Dynamics of two-phase interfaces and surface tensions: A density-functional theory perspective

NASA Astrophysics Data System (ADS)

Yatsyshin, Petr; Sibley, David N.; Duran-Olivencia, Miguel A.; Kalliadasis, Serafim

2016-11-01

Classical density functional theory (DFT) is a statistical mechanical framework for the description of fluids at the nanoscale, where the inhomogeneity of the fluid structure needs to be carefully accounted for. By expressing the grand free-energy of the fluid as a functional of the one-body density, DFT offers a theoretically consistent and computationally accessible way to obtain two-phase interfaces and respective interfacial tensions in a ternary solid-liquid-gas system. The dynamic version of DFT (DDFT) can be rigorously derived from the Smoluchowsky picture of the dynamics of colloidal particles in a solvent. It is generally agreed that DDFT can capture the diffusion-driven evolution of many soft-matter systems. In this context, we use DDFT to investigate the dynamic behaviour of two-phase interfaces in both equilibrium and dynamic wetting and discuss the possibility of defining a time-dependent surface tension, which still remains in debate. We acknowledge financial support from the European Research Council via Advanced Grant No. 247031 and from the Engineering and Physical Sciences Research Council of the UK via Grants No. EP/L027186 and EP/L020564.

Communication: A method to compute the transport coefficient of pure fluids diffusing through planar interfaces from equilibrium molecular dynamics simulations.

PubMed

Vermorel, Romain; Oulebsir, Fouad; Galliero, Guillaume

2017-09-14

The computation of diffusion coefficients in molecular systems ranks among the most useful applications of equilibrium molecular dynamics simulations. However, when dealing with the problem of fluid diffusion through vanishingly thin interfaces, classical techniques are not applicable. This is because the volume of space in which molecules diffuse is ill-defined. In such conditions, non-equilibrium techniques allow for the computation of transport coefficients per unit interface width, but their weak point lies in their inability to isolate the contribution of the different physical mechanisms prone to impact the flux of permeating molecules. In this work, we propose a simple and accurate method to compute the diffusional transport coefficient of a pure fluid through a planar interface from equilibrium molecular dynamics simulations, in the form of a diffusion coefficient per unit interface width. In order to demonstrate its validity and accuracy, we apply our method to the case study of a dilute gas diffusing through a smoothly repulsive single-layer porous solid. We believe this complementary technique can benefit to the interpretation of the results obtained on single-layer membranes by means of complex non-equilibrium methods.

A soft porous drop in linear flows

NASA Astrophysics Data System (ADS)

Young, Yuan-Nan; Miksis, Michael; Mori, Yoichiro; Shelley, Michael

2017-11-01

The cellular cytoplasm consists a viscous fluid filled with fibrous networks that also have their own dynamics. Such fluid-structure interactions have been modeled as a soft porous material immersed in a viscous fluid. In this talk we focus on the hydrodynamics of a viscous drop filled with soft porous material inside. Suspended in a Stokes flow, such a porous viscous drop is allowed to deform, both the drop interface and the porous structures inside. Special focus is on the deformation dynamics of both the porosity and the shape of the drop under simple flows such as a uniform streaming flow and linear flows. We examine the effects of flow boundary conditions at interface between the porous drop and the surrounding viscous fluid. We also examine the dynamics of a porous drop with active stress from the porous network.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antonelli, Perry Edward

A low-level model-to-model interface is presented that will enable independent models to be linked into an integrated system of models. The interface is based on a standard set of functions that contain appropriate export and import schemas that enable models to be linked with no changes to the models themselves. These ideas are presented in the context of a specific multiscale material problem that couples atomistic-based molecular dynamics calculations to continuum calculations of fluid ow. These simulations will be used to examine the influence of interactions of the fluid with an adjacent solid on the fluid ow. The interface willmore » also be examined by adding it to an already existing modeling code, Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) and comparing it with our own molecular dynamics code.« less

Fluid-fluid interfacial mobility from random walks

NASA Astrophysics Data System (ADS)

Barclay, Paul L.; Lukes, Jennifer R.

2017-12-01

Dual control volume grand canonical molecular dynamics is used to perform the first calculation of fluid-fluid interfacial mobilities. The mobility is calculated from one-dimensional random walks of the interface by relating the diffusion coefficient to the interfacial mobility. Three different calculation methods are employed: one using the interfacial position variance as a function of time, one using the mean-squared interfacial displacement, and one using the time-autocorrelation of the interfacial velocity. The mobility is calculated for two liquid-liquid interfaces and one liquid-vapor interface to examine the robustness of the methods. Excellent agreement between the three calculation methods is shown for all the three interfaces, indicating that any of them could be used to calculate the interfacial mobility.

How are soap bubbles blown? Fluid dynamics of soap bubble blowing

NASA Astrophysics Data System (ADS)

Davidson, John; Lambert, Lori; Sherman, Erica; Wei, Timothy; Ryu, Sangjin

2013-11-01

Soap bubbles are a common interfacial fluid dynamics phenomenon having a long history of delighting not only children and artists but also scientists. In contrast to the dynamics of liquid droplets in gas and gas bubbles in liquid, the dynamics of soap bubbles has not been well documented. This is possibly because studying soap bubbles is more challenging due to there existing two gas-liquid interfaces. Having the thin-film interface seems to alter the characteristics of the bubble/drop creation process since the interface has limiting factors such as thickness. Thus, the main objective of this study is to determine how the thin-film interface differentiates soap bubbles from gas bubbles and liquid drops. To investigate the creation process of soap bubbles, we constructed an experimental model consisting of air jet flow and a soap film, which consistently replicates the conditions that a human produces when blowing soap bubbles, and examined the interaction between the jet and the soap film using the high-speed videography and the particle image velocimetry.

Multiphase Fluid Dynamics for Spacecraft Applications

NASA Astrophysics Data System (ADS)

Shyy, W.; Sim, J.

2011-09-01

Multiphase flows involving moving interfaces between different fluids/phases are observed in nature as well as in a wide range of engineering applications. With the recent development of high fidelity computational techniques, a number of challenging multiphase flow problems can now be computed. We introduce the basic notion of the main categories of multiphase flow computation; Lagrangian, Eulerian, and Eulerian-Lagrangian techniques to represent and follow interface, and sharp and continuous interface methods to model interfacial dynamics. The marker-based adaptive Eulerian-Lagrangian method, which is one of the most popular methods, is highlighted with microgravity and space applications including droplet collision and spacecraft liquid fuel tank surface stability.

Active microrheology and simultaneous visualization of sheared phospholipid monolayers

PubMed Central

Choi, S.Q.; Steltenkamp, S.; Zasadzinski, J.A.; Squires, T.M.

2011-01-01

Two-dimensional films of surface-active agents—from phospholipids and proteins to nanoparticles and colloids—stabilize fluid interfaces, which are essential to the science, technology and engineering of everyday life. The 2D nature of interfaces present unique challenges and opportunities: coupling between the 2D films and the bulk fluids complicates the measurement of surface dynamic properties, but allows the interfacial microstructure to be directly visualized during deformation. Here we present a novel technique that combines active microrheology with fluorescence microscopy to visualize fluid interfaces as they deform under applied stress, allowing structure and rheology to be correlated on the micron-scale in monolayer films. We show that even simple, single-component lipid monolayers can exhibit viscoelasticity, history dependence, a yield stress and hours-long time scales for elastic recoil and aging. Simultaneous visualization of the monolayer under stress shows that the rich dynamical response results from the cooperative dynamics and deformation of liquid-crystalline domains and their boundaries. PMID:21587229

Implicit mesh discontinuous Galerkin methods and interfacial gauge methods for high-order accurate interface dynamics, with applications to surface tension dynamics, rigid body fluid-structure interaction, and free surface flow: Part I

NASA Astrophysics Data System (ADS)

Saye, Robert

2017-09-01

In this two-part paper, a high-order accurate implicit mesh discontinuous Galerkin (dG) framework is developed for fluid interface dynamics, facilitating precise computation of interfacial fluid flow in evolving geometries. The framework uses implicitly defined meshes-wherein a reference quadtree or octree grid is combined with an implicit representation of evolving interfaces and moving domain boundaries-and allows physically prescribed interfacial jump conditions to be imposed or captured with high-order accuracy. Part one discusses the design of the framework, including: (i) high-order quadrature for implicitly defined elements and faces; (ii) high-order accurate discretisation of scalar and vector-valued elliptic partial differential equations with interfacial jumps in ellipticity coefficient, leading to optimal-order accuracy in the maximum norm and discrete linear systems that are symmetric positive (semi)definite; (iii) the design of incompressible fluid flow projection operators, which except for the influence of small penalty parameters, are discretely idempotent; and (iv) the design of geometric multigrid methods for elliptic interface problems on implicitly defined meshes and their use as preconditioners for the conjugate gradient method. Also discussed is a variety of aspects relating to moving interfaces, including: (v) dG discretisations of the level set method on implicitly defined meshes; (vi) transferring state between evolving implicit meshes; (vii) preserving mesh topology to accurately compute temporal derivatives; (viii) high-order accurate reinitialisation of level set functions; and (ix) the integration of adaptive mesh refinement. In part two, several applications of the implicit mesh dG framework in two and three dimensions are presented, including examples of single phase flow in nontrivial geometry, surface tension-driven two phase flow with phase-dependent fluid density and viscosity, rigid body fluid-structure interaction, and free surface flow. A class of techniques known as interfacial gauge methods is adopted to solve the corresponding incompressible Navier-Stokes equations, which, compared to archetypical projection methods, have a weaker coupling between fluid velocity, pressure, and interface position, and allow high-order accurate numerical methods to be developed more easily. Convergence analyses conducted throughout the work demonstrate high-order accuracy in the maximum norm for all of the applications considered; for example, fourth-order spatial accuracy in fluid velocity, pressure, and interface location is demonstrated for surface tension-driven two phase flow in 2D and 3D. Specific application examples include: vortex shedding in nontrivial geometry, capillary wave dynamics revealing fine-scale flow features, falling rigid bodies tumbling in unsteady flow, and free surface flow over a submersed obstacle, as well as high Reynolds number soap bubble oscillation dynamics and vortex shedding induced by a type of Plateau-Rayleigh instability in water ripple free surface flow. These last two examples compare numerical results with experimental data and serve as an additional means of validation; they also reveal physical phenomena not visible in the experiments, highlight how small-scale interfacial features develop and affect macroscopic dynamics, and demonstrate the wide range of spatial scales often at play in interfacial fluid flow.

Implicit mesh discontinuous Galerkin methods and interfacial gauge methods for high-order accurate interface dynamics, with applications to surface tension dynamics, rigid body fluid-structure interaction, and free surface flow: Part II

NASA Astrophysics Data System (ADS)

Saye, Robert

2017-09-01

In this two-part paper, a high-order accurate implicit mesh discontinuous Galerkin (dG) framework is developed for fluid interface dynamics, facilitating precise computation of interfacial fluid flow in evolving geometries. The framework uses implicitly defined meshes-wherein a reference quadtree or octree grid is combined with an implicit representation of evolving interfaces and moving domain boundaries-and allows physically prescribed interfacial jump conditions to be imposed or captured with high-order accuracy. Part one discusses the design of the framework, including: (i) high-order quadrature for implicitly defined elements and faces; (ii) high-order accurate discretisation of scalar and vector-valued elliptic partial differential equations with interfacial jumps in ellipticity coefficient, leading to optimal-order accuracy in the maximum norm and discrete linear systems that are symmetric positive (semi)definite; (iii) the design of incompressible fluid flow projection operators, which except for the influence of small penalty parameters, are discretely idempotent; and (iv) the design of geometric multigrid methods for elliptic interface problems on implicitly defined meshes and their use as preconditioners for the conjugate gradient method. Also discussed is a variety of aspects relating to moving interfaces, including: (v) dG discretisations of the level set method on implicitly defined meshes; (vi) transferring state between evolving implicit meshes; (vii) preserving mesh topology to accurately compute temporal derivatives; (viii) high-order accurate reinitialisation of level set functions; and (ix) the integration of adaptive mesh refinement. In part two, several applications of the implicit mesh dG framework in two and three dimensions are presented, including examples of single phase flow in nontrivial geometry, surface tension-driven two phase flow with phase-dependent fluid density and viscosity, rigid body fluid-structure interaction, and free surface flow. A class of techniques known as interfacial gauge methods is adopted to solve the corresponding incompressible Navier-Stokes equations, which, compared to archetypical projection methods, have a weaker coupling between fluid velocity, pressure, and interface position, and allow high-order accurate numerical methods to be developed more easily. Convergence analyses conducted throughout the work demonstrate high-order accuracy in the maximum norm for all of the applications considered; for example, fourth-order spatial accuracy in fluid velocity, pressure, and interface location is demonstrated for surface tension-driven two phase flow in 2D and 3D. Specific application examples include: vortex shedding in nontrivial geometry, capillary wave dynamics revealing fine-scale flow features, falling rigid bodies tumbling in unsteady flow, and free surface flow over a submersed obstacle, as well as high Reynolds number soap bubble oscillation dynamics and vortex shedding induced by a type of Plateau-Rayleigh instability in water ripple free surface flow. These last two examples compare numerical results with experimental data and serve as an additional means of validation; they also reveal physical phenomena not visible in the experiments, highlight how small-scale interfacial features develop and affect macroscopic dynamics, and demonstrate the wide range of spatial scales often at play in interfacial fluid flow.

Deformation of a free interface pierced by a tilted cylinder

NASA Astrophysics Data System (ADS)

Raufaste, C.; Kirstetter, G.; Celestini, F.; Cox, S. J.

2012-07-01

We investigate the interaction between an infinite cylinder and a free fluid-fluid interface governed only by its surface tension. We study the deformation of an initially flat interface when it is deformed by the presence of a cylindrical object, tilted at an arbitrary angle, that the interface “totally wets”. Our simulations predict all significant quantities such as the interface shape, the position of the contact line, and the force exerted by the interface on the cylinder. These results are compared with an experimental study of the penetration of a soap film by a cylindrical liquid jet. This dynamic situation exhibits all the characteristics of a totally wetting interface. We show that whatever the inclination, the force is always perpendicular to the plane of the interface, and its amplitude diverges as the inclination angle increases. Such results should bring new insights in both fluid and solid mechanics, from animal locomotion to surface micro-processing.

Instability of multi-layer fluid configurations in the presence of time-dependent accelerations in a microgravity environment

NASA Technical Reports Server (NTRS)

Lyell, M. J.; Roh, Michael

1991-01-01

The increasing number of research opportunities in a microgravity environment will benefit not only fundamental studies in fluid dynamics, but also technological applications such as those involving materials processing. In particular, fluid configurations which involve fluid-fluid interfaces would occur in a variety of experimental investigations. This work investigates the stability of a configuration involving fluid-fluid interfaces in the presence of a time-dependent forcing. Both periodic (g-jitter) and nonperiodic accelerations are considered. The fluid configuration is multilayered, and infinite in extent. The analysis is linear and inviscid, and the acceleration vector is oriented perpendicular to each interface. A Floquet analysis is employed in the case of the periodic forcing. In the problem of nonperiodic forcing, the resulting system of equations are integrated in time. Specific nondimensional parameters appear in each problem. The configuration behavior is investigated for a range of parameter values.

An interface tracking model for droplet electrocoalescence.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erickson, Lindsay Crowl

This report describes an Early Career Laboratory Directed Research and Development (LDRD) project to develop an interface tracking model for droplet electrocoalescence. Many fluid-based technologies rely on electrical fields to control the motion of droplets, e.g. microfluidic devices for high-speed droplet sorting, solution separation for chemical detectors, and purification of biodiesel fuel. Precise control over droplets is crucial to these applications. However, electric fields can induce complex and unpredictable fluid dynamics. Recent experiments (Ristenpart et al. 2009) have demonstrated that oppositely charged droplets bounce rather than coalesce in the presence of strong electric fields. A transient aqueous bridge forms betweenmore » approaching drops prior to pinch-off. This observation applies to many types of fluids, but neither theory nor experiments have been able to offer a satisfactory explanation. Analytic hydrodynamic approximations for interfaces become invalid near coalescence, and therefore detailed numerical simulations are necessary. This is a computationally challenging problem that involves tracking a moving interface and solving complex multi-physics and multi-scale dynamics, which are beyond the capabilities of most state-of-the-art simulations. An interface-tracking model for electro-coalescence can provide a new perspective to a variety of applications in which interfacial physics are coupled with electrodynamics, including electro-osmosis, fabrication of microelectronics, fuel atomization, oil dehydration, nuclear waste reprocessing and solution separation for chemical detectors. We present a conformal decomposition finite element (CDFEM) interface-tracking method for the electrohydrodynamics of two-phase flow to demonstrate electro-coalescence. CDFEM is a sharp interface method that decomposes elements along fluid-fluid boundaries and uses a level set function to represent the interface.« less

Soft particles at a fluid interface

NASA Astrophysics Data System (ADS)

Mehrabian, Hadi; Harting, Jens; Snoeijer, Jacco H.

2015-11-01

Particles added to a fluid interface can be used as a surface stabilizer in the food, oil and cosmetic industries. As an alternative to rigid particles, it is promising to consider highly deformable particles that can adapt their conformation at the interface. In this study, we compute the shapes of soft elastic particles using molecular dynamics simulations of a cross-linked polymer gel, complemented by continuum calculations based on the linear elasticity. It is shown that the particle shape is not only affected by the Young's modulus of the particle, but also strongly depends on whether the gel is partially or completely wetting the fluid interface. We find that the molecular simulations for the partially wetting case are very accurately described by the continuum theory. By contrast, when the gel is completely wetting the fluid interface the linear theory breaks down and we reveal that molecular details have a strong influence on the equilibrium shape.

Exploring a multi-scale method for molecular simulation in continuum solvent model: Explicit simulation of continuum solvent as an incompressible fluid.

PubMed

Xiao, Li; Luo, Ray

2017-12-07

We explored a multi-scale algorithm for the Poisson-Boltzmann continuum solvent model for more robust simulations of biomolecules. In this method, the continuum solvent/solute interface is explicitly simulated with a numerical fluid dynamics procedure, which is tightly coupled to the solute molecular dynamics simulation. There are multiple benefits to adopt such a strategy as presented below. At this stage of the development, only nonelectrostatic interactions, i.e., van der Waals and hydrophobic interactions, are included in the algorithm to assess the quality of the solvent-solute interface generated by the new method. Nevertheless, numerical challenges exist in accurately interpolating the highly nonlinear van der Waals term when solving the finite-difference fluid dynamics equations. We were able to bypass the challenge rigorously by merging the van der Waals potential and pressure together when solving the fluid dynamics equations and by considering its contribution in the free-boundary condition analytically. The multi-scale simulation method was first validated by reproducing the solute-solvent interface of a single atom with analytical solution. Next, we performed the relaxation simulation of a restrained symmetrical monomer and observed a symmetrical solvent interface at equilibrium with detailed surface features resembling those found on the solvent excluded surface. Four typical small molecular complexes were then tested, both volume and force balancing analyses showing that these simple complexes can reach equilibrium within the simulation time window. Finally, we studied the quality of the multi-scale solute-solvent interfaces for the four tested dimer complexes and found that they agree well with the boundaries as sampled in the explicit water simulations.

Three-dimensional user interfaces for scientific visualization

NASA Technical Reports Server (NTRS)

Vandam, Andries

1995-01-01

The main goal of this project is to develop novel and productive user interface techniques for creating and managing visualizations of computational fluid dynamics (CFD) datasets. We have implemented an application framework in which we can visualize computational fluid dynamics user interfaces. This UI technology allows users to interactively place visualization probes in a dataset and modify some of their parameters. We have also implemented a time-critical scheduling system which strives to maintain a constant frame-rate regardless of the number of visualization techniques. In the past year, we have published parts of this research at two conferences, the research annotation system at Visualization 1994, and the 3D user interface at UIST 1994. The real-time scheduling system has been submitted to SIGGRAPH 1995 conference. Copies of these documents are included with this report.

Dynamic fluid connectivity during steady-state multiphase flow in a sandstone.

PubMed

Reynolds, Catriona A; Menke, Hannah; Andrew, Matthew; Blunt, Martin J; Krevor, Samuel

2017-08-01

The current conceptual picture of steady-state multiphase Darcy flow in porous media is that the fluid phases organize into separate flow pathways with stable interfaces. Here we demonstrate a previously unobserved type of steady-state flow behavior, which we term "dynamic connectivity," using fast pore-scale X-ray imaging. We image the flow of N 2 and brine through a permeable sandstone at subsurface reservoir conditions, and low capillary numbers, and at constant fluid saturation. At any instant, the network of pores filled with the nonwetting phase is not necessarily connected. Flow occurs along pathways that periodically reconnect, like cars controlled by traffic lights. This behavior is consistent with an energy balance, where some of the energy of the injected fluids is sporadically converted to create new interfaces.

Diffuse interface models of locally inextensible vesicles in a viscous fluid

PubMed Central

Aland, Sebastian; Egerer, Sabine; Lowengrub, John; Voigt, Axel

2014-01-01

We present a new diffuse interface model for the dynamics of inextensible vesicles in a viscous fluid with inertial forces. A new feature of this work is the implementation of the local inextensibility condition in the diffuse interface context. Local inextensibility is enforced by using a local Lagrange multiplier, which provides the necessary tension force at the interface. We introduce a new equation for the local Lagrange multiplier whose solution essentially provides a harmonic extension of the multiplier off the interface while maintaining the local inextensibility constraint near the interface. We also develop a local relaxation scheme that dynamically corrects local stretching/compression errors thereby preventing their accumulation. Asymptotic analysis is presented that shows that our new system converges to a relaxed version of the inextensible sharp interface model. This is also verified numerically. To solve the equations, we use an adaptive finite element method with implicit coupling between the Navier-Stokes and the diffuse interface inextensibility equations. Numerical simulations of a single vesicle in a shear flow at different Reynolds numbers demonstrate that errors in enforcing local inextensibility may accumulate and lead to large differences in the dynamics in the tumbling regime and smaller differences in the inclination angle of vesicles in the tank-treading regime. The local relaxation algorithm is shown to prevent the accumulation of stretching and compression errors very effectively. Simulations of two vesicles in an extensional flow show that local inextensibility plays an important role when vesicles are in close proximity by inhibiting fluid drainage in the near contact region. PMID:25246712

Comparing the Richtmyer-Meshkov instability of thermal and ion-species interfaces in two-fluid plasmas

NASA Astrophysics Data System (ADS)

Wheatley, Vincent; Bond, Daryl; Li, Yuan; Samtaney, Ravi; Pullin, Dale

2017-11-01

The Richtmyer-Meshkov instability (RMI) of a shock accelerated perturbed density interface is important in both inertial confinement fusion and astrophysics, where the materials involved are typically in the plasma state. Initial density interfaces can be due to either temperature or ion-species discontinuities. If the Atwood number of the interfaces and specific heat ratios of the fluids are matched, these two cases behave similarly when modeled using the equations of either hydrodynamics or magnetohydrodynamics. In the two-fluid ion-electron plasma model, however, there is a significant difference between them: In the thermal interface case, there is a discontinuity in electron density that is also subject to the RMI, while for the ion-species interface case there is not. It will be shown via ideal two-fluid plasma simulations that this causes substantial differences in the dynamics of the flow between the two cases. This work was partially supported by the KAUST Office of Sponsored Research under Award URF/1/2162-01.

Pairwise Force Smoothed Particle Hydrodynamics model for multiphase flow: Surface tension and contact line dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tartakovsky, Alexandre M.; Panchenko, Alexander

2016-01-01

We present a novel formulation of the Pairwise Force Smoothed Particle Hydrodynamics Model (PF-SPH) and use it to simulate two- and three-phase flows in bounded domains. In the PF-SPH model, the Navier-Stokes equations are discretized with the Smoothed Particle Hydrodynamics (SPH) method and the Young-Laplace boundary condition at the fluid-fluid interface and the Young boundary condition at the fluid-fluid-solid interface are replaced with pairwise forces added into the Navier-Stokes equations. We derive a relationship between the parameters in the pairwise forces and the surface tension and static contact angle. Next, we demonstrate the accuracy of the model under static andmore » dynamic conditions. Finally, to demonstrate the capabilities and robustness of the model we use it to simulate flow of three fluids in a porous material.« less

A numerical method for electro-kinetic flow with deformable fluid interfaces

NASA Astrophysics Data System (ADS)

Booty, Michael; Ma, Manman; Siegel, Michael

2013-11-01

We consider two-phase flow of ionic fluids whose motion is driven by an imposed electric field. At a fluid interface, a screening cloud of ions develops and forms an electro-chemical double layer or Debye layer. The imposed field acts on this induced charge distribution, resulting in a strong slip flow near the interface. We formulate a ``hybrid'' or multiscale numerical method in the thin Debye layer limit that incorporates an asymptotic analysis of the electrostatic potential and fluid dynamics in the Debye layer into a boundary integral solution of the full moving boundary problem. Results of the method are presented that show time-dependent deformation and steady state drop interface shapes when the timescale for charge-up of the Debye layer is either much less than or comparable to the timescale of the flow.

Feedback Controlled Colloidal Assembly at Fluid Interfaces

NASA Astrophysics Data System (ADS)

Bevan, Michael

The autonomous and reversible assembly of colloidal nano- and micro- scale components into ordered configurations is often suggested as a scalable process capable of manufacturing meta-materials with exotic electromagnetic properties. As a result, there is strong interest in understanding how thermal motion, particle interactions, patterned surfaces, and external fields can be optimally coupled to robustly control the assembly of colloidal components into hierarchically structured functional meta-materials. We approach this problem by directly relating equilibrium and dynamic colloidal microstructures to kT-scale energy landscapes mediated by colloidal forces, physically and chemically patterned surfaces, multiphase fluid interfaces, and electromagnetic fields. 3D colloidal trajectories are measured in real-space and real-time with nanometer resolution using an integrated suite of evanescent wave, video, and confocal microscopy methods. Equilibrium structures are connected to energy landscapes via statistical mechanical models. The dynamic evolution of initially disordered colloidal fluid configurations into colloidal crystals in the presence of tunable interactions (electromagnetic field mediated interactions, particle-interface interactions) is modeled using a novel approach based on fitting the Fokker-Planck equation to experimental microscopy and computer simulated assembly trajectories. This approach is based on the use of reaction coordinates that capture important microstructural features of crystallization processes and quantify both statistical mechanical (free energy) and fluid mechanical (hydrodynamic) contributions. Ultimately, we demonstrate real-time control of assembly, disassembly, and repair of colloidal crystals using both open loop and closed loop control to produce perfectly ordered colloidal microstructures. This approach is demonstrated for close packed colloidal crystals of spherical particles at fluid-solid interfaces and is being extended to anisotropic particles and multiphase fluid interfaces.

Numerical Modeling of Fluid Flow, Heat Transfer and Arc-Melt Interaction in Tungsten Inert Gas Welding

NASA Astrophysics Data System (ADS)

Li, Linmin; Li, Baokuan; Liu, Lichao; Motoyama, Yuichi

2017-04-01

The present work develops a multi-region dynamic coupling model for fluid flow, heat transfer and arc-melt interaction in tungsten inert gas (TIG) welding using the dynamic mesh technique. The arc-weld pool unified model is developed on basis of magnetohydrodynamic (MHD) equations and the interface is tracked using the dynamic mesh method. The numerical model for arc is firstly validated by comparing the calculated temperature profiles and essential results with the former experimental data. For weld pool convection solution, the drag, Marangoni, buoyancy and electromagnetic forces are separately validated, and then taken into account. Moreover, the model considering interface deformation is adopted in a stationary TIG welding process with SUS304 stainless steel and the effect of interface deformation is investigated. The depression of weld pool center and the lifting of pool periphery are both predicted. The results show that the weld pool shape calculated with considering the interface deformation is more accurate.

Interfacial fluid instabilities and Kapitsa pendula.

PubMed

Krieger, Madison S

2017-07-01

The onset and development of instabilities is one of the central problems in fluid mechanics. Here we develop a connection between instabilities of free fluid interfaces and inverted pendula. When acted upon solely by the gravitational force, the inverted pendulum is unstable. This position can be stabilized by the Kapitsa phenomenon, in which high-frequency low-amplitude vertical vibrations of the base creates a fictitious force which opposes the gravitational force. By transforming the dynamical equations governing a fluid interface into an appropriate pendulum-type equation, we demonstrate how stability can be induced in fluid systems by properly tuned vibrations. We construct a "dictionary"-type relationship between various pendula and the classical Rayleigh-Taylor, Kelvin-Helmholtz, Rayleigh-Plateau and the self-gravitational instabilities. This makes several results in control theory and dynamical systems directly applicable to the study of tunable fluid instabilities, where the critical wavelength depends on the external forces or the instability is suppressed entirely. We suggest some applications and instances of the effect ranging in scale from microns to the radius of a galaxy.

Nanoparticle Assemblies at Fluid Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Russell, Thomas P.

2015-03-10

A systematic study of the structure and dynamics of nanoparticles (NP) and NP-surfactants was performed. The ligands attached to both the NPs and NP-surfactants dictate the manner in which the nanoscopic materials assemble at fluid interfaces. Studies have shown that a single layer of the nanoscpic materials form at the interface to reduce the interactions between the two immiscible fluids. The shape of the NP is, also, important, where for spherical particles, a disordered, liquid-like monolayer forms, and, for nanorods, ordered domains at the interface is found and, if the monolayers are compressed, the orientation of the nanorods with respectmore » to the interface can change. By associating end-functionalized polymers to the NPs assembled at the interface, NP-surfactants are formed that increase the energetic gain in segregating each NP at the interface which allows the NP-surfactants to jam at the interface when compressed. This has opened the possibility of structuring the two liquids by freezing in shape changes of the liquids.« less

Dynamics and Instabilities of Acoustically Stressed Interfaces

NASA Astrophysics Data System (ADS)

Shi, William Tao

An intense sound field exerts acoustic radiation pressure on a transitional layer between two continuous fluid media, leading to the unconventional dynamical behavior of the interface in the presence of the sound field. An understanding of this behavior has applications in the study of drop dynamics and surface rheology. Acoustic fields have also been utilized in the generation of interfacial instability, which may further encourage the dispersion or coalescence of liquids. Therefore, the study of the dynamics of the acoustically stressed interfaces is essential to infer the mechanism of the various phenomena related to interfacial dynamics and to acquire the properties of liquid surfaces. This thesis studies the dynamics of acoustically stressed interfaces through a theoretical model of surface interactions on both closed and open interfaces. Accordingly, a boundary integral method is developed to simulate the motions of a stressed interface. The method has been employed to determine the deformation, oscillation and instability of acoustically levitated drops. The generalized computations are found to be in good agreement with available experimental results. The linearized theory is also derived to predict the instability threshold of the flat interface, and is then compared with experiments conducted to observe and measure the unstable motions of the horizontal interface. This thesis is devoted to describing and classifying the simplest mechanisms by which acoustic fields provide a surface interaction with a fluid. A physical picture of the competing processes introduced by the evolution of an interface in a sound field is presented. The development of an initial small perturbation into a sharp form is observed on either a drop surface or a horizontal interface, indicating a strong focusing of acoustic energy at certain spots of the interface. Emphasis is placed on understanding the basic coupling mechanisms, rather than on particular applications that may involve this coupling. The dynamical behavior of a stressed drop can be determined in terms of a given form of an incident sound field and three dimensionless quantities. Thus, the behavior of a complex dynamic system has been clarified, permitting the exploration and interpretation of the nature of liquid surface phenomena.

Derivation of a continuum model and the energy law for moving contact lines with insoluble surfactants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zhen, E-mail: matzz@nus.edu.sg; Xu, Shixin, E-mail: matxs@nus.edu.sg; Ren, Weiqing, E-mail: matrw@nus.edu.sg

2014-06-15

A continuous model is derived for the dynamics of two immiscible fluids with moving contact lines and insoluble surfactants based on thermodynamic principles. The continuum model consists of the Navier-Stokes equations for the dynamics of the two fluids and a convection-diffusion equation for the evolution of the surfactant on the fluid interface. The interface condition, the boundary condition for the slip velocity, and the condition for the dynamic contact angle are derived from the consideration of energy dissipations. Different types of energy dissipations, including the viscous dissipation, the dissipations on the solid wall and at the contact line, as wellmore » as the dissipation due to the diffusion of surfactant, are identified from the analysis. A finite element method is developed for the continuum model. Numerical experiments are performed to demonstrate the influence of surfactant on the contact line dynamics. The different types of energy dissipations are compared numerically.« less

Experimental and Numerical Study of the Evaporation of Water at Low Pressures.

PubMed

Kazemi, Mohammad Amin; Nobes, David S; Elliott, Janet A W

2017-05-09

Although evaporation is considered to be a surface phenomenon, the rate of molecular transport across a liquid-vapor boundary is strongly dependent on the coupled fluid dynamics and heat transfer in the bulk fluids. Recent experimental thermocouple measurements of the temperature field near the interface of evaporating water into its vapor have begun to show the role of heat transfer in evaporation. However, the role of fluid dynamics has not been explored sufficiently. Here, we have developed a mathematical model to describe the coupling of the heat, mass, and momentum transfer in the fluids with the transport phenomena at the interface. The model was used to understand the experimentally obtained velocity field in the liquid and temperature profiles in the liquid and vapor, in evaporation from a concave meniscus for various vacuum pressures. By using the model, we have shown that an opposing buoyancy flow suppressed the thermocapillary flow in the liquid during evaporation at low pressures in our experiments. As such, in the absence of thermocapillary convection, the evaporation is controlled by heat transfer to the interface, and the predicted behavior of the system is independent of choosing between the existing theoretical expressions for evaporation flux. Furthermore, we investigated the temperature discontinuity at the interface and confirmed that the discontinuity strongly depends on the heat flux from the vapor side, which depends on the geometrical shape of the interface.

Interfacial layering and capillary roughness in immiscible liquids.

PubMed

Geysermans, P; Pontikis, V

2010-08-21

The capillary roughness and the atomic density profiles of extended interfaces between immiscible liquids are determined as a function of the interface area by using molecular dynamics and Lennard-Jones (12-6) potentials. We found that with increasing area, the interface roughness diverges logarithmically, thus fitting the theoretical mean-field prediction. In systems small enough for the interfacial roughness not to blur the structural details, atomic density profiles across the fluid interface are layered with correlation length in the range of molecular correlations in liquids. On increasing the system size, the amplitude of the thermally excited position fluctuations of the interface increases, thus causing layering to rapidly vanish, if density profiles are computed without special care. In this work, we present and validate a simple method, operating in the direct space, for extracting from molecular dynamics trajectories the "intrinsic" structure of a fluid interface that is the local density profile of the interface cleaned from capillary wave effects. Estimated values of interfacial properties such as the tension, the intrinsic width, and the lower wavelength limit of position fluctuations are in agreement with results collected from the literature.

Diffuse-Interface Capturing Methods for Compressible Two-Phase Flows

NASA Astrophysics Data System (ADS)

Saurel, Richard; Pantano, Carlos

2018-01-01

Simulation of compressible flows became a routine activity with the appearance of shock-/contact-capturing methods. These methods can determine all waves, particularly discontinuous ones. However, additional difficulties may appear in two-phase and multimaterial flows due to the abrupt variation of thermodynamic properties across the interfacial region, with discontinuous thermodynamical representations at the interfaces. To overcome this difficulty, researchers have developed augmented systems of governing equations to extend the capturing strategy. These extended systems, reviewed here, are termed diffuse-interface models, because they are designed to compute flow variables correctly in numerically diffused zones surrounding interfaces. In particular, they facilitate coupling the dynamics on both sides of the (diffuse) interfaces and tend to the proper pure fluid-governing equations far from the interfaces. This strategy has become efficient for contact interfaces separating fluids that are governed by different equations of state, in the presence or absence of capillary effects, and with phase change. More sophisticated materials than fluids (e.g., elastic-plastic materials) have been considered as well.

Molecular mechanics and structure of the fluid-solid interface in simple fluids

NASA Astrophysics Data System (ADS)

Wang, Gerald J.; Hadjiconstantinou, Nicolas G.

2017-09-01

Near a fluid-solid interface, the fluid spatial density profile is highly nonuniform at the molecular scale. This nonuniformity can have profound effects on the dynamical behavior of the fluid and has been shown to play an especially important role when modeling a wide variety of nanoscale heat and momentum transfer phenomena. We use molecular-mechanics arguments and molecular-dynamics (MD) simulations to develop a better understanding of the structure of the first fluid layer directly adjacent to the solid in the layering regime, as delineated by a nondimensional number that compares the effects of wall-fluid interaction to thermal energy. Using asymptotic analysis of the Nernst-Planck equation, we show that features of the fluid density profile close to the wall, such as the areal density of the first layer ΣFL (defined as the number of atoms in this layer per unit of fluid-solid interfacial area), can be expressed as polynomial functions of the fluid average density ρave. This is found to be in agreement with MD simulations, which also show that the width of the first layer hFL is a linear function of the average density and only a weak function of the temperature T . These results can be combined to show that, for system average densities corresponding to a dense fluid (ρave≥0.7 ), the ratio C ≡ΣFLρavehFL, representing a density enhancement with respect to the bulk fluid, depends only weakly on temperature and is essentially independent of density. Further MD simulations suggest that the above results, nominally valid for large systems (solid in contact with semi-infinite fluid), also describe fluid-solid interfaces under considerable nanoconfinement, provided ρave is appropriately defined.

Approaching a flat boundary with a block copolymer coated emulsion drop: late stage drainage dynamics

NASA Astrophysics Data System (ADS)

Rozairo, Damith; Croll, Andrew

Understanding the dynamics of the formation and drainage of the thin fluid film that becomes trapped by a deformable droplet as it approaches another object is crucial to the advancement of many industrial and biomedical applications. Adding amphiphilic diblock copolymers, which are becoming more commonly used in drug delivery and oil recovery, only add to the complexity. Despite their increased use, little is known about how long polymer chains fill an emulsion drop's interface or how the molecules influence hydrodynamic processes. We study the drainage dynamics of a thin water film trapped between mica and a diblock copolymer saturated oil droplet. Specifically, we examine several different polystyrene-b-poly(ethylene oxide) (PS-PEO) molecules self-assembled at a toluene-water interface using laser scanning confocal microscopy. Our experiments reveal that the molecular details of the polymer chains deeply influence the drainage times, indicating that they are not acting as a 'simple' surfactant. The presence of the chains creates a much slower dynamic as fluid is forced to drain through an effective polymer brush, the brush itself determined by chain packing at the interface. We present a simple model which accounts for the basic physics of the interface.

Deconstructing Temperature Gradients across Fluid Interfaces: The Structural Origin of the Thermal Resistance of Liquid-Vapor Interfaces

NASA Astrophysics Data System (ADS)

Muscatello, Jordan; Chacón, Enrique; Tarazona, Pedro; Bresme, Fernando

2017-07-01

The interfacial thermal resistance determines condensation-evaporation processes and thermal transport across material-fluid interfaces. Despite its importance in transport processes, the interfacial structure responsible for the thermal resistance is still unknown. By combining nonequilibrium molecular dynamics simulations and interfacial analyses that remove the interfacial thermal fluctuations we show that the thermal resistance of liquid-vapor interfaces is connected to a low density fluid layer that is adsorbed at the liquid surface. This thermal resistance layer (TRL) defines the boundary where the thermal transport mechanism changes from that of gases (ballistic) to that characteristic of dense liquids, dominated by frequent particle collisions involving very short mean free paths. We show that the thermal conductance is proportional to the number of atoms adsorbed in the TRL, and hence we explain the structural origin of the thermal resistance in liquid-vapor interfaces.

Formation of curvature singularities on the interface between dielectric liquids in a strong vertical electric field.

PubMed

Kochurin, Evgeny A; Zubarev, Nikolay M; Zubareva, Olga V

2013-08-01

The nonlinear dynamics of the interface between two deep dielectric fluids in the presence of a vertical electric field is studied. We consider the limit of a strong external electric field where electrostatic forces dominate over gravitational and capillary forces. The nonlinear integrodifferential equations for the interface motion are derived under the assumption of small interfacial slopes. It is shown in the framework of these equations that, in the generic case, the instability development leads to the formation of root singularities at the interface in a finite time. The interfacial curvature becomes infinite at singular points, while the slope angles remain relatively small. The curvature is negative in the vicinity of singularities if the ratio of the permittivities of the fluids exceeds the inverse ratio of their densities, and it is positive in the opposite case (we consider that the lower fluid is heavier than the upper one). In the intermediate case, the interface evolution equations describe the formation and sharpening of dimples at the interface. The results obtained are applicable for the description of the instability of the interface between two magnetic fluids in a vertical magnetic field.

Surface effects on friction-induced fluid heating in nanochannel flows.

PubMed

Li, Zhigang

2009-02-01

We investigate the mechanism of friction-induced fluid heating under the influence of surfaces. The temperature distributions of liquid argon and helium in nanoscale Poiseuille flows are studied through molecular dynamics simulations. It is found that the fluid heating is mainly caused by the viscous friction in the fluid when the external force is small and there is no slip at the fluid-solid interface. When the external force is larger than the fluid-surface binding force, the friction at the fluid-solid interface dominates over the internal friction of the fluid and is the major contribution to fluid heating. An asymmetric temperature gradient in the fluid is developed in the case of nonidentical walls and the general temperature gradient may change sign as the dominant heating factor changes from internal to interfacial friction with increasing external force. The effect of temperature on the fluid heating is also discussed.

Dynamic modelling of an adsorption storage tank using a hybrid approach combining computational fluid dynamics and process simulation

USGS Publications Warehouse

Mota, J.P.B.; Esteves, I.A.A.C.; Rostam-Abadi, M.

2004-01-01

A computational fluid dynamics (CFD) software package has been coupled with the dynamic process simulator of an adsorption storage tank for methane fuelled vehicles. The two solvers run as independent processes and handle non-overlapping portions of the computational domain. The codes exchange data on the boundary interface of the two domains to ensure continuity of the solution and of its gradient. A software interface was developed to dynamically suspend and activate each process as necessary, and be responsible for data exchange and process synchronization. This hybrid computational tool has been successfully employed to accurately simulate the discharge of a new tank design and evaluate its performance. The case study presented here shows that CFD and process simulation are highly complementary computational tools, and that there are clear benefits to be gained from a close integration of the two. ?? 2004 Elsevier Ltd. All rights reserved.

Importance of curvature evaluation scale for predictive simulations of dynamic gas-liquid interfaces

NASA Astrophysics Data System (ADS)

Owkes, Mark; Cauble, Eric; Senecal, Jacob; Currie, Robert A.

2018-07-01

The effect of the scale used to compute the interfacial curvature on the prediction of dynamic gas-liquid interfaces is investigated. A new interface curvature calculation methodology referred to herein as the Adjustable Curvature Evaluation Scale (ACES) is proposed. ACES leverages a weighted least squares regression to fit a polynomial through points computed on the volume-of-fluid representation of the gas-liquid interface. The interface curvature is evaluated from this polynomial. Varying the least squares weight with distance from the location where the curvature is being computed, adjusts the scale the curvature is evaluated on. ACES is verified using canonical static test cases and compared against second- and fourth-order height function methods. Simulations of dynamic interfaces, including a standing wave and oscillating droplet, are performed to assess the impact of the curvature evaluation scale for predicting interface motions. ACES and the height function methods are combined with two different unsplit geometric volume-of-fluid (VoF) schemes that define the interface on meshes with different levels of refinement. We find that the results depend significantly on curvature evaluation scale. Particularly, the ACES scheme with a properly chosen weight function is accurate, but fails when the scale is too small or large. Surprisingly, the second-order height function method is more accurate than the fourth-order variant for the dynamic tests even though the fourth-order method performs better for static interfaces. Comparing the curvature evaluation scale of the second- and fourth-order height function methods, we find the second-order method is closer to the optimum scale identified with ACES. This result suggests that the curvature scale is driving the accuracy of the dynamics. This work highlights the importance of studying numerical methods with realistic (dynamic) test cases and that the interactions of the various discretizations is as important as the accuracy of one part of the discretization.

Gravity Probe-B Spacecraft attitude control based on the dynamics of slosh wave-induced fluid stress distribution on rotating dewar container of cryogenic propellant

NASA Technical Reports Server (NTRS)

Hung, R. J.; Lee, C. C.; Leslie, F. W.

1991-01-01

The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled rotating fluids, in a full-scale Gravity Probe-B Spacecraft propellant dewar tank imposed by various frequencies of gravity jitters have been investigated. Results show that fluid stress distribution exerted on the outer and inner walls of rotating dewar are closely related to the characteristics of slosh waves excited on the liquid-vapor interface in the rotating dewar tank. This can provide a set of tool for the spacecraft dynamic control leading toward the control of spacecraft unbalance caused by the uneven fluid stress distribution due to slosh wave excitations.

New insights on the complex dynamics of two-phase flow in porous media under intermediate-wet conditions.

PubMed

Rabbani, Harris Sajjad; Joekar-Niasar, Vahid; Pak, Tannaz; Shokri, Nima

2017-07-04

Multiphase flow in porous media is important in a number of environmental and industrial applications such as soil remediation, CO 2 sequestration, and enhanced oil recovery. Wetting properties control flow of immiscible fluids in porous media and fluids distribution in the pore space. In contrast to the strong and weak wet conditions, pore-scale physics of immiscible displacement under intermediate-wet conditions is less understood. This study reports the results of a series of two-dimensional high-resolution direct numerical simulations with the aim of understanding the pore-scale dynamics of two-phase immiscible fluid flow under intermediate-wet conditions. Our results show that for intermediate-wet porous media, pore geometry has a strong influence on interface dynamics, leading to co-existence of concave and convex interfaces. Intermediate wettability leads to various interfacial movements which are not identified under imbibition or drainage conditions. These pore-scale events significantly influence macro-scale flow behaviour causing the counter-intuitive decline in recovery of the defending fluid from weak imbibition to intermediate-wet conditions.

How Does a Liquid Wet a Solid? Hydrodynamics of Dynamic Contact Angles

NASA Technical Reports Server (NTRS)

Rame, Enrique

2001-01-01

A contact line is defined at the intersection of a solid surface with the interface between two immiscible fluids. When one fluid displaces another immiscible fluid along a solid surface, the process is called dynamic wetting and a "moving" contact line (one whose position relative to the solid changes in time) often appears. The physics of dynamic wetting controls such natural and industrial processes as spraying of paints and insecticides, dishwashing, film formation and rupture in the eye and in the alveoli, application of coatings, printing, drying and imbibition of fibrous materials, oil recovery from porous rocks, and microfluidics.

Laboratory and numerical investigations of kinetic interface sensitive tracers transport for immiscible two-phase flow porous media systems

NASA Astrophysics Data System (ADS)

Tatomir, Alexandru Bogdan A. C.; Sauter, Martin

2017-04-01

A number of theoretical approaches estimating the interfacial area between two fluid phases are available (Schaffer et al.,2013). Kinetic interface sensitive (KIS) tracers are used to describe the evolution of fluid-fluid interfaces advancing in two phase porous media systems (Tatomir et al., 2015). Initially developed to offer answers about the supercritical (sc)CO2 plume movement and the efficiency of trapping in geological carbon storage reservoirs, KIS tracers are tested in dynamic controlled laboratory conditions. N-octane and water, analogue to a scCO2 - brine system, are used. The KIS tracer is dissolved in n-octane, which is injected as the non-wetting phase in a fully water saturated porous media column. The porous system is made up of spherical glass beads with sizes of 100-250 μm. Subsequently, the KIS tracer follows a hydrolysis reaction over the n-octane - water interface resulting in an acid and phenol which are both water soluble. The fluid-fluid interfacial area is described numerically with the help of constitutive-relationships derived from the Brooks-Corey model. The specific interfacial area is determined numerically from pore scale calculations, or from different literature sources making use of pore network model calculations (Joekar-Niasar et al., 2008). This research describes the design of the laboratory setup and compares the break-through curves obtained with the forward model and in the laboratory experiment. Furthermore, first results are shown in the attempt to validate the immiscible two phase flow reactive transport numerical model with dynamic laboratory column experiments. Keywords: Fluid-fluid interfacial area, KIS tracers, model validation, CCS, geological storage of CO2

Dynamic stabilization of Rayleigh-Taylor instability: Experiments with Newtonian fluids as surrogates for ablation fronts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez Prieto, G.; Piriz, A. R.; Lopez Cela, J. J.

2013-01-15

A previous theory on dynamic stabilization of Rayleigh-Taylor instability at interfaces between Newtonian fluids is reformulated in order to make evident the analogy of this problem with the related one on dynamic stabilization of ablation fronts in the framework of inertial confinement fusion. Explicit analytical expressions are obtained for the boundaries of the dynamically stable region which turns out to be completely analogue to the stability charts obtained for the case of ablation fronts. These results allow proposing experiments with Newtonian fluids as surrogates for studying the case of ablation fronts. Experiments with Newtonian fluids are presented which demonstrate themore » validity of the theoretical approach and encourage to pursue experimental research on ablation fronts to settle the feasibility of dynamic stabilization in the inertial confinement fusion scenario.« less

Smoothed dissipative particle dynamics model for mesoscopic multiphase flows in the presence of thermal fluctuations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lei, Huan; Baker, Nathan A.; Wu, Lei

2016-08-05

Thermal fluctuations cause perturbations of fluid-fluid interfaces and highly nonlinear hydrodynamics in multiphase flows. In this work, we develop a novel multiphase smoothed dissipative particle dynamics model. This model accounts for both bulk hydrodynamics and interfacial fluctuations. Interfacial surface tension is modeled by imposing a pairwise force between SDPD particles. We show that the relationship between the model parameters and surface tension, previously derived under the assumption of zero thermal fluctuation, is accurate for fluid systems at low temperature but overestimates the surface tension for intermediate and large thermal fluctuations. To analyze the effect of thermal fluctuations on surface tension,more » we construct a coarse-grained Euler lattice model based on the mean field theory and derive a semi-analytical formula to directly relate the surface tension to model parameters for a wide range of temperatures and model resolutions. We demonstrate that the present method correctly models the dynamic processes, such as bubble coalescence and capillary spectra across the interface.« less

Phase behavior of charged colloids at a fluid interface

NASA Astrophysics Data System (ADS)

Kelleher, Colm P.; Guerra, Rodrigo E.; Hollingsworth, Andrew D.; Chaikin, Paul M.

2017-02-01

We study the phase behavior of a system of charged colloidal particles that are electrostatically bound to an almost flat interface between two fluids. We show that, despite the fact that our experimental system consists of only 103-104 particles, the phase behavior is consistent with the theory of melting due to Kosterlitz, Thouless, Halperin, Nelson, and Young. Using spatial and temporal correlations of the bond-orientational order parameter, we classify our samples into solid, isotropic fluid, and hexatic phases. We demonstrate that the topological defect structure we observe in each phase corresponds to the predictions of Kosterlitz-Thouless-Halperin-Nelson-Young theory. By measuring the dynamic Lindemann parameter γL(τ ) and the non-Gaussian parameter α2(τ ) of the displacements of the particles relative to their neighbors, we show that each of the phases displays distinctive dynamical behavior.

Predictive models for moving contact line flows

NASA Technical Reports Server (NTRS)

Rame, Enrique; Garoff, Stephen

2003-01-01

Modeling flows with moving contact lines poses the formidable challenge that the usual assumptions of Newtonian fluid and no-slip condition give rise to a well-known singularity. This singularity prevents one from satisfying the contact angle condition to compute the shape of the fluid-fluid interface, a crucial calculation without which design parameters such as the pressure drop needed to move an immiscible 2-fluid system through a solid matrix cannot be evaluated. Some progress has been made for low Capillary number spreading flows. Combining experimental measurements of fluid-fluid interfaces very near the moving contact line with an analytical expression for the interface shape, we can determine a parameter that forms a boundary condition for the macroscopic interface shape when Ca much les than l. This parameter, which plays the role of an "apparent" or macroscopic dynamic contact angle, is shown by the theory to depend on the system geometry through the macroscopic length scale. This theoretically established dependence on geometry allows this parameter to be "transferable" from the geometry of the measurement to any other geometry involving the same material system. Unfortunately this prediction of the theory cannot be tested on Earth.

Differential Geometry Based Multiscale Models

PubMed Central

Wei, Guo-Wei

2010-01-01

Large chemical and biological systems such as fuel cells, ion channels, molecular motors, and viruses are of great importance to the scientific community and public health. Typically, these complex systems in conjunction with their aquatic environment pose a fabulous challenge to theoretical description, simulation, and prediction. In this work, we propose a differential geometry based multiscale paradigm to model complex macromolecular systems, and to put macroscopic and microscopic descriptions on an equal footing. In our approach, the differential geometry theory of surfaces and geometric measure theory are employed as a natural means to couple the macroscopic continuum mechanical description of the aquatic environment with the microscopic discrete atom-istic description of the macromolecule. Multiscale free energy functionals, or multiscale action functionals are constructed as a unified framework to derive the governing equations for the dynamics of different scales and different descriptions. Two types of aqueous macromolecular complexes, ones that are near equilibrium and others that are far from equilibrium, are considered in our formulations. We show that generalized Navier–Stokes equations for the fluid dynamics, generalized Poisson equations or generalized Poisson–Boltzmann equations for electrostatic interactions, and Newton's equation for the molecular dynamics can be derived by the least action principle. These equations are coupled through the continuum-discrete interface whose dynamics is governed by potential driven geometric flows. Comparison is given to classical descriptions of the fluid and electrostatic interactions without geometric flow based micro-macro interfaces. The detailed balance of forces is emphasized in the present work. We further extend the proposed multiscale paradigm to micro-macro analysis of electrohydrodynamics, electrophoresis, fuel cells, and ion channels. We derive generalized Poisson–Nernst–Planck equations that are coupled to generalized Navier–Stokes equations for fluid dynamics, Newton's equation for molecular dynamics, and potential and surface driving geometric flows for the micro-macro interface. For excessively large aqueous macromolecular complexes in chemistry and biology, we further develop differential geometry based multiscale fluid-electro-elastic models to replace the expensive molecular dynamics description with an alternative elasticity formulation. PMID:20169418

A new model for fluid velocity slip on a solid surface.

PubMed

Shu, Jian-Jun; Teo, Ji Bin Melvin; Chan, Weng Kong

2016-10-12

A general adsorption model is developed to describe the interactions between near-wall fluid molecules and solid surfaces. This model serves as a framework for the theoretical modelling of boundary slip phenomena. Based on this adsorption model, a new general model for the slip velocity of fluids on solid surfaces is introduced. The slip boundary condition at a fluid-solid interface has hitherto been considered separately for gases and liquids. In this paper, we show that the slip velocity in both gases and liquids may originate from dynamical adsorption processes at the interface. A unified analytical model that is valid for both gas-solid and liquid-solid slip boundary conditions is proposed based on surface science theory. The corroboration with the experimental data extracted from the literature shows that the proposed model provides an improved prediction compared to existing analytical models for gases at higher shear rates and close agreement for liquid-solid interfaces in general.

Microfluidic on-chip fluorescence-activated interface control system

PubMed Central

Haiwang, Li; Nguyen, N. T.; Wong, T. N.; Ng, S. L.

2010-01-01

A microfluidic dynamic fluorescence-activated interface control system was developed for lab-on-a-chip applications. The system consists of a straight rectangular microchannel, a fluorescence excitation source, a detection sensor, a signal conversion circuit, and a high-voltage feedback system. Aqueous NaCl as conducting fluid and aqueous glycerol as nonconducting fluid were introduced to flow side by side into the straight rectangular microchannel. Fluorescent dye was added to the aqueous NaCl to work as a signal representing the interface position. Automatic control of the liquid interface was achieved by controlling the electroosmotic effect that exists only in the conducting fluid using a high-voltage feedback system. A LABVIEW program was developed to control the output of high-voltage power supply according the actual interface position, and then the interface position is modified as the output of high-voltage power supply. At last, the interface can be moved to the desired position automatically using this feedback system. The results show that the system presented in this paper can control an arbitrary interface location in real time. The effects of viscosity ratio, flow rates, and polarity of electric field were discussed. This technique can be extended to switch the sample flow and droplets automatically. PMID:21173886

Deformation and breakup of liquid-liquid threads, jets, and drops

NASA Astrophysics Data System (ADS)

Doshi, Pankaj

The formation and breakup of two-fluid jets and drops find application in various industrially important processes like microencapsulation, inkjet printing, dispersion and emulsion formation, micro fluidics. Two important aspects of these problems are studied in this thesis. The first regards the study of the dynamics of a two-fluid jet issuing out of a concentric nozzle and breaking into multiple liquid drops. The second aspect concerns the study of the dynamics of liquid-liquid interface rupture. Highly robust and accurate numerical algorithms based on the Galerkin finite element method (G/FEM) and elliptic mesh generation technique are developed. The most important results of this research are the prediction of compound drop formation and volume partitioning between primary drop and satellite drops, which are of critical importance for microencapsulation technology. Another equally important result is computational and experimental demonstration of a self-similar behavior for the rupture of liquid-liquid interface. The final focus is the study of the pinch-off dynamics of generalized-Newtonian fluids with deformation-rate-dependent rheology using asymptotic analysis and numerical computation. A significant result is the first ever prediction of self-similar pinch-off of liquid threads of generalized Newtonian fluids.

Electrohydrodynamic simulation of an electrospray in a colloid thruster

NASA Astrophysics Data System (ADS)

Jugroot, Manish; Forget, Martin; Malardier-Jugroot, Cecile

2012-02-01

A precise understanding of electrosprays is highly interesting as the complexity of micro-technology (such as nano-material processing, spacecraft propulsion and mass-spectrometers) systems increases. A multi-component CFD-based model coupling fluid dynamics, charged species dynamics and electric field is developed. The simulations describe the charged fluid interface with emphasis on the Taylor cone formation and cone-jet transition under the effect of a electric field. The goal is to recapture this transition from a rounded liquid interface into a Taylor cone from an initial uniform distribution, without making assumptions on the behaviour, geometry or charge distribution of the system. The time evolution of the interface highlights the close interaction among space charge, coulombic forces and the surface tension, which appear as governing and competing processes in the transition. The results from the coupled formalism provide valuable insights on the physical phenomena and will be applied to a colloid thruster for small spacecrafts.

Computer program MCAP-TOSS calculates steady-state fluid dynamics of coolant in parallel channels and temperature distribution in surrounding heat-generating solid

NASA Technical Reports Server (NTRS)

Lee, A. Y.

1967-01-01

Computer program calculates the steady state fluid distribution, temperature rise, and pressure drop of a coolant, the material temperature distribution of a heat generating solid, and the heat flux distributions at the fluid-solid interfaces. It performs the necessary iterations automatically within the computer, in one machine run.

Computational study of a self-cleaning process on superhydrophobic surface

NASA Astrophysics Data System (ADS)

Farokhirad, Samaneh

All substances around us are bounded by interfaces. In general, interface between different phases of materials are categorized as fluid-fluid, solid-fluid, and solid-solid. Fluid-fluid interfaces exhibit a distinct behavior by adapting their shape in response to external stimulus. For example, a liquid droplet on a substrate can undergo different wetting morphologies depending on topography and chemical composition of the surface. Fundamentally, interfacial phenomena arise at the limit between two immiscible phases, namely interface. The interface dynamic governs, to a great extent, physical processes such as impact and spreading of two immiscible media, and stabilization of foams and emulsions from break-up and coalescence. One of the recent challenging problems in the interface-driven fluid dynamics is the self-propulsion mechanism of droplets by means of different types of external forces such as electrical potential, or thermal Marangoni effect. Rapid removal of self-propelled droplet from the surface is an essential factor in terms of expense and efficiency for many applications including self-cleaning and enhanced heat and mass transfer to save energy and natural resources. A recent study on superhydrophobic nature of micro- and nanostructures of cicada wings offers a unique way for the self-propulsion process with no external force, namely coalescence-induced self-propelled jumping of droplet which can act effectively at any orientation. The biological importance of this new mechanism is associated with protecting such surfaces from long term exposure to colloidal particles such as microbial colloids and virus particles. Different interfacial phenomena can occur after out-of-plane jumping of droplet. If the departed droplet is landed back by gravity, it may impact and spread on the surface or coalesce with another droplet and again self-peopled itself to jump away from the surface. The complete removal of the propelled droplet to a sufficient distance beyond the boundary layer of the surface can be accomplished with a surface-parallel shear flow. This thesis presents an investigation of the physics involved in the mechanism of coalescence-induced self-propelled jumping of droplet with and without particle presence, through the use of numerical simulation. (Abstract shortened by ProQuest.).

Centrifugal fingering in a curved Hele-Shaw cell: A generalized Euler's elastica shape for the two-fluid interface

NASA Astrophysics Data System (ADS)

Miranda, Jose; Brandao, Rodolfo

2017-11-01

We study a family of generalized elastica-like equilibrium shapes that arise at the interface separating two fluids in a curved rotating Hele-Shaw cell. This family of stationary interface solutions consists of shapes that balance the competing capillary and centrifugal forces in such a curved flow environment. We investigate how the emerging interfacial patterns are impacted by changes in the geometric properties of the curved Hele-Shaw cell. A vortex-sheet formalism is used to calculate the two-fluid interface curvature, and a gallery of possible shapes is provided to highlight a number of peculiar morphological features. A linear perturbation theory is employed to show that the most prominent aspects of these complex stationary patterns can be fairly well reproduced by the interplay of just two interfacial modes. The connection of these dominant modes to the geometry of the curved cell, as well as to the fluid dynamic properties of the flow, is discussed. We thank CNPq (Brazilian Research Council) for financial support under Grant No. 304821/2015-2.

Parallel Three-Dimensional Computation of Fluid Dynamics and Fluid-Structure Interactions of Ram-Air Parachutes

NASA Technical Reports Server (NTRS)

Tezduyar, Tayfun E.

1998-01-01

This is a final report as far as our work at University of Minnesota is concerned. The report describes our research progress and accomplishments in development of high performance computing methods and tools for 3D finite element computation of aerodynamic characteristics and fluid-structure interactions (FSI) arising in airdrop systems, namely ram-air parachutes and round parachutes. This class of simulations involves complex geometries, flexible structural components, deforming fluid domains, and unsteady flow patterns. The key components of our simulation toolkit are a stabilized finite element flow solver, a nonlinear structural dynamics solver, an automatic mesh moving scheme, and an interface between the fluid and structural solvers; all of these have been developed within a parallel message-passing paradigm.

Advances in modelling of biomimetic fluid flow at different scales

PubMed Central

2011-01-01

The biomimetic flow at different scales has been discussed at length. The need of looking into the biological surfaces and morphologies and both geometrical and physical similarities to imitate the technological products and processes has been emphasized. The complex fluid flow and heat transfer problems, the fluid-interface and the physics involved at multiscale and macro-, meso-, micro- and nano-scales have been discussed. The flow and heat transfer simulation is done by various CFD solvers including Navier-Stokes and energy equations, lattice Boltzmann method and molecular dynamics method. Combined continuum-molecular dynamics method is also reviewed. PMID:21711847

Activity induces traveling waves, vortices and spatiotemporal chaos in a model actomyosin layer

NASA Astrophysics Data System (ADS)

Ramaswamy, Rajesh; Jülicher, Frank

2016-02-01

Inspired by the actomyosin cortex in biological cells, we investigate the spatiotemporal dynamics of a model describing a contractile active polar fluid sandwiched between two external media. The external media impose frictional forces at the interface with the active fluid. The fluid is driven by a spatially-homogeneous activity measuring the strength of the active stress that is generated by processes consuming a chemical fuel. We observe that as the activity is increased over two orders of magnitude the active polar fluid first shows spontaneous flow transition followed by transition to oscillatory dynamics with traveling waves and traveling vortices in the flow field. In the flow-tumbling regime, the active polar fluid also shows transition to spatiotemporal chaos at sufficiently large activities. These results demonstrate that level of activity alone can be used to tune the operating point of actomyosin layers with qualitatively different spatiotemporal dynamics.

Numerical Simulations for Turbulent Drag Reduction Using Liquid Infused Surfaces

NASA Astrophysics Data System (ADS)

Arenas-Navarro, Isnardo

Numerical simulations of the turbulent flow over Super Hydrophobic and Liquid Infused Surfaces have been performed in this work. Three different textured surfaces have been considered: longitudinal square bars, transversal square bars and staggered cubes. The numerical code combines an immersed boundary method to mimic the substrate and a level set method to track the interface. Liquid Infused Surfaces reduce the drag by locking a lubricant within structured roughness to facilitate a slip velocity at the surface interface. The conceptual idea is similar to Super Hydrophobic Surfaces, which rely on a lubricant air layer, whereas liquid-infused surfaces use a preferentially wetting liquid lubricant to create a fluid-fluid interface. This slipping interface has been shown to be an effective method of passively reducing skin friction drag in turbulent flows. Details are given on the effect of the viscosity ratio between the two fluids and the dynamics of the interface on drag reduction. An attempt has been made to reconcile Super-Hydrophobic, Liquid Infused and rough wall under the same framework by correlating the drag to the wall normal velocity fluctuations.

Numerical Simulation of Multiphase Magnetohydrodynamic Flow and Deformation of Electrolyte-Metal Interface in Aluminum Electrolysis Cells

NASA Astrophysics Data System (ADS)

Hua, Jinsong; Rudshaug, Magne; Droste, Christian; Jorgensen, Robert; Giskeodegard, Nils-Haavard

2018-06-01

A computational fluid dynamics based multiphase magnetohydrodynamic (MHD) flow model for simulating the melt flow and bath-metal interface deformation in realistic aluminum reduction cells is presented. The model accounts for the complex physics of the MHD problem in aluminum reduction cells by coupling two immiscible fluids, electromagnetic field, Lorentz force, flow turbulence, and complex cell geometry with large length scale. Especially, the deformation of bath-metal interface is tracked directly in the simulation, and the condition of constant anode-cathode distance (ACD) is maintained by moving anode bottom dynamically with the deforming bath-metal interface. The metal pad deformation and melt flow predicted by the current model are compared to the predictions using a simplified model where the bath-metal interface is assumed flat. The effects of the induced electric current due to fluid flow and the magnetic field due to the interior cell current on the metal pad deformation and melt flow are investigated. The presented model extends the conventional simplified box model by including detailed cell geometry such as the ledge profile and all channels (side, central, and cross-channels). The simulations show the model sensitivity to different side ledge profiles and the cross-channel width by comparing the predicted melt flow and metal pad heaving. In addition, the model dependencies upon the reduction cell operation conditions such as ACD, current distribution on cathode surface and open/closed channel top, are discussed.

Surface capillary currents: Rediscovery of fluid-structure interaction by forced evolving boundary theory

NASA Astrophysics Data System (ADS)

Wang, Chunbai; Mitra, Ambar K.

2016-01-01

Any boundary surface evolving in viscous fluid is driven with surface capillary currents. By step function defined for the fluid-structure interface, surface currents are found near a flat wall in a logarithmic form. The general flat-plate boundary layer is demonstrated through the interface kinematics. The dynamics analysis elucidates the relationship of the surface currents with the adhering region as well as the no-slip boundary condition. The wall skin friction coefficient, displacement thickness, and the logarithmic velocity-defect law of the smooth flat-plate boundary-layer flow are derived with the advent of the forced evolving boundary method. This fundamental theory has wide applications in applied science and engineering.

Dynamics of deformation and pinch-off of a migrating compound droplet in a tube

NASA Astrophysics Data System (ADS)

Borthakur, Manash Pratim; Biswas, Gautam; Bandyopadhyay, Dipankar

2018-04-01

A computational fluid dynamic investigation has been carried out to study the dynamics of a moving compound droplet inside a tube. The motions associated with such a droplet is uncovered by solving the axisymmetric Navier-Stokes equations in which the spatiotemporal evolution of a pair of twin-deformable interfaces has been tracked employing the volume-of-fluid approach. The deformations at the interfaces and their subsequent dynamics are found to be stimulated by the subtle interplay between the capillary and viscous forces. The simulations uncover that when a compound drop composed of concentric inner and outer interfaces migrates inside a tube, initially in the unsteady domain of evolution, the inner drop shifts away from the concentric position to reach a morphology of constant eccentricity at the steady state. The coupled motions of the droplets in the unsteady regime causes a continuous deformation of the inner and outer interfaces to obtain a configuration with a (an) prolate (oblate) shaped outer (inner) interface. The magnitudes of capillary number and viscosity ratio are found to have significant influence on the temporal evolution of the interfacial deformations as well as the eccentricity of the droplets. Further, the simulations uncover that, following the asymmetric deformation of the interfaces, the migrating compound droplet can undergo an uncommon breakup stimulated by a rather irregular pinch-off of the outer shell. The breakup is found to initiate with the thinning of the outer shell followed by the pinch-off. Interestingly, the kinetics of the thinning of outer shell is found to follow two distinct power-law regimes—a swiftly thinning stage at the onset followed by a rate limiting stage before pinch-off, which eventually leads to the uncommon breakup of the migrating compound droplets.

STABILITY OF A CYLINDRICAL SOLUTE-SOLVENT INTERFACE: EFFECT OF GEOMETRY, ELECTROSTATICS, AND HYDRODYNAMICS.

PubMed

Li, B O; Sun, Hui; Zhou, Shenggao

The solute-solvent interface that separates biological molecules from their surrounding aqueous solvent characterizes the conformation and dynamics of such molecules. In this work, we construct a solvent fluid dielectric boundary model for the solvation of charged molecules and apply it to study the stability of a model cylindrical solute-solvent interface. The motion of the solute-solvent interface is defined to be the same as that of solvent fluid at the interface. The solvent fluid is assumed to be incompressible and is described by the Stokes equation. The solute is modeled simply by the ideal-gas law. All the viscous force, hydrostatic pressure, solute-solvent van der Waals interaction, surface tension, and electrostatic force are balanced at the solute-solvent interface. We model the electrostatics by Poisson's equation in which the solute-solvent interface is treated as a dielectric boundary that separates the low-dielectric solute from the high-dielectric solvent. For a cylindrical geometry, we find multiple cylindrically shaped equilibrium interfaces that describe polymodal (e.g., dry and wet) states of hydration of an underlying molecular system. These steady-state solutions exhibit bifurcation behavior with respect to the charge density. For their linearized systems, we use the projection method to solve the fluid equation and find the dispersion relation. Our asymptotic analysis shows that, for large wavenumbers, the decay rate is proportional to wavenumber with the proportionality half of the ratio of surface tension to solvent viscosity, indicating that the solvent viscosity does affect the stability of a solute-solvent interface. Consequences of our analysis in the context of biomolecular interactions are discussed.

Dynamic stabilization of classical Rayleigh-Taylor instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piriz, A. R.; Piriz, S. A.; Tahir, N. A.

2011-09-15

Dynamic stabilization of classical Rayleigh-Taylor instability is studied by modeling the interface vibration with the simplest possible wave form, namely, a sequence of Dirac deltas. As expected, stabilization results to be impossible. However, in contradiction to previously reported results obtained with a sinusoidal driving, it is found that in general the perturbation amplitude is larger than in the classical case. Therefore, no beneficial effect can be obtained from the vertical vibration of a Rayleigh-Taylor unstable interface between two ideal fluids.

Development of an Aeroelastic Modeling Capability for Transient Nozzle Side Load Analysis

NASA Technical Reports Server (NTRS)

Wang, Ten-See; Zhao, Xiang; Zhang, Sijun; Chen, Yen-Sen

2013-01-01

Lateral nozzle forces are known to cause severe structural damage to any new rocket engine in development. Currently there is no fully coupled computational tool to analyze this fluid/structure interaction process. The objective of this study was to develop a fully coupled aeroelastic modeling capability to describe the fluid/structure interaction process during the transient nozzle operations. The aeroelastic model composes of three components: the computational fluid dynamics component based on an unstructured-grid, pressure-based computational fluid dynamics formulation, the computational structural dynamics component developed in the framework of modal analysis, and the fluid-structural interface component. The developed aeroelastic model was applied to the transient nozzle startup process of the Space Shuttle Main Engine at sea level. The computed nozzle side loads and the axial nozzle wall pressure profiles from the aeroelastic nozzle are compared with those of the published rigid nozzle results, and the impact of the fluid/structure interaction on nozzle side loads is interrogated and presented.

Generalized elastica patterns in a curved rotating Hele-Shaw cell

NASA Astrophysics Data System (ADS)

Brandão, Rodolfo; Miranda, José A.

2017-08-01

We study a family of generalized elasticalike equilibrium shapes that arise at the interface separating two fluids in a curved rotating Hele-Shaw cell. This family of stationary interface solutions consists of shapes that balance the competing capillary and centrifugal forces in such a curved flow environment. We investigate how the emerging interfacial patterns are impacted by changes in the geometric properties of the curved Hele-Shaw cell. A vortex-sheet formalism is used to calculate the two-fluid interface curvature, and a gallery of possible shapes is provided to highlight a number of peculiar morphological features. A linear perturbation theory is employed to show that the most prominent aspects of these complex stationary patterns can be fairly well reproduced by the interplay of just two interfacial modes. The connection of these dominant modes to the geometry of the curved cell, as well as to the fluid dynamic properties of the flow, is discussed.

Running interfacial waves in a two-layer fluid system subject to longitudinal vibrations.

PubMed

Goldobin, D S; Pimenova, A V; Kovalevskaya, K V; Lyubimov, D V; Lyubimova, T P

2015-05-01

We study the waves at the interface between two thin horizontal layers of immiscible fluids subject to high-frequency horizontal vibrations. Previously, the variational principle for energy functional, which can be adopted for treatment of quasistationary states of free interface in fluid dynamical systems subject to vibrations, revealed the existence of standing periodic waves and solitons in this system. However, this approach does not provide regular means for dealing with evolutionary problems: neither stability problems nor ones associated with propagating waves. In this work, we rigorously derive the evolution equations for long waves in the system, which turn out to be identical to the plus (or good) Boussinesq equation. With these equations one can find all the time-independent-profile solitary waves (standing solitons are a specific case of these propagating waves), which exist below the linear instability threshold; the standing and slow solitons are always unstable while fast solitons are stable. Depending on initial perturbations, unstable solitons either grow in an explosive manner, which means layer rupture in a finite time, or falls apart into stable solitons. The results are derived within the long-wave approximation as the linear stability analysis for the flat-interface state [D.V. Lyubimov and A.A. Cherepanov, Fluid Dynamics 21, 849 (1986)] reveals the instabilities of thin layers to be long wavelength.

Overview of ICE Project: Integration of Computational Fluid Dynamics and Experiments

NASA Technical Reports Server (NTRS)

Stegeman, James D.; Blech, Richard A.; Babrauckas, Theresa L.; Jones, William H.

2001-01-01

Researchers at the NASA Glenn Research Center have developed a prototype integrated environment for interactively exploring, analyzing, and validating information from computational fluid dynamics (CFD) computations and experiments. The Integrated CFD and Experiments (ICE) project is a first attempt at providing a researcher with a common user interface for control, manipulation, analysis, and data storage for both experiments and simulation. ICE can be used as a live, on-tine system that displays and archives data as they are gathered; as a postprocessing system for dataset manipulation and analysis; and as a control interface or "steering mechanism" for simulation codes while visualizing the results. Although the full capabilities of ICE have not been completely demonstrated, this report documents the current system. Various applications of ICE are discussed: a low-speed compressor, a supersonic inlet, real-time data visualization, and a parallel-processing simulation code interface. A detailed data model for the compressor application is included in the appendix.

Fluid Dynamics Problems of Vehicles Operating Near or in the Air-Sea Interface (Problemes de Dynamique des Fluides des Vehicules Evoluant dans ou pres de L’interface Air-Mer).

DTIC Science & Technology

1999-02-01

articulated rotor systems, the rotor blade can deflect several feet and contact the fuselage of the helicopter, resulting in a "tunnel strike " in...tandem rotor configurations; or the tailboom, resulting in a "tailboom strike " in single rotor configurations. The H-46 Sea Knight, a tandem rotor...helicopter used by the U.S. Navy and Marines, has encountered over 100 tunnel strikes since 1964 and still occasionally experiences them. Most tunnel

Working research codes into fluid dynamics education: a science gateway approach

NASA Astrophysics Data System (ADS)

Mason, Lachlan; Hetherington, James; O'Reilly, Martin; Yong, May; Jersakova, Radka; Grieve, Stuart; Perez-Suarez, David; Klapaukh, Roman; Craster, Richard V.; Matar, Omar K.

2017-11-01

Research codes are effective for illustrating complex concepts in educational fluid dynamics courses, compared to textbook examples, an interactive three-dimensional visualisation can bring a problem to life! Various barriers, however, prevent the adoption of research codes in teaching: codes are typically created for highly-specific `once-off' calculations and, as such, have no user interface and a steep learning curve. Moreover, a code may require access to high-performance computing resources that are not readily available in the classroom. This project allows academics to rapidly work research codes into their teaching via a minimalist `science gateway' framework. The gateway is a simple, yet flexible, web interface allowing students to construct and run simulations, as well as view and share their output. Behind the scenes, the common operations of job configuration, submission, monitoring and post-processing are customisable at the level of shell scripting. In this talk, we demonstrate the creation of an example teaching gateway connected to the Code BLUE fluid dynamics software. Student simulations can be run via a third-party cloud computing provider or a local high-performance cluster. EPSRC, UK, MEMPHIS program Grant (EP/K003976/1), RAEng Research Chair (OKM).

Experimental investigation of the displacement dynamics during biphasic flow in porous media

NASA Astrophysics Data System (ADS)

Ayaz, Monem; Toussaint, Renaud; Måløy, Knut-Jørgen; Schafer, Gerhard

2016-04-01

We experimentally study the interface dynamics of an immiscible fluid as it displaces a fully saturated porous medium. The system is confined by a vertically oriented Hele-Shaw cell, with piezoelectric type acoustic sensors mounted along the centerline. During drainage potential surface energy is stored at the interface up to a given threshold in pressure, at which an instability occurs as new pores are invaded and the radius of curvature of the interface increases locally, the energy gets released, and part of this energy is detectable as acoustic emission. By detecting pore-scale events emanating from the interface at various points, we look to develop techniques for localizing the displacement front. To assess the quality, optical monitoring is done using a high speed camera.In our study we also aim to gain further insight into the interface dynamics by varying parameters such as the effective gravity, and the invasion speed and using other methods of probing the system such as active tomography. We here present our preliminary results of this study.

Fingering dynamics on the adsorbed solute with influence of less viscous and strong sample solvent.

PubMed

Rana, Chinar; Mishra, Manoranjan

2014-12-07

Viscous fingering is a hydrodynamic instability that sets in when a low viscous fluid displaces a high viscous fluid and creates complex patterns in porous media flows. Fundamental facets of the displacement process, such as the solute concentration distribution, spreading length, and the solute mixing, depend strongly on the type of pattern created by the unstable interface of the underlying fluids. In the present study, the frontal interface of the sample shows viscous fingering and the strong solvent causes the retention of the solute to depend on the solvent concentration. This work presents a computational investigation to explore the effect of the underlying physico-chemical phenomena, (i.e., the combined effects of solvent strength, retention, and viscous fingering) on the dynamics of the adsorbed solute. A linear adsorption isotherm has been assumed between the mobile and stationary phases of the solute. We carried out the numerical simulations by considering a rectangular Hele-Shaw cell as an analog to 2D-porous media containing a three component system (displacing fluid, sample solvent, solute) to map out the evolution of the solute concentration. We observed that viscous fingering at the frontal interface of the strong sample solvent intensifies the band broadening of the solute zone. Also notable increase in the spreading dynamics of the solute has been observed for less viscous and strong sample solvent as compared to the high viscous sample slices or in the pure dispersive case. On the contrary, the solute gets intensively mixed at early times for more viscous sample in comparison to less viscous one. The results of the simulations are in qualitative agreement with the behavior observed in the liquid chromatography column experiments.

Domain decomposition algorithms and computation fluid dynamics

NASA Technical Reports Server (NTRS)

Chan, Tony F.

1988-01-01

In the past several years, domain decomposition was a very popular topic, partly motivated by the potential of parallelization. While a large body of theory and algorithms were developed for model elliptic problems, they are only recently starting to be tested on realistic applications. The application of some of these methods to two model problems in computational fluid dynamics are investigated. Some examples are two dimensional convection-diffusion problems and the incompressible driven cavity flow problem. The construction and analysis of efficient preconditioners for the interface operator to be used in the iterative solution of the interface solution is described. For the convection-diffusion problems, the effect of the convection term and its discretization on the performance of some of the preconditioners is discussed. For the driven cavity problem, the effectiveness of a class of boundary probe preconditioners is discussed.

Insect flight on fluid interfaces: a chaotic interfacial oscillator

NASA Astrophysics Data System (ADS)

Mukundarajan, Haripriya; Prakash, Manu

2013-11-01

Flight is critical to the dominance of insect species on our planet, with about 98 percent of insect species having wings. How complex flight control systems developed in insects is unknown, and arboreal or aquatic origins have been hypothesized. We examine the biomechanics of aquatic origins of flight. We recently reported discovery of a novel mode of ``2D flight'' in Galerucella beetles, which skim along an air-water interface using flapping wing flight. This unique flight mode is characterized by a balance between capillary forces from the interface and biomechanical forces exerted by the flapping wings. Complex interactions on the fluid interface form capillary wave trains behind the insect, and produce vertical oscillations at the surface due to non-linear forces arising from deformation of the fluid meniscus. We present both experimental observations of 2D flight kinematics and a dynamic model explaining the observed phenomena. Careful examination of this interaction predicts the chaotic nature of interfacial flight and takeoff from the interface into airborne flight. The role of wingbeat frequency, stroke plane angle and body angle in determining transition between interfacial and fully airborne flight is highlighted, shedding light on the aquatic theory of flight evolution.

Real-Time Wing-Vortex and Pressure Distribution Estimation on Wings Via Displacements and Strains in Unsteady and Transitional Flight Conditions

DTIC Science & Technology

2016-09-07

approach in co simulation with fluid-dynamics solvers is used. An original variational formulation is developed for the inverse problem of...by the inverse solution meshing. The same approach is used to map the structural and fluid interface kinematics and loads during the fluid structure...co-simulation. The inverse analysis is verified by reconstructing the deformed solution obtained with a corresponding direct formulation, based on

Effect of wettability on two-phase quasi-static displacement: Validation of two pore scale modeling approaches

NASA Astrophysics Data System (ADS)

Verma, Rahul; Icardi, Matteo; Prodanović, Maša

2018-05-01

Understanding of pore-scale physics for multiphase flow in porous media is essential for accurate description of various flow phenomena. In particular, capillarity and wettability strongly influence capillary pressure-saturation and relative permeability relationships. Wettability is quantified by the contact angle of the fluid-fluid interface at the pore walls. In this work we focus on the non-trivial interface equilibria in presence of non-neutral wetting and complex geometries. We quantify the accuracy of a volume-of-fluid (VOF) formulation, implemented in a popular open-source computational fluid dynamics code, compared with a new formulation of a level set (LS) method, specifically developed for quasi-static capillarity-dominated displacement. The methods are tested in rhomboidal packings of spheres for a range of contact angles and for different rhomboidal configurations and the accuracy is evaluated against the semi-analytical solutions obtained by Mason and Morrow (1994). While the VOF method is implemented in a general purpose code that solves the full Navier-Stokes (NS) dynamics in a finite volume formulation, with additional terms to model surface tension, the LS method is optimized for the quasi-static case and, therefore, less computationally expensive. To overcome the shortcomings of the finite volume NS-VOF system for low capillary number flows, and its computational cost, we introduce an overdamped dynamics and a local time stepping to speed up the convergence to the steady state, for every given imposed pressure gradient (and therefore saturation condition). Despite these modifications, the methods fundamentally differ in the way they capture the interface, as well as in the number of equations solved and in the way the mean curvature (or equivalently capillary pressure) is computed. This study is intended to provide a rigorous validation study and gives important indications on the errors committed by these methods in solving more complex geometry and dynamics, where usually many sources of errors are interplaying.

Structure and Dynamics of Forsterite-scCO2/H2O Interfaces as a Function of Water Content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerisit, Sebastien N.; Weare, John H.; Felmy, Andrew R.

Molecular dynamics (MD) simulations of forsterite surfaces in contact with supercritical carbon dioxide (scCO2) fluids of varying water content were performed to determine the partition of water between the scCO2 fluid and the mineral surface, the nature of CO2 and H2O bonding at the interface, and the regions of the interface that may be conducive to HxCO3(2-x)- formation. Calculations of the free energy of the associative adsorption of water onto the (010) forsterite surface from the scCO2 phase indicated that the formation of a water film up to three-monolayer thick can be exothermic even for water contents below the watermore » saturation concentration of the scCO2 fluid. In MD simulations of scCO2/H2O mixtures in contact with the (010) forsterite surface, H2O was found to readily displace CO2 at the surface and, therefore, CO2 directly contacted the surface only for water coverages below two monolayers. For thicker water films, a two-monolayer hydration layer formed that CO2 could not penetrate. Simulations of the hydroxylated (010) surface and of the (011) surface suggested that this conclusion can be extended to forsterite surfaces with different surface structures and/or compositions. The density, diffusion, and degree of hydration of CO2 as well as the extent of CO2/H2O mixing at the interface were all predicted to depend strongly on the thickness of the water-rich film, i.e., on the water content of the scCO2 fluid.« less

The middeck 0-gravity dynamics experiment

NASA Technical Reports Server (NTRS)

Crawley, Edward F.; Vanschoor, Marthinus C.; Bokhour, Edward B.

1993-01-01

The Middeck 0-Gravity Dynamics Experiment (MODE), flown onboard the Shuttle STS-48 Mission, consists of three major elements: the Experiment Support Module, a dynamics test bed providing computer experiment control, analog signal conditioning, power conditioning, an operator interface consisting of a keypad and display, experiment electrical and thermal control, and archival data storage: the Fluid Test Article assembly, used to investigate the dynamics of fluid-structure interaction in 0-gravity; and the Structural Test Article for investigating the open-loop dynamics of structures in 0-gravity. Deployable, erectable, and rotary modules were assembled to form three one- and two-dimensional structures, in which variations in bracing wire and rotary joint preload could be introduced. Change in linear modal parameters as well as the change in nonlinear nature of the response is examined. Trends in modal parameters are presented as a function of force amplitude, joint preload, and ambient gravity. An experimental study of the lateral slosh behavior of contained fluids is also presented. A comparison of the measured earth and space results identifies and highlights the effects of gravity on the linear and nonlinear slosh behavior of these fluids.

Hydro-Mechanical Modelling of Slow Slip Phenomena at the Subduction Interface.

NASA Astrophysics Data System (ADS)

Petrini, C.; Gerya, T.; Madonna, C.; van Dinther, Y.

2016-12-01

Subduction zones experience a spectrum of slip phenomena, ranging from large devastating megathrust earthquakes to aseismic slow slip events. Slow slip events, lasting hours to years and being perceptible only by instruments, are believed to have the capability to induce large earthquakes. It is also repeatedly proposed that such slow events are controlled by fluid-rock interactions along the subduction interface, thus calling for development of fully coupled seismo-hydro-mechanical modeling approaches to identify their physics and controlling parameters. We present a newly developed finite difference visco-elasto-plastic numerical code with marker-in-cell technique, which fully couples mechanical deformation and fluid flow. We use this to investigate how the presence of fluids in the pore space of a (de)compacting rock matrix affects elastic stress accumulation and release along a fluid-bearing subduction interface. The model simulates the spontaneous occurrence of quasi-periodic slow slip phenomena along self-consistently forming highly localized shearbands, which accommodate shear displacement between two plates. The produced elastic rebound events show a slip velocity on the order of cm/yr, which is in good agreement with measured data. The governing gradual strength decrease along the slowly propagating shear bands is related to a drop in total pressure caused by shear localization at nearly constant (slightly decreasing) fluid pressure. Gradual reduction of the difference between the total and fluid pressure decreases brittle/plastic strength of fluid-bearing rocks along the shear bands, thus providing a dynamic feedback mechanism for the accumulated elastic stress release at the subduction interface.

Microfluidic flow spectrometer

NASA Astrophysics Data System (ADS)

Vázquez-Vergara, Pamela; Torres Rojas, Aimee M.; Guevara-Pantoja, Pablo E.; Corvera Poiré, Eugenia; Caballero-Robledo, Gabriel A.

2017-07-01

We present a microfluidic device which allows one to study the dynamics of oscillatory flows for a frequency range between 1 and 300 Hz. The fluid in the microdevice could be Newtonian, viscoelastic, or even a biofluid, since the device is made of PMMA, which makes it biocompatible and free of elastomeric elements. Coupling a piezoelectric to a micropiston allows one to impose periodic movement to the fluid, with zero mean flow and amplitudes of up to 20~μ m, within the microchannels in which the dynamics is studied. The use of a fast camera coupled to a microscope allows one to study the dynamics of 1~μ m tracer particles and interfaces at an image acquisition rate as fast as 5000 frames per second. The fabrication of the device is easy and cost-effective, since it is based on the use of a micromilling machine. The dynamics of a Newtonian fluid is studied as a proof of principle.

Mesoscopic electrohydrodynamic simulations of binary colloidal suspensions.

PubMed

Rivas, Nicolas; Frijters, Stefan; Pagonabarraga, Ignacio; Harting, Jens

2018-04-14

A model is presented for the solution of electrokinetic phenomena of colloidal suspensions in fluid mixtures. We solve the discrete Boltzmann equation with a Bhatnagar-Gross-Krook collision operator using the lattice Boltzmann method to simulate binary fluid flows. Solvent-solvent and solvent-solute interactions are implemented using a pseudopotential model. The Nernst-Planck equation, describing the kinetics of dissolved ion species, is solved using a finite difference discretization based on the link-flux method. The colloids are resolved on the lattice and coupled to the hydrodynamics and electrokinetics through appropriate boundary conditions. We present the first full integration of these three elements. The model is validated by comparing with known analytic solutions of ionic distributions at fluid interfaces, dielectric droplet deformations, and the electrophoretic mobility of colloidal suspensions. Its possibilities are explored by considering various physical systems, such as breakup of charged and neutral droplets and colloidal dynamics at either planar or spherical fluid interfaces.

Mesoscopic electrohydrodynamic simulations of binary colloidal suspensions

NASA Astrophysics Data System (ADS)

Rivas, Nicolas; Frijters, Stefan; Pagonabarraga, Ignacio; Harting, Jens

2018-04-01

A model is presented for the solution of electrokinetic phenomena of colloidal suspensions in fluid mixtures. We solve the discrete Boltzmann equation with a Bhatnagar-Gross-Krook collision operator using the lattice Boltzmann method to simulate binary fluid flows. Solvent-solvent and solvent-solute interactions are implemented using a pseudopotential model. The Nernst-Planck equation, describing the kinetics of dissolved ion species, is solved using a finite difference discretization based on the link-flux method. The colloids are resolved on the lattice and coupled to the hydrodynamics and electrokinetics through appropriate boundary conditions. We present the first full integration of these three elements. The model is validated by comparing with known analytic solutions of ionic distributions at fluid interfaces, dielectric droplet deformations, and the electrophoretic mobility of colloidal suspensions. Its possibilities are explored by considering various physical systems, such as breakup of charged and neutral droplets and colloidal dynamics at either planar or spherical fluid interfaces.

Surface Instability of Liquid Propellant under Vertical Oscillatory Forcing

NASA Technical Reports Server (NTRS)

Yang, H. Q.; Peugeot, John

2011-01-01

Fluid motion in a fuel tank produced during thrust oscillations can circulate sub-cooled hydrogen near the liquid-vapor interface resulting in increased condensation and ullage pressure collapse. The first objective of this study is to validate the capabilities of a Computational Fluid Dynamics (CFD) tool, CFD-ACE+, in modeling the fundamental interface transition physics occurring at the propellant surface. The second objective is to use the tool to assess the effects of thrust oscillations on surface dynamics. Our technical approach is to first verify the CFD code against known theoretical solutions, and then validate against existing experiments for small scale tanks and a range of transition regimes. A 2D axisymmetric, multi-phase model of gases, liquids, and solids is used to verify that CFD-ACE+ is capable of modeling fluid-structure interaction and system resonance in a typical thrust oscillation environment. Then, the 3D mode is studied with an assumed oscillatory body force to simulate the thrust oscillating effect. The study showed that CFD modeling can capture all of the transition physics from solid body motion to standing surface wave and to droplet ejection from liquid-gas interface. Unlike the analytical solutions established during the 1960 s, CFD modeling is not limited to the small amplitude regime. It can extend solutions to the nonlinear regime to determine the amplitude of surface waves after the onset of instability. The present simulation also demonstrated consistent trends from numerical experiments through variation of physical properties from low viscous fluid to high viscous fluids, and through variation of geometry and input forcing functions. A comparison of surface wave patterns under various forcing frequencies and amplitudes showed good agreement with experimental observations. It is concluded that thrust oscillations can cause droplet formation at the interface, which results in increased surface area and enhanced heat transfer between the liquid and gas phases as the ejected droplets travel well into the warmer gas region.

Transport Phenomena of Water in Molecular Fluidic Channels

PubMed Central

Vo, Truong Quoc; Kim, BoHung

2016-01-01

In molecular-level fluidic transport, where the discrete characteristics of a molecular system are not negligible (in contrast to a continuum description), the response of the molecular water system might still be similar to the continuum description if the time and ensemble averages satisfy the ergodic hypothesis and the scale of the average is enough to recover the classical thermodynamic properties. However, even in such cases, the continuum description breaks down on the material interfaces. In short, molecular-level liquid flows exhibit substantially different physics from classical fluid transport theories because of (i) the interface/surface force field, (ii) thermal/velocity slip, (iii) the discreteness of fluid molecules at the interface and (iv) local viscosity. Therefore, in this study, we present the result of our investigations using molecular dynamics (MD) simulations with continuum-based energy equations and check the validity and limitations of the continuum hypothesis. Our study shows that when the continuum description is subjected to the proper treatment of the interface effects via modified boundary conditions, the so-called continuum-based modified-analytical solutions, they can adequately predict nanoscale fluid transport phenomena. The findings in this work have broad effects in overcoming current limitations in modeling/predicting the fluid behaviors of molecular fluidic devices. PMID:27650138

Musical Interfaces: Visualization and Reconstruction of Music with a Microfluidic Two-Phase Flow

PubMed Central

Mak, Sze Yi; Li, Zida; Frere, Arnaud; Chan, Tat Chuen; Shum, Ho Cheung

2014-01-01

Detection of sound wave in fluids can hardly be realized because of the lack of approaches to visualize the very minute sound-induced fluid motion. In this paper, we demonstrate the first direct visualization of music in the form of ripples at a microfluidic aqueous-aqueous interface with an ultra-low interfacial tension. The interfaces respond to sound of different frequency and amplitude robustly with sufficiently precise time resolution for the recording of musical notes and even subsequent reconstruction with high fidelity. Our work shows the possibility of sensing and transmitting vibrations as tiny as those induced by sound. This robust control of the interfacial dynamics enables a platform for investigating the mechanical properties of microstructures and for studying frequency-dependent phenomena, for example, in biological systems. PMID:25327509

Pore-scale modeling of phase change in porous media

NASA Astrophysics Data System (ADS)

Juanes, Ruben; Cueto-Felgueroso, Luis; Fu, Xiaojing

2017-11-01

One of the main open challenges in pore-scale modeling is the direct simulation of flows involving multicomponent mixtures with complex phase behavior. Reservoir fluid mixtures are often described through cubic equations of state, which makes diffuse interface, or phase field theories, particularly appealing as a modeling framework. What is still unclear is whether equation-of-state-driven diffuse-interface models can adequately describe processes where surface tension and wetting phenomena play an important role. Here we present a diffuse interface model of single-component, two-phase flow (a van der Waals fluid) in a porous medium under different wetting conditions. We propose a simplified Darcy-Korteweg model that is appropriate to describe flow in a Hele-Shaw cell or a micromodel, with a gap-averaged velocity. We study the ability of the diffuse-interface model to capture capillary pressure and the dynamics of vaporization/condensation fronts, and show that the model reproduces pressure fluctuations that emerge from abrupt interface displacements (Haines jumps) and from the break-up of wetting films.

Atomistic Modeling of the Fluid-Solid Interface in Simple Fluids

NASA Astrophysics Data System (ADS)

Hadjiconstantinou, Nicolas; Wang, Gerald

2017-11-01

Fluids can exhibit pronounced structuring effects near a solid boundary, typically manifested in a layered structure that has been extensively shown to directly affect transport across the interface. We present and discuss several results from molecular-mechanical modeling and molecular-dynamics (MD) simulations aimed at characterizing the structure of the first fluid layer directly adjacent to the solid. We identify a new dimensionless group - termed the Wall number - which characterizes the degree of fluid layering, by comparing the competing effects of wall-fluid interaction and thermal energy. We find that in the layering regime, several key features of the first layer layer - including its distance from the solid, its width, and its areal density - can be described using mean-field-energy arguments, as well as asymptotic analysis of the Nernst-Planck equation. For dense fluids, the areal density and the width of the first layer can be related to the bulk fluid density using a simple scaling relation. MD simulations show that these results are broadly applicable and robust to the presence of a second confining solid boundary, different choices of wall structure and thermalization, strengths of fluid-solid interaction, and wall geometries.

Numerical Treatment of Stokes Solvent Flow and Solute-Solvent Interfacial Dynamics for Nonpolar Molecules.

PubMed

Sun, Hui; Zhou, Shenggao; Moore, David K; Cheng, Li-Tien; Li, Bo

2016-05-01

We design and implement numerical methods for the incompressible Stokes solvent flow and solute-solvent interface motion for nonpolar molecules in aqueous solvent. The balance of viscous force, surface tension, and van der Waals type dispersive force leads to a traction boundary condition on the solute-solvent interface. To allow the change of solute volume, we design special numerical boundary conditions on the boundary of a computational domain through a consistency condition. We use a finite difference ghost fluid scheme to discretize the Stokes equation with such boundary conditions. The method is tested to have a second-order accuracy. We combine this ghost fluid method with the level-set method to simulate the motion of the solute-solvent interface that is governed by the solvent fluid velocity. Numerical examples show that our method can predict accurately the blow up time for a test example of curvature flow and reproduce the polymodal (e.g., dry and wet) states of hydration of some simple model molecular systems.

Numerical Treatment of Stokes Solvent Flow and Solute-Solvent Interfacial Dynamics for Nonpolar Molecules

PubMed Central

Sun, Hui; Zhou, Shenggao; Moore, David K.; Cheng, Li-Tien; Li, Bo

2015-01-01

We design and implement numerical methods for the incompressible Stokes solvent flow and solute-solvent interface motion for nonpolar molecules in aqueous solvent. The balance of viscous force, surface tension, and van der Waals type dispersive force leads to a traction boundary condition on the solute-solvent interface. To allow the change of solute volume, we design special numerical boundary conditions on the boundary of a computational domain through a consistency condition. We use a finite difference ghost fluid scheme to discretize the Stokes equation with such boundary conditions. The method is tested to have a second-order accuracy. We combine this ghost fluid method with the level-set method to simulate the motion of the solute-solvent interface that is governed by the solvent fluid velocity. Numerical examples show that our method can predict accurately the blow up time for a test example of curvature flow and reproduce the polymodal (e.g., dry and wet) states of hydration of some simple model molecular systems. PMID:27365866

A Software Upgrade of the NASA Aeroheating Code "MINIVER"

NASA Technical Reports Server (NTRS)

Louderback, Pierce Mathew

2013-01-01

Computational Fluid Dynamics (CFD) is a powerful and versatile tool simulating fluid and thermal environments of launch and re-entry vehicles alike. Where it excels in power and accuracy, however, it lacks in speed. An alternative tool for this purpose is known as MINIVER, an aeroheating code widely used by NASA and within the aerospace industry. Capable of providing swift, reasonably accurate approximations of the fluid and thermal environment of launch vehicles, MINIVER is used where time is of the essence and accuracy need not be exact. However, MINIVER is an old, aging tool: running on a user-unfriendly, legacy command-line interface, it is difficult for it to keep pace with more modem software tools. Florida Institute of Technology was tasked with the construction of a new Graphical User Interface (GUI) that implemented the legacy version's capabilities and enhanced them with new tools and utilities. This thesis provides background to the legacy version of the program, the progression and final version of a modem user interface, and benchmarks to demonstrate its usefulness.

The growth and breakdown of a vortex-pair in a stably stratified fluid

NASA Astrophysics Data System (ADS)

Advaith, S.; Tinaikar, Aashay; Manu, K. V.; Basu, Saptarshi

2017-11-01

Vortex interaction with density stratification is ubiquitous in nature and applied to various engineering applications. Present study have characterized the spatial and temporal dynamics of the interaction between a vortex and a density stratified interface. The present work is prompted by our research on single tank Thermal Energy Storage (TES) system used in concentrated solar power (CSP) plants where hot and cold fluids are separated by means of density stratification. Rigorous qualitative (High speed Shadowgraph) and quantitative (high speed PIV) studies enable us to have great understanding about vortex formation, propagation, interaction dynamics with density stratified interface, resulted plume characteristics and so on. We have categorized this interaction phenomena in to three different cases based on its nature as non-penetrative, partial penetrative and extensively penetrative. Along with that we have proposed a regime map consisting non-dimensional parameters like Reynolds, Richardson and Atwood numbers which predicts the occurrence above mentioned cases.

The Effect of the Density Ratio on the Nonlinear Dynamics of the Unstable Fluid Interface

NASA Technical Reports Server (NTRS)

Abarzhi, S. I.

2003-01-01

Here we report multiple harmonic theoretical solutions for a complete system of conservation laws, which describe the large-scale coherent dynamics in RTI and RMI for fluids with a finite density ratio in the general three-dimensional case. The analysis yields new properties of the bubble front dynamics. In either RTI or RMI, the obtained dependencies of the bubble velocity and curvature on the density ratio differ qualitatively and quantitatively from those suggested by the models of Sharp (1984), Oron et al. (2001), and Goncharov (2002). We show explicitly that these models violate the conservation laws. For the first time, our theory reveals an important qualitative distinction between the dynamics of the RT and RM bubbles.

Indirect measurement of the solid/liquid interface using the minimization technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, H.; Chun, M.

1985-11-01

The phenomenon of solidification of a flowing fluid in a vertical tube is closely related to the relocation dynamics of molten nuclear fuels in hypothetical core-disruptive accidents of a liquid-metal fast breeder reactor. The knowledge of the transient shape and the position of the liquid/solid interface is of practical importance in analysis of phase change processes. Sparrow and Broadbent directly measured the solid liquid interface via experiments, whereas Viskanta observed the solid/liquid interface motion via a photographic method. In this paper, a new method to predict the transient position of the solid/liquid interface is developed. This method is based onmore » the minimization technique. To use this method one needs the temperature of the wall on which the phase change is to take place. The new technique is useful, in particular, for the case of inward solidification of a flowing fluid in a tube where direct measurement of the solid/liquid interface is not possible, whereas the tube wall temperature measurement is relatively easy.« less

Charging and discharging of single colloidal particles at oil/water interfaces

PubMed Central

Gao, Peng; Xing, XiaoChen; Li, Ye; Ngai, To; Jin, Fan

2014-01-01

The physical behavior of solid colloids trapped at a fluid-fluid interface remains in itself an open fundamental issue. Here, we show that the gradients of surface tension can induce particles to jet towards the oil/water interface with velocities as high as ≈ 60 mm/s when particle suspensions come in contact with the interface. We hypothesize that rubbing between the particles and oil lead to the spontaneous accumulation of negative charges on the hemisphere of those interfacial particles that contact the oil phase by means of triboelectrification. The charging process is highly dependent on the sliding distances, and gives rise to long-ranged repulsions that protect interfacial particles from coagulating at the interface by the presence of electrolyte. These triboelectric charges, however, are compensated within several hours, which affect the stability of interfacial particles. Importantly, by charging different kinds of colloidal particles using various spreading solvents and dispersion methods, we have demonstrated that charging and discharging of single colloidal particles at oil/water interfaces impacts a broad range of dynamical behavior. PMID:24786477

Dynamics of Liquids in Edges and Corners (DYLCO): IML-2 Experiment for the BDPU

NASA Technical Reports Server (NTRS)

Langbein, D.; Weislogel, M.

1998-01-01

Knowledge of the behavior of fluids possessing free surfaces is important to many fluid systems, particularly in space, where the normally subtle effects of surface wettability play a more dramatic and often surprising role. DYLCO for the IML-2 mission was proposed as a simple experiment to probe the particular behavior of capillary surfaces in containers of irregular cross section. Temperature control was utilized to vary the fluid-solid contact angle, a questionable thermodynamic parameter of the system, small changes in which can dramatically influence the configuration, stability, and flow of a capillary surface. Container shapes, test fluid, and temperature ranges were selected for observing both local changes in interface curvature as well as a global change in fluid orientation due to a critical wetting phenomenon. The experiment hardware performed beyond what was expected and fluid interfaces could be readily digitized post flight to show the dependence of the interface curvature on temperature. For each of the containers tested surfaces were observed which did not satisfy the classic equations for the prediction of interface shape with constant contact angle boundary condition. This is explained by the presence of contact angle hysteresis arising from expansion and contraction of the liquid during the heating and cooling steps of the test procedure. More importantly, surfaces exceeding the critical surface curvature required for critical wetting were measured, yet no wetting was observed. These findings are indeed curious and pose key questions concerning the role of hysteresis for this critical wetting phenomena. The stability of such surfaces was determined numerically and it is shown that stability is enhance (reduced) when a surface is in its 'advancing' ('receding') state, The analysis shows complete instability as the critical wetting condition is reached. The case of ideal dynamic wetting is addressed analytically in detail with results of significant flow characteristics presented in closed form. The solutions indicate a square root of T dependence of the capillary 'rise' rate which is corroborated by drop tower tests. The analysis clearly shows that infinite time is necessary for surfaces to reorient at the critical wetting transition.

Blocking Gastric Lipase Adsorption and Displacement Processes with Viscoelastic Biopolymer Adsorption Layers.

PubMed

Scheuble, Nathalie; Lussi, Micha; Geue, Thomas; Carrière, Frédéric; Fischer, Peter

2016-10-10

Delayed fat digestion might help to fight obesity. Fat digestion begins in the stomach by adsorption of gastric lipases to oil/water interfaces. In this study we show how biopolymer covered interfaces can act as a physical barrier for recombinant dog gastric lipase (rDGL) adsorption and thus gastric lipolysis. We used β-lactoglobulin (β-lg) and thermosensitive methylated nanocrystalline cellulose (metNCC) as model biopolymers to investigate the role of interfacial fluid dynamics and morphology for interfacial displacement processes by rDGL and polysorbate 20 (P20) under gastric conditions. Moreover, the influence of the combination of the flexible β-lg and the elastic metNCC was studied. The interfaces were investigated combining interfacial techniques, such as pendant drop, interfacial shear and dilatational rheology, and neutron reflectometry. Displacement of biopolymer layers depended mainly on the fluid dynamics and thickness of the layers, both of which were drastically increased by the thermal induced gelation of metNCC at body temperature. Soft, thin β-lg interfaces were almost fully displaced from the interface, whereas the composite β-lg-metNCC layer thermogelled to a thick interfacial layer incorporating β-lg as filler material and therefore resisted higher shear forces than a pure metNCC layer. Hence, with metNCC alone lipolysis by rDGL was inhibited, whereas the layer performance could be increased by the combination with β-lg.

Effects of Force Fields on Interface Dynamics, in view of Two-Phase Heat Transfer Enhancement and Phase Management for Space Applications

NASA Astrophysics Data System (ADS)

Di Marco, P.; Saccone, G.

2017-11-01

On earth, gravity barely influences the dynamics of interfaces. For what concerns bubbles, buoyancy governs the dynamics of boiling mechanism and thus affects boiling heat transfer capacity. While, for droplets, the coupled effects of wettability and gravity affects interface exchanges. In space, in the lack of gravity, rules are changed and new phenomena come into play. The present work is aimed to study the effects of electric field on the shape and behaviour of bubbles and droplets in order to understand how to handle microgravity applications; in particular, the replacement of gravity with electric field and their coupled effects are evaluated. The experiments spread over different setups, gravity conditions, working fluids, interface conditions. Droplets and bubbles have been analysed with and without electric field, with and without (adiabatic) heat and mass transfer across the interface. Furthermore, the results of the 4 ESA Parabolic Flight Campaigns (PFC 58, 60, 64 & 66), for adiabatic bubbles, adiabatic droplets and evaporating droplets, will be summarized, discussed, and compared with the ground tests.

Structure and Dynamics of Interfaces: Drops and Films

NASA Technical Reports Server (NTRS)

Mann, J. Adin, Jr.; Mann, Elizabeth K.; Meyer, William V.; Neumann, A. Wilhelm; Tavana, Hossein

2015-01-01

We aim to acquire measurements of the structure and dynamics of certain liquid-fluid interfaces using an ensemble of techniques in collaboration: (1) Total internal reflection (TIR) Surface light scattering spectroscopy (SLSS), (2) Brewster angle microscopy (BAM), and (3) Drop-shape analysis. SLSS and BAM can be done on a shared interfacial footprint. Results using a 50-50 mixture of pentane-isohexane, which extends the range of NASA's Confined Vapor Bubble (CVB) experiment, yield surface tension results that differ from the expected Langmuir Fit. These results were confirmed using both the SLSS and drop-shape analysis approaches.

Marangoni-driven chemotaxis, chemotactic collapse, and the Keller-Segel equation

NASA Astrophysics Data System (ADS)

Shelley, Michael; Masoud, Hassan

2013-11-01

Almost by definition, chemotaxis involves the biased motion of motile particles along gradients of a chemical concentration field. Perhaps the most famous model for collective chemotaxis in mathematical biology is the Keller-Segel model, conceived to describe collective aggregation of slime mold colonies in response to an intrinsically produced, and diffusing, chemo-attractant. Heavily studied, particularly in 2D where the system is ``super-critical'', it has been proved that the KS model can develop finite-time singularities - so-called chemotactic collapse - of delta-function type. Here, we study the collective dynamics of immotile particles bound to a 2D interface above a 3D fluid. These particles are chemically active and produce a diffusing field that creates surface-tension gradients along the surface. The resultant Marangoni stresses create flows that carry the particles, possibly concentrating them. Remarkably, we show that this system involving 3D diffusion and fluid dynamics, exactly yields the 2D Keller-Segel model for the surface-flow of active particles. We discuss the consequences of collapse on the 3D fluid dynamics, and generalizations of the fluid-dynamical model.

Molecular simulation of fluid mixtures in bulk and at solid-liquid interfaces

NASA Astrophysics Data System (ADS)

Kern, Jesse L.

The properties of a diverse range of mixture systems at interfaces are investigated using a variety of computational techniques. Molecular simulation is used to examine the thermodynamic, structural, and transport properties of heterogeneous systems of theoretical and practical importance. The study of binary hard-sphere mixtures at a hard wall demonstrates the high accuracy of recently developed classical-density functionals. The study of aluminum--gallium solid--liquid heterogeneous interfaces predicts a significant amount of prefreezing of the liquid by adopting the structure of the solid surface. The study of ethylene-expanded methanol within model silica mesopores shows the effect of confinement and surface functionalzation on the mixture composition and transport inside of the pores. From our molecular-dynamics study of binary hard-sphere fluid mixtures at a hard wall, we obtained high-precision calculations of the wall-fluid interfacial free energies, gamma. We have considered mixtures of varying diameter ratio, alpha = 0.7,0.8,0.9; mole fraction, x 1 = 0.25,0.50,0.75; and packing fraction, eta < 0.50. Using Gibbs-Cahn Integration, gamma is calculated from the system pressure, chemical potentials, and density profiles. Recent classical density-functional theory predictions agree very well with our results. Structural, thermodynamic, and transport properties of the aluminum--gallium solid--liquid interface at 368 K are obtained for the (100), (110), and (111) orientations using molecular dynamics. Density, potential energy, stress, and diffusion profiles perpendicular to the interface are calculated. The layers of Ga that form on the Al surface are strongly adsorbed and take the in-plane structure of the underlying crystal layers for all orientations, which results in significant compressive stress on the Ga atoms. Bulk methanol--ethylene mixtures under vapor-liquid equilibrium conditions have been characterized using Monte Carlo and molecular dynamics. The simulated vapor-liquid coexistence curves for the pure-component and binary mixtures agree well with experiment, as do the mixture volumetric expansion results. Using chemical potentials obtained from the bulk simulations, the filling of a number of model silica mesopores with ethylene and methanol is simulated. We report the compositions of the confined fluid mixtures over a range of pressures and for three degrees of nominal pore hydrophobicity.

Measurements of acoustic surface waves on fluid-filled porous rocks

NASA Astrophysics Data System (ADS)

Adler, Laszlo; Nagy, Peter B.

1994-09-01

Novel experimental techniques to measure ultrasonic velocity and attenuation of surface waves on fluid-filled porous natural rocks are presented. Our experimental results are consistent with the theoretical predictions of Feng and Johnson (1983). Depending on the interface conditions, i.e., whether the surface pores are open or closed, pseudo-Rayleigh, pseudo-Stoneley, and/or Stoneley surface waves may exist on fluid-saturated rocks with closed 'slow' surface wave (true Stoneley mode) on fluid-filled porous rocks with closed surface pores. The velocity and attenuation of the 'slow' surface mode may be used to assess the dynamic permeabilty of porous formations.

How animals drink and swim in fluids

NASA Astrophysics Data System (ADS)

Jung, Sunghwan

2011-10-01

Fluids are essential for most living organisms to maintain a healthy body and also serve as a medium in which they locomote. The fluid bulk or interfaces actively interact with biological structures, which produces highly nonlinear, interesting, and complicated dynamical problems. We studied the lapping of cats and the swimming of Paramecia in various fluidic environments. The problem of the cat drinking can be simplified as the competition between inertia and gravity whereas the problem of Paramecium swimming in viscous fluids results from the competition between viscous drag and thrust. The underlying mechanisms are discussed and understood through laboratory experiments utilizing high-speed photography.

Visual Environments for CFD Research

NASA Technical Reports Server (NTRS)

Watson, Val; George, Michael W. (Technical Monitor)

1994-01-01

This viewgraph presentation gives an overview of the visual environments for computational fluid dynamics (CFD) research. It includes details on critical needs from the future computer environment, features needed to attain this environment, prospects for changes in and the impact of the visualization revolution on the human-computer interface, human processing capabilities, limits of personal environment and the extension of that environment with computers. Information is given on the need for more 'visual' thinking (including instances of visual thinking), an evaluation of the alternate approaches for and levels of interactive computer graphics, a visual analysis of computational fluid dynamics, and an analysis of visualization software.

Visualization of Computational Fluid Dynamics

NASA Technical Reports Server (NTRS)

Gerald-Yamasaki, Michael; Hultquist, Jeff; Bryson, Steve; Kenwright, David; Lane, David; Walatka, Pamela; Clucas, Jean; Watson, Velvin; Lasinski, T. A. (Technical Monitor)

1995-01-01

Scientific visualization serves the dual purpose of exploration and exposition of the results of numerical simulations of fluid flow. Along with the basic visualization process which transforms source data into images, there are four additional components to a complete visualization system: Source Data Processing, User Interface and Control, Presentation, and Information Management. The requirements imposed by the desired mode of operation (i.e. real-time, interactive, or batch) and the source data have their effect on each of these visualization system components. The special requirements imposed by the wide variety and size of the source data provided by the numerical simulation of fluid flow presents an enormous challenge to the visualization system designer. We describe the visualization system components including specific visualization techniques and how the mode of operation and source data requirements effect the construction of computational fluid dynamics visualization systems.

Surface tension dominates insect flight on fluid interfaces.

PubMed

Mukundarajan, Haripriya; Bardon, Thibaut C; Kim, Dong Hyun; Prakash, Manu

2016-03-01

Flight on the 2D air-water interface, with body weight supported by surface tension, is a unique locomotion strategy well adapted for the environmental niche on the surface of water. Although previously described in aquatic insects like stoneflies, the biomechanics of interfacial flight has never been analysed. Here, we report interfacial flight as an adapted behaviour in waterlily beetles (Galerucella nymphaeae) which are also dexterous airborne fliers. We present the first quantitative biomechanical model of interfacial flight in insects, uncovering an intricate interplay of capillary, aerodynamic and neuromuscular forces. We show that waterlily beetles use their tarsal claws to attach themselves to the interface, via a fluid contact line pinned at the claw. We investigate the kinematics of interfacial flight trajectories using high-speed imaging and construct a mathematical model describing the flight dynamics. Our results show that non-linear surface tension forces make interfacial flight energetically expensive compared with airborne flight at the relatively high speeds characteristic of waterlily beetles, and cause chaotic dynamics to arise naturally in these regimes. We identify the crucial roles of capillary-gravity wave drag and oscillatory surface tension forces which dominate interfacial flight, showing that the air-water interface presents a radically modified force landscape for flapping wing flight compared with air. © 2016. Published by The Company of Biologists Ltd.

Surface tension dominates insect flight on fluid interfaces

PubMed Central

Mukundarajan, Haripriya; Bardon, Thibaut C.; Kim, Dong Hyun; Prakash, Manu

2016-01-01

ABSTRACT Flight on the 2D air–water interface, with body weight supported by surface tension, is a unique locomotion strategy well adapted for the environmental niche on the surface of water. Although previously described in aquatic insects like stoneflies, the biomechanics of interfacial flight has never been analysed. Here, we report interfacial flight as an adapted behaviour in waterlily beetles (Galerucella nymphaeae) which are also dexterous airborne fliers. We present the first quantitative biomechanical model of interfacial flight in insects, uncovering an intricate interplay of capillary, aerodynamic and neuromuscular forces. We show that waterlily beetles use their tarsal claws to attach themselves to the interface, via a fluid contact line pinned at the claw. We investigate the kinematics of interfacial flight trajectories using high-speed imaging and construct a mathematical model describing the flight dynamics. Our results show that non-linear surface tension forces make interfacial flight energetically expensive compared with airborne flight at the relatively high speeds characteristic of waterlily beetles, and cause chaotic dynamics to arise naturally in these regimes. We identify the crucial roles of capillary–gravity wave drag and oscillatory surface tension forces which dominate interfacial flight, showing that the air–water interface presents a radically modified force landscape for flapping wing flight compared with air. PMID:26936640

Multiscale Particle-Based Modeling of Flowing Platelets in Blood Plasma Using Dissipative Particle Dynamics and Coarse Grained Molecular Dynamics

PubMed Central

Zhang, Peng; Gao, Chao; Zhang, Na; Slepian, Marvin J.; Deng, Yuefan; Bluestein, Danny

2014-01-01

We developed a multiscale particle-based model of platelets, to study the transport dynamics of shear stresses between the surrounding fluid and the platelet membrane. This model facilitates a more accurate prediction of the activation potential of platelets by viscous shear stresses - one of the major mechanisms leading to thrombus formation in cardiovascular diseases and in prosthetic cardiovascular devices. The interface of the model couples coarse-grained molecular dynamics (CGMD) with dissipative particle dynamics (DPD). The CGMD handles individual platelets while the DPD models the macroscopic transport of blood plasma in vessels. A hybrid force field is formulated for establishing a functional interface between the platelet membrane and the surrounding fluid, in which the microstructural changes of platelets may respond to the extracellular viscous shear stresses transferred to them. The interaction between the two systems preserves dynamic properties of the flowing platelets, such as the flipping motion. Using this multiscale particle-based approach, we have further studied the effects of the platelet elastic modulus by comparing the action of the flow-induced shear stresses on rigid and deformable platelet models. The results indicate that neglecting the platelet deformability may overestimate the stress on the platelet membrane, which in turn may lead to erroneous predictions of the platelet activation under viscous shear flow conditions. This particle-based fluid-structure interaction multiscale model offers for the first time a computationally feasible approach for simulating deformable platelets interacting with viscous blood flow, aimed at predicting flow induced platelet activation by using a highly resolved mapping of the stress distribution on the platelet membrane under dynamic flow conditions. PMID:25530818

Axisymmetric Lattice Boltzmann Model of Droplet Impact on Solid Surfaces

NASA Astrophysics Data System (ADS)

Dalgamoni, Hussein; Yong, Xin

2017-11-01

Droplet impact is a ubiquitous fluid phenomena encountered in scientific and engineering applications such as ink-jet printing, coating, electronics manufacturing, and many others. It is of great technological importance to understand the detailed dynamics of drop impact on various surfaces. The lattice Boltzmann method (LBM) emerges as an efficient method for modeling complex fluid systems involving rapidly evolving fluid-fluid and fluid-solid interfaces with complex geometries. In this work, we model droplet impact on flat solid substrates with well-defined wetting behavior using a two-phase axisymmetric LBM with high density and viscosity contrasts. We extend the two-dimensional Lee and Liu model to capture axisymmetric effect in the normal impact. First we compare the 2D axisymmetric results with the 2D and 3D results reported by Lee and Liu to probe the effect of axisymmetric terms. Then, we explore the effects of Weber number, Ohnesorge number, and droplet-surface equilibrium contact angle on the impact. The dynamic contact angle and spreading factor of the droplet during impact are investigated to qualitatively characterize the impact dynamics.

FAST - A multiprocessed environment for visualization of computational fluid dynamics

NASA Technical Reports Server (NTRS)

Bancroft, Gordon V.; Merritt, Fergus J.; Plessel, Todd C.; Kelaita, Paul G.; Mccabe, R. Kevin

1991-01-01

The paper presents the Flow Analysis Software Toolset (FAST) to be used for fluid-mechanics analysis. The design criteria for FAST including the minimization of the data path in the computational fluid-dynamics (CFD) process, consistent user interface, extensible software architecture, modularization, and the isolation of three-dimensional tasks from the application programmer are outlined. Each separate process communicates through the FAST Hub, while other modules such as FAST Central, NAS file input, CFD calculator, surface extractor and renderer, titler, tracer, and isolev might work together to generate the scene. An interprocess communication package making it possible for FAST to operate as a modular environment where resources could be shared among different machines as well as a single host is discussed.

The Dynamics of Miscible Fluids: A Space Flight Experiment (MIDAS)

NASA Technical Reports Server (NTRS)

Maxworthy, T.; Meiburg, E.; Balasubramaniam, R.; Rashidnia, N.; Lauver, R.

2001-01-01

We propose a space flight experiment to study the dynamics of miscible interfaces. A less viscous fluid displaces one of higher viscosity within a tube. The two fluids are miscible in all proportions. An intruding "finger" forms that occupies a fraction of the tube. As time progresses diffusion at the interface combined with flow induced straining between the two fluids modifies the concentration and velocity distributions within the whole tube. Also, under such circumstances it has been proposed that the interfacial stresses could depend on the local concentration gradients (Korteweg stresses) and that the divergence of the velocity need not be zero, even though the flow is incompressible. We have obtained reasonable agreement for the tip velocity between numerical simulations (that ignored the Korteweg stress and divergence effects) and physical experiments only at high Peelet Numbers. However at moderate to low Pe agreement was poor. As one possibility we attributed this lack of agreement to the disregard of these effects. We propose a space experiment to measure the finger shape, tip velocity, and the velocity and concentration fields. From intercomparisons between the experiment and the calculations we can then extract values for the coefficients of the Korteweg stress terms and confirm or deny the importance of these stresses.

The Dynamics of Miscible Fluids: A Space Flight Experiment (MIDAS)

NASA Technical Reports Server (NTRS)

Maxworthy, T.; Meiburg, E.; Balasubramaniam, R.; Rashidnia, N.; Lauver, R.

2001-01-01

We propose a space flight experiment to study the dynamics of miscible interfaces. A less viscous fluid displaces one of higher viscosity within a tube. The two fluids are miscible in all proportions. An intruding "finger" forms that occupies a fraction of the tube. As time progresses diffusion at the interface combined with flow induced straining between the two fluids modifies the concentration and velocity distributions within the whole tube. Also, under such circumstances it has been proposed that the interfacial stresses could depend on the local concentration gradients (Korteweg stresses) and that the divergence of the velocity need not be zero, even though the flow is incompressible. We have obtained reasonable agreement for the tip velocity between numerical simulations (that ignored the Korteweg stress and divergence effects) and physical experiments only at high Peclet Numbers. However at moderate to low Pe agreement was poor. As one possibility we attributed this lack of agreement to the disregard of these effects. We propose a space experiment to measure the finger shape, tip velocity, and the velocity and concentration fields. From intercomparisons between the experiment and the calculations we can then extract values for the coefficients of the Korteweg stress terms and confirm or deny the importance of these stresses.

Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture

NASA Technical Reports Server (NTRS)

Ostrach, S.

1983-01-01

An attempt is made to unify the current state of knowledge in crystal growth techniques and fluid mechanics. After identifying important fluid dynamic problems for such representative crystal growth processes as closed tube vapor transport, open reactor vapor deposition, and the Czochralski and floating zone melt growth techniques, research results obtained to date are presented. It is noted that the major effort to date has been directed to the description of the nature and extent of bulk transport under realistic conditions, where bulk flow determines the heat and solute transport which strongly influence the temperature and concentration fields in the vicinity of the growth interface. Proper treatment of near field, or interface, problems cannot be given until the far field, or global flow, involved in a given crystal growth technique has been adequately described.

Journal and Wave Bearing Impedance Calculation Software

NASA Technical Reports Server (NTRS)

Hanford, Amanda; Campbell, Robert

2012-01-01

The wave bearing software suite is a MALTA application that computes bearing properties for user-specified wave bearing conditions, as well as plain journal bearings. Wave bearings are fluid film journal bearings with multi-lobed wave patterns around the circumference of the bearing surface. In this software suite, the dynamic coefficients are outputted in a way for easy implementation in a finite element model used in rotor dynamics analysis. The software has a graphical user interface (GUI) for inputting bearing geometry parameters, and uses MATLAB s structure interface for ease of interpreting data. This innovation was developed to provide the stiffness and damping components of wave bearing impedances. The computational method for computing bearing coefficients was originally designed for plain journal bearings and tilting pad bearings. Modifications to include a wave bearing profile consisted of changing the film thickness profile given by an equation, and writing an algorithm to locate the integration limits for each fluid region. Careful consideration was needed to implement the correct integration limits while computing the dynamic coefficients, depending on the form of the input/output variables specified in the algorithm.

Surfactant effects on the dynamics of an intravascular bubble

NASA Astrophysics Data System (ADS)

Zhang, Jie; Eckmann, David; Ayyaswamy, P. S.

2004-11-01

The effects of a surfactant on the dynamics of gas bubble behavior in the arteriolar vasculature are numerically investigated. The equations for momentum in the bulk fluid (blood) and the bubble, and the convection-diffusion equations for mass transport both in the bulk fluid and on the gas-liquid interface are numerically solved using a front tracking method. Both soluble and insoluble surfactants are considered. The adsorption/desorption dynamics of the soluble surfactant is accurately resolved. For a nearly occluded bubble, a faster rate of depletion of the surfactant from the region adjacent to the wall of the vessel is observed. In several cases studied here, the bulk medium is treated as non-Newtonian (power law, Casson), although the majority of cases treat blood as Newtonian. Results show that the adsorbed surfactant serves to prevent blood proteins and other macromolecules from occupying the interface. This prevents clotting or adhesion of the bubble to the vessel wall. The results obtained have significance in the study of intravascular gas embolism. Supported by NIH R01 HL67986

Interfacial instabilities in vibrated fluids

NASA Astrophysics Data System (ADS)

Porter, Jeff; Laverón-Simavilla, Ana; Tinao Perez-Miravete, Ignacio; Fernandez Fraile, Jose Javier

2016-07-01

Vibrations induce a range of different interfacial phenomena in fluid systems depending on the frequency and orientation of the forcing. With gravity, (large) interfaces are approximately flat and there is a qualitative difference between vertical and horizontal forcing. Sufficient vertical forcing produces subharmonic standing waves (Faraday waves) that extend over the whole interface. Horizontal forcing can excite both localized and extended interfacial phenomena. The vibrating solid boundaries act as wavemakers to excite traveling waves (or sloshing modes at low frequencies) but they also drive evanescent bulk modes whose oscillatory pressure gradient can parametrically excite subharmonic surface waves like cross-waves. Depending on the magnitude of the damping and the aspect ratio of the container, these locally generated surfaces waves may interact in the interior resulting in temporal modulation and other complex dynamics. In the case where the interface separates two fluids of different density in, for example, a rectangular container, the mass transfer due to vertical motion near the endwalls requires a counterflow in the interior region that can lead to a Kelvin-Helmholtz type instability and a ``frozen wave" pattern. In microgravity, the dominance of surface forces favors non-flat equilibrium configurations and the distinction between vertical and horizontal applied forcing can be lost. Hysteresis and multiplicity of solutions are more common, especially in non-wetting systems where disconnected (partial) volumes of fluid can be established. Furthermore, the vibrational field contributes a dynamic pressure term that competes with surface tension to select the (time averaged) shape of the surface. These new (quasi-static) surface configurations, known as vibroequilibria, can differ substantially from the hydrostatic state. There is a tendency for the interface to orient perpendicular to the vibrational axis and, in some cases, a bulge or cavity is induced that leads to splitting (fluid separation). We investigate the interaction of these prominent interfacial instabilities in the absence of gravity, concentrating on harmonically vibrated rectangular containers of fluid. We compare vibroequilibria theory with direct numerical simulations and consider the effect of surfaces waves, which can excite sloshing motion of the vibroequilibria. We systematically investigate the saddle-node bifurcation experienced by a symmetric singly connected vibroequilibria solution, for sufficiently deep containers, as forcing is increased. Beyond this instability, the fluid rapidly separates into (at least) two distinct masses. Pronounced hysteresis is associated with this transition, even in the presence of gravity. The interaction of vibroequilibria and frozen waves is investigated in two-fluid systems. Preparations for a parabolic flight experiment on fluids vibrated at high frequencies are discussed.

Consumption, supply and transport: self-organization without direct communication

NASA Technical Reports Server (NTRS)

Kessler, J. O.

1996-01-01

Swimming bacteria of the species Bacillus subtilis require and consume oxygen. In static liquid cultures the cells' swimming behaviour leads them to accumulate up oxygen concentration gradients generated by consumption and supply. Since the density of bacterial cells exceeds that of the fluid in which they live, fluid regions where cells have accumulated are denser than depleted regions. These density variations cause convection. The fluid motion is dynamically maintained by the swimming of the cells toward regions of attraction: the air-fluid interface and the fluctuating advecting attractors, gradients of oxygen concentration that are embedded in the convecting fluid. Because of the fluid dynamical conservation laws, these complex physical and biological factors generate patterns ordered over distances > 10000 bacterial cell diameters. The convection enhances long-range transport and mixing of oxygen, cells and extracellular products by orders of magnitude. Thus, through the interplay of physical and biological factors, a population of undifferentiated selfish cells creates functional dynamic patterns. Populations of bacteria that have organised themselves into regularly patterned regions of vigorous convection and varying cell concentration interact with their environment as if they were one purposeful, coherent multicellular individual. The mathematical and experimental ingredients of these remarkable phenomena are presented here.

Modeling Ullage Dynamics of Tank Pressure Control Experiment during Jet Mixing in Microgravity

NASA Technical Reports Server (NTRS)

Kartuzova, O.; Kassemi, M.

2016-01-01

A CFD model for simulating the fluid dynamics of the jet induced mixing process is utilized in this paper to model the pressure control portion of the Tank Pressure Control Experiment (TPCE) in microgravity1. The Volume of Fluid (VOF) method is used for modeling the dynamics of the interface during mixing. The simulations were performed at a range of jet Weber numbers from non-penetrating to fully penetrating. Two different initial ullage positions were considered. The computational results for the jet-ullage interaction are compared with still images from the video of the experiment. A qualitative comparison shows that the CFD model was able to capture the main features of the interfacial dynamics, as well as the jet penetration of the ullage.

Liquid phase stabilization versus bubble formation at a nanoscale curved interface

NASA Astrophysics Data System (ADS)

Schiffbauer, Jarrod; Luo, Tengfei

2018-03-01

We investigate the nature of vapor bubble formation near a nanoscale-curved convex liquid-solid interface using two models: an equilibrium Gibbs model for homogenous nucleation, and a nonequilibrium dynamic van der Waals-diffuse-interface model for phase change in an initially cool liquid. Vapor bubble formation is shown to occur for sufficiently large radius of curvature and is suppressed for smaller radii. Solid-fluid interactions are accounted for and it is shown that liquid-vapor interfacial energy, and hence Laplace pressure, has limited influence over bubble formation. The dominant factor is the energetic cost of creating the solid-vapor interface from the existing solid-liquid interface, as demonstrated via both equilibrium and nonequilibrium arguments.

Coupled diffusion in lipid bilayers upon close approach

DOE PAGES

Pronk, Sander; Lindahl, Erik; Kasson, Peter M.

2014-12-23

Biomembrane interfaces create regions of slowed water dynamics in their vicinity. When two lipid bilayers come together, this effect is further accentuated, and the associated slowdown can affect the dynamics of larger-scale processes such as membrane fusion. We have used molecular dynamics simulations to examine how lipid and water dynamics are affected as two lipid bilayers approach each other. These two interacting fluid systems, lipid and water, both slow and become coupled when the lipid membranes are separated by a thin water layer. We show in particular that the water dynamics become glassy, and diffusion of lipids in the apposedmore » leaflets becomes coupled across the water layer, while the “outer” leaflets remain unaffected. This dynamic coupling between bilayers appears mediated by lipid–water–lipid hydrogen bonding, as it occurs at bilayer separations where water–lipid hydrogen bonds become more common than water–water hydrogen bonds. We further show that such coupling occurs in simulations of vesicle–vesicle fusion prior to the fusion event itself. As a result, such altered dynamics at membrane–membrane interfaces may both stabilize the interfacial contact and slow fusion stalk formation within the interface region.« less

Coherent structures over Super Hydrophobic and Liquid Infused Surfaces

NASA Astrophysics Data System (ADS)

Arenas, Isnardo; Bernardini, Matteo; Leonardi, Stefano

2017-11-01

Numerical Simulations of two superposed fluids in a turbulent channel have been performed. Both walls of the channel are made of longitudinal riblets with a gas fractions of 0.5 and several pitch values p+ = 18 , 36 , 72 , 144 . For Liquid Infused Surfaces, LIS, with a viscosity ratio m =μ1 /μ2 = 0.4 (where the subscripts 1 and 2 indicate the fluid in the cavities and the overlying fluid respectively) two cases have been considered varying the Weber number: We = 0 , implying an interface sustained by the surface tension and We = 1000 with the dynamics of the interface between the two fluids modeled with a Level Set Approach. Results are compared to the case mimicking water over air (Super hydrophobic Surface SHS m = 0.02) and We = 0 . A smooth channel with one fluid only at Reτ = 180 is used as reference and to assess how the LIS and SHS modify coherent structures near the wall. Numerical simulations were performed on XSEDE TACC under Grant CTS070066. This work was supported by ONR MURI Grants N00014-12-01-0875 and N00014-12-01-0962.

A numerical model of two-phase flow at the micro-scale using the volume-of-fluid method

NASA Astrophysics Data System (ADS)

Shams, Mosayeb; Raeini, Ali Q.; Blunt, Martin J.; Bijeljic, Branko

2018-03-01

This study presents a simple and robust numerical scheme to model two-phase flow in porous media where capillary forces dominate over viscous effects. The volume-of-fluid method is employed to capture the fluid-fluid interface whose dynamics is explicitly described based on a finite volume discretization of the Navier-Stokes equations. Interfacial forces are calculated directly on reconstructed interface elements such that the total curvature is preserved. The computed interfacial forces are explicitly added to the Navier-Stokes equations using a sharp formulation which effectively eliminates spurious currents. The stability and accuracy of the implemented scheme is validated on several two- and three-dimensional test cases, which indicate the capability of the method to model two-phase flow processes at the micro-scale. In particular we show how the co-current flow of two viscous fluids leads to greatly enhanced flow conductance for the wetting phase in corners of the pore space, compared to a case where the non-wetting phase is an inviscid gas.

Contact mechanics for poroelastic, fluid-filled media, with application to cartilage.

PubMed

Persson, B N J

2016-12-21

I study a simple contact mechanics model for a poroelastic, fluid-filled solid squeezed against a rigid, randomly rough substrate. I study how the fluid is squeezed out from the interface, and how the area of contact, and the average interfacial separation, change with time. I present numerical results relevant for a human cartilage. I show that for a fluid filled poroelastic solid the probability of cavitation (and the related wear as the cavities implode), and dynamical scraping (defined below and in Hutt and Persson, J. Chem. Phys. 144, 124903 (2016)), may be suppressed by fluid flow from the poroelastic solid into the (roughness induced) interfacial gap between the solids.

Contact mechanics for poroelastic, fluid-filled media, with application to cartilage

NASA Astrophysics Data System (ADS)

Persson, B. N. J.

2016-12-01

I study a simple contact mechanics model for a poroelastic, fluid-filled solid squeezed against a rigid, randomly rough substrate. I study how the fluid is squeezed out from the interface, and how the area of contact, and the average interfacial separation, change with time. I present numerical results relevant for a human cartilage. I show that for a fluid filled poroelastic solid the probability of cavitation (and the related wear as the cavities implode), and dynamical scraping (defined below and in Hutt and Persson, J. Chem. Phys. 144, 124903 (2016)), may be suppressed by fluid flow from the poroelastic solid into the (roughness induced) interfacial gap between the solids.

Deformation and Metasomatic Evolution at the Subduction Plate Interface As Viewed from Study of HP/UHP Metamorphic Rocks

NASA Astrophysics Data System (ADS)

Bebout, G. E.; Penniston-Dorland, S.

2014-12-01

We provide a view of lithologic makeup, deformation, and fluid-rock interaction along the deep forearc to subarc plate interface, based on insights gained from study of HP/UHP metamorphic rocks. Exposures of plate-boundary shear zones on which we base our perspective represent 30-80 km depths and are on Catalina Island and at Monviso, Syros, and New Caledonia. Each contains highly deformed zones with schistose matrix, commonly with a large ultramafic component, containing bodies of less deformed mafic, sedimentary, and ultramafic rocks. These "blocks" have varying geometries, are up to km-scale, and can preserve disparate P-T histories reflecting dynamics of incorporation and entrainment. Sheared matrices contain high-variance, hydrous mineral assemblages in some cases resembling metasomatic zones ("rinds") at block-matrix contacts, and rinds and matrices have homogenized isotopic compositions reflecting extensive fluid-rock interaction. Shearing and related physical juxtaposition of disparate metasomatic rocks can result in mixed or 'hybrid' chemical compositions. The chlorite-, talc-, and amphibole-rich schists developed by these processes can stabilize H2O to great depth and influence its cycling. Fluids (hydrous fluids, silicate melts) released within slabs necessarily interact with highly deformed, lithologically hybridized zones at the plate interface as they ascend to potentially enter mantle wedges. Fluids bearing chemical/isotopic signatures of hybrid rocks appear capable of producing arc magma compositions interpreted as reflecting multiple, chemically distinct fluids sources. Geophysical signatures of these rheologically weak zones are equivocal but many recognize the presence of zones of low seismic velocity at/near the top of slabs and attribute them to hydrated rocks. Whether rocks from this interface buoyantly ascend into mantle wedges, indicated in some theoretical models, remains largely untested by field and geophysical observations.

Computational and Spectroscopic Investigations of the Molecular Scale Structure and Dynamics of Geologically Important Fluids and Mineral-Fluid Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

R. James Kirkpatrick; Andrey G. Kalinichev

2008-11-25

Research supported by this grant focuses on molecular scale understanding of central issues related to the structure and dynamics of geochemically important fluids, fluid-mineral interfaces, and confined fluids using computational modeling and experimental methods. Molecular scale knowledge about fluid structure and dynamics, how these are affected by mineral surfaces and molecular-scale (nano-) confinement, and how water molecules and dissolved species interact with surfaces is essential to understanding the fundamental chemistry of a wide range of low-temperature geochemical processes, including sorption and geochemical transport. Our principal efforts are devoted to continued development of relevant computational approaches, application of these approaches tomore » important geochemical questions, relevant NMR and other experimental studies, and application of computational modeling methods to understanding the experimental results. The combination of computational modeling and experimental approaches is proving highly effective in addressing otherwise intractable problems. In 2006-2007 we have significantly advanced in new, highly promising research directions along with completion of on-going projects and final publication of work completed in previous years. New computational directions are focusing on modeling proton exchange reactions in aqueous solutions using ab initio molecular dynamics (AIMD), metadynamics (MTD), and empirical valence bond (EVB) approaches. Proton exchange is critical to understanding the structure, dynamics, and reactivity at mineral-water interfaces and for oxy-ions in solution, but has traditionally been difficult to model with molecular dynamics (MD). Our ultimate objective is to develop this capability, because MD is much less computationally demanding than quantum-chemical approaches. We have also extended our previous MD simulations of metal binding to natural organic matter (NOM) to a much longer time scale (up to 10 ns) for significantly larger systems. These calculations have allowed us, for the first time, to study the effects of metal cations with different charges and charge density on the NOM aggregation in aqueous solutions. Other computational work has looked at the longer-time-scale dynamical behavior of aqueous species at mineral-water interfaces investigated simultaneously by NMR spectroscopy. Our experimental NMR studies have focused on understanding the structure and dynamics of water and dissolved species at mineral-water interfaces and in two-dimensional nano-confinement within clay interlayers. Combined NMR and MD study of H2O, Na+, and Cl- interactions with the surface of quartz has direct implications regarding interpretation of sum frequency vibrational spectroscopic experiments for this phase and will be an important reference for future studies. We also used NMR to examine the behavior of K+ and H2O in the interlayer and at the surfaces of the clay minerals hectorite and illite-rich illite-smectite. This the first time K+ dynamics has been characterized spectroscopically in geochemical systems. Preliminary experiments were also performed to evaluate the potential of 75As NMR as a probe of arsenic geochemical behavior. The 75As NMR study used advanced signal enhancement methods, introduced a new data acquisition approach to minimize the time investment in ultra-wide-line NMR experiments, and provides the first evidence of a strong relationship between the chemical shift and structural parameters for this experimentally challenging nucleus. We have also initiated a series of inelastic and quasi-elastic neutron scattering measurements of water dynamics in the interlayers of clays and layered double hydroxides. The objective of these experiments is to probe the correlations of water molecular motions in confined spaces over the scale of times and distances most directly comparable to our MD simulations and on a time scale different than that probed by NMR. This work is being done in collaboration with Drs. C.-K. Loong, N. de Souza, and A.I. Kolesnikov at the Intense Pulsed Neutron Source facility of the Argonne National Lab, and Dr. A. Faraone at the NIST Center for Neutron Research. A manuscript reporting the first results of these experiments, which are highly complimentary to our previous NMR, X-ray, and infra-red results for these phases, is currently in preparation. In total, in 2006-2007 our work has resulted in the publication of 14 peer-reviewed research papers. We also devoted considerable effort to making our work known to a wide range of researchers, as indicated by the 24 contributed abstracts and 14 invited presentations.« less

Ion transfer from an atmospheric pressure ion funnel into a mass spectrometer with different interface options: Simulation-based optimization of ion transmission efficiency.

PubMed

Mayer, Thomas; Borsdorf, Helko

2016-02-15

We optimized an atmospheric pressure ion funnel (APIF) including different interface options (pinhole, capillary, and nozzle) regarding a maximal ion transmission. Previous computer simulations consider the ion funnel itself and do not include the geometry of the following components which can considerably influence the ion transmission into the vacuum stage. Initially, a three-dimensional computer-aided design (CAD) model of our setup was created using Autodesk Inventor. This model was imported to the Autodesk Simulation CFD program where the computational fluid dynamics (CFD) were calculated. The flow field was transferred to SIMION 8.1. Investigations of ion trajectories were carried out using the SDS (statistical diffusion simulation) tool of SIMION, which allowed us to evaluate the flow regime, pressure, and temperature values that we obtained. The simulation-based optimization of different interfaces between an atmospheric pressure ion funnel and the first vacuum stage of a mass spectrometer require the consideration of fluid dynamics. The use of a Venturi nozzle ensures the highest level of transmission efficiency in comparison to capillaries or pinholes. However, the application of radiofrequency (RF) voltage and an appropriate direct current (DC) field leads to process optimization and maximum ion transfer. The nozzle does not hinder the transfer of small ions. Our high-resolution SIMION model (0.01 mm grid unit(-1) ) under consideration of fluid dynamics is generally suitable for predicting the ion transmission through an atmospheric-vacuum system for mass spectrometry and enables the optimization of operational parameters. A Venturi nozzle inserted between the ion funnel and the mass spectrometer permits maximal ion transmission. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Sloshing dynamics modulated fluid angular momentum and moment fluctuations driven by orbital gravity gradient and jitter accelerations in microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Pan, H. L.

1995-01-01

The dynamical behavior of spacecraft propellant affected by the asymmetric combined gravity gradient and jitter accelerations, in particular the effect of surface tension on partially-filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank has been investigated. Three different cases of orbital accelerations: (1) gravity gradient-dominated, (2) equally weighted between gravity gradient and jitter, and (3) gravity jitter-dominated accelerations are studied. The results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient-dominated accelerations provide a torsional moment with tidal motion of bubble oscillations in the rotating dewar. The results are clearly seen from the twisting shape of the bubble oscillations driven by gravity gradient-dominated acceleration. The results of slosh wave excitation along the liquid-vapor interface induced by gravity jitter-dominated acceleration indicate the results of bubble motion in a manner of down-and-up and leftward-and-rightward movement of oscillation when the bubble is rotating with respect to rotating dewar axis. Fluctuations of angular momentum, fluid moment and bubble mass center caused by slosh wave excitations driven by gravity gradient acceleration or gravity jitter acceleration are also investigated.

Inertial effects during irreversible meniscus reconfiguration in angular pores

NASA Astrophysics Data System (ADS)

Ferrari, Andrea; Lunati, Ivan

2014-12-01

In porous media, the dynamics of the invading front between two immiscible fluids is often characterized by abrupt reconfigurations caused by local instabilities of the interface. As a prototype of these phenomena we consider the dynamics of a meniscus in a corner as it can be encountered in angular pores. We investigate this process in detail by means of direct numerical simulations that solve the Navier-Stokes equations in the pore space and employ the Volume of Fluid method (VOF) to track the evolution of the interface. We show that for a quasi-static displacement, the numerically calculated surface energy agrees well with the analytical solutions that we have derived for pores with circular and square cross sections. However, the spontaneous reconfigurations are irreversible and cannot be controlled by the injection rate: they are characterized by the amount of surface energy that is spontaneously released and transformed into kinetic energy. The resulting local velocities can be orders of magnitude larger than the injection velocity and they induce damped oscillations of the interface that possess their own time scales and depend only on fluid properties and pore geometry. In complex media (we consider a network of cubic pores) reconfigurations are so frequent and oscillations last long enough that increasing inertial effects leads to a different fluid distribution by influencing the selection of the next pore to be invaded. This calls into question simple pore-filling rules based only on capillary forces. Also, we demonstrate that inertial effects during irreversible reconfigurations can influence the work done by the external forces that is related to the pressure drop in Darcy's law. This suggests that these phenomena have to be considered when upscaling multiphase flow because local oscillations of the menisci affect macroscopic quantities and modify the constitutive relationships to be used in macro-scale models. These results can be extrapolated to other interface instabilities that are at the origin of fast pore-scale events, such as Haines jumps, snap-off and coalescence.

A dynamic pressure view cell for acoustic stimulation of fluids--Micro-bubble generation and fluid movement in porous media.

PubMed

Stewart, Robert A; Shaw, J M

2015-09-01

The development and baseline operation of an acoustic view cell for observing fluids, and fluid-fluid and fluid-solid interfaces in porous media over the frequency range of 10-5000 Hz is described. This range includes the industrially relevant frequency range 500-5000 Hz that is not covered by existing devices. Pressure waveforms of arbitrary shape are generated in a 17.46 mm ID by 200 mm and 690.5 mm long glass tubes at flow rates up to 200 ml/min using a syringe pump. Peak-to-peak amplitudes exceeding 80 kPa are readily realized at frequencies from 10 to 5000 Hz in bubble free fluids when actuated with 20 Vpp as exemplified using castor oil. At resonant frequencies, peak-to-peak pressure amplitudes exceeding 500 kPa were obtained (castor oil at 2100 Hz when actuated with 20 Vpp). Impacts of vibration on macroscopic liquid-liquid and liquid-vapour interfaces and interface movement are illustrated. Pressure wave transmission and attenuation in a fluid saturated porous medium, randomly packed 250-330 μm spherical silica beads, is also demonstrated. Attenuation differences and frequency shifts in resonant peaks are used to detect the presence and generation of dispersed micro-bubbles (<180 μm diameter), and bubbles within porous media that are not readily visualized. Envisioned applications include assessment of the impacts of vibration on reaction, mass transfer, and flow/flow pattern outcomes. This knowledge will inform laboratory and pilot scale process studies, where nuisance vibrations may affect the interpretation of process outcomes, and large scale or in situ processes in aquifers or hydrocarbon reservoirs where imposed vibration may be deployed to improve aspects of process performance. Future work will include miscible interface observation and quantitative measurements in the bulk and in porous media where the roles of micro-bubbles comprise subjects of special interest.

Using evaporation to control capillary instabilities in micro-systems.

PubMed

Ledesma-Aguilar, Rodrigo; Laghezza, Gianluca; Yeomans, Julia M; Vella, Dominic

2017-12-06

The instabilities of fluid interfaces represent both a limitation and an opportunity for the fabrication of small-scale devices. Just as non-uniform capillary pressures can destroy micro-electrical mechanical systems (MEMS), so they can guide the assembly of novel solid and fluid structures. In many such applications the interface appears during an evaporation process and is therefore only present temporarily. It is commonly assumed that this evaporation simply guides the interface through a sequence of equilibrium configurations, and that the rate of evaporation only sets the timescale of this sequence. Here, we use Lattice-Boltzmann simulations and a theoretical analysis to show that, in fact, the rate of evaporation can be a factor in determining the onset and form of dynamical capillary instabilities. Our results shed light on the role of evaporation in previous experiments, and open the possibility of exploiting diffusive mass transfer to directly control capillary flows in MEMS applications.

The 3D widgets for exploratory scientific visualization

NASA Technical Reports Server (NTRS)

Herndon, Kenneth P.; Meyer, Tom

1995-01-01

Computational fluid dynamics (CFD) techniques are used to simulate flows of fluids like air or water around such objects as airplanes and automobiles. These techniques usually generate very large amounts of numerical data which are difficult to understand without using graphical scientific visualization techniques. There are a number of commercial scientific visualization applications available today which allow scientists to control visualization tools via textual and/or 2D user interfaces. However, these user interfaces are often difficult to use. We believe that 3D direct-manipulation techniques for interactively controlling visualization tools will provide opportunities for powerful and useful interfaces with which scientists can more effectively explore their datasets. A few systems have been developed which use these techniques. In this paper, we will present a variety of 3D interaction techniques for manipulating parameters of visualization tools used to explore CFD datasets, and discuss in detail various techniques for positioning tools in a 3D scene.

Experimental growth of inertial forced Richtmyer-Meshkov instabilities for different Atwood numbers

NASA Astrophysics Data System (ADS)

Redondo, J. M.; Castilla, R.

2009-04-01

Richtmyer-Meshkov instability occurs when a shock wave impinges on an interface separating two fluids having different densities [1,2]. The instability causes perturbations on the interface to grow, bubbles and spikes, producing vortical structures which potentially result in a turbulent mixing layer. In addition to shock tube experiments, the incompressible Richtmyer-Meshkov instability has also been studied by impulsively accelerating containers of incompressible fluids. Castilla and Redondo (1994) [3] first exploited this technique by dropping tanks containing a liquid and air or two liquids onto a cushioned surface. This technique was improved upon by Niederhaus and Jacobs (2003)[4] by mounting the tank onto a rail system and then allowing it to bounce off of a fixed spring. A range of both miscible and inmiscible liquids were used, giving a wide range of Atwood numbers using the combinations of air, water, alcohol, oil and mercury. Experimental results show the different pattern selection of both the bubbles and spikes for the different Atwood numbers. Visual analysis of the marked interfaces allows to distinguish the regions of strong mixing and compare self-similarity growth of the mixing region. [1] Meshkov, E. E. 1969 Instability of the interface of two gases accelerated by a shock wave. Fluid Dynamics 4, 101-104. [2] Brouillette, M. & Sturtevant, B. 1994 Experiments on the Richtmyer-Meshkov instability: single-scale perturbations on a continuous interface. Journal of Fluid Mechanics 263, 271-292. [3] Castilla, R. & Redondo, J. M. 1994 Mixing Front Growth in RT and RM Instabilities. Proceedings of the Fourth International Workshop on the Physics of Compressible Turbulent Mixing, Cambridge, United Kingdom, edited by P. F. Linden, D. L. Youngs, and S. B. Dalziel, 11-31. [4] Niederhaus, C. E. & Jacobs, J. W. 2003 Experimental study of the Richtmyer-Meshkov instability of incompressible fluids. Journal of Fluid Mechanics 485, 243-277.

The Effects of Ultra Thin Films on Dynamic Wetting

NASA Astrophysics Data System (ADS)

Chen, Xia; Garoff, Stephen; Rame, Enrique

2002-11-01

Dynamic wetting, the displacement of one fluid by another immiscible fluid on a surface, controls many natural and technological phenomena, such as coating, printing, spray painting and lubricating. Particularly in coating and spraying applications, contact lines advance across pre-existing fluid films. Most previous work has focused on contact lines advancing across films sufficiently thick that they behave as simple Newtonian fluids. Ultrathin films, where the film thickness may impinge on fundamental length scales in the fluid, have received less attention. In this talk, we will discuss the effects of ultrathin polymer films on dynamic wetting. We measure the interface shape within microns of moving contact lines advancing across preexisting films and compare the measurements to existing models of viscous bending for interfaces advancing across dry surfaces and 'thick' (in the sense that they behave as liquids) films. In the experiments, we advance a contact line of 10-poise and 1-poise polydimethylsiloxane (silicone oil) across pre-coated films of the same fluid with thickness from a single chain thickness (approx. 10 A) through a couple of radii of gyration (100-200 A) to films so thick they are likely bulk in behavior (103 A). All films are physisorbed, i.e. they readily rinse from the surface. Thus, molecules in the film are not anchored to the surface and can move within the film if the hydrodynamics dictate such motion. For films of the thickness of a single chain (approx. 10 A), our experiments indicate that the advancing fluid behaves just as it would if it advanced over a dry surface. For the thicker films (103 A), we find behavior indicating that the molecules in the film are acting as a fluid with the bulk properties. In this regime, results for the two different fluids are identical when the experiments are performed at the same pre-existing film thickness and advancing capillary number, Ca. For film of thickness of a few radii of gyration (approx. 100-200 A), the behavior depends on Ca of the advancing meniscus. At low Ca, the viscous bending of the interface near the contact line does not behave as it would on a dry surface. It has a lower curvature than expected. However, at higher Ca, the viscous bending is described by the model for spreading over a dry surface. These results show that the fluid flow in the film does behave differently than bulk as the film thickness becomes comparable to molecular length scale. But even more intriguing is the unusual velocity dependence of that behavior where the film behaves more solid-like at higher contact line speeds. We will discuss these results in terms of the properties of confined polymer melts.

The Effects of Ultra Thin Films on Dynamic Wetting

NASA Technical Reports Server (NTRS)

Chen, Xia; Garoff, Stephen; Rame, Enrique

2002-01-01

Dynamic wetting, the displacement of one fluid by another immiscible fluid on a surface, controls many natural and technological phenomena, such as coating, printing, spray painting and lubricating. Particularly in coating and spraying applications, contact lines advance across pre-existing fluid films. Most previous work has focused on contact lines advancing across films sufficiently thick that they behave as simple Newtonian fluids. Ultrathin films, where the film thickness may impinge on fundamental length scales in the fluid, have received less attention. In this talk, we will discuss the effects of ultrathin polymer films on dynamic wetting. We measure the interface shape within microns of moving contact lines advancing across preexisting films and compare the measurements to existing models of viscous bending for interfaces advancing across dry surfaces and 'thick' (in the sense that they behave as liquids) films. In the experiments, we advance a contact line of 10-poise and 1-poise polydimethylsiloxane (silicone oil) across pre-coated films of the same fluid with thickness from a single chain thickness (approx. 10 A) through a couple of radii of gyration (100-200 A) to films so thick they are likely bulk in behavior (10(exp 3) A). All films are physisorbed, i.e. they readily rinse from the surface. Thus, molecules in the film are not anchored to the surface and can move within the film if the hydrodynamics dictate such motion. For films of the thickness of a single chain (approx. 10 A), our experiments indicate that the advancing fluid behaves just as it would if it advanced over a dry surface. For the thicker films (10(exp 3) A), we find behavior indicating that the molecules in the film are acting as a fluid with the bulk properties. In this regime, results for the two different fluids are identical when the experiments are performed at the same pre-existing film thickness and advancing capillary number, Ca. For film of thickness of a few radii of gyration (approx. 100-200 A), the behavior depends on Ca of the advancing meniscus. At low Ca, the viscous bending of the interface near the contact line does not behave as it would on a dry surface. It has a lower curvature than expected. However, at higher Ca, the viscous bending is described by the model for spreading over a dry surface. These results show that the fluid flow in the film does behave differently than bulk as the film thickness becomes comparable to molecular length scale. But even more intriguing is the unusual velocity dependence of that behavior where the film behaves more solid-like at higher contact line speeds. We will discuss these results in terms of the properties of confined polymer melts.

Linear stability of an active fluid interface

NASA Astrophysics Data System (ADS)

Nagilla, Amarender; Prabhakar, Ranganathan; Jadhav, Sameer

2018-02-01

Motivated by studies suggesting that the patterns exhibited by the collectively expanding fronts of thin cells during the closing of a wound [S. Mark et al., "Physical model of the dynamic instability in an expanding cell culture," Biophys. J. 98(3), 361-370 (2010)] and the shapes of single cells crawling on surfaces [A. C. Callan-Jones et al., "Viscous-fingering-like instability of cell fragments," Phys. Rev. Lett. 100(25), 258106 (2008)] are due to fingering instabilities, we investigate the stability of actively driven interfaces under the Hele-Shaw confinement. An initially radial interface between a pair of viscous fluids is driven by active agents. Surface tension and bending rigidity resist the deformation of the interface. A point source at the origin and a distributed source are also included to model the effects of injection or suction and growth or depletion, respectively. Linear stability analysis reveals that for any given initial radius of the interface, there are two key dimensionless driving rates that determine interfacial stability. We discuss stability regimes in a state space of these parameters and their implications for biological systems. An interesting finding is that an actively mobile interface is susceptible to the fingering instability irrespective of viscosity contrast.

Study of dynamic fluid-structure coupling with application to human phonation

NASA Astrophysics Data System (ADS)

Saurabh, Shakti; Faber, Justin; Bodony, Daniel

2013-11-01

Two-dimensional direct numerical simulations of a compressible, viscous fluid interacting with a non-linear, viscoelastic solid are used to study the generation of the human voice. The vocal fold (VF) tissues are modeled using a finite-strain fractional derivative constitutive model implemented in a quadratic finite element code and coupled to a high-order compressible Navier-Stokes solver through a boundary-fitted fluid-solid interface. The viscoelastic solver is validated through in-house experiments using Agarose Gel, a human tissue simulant, undergoing static and harmonic deformation measured with load cell and optical diagnostics. The phonation simulations highlight the role tissue nonlinearity and viscosity play in the glottal jet dynamics and in the radiated sound. Supported by the National Science Foundation (CAREER award number 1150439).

Calculation of a solid/liquid surface tension: A methodological study

NASA Astrophysics Data System (ADS)

Dreher, T.; Lemarchand, C.; Soulard, L.; Bourasseau, E.; Malfreyt, P.; Pineau, N.

2018-01-01

The surface tension of a model solid/liquid interface constituted of a graphene sheet surrounded by liquid methane has been computed using molecular dynamics in the Kirkwood-Buff formalism. We show that contrary to the fluid/fluid case, the solid/liquid case can lead to different structurations of the first fluid layer, leading to significantly different values of surface tension. Therefore we present a statistical approach that consists in running a series of molecular simulations of similar systems with different initial conditions, leading to a distribution of surface tensions from which an average value and uncertainty can be extracted. Our results suggest that these distributions converge as the system size increases. Besides we show that surface tension is not particularly sensitive to the choice of the potential energy cutoff and that long-range corrections can be neglected contrary to what we observed in the liquid/vapour interfaces. We have not observed the previously reported commensurability effect.

Translator for Optimizing Fluid-Handling Components

NASA Technical Reports Server (NTRS)

Landon, Mark; Perry, Ernest

2007-01-01

A software interface has been devised to facilitate optimization of the shapes of valves, elbows, fittings, and other components used to handle fluids under extreme conditions. This software interface translates data files generated by PLOT3D (a NASA grid-based plotting-and- data-display program) and by computational fluid dynamics (CFD) software into a format in which the files can be read by Sculptor, which is a shape-deformation- and-optimization program. Sculptor enables the user to interactively, smoothly, and arbitrarily deform the surfaces and volumes in two- and three-dimensional CFD models. Sculptor also includes design-optimization algorithms that can be used in conjunction with the arbitrary-shape-deformation components to perform automatic shape optimization. In the optimization process, the output of the CFD software is used as feedback while the optimizer strives to satisfy design criteria that could include, for example, improved values of pressure loss, velocity, flow quality, mass flow, etc.

The Dynamics of Turbulent Scalar Mixing near the Edge of a Shear Layer

NASA Astrophysics Data System (ADS)

Taveira, R. M. R.; da Silva, C. B.; Pereira, J. C. F.

2011-12-01

In free shear flows a sharp and convoluted turbulent/nonturbulent (T/NT) interface separates the outer fluid region, where the flow is essentially irrotational, from the shear layer turbulent region. It was found recently that the entrainment mechanism is mainly caused by small scale ("nibbling") motions (Westerweel et al. (2005)). The dynamics of this interface is crucial to understand important exchanges of enstrophy and scalars that can be conceived as a three-stage process of entrainment, dispersion and diffusion (Dimotakis (2005)). A thorough understanding of scalar mixing and transport is of indisputable relevance to control turbulent combustion, propulsion and contaminant dispersion (Stanley et al. (2002)). The present work uses several DNS of turbulent jets at Reynolds number ranging from Reλ = 120 to Reλ = 160 (da Silva & Taveira (2010)) and a Schmidt number Sc = 0.7 to analyze the "scalar interface" and turbulent mixing of a passive scalar. Specifically, we employ conditional statistics, denoted by langlerangleI, in order to eliminate the intermittency that affects statistics close to the jet edge. The physical mechanisms behind scalar mixing near the T/NT interfaces, their scales and topology are investigated detail. Analysis of the instantaneous fields showed intense scalar gradient sheet-like structures along regions of persistent strain, in particular at the T/NT interface. The scalar gradient transport equation, at the jet edge, showed that almost all mixing mechanisms are taking place in a confined region, beyond which they become reduced to an almost in perfect balance between production and dissipation of scalar variance. At the T/NT interface transport mechanisms are the ones responsible for the growth in the scalar fluctuations to the entrained fluid, where convection plays a dominant role, smoothing scalar gradients inside the interface and boosting them as far as

Dynamics of immiscible liquids in a rotating horizontal cylinder

NASA Astrophysics Data System (ADS)

Kozlov, N. V.; Kozlova, A. N.; Shuvalova, D. A.

2016-11-01

The dynamics of an interface between two immiscible liquids of different density is studied experimentally in a horizontal cylinder at rotation in the gravity field. Two liquids entirely fill the cavity volume, and the container is rotated sufficiently fast so that the liquids are centrifuged. The light liquid forms a column extended along the rotation axis, and the heavy liquid forms an annular layer. Under the action of gravity, the light liquid column displaces steadily along the radius, downwards in the laboratory frame. As a result, fluid oscillations in the cavity frame are excited at the interface, which lead to the generation of a steady streaming, and the fluid comes into a slow lagging rotation with respect to the cylinder walls. The dynamics of the studied system is determined by the ratio of the gravity acceleration to the centrifugal one—the dimensionless acceleration. In experiments, the system is controlled by the means of variation of the rotation rate, i.e., of the centrifugal force. At a critical value of the dimensionless acceleration the circular interface looses stability, and an azimuthal wave is excited. This leads to a strong increase in the interface differential velocity. A theoretical analysis is done based on the theory of centrifugal waves and a frequency equation is obtained. Experimental results are in good agreement with the theory at the condition of small wave amplitudes. Mechanism of steady streaming generation is analyzed based on previously published theoretical results obtained for the limiting case when the light phase is a solid cylinder. A qualitative agreement is found.

On the physically based modeling of surface tension and moving contact lines with dynamic contact angles on the continuum scale

NASA Astrophysics Data System (ADS)

Huber, M.; Keller, F.; Säckel, W.; Hirschler, M.; Kunz, P.; Hassanizadeh, S. M.; Nieken, U.

2016-04-01

The description of wetting phenomena is a challenging problem on every considerable length-scale. The behavior of interfaces and contact lines on the continuum scale is caused by intermolecular interactions like the Van der Waals forces. Therefore, to describe surface tension and the resulting dynamics of interfaces and contact lines on the continuum scale, appropriate formulations must be developed. While the Continuum Surface Force (CSF) model is well-engineered for the description of interfaces, there is still a lack of treatment of contact lines, which are defined by the intersection of an ending fluid interface and a solid boundary surface. In our approach we use a balance equation for the contact line and extend the Navier-Stokes equations in analogy to the extension of a two-phase interface in the CSF model. Since this model depicts a physically motivated approach on the continuum scale, no fitting parameters are introduced and the deterministic description leads to a dynamical evolution of the system. As verification of our theory, we show a Smoothed Particle Hydrodynamics (SPH) model and simulate the evolution of droplet shapes and their corresponding contact angles.

On the transition between two-phase and single-phase interface dynamics in multicomponent fluids at supercritical pressures

NASA Astrophysics Data System (ADS)

Dahms, Rainer N.; Oefelein, Joseph C.

2013-09-01

A theory that explains the operating pressures where liquid injection processes transition from exhibiting classical two-phase spray atomization phenomena to single-phase diffusion-dominated mixing is presented. Imaging from a variety of experiments have long shown that under certain conditions, typically when the pressure of the working fluid exceeds the thermodynamic critical pressure of the liquid phase, the presence of discrete two-phase flow processes become diminished. Instead, the classical gas-liquid interface is replaced by diffusion-dominated mixing. When and how this transition occurs, however, is not well understood. Modern theory still lacks a physically based model to quantify this transition and the precise mechanisms that lead to it. In this paper, we derive a new model that explains how the transition occurs in multicomponent fluids and present a detailed analysis to quantify it. The model applies a detailed property evaluation scheme based on a modified 32-term Benedict-Webb-Rubin equation of state that accounts for the relevant real-fluid thermodynamic and transport properties of the multicomponent system. This framework is combined with Linear Gradient Theory, which describes the detailed molecular structure of the vapor-liquid interface region. Our analysis reveals that the two-phase interface breaks down not necessarily due to vanishing surface tension forces, but due to thickened interfaces at high subcritical temperatures coupled with an inherent reduction of the mean free molecular path. At a certain point, the combination of reduced surface tension, the thicker interface, and reduced mean free molecular path enter the continuum length scale regime. When this occurs, inter-molecular forces approach that of the multicomponent continuum where transport processes dominate across the interfacial region. This leads to a continuous phase transition from compressed liquid to supercritical mixture states. Based on this theory, a regime diagram for liquid injection is developed that quantifies the conditions under which classical sprays transition to dense-fluid jets. It is shown that the chamber pressure required to support diffusion-dominated mixing dynamics depends on the composition and temperature of the injected liquid and ambient gas. To illustrate the method and analysis, we use conditions typical of diesel engine injection. We also present a companion set of high-speed images to provide experimental validation of the presented theory. The basic theory is quite general and applies to a wide range of modern propulsion and power systems such as liquid rockets, gas turbines, and reciprocating engines. Interestingly, the regime diagram associated with diesel engine injection suggests that classical spray phenomena at typical injection conditions do not occur.

Low torque hydrodynamic lip geometry for bi-directional rotation seals

DOEpatents

Dietle, Lannie L [Houston, TX; Schroeder, John E [Richmond, TX

2009-07-21

A hydrodynamically lubricating geometry for the generally circular dynamic sealing lip of rotary seals that are employed to partition a lubricant from an environment. The dynamic sealing lip is provided for establishing compressed sealing engagement with a relatively rotatable surface, and for wedging a film of lubricating fluid into the interface between the dynamic sealing lip and the relatively rotatable surface in response to relative rotation that may occur in the clockwise or the counter-clockwise direction. A wave form incorporating an elongated dimple provides the gradual convergence, efficient impingement angle, and gradual interfacial contact pressure rise that are conducive to efficient hydrodynamic wedging. Skewed elevated contact pressure zones produced by compression edge effects provide for controlled lubricant movement within the dynamic sealing interface between the seal and the relatively rotatable surface, producing enhanced lubrication and low running torque.

Low torque hydrodynamic lip geometry for rotary seals

DOEpatents

Dietle, Lannie L.; Schroeder, John E.

2015-07-21

A hydrodynamically lubricating geometry for the generally circular dynamic sealing lip of rotary seals that are employed to partition a lubricant from an environment. The dynamic sealing lip is provided for establishing compressed sealing engagement with a relatively rotatable surface, and for wedging a film of lubricating fluid into the interface between the dynamic sealing lip and the relatively rotatable surface in response to relative rotation that may occur in the clockwise or the counter-clockwise direction. A wave form incorporating an elongated dimple provides the gradual convergence, efficient impingement angle, and gradual interfacial contact pressure rise that are conducive to efficient hydrodynamic wedging. Skewed elevated contact pressure zones produced by compression edge effects provide for controlled lubricant movement within the dynamic sealing interface between the seal and the relatively rotatable surface, producing enhanced lubrication and low running torque.

Low torque hydrodynamic lip geometry for bi-directional rotation seals

DOEpatents

Dietle, Lannie L [Houston, TX; Schroeder, John E [Richmond, TX

2011-11-15

A hydrodynamically lubricating geometry for the generally circular dynamic sealing lip of rotary seals that are employed to partition a lubricant from an environment. The dynamic sealing lip is provided for establishing compressed sealing engagement with a relatively rotatable surface, and for wedging a film of lubricating fluid into the interface between the dynamic sealing lip and the relatively rotatable surface in response to relative rotation that may occur in the clockwise or the counter-clockwise direction. A wave form incorporating an elongated dimple provides the gradual convergence, efficient impingement angle, and gradual interfacial contact pressure rise that are conducive to efficient hydrodynamic wedging. Skewed elevated contact pressure zones produced by compression edge effects provide for controlled lubricant movement within the dynamic sealing interface between the seal and the relatively rotatable surface, producing enhanced lubrication and low running torque.

New Type of the Interface Evolution in the Richtmyer-Meshkov Instability

NASA Technical Reports Server (NTRS)

Abarzhi, S. I.; Herrmann, M.

2003-01-01

We performed systematic theoretical and numerical studies of the nonlinear large-scale coherent dynamics in the Richtmyer-Meshkov instability for fluids with contrast densities. Our simulations modeled the interface dynamics for compressible and viscous uids. For a two-fluid system we observed that in the nonlinear regime of the instability the bubble velocity decays and its surface attens, and the attening is accompanied by slight oscillations. We found the theoretical solution for the system of conservation laws, describing the principal influence of the density ratio on the motion of the nonlinear bubble. The solution has no adjustable parameters, and shows that the attening of the bubble front is a distinct property universal for all values of the density ratio. This property follows from the fact that the RM bubbles decelerate. The theoretical and numerical results validate each other, describe the new type of the bubble front evolution in RMI, and identify the bubble curvature as important and sensitive diagnostic parameter.

Active turbulence in a gas of self-assembled spinners

PubMed Central

Kokot, Gašper; Das, Shibananda; Winkler, Roland G.; Aranson, Igor S.; Snezhko, Alexey

2017-01-01

Colloidal particles subject to an external periodic forcing exhibit complex collective behavior and self-assembled patterns. A dispersion of magnetic microparticles confined at the air–liquid interface and energized by a uniform uniaxial alternating magnetic field exhibits dynamic arrays of self-assembled spinners rotating in either direction. Here, we report on experimental and simulation studies of active turbulence and transport in a gas of self-assembled spinners. We show that the spinners, emerging as a result of spontaneous symmetry breaking of clock/counterclockwise rotation of self-assembled particle chains, generate vigorous vortical flows at the interface. An ensemble of spinners exhibits chaotic dynamics due to self-generated advection flows. The same-chirality spinners (clockwise or counterclockwise) show a tendency to aggregate and form dynamic clusters. Emergent self-induced interface currents promote active diffusion that could be tuned by the parameters of the external excitation field. Furthermore, the erratic motion of spinners at the interface generates chaotic fluid flow reminiscent of 2D turbulence. Our work provides insight into fundamental aspects of collective transport in active spinner materials and yields rules for particle manipulation at the microscale. PMID:29158382

Pore-scale modeling of moving contact line problems in immiscible two-phase flow.

NASA Astrophysics Data System (ADS)

Kucala, A.; Noble, D.; Martinez, M. J.

2016-12-01

Two immiscible fluids in static equilibrium form a common interface along a solid surface, characterized as the static contact (wetting) angle and is a function of surface geometry, intermolecular forces, and interfacial surface energies manifested as interfacial tension. This static configuration may become perturbed due to external force imbalances (mass injection, pressure gradients, buoyancy, etc.) and the contact line location and interface curvature becomes dynamic. Accurate modeling of moving contact line (MCL) problems is imperative in predicting capillary pressure vs. saturation curves, permeability, and preferential flow paths for a variety of applications, including geological carbon storage (GCS) and enhanced oil recovery (EOR). Here, we present a model for the moving contact line using pore-scale computational fluid dynamics (CFD) which solves the full, time-dependent Navier-Stokes equations using the Galerkin finite-element method. The MCL is modeled as a surface traction force proportional to the surface tension, dependent on the static properties of the immiscible fluid/solid system. The moving two-phase interface is tracked using the level set method and discretized with the conformal decomposition finite element method (CDFEM), allowing for surface tension effects to be computed at the exact interface location. We present a variety of verification test cases for simple two- and three-dimensional geometries to validate the current model, including threshold pressure predictions in flows through pore-throats for a variety of wetting angles. Simulations involving more complex geometries are also presented to be used in future simulations for GCS and EOR problems. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000

A phase-field method to analyze the dynamics of immiscible fluids in porous media

NASA Astrophysics Data System (ADS)

de Paoli, Marco; Roccon, Alessio; Zonta, Francesco; Soldati, Alfredo

2017-11-01

Liquid carbon dioxide (CO2) injected into geological formations (filled with brine) is not completely soluble in the surrounding fluid. For this reason, complex transport phenomena may occur across the interface that separates the two phases (CO2+brine and brine). Inspired by this geophysical instance, we used a Phase-Field Method (PFM) to describe the dynamics of two immiscible fluids in satured porous media. The basic idea of the PFM is to introduce an order parameter (ϕ) that varies continuously across the interfacial layer between the phases and is uniform in the bulk. The equation that describes the distribution of ϕ is the Cahn-Hilliard (CH) equation, which is coupled with the Darcy equation (to evaluate fluid velocity) through the buoyancy and Korteweg stress terms. The governing equations are solved through a pseudo-spectral technique (Fourier-Chebyshev). Our results show that the value of the surface tension between the two phases strongly influences the initial and the long term dynamics of the system. We believe that the proposed numerical approach, which grants an accurate evaluation of the interfacial fluxes of momentum/energy/species, is attractive to describe the transfer mechanism and the overall dynamics of immiscible and partially miscible phases.

Direct Numerical Simulation of Low Capillary Number Pore Scale Flows

NASA Astrophysics Data System (ADS)

Esmaeilzadeh, S.; Soulaine, C.; Tchelepi, H.

2017-12-01

The arrangement of void spaces and the granular structure of a porous medium determines multiple macroscopic properties of the rock such as porosity, capillary pressure, and relative permeability. Therefore, it is important to study the microscopic structure of the reservoir pores and understand the dynamics of fluid displacements through them. One approach for doing this, is direct numerical simulation of pore-scale flow that requires a robust numerical tool for prediction of fluid dynamics and a detailed understanding of the physical processes occurring at the pore-scale. In pore scale flows with a low capillary number, Eulerian multiphase methods are well-known to produce additional vorticity close to the interface. This is mainly due to discretization errors which lead to an imbalance of capillary pressure and surface tension forces that causes unphysical spurious currents. At the pore scale, these spurious currents can become significantly stronger than the average velocity in the phases, and lead to unphysical displacement of the interface. In this work, we first investigate the capability of the algebraic Volume of Fluid (VOF) method in OpenFOAM for low capillary number pore scale flow simulations. Afterward, we compare VOF results with a Coupled Level-Set Volume of Fluid (CLSVOF) method and Iso-Advector method. It has been shown that the former one reduces the VOF's unphysical spurious currents in some cases, and both are known to capture interfaces sharper than VOF. As the conclusion, we will investigate that whether the use of CLSVOF or Iso-Advector will lead to less spurious velocities and more accurate results for capillary driven pore-scale multiphase flows or not. Keywords: Pore-scale multiphase flow, Capillary driven flows, Spurious currents, OpenFOAM

Droplets and the three-phase contact line at the nano-scale. Statics and dynamics

NASA Astrophysics Data System (ADS)

Yatsyshin, Petr; Sibley, David; Savva, Nikos; Kalliadasis, Serafim

2014-11-01

Understanding the behaviour of the solid-liquid-vapour contact line at the scale of several tens of molecular diameters is important in wetting hydrodynamics with applications in micro- and nano-fluidics, including the design of lab-on-a-chip devices and surfaces with specific wetting properties. Due to the fluid inhomogeneity at the nano-scale, the application of continuum-mechanical approaches is limited, and a natural way to remedy this is to seek descriptions accounting for the non-local molecular-level interactions. Density Functional Theory (DFT) for fluids offers a statistical-mechanical framework based on expressing the free energy of the fluid-solid pair as a functional of the spatially varying fluid density. DFT allows us to investigate small drops deposited on planar substrates whilst keeping track of the microscopic structural details of the fluid. Starting from a model of intermolecular forces, we systematically obtain interfaces, surface tensions, and the microscopic contact angle. Using a dynamic extension of equilibrium DFT, we investigate the diffusion-driven evolution of the three-phase contact line to gain insight into the dynamic behaviour of the microscopic contact angle, which is still under debate.

A fictitious domain finite element method for simulations of fluid-structure interactions: The Navier-Stokes equations coupled with a moving solid

NASA Astrophysics Data System (ADS)

Court, Sébastien; Fournié, Michel

2015-05-01

The paper extends a stabilized fictitious domain finite element method initially developed for the Stokes problem to the incompressible Navier-Stokes equations coupled with a moving solid. This method presents the advantage to predict an optimal approximation of the normal stress tensor at the interface. The dynamics of the solid is governed by the Newton's laws and the interface between the fluid and the structure is materialized by a level-set which cuts the elements of the mesh. An algorithm is proposed in order to treat the time evolution of the geometry and numerical results are presented on a classical benchmark of the motion of a disk falling in a channel.

Sloshing dynamics on rotating helium dewar tank

NASA Technical Reports Server (NTRS)

Hung, R. J.

1993-01-01

The generalized mathematical formulation of sloshing dynamics for partially filled liquid of cryogenic superfluid helium II in dewar containers driven by both the gravity gradient and jitter accelerations applicable to scientific spacecraft which is eligible to carry out spinning motion and/or slew motion for the purpose to perform scientific observation during the normal spacecraft operation are investigated. An example is given with Gravity Probe-B (GP-B) spacecraft which is responsible for the sloshing dynamics. The jitter accelerations include slew motion, spinning motion, atmospheric drag on the spacecraft, spacecraft attitude motions arising from machinery vibrations, thruster firing, pointing control of spacecraft, crew motion, etc. Explicit mathematical expressions to cover these forces acting on the spacecraft fluid systems are derived. The numerical computation of sloshing dynamics were based on the non-inertia frame spacecraft bound coordinate, and solve time dependent, three-dimensional formulations of partial differential equations subject to initial and boundary conditions. The explicit mathematical expressions of boundary conditions to cover capillary force effect on the liquid vapor interface in microgravity environments are also derived. The formulations of fluid moment and angular moment fluctuations in fluid profiles induced by the sloshing dynamics, together with fluid stress and moment fluctuations exerted on the spacecraft dewar containers were derived. Results were widely published in the open journals.

Elastic contact mechanics: percolation of the contact area and fluid squeeze-out.

PubMed

Persson, B N J; Prodanov, N; Krick, B A; Rodriguez, N; Mulakaluri, N; Sawyer, W G; Mangiagalli, P

2012-01-01

The dynamics of fluid flow at the interface between elastic solids with rough surfaces depends sensitively on the area of real contact, in particular close to the percolation threshold, where an irregular network of narrow flow channels prevails. In this paper, numerical simulation and experimental results for the contact between elastic solids with isotropic and anisotropic surface roughness are compared with the predictions of a theory based on the Persson contact mechanics theory and the Bruggeman effective medium theory. The theory predictions are in good agreement with the experimental and numerical simulation results and the (small) deviation can be understood as a finite-size effect. The fluid squeeze-out at the interface between elastic solids with randomly rough surfaces is studied. We present results for such high contact pressures that the area of real contact percolates, giving rise to sealed-off domains with pressurized fluid at the interface. The theoretical predictions are compared to experimental data for a simple model system (a rubber block squeezed against a flat glass plate), and for prefilled syringes, where the rubber plunger stopper is lubricated by a high-viscosity silicon oil to ensure functionality of the delivery device. For the latter system we compare the breakloose (or static) friction, as a function of the time of stationary contact, to the theory prediction.

Three-Dimensional User Interfaces for Immersive Virtual Reality

NASA Technical Reports Server (NTRS)

vanDam, Andries

1997-01-01

The focus of this grant was to experiment with novel user interfaces for immersive Virtual Reality (VR) systems, and thus to advance the state of the art of user interface technology for this domain. Our primary test application was a scientific visualization application for viewing Computational Fluid Dynamics (CFD) datasets. This technology has been transferred to NASA via periodic status reports and papers relating to this grant that have been published in conference proceedings. This final report summarizes the research completed over the past year, and extends last year's final report of the first three years of the grant.

Liquid Microjunction Surface Sampling Probe Fluid Dynamics: Computational and Experimental Analysis of Coaxial Intercapillary Positioning Effects on Sample Manipulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

ElNaggar, Mariam S; Barbier, Charlotte N; Van Berkel, Gary J

A coaxial geometry liquid microjunction surface sampling probe (LMJ-SSP) enables direct extraction of analytes from surfaces for subsequent analysis by techniques like mass spectrometry. Solution dynamics at the probe-to-sample surface interface in the LMJ-SSP has been suspected to influence sampling efficiency and dispersion but has not been rigorously investigated. The effect on flow dynamics and analyte transport to the mass spectrometer caused by coaxial retraction of the inner and outer capillaries from each other and the surface during sampling with a LMJ-SSP was investigated using computational fluid dynamics and experimentation. A transparent LMJ-SSP was constructed to provide the means formore » visual observation of the dynamics of the surface sampling process. Visual observation, computational fluid dynamics (CFD) analysis, and experimental results revealed that inner capillary axial retraction from the flush position relative to the outer capillary transitioned the probe from a continuous sampling and injection mode through an intermediate regime to sample plug formationmode caused by eddy currents at the sampling end of the probe. The potential for analytical implementation of these newly discovered probe operational modes is discussed.« less

Lattice Boltzmann simulations of multiple-droplet interaction dynamics.

PubMed

Zhou, Wenchao; Loney, Drew; Fedorov, Andrei G; Degertekin, F Levent; Rosen, David W

2014-03-01

A lattice Boltzmann (LB) formulation, which is consistent with the phase-field model for two-phase incompressible fluid, is proposed to model the interface dynamics of droplet impingement. The interparticle force is derived by comparing the macroscopic transport equations recovered from LB equations with the governing equations of the continuous phase-field model. The inconsistency between the existing LB implementations and the phase-field model in calculating the relaxation time at the phase interface is identified and an approximation is proposed to ensure the consistency with the phase-field model. It is also shown that the commonly used equilibrium velocity boundary for the binary fluid LB scheme does not conserve momentum at the wall boundary and a modified scheme is developed to ensure the momentum conservation at the boundary. In addition, a geometric formulation of the wetting boundary condition is proposed to replace the popular surface energy formulation and results show that the geometric approach enforces the prescribed contact angle better than the surface energy formulation in both static and dynamic wetting. The proposed LB formulation is applied to simulating droplet impingement dynamics in three dimensions and results are compared to those obtained with the continuous phase-field model, the LB simulations reported in the literature, and experimental data from the literature. The results show that the proposed LB simulation approach yields not only a significant speed improvement over the phase-field model in simulating droplet impingement dynamics on a submillimeter length scale, but also better accuracy than both the phase-field model and the previously reported LB techniques when compared to experimental data. Upon validation, the proposed LB modeling methodology is applied to the study of multiple-droplet impingement and interactions in three dimensions, which demonstrates its powerful capability of simulating extremely complex interface phenomena.

A weak-coupling immersed boundary method for fluid-structure interaction with low density ratio of solid to fluid

NASA Astrophysics Data System (ADS)

Kim, Woojin; Lee, Injae; Choi, Haecheon

2018-04-01

We present a weak-coupling approach for fluid-structure interaction with low density ratio (ρ) of solid to fluid. For accurate and stable solutions, we introduce predictors, an explicit two-step method and the implicit Euler method, to obtain provisional velocity and position of fluid-structure interface at each time step, respectively. The incompressible Navier-Stokes equations, together with these provisional velocity and position at the fluid-structure interface, are solved in an Eulerian coordinate using an immersed-boundary finite-volume method on a staggered mesh. The dynamic equation of an elastic solid-body motion, together with the hydrodynamic force at the provisional position of the interface, is solved in a Lagrangian coordinate using a finite element method. Each governing equation for fluid and structure is implicitly solved using second-order time integrators. The overall second-order temporal accuracy is preserved even with the use of lower-order predictors. A linear stability analysis is also conducted for an ideal case to find the optimal explicit two-step method that provides stable solutions down to the lowest density ratio. With the present weak coupling, three different fluid-structure interaction problems were simulated: flows around an elastically mounted rigid circular cylinder, an elastic beam attached to the base of a stationary circular cylinder, and a flexible plate, respectively. The lowest density ratios providing stable solutions are searched for the first two problems and they are much lower than 1 (ρmin = 0.21 and 0.31, respectively). The simulation results agree well with those from strong coupling suggested here and also from previous numerical and experimental studies, indicating the efficiency and accuracy of the present weak coupling.

Fluid behavior in microgravity environment

NASA Technical Reports Server (NTRS)

Hung, R. J.; Lee, C. C.; Tsao, Y. D.

1990-01-01

The instability of liquid and gas interface can be induced by the presence of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. In a spacecraft design, the requirements of settled propellant are different for tank pressurization, engine restart, venting, or propellent transfer. In this paper, the dynamical behavior of liquid propellant, fluid reorientation, and propellent resettling have been carried out through the execution of a CRAY X-MP super computer to simulate fluid management in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have also been investigated.

Conceptual design of two-phase fluid mechanics and heat transfer facility for spacelab

NASA Technical Reports Server (NTRS)

North, B. F.; Hill, M. E.

1980-01-01

Five specific experiments were analyzed to provide definition of experiments designed to evaluate two phase fluid behavior in low gravity. The conceptual design represents a fluid mechanics and heat transfer facility for a double rack in Spacelab. The five experiments are two phase flow patterns and pressure drop, flow boiling, liquid reorientation, and interface bubble dynamics. Hardware was sized, instrumentation and data recording requirements defined, and the five experiments were installed as an integrated experimental package. Applicable available hardware was selected in the experiment design and total experiment program costs were defined.

The Effect of Welding Energy on the Microstructural and Mechanical Properties of Ultrasonic-Welded Copper Joints

PubMed Central

Yang, Jingwei; Cao, Biao; Lu, Qinghua

2017-01-01

The effects of welding energy on the mechanical and microstructural characteristics of ultrasonic-welded pure copper plates were investigated. Complex dynamic recrystallization and grain growth occurred inside the weld zone during ultrasonic welding. At a low welding energy, a thin band of straight weld interfaces was observed and had an ultra-fine grain structure. With an increase in welding energy, the weld interface progressively changed from flat to sinusoidal, and eventually turned into a convoluted wavy pattern, bearing similarities to shear instabilities, as observed in fluid dynamics. The lap shear load of the joints initially increased and then remained stable as the welding energy increased. The tensile characteristics of the joints significantly depended on the development of plastic deformation at the interface. The influence of the microstructure on the hardness was also discussed. PMID:28772553

The Effect of Welding Energy on the Microstructural and Mechanical Properties of Ultrasonic-Welded Copper Joints.

PubMed

Yang, Jingwei; Cao, Biao; Lu, Qinghua

2017-02-16

The effects of welding energy on the mechanical and microstructural characteristics of ultrasonic-welded pure copper plates were investigated. Complex dynamic recrystallization and grain growth occurred inside the weld zone during ultrasonic welding. At a low welding energy, a thin band of straight weld interfaces was observed and had an ultra-fine grain structure. With an increase in welding energy, the weld interface progressively changed from flat to sinusoidal, and eventually turned into a convoluted wavy pattern, bearing similarities to shear instabilities, as observed in fluid dynamics. The lap shear load of the joints initially increased and then remained stable as the welding energy increased. The tensile characteristics of the joints significantly depended on the development of plastic deformation at the interface. The influence of the microstructure on the hardness was also discussed.

A fictitious domain method for fluid/solid coupling applied to the lithosphere/asthenosphere interaction.

NASA Astrophysics Data System (ADS)

Cerpa, Nestor; Hassani, Riad; Gerbault, Muriel

2014-05-01

A large variety of geodynamical problems can be viewed as a solid/fluid interaction problem coupling two bodies with different physics. In particular the lithosphere/asthenosphere mechanical interaction in subduction zones belongs to this kind of problem, where the solid lithosphere is embedded in the asthenospheric viscous fluid. In many fields (Industry, Civil Engineering,etc.), in which deformations of solid and fluid are "small", numerical modelers consider the exact discretization of both domains and fit as well as possible the shape of the interface between the two domains, solving the discretized physic problems by the Finite Element Method (FEM). Although, in a context of subduction, the lithosphere is submitted to large deformation, and can evolve into a complex geometry, thus leading to important deformation of the surrounding asthenosphere. To alleviate the precise meshing of complex geometries, numerical modelers have developed non-matching interface methods called Fictitious Domain Methods (FDM). The main idea of these methods is to extend the initial problem to a bigger (and simpler) domain. In our version of FDM, we determine the forces at the immersed solid boundary required to minimize (at the least square sense) the difference between fluid and solid velocities at this interface. This method is first-order accurate and the stability depends on the ratio between the fluid background mesh size and the interface discretization. We present the formulation and provide benchmarks and examples showing the potential of the method : 1) A comparison with an analytical solution of a viscous flow around a rigid body. 2) An experiment of a rigid sphere sinking in a viscous fluid (in two and three dimensional cases). 3) A comparison with an analog subduction experiment. Another presentation aims at describing the geodynamical application of this method to Andean subduction dynamics, studying cyclic slab folding on the 660 km discontinuity, and its relationship with flat subduction.

A Diffuse Interface Model with Immiscibility Preservation

PubMed Central

Tiwari, Arpit; Freund, Jonathan B.; Pantano, Carlos

2013-01-01

A new, simple, and computationally efficient interface capturing scheme based on a diffuse interface approach is presented for simulation of compressible multiphase flows. Multi-fluid interfaces are represented using field variables (interface functions) with associated transport equations that are augmented, with respect to an established formulation, to enforce a selected interface thickness. The resulting interface region can be set just thick enough to be resolved by the underlying mesh and numerical method, yet thin enough to provide an efficient model for dynamics of well-resolved scales. A key advance in the present method is that the interface regularization is asymptotically compatible with the thermodynamic mixture laws of the mixture model upon which it is constructed. It incorporates first-order pressure and velocity non-equilibrium effects while preserving interface conditions for equilibrium flows, even within the thin diffused mixture region. We first quantify the improved convergence of this formulation in some widely used one-dimensional configurations, then show that it enables fundamentally better simulations of bubble dynamics. Demonstrations include both a spherical bubble collapse, which is shown to maintain excellent symmetry despite the Cartesian mesh, and a jetting bubble collapse adjacent a wall. Comparisons show that without the new formulation the jet is suppressed by numerical diffusion leading to qualitatively incorrect results. PMID:24058207

User interface concerns

NASA Technical Reports Server (NTRS)

Redhed, D. D.

1978-01-01

Three possible goals for the Numerical Aerodynamic Simulation Facility (NASF) are: (1) a computational fluid dynamics (as opposed to aerodynamics) algorithm development tool; (2) a specialized research laboratory facility for nearly intractable aerodynamics problems that industry encounters; and (3) a facility for industry to use in its normal aerodynamics design work that requires high computing rates. The central system issue for industry use of such a computer is the quality of the user interface as implemented in some kind of a front end to the vector processor.

Translational viscous drags of an ellipsoid straddling an interface between two fluids.

PubMed

Boniello, Giuseppe; Stocco, Antonio; Gross, Michel; In, Martin; Blanc, Christophe; Nobili, Maurizio

2016-07-01

We study the dynamics of individual polystyrene ellipsoids of different aspect ratios trapped at the air-water interface. Using particle tracking and in situ vertical scanning interferometry techniques we are able to measure translational drags and the protrusion in air of the ellipsoids. We report that translational drags on the ellipsoid are unexpectedly enhanced: despite the fact that a noticeable part of the ellipsoid is in air, drags are found larger than the bulk one in water.

MPI implementation of PHOENICS: A general purpose computational fluid dynamics code

NASA Astrophysics Data System (ADS)

Simunovic, S.; Zacharia, T.; Baltas, N.; Spalding, D. B.

1995-03-01

PHOENICS is a suite of computational analysis programs that are used for simulation of fluid flow, heat transfer, and dynamical reaction processes. The parallel version of the solver EARTH for the Computational Fluid Dynamics (CFD) program PHOENICS has been implemented using Message Passing Interface (MPI) standard. Implementation of MPI version of PHOENICS makes this computational tool portable to a wide range of parallel machines and enables the use of high performance computing for large scale computational simulations. MPI libraries are available on several parallel architectures making the program usable across different architectures as well as on heterogeneous computer networks. The Intel Paragon NX and MPI versions of the program have been developed and tested on massively parallel supercomputers Intel Paragon XP/S 5, XP/S 35, and Kendall Square Research, and on the multiprocessor SGI Onyx computer at Oak Ridge National Laboratory. The preliminary testing results of the developed program have shown scalable performance for reasonably sized computational domains.

MPI implementation of PHOENICS: A general purpose computational fluid dynamics code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simunovic, S.; Zacharia, T.; Baltas, N.

1995-04-01

PHOENICS is a suite of computational analysis programs that are used for simulation of fluid flow, heat transfer, and dynamical reaction processes. The parallel version of the solver EARTH for the Computational Fluid Dynamics (CFD) program PHOENICS has been implemented using Message Passing Interface (MPI) standard. Implementation of MPI version of PHOENICS makes this computational tool portable to a wide range of parallel machines and enables the use of high performance computing for large scale computational simulations. MPI libraries are available on several parallel architectures making the program usable across different architectures as well as on heterogeneous computer networks. Themore » Intel Paragon NX and MPI versions of the program have been developed and tested on massively parallel supercomputers Intel Paragon XP/S 5, XP/S 35, and Kendall Square Research, and on the multiprocessor SGI Onyx computer at Oak Ridge National Laboratory. The preliminary testing results of the developed program have shown scalable performance for reasonably sized computational domains.« less

Computer-aided-engineering system for modeling and analysis of ECLSS integration testing

NASA Technical Reports Server (NTRS)

Sepahban, Sonbol

1987-01-01

The accurate modeling and analysis of two-phase fluid networks found in environmental control and life support systems is presently undertaken by computer-aided engineering (CAE) techniques whose generalized fluid dynamics package can solve arbitrary flow networks. The CAE system for integrated test bed modeling and analysis will also furnish interfaces and subsystem/test-article mathematical models. Three-dimensional diagrams of the test bed are generated by the system after performing the requisite simulation and analysis.

Dynamics of ultra-thin polystyrene with and without a (artificial) dead layer studied by resonance enhanced dynamic light scattering

NASA Astrophysics Data System (ADS)

Vianna, S. D. B.; Lin, F. Y.; Plum, M. A.; Duran, H.; Steffen, W.

2017-05-01

Using non-invasive, marker-free resonance enhanced dynamic light scattering, the dynamics of capillary waves on ultrathin polystyrene films' coupling to the viscoelastic and mechanical properties have been studied. The dynamics of ultrathin polymer films is still debated. In particular the question of what influence either the solid substrate and/or the fluid-gas interface has on the dynamics and the mechanical properties of films of glass forming liquids as polymers is in the focus of the present research. As a consequence, e.g., viscosity close to interfaces and thus the average viscosity of very thin films are prone to change. This study is focused on atactic, non-entangled polystyrene thin films on the gold surface. A slow dynamic mode was observed with Vogel-Fulcher-Tammann temperature dependence, slowing down with decreasing film thickness. We tentatively attribute this relaxation mode to overdamped capillary waves because of its temperature dependence and the dispersion with a wave vector which was found. No signs of a more mobile layer at the air/polymer interface or of a "dead layer" at the solid/polymer interface were found. Therefore we investigated the influence of an artificially created dead layer on the capillary wave dynamics by introducing covalently bound polystyrene polymer brushes as anchors. The dynamics was slowed down to a degree more than expected from theoretical work on the increase of density close to the solid liquid interface—instead of a "dead layer" of 2 nm, the interaction seems to extend more than 10 nm into the polymer.

Wetting Hysteresis at the Molecular Scale

NASA Technical Reports Server (NTRS)

Jin, Wei; Koplik, Joel; Banavar, Jayanth R.

1996-01-01

The motion of a fluid-fluid-solid contact line on a rough surface is well known to display hysteresis in the contact angle vs. velocity relationship. In order to understand the phenomenon at a fundamental microscopic level, we have conducted molecular dynamics computer simulations of a Wilhelmy plate experiment in which a solid surface is dipped into a liquid bath, and the force-velocity characteristics are measured. We directly observe a systematic variation of force and contact angle with velocity, which is single-valued for the case of an atomically smooth solid surface. In the microscopically rough case, however, we find (as intuitively expected) an open hysteresis loop. Further characterization of the interface dynamics is in progress.

Non-equilibrium phase stabilization versus bubble nucleation at a nanoscale-curved Interface

NASA Astrophysics Data System (ADS)

Schiffbauer, Jarrod; Luo, Tengfei

Using continuum dynamic van der Waals theory in a radial 1D geometry with a Lennard-Jones fluid model, we investigate the nature of vapor bubble nucleation near a heated, nanoscale-curved convex interface. Vapor bubble nucleation and growth are observed for interfaces with sufficiently large radius of curvature while phase stabilization of a superheated fluid layer occurs at interfaces with smaller radius. The hypothesis that the high Laplace pressure required for stable equilibrium of very small bubbles is responsible for phase stability is tested by effectively varying the parameter which controls liquid-vapor surface tension. In doing so, the liquid-vapor surface tension- hence Laplace pressure-is shown to have limited effect on phase stabilization vs. bubble nucleation. However, the strong dependence of nucleation on leading-order momentum transport, i.e. viscous dissipation, near the heated inner surface is demonstrated. We gratefully acknowledge ND Energy for support through the ND Energy Postdoctoral Fellowship program and the Army Research Office, Grant No. W911NF-16-1-0267, managed by Dr. Chakrapani Venanasi.

Effects of aperture variability and wettability on immiscible displacement in fractures

NASA Astrophysics Data System (ADS)

Yang, Zhibing; Méheust, Yves; Neuweiler, Insa

2017-04-01

Fluid-fluid displacement in porous and fractured media is an important process. Understanding and controlling this process is key to many practical applications, such as hydrocarbon recovery, geological storage of CO2, groundwater remediation, etc. Here, we numerically study fluid-fluid displacement in rough-walled fractures. We focus on the combined effect of wettability and fracture surface topography on displacement patterns and interface growth. We develop a novel numerical model to simulate dynamic fluid invasion under the influence of capillary and viscous forces. The capillary force is calculated using the two principal curvatures (aperture-induced curvature and in-plane curvature) at the fluid-fluid interface, and the viscous force is taken into account by solving the fluid pressure distribution. The aperture field of a fracture is represented by a spatially correlated random field, which is described by a power spectrum for the fracture wall topography and a cutoff wave-length. We numerically produce displacement patterns ranging from stable displacement, capillary fingering, and viscous fingering, as well as the transitions between them. We show that both reducing the aperture variability and increasing the contact angle (from drainage to weak imbibition) stabilize the displacement due to the influence of the in-plane curvature, an effect analogous to that of the cooperative pore filling in porous media. Implications of these results will be discussed.

Modelling low Reynolds number vortex-induced vibration problems with a fixed mesh fluid-solid interaction formulation

NASA Astrophysics Data System (ADS)

González Cornejo, Felipe A.; Cruchaga, Marcela A.; Celentano, Diego J.

2017-11-01

The present work reports a fluid-rigid solid interaction formulation described within the framework of a fixed-mesh technique. The numerical analysis is focussed on the study of a vortex-induced vibration (VIV) of a circular cylinder at low Reynolds number. The proposed numerical scheme encompasses the fluid dynamics computation in an Eulerian domain where the body is embedded using a collection of markers to describe its shape, and the rigid solid's motion is obtained with the well-known Newton's law. The body's velocity is imposed on the fluid domain through a penalty technique on the embedded fluid-solid interface. The fluid tractions acting on the solid are computed from the fluid dynamic solution of the flow around the body. The resulting forces are considered to solve the solid motion. The numerical code is validated by contrasting the obtained results with those reported in the literature using different approaches for simulating the flow past a fixed circular cylinder as a benchmark problem. Moreover, a mesh convergence analysis is also done providing a satisfactory response. In particular, a VIV problem is analyzed, emphasizing the description of the synchronization phenomenon.

ISCFD Nagoya 1989 - International Symposium on Computational Fluid Dynamics, 3rd, Nagoya, Japan, Aug. 28-31, 1989, Technical Papers

NASA Astrophysics Data System (ADS)

Recent advances in computational fluid dynamics are discussed in reviews and reports. Topics addressed include large-scale LESs for turbulent pipe and channel flows, numerical solutions of the Euler and Navier-Stokes equations on parallel computers, multigrid methods for steady high-Reynolds-number flow past sudden expansions, finite-volume methods on unstructured grids, supersonic wake flow on a blunt body, a grid-characteristic method for multidimensional gas dynamics, and CIC numerical simulation of a wave boundary layer. Consideration is given to vortex simulations of confined two-dimensional jets, supersonic viscous shear layers, spectral methods for compressible flows, shock-wave refraction at air/water interfaces, oscillatory flow in a two-dimensional collapsible channel, the growth of randomness in a spatially developing wake, and an efficient simplex algorithm for the finite-difference and dynamic linear-programming method in optimal potential control.

Arresting relaxation in Pickering Emulsions

NASA Astrophysics Data System (ADS)

Atherton, Tim; Burke, Chris

2015-03-01

Pickering emulsions consist of droplets of one fluid dispersed in a host fluid and stabilized by colloidal particles absorbed at the fluid-fluid interface. Everyday materials such as crude oil and food products like salad dressing are examples of these materials. Particles can stabilize non spherical droplet shapes in these emulsions through the following sequence: first, an isolated droplet is deformed, e.g. by an electric field, increasing the surface area above the equilibrium value; additional particles are then adsorbed to the interface reducing the surface tension. The droplet is then allowed to relax toward a sphere. If more particles were adsorbed than can be accommodated by the surface area of the spherical ground state, relaxation of the droplet is arrested at some non-spherical shape. Because the energetic cost of removing adsorbed colloids exceeds the interfacial driving force, these configurations can remain stable over long timescales. In this presentation, we present a computational study of the ordering present in anisotropic droplets produced through the mechanism of arrested relaxation and discuss the interplay between the geometry of the droplet, the dynamical process that produced it, and the structure of the defects observed.

An Alternative Frictional Boundary Condition for Computational Fluid Dynamics Simulation of Friction Stir Welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan

For better application of numerical simulation in optimization and design of friction stir welding (FSW), this paper presents a new frictional boundary condition at the tool/workpiece interface for computational fluid dynamics (CFD) modeling of FSW. The proposed boundary condition is based on an implementation of the Coulomb friction model. Using the new boundary condition, the CFD simulation yields non-uniform distribution of contact state over the tool/workpiece interface, as validated by the experimental weld macrostructure. It is found that interfacial sticking state is present over large area at the tool-workpiece interface, while significant interfacial sliding occurs at the shoulder periphery, themore » lower part of pin side, and the periphery of pin bottom. Due to the interfacial sticking, a rotating flow zone is found under the shoulder, in which fast circular motion occurs. The diameter of the rotating flow zone is smaller than the shoulder diameter, which is attributed to the presence of the interfacial sliding at the shoulder periphery. For the simulated welding condition, the heat generation due to friction and plastic deformation makes up 54.4 and 45.6% of the total heat generation rate, respectively. In conclusion, the simulated temperature field is validated by the good agreement to the experimental measurements.« less

An Alternative Frictional Boundary Condition for Computational Fluid Dynamics Simulation of Friction Stir Welding

DOE PAGES

Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan; ...

2016-07-11

For better application of numerical simulation in optimization and design of friction stir welding (FSW), this paper presents a new frictional boundary condition at the tool/workpiece interface for computational fluid dynamics (CFD) modeling of FSW. The proposed boundary condition is based on an implementation of the Coulomb friction model. Using the new boundary condition, the CFD simulation yields non-uniform distribution of contact state over the tool/workpiece interface, as validated by the experimental weld macrostructure. It is found that interfacial sticking state is present over large area at the tool-workpiece interface, while significant interfacial sliding occurs at the shoulder periphery, themore » lower part of pin side, and the periphery of pin bottom. Due to the interfacial sticking, a rotating flow zone is found under the shoulder, in which fast circular motion occurs. The diameter of the rotating flow zone is smaller than the shoulder diameter, which is attributed to the presence of the interfacial sliding at the shoulder periphery. For the simulated welding condition, the heat generation due to friction and plastic deformation makes up 54.4 and 45.6% of the total heat generation rate, respectively. In conclusion, the simulated temperature field is validated by the good agreement to the experimental measurements.« less

A three-dimensional computational fluid dynamics model of shear stress distribution during neotissue growth in a perfusion bioreactor.

PubMed

Guyot, Y; Luyten, F P; Schrooten, J; Papantoniou, I; Geris, L

2015-12-01

Bone tissue engineering strategies use flow through perfusion bioreactors to apply mechanical stimuli to cells seeded on porous scaffolds. Cells grow on the scaffold surface but also by bridging the scaffold pores leading a fully filled scaffold following the scaffold's geometric characteristics. Current computational fluid dynamic approaches for tissue engineering bioreactor systems have been mostly carried out for empty scaffolds. The effect of 3D cell growth and extracellular matrix formation (termed in this study as neotissue growth), on its surrounding fluid flow field is a challenge yet to be tackled. In this work a combined approach was followed linking curvature driven cell growth to fluid dynamics modeling. The level-set method (LSM) was employed to capture neotissue growth driven by curvature, while the Stokes and Darcy equations, combined in the Brinkman equation, provided information regarding the distribution of the shear stress profile at the neotissue/medium interface and within the neotissue itself during growth. The neotissue was assumed to be micro-porous allowing flow through its structure while at the same time allowing the simulation of complete scaffold filling without numerical convergence issues. The results show a significant difference in the amplitude of shear stress for cells located within the micro-porous neo-tissue or at the neotissue/medium interface, demonstrating the importance of taking along the neotissue in the calculation of the mechanical stimulation of cells during culture.The presented computational framework is used on different scaffold pore geometries demonstrating its potential to be used a design as tool for scaffold architecture taking into account the growing neotissue. Biotechnol. Bioeng. 2015;112: 2591-2600. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

Numerical Simulation of Two-Fluid Mingling Using the Particle Finite Element Method with Applications to Magmatic and Volcanic Processes

NASA Astrophysics Data System (ADS)

de Mier, M.; Costa, F.; Idelsohn, S.

2008-12-01

Many magmatic and volcanic processes (e.g., magma differentiation, mingling, transport in the volcanic conduit) are controlled by the physical properties and flow styles of high-temperature silicate melts. Such processes can be experimentally investigated using analog systems and scaling methods, but it is difficult to find the suitable material and it is generally not possible to quantitatively extrapolate the results to the natural system. An alternative means of studying fluid dynamics in volcanic systems is with numerical models. We have chosen the Particle Finite Element Method (PFEM), which is based on a Delaunay mesh that moves with the fluid velocity, the Navier-Stokes equations in Lagrangian formulation, and linear elements for velocity, pressure, and temperature. Remeshing is performed when the grid becomes too distorted [E. Oñate et al., 2004. The Particle Finite Element Method: An Overview. Int. J. Comput. Meth. 1, 267-307]. The method is ideal for tracking material interfaces between different fluids or media. Methods based on Eulerian reference frames need special techniques, such as level-set or volume-of-fluid, to capture the interface position, and these techniques add a significant numerical diffusion at the interface. We have performed a series of two-dimensional simulations of a classical problem of fluid dynamics in magmatic and volcanic systems: intrusion of a basaltic melt in a silica-rich magma reservoir. We have used realistic physical properties and equations of state for the silicate melts (e.g., temperature, viscosity, and density) and tracked the changes in the system for geologically relevant time scales (up to 100 years). The problem is modeled by the low-Mach-number equations derived from an asymptotic analysis of the compressible Navier-Stokes equations that removes shock waves from the flow but allows however large variations of density due to temperature variations. Non-constant viscosity and volume changes are taken into account in the momentum conservation equation through the full shear-stress tensor. The implications of different magma intrusion rates, volumes, and times will be discussed in the context of mafic-silicic magma mixing and eruption triggers.

Axisymmetric flows from fluid injection into a confined porous medium

NASA Astrophysics Data System (ADS)

Guo, Bo; Zheng, Zhong; Celia, Michael A.; Stone, Howard A.

2016-02-01

We study the axisymmetric flows generated from fluid injection into a horizontal confined porous medium that is originally saturated with another fluid of different density and viscosity. Neglecting the effects of surface tension and fluid mixing, we use the lubrication approximation to obtain a nonlinear advection-diffusion equation that describes the time evolution of the sharp fluid-fluid interface. The flow behaviors are controlled by two dimensionless groups: M, the viscosity ratio of displaced fluid relative to injected fluid, and Γ, which measures the relative importance of buoyancy and fluid injection. For this axisymmetric geometry, the similarity solution involving R2/T (where R is the dimensionless radial coordinate and T is the dimensionless time) is an exact solution to the nonlinear governing equation for all times. Four analytical expressions are identified as asymptotic approximations (two of which are new solutions): (i) injection-driven flow with the injected fluid being more viscous than the displaced fluid (Γ ≪ 1 and M < 1) where we identify a self-similar solution that indicates a parabolic interface shape; (ii) injection-driven flow with injected and displaced fluids of equal viscosity (Γ ≪ 1 and M = 1), where we find a self-similar solution that predicts a distinct parabolic interface shape; (iii) injection-driven flow with a less viscous injected fluid (Γ ≪ 1 and M > 1) for which there is a rarefaction wave solution, assuming that the Saffman-Taylor instability does not occur at the reservoir scale; and (iv) buoyancy-driven flow (Γ ≫ 1) for which there is a well-known self-similar solution corresponding to gravity currents in an unconfined porous medium [S. Lyle et al. "Axisymmetric gravity currents in a porous medium," J. Fluid Mech. 543, 293-302 (2005)]. The various axisymmetric flows are summarized in a Γ-M regime diagram with five distinct dynamic behaviors including the four asymptotic regimes and an intermediate regime. The implications of the regime diagram are discussed using practical engineering projects of geological CO2 sequestration, enhanced oil recovery, and underground waste disposal.

A General Approach for Fluid Patterning and Application in Fabricating Microdevices.

PubMed

Huang, Zhandong; Yang, Qiang; Su, Meng; Li, Zheng; Hu, Xiaotian; Li, Yifan; Pan, Qi; Ren, Wanjie; Li, Fengyu; Song, Yanlin

2018-06-19

Engineering the fluid interface such as the gas-liquid interface is of great significance for solvent processing applications including functional material assembly, inkjet printing, and high-performance device fabrication. However, precisely controlling the fluid interface remains a great challenge owing to its flexibility and fluidity. Here, a general method to manipulate the fluid interface for fluid patterning using micropillars in the microchannel is reported. The principle of fluid patterning for immiscible fluid pairs including air, water, and oils is proposed. This understanding enables the preparation of programmable multiphase fluid patterns and assembly of multilayer functional materials to fabricate micro-optoelectronic devices. This general strategy of fluid patterning provides a promising platform to study the fundamental processes occurring on the fluid interface, and benefits applications in many subjects, such as microfluidics, microbiology, chemical analysis and detection, material synthesis and assembly, device fabrication, etc. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Numerical studies of the surface tension effect of cryogenic liquid helium

NASA Technical Reports Server (NTRS)

Hung, R. J.

1994-01-01

The generalized mathematical formulation of sloshing dynamics for partially filled liquid of cryogenic superfluid helium II in dewar containers driven by both the gravity gradient and jitter accelerations applicable to scientific spacecraft which is eligible to carry out spinning motion and/or slew motion for the purpose of performing scientific observation during the normal spacecraft operation is investigated. An example is given with Gravity Probe-B (GP-B) spacecraft which is responsible for the sloshing dynamics. The jitter accelerations include slew motion, spinning motion, atmospheric drag on the spacecraft, spacecraft attitude motions arising from machinery vibrations, thruster firing, pointing control of spacecraft, crew motion, etc. Explicit mathematical expressions to cover these forces acting on the spacecraft fluid systems are derived. The numerical computation of sloshing dynamics has been based on the non-inertia frame spacecraft bound coordinate, and solve time-dependent, three-dimensional formulations of partial differential equations subject to initial and boundary conditions. The explicit mathematical expressions of boundary conditions to cover capillary force effect on the liquid vapor interface in microgravity environments are also derived. The formulations of fluid moment and angular moment fluctuations in fluid profiles induced by the sloshing dynamics, together with fluid stress and moment fluctuations exerted on the spacecraft dewar containers, have been derived.

A parallel interaction potential approach coupled with the immersed boundary method for fully resolved simulations of deformable interfaces and membranes

NASA Astrophysics Data System (ADS)

Spandan, Vamsi; Meschini, Valentina; Ostilla-Mónico, Rodolfo; Lohse, Detlef; Querzoli, Giorgio; de Tullio, Marco D.; Verzicco, Roberto

2017-11-01

In this paper we show and discuss how the deformation dynamics of closed liquid-liquid interfaces (for example drops and bubbles) can be replicated with use of a phenomenological interaction potential model. This new approach to simulate liquid-liquid interfaces is based on the fundamental principle of minimum potential energy where the total potential energy depends on the extent of deformation of a spring network distributed on the surface of the immersed drop or bubble. Simulating liquid-liquid interfaces using this model require computing ad-hoc elastic constants which is done through a reverse-engineered approach. The results from our simulations agree very well with previous studies on the deformation of drops in standard flow configurations such as a deforming drop in a shear flow or cross flow. The interaction potential model is highly versatile, computationally efficient and can be easily incorporated into generic single phase fluid solvers to also simulate complex fluid-structure interaction problems. This is shown by simulating flow in the left ventricle of the heart with mechanical and natural mitral valves where the imposed flow, motion of ventricle and valves dynamically govern the behaviour of each other. Results from these simulations are compared with ad-hoc in-house experimental measurements. Finally, we present a simple and easy to implement parallelisation scheme, as high performance computing is unavoidable when studying large scale problems involving several thousands of simultaneously deforming bodies in highly turbulent flows.

Controlling the Mobility of the Fluid Interface of Moving Gas Bubbles or Liquid Drops by Using Micellar Solutions of Surfactants

NASA Technical Reports Server (NTRS)

Maldarelli, Charles; Papageorgiou, Demetrios

1998-01-01

Microgravity processes must rely on mechanisms other than buoyancy to move bubbles or droplets from one region to another in a continuous liquid phase. One suggested method is thermocapillary migration in which a temperature gradient is applied to the continuous phase. A significant and as yet unresolved impediment to the use of thermocapillary migration to direct bubble or drop motion is that these migrations can be significantly retarded by the adsorption onto the fluid particle surface of surface active impurities unavoidably present in the continuous or (if the particle is a liquid) droplet phases. The focus of our research was to develop a theory for remobilizing fluid particle interfaces retarded by a surfactant impurity in an effort to make more viable the use of thermocapillary migrations for the management of bubbles and drops in microgravity. We postulated that a surfactant at high bulk concentration which kinetically exchanges rapidly with the surface can restore interface mobility. The scaling arguments along with a discussion of the previous literature is reviewed in the context of the scaling framework. The specific objectives of the research were twofold. The first was to prove the remobilization theory by studying a model problem. As the mechanism for remobilization is independent of the force which drives the particle, the fluid particle shape and the presence of fluid inertia, we chose the simplest model consisting of a spherical bubble rising steadily by buoyancy in creeping flow. We solved the hydrodynamic and surfactant transport equations for rapid kinetic exchange to demonstrate that as the concentration increases, the Marangoni retardation at first increases (the low k behavior) and then decreases (the high k behavior). The second objective was to develop a method to determine the kinetic rate constants of a surfactant molecule, since this information is necessary to select surfactants which will exchange rapidly enough relative to the convective rate in the thermocapillary process of interest. To measure the kinetic rate, we measure the dynamic tension change accompanying adsorption onto an initially clean interface, or the re-equilibration in tension when an equilibrium interface is compressed. The dynamic tension measurements are made by a pendant bubble method, in which surfactant adsorbs onto a pendant bubble, and the tension is measured by analyzing the shape change in the bubble. We conclude this report by detailing the publications, presentations and doctoral thesis completed under the auspices of this grant.

Active turbulence in a gas of self-assembled spinners

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kokot, Gasper; Das, Shibananda; Winkler, Roland G.

Colloidal particles subject to an external periodic forcing exhibit complex collective behavior and self-assembled patterns. A dispersion of magnetic microparticles confined at the air-liquid interface and energized by a uniform uniaxial alternating magnetic field exhibits dynamic arrays of self-assembled spinners rotating in either direction. Here, we report on experimental and simulation studies of active turbulence and transport in a gas of self-assembled spinners. We show that the spinners, emerging as a result of spontaneous symmetry breaking of clock/counterclockwise rotation of self-assembled particle chains, generate vigorous vortical flows at the interface. An ensemble of spinners exhibits chaotic dynamics due to self-generatedmore » advection flows. The same-chirality spinners (clockwise or counterclock-wise) show a tendency to aggregate and form dynamic clusters. Emergent self-induced interface currents promote active diffusion that could be tuned by the parameters of the external excitation field. Furthermore, the erratic motion of spinners at the interface generates chaotic fluid flow reminiscent of 2D turbulence. As a result, our work provides insight into fundamental aspects of collective transport in active spinner materials and yields rules for particle manipulation at the microscale.« less

Numerical Simulation of Dynamic Contact Angles and Contact Lines in Multiphase Flows using Level Set Method

NASA Astrophysics Data System (ADS)

Pendota, Premchand

Many physical phenomena and industrial applications involve multiphase fluid flows and hence it is of high importance to be able to simulate various aspects of these flows accurately. The Dynamic Contact Angles (DCA) and the contact lines at the wall boundaries are a couple of such important aspects. In the past few decades, many mathematical models were developed for predicting the contact angles of the inter-face with the wall boundary under various flow conditions. These models are used to incorporate the physics of DCA and contact line motion in numerical simulations using various interface capturing/tracking techniques. In the current thesis, a simple approach to incorporate the static and dynamic contact angle boundary conditions using the level set method is developed and implemented in multiphase CFD codes, LIT (Level set Interface Tracking) (Herrmann (2008)) and NGA (flow solver) (Desjardins et al (2008)). Various DCA models and associated boundary conditions are reviewed. In addition, numerical aspects such as the occurrence of a stress singularity at the contact lines and grid convergence of macroscopic interface shape are dealt with in the context of the level set approach.

Active turbulence in a gas of self-assembled spinners

DOE PAGES

Kokot, Gasper; Das, Shibananda; Winkler, Roland G.; ...

2017-11-20

Colloidal particles subject to an external periodic forcing exhibit complex collective behavior and self-assembled patterns. A dispersion of magnetic microparticles confined at the air-liquid interface and energized by a uniform uniaxial alternating magnetic field exhibits dynamic arrays of self-assembled spinners rotating in either direction. Here, we report on experimental and simulation studies of active turbulence and transport in a gas of self-assembled spinners. We show that the spinners, emerging as a result of spontaneous symmetry breaking of clock/counterclockwise rotation of self-assembled particle chains, generate vigorous vortical flows at the interface. An ensemble of spinners exhibits chaotic dynamics due to self-generatedmore » advection flows. The same-chirality spinners (clockwise or counterclock-wise) show a tendency to aggregate and form dynamic clusters. Emergent self-induced interface currents promote active diffusion that could be tuned by the parameters of the external excitation field. Furthermore, the erratic motion of spinners at the interface generates chaotic fluid flow reminiscent of 2D turbulence. As a result, our work provides insight into fundamental aspects of collective transport in active spinner materials and yields rules for particle manipulation at the microscale.« less

Fluid Surface Deformation by Objects in the Cheerios Effect

NASA Astrophysics Data System (ADS)

Nguyen, Khoi; Miller, Michael; Mandre, Shreyas; Mandre Lab Team

2012-11-01

Small objects floating on a fluid/air interface deform of the surface depending on material surface properties, density, and geometry. These objects attract each other through capillary interactions, a phenomenon dubbed the ``cheerios effect.'' The attractive force and torque exerted on these objects by the interface can be estimated if the meniscus deformation is known. In addition, the floating objects can also rotate due to such an interaction. We present a series of experiments focused on visualizing the the motions of the floating objects and the deformation of the interface. The experiments involve thin laser-cut acrylic pieces attracting each other on water in a large glass petri dish and a camera set-up to capture the process. Furthermore, optical distortion of a grid pattern is used to visualize the water surface deformation near the edge of the objects. This study of the deformation of the water surface around a floating object, of the attractive/repulsive forces, and of post-contact rotational dynamics are potentially instrumental in the study of colloidal self-assembly.

Qualitative CFD for Rapid Learning in Industrial and Academic Applications

NASA Astrophysics Data System (ADS)

Variano, Evan

2010-11-01

We present a set of tools that allow CFD to be used at an early stage in the design process. Users can rapidly explore the qualitative aspects of fluid flow using real-time simulations that react immediately to design changes. This can guide the design process by fostering an intuitive understanding of fluid dynamics at the prototyping stage. We use an extremely stable Navier-Stokes solver that is available commercially (and free to academic users) plus a custom user interface. The code is designed for the animation and gaming industry, and we exploit the powerful graphical display capabilities to develop a unique human-machine interface. This interface allows the user to efficiently explore the flow in 3D + real time, fostering an intuitive understanding of steady and unsteady flow patterns. There are obvious extensions to use in an academic setting. The trade-offs between accuracy and speed will be discussed in the context of CFD's role in design and education.

Methodologies for launcher-payload coupled dynamic analysis

NASA Astrophysics Data System (ADS)

Fransen, S. H. J. A.

2012-06-01

An important step in the design and verification process of spacecraft structures is the coupled dynamic analysis with the launch vehicle in the low-frequency domain, also referred to as coupled loads analysis (CLA). The objective of such analyses is the computation of the dynamic environment of the spacecraft (payload) in terms of interface accelerations, interface forces, center of gravity (CoG) accelerations as well as the internal state of stress. In order to perform an efficient, fast and accurate launcher-payload coupled dynamic analysis, various methodologies have been applied and developed. The methods are related to substructuring techniques, data recovery techniques, the effects of prestress and fluids and time integration problems. The aim of this paper was to give an overview of these methodologies and to show why, how and where these techniques can be used in the process of launcher-payload coupled dynamic analysis. In addition, it will be shown how these methodologies fit together in a library of procedures which can be used with the MSC.Nastran™ solution sequences.

Establishing mesh topology in multi-material cells: enabling technology for robust and accurate multi-material simulations

DOE PAGES

Kikinzon, Evgeny; Shashkov, Mikhail Jurievich; Garimella, Rao Veerabhadra

2018-05-29

Real world problems are typically multi-material, combining materials such as gases, liquids and solids that have very different properties. The material interfaces may be fixed in time or can be a part of the solution, as in fluid-structure interactions or air-water dynamics, and therefore move and change shape. In such problems the computational mesh may be non-conformal to interfaces due to complexity of these interfaces, presence of small fractions of materials, or because the mesh does not move with the flow, as in the arbitrary Lagrangian–Eulerian (ALE) methods. In order to solve problems of interest on such meshes, interface reconstructionmore » methods are usually used to recover an approximation of material regions within the cells. For a cell intersecting multiple material regions, these approximations of contained subregions can be considered as single-material subcells in a local mesh that we call a minimesh. In this paper, we discuss some of the requirements that discretization methods have on topological information in the resulting hierarchical meshes and present an approach that allows incorporating the buildup of sufficiently detailed topology into the nested dissections based PLIC-type reconstruction algorithms (e.g. Volume-of-Fluid, Moment-of-Fluid) in an efficient and robust manner. Specifically, we describe the X-MOF interface reconstruction algorithm in 2D, which extends the Moment-Of-Fluid (MOF) method to include the topology of minimeshes created inside of multi-material cells and parent-child relations between corresponding mesh entities on different hierarchy levels. X-MOF retains the property of being local to a cell and not requiring external communication, which makes it suitable for massively parallel applications. Here, we demonstrate some scaling results for the X-MOF implementation in Tangram, a modern interface reconstruction framework for exascale computing.« less

Establishing mesh topology in multi-material cells: enabling technology for robust and accurate multi-material simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kikinzon, Evgeny; Shashkov, Mikhail Jurievich; Garimella, Rao Veerabhadra

Real world problems are typically multi-material, combining materials such as gases, liquids and solids that have very different properties. The material interfaces may be fixed in time or can be a part of the solution, as in fluid-structure interactions or air-water dynamics, and therefore move and change shape. In such problems the computational mesh may be non-conformal to interfaces due to complexity of these interfaces, presence of small fractions of materials, or because the mesh does not move with the flow, as in the arbitrary Lagrangian–Eulerian (ALE) methods. In order to solve problems of interest on such meshes, interface reconstructionmore » methods are usually used to recover an approximation of material regions within the cells. For a cell intersecting multiple material regions, these approximations of contained subregions can be considered as single-material subcells in a local mesh that we call a minimesh. In this paper, we discuss some of the requirements that discretization methods have on topological information in the resulting hierarchical meshes and present an approach that allows incorporating the buildup of sufficiently detailed topology into the nested dissections based PLIC-type reconstruction algorithms (e.g. Volume-of-Fluid, Moment-of-Fluid) in an efficient and robust manner. Specifically, we describe the X-MOF interface reconstruction algorithm in 2D, which extends the Moment-Of-Fluid (MOF) method to include the topology of minimeshes created inside of multi-material cells and parent-child relations between corresponding mesh entities on different hierarchy levels. X-MOF retains the property of being local to a cell and not requiring external communication, which makes it suitable for massively parallel applications. Here, we demonstrate some scaling results for the X-MOF implementation in Tangram, a modern interface reconstruction framework for exascale computing.« less

Stabilising falling liquid film flows using feedback control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thompson, Alice B., E-mail: alice.thompson1@imperial.ac.uk; Gomes, Susana N.; Pavliotis, Grigorios A.

2016-01-15

Falling liquid films become unstable due to inertial effects when the fluid layer is sufficiently thick or the slope sufficiently steep. This free surface flow of a single fluid layer has industrial applications including coating and heat transfer, which benefit from smooth and wavy interfaces, respectively. Here, we discuss how the dynamics of the system are altered by feedback controls based on observations of the interface height, and supplied to the system via the perpendicular injection and suction of fluid through the wall. In this study, we model the system using both Benney and weighted-residual models that account for themore » fluid injection through the wall. We find that feedback using injection and suction is a remarkably effective control mechanism: the controls can be used to drive the system towards arbitrary steady states and travelling waves, and the qualitative effects are independent of the details of the flow modelling. Furthermore, we show that the system can still be successfully controlled when the feedback is applied via a set of localised actuators and only a small number of system observations are available, and that this is possible using both static (where the controls are based on only the most recent set of observations) and dynamic (where the controls are based on an approximation of the system which evolves over time) control schemes. This study thus provides a solid theoretical foundation for future experimental realisations of the active feedback control of falling liquid films.« less

Boostream: a dynamic fluid flow process to assemble nanoparticles at liquid interface

NASA Astrophysics Data System (ADS)

Delléa, Olivier; Lebaigue, Olivier

2017-12-01

CEA-LITEN develops an original process called Boostream® to manipulate, assemble and connect micro- or nanoparticles of various materials, sizes, shapes and functions to obtain monolayer colloidal crystals (MCCs). This process uses the upper surface of a liquid film flowing down a ramp to assemble particles in a manner that is close to the horizontal situation of a Langmuir-Blodgett film construction. In presence of particles at the liquid interface, the film down-flow configuration exhibits an unusual hydraulic jump which results from the fluid flow accommodation to the particle monolayer. In order to master our process, the fluid flow has been modeled and experimentally characterized by optical means, such as with the moiré technique that consists in observing the reflection of a succession of periodic black-and-red fringes on the liquid surface mirror. The fringe images are deformed when reflected by the curved liquid surface associated with the hydraulic jump, the fringe deformation being proportional to the local slope of the surface. This original experimental setup allowed us to get the surface profile in the jump region and to measure it along with the main process parameters (liquid flow rate, slope angle, temperature sensitive fluid properties such as dynamic viscosity or surface tension, particle sizes). This work presents the experimental setup and its simple model, the different experimental characterization techniques used and will focus on the way the hydraulic jump relies on the process parameters.

Two-Fluid Models and Interfacial Area Transport in Microgravity Condition

NASA Technical Reports Server (NTRS)

Ishii, Mamoru; Sun, Xiao-Dong; Vasavada, Shilp

2004-01-01

The objective of the present study is to develop a two-fluid model formulation with interfacial area transport equation applicable for microgravity conditions. The new model is expected to make a leapfrog improvement by furnishing the constitutive relations for the interfacial interaction terms with the interfacial area transport equation, which can dynamically model the changes of the interfacial structures. In the first year of this three-year project supported by the U.S. NASA, Office of Biological and Physics Research, the primary focus is to design and construct a ground-based, microgravity two-phase flow simulation facility, in which two immiscible fluids with close density will be used. In predicting the two-phase flow behaviors in any two-phase flow system, the interfacial transfer terms are among the most essential factors in the modeling. These interfacial transfer terms in a two-fluid model specify the rate of phase change, momentum exchange, and energy transfer at the interface between the two phases. For the two-phase flow under the microgravity condition, the stability of the fluid particle interface and the interfacial structures are quite different from those under normal gravity condition. The flow structure may not reach an equilibrium condition and the two fluids may be loosely coupled such that the inertia terms of each fluid should be considered separately by use of the two-fluid model. Previous studies indicated that, unless phase-interaction terms are accurately modeled in the two-fluid model, the complex modeling does not necessarily warrant an accurate solution.

Seeking simplicity for the understanding of multiphase flows

NASA Astrophysics Data System (ADS)

Stone, Howard A.

2017-10-01

Fluid mechanics is a discipline with rich phenomena, with motions occurring over an enormous range of length scales, and spanning a wide range of laminar and turbulent flows, instabilities, and applications in industry, nature, biology, and medicine. The subfield of complex fluids typically refers to those flows where the complexity is introduced, for example, by the presence of suspended particles, multiple phases, soft boundaries, and electrokinetic effects; several distinct multiphase flows of Newtonian fluids make up the examples in this article. Interfaces play a significant role and modify the flow with feedback that further changes the shapes of the interfaces. I will provide examples of our work highlighting (i) new features of classical instabilities triggered by changes in geometry, (ii) multiphase flows relevant to the design of liquid-infused substrates exhibiting effective slip while retaining the trapped liquid, and (iii) unexpected dynamics in flow at a T-junction. The interplay of experiments and mathematical models and/or simulations is critical to the new understanding developed.

Methods for simulation-based analysis of fluid-structure interaction.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barone, Matthew Franklin; Payne, Jeffrey L.

2005-10-01

Methods for analysis of fluid-structure interaction using high fidelity simulations are critically reviewed. First, a literature review of modern numerical techniques for simulation of aeroelastic phenomena is presented. The review focuses on methods contained within the arbitrary Lagrangian-Eulerian (ALE) framework for coupling computational fluid dynamics codes to computational structural mechanics codes. The review treats mesh movement algorithms, the role of the geometric conservation law, time advancement schemes, wetted surface interface strategies, and some representative applications. The complexity and computational expense of coupled Navier-Stokes/structural dynamics simulations points to the need for reduced order modeling to facilitate parametric analysis. The proper orthogonalmore » decomposition (POD)/Galerkin projection approach for building a reduced order model (ROM) is presented, along with ideas for extension of the methodology to allow construction of ROMs based on data generated from ALE simulations.« less

Thermal stability of Ag, Al, Sn, Pb, and Hg films reinforced by 2D (C, Si) crystals and the formation of interfacial fluid states in them upon heating. MD experiment

NASA Astrophysics Data System (ADS)

Polukhin, V. A.; Kurbanova, E. D.

2016-02-01

Molecular dynamics simulation is used to study the thermal stability of the interfacial states of metallic Al, Ag, Sn, Pb, and Hg films (i.e., the structural elements of superconductor composites and conducting electrodes) reinforced by 2D graphene and silicene crystals upon heating up to disordering and to analyze the formation of nonautonomous fluid pseudophases in interfaces. The effect of perforation defects in reinforcing 2D-C and 2D-Si planes with passivated edge covalent bonds on the atomic dynamics is investigated. As compared to Al and Ag, the diffusion coefficients in Pd and Hg films increase monotonically with temperature during thermally activated disordering processes, the interatomic distances decrease, the sizes decrease, drops form, and their density profile grows along the normal. The coagulation of Pb and Hg drops is accompanied by a decrease in the contact angle, the reduction of the interface contact with graphene, and the enhancement of its corrugation (waviness).

Fluid-structure interactions of photo-responsive polymer cantilevers

NASA Astrophysics Data System (ADS)

Bin, Jonghoon; Oates, William S.; Yousuff Hussaini, M.

2013-02-01

A new class of photomechanical liquid crystal networks (LCNs) has emerged, which generate large bending deformation and fast response times that scale with the resonance of the polymer films. Here, a numerical study is presented that describes the photomechanical structural dynamic behavior of an LCN in a fluid medium; however, the methodology is also applicable to fluid-structure interactions of a broader range of adaptive structures. Here, we simulate the oscillation of photomechanical cantilevers excited by light while simultaneously modeling the effect of the surrounding fluid at different ambient pressures. The photoactuated LCN is modeled as an elastic thin cantilever plate, and gradients in photostrain from the external light are computed from the assumptions of light absorption and photoisomerization through the film thickness. Numerical approximations of the equations governing the plate are based on cubic B-spline shape functions and a second order implicit Newmark central scheme for time integration. For the fluid, three dimensional unsteady incompressible Navier-Stokes equations are solved using the arbitrary Lagrangian-Eulerian (ALE) method, which employs a structured body-fitted curvilinear coordinate system where the solid-fluid interface is a mesh line of the system, and the complicated interface boundary conditions are accommodated in a conventional finite-volume formulation. Numerical examples are given which provide new insight into material behavior in a fluid medium as a function of ambient pressure.

Slit-lamp technique of draining interface fluid following Descemet's stripping endothelial keratoplasty.

PubMed

Srinivasan, Sathish; Rootman, David S

2007-09-01

To describe a new slit-lamp technique for draining interface fluid to manage complete donor disc detachments following Descemet's stripping (automated) endothelial keratoplasty (DSEK/DSAEK). Interventional case series. Five DSEK/DSAEK patients presented on the first postoperative day with complete detachment of the donor lenticule. Slit-lamp biomicroscopy showed interface fluid preventing attachment of the donor disc to the host stromal bed. A new slit-lamp technique is described to drain the interface fluid. This technique involved completely filling the anterior chamber with an air bubble using a 30-gauge needle on a 3 ml syringe. Following this, a 0.12 forceps was used to open the inferior mid-peripheral corneal drainage slit to drain the interface fluid. This technique was successful in draining the interface fluid in all five patients, leading to immediate complete reattachment of the donor disc. Donor disc detachments following DSEK/DSAEK can be successfully managed by this slit-lamp technique of draining the interface fluid.

Diffusion-driven fluid dynamics in ideal gases and plasmas

NASA Astrophysics Data System (ADS)

Vold, E. L.; Yin, L.; Taitano, W.; Molvig, K.; Albright, B. J.

2018-06-01

The classical transport theory based on Chapman-Enskog methods provides self-consistent approximations for the kinetic flux of mass, heat, and momentum in a fluid limit characterized with a small Knudsen number. The species mass fluxes relative to the center of mass, or "diffusive fluxes," are expressed as functions of known gradient quantities with kinetic coefficients evaluated using similar analyses for mixtures of gases or plasma components. The sum over species of the diffusive mass fluxes is constrained to be zero in the Lagrange frame, and thus results in a non-zero molar flux leading to a pressure perturbation. At an interface between two species initially in pressure equilibrium, the pressure perturbation driven by the diffusive molar flux induces a center of mass velocity directed from the species of greater atomic mass towards the lighter atomic mass species. As the ratio of the species particle masses increases, this center of mass velocity carries an increasingly greater portion of the mass across the interface and for a particle mass ratio greater than about two, the center of mass velocity carries more mass than the gradient driven diffusion flux. Early time transients across an interface between two species in a 1D plasma regime and initially in equilibrium are compared using three methods; a fluid code with closure in a classical transport approximation, a particle in cell simulation, and an implicit Fokker-Planck solver for the particle distribution functions. The early time transient phenomenology is shown to be similar in each of the computational simulation methods, including a pressure perturbation associated with the stationary "induced" component of the center of mass velocity which decays to pressure equilibrium during diffusion. At early times, the diffusive process generates pressure and velocity waves which propagate outward from the interface and are required to maintain momentum conservation. The energy in the outgoing waves dissipates as heat in viscous regions, and it is hypothesized that these diffusion driven waves may sustain fluctuations in less viscid finite domains after reflections from the boundaries. These fluid dynamic phenomena are similar in gases or plasmas and occur in flow transients with a moderate Knudsen number. The analysis and simulation results show how the kinetic flux, represented in the fluid transport closure, directly modifies the mass averaged flow described with the Euler equations.

Superfluid helium sloshing dynamics induced oscillations and fluctuations of angular momentum, force and moment actuated on spacecraft driven by gravity gradient or jitter acceleration associated with slew motion

NASA Technical Reports Server (NTRS)

Hung, R. J.

1994-01-01

The generalized mathematical formulation of sloshing dynamics for partially filled liquid of cryogenic superfluid helium II in dewar containers driven by the gravity gradient and jitter accelerations associated with slew motion for the purpose to perform scientific observation during the normal spacecraft operation are investigated. An example is given with the Advanced X-Ray Astrophysics Facility-Spectroscopy (AXAF-S) for slew motion which is responsible for the sloshing dynamics. The jitter accelerations include slew motion, spinning motion, atmospheric drag on the spacecraft, spacecraft attitude motions arising from machinery vibrations, thruster firing, pointing control of spacecraft, crew motion, etc. Explicit mathematical expressions to cover these forces acting on the spacecraft fluid systems are derived. The numerical computation of sloshing dynamics is based on the non-inertia frame spacecraft bound coordinate, and solve time-dependent, three-dimensional formulations of partial differential equations subject to initial and boundary conditions. The explicit mathematical expressions of boundary conditions to cover capillary force effect on the liquid-vapor interface in microgravity environments are also derived. The formulations of fluid moment and angular moment fluctuations in fluid profiles induced by the sloshing dynamics, together with fluid stress and moment fluctuations exerted on the spacecraft dewar containers have also been derived. Examples are also given for cases applicable to the AXAF-S spacecraft sloshing dynamics associated with slew motion.

Unified description of the slip phenomena in sheared polymer films: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Priezjev, Nikolai

2010-03-01

The dynamic behavior of the slip length in shear flow of polymer melts past atomically smooth surfaces is investigated using MD simulations. The polymer melt was modeled as a collection of FENE-LJ bead-spring chains. We consider shear flow conditions at low pressures and weak wall-fluid interaction energy so that fluid velocity profiles are linear throughout the channel at all shear rates examined. In agreement with earlier studies we confirm that for shear- thinning fluids the slip length passes through a local minimum at low shear rates and then increases rapidly at higher shear rates. We found that the rate dependence of the slip length depends on the lattice orientation at high shear rates. The MD results show that the ratio of slip length to viscosity follows a master curve when plotted as a function of a single variable that depends on the structure factor, contact density and temperature of the first fluid layer near the solid wall. The universal dependence of the slip length holds for a number of parameters of the interface: fluid density and structure (chain length), wall-fluid interaction energy, wall density, lattice orientation, thermal or solid walls.

Freezing point and solid-liquid interfacial free energy of Stockmayer dipolar fluids: a molecular dynamics simulation study.

PubMed

Wang, Jun; Apte, Pankaj A; Morris, James R; Zeng, Xiao Cheng

2013-09-21

Stockmayer fluids are a prototype model system for dipolar fluids. We have computed the freezing temperatures of Stockmayer fluids at zero pressure using three different molecular-dynamics simulation methods, namely, the superheating-undercooling method, the constant-pressure and constant-temperature two-phase coexistence method, and the constant-pressure and constant-enthalpy two-phase coexistence method. The best estimate of the freezing temperature (in reduced unit) for the Stockmayer (SM) fluid with the dimensionless dipole moment μ*=1, √2, √3 is 0.656 ± 0.001, 0.726 ± 0.002, and 0.835 ± 0.005, respectively. The freezing temperature increases with the dipolar strength. Moreover, for the first time, the solid-liquid interfacial free energies γ of the fcc (111), (110), and (100) interfaces are computed using two independent methods, namely, the cleaving-wall method and the interfacial fluctuation method. Both methods predict that the interfacial free energy increases with the dipole moment. Although the interfacial fluctuation method suggests a weaker interfacial anisotropy, particularly for strongly dipolar SM fluids, both methods predicted the same trend of interfacial anisotropy, i.e., γ100 > γ110 > γ111.

Fluorescent fluid interface position sensor

DOEpatents

Weiss, Jonathan D.

2004-02-17

A new fluid interface position sensor has been developed, which is capable of optically determining the location of an interface between an upper fluid and a lower fluid, the upper fluid having a larger refractive index than a lower fluid. The sensor functions by measurement, of fluorescence excited by an optical pump beam which is confined within a fluorescent waveguide where that waveguide is in optical contact with the lower fluid, but escapes from the fluorescent waveguide where that waveguide is in optical contact with the upper fluid.

COMPUTATIONAL FLUID DYNAMICS MODELING OF SCALED HANFORD DOUBLE SHELL TANK MIXING - CFD MODELING SENSITIVITY STUDY RESULTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

JACKSON VL

2011-08-31

The primary purpose of the tank mixing and sampling demonstration program is to mitigate the technical risks associated with the ability of the Hanford tank farm delivery and celtification systems to measure and deliver a uniformly mixed high-level waste (HLW) feed to the Waste Treatment and Immobilization Plant (WTP) Uniform feed to the WTP is a requirement of 24590-WTP-ICD-MG-01-019, ICD-19 - Interface Control Document for Waste Feed, although the exact definition of uniform is evolving in this context. Computational Fluid Dynamics (CFD) modeling has been used to assist in evaluating scaleup issues, study operational parameters, and predict mixing performance atmore » full-scale.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fujiwara, K., E-mail: ku.fujiwara@screen.co.jp; Department of Mechanical Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871; Shibahara, M., E-mail: siba@mech.eng.osaka-u.ac.jp

A classical molecular dynamics simulation was conducted for a system composed of fluid molecules between two planar solid surfaces, and whose interactions are described by the 12-6 Lennard-Jones form. This paper presents a general description of the pressure components and interfacial tension at a fluid-solid interface obtained by the perturbative method on the basis of statistical thermodynamics, proposes a method to consider the pressure components tangential to an interface which are affected by interactions with solid atoms, and applies this method to the calculation system. The description of the perturbative method is extended to subsystems, and the local pressure componentsmore » and interfacial tension at a liquid-solid interface are obtained and examined in one- and two-dimensions. The results are compared with those obtained by two alternative methods: (a) an evaluation of the intermolecular force acting on a plane, and (b) the conventional method based on the virial expression. The accuracy of the numerical results is examined through the comparison of the results obtained by each method. The calculated local pressure components and interfacial tension of the fluid at a liquid-solid interface agreed well with the results of the two alternative methods at each local position in one dimension. In two dimensions, the results showed a characteristic profile of the tangential pressure component which depended on the direction tangential to the liquid-solid interface, which agreed with that obtained by the evaluation of the intermolecular force acting on a plane in the present study. Such good agreement suggests that the perturbative method on the basis of statistical thermodynamics used in this study is valid to obtain the local pressure components and interfacial tension at a liquid-solid interface.« less

Benard and Marangoni convection in multiple liquid layers

NASA Technical Reports Server (NTRS)

Koster, Jean N.; Prakash, A.; Fujita, D.; Doi, T.

1992-01-01

Convective fluid dynamics of immiscible double and triple liquid layers are considered. First results on multilayer convective flow, in preparation for spaceflight experiment aboard IML-2 (International Microgravity Laboratory), are discussed. Convective flow in liquid layers with one or two horizontal interfaces with heat flow applied parallel to them is one of the systems investigated. The second system comprises two horizontally layered immiscible liquids heated from below and cooled from above, that is, heat flow orthogonal to the interface. In this system convection results due to the classical Benard instability.

Advanced graphical user interface for multi-physics simulations using AMST

NASA Astrophysics Data System (ADS)

Hoffmann, Florian; Vogel, Frank

2017-07-01

Numerical modelling of particulate matter has gained much popularity in recent decades. Advanced Multi-physics Simulation Technology (AMST) is a state-of-the-art three dimensional numerical modelling technique combining the eX-tended Discrete Element Method (XDEM) with Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) [1]. One major limitation of this code is the lack of a graphical user interface (GUI) meaning that all pre-processing has to be made directly in a HDF5-file. This contribution presents the first graphical pre-processor developed for AMST.

Specific interface area in a thin layer system of two immiscible liquids with vapour generation at the contact interface

NASA Astrophysics Data System (ADS)

Pimenova, Anastasiya V.; Gazdaliev, Ilias M.; Goldobin, Denis S.

2017-06-01

For well-stirred multiphase fluid systems the mean interface area per unit volume, or “specific interface area” SV, is a significant characteristic of the system state. In particular, it is important for the dynamics of systems of immiscible liquids experiencing interfacial boiling. We estimate the value of parameter SV as a function of the heat influx {\\dot{Q}}V to the system or the average system overheat <Θ> above the interfacial boiling point. The derived results can be reformulated for the case of an endothermic chemical reaction between two liquid reagents with the gaseous form of one of the reaction products. The final results are restricted to the case of thin layers, where the potential gravitational energy of bubbles leaving the contact interface is small compared to their surface tension energy.

Investigation of Conjugate Heat Transfer in Turbine Blades and Vanes

NASA Technical Reports Server (NTRS)

Kassab, A. J.; Kapat, J. S.

2001-01-01

We report on work carried out to develop a 3-D coupled Finite Volume/BEM-based temperature forward/flux back (TFFB) coupling algorithm to solve the conjugate heat transfer (CHT) which arises naturally in analysis of systems exposed to a convective environment. Here, heat conduction within a structure is coupled to heat transfer to the external fluid which is convecting heat into or out of the solid structure. There are two basic approaches to solving coupled fluid structural systems. The first is a direct coupling where the solution of the different fields is solved simultaneously in one large set of equations. The second approach is a loose coupling strategy where each set of field equations is solved to provide boundary conditions for the other. The equations are solved in turn until an iterated convergence criterion is met at the fluid-solid interface. The loose coupling strategy is particularly attractive when coupling auxiliary field equations to computational fluid dynamics codes. We adopt the latter method in which the BEM is used to solve heat conduction inside a structure which is exposed to a convective field which in turn is resolved by solving the NASA Glenn compressible Navier-Stokes finite volume code Glenn-HT. The BEM code features constant and bi-linear discontinuous elements and an ILU-preconditioned GMRES iterative solver for the resulting non-symmetric algebraic set arising in the conduction solution. Interface of flux and temperature is enforced at the solid/fluid interface, and a radial-basis function scheme is used to interpolated information between the CFD and BEM surface grids. Additionally, relaxation is implemented in passing the fluxes from the conduction solution to the fluid solution. Results from a simple test example are reported.

Particle-induced viscous fingering

NASA Astrophysics Data System (ADS)

Lee, Sungyon

2017-11-01

An inclusion of non-colloidal particles in a Newtonian liquid can fundamentally change the interfacial dynamics and even cause interfacial instabilities. In this talk, we report a particle-induced fingering instability when a mixture of particles and viscous oil is injected radially into a Hele-Shaw cell. Our experimental results show that the onset and characteristics of fingering are most directly affected by the particle volume fraction but also depend on the ratio of the particle diameter to gap size. In particular, the formation of a particle band is observed on the interface only when the particle diameter is comparable to the channel gap thickness. This work demonstrates the complex coupling between suspensions and fluid-fluid interfaces and has broad relevance in suspension processing, particle self-assembly, and oil recovery processes. The physical mechanism behind the instability and a quantitative model are also discussed.

Numerical Simulations of Free Surface Magnetohydrodynamic Flows

NASA Astrophysics Data System (ADS)

Samulyak, Roman; Glimm, James; Oh, Wonho; Prykarpatskyy, Yarema

2003-11-01

We have developed a numerical algorithm and performed simulations of magnetohydrodynamic (MHD) free surface flows. The corresponding system of MHD equations is a system of strongly coupled hyperbolic and parabolic/elliptic equations in moving and geometrically complex domains. The hyperbolic system is solved using the front tracking technique for the free fluid interface. Parallel algorithms for solving elliptic and parabolic equations are based on a finite element discretization on moving grids dynamically conforming to fluid interfaces. The method has been implemented as an MHD extension of the FronTier code. The code has been applied for modeling the behavior of lithium and mercury jets in magnetic fields, laser ablation plumes, and the Richtmyer-Meshkov instability of a liquid mercury jet interacting with a high energy proton pulse in a strong magnetic field. Such an instability occurs in the target for the Muon Collider.

Temperature anisotropy at equilibrium reveals nonlocal entropic contributions to interfacial properties.

PubMed

Wilhelmsen, Øivind; Trinh, Thuat T; Lervik, Anders

2018-01-01

Density gradient theory for fluids has played a key role in the study of interfacial phenomena for a century. In this work, we revisit its fundamentals by examining the vapor-liquid interface of argon, represented by the cut and shifted Lennard-Jones fluid. The starting point has traditionally been a Helmholtz energy functional using mass densities as arguments. By using rather the internal energy as starting point and including the entropy density as an additional argument, following thereby the phenomenological approach from classical thermodynamics, the extended theory suggests that the configurational part of the temperature has different contributions from the parallel and perpendicular directions at the interface, even at equilibrium. We find a similar anisotropy by examining the configurational temperature in molecular dynamics simulations and obtain a qualitative agreement between theory and simulations. The extended theory shows that the temperature anisotropy originates in nonlocal entropic contributions, which are currently missing from the classical theory. The nonlocal entropic contributions discussed in this work are likely to play a role in the description of both equilibrium and nonequilibrium properties of interfaces. At equilibrium, they influence the temperature- and curvature-dependence of the surface tension. Across the vapor-liquid interface of the Lennard Jones fluid, we find that the maximum in the temperature anisotropy coincides precisely with the maximum in the thermal resistivity relative to the equimolar surface, where the integral of the thermal resistivity gives the Kapitza resistance. This links the temperature anisotropy at equilibrium to the Kapitza resistance of the vapor-liquid interface at nonequilibrium.

Diffusion-limited retention of porous particles at density interfaces

PubMed Central

Kindler, Kolja; Khalili, Arzhang; Stocker, Roman

2010-01-01

Downward carbon flux in the ocean is largely governed by particle settling. Most marine particles settle at low Reynolds numbers and are highly porous, yet the fluid dynamics of this regime have remained unexplored. We present results of an experimental investigation of porous particles settling through a density interface at Reynolds numbers between 0.1 and 1. We tracked 100 to 500 μm hydrogel spheres with 95.5% porosity and negligible permeability. We found that a small negative initial excess density relative to the lower (denser) fluid layer, a common scenario in the ocean, results in long retention times of particles at the interface. We hypothesized that the retention time was determined by the diffusive exchange of the stratifying agent between interstitial and ambient fluid, which increases excess density of particles that have stalled at the interface, enabling their settling to resume. This hypothesis was confirmed by observations, which revealed a quadratic dependence of retention time on particle size, consistent with diffusive exchange. These results demonstrate that porosity can control retention times and therefore accumulation of particles at density interfaces, a mechanism that could underpin the formation of particle layers frequently observed at pycnoclines in the ocean. We estimate retention times of 3 min to 3.3 d for the characteristic size range of marine particles. This enhancement in retention time can affect carbon transformation through increased microbial colonization and utilization of particles and release of dissolved organics. The observed size dependence of the retention time could further contribute to improve quantifications of vertical carbon flux. PMID:21135242

Temperature anisotropy at equilibrium reveals nonlocal entropic contributions to interfacial properties

NASA Astrophysics Data System (ADS)

Wilhelmsen, Øivind; Trinh, Thuat T.; Lervik, Anders

2018-01-01

Density gradient theory for fluids has played a key role in the study of interfacial phenomena for a century. In this work, we revisit its fundamentals by examining the vapor-liquid interface of argon, represented by the cut and shifted Lennard-Jones fluid. The starting point has traditionally been a Helmholtz energy functional using mass densities as arguments. By using rather the internal energy as starting point and including the entropy density as an additional argument, following thereby the phenomenological approach from classical thermodynamics, the extended theory suggests that the configurational part of the temperature has different contributions from the parallel and perpendicular directions at the interface, even at equilibrium. We find a similar anisotropy by examining the configurational temperature in molecular dynamics simulations and obtain a qualitative agreement between theory and simulations. The extended theory shows that the temperature anisotropy originates in nonlocal entropic contributions, which are currently missing from the classical theory. The nonlocal entropic contributions discussed in this work are likely to play a role in the description of both equilibrium and nonequilibrium properties of interfaces. At equilibrium, they influence the temperature- and curvature-dependence of the surface tension. Across the vapor-liquid interface of the Lennard Jones fluid, we find that the maximum in the temperature anisotropy coincides precisely with the maximum in the thermal resistivity relative to the equimolar surface, where the integral of the thermal resistivity gives the Kapitza resistance. This links the temperature anisotropy at equilibrium to the Kapitza resistance of the vapor-liquid interface at nonequilibrium.

A smoothed particle hydrodynamics model for droplet and film flow on smooth and rough fracture surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kordilla, Jannes; Tartakovsky, Alexandre M.; Geyer, Tobias

2013-09-01

Flow on fracture surfaces has been identified by many authors as an important flow process in unsaturated fractured rock formations. Given the complexity of flow dynamics on such small scales, robust numerical methods have to be employed in order to capture the highly dynamic interfaces and flow intermittency. In this work we present microscale free-surface flow simulations using a three-dimensional multiphase Smoothed Particle Hydrodynamics (SPH) code. Pairwise solid-fluid and fluid-fluid interaction forces are used to control the wetting behavior and cover a wide range of static and transient contact angles as well as Reynolds numbers encountered in droplet flow onmore » rock surfaces. We validate our model via comparison with existing empirical and semi-analyical solutions for droplet flow. We use the model to investigate the occurence of adsorbed trailing films of droplets under various flow conditions and its importance for the flow dynamics when films and droplets coexist. We show that flow velocities are higher on prewetted surfaces covered by a thin film which is qualitatively attributed to the enhanced dynamic wetting and dewetting at the trailing and advancing contact line.« less

A variational approach to the strongly nonlinear regime of the Rayleigh-Taylor instability

NASA Astrophysics Data System (ADS)

Yoshikawa, Toshio

The Rayleigh-Taylor instability is the instability of the interface between two fluids of different densities. When a heavy fluid is superposed over a light fluid. small disturbances on the interface develop into a complex form with heavy fluid ``fingers'' and light fluid ``bubbles.'' We propose a variational method for the description of the evolution of the fingers and bubbles in the late stage of the instability. In this method, the fluid region is represented as the image of a time-dependent conformal mapping; the dynamics of the mapping is determined by the least action principle for the Lagrangian. i.e., the kinetic energy minus the potential energy. The evolution of a single finger and bubble is investigated by this method. We first consider a symmetric finger and bubble in a zero gravitational field. We derive an integrable Hamiltonian system with two degrees of freedom that governs the dynamics of the symmetric finger and bubble. We present a general solution of the system. The solution predicts the linear growth of the finger and the saturation of the bubble growth. It is shown that this solution is asymptotically exact. We consider a symmetric finger and bubble with perturbations. We show that the dynamics of the finger and bubble and that of the perturbations are decoupled. We next consider an inclined finger and bubble in a zero gravitational field. We derive a Hamiltonian system with four degrees of freedom that governs the dynamics of the inclined finger and bubble. The system has four integrals of motion, one of them depends on time explicitly. When there is no lateral motion, the system reduces to an integrable Hamiltonian system with three degrees of freedom. A general solution of the system is presented. The solution predicts the linear growth of the finger toward a direction and the saturation of the bubble growth. Finally, we consider a symmetric finger and bubble in a uniform gravitational field. We derive a Hamiltonian system with two degrees of freedom that governs the dynamics of the symmetric finger and bubble. Since the system includes a potential energy term, it is not integrable in general. However, we present a general solution in the case of the total energy being zero. This case corresponds to an interesting case where the evolution starts from a flat surface. The solution predicts that the finger grows as the square of time, and the bubble as the square root of time.

Particles at fluid-fluid interfaces: A new Navier-Stokes-Cahn-Hilliard surface- phase-field-crystal model.

PubMed

Aland, Sebastian; Lowengrub, John; Voigt, Axel

2012-10-01

Colloid particles that are partially wetted by two immiscible fluids can become confined to fluid-fluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids form an emulsion with interesting material properties and offer an important route to new soft materials. A promising approach to simulate these emulsions was presented in Aland et al. [Phys. Fluids 23, 062103 (2011)], where a Navier-Stokes-Cahn-Hilliard model for the macroscopic two-phase fluid system was combined with a surface phase-field-crystal model for the microscopic colloidal particles along the interface. Unfortunately this model leads to spurious velocities which require very fine spatial and temporal resolutions to accurately and stably simulate. In this paper we develop an improved Navier-Stokes-Cahn-Hilliard-surface phase-field-crystal model based on the principles of mass conservation and thermodynamic consistency. To validate our approach, we derive a sharp interface model and show agreement with the improved diffuse interface model. Using simple flow configurations, we show that the new model has much better properties and does not lead to spurious velocities. Finally, we demonstrate the solid-like behavior of the crystallized interface by simulating the fall of a solid ball through a colloid-laden multiphase fluid.

Fluid management systems technology summaries

NASA Technical Reports Server (NTRS)

Stark, J. A.; Blatt, M. H.; Bennett, F. O., Jr.; Campbell, B. J.

1974-01-01

A summarization and categorization of the pertinent literature associated with fluid management systems technology having potential application to in-orbit fluid transfer and/or associated storage are presented. A literature search was conducted to obtain pertinent documents for review. Reports determined to be of primary significance were summarized in the following manner: (1) report identification, (2) objective(s) of the work, (3) description of pertinent work performed, (4) major results, and (5) comments of the reviewer. Pertinent figures are presented on a single facing page separate from the text. Specific areas covered are: fluid line dynamics and thermodynamics, low-g mass gauging, other instrumentation, stratification/pressurization, low-g vent systems, fluid mixing refrigeration and reliquefaction, and low-g interface control and liquid acquisition systems. Reports which were reviewed and not summarized, along with reasons for not summarizing, are also listed.

Numerical Investigation of an Oscillating Flat Plate Airfoil

NASA Astrophysics Data System (ADS)

Mohaghegh, Fazlolah; Janechek, Matthew; Buchholz, James; Udaykumar, Hs

2017-11-01

This research investigates the vortex dynamics of a plunging flat plate airfoil by analyzing the vorticity transport in 2D simulations. A horizontal airfoil is subject to a freestream flow at Re =10000. A prescribed vertical sinusoidal motion is applied to the airfoil. Smoothed Profile Method (SPM) models the fluid-structure interaction. SPM as a diffuse interface model considers a thickness for the interface and applies a smooth transition from solid to fluid. As the forces on the airfoil are highly affected by the interaction of the generated vortices from the surface, it is very important to find out whether a diffuse interface solver can model a flow dominated by vorticities. The results show that variation of lift coefficient with time agrees well with the experiment. Study of vortex evolution shows that similar to experiments, when the plate starts moving downward from top, the boundary layer is attached to the surface and the leading-edge vortex (LEV) is very small. By time, LEV grows and rolls up and a secondary vortex emerges. Meanwhile, the boundary layer starts to separate and finally LEV detaches from the surface. In overall, SPM as a diffuse interface model can predict the lift force and vortex pattern accurately.

Numerical study of drop spreading on a flat surface

NASA Astrophysics Data System (ADS)

Wang, Sheng; Desjardins, Olivier

2017-11-01

In this talk, we perform a numerical study of a droplet on a flat surface with special emphasis on capturing the spreading dynamics. The computational methodology employed is tailored for simulating large-scale two-phase flows within complex geometries. It combines a conservative level-set method to capture the liquid-gas interface, a conservative immersed boundary method to represent the solid-fluid interface, and a sub-grid curvature model at the triple-point to implicitly impose the contact angle of the liquid-gas interface. The performance of the approach is assessed in the inertial droplet spreading regime, the viscous spreading regime of high viscosity drops, and with the capillary oscillation of low viscosity droplets.

Finite volume solution for two-phase flow in a straight capillary

NASA Astrophysics Data System (ADS)

Yelkhovsky, Alexander; Pinczewski, W. Val

2018-04-01

The problem of two-phase flow in straight capillaries of polygonal cross section displays many of the dynamic characteristics of rapid interfacial motions associated with pore-scale displacements in porous media. Fluid inertia is known to be important in these displacements but is usually ignored in network models commonly used to predict macroscopic flow properties. This study presents a numerical model for two-phase flow which describes the spatial and temporal evolution of the interface between the fluids. The model is based on an averaged Navier-Stokes equation and is shown to be successful in predicting the complex dynamics of both capillary rise in round capillaries and imbibition along the corners of polygonal capillaries. The model can form the basis for more realistic network models which capture the effect of capillary, viscous, and inertial forces on pore-scale interfacial dynamics and consequent macroscopic flow properties.

Atomization and dense-fluid breakup regimes in liquid rocket engines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oefelein, Joseph; Dahms, Rainer Norbert Uwe

Until recently, modern theory has lacked a fundamentally based model to predict the operating pressures where classical sprays transition to dense-fluid mixing with diminished surface tension. In this paper, such a model is presented to quantify this transition for liquid-oxygen–hydrogen and n-decane–gaseous-oxygen injection processes. The analysis reveals that respective molecular interfaces break down not necessarily because of vanishing surface tension forces but instead because of the combination of broadened interfaces and a reduction in mean free molecular path. When this occurs, the interfacial structure itself enters the continuum regime, where transport processes rather than intermolecular forces dominate. Using this model,more » regime diagrams for the respective systems are constructed that show the range of operating pressures and temperatures where this transition occurs. The analysis also reveals the conditions where classical spray dynamics persists even at high supercritical pressures. As a result, it demonstrates that, depending on the composition and temperature of the injected fluids, the injection process can exhibit either classical spray atomization, dense-fluid diffusion-dominated mixing, or supercritical mixing phenomena at chamber pressures encountered in state-of-the-art liquid rocket engines.« less

Atomization and dense-fluid breakup regimes in liquid rocket engines

DOE PAGES

Oefelein, Joseph; Dahms, Rainer Norbert Uwe

2015-04-20

Until recently, modern theory has lacked a fundamentally based model to predict the operating pressures where classical sprays transition to dense-fluid mixing with diminished surface tension. In this paper, such a model is presented to quantify this transition for liquid-oxygen–hydrogen and n-decane–gaseous-oxygen injection processes. The analysis reveals that respective molecular interfaces break down not necessarily because of vanishing surface tension forces but instead because of the combination of broadened interfaces and a reduction in mean free molecular path. When this occurs, the interfacial structure itself enters the continuum regime, where transport processes rather than intermolecular forces dominate. Using this model,more » regime diagrams for the respective systems are constructed that show the range of operating pressures and temperatures where this transition occurs. The analysis also reveals the conditions where classical spray dynamics persists even at high supercritical pressures. As a result, it demonstrates that, depending on the composition and temperature of the injected fluids, the injection process can exhibit either classical spray atomization, dense-fluid diffusion-dominated mixing, or supercritical mixing phenomena at chamber pressures encountered in state-of-the-art liquid rocket engines.« less

Local mass and energy transports in evaporation processes from a vapor-liquid interface in a slit pore based on molecular dynamics

NASA Astrophysics Data System (ADS)

Fujiwara, K.; Shibahara, M.

2018-02-01

Molecular evaporation processes from a vapor-liquid interface formed in a slit-like pore were examined based on the classical molecular dynamics method, in order to elucidate a molecular mechanism of local mass and energy transports in a slit. The calculation system consisted of monatomic molecules and atoms which interact through the 12-6 Lennard-Jones potential. At first, a liquid was situated in a slit with a vapor-liquid interface, and instantaneous amounts of the mass and energy fluxes defined locally in the slit were obtained in two dimensions to reveal local fluctuation properties of the fluid in equilibrium states. Then, imposing a temperature gradient in the calculation system, non-equilibrium evaporation processes in the slit were investigated in details based on the local mass and energy fluxes. In this study, we focused on the fluid which is in the vicinity of the solid surface and in contact with the vapor phase. In the non-equilibrium evaporation processes, the results revealed that the local energy transport mechanism in the vicinity of the solid surface is different from that of the vapor phase, especially in the case of the relatively strong fluid-solid interaction. The results also revealed that the local mass transport in the vicinity of the solid surface can be interpreted based on the mechanism of the local energy transport, and the mechanism provides valuable information about pictures of the evaporation phenomena especially in the vicinity of the hydrophilic surfaces. It suggests that evaluating and changing this mechanism of the local energy transport are necessary to control the local mass flux more precisely in the vicinity of the solid surface.

Development, Verification and Validation of Parallel, Scalable Volume of Fluid CFD Program for Propulsion Applications

NASA Technical Reports Server (NTRS)

West, Jeff; Yang, H. Q.

2014-01-01

There are many instances involving liquid/gas interfaces and their dynamics in the design of liquid engine powered rockets such as the Space Launch System (SLS). Some examples of these applications are: Propellant tank draining and slosh, subcritical condition injector analysis for gas generators, preburners and thrust chambers, water deluge mitigation for launch induced environments and even solid rocket motor liquid slag dynamics. Commercially available CFD programs simulating gas/liquid interfaces using the Volume of Fluid approach are currently limited in their parallel scalability. In 2010 for instance, an internal NASA/MSFC review of three commercial tools revealed that parallel scalability was seriously compromised at 8 cpus and no additional speedup was possible after 32 cpus. Other non-interface CFD applications at the time were demonstrating useful parallel scalability up to 4,096 processors or more. Based on this review, NASA/MSFC initiated an effort to implement a Volume of Fluid implementation within the unstructured mesh, pressure-based algorithm CFD program, Loci-STREAM. After verification was achieved by comparing results to the commercial CFD program CFD-Ace+, and validation by direct comparison with data, Loci-STREAM-VoF is now the production CFD tool for propellant slosh force and slosh damping rate simulations at NASA/MSFC. On these applications, good parallel scalability has been demonstrated for problems sizes of tens of millions of cells and thousands of cpu cores. Ongoing efforts are focused on the application of Loci-STREAM-VoF to predict the transient flow patterns of water on the SLS Mobile Launch Platform in order to support the phasing of water for launch environment mitigation so that vehicle determinantal effects are not realized.

Phase behavior of charged hydrophobic colloids on flat and spherical surfaces

NASA Astrophysics Data System (ADS)

Kelleher, Colm P.

For a broad class of two-dimensional (2D) materials, the transition from isotropic fluid to crystalline solid is described by the theory of melting due to Kosterlitz, Thouless, Halperin, Nelson and Young (KTHNY). According to this theory, long-range order is achieved via elimination of the topological defects which proliferate in the fluid phase. However, many natural and man-made 2D systems posses spatial curvature and/or non-trivial topology, which require the presence of topological defects, even at T=0. In principle, the presence of these defects could profoundly affect the phase behavior of such a system. In this thesis, we develop and characterize an experimental system of charged colloidal particles that bind electrostatically to the interface between an oil and an aqueous phase. Depending on how we prepare the sample, this fluid interface may be flat, spherical, or have a more complicated geometry. Focusing on the cases where the interface is flat or spherical, we measure the interactions between the particles, and probe various aspects of their phase behavior. On flat interfaces, this phase behavior is well-described by KTHNY theory. In spherical geometries, however, we observe spatial structures and inhomogeneous dynamics that cannot be captured by the measures traditionally used to describe flat-space phase behavior. We show that, in the spherical system, ordering is achieved by a novel mechanism: sequestration of topological defects into freely-terminating grain boundaries ("scars"), and simultaneous spatial organization of the scars themselves on the vertices of an icosahedron. The emergence of icosahedral order coincides with the localization of mobility into isolated "lakes" of fluid or glassy particles, situated at the icosahedron vertices. These lakes are embedded in a rigid, connected "continent" of locally crystalline particles.

Simulations of laser thrombolysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chapyak, E.J.; Godwin, R.P.

1999-03-01

The authors have shown that bubble expansion and collapse near the interface between two materials with modest property differences produces jet-like interpenetration of the two materials. The bubble dynamics at a water-viscous fluid interface is compared with that at the interface of water with a weak elastic-plastic material. The authors find that, despite rather similar behavior during bubble growth and the initial portion of bubble collapse, the terminal jetting behavior is quite different, even in direction. The elastic-plastic properties chosen realistically represent real and surrogate thrombus. Simulations using the elastic-plastic model quantitatively agree with laboratory thrombolysis mass removal experiments. Inmore » the earlier simulations of laboratory experiments, walls have been remote so as to not effect the dynamics. Here the authors present two-dimensional simulations of thrombolysis with water over elastic-plastic surrogate thrombus in a geometry representative of the clinical situation. The calculations include thin cylindrical elastic walls with properties and dimensions appropriate for arteries. The presence of these artery walls does not substantially change the interface jetting predicted in unconfined simulations.« less

Influence of Turbulent Flows in the Nozzle on Melt Flow Within a Slab Mold and Stability of the Metal-Flux Interface

NASA Astrophysics Data System (ADS)

Calderon-Ramos, Ismael; Morales, R. D.

2016-06-01

The design of the ports of a casting nozzle has profound effects on the fluid flow patterns in slab molds. The influence of these outlets have also considerable effects on the turbulent flow and turbulence variables inside the nozzle itself. To understand the effects of nozzle design, three approaches were employed: a theoretical analysis based on the turbulent viscosity hypothesis, dimensional analysis (both analyses aided by computer fluid dynamics), and experiments using particle image velocimetry. The first approach yields a linear relation between calculated magnitudes of scalar fields of ɛ (dissipation rate of kinetic energy) and k 2 (square of the turbulent kinetic energy), which is derived from the wall and the logarithmic-wall laws in the boundary layers. The smaller the slope of this linear relation is, the better the performance of a given nozzle is for maintaining the stability of the melt-flux interface. The second approach yields also a linear relation between flow rate of liquid metal and the cubic root of the dissipation rate of kinetic energy. In this case, the larger the slope of the linear relation is, the better the performance of a given nozzle is for maintaining the stability of the melt-flux interface. Finally, PIV measurements in a mold water model, together with equations for estimation of critical melt velocities for slag entrainment, were used to quantify the effects of nozzle design on the dynamics of the metal-slag interface. The three approaches agree in the characterization of turbulent flows in continuous casting molds using different nozzles.

Formation and organization of protein domains in the immunological synapse

NASA Astrophysics Data System (ADS)

Carlson, Andreas; Mahadevan, L.

2014-11-01

The cellular basis for the adaptive immune response during antigen recognition relies on a specialized protein interface known as the immunological synapse. Here, we propose a minimal mathematical model for the dynamics of the IS that encompass membrane mechanics, hydrodynamics and protein kinetics. Simple scaling laws describe the dynamics of protein clusters as a function of membrane stiffness, rigidity of the adhesive proteins, and fluid flow in the synaptic cleft. Numerical simulations complement the scaling laws by quantifying the nucleation, growth and stabilization of proteins domains on the size of the cell. Direct comparison with experiment suggests that passive dynamics suffices to describe the short-time formation and organization of protein clusters, while the stabilization and long time dynamics of the synapse is likely determined by active cytoskeleton processes triggered by receptor binding. Our study reveals that the fluid flow generated by the interplay between membrane deformation and protein binding kinetics can assist immune cells in regulating protein sorting.

Spectral analysis of the turbulent mixing of two fluids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steinkamp, M.J.

1996-02-01

The authors describe a spectral approach to the investigation of fluid instability, generalized turbulence, and the interpenetration of fluids across an interface. The technique also applies to a single fluid with large variations in density. Departures of fluctuating velocity components from the local mean are far subsonic, but the mean Mach number can be large. Validity of the description is demonstrated by comparisons with experiments on turbulent mixing due to the late stages of Rayleigh-Taylor instability, when the dynamics become approximately self-similar in response to a constant body force. Generic forms for anisotropic spectral structure are described and used asmore » a basis for deriving spectrally integrated moment equations that can be incorporated into computer codes for scientific and engineering analyses.« less

Topics in viscous potential flow of two-phase systems

NASA Astrophysics Data System (ADS)

Padrino Inciarte, Juan Carlos

Two-phase flows are ubiquitous, from natural and domestic environments to industrial settings. However, due to their complexity, modeling these fluid systems remains a challenge from both the perspective of fundamental questions on the dynamics of an individual, smooth interface, and the perspective of integral analyses, which involve averaging of the conservation laws over large domains, thereby missing local details of the flow. In this work, we consider a set of five problems concerning the linear and non-linear dynamics of an interface or free surface and the study of cavitation inception. Analyses are carried out by assuming the fluid motion to be irrotational, that is, with zero vorticity, and the fluids to be viscous, although results from rotational analyses are presented for the purpose of comparison. The problems considered here are the following: First, we analyze the non-linear deformation and break-up of a bubble or drop immersed in a uniaxial extensional flow of an incompressible viscous fluid. The method of viscous potential flow, in which the flow field is irrotational and viscosity enters through the balance of normal stresses at the interface, is used in the analysis. The governing equations are solved numerically to track the motion of the interface by coupling a boundary element method with a time-integration routine. When break-up occurs, the break-up time computed here is compared with results obtained elsewhere from numerical simulations of the Navier.Stokes equations, which thus keeps vorticity in the analysis, for several combinations of the relevant dimensionless parameters of the problem. For the bubble, for Weber numbers 3 ≤ We ≤ 6, predictions from viscous potential flow shows good agreement with the results from the Navier.Stokes equations for the bubble break-up time, whereas for larger We, the former underpredicts the results given by the latter. Including viscosity increases the break-up time with respect to the inviscid case. For the drop, as expected, increasing the viscous effects of the irrotational motion produces large, elongated drops that take longer to break up in comparison with results for inviscid fluids. In the second problem, we compute the force acting on a spherical bubble of variable radius moving within a liquid with an outer spherical boundary. Viscous potential flow and the dissipation method, which is another purely irrotational approach stemming from the mechanical energy equation, are both systematically implemented. This exposes the role of the choice of the outer boundary condition for the stress on the drag, an issue not explained in the literature known to us. By means of the well-known "cell-model" analysis, the results for the drag are then applied to the case of a swarm of rising bubbles having a certain void fraction. Computations from the dissipation method for the drag coefficient and rise velocity for a bubble swarm agree with numerical solutions; evaluation against experimental data for high Reynolds and low Weber numbers shows that all the models considered, including those given in the literature, overpredict the bubble swarm rise velocity. In the next two problems, we apply the analysis of viscous potential flow and the dissipation method to study the linear dynamics of waves of "small" amplitude acting either on a plane or on a spherical interface separating a liquid from a dynamically inactive fluid. It is shown that the viscous irrational theories exhibit the features of the wave dynamics by comparing with the exact solution. The range of parameters for which good agreement with the exact solution exists is presented. The general trend shows that for long waves the dissipation method results in the best approximation, whereas for short waves, even for very viscous liquids, viscous potential flow demonstrates better agreement. Finally, the problem of cavitation inception for the flow of a viscous liquid past a stationary sphere is studied by means of the theory of stress-induced cavitation. The flow field for a single phase needed in the analysis is found from three different methods, namely, the numerical solution of the Navier--Stokes equations, the irrotational motion of a viscous fluid, and, in the limit of no inertia, the Stokes flow formulation. The new predictions are then compared with those obtained from the classical pressure criterion. The main finding is that at a fixed cavitation number more viscous liquids are at greater risk to cavitation.

A preliminary investigation of the growth of an aneurysm with a multiscale monolithic Fluid-Structure interaction solver

NASA Astrophysics Data System (ADS)

Cerroni, D.; Manservisi, S.; Pozzetti, G.

2015-11-01

In this work we investigate the potentialities of multi-scale engineering techniques to approach complex problems related to biomedical and biological fields. In particular we study the interaction between blood and blood vessel focusing on the presence of an aneurysm. The study of each component of the cardiovascular system is very difficult due to the fact that the movement of the fluid and solid is determined by the rest of system through dynamical boundary conditions. The use of multi-scale techniques allows us to investigate the effect of the whole loop on the aneurysm dynamic. A three-dimensional fluid-structure interaction model for the aneurysm is developed and coupled to a mono-dimensional one for the remaining part of the cardiovascular system, where a point zero-dimensional model for the heart is provided. In this manner it is possible to achieve rigorous and quantitative investigations of the cardiovascular disease without loosing the system dynamic. In order to study this biomedical problem we use a monolithic fluid-structure interaction (FSI) model where the fluid and solid equations are solved together. The use of a monolithic solver allows us to handle the convergence issues caused by large deformations. By using this monolithic approach different solid and fluid regions are treated as a single continuum and the interface conditions are automatically taken into account. In this way the iterative process characteristic of the commonly used segregated approach, it is not needed any more.

Sound-induced Interfacial Dynamics in a Microfluidic Two-phase Flow

NASA Astrophysics Data System (ADS)

Mak, Sze Yi; Shum, Ho Cheung

2014-11-01

Retrieving sound wave by a fluidic means is challenging due to the difficulty in visualizing the very minute sound-induced fluid motion. This work studies the interfacial response of multiphase systems towards fluctuation in the flow. We demonstrate a direct visualization of music in the form of ripples at a microfluidic aqueous-aqueous interface with an ultra-low interfacial tension. The interface shows a passive response to sound of different frequencies with sufficiently precise time resolution, enabling the recording of musical notes and even subsequent reconstruction with high fidelity. This suggests that sensing and transmitting vibrations as tiny as those induced by sound could be realized in low interfacial tension systems. The robust control of the interfacial dynamics could be adopted for droplet and complex-fiber generation.

OpenFLUID: an open-source software environment for modelling fluxes in landscapes

NASA Astrophysics Data System (ADS)

Fabre, Jean-Christophe; Rabotin, Michaël; Crevoisier, David; Libres, Aline; Dagès, Cécile; Moussa, Roger; Lagacherie, Philippe; Raclot, Damien; Voltz, Marc

2013-04-01

Integrative landscape functioning has become a common concept in environmental management. Landscapes are complex systems where many processes interact in time and space. In agro-ecosystems, these processes are mainly physical processes, including hydrological-processes, biological processes and human activities. Modelling such systems requires an interdisciplinary approach, coupling models coming from different disciplines, developed by different teams. In order to support collaborative works, involving many models coupled in time and space for integrative simulations, an open software modelling platform is a relevant answer. OpenFLUID is an open source software platform for modelling landscape functioning, mainly focused on spatial fluxes. It provides an advanced object-oriented architecture allowing to i) couple models developed de novo or from existing source code, and which are dynamically plugged to the platform, ii) represent landscapes as hierarchical graphs, taking into account multi-scale, spatial heterogeneities and landscape objects connectivity, iii) run and explore simulations in many ways : using the OpenFLUID software interfaces for users (command line interface, graphical user interface), or using external applications such as GNU R through the provided ROpenFLUID package. OpenFLUID is developed in C++ and relies on open source libraries only (Boost, libXML2, GLib/GTK, OGR/GDAL, …). For modelers and developers, OpenFLUID provides a dedicated environment for model development, which is based on an open source toolchain, including the Eclipse editor, the GCC compiler and the CMake build system. OpenFLUID is distributed under the GPLv3 open source license, with a special exception allowing to plug existing models licensed under any license. It is clearly in the spirit of sharing knowledge and favouring collaboration in a community of modelers. OpenFLUID has been involved in many research applications, such as modelling of hydrological network transfer, diagnosis and prediction of water quality taking into account human activities, study of the effect of spatial organization on hydrological fluxes, modelling of surface-subsurface water exchanges, … At LISAH research unit, OpenFLUID is the supporting development platform of the MHYDAS model, which is a distributed model for agrosystems (Moussa et al., 2002, Hydrological Processes, 16, 393-412). OpenFLUID web site : http://www.openfluid-project.org

Electric Field Induced Interfacial Instabilities

NASA Technical Reports Server (NTRS)

Kusner, Robert E.; Min, Kyung Yang; Wu, Xiao-lun; Onuki, Akira

1999-01-01

The study of the interface in a charge-free, critical and near-critical binary fluid in the presence of an externally applied electric field is presented. At sufficiently large fields, the interface between the two phases of the binary fluid should become unstable and exhibit an undulation with a predefined wavelength on the order of the capillary length. As the critical point is approached, this wavelength is reduced, potentially approaching length-scales such as the correlation length or critical nucleation radius. At this point the critical properties of the system may be affected. In this paper, the flat interface of a marginally polar binary fluid mixture is stressed by a perpendicular alternating electric field and the resulting instability is characterized by the critical electric field E(sub c) and the pattern observed. The character of the surface dynamics at the onset of instability is found to be strongly dependent on the frequency f of the field applied. The plot of E(sub c) vs. f for a fixed temperature shows a sigmoidal shape, whose low and high frequency limits are well described by a power-law relationship, E(sub c) = epsilon(exp zeta) with zeta = 0.35 and zeta = 0.08, respectively. The low-limit exponent compares well with the value zeta = 4 for a system of conducting and non-conducting fluids. On the other hand, the high-limit exponent coincides with what was first predicted by Onuki. The instability manifests itself as the conducting phase penetrates the non-conducting phase. As the frequency increases, the shape of the pattern changes from an array of bifurcating strings to an array of column-like (or rod-like) protrusions, each of which spans the space between the plane interface and one of the electrodes. For an extremely high frequency, the disturbance quickly grows into a parabolic cone pointing toward the upper plate. As a result, the interface itself changes its shape from that of a plane to that of a high sloping pyramid.

Particles at fluid-fluid interfaces: A new Navier-Stokes-Cahn-Hilliard surface-phase-field-crystal model

PubMed Central

Aland, Sebastian; Lowengrub, John; Voigt, Axel

2013-01-01

Colloid particles that are partially wetted by two immiscible fluids can become confined to fluid-fluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids form an emulsion with interesting material properties and offer an important route to new soft materials. A promising approach to simulate these emulsions was presented in Aland et al. [Phys. Fluids 23, 062103 (2011)], where a Navier-Stokes-Cahn-Hilliard model for the macroscopic two-phase fluid system was combined with a surface phase-field-crystal model for the microscopic colloidal particles along the interface. Unfortunately this model leads to spurious velocities which require very fine spatial and temporal resolutions to accurately and stably simulate. In this paper we develop an improved Navier-Stokes-Cahn-Hilliard-surface phase-field-crystal model based on the principles of mass conservation and thermodynamic consistency. To validate our approach, we derive a sharp interface model and show agreement with the improved diffuse interface model. Using simple flow configurations, we show that the new model has much better properties and does not lead to spurious velocities. Finally, we demonstrate the solid-like behavior of the crystallized interface by simulating the fall of a solid ball through a colloid-laden multiphase fluid. PMID:23214691

High Accuracy Liquid Propellant Slosh Predictions Using an Integrated CFD and Controls Analysis Interface

NASA Technical Reports Server (NTRS)

Marsell, Brandon; Griffin, David; Schallhorn, Dr. Paul; Roth, Jacob

2012-01-01

Coupling computational fluid dynamics (CFD) with a controls analysis tool elegantly allows for high accuracy predictions of the interaction between sloshing liquid propellants and th e control system of a launch vehicle. Instead of relying on mechanical analogs which are not valid during aU stages of flight, this method allows for a direct link between the vehicle dynamic environments calculated by the solver in the controls analysis tool to the fluid flow equations solved by the CFD code. This paper describes such a coupling methodology, presents the results of a series of test cases, and compares said results against equivalent results from extensively validated tools. The coupling methodology, described herein, has proven to be highly accurate in a variety of different cases.

Integrated CFD and Controls Analysis Interface for High Accuracy Liquid Propellant Slosh Predictions

NASA Technical Reports Server (NTRS)

Marsell, Brandon; Griffin, David; Schallhorn, Paul; Roth, Jacob

2012-01-01

Coupling computational fluid dynamics (CFD) with a controls analysis tool elegantly allows for high accuracy predictions of the interaction between sloshing liquid propellants and the control system of a launch vehicle. Instead of relying on mechanical analogs which are n0t va lid during all stages of flight, this method allows for a direct link between the vehicle dynamic environments calculated by the solver in the controls analysis tool to the fluid now equations solved by the CFD code. This paper describes such a coupling methodology, presents the results of a series of test cases, and compares said results against equivalent results from extensively validated tools. The coupling methodology, described herein, has proven to be highly accurate in a variety of different cases.

Experimental Flow Models for SSME Flowfield Characterization

NASA Technical Reports Server (NTRS)

Abel, L. C.; Ramsey, P. E.

1989-01-01

Full scale flow models with extensive instrumentation were designed and manufactured to provide data necessary for flow field characterization in rocket engines of the Space Shuttle Main Engine (SSME) type. These models include accurate flow path geometries from the pre-burner outlet through the throat of the main combustion chamber. The turbines are simulated with static models designed to provide the correct pressure drop and swirl for specific power levels. The correct turbopump-hot gas manifold interfaces were designed into the flow models to permit parametric/integration studies for new turbine designs. These experimental flow models provide a vehicle for understanding the fluid dynamics associated with specific engine issues and also fill the more general need for establishing a more detailed fluid dynamic base to support development and verification of advanced math models.

Controlled assembly of jammed colloidal shells on fluid droplets.

PubMed

Subramaniam, Anand Bala; Abkarian, Manouk; Stone, Howard A

2005-07-01

Assembly of colloidal particles on fluid interfaces is a promising technique for synthesizing two-dimensional microcrystalline materials useful in fields as diverse as biomedicine, materials science, mineral flotation and food processing. Current approaches rely on bulk emulsification methods, require further chemical and thermal treatments, and are restrictive with respect to the materials used. The development of methods that exploit the great potential of interfacial assembly for producing tailored materials have been hampered by the lack of understanding of the assembly process. Here we report a microfluidic method that allows direct visualization and understanding of the dynamics of colloidal crystal growth on curved interfaces. The crystals are periodically ejected to form stable jammed shells, which we refer to as colloidal armour. We propose that the energetic barriers to interfacial crystal growth and organization can be overcome by targeted delivery of colloidal particles through hydrodynamic flows. Our method allows an unprecedented degree of control over armour composition, size and stability.

Controlled assembly of jammed colloidal shells on fluid droplets

NASA Astrophysics Data System (ADS)

Subramaniam, Anand Bala; Abkarian, Manouk; Stone, Howard A.

2005-07-01

Assembly of colloidal particles on fluid interfaces is a promising technique for synthesizing two-dimensional microcrystalline materials useful in fields as diverse as biomedicine, materials science, mineral flotation and food processing. Current approaches rely on bulk emulsification methods, require further chemical and thermal treatments, and are restrictive with respect to the materials used. The development of methods that exploit the great potential of interfacial assembly for producing tailored materials have been hampered by the lack of understanding of the assembly process. Here we report a microfluidic method that allows direct visualization and understanding of the dynamics of colloidal crystal growth on curved interfaces. The crystals are periodically ejected to form stable jammed shells, which we refer to as colloidal armour. We propose that the energetic barriers to interfacial crystal growth and organization can be overcome by targeted delivery of colloidal particles through hydrodynamic flows. Our method allows an unprecedented degree of control over armour composition, size and stability.

Pressure gradients fail to predict diffusio-osmosis

NASA Astrophysics Data System (ADS)

Liu, Yawei; Ganti, Raman; Frenkel, Daan

2018-05-01

We present numerical simulations of diffusio-osmotic flow, i.e. the fluid flow generated by a concentration gradient along a solid-fluid interface. In our study, we compare a number of distinct approaches that have been proposed for computing such flows and compare them with a reference calculation based on direct, non-equilibrium molecular dynamics simulations. As alternatives, we consider schemes that compute diffusio-osmotic flow from the gradient of the chemical potentials of the constituent species and from the gradient of the component of the pressure tensor parallel to the interface. We find that the approach based on treating chemical potential gradients as external forces acting on various species agrees with the direct simulations, thereby supporting the approach of Marbach et al (2017 J. Chem. Phys. 146 194701). In contrast, an approach based on computing the gradients of the microscopic pressure tensor does not reproduce the direct non-equilibrium results.

Lattice Boltzmann Method for Spacecraft Propellant Slosh Simulation

NASA Technical Reports Server (NTRS)

Orr, Jeb S.; Powers, Joseph F.; Yang, Hong Q

2015-01-01

A scalable computational approach to the simulation of propellant tank sloshing dynamics in microgravity is presented. In this work, we use the lattice Boltzmann equation (LBE) to approximate the behavior of two-phase, single-component isothermal flows at very low Bond numbers. Through the use of a non-ideal gas equation of state and a modified multiple relaxation time (MRT) collision operator, the proposed method can simulate thermodynamically consistent phase transitions at temperatures and density ratios consistent with typical spacecraft cryogenic propellants, for example, liquid oxygen. Determination of the tank forces and moments is based upon a novel approach that relies on the global momentum conservation of the closed fluid domain, and a parametric wall wetting model allows tuning of the free surface contact angle. Development of the interface is implicit and no interface tracking approach is required. A numerical example illustrates the method's application to prediction of bulk fluid behavior during a spacecraft ullage settling maneuver.

Lattice Boltzmann Method for Spacecraft Propellant Slosh Simulation

NASA Technical Reports Server (NTRS)

Orr, Jeb S.; Powers, Joseph F.; Yang, Hong Q.

2015-01-01

A scalable computational approach to the simulation of propellant tank sloshing dynamics in microgravity is presented. In this work, we use the lattice Boltzmann equation (LBE) to approximate the behavior of two-phase, single-component isothermal flows at very low Bond numbers. Through the use of a non-ideal gas equation of state and a modified multiple relaxation time (MRT) collision operator, the proposed method can simulate thermodynamically consistent phase transitions at temperatures and density ratios consistent with typical spacecraft cryogenic propellants, for example, liquid oxygen. Determination of the tank forces and moments relies upon the global momentum conservation of the fluid domain, and a parametric wall wetting model allows tuning of the free surface contact angle. Development of the interface is implicit and no interface tracking approach is required. Numerical examples illustrate the method's application to predicting bulk fluid motion including lateral propellant slosh in low-g conditions.

Contact angle distribution of particles at fluid interfaces.

PubMed

Snoeyink, Craig; Barman, Sourav; Christopher, Gordon F

2015-01-27

Recent measurements have implied a distribution of interfacially adsorbed particles' contact angles; however, it has been impossible to measure statistically significant numbers for these contact angles noninvasively in situ. Using a new microscopy method that allows nanometer-scale resolution of particle's 3D positions on an interface, we have measured the contact angles for thousands of latex particles at an oil/water interface. Furthermore, these measurements are dynamic, allowing the observation of the particle contact angle with high temporal resolution, resulting in hundreds of thousands of individual contact angle measurements. The contact angle has been found to fit a normal distribution with a standard deviation of 19.3°, which is much larger than previously recorded. Furthermore, the technique used allows the effect of measurement error, constrained interfacial diffusion, and particle property variation on the contact angle distribution to be individually evaluated. Because of the ability to measure the contact angle noninvasively, the results provide previously unobtainable, unique data on the dynamics and distribution of the adsorbed particles' contact angle.

Toward direct pore-scale modeling of three-phase displacements

NASA Astrophysics Data System (ADS)

Mohammadmoradi, Peyman; Kantzas, Apostolos

2017-12-01

A stable spreading film between water and gas can extract a significant amount of bypassed non-aqueous phase liquid (NAPL) through immiscible three-phase gas/water injection cycles. In this study, the pore-scale displacement mechanisms by which NAPL is mobilized are incorporated into a three-dimensional pore morphology-based model under water-wet and capillary equilibrium conditions. The approach is pixel-based and the sequence of invasions is determined by the fluids' connectivity and the threshold capillary pressure of the advancing interfaces. In addition to the determination of three-phase spatial saturation profiles, residuals, and capillary pressure curves, dynamic finite element simulations are utilized to predict the effective permeabilities of the rock microtomographic images as reasonable representations of the geological formations under study. All the influential features during immiscible fluid flow in pore-level domains including wetting and spreading films, saturation hysteresis, capillary trapping, connectivity, and interface development strategies are taken into account. The capabilities of the model are demonstrated by the successful prediction of saturation functions for Berea sandstone and the accurate reconstruction of three-phase fluid occupancies through a micromodel.

A Multiscale Model for Virus Capsid Dynamics

PubMed Central

Chen, Changjun; Saxena, Rishu; Wei, Guo-Wei

2010-01-01

Viruses are infectious agents that can cause epidemics and pandemics. The understanding of virus formation, evolution, stability, and interaction with host cells is of great importance to the scientific community and public health. Typically, a virus complex in association with its aquatic environment poses a fabulous challenge to theoretical description and prediction. In this work, we propose a differential geometry-based multiscale paradigm to model complex biomolecule systems. In our approach, the differential geometry theory of surfaces and geometric measure theory are employed as a natural means to couple the macroscopic continuum domain of the fluid mechanical description of the aquatic environment from the microscopic discrete domain of the atomistic description of the biomolecule. A multiscale action functional is constructed as a unified framework to derive the governing equations for the dynamics of different scales. We show that the classical Navier-Stokes equation for the fluid dynamics and Newton's equation for the molecular dynamics can be derived from the least action principle. These equations are coupled through the continuum-discrete interface whose dynamics is governed by potential driven geometric flows. PMID:20224756

Fluid and mass transfer at subduction interfaces-The field metamorphic record

NASA Astrophysics Data System (ADS)

Bebout, Gray E.; Penniston-Dorland, Sarah C.

2016-01-01

The interface between subducting oceanic slabs and the hanging wall is a structurally and lithologically complex region. Chemically disparate lithologies (sedimentary, mafic and ultramafic rocks) and mechanical mixtures thereof show heterogeneous deformation. These lithologies are tectonically juxtaposed at mm to km scales, particularly in more intensely sheared regions (mélange zones, which act as fluid channelways). This juxtaposition, commonly in the presence of a mobile fluid phase, offers up huge potential for mass transfer and related metasomatic alteration. Fluids in this setting appear capable of transporting mass over scales of kms, along flow paths with widely varying geometries and P-T trajectories. Current models of arc magmatism require km-scale migration of fluids from the interface into mantle wedge magma source regions and implicit in these models is the transport of any fluids generated in the subducting slab along and ultimately through the subduction interface. Field and geochemical studies of high- and ultrahigh-pressure metamorphic rocks elucidate the sources and compositions of fluids in subduction interfaces and the interplay between deformation and fluid and mass transfer in this region. Recent geophysical studies of the subduction interface - its thickness, mineralogy, density, and H2O content - indicate that its rheology greatly influences the ways in which the subducting plate is coupled with the hanging wall. Field investigation of the magnitude and styles of fluid-rock interaction in metamorphic rocks representing "seismogenic zone" depths (and greater) yields insight regarding the roles of fluids and elevated fluid pore pressure in the weakening of plate interface rocks and the deformation leading to seismic events. From a geochemical perspective, the plate interface contributes to shaping the "slab signature" observed in studies of the composition of arc volcanic rocks. Understanding the production of fluids with hybridized chemical/isotopic compositions could improve models aimed at identifying the relative contributions of end-member rock reservoirs through analyses of arc volcanic rocks. Production of rocks rich in hydrous minerals, along the subduction interface, could stabilize H2O to great depths in subduction zones and influence deep-Earth H2O cycling. Enhancement of decarbonation reactions and dissolution by fluid infiltration facilitated by deformation at the interface could influence the C flux from subducting slabs entering the sub-arc mantle wedge and various forearc reservoirs. In this paper, we consider records of fluid and mass transfer at localities representing various depths and structural expressions of evolving paleo-interfaces, ranging widely in structural character, the rock types involved (ultramafic, mafic, sedimentary), and the rheology of these rocks. We stress commonalities in styles of fluid and mass transfer as related to deformation style and the associated geometries of fluid mobility at subduction interfaces. Variations in thermal structure among individual margins will lead to significant differences in not only the rheology of subducting rocks, and thus seismicity, but also the profiles of devolatilization and melting, through the forearc and subarc, and the element/mineral solubilities in any aqueous fluids or silicate melts that are produced. One key factor in considering fluid and mass transfer in the subduction interface, influencing C cycling and other chemical additions to arcs, is the uncertain degree to which sub-crustal ultramafic rocks in downgoing slabs are hydrated and release H2O-rich fluids.

Oscillatory interfacial instability between miscible fluids

NASA Astrophysics Data System (ADS)

Shevtsova, Valentina; Gaponenko, Yuri; Mialdun, Aliaksandr; Torregrosa, Marita; Yasnou, Viktar

Interfacial instabilities occurring between two fluids are of fundamental interest in fluid dynamics, biological systems and engineering applications such as liquid storage, solvent extraction, oil recovery and mixing. Horizontal vibrations applied to stratified layers of immiscible liquids may generate spatially periodic waving of the interface, stationary in the reference frame of the vibrated cell, referred to as a "frozen wave". We present experimental evidence that frozen wave instability exists between two ordinary miscible liquids of similar densities and viscosities. At the experiments and at the numerical model, two superimposed layers of ordinary liquids, water-alcohol of different concentrations, are placed in a closed cavity in a gravitationally stable configuration. The density and viscosity of these fluids are somewhat similar. Similar to the immiscible fluids this instability has a threshold. When the value of forcing is increased the amplitudes of perturbations grow continuously displaying a saw-tooth structure. The decrease of gravity drastically changes the structure of frozen waves.

Dynamics of liquid bridges inside microchannels subject to pure oscillatory flows

NASA Astrophysics Data System (ADS)

Ahmadlouydarab, Majid; Azaiez, Jalel; Chen, Zhangxin

2014-11-01

We report on 2D simulations of liquid bridges' dynamics in microchannels of uniform wettability and subject to external oscillatory flows. The flow equations were solved using the Cahn-Hilliard diffuse-interface formulation and the finite element method with unstructured grid. It was found that regardless of the wettability properties of the microchannel walls, there is a critical frequency above which the bridge shows perpetual periodic oscillatory motion. Below that critical frequency, the liquid bridge ruptures when the channel walls are philic and detaches from the surface when they are phobic. This critical frequency depends on the viscosity ratio, oscillation amplitude and geometric aspect ratio of the bridge. It was also found that the flow velocity is out of phase with the footprint/throat lengths and that the latter two show a phase difference. These differences were explained in terms of the motion of the two contact lines on the substrates and the deformation of the fluid-fluid interfaces. To characterize the behavior of the liquid bridge, two quantitative parameters; the liquid bridge-solid interfacial length and the length of the throat of the liquid bridge were used. Variations of the interfacial morphology development of the bridge were analyzed to understand the bridge response.

Partial coalescence of drops at liquid interfaces

NASA Astrophysics Data System (ADS)

Blanchette, François; Bigioni, Terry P.

2006-04-01

When two separate masses of the same fluid are brought gently into contact, they are expected to fully merge into a single larger mass to minimize surface energy. However, when a stationary drop coalesces with an underlying reservoir of identical fluid, merging does not always proceed to completion. Occasionally, a drop in the process of merging apparently defies surface tension by `pinching off' before total coalescence occurs, leaving behind a smaller daughter droplet. Moreover, this process can repeat itself for subsequent generations of daughter droplets, resulting in a cascade of self-similar events. Such partial coalescence behaviour has implications for the dynamics of a variety of systems, including the droplets in clouds, ocean mist and airborne salt particles, emulsions, and the generation of vortices near an interface. Although it was first observed almost half a century ago, little is known about its precise mechanism. Here, we combine high-speed video imaging with numerical simulations to determine the conditions under which partial coalescence occurs, and to reveal a dynamic pinch-off mechanism. This mechanism is critically dependent on the ability of capillary waves to vertically stretch the drop by focusing energy on its summit.

Visual analysis of fluid dynamics at NASA's numerical aerodynamic simulation facility

NASA Technical Reports Server (NTRS)

Watson, Velvin R.

1991-01-01

A study aimed at describing and illustrating visualization tools used in Computational Fluid Dynamics (CFD) and indicating how these tools are likely to change by showing a projected resolution of the human computer interface is presented. The following are outlined using a graphically based test format: the revolution of human computer environments for CFD research; comparison of current environments; current environments with the ideal; predictions for the future CFD environments; what can be done to accelerate the improvements. The following comments are given: when acquiring visualization tools, potential rapid changes must be considered; environmental changes over the next ten years due to human computer interface cannot be fathomed; data flow packages such as AVS, apE, Explorer and Data Explorer are easy to learn and use for small problems, excellent for prototyping, but not so efficient for large problems; the approximation techniques used in visualization software must be appropriate for the data; it has become more cost effective to move jobs that fit on workstations and run only memory intensive jobs on the supercomputer; use of three dimensional skills will be maximized when the three dimensional environment is built in from the start.

Interaction of vortex ring with a stratified finite thickness interface

NASA Astrophysics Data System (ADS)

Advaith, S.; Manu, K. V.; Tinaikar, Aashay; Chetia, Utpal Kumar; Basu, Saptarshi

2017-09-01

This work experimentally investigates the dynamics of interaction between a propagating vortex ring and density stratified interface of finite thickness. The flow evolution has been quantified using a high speed shadowgraph technique and particle image velocimetry. The spatial and temporal behaviours of the vortex in the near and far field of the interface and the plume structure formed due to buoyancy are investigated systematically by varying the vortex strength (Reynolds number, Re) and the degree of stratification (Atwood number, At). Maximum penetration length (Lpmax) of the vortex ring through the interface is measured over a range of Reynolds (1350 ≤ Re ≤ 4600) and Richardson (0.1 ≤ Ri ≤ 4) numbers. It is found that for low Froude number values, the maximum penetration length varies linearly with the Froude number as in the study of Orlandi et al. ["Vortex rings descending in a stratified fluid," Phys. Fluids 10, 2819-2827 (1998)]. However, for high Reynolds and Richardson numbers (Ri), anomalous behaviour in maximum penetration is observed. The Lpmax value is used to characterize the vortex-interface interactions into non-penetrative, partially-penetrative, and extensively penetrative regimes. Flow visualization revealed the occurrence of short-wavelength instability of a plume structure, particularly in a partially penetrative regime. Fluid motion exhibits chaotic behaviour in an extensively penetrative regime. Detailed analyses of plume structure propagation are performed by measuring the plume length and plume rise. Appropriate scaling for the plume length and plume rise is derived, which allows universal collapse of the data for different flow conditions. Some information concerning the instability of the plume structure and decay of the vortex ring is obtained using proper orthogonal decomposition.

Fluid dynamic instabilities: theory and application to pattern forming in complex media

PubMed Central

Brun, P.-T.

2017-01-01

In this review article, we exemplify the use of stability analysis tools to rationalize pattern formation in complex media. Specifically, we focus on fluid flows, and show how the destabilization of their interface sets the blueprint of the patterns they eventually form. We review the potential use and limitations of the theoretical methods at the end, in terms of their applications to practical settings, e.g. as guidelines to design and fabricate structures while harnessing instabilities. This article is part of the themed issue ‘Patterning through instabilities in complex media: theory and applications’. PMID:28373378

Ion distributions in electrolyte confined by multiple dielectric interfaces

NASA Astrophysics Data System (ADS)

Jing, Yufei; Zwanikken, Jos W.; Jadhao, Vikram; de La Cruz, Monica

2014-03-01

The distribution of ions at dielectric interfaces between liquids characterized by different dielectric permittivities is crucial to nanoscale assembly processes in many biological and synthetic materials such as cell membranes, colloids and oil-water emulsions. The knowledge of ionic structure of these systems is also exploited in energy storage devices such as double-layer super-capacitors. The presence of multiple dielectric interfaces often complicates computing the desired ionic distributions via simulations or theory. Here, we use coarse-grained models to compute the ionic distributions in a system of electrolyte confined by two planar dielectric interfaces using Car-Parrinello molecular dynamics simulations and liquid state theory. We compute the density profiles for various electrolyte concentrations, stoichiometric ratios and dielectric contrasts. The explanations for the trends in these profiles and discuss their effects on the behavior of the confined charged fluid are also presented.

Modelling Earthquakes Using a Poro-Elastic Two-Phase Flow Formulation

NASA Astrophysics Data System (ADS)

Petrini, C.; Gerya, T.; van Dinther, Y.; Connolly, J. A.; Madonna, C.

2017-12-01

Seismicity along subduction zones ranges from large devastating megathrust earthquakes to aseismic slow slip events. These different slip phenomena are widely believed to be influenced by fluids and interactions of fluids with the host rock. To understand the slip or strain mode along the megathrust interface, it is thus crucial to understand the role of fluids. Considering the spatiotemporal limitations of observations, a promising approach is to develop a numerical model that couples the deformation of both fluids and solids in a single framework. The objective of this study is the development of such a seismo-hydro-mechanical approach and the subsequent identification of parameters that control the mode of slip. We present a newly developed finite difference visco-elasto-plastic numerical code with marker-in-cell technique, which fully couples inertial mechanical deformation and fluid flow. It allows for the accurate treatment of localised brittle/plastic deformation through global iterations. To accurately simulate both long- and short-term deformation an adaptive time step is introduced. This makes it possible to resolve seismic event with time steps on the order of milliseconds. We use this new tool to investigate how the presence of fluids in the pore space of an visco-elasto-brittle/plastic (de)compacting rock matrix affects elastic stress accumulation and release along a fluid-bearing subduction interface. The model is able to simulate spontaneous quasi-periodic seismic events, nucleating near the brittle-ductile transition zone, along self-consistently forming highly localized ruptures, which accommodate shear displacement between two plates. The generated elastic rebound events show slip velocities on the order of m/s. The governing gradual strength decrease along the propagating fracture is related to a drop in total pressure due to shear localization in combination with an increase in fluid pressure due to elastic compaction of the pore space in a rock with low permeability (6e-19 m2). Reduction of the differential pressure decreases brittle/plastic strength of fluid-bearing rocks along the rupture, thus providing a dynamic feedback mechanism for the accumulated elastic stress release at the subduction interface.

The Impact of Solid Surface Features on Fluid-Fluid Interface Configuration

NASA Astrophysics Data System (ADS)

Araujo, J. B.; Brusseau, M. L. L.

2017-12-01

Pore-scale fluid processes in geological media are critical for a broad range of applications such as radioactive waste disposal, carbon sequestration, soil moisture distribution, subsurface pollution, land stability, and oil and gas recovery. The continued improvement of high-resolution image acquisition and processing have provided a means to test the usefulness of theoretical models developed to simulate pore-scale fluid processes, through the direct quantification of interfaces. High-resolution synchrotron X-ray microtomography is used in combination with advanced visualization tools to characterize fluid distributions in natural geologic media. The studies revealed the presence of fluid-fluid interface associated with macroscopic features on the surfaces of the solids such as pits and crevices. These features and respective fluid interfaces, which are not included in current theoretical or computational models, may have a significant impact on accurate simulation and understanding of multi-phase flow, energy, heat and mass transfer processes.

Interface fluctuations during rapid drainage

NASA Astrophysics Data System (ADS)

Ayaz, Monem; Toussaint, Renaud; Schäfer, Gerhard; Jørgen Måløy, Knut; Moura, Marcel

2017-04-01

We experimentally study the interface dynamics of an immiscible fluid as it invades a monolayer of saturated porous medium through rapid drainage. The seemingly stable and continuous motion of the interface at macroscale, involves numerous abrupt pore-scale jumps and local reconfigurations of the interface. By computing the velocity fluctuations along the invasion front from sequences of images captured at high frame rate, we are able to study both the local and global behavior. The latter displays an intermittent behavior with power-law distributed avalanches in size and duration. As the system is drained potential surface energy is stored at the interface up to a given threshold in pressure. The energy released generates elastic waves at the confining plate, which we detect using piezoelectric type acoustic sensors. By detecting pore-scale events emanating from the depinning of the interface, we look to develop techniques for localizing the displacement front. To assess the quality of these techniques, optical monitoring is done in parallel using a high speed camera.

Atomization simulations using an Eulerian-VOF-Lagrangian method

NASA Technical Reports Server (NTRS)

Chen, Yen-Sen; Shang, Huan-Min; Liaw, Paul; Chen, C. P.

1994-01-01

This paper summarizes the technical development and validation of a multiphase computational fluid dynamics (CFD) numerical method using the volume-of-fluid (VOF) model and a Lagrangian tracking model which can be employed to analyze general multiphase flow problems with free surface mechanism. The gas-liquid interface mass, momentum and energy conservations are modeled by continuum surface mechanisms. A new solution method is developed such that the present VOF model can be applied for all-speed flow regimes. The objectives of the present study are to develop and verify the fractional volume-of-fluid cell partitioning approach into a predictor-corrector algorithm and to demonstrate the effectiveness of the present innovative approach by simulating benchmark problems including the coaxial jet atomization.

Dynamics of Wetting of Ultra Hydrophobic Surfaces

NASA Astrophysics Data System (ADS)

Mohammad Karim, Alireza; Kim, Jeong-Hyun; Rothstein, Jonathan; Kavehpour, Pirouz; Mechanical and Industrial Engineering, University of Massachusetts, Amherst Collaboration

2013-11-01

Controlling the surface wettability of hydrophobic and super hydrophobic surfaces has extensive industrial applications ranging from coating, painting and printing technology and waterproof clothing to efficiency increase in power and water plants. This requires enhancing the knowledge about the dynamics of wetting on these hydrophobic surfaces. We have done experimental investigation on the dynamics of wetting on hydrophobic surfaces by looking deeply in to the dependency of the dynamic contact angles both advancing and receding on the velocity of the three-phase boundary (Solid/Liquid/Gas interface) using the Wilhelmy plate method with different ultra-hydrophobic surfaces. Several fluids with different surface tension and viscosity are used to study the effect of physical properties of liquids on the governing laws.

Multiphase fluid-solid coupled analysis of shock-bubble-stone interaction in shockwave lithotripsy.

PubMed

Wang, Kevin G

2017-10-01

A novel multiphase fluid-solid-coupled computational framework is applied to investigate the interaction of a kidney stone immersed in liquid with a lithotripsy shock wave (LSW) and a gas bubble near the stone. The main objective is to elucidate the effects of a bubble in the shock path to the elastic and fracture behaviors of the stone. The computational framework couples a finite volume 2-phase computational fluid dynamics solver with a finite element computational solid dynamics solver. The surface of the stone is represented as a dynamic embedded boundary in the computational fluid dynamics solver. The evolution of the bubble surface is captured by solving the level set equation. The interface conditions at the surfaces of the stone and the bubble are enforced through the construction and solution of local fluid-solid and 2-fluid Riemann problems. This computational framework is first verified for 3 example problems including a 1D multimaterial Riemann problem, a 3D shock-stone interaction problem, and a 3D shock-bubble interaction problem. Next, a series of shock-bubble-stone-coupled simulations are presented. This study suggests that the dynamic response of a bubble to LSW varies dramatically depending on its initial size. Bubbles with an initial radius smaller than a threshold collapse within 1 μs after the passage of LSW, whereas larger bubbles do not. For a typical LSW generated by an electrohydraulic lithotripter (p max  = 35.0MPa, p min  =- 10.1MPa), this threshold is approximately 0.12mm. Moreover, this study suggests that a noncollapsing bubble imposes a negative effect on stone fracture as it shields part of the LSW from the stone. On the other hand, a collapsing bubble may promote fracture on the proximal surface of the stone, yet hinder fracture from stone interior. Copyright © 2016 John Wiley & Sons, Ltd.

VOF simulations of the contact angle dynamics during the drop spreading: standard models and a new wetting force model.

PubMed

Malgarinos, Ilias; Nikolopoulos, Nikolaos; Marengo, Marco; Antonini, Carlo; Gavaises, Manolis

2014-10-01

In this study,a novel numerical implementation for the adhesion of liquid droplets impacting normally on solid dry surfaces is presented. The advantage of this new approach, compared to the majority of existing models, is that the dynamic contact angle forming during the surface wetting process is not inserted as a boundary condition, but is derived implicitly by the induced fluid flow characteristics (interface shape) and the adhesion physics of the gas-liquid-surface interface (triple line), starting only from the advancing and receding equilibrium contact angles. These angles are required in order to define the wetting properties of liquid phases when interacting with a solid surface. The physical model is implemented as a source term in the momentum equation of a Navier-Stokes CFD flow solver as an "adhesion-like" force which acts at the triple-phase contact line as a result of capillary interactions between the liquid drop and the solid substrate. The numerical simulations capture the liquid-air interface movement by considering the volume of fluid (VOF) method and utilizing an automatic local grid refinement technique in order to increase the accuracy of the predictions at the area of interest, and simultaneously minimize numerical diffusion of the interface. The proposed model is validated against previously reported experimental data of normal impingement of water droplets on dry surfaces at room temperature. A wide range of impact velocities, i.e. Weber numbers from as low as 0.2 up to 117, both for hydrophilic (θadv=10°-70°) and hydrophobic (θadv=105°-120°) surfaces, has been examined. Predictions include in addition to droplet spreading dynamics, the estimation of the dynamic contact angle; the latter is found in reasonable agreement against available experimental measurements. It is thus concluded that theimplementation of this model is an effective approach for overcoming the need of a pre-defined dynamic contact angle law, frequently adopted as an approximate boundary condition for such simulations. Clearly, this model is mostly influential during the spreading phase for the cases of low We number impacts (We<˜80) since for high impact velocities, inertia dominates significantly over capillary forces in the initial phase of spreading. Copyright © 2014 Elsevier B.V. All rights reserved.

On relation between scalar interfaces and vorticity in inviscid flows

NASA Astrophysics Data System (ADS)

Ramesh, O. N.; Patwardhan, Saurabh

2013-11-01

A great variety of applications like pollutant mixing in the atmosphere, mixing of reactants in combustion highlight the importance of passive scalar dynamics in fluid flows. The other dynamically important variable in the study of fluid flow is the vorticity. Vorticity though, unlike a passive scalar, does affect the fluid motion. The dynamics of scalar (linear) and vorticity (non-linear) are governed by the equations which inherently have different characteristics. This paper addresses the question of the faithfulness of representation of vorticity by scalar marker and the motivation for this comes from the experiment of Head and Bandyopadhyay (1981) which showed the existence of coherent vortices by using smoke flow visualization in a turbulent boundary layer. We will show analytically in regions where the molecular diffusion effects are negligible, the vorticity and scalar gradients are orthogonal to each other. The iso- surface of scalar follows the vorticity in an inviscid situation. Also, we will demonstrate that in the case of unsteady burgers vortex and vortex shedding behind a finite circular cylinder, the scalar gradient is orthogonal to vorticity and inner product of vorticity and scalar gradients is zero in regions away from the wall.

Effect of Baffle on Gravity-Gradient-Excited Slosh Waves and Spacecraft Moment and Angular-Momentum Fluctuations in Microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Lee, C. C.

1995-01-01

The dynamical behavior of fluids affected by the asymmetric gravity gradient acceleration has been investigated. In particular, the effects of surface tension on partially filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank with and without baffles are studied. Results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient acceleration indicate that the gravity gradient acceleration is equivalent to the combined effect of a twisting force and a torsional moment acting on the spacecraft. The results are clearly seen from one-up one-down and one-down one-up oscillations in the cross-section profiles of two bubbles in the vertical (r, z)-plane of the rotating dewar, and from the eccentric contour of the bubble rotating around the axis of the dewar in a horizontal (r, theta)-plane. As the viscous force, between liquid and solid interface, greatly contributes to the damping of slosh wave excitation, a rotating dewar with baffles provides more areas of liquid-solid interface than that of a rotating dewar without baffles. Results show that the damping effect provided by the baffles reduces the amplitude of slosh wave excitation and lowers the degree of asymmetry in liquid-vapor distribution. Fluctuations of angular momentum and fluid moment caused by the slosh wave excited by gravity gradient acceleration with and without baffle boards are also investigated. It is also shown that the damping effect provided by the baffles greatly reduces the amplitudes of angular momentum and fluid moment fluctuations.

Finite-element lattice Boltzmann simulations of contact line dynamics

NASA Astrophysics Data System (ADS)

Matin, Rastin; Krzysztof Misztal, Marek; Hernández-García, Anier; Mathiesen, Joachim

2018-01-01

The lattice Boltzmann method has become one of the standard techniques for simulating a wide range of fluid flows. However, the intrinsic coupling of momentum and space discretization restricts the traditional lattice Boltzmann method to regular lattices. Alternative off-lattice Boltzmann schemes exist for both single- and multiphase flows that decouple the velocity discretization from the underlying spatial grid. The current study extends the applicability of these off-lattice methods by introducing a finite element formulation that enables simulating contact line dynamics for partially wetting fluids. This work exemplifies the implementation of the scheme and furthermore presents benchmark experiments that show the scheme reduces spurious currents at the liquid-vapor interface by at least two orders of magnitude compared to a nodal implementation and allows for predicting the equilibrium states accurately in the range of moderate contact angles.

The interaction of evaporative and convective instabilities

NASA Astrophysics Data System (ADS)

Ozen, O.

Evaporative convection arises in a variety of natural and industrial processes, such as drying of lakebeds, heat pipe technology and dry-eye syndrome. The phenomenon of evaporative convection leads to an interfacial instability where an erstwhile flat surface becomes undulated as a control variable, such as temperature drop, exceeds a critical value. This instability has been investigated by others assuming that the vapor phase is infinitely deep and passive, i.e. vapor fluid dynamics has been ignored. However, when we look at some engineering processes, such as distillation columns, heat pipes and drying technologies where phase change takes place we might imagine that the assumption of an infinitely deep vapor layer or at least that of a passive vapor is inappropriate. Previous work on convection in bilayer systems with no phase-change suggests that active vapor layers play a major role in determining the stability of an interface. Hence, for the case of convection with phase-change, we will address this issue and try to answer the question whether the infinitely deep and passive vapor layer is a valid assumption. We have also investigated, theoretically, the gravity and surface tension gradient-driven instabilities occurring during the evaporation of a liquid into its own vapor taking into account the fluid dynamics of both phases and the finiteness of the domains of each phase, i.e. the liquid and its vapor are assumed to be confined between two horizontal plates, and different heating arrangements are applied. The effects of fluid layer depths, the evaporation rate and the temperature gradient applied across the fluids on the stability of the interface are studied. The modes of the flow pattern are determined for each scenario. The physics of the instability are explained and a comparison is made with the results of similar, yet physically different problems.

Investigate the complex process in particle-fluid based surface generation technology using reactive molecular dynamics method

NASA Astrophysics Data System (ADS)

Han, Xuesong; Li, Haiyan; Zhao, Fu

2017-07-01

Particle-fluid based surface generation process has already become one of the most important materials processing technology for many advanced materials such as optical crystal, ceramics and so on. Most of the particle-fluid based surface generation technology involves two key process: chemical reaction which is responsible for surface softening; physical behavior which is responsible for materials removal/deformation. Presently, researchers cannot give a reasonable explanation about the complex process in the particle-fluid based surface generation technology because of the small temporal-spatial scale and the concurrent influence of physical-chemical process. Molecular dynamics (MD) method has already been proved to be a promising approach for constructing effective model of atomic scale phenomenon and can serve as a predicting simulation tool in analyzing the complex surface generation mechanism and is employed in this research to study the essence of surface generation. The deformation and piles of water molecule is induced with the feeding of abrasive particle which justifies the property mutation of water at nanometer scale. There are little silica molecule aggregation or materials removal because the water-layer greatly reduce the strength of mechanical interaction between particle and materials surface and minimize the stress concentration. Furthermore, chemical effect is also observed at the interface: stable chemical bond is generated between water and silica which lead to the formation of silconl and the reaction rate changes with the amount of water molecules in the local environment. Novel ring structure is observed in the silica surface and it is justified to be favored of chemical reaction with water molecule. The siloxane bond formation process quickly strengthened across the interface with the feeding of abrasive particle because of the compressive stress resulted by the impacting behavior.

Acquisition of Long-Duration, Low-Gravity Slosh Data Utilizing Existing ISS Equipment (SPHERES) for Calibration of CFD Models of Coupled Fluid-Vehicle Behavior

NASA Technical Reports Server (NTRS)

Schallhorn, Paul; Roth, Jacob; Marsell, Brandon; Kirk, Daniel; Gutierrez, Hector; Saenz-Otero, Alvar; Dorney, Daniel; Moder, Jeffrey

2013-01-01

Accurate prediction of coupled fluid slosh and launch vehicle or spacecraft dynamics (e.g., nutation/precessional movement about various axes, attitude changes, ect.) requires Computational Fluid Dynamics (CFD) models calibrated with low-gravity, long duration slosh data. Recently completed investigations of reduced gravity slosh behavior have demonstrated the limitations of utilizing parabolic flights on specialized aircraft with respect to the specific objectives of the experiments. Although valuable data was collected, the benefits of longer duration low-gravity environments were clearly established. The proposed research provides the first data set from long duration tests in zero gravity that can be directly used to benchmark CFD models, including the interaction between the sloshing fluid and the tank/vehicle dynamics. To explore the coupling of liquid slosh with the motion of an unconstrained tank in microgravity, NASA's Kennedy Space Center, Launch Services Program has teamed up with the Florida Institute of Technology (FIT), Massachusetts Institute of Technology (MIT) and the NASA Game Changing Development Program (GCD) to perform a series of slosh dynamics experiments on the International Space Station using the SPHERES platform. The Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) testbed provides a unique, free-floating instrumented platform on ISS that can be utilized in a manner that would solve many of the limitations of the current knowledge related to propellant slosh dynamics on launch vehicle and spacecraft fuel tanks. The six degree of freedom (6-DOF) motion of the SPHERES free-flyer is controlled by an array of cold-flow C02 thrusters, supplied from a built-in liquid C02 tank. These SPHERES can independently navigate and re-orient themselves within the ISS. The intent of this project is to design an externally mounted tank to be driven inside the ISS by a set of two SPHERES devices (Figure 1). The tank geometry simulates a launch vehicle upper stage propellant tank and the maneuvers replicate those of real vehicles. The design includes inertial sensors, data acquisition, image capture and data storage interfaces to the SPHERES VERTIGO computer system on board the flight article assembly. The design also includes mechanical and electronic interfaces to the existing SPHERES hardware, which include self-contained packages that can operate in conjunction with the existing SPHERES electronics

Acquisition of Long-Duration, Low-Gravity Slosh Data Utilizing Existing ISS Equipment (SPHERES) for Calibration of CFD Models of Coupled Fluid-Vehicle Behavior

NASA Technical Reports Server (NTRS)

Schallhorn, Paul; Roth, Jacob; Marsell, Brandon; Kirk, Daniel; Gutierrez, Hector; Saenz-Otero, Alvar; Dorney, Daniel; Moder, Jeffrey

2012-01-01

Accurate prediction of coupled fluid slosh and launch vehicle or spacecraft dynamics (e.g., nutation/precessional movement about various axes, attitude changes, ect.) requires Computational Fluid Dynamics (CFD) models calibrated with low-gravity, long duration slosh data. Recently completed investigations of reduced gravity slosh behavior have demonstrated the limitations of utilizing parabolic flights on specialized aircraft with respect to the specific objectives of the experiments. Although valuable data was collected, the benefits of longer duration low-gravity environments were clearly established. The proposed research provides the first data set from long duration tests in zero gravity that can be directly used to benchmark CFD models, including the interaction between the sloshing fluid and the tank/vehicle dynamics. To explore the coupling of liquid slosh with the motion of an unconstrained tank in microgravity, NASA's Kennedy Space Center, Launch Services Program has teamed up with the Florida Institute of Technology (FIT), Massachusetts Institute of Technology (MIT) and the Office of the Chief Technologist (OCT) to perform a series of slosh dynamics experiments on the International Space Station using the SPHERES platform. The Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) testbed provides a unique, free-floating instrumented platform on ISS that can be utilized in a manner that would solve many of the limitations of the current knowledge related to propellant slosh dynamics on launch vehicle and spacecraft fuel tanks. The six degree of freedom (6-DOF) motion of the SPHERES free-flyer is controlled by an array of cold-flow C02 thrusters, supplied from a built-in liquid C02 tank. These SPHERES can independently navigate and re-orient themselves within the ISS. The intent of this project is to design an externally mounted tank to be driven inside the ISS by a set of two SPHERES devices (Figure 1 ). The tank geometry simulates a launch vehicle upper stage propellant tank and the maneuvers replicate those of real vehicles. The design includes inertial sensors, data acquisition, image capture and data storage interfaces to the SPHERES VERTIGO computer system on board the flight article assembly. The design also includes mechanical and electronic interfaces to the existing SPHERES hardware, which include self-contained packages that can operate in conjunction with the existing SPHERES electronics.

Potential application of artificial concepts to aerodynamic simulation

NASA Technical Reports Server (NTRS)

Kutler, P.; Mehta, U. B.; Andrews, A.

1984-01-01

The concept of artificial intelligence as it applies to computational fluid dynamics simulation is investigated. How expert systems can be adapted to speed the numerical aerodynamic simulation process is also examined. A proposed expert grid generation system is briefly described which, given flow parameters, configuration geometry, and simulation constraints, uses knowledge about the discretization process to determine grid point coordinates, computational surface information, and zonal interface parameters.

Effect of fluid-colloid interactions on the mobility of a thermophoretic microswimmer in non-ideal fluids.

PubMed

Fedosov, Dmitry A; Sengupta, Ankush; Gompper, Gerhard

2015-09-07

Janus colloids propelled by light, e.g., thermophoretic particles, offer promising prospects as artificial microswimmers. However, their swimming behavior and its dependence on fluid properties and fluid-colloid interactions remain poorly understood. Here, we investigate the behavior of a thermophoretic Janus colloid in its own temperature gradient using numerical simulations. The dissipative particle dynamics method with energy conservation is used to investigate the behavior in non-ideal and ideal-gas like fluids for different fluid-colloid interactions, boundary conditions, and temperature-controlling strategies. The fluid-colloid interactions appear to have a strong effect on the colloid behavior, since they directly affect heat exchange between the colloid surface and the fluid. The simulation results show that a reduction of the heat exchange at the fluid-colloid interface leads to an enhancement of colloid's thermophoretic mobility. The colloid behavior is found to be different in non-ideal and ideal fluids, suggesting that fluid compressibility plays a significant role. The flow field around the colloid surface is found to be dominated by a source-dipole, in agreement with the recent theoretical and simulation predictions. Finally, different temperature-control strategies do not appear to have a strong effect on the colloid's swimming velocity.

Understanding the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions

NASA Astrophysics Data System (ADS)

Dahms, Rainer N.

2016-04-01

A generalized framework for multi-component liquid injections is presented to understand and predict the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions. The analysis focuses on the thermodynamic structure and the immiscibility state of representative gas-liquid interfaces. The most modern form of Helmholtz energy mixture state equation is utilized which exhibits a unique and physically consistent behavior over the entire two-phase regime of fluid densities. It is combined with generalized models for non-linear gradient theory and for liquid injections to quantify multi-component two-phase interface structures in global thermal equilibrium. Then, the Helmholtz free energy is minimized which determines the interfacial species distribution as a consequence. This minimal free energy state is demonstrated to validate the underlying assumptions of classic two-phase theory and spray atomization. However, under certain engine-relevant conditions for which corroborating experimental data are presented, this requirement for interfacial thermal equilibrium becomes unsustainable. A rigorously derived probability density function quantifies the ability of the interface to develop internal spatial temperature gradients in the presence of significant temperature differences between injected liquid and ambient gas. Then, the interface can no longer be viewed as an isolated system at minimal free energy. Instead, the interfacial dynamics become intimately connected to those of the separated homogeneous phases. Hence, the interface transitions toward a state in local equilibrium whereupon it becomes a dense-fluid mixing layer. A new conceptual view of a transitional liquid injection process emerges from a transition time scale analysis. Close to the nozzle exit, the two-phase interface still remains largely intact and more classic two-phase processes prevail as a consequence. Further downstream, however, the transition to dense-fluid mixing generally occurs before the liquid length is reached. The significance of the presented modeling expressions is established by a direct comparison to a reduced model, which utilizes widely applied approximations but fundamentally fails to capture the physical complexity discussed in this paper.

Adapting SAFT-γ perturbation theory to site-based molecular dynamics simulation. II. Confined fluids and vapor-liquid interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghobadi, Ahmadreza F.; Elliott, J. Richard, E-mail: elliot1@uakron.edu

2014-07-14

In this work, a new classical density functional theory is developed for group-contribution equations of state (EOS). Details of implementation are demonstrated for the recently-developed SAFT-γ WCA EOS and selective applications are studied for confined fluids and vapor-liquid interfaces. The acronym WCA (Weeks-Chandler-Andersen) refers to the characterization of the reference part of the third-order thermodynamic perturbation theory applied in formulating the EOS. SAFT-γ refers to the particular form of “statistical associating fluid theory” that is applied to the fused-sphere, heteronuclear, united-atom molecular models of interest. For the monomer term, the modified fundamental measure theory is extended to WCA-spheres. A newmore » chain functional is also introduced for fused and soft heteronuclear chains. The attractive interactions are taken into account by considering the structure of the fluid, thus elevating the theory beyond the mean field approximation. The fluctuations of energy are also included via a non-local third-order perturbation theory. The theory includes resolution of the density profiles of individual groups such as CH{sub 2} and CH{sub 3} and satisfies stoichiometric constraints for the density profiles. New molecular simulations are conducted to demonstrate the accuracy of each Helmholtz free energy contribution in reproducing the microstructure of inhomogeneous systems at the united-atom level of coarse graining. At each stage, comparisons are made to assess where the present theory stands relative to the current state of the art for studying inhomogeneous fluids. Overall, it is shown that the characteristic features of real molecular fluids are captured both qualitatively and quantitatively. For example, the average pore density deviates ∼2% from simulation data for attractive pentadecane in a 2-nm slit pore. Another example is the surface tension of ethane/heptane mixture, which deviates ∼1% from simulation data while the theory reproduces the excess accumulation of ethane at the interface.« less

Transport properties at fluids interfaces: a molecular study for a macroscopic modelling

NASA Astrophysics Data System (ADS)

Russo, Antonio; Morciano, Matteo; Sibley, David N.; Nold, Andreas; Goddard, Benjamin D.; Asinari, Pietro; Kalliadasis, Serafim

2017-11-01

Rapid developments in the field of micro- and nano-fluidics require detailed analysis of the properties of matter at the molecular level. But despite numerous works in the literature, appropriate macroscopic relations able to integrate a microscopic description of fluid and soft matter properties at liquid-vapour and multi-fluid interfaces are missing. As a consequence, studies on interfacial phenomena and micro-device designs often rely on oversimplified assumptions, e.g. that the viscosities can be considered constant across interfaces. In our work, we present non-equilibrium MD simulations to scrutinise efficiently and systematically, through the tools of statistical mechanics, the anisotropic properties of fluids, namely density variations, stress tensor, and shear viscosity, at the fluid interfaces between liquid and vapour and between two partially miscible fluids. Our analysis has led to the formulation of a general relation between shear viscosity and density variations validated for a wide spectrum of interfacial fluid problems. In addition, it provides a rational description of other interfacial quantities of interest, including surface tension and its origins, and more generally, it offers valuable insight of molecular transport phenomena at interfaces.

Computational fluid dynamics (CFD) insights into agitation stress methods in biopharmaceutical development.

PubMed

Bai, Ge; Bee, Jared S; Biddlecombe, James G; Chen, Quanmin; Leach, W Thomas

2012-02-28

Agitation of small amounts of liquid is performed routinely in biopharmaceutical process, formulation, and packaging development. Protein degradation commonly results from agitation, but the specific stress responsible or degradation mechanism is usually not well understood. Characterization of the agitation stress methods is critical to identifying protein degradation mechanisms or specific sensitivities. In this study, computational fluid dynamics (CFD) was used to model agitation of 1 mL of fluid by four types of common laboratory agitation instruments, including a rotator, orbital shaker, magnetic stirrer and vortex mixer. Fluid stresses in the bulk liquid and near interfaces were identified, quantified and compared. The vortex mixer provides the most intense stresses overall, while the stir bar system presented locally intense shear proximal to the hydrophobic stir bar surface. The rotator provides gentler fluid stresses, but the air-water interfacial area and surface stresses are relatively high given its low rotational frequency. The orbital shaker provides intermediate-level stresses but with the advantage of a large stable platform for consistent vial-to-vial homogeneity. Selection of experimental agitation methods with targeted types and intensities of stresses can facilitate better understanding of protein degradation mechanisms and predictability for "real world" applications. Copyright © 2011 Elsevier B.V. All rights reserved.

Settling of a sphere through a fluid-fluid interface: influence of the Reynolds number

NASA Astrophysics Data System (ADS)

Pierson, Jean-Lou; Magnaudet, Jacques

2015-11-01

When a particle sediments through a horizontal fluid-fluid interface (a situation frequently encountered in oceanography as well as in coating processes), it often tows a tail of the upper fluid into the lower one. This feature is observed in both inertia- and viscosity-dominated regimes. Nevertheless the tail evolution and the particle motion are found to highly depend on the ratio of the two effects, i.e. on the Reynolds number. In this work we study numerically the settling of a sphere through a horizontal fluid-fluid interface using an Immersed Boundary Method combined with a Volume of Fluid approach. To get some more insight into the underlying physical mechanisms, we combine this computational approach with a semi-analytical description based on the concept of Darwin ''drift'' which allows us to predict the interface evolution, hence the thickness of the film encapsulating the sphere, in the two limits of Stokes flow and potential flow. This work was funded by DGA whose financial support is greatly appreciated.

Droplet Deformation in an Extensional Flow: The Role of Surfactant Physical Chemistry

NASA Technical Reports Server (NTRS)

Stebe, Kathleen J.

1996-01-01

Surfactant-induced Marangoni effects strongly alter the stresses exerted along fluid particle interfaces. In low gravity processes, these stresses can dictate the system behavior. The dependence of Marangoni effects on surfactant physical chemistry is not understood, severely impacting our ability to predict and control fluid particle flows. A droplet in an extensional flow allows the controlled study of stretching and deforming interfaces. The deformations of the drop allow both Marangoni stresses, which resist tangential shear, and Marangoni elasticities, which resist surface dilatation, to develop. This flow presents an ideal model system for studying these effects. Prior surfactant-related work in this flow considered a linear dependence of the surface tension on the surface concentration, valid only at dilute surface concentrations, or a non-linear framework at concentrations sufficiently dilute that the linear approximation was valid. The linear framework becomes inadequate for several reasons. The finite dimensions of surfactant molecules must be taken into account with a model that includes surfaces saturation. Nonideal interactions between adsorbed surfactant molecules alter the partitioning of surfactant between the bulk and the interface, the dynamics of surfactant adsorptive/desorptive exchange, and the sensitivity of the surface tension to adsorbed surfactant. For example, cohesion between hydrocarbon chains favors strong adsorption. Cohesion also slows the rate of desorption from interfaces, and decreases the sensitivity of the surface tension to adsorbed surfactant. Strong cohesive interactions result in first order surface phase changes with a plateau in the surface tension vs surface concentration. Within this surface concentration range, the surface tension is decoupled from surface concentration gradients. We are engaged in the study of the role of surfactant physical chemistry in determining the Marangoni stresses on a drop in an extensional flow in a numerical and experimental program. Using surfactants whose dynamics and equilibrium behavior have been characterized in our laboratory, drop deformation will be studied in ground-based experiment. In an accompanying numerical study, predictive drop deformations will be determined based on the isotherm and equation of state determined in our laboratory. This work will improve our abilities to predict and control all fluid particle flows.

The importance of experimental design on measurement of dynamic interfacial tension and interfacial rheology in diffusion-limited surfactant systems

DOE PAGES

Reichert, Matthew D.; Alvarez, Nicolas J.; Brooks, Carlton F.; ...

2014-09-24

Pendant bubble and drop devices are invaluable tools in understanding surfactant behavior at fluid–fluid interfaces. The simple instrumentation and analysis are used widely to determine adsorption isotherms, transport parameters, and interfacial rheology. However, much of the analysis performed is developed for planar interfaces. Moreover, the application of a planar analysis to drops and bubbles (curved interfaces) can lead to erroneous and unphysical results. We revisit this analysis for a well-studied surfactant system at air–water interfaces over a wide range of curvatures as applied to both expansion/contraction experiments and interfacial elasticity measurements. The impact of curvature and transport on measured propertiesmore » is quantified and compared to other scaling relationships in the literature. Our results provide tools to design interfacial experiments for accurate determination of isotherm, transport and elastic properties.« less

An immersed boundary method for fluid-structure interaction with compressible multiphase flows

NASA Astrophysics Data System (ADS)

Wang, Li; Currao, Gaetano M. D.; Han, Feng; Neely, Andrew J.; Young, John; Tian, Fang-Bao

2017-10-01

This paper presents a two-dimensional immersed boundary method for fluid-structure interaction with compressible multiphase flows involving large structure deformations. This method involves three important parts: flow solver, structure solver and fluid-structure interaction coupling. In the flow solver, the compressible multiphase Navier-Stokes equations for ideal gases are solved by a finite difference method based on a staggered Cartesian mesh, where a fifth-order accuracy Weighted Essentially Non-Oscillation (WENO) scheme is used to handle spatial discretization of the convective term, a fourth-order central difference scheme is employed to discretize the viscous term, the third-order TVD Runge-Kutta scheme is used to discretize the temporal term, and the level-set method is adopted to capture the multi-material interface. In this work, the structure considered is a geometrically non-linear beam which is solved by using a finite element method based on the absolute nodal coordinate formulation (ANCF). The fluid dynamics and the structure motion are coupled in a partitioned iterative manner with a feedback penalty immersed boundary method where the flow dynamics is defined on a fixed Lagrangian grid and the structure dynamics is described on a global coordinate. We perform several validation cases (including fluid over a cylinder, structure dynamics, flow induced vibration of a flexible plate, deformation of a flexible panel induced by shock waves in a shock tube, an inclined flexible plate in a hypersonic flow, and shock-induced collapse of a cylindrical helium cavity in the air), and compare the results with experimental and other numerical data. The present results agree well with the published data and the current experiment. Finally, we further demonstrate the versatility of the present method by applying it to a flexible plate interacting with multiphase flows.

Development of a contact heat exchanger for a constructable radiator system

NASA Technical Reports Server (NTRS)

Howell, H. R.

1983-01-01

A development program for a contact heat exchanger to be used to transfer heat from a spacecraft coolant loop to a heat pipe radiator is described. The contact heat exchanger provides for a connectable/disconnectable joint which allows for on-orbit assembly of the radiator system and replacement or exchange of radiator panels for repair and maintenance. The contact heat exchanger does not require the transfer of fluid across the joint; the spacecraft coolant loop remains contained in an all welded system with no static or dynamic fluid seals. The contact interface is also "dry' with no conductive grease or interstitial material required.

Hybrid multiphase CFD simulation for liquid-liquid interfacial area prediction in annular centrifugal contactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wardle, K.E.

2013-07-01

Liquid-liquid contacting equipment used in solvent extraction processes has the dual purpose of mixing and separating two immiscible fluids. Consequently, such devices inherently encompass a wide variety of multiphase flow regimes. A hybrid multiphase computational fluid dynamics (CFD) solver which combines the Eulerian multi-fluid method with VOF (volume of fluid) sharp interface capturing has been developed for application to annular centrifugal contactors. This solver has been extended to enable prediction of mean droplet size and liquid-liquid interfacial area through a single moment population balance method. Simulations of liquid-liquid mixing in a simplified geometry and a model annular centrifugal contactor aremore » reported with droplet breakup/coalescence models being calibrated versus available experimental data. Quantitative comparison is made for two different housing vane geometries and it is found that the predicted droplet size is significantly smaller for vane geometries which result in higher annular liquid holdup.« less

Potential pressurized payloads: Fluid and thermal experiments

NASA Technical Reports Server (NTRS)

Swanson, Theodore D.

1992-01-01

Space Station Freedom (SSF) presents the opportunity to perform long term fluid and thermal experiments in a microgravity environment. This presentation provides perspective on the need for fluids/thermal experimentation in a microgravity environment, addresses previous efforts, identifies possible experiments, and discusses the capabilities of a proposed fluid physics/dynamics test facility. Numerous spacecraft systems use fluids for their operation. Thermal control, propulsion, waste management, and various operational processes are examples of such systems. However, effective ground testing is very difficult. This is because the effect of gravity induced phenomena, such as hydrostatic pressure, buoyant convection, and stratification, overcome such forces as surface tension, diffusion, electric potential, etc., which normally dominate in a microgravity environment. Hence, space experimentation is necessary to develop and validate a new fluid based technology. Two broad types of experiments may be performed on SSF: basic research and applied research. Basic research might include experiments focusing on capillary phenomena (with or without thermal and/or solutal gradients), thermal/solutal convection, phase transitions, and multiphase flow. Representative examples of applied research might include two-phase pressure drop, two-phase flow instabilities, heat transfer coefficients, fluid tank fill/drain, tank slosh dynamics, condensate removal enhancement, and void formation within thermal energy storage materials. In order to better support such fluid/thermal experiments on board SSF, OSSA has developed a conceptual design for a proposed Fluid Physics/Dynamics Facility (FP/DF). The proposed facility consists of one facility rack permanently located on SSF and one experimenter rack which is changed out as needed to support specific experiments. This approach will minimize the on-board integration/deintegration required for specific experiments. The FP/DF will have acceleration/vibration compensation, power and thermal interfaces, computer command/data collection, a video imaging system, and a portable glove box for operations. This facility will allow real-time astronaut interaction with the testing.

Brownian microhydrodynamics of active filaments.

PubMed

Laskar, Abhrajit; Adhikari, R

2015-12-21

Slender bodies capable of spontaneous motion in the absence of external actuation in an otherwise quiescent fluid are common in biological, physical and technological contexts. The interplay between the spontaneous fluid flow, Brownian motion, and the elasticity of the body presents a challenging fluid-structure interaction problem. Here, we model this problem by approximating the slender body as an elastic filament that can impose non-equilibrium velocities or stresses at the fluid-structure interface. We derive equations of motion for such an active filament by enforcing momentum conservation in the fluid-structure interaction and assuming slow viscous flow in the fluid. The fluid-structure interaction is obtained, to any desired degree of accuracy, through the solution of an integral equation. A simplified form of the equations of motion, which allows for efficient numerical solutions, is obtained by applying the Kirkwood-Riseman superposition approximation to the integral equation. We use this form of equation of motion to study dynamical steady states in free and hinged minimally active filaments. Our model provides the foundation to study collective phenomena in momentum-conserving, Brownian, active filament suspensions.

Diffuse-Interface Methods in Fluid Mechanics

NASA Technical Reports Server (NTRS)

Anderson, D. M.; McFadden, G. B.; Wheeler, A. A.

1997-01-01

The authors review the development of diffuse-interface models of hydrodynamics and their application to a wide variety of interfacial phenomena. The authors discuss the issues involved in formulating diffuse-interface models for single-component and binary fluids. Recent applications and computations using these models are discussed in each case. Further, the authors address issues including sharp-interface analyses that relate these models to the classical free-boundary problem, related computational approaches to describe interfacial phenomena, and related approaches describing fully-miscible fluids.

Chemical reaction fouling model for single-phase heat transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panchal, C.B.; Watkinson, A.P.

1993-08-01

A fouling model was developed on the premise that the chemical reaction for generation of precursor can take place in the bulk fluid, in the thermalboundary layer, or at the fluid/wall interface, depending upon the interactive effects of flu id dynamics, heat and mass transfer, and the controlling chemical reaction. The analysis was used to examine the experimental data for fouling deposition of polyperoxides produced by autoxidation of indene in kerosene. The effects of fluid and wall temperatures for two flow geometries were analyzed. The results showed that the relative effects of physical parameters on the fouling rate would differmore » for the three fouling mechanisms; therefore, it is important to identify the controlling mechanism in applying the closed-flow-loop data to industrial conditions.« less

Numerical modeling of spray combustion with an advanced VOF method

NASA Technical Reports Server (NTRS)

Chen, Yen-Sen; Shang, Huan-Min; Shih, Ming-Hsin; Liaw, Paul

1995-01-01

This paper summarizes the technical development and validation of a multiphase computational fluid dynamics (CFD) numerical method using the volume-of-fluid (VOF) model and a Lagrangian tracking model which can be employed to analyze general multiphase flow problems with free surface mechanism. The gas-liquid interface mass, momentum and energy conservation relationships are modeled by continuum surface mechanisms. A new solution method is developed such that the present VOF model can be applied for all-speed flow regimes. The objectives of the present study are to develop and verify the fractional volume-of-fluid cell partitioning approach into a predictor-corrector algorithm and to demonstrate the effectiveness of the present approach by simulating benchmark problems including laminar impinging jets, shear coaxial jet atomization and shear coaxial spray combustion flows.

Asymmetric bubble collapse and jetting in generalized Newtonian fluids

NASA Astrophysics Data System (ADS)

Shukla, Ratnesh K.; Freund, Jonathan B.

2017-11-01

The jetting dynamics of a gas bubble near a rigid wall in a non-Newtonian fluid are investigated using an axisymmetric simulation model. The bubble gas is assumed to be homogeneous, with density and pressure related through a polytropic equation of state. An Eulerian numerical description, based on a sharp interface capturing method for the shear-free bubble-liquid interface and an incompressible Navier-Stokes flow solver for generalized fluids, is developed specifically for this problem. Detailed simulations for a range of rheological parameters in the Carreau model show both the stabilizing and destabilizing non-Newtonian effects on the jet formation and impact. In general, for fixed driving pressure ratio, stand-off distance and reference zero-shear-rate viscosity, shear-thinning and shear-thickening promote and suppress jet formation and impact, respectively. For a sufficiently large high-shear-rate limit viscosity, the jet impact is completely suppressed. Thresholds are also determined for the Carreau power-index and material time constant. The dependence of these threshold rheological parameters on the non-dimensional driving pressure ratio and wall stand-off distance is similarly established. Implications for tissue injury in therapeutic ultrasound will be discussed.

Systems and methods for separating particles and/or substances from a sample fluid

DOEpatents

Mariella, Jr., Raymond P.; Dougherty, George M.; Dzenitis, John M.; Miles, Robin R.; Clague, David S.

2016-11-01

Systems and methods for separating particles and/or toxins from a sample fluid. A method according to one embodiment comprises simultaneously passing a sample fluid and a buffer fluid through a chamber such that a fluidic interface is formed between the sample fluid and the buffer fluid as the fluids pass through the chamber, the sample fluid having particles of interest therein; applying a force to the fluids for urging the particles of interest to pass through the interface into the buffer fluid; and substantially separating the buffer fluid from the sample fluid.

Novel Colloidal and Dynamic Interfacial Phenomena in Liquid Crystalline Systems

DTIC Science & Technology

2014-09-13

Pablo. Effects of anchoring strength on the diffusivity of nanoparticles in model liquid-crystalline fluids, Soft Matter, (03 2011): 6828. doi...10.1021/la103975s Santanu Kumar Pal, Claribel Acevedo-Ve?lez, Jacob T. Hunter, Nicholas L. Abbott. Effects of Divalent Ligand Interactions on Surface...peer-reviewed journals: (c) Presentations 7 Presentation #1 (a) Electrical double layer and specific ion effects at interfaces between thermotropic

Propagation of a viscous thin film over an elastic membran

NASA Astrophysics Data System (ADS)

Zheng, Zhong; Griffiths, Ian; Stone, Howard

2016-11-01

We study the buoyancy-driven spreading of a thin viscous film over a thin elastic membrane. Neglecting the effects of membrane bending and the membrane weight, we study the case of constant fluid injection and obtain a system of coupled partial differential equations to describe the shape of the air-liquid interface, and the deformation and the radial tension of the stretched membrane. We obtain self-similar solutions to describe the dynamics. In particular, in the early time period, the dynamics is dominated by buoyancy-driven spreading of the liquid film, and membrane stretching is a response to the buoyancy-controlled distribution of liquid weight; the location of the liquid front obeys the power-law form rf (t) t 1 / 2 . However, in the late time period, the system is quasi-steady, the air-liquid interface is flat, and membrane stretching, due to the liquid weight, causes the spreading of the liquid front; the location of the front obeys a different power-law form rf (t) t 1 / 4 before the edge effects of the membrane become significant. In addition, we report laboratory experiments for constant fluid injection using different viscous liquids and thin elastic membranes. Very good agreement is obtained between the theory and experiments.

A mass-conserving lattice Boltzmann method with dynamic grid refinement for immiscible two-phase flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fakhari, Abbas, E-mail: afakhari@nd.edu; Geier, Martin; Lee, Taehun

2016-06-15

A mass-conserving lattice Boltzmann method (LBM) for multiphase flows is presented in this paper. The proposed LBM improves a previous model (Lee and Liu, 2010 [21]) in terms of mass conservation, speed-up, and efficiency, and also extends its capabilities for implementation on non-uniform grids. The presented model consists of a phase-field lattice Boltzmann equation (LBE) for tracking the interface between different fluids and a pressure-evolution LBM for recovering the hydrodynamic properties. In addition to the mass conservation property and the simplicity of the algorithm, the advantages of the current phase-field LBE are that it is an order of magnitude fastermore » than the previous interface tracking LBE proposed by Lee and Liu (2010) [21] and it requires less memory resources for data storage. Meanwhile, the pressure-evolution LBM is equipped with a multi-relaxation-time (MRT) collision operator to facilitate attainability of small relaxation rates thereby allowing simulation of multiphase flows at higher Reynolds numbers. Additionally, we reformulate the presented MRT-LBM on nonuniform grids within an adaptive mesh refinement (AMR) framework. Various benchmark studies such as a rising bubble and a falling drop under buoyancy, droplet splashing on a wet surface, and droplet coalescence onto a fluid interface are conducted to examine the accuracy and versatility of the proposed AMR-LBM. The proposed model is further validated by comparing the results with other LB models on uniform grids. A factor of about 20 in savings of computational resources is achieved by using the proposed AMR-LBM. As a more demanding application, the Kelvin–Helmholtz instability (KHI) of a shear-layer flow is investigated for both density-matched and density-stratified binary fluids. The KHI results of the density-matched fluids are shown to be in good agreement with the benchmark AMR results based on the sharp-interface approach. When a density contrast between the two fluids exists, a typical chaotic structure in the flow field is observed at a Reynolds number of 10000, which indicates that the proposed model is a promising tool for direct numerical simulation of two-phase flows.« less

An investigation of matched index of refraction technique and its application in optical measurements of fluid flow

NASA Astrophysics Data System (ADS)

Amini, Noushin; Hassan, Yassin A.

2012-12-01

Optical distortions caused by non-uniformities of the refractive index within the measurement volume is a major impediment for all laser diagnostic imaging techniques applied in experimental fluid dynamic studies. Matching the refractive indices of the working fluid and the test section walls and interfaces provides an effective solution to this problem. The experimental set-ups designed to be used along with laser imaging techniques are typically constructed of transparent solid materials. In this investigation, different types of aqueous salt solutions and various organic fluids are studied for refractive index matching with acrylic and fused quartz, which are commonly used in construction of the test sections. One aqueous CaCl2·2H2O solution (63 % by weight) and two organic fluids, Dibutyl Phthalate and P-Cymene, are suggested for refractive index matching with fused quartz and acrylic, respectively. Moreover, the temperature dependence of the refractive indices of these fluids is investigated, and the Thermooptic Constant is calculated for each fluid. Finally, the fluid viscosity for different shear rates is measured as a function of temperature and is applied to characterize the physical behavior of the proposed fluids.

Cryogenic fluid management experiment

NASA Technical Reports Server (NTRS)

Eberhardt, R. N.; Bailey, W. J.; Fester, D. A.

1981-01-01

The cryogenic fluid management experiment (CFME), designed to characterize subcritical liquid hydrogen storage and expulsion in the low-q space environment, is discussed. The experiment utilizes a fine mesh screen fluid management device to accomplish gas-free liquid expulsion and a thermodynamic vent system to intercept heat leak and control tank pressure. The experiment design evolved from a single flight prototype to provision for a multimission (up to 7) capability. A detailed design of the CFME, a dynamic test article, and dedicated ground support equipment were generated. All materials and parts were identified, and components were selected and specifications prepared. Long lead titanium pressurant spheres and the flight tape recorder and ground reproduce unit were procured. Experiment integration with the shuttle orbiter, Spacelab, and KSC ground operations was coordinated with the appropriate NASA centers, and experiment interfaces were defined. Phase 1 ground and flight safety reviews were conducted. Costs were estimated for fabrication and assembly of the CFME, which will become the storage and supply tank for a cryogenic fluid management facility to investigate fluid management in space.

right-sized dimple evaluator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez, Sal

2017-08-24

The code (aka computer program written as a Matlab script) uses a unique set of n independent equations to solve for n turbulence variables. The code requires the input of a characteristic dimension, a characteristic fluid velocity, the fluid dynamic viscosity, and the fluid density. Most importantly, the code estimates the size of three key turbulent eddies: Kolmogorov, Taylor, and integral. Based on the eddy sizes, dimples dimensions are prescribed such that the key eddies (principally Taylor, and sometimes Kolmogorov), can be generated by the dimple rim and flow unimpeded through the dimple’s concave cavity. It is hypothesized that turbulentmore » eddies are generated by the dimple rim at the dimple-surface interface. The newly-generated eddies in turn entrain the movement of surrounding regions of fluid, creating more mixing. The eddies also generate lift near the wall surrounding the dimple, as they accelerate and reduce pressure in the regions near and at the dimple cavity, thereby minimizing the fluid drag.« less

A mixed-penalty biphasic finite element formulation incorporating viscous fluids and material interfaces.

PubMed

Chan, B; Donzelli, P S; Spilker, R L

2000-06-01

The fluid viscosity term of the fluid phase constitutive equation and the interface boundary conditions between biphasic, solid and fluid domains have been incorporated into a mixed-penalty finite element formulation of the linear biphasic theory for hydrated soft tissue. The finite element code can now model a single-phase viscous incompressible fluid, or a single-phase elastic solid, as limiting cases of a biphasic material. Interface boundary conditions allow the solution of problems involving combinations of biphasic, fluid and solid regions. To incorporate these conditions, the volume-weighted mixture velocity is introduced as a degree of freedom at interface nodes so that the kinematic continuity conditions are satisfied by conventional finite element assembly techniques. Results comparing our numerical method with an independent, analytic solution for the problem of Couette flow over rigid and deformable porous biphasic layers show that the finite element code accurately predicts the viscous fluid flows and deformation in the porous biphasic region. Thus, the analysis can be used to model the interface between synovial fluid and articular cartilage in diarthrodial joints. This is an important step toward modeling and understanding the mechanisms of joint lubrication and another step toward fully modeling the in vivo behavior of a diarthrodial joint.

The influence of interfacial slip on two-phase flow in rough pores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kucala, Alec; Martinez, Mario J.; Wang, Yifeng

The migration and trapping of supercritical CO 2 (scCO 2) in geologic carbon storage is strongly dependent on the geometry and wettability of the pore network in the reservoir rock. During displacement, resident fluids may become trapped in the pits of a rough pore surface forming an immiscible two-phase fluid interface with the invading fluid, allowing apparent slip flow at this interface. We present a two-phase fluid dynamics model, including interfacial tension, to characterize the impact of mineral surface roughness on this slip flow. We show that the slip flow can be cast in more familiar terms as a contact-anglemore » (wettability)-dependent effective permeability to the invading fluid, a nondimensional measurement which relates the interfacial slip to the pore geometry. The analysis shows the surface roughness-induced slip flow can effectively increase or decrease this effective permeability, depending on the wettability and roughness of the mineral surfaces. Configurations of the pore geometry where interfacial slip has a tangible influence on permeability have been identified. The results suggest that for large roughness features, permeability to CO 2 may be enhanced by approximately 30% during drainage, while the permeability to brine during reimbibition may be enhanced or diminished by 60%, depending on the contact angle with the mineral surfaces and degrees of roughness. For smaller roughness features, the changes in permeability through interfacial slip are small. As a result, a much larger range of effective permeabilities are suggested for general fluid pairs and contact angles, including occlusion of the pore by the trapped phase.« less

The influence of interfacial slip on two-phase flow in rough pores

DOE PAGES

Kucala, Alec; Martinez, Mario J.; Wang, Yifeng; ...

2017-08-01

The migration and trapping of supercritical CO 2 (scCO 2) in geologic carbon storage is strongly dependent on the geometry and wettability of the pore network in the reservoir rock. During displacement, resident fluids may become trapped in the pits of a rough pore surface forming an immiscible two-phase fluid interface with the invading fluid, allowing apparent slip flow at this interface. We present a two-phase fluid dynamics model, including interfacial tension, to characterize the impact of mineral surface roughness on this slip flow. We show that the slip flow can be cast in more familiar terms as a contact-anglemore » (wettability)-dependent effective permeability to the invading fluid, a nondimensional measurement which relates the interfacial slip to the pore geometry. The analysis shows the surface roughness-induced slip flow can effectively increase or decrease this effective permeability, depending on the wettability and roughness of the mineral surfaces. Configurations of the pore geometry where interfacial slip has a tangible influence on permeability have been identified. The results suggest that for large roughness features, permeability to CO 2 may be enhanced by approximately 30% during drainage, while the permeability to brine during reimbibition may be enhanced or diminished by 60%, depending on the contact angle with the mineral surfaces and degrees of roughness. For smaller roughness features, the changes in permeability through interfacial slip are small. As a result, a much larger range of effective permeabilities are suggested for general fluid pairs and contact angles, including occlusion of the pore by the trapped phase.« less

The influence of interfacial slip on two-phase flow in rough pores

NASA Astrophysics Data System (ADS)

Kucala, Alec; Martinez, Mario J.; Wang, Yifeng; Noble, David R.

2017-08-01

The migration and trapping of supercritical CO2 (scCO2) in geologic carbon storage is strongly dependent on the geometry and wettability of the pore network in the reservoir rock. During displacement, resident fluids may become trapped in the pits of a rough pore surface forming an immiscible two-phase fluid interface with the invading fluid, allowing apparent slip flow at this interface. We present a two-phase fluid dynamics model, including interfacial tension, to characterize the impact of mineral surface roughness on this slip flow. We show that the slip flow can be cast in more familiar terms as a contact-angle (wettability)-dependent effective permeability to the invading fluid, a nondimensional measurement which relates the interfacial slip to the pore geometry. The analysis shows the surface roughness-induced slip flow can effectively increase or decrease this effective permeability, depending on the wettability and roughness of the mineral surfaces. Configurations of the pore geometry where interfacial slip has a tangible influence on permeability have been identified. The results suggest that for large roughness features, permeability to CO2 may be enhanced by approximately 30% during drainage, while the permeability to brine during reimbibition may be enhanced or diminished by 60%, depending on the contact angle with the mineral surfaces and degrees of roughness. For smaller roughness features, the changes in permeability through interfacial slip are small. A much larger range of effective permeabilities are suggested for general fluid pairs and contact angles, including occlusion of the pore by the trapped phase.

Three-Dimensional Simulation of Liquid Drop Dynamics Within Unsaturated Vertical Hele-Shaw Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hai Huang; Paul Meakin

A three-dimensional, multiphase fluid flow model with volume of fluid-interface tracking was developed and applied to study the multiphase dynamics of moving liquid drops of different sizes within vertical Hele-Shaw cells. The simulated moving velocities are significantly different from those obtained from a first-order analytical approximation, based on simple force-balance concepts. The simulation results also indicate that the moving drops can exhibit a variety of shapes and that the transition among these different shapes is largely determined by the moving velocities. More important, there is a transition from a linear moving regime at small capillary numbers, in which the capillarymore » number scales linearly with the Bond number, to a nonlinear moving regime at large capillary numbers, in which the moving drop releases a train of droplets from its trailing edge. The train of droplets forms a variety of patterns at different moving velocities.« less

Pressurized-Flat-Interface Heat Exchanger

NASA Technical Reports Server (NTRS)

Voss, F. E.; Howell, H. R.; Winkler, R. V.

1990-01-01

High thermal conductance obtained without leakage between loops. Heat-exchanger interface enables efficient transfer of heat between two working fluids without allowing fluids to intermingle. Interface thin, flat, and easy to integrate into thermal system. Possible application in chemical or pharmaceutical manufacturing when even trace contamination of process stream with water or other coolant ruins product. Reduces costs when highly corrosive fluids must be cooled or heated.

Computer Aided Grid Interface: An Interactive CFD Pre-Processor

NASA Technical Reports Server (NTRS)

Soni, Bharat K.

1997-01-01

NASA maintains an applications oriented computational fluid dynamics (CFD) efforts complementary to and in support of the aerodynamic-propulsion design and test activities. This is especially true at NASA/MSFC where the goal is to advance and optimize present and future liquid-fueled rocket engines. Numerical grid generation plays a significant role in the fluid flow simulations utilizing CFD. An overall goal of the current project was to develop a geometry-grid generation tool that will help engineers, scientists and CFD practitioners to analyze design problems involving complex geometries in a timely fashion. This goal is accomplished by developing the CAGI: Computer Aided Grid Interface system. The CAGI system is developed by integrating CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) geometric system output and/or Initial Graphics Exchange Specification (IGES) files (including all the NASA-IGES entities), geometry manipulations and generations associated with grid constructions, and robust grid generation methodologies. This report describes the development process of the CAGI system.

Computer Aided Grid Interface: An Interactive CFD Pre-Processor

NASA Technical Reports Server (NTRS)

Soni, Bharat K.

1996-01-01

NASA maintains an applications oriented computational fluid dynamics (CFD) efforts complementary to and in support of the aerodynamic-propulsion design and test activities. This is especially true at NASA/MSFC where the goal is to advance and optimize present and future liquid-fueled rocket engines. Numerical grid generation plays a significant role in the fluid flow simulations utilizing CFD. An overall goal of the current project was to develop a geometry-grid generation tool that will help engineers, scientists and CFD practitioners to analyze design problems involving complex geometries in a timely fashion. This goal is accomplished by developing the Computer Aided Grid Interface system (CAGI). The CAGI system is developed by integrating CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) geometric system output and / or Initial Graphics Exchange Specification (IGES) files (including all the NASA-IGES entities), geometry manipulations and generations associated with grid constructions, and robust grid generation methodologies. This report describes the development process of the CAGI system.

Fluid Interfaces of Triangular Containers in Reduced Gravity Environments

NASA Technical Reports Server (NTRS)

Guttromson, Jayleen; Manning, Robert; Collicott, Steven H.

2002-01-01

Capillary dominated fluid dynamics will be examined in a reduced-gravity environment onboard the KC-135; in particular, the behavior of the lower portion of the meniscus in triangular tank geometries. Seven clear acrylic tanks were constructed to view seven angles of the four geometries. Silicon oil with two different viscosities, 2cs and 5cs silicon oil, were used on different days of the flight. Six tanks and one control tank are filled with a certain viscosity fluid for each flight day. During each parabola, three tanks are tested at time. The experimental tanks are exchanged between parabola sets on the KC-135. The 60deg -60deg -60deg control tank is viewed throughout the flight. To gather data, two digital video cameras and one digital still camera are placed perpendicular the viewing surface. To provide a greater contrast in the meniscus, an EL backlighting sheet was used to backlight the tanks. These images and video are then digitized, passed through NASA's mini-tracker software, and compared to a theory published my M. M. Weislogel, "Fluid Interface Phenomena in a Low-Gravity Environment: Recent Results from Drop Tower Experimentation." By focusing on a lower portion of the meniscus and using longer periods of reduced gravity, this experiment may confirm that a stationary point exists on the fluid surface. This information will enable better designing of propellant management devices, especially satellite propellant refilling and gas venting. Also, biological and material processing systems in reduced gravity environments will benefit from this data.

Single-bubble dynamics in pool boiling of one-component fluids.

PubMed

Xu, Xinpeng; Qian, Tiezheng

2014-06-01

We numerically investigate the pool boiling of one-component fluids with a focus on the effects of surface wettability on the single-bubble dynamics. We employed the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007)], a diffuse-interface model for liquid-vapor flows involving liquid-vapor transition in nonuniform temperature fields. We first perform simulations for bubbles on homogeneous surfaces. We find that an increase in either the contact angle or the surface superheating can enhance the bubble spreading over the heating surface and increase the bubble departure diameter as well and therefore facilitate the transition into film boiling. We then examine the dynamics of bubbles on patterned surfaces, which incorporate the advantages of both hydrophobic and hydrophilic surfaces. The central hydrophobic region increases the thermodynamic probability of bubble nucleation while the surrounding hydrophilic region hinders the continuous bubble spreading by pinning the contact line at the hydrophobic-hydrophilic intersection. This leads to a small bubble departure diameter and therefore prevents the transition from nucleate boiling into film boiling. With the bubble nucleation probability increased and the bubble departure facilitated, the efficiency of heat transfer on such patterned surfaces is highly enhanced, as observed experimentally [Int. J. Heat Mass Transfer 57, 733 (2013)]. In addition, the stick-slip motion of contact line on patterned surfaces is demonstrated in one-component fluids, with the effect weakened by surface superheating.

Nano- and microparticles at fluid and biological interfaces.

PubMed

Dasgupta, S; Auth, T; Gompper, G

2017-09-20

Systems with interfaces are abundant in both technological applications and biology. While a fluid interface separates two fluids, membranes separate the inside of vesicles from the outside, the interior of biological cells from the environment, and compartmentalize cells into organelles. The physical properties of interfaces are characterized by interface tension, those of membranes are characterized by bending and stretching elasticity. Amphiphilic molecules like surfactants that are added to a system with two immiscible fluids decrease the interface tension and induce a bending rigidity. Lipid bilayer membranes of vesicles can be stretched or compressed by osmotic pressure; in biological cells, also the presence of a cytoskeleton can induce membrane tension. If the thickness of the interface or the membrane is small compared with its lateral extension, both can be described using two-dimensional mathematical surfaces embedded in three-dimensional space. We review recent work on the interaction of particles with interfaces and membranes. This can be micrometer-sized particles at interfaces that stabilise emulsions or form colloidosomes, as well as typically nanometer-sized particles at membranes, such as viruses, parasites, and engineered drug delivery systems. In both cases, we first discuss the interaction of single particles with interfaces and membranes, e.g. particles in external fields, non-spherical particles, and particles at curved interfaces, followed by interface-mediated interaction between two particles, many-particle interactions, interface and membrane curvature-induced phenomena, and applications.

Nano- and microparticles at fluid and biological interfaces

NASA Astrophysics Data System (ADS)

Dasgupta, S.; Auth, T.; Gompper, G.

2017-09-01

Systems with interfaces are abundant in both technological applications and biology. While a fluid interface separates two fluids, membranes separate the inside of vesicles from the outside, the interior of biological cells from the environment, and compartmentalize cells into organelles. The physical properties of interfaces are characterized by interface tension, those of membranes are characterized by bending and stretching elasticity. Amphiphilic molecules like surfactants that are added to a system with two immiscible fluids decrease the interface tension and induce a bending rigidity. Lipid bilayer membranes of vesicles can be stretched or compressed by osmotic pressure; in biological cells, also the presence of a cytoskeleton can induce membrane tension. If the thickness of the interface or the membrane is small compared with its lateral extension, both can be described using two-dimensional mathematical surfaces embedded in three-dimensional space. We review recent work on the interaction of particles with interfaces and membranes. This can be micrometer-sized particles at interfaces that stabilise emulsions or form colloidosomes, as well as typically nanometer-sized particles at membranes, such as viruses, parasites, and engineered drug delivery systems. In both cases, we first discuss the interaction of single particles with interfaces and membranes, e.g. particles in external fields, non-spherical particles, and particles at curved interfaces, followed by interface-mediated interaction between two particles, many-particle interactions, interface and membrane curvature-induced phenomena, and applications.

Incorporating contact angles in the surface tension force with the ACES interface curvature scheme

NASA Astrophysics Data System (ADS)

Owkes, Mark

2017-11-01

In simulations of gas-liquid flows interacting with solid boundaries, the contact line dynamics effect the interface motion and flow field through the surface tension force. The surface tension force is directly proportional to the interface curvature and the problem of accurately imposing a contact angle must be incorporated into the interface curvature calculation. Many commonly used algorithms to compute interface curvatures (e.g., height function method) require extrapolating the interface, with defined contact angle, into the solid to allow for the calculation of a curvature near a wall. Extrapolating can be an ill-posed problem, especially in three-dimensions or when multiple contact lines are near each other. We have developed an accurate methodology to compute interface curvatures that allows for contact angles to be easily incorporated while avoiding extrapolation and the associated challenges. The method, known as Adjustable Curvature Evaluation Scale (ACES), leverages a least squares fit of a polynomial to points computed on the volume-of-fluid (VOF) representation of the gas-liquid interface. The method is tested by simulating canonical test cases and then applied to simulate the injection and motion of water droplets in a channel (relevant to PEM fuel cells).

Locking of the Chile subduction zone controlled by fluid pressure before the 2010 earthquake

NASA Astrophysics Data System (ADS)

Moreno, Marcos; Haberland, Christian; Oncken, Onno; Rietbrock, Andreas; Angiboust, Samuel; Heidbach, Oliver

2014-04-01

Constraints on the potential size and recurrence time of strong subduction-zone earthquakes come from the degree of locking between the down-going and overriding plates, in the period between large earthquakes. In many cases, this interseismic locking degree correlates with slip during large earthquakes or is attributed to variations in fluid content at the plate interface. Here we use geodetic and seismological data to explore the links between pore-fluid pressure and locking patterns at the subduction interface ruptured during the magnitude 8.8 Chile earthquake in 2010. High-resolution three-dimensional seismic tomography reveals variations in the ratio of seismic P- to S-wave velocities (Vp/Vs) along the length of the subduction-zone interface. High Vp/Vs domains, interpreted as zones of elevated pore-fluid pressure, correlate spatially with parts of the plate interface that are poorly locked and slip aseismically. In contrast, low Vp/Vs domains, interpreted as zones of lower pore-fluid pressure, correlate with locked parts of the plate interface, where unstable slip and earthquakes occur. Variations in pore-fluid pressure are caused by the subduction and dehydration of a hydrothermally altered oceanic fracture zone. We conclude that variations in pore-fluid pressure at the plate interface control the degree of interseismic locking and therefore the slip distribution of large earthquake ruptures.

Fluid-structure interaction modeling of wind turbines: simulating the full machine

NASA Astrophysics Data System (ADS)

Hsu, Ming-Chen; Bazilevs, Yuri

2012-12-01

In this paper we present our aerodynamics and fluid-structure interaction (FSI) computational techniques that enable dynamic, fully coupled, 3D FSI simulation of wind turbines at full scale, and in the presence of the nacelle and tower (i.e., simulation of the "full machine"). For the interaction of wind and flexible blades we employ a nonmatching interface discretization approach, where the aerodynamics is computed using a low-order finite-element-based ALE-VMS technique, while the rotor blades are modeled as thin composite shells discretized using NURBS-based isogeometric analysis (IGA). We find that coupling FEM and IGA in this manner gives a good combination of efficiency, accuracy, and flexibility of the computational procedures for wind turbine FSI. The interaction between the rotor and tower is handled using a non-overlapping sliding-interface approach, where both moving- and stationary-domain formulations of aerodynamics are employed. At the fluid-structure and sliding interfaces, the kinematic and traction continuity is enforced weakly, which is a key ingredient of the proposed numerical methodology. We present several simulations of a three-blade 5~MW wind turbine, with and without the tower. We find that, in the case of no tower, the presence of the sliding interface has no effect on the prediction of aerodynamic loads on the rotor. From this we conclude that weak enforcement of the kinematics gives just as accurate results as the strong enforcement, and thus enables the simulation of rotor-tower interaction (as well as other applications involving mechanical components in relative motion). We also find that the blade passing the tower produces a 10-12 % drop (per blade) in the aerodynamic torque. We feel this finding may be important when it comes to the fatigue-life analysis and prediction for wind turbine blades.

Rayleigh-Taylor instability at spherical interfaces between viscous fluids: Fluid/vacuum interface

DOE PAGES

Terrones, Guillermo; Carrara, Mark D.

2015-05-01

For a spherical interface of radius R separating two different homogeneous regions of incompressible viscous fluids under the action of a radially directed acceleration, we perform a linear stability analysis in terms of spherical surface harmonics Y n to derive the dispersion relation. The instability behavior is investigated by computing the growth rates and the most-unstable modes as a function of the spherical harmonic degree n. This general methodology is applicable to the entire parameter space spanned by the Atwood number, the viscosity ratio, and the dimensionless number B = (α RΡ² 2/μ² ²)¹ /³ R (where α R, Ρmore » 2 and μ 2 are the local radial acceleration at the interface, and the density and viscosity of the denser overlying fluid, respectively). While the mathematical formulation here is general, this paper focuses on instability that arises at a spherical viscous fluid/vacuum interface as there is a great deal to be learned from the effects of one-fluid viscosity and sphericity alone. To quantify and understand the effect that curvature and radial accelerationhave on the Rayleigh-Taylor instability, a comparison of the growth rates, under homologous driving conditions, between the planar and spherical interfaces is performed. The derived dispersion relation for the planar interface accounts for an underlying finite fluid region of thickness L and normal acceleration α R. Under certain conditions, the development of the most-unstable modes at a spherical interface can take place via the superposition of two adjacent spherical harmonics Y n and Y n+1. This bimodality in the evolution of disturbances in the linear regime does not have a counterpart in the planar configuration where the most-unstable modes are associated with a unique wave number.« less

Statistical substantiation of the van der Waals theory of inhomogeneous fluids

NASA Astrophysics Data System (ADS)

Baidakov, V. G.; Protsenko, S. P.; Chernykh, G. G.; Boltachev, G. Sh.

2002-04-01

Computer experiments on simulation of thermodynamic properties and structural characteristics of a Lennard-Jones fluid in one- and two-phase models have been performed for the purpose of checking the base concepts of the van der Waals theory. Calculations have been performed by the method of molecular dynamics at cutoff radii of the intermolecular potential rc,1=2.6σ and rc,2=6.78σ. The phase equilibrium parameters, surface tension, and density distribution have been determined in a two-phase model with a flat liquid-vapor interface. The strong dependence of these properties on the value of rc is shown. The p,ρ,T properties and correlation functions have been calculated in a homogeneous model for a stable and a metastable fluid. An equation of state for a Lennard-Jones fluid describing stable, metastable, and labile regions has been built. It is shown that at T>=1.1 the properties of a flat interface within the computer experimental error can be described by the van der Waals square-gradient theory with an influence parameter κ independent of the density. Taking into account the density dependence of κ through the second moment of the direct correlation function will deteriorate the agreement of the theory with data of computer simulation. The contribution of terms of a higher order than (∇ρ)2 to the Helmholtz free energy of an inhomogeneous system has been considered. It is shown that taking into account terms proportional to (∇ρ)4 leaves no way of obtaining agreement between the theory and simulation data, while taking into consideration of terms proportional to (∇ρ)6 makes it possible to describe with adequate accuracy all the properties of a flat interface in the temperature range from the triple to the critical point.

The complex fluid dynamics of simple diffusion

NASA Astrophysics Data System (ADS)

Vold, Erik

2017-11-01

Diffusion as the mass transport process responsible for mixing fluids at the atomic level is often underestimated in its complexity. An initial discontinuity between two species of different atomic masses exhibits a mass density discontinuity under isothermal pressure equilibrium implying equal species molar densities. The self-consistent kinetic transport processes across such an interface leads to a zero sum of mass flux relative to the center of mass and so diffusion alone cannot relax an initially stationary mass discontinuity nor broaden the density profile at the interface. The diffusive mixing leads to a molar imbalance which drives a center of mass velocity which moves the heavier species toward the lighter species leading to the interfacial density relaxation. Simultaneously, the species non-zero molar flux modifies the pressure profile in a transient wave and in a local perturbation. The resulting center of mass velocity has two components; one, associated with the divergence of the flow, persists in the diffusive mixing region throughout the diffusive mixing process, and two, travelling waves at the front of the pressure perturbations propagate away from the mixing region. The momentum in these waves is necessary to maintain momentum conservation in the center of mass frame. Thus, in a number of ways, the diffusive mixing provides feedback into the small scale advective motions. Numerical methods which diffuse all species assuming P-T equilibrium may not recover the subtle dynamics of mass transport at an interface. Work performed by the LANS, LLC, under USDOE Contract No. DE-AC52-06NA25396, funded by the (ASC) Program.

Recent advances in quantitative analysis of fluid interfaces in multiphase fluid flow measured by synchrotron-based x-ray microtomography

NASA Astrophysics Data System (ADS)

Schlueter, S.; Sheppard, A.; Wildenschild, D.

2013-12-01

Imaging of fluid interfaces in three-dimensional porous media via x-ray microtomography is an efficient means to test thermodynamically derived predictions on the relationship between capillary pressure, fluid saturation and specific interfacial area (Pc-Sw-Anw) in partially saturated porous media. Various experimental studies exist to date that validate the uniqueness of the Pc-Sw-Anw relationship under static conditions and with current technological progress direct imaging of moving interfaces under dynamic conditions is also becoming available. Image acquisition and subsequent image processing currently involves many steps each prone to operator bias, like merging different scans of the same sample obtained at different beam energies into a single image or the generation of isosurfaces from the segmented multiphase image on which the interface properties are usually calculated. We demonstrate that with recent advancements in (i) image enhancement methods, (ii) multiphase segmentation methods and (iii) methods of structural analysis we can considerably decrease the time and cost of image acquisition and the uncertainty associated with the measurement of interfacial properties. In particular, we highlight three notorious problems in multiphase image processing and provide efficient solutions for each: (i) Due to noise, partial volume effects, and imbalanced volume fractions, automated histogram-based threshold detection methods frequently fail. However, these impairments can be mitigated with modern denoising methods, special treatment of gray value edges and adaptive histogram equilization, such that most of the standard methods for threshold detection (Otsu, fuzzy c-means, minimum error, maximum entropy) coincide at the same set of values. (ii) Partial volume effects due to blur may produce apparent water films around solid surfaces that alter the specific fluid-fluid interfacial area (Anw) considerably. In a synthetic test image some local segmentation methods like Bayesian Markov random field, converging active contours and watershed segmentation reduced the error in Anw associated with apparent water films from 21% to 6-11%. (iii) The generation of isosurfaces from the segmented data usually requires a lot of postprocessing in order to smooth the surface and check for consistency errors. This can be avoided by calculating specific interfacial areas directly on the segmented voxel image by means of Minkowski functionals which is highly efficient and less error prone.

Direct Numerical Simulations of Dynamic Drainage and Imbibition to Investigate Capillary Pressure-Saturation-Interfacial Area Relation

NASA Astrophysics Data System (ADS)

Konangi, S.; Palakurthi, N. K.; Karadimitriou, N.; Comer, K.; Ghia, U.

2017-12-01

We present results of pore-scale direct numerical simulations (DNS) of drainage and imbibition in a quasi-two-dimensional (40µm thickness) porous medium with a randomly distributed packing of cylindrical obstructions. The Navier-Stokes (NS) equations are solved in the pore space on an Eulerian mesh using the open-source finite-volume computational fluid dynamics (CFD) code, OpenFOAM. The Volume-of-Fluid (VOF) method is employed to track the evolution of the fluid-fluid interface; a static contact angle is used to account for wall adhesion. From the DNS data, we focus on the macroscopic capillary pressure-saturation (Pc-Sw) relation, which is known to be hysteretic, i.e., this relation is flow process (such as drainage, imbibition and scanning curves) and history dependent. In order to overcome the problem of hysteresis, extended theories of multiphase flow hypothesized that the inclusion of specific interfacial area as a state variable will result in a unique relation between capillary pressure, saturation and interfacial area (Pc-Sw-awn). We study the role of specific interfacial area on hysteresis in the macroscopic Pc-Sw relation under non-equilibrium (dynamic) conditions. Under dynamic conditions, capillary pressure depends on the rate of change of the wetting phase saturation, and the dynamic Pc-Sw relation includes the changes caused by viscous effects. Simulations of drainage and imbibition are performed for two capillary numbers by controlling the flow rate of the non-wetting (polydimenthlysiloxane oil) and wetting (water) fluids. From these simulations, the Pc-Sw curves will be estimated; the Pc-S-awn surface will be constructed to determine whether the data points from drainage and imbibition processes fall on a unique surface under transient conditions. Different macroscopic capillary pressure definitions based on phase-averaged pressures and interfacial area will be evaluated. Understanding macroscopic capillary pressure definitions and the uniqueness of the Pc-S- awn relation is step towards complete description of two-phase flow at the Darcy scale.

Evolution of oil/water interface in the presence of SDBS detected by dual polarization interferometry

NASA Astrophysics Data System (ADS)

Duan, Ming; Ding, Ziling; Wang, Hu; Xiong, Yan; Fang, Shenwen; Shi, Peng; Liu, Shuai

2018-01-01

In this work, the technique of dual polarization interferometry (DPI) was applied to establish a new method to monitor the real-time evolution of oil/water interface in the presence of sodium dodecyl benzene sulfonate (SDBS) at molecular level. A three-stage model of adsorption-desorption-detachment had been proposed and was systematically discussed upon the addition of different SDBS concentrations based on the variation of the interfacial mass with time. The results demonstrated two patterns of adsorption morphology at the oil/water interface, SDBS mono-molecules and SDBS hemi-micelles at SDBS concentrations below and above cmc respectively according to the relaxation time obtained by theoretical model and the reaction order calculated by integral method in the analysis of adsorbed dynamics. The capability of oil detachment with the aid of SDBS as well as the properties of the outlet fluid were investigated under two patterns of adsorption morphologies, which showed different effects of oil detachment with the aid of SDBS molecules. The speed of oil detachment and the fluorescence intensity of the outlet fluid during the detachment process indicated the fact that the oil detachment capability was significantly promoted by the morphology of the absorbed hemi-micelles. The findings in the present study are crucial for fully understanding the interfacial behavior of surfactants applied in oil/water interface, which is of great significance in enhanced oil recovery and pollution industry.

Stereo Imaging Velocimetry of Mixing Driven by Buoyancy Induced Flow Fields

NASA Technical Reports Server (NTRS)

Duval, W. M. B.; Jacqmin, D.; Bomani, B. M.; Alexander, I. J.; Kassemi, M.; Batur, C.; Tryggvason, B. V.; Lyubimov, D. V.; Lyubimova, T. P.

2000-01-01

Mixing of two fluids generated by steady and particularly g-jitter acceleration is fundamental towards the understanding of transport phenomena in a microgravity environment. We propose to carry out flight and ground-based experiments to quantify flow fields due to g-jitter type of accelerations using Stereo Imaging Velocimetry (SIV), and measure the concentration field using laser fluorescence. The understanding of the effects of g-jitter on transport phenomena is of great practical interest to the microgravity community and impacts the design of experiments for the Space Shuttle as well as the International Space Station. The aim of our proposed research is to provide quantitative data to the community on the effects of g-jitter on flow fields due to mixing induced by buoyancy forces. The fundamental phenomenon of mixing occurs in a broad range of materials processing encompassing the growth of opto-electronic materials and semiconductors, (by directional freezing and physical vapor transport), to solution and protein crystal growth. In materials processing of these systems, crystal homogeneity, which is affected by the solutal field distribution, is one of the major issues. The understanding of fluid mixing driven by buoyancy forces, besides its importance as a topic in fundamental science, can contribute towards the understanding of how solutal fields behave under various body forces. The body forces of interest are steady acceleration and g-jitter acceleration as in a Space Shuttle environment or the International Space Station. Since control of the body force is important, the flight experiment will be carried out on a tunable microgravity vibration isolation mount, which will permit us to precisely input the desired forcing function to simulate a range of body forces. To that end, we propose to design a flight experiment that can only be carried out under microgravity conditions to fully exploit the effects of various body forces on fluid mixing. Recent flight experiments, by the P.I. through collaboration with the Canadian Space Agency (STS-85, August 1997), aimed at determining the stability of the interface between two miscible liquids inside an enclosure show that a long liquid column (5 cm) under microgravity isolation conditions can be stable, i.e. the interface remains sharp and vertical over a short time scale; thus transport occurs by molecular mass diffusion. On the other hand, when the two liquids were excited from a controlled vibration source (Microgravity Vibration Isolation Mount) two to four mode large amplitude quasi-stationary waves were observed. The data was limited to CCD recording of the dynamics of the interface between the two fluids. We propose to carry out flight experiments to quantify the dynamics of the flow field using Stereo Imaging Velocimetry and measure the concentration field using laser fluorescence. The results will serve as a basis to understand effects of g-jitter on transport phenomena, in this case mass diffusion. As the measurement of the kinematics of the flow field will shed light on the instability mechanism. The research will allow measurement of the flow field in microgravity environment to prove two hypotheses: (1) Maxwell's hypothesis: finite convection always exists in diffusing systems, and (2) Quasi-stationary waves inside a bounded enclosure in a microgravity environment is generated by Kelvin-Helmholtz instability; resonance of the interface which produces incipient mixing is due to Rayleigh-Taylor instability. The first hypothesis can be used as a benchmark experiment to illustrate diffusive mixing. The second hypothesis will lead to the understanding of g-jitter effects on buoyancy driven flow fields which occur in many situations involving materials processing, and other basic fluid physics phenomena. In addition, the second hypothesis will also provide insight in how Rayleigh-Taylor and Kelvin-Helmholtz instabilities propagate concentration fronts during mixing. Measurement of the flow field using SIV is important because it is the flow field which causes instability at the interface between the two fluids. Mixing driven by buoyancy induced flow fields will be addressed both experimentally and computationally. The experimental effort will address the kinematics of mixing: stretching, transport and chaos. Quantification of the mechanisms of mixing will consists of measuring the flow field using the SIV system at Glenn and capturing the dynamics of the interface, to measure mass transport, using a CCD camera. These experiments will be carried out within the framework of Earth's gravity and g-jitter microgravity acceleration as in a Space Shuttle environment or the International Space Station. The g-jitter will be induced and controlled using a tunable vibration isolation platform to isolate against vibration as well as input periodic and random vibration to the system. The parametric range of the microgravity experiment will be extended from the experiments on STS-85 to investigate higher mode quasi-stationary waves (8 to 12), as well as resonance regions which leads to chaos and turbulence. Ground-based experiments will focus on effects of vibration on stably stratified fluid layers in order to scale for possible scenarios in a microgravity environment. These vibrations will be subjected perpendicular to the concentration field on the ground since the parallel case can only be carried out in a microgravity environment. The concept of dynamical similarity will be applied to tune the experiments as closely as possible to a Space Shuttle environment or the International Space Station. The computational effort will take advantage of the Computational Laboratory at Glenn to corroborate the experimental findings with predictions of the dynamics of the flow field using the codes FLUENT (finite difference based) and FIDAP (finite element based). We will investigate two important cases, single-fluid model to address dilute systems with negligible jump in viscosity and the more general two-fluid model which accounts for finite jump in viscosity. Apart from its microgravity relevance, this experiment is well suited to study dynamics in nonlinear systems.

OFF, Open source Finite volume Fluid dynamics code: A free, high-order solver based on parallel, modular, object-oriented Fortran API

NASA Astrophysics Data System (ADS)

Zaghi, S.

2014-07-01

OFF, an open source (free software) code for performing fluid dynamics simulations, is presented. The aim of OFF is to solve, numerically, the unsteady (and steady) compressible Navier-Stokes equations of fluid dynamics by means of finite volume techniques: the research background is mainly focused on high-order (WENO) schemes for multi-fluids, multi-phase flows over complex geometries. To this purpose a highly modular, object-oriented application program interface (API) has been developed. In particular, the concepts of data encapsulation and inheritance available within Fortran language (from standard 2003) have been stressed in order to represent each fluid dynamics "entity" (e.g. the conservative variables of a finite volume, its geometry, etc…) by a single object so that a large variety of computational libraries can be easily (and efficiently) developed upon these objects. The main features of OFF can be summarized as follows: Programming LanguageOFF is written in standard (compliant) Fortran 2003; its design is highly modular in order to enhance simplicity of use and maintenance without compromising the efficiency; Parallel Frameworks Supported the development of OFF has been also targeted to maximize the computational efficiency: the code is designed to run on shared-memory multi-cores workstations and distributed-memory clusters of shared-memory nodes (supercomputers); the code's parallelization is based on Open Multiprocessing (OpenMP) and Message Passing Interface (MPI) paradigms; Usability, Maintenance and Enhancement in order to improve the usability, maintenance and enhancement of the code also the documentation has been carefully taken into account; the documentation is built upon comprehensive comments placed directly into the source files (no external documentation files needed): these comments are parsed by means of doxygen free software producing high quality html and latex documentation pages; the distributed versioning system referred as git has been adopted in order to facilitate the collaborative maintenance and improvement of the code; CopyrightsOFF is a free software that anyone can use, copy, distribute, study, change and improve under the GNU Public License version 3. The present paper is a manifesto of OFF code and presents the currently implemented features and ongoing developments. This work is focused on the computational techniques adopted and a detailed description of the main API characteristics is reported. OFF capabilities are demonstrated by means of one and two dimensional examples and a three dimensional real application.

Interfacing supercritical fluid reaction apparatus with on-line liquid chromatography: monitoring the progress of a synthetic organic reaction performed in supercritical fluid solution.

PubMed

Ramsey, Edward D; Li, Ben; Guo, Wei; Liu, Jing Y

2015-04-03

An interface has been developed that connects a supercritical fluid reaction (SFR) vessel directly on-line to a liquid chromatograph. The combined SFR-LC system has enabled the progress of the esterification reaction between phenol and benzoyl chloride to synthesize phenyl benzoate in supercritical fluid carbon dioxide solution to be dynamically monitored. This was achieved by the periodic SFR-LC analysis of samples directly withdrawn from the esterification reaction mixture. Using the series of SFR-LC analysis results obtained for individual esterification reactions, the reaction progress profile for each esterification reaction was obtained by expressing the measured yield of phenyl benzoate as a function of reaction time. With reaction temperature fixed at 75°C, four sets (n=3) of SFR-LC reaction progress profiles were obtained at four different SFR pressures ranging from 13.79 to 27.58 MPa. The maximum SFR yield obtained for phenyl benzoate using a standard set of reactant concentrations was 85.2% (R.S.D. 4.2%) when the reaction was performed at 13.79 MPa for 90 min. In comparison, a phenyl benzoate yield of less than 0.3% was obtained using the same standard reactant concentrations after 90 min reaction time at 75°C using either: heptane, ethyl acetate or acetonitrile as conventional organic reaction solvents. Copyright © 2015 Elsevier B.V. All rights reserved.

Boundary slip and wetting properties of interfaces: correlation of the contact angle with the slip length.

PubMed

Voronov, Roman S; Papavassiliou, Dimitrios V; Lee, Lloyd L

2006-05-28

Correlations between contact angle, a measure of the wetting of surfaces, and slip length are developed using nonequilibrium molecular dynamics for a Lennard-Jones fluid in Couette flow between graphitelike hexagonal-lattice walls. The fluid-wall interaction is varied by modulating the interfacial energy parameter epsilonr=epsilonsfepsilonff and the size parameter sigmar=sigmasfsigmaff, (s=solid, f=fluid) to achieve hydrophobicity (solvophobicity) or hydrophilicity (solvophilicity). The effects of surface chemistry, as well as the effects of temperature and shear rate on the slip length are determined. The contact angle increases from 25 degrees to 147 degrees on highly hydrophobic surfaces (as epsilonr decreases from 0.5 to 0.1), as expected. The slip length is functionally dependent on the affinity strength parameters epsilonr and sigmar: increasing logarithmically with decreasing surface energy epsilonr (i.e., more hydrophobic), while decreasing with power law with decreasing size sigmar. The mechanism for the latter is different from the energetic case. While weak wall forces (small epsilonr) produce hydrophobicity, larger sigmar smoothes out the surface roughness. Both tend to increase the slip. The slip length grows rapidly with a high shear rate, as wall velocity increases three decades from 100 to 10(5) ms. We demonstrate that fluid-solid interfaces with low epsilonr and high sigmar should be chosen to increase slip and are prime candidates for drag reduction.

Dynamic properties of interfaces in soft matter: Experiments and theory

NASA Astrophysics Data System (ADS)

Sagis, Leonard M. C.

2011-10-01

The dynamic properties of interfaces often play a crucial role in the macroscopic dynamics of multiphase soft condensed matter systems. These properties affect the dynamics of emulsions, of dispersions of vesicles, of biological fluids, of coatings, of free surface flows, of immiscible polymer blends, and of many other complex systems. The study of interfacial dynamic properties, surface rheology, is therefore a relevant discipline for many branches of physics, chemistry, engineering, and life sciences. In the past three to four decades a vast amount of literature has been produced dealing with the rheological properties of interfaces stabilized by low molecular weight surfactants, proteins, (bio)polymers, lipids, colloidal particles, and various mixtures of these surface active components. In this paper recent experiments are reviewed in the field of surface rheology, with particular emphasis on the models used to analyze surface rheological data. Most of the models currently used are straightforward generalizations of models developed for the analysis of rheological data of bulk phases. In general the limits on the validity of these generalizations are not discussed. Not much use is being made of recent advances in nonequilibrium thermodynamic formalisms for multiphase systems, to construct admissible models for the stress-deformation behavior of interfaces. These formalisms are ideally suited to construct thermodynamically admissible constitutive equations for rheological behavior that include the often relevant couplings to other fluxes in the interface (heat and mass), and couplings to the transfer of mass from the bulk phase to the interface. In this review recent advances in the application of classical irreversible thermodynamics, extended irreversible thermodynamics, rational thermodynamics, extended rational thermodynamics, and the general equation for the nonequilibrium reversible-irreversible coupling formalism to multiphase systems are also discussed, and shown how these formalisms can be used to generate a wide range of thermodynamically admissible constitutive models for the surface stress tensor. Some of the generalizations currently in use are shown to have only limited validity. The aim of this review is to stimulate new developments in the fields of experimental surface rheology and constitutive modeling of multiphase systems using nonequilibrium thermodynamic formalisms and to promote a closer integration of these disciplines.

Time-Dependent Thermally-Driven Interfacial Flows in Multilayered Fluid Structures

NASA Technical Reports Server (NTRS)

Haj-Hariri, Hossein; Borhan, A.

1996-01-01

A computational study of thermally-driven convection in multilayered fluid structures will be performed to examine the effect of interactions among deformable fluid-fluid interfaces on the structure of time-dependent flow in these systems. Multilayered fluid structures in two models configurations will be considered: the differentially heated rectangular cavity with a free surface, and the encapsulated cylindrical liquid bridge. An extension of a numerical method developed as part of our recent NASA Fluid Physics grant will be used to account for finite deformations of fluid-fluid interfaces.

Object-oriented design and implementation of CFDLab: a computer-assisted learning tool for fluid dynamics using dual reciprocity boundary element methodology

NASA Astrophysics Data System (ADS)

Friedrich, J.

1999-08-01

As lecturers, our main concern and goal is to develop more attractive and efficient ways of communicating up-to-date scientific knowledge to our students and facilitate an in-depth understanding of physical phenomena. Computer-based instruction is very promising to help both teachers and learners in their difficult task, which involves complex cognitive psychological processes. This complexity is reflected in high demands on the design and implementation methods used to create computer-assisted learning (CAL) programs. Due to their concepts, flexibility, maintainability and extended library resources, object-oriented modeling techniques are very suitable to produce this type of pedagogical tool. Computational fluid dynamics (CFD) enjoys not only a growing importance in today's research, but is also very powerful for teaching and learning fluid dynamics. For this purpose, an educational PC program for university level called 'CFDLab 1.1' for Windows™ was developed with an interactive graphical user interface (GUI) for multitasking and point-and-click operations. It uses the dual reciprocity boundary element method as a versatile numerical scheme, allowing to handle a variety of relevant governing equations in two dimensions on personal computers due to its simple pre- and postprocessing including 2D Laplace, Poisson, diffusion, transient convection-diffusion.

A high-pressure atomic force microscope for imaging in supercritical carbon dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lea, Alan S.; Higgins, Steven R.; Knauss, Kevin G.

2011-04-26

A high-pressure atomic force microscope (AFM) that enables in-situ, atomic scale measurements of topography of solid surfaces in contact with supercritical CO2 (scCO2) fluids has been developed. This apparatus overcomes the pressure limitations of the hydrothermal AFM and is designed to handle pressures up to 100 atm at temperatures up to ~ 350 K. A standard optically-based cantilever deflection detection system was chosen. When imaging in compressible supercritical fluids such as scCO2, precise control of pressure and temperature in the fluid cell is the primary technical challenge. Noise levels and imaging resolution depend on minimization of fluid density fluctuations thatmore » change the fluid refractive index and hence the laser path. We demonstrate with our apparatus in-situ atomic scale imaging of a calcite (CaCO3) mineral surface in scCO2; both single, monatomic steps and dynamic processes occurring on the (10¯14) surface are presented. This new AFM provides unprecedented in-situ access to interfacial phenomena at solid-fluid interfaces under pressure.« less

Matching refractive indices of two fluids and finding interfacial tension for the purpose of fuel spray imaging

NASA Astrophysics Data System (ADS)

Liang, Y. H.

2017-06-01

This study attempts to prepare a fluid pair for use in spray dynamics investigations. Better understanding the behavior of fuel sprays is one of the things that can help improve the efficiency of internal combustion engines. To address the scattering issue in current imaging methods, the refractive index difference between the injected fluid and the medium that it is injected into is eliminated. Two immiscible fluids (sucrose solution and silicone oil) with the same refractive index was identified, their surface tension to build a model fluid engine system injection was also studied. At the same time, Weber number is found to help correct the difference. Results show that 63.7% mass sucrose solution has the same refractive index as silicone oil, and the sucrose solution/silicone oil interface has a surface tension of 0.08941 N/m, which is roughly four times larger than that of ethanol/air. This means using the sucrose/silicone oil fluid pair to model fuel spray will involve some adjustments to be accurate.

Pore-Scale Geochemical Reactivity Associated with CO2 Storage: New Frontiers at the Fluid-Solid Interface.

PubMed

Noiriel, Catherine; Daval, Damien

2017-04-18

The reactivity of carbonate and silicate minerals is at the heart of porosity and pore geometry changes in rocks injected with CO 2 , which ultimately control the evolution of flow and transport properties of fluids in porous and/or fractured geological reservoirs. Modeling the dynamics of CO 2 -water-rock interactions is challenging because of the resulting large geochemical disequilibrium, the reservoir heterogeneities, and the large space and time scales involved in the processes. In particular, there is a lack of information about how the macroscopic properties of a reservoir, e.g., the permeability, will evolve as a result of geochemical reactions at the molecular scale. Addressing this point requires a fundamental understanding of how the microstructures influence the macroscopic properties of rocks. The pore scale, which ranges from a few nanometers to centimeters, has stood out as an essential scale of observation of geochemical processes in rocks. Transport or surface reactivity limitations due to the pore space architecture, for instance, are best described at the pore scale itself. It can be also considered as a mesoscale for aggregating and increasing the gain of fundamental understanding of microscopic interfacial processes. Here we focus on the potential application of a combination of physicochemical measurements coupled with nanoscale and microscale imaging techniques during laboratory experiments to improve our understanding of the physicochemical mechanisms that occur at the fluid-solid interface and the dynamics of the coupling between the geochemical reactions and flow and transport modifications at the pore scale. Imaging techniques such as atomic force microscopy, vertical scanning interferometry, focused ion beam transmission electron microscopy, and X-ray microtomography, are ideal for investigating the reactivity dynamics of these complex materials. Minerals and mineral assemblages, i.e., rocks, exhibit heterogeneous and anisotropic reactivity, which challenges the continuum description of porous media and assumptions required for reactive transport modeling at larger scales. The conventional approach, which consists of developing dissolution rate laws normalized to the surface area, should be revisited to account for both the anisotropic crystallographic structure of minerals and the transport of chemical species near the interface, which are responsible for the intrinsic evolution of the mineral dissolution rate as the reaction progresses. In addition, the crystal morphology and the mineral assemblage composition, texture, and structural heterogeneities are crucial in determining whether the permeability and transport properties of the reservoir will be altered drastically or maintain the sealing properties required to ensure the safe sequestration of CO 2 for hundreds of years. Investigating the transport properties in nanometer- to micrometer-thick amorphous Si-rich surface layers (ASSLs), which develop at the fluid-mineral interface in silicates, provides future direction, as ASSLs may prevent contact between the dissolving solids and the pore fluid, potentially inhibiting the dissolution/carbonation process. Equally, at a larger scale, the growth of micrometer- to millimeter-thick alteration layers, which result from the difference in reactivity between silicates and carbonates, slows the transport in the vicinity of the fluid-solid interface in polymineralic rocks, thus limiting the global reactivity of the carbonate matrix. In contrast, in pure limestone, the global reactivity of the monomineralic rock decreases because the flow localization promotes the local reactivity within the forming channels, thus enhancing permeability changes compared with more homogeneous dissolution of the rock matrix. These results indicate that the transformation of the rock matrix should control the evolution of the transport properties in reservoirs injected with CO 2 to the same extent as the intrinsic chemical reactivity of the minerals and the reservoir hydrodynamics. This process, which is currently not captured by large-scale modeling of reactive transport, should benefit from the increasing capabilities of noninvasive and nondestructive characterization tools for pore-scale processes, ultimately constraining reactive transport modeling and improving the reliability of predictions.

Fast fluid-flow events within a subduction-related vein system in oceanic eclogite: implications for pore fluid pressure at the plate interface

NASA Astrophysics Data System (ADS)

Taetz, Stephan; John, Timm; Bröcker, Michael; Spandler, Carl; Stracke, Andreas

2017-04-01

A better understanding of the subduction zone fluid cycle and its mechanical feedback requires in-depth knowledge of how fluids flow within and out of the descending slabs. In order to develop reliable quantitative models of fluid flow, the general relationship between dehydration reactions, fluid pathway formation, and the dimensions and timescales of distinct fluid flow events have to be explored. The high-pressure/low-temperature metamorphic rocks of the Pouébo Eclogite Mélange in New Caledonia provide an excellent opportunity to study the fluid flux in a subduction zone setting. Fluid dynamics are recorded by high-pressure veins that cross-cut eclogite facies mélange blocks from this occurrence. Two types of garnet-quartz-phengite veins can be distinguished. These veins record both synmetamorphic internal fluid release by mineral breakdown reactions (type I veins) as well as infiltration of an external fluid (type II veins) and the associated formation of a reaction halo. The overall dehydration, fluid accumulation and fluid migration documented by the type I veins occurred on a timescale of 10^5-106 years that is mainly given by the geometry and convergence rate of the subduction system. In order to quantify the timeframe of fluid-rock interaction between the external fluid and the wall-rock, we have applied Li-isotope chronology. A continuous profile was sampled perpendicular to a type II vein including material from the vein, the reaction selvage and the immediate host rock. Additional drill cores were taken from parts of the outcrop that most likely remained completely unaffected by fluid infiltration-induced alteration. Different Li concentrations in the internal and external fluid reservoirs produced a distinct diffusion profile of decreasing Li concentration and increasing δ7Li as the reaction front propagated into the host-rock. Li-chronometric constraints indicate that fluid-rock interaction related to the formation of the type II veins and had been completed within ca. 3 years. The short-lived, pulse-like character of this process is in accordance with the notion that fluid flow related to oceanic crust dehydration at the blueschist-to-eclogite transition contributes to or even dominates episodic pore fluid pressure increases at the plate interface which may trigger slip events reported from many subduction zones.

System and Method for Wirelessly Determining Fluid Volume

NASA Technical Reports Server (NTRS)

Woodard, Stanley E. (Inventor); Taylor, Bryant D. (Inventor)

2009-01-01

A system and method are provided for determining the volume of a fluid in container. Sensors are positioned at distinct locations in a container of a fluid. Each sensor is sensitive to an interface defined by the top surface of the fluid. Interfaces associated with at least three of the sensors are determined and used to find the volume of the fluid in the container in a geometric process.

Fluid content along the subduction plate interface: how it impacts the long- (and short-) term rheology and exhumation modes

NASA Astrophysics Data System (ADS)

Agard, Philippe; Angiboust, Samuel; Guillot, Stéphane; Burov, Evgueni

2015-04-01

Over the last decade, many studies based on field, petrological and geophysical evidence have emphasized the link between mineral reactions, fluid release and seismogenesis, either along the whole plate interface (eg., Hacker et al., 2003) or at specific depths (e.g., ~30 km: Audet et al., 2009; ~70-80 km: Angiboust et al., 2012). Although they argue for a crucial influence of fluids on subduction processes, large uncertainties remain when assessing their impact on the rheology of the plate interface across space and time. Kilometer-scale accreted terranes/units in both ancient and present-day subduction zones potentially allow to track changes in mechanical coupling along the plate interface. Despite some potential biases (exhumation is limited and episodic, lasting no more than a few My if any, from prefered depths -- mainly 30-40 and 70-80 km, and there are so far only few examples precisely located with respect to the plate interface) their record of changes in fluid regime and strain localisation is extremely valuable. One striking example of the role of fluids on plate interface rheology during nascent subduction is provided by metamorphic soles (i.e., ~500 m thick tectonic slices welded to the base of ophiolites). We show that their accretion to the ophiolite indeed only happens across a transient, optimal time-T-P window (after < 1-2 My, at 1±0.2 GPa, 750-850°C) associated with fluid release and infiltration, leading to similar effective rheology on both sides (i.e., downgoing crust and mantle wedge). This maximizes interplate mechanical coupling, as deformation gets distributed over a large band encompassing the plate interface (i.e., a few km), and promotes detachment of the sole from the sinking slab. We also show how tectonic slicing during mature subduction likely relates to short-term fluid release and repeated seismicity, based on the Monviso exposures (W. Alps, a relatively continuous, 15 km long fragment of oceanic lithosphere exhumed from ~80 km depths), which preserve evidence of intraslab fluid flow and eclogitic, intermediate-depth seismicity of Mw ~4. We finally address how, in the long-term and at subduction scale, the overall fluid content and fluid regime may control the slicing, size and metastability of exhumed units. We propose that mechanical coupling varies through time, from weak to strong, as a function of the contrast of effective viscosity on either side of the interface: a young and wet subduction interface will promote the formation of knockers and sole accretion, whereas a fluid-present yet drier and colder one will lead to mainly metasedimentary underplated material and large-scale slivers of (metastable) oceanic lithosphere. This interpretation is supported by bi-phase numerical models (allowing for fluid migration driven by concentrations in the rocks, non-lithostatic pressure gradients and deformation, mantle wedge hydration and mechanical weakening of the plate interface) showing that the detachment of large-scale oceanic tectonic slices is in particular promoted by fluid migration along the subduction interface. [Hacker et al., Journal of Geophysical Research 2003; Audet et al., Nature, 2009; Angiboust et al., Geology 2012

Identification of fluids and an interface between fluids

DOEpatents

Lee, D.O.; Wayland, J.R. Jr.

1988-03-10

Complex impedance measured over a predefined frequency range is used to determine the identity of different oils in a column. The location of an interface between the oils is determined from the percent frequency effects of the complex impedance measured across the interface. 4 figs.

Solutal convection induced by dissolution. Influence on erosion dynamics and interface shaping.

NASA Astrophysics Data System (ADS)

Berhanu, Michael; Philippi, Julien; Cohen, Caroline; Derr, Julien; Courrech du Pont, Sylvain

2017-04-01

Rock fractures invaded by a water flow, are often subjected to dissolution, which let grow and evolve the initial fracture network, by evacuating the eroded minerals under a solute form. In the case of fast kinetic of dissolution, local erosion rate is set by the advection of the solute. The erosion velocity decreases indeed with the solute concentration at the interface and vanishes when this concentration reaches the saturation value. Even in absence of an imposed or external flow, advection can drive the dissolution, when buoyancy effects due to gravity induce a solutal convection flow, which controls the erosive dynamics and modifies the shape of the dissolving interface. Here, we investigate using model experiments with fast dissolving materials and numerical simulations in simplified situations, solutal convection induced by dissolution. Results are interpreted regarding a linear stability analysis of the corresponding solutal Rayleigh-Benard instability. A dissolving surface is suspended above a water height, initially at rest. In a first step, solute flux is transported through a growing diffusion layer. Then after an onset time, once the layer exceeds critical width, convection flow starts under the form of falling plumes. A dynamic equilibrium results in average from births and deaths of intermittent plumes, setting the size of the solute concentration boundary layer at the interface and thus the erosion velocity. Solutal convection can also induce a pattern on the dissolving interface. We show experimentally with suspended and inclined blocks of salt and sugar, that in a linear stage, the first wavelength of the dissolution pattern corresponds to the wavelength of the convection instability. Then pattern evolves to more complex shapes due to non-linear interactions between the flow and the eroded interface. More generally, we inquire what are the conditions to observe a such solutal convection instability in geological situations and if the properties of dissolution patterns can be related to the characteristic of the convective flow. C. Oltéan, F. Golfier and M.A. Buès, Numerical and experimental investigation of buoyancy-driven dissolution in vertical fracture, J. Geophys. Res. Solid Earth, 118(5), 2038-2048 (2013) C. Cohen, M. Berhanu, J. Derr and S. Courrech du Pont, Erosion patterns on dissolving and melting bodies (2015 Gallery of Fluid motion), Phys. Rev. Fluids, 1, 050508 (2016) T. S. Sullivan, Y. Liu, and R. E. Ecke, Turbulent solutal convection and surface patterning in solid dissolution, Phys. Rev. E 54, 486 (1996)

International Conference on Numerical Methods in Fluid Dynamics, 7th, Stanford University, Stanford and Moffett Field, CA, June 23-27, 1980, Proceedings

NASA Technical Reports Server (NTRS)

Reynolds, W. C. (Editor); Maccormack, R. W.

1981-01-01

Topics discussed include polygon transformations in fluid mechanics, computation of three-dimensional horseshoe vortex flow using the Navier-Stokes equations, an improved surface velocity method for transonic finite-volume solutions, transonic flow calculations with higher order finite elements, the numerical calculation of transonic axial turbomachinery flows, and the simultaneous solutions of inviscid flow and boundary layer at transonic speeds. Also considered are analytical solutions for the reflection of unsteady shock waves and relevant numerical tests, reformulation of the method of characteristics for multidimensional flows, direct numerical simulations of turbulent shear flows, the stability and separation of freely interacting boundary layers, computational models of convective motions at fluid interfaces, viscous transonic flow over airfoils, and mixed spectral/finite difference approximations for slightly viscous flows.

The Properties of Confined Water and Fluid Flow at the Nanoscale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwegler, E; Reed, J; Lau, E

This project has been focused on the development of accurate computational tools to study fluids in confined, nanoscale geometries, and the application of these techniques to probe the structural and electronic properties of water confined between hydrophilic and hydrophobic substrates, including the presence of simple ions at the interfaces. In particular, we have used a series of ab-initio molecular dynamics simulations and quantum Monte Carlo calculations to build an understanding of how hydrogen bonding and solvation are modified at the nanoscale. The properties of confined water affect a wide range of scientific and technological problems - including protein folding, cell-membranemore » flow, materials properties in confined media and nanofluidic devices.« less

Interface Fluid Syndrome After Laser In Situ Keratomileusis (LASIK) Because of Fuchs Endothelial Dystrophy Reversed by Descemet Membrane Endothelial Keratoplasty (DMEK).

PubMed

Luceri, Salvatore; Baksoellah, Zainab; Ilyas, Abbas; Baydoun, Lamis; Melles, Gerrit R J

2016-12-01

To describe a case that developed "interface fluid syndrome" after previous laser in situ keratomileusis (LASIK) because of Fuchs endothelial dystrophy (FED), which was reversed by Descemet membrane endothelial keratoplasty (DMEK). A 58-year-old male patient presented with bilateral visual impairment owing to FED and visually significant cataract. Cataract surgery was carried out in both eyes followed by DMEK in his left eye. After cataract surgery, visual acuity did not improve sufficiently because corneal thickness increased and a fine cleft with interface fluid developed between the LASIK-flap and the residual stromal bed. After uneventful DMEK in his left eye, the fluid resolved within a week and visual acuity improved rapidly. This case demonstrates that "interface fluid syndrome" after LASIK caused by concomitant endothelial dysfunction may be reversed by DMEK allowing fast visual recovery.

Dynamics of tokamak plasma surface current in 3D ideal MHD model

NASA Astrophysics Data System (ADS)

Galkin, Sergei A.; Svidzinski, V. A.; Zakharov, L. E.

2013-10-01

Interest in the surface current which can arise on perturbed sharp plasma vacuum interface in tokamaks was recently generated by a few papers (see and references therein). In dangerous disruption events with plasma-touching-wall scenarios, the surface current can be shared with the wall leading to the strong, damaging forces acting on the wall A relatively simple analytic definition of δ-function surface current proportional to a jump of tangential component of magnetic field nevertheless leads to a complex computational problem on the moving plasma-vacuum interface, requiring the incorporation of non-linear 3D plasma dynamics even in one-fluid ideal MHD. The Disruption Simulation Code (DSC), which had recently been developed in a fully 3D toroidal geometry with adaptation to the moving plasma boundary, is an appropriate tool for accurate self-consistent δfunction surface current calculation. Progress on the DSC-3D development will be presented. Self-consistent surface current calculation under non-linear dynamics of low m kink mode and VDE will be discussed. Work is supported by the US DOE SBIR grant #DE-SC0004487.

Identification of fluids and an interface between fluids by measuring complex impedance

DOEpatents

Lee, David O.; Wayland, Jr., James R.

1989-01-01

Complex impedance measured over a predefined frequency range is used to determine the identity of different oils in a column. The location of an interface between the oils is determined from the percent frequency effects of the complex impedance measured across the interface.

Controlling Hydrogel Mechanics via Bio-Inspired Polymer-Nanoparticle Bond Dynamics.

PubMed

Li, Qiaochu; Barrett, Devin G; Messersmith, Phillip B; Holten-Andersen, Niels

2016-01-26

Interactions between polymer molecules and inorganic nanoparticles can play a dominant role in nanocomposite material mechanics, yet control of such interfacial interaction dynamics remains a significant challenge particularly in water. This study presents insights on how to engineer hydrogel material mechanics via nanoparticle interface-controlled cross-link dynamics. Inspired by the adhesive chemistry in mussel threads, we have incorporated iron oxide nanoparticles (Fe3O4 NPs) into a catechol-modified polymer network to obtain hydrogels cross-linked via reversible metal-coordination bonds at Fe3O4 NP surfaces. Unique material mechanics result from the supra-molecular cross-link structure dynamics in the gels; in contrast to the previously reported fluid-like dynamics of transient catechol-Fe(3+) cross-links, the catechol-Fe3O4 NP structures provide solid-like yet reversible hydrogel mechanics. The structurally controlled hierarchical mechanics presented here suggest how to develop hydrogels with remote-controlled self-healing dynamics.

Interface proliferation and the growth of labyrinths in a reaction-diffusion system

NASA Astrophysics Data System (ADS)

Goldstein, Raymond E.; Muraki, David J.; Petrich, Dean M.

1996-04-01

In the bistable regime of the FitzHugh-Nagumo model of reaction-diffusion systems, spatially homogeneous patterns may be nonlinearly unstable to the formation of compact "localized states." The formation of space-filling patterns from instabilities of such structures is studied in the context of a nonlocal contour dynamics model for the evolution of boundaries between high and low concentrations of the activator. An earlier heuristic derivation [D. M. Petrich and R. E. Goldstein,

Three-Dimensional Smoothed Particle Hydrodynamics Modeling of Preferential Flow Dynamics at Fracture Intersections on a High-Performance Computing Platform

NASA Astrophysics Data System (ADS)

Kordilla, J.; Bresinsky, L. T.

2017-12-01

The physical mechanisms that govern preferential flow dynamics in unsaturated fractured rock formations are complex and not well understood. Fracture intersections may act as an integrator of unsaturated flow, leading to temporal delay, intermittent flow and partitioning dynamics. In this work, a three-dimensional Pairwise-Force Smoothed Particle Hydrodynamics (PF-SPH) model is being applied in order to simulate gravity-driven multiphase flow at synthetic fracture intersections. SPH, as a meshless Lagrangian method, is particularly suitable for modeling deformable interfaces, such as three-phase contact dynamics of droplets, rivulets and free-surface films. The static and dynamic contact angle can be recognized as the most important parameter of gravity-driven free-surface flow. In SPH, surface tension and adhesion naturally emerges from the implemented pairwise fluid-fluid (sff) and solid-fluid (ssf) interaction force. The model was calibrated to a contact angle of 65°, which corresponds to the wetting properties of water on Poly(methyl methacrylate). The accuracy of the SPH simulations were validated against an analytical solution of Poiseuille flow between two parallel plates and against laboratory experiments. Using the SPH model, the complex flow mode transitions from droplet to rivulet flow of an experimental study were reproduced. Additionally, laboratory dimensionless scaling experiments of water droplets were successfully replicated in SPH. Finally, SPH simulations were used to investigate the partitioning dynamics of single droplets into synthetic horizontal fractures with various apertures (Δdf = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0 mm) and offsets (Δdoff = -1.5, -1.0, -0.5, 0, 1.0, 2.0, 3.0 mm). Fluid masses were measured in the domains R1, R2 and R3. The perfect conditions of ideally smooth surfaces and the SPH inherent advantage of particle tracking allow the recognition of small scale partitioning mechanisms and its importance for bulk flow behavior.

Understanding the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahms, Rainer N.

A generalized framework for multi-component liquid injections is presented to understand and predict the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions. The analysis focuses on the thermodynamic structure and the immiscibility state of representative gas-liquid interfaces. The most modern form of Helmholtz energy mixture state equation is utilized which exhibits a unique and physically consistent behavior over the entire two-phase regime of fluid densities. It is combined with generalized models for non-linear gradient theory and for liquid injections to quantify multi-component two-phase interface structures in global thermal equilibrium. Then, the Helmholtz free energy is minimized whichmore » determines the interfacial species distribution as a consequence. This minimal free energy state is demonstrated to validate the underlying assumptions of classic two-phase theory and spray atomization. However, under certain engine-relevant conditions for which corroborating experimental data are presented, this requirement for interfacial thermal equilibrium becomes unsustainable. A rigorously derived probability density function quantifies the ability of the interface to develop internal spatial temperature gradients in the presence of significant temperature differences between injected liquid and ambient gas. Then, the interface can no longer be viewed as an isolated system at minimal free energy. Instead, the interfacial dynamics become intimately connected to those of the separated homogeneous phases. Hence, the interface transitions toward a state in local equilibrium whereupon it becomes a dense-fluid mixing layer. A new conceptual view of a transitional liquid injection process emerges from a transition time scale analysis. Close to the nozzle exit, the two-phase interface still remains largely intact and more classic two-phase processes prevail as a consequence. Further downstream, however, the transition to dense-fluid mixing generally occurs before the liquid length is reached. As a result, the significance of the presented modeling expressions is established by a direct comparison to a reduced model, which utilizes widely applied approximations but fundamentally fails to capture the physical complexity discussed in this paper.« less

Understanding the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahms, Rainer N., E-mail: Rndahms@sandia.gov

A generalized framework for multi-component liquid injections is presented to understand and predict the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions. The analysis focuses on the thermodynamic structure and the immiscibility state of representative gas-liquid interfaces. The most modern form of Helmholtz energy mixture state equation is utilized which exhibits a unique and physically consistent behavior over the entire two-phase regime of fluid densities. It is combined with generalized models for non-linear gradient theory and for liquid injections to quantify multi-component two-phase interface structures in global thermal equilibrium. Then, the Helmholtz free energy is minimized whichmore » determines the interfacial species distribution as a consequence. This minimal free energy state is demonstrated to validate the underlying assumptions of classic two-phase theory and spray atomization. However, under certain engine-relevant conditions for which corroborating experimental data are presented, this requirement for interfacial thermal equilibrium becomes unsustainable. A rigorously derived probability density function quantifies the ability of the interface to develop internal spatial temperature gradients in the presence of significant temperature differences between injected liquid and ambient gas. Then, the interface can no longer be viewed as an isolated system at minimal free energy. Instead, the interfacial dynamics become intimately connected to those of the separated homogeneous phases. Hence, the interface transitions toward a state in local equilibrium whereupon it becomes a dense-fluid mixing layer. A new conceptual view of a transitional liquid injection process emerges from a transition time scale analysis. Close to the nozzle exit, the two-phase interface still remains largely intact and more classic two-phase processes prevail as a consequence. Further downstream, however, the transition to dense-fluid mixing generally occurs before the liquid length is reached. The significance of the presented modeling expressions is established by a direct comparison to a reduced model, which utilizes widely applied approximations but fundamentally fails to capture the physical complexity discussed in this paper.« less

Understanding the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions

DOE PAGES

Dahms, Rainer N.

2016-04-26

A generalized framework for multi-component liquid injections is presented to understand and predict the breakdown of classic two-phase theory and spray atomization at engine-relevant conditions. The analysis focuses on the thermodynamic structure and the immiscibility state of representative gas-liquid interfaces. The most modern form of Helmholtz energy mixture state equation is utilized which exhibits a unique and physically consistent behavior over the entire two-phase regime of fluid densities. It is combined with generalized models for non-linear gradient theory and for liquid injections to quantify multi-component two-phase interface structures in global thermal equilibrium. Then, the Helmholtz free energy is minimized whichmore » determines the interfacial species distribution as a consequence. This minimal free energy state is demonstrated to validate the underlying assumptions of classic two-phase theory and spray atomization. However, under certain engine-relevant conditions for which corroborating experimental data are presented, this requirement for interfacial thermal equilibrium becomes unsustainable. A rigorously derived probability density function quantifies the ability of the interface to develop internal spatial temperature gradients in the presence of significant temperature differences between injected liquid and ambient gas. Then, the interface can no longer be viewed as an isolated system at minimal free energy. Instead, the interfacial dynamics become intimately connected to those of the separated homogeneous phases. Hence, the interface transitions toward a state in local equilibrium whereupon it becomes a dense-fluid mixing layer. A new conceptual view of a transitional liquid injection process emerges from a transition time scale analysis. Close to the nozzle exit, the two-phase interface still remains largely intact and more classic two-phase processes prevail as a consequence. Further downstream, however, the transition to dense-fluid mixing generally occurs before the liquid length is reached. As a result, the significance of the presented modeling expressions is established by a direct comparison to a reduced model, which utilizes widely applied approximations but fundamentally fails to capture the physical complexity discussed in this paper.« less

Kuipers during photo documentation of the fluid and electrical interfaces on the UIA

NASA Image and Video Library

2012-01-27

ISS030-E-156468 (27 Jan. 2012) --- European Space Agency astronaut Andre Kuipers, Expedition 30 flight engineer, is pictured in the Quest airlock of the International Space Station during photo documentation of the fluid and electrical interfaces on the Umbilical Interface Assembly (UIA) Connector Shelf.

Identification of fluids and an interface between fluids by measuring complex impedance

DOEpatents

Lee, D.O.; Wayland, J.R. Jr.

1989-12-05

Complex impedance measured over a predefined frequency range is used to determine the identity of different oils in a column. The location of an interface between the oils is determined from the percent frequency effects of the complex impedance measured across the interface. 5 figs.

Accurate prediction of complex free surface flow around a high speed craft using a single-phase level set method

NASA Astrophysics Data System (ADS)

Broglia, Riccardo; Durante, Danilo

2017-11-01

This paper focuses on the analysis of a challenging free surface flow problem involving a surface vessel moving at high speeds, or planing. The investigation is performed using a general purpose high Reynolds free surface solver developed at CNR-INSEAN. The methodology is based on a second order finite volume discretization of the unsteady Reynolds-averaged Navier-Stokes equations (Di Mascio et al. in A second order Godunov—type scheme for naval hydrodynamics, Kluwer Academic/Plenum Publishers, Dordrecht, pp 253-261, 2001; Proceedings of 16th international offshore and polar engineering conference, San Francisco, CA, USA, 2006; J Mar Sci Technol 14:19-29, 2009); air/water interface dynamics is accurately modeled by a non standard level set approach (Di Mascio et al. in Comput Fluids 36(5):868-886, 2007a), known as the single-phase level set method. In this algorithm the governing equations are solved only in the water phase, whereas the numerical domain in the air phase is used for a suitable extension of the fluid dynamic variables. The level set function is used to track the free surface evolution; dynamic boundary conditions are enforced directly on the interface. This approach allows to accurately predict the evolution of the free surface even in the presence of violent breaking waves phenomena, maintaining the interface sharp, without any need to smear out the fluid properties across the two phases. This paper is aimed at the prediction of the complex free-surface flow field generated by a deep-V planing boat at medium and high Froude numbers (from 0.6 up to 1.2). In the present work, the planing hull is treated as a two-degree-of-freedom rigid object. Flow field is characterized by the presence of thin water sheets, several energetic breaking waves and plungings. The computational results include convergence of the trim angle, sinkage and resistance under grid refinement; high-quality experimental data are used for the purposes of validation, allowing to compare the hydrodynamic forces and the attitudes assumed at different velocities. A very good agreement between numerical and experimental results demonstrates the reliability of the single-phase level set approach for the predictions of high Froude numbers flows.

Geochemical and Geomechanical Effects on Wellbore Cement Fractures

DOE PAGES

Um, Wooyong; Jung, Hun Bok; Kabilan, Senthil; ...

2014-12-31

Experimental studies were conducted using batch reactors, X-ray microtomograpy (XMT), and computational fluid dynamics (CFD) simulation to determine changes in cement fracture surfaces, fluid flow pathways, and permeability with geochemical and geomechanical processes. Composite Portland cement-basalt caprock core with artificial fractures was prepared and reacted with CO2-saturated groundwater at 50°C and 10 MPa for 3 to 3.5 months under static conditions to understand the geochemical and geomechanical effects on the integrity of wellbores containing defects. Cement-basalt interface samples were subjected to mechanical stress at 2.7 MPa before the CO2 reaction. XMT provided three-dimensional (3-D) visualization of the opening and interconnectionmore » of cement fractures due to mechanical stress. After the CO2 reaction, XMT images revealed that calcium carbonate precipitation occurred extensively within the fractures in the cement matrix, but only partially along fractures located at the cement-basalt interface. The permeability calculated based on CFD simulation was in agreement with the experimentally measured permeability. The experimental results imply that the wellbore cement with fractures is likely to be healed during exposure to CO2-saturated groundwater under static conditions, whereas fractures along the cement-caprock interface are still likely to remain vulnerable to the leakage of CO2. CFD simulation for the flow of different fluids (CO2-saturated brine and supercritical CO2) using a pressure difference of 20 kPa and 200 kPa along ~2 cm-long cement fractures showed that a pressure gradient increase resulted in an increase of CO2 fluids flux by a factor of only ~3-9 because the friction of CO2 fluids on cement fracture surfaces increased with higher flow rate as well. At the same pressure gradient, the simulated flow rate was higher for supercritical CO2 than CO2-saturated brine by a factor of only ~2-3, because the viscosity of supercritical CO2 is much lower than that of CO2-saturated brine. The study suggests that in deep geological reservoirs the geochemical and geomechanical processes have coupled effects on the wellbore cement fracture evolution and fluid flow along the fracture surfaces.« less

Deriving a blood-mimicking fluid for particle image velocimetry in Sylgard-184 vascular models.

PubMed

Yousif, Majid Y; Holdsworth, David W; Poepping, Tamie L

2009-01-01

A new blood-mimicking fluid (BMF) has been developed for particle image velocimetry (PIV), which enables flow studies in vascular models (phantoms). A major difficulty in PIV that affects measurement accuracy is the refraction and distortion of light passing through the interface between the model and the fluid, due to the difference in refractive index (n) between the two materials. The problem can be eliminated by using a fluid with a refractive index matching that of the model. Such fluids are not commonly available, especially for vascular research where the fluid should also have a viscosity similar to human blood. In this work, a blood-mimicking fluid, composed of water (47.38% by weight), glycerol (36.94% by weight) and sodium iodide salt (15.68% by weight), was developed for compatibility with our silicone (Sylgard 184; n = 1.414) phantoms. The fluid exhibits a dynamic viscosity of 4.31+/-0.03 cP which lies within the range of human blood viscosity (4.4+/-0.6 cP). Both refractive index and viscosity were attained at 22.2+/-0.2 degrees C, which is a feasible room temperature, thus eliminating the need for a temperature-control system. The fluid will be used to study hemodynamics in vascular flow models fabricated from Sylgard 184.

Interfacing a General Purpose Fluid Network Flow Program with the SINDA/G Thermal Analysis Program

NASA Technical Reports Server (NTRS)

Schallhorn, Paul; Popok, Daniel

1999-01-01

A general purpose, one dimensional fluid flow code is currently being interfaced with the thermal analysis program Systems Improved Numerical Differencing Analyzer/Gaski (SINDA/G). The flow code, Generalized Fluid System Simulation Program (GFSSP), is capable of analyzing steady state and transient flow in a complex network. The flow code is capable of modeling several physical phenomena including compressibility effects, phase changes, body forces (such as gravity and centrifugal) and mixture thermodynamics for multiple species. The addition of GFSSP to SINDA/G provides a significant improvement in convective heat transfer modeling for SINDA/G. The interface development is conducted in multiple phases. This paper describes the first phase of the interface which allows for steady and quasi-steady (unsteady solid, steady fluid) conjugate heat transfer modeling.

A portable self-sensing rheometer for investigation and therapy of swallowing disorders.

PubMed

O'Leary, Mark T; Hanson, Ben

2010-01-01

Dysphagia is a medical condition in which the safety or efficiency of eating and drinking is compromised. Thin, watery fluids flow too quickly through the oral anatomy during an abnormal swallow, pre-empting airway protective mechanisms, and potentially resulting in fluid entry into the lung. Dysphagia therapy consists of reducing flow speed during swallowing by increasing fluid viscosity using thickeners. Bolus viscosity must be specified and presented to the patient within a well-defined range for effective therapy. Thickeners produce non-Newtonian fluids, rendering current subjective methods for fluid assessment unreliable. Widespread quantification of fluid viscosity is presently impractical as rheometers are costly and complicated to use. Alternative techniques also have disadvantages such as operation at shear rates inappropriate to fluid use. A simple and inexpensive rheometer has been constructed to remedy this situation using a self-sensing electromagnetic actuator. This avoids the need for separate force and displacement sensors, with benefits for simplicity and robustness. The actuator and fluid interface were designed for viscosities consistent with those used for dysphagia therapy. The self-sensing rheometer was found to be able to resolve the different dynamic viscosities obtained from three commonly used therapeutic fluid consistency levels in close agreement with results from a reference laboratory rheometer. Widespread use of the rheometer could remove the subjectivity of fluid assessment, increasing accuracy of fluid specification and therapy across all consistencies and fluid types.

Enhanced reaction kinetics and reactive mixing scale dynamics in mixing fronts under shear flow for arbitrary Damköhler numbers

NASA Astrophysics Data System (ADS)

Bandopadhyay, Aditya; Le Borgne, Tanguy; Méheust, Yves; Dentz, Marco

2017-02-01

Mixing fronts, where fluids of different chemical compositions mix with each other, are known to represent hotspots of chemical reaction in hydrological systems. These fronts are typically subjected to velocity gradients, ranging from the pore scale due to no slip boundary conditions at fluid solid interfaces, to the catchment scale due to permeability variations and complex geometry of the Darcy velocity streamlines. A common trait of these processes is that the mixing interface is strained by shear. Depending on the Péclet number Pe , which represents the ratio of the characteristic diffusion time to the characteristic shear time, and the Damköhler number Da , which represents the ratio of the characteristic diffusion time to the characteristic reaction time, the local reaction rates can be strongly impacted by the dynamics of the mixing interface. So far, this impact has been characterized mostly either in kinetics-limited or in mixing-limited conditions, that is, for either low or high Da. Here the coupling of shear flow and chemical reactivity is investigated for arbitrary Damköhler numbers, for a bimolecular reaction and an initial interface with separated reactants. Approximate analytical expressions for the global production rate and reactive mixing scale are derived based on a reactive lamella approach that allows for a general coupling between stretching enhanced mixing and chemical reactions. While for Pe < Da , reaction kinetics and stretching effects are decoupled, a scenario which we name "weak stretching", for Pe > Da , we uncover a "strong stretching" scenario where new scaling laws emerge from the interplay between reaction kinetics, diffusion, and stretching. The analytical results are validated against numerical simulations. These findings shed light on the effect of flow heterogeneity on the enhancement of chemical reaction and the creation of spatially localized hotspots of reactivity for a broad range of systems ranging from kinetic limited to mixing limited situations.

On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

NASA Astrophysics Data System (ADS)

Yellin-Bergovoy, Ron; Heifetz, Eyal; Umurhan, Orkan M.

2016-05-01

The dynamical response of edge waves under the influence of self-gravity is examined in an idealised two-dimensional model of a proto-stellar disc, characterised in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius ?. The fluid in basic state is prescribed to rotate with a Keplerian profile ? modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabiliser irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of vorticity edge waves. The roles of both Boussinesq and non-Boussinesq effects upon the stability and propagation of these waves with and without the inclusion of self-gravity are then quantified. The dynamics involved with self-gravity non-Boussinesq effect is shown to be a source of vorticity production where there is a jump in the basic state density In addition, self-gravity also alters the dynamics via the radial main pressure gradient, which is a Boussinesq effect. Further applications of these mechanical insights are presented in the conclusion including the ways in which multiple density jumps or gaps may or may not be stable.

Introduction to the Focus Issue: Chemo-Hydrodynamic Patterns and Instabilities

NASA Astrophysics Data System (ADS)

De Wit, A.; Eckert, K.; Kalliadasis, S.

2012-09-01

Pattern forming instabilities are often encountered in a wide variety of natural phenomena and technological applications, from self-organization in biological and chemical systems to oceanic or atmospheric circulation and heat and mass transport processes in engineering systems. Spatio-temporal structures are ubiquitous in hydrodynamics where numerous different convective instabilities generate pattern formation and complex spatiotemporal dynamics, which have been much studied both theoretically and experimentally. In parallel, reaction-diffusion processes provide another large family of pattern forming instabilities and spatio-temporal structures which have been analyzed for several decades. At the intersection of these two fields, "chemo-hydrodynamic patterns and instabilities" resulting from the coupling of hydrodynamic and reaction-diffusion processes have been less studied. The exploration of the new instability and symmetry-breaking scenarios emerging from the interplay between chemical reactions, diffusion and convective motions is a burgeoning field in which numerous exciting problems have emerged during the last few years. These problems range from fingering instabilities of chemical fronts and reactive fluid-fluid interfaces to the dynamics of reaction-diffusion systems in the presence of chaotic mixing. The questions to be addressed are at the interface of hydrodynamics, chemistry, engineering or environmental sciences to name a few and, as a consequence, they have started to draw the attention of several communities including both the nonlinear chemical dynamics and hydrodynamics communities. The collection of papers gathered in this Focus Issue sheds new light on a wide range of phenomena in the general area of chemo-hydrodynamic patterns and instabilities. It also serves as an overview of the current research and state-of-the-art in the field.

Capillary bending of a thin polymer film floating on a liquid bath

NASA Astrophysics Data System (ADS)

Twohig, Timothy; Croll, Andrew B.

Thin elastic films and shells are very important in schemes for the encapsulation and protection of fluids from their environment. Capillary origami is a particularly poignant example of how useful fluid/film structures can be formed. The interactions of fluids on thin-films which themselves lie on another surface (fluid or low friction solid) need to be studied if the differences from fluid-fluid and fluid-solid film interfaces are to be fully appreciated. In this experiment, we examine the triple line that occurs when a fluid is resting on a thin polymer film which is itself floating on a second fluid. The top fluid has a high-energy air/fluid interface which can be minimized by deforming the film in a manner that reduces the total air/fluid interface. We create a one-dimensional experiment in order to isolate the basic physics that occurs as the tension of the top fluid pulls on the thin film. Notably, the 1D geometry removes all the complexity incurred by thin films in biaxial stress states (such as wrinkling, folding and crumpling) from the problem. AFOSR under the Young Investigator Program (FA9550-15-1-0168).

Dynamic Asphaltene-Stearic Acid Competition at the Oil-Water Interface.

PubMed

Sauerer, Bastian; Stukan, Mikhail; Buiting, Jan; Abdallah, Wael; Andersen, Simon

2018-05-15

Interfacial tension (IFT) is one of the major parameters which govern the fluid flow in oil production and recovery. This paper investigates the interfacial activity of different natural surfactants found in crude oil. The main objective was to better understand the competition between carboxylic acids and asphaltenes on toluene/water interfaces. Dynamic IFT was measured for water-in-oil pendant drops contrary to most studies using oil-in-water drops. Stearic acid (SA) was used as model compound for surface-active carboxylic acids in crude. The influence of concentration of these species on dynamic IFT between model oil and deionized water was examined. The acid concentrations were of realistic values (total acid number 0.1 to 2 mg KOH/g oil) while asphaltene concentrations were low and set between 10 and 100 ppm. In mixtures, the initial surface pressure was entirely determined by the SA content while asphaltenes showed a slow initial diffusion to the interface followed by increased adsorption at longer times. The final surface pressure was higher for asphaltenes compared to SA, but for binaries, the final surface pressure was always lower than the sum of the individuals. At high SA concentration, surface pressures of mixtures were dominated entirely by the SA, although, Langmuir isotherm analysis shows that asphaltenes bind to the interface 200-250 times stronger than SA. The surface area/molecule for both SA and asphaltenes were found to be larger than the values reported in recent literature. Various approaches to dynamic surface adsorption were tested, showing that apparent diffusivity of asphaltenes is very low, in agreement with other works. Hence, the adsorption is apparently under barrier control. A possible hypothesis is that at the initial phase of the experiment and at lower concentration of asphaltenes, the interface is occupied by stearic acid molecules forming a dense layer of hydrocarbon chains that may repel the asphaltenes.

Single-bubble dynamics in pool boiling of one-component fluids

NASA Astrophysics Data System (ADS)

Xu, Xinpeng; Qian, Tiezheng

2014-06-01

We numerically investigate the pool boiling of one-component fluids with a focus on the effects of surface wettability on the single-bubble dynamics. We employed the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007), 10.1103/PhysRevE.75.036304], a diffuse-interface model for liquid-vapor flows involving liquid-vapor transition in nonuniform temperature fields. We first perform simulations for bubbles on homogeneous surfaces. We find that an increase in either the contact angle or the surface superheating can enhance the bubble spreading over the heating surface and increase the bubble departure diameter as well and therefore facilitate the transition into film boiling. We then examine the dynamics of bubbles on patterned surfaces, which incorporate the advantages of both hydrophobic and hydrophilic surfaces. The central hydrophobic region increases the thermodynamic probability of bubble nucleation while the surrounding hydrophilic region hinders the continuous bubble spreading by pinning the contact line at the hydrophobic-hydrophilic intersection. This leads to a small bubble departure diameter and therefore prevents the transition from nucleate boiling into film boiling. With the bubble nucleation probability increased and the bubble departure facilitated, the efficiency of heat transfer on such patterned surfaces is highly enhanced, as observed experimentally [Int. J. Heat Mass Transfer 57, 733 (2013), 10.1016/j.ijheatmasstransfer.2012.10.080]. In addition, the stick-slip motion of contact line on patterned surfaces is demonstrated in one-component fluids, with the effect weakened by surface superheating.

Basal melting driven by turbulent thermal convection

NASA Astrophysics Data System (ADS)

Rabbanipour Esfahani, Babak; Hirata, Silvia C.; Berti, Stefano; Calzavarini, Enrico

2018-05-01

Melting and, conversely, solidification processes in the presence of convection are key to many geophysical problems. An essential question related to these phenomena concerns the estimation of the (time-evolving) melting rate, which is tightly connected to the turbulent convective dynamics in the bulk of the melt fluid and the heat transfer at the liquid-solid interface. In this work, we consider a convective-melting model, constructed as a generalization of the Rayleigh-Bénard system, accounting for the basal melting of a solid. As the change of phase proceeds, a fluid layer grows at the heated bottom of the system and eventually reaches a turbulent convection state. By means of extensive lattice-Boltzmann numerical simulations employing an enthalpy formulation of the governing equations, we explore the model dynamics in two- and three-dimensional configurations. The focus of the analysis is on the scaling of global quantities like the heat flux and the kinetic energy with the Rayleigh number, as well as on the interface morphology and the effects of space dimensionality. Independently of dimensionality, we find that the convective-melting system behavior shares strong resemblances with that of the Rayleigh-Bénard one, and that the heat flux is only weakly enhanced with respect to that case. Such similarities are understood, at least to some extent, considering the resulting slow motion of the melting front (with respect to the turbulent fluid velocity fluctuations) and its generally little roughness (compared to the height of the fluid layer). Varying the Stefan number, accounting for the thermodynamical properties of the material, also seems to have only a mild effect, which implies the possibility of extrapolating results in numerically delicate low-Stefan setups from more convenient high-Stefan ones. Finally, we discuss the implications of our findings for the geophysically relevant problem of modeling Arctic ice melt ponds.

Comparison of Microleakage of Composite Resin Veneering Systems at the Alloy Interface

DTIC Science & Technology

1988-09-01

of oral fluids at the metal- resin interface and breakdown of the acrylic resin were factors that have limited the acceptance and widespread use of...percolation of oral fluids at the resin -metal interface, and low resistance to toothbrush abrasion. If chemical means could be used to achieve resin -metal...bonding, 1) esthetics could be improved because of a more uniform layer of the opaque and composite resin , and 2) percolation of fluids at the metal

An analytical study of reduced-gravity flow dynamics

NASA Technical Reports Server (NTRS)

Bradshaw, R. D.; Kramer, J. L.; Zich, J. L.

1976-01-01

Addition of surface tension forces to a marker-and-cell code and the performance of four incompressible fluid simulations in reduced gravity, were studied. This marker-and-cell code has a variable grid capability with arbitrary curved boundaries and time dependent acceleration fields. The surface tension logic includes a spline fit of surface marker particles as well as contact angle logic for straight and curved wall boundaries. Three types of flow motion were simulated with the improved code: impulsive settling in a model Centaur LH2 tank, continuous settling in a model and full scale Centaur LO2 tank and mixing in a Centaur LH2 tank. The impulsive settling case confirmed a drop tower analysis which indicated more orderly fluid collection flow patterns with this method providing a potential savings in settling propellants. In the LO2 tank, fluid collection and flow simulation into the thrust barrel were achieved. The mixing simulation produced good results indicating both the development of the flow field and fluid interface behavior.

Multiphase Flow Modeling of Slag Entrainment During Ladle Change-Over Operation

NASA Astrophysics Data System (ADS)

Morales, Rodolfo D.; Garcia-Hernandez, Saul; Barreto, Jose de Jesus; Ceballos-Huerta, Ariana; Calderon-Ramos, Ismael; Gutierrez, Enif

2016-08-01

Steel transfer from the ladle to a single-strand tundish using a conventional ladle shroud (CLS), and a dissipative ladle shroud (DLS) is studied during the transient period of ladle change-over operation. Fluid velocities and fluid flow turbulence statistics during this unsteady operation were recorded by an ultrasound velocimetry probe in a 1/3 scale water-oil-air analog model (to emulate steel-slag-air system). Reynolds stress model and volume of fluid model allow the tracking of water-oil, water-air, and oil-air interfaces during this operation. Velocity measurements indicate a very high turbulence with the formation of a water-air bubbles-oil emulsion. Flow turbulence and the intensity of the emulsification decrease considerably due to an efficient dissipation of the turbulent kinetic energy employing the DLS instead of the CLS. The modeling results indicate that DLS is widely recommended to substitute flow control devices to improve the fluid dynamics of liquid steel during this transient operation.

Coarsening dynamics of binary liquids with active rotation.

PubMed

Sabrina, Syeda; Spellings, Matthew; Glotzer, Sharon C; Bishop, Kyle J M

2015-11-21

Active matter comprised of many self-driven units can exhibit emergent collective behaviors such as pattern formation and phase separation in both biological (e.g., mussel beds) and synthetic (e.g., colloidal swimmers) systems. While these behaviors are increasingly well understood for ensembles of linearly self-propelled "particles", less is known about the collective behaviors of active rotating particles where energy input at the particle level gives rise to rotational particle motion. A recent simulation study revealed that active rotation can induce phase separation in mixtures of counter-rotating particles in 2D. In contrast to that of linearly self-propelled particles, the phase separation of counter-rotating fluids is accompanied by steady convective flows that originate at the fluid-fluid interface. Here, we investigate the influence of these flows on the coarsening dynamics of actively rotating binary liquids using a phenomenological, hydrodynamic model that combines a Cahn-Hilliard equation for the fluid composition with a Navier-Stokes equation for the fluid velocity. The effect of active rotation is introduced though an additional force within the Navier-Stokes equations that arises due to gradients in the concentrations of clockwise and counter-clockwise rotating particles. Depending on the strength of active rotation and that of frictional interactions with the stationary surroundings, we observe and explain new dynamical behaviors such as "active coarsening" via self-generated flows as well as the emergence of self-propelled "vortex doublets". We confirm that many of the qualitative behaviors identified by the continuum model can also be found in discrete, particle-based simulations of actively rotating liquids. Our results highlight further opportunities for achieving complex dissipative structures in active materials subject to distributed actuation.

Three dimensional contact/impact methodology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulak, R.F.

1987-01-01

The simulation of three-dimensional interface mechanics between reactor components and structures during static contact or dynamic impact is necessary to realistically evaluate their structural integrity to off-normal loads. In our studies of postulated core energy release events, we have found that significant structure-structure interactions occur in some reactor vessel head closure designs and that fluid-structure interactions occur within the reactor vessel. Other examples in which three-dimensional interface mechanics play an important role are: (1) impact response of shipping casks containing spent fuel, (2) whipping pipe impact on reinforced concrete panels or pipe-to-pipe impact after a pipe break, (3) aircraft crashmore » on secondary containment structures, (4) missiles generated by turbine failures or tornados, and (5) drops of heavy components due to lifting accidents. The above is a partial list of reactor safety problems that require adequate treatment of interface mechanics and are discussed in this paper.« less

Benchmarking sheath subgrid boundary conditions for macroscopic-scale simulations

NASA Astrophysics Data System (ADS)

Jenkins, T. G.; Smithe, D. N.

2015-02-01

The formation of sheaths near metallic or dielectric-coated wall materials in contact with a plasma is ubiquitous, often giving rise to physical phenomena (sputtering, secondary electron emission, etc) which influence plasma properties and dynamics both near and far from the material interface. In this paper, we use first-principles PIC simulations of such interfaces to formulate a subgrid sheath boundary condition which encapsulates fundamental aspects of the sheath behavior at the interface. Such a boundary condition, based on the capacitive behavior of the sheath, is shown to be useful in fluid simulations wherein sheath scale lengths are substantially smaller than scale lengths for other relevant physical processes (e.g. radiofrequency wavelengths), in that it enables kinetic processes associated with the presence of the sheath to be numerically modeled without explicit resolution of spatial and temporal sheath scales such as electron Debye length or plasma frequency.

Clinopyroxene dissolution in basaltic melt

NASA Astrophysics Data System (ADS)

Chen, Yang; Zhang, Youxue

2009-10-01

The history of magmatic systems may be inferred from reactions between mantle xenoliths and host basalt if the thermodynamics and kinetics of the reactions are quantified. To study diffusive and convective clinopyroxene dissolution in silicate melts, diffusive clinopyroxene dissolution experiments were conducted at 0.47-1.90 GPa and 1509-1790 K in a piston-cylinder apparatus. Clinopyroxene saturation is found to be roughly determined by MgO and CaO content. The effective binary diffusivities, DMgO and DCaO, and the interface melt saturation condition, C0MgO×C0CaO, are extracted from the experiments. DMgO and DCaO show Arrhenian dependence on temperature. The pressure dependence is small and not resolved within 0.47-1.90 GPa. C0MgO×C0CaO in the interface melt increases with increasing temperature, but decreases with increasing pressure. Convective clinopyroxene dissolution, where the convection is driven by the density difference between the crystal and melt, is modeled using the diffusivities and interface melt saturation condition. Previous studies showed that the convective dissolution rate depends on the thermodynamics, kinetics and fluid dynamics of the system. Comparing our results for clinopyroxene dissolution to results from a previous study on convective olivine dissolution shows that the kinetic and fluid dynamic aspects of the two minerals are quite similar. However, the thermodynamics of clinopyroxene dissolution depends more strongly on the degree of superheating and composition of the host melt than that of olivine dissolution. The models for clinopyroxene and olivine dissolution are tested against literature experiments on mineral-melt interaction. They are then applied to previously proposed reactions between Hawaii basalts and mantle minerals, mid-ocean ridge basalts and mantle minerals, and xenoliths digestion in a basalt at Kuandian, Northeast China.

Modeling mass transfer and reaction of dilute solutes in a ternary phase system by the lattice Boltzmann method

NASA Astrophysics Data System (ADS)

Fu, Yu-Hang; Bai, Lin; Luo, Kai-Hong; Jin, Yong; Cheng, Yi

2017-04-01

In this work, we propose a general approach for modeling mass transfer and reaction of dilute solute(s) in incompressible three-phase flows by introducing a collision operator in lattice Boltzmann (LB) method. An LB equation was used to simulate the solute dynamics among three different fluids, in which the newly expanded collision operator was used to depict the interface behavior of dilute solute(s). The multiscale analysis showed that the presented model can recover the macroscopic transport equations derived from the Maxwell-Stefan equation for dilute solutes in three-phase systems. Compared with the analytical equation of state of solute and dynamic behavior, these results are proven to constitute a generalized framework to simulate solute distributions in three-phase flows, including compound soluble in one phase, compound adsorbed on single-interface, compound in two phases, and solute soluble in three phases. Moreover, numerical simulations of benchmark cases, such as phase decomposition, multilayered planar interfaces, and liquid lens, were performed to test the stability and efficiency of the model. Finally, the multiphase mass transfer and reaction in Janus droplet transport in a straight microchannel were well reproduced.

Numerical study on the effect of temperature oscillations on the crystallization front shape during Czochralski growth of gadolinium gallium garnet crystal

NASA Astrophysics Data System (ADS)

Faiez, Reza; Rezaei, Yazdan

2017-10-01

Time-dependent, finite volume method calculations of momentum and heat transfer were carried out to investigate the correlation between oscillatory convection and the crystallization front dynamics during the Czochralski (Cz) growth of an oxide material. The present modeling allows us to illustrate the modification of the interface shape during the time period of oscillation of the flow manifesting as the formation of a cold plume beneath the phase boundary. It was shown that the instability mechanism is associated with an irreversible dramatic change in the interface shape, which occurs at a critical Reynolds number significantly lower than that is predicted by the quasi-stationary global model analysis of the Cz growth system. The baroclinic term which appears in the vorticity equation in a rotating stratified fluid is used to describe the numerical results of the model. The properties of the thermal waves were studied in the monitoring points located nearby the interface. The waves are regular but not in fact vertically correlated as observed in the case of baroclinic waves. The Rayleigh-Benard dynamics is suggested to be the predominant mechanism even though the instability is primarily baroclinic.

New Laboratory Observations of Thermal Pressurization Weakening

NASA Astrophysics Data System (ADS)

Badt, N.; Tullis, T. E.; Hirth, G.

2017-12-01

Dynamic frictional weakening due to pore fluid thermal pressurization has been studied under elevated confining pressure in the laboratory, using a rotary-shear apparatus having a sample with independent pore pressure and confining pressure systems. Thermal pressurization is directly controlled by the permeability of the rocks, not only for the initiation of high-speed frictional weakening but also for a subsequent sequence of high-speed sliding events. First, the permeability is evaluated at different effective pressures using a method where the pore pressure drop and the flow-through rate are compared using Darcy's Law as well as a pore fluid oscillation method, the latter method also permitting measurement of the storage capacity. Then, the samples undergo a series of high-speed frictional sliding segments at a velocity of 2.5 mm/s, under an applied confining pressure and normal stress of 45 MPa and 50 MPa, respectively, and an initial pore pressure of 25 MPa. Finally the rock permeability and storage capacity are measured again to assess the evolution of the rock's pore fluid properties. For samples with a permeability of 10-20 m2 thermal pressurization promotes a 40% decrease in strength. However, after a sequence of three high-speed sliding events, the magnitude of weakening diminishes progressively from 40% to 15%. The weakening events coincide with dilation of the sliding interface. Moreover, the decrease in the weakening degree with progressive fast-slip events suggest that the hydraulic diffusivity may increase locally near the sliding interface during thermal pressurization-enhanced slip. This could result from stress- or thermally-induced damage to the host rock, which would perhaps increase both permeability and storage capacity, and so possibly decrease the susceptibility of dynamic weakening due to thermal pressurization in subsequent high-speed sliding events.

Micro-scale dynamic simulation of erythrocyte-platelet interaction in blood flow.

PubMed

AlMomani, T; Udaykumar, H S; Marshall, J S; Chandran, K B

2008-06-01

Platelet activation, adhesion, and aggregation on the blood vessel and implants result in the formation of mural thrombi. Platelet dynamics in blood flow is influenced by the far more numerous erythrocytes (RBCs). This is particularly the case in the smaller blood vessels (arterioles) and in constricted regions of blood flow (such as in valve leakage and hinge regions) where the dimensions of formed elements of blood become comparable with that of the flow geometry. In such regions, models to predict platelet motion, activation, aggregation and adhesion must account for platelet-RBC interactions. This paper studies platelet-RBC interactions in shear flows by performing simulations of micro-scale dynamics using a computational fluid dynamics (CFD) model. A level-set sharp-interface immersed boundary method is employed in the computations in which RBC and platelet boundaries are tracked on a two-dimensional Cartesian grid. The RBCs are assumed to have an elliptical shape and to deform elastically under fluid forces while the platelets are assumed to behave as rigid particles of circular shape. Forces and torques between colliding blood cells are modeled using an extension of the soft-sphere model for elliptical particles. RBCs and platelets are transported under the forces and torques induced by fluid flow and cell-cell and cell-platelet collisions. The simulations show that platelet migration toward the wall is enhanced with increasing hematocrit, in agreement with past experimental observations. This margination is seen to occur due to hydrodynamic forces rather than collisional forces or volumetric exclusion effects. The effect of fluid shear forces on the platelets increases exponentially as a function of hematocrit for the range of parameters covered in this study. The micro-scale analysis can be potentially employed to obtain a deterministic relationship between fluid forces and platelet activation and aggregation in blood flow past cardiovascular implants.

An adaptive extended finite element method for the analysis of agglomeration of colloidal particles in a flowing fluid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Young Joon; Jorshari, Razzi Movassaghi; Djilali, Ned

2015-03-10

Direct numerical simulations of the flow-nanoparticle interaction in a colloidal suspension are presented using an extended finite element method (XFEM) in which the dynamics of the nanoparticles is solved in a fully-coupled manner with the flow. The method is capable of accurately describing solid-fluid interfaces without the need of boundary-fitted meshes to investigate the dynamics of particles in complex flows. In order to accurately compute the high interparticle shear stresses and pressures while minimizing computing costs, an adaptive meshing technique is incorporated with the fluid-structure interaction algorithm. The particle-particle interaction at the microscopic level is modeled using the Lennard-Jones (LJ)more » potential and the corresponding potential parameters are determined by a scaling procedure. The study is relevant to the preparation of inks used in the fabrication of catalyst layers for fuel cells. In this paper, we are particularly interested in investigating agglomeration of the nanoparticles under external shear flow in a sliding bi-periodic Lees-Edwards frame. The results indicate that the external shear has a crucial impact on the structure formation of colloidal particles in a suspension.« less

Time-dependent and outflow boundary conditions for Dissipative Particle Dynamics

PubMed Central

Lei, Huan; Fedosov, Dmitry A.; Karniadakis, George Em

2011-01-01

We propose a simple method to impose both no-slip boundary conditions at fluid-wall interfaces and at outflow boundaries in fully developed regions for Dissipative Particle Dynamics (DPD) fluid systems. The procedure to enforce the no-slip condition is based on a velocity-dependent shear force, which is a generalized force to represent the presence of the solid-wall particles and to maintain locally thermodynamic consistency. We show that this method can be implemented in both steady and time-dependent fluid systems and compare the DPD results with the continuum limit (Navier-Stokes) results. We also develop a force-adaptive method to impose the outflow boundary conditions for fully developed flow with unspecified outflow velocity profile or pressure value. We study flows over the backward-facing step and in idealized arterial bifurcations using a combination of the two new boundary methods with different flow rates. Finally, we explore the applicability of the outflow method in time-dependent flow systems. The outflow boundary method works well for systems with Womersley number of O(1), i.e., when the pressure and flowrate at the outflow are approximately in-phase. PMID:21499548

Nonlinear interfacial stability of core-annular film flows in the presence of surfactants

NASA Astrophysics Data System (ADS)

Kas-Danouche, Said A.

This work is an analytical and computational study of the nonlinear interfacial instabilities found in core-annular flows in the presence of surfactants. Core-annular flows arise when two immiscible fluids (for example water and oil) are caused to flow in a pipe under the action of an axial pressure gradient. In one typical type of flow regime, the fluids arrange themselves so that the less viscous (e.g. water) lies in the region of high shear near the pipe wall, with the more viscous fluid occupying the core region. Technologically, this arrangement provides an advantage since the highly viscous fluid is lubricated by the less viscous annulus and for a given pressure gradient the core-fluid flux can be greatly increased. The stability of these flows is of fundamental scientific and practical importance. The sharp interface between the two phases can become unstable by several physical mechanisms and one such mechanism of practical importance is surface tension. In this work we incorporate into our model the effects of insoluble surfactants on the instability. The full problem is derived with particular emphasis paid to the surfactant transport equation which is novel. We then carry out an asymptotic solution of the problem when the annular layer is thin compared to the core-fluid radius and for waves which are of the order of the pipe radius (that is long compared to the annular layer thickness); these scales are in accord with both linear theory as well as experimental observations. The result of the matched asymptotic analysis is a system of coupled nonlinear partial differential equations for the interfacial amplitude and the surfactant concentration on the interface. In the absence of surfactants, the system reduces to the Kuramoto-Sivashinsky equation which has been extensively studied as a paradigm for one-dimensional turbulence in dissipative systems. The surfactant modifies the flow by inducing Marangoni forces along the interface which in turn modify both the velocities and interfacial amplitudes. There are two parameters present in the nonlinear system, the length of the system and a surface Peclet number which measures the diffusion of surfactant on the interface. In order to gain an understanding of the dynamics, we carry out extensive computations using accurate and stable numerical methods capable of following the solution for long times. We map out the dynamics by numerically solving initial value problems on spatially periodic domains where the length of the system is the bifurcation parameter, keeping the Peclet number fixed and equal to one. We find that surfactant acts to suppress chaotic behavior found in its absence for extensive ranges of the bifurcation parameter. The new flow consists of successive windows (in parameter space) of steady-state traveling waves separated by time-periodic attractors. As the length of the system increases a self-similar structure has been found to govern the shapes of the traveling waves as we move from a given window to a lower one. This is elucidated analytically and numerically.

Dynamic Stability of the Rate, State, Temperature, and Pore Pressure Friction Model at a Rock Interface

NASA Astrophysics Data System (ADS)

Sinha, Nitish; Singh, Arun K.; Singh, Trilok N.

2018-05-01

In this article, we study numerically the dynamic stability of the rate, state, temperature, and pore pressure friction (RSTPF) model at a rock interface using standard spring-mass sliding system. This particular friction model is a basically modified form of the previously studied friction model namely the rate, state, and temperature friction (RSTF). The RSTPF takes into account the role of thermal pressurization including dilatancy and permeability of the pore fluid due to shear heating at the slip interface. The linear stability analysis shows that the critical stiffness, at which the sliding becomes stable to unstable or vice versa, increases with the coefficient of thermal pressurization. Critical stiffness, on the other hand, remains constant for small values of either dilatancy factor or hydraulic diffusivity, but the same decreases as their values are increased further from dilatancy factor (˜ 10^{ - 4} ) and hydraulic diffusivity (˜ 10^{ - 9} {m}2 {s}^{ - 1} ) . Moreover, steady-state friction is independent of the coefficient of thermal pressurization, hydraulic diffusivity, and dilatancy factor. The proposed model is also used for predicting time of failure of a creeping interface of a rock slope under the constant gravitational force. It is observed that time of failure decreases with increase in coefficient of thermal pressurization and hydraulic diffusivity, but the dilatancy factor delays the failure of the rock fault under the condition of heat accumulation at the creeping interface. Moreover, stiffness of the rock-mass also stabilizes the failure process of the interface as the strain energy due to the gravitational force accumulates in the rock-mass before it transfers to the sliding interface. Practical implications of the present study are also discussed.

ls1 mardyn: The Massively Parallel Molecular Dynamics Code for Large Systems.

PubMed

Niethammer, Christoph; Becker, Stefan; Bernreuther, Martin; Buchholz, Martin; Eckhardt, Wolfgang; Heinecke, Alexander; Werth, Stephan; Bungartz, Hans-Joachim; Glass, Colin W; Hasse, Hans; Vrabec, Jadran; Horsch, Martin

2014-10-14

The molecular dynamics simulation code ls1 mardyn is presented. It is a highly scalable code, optimized for massively parallel execution on supercomputing architectures and currently holds the world record for the largest molecular simulation with over four trillion particles. It enables the application of pair potentials to length and time scales that were previously out of scope for molecular dynamics simulation. With an efficient dynamic load balancing scheme, it delivers high scalability even for challenging heterogeneous configurations. Presently, multicenter rigid potential models based on Lennard-Jones sites, point charges, and higher-order polarities are supported. Due to its modular design, ls1 mardyn can be extended to new physical models, methods, and algorithms, allowing future users to tailor it to suit their respective needs. Possible applications include scenarios with complex geometries, such as fluids at interfaces, as well as nonequilibrium molecular dynamics simulation of heat and mass transfer.

Alveolar Thin Layer Flows and Surfactant Dynamics

NASA Astrophysics Data System (ADS)

Roumie, Ahmad; Jbaily, Abdulrahman; Szeri, Andrew J.

2017-11-01

Pulmonary surfactants play a vital role in everyday respiration. They regulate surface tension in the lungs by diffusing through the hypophase, a liquid layer that lines the interior surface of the alveoli, and adsorbing to the existing air-fluid interface. This decreases the equilibrium surface tension value by as much as a factor of 3, minimizing breathing effort and preventing lung collapse at the end of exhalation. Given that the hypophase thickness h lies within the range 0.1 μm < h <0.5 μm , and that the average alveolar radius R is 100 μm , for some purposes the hypophase may usefully be modeled as a fluid layer on a flat sheet representing the alveolar wall. Moreover, because of the large aspect ratio, the lubrication approximation can be applied. The aim of the present work is to study the interaction between the straining of the alveolar wall and the fluid flow in the hypophase. The analysis is governed by the relative magnitudes of the time scales of surfactant diffusion, adsorption, desorption, viscous dissipation and sheet straining. Cases of particular interest include non-uniform surfactant concentration at the interface, leading to Marangoni flows and a non-uniform hypophase thickness profile. The analytical formulation and numerical simulations are presented. This work is motivated by a need to understand alveolar deformation during breathing, and to do so in a way that derives from improved understanding of the fluid mechanics of the problem.

Stokesian swimming of a helical swimmer across an interface

NASA Astrophysics Data System (ADS)

Godinez, Francisco; Ramos, Armando; Zenit, Roberto

2016-11-01

Microorganisms swim in flows dominated by viscous effects but in many instances the motion occurs across heterogeneous environments where the fluid properties may vary. To our knowledge, the effect of such in-homogeneity has not been addressed in depth. We conduct experiments in which a magnetic self-propelled helical swimmer displaces across the interface between two immiscible density stratified fluids. As the swimmer crosses the interface, at a fixed rotation rate, its speed is reduced and a certain volume of the lower fluid is dragged across. We quantify the drift volume and the change of swimming speed for different swimming speeds and different fluid combinations. We relate the reduction of the swimming speed with the interfacial tension of the interface. We also compare the measurements of the drift volume with some recent calculations found in the literature.

The rotating movement of three immiscible fluids - A benchmark problem

USGS Publications Warehouse

Bakker, M.; Oude, Essink G.H.P.; Langevin, C.D.

2004-01-01

A benchmark problem involving the rotating movement of three immiscible fluids is proposed for verifying the density-dependent flow component of groundwater flow codes. The problem consists of a two-dimensional strip in the vertical plane filled with three fluids of different densities separated by interfaces. Initially, the interfaces between the fluids make a 45??angle with the horizontal. Over time, the fluids rotate to the stable position whereby the interfaces are horizontal; all flow is caused by density differences. Two cases of the problem are presented, one resulting in a symmetric flow field and one resulting in an asymmetric flow field. An exact analytical solution for the initial flow field is presented by application of the vortex theory and complex variables. Numerical results are obtained using three variable-density groundwater flow codes (SWI, MOCDENS3D, and SEAWAT). Initial horizontal velocities of the interfaces, as simulated by the three codes, compare well with the exact solution. The three codes are used to simulate the positions of the interfaces at two times; the three codes produce nearly identical results. The agreement between the results is evidence that the specific rotational behavior predicted by the models is correct. It also shows that the proposed problem may be used to benchmark variable-density codes. It is concluded that the three models can be used to model accurately the movement of interfaces between immiscible fluids, and have little or no numerical dispersion. ?? 2003 Elsevier B.V. All rights reserved.

System for concentrating and analyzing particles suspended in a fluid

DOEpatents

Fiechtner, Gregory J [Bethesda, MD; Cummings, Eric B [Livermore, CA; Singh, Anup K [Danville, CA

2011-04-26

Disclosed is a device for separating and concentrating particles suspended in a fluid stream by using dielectrophoresis (DEP) to trap and/or deflect those particles as they migrate through a fluid channel. The method uses fluid channels designed to constrain a liquid flowing through it to uniform electrokinetic flow velocities. This behavior is achieved by connecting deep and shallow sections of channels, with the channel depth varying abruptly along an interface. By careful design of abrupt changes in specific permeability at the interface, an abrupt and spatially uniform change in electrokinetic force can be selected. Because these abrupt interfaces also cause a sharp gradient in applied electric fields, a DEP force also can be established along the interface. Depending on the complex conductivity of the suspended particles and the immersion liquid, the DEP force can controllably complement or oppose the local electrokinetic force transporting the fluid through the channel allowing for manipulation of particles suspended in the transporting liquid.

Apparatus and method for concentrating and filtering particles suspended in a fluid

DOEpatents

Fiechtner, Gregory J [Bethesda, MD; Cummings, Eric B [Livermore, CA; Singh, Anup K [Danville, CA

2009-05-19

Disclosed is a device for separating and concentrating particles suspended in a fluid stream by using dielectrophoresis (DEP) to trap and/or deflect those particles as they migrate through a fluid channel. The method uses fluid channels designed to constrain a liquid flowing through it to uniform electrokinetic flow velocities. This behavior is achieved by connecting deep and shallow sections of channels, with the channel depth varying abruptly along an interface. By careful design of abrupt changes in specific permeability at the interface, an abrupt and spatially uniform change in electrokinetic force can be selected. Because these abrupt interfaces also cause a sharp gradient in applied electric fields, a DEP force also can be established along the interface. Depending on the complex conductivity of the suspended particles and the immersion liquid, the DEP force can controllably complement or oppose the local electrokinetic force transporting the fluid through the channel allowing for manipulation of particles suspended in the transporting liquid.

Numerical modeling of interface displacement in heterogeneously wetting porous media

NASA Astrophysics Data System (ADS)

Hiller, T.; Brinkmann, M.; Herminghaus, S.

2013-12-01

We use the mesoscopic particle method stochastic rotation dynamics (SRD) to simulate immiscible multi-phase flow on the pore and sub-pore scale in three dimensions. As an extension to the standard SRD method, we present an approach on implementing complex wettability on heterogeneous surfaces. We use 3D SRD to simulate immiscible two-phase flow through a model porous medium (disordered packing of spherical beads) where the substrate exhibits different spatial wetting patterns. The simulations are designed to resemble experimental measurements of capillary pressure saturation. We show that the correlation length of the wetting patterns influences the temporal evolution of the interface and thus percolation, residual saturation and work dissipated during the fluid displacement. Our numerical results are in qualitatively good agreement with the experimental data. Besides of modeling flow in porous media, our SRD implementation allows us to address various questions of interfacial dynamics, e.g. the formation of capillary bridges between spherical beads or droplets in microfluidic applications to name only a few.

Governing Influence of Thermodynamic and Chemical Equilibria on the Interfacial Properties in Complex Fluids.

PubMed

Harikrishnan, A R; Dhar, Purbarun; Gedupudi, Sateesh; Das, Sarit K

2018-04-12

We propose a comprehensive analysis and a quasi-analytical mathematical formalism to predict the surface tension and contact angles of complex surfactant-infused nanocolloids. The model rests on the foundations of the interaction potentials for the interfacial adsorption-desorption dynamics in complex multicomponent colloids. Surfactant-infused nanoparticle-laden interface problems are difficult to deal with because of the many-body interactions and interfaces involved at the meso-nanoscales. The model is based on the governing role of thermodynamic and chemical equilibrium parameters in modulating the interfacial energies. The influence of parameters such as the presence of surfactants, nanoparticles, and surfactant-capped nanoparticles on interfacial dynamics is revealed by the analysis. Solely based on the knowledge of interfacial properties of independent surfactant solutions and nanocolloids, the same can be deduced for complex surfactant-based nanocolloids through the proposed approach. The model accurately predicts the equilibrium surface tension and contact angle of complex nanocolloids available in the existing literature and present experimental findings.

Revisiting kinetic boundary conditions at the surface of fuel droplet hydrocarbons: An atomistic computational fluid dynamics simulation

PubMed Central

Nasiri, Rasoul

2016-01-01

The role of boundary conditions at the interface for both Boltzmann equation and the set of Navier-Stokes equations have been suggested to be important for studying of multiphase flows such as evaporation/condensation process which doesn’t always obey the equilibrium conditions. Here we present aspects of transition-state theory (TST) alongside with kinetic gas theory (KGT) relevant to the study of quasi-equilibrium interfacial phenomena and the equilibrium gas phase processes, respectively. A two-state mathematical model for long-chain hydrocarbons which have multi-structural specifications is introduced to clarify how kinetics and thermodynamics affect evaporation/condensation process at the surface of fuel droplet, liquid and gas phases and then show how experimental observations for a number of n-alkane may be reproduced using a hybrid framework TST and KGT with physically reasonable parameters controlling the interface, gas and liquid phases. The importance of internal activation dynamics at the surface of n-alkane droplets is established during the evaporation/condensation process. PMID:27215897

Critical conditions for the buoyancy-driven detachment of a wall-bound pendant drop

NASA Astrophysics Data System (ADS)

Lamorgese, A.; Mauri, R.

2016-03-01

We investigate numerically the critical conditions for detachment of an isolated, wall-bound emulsion droplet acted upon by surface tension and wall-normal buoyancy forces alone. To that end, we present a simple extension of a diffuse-interface model for partially miscible binary mixtures that was previously employed for simulating several two-phase flow phenomena far and near the critical point [A. G. Lamorgese et al. "Phase-field approach to multiphase flow modeling," Milan J. Math. 79(2), 597-642 (2011)] to allow for static contact angles other than 90°. We use the same formulation of the Cahn boundary condition as first proposed by Jacqmin ["Contact-line dynamics of a diffuse fluid interface," J. Fluid Mech. 402, 57-88 (2000)], which accommodates a cubic (Hermite) interpolation of surface tensions between the wall and each phase at equilibrium. We show that this model can be successfully employed for simulating three-phase contact line problems in stable emulsions with nearly immiscible components. We also show a numerical determination of critical Bond numbers as a function of static contact angle by phase-field simulation.

Characterizing Droplet Formation from Non-Linear Slosh in a Propellant Tank

NASA Technical Reports Server (NTRS)

Brodnick, Jacob; Yang, Hong; West, Jeffrey

2015-01-01

The Fluid Dynamics Branch (ER42) at the Marshall Space Flight Center (MSFC) was tasked with characterizing the formation and evolution of liquid droplets resulting from nonlinear propellant slosh in a storage tank. Lateral excitation of propellant tanks can produce high amplitude nonlinear slosh waves through large amplitude excitations and or excitation frequencies near a resonance frequency of the tank. The high amplitude slosh waves become breaking waves upon attaining a certain amplitude or encountering a contracting geometry such as the upper dome section of a spherical tank. Inherent perturbations in the thinning regions of breaking waves result in alternating regions of high and low pressure within the fluid. Droplets form once the force from the local pressure differential becomes larger than the force maintaining the fluid interface shape due to surface tension. Droplets released from breaking waves in a pressurized tank may lead to ullage collapse given the appropriate conditions due to the increased liquid surface area and thus heat transfer between the fluids. The goal of this project is to create an engineering model that describes droplet formation as a function of propellant slosh for use in the evaluation of ullage collapse during a sloshing event. The Volume of Fluid (VOF) model in the production level Computational Fluid Dynamics (CFD) code Loci-Stream was used to predict droplet formation from breaking waves with realistic surface tension characteristics. Various excitation frequencies and amplitudes were investigated at multiple fill levels for a single storage tank to create the engineering model of droplet formation from lateral propellant slosh.

Smoothed particle hydrodynamics model for Landau-Lifshitz-Navier-Stokes and advection-diffusion equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kordilla, Jannes, E-mail: jkordil@gwdg.de; Pan, Wenxiao, E-mail: Wenxiao.Pan@pnnl.gov; Tartakovsky, Alexandre, E-mail: alexandre.tartakovsky@pnnl.gov

2014-12-14

We propose a novel smoothed particle hydrodynamics (SPH) discretization of the fully coupled Landau-Lifshitz-Navier-Stokes (LLNS) and stochastic advection-diffusion equations. The accuracy of the SPH solution of the LLNS equations is demonstrated by comparing the scaling of velocity variance and the self-diffusion coefficient with kinetic temperature and particle mass obtained from the SPH simulations and analytical solutions. The spatial covariance of pressure and velocity fluctuations is found to be in a good agreement with theoretical models. To validate the accuracy of the SPH method for coupled LLNS and advection-diffusion equations, we simulate the interface between two miscible fluids. We study formationmore » of the so-called “giant fluctuations” of the front between light and heavy fluids with and without gravity, where the light fluid lies on the top of the heavy fluid. We find that the power spectra of the simulated concentration field are in good agreement with the experiments and analytical solutions. In the absence of gravity, the power spectra decay as the power −4 of the wavenumber—except for small wavenumbers that diverge from this power law behavior due to the effect of finite domain size. Gravity suppresses the fluctuations, resulting in much weaker dependence of the power spectra on the wavenumber. Finally, the model is used to study the effect of thermal fluctuation on the Rayleigh-Taylor instability, an unstable dynamics of the front between a heavy fluid overlaying a light fluid. The front dynamics is shown to agree well with the analytical solutions.« less

Smoothed particle hydrodynamics model for Landau-Lifshitz-Navier-Stokes and advection-diffusion equations.

PubMed

Kordilla, Jannes; Pan, Wenxiao; Tartakovsky, Alexandre

2014-12-14

We propose a novel smoothed particle hydrodynamics (SPH) discretization of the fully coupled Landau-Lifshitz-Navier-Stokes (LLNS) and stochastic advection-diffusion equations. The accuracy of the SPH solution of the LLNS equations is demonstrated by comparing the scaling of velocity variance and the self-diffusion coefficient with kinetic temperature and particle mass obtained from the SPH simulations and analytical solutions. The spatial covariance of pressure and velocity fluctuations is found to be in a good agreement with theoretical models. To validate the accuracy of the SPH method for coupled LLNS and advection-diffusion equations, we simulate the interface between two miscible fluids. We study formation of the so-called "giant fluctuations" of the front between light and heavy fluids with and without gravity, where the light fluid lies on the top of the heavy fluid. We find that the power spectra of the simulated concentration field are in good agreement with the experiments and analytical solutions. In the absence of gravity, the power spectra decay as the power -4 of the wavenumber-except for small wavenumbers that diverge from this power law behavior due to the effect of finite domain size. Gravity suppresses the fluctuations, resulting in much weaker dependence of the power spectra on the wavenumber. Finally, the model is used to study the effect of thermal fluctuation on the Rayleigh-Taylor instability, an unstable dynamics of the front between a heavy fluid overlaying a light fluid. The front dynamics is shown to agree well with the analytical solutions.

Smoothed particle hydrodynamics model for Landau-Lifshitz Navier-Stokes and advection-diffusion equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kordilla, Jannes; Pan, Wenxiao; Tartakovsky, Alexandre M.

2014-12-14

We propose a novel Smoothed Particle Hydrodynamics (SPH) discretization of the fully-coupled Landau-Lifshitz-Navier-Stokes (LLNS) and advection-diffusion equations. The accuracy of the SPH solution of the LLNS equations is demonstrated by comparing the scaling of velocity variance and self-diffusion coefficient with kinetic temperature and particle mass obtained from the SPH simulations and analytical solutions. The spatial covariance of pressure and velocity fluctuations are found to be in a good agreement with theoretical models. To validate the accuracy of the SPH method for the coupled LLNS and advection-diffusion equations, we simulate the interface between two miscible fluids. We study the formation ofmore » the so-called giant fluctuations of the front between light and heavy fluids with and without gravity, where the light fluid lays on the top of the heavy fluid. We find that the power spectra of the simulated concentration field is in good agreement with the experiments and analytical solutions. In the absence of gravity the the power spectra decays as the power -4 of the wave number except for small wave numbers which diverge from this power law behavior due to the effect of finite domain size. Gravity suppresses the fluctuations resulting in the much weaker dependence of the power spectra on the wave number. Finally the model is used to study the effect of thermal fluctuation on the Rayleigh-Taylor instability, an unstable dynamics of the front between a heavy fluid overlying a light fluid. The front dynamics is shown to agree well with the analytical solutions.« less

Electrohydrodynamics of drops in strong electric fields: Simulations and theory

NASA Astrophysics Data System (ADS)

Saintillan, David; Das, Debasish

2016-11-01

Weakly conducting dielectric liquid drops suspended in another dielectric liquid exhibit a wide range of dynamical behaviors when subject to an applied uniform electric field contingent on field strength and material properties. These phenomena are best described by the much celebrated Maylor-Taylor leaky dielectric model that hypothesizes charge accumulation on the drop-fluid interface and prescribes a balance between charge relaxation, the jump in Ohmic currents and charge convection by the interfacial fluid flow. Most previous numerical simulations based on this model have either neglected interfacial charge convection or restricted themselves to axisymmetric drops. In this work, we develop a three-dimensional boundary element method for the complete leaky dielectric model to systematically study the deformation and dynamics of liquid drops in electric fields. The inclusion of charge convection in our simulation permits us to investigate drops in the Quincke regime, in which experiments have demonstrated symmetry-breaking bifurcations leading to steady electrorotation. Our simulation results show excellent agreement with existing experimental data and small deformation theories. ACSPRF Grant 53240-ND9.

3D numerical simulations of oblique droplet impact onto a deep liquid pool

NASA Astrophysics Data System (ADS)

Gelderblom, Hanneke; Reijers, Sten A.; Gielen, Marise; Sleutel, Pascal; Lohse, Detlef; Xie, Zhihua; Pain, Christopher C.; Matar, Omar K.

2017-11-01

We study the fluid dynamics of three-dimensional oblique droplet impact, which results in phenomena that include splashing and cavity formation. An adaptive, unstructured mesh modelling framework is employed here, which can modify and adapt unstructured meshes to better represent the underlying physics of droplet dynamics, and reduce computational effort without sacrificing accuracy. The numerical framework consists of a mixed control-volume and finite-element formulation, a volume-of-fluid-type method for the interface-capturing based on a compressive control-volume advection method. The framework also features second-order finite-element methods, and a force-balanced algorithm for the surface tension implementation, minimising the spurious velocities often found in many simulations involving capillary-driven flows. The numerical results generated using this framework are compared with high-speed images of the interfacial shapes of the deformed droplet, and the cavity formed upon impact, yielding good agreement. EPSRC, UK, MEMPHIS program Grant (EP/K003976/1), RAEng Research Chair (OKM).

Evaluation of space shuttle main engine fluid dynamic frequency response characteristics

NASA Technical Reports Server (NTRS)

Gardner, T. G.

1980-01-01

In order to determine the POGO stability characteristics of the space shuttle main engine liquid oxygen (LOX) system, the fluid dynamic frequency response functions between elements in the SSME LOX system was evaluated, both analytically and experimentally. For the experimental data evaluation, a software package was written for the Hewlett-Packard 5451C Fourier analyzer. The POGO analysis software is documented and consists of five separate segments. Each segment is stored on the 5451C disc as an individual program and performs its own unique function. Two separate data reduction methods, a signal calibration, coherence or pulser signal based frequency response function blanking, and automatic plotting features are included in the program. The 5451C allows variable parameter transfer from program to program. This feature is used to advantage and requires only minimal user interface during the data reduction process. Experimental results are included and compared with the analytical predictions in order to adjust the general model and arrive at a realistic simulation of the POGO characteristics.

Fluctuating chemohydrodynamics and the stochastic motion of self-diffusiophoretic particles

NASA Astrophysics Data System (ADS)

Gaspard, Pierre; Kapral, Raymond

2018-04-01

The propulsion of active particles by self-diffusiophoresis is driven by asymmetric catalytic reactions on the particle surface that generate a mechanochemical coupling between the fluid velocity and the concentration fields of fuel and product in the surrounding solution. Because of thermal and molecular fluctuations in the solution, the motion of micrometric or submicrometric active particles is stochastic. Coupled Langevin equations describing the translation, rotation, and reaction of such active particles are deduced from fluctuating chemohydrodynamics and fluctuating boundary conditions at the interface between the fluid and the particle. These equations are consistent with microreversibility and the Onsager-Casimir reciprocal relations between affinities and currents and provide a thermodynamically consistent basis for the investigation of the dynamics of active particles propelled by diffusiophoretic mechanisms.

Cryogenic Fluid Technologies for Long Duration In-Space Operations

NASA Technical Reports Server (NTRS)

Motil, Susan M.; Tramel, Terri L.

2008-01-01

Reliable knowledge of low-gravity cryogenic fluid management behavior is lacking and yet is critical in the areas of storage, distribution, and low-gravity propellant management. The Vision for Space Exploration mission objectives will require the use of high performance cryogenic propellants (hydrogen, oxygen, and methane). Additionally, lunar missions will require success in storing and transferring liquid and gas commodities on the surface. The fundamental challenges associated with the in-space use of cryogens are their susceptibility to environmental heat, their complex thermodynamic and fluid dynamic behavior in low gravity and the uncertainty of the position of the liquid-vapor interface if the propellants are not settled. The Cryogenic Fluid Management (CFM) project is addressing these issues through ground testing and analytical model development, and has crosscutting applications and benefits to virtually all missions requiring in-space operations with cryogens. Such knowledge can significantly reduce or even eliminate tank fluid boil-off losses for long term missions, reduce propellant launch mass and on-orbit margins, and simplify vehicle operations. The Cryogenic Fluid Management (CFM) Project is conducting testing and performing analytical evaluation of several areas to enable NASA s Exploration Vision. This paper discusses the content and progress of the technology focus areas within CFM.

A magnetic fluid seal for rotary blood pumps: Behaviors of magnetic fluids in a magnetic fluid seal.

PubMed

Mitamura, Yoshinori; Yano, Tetsuya; Nakamura, Wataru; Okamoto, Eiji

2013-01-01

A magnetic fluid (MF) seal has excellent durability. The performance of an MF seal, however, has been reported to decrease in liquids (several days). We have developed an MF seal that has a shield mechanism. The seal was perfect for 275 days in water. To investigate the effect of a shield, behaviors of MFs in a seal in water were studied both experimentally and computationally. (a) Two kinds of MF seals, one with a shield and one without a shield, were installed in a centrifugal pump. Behaviors of MFs in the seals in water were observed with a video camera and high-speed microscope. In the seal without a shield, the surface of the water in the seal waved and the turbulent flow affected behaviors of the MFs. In contrast, MFs rotated stably in the seal with a shield in water even at high rotational speeds. (b) Computational fluid dynamics analysis revealed that a stationary secondary flow pattern in the seal and small velocity difference between magnetic fluid and water at the interface. These MF behaviors prolonged the life of an MF seal in water.

Monitoring transient changes within overpressured regions of subduction zones using ambient seismic noise.

PubMed

Chaves, Esteban J; Schwartz, Susan Y

2016-01-01

In subduction zones, elevated pore fluid pressure, generally linked to metamorphic dehydration reactions, has a profound influence on the mechanical behavior of the plate interface and forearc crust through its control on effective stress. We use seismic noise-based monitoring to characterize seismic velocity variations following the 2012 Nicoya Peninsula, Costa Rica earthquake [M w (moment magnitude) 7.6] that we attribute to the presence of pressurized pore fluids. Our study reveals a strong velocity reduction (~0.6%) in a region where previous work identified high forearc pore fluid pressure. The depth of this velocity reduction is constrained to be below 5 km and therefore not the result of near-surface damage due to strong ground motions; rather, we posit that it is caused by fracturing of the fluid-pressurized weakened crust due to dynamic stresses. Although pressurized fluids have been implicated in causing coseismic velocity reductions beneath the Japanese volcanic arc, this is the first report of a similar phenomenon in a subduction zone setting. It demonstrates the potential to identify pressurized fluids in subduction zones using temporal variations of seismic velocity inferred from ambient seismic noise correlations.

Wettability control on fluid-fluid displacements in patterned microfluidics and porous media

NASA Astrophysics Data System (ADS)

Juanes, Ruben; Trojer, Mathias; Zhao, Benzhong

2014-11-01

While it is well known that the wetting properties are critical in two-phase flows in porous media, the effect of wettability on fluid displacement continues to challenge our microscopic and macroscopic descriptions. Here we study this problem experimentally, starting with the classic experiment of two-phase flow in a capillary tube. We image the shape of the meniscus and measure the associated capillary pressure for a wide range of capillary numbers. We synthesize new observations on the dependence of the dynamic capillary pressure on wetting properties (contact angle) and flow conditions (viscosity contrast and capillary number). We then conduct experiments on a planar microfluidic device patterned with vertical posts. We track the evolution of the fluid-fluid interface and elucidate the impact of wetting on the cooperative nature of fluid displacement during pore invasion events. We use the insights gained from the capillary tube and patterned microfluidics experiments to elucidate the effect of wetting properties on viscous fingering and capillary fingering in a Hele-Shaw cell filled with glass beads, where we observe a contact-angle-dependent stabilizing behavior for the emerging flow instabilities, as the system transitions from drainage to imbibition.

The dynamical simulation of transient three-dimensional cryogenic liquid sloshing oscillations under low-gravity and microgravity

NASA Astrophysics Data System (ADS)

Chi, Yong Mann

A numerical simulation model has been developed for the dynamical behavior of spacecraft propellant, both during the draining and the closing of the tank outlet at the onset of suction dip affected by the asymmetric combined gravity gradient and gravity jitter accelerations. In particular the effect of the surface tension of the fluids in the partially filled dewar (applicable to the Gravity Probe-B spacecraft dewar tank and fuel tanks for a liquid rocket) with rotation has been simulated and investigated. Two different cases of accelerations, one with gravity jitter dominated and the other equally weighted between gravity gradient and gravity jitter accelerations, are studied. In the development of this numerical simulation model, the NASA-VOF3D has been used as a supplement to the numerical program of this dissertation. The NASA-VOF3D code has been used for performing the three-dimensional incompressible flows with free surface. This is also used for controlling liquid sloshing inside the tank when the spacecraft is orbiting. To keep track of the location of the liquid, the fractional volume of fluid (VOF) technique was used. The VOF is based on the indicator function of the region occupied by the liquid with an Eulerian approach to solve the free surface phenomena between liquid and gas phases. For the calculation of surface tension force, the VOF model is also used. The newly developed simulation model is used to investigate the characteristics of liquid hydrogen draining in terms of the residual amount of trapped liquid at the onset of the suction dip and residual liquid volume at the time the dip of the liquid-vapor interface formed. This investigation simulates the characteristics of liquid oscillations due to liquid container outlet shut-off at the onset of suction dip. These phenomena checked how these mechanisms affected the excitation of slosh waves during the course of liquid draining and after shut-off tank outlet. In the present study, the dynamical evolution of sloshing dynamics excited by fluid stress forces, fluid stress moments, and the arm of fluid moment exerted on the dewar container, is considered. This excitation was driven by the combined gravity gradient and gravity jitter acceleration inside the tank during the draining process and closing the tank outlet. The time evolution of the liquid-vapor interface profiles and the bubble mass center fluctuation, as well as liquid mass center and fluctuations of angular momentum caused by slosh wave excitations with 0.1 rpm in a reduced gravity, are also investigated and simulated. Force, angular momentum, and torque vector time histories and Power Spectral Density (PSD) are also plotted and discussed. The results of this investigation may be applied to determine the magnitude and nature of control forces and torques needed to minimize influence of slosh on the dynamics of liquid fueled vehicles in near earth orbit. Results show that induced fluid forces (or angular momentum) exerted on the container wall along x and y-axes, which are non-existent at the beginning, are introduced by the slosh waves excited by asymmetric gravity gradient and the gravity jitter acceleration.

Primary drainage in geological fractures: Effects of aperture variability and wettability

NASA Astrophysics Data System (ADS)

Yang, Z.; Méheust, Y.; Neuweiler, I.

2017-12-01

Understanding and controlling fluid-fluid displacement in porous and fractured media is a key asset for many practical applications, such as the geological storage of CO2, hydrocarbon recovery, groundwater remediation, etc. We numerically investigate fluid-fluid displacement in rough-walled fractures with a focus on the combined effect of wettability, the viscous contrast between the two fluids, and fracture surface topography on drainage patterns and interface growth. A model has been developed to simulate the dynamic displacement of one fluid by another immiscible one in a rough geological fracture; the model takes both capillary and viscous forces into account. Capillary pressures at the fluid-fluid interface are calculated based on the Young-Laplace equation using the two principal curvatures (aperture-induced curvature and in-plane curvature) [1], while viscous forces are calculated by continuously solving the fluid pressure field in the fracture. The aperture field of a fracture is represented by a spatially correlated random field, with a power spectral density of the fracture wall topographies scaling as a power law, and a cutoff wave-length above which the Fourier modes of the two walls are identical [2]. We consider flow scenarios with both rectangular and radial configurations. Results show that the model is able to produce displacement patterns of compact displacement, capillary fingering, and viscous fingering, as well as the transitions between them. Both reducing the aperture variability and increasing the contact angle (from drainage to weak imbibition) can stabilize the displacement due to the influence of the in-plane curvature, an effect analogous to that of the cooperative pore filling in porous media. These results suggest that for geometries typical of geological fractures we can extend the phase diagram in the parameter space of capillary number and mobility ratio by another dimension to take into account the combined effect of wettability and fracture aperture topography. References: [1] Yang, Z. et al. (2012), A generalized approach for estimation of in-plane curvature in invasion percolation models for drainage in fractures. Wat. Resour. Res., 48(9), W09507. [2] Yang, Z. et al. (2016), Fluid trapping during capillary displacement in fractures. Adv. Water Resour., 95, 264-275.

Mobile interfaces: Liquids as a perfect structural material for multifunctional, antifouling surfaces

DOE PAGES

Grinthal, Alison; Aizenberg, Joanna

2013-10-14

Life creates some of its most robust, extreme surface materials not from solids but from liquids: a purely liquid interface, stabilized by underlying nanotexture, makes carnivorous plant leaves ultraslippery, the eye optically perfect and dirt-resistant, our knees lubricated and pressure-tolerant, and insect feet reversibly adhesive and shape-adaptive. Novel liquid surfaces based on this idea have recently been shown to display unprecedented omniphobic, self-healing, anti-ice, antifouling, optical, and adaptive properties. In this Perspective, we present a framework and a path forward for developing and designing such liquid surfaces into sophisticated, versatile multifunctional materials. Drawing on concepts from solid materials design andmore » fluid dynamics, we outline how the continuous dynamics, responsiveness, and multiscale patternability of a liquid surface layer can be harnessed to create a wide range of unique, active interfacial functions-able to operate in harsh, changing environments-not achievable with static solids. We discuss how, in partnership with the underlying substrate, the liquid surface can be programmed to adaptively and reversibly reconfigure from a defect-free, molecularly smooth, transparent interface through a range of finely tuned liquid topographies in response to environmental stimuli. In conclusion, with nearly unlimited design possibilities and unmatched interfacial properties, liquid materials-as long-term stable interfaces yet in their fully liquid state-may potentially transform surface design everywhere from medicine to architecture to energy infrastructure.« less

Single-interface Richtmyer-Meshkov turbulent mixing at the Los Alamos Vertical Shock Tube

DOE PAGES

Wilson, Brandon Merrill; Mejia Alvarez, Ricardo; Prestridge, Katherine Philomena

2016-04-12

We studied Mach number and initial conditions effects on Richtmyer–Meshkov (RM) mixing by the vertical shock tube (VST) at Los Alamos National Laboratory (LANL). At the VST, a perturbed stable light-to-heavy (air–SF 6, A=0.64) interface is impulsively accelerated with a shock wave to induce RM mixing. We investigate changes to both large and small scales of mixing caused by changing the incident Mach number (Ma=1.3 and 1.45) and the three-dimensional (3D) perturbations on the interface. Simultaneous density (quantitative planar laser-induced fluorescence (PLIF)) and velocity (particle image velocimetry (PIV)) measurements are used to characterize preshock initial conditions and the dynamic shockedmore » interface. Initial conditions and fluid properties are characterized before shock. Using two types of dynamic measurements, time series (N=5 realizations at ten locations) and statistics (N=100 realizations at a single location) of the density and velocity fields, we calculate several mixing quantities. Mix width, density-specific volume correlations, density–vorticity correlations, vorticity, enstrophy, strain, and instantaneous dissipation rate are examined at one downstream location. Results indicate that large-scale mixing, such as the mix width, is strongly dependent on Mach number, whereas small scales are strongly influenced by initial conditions. Lastly, the enstrophy and strain show focused mixing activity in the spike regions.« less

A hybrid framework for coupling arbitrary summation-by-parts schemes on general meshes

NASA Astrophysics Data System (ADS)

Lundquist, Tomas; Malan, Arnaud; Nordström, Jan

2018-06-01

We develop a general interface procedure to couple both structured and unstructured parts of a hybrid mesh in a non-collocated, multi-block fashion. The target is to gain optimal computational efficiency in fluid dynamics simulations involving complex geometries. While guaranteeing stability, the proposed procedure is optimized for accuracy and requires minimal algorithmic modifications to already existing schemes. Initial numerical investigations confirm considerable efficiency gains compared to non-hybrid calculations of up to an order of magnitude.

Nonlinear effects on the natural modes of oscillation of a finite length inviscid fluid column, supplement 2

NASA Technical Reports Server (NTRS)

Lyell, M. J.; Zhang, L.

1994-01-01

The aspects of nonlinear behavior of a finite length liquid column is investigated with an emphasis on bridge dynamics. The primary objectives are to determine the nonlinear corrections to the interface shape of a naturally oscillating finite length liquid column and to determine the nonlinear corrections to the oscillation frequencies for various modes of oscillation. Application of the Lindstedt-Poincare expansion in conjunction with the domain perturbation techniques results in an hierarchical system of equations.

An upper bound on the particle-laden dependency of shear stresses at solid-fluid interfaces

NASA Astrophysics Data System (ADS)

Zohdi, T. I.

2018-03-01

In modern advanced manufacturing processes, such as three-dimensional printing of electronics, fine-scale particles are added to a base fluid yielding a modified fluid. For example, in three-dimensional printing, particle-functionalized inks are created by adding particles to freely flowing solvents forming a mixture, which is then deposited onto a surface, which upon curing yields desirable solid properties, such as thermal conductivity, electrical permittivity and magnetic permeability. However, wear at solid-fluid interfaces within the machinery walls that deliver such particle-laden fluids is typically attributed to the fluid-induced shear stresses, which increase with the volume fraction of added particles. The objective of this work is to develop a rigorous strict upper bound for the tolerable volume fraction of particles that can be added, while remaining below a given stress threshold at a fluid-solid interface. To illustrate the bound's utility, the expression is applied to a series of classical flow regimes.

On Energy Inequality for the Problem on the Evolution of Two Fluids of Different Types Without Surface Tension

NASA Astrophysics Data System (ADS)

Denisova, Irina Vlad.

2015-03-01

The paper deals with the motion of two immiscible viscous fluids in a container, one of the fluids being compressible while another one being incompressible. The interface between the fluids is an unknown closed surface where surface tension is neglected. We assume the compressible fluid to be barotropic, the pressure being given by an arbitrary smooth increasing function. This problem is considered in anisotropic Sobolev-Slobodetskiǐ spaces. We show that the L 2-norms of the velocity and deviation of compressible fluid density from the mean value decay exponentially with respect to time. The proof is based on a local existence theorem (Denisova, Interfaces Free Bound 2:283-312, 2000) and on the idea of constructing a function of generalized energy, proposed by Padula (J Math Fluid Mech 1:62-77, 1999). In addition, we eliminate the restrictions for the viscosities which appeared in Denisova (Interfaces Free Bound 2:283-312, 2000).

Multiscale X-ray and Proton Imaging of Bismuth-Tin Solidification

NASA Astrophysics Data System (ADS)

Gibbs, P. J.; Imhoff, S. D.; Morris, C. L.; Merrill, F. E.; Wilde, C. H.; Nedrow, P.; Mariam, F. G.; Fezzaa, K.; Lee, W.-K.; Clarke, A. J.

2014-08-01

The formation of structural patterns during metallic solidification is complex and multiscale in nature, ranging from the nanometer scale, where solid-liquid interface properties are important, to the macroscale, where casting mold filling and intended heat transfer are crucial. X-ray and proton imaging can directly interrogate structure, solute, and fluid flow development in metals from the microscale to the macroscale. X-rays permit high spatio-temporal resolution imaging of microscopic solidification dynamics in thin metal sections. Similarly, high-energy protons permit imaging of mesoscopic and macroscopic solidification dynamics in large sample volumes. In this article, we highlight multiscale x-ray and proton imaging of bismuth-tin alloy solidification to illustrate dynamic measurement of crystal growth rates and solute segregation profiles that can be that can be acquired using these techniques.

Sharp Interface Tracking in Rotating Microflows of Solvent Extraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glimm, James; Almeida, Valmor de; Jiao, Xiangmin

2013-01-08

The objective of this project is to develop a specialized sharp interface tracking simulation capability for predicting interaction of micron-sized drops and bubbles in rotating flows relevant to optimized design of contactor devices used in solvent extraction processes of spent nuclear fuel reprocessing. The primary outcomes of this project include the capability to resolve drops and bubbles micro-hydrodynamics in solvent extraction contactors, determining from first principles continuum fluid mechanics how micro-drops and bubbles interact with each other and the surrounding shearing fluid for realistic flows. In the near term, this effort will play a central role in providing parameters andmore » insight into the flow dynamics of models that average over coarser scales, say at the millimeter unit length. In the longer term, it will prove to be the platform to conduct full-device, detailed simulations as parallel computing power reaches the exaflop level. The team will develop an accurate simulation tool for flows containing interacting droplets and bubbles with sharp interfaces under conditions that mimic those found in realistic contactor operations. The main objective is to create an off-line simulation capability to model drop and bubble interactions in a domain representative of the averaged length scale. The technical approach is to combine robust interface tracking software, subgrid modeling, validation quality experiments, powerful computational hardware, and a team with simulation modeling, physical modeling and technology integration experience. Simulations will then fully resolve the microflow of drops and bubbles at the microsecond time scale. This approach is computationally intensive but very accurate in treating important coupled physical phenomena in the vicinity of interfaces. The method makes it possible to resolve spatial scales smaller than the typical distance between bubbles and to model some non-equilibrium thermodynamic features such as finite critical tension in cavitating liquids« less

Passive scalars chaotic dynamics induced by two vortices in a two-layer geophysical flow with shear and rotation

NASA Astrophysics Data System (ADS)

Ryzhov, Eugene

2015-11-01

Vortex motion in shear flows is of great interest from the point of view of nonlinear science, and also as an applied problem to predict the evolution of vortices in nature. Considering applications to the ocean and atmosphere, it is well-known that these media are significantly stratified. The simplest way to take stratification into account is to deal with a two-layer flow. In this case, vortices perturb the interface, and consequently, the perturbed interface transits the vortex influences from one layer to another. Our aim is to investigate the dynamics of two point vortices in an unbounded domain where a shear and rotation are imposed as the leading order influence from some generalized perturbation. The two vortices are arranged within the bottom layer, but an emphasis is on the upper-layer fluid particle motion. Point vortices induce singular velocity fields in the layer they belong to, however, in the other layers of a multi-layer flow, they induce regular velocity fields. The main feature is that singular velocity fields prohibit irregular dynamics in the vicinity of the singular points, but regular velocity fields, provided optimal conditions, permit irregular dynamics to extend almost in every point of the corresponding phase space.

Wave turbulence in a two-layer fluid: Coupling between free surface and interface waves

NASA Astrophysics Data System (ADS)

Falcon, Eric; Issenmann, Bruno; Laroche, Claude

2017-11-01

We experimentally study gravity-capillary wave turbulence on the interface between two immiscible fluids of close density with free upper surface. We locally measure the wave height at the interface between both fluids by means of a highly sensitive laser Doppler vibrometer. We show that the inertial range of the capillary wave turbulence regime is significantly extended when the upper fluid depth is increased: The crossover frequency between the gravity and capillary wave turbulence regimes is found to decrease whereas the dissipative cut-off frequency of the spectrum is found to increase. We explain these observations by the progressive decoupling between waves propagating at the interface and the ones at the free surface, using the full dispersion relation of gravity-capillary waves in a two-layer fluid of finite depths. The cut-off evolution is due to the disappearance of parasitic capillaries responsible for the main wave dissipation for a single fluid. B. Issenmann, C. Laroche & E. Falcon, EPL 116, 64005 (2016) published online 16 feb. 2017. This work has been partially supported by CNRS (1-year postdoctoral funding), ANR Turbulon 12-BS04-0005, and ANR Dysturb 2017.

Dust Tolerant Commodity Transfer Interface Mechanisms for Planetary Surfaces

NASA Technical Reports Server (NTRS)

Townsend, Ivan I.; Mueller, Robert P.; Tamasy, Gabor J.

2014-01-01

Regolith is present on most planetary surfaces such as Earth's moon, Mars, and Asteroids. If human crews and robotic machinery are to operate on these regolith covered surfaces, they must face the consequences of interacting with regolith fines which consist of particles below 100 microns in diameter down to as small as submicron scale particles. Such fine dust will intrude into mechanisms and interfaces causing a variety of problems such as contamination of clean fluid lines, jamming of mechanisms and damaging connector seals and couplings. Since multiple elements must be assembled in space for system level functionality, it will be inevitable that interfaces will be necessary for structural connections, and to pass commodities such as cryogenic liquid propellants, purge and buffer gases, water, breathing air, pressurizing gases, heat exchange fluids, power and data. When fine regolith dust is present in the environment it can be lofted into interfaces where it can compromise the utility of the interface by preventing the connections from being successfully mated, or by inducing fluid leaks or degradation of power and data transmission. A dust tolerant, hand held "quick-disconnect" cryogenic fluids connector housing has been developed at NASA KSC which can be used by astronaut crews to connect flex lines that will transfer propellants and other useful fluids to the end user. In addition, a dust tolerant, automated, cryogenic fluid, multiple connector, power and data interface mechanism prototype has been developed, fabricated and demonstrated by NASA at Kennedy Space Center (KSC). The design and operation of these prototypes are explained and discussed.

Control of Meridional Flow by a Non-Uniform Rotational Magnetic Field

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin; Ramachandran, Narayanan

1999-01-01

The diffusive mass transfer of species during crystal growth in vertical ampoules is significantly affected by fluid flow in the liquid mother phase (melt). For electrically conductive melts, an elegant way of remotely inducing and controlling this flow is by utilizing a uniform rotational magnetic field (RMF) in the transverse direction. It induces an azimuthal flow which tends to homogenize the thermal and solutal fields. The rotating field also reduces the diffusion boundary layer, stabilizes temperature fluctuations, and promotes better overall crystal growth. For moderate strengths of the applied magnetic field (2-20 m Tesla) with frequencies of up to 400 Hz, the induced secondary meridional flow becomes significant. It typically consists of one roll at the bottom of the liquid column and a second roll (vortex) at the top. The flow along the centerline (ampoule axis) is directed from the growing solid (interface) towards the liquid (melt). In case of convex interfaces (e.g. in floating zone crystal growth) such flow behavior is beneficial since it suppresses diffusion at the center. However, for concave interfaces (e.g. vertical Bridgman crystal growth) such a flow tends to exacerbate the situation in making the interface shape more concave. It would be beneficial to have some control of this meridional flow- for example, a single recirculating cell with controllable direction and flow magnitude will make this technique even more attractive for crystal growth. Such flow control is a possibility if a non-uniform PNE field is utilized for this purpose. Although this idea has been proposed earlier, it has not been conclusively demonstrated so far. In this work, we derive the governing equations for the fluid dynamics for such a system and obtain solutions for a few important cases. Results from parallel experimental measurements of fluid flow in a mercury column subjected to non-uniform RMF will also be presented.

The Dynamics of Miscible Interfaces: Simulations

NASA Technical Reports Server (NTRS)

Meiburg, Eckart

2005-01-01

This research project focuses on the dynamics of interfacial regions between miscible fluids. While much attention has focused on immiscible interfaces in the past, miscible interfaces have been explored to a much lesser degree, so that there are many open questions regarding their dynamics at this time. Among the more pressing issues is the role that nonconventional stresses can play in such interfacial regions. Such stresses are typically not accounted for in efforts to model the dynamics of miscible flows. Our research aims to clarify under which circumstances these stresses do have to be taken into account, and what quantitative approaches are most suitable in this regard. In order to address these issues, we have focused on conducting linear stability analyses and nonlinear simulations for capillary tube and Hele-Shaw flows, and to compare the results with corresponding experiments performed in the labs of our co-investigators Prof. Maxworthy at USC, and Dr. Balasubramaniam at NASA. Over the duration of the project we have, among other things, focused on the effects of variable diffusion coefficients in such flows, and specifically on their influence in the growth of instabilities. Furthermore, our three-dimensional spectral element simulations have made good progress, so that we have come to a point where we can conduct more detailed comparisons with experimental observations. We are currently focusing our efforts on reproducing the tip-splitting instability observed by Maxworthy. Finally, we have discovered a new core-annular flow instability in the Stokes flow regime during the last year. This represents a significant finding, as this instability does not have an immiscible counterpart.

Consistent Temperature Coupling with Thermal Fluctuations of Smooth Particle Hydrodynamics and Molecular Dynamics

PubMed Central

Ganzenmüller, Georg C.; Hiermaier, Stefan; Steinhauser, Martin O.

2012-01-01

We propose a thermodynamically consistent and energy-conserving temperature coupling scheme between the atomistic and the continuum domain. The coupling scheme links the two domains using the DPDE (Dissipative Particle Dynamics at constant Energy) thermostat and is designed to handle strong temperature gradients across the atomistic/continuum domain interface. The fundamentally different definitions of temperature in the continuum and atomistic domain – internal energy and heat capacity versus particle velocity – are accounted for in a straightforward and conceptually intuitive way by the DPDE thermostat. We verify the here-proposed scheme using a fluid, which is simultaneously represented as a continuum using Smooth Particle Hydrodynamics, and as an atomistically resolved liquid using Molecular Dynamics. In the case of equilibrium contact between both domains, we show that the correct microscopic equilibrium properties of the atomistic fluid are obtained. As an example of a strong non-equilibrium situation, we consider the propagation of a steady shock-wave from the continuum domain into the atomistic domain, and show that the coupling scheme conserves both energy and shock-wave dynamics. To demonstrate the applicability of our scheme to real systems, we consider shock loading of a phospholipid bilayer immersed in water in a multi-scale simulation, an interesting topic of biological relevance. PMID:23300586

A novel method for calculating the dynamic capillary force and correcting the pressure error in micro-tube experiment.

PubMed

Wang, Shuoliang; Liu, Pengcheng; Zhao, Hui; Zhang, Yuan

2017-11-29

Micro-tube experiment has been implemented to understand the mechanisms of governing microcosmic fluid percolation and is extensively used in both fields of micro electromechanical engineering and petroleum engineering. The measured pressure difference across the microtube is not equal to the actual pressure difference across the microtube. Taking into account the additional pressure losses between the outlet of the micro tube and the outlet of the entire setup, we propose a new method for predicting the dynamic capillary pressure using the Level-set method. We first demonstrate it is a reliable method for describing microscopic flow by comparing the micro-model flow-test results against the predicted results using the Level-set method. In the proposed approach, Level-set method is applied to predict the pressure distribution along the microtube when the fluids flow along the microtube at a given flow rate; the microtube used in the calculation has the same size as the one used in the experiment. From the simulation results, the pressure difference across a curved interface (i.e., dynamic capillary pressure) can be directly obtained. We also show that dynamic capillary force should be properly evaluated in the micro-tube experiment in order to obtain the actual pressure difference across the microtube.

Seismoelectric couplings in a poroelastic material containing two immiscible fluid phases

NASA Astrophysics Data System (ADS)

Jardani, A.; Revil, A.

2015-08-01

A new approach of seismoelectric imaging has been recently proposed to detect saturation fronts in which seismic waves are focused in the subsurface to scan its heterogeneous nature and determine saturation fronts. Such type of imaging requires however a complete modelling of the seismoelectric properties of porous media saturated by two immiscible fluid phases, one being usually electrically insulating (for instance water and oil). We combine an extension of Biot dynamic theory, valid for porous media containing two immiscible Newtonian fluids, with an extension of the electrokinetic theory based on the notion of effective volumetric charge densities dragged by the flow of each fluid phase. These effective charge densities can be related directly to the permeability and saturation of each fluid phase. The coupled partial differential equations are solved with the finite element method. We also derive analytically the transfer function connecting the macroscopic electrical field to the acceleration of the fast P wave (coseismic electrical field) and we study the influence of the water content on this coupling. We observe that the amplitude of the co-seismic electrical disturbance is very sensitive to the water content with an increase in amplitude with water saturation. We also investigate the seismoelectric conversions (interface effect) occurring at the water table. We show that the conversion response at the water table can be identifiable only when the saturation contrasts between the vadose and saturated zones are sharp enough. A relatively dry vadose zone represents the best condition to identify the water table through seismoelectric measurements. Indeed, in this case, the coseismic electrical disturbances are vanishingly small compared to the seismoelectric interface response.

Simulating the frontal instability of lock-exchange density currents with dissipative particle dynamics

NASA Astrophysics Data System (ADS)

Li, Yanggui; Geng, Xingguo; Wang, Heping; Zhuang, Xin; Ouyang, Jie

2016-06-01

The frontal instability of lock-exchange density currents is numerically investigated using dissipative particle dynamics (DPD) at the mesoscopic particle level. For modeling two-phase flow, the “color” repulsion model is adopted to describe binary fluids according to Rothman-Keller method. The present DPD simulation can reproduce the flow phenomena of lock-exchange density currents, including the lobe-and-cleft instability that appears at the head, as well as the formation of coherent billow structures at the interface behind the head due to the growth of Kelvin-Helmholtz instability. Furthermore, through the DPD simulation, some small-scale characteristics can be observed, which are difficult to be captured in macroscopic simulation and experiment.

Vapor-Gas Bubble Evolution and Growth in Extremely Viscous Fluids Under Vacuum

NASA Technical Reports Server (NTRS)

Kizito, John; Balasubramaniam, R.; Nahra, Henry; Agui, Juan; Truong, Duc

2008-01-01

Formation of vapor and gas bubbles and voids is normal and expected in flow processes involving extremely viscous fluids in normal gravity. Practical examples of extremely viscous fluids are epoxy-like filler materials before the epoxy fluids cure to their permanent form to create a mechanical bond between two substrates. When these fluids flow with a free liquid interface exposed to vacuum, rapid bubble expansion process may ensue. Bubble expansion might compromise the mechanical bond strength. The potential sources for the origin of the gases might be incomplete out-gassing process prior to filler application; regasification due to seal leakage in the filler applicator; and/or volatiles evolved from cure reaction products formed in the hardening process. We embarked on a study that involved conducting laboratory experiments with imaging diagnostics in order to deduce the seriousness of bubbling caused by entrained air and volatile fluids under space vacuum and low gravity environment. We used clear fluids with the similar physical properties as the epoxy-like filler material to mimic the dynamics of bubbles. Another aspect of the present study was to determine the likelihood of bubbling resulting from dissolved gases nucleating from solution. These experimental studies of the bubble expansion are compared with predictions using a modified Rayleigh- Plesset equation, which models the bubble expansion.

Desertification of the peritoneum by thin-film evaporation during laparoscopy.

PubMed

Ott, Douglas E

2003-01-01

To assess the effects of gas flow during insufflation on peritoneal fluid and peritoneal tissue regarding transient thermal behavior and thin-film evaporation. The effects of laparoscopic gas on peritoneal cell desiccation and peritoneal fluid thin-film evaporation were analyzed. Measurment of tissue and peritoneal fluid and analysis of gas flow dynamics during laparoscopy. High-velocity gas interface conditions during laparoscopic gas insufflation result in peritoneal surface temperature and decreases up to 20 degrees C/second due to rapid thin-film evaporation of the peritoneal fluid. Evaporation of the thin film of peritoneal fluid extends quickly to the peritoneal cell membrane, causing peritoneal cell desiccation, internal cytoplasmic stress, and disruption of the cell membrane, resulting in loss of peritoneal surface continuity and integrity. Changing the gas conditions to 35 degrees C and 95% humidity maintains normal peritoneal fluid thin-film characteristics, cellular integrity, and prevents evaporative losses. Cold, dry gas and the characteristics of the laparoscopic gas delivery apparatus cause local peritoneal damaging alterations by high-velocity gas flow with extremely dry gas, creating extreme arid surface conditions, rapid evaporative and hydrological changes, tissue desiccation, and peritoneal fluid alterations that contribute to the process of desertification and thin-film evaporation. Peritoneal desertification is preventable by preconditioning the gas to 35 degrees C and 95% humidity.

Molecular dynamic approach to the study of the intense heat and mass transfer processes on the vapor-liquid interface

NASA Astrophysics Data System (ADS)

Levashov, V. Yu; Kamenov, P. K.

2017-10-01

The paper is devoted to research of the heat and mass transfer processes on the vapor-liquid interface. These processes can be realized for example at metal tempering, accidents at nuclear power stations, followed by the release of the corium into the heat carrier, getting hot magma into the water during volcanic eruptions and other. In all these examples the vapor film can arise on the heated body surface. In this paper the vapor film formation process will be considered with help of molecular dynamics simulation methods. The main attention during this process modeling will be focused on the subject of the fluid and vapor interactions with the heater surface. Another direction of this work is to study of the processes inside the droplet that may take place as result of impact of the high-power laser radiation. Such impact can lead to intensive evaporation and explosive destruction of the droplet. At that the duration of heat and mass transfer processes in droplet substance is tens of femtoseconds. Thus, the methods of molecular dynamics simulation can give the possibilities describe the heat and mass transfer processes in the droplet and the vapor phase formation.

Predicting the pKa and stability of organic acids and bases at an oil-water interface.

PubMed

Andersson, M P; Olsson, M H M; Stipp, S L S

2014-06-10

We have used density functional theory and the implicit solvent model, COSMO-RS, to investigate how the acidity constant, pKa, of organic acids and bases adsorbed at the organic compound-aqueous solution interface changes, compared to its value in the aqueous phase. The pKa determine the surface charge density of the molecules that accumulate at the fluid-fluid interface. We have estimated the pKa by comparing the stability of the protonated and unprotonated forms of a series of molecules in the bulk aqueous solution and at an interface where parts of each molecule reside in the hydrophobic phase and the rest remains in the hydrophilic phase. We found that the pKa for acids is shifted by ∼1 pH unit to higher values compared to the bulk water pKa, whereas they are shifted to lower values by a similar amount for bases. Because this pKa shift is similar in magnitude for each of the molecules studied, we propose that the pKa for molecules at a water-organic compound interface can easily be predicted by adding a small shift to the aqueous pKa. This shift is general and correlates with the functional group. We also found that the relative composition of molecules at the fluid-fluid interface is not the same as in the bulk. For example, species such as carboxylic acids are enriched at the interface, where they can dominate surface properties, even when they are a modest component in the bulk fluid. For high surface concentrations of carboxylic acid groups at an interface, such as a self-assembled monolayer, we have demonstrated that the pKa depends on the degree of deprotonation through direct hydrogen bonding between protonated and deprotonated acidic headgroups.

A Steady State and Quasi-Steady Interface Between the Generalized Fluid System Simulation Program and the SINDA/G Thermal Analysis Program

NASA Technical Reports Server (NTRS)

Schallhorn, Paul; Majumdar, Alok; Tiller, Bruce

2001-01-01

A general purpose, one dimensional fluid flow code is currently being interfaced with the thermal analysis program SINDA/G. The flow code, GFSSP, is capable of analyzing steady state and transient flow in a complex network. The flow code is capable of modeling several physical phenomena including compressibility effects, phase changes, body forces (such as gravity and centrifugal) and mixture thermodynamics for multiple species. The addition of GFSSP to SINDA/G provides a significant improvement in convective heat transfer modeling for SINDA/G. The interface development is conducted in multiple phases. This paper describes the first phase of the interface which allows for steady and quasisteady (unsteady solid, steady fluid) conjugate heat transfer modeling.

Mechanically Enhanced Liquid Interfaces at Human Body Temperature Using Thermosensitive Methylated Nanocrystalline Cellulose.

PubMed

Scheuble, N; Geue, T; Kuster, S; Adamcik, J; Mezzenga, R; Windhab, E J; Fischer, P

2016-02-09

The mechanical performance of materials at oil/water interfaces after consumption is a key factor affecting hydrophobic drug release. In this study, we methylated the surface of nanocrystalline cellulose (NCC) by mercerization and dimethyl sulfate exposure to produce thermosensitive biopolymers. These methylated NCC (metNCC) were used to investigate interfacial thermogelation at air/water and medium-chain triglyceride (MCT)/water interfaces at body temperature. In contrast to bulk fluid dynamics, elastic layers were formed at room temperature, and elasticity increased significantly at body temperature, which was measured by interfacial shear and dilatational rheology in situ. This unique phenomenon depends on solvent quality, temperature, and polymer concentration at interfaces. Thus, by adjusting the degree of hydrophobicity of metNCC, the interfacial elasticity and thermogelation of the interfaces could be varied. In general, these new materials (metNCC) formed more brittle interfacial layers compared to commercial methylcellulose (MC A15). Thermogelation of methylcellulose promotes attractive intermolecular forces, which were reflected in a change in self-assembly of metNCC at the interface. As a consequence, layer thickness and density increased as a function of temperature. These effects were measured by atomic force microscopy (AFM) images of the displaced interface and confirmed by neutron reflection. The substantial structural and mechanical change of methylcellulose interfaces at body temperature represents a controllable encapsulation parameter allowing optimization of lipid-based drug formulations.

Full Multigrid Flow Solver

NASA Technical Reports Server (NTRS)

Mineck, Raymond E.; Thomas, James L.; Biedron, Robert T.; Diskin, Boris

2005-01-01

FMG3D (full multigrid 3 dimensions) is a pilot computer program that solves equations of fluid flow using a finite difference representation on a structured grid. Infrastructure exists for three dimensions but the current implementation treats only two dimensions. Written in Fortran 90, FMG3D takes advantage of the recursive subroutine feature, dynamic memory allocation, and structured-programming constructs of that language. FMG3D supports multi-block grids with three types of block-to-block interfaces: periodic, C-zero, and C-infinity. For all three types, grid points must match at interfaces. For periodic and C-infinity types, derivatives of grid metrics must be continuous at interfaces. The available equation sets are as follows: scalar elliptic equations, scalar convection equations, and the pressure-Poisson formulation of the Navier-Stokes equations for an incompressible fluid. All the equation sets are implemented with nonzero forcing functions to enable the use of user-specified solutions to assist in verification and validation. The equations are solved with a full multigrid scheme using a full approximation scheme to converge the solution on each succeeding grid level. Restriction to the next coarser mesh uses direct injection for variables and full weighting for residual quantities; prolongation of the coarse grid correction from the coarse mesh to the fine mesh uses bilinear interpolation; and prolongation of the coarse grid solution uses bicubic interpolation.

Drag penalty due to the asperities in the substrate of super-hydrophobic and liquid infused surfaces

NASA Astrophysics Data System (ADS)

Garcia Cartagena, Edgardo J.; Arenas, Isnardo; Leonardi, Stefano

2017-11-01

Direct numerical simulations of two superposed fluids in a turbulent channel with a textured surface made of pinnacles of random height have been performed. The viscosity ratio between the two fluids are N =μo /μi = 50 (μo and μi are the viscosities of outer and inner fluid respectively) mimicking a super-hydrophobic surface (water over air) and N=2.5 (water over heptane) resembling a liquid infused surface. Two set of simulations have been performed varying the Reynolds number, Reτ = 180 and Reτ = 390 . The interface between the two fluids is flat simulating infinite surface tension. The position of the interface between the two fluids has been varied in the vertical direction from the base of the substrate (what would be a rough wall) to the highest point of the roughness. Drag reduction is very sensitive to the position of the interface between the two fluids. Asperities above the interface induce a large form drag and diminish considerably the drag reduction. When the mean height of the surface measured from the interface in the outer fluid is greater than one wall unit, k+ > 1 , the drag increases with respect to a smooth wall. Present results provide a guideline to the accuracy required in manufacturing super-hydrophobic and liquid infused surfaces. This work was supported under ONR MURI Grants N00014-12-0875 and N00014-12- 1-0962, Program Manager Dr. Ki-Han Kim. Numerical simulations were performed on the Texas Advanced Computer Center.

Effects of surface tension and intraluminal fluid on mechanics of small airways.

PubMed

Hill, M J; Wilson, T A; Lambert, R K

1997-01-01

Airway constriction is accompanied by folding of the mucosa to form ridges that run axially along the inner surface of the airways. The mucosa has been modeled (R. K. Lambert. J. Appl. Physiol. 71:666-673, 1991) as a thin elastic layer with a finite bending stiffness, and the contribution of its bending stiffness to airway elastance has been computed. In this study, we extend that work by including surface tension and intraluminal fluid in the model. With surface tension, the pressure on the inner surface of the elastic mucosa is modified by the pressure difference across the air-liquid interface. As folds form in the mucosa, intraluminal fluid collects in pools in the depressions formed by the folds, and the curvature of the air-liquid interface becomes nonuniform. If the amount of intraluminal fluid is small, < 2% of luminal volume, the pools of intraluminal fluid are small, the air-liquid interface nearly coincides with the surface of the mucosa, and the area of the air-liquid interface remains constant as airway cross-sectional area decreases. In that case, surface energy is independent of airway area, and surface tension has no effect on airway mechanics. If the amount of intraluminal fluid is > 2%, the area of the air-liquid interface decreases as airway cross-sectional area decreases. and surface tension contributes to airway compression. The model predicts that surface tension plus intraluminal fluid can cause an instability in the area-pressure curve of small airways. This instability provides a mechanism for abrupt airway closure and abrupt reopening at a higher opening pressure.

Self-Healing Nanocomposite Hydrogel with Well-Controlled Dynamic Mechanics

NASA Astrophysics Data System (ADS)

Li, Qiaochu; Mishra, Sumeet; Chen, Pangkuan; Tracy, Joseph; Holten-Andersen, Niels

Network dynamics is a crucial factor that determines the macroscopic self-healing rate and efficiency in polymeric hydrogel materials, yet its controllability is seldom studied in most reported self-healing hydrogel systems. Inspired by mussel's adhesion chemistry, we developed a novel approach to assemble inorganic nanoparticles and catechol-decorated PEG polymer into a hydrogel network. When utilized as reversible polymer-particle crosslinks, catechol-metal coordination bonds yield a unique gel network with dynamic mechanics controlled directly by interfacial crosslink structure. Taking advantage of this structure-property relationship at polymer-particle interfaces, we next designed a hierarchically structured hybrid gel with two distinct relaxation timescales. By tuning the relative contribution of the two hierarchical relaxation modes, we are able to finely control the gel's dynamic mechanical behavior from a viscoelastic fluid to a stiff solid, yet preserving its fast self-healing property without the need for external stimuli.

Rapid Self-healing Nanocomposite Hydrogel with Tunable Dynamic Mechanics

NASA Astrophysics Data System (ADS)

Li, Qiaochu; Mishra, Sumeet; Chapman, Brian; Chen, Pangkuan; Tracy, Joseph; Holten-Andersen, Niels

The macroscopic healing rate and efficiency in self-repairing hydrogel materials are largely determined by the dissociation dynamics of their polymer network, which is hardly achieved in a controllable manner. Inspired by mussel's adhesion chemistry, we developed a novel approach to assemble inorganic nanoparticles and catechol-decorated PEG polymer into a hydrogel network. When utilized as reversible polymer-particle crosslinks, catechol-metal coordination bonds yield a unique gel network with dynamic mechanics controlled directly by interfacial crosslink structure. Taking advantage of this structure-property relationship at polymer-particle interfaces, we designed a hierarchically structured hybrid gel with two distinct relaxation timescales. By tuning the relative contribution of the two relaxation modes, we are able to finely control the gel's dynamic mechanical behavior from a viscoelastic fluid to a stiff solid, yet preserving its rapid self-healing property without the need for external stimuli.

Resonant Formation and Control of m-Fold Symmetric V-States

NASA Astrophysics Data System (ADS)

Friedland, Lazar; Shagalov, Arkadi

2000-10-01

Magnetized, pure electron plasmas trapped in a Malmberg-Penning trap can be modeled (in the drift approximation) by two-dimensional Euler equations of ideal fluids. The plasma density in this approximation is analogous to vorticity, while the radial electric field potential to the stream function of the fluid velocity field. For instance, electron plasma cylinder aligned with the magnetic field is analogous to a circular vortex patch solution of an ideal fluid. We shall show that by starting in such a circular equilibrium one can drive an m-fold symmetric interface (vortex) waves in two dimensions (V-states, discovered by Deem and Zabusky [1] nearly 20 years ago)into a highly nonlinear excitation by applying a weak external oscillating potential of appropriate symmetry and slowly varying the frequency of these oscillations. The phenomenon is due to autoresonance [2,3] in the system as the excited plasma (vortex) boundary preserves its functional form despite the drive, but self-adjusts the aspect ratio to synchronize with the driving potential oscillations. A similar approach can be used in controlling interface dynamics subject to global constraints in many other fields of physics. Work supported by Israel Science Foundation grant 607-97 and INTAS grant 99-1068. [1] G. Deem and N. Zabusky, Phys. Rev. Lett. 40, 859 (1978). [2] L. Friedland, Phys. Rev. E, 4106 (1999). [3] J. Fajans, E. Gilson, and L. Friedland, Phys. Rev. Lett. 82, 4444 (1999).

Crustal fingering: solidification on a viscously unstable interface

NASA Astrophysics Data System (ADS)

Fu, Xiaojing; Jimenez-Martinez, Joaquin; Cueto-Felgueroso, Luis; Porter, Mark; Juanes, Ruben

2017-11-01

Motivated by the formation of gas hydrates in seafloor sediments, here we study the volumetric expansion of a less viscous gas pocket into a more viscous liquid when the gas-liquid interfaces readily solidify due to hydrate formation. We first present a high-pressure microfluidic experiment to study the depressurization-controlled expansion of a Xenon gas pocket in a water-filled Hele-Shaw cell. The evolution of the pocket is controlled by three processes: (1) volumetric expansion of the gas; (2) rupturing of existing hydrate films on the gas-liquid interface; and (3) formation of new hydrate films. These result in gas fingering leading to a complex labyrinth pattern. To reproduce these observations, we propose a phase-field model that describes the formation of hydrate shell on viscously unstable interfaces. We design the free energy of the three-phase system to rigorously account for interfacial effects, gas compressibility and phase transitions. We model the hydrate shell as a highly viscous fluid with shear-thinning rheology to reproduce shell-rupturing behavior. We present high-resolution numerical simulations of the model, which illustrate the emergence of complex crustal fingering patterns as a result of gas expansion dynamics modulated by hydrate growth at the interface.

Adjustable Autonomy Testbed

NASA Technical Reports Server (NTRS)

Malin, Jane T.; Schrenkenghost, Debra K.

2001-01-01

The Adjustable Autonomy Testbed (AAT) is a simulation-based testbed located in the Intelligent Systems Laboratory in the Automation, Robotics and Simulation Division at NASA Johnson Space Center. The purpose of the testbed is to support evaluation and validation of prototypes of adjustable autonomous agent software for control and fault management for complex systems. The AA T project has developed prototype adjustable autonomous agent software and human interfaces for cooperative fault management. This software builds on current autonomous agent technology by altering the architecture, components and interfaces for effective teamwork between autonomous systems and human experts. Autonomous agents include a planner, flexible executive, low level control and deductive model-based fault isolation. Adjustable autonomy is intended to increase the flexibility and effectiveness of fault management with an autonomous system. The test domain for this work is control of advanced life support systems for habitats for planetary exploration. The CONFIG hybrid discrete event simulation environment provides flexible and dynamically reconfigurable models of the behavior of components and fluids in the life support systems. Both discrete event and continuous (discrete time) simulation are supported, and flows and pressures are computed globally. This provides fast dynamic simulations of interacting hardware systems in closed loops that can be reconfigured during operations scenarios, producing complex cascading effects of operations and failures. Current object-oriented model libraries support modeling of fluid systems, and models have been developed of physico-chemical and biological subsystems for processing advanced life support gases. In FY01, water recovery system models will be developed.

Smoothed particle hydrodynamics simulations of evaporation and explosive boiling of liquid drops in microgravity.

PubMed

Sigalotti, Leonardo Di G; Troconis, Jorge; Sira, Eloy; Peña-Polo, Franklin; Klapp, Jaime

2015-07-01

The rapid evaporation and explosive boiling of a van der Waals (vdW) liquid drop in microgravity is simulated numerically in two-space dimensions using the method of smoothed particle hydrodynamics. The numerical approach is fully adaptive and incorporates the effects of surface tension, latent heat, mass transfer across the interface, and liquid-vapor interface dynamics. Thermocapillary forces are modeled by coupling the hydrodynamics to a diffuse-interface description of the liquid-vapor interface. The models start from a nonequilibrium square-shaped liquid of varying density and temperature. For a fixed density, the drop temperature is increased gradually to predict the point separating normal boiling at subcritical heating from explosive boiling at the superheat limit for this vdW fluid. At subcritical heating, spontaneous evaporation produces stable drops floating in a vapor atmosphere, while at near-critical heating, a bubble is nucleated inside the drop, which then collapses upon itself, leaving a smaller equilibrated drop embedded in its own vapor. At the superheat limit, unstable bubble growth leads to either fragmentation or violent disruption of the liquid layer into small secondary drops, depending on the liquid density. At higher superheats, explosive boiling occurs for all densities. The experimentally observed wrinkling of the bubble surface driven by rapid evaporation followed by a Rayleigh-Taylor instability of the thin liquid layer and the linear growth of the bubble radius with time are reproduced by the simulations. The predicted superheat limit (T(s)≈0.96) is close to the theoretically derived value of T(s)=1 at zero ambient pressure for this vdW fluid.

The Investigation of Ghost Fluid Method for Simulating the Compressible Two-Medium Flow

NASA Astrophysics Data System (ADS)

Lu, Hai Tian; Zhao, Ning; Wang, Donghong

2016-06-01

In this paper, we investigate the conservation error of the two-dimensional compressible two-medium flow simulated by the front tracking method. As the improved versions of the original ghost fluid method, the modified ghost fluid method and the real ghost fluid method are selected to define the interface boundary conditions, respectively, to show different effects on the conservation error. A Riemann problem is constructed along the normal direction of the interface in the front tracking method, with the goal of obtaining an efficient procedure to track the explicit sharp interface precisely. The corresponding Riemann solutions are also used directly in these improved ghost fluid methods. Extensive numerical examples including the sod tube and the shock-bubble interaction are tested to calculate the conservation error. It is found that these two ghost fluid methods have distinctive performances for different initial conditions of the flow field, and the related conclusions are made to suggest the best choice for the combination.

Interface projection techniques for fluid-structure interaction modeling with moving-mesh methods

NASA Astrophysics Data System (ADS)

Tezduyar, Tayfun E.; Sathe, Sunil; Pausewang, Jason; Schwaab, Matthew; Christopher, Jason; Crabtree, Jason

2008-12-01

The stabilized space-time fluid-structure interaction (SSTFSI) technique developed by the Team for Advanced Flow Simulation and Modeling (T★AFSM) was applied to a number of 3D examples, including arterial fluid mechanics and parachute aerodynamics. Here we focus on the interface projection techniques that were developed as supplementary methods targeting the computational challenges associated with the geometric complexities of the fluid-structure interface. Although these supplementary techniques were developed in conjunction with the SSTFSI method and in the context of air-fabric interactions, they can also be used in conjunction with other moving-mesh methods, such as the Arbitrary Lagrangian-Eulerian (ALE) method, and in the context of other classes of FSI applications. The supplementary techniques currently consist of using split nodal values for pressure at the edges of the fabric and incompatible meshes at the air-fabric interfaces, the FSI Geometric Smoothing Technique (FSI-GST), and the Homogenized Modeling of Geometric Porosity (HMGP). Using split nodal values for pressure at the edges and incompatible meshes at the interfaces stabilizes the structural response at the edges of the membrane used in modeling the fabric. With the FSI-GST, the fluid mechanics mesh is sheltered from the consequences of the geometric complexity of the structure. With the HMGP, we bypass the intractable complexities of the geometric porosity by approximating it with an “equivalent”, locally-varying fabric porosity. As test cases demonstrating how the interface projection techniques work, we compute the air-fabric interactions of windsocks, sails and ringsail parachutes.

First Principle Estimation of Geochemically Important Transition Metal Oxide Properties: Structure and Dynamics of the Bulk, Surface and Mineral/Aqueous Fluid Interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Ying; Bylaska, Eric J.; Weare, John H.

Reactions in the mineral surface/reservoir fluid interface control many geochemical processes such as the dissolution and growth of minerals (Yanina and Rosso 2008), heterogeneous oxidation/reduction (Hochella 1990, Brown 2001, Hochella, Lower et al. 2008, Navrotsky, Mazeina et al. 2008), and inorganic respiration (Newman 2010). Key minerals involved in these processes are the transition metal oxides and oxyhydroxides (e.g., hematite, Fe2O3, and goethite, FeOOH)(Brown, Henrich et al. 1999, Brown 2001, Hochella, Lower et al. 2008, Navrotsky, Mazeina et al. 2008). To interpret and predict these processes, it is necessary to have a high level of understanding of the interactions between themore » formations containing these minerals and their reservoir fluids. However, these are complicated chemical events occurring under a wide range of T, P, and X conditions and the interpretation is complicated by the highly heterogeneous nature of natural environments (Hochella 1990, Hochella, Lower et al. 2008, Navrotsky, Mazeina et al. 2008) and the electronic and structural complexity of the oxide materials involved(Cox 1992, Kotliar and Vollhardt 2004, Navrotsky, Mazeina et al. 2008). In addition, also because of the complexity of the minerals involved and the heterogeneous nature of natural systems, the direct observation of these reactions at the atomic level is experimentally extremely difficult. Theoretical simulations will provide important support for analysis of the geochemistry of the mineral surface/fluid region as well as provide essential tools to extrapolate laboratory measurements to the field environment.« less

Interface behavior of a multi-layer fluid configuration subject to acceleration in a microgravity environment, supplement 1. M.S. Thesis

NASA Technical Reports Server (NTRS)

Lyell, M. J.; Roh, Michael

1991-01-01

With the increasing opportunities for research in a microgravity environment, there arises a need for understanding fluid mechanics under such conditions. In particular, a number of material processing configurations involve fluid-fluid interfaces which may experience instabilities in the presence of external forcing. In a microgravity environment, these accelerations may be periodic or impulse-type in nature. This research investigates the behavior of a multi-layer idealized fluid configuration which is infinite in extent. The analysis is linear, and each fluid region is considered inviscid, incompressible, and immiscible. An initial parametric study of confiquration stability in the presence of a constant acceleration field is performed. The zero mean gravity limit case serves as the base state for the subsequent time-dependent forcing cases. A stability analysis of the multi-layer fluid system in the presence of periodic forcing is investigated. Floquet theory is utilized. A parameter study is performed, and regions of stability are identified. For the impulse-type forcing case, asymptotic stability is established for the configuration. Using numerical integration, the time response of the interfaces is determined.

Charge fluctuations in nanoscale capacitors.

PubMed

Limmer, David T; Merlet, Céline; Salanne, Mathieu; Chandler, David; Madden, Paul A; van Roij, René; Rotenberg, Benjamin

2013-09-06

The fluctuations of the charge on an electrode contain information on the microscopic correlations within the adjacent fluid and their effect on the electronic properties of the interface. We investigate these fluctuations using molecular dynamics simulations in a constant-potential ensemble with histogram reweighting techniques. This approach offers, in particular, an efficient, accurate, and physically insightful route to the differential capacitance that is broadly applicable. We demonstrate these methods with three different capacitors: pure water between platinum electrodes and a pure as well as a solvent-based organic electrolyte each between graphite electrodes. The total charge distributions with the pure solvent and solvent-based electrolytes are remarkably Gaussian, while in the pure ionic liquid the total charge distribution displays distinct non-Gaussian features, suggesting significant potential-driven changes in the organization of the interfacial fluid.

Charge Fluctuations in Nanoscale Capacitors

NASA Astrophysics Data System (ADS)

Limmer, David T.; Merlet, Céline; Salanne, Mathieu; Chandler, David; Madden, Paul A.; van Roij, René; Rotenberg, Benjamin

2013-09-01

The fluctuations of the charge on an electrode contain information on the microscopic correlations within the adjacent fluid and their effect on the electronic properties of the interface. We investigate these fluctuations using molecular dynamics simulations in a constant-potential ensemble with histogram reweighting techniques. This approach offers, in particular, an efficient, accurate, and physically insightful route to the differential capacitance that is broadly applicable. We demonstrate these methods with three different capacitors: pure water between platinum electrodes and a pure as well as a solvent-based organic electrolyte each between graphite electrodes. The total charge distributions with the pure solvent and solvent-based electrolytes are remarkably Gaussian, while in the pure ionic liquid the total charge distribution displays distinct non-Gaussian features, suggesting significant potential-driven changes in the organization of the interfacial fluid.

Dogs lap using acceleration-driven open pumping

PubMed Central

Gart, Sean; Socha, John J.; Vlachos, Pavlos P.; Jung, Sunghwan

2015-01-01

Dogs lap because they have incomplete cheeks and cannot suck. When lapping, a dog’s tongue pulls a liquid column from the bath, suggesting that the hydrodynamics of column formation are critical to understanding how dogs drink. We measured lapping in 19 dogs and used the results to generate a physical model of the tongue’s interaction with the air–fluid interface. These experiments help to explain how dogs exploit the fluid dynamics of the generated column. The results demonstrate that effects of acceleration govern lapping frequency, which suggests that dogs curl the tongue to create a larger liquid column. Comparing lapping in dogs and cats reveals that, despite similar morphology, these carnivores lap in different physical regimes: an unsteady inertial regime for dogs and steady inertial regime for cats. PMID:26668382

Opportunities of hydrostatically coupled dielectric elastomer actuators for haptic interfaces

NASA Astrophysics Data System (ADS)

Carpi, Federico; Frediani, Gabriele; De Rossi, Danilo

2011-04-01

As a means to improve versatility and safety of dielectric elastomer actuators (DEAs) for several fields of application, so-called 'hydrostatically coupled' DEAs (HC-DEAs) have recently been described. HC-DEAs are based on an incompressible fluid that mechanically couples a DE-based active part to a passive part interfaced to the load, so as to enable hydrostatic transmission. This paper presents ongoing developments of HC-DEAs and potential applications in the field of haptics. Three specific examples are considered. The first deals with a wearable tactile display used to provide users with tactile feedback during electronic navigation in virtual environments. The display consists of HCDEAs arranged in contact with finger tips. As a second example, an up-scaled prototype version of an 8-dots refreshable cell for dynamic Braille displays is shown. Each Braille dot consists of a miniature HC-DEA, with a diameter lower than 2 mm. The third example refers to a device for finger rehabilitation, conceived to work as a sort of active version of a rehabilitation squeezing ball. The device is designed to dynamically change its compliance according to an electric control. The three examples of applications intend to show the potential of the new technology and the prospective opportunities for haptic interfaces.

Quantification of the Mass Transfer at Fluid Interfaces in Microfluidic Channels

NASA Astrophysics Data System (ADS)

Wismeth, Carina; Manhart, Michael; Niessner, Reinhard; Baumann, Thomas

2017-04-01

Mass transfer rates at interfaces in a complex porous media are relevant in many environmental applications and control the functions of natural filter systems in subsurface environments. The mass transfer at fluid interfaces is associated with interface convection caused by local inhomogeneities in interface tension and hydrodynamic instabilities at the interface. If there is a surface tension gradient along the surface a shear stress jump is generated that results in fluid motion along the surface that is called Marangoni effect. These spontaneous convection currents can lead to an increased mass transfer of the transition component at the phase boundary and to an increased mixing of the phases. Therefore compensatory currents at the interface can have a significant influence on the subsurface transport of contaminants in the groundwater area, especially in the vadose zone. Using microfluidic channels and advanced experimental techniques it is possible to measure the fluid flow and mass transfer rates directly and to quantify the effect of the Marangoni convection on the mass transfer at interfaces between a non-aqueous liquid and water with high temporal and spatial resolution. The use of fluorescent particles as well as the recording and analysis of their trajectories is intended to visualize interfacial processes and to quantify the mass transfer at fluid phase boundaries. Concentration gradients at the interface are analysed by spectroscopic methods and allow an assessment of the enrichment and depletion at the phase boundaries. Extensive test series provide the experimental basis for quantifying and analysing the impact of the Marangoni effect on the mass transfer rates at interfaces in porous media in subsurface aquatic environments. Within this research project we concentrate on the effect of Marangoni convection on the mass transfer near an 1-octanol-water interface, which serves as a well defined proxy for non-aqueous phase liquids in porous media. Experiments and a numerical simulation are closely coupled to provide a generic data set with high reproducibility and used to obtain highly resolved three-dimensional data of mass transfer in two- and three-phase systems to foster the understanding of subsurface transport, especially in the vadose zone.

Calculation of nanodrop profile from fluid density distribution.

PubMed

Berim, Gersh O; Ruckenstein, Eli

2016-05-01

Two approaches are examined, which can be used to determine the drop profile from the fluid density distributions (FDDs) obtained on the basis of microscopic theories. For simplicity, only two-dimensional (cylindrical, or axisymmetrical) distributions are examined and it is assumed that the fluid is either in contact with a smooth solid or separated from the smooth solid by a lubricating liquid film. The first approach is based on the sharp-kink interface approximation in which the density of the liquid inside and the density of the vapor outside the drop are constant with the exception of the surface layer of the drop where the density is different from the above ones. In this case, the drop profile was calculated by minimizing the total potential energy of the system. The second approach is based on a nonuniform FDD obtained either by the density functional theory or molecular dynamics simulations. To determine the drop profile from such an FDD, which does not contain sharp interfaces, three procedures can be used. In the first two procedures, P1 and P2, the one-dimensional FDDs along straight lines which are parallel to the surface of the solid are extracted from the two-dimensional FDD. Each of those one-dimensional FDDs has a vapor-liquid interface at which the fluid density changes from vapor-like to liquid-like values. Procedure P1 uses the locations of the equimolar dividing surfaces for the one-dimensional FDDs as points of the drop profile. Procedure P2 is based on the assumption that the fluid density is constant on the surface of the drop, that density being selected either arbitrarily or as a fluid density at the location of the equimolar dividing surface for one of the one-dimensional FDDs employed in procedure P1. In the third procedure, P3, which is suggested for the first time in this paper, the one-dimensional FDDs are taken along the straight lines passing through a selected point inside the drop (radial line). Then, the drop profile is calculated like in procedure P1. It is shown, that procedure P3 provides a drop profile which is more reasonable than the other ones. Relationship of the discussed procedures to those used in image analysis is briefly discussed. Copyright © 2016 Elsevier B.V. All rights reserved.

Analytical solution for the transient wave propagation of a buried cylindrical P-wave line source in a semi-infinite elastic medium with a fluid surface layer

NASA Astrophysics Data System (ADS)

Shan, Zhendong; Ling, Daosheng

2018-02-01

This article develops an analytical solution for the transient wave propagation of a cylindrical P-wave line source in a semi-infinite elastic solid with a fluid layer. The analytical solution is presented in a simple closed form in which each term represents a transient physical wave. The Scholte equation is derived, through which the Scholte wave velocity can be determined. The Scholte wave is the wave that propagates along the interface between the fluid and solid. To develop the analytical solution, the wave fields in the fluid and solid are defined, their analytical solutions in the Laplace domain are derived using the boundary and interface conditions, and the solutions are then decomposed into series form according to the power series expansion method. Each item of the series solution has a clear physical meaning and represents a transient wave path. Finally, by applying Cagniard's method and the convolution theorem, the analytical solutions are transformed into the time domain. Numerical examples are provided to illustrate some interesting features in the fluid layer, the interface and the semi-infinite solid. When the P-wave velocity in the fluid is higher than that in the solid, two head waves in the solid, one head wave in the fluid and a Scholte wave at the interface are observed for the cylindrical P-wave line source.

The importance of fluctuations in fluid mixing.

PubMed

Kadau, Kai; Rosenblatt, Charles; Barber, John L; Germann, Timothy C; Huang, Zhibin; Carlès, Pierre; Alder, Berni J

2007-05-08

A ubiquitous example of fluid mixing is the Rayleigh-Taylor instability, in which a heavy fluid initially sits atop a light fluid in a gravitational field. The subsequent development of the unstable interface between the two fluids is marked by several stages. At first, each interface mode grows exponentially with time before transitioning to a nonlinear regime characterized by more complex hydrodynamic mixing. Unfortunately, traditional continuum modeling of this process has generally been in poor agreement with experiment. Here, we indicate that the natural, random fluctuations of the flow field present in any fluid, which are neglected in continuum models, can lead to qualitatively and quantitatively better agreement with experiment. We performed billion-particle atomistic simulations and magnetic levitation experiments with unprecedented control of initial interface conditions. A comparison between our simulations and experiments reveals good agreement in terms of the growth rate of the mixing front as well as the new observation of droplet breakup at later times. These results improve our understanding of many fluid processes, including interface phenomena that occur, for example, in supernovae, the detachment of droplets from a faucet, and ink jet printing. Such instabilities are also relevant to the possible energy source of inertial confinement fusion, in which a millimeter-sized capsule is imploded to initiate nuclear fusion reactions between deuterium and tritium. Our results suggest that the applicability of continuum models would be greatly enhanced by explicitly including the effects of random fluctuations.

A magnetic fluid seal for rotary blood pumps: image and computational analyses of behaviors of magnetic fluids.

PubMed

Mitamura, Yoshinori; Yano, Tetsuya; Okamoto, Eiji

2013-01-01

A magnetic fluid (MF) seal has excellent durability. The performance of an MF seal, however, has been reported to decrease in liquids (several days). We have developed an MF seal that has a shield mechanism. The seal was perfect for 275 days in water. To investigate the effect of a shield, behaviors of MFs in a seal in water were studied both experimentally and computationally. (a) Two kinds of MF seals, one with a shield and one without a shield, were installed in a centrifugal pump. Behaviors of MFs in the seals in water were observed with a video camera and high-speed microscope. In the seal without a shield, the surface of the water in the seal waved and the turbulent flow affected behaviors of the MFs. In contrast, MFs rotated stably in the seal with a shield in water even at high rotational speeds. (b) Computational fluid dynamics analysis revealed that a stationary secondary flow pattern in the seal and small velocity difference between magnetic fluid and water at the interface. These MF behaviors prolonged the life of an MF seal in water.

Bed Erosion Process in Geophysical Viscoplastic Fluid

NASA Astrophysics Data System (ADS)

Luu, L. H.; Philippe, P.; Chambon, G.; Vigneaux, P.; Marly, A.

2017-12-01

The bulk behavior of materials involved in geophysical fluid dynamics such as snow avalanches or debris flows has often been modeled as viscoplastic fluid that starts to flow once its stress state overcomes a critical yield value. This experimental and numerical study proposes to interpret the process of erosion in terms of solid-fluid transition for these complex materials. The experimental setup consists in a closed rectangular channel with a cavity in its base. By means of high-resolution optical velocimetry (PIV), we properly examine the typical velocity profiles of a model elasto-viscoplastic flow (Carbopol) at the vicinity of the solid-fluid interface, separating a yielded flowing layer above from an unyielded dead zone below. In parallel, numerical simulations in this expansion-contraction geometry with Augmented Lagrangian and Finite-Differences methods intend to discuss the possibility to describe the specific flow related to the existence of a dead zone, with a simple Bingham rheology. First results of this comparative analysis show a good numerical ability to capture the main scalings and flow features, such as the non-monotonous evolution of the shear stress in the boundary layer between the central plug zone and the dead zone at the bottom of the cavity.

Fluid Pressures at the Shoe-Floor-Contaminant Interface During Slips: Effects of Tread & Implications on Slip Severity

PubMed Central

Beschorner, Kurt E.; Albert, Devon L.; Chambers, April J.; Redfern, Mark S.

2018-01-01

Previous research on slip and fall accidents has suggested that pressurized fluid between the shoe and floor is responsible for initiating slips yet this effect has not been verified experimentally. This study aimed to 1) measure hydrodynamic pressures during slipping for treaded and untreaded conditions; 2) determine the effects of fluid pressure on slip severity; and 3) quantify how fluid pressures vary with instantaneous resultant slipping speed, position on the shoe surface, and throughout the progression of the slip. Eighteen subjects walked on known dry and unexpected slippery floors, while wearing treaded and untreaded shoes. Fluid pressure sensors, embedded in the floor, recorded hydrodynamic pressures during slipping. The maximum fluid pressures (mean+/−standard deviation) were significantly higher for the untreaded conditions (124 +/−75 kPa) than the treaded conditions (1.1 +/−0.29 kPa). Maximum fluid pressures were positively correlated with peak slipping speed (r = 0.87), suggesting that higher fluid pressures, which are associated with untreaded conditions, resulted in more severe slips. Instantaneous resultant slipping speed and position of sensor relative to the shoe sole and walking direction explained 41% of the fluid pressure variability. Fluid pressures were primarily observed for untreaded conditions. This study confirms that fluid pressures are relevant to slipping events, consistent with fluid dynamics theory (i.e. the Reynolds equation), and can be modified with shoe tread design. The results suggest that the occurrence and severity of unexpected slips can be reduced by designing shoes/floors that reduce underfoot fluid pressures. PMID:24267270

Impact of an irregular friction formulation on dynamics of a minimal model for brake squeal

NASA Astrophysics Data System (ADS)

Stender, Merten; Tiedemann, Merten; Hoffmann, Norbert; Oberst, Sebastian

2018-07-01

Friction-induced vibrations are of major concern in the design of reliable, efficient and comfortable technical systems. Well-known examples for systems susceptible to self-excitation can be found in fluid structure interaction, disk brake squeal, rotor dynamics, hip implants noise and many more. While damping elements and amplitude reduction are well-understood in linear systems, nonlinear systems and especially self-excited dynamics still constitute a challenge for damping element design. Additionally, complex dynamical systems exhibit deterministic chaotic cores which add severe sensitivity to initial conditions to the system response. Especially the complex friction interface dynamics remain a challenging task for measurements and modeling. Today, mostly simple and regular friction models are investigated in the field of self-excited brake system vibrations. This work aims at investigating the effect of high-frequency irregular interface dynamics on the nonlinear dynamical response of a self-excited structure. Special focus is put on the characterization of the system response time series. A low-dimensional minimal model is studied which features self-excitation, gyroscopic effects and friction-induced damping. Additionally, the employed friction formulation exhibits temperature as inner variable and superposed chaotic fluctuations governed by a Lorenz attractor. The time scale of the irregular fluctuations is chosen one order smaller than the overall system dynamics. The influence of those fluctuations on the structural response is studied in various ways, i.e. in time domain and by means of recurrence analysis. The separate time scales are studied in detail and regimes of dynamic interactions are identified. The results of the irregular friction formulation indicate dynamic interactions on multiple time scales, which trigger larger vibration amplitudes as compared to regular friction formulations conventionally studied in the field of friction-induced vibrations.

Deciphering the 3-D distribution of fluid along the shallow Hikurangi subduction zone using P- and S-wave attenuation

NASA Astrophysics Data System (ADS)

Eberhart-Phillips, Donna; Bannister, Stephen; Reyners, Martin

2017-11-01

We use local earthquake velocity spectra to solve for the 3-D distribution of P- and S-wave attenuation in the shallow Hikurangi subduction zone in the North Island of New Zealand to gain insight into how fluids control both the distribution of slip rate deficit and slow-slip events at the shallow plate interface. Qs/Qp gives us information on the 3-D distribution of fluid saturation, which we can compare with the previously determined 3-D distribution of Vp/Vs, which gives information on pore fluid pressure. The Hikurangi margin is unusual, in that a large igneous province (the Hikurangi Plateau) is being subducted. This plateau has had two episodes of subduction-first at 105-100 Ma during north-south convergence with Gondwana, and currently during east-west convergence between the Pacific and Australian plates. We find that in the southern part of the subduction zone, where there is a large deficit in slip rate at the plate interface, the plate interface region is only moderately fluid-rich because the underlying plateau had already had an episode of dehydration during Gondwana subduction. But fluid pressure is relatively high, due to an impermeable terrane in the upper plate trapping fluids below the plate interface. The central part of the margin, where the slip rate deficit is very low, is the most fluid-rich part of the shallow subduction zone. We attribute this to an excess of fluid from the subducted plateau. Our results suggest this part of the plateau has unusually high fracture permeability, on account of it having had two episodes of bending-first at the Gondwana trench and now at the Hikurangi Trough. Qs/Qp is consistent with fluids migrating across the plate interface in this region, leaving it drained and producing high fluid pressure in the overlying plate. The northern part of the margin is a region of heterogeneous deficit in slip rate. Here the Hikurangi Plateau is subducting for the first time, so there is less fluid available from its dehydration than in the central region. Fluid pressure in the overlying plate is high, but Qs/Qp indicates that it is not uniformly fluid-rich. This heterogeneity is consistent with the rough topography of the plateau, including seamounts which entrain fluid-rich sediments. Deep slow-slip events in the southern part of the margin occur where the Moho of the overlying plate meets the plate interface, as typically seen in other deep slow-slip events worldwide. But in the central and northern parts of the margin, the locations of shallow slow-slip events appear to be controlled by a shallow brittle-viscous transition within the fluid-rich upper plate. There is also evidence that a major fault zone in the overlying plate might bleed off some of the high fluid pressure promoting slow-slip events.

Hydraulic pressures generated in magnetic ionic liquids by paramagnetic fluid/air interfaces inside of uniform tangential magnetic fields.

PubMed

Scovazzo, Paul; Portugal, Carla A M; Rosatella, Andreia A; Afonso, Carlos A M; Crespo, João G

2014-08-15

Magnetic Ionic Liquid (MILs), novel magnetic molecules that form "pure magnetic liquids," will follow the Ferrohydrodynamic Bernoulli Relationship. Based on recent literature, the modeling of this fluid system is an open issue and potentially controversial. We imposed uniform magnetic fields parallel to MIL/air interfaces where the capillary forces were negligible, the Quincke Problem. The size and location of the bulk fluid as well as the size and location of the fluid/air interface inside of the magnetic field were varied. MIL properties varied included the density, magnetic susceptibility, chemical structure, and magnetic element. Uniform tangential magnetic fields pulled the MILs up counter to gravity. The forces per area were not a function of the volume, the surface area inside of the magnetic field, or the volume displacement. However, the presence of fluid/air interfaces was necessary for the phenomena. The Ferrohydrodynamic Bernoulli Relationship predicted the phenomena with the forces being directly related to the fluid's volumetric magnetic susceptibility and the square of the magnetic field strength. [emim][FeCl4] generated the greatest hydraulic head (64-mm or 910 Pa at 1.627 Tesla). This work could aid in experimental design, when free surfaces are involved, and in the development of MIL applications. Copyright © 2014 Elsevier Inc. All rights reserved.

Can numerical simulations accurately predict hydrodynamic instabilities in liquid films?

NASA Astrophysics Data System (ADS)

Denner, Fabian; Charogiannis, Alexandros; Pradas, Marc; van Wachem, Berend G. M.; Markides, Christos N.; Kalliadasis, Serafim

2014-11-01

Understanding the dynamics of hydrodynamic instabilities in liquid film flows is an active field of research in fluid dynamics and non-linear science in general. Numerical simulations offer a powerful tool to study hydrodynamic instabilities in film flows and can provide deep insights into the underlying physical phenomena. However, the direct comparison of numerical results and experimental results is often hampered by several reasons. For instance, in numerical simulations the interface representation is problematic and the governing equations and boundary conditions may be oversimplified, whereas in experiments it is often difficult to extract accurate information on the fluid and its behavior, e.g. determine the fluid properties when the liquid contains particles for PIV measurements. In this contribution we present the latest results of our on-going, extensive study on hydrodynamic instabilities in liquid film flows, which includes direct numerical simulations, low-dimensional modelling as well as experiments. The major focus is on wave regimes, wave height and wave celerity as a function of Reynolds number and forcing frequency of a falling liquid film. Specific attention is paid to the differences in numerical and experimental results and the reasons for these differences. The authors are grateful to the EPSRC for their financial support (Grant EP/K008595/1).

Diffuse interface immersed boundary method for multi-fluid flows with arbitrarily moving rigid bodies

NASA Astrophysics Data System (ADS)

Patel, Jitendra Kumar; Natarajan, Ganesh

2018-05-01

We present an interpolation-free diffuse interface immersed boundary method for multiphase flows with moving bodies. A single fluid formalism using the volume-of-fluid approach is adopted to handle multiple immiscible fluids which are distinguished using the volume fractions, while the rigid bodies are tracked using an analogous volume-of-solid approach that solves for the solid fractions. The solution to the fluid flow equations are carried out using a finite volume-immersed boundary method, with the latter based on a diffuse interface philosophy. In the present work, we assume that the solids are filled with a "virtual" fluid with density and viscosity equal to the largest among all fluids in the domain. The solids are assumed to be rigid and their motion is solved using Newton's second law of motion. The immersed boundary methodology constructs a modified momentum equation that reduces to the Navier-Stokes equations in the fully fluid region and recovers the no-slip boundary condition inside the solids. An implicit incremental fractional-step methodology in conjunction with a novel hybrid staggered/non-staggered approach is employed, wherein a single equation for normal momentum at the cell faces is solved everywhere in the domain, independent of the number of spatial dimensions. The scalars are all solved for at the cell centres, with the transport equations for solid and fluid volume fractions solved using a high-resolution scheme. The pressure is determined everywhere in the domain (including inside the solids) using a variable coefficient Poisson equation. The solution to momentum, pressure, solid and fluid volume fraction equations everywhere in the domain circumvents the issue of pressure and velocity interpolation, which is a source of spurious oscillations in sharp interface immersed boundary methods. A well-balanced algorithm with consistent mass/momentum transport ensures robust simulations of high density ratio flows with strong body forces. The proposed diffuse interface immersed boundary method is shown to be discretely mass-preserving while being temporally second-order accurate and exhibits nominal second-order accuracy in space. We examine the efficacy of the proposed approach through extensive numerical experiments involving one or more fluids and solids, that include two-particle sedimentation in homogeneous and stratified environment. The results from the numerical simulations show that the proposed methodology results in reduced spurious force oscillations in case of moving bodies while accurately resolving complex flow phenomena in multiphase flows with moving solids. These studies demonstrate that the proposed diffuse interface immersed boundary method, which could be related to a class of penalisation approaches, is a robust and promising alternative to computationally expensive conformal moving mesh algorithms as well as the class of sharp interface immersed boundary methods for multibody problems in multi-phase flows.

Nanopore Confinement of C-O-H Fluids Relevant to Subsurface Energy Systems

NASA Astrophysics Data System (ADS)

Cole, D. R.

2016-12-01

Complex intermolecular interactions of C-O-H fluids (e.g., H2O, CO2, CH4) result in their unique thermophysical properties, including large deviations in the volumetric properties from ideality, vapor-liquid equilibria, and critical phenomena as these fluids encounter different pressure-temperature-pore network conditions in the crust. Development of a comprehensive understanding of the structures, dynamics, and reactivity at multiple length scales (molecular to macroscopic) over wide ranges of state conditions and composition is foundational to advances in quantifying geochemical processes involving mineral-fluid interfaces. The size, distribution and connectivity of these confined geometries dictate how fluids migrate into and through these micro- and nano-environments, wet and react with the solid. This presentation will provide an overview of the application of state-of-the-art experimental, analytical and computational tools to assess key features of the fluid-matrix interaction. The multidisciplinary approaches highlighted will include neutron scattering and NMR experiments, thermodynamic measurements and molecular-level simulations to quantitatively assess molecular properties of different mixtures of C-O-H fluids in nanpores. Key results include: (1) The addition of a second carbon-bearing phase or water has a profound effect on the competition for sorption sites, phase chemistry and the dynamical properties of all phases present in the pore. (2) Low solubility phases such as methane may exhibit profound increases in concentration in nanopores in the presence of water at elevated pressures and ambient temperature compared to bulk values. (3) Methane permeability through the hydrated pores is strongly dependent on the solid substrate and local properties of confined water, including its structure and, more importantly, evolution of solvation free energy and hydrogen bond structure. (4) Under certain conditions preferential adsorption of the fluids in the narrow pores can produce a shift in the equilibrium distribution of mixed volatiles present in adjoining fractures (aka the bulk portion of the system).

Diffuse-Interface Modelling of Flow in Porous Media

NASA Astrophysics Data System (ADS)

Addy, Doug; Pradas, Marc; Schmuck, Marcus; Kalliadasis, Serafim

2016-11-01

Multiphase flows are ubiquitous in a wide spectrum of scientific and engineering applications, and their computational modelling often poses many challenges associated with the presence of free boundaries and interfaces. Interfacial flows in porous media encounter additional challenges and complexities due to their inherently multiscale behaviour. Here we investigate the dynamics of interfaces in porous media using an effective convective Cahn-Hilliard (CH) equation recently developed in from a Stokes-CH equation for microscopic heterogeneous domains by means of a homogenization methodology, where the microscopic details are taken into account as effective tensor coefficients which are given by a Poisson equation. The equations are decoupled under appropriate assumptions and solved in series using a classic finite-element formulation with the open-source software FEniCS. We investigate the effects of different microscopic geometries, including periodic and non-periodic, at the bulk fluid flow, and find that our model is able to describe the effective macroscopic behaviour without the need to resolve the microscopic details.

Inertial particle manipulation in microscale oscillatory flows

NASA Astrophysics Data System (ADS)

Agarwal, Siddhansh; Rallabandi, Bhargav; Raju, David; Hilgenfeldt, Sascha

2017-11-01

Recent work has shown that inertial effects in oscillating flows can be exploited for simultaneous transport and differential displacement of microparticles, enabling size sorting of such particles on extraordinarily short time scales. Generalizing previous theory efforts, we here derive a two-dimensional time-averaged version of the Maxey-Riley equation that includes the effect of an oscillating interface to model particle dynamics in such flows. Separating the steady transport time scale from the oscillatory time scale results in a simple and computationally efficient reduced model that preserves all slow-time features of the full unsteady Maxey-Riley simulations, including inertial particle displacement. Comparison is made not only to full simulations, but also to experiments using oscillating bubbles as the driving interfaces. In this case, the theory predicts either an attraction to or a repulsion from the bubble interface due to inertial effects, so that versatile particle manipulation is possible using differences in particle size, particle/fluid density contrast and streaming strength. We also demonstrate that these predictions are in agreement with experiments.

Wrinkles, folds, and plasticity in granular rafts

NASA Astrophysics Data System (ADS)

Jambon-Puillet, Etienne; Josserand, Christophe; Protière, Suzie

2017-09-01

We investigate the mechanical response of a compressed monolayer of large and dense particles at a liquid-fluid interface: a granular raft. Upon compression, rafts first wrinkle; then, as the confinement increases, the deformation localizes in a unique fold. This characteristic buckling pattern is usually associated with floating elastic sheets, and as a result, particle laden interfaces are often modeled as such. Here, we push this analogy to its limits by comparing quantitative measurements of the raft morphology to a theoretical continuous elastic model of the interface. We show that, although powerful to describe the wrinkle wavelength, the wrinkle-to-fold transition, and the fold shape, this elastic description does not capture the finer details of the experiment. We describe an unpredicted secondary wavelength, a compression discrepancy with the model, and a hysteretic behavior during compression cycles, all of which are a signature of the intrinsic discrete and frictional nature of granular rafts. It suggests also that these composite materials exhibit both plastic transition and jamming dynamics.

A molecular theory of liquid interfaces.

PubMed

Kovalenko, Andriy; Hirata, Fumio

2005-04-21

We propose a site site generalization of the Lovett-Mow-Buff-Wertheim integro-differential equation for the one-particle density distributions to polyatomic fluids. The method provides microscopic description of liquid interfaces of molecular fluids and solutions. It uses the inhomogeneous site-site direct correlation function of molecular fluid consistently constructed by nonlinear interpolation between the homogeneous ones. The site site correlations of the coexisting bulk phases are obtained from the reference interaction site model (RISM) integral equation with our closure approximation. For illustration, we calculated the structure of the planar liquid-vapor as well as liquid-liquid interfaces of n-hexane and methanol at ambient conditions.

Stability of miscible core?annular flows with viscosity stratification

NASA Astrophysics Data System (ADS)

Selvam, B.; Merk, S.; Govindarajan, Rama; Meiburg, E.

The linear stability of variable viscosity, miscible core-annular flows is investigated. Consistent with pipe flow of a single fluid, the flow is stable at any Reynolds number when the magnitude of the viscosity ratio is less than a critical value. This is in contrast to the immiscible case without interfacial tension, which is unstable at any viscosity ratio. Beyond the critical value of the viscosity ratio, the flow can be unstable even when the more viscous fluid is in the core. This is in contrast to plane channel flows with finite interface thickness, which are always stabilized relative to single fluid flow when the less viscous fluid is in contact with the wall. If the more viscous fluid occupies the core, the axisymmetric mode usually dominates over the corkscrew mode. It is demonstrated that, for a less viscous core, the corkscrew mode is inviscidly unstable, whereas the axisymmetric mode is unstable for small Reynolds numbers at high Schmidt numbers. For the parameters under consideration, the switchover occurs at an intermediate Schmidt number of about 500. The occurrence of inviscid instability for the corkscrew mode is shown to be consistent with the Rayleigh criterion for pipe flows. In some parameter ranges, the miscible flow is seen to be more unstable than its immiscible counterpart, and the physical reasons for this behaviour are discussed.A detailed parametric study shows that increasing the interface thickness has a uniformly stabilizing effect. The flow is least stable when the interface between the two fluids is located at approximately 0.6 times the tube radius. Unlike for channel flow, there is no sudden change in the stability with radial location of the interface. The instability originates mainly in the less viscous fluid, close to the interface.

Competitive Adsorption between Nanoparticles and Surface Active Ions for the Oil-Water Interface.

PubMed

Hua, Xiaoqing; Bevan, Michael A; Frechette, Joelle

2018-04-24

Nanoparticles (NPs) can add functionality (e.g., catalytic, optical, rheological) to an oil-water interface. Adsorption of ∼10 nm NPs can be reversible; however, the mechanisms for adsorption and its effects on surface pressure remain poorly understood. Here we demonstrate how the competitive reversible adsorption of NPs and surfactants at fluid interfaces can lead to independent control of both the adsorbed amount and surface pressure. In contrast to prior work, both species investigated (NPs and surfactants) interact reversibly with the interface and without the surface active species binding to NPs. Independent measurements of the adsorption and surface pressure isotherms allow determination of the equation of state (EOS) of the interface under conditions where the NPs and surfactants are both in dynamic equilibrium with the bulk phase. The adsorption and surface pressure measurements are performed with gold NPs of two different sizes (5 and 10 nm), at two pH values, and across a wide concentration range of surfactant (tetrapentylammonium, TPeA + ) and NPs. We show that free surface active ions compete with NPs for the interface and give rise to larger surface pressures upon the adsorption of NPs. Through a competitive adsorption model, we decouple the contributions of NPs wetting at the interface and their surface activity on the measured surface pressure. We also demonstrate reversible control of adsorbed amount via changes in the surfactant concentration or the aqueous phase pH.

A sharp interface Cartesian grid method for viscous simulation of shocked particle-laden flows

NASA Astrophysics Data System (ADS)

Das, Pratik; Sen, Oishik; Jacobs, Gustaaf; Udaykumar, H. S.

2017-09-01

A Cartesian grid-based sharp interface method is presented for viscous simulations of shocked particle-laden flows. The moving solid-fluid interfaces are represented using level sets. A moving least-squares reconstruction is developed to apply the no-slip boundary condition at solid-fluid interfaces and to supply viscous stresses to the fluid. The algorithms developed in this paper are benchmarked against similarity solutions for the boundary layer over a fixed flat plate and against numerical solutions for moving interface problems such as shock-induced lift-off of a cylinder in a channel. The framework is extended to 3D and applied to calculate low Reynolds number steady supersonic flow over a sphere. Viscous simulation of the interaction of a particle cloud with an incident planar shock is demonstrated; the average drag on the particles and the vorticity field in the cloud are compared to the inviscid case to elucidate the effects of viscosity on momentum transfer between the particle and fluid phases. The methods developed will be useful for obtaining accurate momentum and heat transfer closure models for macro-scale shocked particulate flow applications such as blast waves and dust explosions.

A computational method for sharp interface advection.

PubMed

Roenby, Johan; Bredmose, Henrik; Jasak, Hrvoje

2016-11-01

We devise a numerical method for passive advection of a surface, such as the interface between two incompressible fluids, across a computational mesh. The method is called isoAdvector, and is developed for general meshes consisting of arbitrary polyhedral cells. The algorithm is based on the volume of fluid (VOF) idea of calculating the volume of one of the fluids transported across the mesh faces during a time step. The novelty of the isoAdvector concept consists of two parts. First, we exploit an isosurface concept for modelling the interface inside cells in a geometric surface reconstruction step. Second, from the reconstructed surface, we model the motion of the face-interface intersection line for a general polygonal face to obtain the time evolution within a time step of the submerged face area. Integrating this submerged area over the time step leads to an accurate estimate for the total volume of fluid transported across the face. The method was tested on simple two-dimensional and three-dimensional interface advection problems on both structured and unstructured meshes. The results are very satisfactory in terms of volume conservation, boundedness, surface sharpness and efficiency. The isoAdvector method was implemented as an OpenFOAM ® extension and is published as open source.

An efficient mass-preserving interface-correction level set/ghost fluid method for droplet suspensions under depletion forces

NASA Astrophysics Data System (ADS)

Ge, Zhouyang; Loiseau, Jean-Christophe; Tammisola, Outi; Brandt, Luca

2018-01-01

Aiming for the simulation of colloidal droplets in microfluidic devices, we present here a numerical method for two-fluid systems subject to surface tension and depletion forces among the suspended droplets. The algorithm is based on an efficient solver for the incompressible two-phase Navier-Stokes equations, and uses a mass-conserving level set method to capture the fluid interface. The four novel ingredients proposed here are, firstly, an interface-correction level set (ICLS) method; global mass conservation is achieved by performing an additional advection near the interface, with a correction velocity obtained by locally solving an algebraic equation, which is easy to implement in both 2D and 3D. Secondly, we report a second-order accurate geometric estimation of the curvature at the interface and, thirdly, the combination of the ghost fluid method with the fast pressure-correction approach enabling an accurate and fast computation even for large density contrasts. Finally, we derive a hydrodynamic model for the interaction forces induced by depletion of surfactant micelles and combine it with a multiple level set approach to study short-range interactions among droplets in the presence of attracting forces.

Statistics of chemical gradients in heterogeneous porous media

NASA Astrophysics Data System (ADS)

Le Borgne, T.; Huck, P. D.; Dentz, M.; Villermaux, E.

2017-12-01

As they create chemical disequilibrium and drive mixing fluxes, spatial gradients in solute concentrations exert a strong control on mixing and biogeochemical reactions in the subsurface. Large concentration gradients may develop in particular at interfaces between surface water and groundwater bodies, such as hyporheic zones, sea water - surface water interfaces or recharge areas. They also develop around contaminant plumes and fluids injected in subsurface operations. While macrodispersion theories predict smooth gradients, decaying in time due to dispersive dissipation, we show that concentration gradients are sustained by flow heterogeneity and have broadly distributed values. We present a general theory predicting the statistics of concentration gradients from the flow heterogeneity (Le Borgne et al., 2017). Analytical predictions are validated from high resolution simulations of transport in heterogeneous Darcy fields ranging from low to high permeability variances and low to high Peclet numbers. This modelling framework hence opens new perspectives for quantifying the dynamics of chemical gradients and the kinetics of associated biogeochemical reactions in heterogeneous subsurface environments.Reference:Le Borgne T., P.D. Huck, M. Dentz and E. Villermaux (2017) Scalar gradients in stirred mixtures and the deconstruction of random fields, J. of Fluid Mech. vol. 812, pp. 578-610 doi:10.1017/jfm.2016.799

The buoyancy-driven motion of a single skirted bubble or drop rising through a viscous liquid

NASA Astrophysics Data System (ADS)

Ohta, Mitsuhiro; Sussman, Mark

2012-11-01

The buoyancy-driven motion of a single skirted bubble or drop rising through a viscous liquid is computationally explored by way of 3d-axisymmetric computations. The Navier-Stokes equations for incompressible two-fluid flow are solved numerically in which the coupled level-set and volume-of-fluid method is used to simulate the deforming bubble/drop boundary and the interface jump conditions on the deforming boundary are enforced through a sharp interface numerical treatment. Dynamic, block structured adaptive grid refinement is employed in order to sufficiently resolve the thin skirts. Results on the sensitivity of the thickness of trailing bubble/drop skirts to the density ratio and viscosity ratio are reported. It is shown that both the density ratio (not the density difference) and the viscosity ratio effect the skirt thickness. Previous theory for predicting skirt thickness can be refined as a result of our calculations. It is also discovered that the formation of thin skirts for bubbles and drops have little effect on the rise velocity. In other words, the measured Re number for cases without skirt formation have almost the same values for Re as cases with a thin skirt.

Splay fault branching from the Hikurangi subduction shear zone: Implications for slow slip and fluid flow

NASA Astrophysics Data System (ADS)

Plaza-Faverola, A.; Henrys, S.; Pecher, I.; Wallace, L.; Klaeschen, D.

2016-12-01

Prestack depth migration data across the Hikurangi margin, East Coast of the North Island, New Zealand, are used to derive subducting slab geometry, upper crustal structure, and seismic velocities resolved to ˜14 km depth. We investigate the potential relationship between the crustal architecture, fluid migration, and short-term geodetically determined slow slip events. The subduction interface is a shallow dipping thrust at <7 km depth near the trench and steps down to 14 km depth along an ˜18 km long ramp, beneath Porangahau Ridge. This apparent step in the décollement is associated with splay fault branching and coincides with a zone of maximum slip (90 mm) inferred on the subduction interface during slow slip events in June and July 2011. A low-velocity zone beneath the plate interface, updip of the plate interface ramp, is interpreted as fluid-rich overpressured sediments capped with a low permeability condensed layer of chalk and interbedded mudstones. Fluid-rich sediments have been imbricated by splay faults in a region that coincides with the step down in the décollement from the top of subducting sediments to the oceanic crust and contribute to spatial variation in frictional properties of the plate interface that may promote slow slip behavior in the region. Further, transient fluid migration along splay faults at Porangahau Ridge may signify stress changes during slow slip.

Interface Configuration Experiments (ICE) Explore the Effects of Microgravity on Fluids

NASA Technical Reports Server (NTRS)

1996-01-01

The Interface Configuration Experiment (ICE) is actually a series of experiments that explore the striking behavior of liquid-vapor interfaces (i.e., fluid surfaces) in a low gravity environment under which major shifts in liquid position can arise from small changes in container shape or contact angle. Although these experiments are designed to test current mathematical theory, there are numerous practical applications that could result from these studies. When designing fluid management systems for space-based operations, it is important to be able to predict the locations and configurations that fluids will assume in containers under low-gravity conditions. The increased ability to predict, and hence control, fluid interfaces is vital to systems and/or processes where capillary forces play a significant role both in space and on the Earth. Some of these applications are in general coating processes (paints, pesticides, printing, etc.), fluid transport in porous media (ground water flows, oil recovery, etc.), liquid propellant systems in space (liquid fuel and oxygen), capillary-pumped loops and heat pipes, and space-based life-support systems. In space, almost every fluid system is affected, if not dominated, by capillarity. Knowledge of the liquid-vapor interface behavior, and in particular the interface shape from which any analysis must begin, is required as a foundation to predict how these fluids will react in microgravity and on Earth. With such knowledge, system designs can be optimized, thereby decreasing costs and complexity, while increasing performance and reliability. ICE has increased, and will continue to increase this knowledge, as it probes the specific peculiarities of current theory upon which our current understanding of these effects is based. Several versions of ICE were conducted in NASA Lewis Research Center's drop towers and on the space shuttle during the first and second United States Microgravity Laboratory missions (USML-1 and USML-2). Additional tests are planned for the space shuttle and for the Russian Mir space station. These studies will focus on interfacial problems concerning surface existence, uniqueness, configuration, stability, and flow characteristics.

Rational rates of uniform decay for strong solutions to a fluid-structure PDE system

NASA Astrophysics Data System (ADS)

Avalos, George; Bucci, Francesca

2015-06-01

In this work we investigate the uniform stability properties of solutions to a well-established partial differential equation (PDE) model for a fluid-structure interaction. The PDE system under consideration comprises a Stokes flow which evolves within a three-dimensional cavity; moreover, a Kirchhoff plate equation is invoked to describe the displacements along a (fixed) portion - say, Ω - of the cavity wall. Contact between the respective fluid and structure dynamics occurs on the boundary interface Ω. The main result in the paper is as follows: the solutions to the composite PDE system, corresponding to smooth initial data, decay at the rate of O (1 / t). Our method of proof hinges upon the appropriate invocation of a relatively recent resolvent criterion for polynomial decays of C0-semigroups. While the characterization provided by said criterion originates in the context of operator theory and functional analysis, the work entailed here is wholly within the realm of PDE.

Lagrangian particle method for compressible fluid dynamics

NASA Astrophysics Data System (ADS)

Samulyak, Roman; Wang, Xingyu; Chen, Hsin-Chiang

2018-06-01

A new Lagrangian particle method for solving Euler equations for compressible inviscid fluid or gas flows is proposed. Similar to smoothed particle hydrodynamics (SPH), the method represents fluid cells with Lagrangian particles and is suitable for the simulation of complex free surface/multiphase flows. The main contributions of our method, which is different from SPH in all other aspects, are (a) significant improvement of approximation of differential operators based on a polynomial fit via weighted least squares approximation and the convergence of prescribed order, (b) a second-order particle-based algorithm that reduces to the first-order upwind method at local extremal points, providing accuracy and long term stability, and (c) more accurate resolution of entropy discontinuities and states at free interfaces. While the method is consistent and convergent to a prescribed order, the conservation of momentum and energy is not exact and depends on the convergence order. The method is generalizable to coupled hyperbolic-elliptic systems. Numerical verification tests demonstrating the convergence order are presented as well as examples of complex multiphase flows.

Growth and Morphology of Supercritical Fluids Studied in Microgravity on Mir

NASA Technical Reports Server (NTRS)

Wilkinson, R. Allen

2000-01-01

The Growth and Morphology of Supercritical Fluids (GMSF) is an international experiment facilitated by the NASA Glenn Research Center at Lewis Field and under the guidance of U.S. principal investigator Professor John Hegseth of the University of New Orleans and three French coinvestigators Daniel Beysens, Yves Garrabos, and Carole Chabot. In early 1999, GMSF experiments were operated for 20 days on the Russian Space Station Mir. Mir astronauts performed experiments One through Seven, which spanned the three science themes of near-critical phase separation rates, interface dynamics in near-critical boiling, and measurement of the spectrum of density fluctuation length scales very close to the critical point. The fluids used were pure CO2 or SF6. Three of the five thermostats used could adjust the sample volume with the scheduled crew time. Such a volume adjustment enabled variable sample densities around the critical density as well as pressure steps (as distinct from the usual temperature steps) to be applied to the sample.

Direct measurement of friction of a fluctuating contact line

NASA Astrophysics Data System (ADS)

Guo, Shuo; Gao, Min; Xiong, Xiaomin; Wang, Yong Jian; Wang, Xiaoping; Sheng, Ping; Tong, Penger

2013-03-01

What happens at a moving contact line, where one fluid displaces another (immiscible) fluid over a solid surface, is a fundamental issue in fluid dynamics. In this presentation, we report a direct measurement of the friction coefficient in the immediate vicinity of a fluctuating contact line using a micron-sized vertical glass fiber with one end glued to an atomic force microscope (AFM) cantilever beam and the other end touching a liquid-air interface. By measuring the broadening of the resonance peak of the cantilever system with varying liquid viscosity η, we obtain the friction coefficient ξc associated with the contact line fluctuations on the glass fiber of diameter d and find it has the universal form, ξc = 0 . 8 πdη , independent of the contact angle. The result is further confirmed by using a soap film system whose bulk effect is negligibly small. This is the first time that the friction coefficient of a fluctuating contact line is measured. *Work supported by the Research Grants Council of Hong Kong SAR.

Dynamical Modeling of Surface Tension

NASA Technical Reports Server (NTRS)

Brackbill, Jeremiah U.; Kothe, Douglas B.

1996-01-01

In a recent review it is said that free-surface flows 'represent some of the difficult remaining challenges in computational fluid dynamics'. There has been progress with the development of new approaches to treating interfaces, such as the level-set method and the improvement of older methods such as the VOF method. A common theme of many of the new developments has been the regularization of discontinuities at the interface. One example of this approach is the continuum surface force (CSF) formulation for surface tension, which replaces the surface stress given by Laplace's equation by an equivalent volume force. Here, we describe how CSF formulation might be made more useful. Specifically, we consider a derivation of the CSF equations from a minimization of surface energy as outlined by Jacqmin (1996). This reformulation suggests that if one eliminates the computation of curvature in terms of a unit normal vector, parasitic currents may be eliminated. For this reformulation to work, it is necessary that transition region thickness be controlled. Various means for this, in addition to the one discussed by Jacqmin (1996), are discussed.

Multi-layer porous fiber-reinforced composites for implants: in vitro calcium phosphate formation in the presence of bioactive glass.

PubMed

Nganga, Sara; Zhang, Di; Moritz, Niko; Vallittu, Pekka K; Hupa, Leena

2012-11-01

Glass-fiber-reinforced composites (FRCs), based on bifunctional methacrylate resin, have recently shown their potential for use as durable cranioplasty, orthopedic and oral implants. In this study we suggest a multi-component sandwich implant structure with (i) outer layers out of porous FRC, which interface the cortical bone, and (ii) inner layers encompassing bioactive glass granules, which interface with the cancellous bone. The capability of Bioglass(®) 45S5 granules (100-250μm) to induce calcium phosphate formation on the surface of the FRC was explored by immersing the porous FRC-Bioglass laminates in simulated body fluid (SBF) for up to 28d. In both static (agitated) and dynamic conditions, bioactive glass granules induced precipitation of calcium phosphate at the laminate surfaces as confirmed by scanning electron microscopy. The proposed dynamic flow system is useful for the in vitro simulation of bone-like apatite formation on various new porous implant designs containing bioactive glass and implant material degradation. Copyright © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Implementation of Interaction Algorithm to Non-Matching Discrete Interfaces Between Structure and Fluid Mesh

NASA Technical Reports Server (NTRS)

Chen, Shu-Po

1999-01-01

This paper presents software for solving the non-conforming fluid structure interfaces in aeroelastic simulation. It reviews the algorithm of interpolation and integration, highlights the flexibility and the user-friendly feature that allows the user to select the existing structure and fluid package, like NASTRAN and CLF3D, to perform the simulation. The presented software is validated by computing the High Speed Civil Transport model.

Attachment of composite porous supra-particles to air-water and oil-water interfaces: theory and experiment.

PubMed

Paunov, Vesselin N; Al-Shehri, Hamza; Horozov, Tommy S

2016-09-29

We developed and tested a theoretical model for the attachment of fluid-infused porous supra-particles to a fluid-liquid interface. We considered the wetting behaviour of agglomerated clusters of particles, typical of powdered materials dispersed in a liquid, as well as of the adsorption of liquid-infused colloidosomes at the liquid-fluid interface. The free energy of attachment of a composite spherical porous supra-particle made from much smaller aggregated spherical particles to the oil-water interface was calculated. Two cases were considered: (i) a water-filled porous supra-particle adsorbed at the oil-water interface from the water phase, and, (ii) an oil-filled porous supra-particle adsorbed at the oil-water interface from the oil-phase. We derived equations relating the three-phase contact angle of the smaller "building block" particles and the contact angle of the liquid-infused porous supra-particles. The theory predicts that the porous supra-particle contact angle attached at the liquid interface strongly depends on the type of fluid infused in the particle pores and the fluid phase from which it approaches the liquid interface. We tested the theory by using millimetre-sized porous supra-particles fabricated by evaporation of droplets of polystyrene latex suspension on a pre-heated super-hydrophobic surface, followed by thermal annealing at the glass transition temperature. Such porous particles were initially infused with water or oil and approached to the oil-water interface from the infusing phase. The experiment showed that when attaching at the hexadecane-water interface, the porous supra-particles behaved as hydrophilic when they were pre-filled with water and hydrophobic when they were pre-filled with hexadecane. The results agree with the theoretically predicted contact angles for the porous composite supra-particles based on the values of the contact angles of their building block latex particles measured with the Gel Trapping Technique. The experimental data for the attachment of porous supra particles to the air-water interface from both air and water also agree with the theoretical model. This study gives important insights about how porous particles and particle aggregates attach to the oil-water interface in Pickering emulsions and the air-water surface in particle-stabilised aqueous foams relevant in ore flotation and a range of cosmetic, pharmaceutical, food, home and personal care formulations.

Effect of a relative phase of waves constituting the initial perturbation and the wave interference on the dynamics of strong-shock-driven Richtmyer-Meshkov flows

NASA Astrophysics Data System (ADS)

Pandian, Arun; Stellingwerf, Robert F.; Abarzhi, Snezhana I.

2017-07-01

While it is a common wisdom that initial conditions influence the evolution of the Richtmyer-Meshkov instability (RMI), the research in this area is focused primarily on the effects of the wavelength and amplitude of the interface perturbation. The information has hitherto largely ignored the influences on RMI dynamics of the relative phase of waves constituting a multiwave initial perturbation and the interference of the perturbation waves. In this work we systematically study the influence of the relative phase and the interference of waves constituting a multiwave initial perturbation on a strong-shock-driven Richtmyer-Meshkov unstable interface separating ideal fluids with contrast densities. We apply group theory analysis and smoothed particle hydrodynamics numerical simulations. For verification and validation of the simulations, qualitative and quantitative comparisons are performed with rigorous zeroth-order, linear, and nonlinear theories as well as with gas dynamics experiments achieving good agreement. For a sample case of a two-wave (two-mode) initial perturbation we select the first-wave amplitude enabling the maximum initial growth rate of the RMI and we vary the second-wave amplitude from 1% to 100% of the first-wave amplitude. We also vary the relative phase of the first and second waves and consider the in-phase, the antiphase and the random-phase cases. We find that the relative phase and the interference of waves are important factors of RMI dynamics influencing qualitatively and quantitatively the symmetry, morphology, and growth rate of the Richtmyer-Meshkov unstable interface, as well as the order and disorder in strong-shock-driven RMI.

Detonation Propagation through Nitromethane Embedded Metal Foam

NASA Astrophysics Data System (ADS)

Lieberthal, Brandon; Maines, Warren R.; Stewart, D. Scott

2015-11-01

There is considerable interest in developing a better understanding of dynamic behaviors of multicomponent systems. We report results of Eulerian hydrodynamic simulations of shock waves propagating through metal foam at approximately 20% relative density and various porosities using a reactive flow model in the ALE3D software package. We investigate the applied pressure and energy of the shock wave and its effects on the fluid and the inert material interface. By varying pore sizes, as well as metal impedance, we predict the overall effects of heterogeneous material systems at the mesoscale. In addition, we observe a radially expanding blast front in these heterogeneous models and apply the theory of Detonation Shock Dynamics to the convergence behavior of the lead shock.

Self-Assembled Magnetic Surface Swimmers: Theoretical Model

NASA Astrophysics Data System (ADS)

Aranson, Igor; Belkin, Maxim; Snezhko, Alexey

2009-03-01

The mechanisms of self-propulsion of living microorganisms are a fascinating phenomenon attracting enormous attention in the physics community. A new type of self-assembled micro-swimmers, magnetic snakes, is an excellent tool to model locomotion in a simple table-top experiment. The snakes self-assemble from a dispersion of magnetic microparticles suspended on the liquid-air interface and subjected to an alternating magnetic field. Formation and dynamics of these swimmers are captured in the framework of theoretical model coupling paradigm equation for the amplitude of surface waves, conservation law for the density of particles, and the Navier-Stokes equation for hydrodynamic flows. The results of continuum modeling are supported by hybrid molecular dynamics simulations of magnetic particles floating on the surface of fluid.

Experimental study of the heated contact line region for a pure fluid and binary fluid mixture in microgravity.

PubMed

Nguyen, Thao T T; Kundan, Akshay; Wayner, Peter C; Plawsky, Joel L; Chao, David F; Sicker, Ronald J

2017-02-15

Understanding the dynamics of phase change heat and mass transfer in the three-phase contact line region is a critical step toward improving the efficiency of phase change processes. Phase change becomes especially complicated when a fluid mixture is used. In this paper, a wickless heat pipe was operated on the International Space Station (ISS) to study the contact line dynamics of a pentane/isohexane mixture. Different interfacial regions were identified, compared, and studied. Using high resolution (50×), interference images, we calculated the curvature gradient of the liquid-vapor interface at the contact line region along the edges of the heat pipe. We found that the curvature gradient in the evaporation region increases with increasing heat flux magnitude and decreasing pentane concentration. The curvature gradient for the mixture case is larger than for the pure pentane case. The difference between the two cases increases as pentane concentration decreases. Our data showed that the curvature gradient profile within the evaporation section is separated into two regions with the boundary between the two corresponding to the location of a thick, liquid, "central drop" region at the point of maximum internal local heat flux. We found that the curvature gradients at the central drop and on the flat surfaces where condensation begins are one order of magnitude smaller than the gradients in the corner meniscus indicating the driving forces for fluid flow are much larger in the corners. Copyright © 2016 Elsevier Inc. All rights reserved.

An experimental study of miscible viscous fingering of annular ring

NASA Astrophysics Data System (ADS)

Nagatsu, Yuichiro; Othman, Hamirul Bin; Mishra, Manoranjan

2017-11-01

Understanding the viscous fingering (VF) dynamics of finite width sample is important in the fields especially such as liquid chromatography and groundwater contamination and mixing in microfluidics. In this paper, we experimentally investigate such hydrodynamical morphology of VF using a Hele-Shaw flow system in which a miscible annular ring of fluid is displaced radially. Experiments are performed to investigate the effects of the sample volume, the effects of dispersion and log mobility ratio R on the dynamics of VF pattern and onset of such instability. Depending whether the finite width ring is more or less viscous than the carrier fluid, the log mobility ratio R becomes positive or negative respectively. The experiments are successfully conducted to obtain the VF patterns for R>0 and R<0, of the finite annular ring at the inner and outer radial interfaces, respectively. It is found that in the radial displacement, the inward finger moves slower than the outward finger. The experimental results are found to be qualitatively in good agreement with the corresponding linear stability analysis and non-linear simulations results available in the literature.

Immersed boundary methods for simulating fluid-structure interaction

NASA Astrophysics Data System (ADS)

Sotiropoulos, Fotis; Yang, Xiaolei

2014-02-01

Fluid-structure interaction (FSI) problems commonly encountered in engineering and biological applications involve geometrically complex flexible or rigid bodies undergoing large deformations. Immersed boundary (IB) methods have emerged as a powerful simulation tool for tackling such flows due to their inherent ability to handle arbitrarily complex bodies without the need for expensive and cumbersome dynamic re-meshing strategies. Depending on the approach such methods adopt to satisfy boundary conditions on solid surfaces they can be broadly classified as diffused and sharp interface methods. In this review, we present an overview of the fundamentals of both classes of methods with emphasis on solution algorithms for simulating FSI problems. We summarize and juxtapose different IB approaches for imposing boundary conditions, efficient iterative algorithms for solving the incompressible Navier-Stokes equations in the presence of dynamic immersed boundaries, and strong and loose coupling FSI strategies. We also present recent results from the application of such methods to study a wide range of problems, including vortex-induced vibrations, aquatic swimming, insect flying, human walking and renewable energy. Limitations of such methods and the need for future research to mitigate them are also discussed.

Fluid Dynamics of Competitive Swimming: A Computational Study

NASA Astrophysics Data System (ADS)

Mittal, Rajat; Loebbeck, Alfred; Singh, Hersh; Mark, Russell; Wei, Timothy

2004-11-01

The dolphin kick is an important component in competitive swimming and is used extensively by swimmers immediately following the starting dive as well as after turns. In this stroke, the swimmer swims about three feet under the water surface and the stroke is executed by performing an undulating wave-like motion of the body that is quite similar to the anguilliform propulsion mode in fish. Despite the relatively simple kinematics of this stoke, considerable variability in style and performance is observed even among Olympic level swimmers. Motivated by this, a joint experimental-numerical study has been initiated to examine the fluid-dynamics of this stroke. The current presentation will describe the computational portion of this study. The computations employ a sharp interface immersed boundary method (IBM) which allows us to simulate flows with complex moving boudnaries on stationary Cartesian grids. 3D body scans of male and female Olympic swimmers have been obtained and these are used in conjuction with high speed videos to recreate a realistic dolphin kick for the IBM solver. Preliminary results from these computations will be presented.

Advances in the Application of High-order Techniques in Simulation of Multi-disciplinary Phenomena

NASA Astrophysics Data System (ADS)

Gaitonde, D. V.; Visbal, M. R.

2003-03-01

This paper describes the development of a comprehensive high-fidelity algorithmic framework to simulate the three-dimensional fields associated with multi-disciplinary physics. A wide range of phenomena is considered, from aero-acoustics and turbulence to electromagnetics, non-linear fluid-structure interactions, and magnetogasdynamics. The scheme depends primarily on "spectral-like," up to sixth-order accurate compact-differencing and up to tenth-order filtering techniques. The tightly coupled procedure suppresses numerical instabilities commonly encountered with high-order methods on non-uniform meshes, near computational boundaries or in the simulation of nonlinear dynamics. Particular emphasis is placed on developing the proper metric evaluation procedures for three-dimensional moving and curvilinear meshes so that the advantages of higher-order schemes are retained in practical calculations. A domain-decomposition strategy based on finite-sized overlap regions and interface boundary treatments enables the development of highly scalable solvers. The utility of the method to simulate problems governed by widely disparate governing equations is demonstrated with several examples encompassing vortex dynamics, wave scattering, electro-fluid plasma interactions, and panel flutter.

Steady-state and dynamic models for particle engulfment during solidification

NASA Astrophysics Data System (ADS)

Tao, Yutao; Yeckel, Andrew; Derby, Jeffrey J.

2016-06-01

Steady-state and dynamic models are developed to study the physical mechanisms that determine the pushing or engulfment of a solid particle at a moving solid-liquid interface. The mathematical model formulation rigorously accounts for energy and momentum conservation, while faithfully representing the interfacial phenomena affecting solidification phase change and particle motion. A numerical solution approach is developed using the Galerkin finite element method and elliptic mesh generation in an arbitrary Lagrangian-Eulerian implementation, thus allowing for a rigorous representation of forces and dynamics previously inaccessible by approaches using analytical approximations. We demonstrate that this model accurately computes the solidification interface shape while simultaneously resolving thin fluid layers around the particle that arise from premelting during particle engulfment. We reinterpret the significance of premelting via the definition an unambiguous critical velocity for engulfment from steady-state analysis and bifurcation theory. We also explore the complicated transient behaviors that underlie the steady states of this system and posit the significance of dynamical behavior on engulfment events for many systems. We critically examine the onset of engulfment by comparing our computational predictions to those obtained using the analytical model of Rempel and Worster [29]. We assert that, while the accurate calculation of van der Waals repulsive forces remains an open issue, the computational model developed here provides a clear benefit over prior models for computing particle drag forces and other phenomena needed for the faithful simulation of particle engulfment.

Diffuse-interface approach to rotating Hele-Shaw flows.

PubMed

Chen, Ching-Yao; Huang, Yu-Sheng; Miranda, José A

2011-10-01

When two fluids of different densities move in a rotating Hele-Shaw cell, the interface between them becomes centrifugally unstable and deforms. Depending on the viscosity contrast of the system, distinct types of complex patterns arise at the fluid-fluid boundary. Deformations can also induce the emergence of interfacial singularities and topological changes such as droplet pinch-off and self-intersection. We present numerical simulations based on a diffuse-interface model for this particular two-phase displacement that capture a variety of pattern-forming behaviors. This is implemented by employing a Boussinesq Hele-Shaw-Cahn-Hilliard approach, considering the whole range of possible values for the viscosity contrast, and by including inertial effects due to the Coriolis force. The role played by these two physical contributions on the development of interface singularities is illustrated and discussed.

A continuum treatment of sliding in Eulerian simulations of solid-solid and solid-fluid interfaces

NASA Astrophysics Data System (ADS)

Subramaniam, Akshay; Ghaisas, Niranjan; Lele, Sanjiva

2017-11-01

A novel treatment of sliding is developed for use in an Eulerian framework for simulating elastic-plastic deformations of solids coupled with fluids. In this method, embedded interfacial boundary conditions for perfect sliding are imposed by enforcing the interface normal to be a principal direction of the Cauchy stress and appropriate consistency conditions ensure correct transmission and reflection of waves at the interface. This sliding treatment may be used either to simulate a solid-solid sliding interface or to incorporate an internal slip boundary condition at a solid-fluid interface. Sliding laws like the Coulomb friction law can also be incorporated with relative ease into this framework. Simulations of sliding interfaces are conducted using a 10th order compact finite difference scheme and a Localized Artificial Diffusivity (LAD) scheme for shock and interface capturing. 1D and 2D simulations are used to assess the accuracy of the sliding treatment. The Richmyer-Meshkov instability between copper and aluminum is simulated with this sliding treatment as a demonstration test case. Support for this work was provided through Grant B612155 from the Lawrence Livermore National Laboratory, US Department of Energy.