Hydrodynamical Dispersion in Taylor-Couette Cells
NASA Astrophysics Data System (ADS)
Piva, M.; Calvo, A.; Aguirre, A.; Callegari, G.; Gabbanelli, S.; Rosen, M.; Wesfreid, J. E.
1997-04-01
In this article we study the mass tracer dispersion in organized flows. For this purpose we performed experiments in the flow arising from the Taylor-Couette hydrodynamic instability combined with axial flow. The tracer evolution is followed by means of optical measurements of the concentration. In this way transmission curves are obtained. We compare these curves with the solutions of the Gaussian models of mass diffusion and with phenomenological models including tracer trapping in the cells. This comparison gives us physical parameters related to the typical time and distances involved in the diffusive behaviour of tracers in the regions with recirculations and trapping.
Structure parameters in rotating Couette-Poiseuille channel flow
NASA Technical Reports Server (NTRS)
Knightly, George H.; Sather, D.
1986-01-01
It is well-known that a number of steady state problems in fluid mechanics involving systems of nonlinear partial differential equations can be reduced to the problem of solving a single operator equation of the form: v + lambda Av + lambda B(v) = 0, v is the summation of H, lambda is the summation of one-dimensional Euclid space, where H is an appropriate (real or complex) Hilbert space. Here lambda is a typical load parameter, e.g., the Reynolds number, A is a linear operator, and B is a quadratic operator generated by a bilinear form. In this setting many bifurcation and stability results for problems were obtained. A rotating Couette-Poiseuille channel flow was studied, and it showed that, in general, the superposition of a Poiseuille flow on a rotating Couette channel flow is destabilizing.
Computational modeling of flow and combustion in a couette channel simulating microgravity
NASA Astrophysics Data System (ADS)
Hamdan, Ghaleb
Theoretically a Couette flow in a narrow channel can be utilized to simulate microgravity conditions experienced by a surface flame due to the linear velocity profile. Hence, the Couette channel is a potential apparatus for the study of flame spread in an environment that recreated microgravity flow conditions. Simulated microgravity conditions were achieved by limiting the vertical extent over and under the flame to suppress buoyancy. This numerical study was done for a 2-D channel using Fire Dynamics Simulator (FDS). This thesis is divided into two sections; the first is the study of Couette flow with a non-reacting cold flow in a finite length channel, a subject with surprisingly little past research, despite the ubiquity of "infinite" Couette channels in text books. The channel was placed in a room to allow for a better representation of a realistic channel and allow the flow and pressure field to develop without forcing them at the inlet and outlet. The plate's velocities, channel's gap and the channel's length were varied and the results of the u-velocity profile, w-velocity profile and pressure were investigated. The entrance length relationship with Reynolds number for a finite Couette Channel was determined for the first time - as far as the author knows - in order to ensure the flame occurs in a fully developed flow. In contrast to an infinite channel, the u-velocity was found to be nonlinear due to an adverse pressure differential created along the channel attributed to the pull force along the entrance of the channel created by the top plate a well as the pressure differential created by the flow exiting the channel. The linearity constant was derived for the one moving plate case. The domain consisted of a rectangular region with the top plate moving and the bottom plate fixed except for a few cases in which the bottom plate also moved and were compared with only one moving plate. The second section describes the combustion of a thin cellulose sample
Nondecaying Hydrodynamic Interactions along Narrow Channels
NASA Astrophysics Data System (ADS)
Misiunas, Karolis; Pagliara, Stefano; Lauga, Eric; Lister, John R.; Keyser, Ulrich F.
2015-07-01
Particle-particle interactions are of paramount importance in every multibody system as they determine the collective behavior and coupling strength. Many well-known interactions such as electrostatic, van der Waals, or screened Coulomb interactions, decay exponentially or with negative powers of the particle spacing r . Similarly, hydrodynamic interactions between particles undergoing Brownian motion decay as 1 /r in bulk, and are assumed to decay in small channels. Such interactions are ubiquitous in biological and technological systems. Here we confine two particles undergoing Brownian motion in narrow, microfluidic channels and study their coupling through hydrodynamic interactions. Our experiments show that the hydrodynamic particle-particle interactions are distance independent in these channels. This finding is of fundamental importance for the interpretation of experiments where dense mixtures of particles or molecules diffuse through finite length, water-filled channels or pore networks.
Nondecaying Hydrodynamic Interactions along Narrow Channels.
Misiunas, Karolis; Pagliara, Stefano; Lauga, Eric; Lister, John R; Keyser, Ulrich F
2015-07-17
Particle-particle interactions are of paramount importance in every multibody system as they determine the collective behavior and coupling strength. Many well-known interactions such as electrostatic, van der Waals, or screened Coulomb interactions, decay exponentially or with negative powers of the particle spacing r. Similarly, hydrodynamic interactions between particles undergoing Brownian motion decay as 1/r in bulk, and are assumed to decay in small channels. Such interactions are ubiquitous in biological and technological systems. Here we confine two particles undergoing Brownian motion in narrow, microfluidic channels and study their coupling through hydrodynamic interactions. Our experiments show that the hydrodynamic particle-particle interactions are distance independent in these channels. This finding is of fundamental importance for the interpretation of experiments where dense mixtures of particles or molecules diffuse through finite length, water-filled channels or pore networks. PMID:26230830
Hydrodynamic resistance and mobility of deformable objects in microfluidic channels
Sajeesh, P.; Doble, M.; Sen, A. K.
2014-01-01
This work reports experimental and theoretical studies of hydrodynamic behaviour of deformable objects such as droplets and cells in a microchannel. Effects of mechanical properties including size and viscosity of these objects on their deformability, mobility, and induced hydrodynamic resistance are investigated. The experimental results revealed that the deformability of droplets, which is quantified in terms of deformability index (D.I.), depends on the droplet-to-channel size ratio ρ and droplet-to-medium viscosity ratio λ. Using a large set of experimental data, for the first time, we provide a mathematical formula that correlates induced hydrodynamic resistance of a single droplet ΔRd with the droplet size ρ and viscosity λ. A simple theoretical model is developed to obtain closed form expressions for droplet mobility ϕ and ΔRd. The predictions of the theoretical model successfully confront the experimental results in terms of the droplet mobility ϕ and induced hydrodynamic resistance ΔRd. Numerical simulations are carried out using volume-of-fluid model to predict droplet generation and deformation of droplets of different size ratio ρ and viscosity ratio λ, which compare well with that obtained from the experiments. In a novel effort, we performed experiments to measure the bulk induced hydrodynamic resistance ΔR of different biological cells (yeast, L6, and HEK 293). The results reveal that the bulk induced hydrodynamic resistance ΔR is related to the cell concentration and apparent viscosity of the cells. PMID:25538806
Hydrodynamic resistance and mobility of deformable objects in microfluidic channels.
Sajeesh, P; Doble, M; Sen, A K
2014-09-01
This work reports experimental and theoretical studies of hydrodynamic behaviour of deformable objects such as droplets and cells in a microchannel. Effects of mechanical properties including size and viscosity of these objects on their deformability, mobility, and induced hydrodynamic resistance are investigated. The experimental results revealed that the deformability of droplets, which is quantified in terms of deformability index (D.I.), depends on the droplet-to-channel size ratio [Formula: see text] and droplet-to-medium viscosity ratio [Formula: see text]. Using a large set of experimental data, for the first time, we provide a mathematical formula that correlates induced hydrodynamic resistance of a single droplet [Formula: see text] with the droplet size [Formula: see text] and viscosity [Formula: see text]. A simple theoretical model is developed to obtain closed form expressions for droplet mobility [Formula: see text] and [Formula: see text]. The predictions of the theoretical model successfully confront the experimental results in terms of the droplet mobility [Formula: see text] and induced hydrodynamic resistance [Formula: see text]. Numerical simulations are carried out using volume-of-fluid model to predict droplet generation and deformation of droplets of different size ratio [Formula: see text] and viscosity ratio [Formula: see text], which compare well with that obtained from the experiments. In a novel effort, we performed experiments to measure the bulk induced hydrodynamic resistance [Formula: see text] of different biological cells (yeast, L6, and HEK 293). The results reveal that the bulk induced hydrodynamic resistance [Formula: see text] is related to the cell concentration and apparent viscosity of the cells. PMID:25538806
Smoothed Particle Hydrodynamics for water wave propagation in a channel
NASA Astrophysics Data System (ADS)
Omidvar, Pourya; Norouzi, Hossein; Zarghami, Ahad
2015-01-01
In this paper, Smoothed Particle Hydrodynamics (SPH) is used to simulate the propagation of waves in an intermediate depth water channel. The major advantage of using SPH is that no special treatment of the free surface is required, which is advantageous for simulating highly nonlinear flows with possible wave breaking. The SPH method has an option of different formulations with their own advantages and drawbacks to be implemented. Here, we apply the classical and Arbitrary Lagrange-Euler (ALE) formulation for wave propagation in a water channel. The classical SPH should come with an artificial viscosity which stabilizes the numerical algorithm and increases the accuracy. Here, we will show that the use of classical SPH with an artificial viscosity may cause the waves in the channel to decay. On the other hand, we will show that using the ALE-SPH algorithm with a Riemann solver is more stable, and in addition to producing the pressure fields with much less numerical noise, the waves propagate in the channel without dissipation.
Fluidic Channels Produced by Electro Hydrodynamic Viscous Fingering
NASA Astrophysics Data System (ADS)
Behler, Kristopher; Wetzel, Eric
2010-03-01
Viscous fingering is a term describing fingerlike extensions of liquid from a column of low viscosity liquid that has been injected into a more viscous liquid. The modification of viscous fingering, known as electro hydrodynamic viscous fingering (EHVF), utilizes large electrical potentials of 10-60 kV. The fingers see a reduction in size and increase in branching behavior due to the potential applied to the system. The resulting finely structured patterns are analogous to biological systems such as blood vessels and the lymphatic system. In this study silicone oils and water were studied in thin channel Hele-Shaw cells. The interfacial tension was optimized by altering the surfactant concentration in the silicone oils. EHVF of liquid filled packed beds consisting of beads and silicone oils showed retardation of the relaxation of the fingers after the voltage was turned off. Decreased relaxation provides a means to solidify patterns into a curable material, such as polydimethylsiloxane (PDMS). After the water is evacuated from the fingers, the cured materials then possess hollow channels that can be refilled and emptied, thus creating an artificial circulatory system.
The Hydrodynamic Stability of Channel Flow with Compliant Boundaries
NASA Astrophysics Data System (ADS)
Gajjar, J. S. B.; Sibanda, P.
1996-03-01
An asymptotic theory is developed for the hydrodynamic stability of an incompressible fluid flowing in a channel in which one wall is rigid and the other is compliant. We exploit the multideck structure of the flow to investigate theoretically the development of disturbances to the flow in the limit of large Reynolds numbers. A simple spring-plate model is used to describe the motion of the compliant wall, and this study considers the effect of the various wall parameters, such as tension, inertia, and damping, on the stability properties. An amplitude equation for a modulated wavetrain is derived and the properties of this equation are studied for a number of cases including linear and nonlinear theory. It is shown that in general the effect of viscoelastic damping is destabilizing. In particular, for large damping, the analysis points to a fast travelling wave, short-scale instability, which may be related to a flutter instability observed in some experiments. This work also demonstrates that the conclusions obtained by previous investigators in which the effect of tension, inertia, and other parameters is neglected, may be misleading. Finally it is shown that a set of compliant-wall parameters exists for which the Haberman type of critical layer analysis leads to stable equilibrium amplitudes, in contrast to many other stability problems where such equilibrium amplitudes are unstable.
Juice irradiation with Taylor-Couette flow: UV inactivation of Escherichia coli.
Forney, L J; Pierson, J A; Ye, Z
2004-11-01
A novel reactor is described with flow characteristics that approach that of ideal plug flow but with a residence time that is uncoupled from the hydrodynamics or boundary layer characteristics. The design described consists of an inner cylinder that rotates within a stationary but larger outer cylinder. At low rotation rates, a laminar, hydrodynamic configuration called Taylor-Couette flow is established, which consists of a system of circumferential vortices within the annular fluid gap. The latter constitutes a spatially periodic flow that is the hydrodynamic equivalent to cross flow over a tube bank or lamp array. These vortices provide radial mixing, reduce the boundary layer thickness, and are independent of the axial flow rate and thus the fluid residence time. An additional feature of the rotating design is the repetitive exposure of the fluid parcels to a minimum number of lamps, which substantially reduces the maintenance requirements. Inactivation data for Escherichia coli (ATCC 15597) were recorded in commercial apple and grape juice that are relatively opaque to UV radiation. With initial E. coli concentrations of approximately 10(6) CFU/ml, Taylor-Couette flow was found to provide a 3- to 5-log improvement in the inactivation efficiency compared with simple channel flow between concentric cylinders. PMID:15553621
Coevolution of hydrodynamics, vegetation and channel evolution in wetlands of a semi-arid floodplain
NASA Astrophysics Data System (ADS)
Seoane, Manuel; Rodriguez, Jose Fernando; Rojas, Steven Sandi; Saco, Patricia Mabel; Riccardi, Gerardo; Saintilan, Neil; Wen, Li
2015-04-01
The Macquarie Marshes are located in the semi-arid region in north western NSW, Australia, and constitute part of the northern Murray-Darling Basin. The Marshes are comprised of a system of permanent and semi-permanent marshes, swamps and lagoons interconnected by braided channels. The wetland complex serves as nesting place and habitat for many species of water birds, fish, frogs and crustaceans, and portions of the Marshes was listed as internationally important under the Ramsar Convention. Some of the wetlands have undergone degradation over the last four decades, which has been attributed to changes in flow management upstream of the marshes. Among the many characteristics that make this wetland system unique is the occurrence of channel breakdown and channel avulsion, which are associated with decline of river flow in the downstream direction typical of dryland streams. Decrease in river flow can lead to sediment deposition, decrease in channel capacity, vegetative invasion of the channel, overbank flows, and ultimately result in channel breakdown and changes in marsh formation. A similar process on established marshes may also lead to channel avulsion and marsh abandonment, with the subsequent invasion of terrestrial vegetation. All the previous geomorphological evolution processes have an effect on the established ecosystem, which will produce feedbacks on the hydrodynamics of the system and affect the geomorphology in return. In order to simulate the complex dynamics of the marshes we have developed an ecogeomorphological modelling framework that combines hydrodynamic, vegetation and channel evolution modules and in this presentation we provide an update on the status of the model. The hydrodynamic simulation provides spatially distributed values of inundation extent, duration, depth and recurrence to drive a vegetation model based on species preference to hydraulic conditions. It also provides velocities and shear stresses to assess geomorphological
NASA Astrophysics Data System (ADS)
Tallapragada, Phanindra; Hasabnis, Nilesh; Katuri, Kalyan; Sudarsanam, Senbagaraman; Joshi, Ketaki; Ramasubramanian, Melur
2015-08-01
The hydrodynamic separation of spherical particles in flows at low Reynolds numbers is a very active area of research in microfluidic engineering due to the many important biomedical applications. In particular, curved channels such as spiral channels are of growing interest because the lift and drag force exerted on inertial particles can be used to hydrodynamically separate the particles. In this paper we present a scale invariant classification of the lateral focusing of particles in highly curved spiral micro channels with a square cross section. We then use this scale invariant classification to demonstrate the separation of particles in two-particle mixtures across a large range of sizes. We thus show that our results can be used to systematically design the geometry of devices and select flow parameters to separate particles by size in a mixture.
NASA Astrophysics Data System (ADS)
Qi, Zhiyuan; Nguyen, Zoom; Park, Cheol; Maclennan, Joe; Maclennan, Matt; Clark, Noel
2012-02-01
The quantization of film thickness in freely suspended fluid smectic liquid crystal film enables the study of the hydrodynamics of drops and interfaces in 2D. We report microfluidic experiments, in which we observe the hydrodynamics of 2D drops flowing in channels. Using high-speed video microscopy, we track the shape of 2D drops and interfaces, visualizing the deterministic lateral displacement-based separation and pinched flow separation phenomena previously observed only in 3D. Finally, we demonstrate techniques for 2D drop generation and sorting, which will be used for 2D microfluidic applications.
Hydrodynamics and heat transfer in a laminar flow of viscoelastic fluid in a flat slot channel
NASA Astrophysics Data System (ADS)
Ananyev, D. V.; Halitova, G. R.; Vachagina, E. K.
2015-01-01
Results of the numerical study of hydrodynamics and heat transfer in a laminar flow of viscoelastic fluid in a flat slot channel are presented in the present paper. The model of nonlinear viscoelastic fluid of Phan-Thien—Tanner is used to describe the viscoelastic properties of fluid. The solution to the stated problem by software package "COMSOL Multiphysics" is considered. The method of solution is verified, and results are compared with data of the other authors. It is determined that in the flow of viscoelastic fluid in a flat slot channel, the maximal contribution of heating due to dissipation is approximately 7-8 %.
Hydrodynamic chromatography and field flow fractionation in finite aspect ratio channels.
Shendruk, T N; Slater, G W
2014-04-25
Hydrodynamic chromatography (HC) and field-flow fractionation (FFF) separation methods are often performed in 3D rectangular channels, though ideal retention theory assumes 2D systems. Devices are commonly designed with large aspect ratios; however, it can be unavoidable or desirable to design rectangular channels with small or even near-unity aspect ratios. To assess the significance of finite-aspect ratio effects and interpret experimental retention results, an ideal, analytical retention theory is needed. We derive a series solution for the ideal retention ratio of HC and FFF rectangular channels. Rather than limiting devices' ability to resolve samples, our theory predicts that retention curves for normal-mode FFF are well approximated by the infinite plate solution and that the performance of HC is actually improved. These findings suggest that FFF devices need not be designed with large aspect ratios and that rectangular HC channels are optimal when the aspect ratio is unity. PMID:24674643
PREFACE: The 15th International Couette-Taylor Worskhop
NASA Astrophysics Data System (ADS)
Mutabazi, Innocent; Crumeyrolle, Olivier
2008-07-01
The 15th International Couette-Taylor Worskhop (ICTW15) was held in Le Havre, France from 9-12 July 2007. This regular international conference started in 1979 in Leeds, UK when the research interest in simple models of fluid flows was revitalized by systematic investigation of Rayleigh-Bénard convection and the Couette-Taylor flow. These two flow systems are good prototypes for the study of the transition to chaos and turbulence in closed flows. The workshop themes have been expanded from the original Couette-Taylor flow to include other centrifugal instabilities (Dean, Görtler, Taylor-Dean), spherical Couette flows, thermal convection instabilities, MHD, nonlinear dynamics and chaos, transition to turbulence, development of numerical and experimental techniques. The impressive longevity of the ICTW is due to the close interaction and fertile exchanges between international research groups from different disciplines: Physics and Astrophysics, Applied Mathematics, Mechanical Engineering, Chemical Engineering. The present workshop was attended by 100 participants, the program included over 83 contributions with 4 plenary lectures, 68 oral communications and 17 posters. The topics include, besides the classical Couette-Taylor flows, the centrifugal flows with longitudinal vortices, the shear flows, the thermal convection in curved geometries, the spherical Couette-Taylor flow, the geophysical flows, the magneto-hydrodynamic effects including the dynamo effect, the complex flows (viscoelasticity, immiscible fluids, bubbles and migration). Selected papers have been processed through the peer review system and are published in this issue of the Journal of Physics: Conference Series. The Workshop has been sponsored by Le Havre University, the Region Council of Haute-Normandie, Le Havre City Council, CNRS (ST2I, GdR-DYCOEC), and the European Space Agency through GEOFLOW program. The French Ministry of Defense (DGA), the Ministry of Foreign Affairs, the Ministry of
Scaling Hydrodynamic Boundary Conditions of Microstructured Surfaces in the Thin Channel Limit.
Pilkington, Georgia A; Gupta, Rohini; Fréchette, Joëlle
2016-03-15
Despite its importance in many applications and processes, a complete and unified view on how nano- and microscale asperities influence hydrodynamic interactions has yet to be reached. In particular, the effects of surface structure can be expected to become more dominant when the length scale of the asperities or textures becomes comparable to that of the fluid flow. Here we analyze the hydrodynamic drainage of a viscous silicone oil squeezed between a smooth plane and a surface decorated with hexagonal arrays of lyophilic microsized cylindrical posts. For all micropost arrays studied, the periodicity of the structures was much larger than the separation range of our measurements. In this thin channel geometry, we find the hydrodynamic drainage and separation forces for the micropost arrays cannot be fully described by existing boundary condition models for interfacial slip or a no-slip shifted plane. Instead, our results show that the influence of the microposts on the hydrodynamic drag exhibits three distinct regimes as a function of separation. For large separations, a no slip boundary condition (Reynolds theory) is observed for all surfaces until a critical (intermediate) separation, below which the position of the no-slip plane scales with surface separation until reaching a maximum, just before contact. Below this separation, a sharp decrease in the no-slip plane position then suggests that a boundary condition of a smooth surface is recovered at contact. PMID:26901492
Hydrodynamic analysis of flagellated bacteria swimming in corners of rectangular channels
NASA Astrophysics Data System (ADS)
Shum, Henry; Gaffney, Eamonn A.
2015-12-01
The influence of nearby solid surfaces on the motility of bacteria is of fundamental importance as these interactions govern the ability of the microorganisms to explore their environment and form sessile colonies. Reducing biofouling in medical implants and controlling the transport of bacterial cells in a microfluidic device are two applications that could benefit from a detailed understanding of swimming in microchannels. In this study, we investigate the self-propelled motion of a model bacterium, driven by rotating a single helical flagellum, in such an environment. In particular, we focus on the corner region of a large channel modeled as two perpendicular sections of no-slip planes joined with a rounded corner. We numerically solve the equations of Stokes flow using the boundary element method to obtain the swimming velocities at different positions and orientations relative to the channel corner. From these velocities, we construct many trajectories to ascertain the general behavior of the swimmers. Considering only hydrodynamic interactions between the bacterium and the channel walls, we show that some swimmers can become trapped near the corner while moving, on average, along the axis of the channel. This result suggests that such bacteria may be found at much higher densities in corners than in other parts of the channel. Another implication is that these corner accumulating bacteria may travel quickly through channels since they are guided directly along the corner and do not turn back or swim transversely across the channel.
Hydrodynamics and sediment suspension in shallow tidal channels intersecting a tidal flat
NASA Astrophysics Data System (ADS)
Pieterse, Aline; Puleo, Jack A.; McKenna, Thomas E.
2016-05-01
A field study was conducted on a tidal flat intersected by small tidal channels (depth <0.1 m, width <2 m) within a tidal marsh. Data were collected in the channels, and on the adjacent tidal flat that encompasses approximately 1600 m2 in planform area. Hydrodynamic processes and sediment suspension between the channels and adjacent flat were compared. Shear stress and turbulent kinetic energy were computed from high frequency velocity measurements. Maximum water depth at the field site varied from 0.11 m during the lowest neap high tide to 0.58 m during a storm event. In the channel intersecting the tidal flat, the shear stress, turbulence and along-channel velocity were ebb dominant; e.g. 0.33 m/s peak velocity for ebb compared to 0.19 m/s peak velocity for flood. Distinct pulses in velocity occurred when the water level was near the tidal flat level. The velocity pulse during flood tide occurred at a higher water level than during ebb tide. No corresponding velocity pulse on the tidal flat was observed. Sediment concentrations peaked at the beginning and end of each tidal cycle, and often had a secondary peak close to high tide, assumed to be related to sediment advection. The influence of wind waves on bed shear stress and sediment suspension was negligible. Water levels were elevated during a storm event such that the tidal flat remained inundated for 4 tidal cycles. The water did not drain from the tidal flat into the channels during the storm, and no velocity pulses occurred. Along-channel velocities, turbulent kinetic energy, and shear stresses were therefore smaller in the channels during storm conditions than during non-storm conditions.
NASA Astrophysics Data System (ADS)
de Pablo, Juan
2009-03-01
The flow and translocation of long DNA molecules are of considerable applied and fundamental interest. Design of effective genomic devices requires control of molecular shape and positioning at the level of microns and nanometers, and understanding the manner in which DNA is packaged into small channels and cavities is of interest to biology and medicine. This presentation will present an overview of hierarchical models and computational approaches developed by our research group to investigate the effects of confinement, hydrodynamic interactions, and salt concentration, on the structure and properties of DNA, both at equilibrium and beyond equilibrium. The talk will include a discussion of coarse grain descriptions of the flow of DNA in microfluidic and nanofluidic channels over multiple length and time scales, and a discussion of emerging, detailed models that are capable of describing melting and rehybridization at the single nucleotide level, as well as the packaging of DNA into viral capsids and small pores.
Channeling of fast ions through the bent carbon nanotubes: The extended two-fluid hydrodynamic model
NASA Astrophysics Data System (ADS)
Lazar, Karbunar; Duško, Borka; Ivan, Radović; Zoran, L. Mišković
2016-04-01
We investigate the interactions of charged particles with straight and bent single-walled carbon nanotubes (SWNTs) under channeling conditions in the presence of dynamic polarization of the valence electrons in carbon. This polarization is described by a cylindrical, two-fluid hydrodynamic model with the parameters taken from the recent modelling of several independent experiments on electron energy loss spectroscopy of carbon nano-structures. We use the hydrodynamic model to calculate the image potential for protons moving through four types of SWNTs at a speed of 3 atomic units. The image potential is then combined with the Doyle–Turner atomic potential to obtain the total potential in the bent carbon nanotubes. Using that potential, we also compute the spatial and angular distributions of protons channeled through the bent carbon nanotubes, and compare the results with the distributions obtained without taking into account the image potential. Project supported by the Funds from the Ministry of Education, Science and Technological Development of the Republic of Serbia (Grant No. 45005). Z. L. Mišković thanks the Natural Sciences and Engineering Research Council of Canada for Finacial Support.
Taylor-Couette flow of unmagnetized plasma
Collins, C.; Cooper, C. M.; Flanagan, K.; Khalzov, I. V.; Nornberg, M. D.; Forest, C. B.; Clark, M.; Seidlitz, B.; Wallace, J.
2014-04-15
Differentially rotating flows of unmagnetized, highly conducting plasmas have been created in the Plasma Couette Experiment. Previously, hot-cathodes have been used to control plasma rotation by a stirring technique [C. Collins et al., Phys. Rev. Lett. 108, 115001 (2012)] on the outer cylindrical boundary—these plasmas were nearly rigid rotors, modified only by the presence of a neutral particle drag. Experiments have now been extended to include stirring from an inner boundary, allowing for generalized circular Couette flow and opening a path for both hydrodynamic and magnetohydrodynamic experiments, as well as fundamental studies of plasma viscosity. Plasma is confined in a cylindrical, axisymmetric, multicusp magnetic field, with T{sub e} < 10 eV, T{sub i} < 1 eV, and n{sub e}<10{sup 11} cm{sup −3}. Azimuthal flows (up to 12 km/s, M = V∕c{sub s} ∼ 0.7) are driven by edge J × B torques in helium, neon, argon, and xenon plasmas, and the experiment has already achieved Rm ∼ 65 and Pm∼0.2−12. We present measurements of a self-consistent, rotation-induced, species-dependent radial electric field, which acts together with pressure gradient to provide the centripetal acceleration for the ions. The maximum flow speeds scale with the Alfvén critical ionization velocity, which occurs in partially ionized plasma. A hydrodynamic stability analysis in the context of the experimental geometry and achievable parameters is also explored.
NASA Astrophysics Data System (ADS)
Lunn, R. J.; El Mountassir, G.; MacLachlan, E.; Moir, H.
2013-12-01
Evidence of fossilized microorganisms embedded within mineral veins and mineral-filled fractures has been observed in a wide range of geological environments. Microorganisms can act as sites for mineral nucleation and also contribute to mineral precipitation by inducing local geochemical changes. In this study, we explore fundamental controls on microbially induced mineralization in rock fractures. Specifically, we systematically investigate the influence of hydrodynamics (velocity, flow rate, aperture) on microbially mediated calcite precipitation. We use a case study of microbially induced calcite precipitation as a model biomineralization system to investigate potential feedback mechanisms between the temporally varying patterns of mineral precipitation within a fracture and the resulting variations in the local velocity field. Fractures are represented as a series of precision-etched parallel channels between a pair of sealed Perspex plates. Multiple channels are designed to maintain a constant flow rate, whilst independently adjusting channel aperture and width to explore the effects of aperture and fluid velocity on biomineral precipitation. Our experimental results demonstrate that a feedback mechanism exists between the gradual reduction in fracture aperture due to precipitation, and its effect on the local fluid velocity. This feedback results in mineral fill distributions that focus flow into a small number of self-organizing channels that remain open, ultimately controlling the final aperture profile that governs flow within the fracture. This feedback mechanism exists because precipitation on the fracture walls (as opposed to in solution) requires the bacteria to be transported to the fracture surface. Bacteria settle out of a quiescent solution at a velocity that is dependent on individual floc size and density. This settling velocity competes with the bed shear velocity, inhibiting deposition via entrainment. As precipitation progresses, the flow
NASA Astrophysics Data System (ADS)
Hill, Craig; Kozarek, Jessica; Sotiropoulos, Fotis; Guala, Michele
2016-02-01
An investigation into the interactions between a model axial-flow hydrokinetic turbine (rotor diameter, dT = 0.15 m) and the complex hydrodynamics and sediment transport processes within a meandering channel was carried out in the Outdoor StreamLab research facility at the University of Minnesota St. Anthony Falls Laboratory. This field-scale meandering stream with bulk flow and sediment discharge control provided a location for high spatiotemporally resolved measurements of bed and water surface elevations around the model turbine. The device was installed within an asymmetric, erodible channel cross section under migrating bed form and fixed outer bank conditions. A comparative analysis between velocity and topographic measurements, with and without the turbine installed, highlights the local and nonlocal features of the turbine-induced scour and deposition patterns. In particular, it shows how the cross-section geometry changes, how the bed form characteristics are altered, and how the mean flow field is distorted both upstream and downstream of the turbine. We further compare and discuss how current energy conversion deployments in meander regions would result in different interactions between the turbine operation and the local and nonlocal bathymetry compared to straight channels.
Hydrodynamic and Sediment Responses of Open Channels to Exposed Pipe Encasements.
Mao, J Q; Zhang, H Q; Dai, H C; Yuan, B H; Hu, T F
2015-01-01
The effects of exposed pipe encasements on the local variation of hydrodynamic and sediment conditions in a river channel are examined. Laboratory experiments are performed to assess the response of water level, flow regime and bed deformation to several representative types of concrete encasements. The experimental conditions considered are: three types of exposed pipe encasements exposed on the bed, including trapezoidal shape, circular-arc shape and polygonal shape, and three sets of discharges, including annual discharge, once-in-3-year flood, and once-in-50-year flood. Our experiments show that: (1) the amount of backwater definitely depends on the encasement geometric shape and the background discharge; (2) smaller discharges generally tend to induce local scour of river bed downstream of the encasement, and the order of sensitivity of bed deformation to the encasement geometric shape is trapezoidal > circular-arc > polygonal; (3) comparatively speaking, the polygonal encasement may be considered as a suitable protective structure for pipelines across alluvial rivers, with relatively modest effects on the local hydrodynamic conditions and bed stabilization. PMID:26588840
Hydrodynamic studies of post dryout two-phase downflow in narrow channels
Eberle, C.S.; Ishii, M.; Revankar, S.T.
1995-07-01
An experimental study of the hydrodynamics of a narrow channel was performed in order to obtain the heat transfer mechanisms and influences contributing to the flow regime transition from inverted annular to inverted slug flows for post dryout downflow. The experimental series consisted of both adiabatic and diabatic visualization tests over a wide range of fluid and thermal parameters. The system inlet gas velocities ranged from 0 to 14 meters per second while the inlet fluid velocities ranged from 1 to 3 meters per second. Full extent visualization of the flow regime was possible due to a quartz tube in tube construction with a clear heating fluid. Constant temperature heating of the freon was accomplished at bulk fluid temperatures above the critical heat flux temperature. For each hydrodynamic flow condition, one to three minuets of VHS-video filming was performed to acquire both flow regime and break-up length data. In addition to this the flow field parameters were recorded simultaneously with the filming.
Hydrodynamic and Sediment Responses of Open Channels to Exposed Pipe Encasements
Mao, J. Q.; Zhang, H. Q.; Dai, H. C.; Yuan, B. H.; Hu, T. F.
2015-01-01
The effects of exposed pipe encasements on the local variation of hydrodynamic and sediment conditions in a river channel are examined. Laboratory experiments are performed to assess the response of water level, flow regime and bed deformation to several representative types of concrete encasements. The experimental conditions considered are: three types of exposed pipe encasements exposed on the bed, including trapezoidal shape, circular-arc shape and polygonal shape, and three sets of discharges, including annual discharge, once-in-3-year flood, and once-in-50-year flood. Our experiments show that: (1) the amount of backwater definitely depends on the encasement geometric shape and the background discharge; (2) smaller discharges generally tend to induce local scour of river bed downstream of the encasement, and the order of sensitivity of bed deformation to the encasement geometric shape is trapezoidal > circular-arc > polygonal; (3) comparatively speaking, the polygonal encasement may be considered as a suitable protective structure for pipelines across alluvial rivers, with relatively modest effects on the local hydrodynamic conditions and bed stabilization. PMID:26588840
Helical magnetorotational instability in a Taylor-Couette flow with strongly reduced Ekman pumping.
Stefani, Frank; Gerbeth, Gunter; Gundrum, Thomas; Hollerbach, Rainer; Priede, Jānis; Rüdiger, Günther; Szklarski, Jacek
2009-12-01
The magnetorotational instability (MRI) is thought to play a key role in the formation of stars and black holes by sustaining the turbulence in hydrodynamically stable Keplerian accretion disks. In previous experiments the MRI was observed in a liquid metal Taylor-Couette flow at moderate Reynolds numbers by applying a helical magnetic field. The observation of this helical MRI (HMRI) was interfered with a significant Ekman pumping driven by solid end caps that confined the instability only to a part of the Taylor-Couette cell. This paper describes the observation of the HMRI in an improved Taylor-Couette setup with the Ekman pumping significantly reduced by using split end caps. The HMRI, which now spreads over the whole height of the cell, appears much sharper and in better agreement with numerical predictions. By analyzing various parameter dependencies we conclude that the observed HMRI represents a self-sustained global instability rather than a noise-sustained convective one. PMID:20365263
Turbulent plane Couette flow subject to strong system rotation
NASA Astrophysics Data System (ADS)
Bech, Knut H.; Andersson, Helge I.
1997-09-01
System rotation is known to substantially affect the mean flow pattern as well as the turbulence structure in rotating channel flows. In a numerical study of plane Couette flow rotating slowly about an axis aligned with the mean vorticity, Bech & Andersson (1996a) found that the turbulence level was damped in the presence of anticyclonic system rotation, in spite of the occurrence of longitudinal counter-rotating roll cells. Moreover, the turbulence anisotropy was practically unaffected by the weak rotation, for which the rotation number Ro, defined as the ratio of twice the imposed angular vorticity [Omega] to the shear rate of the corresponding laminar flow, was ±0.01. The aim of the present paper is to explore the effects of stronger anticyclonic system rotation on directly simulated turbulent plane Couette flow. Turbulence statistics like energy, enstrophy and Taylor lengthscales, both componental and directional, were computed from the statistically steady flow fields and supplemented by structural information obtained by conditional sampling.
NASA Astrophysics Data System (ADS)
Ryu, Brian; Dhong, Charles; Frechette, Joelle
While it is well known that surface asperities and roughness alter the hydrodynamic drag of a non-colloidal sphere down an inclined plane, less is known about how the hydrodynamic drag is modified if the asperities and roughness are connected through a network of drainage channels, which allows the movement of fluid between asperities. We investigate the rotational and translation motion of spheres on several pairs of surfaces that have the same porosity and asperity size, but one surface has interconnected drainage channels whereas the other does not. These can have direct relevance to lubricated surfaces such as ball bearings in industrial settings, or biological relevance of leucocyte movement across rough surfaces. Provost's Undergraduate Research Awards, Office of Naval Research, National Science Foundation.
NASA Astrophysics Data System (ADS)
Gorla, R. S. R.; Gireesha, B. J.
2015-12-01
An analysis has been provided to determine the transient velocity and steady state entropy generation in a microfluidic Couette flow influenced by electro-kinetic effect of charged nanoparticles. The equation for calculating the Couette flow velocity profile is derived for transient flow. The solutions for momentum and energy equations are used to get the exact solution for the dimensionless velocity ratio and dimensionless entropy generation number. The effects of the dimensionless entropy generation number, Bejan number, irreversibility ratio, entropy generation due to fluid friction and due to heat transfer on dimensionless time, relative channel height, Brinkman number, dimensionless temperature ratio, nanoparticle volume fraction are analyzed.
Monolithic cell counter based on 3D hydrodynamic focusing in microfluidic channels
NASA Astrophysics Data System (ADS)
Paiè, Petra; Bragheri, Francesca; Osellame, Roberto
2014-03-01
Hydrodynamic focusing is a powerful technique frequently used in microfluidics that presents a wide range of applications since it allows focusing the sample flowing in the device to a narrow region in the center of the microchannel. In fact thanks to the laminarity of the fluxes in microchannels it is possible to confine the sample solution with a low flow rate by using a sheath flow with a higher flow rate. This in turn allows the flowing of one sample element at a time in the detection region, thus enabling analysis on single particles. Femtosecond laser micromachining is ideally suited to fabricate device integrating full hydrodynamic focusing functionalities thanks to the intrinsic 3D nature of this technique, especially if compared to expensive and complicated lithographic multi-step fabrication processes. Furthermore, because of the possibility to fabricate optical waveguides with the same technology, it is possible to obtain compact optofluidic devices to perform optical analysis of the sample even at the single cell level, as is the case for optical cell stretchers and sorters. In this work we show the fabrication and the fluidic characterization of extremely compact devices having only two inlets for 2D (both in vertical and horizontal planes) as well as full 3D symmetric hydrodynamic focusing. In addition we prove one of the possible application of the hydrodynamic focusing module, by fabricating and validating (both with polystyrene beads and erythrocytes) a monolithic cell counter obtained by integrating optical waveguides in the 3D hydrodynamic focusing device.
Velocity Inversion In Cylindrical Couette Gas Flows
NASA Astrophysics Data System (ADS)
Dongari, Nishanth; Barber, Robert W.; Emerson, David R.; Zhang, Yonghao; Reese, Jason M.
2012-05-01
We investigate a power-law probability distribution function to describe the mean free path of rarefied gas molecules in non-planar geometries. A new curvature-dependent model is derived by taking into account the boundary-limiting effects on the molecular mean free path for surfaces with both convex and concave curvatures. In comparison to a planar wall, we find that the mean free path for a convex surface is higher at the wall and exhibits a sharper gradient within the Knudsen layer. In contrast, a concave wall exhibits a lower mean free path near the surface and the gradients in the Knudsen layer are shallower. The Navier-Stokes constitutive relations and velocity-slip boundary conditions are modified based on a power-law scaling to describe the mean free path, in accordance with the kinetic theory of gases, i.e. transport properties can be described in terms of the mean free path. Velocity profiles for isothermal cylindrical Couette flow are obtained using the power-law model. We demonstrate that our model is more accurate than the classical slip solution, especially in the transition regime, and we are able to capture important non-linear trends associated with the non-equilibrium physics of the Knudsen layer. In addition, we establish a new criterion for the critical accommodation coefficient that leads to the non-intuitive phenomena of velocity-inversion. Our results are compared with conventional hydrodynamic models and direct simulation Monte Carlo data. The power-law model predicts that the critical accommodation coefficient is significantly lower than that calculated using the classical slip solution and is in good agreement with available DSMC data. Our proposed constitutive scaling for non-planar surfaces is based on simple physical arguments and can be readily implemented in conventional fluid dynamics codes for arbitrary geometric configurations.
Experimental research of the couette flow with cross flow
NASA Astrophysics Data System (ADS)
Nobis, Matthias; Stücke, Peter; Schmidt, Marcus
2012-04-01
When a solid cylinder is rotating inside a hollow cylinder, a characteristic fluid flow occurs inside the gap between the two cylinders, caused by the adhesion of the fluid at the walls. This flow problem is widely known as the Couette-flow. If an additional flow entrances through a radial located feedhole at the outer hollow cylinder, there is an interaction between the cross flow and the Couette-flow. In result there are complex three dimensional flow structures in the gap at the area around the feedhole. These arising flow structures are closely related with the technical important flow inside the gap of hydrodynamic lubricated journal bearings. When the flow conditions inside the bearing gap are well explored and appreciated, it will be possible to give suggestions for constructive details like the design, the location and the dimension of the feedhole for longer lifecycles or an even more efficiently running. In this paper the test rig of the bearing model will be presented. Moreover some representative results from researches with a Laser-Doppler-Velocimeter (LDV) in comparison with the output of three dimensional numerical simulations will be illustrated.
NASA Astrophysics Data System (ADS)
Narsimhan, Vivek; Zhao, Hong; Shaqfeh, Eric S. G.
2013-06-01
We develop a coarse-grained theory to predict the concentration distribution of a suspension of vesicles or red blood cells in a wall-bound Couette flow. This model balances the wall-induced hydrodynamic lift on deformable particles with the flux due to binary collisions, which we represent via a second-order kinetic master equation. Our theory predicts a depletion of particles near the channel wall (i.e., the Fahraeus-Lindqvist effect), followed by a near-wall formation of particle layers. We quantify the effect of channel height, viscosity ratio, and shear-rate on the cell-free layer thickness (i.e., the Fahraeus-Lindqvist effect). The results agree with in vitro experiments as well as boundary integral simulations of suspension flows. Lastly, we examine a new type of collective particle motion for red blood cells induced by hydrodynamic interactions near the wall. These "swapping trajectories," coined by Zurita-Gotor et al. [J. Fluid Mech. 592, 447-469 (2007), 10.1017/S0022112007008701], could explain the origin of particle layering near the wall. The theory we describe represents a significant improvement in terms of time savings and predictive power over current large-scale numerical simulations of suspension flows.
NASA Astrophysics Data System (ADS)
Chang, Tsang-Jung; Chang, Kao-Hua; Kao, Hong-Ming
2014-11-01
A new approach to model weakly nonhydrostatic shallow water flows in open channels is proposed by using a Lagrangian meshless method, smoothed particle hydrodynamics (SPH). The Lagrangian form of the Boussinesq equations is solved through SPH to merge the local and convective derivatives as the material derivative. In the numerical SPH procedure, the present study uses a predictor-corrector method, in which the pure space derivative terms (the hydrostatic and source terms) are explicitly solved and the mixed space and time derivatives term (the material term of B1 and B2) is computed with an implicit scheme. It is thus a convenient tool in the processes of the space discretization compared to other Eulerian approaches. Four typical benchmark problems in weakly nonhydrostatic shallow water flows, including solitary wave propagation, nonlinear interaction of two solitary waves, dambreak flow propagation, and undular bore development, are selected to employ model validation under the closed and open boundary conditions. Numerical results are compared with the analytical solutions or published laboratory and numerical results. It is found that the proposed approach is capable of resolving weakly nonhydrostatic shallow water flows. Thus, the proposed SPH approach can supplement the lack of the SPH-Boussinesq researches in the literatures, and provide an alternative to model weakly nonhydrostatic shallow water flows in open channels.
Logarithmic Boundary Layers in Strong Taylor-Couette Turbulence
NASA Astrophysics Data System (ADS)
Huisman, Sander G.; Scharnowski, Sven; Cierpka, Christian; Kähler, Christian J.; Lohse, Detlef; Sun, Chao
2013-06-01
We provide direct measurements of the boundary layer properties in highly turbulent Taylor-Couette flow up to Re=2×106 (Ta=6.2×1012) using high-resolution particle image velocimetry and particle tracking velocimetry. We find that the mean azimuthal velocity profile at the inner and outer cylinder can be fitted by the von Kármán log law u+=1/κlny++B. The von Kármán constant κ is found to depend on the driving strength Ta and for large Ta asymptotically approaches κ≈0.40. The variance profiles of the local azimuthal velocity have a universal peak around y+≈12 and collapse when rescaled with the driving velocity (and not with the friction velocity), displaying a log dependence of y+ as also found for channel and pipe flows.
Hydrodynamic behavior in the outer shear layer of partly obstructed open channels
NASA Astrophysics Data System (ADS)
Ben Meftah, Mouldi; De Serio, Francesca; Mossa, Michele
2014-06-01
Despite the many studies on flow in partly obstructed open channels, this issue remains of fundamental importance in order to better understand the interaction between flow behavior and the canopy structure. In the first part of this study we suggest a new theoretical approach able to model the flow pattern within the shear layer in the unobstructed domain, adjacent to the canopy area. Differently from previous studies, the new analytical solution of flow momentum equations takes into account the transversal velocity component of the flow, which is modelled as a linear function of the streamwise velocity. The proposed theoretical model is validated by different experiments carried out on a physical model of a very large rectangular channel by the research group of the Department of Civil, Environmental, Building Engineering and Chemistry of the Technical University of Bari. An array of vertical, rigid, and circular steel cylinders was partially mounted on the bottom in the central part of the flume, leaving two lateral areas of free flow circulation near the walls. The three-dimensional flow velocity components were measured using a 3D Acoustic Doppler Velocimeter. A comparison of the measured and predicted data of the present study with those obtained in other previous studies, carried out with different canopy density, show a non-dependence of this analytical solution on the array density and the Reynolds number. In the second part of the paper, detailed observations of turbulent intensities and spanwise Reynolds stresses in the unobstructed flow are analyzed and discussed. Differently from some earlier studies, it was observed that the peak of the turbulence intensity and that of the spanwise Reynolds stress are significantly shifted toward the center of the shear layer.
NASA Astrophysics Data System (ADS)
Lewis, K.; Allen, J. I.
2009-05-01
Evaluation is essential if ecosystem models are to be used to simulate short-term and climate scale forecasts. A three-dimensional hydrodynamic-ecosystem model (ERSEM-POLCOMS) simulation of the western English Channel for the period 2003-2005 has been validated with a series of univariate and multivariate tests using physical, biological and chemical data collected routinely at time-series station L4 (50° 15'N, 04° 13'W). Our assessment indicates a varying confidence in model ability to simulate different variables: In terms of high frequency variability there is a high level of confidence in temperature, some confidence in nutrients, especially nitrate, but much development needs to be done before there will be confidence in the model ability to simulate phytoplankton, zooplankton and bacteria at sub weekly timescales. In terms of seasonal timescales, the model captures the phytoplankton succession when diatoms and flagellates dominate the system, but performs less well when dinoflagellate blooms are dominant. The evaluation provides a benchmark for future model development, and highlights the importance of data collection for model validation and the need to expand the range of biological variables sampled. The potential for coastal observatories to play a key role in the future development of marine ecosystem models is discussed.
NASA Astrophysics Data System (ADS)
Rowghanian, Payam; Grosberg, Alexander Y.
2013-07-01
We illustrate an Onsager-type linear response theory of electrohydrodynamic coupling for two examples, namely, a long nano-channel blocked partially by a rigid polymer and a gel of semi-flexible polyelectrolyte chains. We calculate the hydrodynamic and electric currents driven by an external voltage and pressure and the corresponding Onsager coefficients for these systems. Our consideration clarifies the effect of the electro-osmotic flow on the effective charge of the polymer inside the channel. It also makes it possible to explore the dependence of the currents through the gel on the electric screening radius and salt concentration.
Circulation in a Short Cylindrical Couette System
Akira Kageyama; Hantao Ji; Jeremy Goodman
2003-07-08
In preparation for an experimental study of magnetorotational instability (MRI) in liquid metal, we explore Couette flows having height comparable to the gap between cylinders, centrifugally stable rotation, and high Reynolds number. Experiments in water are compared with numerical simulations. The flow is very different from that of an ideal, infinitely long Couette system. Simulations show that endcaps co-rotating with the outer cylinder drive a strong poloidal circulation that redistributes angular momentum. Predicted toroidal flow profiles agree well with experimental measurements. Spin-down times scale with Reynolds number as expected for laminar Ekman circulation; extrapolation from two-dimensional simulations at Re less than or equal to 3200 agrees remarkably well with experiment at Re approximately equal to 106. This suggests that turbulence does not dominate the effective viscosity. Further detailed numerical studies reveal a strong radially inward flow near both endcaps. After turning vertically along the inner cylinder, these flows converge at the midplane and depart the boundary in a radial jet. To minimize this circulation in the MRI experiment, endcaps consisting of multiple, differentially rotating rings are proposed. Simulations predict that an adequate approximation to the ideal Couette profile can be obtained with a few rings.
Measurements of particle dynamics in slow, dense granular Couette flow
NASA Astrophysics Data System (ADS)
Mueth, Daniel M.
Experimental measurements of particle dynamics on the lower surface of a 3D Couette cell containing monodisperse spheres are reported. The average radial density and velocity profiles are similar to those previously measured within the bulk and on the lower surface of the 3D cell filled with mustard seeds. Observations of the evolution of particle velocities over time reveal distinct motion events, intervals where previously stationary particles move for a short duration before jamming again. The cross-correlation between the velocities of two particles at a given distance r from the moving wall reveals a characteristic lengthscale over which the particles are correlated. The autocorrelation of a single particle's velocity reveals a characteristic timescale tau which decreases with distance from the inner moving wall. This may be attributed to the increasing rarity at which the discrete motion events occur and the reduced duration of those events at large r. The radial profile of the velocity fluctuations about their mean, deltavtheta(r), was found to be almost identical in shape to the Gaussian component of the velocity profile vtheta(r). The relationship between the RMS azimuthal velocity fluctuations, delta vtheta(r), and average shear rate, ġ (r), was found to be deltav theta ∝ ġ alpha with alpha = 0.52 +/- 0.04. These observations are compared with other recent experiments and with the modified hydrodynamic model recently introduced by Bocquet et al.
Measurements of particle dynamics in slow, dense granular Couette flow
NASA Astrophysics Data System (ADS)
Mueth, Daniel M.
2003-01-01
Experimental measurements of particle dynamics on the lower surface of a three-dimensional (3D) Couette cell containing monodisperse spheres are reported. The average radial density and velocity profiles are similar to those previously measured within the bulk and on the lower surface of the 3D cell filled with mustard seeds. Observations of the evolution of particle velocities over time reveal distinct motion events, intervals where previously stationary particles move for a short duration before jamming again. The cross correlation between the velocities of two particles at a given distance r from the moving wall reveals a characteristic length scale over which the particles are correlated. The autocorrelation of a single particle’s velocity reveals a characteristic time scale τ, which decreases with increasing distance from the inner moving wall. This may be attributed to the increasing rarity at which the discrete motion events occur and the reduced duration of those events at large r. The relationship between the rms azimuthal velocity fluctuations, δvθ(r), and average shear rate, γ˙(r), was found to be δvθ∝γ˙α with α=0.52±0.04. These observations are compared with other recent experiments and with the modified hydrodynamic model recently introduced by Bocquet et al.
A novel control strategy for a Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Bouabdallah, A.; Oualli, H.; Mekadem, M.; Boukrif, M.; Saad, S.; Gad-El-Hak, M.
2015-11-01
Advancing transition is desired in applications where heat, mass, or momentum transfer needs to be augmented. On the other hand, delaying transition is imperative in crystal growth devices, where all instabilities are to be avoided in order to prevent the appearance of geometrical irregularities in the resulting crystal. The hydrodynamic stability of a viscous flow in a closed, fully filled Taylor-Couette system is considered in the present numerical study. The fluid evolves in an annular cavity between the rotating inner cylinder and the outer fixed one. The base flow is axis-symmetric with two counter-rotating vortices each wavelength. The Taylor number varies in the range of 0-50. Numerical simulations are implemented on a finite-volume CFD code. The control strategy involves a pulsatile motion superimposed separately on the inner and outer cylinder's cross-section, with maximum amplitude of, respectively, 5% and 15% of the radius. The frequency varies in the range of 0-100 Hz. The objective is to localize the transition and to assess the flow's response to the imposed boundary motions. Substantial advancement of transition is found when the inner cylinder's cross-section is varied, while this transition is delayed when the outer cylinder's cross-section is pulsating.
System Developed for Bulk Flow Imaging of a Two-Phase Fluid in a Cylindrical Couette
NASA Technical Reports Server (NTRS)
Juergens, Jeffrey R.; Wagner, James D.
2005-01-01
The Microgravity Observation of Bubble Interactions (MOBI) experiment is working to better understand the physics of gas-liquid suspensions. To study such suspensions, researchers generate bubbles in a large cylindrical flow channel. Then, they use various types of instrumentation, including video imaging, to study the bubbly suspension. Scientists will need a camera view of the majority of the gas-liquid suspension inside of the couette in order to gather the information needed from the MOBI experiment. This will provide the scientists with a qualitative picture of the flow that may indicate flow instabilities or imperfect axial mixing inside the couette. These requirements pose a significant challenge because the imaging and lighting system must be confined to a very tight space since the space available on the International Space Station experiment racks is very limited. In addition, because of the large field of view needed and the detail needed to see the gas-liquid suspension behavior in the image, a digital video camera with high resolution (1024 by 1024 pixels) had to be used. Although the high-resolution camera will provide scientists with the image quality they need, it left little space on the experiment rack for the lighting system. Many configurations were considered for the lighting system, including front-lighting and back-lighting, but because of mechanical design limitations with the couette, back-lighting was not an option.
NASA Astrophysics Data System (ADS)
Kawata, Takuya; Alfredsson, P. Henrik
2016-07-01
Plane Couette flow under spanwise, anticyclonic system rotation [rotating plane Couette flow (RPCF)] is studied experimentally using stereoscopic particle image velocimetry for different Reynolds and rotation numbers in the fully turbulent regime. Similar to the laminar regime, the turbulent flow in RPCF is characterized by roll cells, however both instantaneous snapshots of the velocity field and space correlations show that the roll cell structure varies with the rotation number. All three velocity components are measured and both the mean flow and all four nonzero Reynolds stresses are obtained across the central parts of the channel. This also allows us to determine the wall shear stress from the viscous stress and the Reynolds stress in the center of the channel, and for low rotation rates the wall shear stress increases with increasing rotation rate as expected. The results show that zero absolute vorticity is established in the central parts of the channel of turbulent RPCF for high enough rotation rates, but also that the mean velocity profile for certain parameter ranges shows an S shape giving rise to a negative velocity gradient in the center of the channel. We find that from an analysis of the Reynolds stress transport equation using the present data there is a transport of the Reynolds shear stress towards the center of the channel, which may then result in a negative mean velocity gradient there.
Characterizing the danger of in-channel river hazards using LIDAR and a 2D hydrodynamic model
NASA Astrophysics Data System (ADS)
Strom, M. A.; Pasternack, G. B.
2014-12-01
Despite many injuries and deaths each year worldwide, no analytically rigorous attempt exists to characterize and quantify the dangers to boaters, swimmers, fishermen, and other river enthusiasts. While designed by expert boaters, the International Scale of River Difficulty provides a whitewater classification that uses qualitative descriptions and subjective scoring. The purpose of this study was to develop an objective characterization of in-channel hazard dangers across spatial scales from a single boulder to an entire river segment for application over a wide range of discharges and use in natural hazard assessment and mitigation, recreational boating safety, and river science. A process-based conceptualization of river hazards was developed, and algorithms were programmed in R to quantify the associated dangers. Danger indicators included the passage proximity and reaction time posed to boats and swimmers in a river by three hazards: emergent rocks, submerged rocks, and hydraulic jumps or holes. The testbed river was a 12.2 km mixed bedrock-alluvial section of the upper South Yuba River between Lake Spaulding and Washington, CA in the Sierra Mountains. The segment has a mean slope of 1.63%, with 8 reaches varying from 1.07% to 3.30% slope and several waterfalls. Data inputs to the hazard analysis included sub-decimeter aerial color imagery, airborne LIDAR of the river corridor, bathymetric data, flow inputs, and a stage-discharge relation for the end of the river segment. A key derived data product was the location and configuration of boulders and boulder clusters as these were potential hazards. Two-dimensional hydrodynamic modeling was used to obtain the meter-scale spatial pattern of depth and velocity at discharges ranging from baseflow to modest flood stages. Results were produced for four discharges and included the meter-scale spatial pattern of the passage proximity and reaction time dangers for each of the three hazards investigated. These results
Couette flow of two-dimensional foams
NASA Astrophysics Data System (ADS)
Katgert, G.; Tighe, B. P.; Möbius, M. E.; van Hecke, M.
2010-06-01
We experimentally investigate flow of quasi-two-dimensional disordered foams in Couette geometries, both for foams squeezed below a top plate and for freely floating foams (bubble rafts). With the top plate, the flows are strongly localized and rate dependent. For the bubble rafts the flow profiles become essentially rate independent, the local and global rheology do not match, and in particular the foam flows in regions where the stress is below the global yield stress. We attribute this to nonlocal effects and show that the "fluidity" model recently introduced by Goyon et al. (Nature, 454 (2008) 84) captures the essential features of flow both with and without a top plate.
Linear magnetohydrodynamic Taylor-Couette instability for liquid sodium
NASA Astrophysics Data System (ADS)
Rüdiger, Günther; Schultz, Manfred; Shalybkov, Dima
2003-04-01
The linear stability of MHD Taylor-Couette flow of infinite vertical extension is considered for liquid sodium with its small magnetic Prandtl number Pm of order 10-5. The calculations are performed for a container with Rout=2Rin, with an axial uniform magnetic field and with boundary conditions for both vacuum and perfect conductions. For resting outer cylinder subcritical excitation in comparison to the hydrodynamical case occurs for large Pm but it disappears for small Pm. For rotating outer cylinder the Rayleigh line plays an exceptional role. The hydromagnetic instability exists with Reynolds numbers exactly scaling with Pm-1/2 so that the moderate values of order 104 (for Pm=10-5) result. For the smallest step beyond the Rayleigh line, however, the Reynolds numbers scale as 1/Pm leading to much higher values of order 106. Then it is the magnetic Reynolds number Rm that directs the excitation of the instability. It results as lower for insulating than for conducting walls. The magnetic Reynolds number has to exceed here values of order 10 leading to frequencies of about 20 Hz for the rotation of the inner cylinder if containers with (say) 10 cm radius are considered. With vacuum boundary conditions the excitation of nonaxisymmetric modes is always more difficult than the excitation of axisymmetric modes. For conducting walls, however, crossovers of the lines of marginal stability exist for both resting and rotating outer cylinders, and this might be essential for future dynamo experiments. In this case the instability also can onset as an overstability.
Centrifugal instability of pulsed Taylor-Couette flow in a Maxwell fluid.
Riahi, Mehdi; Aniss, Saïd; Ouazzani Touhami, Mohamed; Skali Lami, Salah
2016-08-01
Centrifugal instability of a pulsed flow in a viscoelastic fluid confined in a Taylor-Couette system is investigated. Both cylinders are subject to an out-of-phase modulation of rotation with equal modulation amplitude and modulation frequency. The fluid is assumed to obey a linear Maxwell fluid with a relaxation time and a constant viscosity. Attention is focused on the linear stability analysis and on the effect of Deborah and frequency numbers on the critical values of the Taylor and wave numbers. Using Floquet theory, we show that in the limit of low frequency, the Deborah number has no effect on the stability of the basic state which tends to the classical configuration of steady circular Couette flow. When the frequency number increases, the stability of the basic flow is enhanced and the Deborah number has a destabilizing effect which is strongly pronounced in the high-frequency limit. In this frequency limit, the critical parameters tend to constant values independently of the frequency number. These numerical results are in good agreement with the asymptotic solutions obtained in the limit of low and high frequencies. Moreover, a correlation between the rheological proprieties of the fluid in a rheometric experience, especially the loss and storage modulus, and this hydrodynamical instability behavior is presented. PMID:27589859
Transient growth of Ekman-Couette flow.
Shi, Liang; Hof, Björn; Tilgner, Andreas
2014-01-01
Coriolis force effects on shear flows are important in geophysical and astrophysical contexts. We report a study on the linear stability and the transient energy growth of the plane Couette flow with system rotation perpendicular to the shear direction. External rotation causes linear instability. At small rotation rates, the onset of linear instability scales inversely with the rotation rate and the optimal transient growth in the linearly stable region is slightly enhanced ∼Re2. The corresponding optimal initial perturbations are characterized by roll structures inclined in the streamwise direction and are twisted under external rotation. At large rotation rates, the transient growth is significantly inhibited and hence linear stability analysis is a reliable indicator for instability. PMID:24580314
Stability of oscillatory two phase Couette flow
NASA Technical Reports Server (NTRS)
Coward, Adrian V.; Papageorgiou, Demetrios T.
1993-01-01
We investigate the stability of two phase Couette flow of different liquids bounded between plane parallel plates. One of the plates has a time dependent velocity in its own plane, which is composed of a constant steady part and a time harmonic component. In the absence of time harmonic modulations, the flow can be unstable to an interfacial instability if the viscosities are different and the more viscous fluid occupies the thinner of the two layers. Using Floquet theory, we show analytically in the limit of long waves, that time periodic modulations in the basic flow can have a significant influence on flow stability. In particular, flows which are otherwise unstable for extensive ranges of viscosity ratios, can be stabilized completely by the inclusion of background modulations, a finding that can have useful consequences in many practical applications.
NASA Astrophysics Data System (ADS)
Chen, X.; Chen, L.; Zhao, J.; Yu, Z.
2015-09-01
This study applied the two-dimensional AdH (adaptive hydraulics) hydrodynamic model to a river reach to analyze flood hydraulics on complex floodplains. Using the AdH model combined with bathymetry and topographic data from the United States Geological Survey (USGS) seamless server and the United States Army Corps of Engineers (USACE), we intended to examine the interactions between the channel and floodplain of a 10 km stretch at McCarran Ranch, which is located at the lower Truckee River in Nevada. After calibrating the model, we tested the dependence of the modeling results on mesh density, input parameters, and time steps and compared the modeling results to the existing gauged data (both the discharge and water stage heights). Results show that the accuracy of prediction from the AdH model may decline slightly at higher discharges and water levels. The modeling results are more sensitive to the roughness coefficient of the main channel, which suggests that the model calibration should give priority to the main channel roughness. A detailed analysis of the floodwater dynamics was then conducted using the modeling approach to examine the hydraulic linkage between the main channel and floodplains. We found that large flood events could lead to a significantly higher proportion of total flow being routed through the floodplains. During peak discharges, a river channel diverted as much as 65 % of the total discharge into the floodplain. During the periods of overbank flow, the transboundary flux ratio was approximately 5 to 45 % of the total river discharge, which indicates substantial exchange between the main channel and floodplains. The results also showed that both the relations of the inundation area and volume versus the discharge exhibit an apparent looped curve form, which suggests that flood routing has an areal hysteresis effect on floodplains.
MHD Couette two-fluid flow and heat transfer in presence of uniform inclined magnetic field
NASA Astrophysics Data System (ADS)
Nikodijevic, D.; Milenkovic, D.; Stamenkovic, Z.
2011-12-01
The MHD Couette flow of two immiscible fluids in a parallel plate channel in the presence of an applied electric and inclined magnetic field is investigated in the paper. One of the fluids is assumed to be electrically conducting, while the other fluid and the channel plates are assumed to be electrically insulating. Separate solutions with appropriate boundary conditions for each fluid are obtained and these solutions are matched at the interface using suitable matching conditions. The partial differential equations governing the flow and heat transfer are transformed to ordinary differential equations and closed-form solutions are obtained in both fluid regions of the channel. The results for various values of the Hartmann number, the angle of magnetic field inclination, the loading parameter and the ratio of the heights of the fluids are presented graphically to show their effect on the flow and heat transfer characteristics.
Computer simulations of an impurity in a granular gas under planar Couette flow
NASA Astrophysics Data System (ADS)
Vega Reyes, F.; Santos, A.; Garzó, V.
2011-07-01
We present in this work results from numerical solutions, obtained by means of the direct simulation Monte Carlo (DSMC) method, of the Boltzmann and Boltzmann-Lorentz equations for an impurity immersed in a granular gas under planar Couette flow. The DSMC results are compared with the exact solution of a recent kinetic model for the same problem. The results confirm that, in steady states and over a wide range of parameter values, the state of the impurity is enslaved to that of the host gas: it follows the same flow velocity profile, its concentration (relative to that of the granular gas) is constant in the bulk region, and the impurity/gas temperature ratio is also constant. We determine also the rheological properties and nonlinear hydrodynamic transport coefficients for the impurity, finding a good semi-quantitative agreement between the DSMC results and the theoretical predictions.
Development of a Couette-Taylor flow device with active minimization of secondary circulation
Ethan Schartman
2009-01-27
A novel Taylor-Couette experiment has been developed to produce rotating shear ows for the study of hydrodynamic and magnetohydrodynamic instabilities which are believed to drive angular momentum transport in astrophysical accretion disks. High speed, concentric, corotating cylinders generate the flow where the height of the cylinders is twice the radial gap width. Ekman pumping is controlled and minimized by splitting the vertical boundaries into pairs of nested, differentially rotating rings. The end rings and cylinders comprise four independently driven rotating components which provide exibility in developing flow profiles. The working fluids of the experiment are water, a water-glycerol mix, or a liquid gallium alloy. The mechanical complexity of the apparatus and large dynamic pressures generated by high speed operation with the gallium alloy presented unique challenges. The mechanical implementation of the experiment and some representative results obtained with Laser Doppler Velocimetry in water are discussed.
Sensitivity analysis of hydrodynamic stability operators
NASA Technical Reports Server (NTRS)
Schmid, Peter J.; Henningson, Dan S.; Khorrami, Mehdi R.; Malik, Mujeeb R.
1992-01-01
The eigenvalue sensitivity for hydrodynamic stability operators is investigated. Classical matrix perturbation techniques as well as the concept of epsilon-pseudoeigenvalues are applied to show that parts of the spectrum are highly sensitive to small perturbations. Applications are drawn from incompressible plane Couette, trailing line vortex flow and compressible Blasius boundary layer flow. Parametric studies indicate a monotonically increasing effect of the Reynolds number on the sensitivity. The phenomenon of eigenvalue sensitivity is due to the non-normality of the operators and their discrete matrix analogs and may be associated with large transient growth of the corresponding initial value problem.
Axially localized states in Taylor Couette flows
NASA Astrophysics Data System (ADS)
Lopez, Jose M.; Marques, Francisco
2014-11-01
We present numerical simulations of the flow in a Taylor Couette system with the inner cylinder rotating and aspect ratio Γ restricted to 0 . 86 <Γ/N < 0 . 95 , being N the number of Taylor vortices. For these values a complex experimental bifurcation scenario has been reported. The transition from wavy vortex flow (WVF) to a very low frequency mode VLF happens via an axisymmetric eigenfunction. The VLF plays an essential role in the dynamics, leading to chaos through a two-tori period-doubling route. This chaotic regime vanishes with further increase in Re and gives rise to a new flow regime ALS characterized by the existence of large jet oscillations localized in some pairs of vortices. The aim of this numerical study is to extend the available information on ALS by means of a detailed exploration of the parameter space in which it occurs. Frequency analysis from time series simultaneously recorded at several points of the domain has been applied to identify the different transitions taking place. The VLF occurs in a wide range of control parameters and its interaction with the axially localized states is crucial is most transitions, either between different ALS or to the chaotic regime. Spanish Ministry of Education and Science Grants (with FEDER funds) FIS2013-40880 and BES-2010-041542.
Rapid MRI and velocimetry of cylindrical Couette flow.
Hanlon, A D; Gibbs, S J; Hall, L D; Haycock, D E; Frith, W J; Ablett, S
1998-10-01
A narrow-gap, temperature-controlled Couette flow rheometer has been developed to study fluid velocities within the annular gap between two concentric cylinders by nuclear magnetic resonance (NMR) imaging and velocimetry. Alternative pulsed-field-gradient-based nuclear magnetic resonance imaging strategies which may be used for measurement of velocity within the Couette flow device have been evaluated. These include two-dimensional (2-D) imaging techniques with acquisition times of several minutes and a one-dimensional (1-D) projection method which exploits the symmetry of the device to reduce overall measurement time to less than 1 min. Velocity measurements made using each technique are presented for a Newtonian fluid undergoing Couette flow at shear rates of approximately 20 and 60 s(-1). PMID:9814778
Low Reynolds number Couette flow facility for drag measurements.
Johnson, Tyler J; Lang, Amy W; Wheelus, Jennifer N; Westcott, Matthew
2010-09-01
For this study a new low Reynolds number Couette facility was constructed to investigate surface drag. In this facility, mineral oil was used as the working fluid to increase the shear stress across the surface of the experimental models. A mounted conveyor inside a tank creates a flow above which an experimental model of a flat plate was suspended. The experimental plate was attached to linear bearings on a slide system that connects to a force gauge used to measure the drag. Within the gap between the model and moving belt a Couette flow with a linear velocity profile was created. Digital particle image velocimetry was used to confirm the velocity profile. The drag measurements agreed within 5% of the theoretically predicted Couette flow value. PMID:20887004
NASA Astrophysics Data System (ADS)
Khanwale, Makrand; Khadamkar, Hrushikesh; Mathpati, Channamallikarjun
2015-11-01
The physics of drop rise with continuous transfer of interfacial tension depressant (acetone), is mainly influenced by the coupling of mass transfer of interfacial depressent fluid, relative motion of two phases, and interface deformation. We present a investigation which focuses on the nature of hydrodynamic causation of aforementioned mass transfer process, which arise due to non-uniform shear at the interface, also known as the Marangoni instabilities. The effects of relative motion of two phases, and interface deformation are eliminated by operating in the spherical shape range (Eötvös number, Eo = 1 . 95 , and Morton number, M = 78 . 20) with creeping flow particle Reynolds number (Rep = 0 . 053). A improved technique for measurement and processing of data acquired from simultaneous planar PIV-PLIF is used to obtain velocity and concentration fields around the drop. A progressive non-Gaussian behaviour from large scales to small scales is seen, in scale wise wavelet energy decomposition of vorticity and concentration fields. This suggests similarity with high Schmidt and Reynolds number intermittent turbulence, even in the creeping flow region. Fourier spectra of concentration and velocity shows the plethora of length scales generated by the Marangoni instabilities. financial support by DAE-India, and TEQIP-India (COE-PI).
Direct velocity measurement of a turbulent shear flow in a planar Couette cell
NASA Astrophysics Data System (ADS)
Niebling, Michael J.; Tallakstad, Ken Tore; Toussaint, Renaud; Mâløy, Knut Jørgen
2014-01-01
In a plane Couette cell a thin fluid layer consisting of water is sheared between the sides of a transparent band at Reynolds numbers ranging from 300 to 1400. The length of the cell's flow channel is large compared to the film separation. To extract the flow velocity in the experiments, a correlation image velocimetry method is used on pictures recorded with a high-speed camera. The flow is recorded at a resolution that allows us to analyze flow patterns similar in size to the film separation. The fluid flow is then studied by calculating flow velocity autocorrelation functions. The turbulent patterns that arise on this scale above a critical Reynolds number of Re =360 display characteristic patterns that are proven by use of the calculated velocity autocorrelation functions. The patterns are metastable and reappear at different positions and times throughout the experiments. Typically these patterns are turbulent rolls which are elongated in the stream direction, which is the direction in which the band is moving. Although the flow states are metastable they possess similarities to the steady Taylor vortices known to appear in circular Taylor Couette cells.
Czuba, Christiana; Czuba, Jonathan A.; Gendaszek, Andrew S.; Magirl, Christopher S.
2010-01-01
The Cedar River in Washington State originates on the western slope of the Cascade Range and provides the City of Seattle with most of its drinking water, while also supporting a productive salmon habitat. Water-resource managers require detailed information on how best to manage high-flow releases from Chester Morse Lake, a large reservoir on the Cedar River, during periods of heavy precipitation to minimize flooding, while mitigating negative effects on fish populations. Instream flow-management practices include provisions for adaptive management to promote and maintain healthy aquatic habitat in the river system. The current study is designed to understand the linkages between peak flow characteristics, geomorphic processes, riverine habitat, and biological responses. Specifically, two-dimensional hydrodynamic modeling is used to simulate and quantify the effects of the peak-flow magnitude, duration, and frequency on the channel morphology and salmon-spawning habitat. Two study reaches, representative of the typical geomorphic and ecologic characteristics of the Cedar River, were selected for the modeling. Detailed bathymetric data, collected with a real-time kinematic global positioning system and an acoustic Doppler current profiler, were combined with a LiDAR-derived digital elevation model in the overbank area to develop a computational mesh. The model is used to simulate water velocity, benthic shear stress, flood inundation, and morphologic changes in the gravel-bedded river under the current and alternative flood-release strategies. Simulations of morphologic change and salmon-redd scour by floods of differing magnitude and duration enable water-resource managers to incorporate model simulation results into adaptive management of peak flows in the Cedar River. PDF version of a presentation on hydrodynamic modelling in the Cedar River in Washington state. Presented at the American Geophysical Union Fall Meeting 2010.
Rubber Bands as Model Polymers in Couette Flow
ERIC Educational Resources Information Center
Dunstan, Dave E.
2008-01-01
We present a simple device for demonstrating the essential aspects of polymers in flow in the classroom. Rubber bands are used as a macroscopic model of polymers to allow direct visual observation of the flow-induced changes in orientation and conformation. A transparent Perspex Couette cell, constructed from two sections of a tube, is used to…
Falcini, Federico; Palatella, Luigi; Cuttitta, Angela; Buongiorno Nardelli, Bruno; Lacorata, Guglielmo; Lanotte, Alessandra S.; Patti, Bernardino; Santoleri, Rosalia
2015-01-01
Knowledge of the link between ocean hydrodynamics and distribution of small pelagic fish species is fundamental for the sustainable management of fishery resources. Both commercial and scientific communities are indeed seeking to provide services that could “connect the dots” among in situ and remote observations, numerical ocean modelling, and fisheries. In the Mediterranean Sea and, in particular, in the Sicily Channel the reproductive strategy of the European Anchovy (Engraulis encrasicolus) is strongly influenced by the oceanographic patterns, which are often visible in sea surface temperature satellite data. Based on these experimental evidences, we propose here a more general approach where the role of ocean currents, wind effects, and mesoscale activity are tied together. To investigate how these features affect anchovy larvae distribution, we pair ichthyoplankton observations to a wide remote sensing data set, and to Lagrangian numerical simulations for larval transport. Our analysis shows that while the wind-induced coastal current is able to transport anchovy larvae from spawning areas to the recruiting area off the Sicilian south-eastern tip, significant cross-shore transport due to the combination of strong northwesterly mistral winds and topographic effects delivers larvae away from the coastal conveyor belt. We then use a potential vorticity approach to describe the occurrence of larvae cross-shore transport. We conclude that monitoring and quantifying the upwelling on the southern Sicilian coast during the spawning season allows to estimate the cross-shore transport of larvae and the consequent decrease of individuals within the recruiting area. PMID:25915489
Falcini, Federico; Palatella, Luigi; Cuttitta, Angela; Buongiorno Nardelli, Bruno; Lacorata, Guglielmo; Lanotte, Alessandra S; Patti, Bernardino; Santoleri, Rosalia
2015-01-01
Knowledge of the link between ocean hydrodynamics and distribution of small pelagic fish species is fundamental for the sustainable management of fishery resources. Both commercial and scientific communities are indeed seeking to provide services that could "connect the dots" among in situ and remote observations, numerical ocean modelling, and fisheries. In the Mediterranean Sea and, in particular, in the Sicily Channel the reproductive strategy of the European Anchovy (Engraulis encrasicolus) is strongly influenced by the oceanographic patterns, which are often visible in sea surface temperature satellite data. Based on these experimental evidences, we propose here a more general approach where the role of ocean currents, wind effects, and mesoscale activity are tied together. To investigate how these features affect anchovy larvae distribution, we pair ichthyoplankton observations to a wide remote sensing data set, and to Lagrangian numerical simulations for larval transport. Our analysis shows that while the wind-induced coastal current is able to transport anchovy larvae from spawning areas to the recruiting area off the Sicilian south-eastern tip, significant cross-shore transport due to the combination of strong northwesterly mistral winds and topographic effects delivers larvae away from the coastal conveyor belt. We then use a potential vorticity approach to describe the occurrence of larvae cross-shore transport. We conclude that monitoring and quantifying the upwelling on the southern Sicilian coast during the spawning season allows to estimate the cross-shore transport of larvae and the consequent decrease of individuals within the recruiting area. PMID:25915489
Solution of the Problem of the Couette Flow for a Fermi Gas with Almost Specular Boundary Conditions
NASA Astrophysics Data System (ADS)
Bedrikova, E. A.; Latyshev, A. V.
2016-06-01
A solution of the Couette problem for a Fermi gas is constructed. The kinetic Bhatnagar-Gross-Krook (BGK) equation is used. Almost specular boundary conditions are considered. Formulas for the mass flux and the heat flux of the gas are obtained. These fluxes are proportional to the difference of the tangential momentum accommodation coefficients of the molecules. An expression for the viscous drag force acting on the walls of the channel is also found. An analysis of the macroparameters of the gas is performed. The limit to classical gases is taken. The obtained results are found to go over to the known results in this limit.
NASA Astrophysics Data System (ADS)
Borrero-Echeverrry, Daniel; Morrison, Benjamin; Peairs, Evan
2015-11-01
Despite centuries of study, fluid dynamicists are still unable to explain why a large class of flows, including pipe flow and plane Couette flow, become turbulent. Hydrodynamic stability theory predicts these flows should be stable to infinitesimal perturbations, which means finite-amplitude perturbations need to be applied to destabilize them. We present the results of a series of experiments studying such subcritical transitions to turbulence in linearly-stable configurations of Taylor-Couette flow. In particular, we discuss how the stability of these flows depends on the size and duration of the applied perturbation as the aspect ratio of the experimental apparatus is varied. We show that for experimental configurations where the end caps rotate with the outer cylinder, the stability of the flow is enhanced at small aspect ratios. We find that at sufficiently high Reynolds numbers, perturbations must exceed a critical amplitude before the transition to turbulence can be triggered. The scaling of this threshold with Re appears to be different than that which has been reported for other linearly-stable shear flows. This work was supported by Reed College's Summer Scholarship Fund, the James Borders Physics Student Fellowship, and the Reed College Science Research Fellowship. We also thank H.L. Swinney, who kindly donated the apparatus used in these experiments.
NASA Technical Reports Server (NTRS)
Ji, H.; Burin, M.; Schartman, E.; Goodman, J.; Liu, W.
2006-01-01
Two plausible mechanisms have been proposed to explain rapid angular momentum transport during accretion processes in astrophysical disks: nonlinear hydrodynamic instabilities and magnetorotational instability (MRI). A laboratory experiment in a short Taylor-Couette flow geometry has been constructed in Princeton to study both mechanisms, with novel features for better controls of the boundary-driven secondary flows (Ekman circulation). Initial results on hydrodynamic stability have shown negligible angular momentum transport in Keplerian-like flows with Reynolds numbers approaching one million, casting strong doubt on the viability of nonlinear hydrodynamic instability as a source for accretion disk turbulence.
NASA Astrophysics Data System (ADS)
Osaci-Costache, G.; Armas, I.; Gogoase Nistoran, D.; Gheorghe, D.
2010-05-01
The objective of the study is to analyze the relationship between morphological transformations observed during the last 200 years along a 20 km reach of Prahova river, and hydrodynamic behavior during high intensity flood periods, in the context of erosion-control works and environmental changes. Along this sub-Carpathian reach, Prahova is a typical mountain river, partially regulated, flowing under fluvial and torrential regime and having a mean thalweg slope of about 1%. Riverbed material consists in cobbles and boulders. Its valley has gradually been cut; therefore four terraces may clearly be identified in the subbasin areas of Breaza and Câmpina. The Holocene floodplain is asymmetrical, and during the last decades an incision of about 3-4 m has clearly been observed in the main channel. This also led to an evolution from an anabranching river aspect to a meandering one along the studied reach. Reasons to explain these changes are a positive neotectonic background coupled with an increased anthropic component (granular material extraction, channel regulation for construction purposes of roads, bridges, railways, layout of gas and oil pipelines, vegetation cutoff etc.). The data obtained from 1900-1980 topographical maps and 1997-2002 satellite images and orthophotos were coupled with topo-bathymetric surveys carried out in 57 cross-sections, in order to obtain the DTM of the studied area. These cross-sections were used to build up the geometry of a 1D hydraulic model by using the HEC-RAS software (USACE, version 3.1.3). Simulations were obtained under steady flow conditions for 1% and 2% return periods (360-400 mc/s and 450-500 mc/s). Calibration of Manning roughness factors was performed on stages measured at the two upstream and downstream gauging stations. High values of computed shear stresses and velocities show areas of potential erosion leading to morphological changes, bank collapsing and incision observed during the last decades and predicted for the
NASA Astrophysics Data System (ADS)
du Bois, P. Bailly; Dumas, F.
The database for medium- and long-term model validation using 125Sb released by the La Hague reprocessing plant includes 1400 measurements performed between 1987 and 1994 in the English Channel and the North Sea and data for each release since 1982. Antimony-125 has a conservative behaviour in water masses over a period of several years. These data can be used qualitatively and quantitatively to compare the measured concentrations with the calculated ones and quantities of tracers. Tritium measurements are also available for model calibration. A two-dimensional hydrodynamic model has been developed to allow repetitive long-term simulations. This model uses a database of residual tidal currents calculated using the Lagrangian barycentric method [Salomon, J.C., Guéguéniat, P., Orbi, A., Baron, Y., 1988. A Lagrangian model for long-term tidally induced transport and mixing. Verification by artificial radionuclide concentrations. In: Guary, J.C., Guéguéniat, P., Pentreath, R.J. (Eds.), Radionuclides: A Tool for Oceanography, Cherbourg 1-5 June, 1987. Elsevier Applied Science Publishers, London, New York, pp. 384-394]. The area covered by the model includes the English Channel, the southern North Sea and the Irish Sea with a mesh size of 1 km. The main adjustment parameters of this model are the sources of wind data used and the calculation method for evaluating wind stress at the sea surface. With these parameters, the fluxes of radionuclides and water masses in the English Channel and the North Sea were balanced for the whole period of field measurements (1987-1994). The correlation factor between individual measurements in seawater and calculation results is 0.88 with an average error of ±54%, the error attributable to the measurement process being 15% on average. The mean flux through the Dover Strait is 126,000 m 3 s -1, close from the one obtained from previous studies [Salomon, J.C., Breton, M., Guéguéniat, P. 1993. Computed residual flow through the Dover
Superadiabatic evolution of acoustic and vorticity perturbations in Couette flow
NASA Astrophysics Data System (ADS)
Favraud, Gael; Pagneux, Vincent
2014-03-01
Nonadiabatic transitions between the acoustic and the vorticity modes perturbing a plane Couette flow are examined in the context of higher-order WKB asymptotics. In the case of the Schrödinger equation, it is known that looking at the solution expressed in the superadiabatic base, composed of higher-order asymptotic solutions, smoothes quantum state transitions. Then, increasing the order of the superadiabatic base causes these transitions to tend to the Gauss error function, and, once an optimal order is reached, the asymptotic process starts to diverge. We show that for perturbations in Couette flow, similar results can be applied on the amplitudes of the vorticity and acoustic modes. This allows us to more closely track the emergence of the acoustic modes in the presence of the vorticity mode.
Measurements of small radius ratio turbulent Taylor-Couette flow
NASA Astrophysics Data System (ADS)
van der Veen, Roeland; Huisman, Sander; Merbold, Sebastian; Sun, Chao; Harlander, Uwe; Egbers, Christoph; Lohse, Detlef
2014-11-01
In Taylor-Couette flows, the radius ratio (η =ri /ro) is one of the key parameters of the system. For small η, the asymmetry of the inner and outer boundary layer becomes more important, affecting the general flow structure and boundary layer characteristics. Using high-resolution particle image velocimetry we measure flow profiles, local transport, and statistical properties of the flow for a radius ratio of 0.5 and a Reynolds number of up to 4 .104 . By measuring flow profiles at varying heights, roll structures are characterized for two different rotation ratios of the inner and outer cylinder. In addition, we systematically vary the rotation ratio and the Reynolds number. These results exemplify how curvature affects flow in strongly turbulent Taylor-Couette Flow.
Structures in Transitional Taylor-Couette Flows Identified using POD
NASA Astrophysics Data System (ADS)
Balabani, Stavroula; Imomoh, Eboshogwe; Dusting, Jonathan
2009-11-01
The flow in the gap between concentric cylinders, or Taylor-Couette flow, has been used to study transition to turbulence for decades, and is also utilised for various biotechnological and industrial processes. Transitional flow states depend highly on vessel geometry; they are also three-dimensional and often time dependent limiting the use of experimental techniques for their characterisation. In this talk the transition to turbulence in a Taylor-Couette flow is studied by means of time resolved PIV velocity fields and Proper Orthogonal Decomposition (POD). It is found that for the particular geometry studied the transition to turbulence occurs via a quasi periodic regime characterised by a fast moving azimuthal wave (FMAW). Aspects of the FMAW structure, such as a series of co-rotating vortices that increase in strength away from the endwalls, are also revealed by spatially resolved POD.
Split rheometer Couette attachment to enable sample extraction
NASA Astrophysics Data System (ADS)
Guthrie, Sarah E.; Idziak, Stefan H. J.
2005-02-01
We report on the development of a Couette attachment insert for a rheometer, which is designed to split in half, enabling intact sample extraction of cocoa butter crystallized from the melt under known dynamic stress conditions. This cell is capable of producing a sample 1mm thick. At shear rates of 90-720s-1 and final temperatures of 18-20°C it was shown that the sample will completely separate from the cell surface intact.
Traveling hairpin-shaped fluid vortices in plane Couette flow
NASA Astrophysics Data System (ADS)
Deguchi, K.; Nagata, M.
2010-11-01
Traveling-wave solutions are discovered in plane Couette flow. They are obtained when the so-called steady hairpin vortex state found recently by Gibson [J. Fluid Mech. 638, 243 (2009)]10.1017/S0022112009990863 and Itano and Generalis [Phys. Rev. Lett. 102, 114501 (2009)]10.1103/PhysRevLett.102.114501 is continued to sliding Couette flow geometry between two concentric cylinders by using the radius ratio as a homotopy parameter. It turns out that in the plane Couette flow geometry two traveling waves having the phase velocities with opposite signs are associated with their appearance from the steady hairpin vortex state, where the amplitude of the phase velocities increases gradually from zero as the Reynolds number is increased. The solutions obviously inherit the streaky structure of the hairpin vortex state, but shape preserving flow patterns propagate in the streamwise direction. Other striking features of the solution are asymmetric mean flow profiles and strong quasistreamwise vortices which occupy the vicinity of only the top or bottom moving boundary, depending on the sign of the phase velocity. Furthermore, we find that the pitchfork bifurcation associated with the appearance of the solution becomes imperfect when the flow is perturbed by a Poiseuille flow component.
Excitation of inertial modes in an experimental spherical Couette flow.
Rieutord, Michel; Triana, Santiago Andrés; Zimmerman, Daniel S; Lathrop, Daniel P
2012-08-01
Spherical Couette flow (flow between concentric rotating spheres) is one of flows under consideration for the laboratory magnetic dynamos. Recent experiments have shown that such flows may excite Coriolis restored inertial modes. The present work aims to better understand the properties of the observed modes and the nature of their excitation. Using numerical solutions describing forced inertial modes of a uniformly rotating fluid inside a spherical shell, we first identify the observed oscillations of the Couette flow with nonaxisymmetric, retrograde, equatorially antisymmetric inertial modes, confirming first attempts using a full sphere model. Although the model has no differential rotation, identification is possible because a large fraction of the fluid in a spherical Couette flow rotates rigidly. From the observed sequence of the excited modes appearing when the inner sphere is slowed down by step, we identify a critical Rossby number associated with a given mode, below which it is excited. The matching between this critical number and the one derived from the phase velocity of the numerically computed modes shows that these modes are excited by an instability likely driven by the critical layer that develops in the shear layer, staying along the tangent cylinder of the inner sphere. PMID:23005851
High-Reynolds Number Taylor-Couette Turbulence
NASA Astrophysics Data System (ADS)
Grossmann, Siegfried; Lohse, Detlef; Sun, Chao
2016-01-01
Taylor-Couette flow, the flow between two coaxial co- or counter-rotating cylinders, is one of the paradigmatic systems in the physics of fluids. The (dimensionless) control parameters are the Reynolds numbers of the inner and outer cylinders, the ratio of the cylinder radii, and the aspect ratio. One key response of the system is the torque required to retain constant angular velocities, which can be connected to the angular velocity transport through the gap. Whereas the low-Reynolds number regime was well explored in the 1980s and 1990s of the past century, in the fully turbulent regime major research activity developed only in the past decade. In this article, we review this recent progress in our understanding of fully developed Taylor-Couette turbulence from the experimental, numerical, and theoretical points of view. We focus on the parameter dependence of the global torque and on the local flow organization, including velocity profiles and boundary layers. Next, we discuss transitions between different (turbulent) flow states. We also elaborate on the relevance of this system for astrophysical disks (quasi-Keplerian flows). The review ends with a list of challenges for future research on turbulent Taylor-Couette flow.
Recovery of short-lived chemical species in a couette flow reactor
Ouyang, Q.; Swinney, H.L. ); Roux, J.C.; Kepper, P.; Boissonade, J. )
1992-04-01
This paper reports on a new technique for studying and recovering short-lived chemical intermediate species that has been developed using a Couette reactor, which is an open one-dimensional reaction-diffusion system. Reaction occurs in the annulus between concentric cylinders with the inner one rotating and the outer one at rest. Fresh reagents are in contact with the ends of the annulus, but there is no net axial flow. The axial transport arising from the hydrodynamic motion is effectively diffusive, but has a diffusion coefficient 3 to 5 order of magnitude larger than that of molecular diffusion. The oxidant (ClO{sub 2}{sup {minus}}) and reductant (I{sup {minus}}) of an autocatalytic reaction are fed at opposite ends of the reactor. The reactants diffuse toward each other and react, forming a steady, sharp chemical front and a stable spatial concentration band of unstable intermediate species (HOCl) in the front region. Unstable intermediate species are thus stabilized at a well-defined spatial position where they can be recovered and studied. The experiments and numerical simulations demonstrate that the faster the reaction rate, the stabler the chemical front and the more effective the recovery of unstable intermediate species.
Hydromagnetic Dynamics and Magnetic Field Enhancement in a Turbulent Spherical Couette Experiment
NASA Astrophysics Data System (ADS)
Stone, Douglas; Adams, Matthew; Kara, Onur; Lathrop, Daniel
2015-11-01
The University of Maryland Three Meter Geodynamo, a spherical Couette experiment filled with liquid sodium and geometrically similar to the earth's core, is used to study hydrodynamic and hydromagnetic phenomena in rapidly rotating turbulence. An external coil applies a magnetic field in order to study hydromagnetic effects relevant to the earth's outer core such as dynamo action, while an array of 31 external Hall sensors measures the Gauss coefficients of the resulting magnetic field. The flow state is strongly dependent on Rossby number, Ro = (ΩI -ΩO) /ΩO , where ΩI and ΩO are the inner and outer sphere rotation frequencies. The flow state is inferred from the torque required to drive the inner sphere. The generation of internal toroidal magnetic field through the Ω-effect is measured by a Hall probe inserted into the sodium. A self-sustaining dynamo has not yet been observed at rotation speeds up to ΩO=3 Hz, which is three-fourths of the design maximum of the experiment. However, continuous dipole amplification up to 12% of a small applied field has been observed at Ro=?17.7 while bursts of dipole field have been observed up to 15% of a large external applied field at Ro=+6.0 and up to 20% of a small applied field at Ro=+2.15.
Hydromagnetic Dynamics and Magnetic Field Enhancement in a Turbulent Spherical Couette Experiment
NASA Astrophysics Data System (ADS)
Stone, D. S.; Liu, Q.; Zimmerman, D. S.; Triana, S. A.; Nataf, H. C.; Lathrop, D. P.
2014-11-01
The University of Maryland Three Meter Geodynamo, a spherical Couette experiment filled with liquid sodium and geometrically similar to the earth's core, is used to study hydrodynamic and hydromagnetic phenomena in rapidly rotating turbulence. Turbulent flow is driven in the sodium by differential rotation of the inner and outer spherical shells, while an external coil applies a magnetic field in order to study hydromagnetic effects relevant to the earth's outer core such as dynamo action. An array of 31 external Hall sensors measures the Gauss coefficients of the resulting magnetic field. The flow state is strongly dependent on Rossby number Ro = (ΩI -ΩO) /ΩO , where ΩI and ΩO are the inner and outer sphere rotation frequencies. The flow state is inferred from the torque required to drive the inner sphere and the generation of internal toroidal magnetic field through the Ω-effect, which is measured by a Hall probe inserted into the sodium. A self-sustaining dynamo has not yet been observed at rotation speeds up to about half of the design maximum. However, continuous dipole amplification up to 12% of a small applied field has been observed at Ro = - 17 . 7 while bursts of dipole field have been observed up to 15% of a large external applied field at Ro = + 6 . 0 and up to 20% of a small applied field at Ro = + 2 . 15 .
A study of eigenvalue sensitivity for hydrodynamic stability operators
NASA Technical Reports Server (NTRS)
Schmid, Peter J.; Henningson, Dan S.; Khorrami, Mehdi R.; Malik, Mujeeb R.
1993-01-01
The eigenvalue sensitivity for hydrodynamic stability operators is investigated. Classical matrix perturbation techniques as well as the concept of epsilon-pseudospectra are applied to show that parts of the spectrum are highly sensitive to small perturbations. Applications are drawn from incompressible plane Couette flow, trailing line vortex flow, and compressible Blasius boundary-layer flow. Parameter studies indicate a monotonically increasing effect of the Reynolds number on the sensitivity. The phenomenon of eigenvalue sensitivity is due to the nonnormality of the operators and their discrete matrix analogs and may be associated with large transient growth of the corresponding initial value problem.
Hydrodynamic particle interactions in sheared microflows
NASA Astrophysics Data System (ADS)
Marin, Alvaro; Rossi, Massimiliano; Zurita-Gotor, Mauricio; Kähler, Christian J.
2012-11-01
Multiphase flows in micro-confined geometries are non-trivial problems: drops and particles introduce a high degree of complexity into the otherwise linear Stokes flows. Very recently, new mechanisms of instability have been identified in simulations in shear-flows of non-Brownian particle solutions (Zurita-Gotor et al., J. Fluid Mech. 592, 2007, and Phys. Rev. Lett. 108, 2012), which might be the cause for anomalous self-diffusion measured experimentally by Zarraga and Leighton (Phys. Fluids 14, 2002). Using a 3D particle tracking technique (Astigmatism-PTV), we perform experiments in a microconfined cone-plate couette flow with a dilute suspension of non-brownian particles. The A-PTV technique permits us to track individual particles trajectories revealing particle-particle hydrodynamic interactions. Our experiments show an abnormal dispersion in the velocity field and non-homogeneous particle distribution which can be related with the swapping mechanism (JFM 592, 2007; PRL 108, 2012).
Periodic orbits near onset of chaos in plane Couette flow.
Kreilos, Tobias; Eckhardt, Bruno
2012-12-01
We track the secondary bifurcations of coherent states in plane Couette flow and show that they undergo a periodic doubling cascade that ends with a crisis bifurcation. We introduce a symbolic dynamics for the orbits and show that the ones that exist fall into the universal sequence described by Metropolis, Stein and Stein for unimodal maps. The periodic orbits cover much of the turbulent dynamics in that their temporal evolution overlaps with turbulent motions when projected onto a plane spanned by energy production and dissipation. PMID:23278091
ERIC Educational Resources Information Center
Lafrance, Pierre
1978-01-01
Explores in a non-mathematical treatment some of the hydrodynamical phenomena and forces that affect the operation of ships, especially at high speeds. Discusses the major components of ship resistance such as the different types of drags and ways to reduce them and how to apply those principles for the hovercraft. (GA)
NASA Astrophysics Data System (ADS)
Mihalas, Dimitri
Basic Radiation Theory Specific Intensity Photon Number Density Photon Distribution Function Mean Intensity Radiation Energy Density Radiation Energy Flux Radiation Momentum Density Radiation Stress Tensor (Radiation Pressure Tensor) Thermal Radiation Thermodynamics of Thermal Radiation and a Perfect Gas The Transfer Equation Absorption, Emission, and Scattering The Equation of Transfer Moments of the Transfer Equation Lorentz Transformation of the Transfer Equation Lorentz Transformation of the Photon 4-Momentum Lorentz Transformation of the Specific Intensity, Opacity, and - Emissivity Lorentz Transformation of the Radiation Stress Energy Tensor The Radiation 4-Force Density Vector Covariant Form of the Transfer Equation Inertial-Frame Equations of Radiation Hydrodynamics Inertial-Frame Radiation Equations Inertial-Frame Equations of Radiation Hydrodynamics Comoving-Frame Equation of Transfer Special Relativistic Derivation (D. Mihalas) Consistency Between Comoving-Frame and Inertial-Frame Equations Noninertial Frame Derivation (J. I. Castor) Analysis of O (v/c) Terms Lagrangian Equations of Radiation Hydrodynamics Momentum Equation Gas Energy Equation First Law of Thermodynamics for the Radiation Field First Law of Thermodynamics for the Radiating Fluid Mechanical Energy Equation Total Energy Equation Consistency of Different Forms of the Radiating-Fluid Energy - and Momentum Equations Consistency of Inertial-Frame and Comoving-Frame Radiation Energy - and Momentum Equations Radiation Diffusion Radiation Diffusion Nonequilibrium Diffusion The Problem of Flux Limiting Shock Propagation: Numerical Methods Acoustic Waves Numerical Stability Systems of Equations Implications of Shock Development Implications of Diffusive Energy Transport Illustrative Example Numerical Radiation Hydrodynamics Radiating Fluid Energy and Momentum Equations Computational Strategy Energy Conservation Formal Solution Multigroup Equations An Astrophysical Example Adaptive-Grid Radiation
NASA Technical Reports Server (NTRS)
2006-01-01
[figure removed for brevity, see original site] Context image for PIA03693 Channel
This channel is located south of Iani Chaos.
Image information: VIS instrument. Latitude -10.9N, Longitude 345.5E. 17 meter/pixel resolution.
Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.
NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.
A two-dimensional Couette viscometer for Langmuir monolayers
NASA Astrophysics Data System (ADS)
Ghaskadvi, R. S.; Dennin, Michael
1998-10-01
We have developed an apparatus that is capable of simultaneously measuring the viscosity of Langmuir monolayers and visualizing their flow. It consists of a circular trough with a nearly circular elastic barrier that can be rotated to generate two-dimensional Couette flow. The "inner cylinder" is a Teflon knife-edge disk that is hung by a thin wire. The torque on the inner cylinder is determined by measuring the angular displacement of the disk. A stepper motor controls the barrier rotation. Viscosity can be measured in two different ways: by oscillating the torsion pendulum and by generating Couette flow. The dynamic viscosity range of the apparatus is 10-4<η<103g/s. Typical shear rates range from 10-4 to 101 s-1. A Brewster angle microscope is mounted on the apparatus. This is used to study various properties of the monolayer such as: velocity profiles, domain shape during shear, domain relaxation after shear, and size distribution of domains.
Geometry of state space in plane Couette flow
NASA Astrophysics Data System (ADS)
Cvitanović, P.; Gibson, J. F.
A large conceptual gap separates the theory of low-dimensional chaotic dynamics from the infinite-dimensional nonlinear dynamics of turbulence. Recent advances in experimental imaging, computational methods, and dynamical systems theory suggest a way to bridge this gap in our understanding of turbulence. Recent discoveries show that recurrent coherent structures observed in wall-bounded shear flows (such as pipes and plane Couette flow) result from close passes to weakly unstable invariant solutions of the Navier-Stokes equations. These 3D, fully nonlinear solutions (equilibria, traveling waves, and periodic orbits) structure the state space of turbulent flows and provide a skeleton for analyzing their dynamics. We calculate a hierarchy of invariant solutions for plane Couette, a canonical wall-bounded shear flow. These solutions reveal organization in the flow's turbulent dynamics and can be used to predict directly from the fundamental equations physical quantities such as bulk flow rate and mean wall drag. All results and the code that generates them are disseminated through through our group's open-source CFD software and solution database Channelflow.org and the collaborative e-book ChaosBook.org.
Transition to turbulence in Taylor-Couette ferrofluidic flow
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
It is known that in classical fluids turbulence typically occurs at high Reynolds numbers. But can turbulence occur at low Reynolds numbers? Here we investigate the transition to turbulence in the classic Taylor-Couette system in which the rotating fluids are manufactured ferrofluids with magnetized nanoparticles embedded in liquid carriers. We find that, in the presence of a magnetic field transverse to the symmetry axis of the system, turbulence can occur at Reynolds numbers that are at least one order of magnitude smaller than those in conventional fluids. This is established by extensive computational ferrohydrodynamics through a detailed investigation of transitions in the flow structure, and characterization of behaviors of physical quantities such as the energy, the wave number, and the angular momentum through the bifurcations. A finding is that, as the magnetic field is increased, onset of turbulence can be determined accurately and reliably. Our results imply that experimental investigation of turbulence may be feasible by using ferrofluids. Our study of transition to and evolution of turbulence in the Taylor-Couette ferrofluidic flow system provides insights into the challenging problem of turbulence control. PMID:26065572
Transition to turbulence in Taylor-Couette ferrofluidic flow.
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
It is known that in classical fluids turbulence typically occurs at high Reynolds numbers. But can turbulence occur at low Reynolds numbers? Here we investigate the transition to turbulence in the classic Taylor-Couette system in which the rotating fluids are manufactured ferrofluids with magnetized nanoparticles embedded in liquid carriers. We find that, in the presence of a magnetic field transverse to the symmetry axis of the system, turbulence can occur at Reynolds numbers that are at least one order of magnitude smaller than those in conventional fluids. This is established by extensive computational ferrohydrodynamics through a detailed investigation of transitions in the flow structure, and characterization of behaviors of physical quantities such as the energy, the wave number, and the angular momentum through the bifurcations. A finding is that, as the magnetic field is increased, onset of turbulence can be determined accurately and reliably. Our results imply that experimental investigation of turbulence may be feasible by using ferrofluids. Our study of transition to and evolution of turbulence in the Taylor-Couette ferrofluidic flow system provides insights into the challenging problem of turbulence control. PMID:26065572
Zonal Flow Velocimetry in Spherical Couette Flow using Acoustic Modes
NASA Astrophysics Data System (ADS)
Adams, Matthew M.; Mautino, Anthony R.; Stone, Douglas R.; Triana, Santiago A.; Lekic, Vedran; Lathrop, Daniel P.
2015-11-01
We present studies of spherical Couette flows using the technique of acoustic mode Doppler velocimetry. This technique uses rotational splittings of acoustic modes to infer the azimuthal velocity profile of a rotating flow, and is of special interest in experiments where direct flow visualization is impractical. The primary experimental system consists of a 60 cm diameter outer spherical shell concentric with a 20 cm diameter sphere, with air or nitrogen gas serving as the working fluid. The geometry of the system approximates that of the Earth's core, making these studies geophysically relevant. A turbulent shear flow is established in the system by rotating the inner sphere and outer shell at different rates. Acoustic modes of the fluid volume are excited using a speaker and measured via microphones, allowingdetermination of rotational splittings. Preliminary results comparing observed splittings with those predicted by theory are presented. While the majority of these studies were performed in the 60 cm diameter device using nitrogen gas, some work has also been done looking at acoustic modes in the 3 m diameter liquid sodium spherical Couette experiment. Prospects for measuring zonal velocity profiles in a wide variety of experiments are discussed.
NASA Astrophysics Data System (ADS)
Chefranov, Sergey; Chefranov, Alexander
2016-04-01
Linear hydrodynamic stability theory for the Hagen-Poiseuille (HP) flow yields a conclusion of infinitely large threshold Reynolds number, Re, value. This contradiction to the observation data is bypassed using assumption of the HP flow instability having hard type and possible for sufficiently high-amplitude disturbances. HP flow disturbance evolution is considered by nonlinear hydrodynamic stability theory. Similar is the case of the plane Couette (PC) flow. For the plane Poiseuille (PP) flow, linear theory just quantitatively does not agree with experimental data defining the threshold Reynolds number Re= 5772 ( S. A. Orszag, 1971), more than five-fold exceeding however the value observed, Re=1080 (S. J. Davies, C. M. White, 1928). In the present work, we show that the linear stability theory conclusions for the HP and PC on stability for any Reynolds number and evidently too high threshold Reynolds number estimate for the PP flow are related with the traditional use of the disturbance representation assuming the possibility of separation of the longitudinal (along the flow direction) variable from the other spatial variables. We show that if to refuse from this traditional form, conclusions on the linear instability for the HP and PC flows may be obtained for finite Reynolds numbers (for the HP flow, for Re>704, and for the PC flow, for Re>139). Also, we fit the linear stability theory conclusion on the PP flow to the experimental data by getting an estimate of the minimal threshold Reynolds number as Re=1040. We also get agreement of the minimal threshold Reynolds number estimate for PC with the experimental data of S. Bottin, et.al., 1997, where the laminar PC flow stability threshold is Re = 150. Rogue waves excitation mechanism in oppositely directed currents due to the PC flow linear instability is discussed. Results of the new linear hydrodynamic stability theory for the HP, PP, and PC flows are published in the following papers: 1. S.G. Chefranov, A
Castor, J I
2003-10-16
The discipline of radiation hydrodynamics is the branch of hydrodynamics in which the moving fluid absorbs and emits electromagnetic radiation, and in so doing modifies its dynamical behavior. That is, the net gain or loss of energy by parcels of the fluid material through absorption or emission of radiation are sufficient to change the pressure of the material, and therefore change its motion; alternatively, the net momentum exchange between radiation and matter may alter the motion of the matter directly. Ignoring the radiation contributions to energy and momentum will give a wrong prediction of the hydrodynamic motion when the correct description is radiation hydrodynamics. Of course, there are circumstances when a large quantity of radiation is present, yet can be ignored without causing the model to be in error. This happens when radiation from an exterior source streams through the problem, but the latter is so transparent that the energy and momentum coupling is negligible. Everything we say about radiation hydrodynamics applies equally well to neutrinos and photons (apart from the Einstein relations, specific to bosons), but in almost every area of astrophysics neutrino hydrodynamics is ignored, simply because the systems are exceedingly transparent to neutrinos, even though the energy flux in neutrinos may be substantial. Another place where we can do ''radiation hydrodynamics'' without using any sophisticated theory is deep within stars or other bodies, where the material is so opaque to the radiation that the mean free path of photons is entirely negligible compared with the size of the system, the distance over which any fluid quantity varies, and so on. In this case we can suppose that the radiation is in equilibrium with the matter locally, and its energy, pressure and momentum can be lumped in with those of the rest of the fluid. That is, it is no more necessary to distinguish photons from atoms, nuclei and electrons, than it is to distinguish
NASA Astrophysics Data System (ADS)
Lauga, Eric
2016-01-01
Bacteria predate plants and animals by billions of years. Today, they are the world's smallest cells, yet they represent the bulk of the world's biomass and the main reservoir of nutrients for higher organisms. Most bacteria can move on their own, and the majority of motile bacteria are able to swim in viscous fluids using slender helical appendages called flagella. Low-Reynolds number hydrodynamics is at the heart of the ability of flagella to generate propulsion at the micrometer scale. In fact, fluid dynamic forces impact many aspects of bacteriology, ranging from the ability of cells to reorient and search their surroundings to their interactions within mechanically and chemically complex environments. Using hydrodynamics as an organizing framework, I review the biomechanics of bacterial motility and look ahead to future challenges.
Scaling laws of turbulent Couette flow with wall-normal transpiration
NASA Astrophysics Data System (ADS)
Kraheberger, Stephanie; Oberlack, Martin; Hoyas, Sergio
2015-11-01
An extensive DNS study of turbulent plane Couette flows with permeable boundary conditions, i.e. wall-normal transpiration, was conducted at Reτ = 250 , 500 , 1000 and varying transpiration velocities v0 . The discretization employed is speudo-spectral in wall-parallel and compact finite differences in wall-normal direction (see Hoyas et al., Phys. Fluids 2006). We derived a global stress relation for the flow, balancing total shear stresses, with very different friction velocities at lower and upper wall. This, in turn, was used to validate convergence of DNS statistics. Most important, we derived a viscous sublayer velocity scaling for the suction wall employing asymptotic methods. Moreover, using Lie group symmetry analysis applied to the multi-point correlation equation we derived scaling laws for the near-wall region on the blowing wall and the channel center, predicting mean velocity
High Reynolds number decay of turbulent Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Verschoof, Ruben A.; Huisman, Sander G.; van der Veen, Roeland C. A.; Sun, Chao; Lohse, Detlef
2015-11-01
We study the decay of high-Reynolds number turbulence in a Taylor-Couette facility for pure inner cylinder rotation. The rotation of the inner cylinder (Rei = 2 ×106) is suddenly decelerated as fast as possible, thus removing the energy input within seconds. Local velocity measurements show that the decay in this wall-bounded inhomogeneous flow is faster than observed for homogeneous isotropic turbulent flows, due to the strong viscous drag applied by the inner and outer cylinder surfaces. We found that the decay over time can be described with the differential equation Re . (t) =cf (Re)Re2 , where the effects of the walls are included through the friction coefficient. A self-similar behavior of the azimuthal velocity is found: its normalized velocity profile as a function of the radius collapses over time during the decay process.
Logarithmic Boundary Layers in Strong Taylor-Couette Turbulence
NASA Astrophysics Data System (ADS)
Lohse, Detlef; Huisman, Sander; Ostilla, Rodolfo; Scharnowski, Sven; Cierpka, Christian; Kähler, Christian; Verzicco, Roberto; Sun, Chao; Grossmann, Siegfried
2013-11-01
We provide direct measurements of boundary layer profiles in highly turbulent Taylor-Couette flow up to Re = 2 ×106 using high-resolution particle image velocimetry and particle tracking velocimetry, complemented by DNS data on the same system up to Re =105 . We find that the mean azimuthal velocity profile at the inner and outer cylinder can be fitted by the von Kármán log law, but with corrections due to the curvature of the cylinder, which we theoretically account for, based on the Navier-Stokes equation and a closure assumption for the turbulent diffusivity. In particular, we study how these corrections depend on the cylinder radius ratio and show that they are different for the boundary layers at the inner and at the outer cylinder.
Multiple states in highly turbulent Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Huisman, Sander G.; van der Veen, Roeland C. A.; Sun, Chao; Lohse, Detlef
2014-05-01
The ubiquity of turbulent flows in nature and technology makes it of utmost importance to fundamentally understand turbulence. Kolmogorov’s 1941 paradigm suggests that for strongly turbulent flows with many degrees of freedom and large fluctuations, there would only be one turbulent state as the large fluctuations would explore the entire higher dimensional phase space. Here we report the first conclusive evidence of multiple turbulent states for large Reynolds number, Re(106) (Taylor number Ta(1012)) Taylor-Couette flow in the regime of ultimate turbulence, by probing the phase space spanned by the rotation rates of the inner and outer cylinder. The manifestation of multiple turbulent states is exemplified by providing combined global torque- and local-velocity measurements. This result verifies the notion that bifurcations can occur in high-dimensional flows (that is, very large Re) and questions Kolmogorov’s paradigm.
Multiple states in highly turbulent Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Huisman, Sander; van der Veen, Roeland; Sun, Chao; Lohse, Detlef
2014-11-01
The ubiquity of turbulent flows in nature and technology makes it of utmost importance to fundamentally understand turbulence. Kolmogorov's 1941 paradigm suggests that for strongly turbulent flows with many degrees of freedom and its large fluctuations, there would only be one turbulent state as the large fluctuations would explore the entire higher-dimensional phase space. Here we report the first conclusive evidence of multiple turbulent states for large Reynolds number Re = O (106) (Taylor number Ta = O (1012) Taylor-Couette flow in the regime of ultimate turbulence, by probing the phase space spanned by the rotation rates of the inner and outer cylinder. The manifestation of multiple turbulent states is exemplified by providing combined global torque and local velocity measurements. This result verifies the notion that bifurcations can occur in high-dimensional flows (i.e. very large Re) and questions Kolmogorov's paradigm.
Directed percolation phase transition to sustained turbulence in Couette flow
NASA Astrophysics Data System (ADS)
Lemoult, Grégoire; Shi, Liang; Avila, Kerstin; Jalikop, Shreyas V.; Avila, Marc; Hof, Björn
2016-03-01
Turbulence is one of the most frequently encountered non-equilibrium phenomena in nature, yet characterizing the transition that gives rise to turbulence in basic shear flows has remained an elusive task. Although, in recent studies, critical points marking the onset of sustained turbulence have been determined for several such flows, the physical nature of the transition could not be fully explained. In extensive experimental and computational studies we show for the example of Couette flow that the onset of turbulence is a second-order phase transition and falls into the directed percolation universality class. Consequently, the complex laminar-turbulent patterns distinctive for the onset of turbulence in shear flows result from short-range interactions of turbulent domains and are characterized by universal critical exponents. More generally, our study demonstrates that even high-dimensional systems far from equilibrium such as turbulence exhibit universality at onset and that here the collective dynamics obeys simple rules.
Couette flow regimes with heat transfer in rarefied gas
Abramov, A. A. Butkovskii, A. V.
2013-06-15
Based on numerical solution of the Boltzmann equation by direct statistic simulation, the Couette flow with heat transfer is studied in a broad range of ratios of plate temperatures and Mach numbers of a moving plate. Flow regime classification by the form of the dependences of the energy flux and friction stress on the Knudsen number Kn is proposed. These dependences can be simultaneously monotonic and nonmonotonic and have maxima. Situations are possible in which the dependence of the energy flux transferred to a plate on Kn has a minimum, while the dependence of the friction stress is monotonic or even has a maximum. Also, regimes exist in which the dependence of the energy flux on Kn has a maximum, while the dependence of the friction stress is monotonic, and vice versa.
On the linear stability of compressible plane Couette flow
NASA Technical Reports Server (NTRS)
Duck, Peter W.; Erlebacher, Gordon; Hussaini, M. Yousuff
1991-01-01
The linear stability of compressible plane Couette flow is investigated. The correct and proper basic velocity and temperature distributions are perturbed by a small amplitude normal mode disturbance. The full small amplitude disturbance equations are solved numerically at finite Reynolds numbers, and the inviscid limit of these equations is then investigated in some detail. It is found that instability can occur, although the stability characteristics of the flow are quite different from unbounded flows. The effects of viscosity are also calculated, asymptotically, and shown to have a stabilizing role in all the cases investigated. Exceptional regimes to the problem occur when the wavespeed of the disturbances approaches the velocity of either of the walls, and these regimes are also analyzed in some detail. Finally, the effect of imposing radiation-type boundary conditions on the upper (moving) wall (in place of impermeability) is investigated, and shown to yield results common to both bounded and unbounded flows.
Shercliff layers in strongly magnetic cylindrical Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Hollerbach, Rainer; Hulot, Deborah
2016-07-01
We numerically compute the axisymmetric Taylor-Couette flow in the presence of axially periodic magnetic fields, with Hartmann numbers up to Ha2 =107. The geometry of the field singles out special field lines on which Shercliff layers form. These are simple shear layers for insulating boundaries, versus super-rotating or counter-rotating layers for conducting boundaries. Some field configurations have previously studied spherical analogs, but fundamentally new configurations also exist, having no spherical analogs. Finally, we explore the influence of azimuthal fields Bϕ ∼r-1eˆϕ on these layers, and show that the flow is suppressed for conducting boundaries, but enhanced for insulating boundaries. xml:lang="fr"
Symmetry and stability in Taylor-Couette flow
NASA Technical Reports Server (NTRS)
Golubitsky, M.; Stewart, I.
1986-01-01
The flow of a fluid between concentric rotating cylinders (the Taylor problem) is studied by exploiting the symmetries of the system. The Navier-Stokes equations, linearized about Couette flow, possess two zero and four purely imaginary eigenvalues at a suitable value of the speed of rotation of the outer cylinder. There is thus a reduced bifurcation equation on a six-dimensonal space which can be shown to commute with an action of the symmetry group 0(2) x S0(2). The group structure is used to analyze this bifurcation equation in the simplest (nondegenerate) case, and to compute the stabilities of solutions. In particular, when the outer cylinder is counterrotated, transitions which seem to agree with recent experiments of Andereck, Liu, and Swinney (1984) are obtained. It is also possible to obtain the 'main sequence' in this model. This sequence is normally observed in experiments when the outer cylinder is held fixed.
Saturation of nonaxisymmetric instabilities of magnetized spherical Couette flow.
Kaplan, E J
2014-06-01
We numerically investigate the saturation of the hydromagnetic instabilities of a magnetized spherical Couette flow. Previous simulations demonstrated a region where the axisymmetric flow, calculated from a 2D simulation, was linearly unstable to nonaxisymmetric perturbations. Full, nonlinear, 3d simulations showed that the saturated state would consist only of harmonics of one azimuthal wave number, though there were bifurcations and transitions as nondimensional parameters (Re, Ha) were varied. Here, the energy transfer between different azimuthal modes is formulated as a network. This demonstrates a mechanism for the saturation of one mode and for the suppression of other unstable modes. A given mode grows by extracting energy from the axisymmetric flow, and then saturates as the energy transfer to its second harmonic equals this inflow. At the same time, this mode suppresses other unstable modes by facilitating an energy transfer to linearly stable modes. PMID:25019888
Optimal Taylor-Couette flow: radius ratio dependence
NASA Astrophysics Data System (ADS)
Ostilla-Mónico, Rodolfo; Huisman, Sander G.; Jannink, Tim J. G.; Van Gils, Dennis P. M.; Verzicco, Roberto; Grossmann, Siegfried; Sun, Chao; Lohse, Detlef
2014-05-01
Taylor-Couette flow with independently rotating inner (i) and outer (o) cylinders is explored numerically and experimentally to determine the effects of the radius ratio {\\eta} on the system response. Numerical simulations reach Reynolds numbers of up to Re_i=9.5 x 10^3 and Re_o=5x10^3, corresponding to Taylor numbers of up to Ta=10^8 for four different radius ratios {\\eta}=r_i/r_o between 0.5 and 0.909. The experiments, performed in the Twente Turbulent Taylor-Couette (T^3C) setup, reach Reynolds numbers of up to Re_i=2x10^6$ and Re_o=1.5x10^6, corresponding to Ta=5x10^{12} for {\\eta}=0.714-0.909. Effective scaling laws for the torque J^{\\omega}(Ta) are found, which for sufficiently large driving Ta are independent of the radius ratio {\\eta}. As previously reported for {\\eta}=0.714, optimum transport at a non-zero Rossby number Ro=r_i|{\\omega}_i-{\\omega}_o|/[2(r_o-r_i){\\omega}_o] is found in both experiments and numerics. Ro_opt is found to depend on the radius ratio and the driving of the system. At a driving in the range between {Ta\\sim3\\cdot10^8} and {Ta\\sim10^{10}}, Ro_opt saturates to an asymptotic {\\eta}-dependent value. Theoretical predictions for the asymptotic value of Ro_{opt} are compared to the experimental results, and found to differ notably. Furthermore, the local angular velocity profiles from experiments and numerics are compared, and a link between a flat bulk profile and optimum transport for all radius ratios is reported.
Chabchoub, A; Hoffmann, N; Onorato, M; Genty, G; Dudley, J M; Akhmediev, N
2013-08-01
We report the experimental observation of multi-bound-soliton solutions of the nonlinear Schrödinger equation (NLS) in the context of hydrodynamic surface gravity waves. Higher-order N-soliton solutions with N=2, 3 are studied in detail and shown to be associated with self-focusing in the wave group dynamics and the generation of a steep localized carrier wave underneath the group envelope. We also show that for larger input soliton numbers, the wave group experiences irreversible spectral broadening, which we refer to as a hydrodynamic supercontinuum by analogy with optics. This process is shown to be associated with the fission of the initial multisoliton into individual fundamental solitons due to higher-order nonlinear perturbations to the NLS. Numerical simulations using an extended NLS model described by the modified nonlinear Schrödinger equation, show excellent agreement with experiment and highlight the universal role that higher-order nonlinear perturbations to the NLS play in supercontinuum generation. PMID:23952405
NASA Astrophysics Data System (ADS)
White, James M.; Muller, Susan J.
2002-11-01
A number of questions regarding the effects of viscous dissipation on the stability of Newtonian Taylor-Couette flows are addressed through flow visualization experiments. Studies with three types of fluids of varying thermal sensitivity reveal that the instability is caused by a coupling of centrifugal destabilization and thermally induced gradients in viscosity. These tests also demonstrate that the Nahme number is the appropriate variable with which to describe dissipative effects on the hydrodynamic stability. Additional tests are performed to elucidate the effects of centrifugal destabilization by varying the amount of outer and inner cylinder co-rotation with the Reynolds number and Nahme number fixed. Lastly, a small hysteresis loop in the critical conditions is revealed by performing ramp tests in which the instability is approached from either above or below the critical condition; this indicates that the instability is weakly subcritical.
Pomraning, G.C.
1982-12-31
This course was intended to provide the participant with an introduction to the theory of radiative transfer, and an understanding of the coupling of radiative processes to the equations describing compressible flow. At moderate temperatures (thousands of degrees), the role of the radiation is primarily one of transporting energy by radiative processes. At higher temperatures (millions of degrees), the energy and momentum densities of the radiation field may become comparable to or even dominate the corresponding fluid quantities. In this case, the radiation field significantly affects the dynamics of the fluid, and it is the description of this regime which is generally the charter of radiation hydrodynamics. The course provided a discussion of the relevant physics and a derivation of the corresponding equations, as well as an examination of several simplified models. Practical applications include astrophysics and nuclear weapons effects phenomena.
NASA Astrophysics Data System (ADS)
Zhang, Rui; Roberts, Tyler; de Pablo, Juan; dePablo Team
2014-11-01
Liquid crystals (LC) posses anisotropic viscoelastic properties, and, as such, LC flow can be incredibly complicated. Here we employ a hybrid lattice Boltzmann method (pioneered by Deniston, Yeomans and Cates) to systematically study the hydrodynamics of nematic liquid crystals (LCs) with and without solid particles. This method evolves the velocity field through lattice Boltzmann and the LC-order parameter via a finite-difference solver of the Beris-Edwards equation. The evolution equation of the boundary points with finite anchoring is obtained through Poisson bracket formulation. Our method has been validated by matching the Ericksen-Leslie theory. We demonstrate two applications in the flow alignment regime. We first investigate a hybrid channel flow in which the top and bottom walls have different anchoring directions. By measuring the apparent shear viscosity in terms of Couette flow, we achieve a viscosity inhomogeneous system which may be applicable to nano particle processing. In the other example, we introduce a homeotropic spherical particle to the channel, and focus on the deformations of the defect ring due to anchorings and flow. The results are then compared to the molecular dynamics simulations of a colloid particle in an LC modeled by a Gay-Berne potential.
Huizinga, Richard J.
2007-01-01
The Blue River Channel Modification project being implemented by the U.S. Army Corps of Engineers (USACE) is intended to provide flood protection within the Blue River valley in the Kansas City, Mo., metropolitan area. In the latest phase of the project, concerns have arisen about preserving the Civil War historic area of Byram's Ford and the associated Big Blue Battlefield while providing flood protection for the Byram's Ford Industrial Park. In 1996, the USACE used a physical model built at the Waterways Experiment Station (WES) in Vicksburg, Miss., to examine the feasibility of a proposed grade control structure (GCS) that would be placed downstream from the historic river crossing of Byram's Ford to provide a subtle transition of flow from the natural channel to the modified channel. The U.S. Geological Survey (USGS), in cooperation with the USACE, modified an existing two-dimensional finite element surface-water model of the river between 63d Street and Blue Parkway (the 'original model'), used the modified model to simulate the existing (as of 2006) unimproved channel and the proposed channel modifications and GCS, and analyzed the results from the simulations and those from the WES physical model. Modifications were made to the original model to create a model that represents existing (2006) conditions between the north end of Swope Park immediately upstream from 63d Street and the upstream limit of channel improvement on the Blue River (the 'model of existing conditions'). The model of existing conditions was calibrated to two measured floods. The model of existing conditions also was modified to create a model that represents conditions along the same reach of the Blue River with proposed channel modifications and the proposed GCS (the 'model of proposed conditions'). The models of existing conditions and proposed conditions were used to simulate the 30-, 50-, and 100-year recurrence floods. The discharge from the calibration flood of May 15, 1990, also
NASA Astrophysics Data System (ADS)
Avila, Kerstin; Hof, Björn
2013-06-01
A novel Taylor-Couette system has been constructed for investigations of transitional as well as high Reynolds number turbulent flows in very large aspect ratios. The flexibility of the setup enables studies of a variety of problems regarding hydrodynamic instabilities and turbulence in rotating flows. The inner and outer cylinders and the top and bottom endplates can be rotated independently with rotation rates of up to 30 Hz, thereby covering five orders of magnitude in Reynolds numbers (Re = 101-106). The radius ratio can be easily changed, the highest realized one is η = 0.98 corresponding to an aspect ratio of 260 gap width in the vertical and 300 in the azimuthal direction. For η < 0.98 the aspect ratio can be dynamically changed during measurements and complete transparency in the radial direction over the full length of the cylinders is provided by the usage of a precision glass inner cylinder. The temperatures of both cylinders are controlled independently. Overall this apparatus combines an unmatched variety in geometry, rotation rates, and temperatures, which is provided by a sophisticated high-precision bearing system. Possible applications are accurate studies of the onset of turbulence and spatio-temporal intermittent flow patterns in very large domains, transport processes of turbulence at high Re, the stability of Keplerian flows for different boundary conditions, and studies of baroclinic instabilities.
Avila, Kerstin; Hof, Björn
2013-06-01
A novel Taylor-Couette system has been constructed for investigations of transitional as well as high Reynolds number turbulent flows in very large aspect ratios. The flexibility of the setup enables studies of a variety of problems regarding hydrodynamic instabilities and turbulence in rotating flows. The inner and outer cylinders and the top and bottom endplates can be rotated independently with rotation rates of up to 30 Hz, thereby covering five orders of magnitude in Reynolds numbers (Re = 10(1)-10(6)). The radius ratio can be easily changed, the highest realized one is η = 0.98 corresponding to an aspect ratio of 260 gap width in the vertical and 300 in the azimuthal direction. For η < 0.98 the aspect ratio can be dynamically changed during measurements and complete transparency in the radial direction over the full length of the cylinders is provided by the usage of a precision glass inner cylinder. The temperatures of both cylinders are controlled independently. Overall this apparatus combines an unmatched variety in geometry, rotation rates, and temperatures, which is provided by a sophisticated high-precision bearing system. Possible applications are accurate studies of the onset of turbulence and spatio-temporal intermittent flow patterns in very large domains, transport processes of turbulence at high Re, the stability of Keplerian flows for different boundary conditions, and studies of baroclinic instabilities. PMID:23822377
NASA Astrophysics Data System (ADS)
Jayaraman, Balaji; Brasseur, James; Wang, Yanxing
2015-11-01
Drug dissolution rates from powdered formulations are commonly measured in in vitro devices. Both measurements and models commonly assume perfect mixing of drug and particle within the device. In this study we analyze the potential importance of heterogeneity in particle concentration and distribution using CFD that incorporates physically accurate mathematical representations of hydrodynamic enhancement of mass transport from shear as applicable to drug dissolution in vivo as well as in vitro. We have developed a high-fidelity computational formulation using the Lattice Boltzmann Method (LBM) with the parallel particle tracking for a polydisperse collection transported by the flow. Drug release from the small (<100 μm) Lagrangian `point' particles is modeled using a mathematical framework that is built on a validated first principles `quasi-steady state' approximation with correlations for shear enhancement and integrated with the coarser Eulerian LBM flow field using a subgrid formulation Our Eulerian-Lagrangian formulation takes into account spatial variations in particle `bulk' concentration from polydisperse particle distributions with specified particle distribution heterogeneities. We shall discuss the primary influences of heterogeneous bulk concentrations surrounding individual particles and non-homogeneous particle distributions in an in vitro Couette flow device to quantify the relative influences of shear enhancement on drug dissolution in vivo vs. in vitro
Geometry Mediated Drag Reduction in Taylor-Couette Flows
NASA Astrophysics Data System (ADS)
Raayai, Shabnam; McKinley, Gareth
2015-11-01
Micro-scale ribbed surfaces have been shown to be able to modify surface properties such as skin friction on both natural and fabricated surfaces. Previous experiments have shown that ribbed surfaces can reduce skin friction in turbulent flow by up to 4-8% in the presence of zero or mild pressure gradients. Our previous computations have shown a substantial reduction in skin friction using micro-scaled ribs of sinusoidal form in high Reynolds number laminar boundary layer flow. The mechanism of this reduction is purely viscous, through a geometrically-controlled retardation of the flow in the grooves of the surface. The drag reduction achieved depends on the ratio of the amplitude to the wavelength of the surface features and can be presented as a function of the wavelength expressed in dimensionless wall units. Here we extend this work, both experimentally and numerically, to consider the effect of similar ribs on steady viscous flow between concentric cylinders (Taylor-Couette flow). For the experimental work, the inner rotating cylinder (rotor) is machined with stream-wise V-groove structures and experiments are performed with fluids of different viscosity to compare the measured frictional torques to the corresponding values on a smooth flat rotor as a measure of drag reduction. The numerical work is performed using the OpenFOAM®open source software to compare the results and understand the physical mechanisms underlying this drag reduction phenomenon.
Frictional drag reduction in bubbly Couette-Taylor flow
NASA Astrophysics Data System (ADS)
Murai, Yuichi; Oiwa, Hiroshi; Takeda, Yasushi
2008-03-01
Frictional drag reduction due to the presence of small bubbles is investigated experimentally using a Couette-Taylor flow system; i.e., shear flow between concentric cylinders. Torque and bubble behavior are measured as a function of Reynolds number up to Re =5000 while air bubbles are injected constantly and rise through an array of vortical cells. Silicone oil is used to avoid the uncertain interfacial property of bubbles and to produce nearly monosized bubble distributions. The effect of drag reduction on sensitivity and power gain are assessed. The sensitivity exceeds unity at Re <2000, proving that the effect of the reduction in drag is greater than that of the reduction in mixture density. This is due to the accumulation of bubbles toward the rotating inner cylinder, which is little affected by turbulence. The power gain, which is defined by the power saving from the drag reduction per the pumping power of bubble injection, has a maximum value of O(10) at higher Re numbers around 2500. An image processing measurement shows this is because of the disappearance of azimuthal waves when the organized bubble distribution transforms from toroidal to spiral modes. Moreover, the axial spacing of bubble clouds expands during the transition, which results in an effective reduction in the momentum exchange.
Nonaxisymmetric linear instability of cylindrical magnetohydrodynamic Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Child, Adam; Kersalé, Evy; Hollerbach, Rainer
2015-09-01
We consider the nonaxisymmetric modes of instability present in Taylor-Couette flow under the application of helical magnetic fields, mainly for magnetic Prandtl numbers close to the inductionless limit, and conduct a full examination of marginal stability in the resulting parameter space. We allow for the azimuthal magnetic field to be generated by a combination of currents in the inner cylinder and fluid itself and introduce a parameter governing the relation between the strength of these currents. A set of governing eigenvalue equations for the nonaxisymmetric modes of instability are derived and solved by spectral collocation with Chebyshev polynomials over the relevant parameter space, with the resulting instabilities examined in detail. We find that by altering the azimuthal magnetic field profiles the azimuthal magnetorotational instability, nonaxisymmetric helical magnetorotational instability, and Tayler instability yield interesting dynamics, such as different preferred mode types and modes with azimuthal wave number m >1 . Finally, a comparison is given to the recent WKB analysis performed by Kirillov et al. [Kirillov, Stefani, and Fukumoto, J. Fluid Mech. 760, 591 (2014), 10.1017/jfm.2014.614] and its validity in the linear regime.
Helical magnetorotational instability in magnetized Taylor-Couette flow
Liu Wei; Ji Hantao; Goodman, Jeremy; Herron, Isom
2006-11-15
Hollerbach and Ruediger have reported a new type of magnetorotational instability (MRI) in magnetized Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields. The salient advantage of this 'helical' MRI (HMRI) is that marginal instability occurs at arbitrarily low magnetic Reynolds and Lundquist numbers, suggesting that HMRI might be easier to realize than standard MRI (axial field only), and that it might be relevant to cooler astrophysical disks, especially those around protostars, which may be quite resistive. We confirm previous results for marginal stability and calculate HMRI growth rates. We show that in the resistive limit, HMRI is a weakly destabilized inertial oscillation propagating in a unique direction along the axis. But we report other features of HMRI that make it less attractive for experiments and for resistive astrophysical disks. Large axial currents are required. More fundamentally, instability of highly resistive flow is peculiar to infinitely long or periodic cylinders: finite cylinders with insulating endcaps are shown to be stable in this limit, at least if viscosity is neglected. Also, Keplerian rotation profiles are stable in the resistive limit regardless of axial boundary conditions. Nevertheless, the addition of a toroidal field lowers thresholds for instability even in finite cylinders.
Direct Simulation Monte Carlo Investigation of Noncontinuum Couette Flow
NASA Astrophysics Data System (ADS)
Torczynski, J. R.; Gallis, M. A.
2009-11-01
The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics is used to study noncontinuum effects in Couette flow. The walls have equal temperatures and equal accommodation coefficients but unequal tangential velocities. Simulations are performed for near-free-molecular to near-continuum gas pressures with accommodation coefficients of 0.25, 0.5, and 1. Ten gases are examined: argon, helium, nitrogen, sea-level air, and six Inverse-Power-Law (IPL) gases with viscosity temperature exponents of 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0, as represented by the Variable Soft Sphere (VSS) interaction. In all cases, the wall shear stress is proportional to the slip velocity. The momentum transfer coefficient relating these two quantities can be accurately correlated in terms of the Knudsen number based on the wall separation. The two dimensionless parameters in the correlation are similar for all gases examined. 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.
The stability of Taylor-Couette flow with radial heating
NASA Astrophysics Data System (ADS)
Ali, Mohamed El-Sayed
The stability of circular Couette flow with radial heating across vertically oriented coaxial cylinders is investigated using linearized stability theory. The physical problem is governed by five parameters: the Taylor number Ta, the Groshof number G, the Prandtl number Pr, the cylinder aspect ration A, and the radius ratio eta. In the model infinite aspect ratio is assumed and critical stability boundaries are calculated for a conduction regime base flow. A rational analysis is made to derive the full governing perturbation equations and test flow stability subject to both axisymmetric and nonaxisymmetric disturbances. The flow may be driven to instability by competition between centrifugal, buoyancy, and shear force mechanisms. In spite of this complexity, the existence of solution symmetries of the perturbation equations with respect to the sense of radial heating and the sense of cylinder rotation are proven. The linear boundary-value problem defined by 16 first-order differential equations is solved using the software package SUPORT in combination with the nonlinear equation solver SNSQE. Critical stability boundaries at fixed Pr and eta were determined by searching for the minimum value of either Ta or G over all wavelengths K and mode numbers n.
Effect of the radial buoyancy on a circular Couette flow
NASA Astrophysics Data System (ADS)
Meyer, Antoine; Yoshikawa, Harunori N.; Mutabazi, Innocent
2015-11-01
The effect of a radial temperature gradient on the stability of a circular Couette flow is investigated when the gravitational acceleration is neglected. The induced radial stratification of the fluid density coupled with the centrifugal acceleration generates radial buoyancy which is centrifugal for inward heating and centripetal for outward heating. This radial buoyancy modifies the Rayleigh discriminant and induces the asymmetry between inward heating and outward heating in flow behavior. The critical modes are axisymmetric and stationary for inward heating while for outward heating, they can be oscillatory axisymmetric or nonaxisymmetric depending on fluid diffusion properties, i.e., on the Prandtl number Pr. The dependence of the critical modes on Pr is explored for different values of the radius ratio of the annulus. The power input of the radial buoyancy is compared with other power terms. The critical frequency of the oscillatory axisymmetric modes is linked to the Brunt-Väisälä frequency due to the density stratification in the radial gravity field induced by the rotation. These modes are associated with inertial waves. The dispersion relation of the oscillatory axisymmetric modes is derived in the vicinity of the critical conditions. A weakly nonlinear amplitude equation with a forcing term is proposed to explain the domination of these axisymmetric oscillatory modes over the stationary centrifugal mode.
Characteristics of electrohydrodynamic roll structures in laminar planar Couette flow
NASA Astrophysics Data System (ADS)
Kourmatzis, Agisilaos; Shrimpton, John S.
2016-02-01
The behaviour of an incompressible dielectric liquid subjected to a laminar planar Couette flow with unipolar charge injection is investigated numerically in two dimensions. The computations show new morphological characteristics of roll structures that arise in this forced electro-convection problem. The charge and velocity magnitude distributions between the two parallel electrodes are discussed as a function of the top wall velocity and the EHD Rayleigh number, T for the case of strong charge injection. A wide enough parametric space is investigated such that the observed EHD roll structures progress through three regimes. These regimes are defined by the presence of a single or double-roll free convective structure as observed elsewhere (Vazquez et al 2008 J. Phys. D 41 175303), a sheared or stretched roll structure, and finally by a regime where the perpendicular velocity gradient is sufficient to prevent the generation of a roll. These three regimes have been delineated as a function of the wall to ionic drift velocity {{U}\\text{W}}/κ E , and the T number. In the stretched regime, an increase in {{U}\\text{W}}/κ E can reduce charge and momentum fluctuations whilst in parallel de-stratify charge in the region between the two electrodes. The stretched roll regime is also characterised by a substantial influence of {{U}\\text{W}}/κ E on the steady development time, however in the traditional non-stretched roll structure regime, no influence of {{U}\\text{W}}/κ E on the development time is noted.
Transient growth in linearly stable Taylor-Couette flows
NASA Astrophysics Data System (ADS)
Maretzke, Simon; Hof, Björn; Avila, Marc
2014-03-01
Non-normal transient growth of disturbances is considered as an essential prerequisite for subcritical transition in shear flows, i.e. transition to turbulence despite linear stability of the laminar flow. In this work we present numerical and analytical computations of linear transient growth covering all linearly stable regimes of Taylor--Couette flow. Our numerical experiments reveal comparable energy amplifications in the different regimes. For high shear Reynolds numbers Re the optimal transient energy growth always follows a 2/3-scaling with Re, which allows for large amplifications even in regimes where the presence of turbulence remains debated. In co-rotating Rayleigh-stable flows the optimal perturbations become increasingly columnar in their structure, as the optimal axial wavenumber goes to zero. In this limit of axially invariant perturbations we show that linear stability and transient growth are independent of the cylinders' rotation-ratio and we derive a universal 2/3-scaling of optimal energy growth with Re using WKB-theory. Based on this, a semi-empirical formula for the estimation of linear transient growth valid in all regimes is obtained.
Dynamics of axially localized states in Taylor-Couette flows.
Lopez, Jose M; Marques, Francisco
2015-05-01
We present numerical simulations of the flow confined in a wide gap Taylor-Couette system, with a rotating inner cylinder and variable length-to-gap aspect ratio. A complex experimental bifurcation scenario differing from the classical Ruelle-Takens route to chaos has been experimentally reported in this geometry. The wavy vortex flow becomes quasiperiodic due to an axisymmetric very low frequency mode. This mode plays a key role in the dynamics of the system, leading to the occurrence of chaos via a period-doubling scenario. Further increasing the rotation of the inner cylinder results in the appearance of a new flow pattern which is characterized by large amplitude oscillations localized in some of the vortex pairs. The purpose of this paper is to study numerically the dynamics of these axially localized states, paying special attention to the transition to chaos. Frequency analysis from time series simultaneously recorded at several points has been applied in order to identify the flow transitions taking place. It has been found that the very low frequency mode is essential to explain the behavior associated with the different transitions towards chaos including localized states. PMID:26066253
Couette flows of a granular monolayer: An experimental study
Elliott, K.E.; Ahmadi, G.; Kvasnak, W.
1995-03-01
An experimental study concerning rapid flows of granular materials in a two dimensional planar granular Couette flow apparatus is performed. The device is capable of generating particulate flows in grain-inertia regime at different shearing rates and solid volume fractions. Multi-color spherical glass particles are sheared across an annular test-section for several wall angular velocities. A video recorder is used to record the motion of particles, and consecutive images are stored and analyzed by an image processing technique for evaluating individual grain velocities. Experimental data for the mean velocity, the root mean-square fluctuation velocity components and the solid volume fraction profile are obtained. The resulting mean velocity profiles have a roughly linear variation for the range of solid volume fractions and shear rates studied. The solid volume fraction profiles exhibit nonuniform variations with the highest concentration occuring near the center of the shearing cell. The RMS-fluctuation velocities are roughly constant, with the streamwise fluctuation being somewhat larger than the cross-stream direction. The experimentally measured flow properties are in reasonable agreement with the earlier theoretical and simulation results.
Rheophysics of highly concentrated coarse-particle suspensions in a wide-gap Couette rheometer
NASA Astrophysics Data System (ADS)
Wiederseiner, S.; Ancey, C.; Rentschler, M.; Andreini, N.
2009-06-01
An optical visualization apparatus has been designed to measure the particle-velocity and solid-concentration profiles of highly concentrated coarse-particle suspensions in a wide-gap Couette rheometer. The main objective is to investigate the frictional-viscous transition, a phenomenon that has been already reported in recent papers [1, 2, 3, 4], but still remains partially understood. For wide-gap viscometers and complex fluids, a related issue is the Couette problem, which underpins the rheometrical treatment for viscometric flows in coaxial-cylinder rheometers; we compare shear-rate computations obtained by solving the Couette problem (bulk estimate) and by differentiating the velocity and concentration profiles (local measurement).
Shear stress related blood damage in laminar couette flow.
Paul, Reinhard; Apel, Jörn; Klaus, Sebastian; Schügner, Frank; Schwindke, Peter; Reul, Helmut
2003-06-01
Artificial organs within the blood stream are generally associated with flow-induced blood damage, particularly hemolysis of red blood cells. These damaging effects are known to be dependent on shear forces and exposure times. The determination of a correlation between these flow-dependent properties and actual hemolysis is the subject of this study. For this purpose, a Couette device has been developed. A fluid seal based on fluorocarbon is used to separate blood from secondary external damage effects. The shear rate within the gap is controlled by the rotational speed of the inner cylinder, and the exposure time by the amount of blood that is axially pumped through the device per given time. Blood damage is quantified by the index of hemolysis (IH), which is calculated from photometric plasma hemoglobin measurements. Experiments are conducted at exposure times from texp=25 - 1250 ms and shear rates ranging from tau=30 up to 450 Pa ensuring Taylor-vortex free flow characteristics. Blood damage is remarkably low over a broad range of shear rates and exposure times. However, a significant increase in blood damage can be observed for shear stresses of tau>or= 425 Pa and exposure times of texp>or= 620 ms. Maximum hemolysis within the investigated range is IH=3.5%. The results indicate generally lower blood damage than reported in earlier studies with comparable devices, and the measurements clearly indicate a rather abrupt (i.e., critical levels of shear stresses and exposure times) than gradual increase in hemolysis, at least for the investigated range of shear rates and exposure times. PMID:12780506
Hydrodynamic dispersion within porous biofilms.
Davit, Y; Byrne, H; Osborne, J; Pitt-Francis, J; Gavaghan, D; Quintard, M
2013-01-01
Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher's equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels' network; (2) the solute's diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport. PMID:23410370
Preferential accumulation of bubbles in Couette-Taylor flow patterns
NASA Astrophysics Data System (ADS)
Climent, Eric; Simonnet, Marie; Magnaudet, Jacques
2007-08-01
We investigate the migration of bubbles in several flow patterns occurring within the gap between a rotating inner cylinder and a concentric fixed outer cylinder. The time-dependent evolution of the two-phase flow is predicted through three-dimensional Euler-Lagrange simulations. Lagrangian tracking of spherical bubbles is coupled with direct numerical simulation of the Navier-Stokes equations. We assume that bubbles do not influence the background flow (one-way coupling simulations). The force balance on each bubble takes into account buoyancy, added-mass, viscous drag, and shear-induced lift forces. For increasing velocities of the rotating inner cylinder, the flow in the fluid gap evolves from the purely azimuthal steady Couette flow to Taylor toroidal vortices and eventually a wavy vortex flow. The migration of bubbles is highly dependent on the balance between buoyancy and centripetal forces (mostly due to the centripetal pressure gradient) directed toward the inner cylinder and the vortex cores. Depending on the rotation rate of the inner cylinder, bubbles tend to accumulate alternatively along the inner wall, inside the core of Taylor vortices or at particular locations within the wavy vortices. A stability analysis of the fixed points associated with bubble trajectories provides a clear understanding of their migration and preferential accumulation. The location of the accumulation points is parameterized by two dimensionless parameters expressing the balance of buoyancy, centripetal attraction toward the inner rotating cylinder, and entrapment in Taylor vortices. A complete phase diagram summarizing the various regimes of bubble migration is built. Several experimental conditions considered by Djéridi, Gabillet, and Billard [Phys. Fluids 16, 128 (2004)] are reproduced; the numerical results reveal a very good agreement with the experiments. When the rotation rate is increased further, the numerical results indicate the formation of oscillating bubble
Lin, Jau-Wen
2014-08-07
This study investigated the structuring of water molecules in a nanoscale Couette flow with the upper plate subjected to lateral forces with various magnitudes and water slipping against a metal wall. It was found that when the upper plate is subjected to a force, the water body deforms into a parallelepiped. Water molecules in the channel are then gradually arranged into lattice positions, creating a layered structure. The structural arrangement of water molecules is caused by the water molecules accommodating themselves to the increase in energy under the application of a lateral force on the moving plate. The ordering arrangement of water molecules increases the rotational degree of freedom, allowing the molecules to increase their Coulomb potential energy through polar rotation that accounts for the energy input through the upper plate. With a force continuously applied to the upper plate, the water molecules in contact with the upper plate move forward until slip between the water and upper plate occurs. The relation between the structural arrangement of water molecules, slip at the wall, and the shear force is studied. The relation between the slip and the locking/unlocking of water molecules to metal atoms is also studied.
NASA Astrophysics Data System (ADS)
Jiang, Shidong; Luo, Li-Shi
2016-07-01
The integral equation for the flow velocity u (x ; k) in the steady Couette flow derived from the linearized Bhatnagar-Gross-Krook-Welander kinetic equation is studied in detail both theoretically and numerically in a wide range of the Knudsen number k between 0.003 and 100.0. First, it is shown that the integral equation is a Fredholm equation of the second kind in which the norm of the compact integral operator is less than 1 on Lp for any 1 ≤ p ≤ ∞ and thus there exists a unique solution to the integral equation via the Neumann series. Second, it is shown that the solution is logarithmically singular at the endpoints. More precisely, if x = 0 is an endpoint, then the solution can be expanded as a double power series of the form ∑n=0∞∑m=0∞cn,mxn(xln x) m about x = 0 on a small interval x ∈ (0 , a) for some a > 0. And third, a high-order adaptive numerical algorithm is designed to compute the solution numerically to high precision. The solutions for the flow velocity u (x ; k), the stress Pxy (k), and the half-channel mass flow rate Q (k) are obtained in a wide range of the Knudsen number 0.003 ≤ k ≤ 100.0; and these solutions are accurate for at least twelve significant digits or better, thus they can be used as benchmark solutions.
NASA Astrophysics Data System (ADS)
Saati, Abdulmannan Abdulhamid
1991-02-01
The direct numerical simulation of the stability and transition of compressible Couette flow is studied. The effects of a constant body force along the vertical direction are also studied. Cartesian geometry is adopted to approximate Couette flow produced in the gap between two coaxial cylinders rotating at high-speed, with the body force representing the effects of the centrifugal force. A new, compressible flow solver for two- and three-dimensional, time dependent Navier-Stokes equations, using both the MacCormack and the high-order Two-Four methods was developed. In order to facilitate the simulations with greater detail and accuracy, a high-speed supercomputer with large core memory is required. Thus, the computer code was written in FORTRAN for its execution on the CRAY2, at NASA Langley. In a concurrent effort, in order to study the feasibility and efficiency of massively parallel super-computers and to speed up the computations, the work was further extended by rewriting the computer code in both C* and PARIS languages, for execution on the massively parallel Connection Machine CM 2 at the University of Colorado. Extensive testing of this new computer code was performed using wave propagation problems involving small- and large-amplitude two- and three-dimensional disturbances. Numerical simulations on the stability of compressible Couette flow between two infinite, parallel plates, with the inclusion of (1) a sudden body force, and (2) a body force in equilibrium, were performed. First, two-dimensional disturbances were considered and then the work was extended by considering three-dimensional disturbances on the rectangular Couette flow problem. Effects of body force magnitude, Mach number, and Reynolds number were also investigated. The simulations provide excellent agreement with the linear theory, thus documenting the phase and amplitude accuracy of the computed results; the overall amplitude error remains less than one percent. The results show that
NASA Astrophysics Data System (ADS)
Takahashi, R.; Matsuo, M.; Ono, M.; Harii, K.; Chudo, H.; Okayasu, S.; Ieda, J.; Takahashi, S.; Maekawa, S.; Saitoh, E.
2016-01-01
Magnetohydrodynamic generation is the conversion of fluid kinetic energy into electricity. Such conversion, which has been applied to various types of electric power generation, is driven by the Lorentz force acting on charged particles and thus a magnetic field is necessary. On the other hand, recent studies of spintronics have revealed the similarity between the function of a magnetic field and that of spin-orbit interactions in condensed matter. This suggests the existence of an undiscovered route to realize the conversion of fluid dynamics into electricity without using magnetic fields. Here we show electric voltage generation from fluid dynamics free from magnetic fields; we excited liquid-metal flows in a narrow channel and observed longitudinal voltage generation in the liquid. This voltage has nothing to do with electrification or thermoelectric effects, but turned out to follow a universal scaling rule based on a spin-mediated scenario. The result shows that the observed voltage is caused by spin-current generation from a fluid motion: spin hydrodynamic generation. The observed phenomenon allows us to make mechanical spin-current and electric generators, opening a door to fluid spintronics.
Nonlinear dynamics in eccentric Taylor-Couette-Poiseuille flow
NASA Astrophysics Data System (ADS)
Pier, Benoît; Caulfield, C. P.
2015-11-01
The flow in the gap between two parallel but eccentric cylinders and driven by an axial pressure gradient and inner cylinder rotation is characterized by two geometrical parameters (radius ratio and eccentricity) and two dynamic parameters (axial and azimuthal Reynolds numbers). Such a theoretical configuration is a model for the flow between drill string and wellbore in the hydrocarbon drilling industry. The linear convective and absolute instability properties have been systematically derived in a recent study [Leclercq, Pier & Scott, J. Fluid Mech. 2013 and 2014]. Here we address the nonlinear dynamics resulting after saturation of exponentially growing small-amplitude perturbations. By using direct numerical simulations, a range of finite-amplitude states are found and characterized: nonlinear traveling waves (an eccentric counterpart of Taylor vortices, associated with constant hydrodynamic loading on the inner cylinder), modulated nonlinear waves (with time-periodic torque and flow rate) and more irregular states. In the nonlinear regime, the hydrodynamic forces are found to depart significantly from those prevailing for the base flow, even in situations of weak linear instability.
NASA Astrophysics Data System (ADS)
Liu, Wei
2007-08-01
The magnetorotational instability (MRI) is probably the main cause of turbulence and accretion in sufficiently ionized astrophysical disks. However, despite much theoretical and computational work, the nonlinear saturation of MRI is imperfectly understood. In Chap. 2 and Chap. 3 of this thesis we present non-ideal magnetohydrodynamic simulations of the Princeton MRI experiment. In vertically infinite or periodic cylinders, MRI saturates in a resistive current-sheet with a significant reduction of the mean shear, and with poloidal circulation scaling as the square root of resistivity. Angular momentum transport scales as the reciprocal square root of viscosity but only weakly depends on resistivity. For finite cylinders with insulating end caps, a method for implementing the fully insulating boundary condition is introduced. MRI grows with a clear linear phase from small amplitudes at rates in good agreement with linear analysis. In the final state one inflowing "jet" opposite to the usual Ekman "jet" is found near the inner cylinder. The MRI enhances the angular momentum transport at saturation. Under proper conditions, our experimental facility is a good platform to show that MRI could be suppressed by a strong magnetic field. Recently, Hollerbach and Rüdiger have reported that MRI modes may grow at much reduced magnetic Reynolds number ( Re m ) and Lundquist number S in the presence of a helical background field, a current-free combination of axial and toroidal field. We have investigated these helical MRI modes in Chap. 4 and Chap. 5. In vertically infinite or periodic cylinders, resistive HMRI is a weakly destabilized hydrodynamic inertial oscillation propagating axially along the background Poynting flux. Growth rates are small, however, and require large axial currents. Furthermore, finite cylinders with insulating endcaps were shown to reduce the growth rate and to stabilize highly resistive, inviscid flows entirely, and the new mode is stable in Keplerian
Exploring the phase space of multiple states in highly turbulent Taylor-Couette flow
NASA Astrophysics Data System (ADS)
van der Veen, Roeland; Huisman, Sander; Dung, On Yu; Tang, Ho Lun; Sun, Chao; Lohse, Detlef
2015-11-01
It was recently found that multiple turbulent states exist for large Reynolds number (Re =106) Taylor-Couette flow in the regime of ultimate turbulence. Here we investigate how the transitions between the multiple states depend on the Reynolds number in the range of Re =105 to 2 .106 , by measuring global torque and local velocity while probing the phase space spanned by the rotation rates of the inner and outer cylinder. This sheds light on the question whether multiple states persist for Reynolds numbers beyond those currently reached. By mapping the flow structures for various rotation ratios in two Taylor-Couette setups with equal radius ratio but different aspect ratio, we furthermore investigate the influence of aspect ratio on the characteristics of the multiple states.
Exploring the phase space of multiple states in highly turbulent Taylor-Couette flow
NASA Astrophysics Data System (ADS)
van der Veen, Roeland C. A.; Huisman, Sander G.; Dung, On-Yu; Tang, Ho L.; Sun, Chao; Lohse, Detlef
2016-06-01
We investigate the existence of multiple turbulent states in highly turbulent Taylor-Couette flow in the range of Ta =1011 to 9 ×1012 by measuring the global torques and the local velocities while probing the phase space spanned by the rotation rates of the inner and outer cylinders. The multiple states are found to be very robust and are expected to persist beyond Ta =1013 . The rotation ratio is the parameter that most strongly controls the transitions between the flow states; the transitional values only weakly depend on the Taylor number. However, complex paths in the phase space are necessary to unlock the full region of multiple states. By mapping the flow structures for various rotation ratios in a Taylor-Couette setup with an equal radius ratio but a larger aspect ratio than before, multiple states are again observed. Here they are characterized by even richer roll structure phenomena, including an antisymmetrical roll state.
NASA Astrophysics Data System (ADS)
Sone, Yoshio; Sugimoto, Hiroshi; Aoki, Kazuo
1999-02-01
A rarefied gas between two coaxial circular cylinders made of the condensed phase of the gas is considered, where each cylinder is kept at a uniform temperature and is rotating at a constant angular velocity around its axis (cylindrical Couette flows of a rarefied gas with evaporation or condensation on the cylinders). The steady behavior of the gas, with special interest in bifurcation of a flow, is studied on the basis of kinetic theory from the continuum to the Knudsen limit. The solution shows profound variety: reversal of direction of evaporation-condensation with variation of the speed of rotation of the cylinders; contrary to the conventional cylindrical Couette flow without evaporation and condensation, bifurcation of a flow in a simple case where the state of the gas is circumferentially and axially uniform.
Transition to two-dimensionality in magnetohydrodynamic turbulent Taylor-Couette flow.
Zhao, Yurong; Tao, Jianjun; Zikanov, Oleg
2014-03-01
Transition from a Taylor-Couette turbulent flow to a completely two-dimensional axisymmetric turbulent state is realized numerically by increasing gradually the strength of the azimuthal magnetic field produced by electric current flowing through the axial rod. With the increase of the Hartmann number, the Taylor-vortex-like structures shrink, move closer to the inner cylinder, and turn into unsteady but perfect tori at sufficiently high Hartmann numbers. PMID:24730932
Chinyoka, T.; Makinde, O. D.
2013-01-01
The thermodynamic second law analysis is utilized to investigate the inherent irreversibility in an unsteady hydromagnetic generalized Couette flow with variable electrical conductivity in the presence of induced electric field. Based on some simplified assumption, the model nonlinear governing equations are obtained and solved numerically using semidiscretization finite difference techniques. Effects of various thermophysical parameters on the fluid velocity, temperature, current density, skin friction, the Nusselt number, entropy generation number, and the Bejan number are presented graphically and discussed quantitatively. PMID:23956691
Observation of Magnetocoriolis Waves in a Liquid Metal Taylor-Couette Experiment
Nornberg, M. D.; Ji, H.; Schartman, E.; Roach, A.; Goodman, J.
2009-09-14
The first observation of fast and slow magnetocoriolis (MC) waves in a laboratory experiment is reported. Rotating nonaxisymmetric modes arising from a magnetized turbulent Taylor-Couette flow of liquid metal are identified as the fast and slow MC waves by the dependence of the rotation frequency on the applied field strength. The observed slow MC wave is marginally damped but will become destabilized by the magnetorotational instability with a modest increase in rotation rate.
Modeling and Applications of the Cylindrical Couette Flow of a Rarefied Gas
Dankov, D.; Roussinov, V.
2008-10-30
The cylindrical Couette flow of a rarefied gas is studied in the case when the inner cylinder is rotating while the outer cylinder is at rest. Velocity, density and temperature profiles are investigated by a Direct Monte Carlo Simulation method and a numerical solution of the Navier-Stokes equations is found. The results prove good agreement between flow macro-characteristic values obtained by the two methods.
Observation of Magnetocoriolis Waves in a Liquid Metal Taylor-Couette Experiment
Nornberg, M. D.; Ji, H.; Schartman, E.; Roach, A.; Goodman, J.
2010-02-19
The first observation of fast and slow magnetocoriolis (MC) waves in a laboratory experiment is reported. Rotating nonaxisymmetric modes arising from a magnetized turbulent Taylor-Couette flow of liquid metal are identified as the fast and slow MC waves by the dependence of the rotation frequency on the applied field strength. The observed slow MC wave is damped but the observation provides a means for predicting the onset of the magnetorotational instability.
Angular momentum transport and flow super-rotation in Rayleigh stable Taylor-Couette
NASA Astrophysics Data System (ADS)
Nordsiek, Freja; Huisman, Sander; van der Veen, Roeland; Sun, Chao; Lohse, Detlef; Lathrop, Daniel
2013-11-01
We present experimental velocimetry and torque measurements for Taylor-Couette flow in the Rayleigh stable regime. Measurements are taken on two geometrically similar experiments, both of which had axial boundaries attatched to the outer cylinder, which is known to cause Ekman pumping. The Twente experiment has a radius ratio of 0.716, an aspect ratio of 11.68, and measures azimuthal velocities by Laser Doppler Anenometry. The Maryland experiment has a radius ratio of 0.725, an aspect ratio of 11.47, and measures the torque required to rotate the inner cylinder. The torque on the inner cylinder is observed to be greater than that of the analytical Couette profile and has a complex dependence on the Reynolds number and Ωi /Ωo . The azimuthal velocity profiles also deviate from the laminar Couette profile. Signficantly, super-rotation in the angular velocity has been observed for 1 >Ωi /Ωo > 0 . In the quasi-Keplerian regime, the angular momentum profiles consist of an approximately constant inner region connected to an outer region approximately in solid-body rotation at Ωo, which suggests that angular momentum is being actively transported from the inner region to the axial boundaries.
Homoclinic snaking in plane Couette flow: bending, skewing and finite-size effects
NASA Astrophysics Data System (ADS)
Gibson, J. F.; Schneider, T. M.
2016-05-01
Invariant solutions of shear flows have recently been extended from spatially periodic solutions in minimal flow units to spatially localized solutions on extended domains. One set of spanwise-localized solutions of plane Couette flow exhibits homoclinic snaking, a process by which steady-state solutions grow additional structure smoothly at their fronts when continued parametrically. Homoclinic snaking is well understood mathematically in the context of the one-dimensional Swift-Hohenberg equation. Consequently, the snaking solutions of plane Couette flow form a promising connection between the largely phenomenological study of laminar-turbulent patterns in viscous shear flows and the mathematically well-developed field of pattern-formation theory. In this paper we present a numerical study of the snaking solutions, generalizing beyond the fixed streamwise wavelength of previous studies. We find a number of new solution features, including bending, skewing, and finite-size effects. We show that the finite-size effects result from the shift-reflect symmetry of the traveling wave and establish the parameter regions over which snaking occurs. A new winding solution of plane Couette flow is derived from a strongly skewed localized equilibrium.
NASA Astrophysics Data System (ADS)
Crowley, Christopher; Krygier, Michael; Borrero-Echeverry, Daniel; Grigoriev, Roman; Schatz, Michael
2015-11-01
The transition to turbulence in counter-rotating Taylor-Couette flow typically occurs through a sequence of supercritical bifurcations of stable flow states (e.g. spiral vortices, interpenetrating spirals (IPS), and wavy interpenetrating spirals). Coughlin and Marcus have proposed a mechanism by which these laminar spiral flows undergo a secondary instability that leads to turbulence. We report the discovery of a counter-rotating regime (Reout = - 1000 , Rein ~ 640) of small aspect ratio/large radius ratio Taylor-Couette flow (Γ = 5 . 26 / η = 0 . 91), where the system bypasses the primary instability to stable laminar spirals and instead undergoes a direct transition to turbulence as the inner cylinder rotation rate is slowly increased. This transition is mediated by an unstable IPS state. We study the transition experimentally using flow visualization and tomographic PIV, and show that it is both highly repeatable and that it shows hysteresis as the inner cylinder rotation rate is decreased. As Rein is decreased, the turbulent flow relaminarizes into an intermediate, stable IPS state. Decreasing Rein further returns the system back to circular Couette flow. This study was supported by NSF DMS-1125302 and NSF CMMI-1234436.
Spatiotemporal intermittency in the torsional Couette flow between a rotating and a stationary disk
NASA Astrophysics Data System (ADS)
Cros, A.; Le Gal, P.
2002-11-01
This work is devoted to the experimental study of the transition to turbulence of a flow confined in a narrow gap between a rotating and a stationary disk. When the fluid layer thickness is of the same order of magnitude as the boundary layer depths, the azimuthal velocity axial gradient is nearly constant and this rotating disk flow tends to be a torsional Couette flow. As in the plane Couette flow or the Taylor-Couette flow, transition to turbulence occurs via the appearance of turbulent domains inside a laminar background. In the rotating disk case, the nucleation of turbulent spirals, previously called "solitary waves" in the rotating disk flow literature, is connected to the birth of structural defects in a periodic underlying roll pattern. As the rotation rate is increased, the lifetime of these turbulent structures increases until a threshold is reached where they then form permanent turbulent spirals arranged nearly periodically all around a circumference. However, since the number of these turbulent spirals decreases with the rotational frequency, the transition to a fully turbulent regime is not achieved. Thus the turbulent fraction of the pattern saturates to a value lower than 0.5. After a geometrical description of the structures, we present a statistical analysis of sizes and lifetimes of the turbulent and laminar domains in order to compare this transition to already observed spatiotemporal intermittent behavior.
Hydrodynamic effects in proteins
NASA Astrophysics Data System (ADS)
Szymczak, Piotr; Cieplak, Marek
2011-01-01
Experimental and numerical results pertaining to flow-induced effects in proteins are reviewed. Special emphasis is placed on shear-induced unfolding and on the role of solvent mediated hydrodynamic interactions in the conformational transitions in proteins.
Hydrodynamic effects in proteins.
Szymczak, Piotr; Cieplak, Marek
2011-01-26
Experimental and numerical results pertaining to flow-induced effects in proteins are reviewed. Special emphasis is placed on shear-induced unfolding and on the role of solvent mediated hydrodynamic interactions in the conformational transitions in proteins. PMID:21406855
NASA Astrophysics Data System (ADS)
Olsen, Thomas; Hou, Yu; Kowalski, Adam; Wiener, Richard
2006-05-01
The Reaction-Diffusion model predicted a period doubling cascade to chaos in a situation analagous Taylor- Couette flow with hourglass geometry. This cascade to chaos was discovered in the actual fluid flow experiments. We model Taylor-Couette flow in a cylindrical geometry with multiple waists of super-critical flow connected by regions of barely super-critical flow by corresponding Reaction-Diffusion models. We compare our results to the findings of an ongoing experimental program. H. Riecke and H.-G. Paap, Europhys. Lett. 14, 1235 (1991). Richard J. Wiener et al, Phys. Rev. E 55, 5489 (1997).
NASA Astrophysics Data System (ADS)
Miroshnikov, Stanislav
2011-11-01
The effect of the period of perturbations on the spatiotemporal statistics of the Kolmogorov-like cascades of the transitional Couette flow is explored using a new method of arbitrary-precision differentiation of trigonometric, hyperbolic, and elliptic structures. The trigonometric, hyperbolic, and elliptic structures are constructed and their differentiation is reduced to an algebraic processing, which may be executed with symbolic and numeric parameters. Computation of high-order derivatives by the arbitrary-precision differentiation and summation of the Boussinesq-Rayleigh-Taylor series for the perturbed Couette flow is implemented in Maple, Python, and C++. Performance of the proposed algorithms is compared both for workstations and clusters.
Identification of complex flows in Taylor-Couette counter-rotating cavities
NASA Technical Reports Server (NTRS)
Czarny, O.; Serre, E.; Bontoux, P.; Lueptow, R. M.
2001-01-01
The transition in confined rotating flows is a topical problem with many industrial and fundamental applications. The purpose of this study is to investigate the Taylor-Couette flow in a finite-length cavity with counter-rotating walls, for two aspect ratios L=5 or L=6. Two complex regimes of wavy vortex and spirals are emphasized for the first time via direct numerical simulation, by using a three-dimensional spectral method. The spatio-temporal behavior of the solutions is analyzed and compared to the few data actually available. c2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
Viscoelastic Taylor-Couette instability as analog of the magnetorotational instability
NASA Astrophysics Data System (ADS)
Bai, Yang; Crumeyrolle, Olivier; Mutabazi, Innocent
2015-09-01
A linear stability analysis and an experimental study of a viscoelastic Taylor-Couette flow corotating in the Keplerian ratio allow us to elucidate the analogy between the viscoelastic instability and the magnetorotational instability (MRI). A generalized Rayleigh criterion allows us to determine the potentially unstable zone to pure-elasticity-driven perturbations. Experiments with a viscoelastic polymer solution yield four modes: one pure-elasticity mode and three elastorotational instability (ERI) modes that represent the MRI-analog modes. The destabilization by the polymer viscosity is evidenced for the ERI modes.
On MHD unsteady reactive Couette flow with heat transfer and variable properties
NASA Astrophysics Data System (ADS)
Makinde, Oluwole Daniel; Franks, Oswald
2014-03-01
This study is devoted to investigate the effect of magnetic field on a reactive unsteady generalized Couette flow with temperature dependent viscosity and thermal conductivity. It is assumed that conducting incompressible fluid is subjected to an exothermic reaction under Arrhenius kinetics, neglecting the consumption of the material. The model nonlinear differential equations governing the transient momentum and energy balance are obtained and tackled numerically using a semi-discretization finite difference technique coupled with Runge-Kutta Fehlberg integration scheme. Important properties of the velocity and temperature fields including thermal stability conditions are presented graphically and discussed quantitatively.
Elongational flow effects on the vortex growth out of Couette flow in ferrofluids.
Altmeyer, S; Leschhorn, A; Hoffmann, Ch; Lücke, M
2013-05-01
The growth behavior of stationary axisymmetric vortices and of oscillatory, nonaxisymmetric spiral vortices in Taylor-Couette flow of a ferrofluid in between differentially rotating cylinders is analyzed using a numerical linear stability analysis. The investigation is done as a function of the inner and outer cylinder's rotation rates, the axial wave number of the vortex flows, and the magnitude of an applied homogeneous axial magnetic field. In particular, the consequences of incorporating elongational flow effects in the magnetization balance equation on the marginal control parameters that separate growth from decay behavior are determined. That is done for several values of the transport coefficient that measures the strength of these effects. PMID:23767623
Perturbation Enstrophy Decay in Poiseuille and Couette Flows according to Synge's Method
NASA Astrophysics Data System (ADS)
Domenicale, Loris; Fraternale, Federico; Staffilani, Gigliola; Tordella, Daniela
2015-11-01
In this work we derive the conditions for no enstrophy growth for bidimensional perturbations in the plane Couette and Poiseuille flows. We follow the method of vorticity proposed by Synge in 1938 (see the Semi-Centennial Puplication of the Amer. Math. Soc., equation 12.13, and the more detailed version in the Proc. of the Fifth Inter. Congress of Applied Mechanics, pages 326-332), which is actually based on the analysis of the spatially averaged enstrophy. We find that the limit curve in the perturbation wavenumber-Reynolds number map differs from the limit for no energy growth (see e.g. Reddy 1993). In particular, the absolute stability region for the enstrophy is wider than that of the kinetic energy, and the maximum Reynolds number giving the monotonic enstrophy decay, at all wavenumbers, is 155 and 80 for the Poiseuille and Couette flows, respectively. It should be noted that in past literature the energy-based analysis was preferred to Synge's enstrophy analysis. This, possibly, for two reasons: the low diffusivity of the 1938 Vth ICAM proceedings and the objectively very complicated analytical treatment required. Nevertheless, the potentiality of this method seems high and therefore it is interesting nowadays to exploit it by means of the symbolic calculus. MITOR-MISTI SEEDS GRANT http://web.mit.edu/mitor/recipients/faculty.html
NASA Astrophysics Data System (ADS)
Guseva, A.; Willis, A. P.; Hollerbach, R.; Avila, M.
2015-09-01
The magnetorotational instability (MRI) is thought to be a powerful source of turbulence and momentum transport in astrophysical accretion discs, but obtaining observational evidence of its operation is challenging. Recently, laboratory experiments of Taylor-Couette flow with externally imposed axial and azimuthal magnetic fields have revealed the kinematic and dynamic properties of the MRI close to the instability onset. While good agreement was found with linear stability analyses, little is known about the transition to turbulence and transport properties of the MRI. We here report on a numerical investigation of the MRI with an imposed azimuthal magnetic field. We show that the laminar Taylor-Couette flow becomes unstable to a wave rotating in the azimuthal direction and standing in the axial direction via a supercritical Hopf bifurcation. Subsequently, the flow features a catastrophic transition to spatio-temporal defects which is mediated by a subcritical subharmonic Hopf bifurcation. Our results are in qualitative agreement with the PROMISE experiment and dramatically extend their realizable parameter range. We find that as the Reynolds number increases defects accumulate and grow into turbulence, yet the momentum transport scales weakly.
Viscoelastic Taylor-Couette instability as an anolog of Magnetorotational instability
NASA Astrophysics Data System (ADS)
Mutabazi, Innocent; Bai, Yang; Crumeyrolle, Olivier
2014-11-01
Our investigation of the viscoelastic instability (VEI) in the corotating Couette-Taylor system is motivated by the prediction of Ogilvie et. al that such an instability is analogous to the MRI (magneto-rotational instability) which is believed to play a key role in the angular momentum transport in accretion disks. This analogy is supported by stretched spring argument developed by Balbus and Hawley which is similar to that of the polymer stretching model in viscoelastic solutions. To our best knowledge, only one experiment by Boldyrev et al. has been reported for the search of the analogy VEI-MRI. We present both theoretical and experimental results obtained in the viscoelastic Couette-Taylor system when both the cylinders are constrained to rotate along the Keplerian and anti-Keplerian lines. The polymer solutions have a constant solution with respect to shear rate and can be described by the Odlroyd-B model. The control parameters are the aspect ratio Γ, the radius ratio η, the Reynolds number Re , the elastic number E = Wi / Re and the viscosity ratio S =μp / μ . After linear stability analysis, critical modes are oscillatory and non-axisymmetric. The observed modes are either stationary or oscillatory modes. A state diagram allows for a comparison to MRI Partial support from the French National Research Agency (ANR) through the program Investissements d'Avenir (ANR-10 LABX-09-01), LABEX EMC3.
Ring-bursting behavior en route to turbulence in narrow-gap Taylor-Couette flows.
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-11-01
We investigate the Taylor-Couette system where the radius ratio is close to unity. Systematically increasing the Reynolds number, we observe a number of previously known transitions, such as one from the classical Taylor vortex flow (TVF) to wavy vortex flow (WVF) and the transition to fully developed turbulence. Prior to the onset of turbulence, we observe intermittent bursting patterns of localized turbulent patches, confirming the experimentally observed pattern of very short wavelength bursts (VSWBs). A striking finding is that, for a Reynolds number larger than that for the onset of VSWBs, a new type of intermittently bursting behavior emerges: patterns of azimuthally closed rings of various orders. We call them ring-bursting patterns, which surround the cylinder completely but remain localized and separated in the axial direction through nonturbulent wavy structures. We employ a number of quantitative measures including the cross-flow energy to characterize the ring-bursting patterns and to distinguish them from the background flow. These patterns are interesting because they do not occur in the wide-gap Taylor-Couette flow systems. The narrow-gap regime is less studied but certainly deserves further attention to gain deeper insights into complex flow dynamics in fluids. PMID:26651790
Effect of intermolecular potential on compressible Couette flow in slip and transitional regimes
NASA Astrophysics Data System (ADS)
Weaver, Andrew B.; Venkattraman, A.; Alexeenko, Alina A.
2014-10-01
The effect of intermolecular potentials on compressible, planar flow in slip and transitional regimes is investigated using the direct simulation Monte Carlo method. Two intermolecular interaction models, the variable hard sphere (VHS) and the Lennard-Jones (LJ) models, are first compared for subsonic and supersonic Couette flows of argon at temperatures of 40, 273, and 1,000 K, and then for Couette flows in the transitional regime ranging from Knudsen numbers (Kn) of 0.0051 to 1. The binary scattering model for elastic scattering using the Lennard-Jones (LJ) intermolecular potential proposed recently [A. Venkattraman and A. Alexeenko, "Binary scattering model for Lennard-Jones potential: Transport coefficients and collision integrals for non-equilibrium gas flow simulations," Phys. Fluids 24, 027101 (2012)] is shown to accurately reproduce both the theoretical collision frequency in an equilibrium gas as well as the theoretical viscosity variation with temperature. The use of a repulsive-attractive instead of a purely repulsive potential is found to be most important in the continuum and slip regimes as well as in flows with large temperature variations. Differences in shear stress of up to 28% between the VHS and LJ models is observed at Kn=0.0051 and is attributed to differences in collision frequencies, ultimately affecting velocity gradients at the wall. For Kn=1 where the Knudsen layer expands the entire domain, the effect of the larger collision frequency in the LJ model relative to VHS diminishes, and a 7% difference in shear stress is observed.
Design of a High Viscosity Couette Flow Facility for Patterned Surface Drag Measurements
NASA Astrophysics Data System (ADS)
Johnson, Tyler; Lang, Amy
2009-11-01
Direct drag measurements can be difficult to obtain with low viscosity fluids such as air or water. In this facility, mineral oil is used as the working fluid to increase the shear stress across the surface of experimental models. A mounted conveyor creates a flow within a plexiglass tank. The experimental model of a flat or patterned surface is suspended above a moving belt. Within the gap between the model and moving belt a Couette flow with a linear velocity profile is created. PIV measurements are used to determine the exact velocities and the Reynolds numbers for each experiment. The model is suspended by bars that connect to the pillow block housing of each bearing. Drag is measured by a force gauge connected to linear roller bearings that slide along steel rods. The patterned surfaces, initially consisting of 2-D cavities, are embedded in a plexiglass plate so as to keep the total surface area constant for each experiment. First, the drag across a flat plate is measured and compared to theoretical values for laminar Couette flow. The drag for patterned surfaces is then measured and compared to a flat plate.
Ring-bursting behavior en route to turbulence in narrow-gap Taylor-Couette flows
NASA Astrophysics Data System (ADS)
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-11-01
We investigate the Taylor-Couette system where the radius ratio is close to unity. Systematically increasing the Reynolds number, we observe a number of previously known transitions, such as one from the classical Taylor vortex flow (TVF) to wavy vortex flow (WVF) and the transition to fully developed turbulence. Prior to the onset of turbulence, we observe intermittent bursting patterns of localized turbulent patches, confirming the experimentally observed pattern of very short wavelength bursts (VSWBs). A striking finding is that, for a Reynolds number larger than that for the onset of VSWBs, a new type of intermittently bursting behavior emerges: patterns of azimuthally closed rings of various orders. We call them ring-bursting patterns, which surround the cylinder completely but remain localized and separated in the axial direction through nonturbulent wavy structures. We employ a number of quantitative measures including the cross-flow energy to characterize the ring-bursting patterns and to distinguish them from the background flow. These patterns are interesting because they do not occur in the wide-gap Taylor-Couette flow systems. The narrow-gap regime is less studied but certainly deserves further attention to gain deeper insights into complex flow dynamics in fluids.
Ekman and Taylor Vortices' Destruction and Mixing Enhancement in a Taylor-Couette System
NASA Astrophysics Data System (ADS)
Oualli, H.; Mekadem, M.; Bentsabet, A.; Abada, M.; Bouabdallah, A.; Gad-El-Hak, M.
2014-11-01
Suppression of Ekman and Taylor vortices is sought in several industrial processes such as cylindrical crystal growth and osmotic/photonic water purification. Last meeting, we investigated experimentally and numerically an active flow control strategy to obliterate vortices in a Taylor-Couette flow. The control consists of effecting minute radial pulsatile motion of the rotating inner cylinder's cross-section. The results showed that destruction of either type of vortices occurs at different pulsatile frequencies, requiring one order of magnitude higher frequency to obliterate the Ekman type. This problem is revisited with identical parameters and conditions for the controlling strategy but the Taylor-Couette system is now inclined relative to the horizontal direction in such a way that gravitational effects are no longer negligible. It is found that body forces contribute to the complete destruction of Taylor and Ekman vortices, reducing the optimum frequency by more than 50% for even a modest inclination angle of θ =15° . Furthermore, the axial and azimuthal velocity fluctuations are increased by one order of magnitude, thus yielding substantial enhancement in flow mixing.
The onset of steady vortices in Taylor-Couette flow: The role of approximate symmetry
NASA Astrophysics Data System (ADS)
Cliffe, K. A.; Mullin, T.; Schaeffer, D.
2012-06-01
The onset of steady cellular motion in Taylor-Couette flow between a pair of finite length cylinders is studied. This is most often portrayed in the literature as an example of a simple pitchfork bifurcation where the trivial state of rotary Couette flow is replaced by cellular motion above a critical Reynolds number. However, numerous experiments and simulations of the Navier-Stokes equations, as well as the detailed numerical bifurcation study reported here, all lead to the following, seemingly paradoxical, conclusion: On the one hand, no matter how long the apparatus, finite-length effects greatly perturb the disconnected branch of the pitchfork of the periodic model. This corresponds to anomalous-mode flows which are observed to exist above a range of Reynolds number that is at least a factor of two greater than the value corresponding to the onset of cells. On the other hand, in long cylinders these effects appear to change the connected branch of normal-mode flows only minimally. We propose a resolution of this paradox in terms of a symmetry breaking bifurcation. The relevant symmetry, which is only approximate, is between two normal-mode flows with large, and nearly equal, numbers of cells. Additionally, our numerical calculations establish a scaling law that quantifies the magnitude of finite-length effects on normal-mode flows at large lengths.
Influence of energetics on the stability of viscoelastic Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Al-Mubaiyedh, U. A.; Sureshkumar, R.; Khomami, B.
1999-11-01
Previously reported isothermal linear stability analyses of viscoelastic Taylor-Couette flow have predicted transitions to nonaxisymmetric and time-dependent secondary flows for elasticity numbers E≡De/Re>0.01. In contrast, recent experiments by Baumert and Muller using constant viscosity Boger fluids have shown that the primary flow transition leads to axisymmetric and stationary Taylor-type toroidal vortices. Moreover, experimentally observed onset Deborah number is an order of magnitude lower than that predicted by isothermal linear stability analyses. In this work, we explore the influence of energetics on the stability characteristics of the viscoelastic Taylor-Couette flow. Our analysis is based on a thermodynamically consistent reformulation of the Oldroyd-B constitutive model that takes into account the influence of thermal history on polymeric stress, and an energy equation that takes into account viscous dissipation effects. Our calculations reveal that for experimentally realizable values of Peclet and Brinkman numbers, the most dangerous eigenvalue is real, corresponding to a stationary and axisymmetric mode of instability. Moreover, the critical Deborah number associated with this eigenvalue is an order of magnitude lower than those associated with the nonisothermal extensions of the most dangerous eigenvalues of the isothermal flow. Eigenfunction analysis shows stratification of perturbation hoop stress across the gap width drives a radial secondary flow. The convection of base state temperature gradients by this radial velocity perturbation leads to this new mode of instability. The influence of geometric and kinematic parameters on this instability is also investigated.
Pulsed Taylor-Couette flow in a viscoelastic fluid under inner cylinder modulation
NASA Astrophysics Data System (ADS)
Riahi, Mehdi; Aniss, Saïd; Ouazzani Touhami, Mohamed; Skali Lami, Salah
2015-12-01
The influence of elasticity on pulsed Taylor-Couette flow in a linear Maxwell fluid is investigated. We consider the case, in which the inner cylinder is oscillating with a periodic angular velocity, Ω0cos(ω t), and the outer cylinder is fixed. Attention is focused on the linear stability analysis which is solved using the Floquet theory and a technique of converting a boundary value problem to an initial value problem. Results obtained in this framework show that, in the high-frequency limit, the Deborah number has a destabilizing effect and the critical Taylor and wave numbers tend toward constant values independently of the frequency number. However, in the low-frequency limit, the Maxwell fluid behaves as a Newtonien one and the Deborah number has no effect on the stability of the basic state which tends to the classical configuration of steady circular Couette flow. These numerical results are in good agreement with the asymptotic analysis performed in the limit of low and high frequencies.
Resurgence in extended hydrodynamics
NASA Astrophysics Data System (ADS)
Aniceto, Inês; Spaliński, Michał
2016-04-01
It has recently been understood that the hydrodynamic series generated by the Müller-Israel-Stewart theory is divergent and that this large-order behavior is consistent with the theory of resurgence. Furthermore, it was observed that the physical origin of this is the presence of a purely damped nonhydrodynamic mode. It is very interesting to ask whether this picture persists in cases where the spectrum of nonhydrodynamic modes is richer. We take the first step in this direction by considering the simplest hydrodynamic theory which, instead of the purely damped mode, contains a pair of nonhydrodynamic modes of complex conjugate frequencies. This mimics the pattern of black brane quasinormal modes which appear on the gravity side of the AdS/CFT description of N =4 supersymmetric Yang-Mills plasma. We find that the resulting hydrodynamic series is divergent in a way consistent with resurgence and precisely encodes information about the nonhydrodynamic modes of the theory.
Synchronization via Hydrodynamic Interactions
NASA Astrophysics Data System (ADS)
Kendelbacher, Franziska; Stark, Holger
2013-12-01
An object moving in a viscous fluid creates a flow field that influences the motion of neighboring objects. We review examples from nature in the microscopic world where such hydrodynamic interactions synchronize beating or rotating filaments. Bacteria propel themselves using a bundle of rotating helical filaments called flagella which have to be synchronized in phase. Other micro-organisms are covered with a carpet of smaller filaments called cilia on their surfaces. They beat highly synchronized so that metachronal waves propagate along the cell surfaces. We explore both examples with the help of simple model systems and identify generic properties for observing synchronization by hydrodynamic interactions.
Microflow Cytometers with Integrated Hydrodynamic Focusing
Frankowski, Marcin; Theisen, Janko; Kummrow, Andreas; Simon, Peter; Ragusch, Hülya; Bock, Nicole; Schmidt, Martin; Neukammer, Jörg
2013-01-01
This study demonstrates the suitability of microfluidic structures for high throughput blood cell analysis. The microfluidic chips exploit fully integrated hydrodynamic focusing based on two different concepts: Two-stage cascade focusing and spin focusing (vortex) principle. The sample—A suspension of micro particles or blood cells—is injected into a sheath fluid streaming at a substantially higher flow rate, which assures positioning of the particles in the center of the flow channel. Particle velocities of a few m/s are achieved as required for high throughput blood cell analysis. The stability of hydrodynamic particle positioning was evaluated by measuring the pulse heights distributions of fluorescence signals from calibration beads. Quantitative assessment based on coefficient of variation for the fluorescence intensity distributions resulted in a value of about 3% determined for the micro-device exploiting cascade hydrodynamic focusing. For the spin focusing approach similar values were achieved for sample flow rates being 1.5 times lower. Our results indicate that the performances of both variants of hydrodynamic focusing suit for blood cell differentiation and counting. The potential of the micro flow cytometer is demonstrated by detecting immunologically labeled CD3 positive and CD4 positive T-lymphocytes in blood. PMID:23571670
Lattice Models for Granular-Like Velocity Fields: Hydrodynamic Description
NASA Astrophysics Data System (ADS)
Manacorda, Alessandro; Plata, Carlos A.; Lasanta, Antonio; Puglisi, Andrea; Prados, Antonio
2016-07-01
A recently introduced model describing—on a 1d lattice—the velocity field of a granular fluid is discussed in detail. The dynamics of the velocity field occurs through next-neighbours inelastic collisions which conserve momentum but dissipate energy. The dynamics is described through the corresponding Master Equation for the time evolution of the probability distribution. In the continuum limit, equations for the average velocity and temperature fields with fluctuating currents are derived, which are analogous to hydrodynamic equations of granular fluids when restricted to the shear modes. Therefore, the homogeneous cooling state, with its linear instability, and other relevant regimes such as the uniform shear flow and the Couette flow states are described. The evolution in time and space of the single particle probability distribution, in all those regimes, is also discussed, showing that the local equilibrium is not valid in general. The noise for the momentum and energy currents, which are correlated, are white and Gaussian. The same is true for the noise of the energy sink, which is usually negligible.
Destabilization of hydrodynamically stable rotation laws by azimuthal magnetic fields
NASA Astrophysics Data System (ADS)
Rüdiger, Günther; Hollerbach, Rainer; Schultz, Manfred; Elstner, Detlef
2007-06-01
We consider the effect of toroidal magnetic fields on hydrodynamically stable Taylor-Couette differential rotation flows. For current-free magnetic fields a non-axisymmetric m = 1 magnetorotational instability arises when the magnetic Reynolds number exceeds O(100). We then consider how this `azimuthal magnetorotational instability' (AMRI) is modified if the magnetic field is not current-free, but also has an associated electric current throughout the fluid. This gives rise to current-driven Tayler instabilities (TIs) that exist even without any differential rotation at all. The interaction of the AMRI and the TI is then considered when both electric currents and differential rotation are present simultaneously. The magnetic Prandtl number Pm turns out to be crucial in this case. Large Pm have a destabilizing influence, and lead to a smooth transition between the AMRI and the TI. In contrast, small Pm have a stabilizing influence, with a broad stable zone separating the AMRI and the TI. In this region the differential rotation is acting to stabilize the TIs, with possible astrophysical applications (Ap stars). The growth rates of both the AMRI and the TI are largely independent of Pm, with the TI acting on the time-scale of a single rotation period, and the AMRI slightly slower, but still on the basic rotational time-scale. The azimuthal drift time-scale is ~20 rotations, and may thus be a (flip-flop) time-scale of stellar activity between the rotation period and the diffusion time.
Lattice Models for Granular-Like Velocity Fields: Hydrodynamic Description
NASA Astrophysics Data System (ADS)
Manacorda, Alessandro; Plata, Carlos A.; Lasanta, Antonio; Puglisi, Andrea; Prados, Antonio
2016-08-01
A recently introduced model describing—on a 1d lattice—the velocity field of a granular fluid is discussed in detail. The dynamics of the velocity field occurs through next-neighbours inelastic collisions which conserve momentum but dissipate energy. The dynamics is described through the corresponding Master Equation for the time evolution of the probability distribution. In the continuum limit, equations for the average velocity and temperature fields with fluctuating currents are derived, which are analogous to hydrodynamic equations of granular fluids when restricted to the shear modes. Therefore, the homogeneous cooling state, with its linear instability, and other relevant regimes such as the uniform shear flow and the Couette flow states are described. The evolution in time and space of the single particle probability distribution, in all those regimes, is also discussed, showing that the local equilibrium is not valid in general. The noise for the momentum and energy currents, which are correlated, are white and Gaussian. The same is true for the noise of the energy sink, which is usually negligible.
Hydrodynamic slip length as a surface property.
Ramos-Alvarado, Bladimir; Kumar, Satish; Peterson, G P
2016-02-01
Equilibrium and nonequilibrium molecular dynamics simulations were conducted in order to evaluate the hypothesis that the hydrodynamic slip length is a surface property. The system under investigation was water confined between two graphite layers to form nanochannels of different sizes (3-8 nm). The water-carbon interaction potential was calibrated by matching wettability experiments of graphitic-carbon surfaces free of airborne hydrocarbon contamination. Three equilibrium theories were used to calculate the hydrodynamic slip length. It was found that one of the recently reported equilibrium theories for the calculation of the slip length featured confinement effects, while the others resulted in calculations significantly hindered by the large margin of error observed between independent simulations. The hydrodynamic slip length was found to be channel-size independent using equilibrium calculations, i.e., suggesting a consistency with the definition of a surface property, for 5-nm channels and larger. The analysis of the individual trajectories of liquid particles revealed that the reason for observing confinement effects in 3-nm nanochannels is the high mobility of the bulk particles. Nonequilibrium calculations were not consistently affected by size but by noisiness in the smallest systems. PMID:26986407
Hydrodynamic slip length as a surface property
NASA Astrophysics Data System (ADS)
Ramos-Alvarado, Bladimir; Kumar, Satish; Peterson, G. P.
2016-02-01
Equilibrium and nonequilibrium molecular dynamics simulations were conducted in order to evaluate the hypothesis that the hydrodynamic slip length is a surface property. The system under investigation was water confined between two graphite layers to form nanochannels of different sizes (3-8 nm). The water-carbon interaction potential was calibrated by matching wettability experiments of graphitic-carbon surfaces free of airborne hydrocarbon contamination. Three equilibrium theories were used to calculate the hydrodynamic slip length. It was found that one of the recently reported equilibrium theories for the calculation of the slip length featured confinement effects, while the others resulted in calculations significantly hindered by the large margin of error observed between independent simulations. The hydrodynamic slip length was found to be channel-size independent using equilibrium calculations, i.e., suggesting a consistency with the definition of a surface property, for 5-nm channels and larger. The analysis of the individual trajectories of liquid particles revealed that the reason for observing confinement effects in 3-nm nanochannels is the high mobility of the bulk particles. Nonequilibrium calculations were not consistently affected by size but by noisiness in the smallest systems.
Skew resisting hydrodynamic seal
Conroy, William T.; Dietle, Lannie L.; Gobeli, Jeffrey D.; Kalsi, Manmohan S.
2001-01-01
A novel hydrodynamically lubricated compression type rotary seal that is suitable for lubricant retention and environmental exclusion. Particularly, the seal geometry ensures constraint of a hydrodynamic seal in a manner preventing skew-induced wear and provides adequate room within the seal gland to accommodate thermal expansion. The seal accommodates large as-manufactured variations in the coefficient of thermal expansion of the sealing material, provides a relatively stiff integral spring effect to minimize pressure-induced shuttling of the seal within the gland, and also maintains interfacial contact pressure within the dynamic sealing interface in an optimum range for efficient hydrodynamic lubrication and environment exclusion. The seal geometry also provides for complete support about the circumference of the seal to receive environmental pressure, as compared the interrupted character of seal support set forth in U.S. Pat. Nos. 5,873,576 and 6,036,192 and provides a hydrodynamic seal which is suitable for use with non-Newtonian lubricants.
Filter-less submicron hydrodynamic size sorting.
Fouet, M; Mader, M-A; Iraïn, S; Yanha, Z; Naillon, A; Cargou, S; Gué, A-M; Joseph, P
2016-02-21
We propose a simple microfluidic device able to separate submicron particles (critical size ∼0.1 μm) from a complex sample with no filter (minimum channel dimension being 5 μm) by hydrodynamic filtration. A model taking into account the actual velocity profile and hydrodynamic resistances enables prediction of the chip sorting properties for any geometry. Two design families are studied to obtain (i) small sizes within minutes (low-aspect ratio, two-level chip) and (ii) micron-sized sorting with a μL flow rate (3D architecture based on lamination). We obtain quantitative agreement of sorting performances both with experiments and with numerical solving, and determine the limits of the approach. We therefore demonstrate a passive, filter-less sub-micron size sorting with a simple, robust, and easy to fabricate design. PMID:26778818
Simulating hydrodynamics on tidal mudflats
NASA Astrophysics Data System (ADS)
Cook, S.; Lippmann, T. C.
2014-12-01
Biogeochemical cycling in estuaries is governed by fluxes from both riverine sources and through estuarine sediment deposits. Although estimates from river sources are relatively common and easily sampled, estimates of nutrient fluxes through the fluid-sediment interface are less common and limited to deeper portions of the bays away from intertidal areas. Lack of quantifiable shear stress estimates over intertidal areas limits our overall understanding of nutrient budgets in estuaries. Unfortunately, observation of intertidal hydrodynamics and nutrient fluxes over tidal flats and near the water's edge is difficult owing to the temporally varying and spatially extensive region where the tides inundate, and thus numerical modeling is often employed. In this work, the Regional Ocean Modeling System (ROMS), a three dimensional numerical hydrodynamic model was used to investigate the shear stresses over intertidal mudflats in the Great Bay, a tidally-dominated New England estuary cut by several tidal channels and with over 50% of the estuary exposed at low tide. The ROMS wetting and drying scheme was used to simulate the rising and falling tide on the flats, a successful approach adapted in other regions of the world but not always inclusive of tidal channels. Bathymetric data obtained in 2009 and 2013 was used to define the model grid. Predicted tides are forced at Adam's Pt., a natural constriction in the estuary about 20 km upstream of the mouth and at the entrance to the Great Bay. Of particular interest are fluxes of material on-to and off-of the tidal flats which contribute to water quality conditions in the estuary, and are largely governed by shear stresses that drive nutrient fluxes at the fluid-sediment interface. Basin wide estimates of near-bottom shear stresses can be used to estimate first order nutrient fluxes over a tidal cycle and hence describe general biogeochemical dynamics of the estuary. Future work will include enhanced forcing of currents by
NASA Astrophysics Data System (ADS)
Makinde, O. D.
2014-12-01
In this paper, the steady generalized axial Couette flow of Ostwald-de Waele power law reactive fluids between concentric cylindrical pipes is investigated. It is assumed that the outer cylinder is stationary and exchanges heat with the ambient surrounding following Newton's law of cooling, while the inner cylinder with isothermal surface is set in motion in the axial direction. The model nonlinear differential equations for the momentum and energy balance are obtained and tackled numerically using the shooting method coupled with the Runge-Kutta-Fehlberg integration technique. The effects of various embedded thermophysical parameters on the velocity and temperature fields including skin friction, Nusselt number and thermal criticality conditions are presented graphically and discussed quantitatively.
NASA Technical Reports Server (NTRS)
Coriell, S. R.; Mcfadden, G. B.; Boisvert, R. F.; Sekerka, R. F.
1984-01-01
The effect of a forced Couette flow, parallel to a horizontal crystal-melt interface during directional solidification of an alloy of lead containing tin, on the onset of convective and morphological instabilities, is calculated numerically via a linear stability analysis. Such a flow does not affect perturbations with wave vectors perpendicular to the flow. For perturbations with wave vectors parallel to the flow, the onset of morphological instability is somewhat suppressed and thermosolutal convection is greatly suppressed. When instabilities occur, they are oscillatory and correspond to travelling waves. For values of the crystal growth velocity for which mixed morphological and convective modes occur, the presence of a forced flow produces sufficient decoupling to allow otherwise degenerate branches to be identified.
Noise-Sustained Convective Instability in a Magnetized Taylor-Couette Flow
W. Liu
2009-02-20
The helical magnetorotational instability of the magnetized Taylor-Couette flow is studied numerically in a finite cylinder. A distant upstream insulating boundary is shown to stabilize the convective instability entirely while reducing the growth rate of the absolute instability. The reduction is less severe with larger height. After modeling the boundary conditions properly, the wave patterns observed in the experiment turn out to be a noise-sustained convective instability. After the source of the noise resulted from unstable Ekman and Stewartson layers is switched off, a slowly-decaying inertial oscillation is observed in the simulation. We reach the conclusion that the experiments completed to date have not yet reached the regime of absolute instability.
Noise-sustained convective instability in a magnetized Taylor-Couette flow
Liu, Wei
2008-01-01
The helical magnetorotational instability of the magnetized Taylor-Couette flow is studied numerically in a finite cylinder. A distant upstream insulating boundary is shown to stabilize the convective instability entirely while reducing the growth rate of the absolute instability. The reduction is less severe with larger height. After modeling the boundary conditions properly, the wave patterns observed in the experiment turn out to be a noise-sustained convective instability. After the source of the noise resulted from unstable Ekman and Stewartson layers is switched off, a slowly-decaying inertial oscillation is observed in the simulation. We reach the conclusion that the experiments completed to date have not yet reached the regime of absolute instability.
Localization in a spanwise-extended model of plane Couette flow.
Chantry, M; Kerswell, R R
2015-04-01
We consider a nine-partial-differential-equation (1-space and 1-time) model of plane Couette flow in which the degrees of freedom are severely restricted in the streamwise and cross-stream directions to study spanwise localization in detail. Of the many steady Eckhaus (spanwise modulational) instabilities identified of global steady states, none lead to a localized state. Spatially localized, time-periodic solutions were found instead, which arise in saddle node bifurcations in the Reynolds number. These solutions appear global (domain filling) in narrow (small spanwise) domains yet can be smoothly continued out to fully spanwise-localized states in very wide domains. This smooth localization behavior, which has also been seen in fully resolved duct flow (S. Okino, Ph.D. thesis, Kyoto University, Kyoto, 2011), indicates that an apparently global flow structure does not have to suffer a modulational instability to localize in wide domains. PMID:25974578
Drag reduction over liquid-infused surfaces in turbulent Taylor-Couette flow
NASA Astrophysics Data System (ADS)
van Buren, Tyler; Rosenberg, Brian; Smits, Alexander
2015-11-01
We present an experimental study on aqueous turbulent flow over a liquid-infused textured surface for the purpose of drag reduction. Taylor-Couette flow experiments are performed over a range of laminar to turbulent conditions (Re = 1500 to 7000), where the skin friction is compared to (i) a baseline case that consists of a textured surface with no impregnated fluid and (ii) an air-impregnated superhydrophic surface. We achieve drag reduction as high as 11% with superhydrophic surfaces and 4% with liquid infused surfaces. Of particular interest in this study is (1) the impact of surface texture shape and gap size on the resulting surface skin friction, (2) the importance of the viscosity ratios of the two fluids and its relationship to drag reduction, and (3) longevity of effectiveness when comparing liquid- to air-infused surfaces. This work was supported by the Office of Naval Research under MURI grant numbers: N000141210875, N000141210962, and N000141310458.
NASA Astrophysics Data System (ADS)
Jones, Robert; Lang, Amy
2010-11-01
Recent research has shown that symmetric, embedded square cavities can reduce the net drag acting on a surface through the formation of embedded vortices. It is hypothesized that the scales on butterfly wings (approximately 100 microns in length), though asymmetric, may act in a similar way resulting in greater flying efficiency. In this experimental study, cavities were modeled based on the geometry observed for bristled butterfly scales. Plates were designed to have parallelogram-shaped embedded cavities with an approximate 2:1 length to depth aspect ratio. The plates were suspended in high viscosity mineral oil above a rotating belt to generate a Couette flow condition such that the cavity Re was maintained in a similar regime as that occurring for the flow over butterfly scales. The net drag forces were measured with a force gauge and compared to flat plate measurements in the same facility. The variation in drag over a range of Reynolds numbers was analyzed.
Unstable periodic orbits in plane Couette flow with the Smagorinsky model
NASA Astrophysics Data System (ADS)
SASAKI, Eiichi; KAWAHARA, Genta; SEKIMOTO, Atsushi; JIMÉNEZ, Javier
2016-04-01
We aim at a description of the logarithmic velocity profile of wall turbulence in terms of unstable periodic orbits (UPOs) for plane Couette flow with a Smagorinsky-type eddy viscosity model. We study the bifurcation structure with respect to the Smagorinsky constant, arising from the gentle UPO reported by Kawahara and Kida [1] for the Navier-Stokes (NS) equation. We find that the obtained UPOs in the large eddy simulation (LES) system connect to those in the NS system, and that the gentle UPO in the LES system is an edge state branch whose stable manifold separates LES turbulence from an LES ‘laminar’ state. As the Reynolds number decreases this solution arises as the saddle solution of the saddle-node bifurcation. Meanwhile, the mean and root-mean-square velocity profiles of the node solution of the LES gentle UPO are in good agreement with those of LES turbulence.
Taylor-Couette Flow with Hourglass Geometry of Varying Lengths Simulated by Reaction-Diffusion
NASA Astrophysics Data System (ADS)
Zhao, Yunjie; Halmstad, Andrew; Olsen, Thomas; Wiener, Richard
2008-11-01
Previously, we have observed chaotic formation of Taylor-Vortex pairs in Modified Taylor- Couette Flow with Hourglass Geometry. In the experiment, the chaotic formation in a shorter system has been restricted to a narrow band about the waist of the hourglass. Such behavior has been modeled by The Reaction-Diffusion equation, which has been previously studied, by Riecke and Paap. Their calculation suggested that quadrupling length of the system would lead to spatial chaos in the vortex formation. We present a careful recreation of this result and consider an intermediate length. We demonstrate that doubling the length should be sufficient to observe spatially chaotic behavior. Richard J. Wiener et al, Phys. Rev. E 55, 5489 (1997). H. Riecke and H.-G. Paap, Europhys. Lett. 14, 1235 (1991).
NASA Astrophysics Data System (ADS)
Merbold, S.; Brauckmann, H. J.; Egbers, C.
2013-02-01
We investigate experimentally and numerically turbulent Taylor-Couette flow with independently rotating cylinders and radius ratio η=0.5. The torque acting on the inner wall is measured to analyze the transverse current of azimuthal motion Jω. The scaling of the torque with shear Reynolds number is determined for the outer cylinder at rest. For constant shear Reynolds number we investigate various ratios of angular velocities and find a torque maximum for counter-rotating cylinders that deviates from the prediction suggested by van Gils [J. Fluid Mech.10.1017/jfm.2012.236 706, 118 (2012)]. The direct comparison between the experiment and the numerical simulation shows a good agreement in the torques.
NASA Astrophysics Data System (ADS)
Saranadhi, Dhananjai; Chen, Dayong; Kleingartner, Justin; Srinivasan, Siddarth; Cohen, Robert; McKinley, Gareth
2015-11-01
A submerged body can be heated past its Leidenfrost temperature to form a thick, continuous film of steam between itself and the water. Here we employ a superhydrophobic surface to drastically reduce the energy input required to create and sustain such a boiling film, and use the resulting slip boundary condition to achieve skin friction drag reduction on the inner rotor of a bespoke Taylor-Couette apparatus. We find that skin friction can be reduced by over 90% relative to an unheated superhydrophobic surface at Re = 19,200, and derive a boundary layer and slip theory to fit the data to a model that calculates a slip length of 3.12 +/- 0.4 mm. This indicates that the boiling film has a thickness of 112 μm, which is consistent with literature.
CFD simulation of shear-induced aggregation and breakage in turbulent Taylor-Couette flow.
Wang, Liguang; Vigil, R Dennis; Fox, Rodney O
2005-05-01
An experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of approximately 10 microm latex spheres suspended in an aqueous solution undergoing turbulent Taylor-Couette flow was carried out. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry experiments. Subsequently, the quadrature method of moments (QMOM) was implemented into the CFD code to obtain predictions for mean particle size that account for the effects of local shear rate on the aggregation and breakage. These predictions were then compared with experimental data for latex sphere aggregates (using an in situ optical imaging method). Excellent agreement between the CFD-QMOM and experimental results was observed for two Reynolds numbers in the turbulent-flow regime. PMID:15797411
Asymptotic theory of neutral stability curve of the Couette flow of vibrationally excited gas
NASA Astrophysics Data System (ADS)
Grigor'ev, Yu N.; Ershov, I. V.
2016-06-01
The asymptotic theory of neutral stability curve of the supersonic plane Couette flow of vibrationally excited gas is constructed. The system of two-temperature viscous gas dynamics equations was used as original mathematical model. Spectral problem for an eighth order linear system of ordinary differential equations was obtained from the system within framework of classical theory of linear stability. Transformations of the spectral problem universal for all shear flows were carried along the classical Dunn — Lin scheme. As a result the problem was reduced to secular algebraic equation with a characteristic division on “inviscid” and “viscous” parts which was solved numerically. The calculated neutral stability curves coincide in limits of 10% with corresponding results of direct numerical solution of original spectral problem.
Numerical study of bubble generation in a turbulent two-phase Couette flow
NASA Astrophysics Data System (ADS)
Ovsyannikov, Andrey; Mani, Ali; Moin, Parviz; Kim, Dokyun
2014-11-01
The objective of this work is to develop an understanding bubble generation mechanism due to interactions between free surfaces and turbulent boundary layers as commonly seen near ship walls. To this end, we have focused on a canonical problem that involves Couette flow between two vertical parallel walls with an air-water interface in between. We have considered flow at Reynolds number of 8000 and Froude number of 3.6, both based on half domain dimension and water properties. Our calculations resolve both Kolmogorov lengths and the Hinze scale. Additionally, a conservative VOF method coupled to a subgrid Lagrangian breakup model is used to represent the ligament breakup phenomena and their resulting bubbles and drops. We will present results from these calculations revealing bubble formation rates, bubble size distribution, and effects of bubbles on modulation of turbulence Supported by ONR.
Localization in a spanwise-extended model of plane Couette flow
NASA Astrophysics Data System (ADS)
Chantry, M.; Kerswell, R. R.
2015-04-01
We consider a nine-partial-differential-equation (1-space and 1-time) model of plane Couette flow in which the degrees of freedom are severely restricted in the streamwise and cross-stream directions to study spanwise localization in detail. Of the many steady Eckhaus (spanwise modulational) instabilities identified of global steady states, none lead to a localized state. Spatially localized, time-periodic solutions were found instead, which arise in saddle node bifurcations in the Reynolds number. These solutions appear global (domain filling) in narrow (small spanwise) domains yet can be smoothly continued out to fully spanwise-localized states in very wide domains. This smooth localization behavior, which has also been seen in fully resolved duct flow (S. Okino, Ph.D. thesis, Kyoto University, Kyoto, 2011), indicates that an apparently global flow structure does not have to suffer a modulational instability to localize in wide domains.
Linear stability of a circular Couette flow under a radial thermoelectric body force
NASA Astrophysics Data System (ADS)
Yoshikawa, H. N.; Meyer, A.; Crumeyrolle, O.; Mutabazi, I.
2015-03-01
The stability of the circular Couette flow of a dielectric fluid is analyzed by a linear perturbation theory. The fluid is confined between two concentric cylindrical electrodes of infinite length with only the inner one rotating. A temperature difference and an alternating electric tension are applied to the electrodes to produce a radial dielectrophoretic body force that can induce convection in the fluid. We examine the effects of superposition of this thermoelectric force with the centrifugal force including its thermal variation. The Earth's gravity is neglected to focus on the situations of a vanishing Grashof number such as microgravity conditions. Depending on the electric field strength and of the temperature difference, critical modes are either axisymmetric or nonaxisymmetric, occurring in either stationary or oscillatory states. An energetic analysis is performed to determine the dominant destabilizing mechanism. When the inner cylinder is hotter than the outer one, the circular Couette flow is destabilized by the centrifugal force for weak and moderate electric fields. The critical mode is steady axisymmetric, except for weak fields within a certain range of the Prandtl number and of the radius ratio of the cylinders, where the mode is oscillatory and axisymmetric. The frequency of this oscillatory mode is correlated with a Brunt-Väisälä frequency due to the stratification of both the density and the electric permittivity of the fluid. Under strong electric fields, the destabilization by the dielectrophoretic force is dominant, leading to oscillatory nonaxisymmetric critical modes with a frequency scaled by the frequency of the inner-cylinder rotation. When the outer cylinder is hotter than the inner one, the instability is again driven by the centrifugal force. The critical mode is axisymmetric and either steady under weak electric fields or oscillatory under strong electric fields. The frequency of the oscillatory mode is also correlated with the
Linear stability of radially-heated circular Couette flow with simulated radial gravity
NASA Astrophysics Data System (ADS)
Tagg, Randy; Weidman, Patrick D.
2007-05-01
The stability of circular Couette flow between vertical concentric cylinders in the presence of a radial temperature gradient is considered with an effective “radial gravity.” In addition to terrestrial buoyancy - ρg e z we include the term - ρg m f(r)e r where g m f(r) is the effective gravitational acceleration directed radially inward across the gap. Physically, this body force arises in experiments using ferrofluid in the annular gap of a Taylor Couette cell whose inner cylinder surrounds a vertical stack of equally spaced disk magnets. The radial dependence f(r) of this force is proportional to the modified Bessel function K 1(κr), where 2π/κ is the spatial period of the magnetic stack and r is the radial coordinate. Linear stability calculations made to compare with conditions reported by Ali and Weidman (J. Fluid Mech., 220, 1990) show strong destabilization effects, measured by the onset Rayleigh number R, when the inner wall is warmer, and strong stabilization effects when the outer wall is warmer, with increasing values of the dimensionless radial gravity γ = g m /g. Further calculations presented for the geometry and fluid properties of a terrestrial laboratory experiment reveal a hitherto unappreciated structure of the stability problem for differentially-heated cylinders: multiple wavenumber minima exist in the marginal stability curves. Transitions in global minima among these curves give rise to a competition between differing instabilities of the same spiral mode number, but widely separated axial wavenumbers.
Vegetation Hydrodynamics - Recent Developments and Future Challenges
NASA Astrophysics Data System (ADS)
Nepf, H. M.
2014-12-01
For over a century vegetation has been removed from channels and coastal zones to facilitate navigation and development. In recent decades, however, we have recognized the ecologic and economic benefits of aquatic vegetation. It buffers against coastal eutrophication, damps waves and coastal storm surge, provides habitat, inhibits bank erosion, and provides significant carbon storage. The management of watersheds and coastal zones has turned from vegetation removal to restoration. In the past 20 years, the study of vegetation hydrodynamics has accelerated to meet the need to understand feedbacks between vegetation, flow and sediment transport. This presentation will describe key features of vegetation hydrodynamics, first at the meadow scale and then at the scale of individual patches, examining how vegetation density and meadow (or patch) morphology impact flow, with subsequent implications for sediment fate. Finally, the talk highlights differences in turbulence generation between bare and vegetated beds that may limit the transfer of open channel sediment transport models to vegetated channels, creating the future challenge of defining sediment transport models appropriate for vegetated regions.
Hydrodynamics of Turning Flocks.
Yang, Xingbo; Marchetti, M Cristina
2015-12-18
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational inertia and alignment strength, are derived by coarse-graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields anisotropic spin waves that mediate the propagation of turning information throughout the flock. The coupling between spin-current density to the local vorticity field through a nonlinear friction gives rise to a hydrodynamic mode with angular-dependent propagation speed at long wavelengths. This mode becomes unstable as a result of the growth of bend and splay deformations augmented by the spin wave, signaling the transition to complex spatiotemporal patterns of continuously turning and swirling flocks. PMID:26722945
Hydrodynamics of Turning Flocks
NASA Astrophysics Data System (ADS)
Yang, Xingbo; Marchetti, M. Cristina
2015-12-01
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational inertia and alignment strength, are derived by coarse-graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields anisotropic spin waves that mediate the propagation of turning information throughout the flock. The coupling between spin-current density to the local vorticity field through a nonlinear friction gives rise to a hydrodynamic mode with angular-dependent propagation speed at long wavelengths. This mode becomes unstable as a result of the growth of bend and splay deformations augmented by the spin wave, signaling the transition to complex spatiotemporal patterns of continuously turning and swirling flocks.
Fluctuations in relativistic causal hydrodynamics
NASA Astrophysics Data System (ADS)
Kumar, Avdhesh; Bhatt, Jitesh R.; Mishra, Ananta P.
2014-05-01
Formalism to calculate the hydrodynamic fluctuations by applying the Onsager theory to the relativistic Navier-Stokes equation is already known. In this work, we calculate hydrodynamic fluctuations within the framework of the second order hydrodynamics of Müller, Israel and Stewart and its generalization to the third order. We have also calculated the fluctuations for several other causal hydrodynamical equations. We show that the form for the Onsager-coefficients and form of the correlation functions remain the same as those obtained by the relativistic Navier-Stokes equation and do not depend on any specific model of hydrodynamics. Further we numerically investigate evolution of the correlation function using the one dimensional boost-invariant (Bjorken) flow. We compare the correlation functions obtained using the causal hydrodynamics with the correlation function for the relativistic Navier-Stokes equation. We find that the qualitative behavior of the correlation functions remains the same for all the models of the causal hydrodynamics.
Hydrodynamics of insect spermatozoa
NASA Astrophysics Data System (ADS)
Pak, On Shun; Lauga, Eric
2010-11-01
Microorganism motility plays important roles in many biological processes including reproduction. Many microorganisms propel themselves by propagating traveling waves along their flagella. Depending on the species, propagation of planar waves (e.g. Ceratium) and helical waves (e.g. Trichomonas) were observed in eukaryotic flagellar motion, and hydrodynamic models for both were proposed in the past. However, the motility of insect spermatozoa remains largely unexplored. An interesting morphological feature of such cells, first observed in Tenebrio molitor and Bacillus rossius, is the double helical deformation pattern along the flagella, which is characterized by the presence of two superimposed helical flagellar waves (one with a large amplitude and low frequency, and the other with a small amplitude and high frequency). Here we present the first hydrodynamic investigation of the locomotion of insect spermatozoa. The swimming kinematics, trajectories and hydrodynamic efficiency of the swimmer are computed based on the prescribed double helical deformation pattern. We then compare our theoretical predictions with experimental measurements, and explore the dependence of the swimming performance on the geometric and dynamical parameters.
Hydrodynamics of fossil fishes.
Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert
2014-08-01
From their earliest origins, fishes have developed a suite of adaptations for locomotion in water, which determine performance and ultimately fitness. Even without data from behaviour, soft tissue and extant relatives, it is possible to infer a wealth of palaeobiological and palaeoecological information. As in extant species, aspects of gross morphology such as streamlining, fin position and tail type are optimized even in the earliest fishes, indicating similar life strategies have been present throughout their evolutionary history. As hydrodynamical studies become more sophisticated, increasingly complex fluid movement can be modelled, including vortex formation and boundary layer control. Drag-reducing riblets ornamenting the scales of fast-moving sharks have been subjected to particularly intense research, but this has not been extended to extinct forms. Riblets are a convergent adaptation seen in many Palaeozoic fishes, and probably served a similar hydrodynamic purpose. Conversely, structures which appear to increase skin friction may act as turbulisors, reducing overall drag while serving a protective function. Here, we examine the diverse adaptions that contribute to drag reduction in modern fishes and review the few attempts to elucidate the hydrodynamics of extinct forms. PMID:24943377
Hydrodynamics of fossil fishes
Fletcher, Thomas; Altringham, John; Peakall, Jeffrey; Wignall, Paul; Dorrell, Robert
2014-01-01
From their earliest origins, fishes have developed a suite of adaptations for locomotion in water, which determine performance and ultimately fitness. Even without data from behaviour, soft tissue and extant relatives, it is possible to infer a wealth of palaeobiological and palaeoecological information. As in extant species, aspects of gross morphology such as streamlining, fin position and tail type are optimized even in the earliest fishes, indicating similar life strategies have been present throughout their evolutionary history. As hydrodynamical studies become more sophisticated, increasingly complex fluid movement can be modelled, including vortex formation and boundary layer control. Drag-reducing riblets ornamenting the scales of fast-moving sharks have been subjected to particularly intense research, but this has not been extended to extinct forms. Riblets are a convergent adaptation seen in many Palaeozoic fishes, and probably served a similar hydrodynamic purpose. Conversely, structures which appear to increase skin friction may act as turbulisors, reducing overall drag while serving a protective function. Here, we examine the diverse adaptions that contribute to drag reduction in modern fishes and review the few attempts to elucidate the hydrodynamics of extinct forms. PMID:24943377
Lindfors, Lennart; Jonsson, Malin; Weibull, Emelie; Brasseur, James G; Abrahamsson, Bertil
2015-09-01
The aim of this study was to understand and predict the influence of hydrodynamic effects in the small intestine on dissolution of primary and aggregated drug particles. Dissolution tests of suspensions with a low-solubility drug, felodipine, were performed in a Couette cell under hydrodynamic test conditions corresponding to the fed small intestine. Dissolution was also performed in the USP II apparatus at two paddle speeds of 25 and 200 rpm and at different surfactant concentrations below critical micelle concentration. The experimental dissolution rates were compared with theoretical calculations. The different levels of shear stress in the in vitro tests did not influence the dissolution of primary or aggregated particles and experimental dissolution rates corresponded very well to calculations. The dissolution rate for the aggregated drug particles increased after addition of surfactant because of deaggregation, but there were still no effect of hydrodynamics. In conclusion, hydrodynamics do not influence dissolution and deaggregation of micronized drug particles in the small intestine of this model drug. Surface tension has a strong effect on the deaggregation and subsequent dissolution. Addition of surfactants at in vivo relevant surface tension levels is thus critical for in vivo predictive in vitro dissolution testing. PMID:25980801
Colgate, Stirling A.; Beckley, Howard; Si, Jiahe; Martinic, Joe; Westpfahl, David; Slutz, James; Westrom, Cebastian; Klein, Brianna; Schendel, Paul; Scharle, Cletus; McKinney, Travis; Ginanni, Rocky; Bentley, Ian; Mickey, Timothy; Ferrel, Regnar; Li, Hui; Pariev, Vladimir; Finn, John
2011-04-29
The {Omega} phase of the liquid sodium {alpha}-{Omega} dynamo experiment at New Mexico Institute of Mining and Technology in cooperation with Los Alamos National Laboratory has demonstrated a high toroidal field B{sub {phi}} that is {approx_equal}8xB{sub r}, where B{sub r} is the radial component of an applied poloidal magnetic field. This enhanced toroidal field is produced by the rotational shear in stable Couette flow within liquid sodium at a magnetic Reynolds number Rm{approx_equal}120. Small turbulence in stable Taylor-Couette flow is caused by Ekman flow at the end walls, which causes an estimated turbulence energy fraction of ({delta}v/v){sup 2{approx}}10{sup -3}.
Colgate, Stirling; Li, Jui; Finn, John; Pariev, Vladimir; Beckley, Howard; Si, Jiahe; Martinic, Joe; Westpfahl, David; Slutz, James; Westrom, Zeb; Klein, Brianna
2010-11-08
The {Omega}-phase of the liquid sodium {alpha}-{Omega} dynamo experiment at NMIMT in cooperation with LANL has successfully demonstrated the production of a high toroidal field, B{sub {phi}} {approx_equal} 8 x B{sub r} from the radial component of an applied poloidal magnetic field, B{sub r}. This enhanced toroidal field is produced by rotational shear in stable Couette Row within liquid sodium at Rm {approx_equal} 120. The small turbulence in stable Taylor-Couette Row is caused by Ekman Row where ({delta}v/v){sup 2} {approx} 10{sup -3}. This high {Omega}-gain in low turbulence flow contrasts with a smaller {Omega}-gain in higher turbulence, Helmholtz-unstable shear flows. This result supports the ansatz that large scale astrophysical magnetic fields are created within semi-coherent large scale motions in which turbulence plays a diffusive role that enables magnetic flux linkage.
NASA Astrophysics Data System (ADS)
Nordsiek, Freja; Huisman, Sander G.; van der Veen, Roeland C. A.; Sun, Chao; Lohse, Detlef; Lathrop, Daniel P.
2015-07-01
We present azimuthal velocity profiles measured in a Taylor-Couette apparatus, which has been used as a model of stellar and planetary accretion disks. The apparatus has a cylinder radius ratio of $\\eta = 0.716$, an aspect-ratio of $\\Gamma = 11.74$, and the plates closing the cylinders in the axial direction are attached to the outer cylinder. We investigate angular momentum transport and Ekman pumping in the Rayleigh-stable regime. The regime is linearly stable and is characterized by radially increasing specific angular momentum. We present several Rayleigh-stable profiles for shear Reynolds numbers $Re_S \\sim O(10^5) \\,$, both for $\\Omega_i > \\Omega_o > 0$ (quasi-Keplerian regime) and $\\Omega_o > \\Omega_i > 0$ (sub-rotating regime) where $\\Omega_{i,o}$ is the inner/outer cylinder rotation rate. None of the velocity profiles matches the non-vortical laminar Taylor-Couette profile. The deviation from that profile increased as solid-body rotation is approached at fixed $Re_S$. Flow super-rotation, an angular velocity greater than that of both cylinders, is observed in the sub-rotating regime. The velocity profiles give lower bounds for the torques required to rotate the inner cylinder that were larger than the torques for the case of laminar Taylor-Couette flow. The quasi-Keplerian profiles are composed of a well mixed inner region, having approximately constant angular momentum, connected to an outer region in solid-body rotation with the outer cylinder and attached axial boundaries. These regions suggest that the angular momentum is transported axially to the axial boundaries. Therefore, Taylor-Couette flow with closing plates attached to the outer cylinder is an imperfect model for accretion disk flows, especially with regard to their stability.
Liquid-liquid extraction based on a new flow pattern: Two-fluid Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Baier, Gretchen
The exploitation of flow instabilities that can occur in rotating flows is investigated as a new approach to liquid extraction. Two immiscible liquids are radially stratified by centrifugal force in the annulus between corotating coaxial cylinders. The inner cylinder is rotated above a critical speed to form Taylor vortices in one or both of the fluids. This flow pattern produces a relatively small amount interfacial surface area that is of highly active for interphase mass transfer. Continuous processing is also possible with the addition of countercurrent axial flow. The present study includes: (1)A review of aqueous- aqueous and reversed micelle extraction techniques, the commercially available centrifugal extractors, and one fluid Taylor-Couette flow and its variations. (2)A theoretical analysis to predict the onset of the two- fluid Taylor-Couette instability in the presence of countercurrent axial flow. (3)Theoretical predictions for interphase mass transfer using penetration theory and computational fluid dynamics. (4)The demonstration of two-fluid Taylor-Couette flow with countercurrent axial flow in the laboratory, including: (1) fluid mechanics studies to determine the onset of vortices, and (2) mass transfer studies to characterize intraphase and interphase mass transfer. The agreement between the experiments and theory is good for both the fluid mechanics and the mass transfer. Furthermore, the extraction performance is quite promising with the mass transfer coefficient approximately proportional to the vortex strength. Even higher extraction efficiencies should be obtainable with even larger relative rotation rates or cylinder modification to promote vortex formation. Besides two-fluid Taylor-Couette flow, other instabilities can also occur. With low viscosity fluids at low rotation rates, the ``barber pole'' pattern is observed experimentally and is believed to be a lingering gravitational effect. At high countercurrent axial flowrates, the linear
Hydrodynamic modes for granular gases.
Dufty, James W; Brey, J Javier
2003-09-01
The eigenfunctions and eigenvalues of the linearized Boltzmann equation for inelastic hard spheres (d=3) or disks (d=2) corresponding to d+2 hydrodynamic modes are calculated in the long wavelength limit for a granular gas. The transport coefficients are identified and found to agree with those from the Chapman-Enskog solution. The dominance of hydrodynamic modes at long times and long wavelengths is studied via an exactly solvable kinetic model. A collisional continuum is bounded away from the hydrodynamic spectrum, assuring a hydrodynamic description at long times. The bound is closely related to the power law decay of the velocity distribution in the reference homogeneous cooling state. PMID:14524742
Molecular Hydrodynamics from Memory Kernels.
Lesnicki, Dominika; Vuilleumier, Rodolphe; Carof, Antoine; Rotenberg, Benjamin
2016-04-01
The memory kernel for a tagged particle in a fluid, computed from molecular dynamics simulations, decays algebraically as t^{-3/2}. We show how the hydrodynamic Basset-Boussinesq force naturally emerges from this long-time tail and generalize the concept of hydrodynamic added mass. This mass term is negative in the present case of a molecular solute, which is at odds with incompressible hydrodynamics predictions. Lastly, we discuss the various contributions to the friction, the associated time scales, and the crossover between the molecular and hydrodynamic regimes upon increasing the solute radius. PMID:27104730
Load responsive hydrodynamic bearing
Kalsi, Manmohan S.; Somogyi, Dezso; Dietle, Lannie L.
2002-01-01
A load responsive hydrodynamic bearing is provided in the form of a thrust bearing or journal bearing for supporting, guiding and lubricating a relatively rotatable member to minimize wear thereof responsive to relative rotation under severe load. In the space between spaced relatively rotatable members and in the presence of a liquid or grease lubricant, one or more continuous ring shaped integral generally circular bearing bodies each define at least one dynamic surface and a plurality of support regions. Each of the support regions defines a static surface which is oriented in generally opposed relation with the dynamic surface for contact with one of the relatively rotatable members. A plurality of flexing regions are defined by the generally circular body of the bearing and are integral with and located between adjacent support regions. Each of the flexing regions has a first beam-like element being connected by an integral flexible hinge with one of the support regions and a second beam-like element having an integral flexible hinge connection with an adjacent support region. A least one local weakening geometry of the flexing region is located intermediate the first and second beam-like elements. In response to application of load from one of the relatively rotatable elements to the bearing, the beam-like elements and the local weakening geometry become flexed, causing the dynamic surface to deform and establish a hydrodynamic geometry for wedging lubricant into the dynamic interface.
Hydrodynamics of pronuclear migration
NASA Astrophysics Data System (ADS)
Nazockdast, Ehssan; Needleman, Daniel; Shelley, Michael
2014-11-01
Microtubule (MT) filaments play a key role in many processes involved in cell devision including spindle formation, chromosome segregation, and pronuclear positioning. We present a direct numerical technique to simulate MT dynamics in such processes. Our method includes hydrodynamically mediated interactions between MTs and other cytoskeletal objects, using singularity methods for Stokes flow. Long-ranged many-body hydrodynamic interactions are computed using a highly efficient and scalable fast multipole method, enabling the simulation of thousands of MTs. Our simulation method also takes into account the flexibility of MTs using Euler-Bernoulli beam theory as well as their dynamic instability. Using this technique, we simulate pronuclear migration in single-celled Caenorhabditis elegans embryos. Two different positioning mechanisms, based on the interactions of MTs with the motor proteins and the cell cortex, are explored: cytoplasmic pulling and cortical pushing. We find that although the pronuclear complex migrates towards the center of the cell in both models, the generated cytoplasmic flows are fundamentally different. This suggest that cytoplasmic flow visualization during pronuclear migration can be utilized to differentiate between the two mechanisms.
Malik, M; Dey, J; Alam, Meheboob
2008-03-01
Linear stability and the nonmodal transient energy growth in compressible plane Couette flow are investigated for two prototype mean flows: (a) the uniform shear flow with constant viscosity, and (b) the nonuniform shear flow with stratified viscosity. Both mean flows are linearly unstable for a range of supersonic Mach numbers (M). For a given M , the critical Reynolds number (Re) is significantly smaller for the uniform shear flow than its nonuniform shear counterpart; for a given Re, the dominant instability (over all streamwise wave numbers, alpha ) of each mean flow belongs to different modes for a range of supersonic M . An analysis of perturbation energy reveals that the instability is primarily caused by an excess transfer of energy from mean flow to perturbations. It is shown that the energy transfer from mean flow occurs close to the moving top wall for "mode I" instability, whereas it occurs in the bulk of the flow domain for "mode II." For the nonmodal transient growth analysis, it is shown that the maximum temporal amplification of perturbation energy, G(max), and the corresponding time scale are significantly larger for the uniform shear case compared to those for its nonuniform counterpart. For alpha=0 , the linear stability operator can be partitioned into L ~ L+Re(2) L(p), and the Re-dependent operator L(p) is shown to have a negligibly small contribution to perturbation energy which is responsible for the validity of the well-known quadratic-scaling law in uniform shear flow: G(t/Re) ~ Re(2). In contrast, the dominance of L(p) is responsible for the invalidity of this scaling law in nonuniform shear flow. An inviscid reduced model, based on Ellingsen-Palm-type solution, has been shown to capture all salient features of transient energy growth of full viscous problem. For both modal and nonmodal instability, it is shown that the viscosity stratification of the underlying mean flow would lead to a delayed transition in compressible Couette flow
Hydrodynamics, resurgence, and transasymptotics
NASA Astrophysics Data System (ADS)
Başar, Gökçe; Dunne, Gerald V.
2015-12-01
The second order hydrodynamical description of a homogeneous conformal plasma that undergoes a boost-invariant expansion is given by a single nonlinear ordinary differential equation, whose resurgent asymptotic properties we study, developing further the recent work of Heller and Spalinski [Phys. Rev. Lett. 115, 072501 (2015)]. Resurgence clearly identifies the nonhydrodynamic modes that are exponentially suppressed at late times, analogous to the quasinormal modes in gravitational language, organizing these modes in terms of a trans-series expansion. These modes are analogs of instantons in semiclassical expansions, where the damping rate plays the role of the instanton action. We show that this system displays the generic features of resurgence, with explicit quantitative relations between the fluctuations about different orders of these nonhydrodynamic modes. The imaginary part of the trans-series parameter is identified with the Stokes constant, and the real part with the freedom associated with initial conditions.
Hydrodynamics of Peristaltic Propulsion
NASA Astrophysics Data System (ADS)
Athanassiadis, Athanasios; Hart, Douglas
2014-11-01
A curious class of animals called salps live in marine environments and self-propel by ejecting vortex rings much like jellyfish and squid. However, unlike other jetting creatures that siphon and eject water from one side of their body, salps produce vortex rings by pumping water through siphons on opposite ends of their hollow cylindrical bodies. In the simplest cases, it seems like some species of salp can successfully move by contracting just two siphons connected by an elastic body. When thought of as a chain of timed contractions, salp propulsion is reminiscent of peristaltic pumping applied to marine locomotion. Inspired by salps, we investigate the hydrodynamics of peristaltic propulsion, focusing on the scaling relationships that determine flow rate, thrust production, and energy usage in a model system. We discuss possible actuation methods for a model peristaltic vehicle, considering both the material and geometrical requirements for such a system.
Hydrodynamics of Turning Flocks
NASA Astrophysics Data System (ADS)
Yang, Xingbo; Marchetti, M. Cristina
2015-03-01
We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well polarized flocks. The continuum equations are derived by coarse graining the inertial spin model recently proposed by Cavagna et al. The interplay between orientational inertia and bend elasticity of the flock yields spin waves that mediate the propagation of turning information throughout the flock. When the inertia is large, we find a novel instability that signals the transition to complex spatio-temporal patterns of continuously turning and swirling flocks. This work was supported by the NSF Awards DMR-1305184 and DGE-1068780 at Syracuse University and NSF Award PHY11-25915 and the Gordon and Betty Moore Foundation Grant No. 2919 at the KITP at the University of California, Santa Barbara.
Hydrodynamic effects on coalescence.
Dimiduk, Thomas G.; Bourdon, Christopher Jay; Grillet, Anne Mary; Baer, Thomas A.; de Boer, Maarten Pieter; Loewenberg, Michael; Gorby, Allen D.; Brooks, Carlton, F.
2006-10-01
The goal of this project was to design, build and test novel diagnostics to probe the effect of hydrodynamic forces on coalescence dynamics. Our investigation focused on how a drop coalesces onto a flat surface which is analogous to two drops coalescing, but more amenable to precise experimental measurements. We designed and built a flow cell to create an axisymmetric compression flow which brings a drop onto a flat surface. A computer-controlled system manipulates the flow to steer the drop and maintain a symmetric flow. Particle image velocimetry was performed to confirm that the control system was delivering a well conditioned flow. To examine the dynamics of the coalescence, we implemented an interferometry capability to measure the drainage of the thin film between the drop and the surface during the coalescence process. A semi-automated analysis routine was developed which converts the dynamic interferogram series into drop shape evolution data.
Synchronization and hydrodynamic interactions
NASA Astrophysics Data System (ADS)
Powers, Thomas; Qian, Bian; Breuer, Kenneth
2008-03-01
Cilia and flagella commonly beat in a coordinated manner. Examples include the flagella that Volvox colonies use to move, the cilia that sweep foreign particles up out of the human airway, and the nodal cilia that set up the flow that determines the left-right axis in developing vertebrate embryos. In this talk we present an experimental study of how hydrodynamic interactions can lead to coordination in a simple idealized system: two nearby paddles driven with fixed torques in a highly viscous fluid. The paddles attain a synchronized state in which they rotate together with a phase difference of 90 degrees. We discuss how synchronization depends on system parameters and present numerical calculations using the method of regularized stokeslets.
Hydrodynamics of sediment threshold
NASA Astrophysics Data System (ADS)
Ali, Sk Zeeshan; Dey, Subhasish
2016-07-01
A novel hydrodynamic model for the threshold of cohesionless sediment particle motion under a steady unidirectional streamflow is presented. The hydrodynamic forces (drag and lift) acting on a solitary sediment particle resting over a closely packed bed formed by the identical sediment particles are the primary motivating forces. The drag force comprises of the form drag and form induced drag. The lift force includes the Saffman lift, Magnus lift, centrifugal lift, and turbulent lift. The points of action of the force system are appropriately obtained, for the first time, from the basics of micro-mechanics. The sediment threshold is envisioned as the rolling mode, which is the plausible mode to initiate a particle motion on the bed. The moment balance of the force system on the solitary particle about the pivoting point of rolling yields the governing equation. The conditions of sediment threshold under the hydraulically smooth, transitional, and rough flow regimes are examined. The effects of velocity fluctuations are addressed by applying the statistical theory of turbulence. This study shows that for a hindrance coefficient of 0.3, the threshold curve (threshold Shields parameter versus shear Reynolds number) has an excellent agreement with the experimental data of uniform sediments. However, most of the experimental data are bounded by the upper and lower limiting threshold curves, corresponding to the hindrance coefficients of 0.2 and 0.4, respectively. The threshold curve of this study is compared with those of previous researchers. The present model also agrees satisfactorily with the experimental data of nonuniform sediments.
Taylor–Couette turbulence at radius ratio : scaling, flow structures and plumes
NASA Astrophysics Data System (ADS)
van der Veen, Roeland C. A.; Huisman, Sander G.; Merbold, Sebastian; Harlander, Uwe; Egbers, Christoph; Lohse, Detlef; Sun, Chao
2016-07-01
Using high-resolution particle image velocimetry we measure velocity profiles, the wind Reynolds number and characteristics of turbulent plumes in Taylor-Couette flow for a radius ratio of 0.5 and Taylor number of up to $6.2\\cdot10^9$. The extracted angular velocity profiles follow a log-law more closely than the azimuthal velocity profiles due to the strong curvature of this $\\eta=0.5$ setup. The scaling of the wind Reynolds number with the Taylor number agrees with the theoretically predicted 3/7-scaling for the classical turbulent regime, which is much more pronounced than for the well-explored $\\eta=0.71$ case, for which the ultimate regime sets in at much lower Ta. By measuring at varying axial positions, roll structures are found for counter-rotation while no clear coherent structures are seen for pure inner cylinder rotation. In addition, turbulent plumes coming from the inner and outer cylinder are investigated. For pure inner cylinder rotation, the plumes in the radial velocity move away from the inner cylinder, while the plumes in the azimuthal velocity mainly move away from the outer cylinder. For counter-rotation, the mean radial flow in the roll structures strongly affects the direction and intensity of the turbulent plumes. Furthermore, it is experimentally confirmed that in regions where plumes are emitted, boundary layer profiles with a logarithmic signature are created.
NASA Astrophysics Data System (ADS)
Krygier, Michael; Grigoriev, Roman
2015-11-01
A direct transition from laminar to turbulent flow has recently been discovered experimentally in the small-gap Taylor-Couette flow with counter-rotating cylinders. The subcritical nature of this transition is a result of relatively small aspect ratio, Γ = 5 . 26 for large Γ the transition is supercritical and involves an intermediate stable state (Coughlin & Marcus, 1996) - interpenetrating spirals (IPS). We investigate this transition numerically to probe the dynamics in regimes inaccessible to experiments for a fixed Reo = - 1000 by varying Rei . The numerics reproduce all the experimentally observed features and confirm the hysteretic nature of the transition. As Rei is increased, the laminar flow transitions to turbulence, with an unstable IPS state mediating the transition, similar to the Tollmien-Schlichting waves in plane Poiseuille flow. As Rei is decreased, turbulent flow transitions to a stable, temporally chaotic IPS state. This IPS state further transitions to either laminar or turbulent flow as Rei is decreased or increased. The stable IPS state is reminiscent of the pre-turbulent chaotic states found numerically in plane Poiseuille flow (Zammert & Eckhardt, 2015), but previously never observed experimentally.
Mechanical and statistical study of the laminar hole formation in transitional plane Couette flow
NASA Astrophysics Data System (ADS)
Rolland, Joran
2015-03-01
This article is concerned with the numerical study and modelling of two aspects the formation of laminar holes in transitional turbulence of plane Couette flow (PCF). On the one hand, we consider quenches: sudden decreases of the Reynolds number R which force the formation of holes. The Reynolds number is decreased from featureless turbulence to the range of existence of the oblique laminar-turbulent bands [ R g; R t]. The successive stages of the quench are studied by means of visualisations and measurements of kinetic energy and turbulent fraction. The behaviour of the kinetic energy is explained using a kinetic energy budget: it shows that viscosity causes quasi modal decay until lift-up equals it and creates a new balance. Moreover, the budget confirms that the physical mechanisms at play are independent of the way the quench is performed. On the other hand we consider the natural formation of laminar holes in the bands, near R g. The direct numerical simulations (DNS) show that holes in the turbulent bands provide a mechanism for the fragmented bands regime and orientation fluctuations near R g. Moreover the analysis of the fluctuations of kinetic energy toward low values demonstrates that the disappearance of turbulence in the bands can be described within the framework of large deviations. A large deviation function is extracted from the probability density function of the kinetic energy.
NASA Astrophysics Data System (ADS)
Srinivasan, Siddarth; Kleingartner, Justin A.; Gilbert, Jonathan B.; Cohen, Robert E.; Milne, Andrew J. B.; McKinley, Gareth H.
2015-01-01
We demonstrate a reduction in the measured inner wall shear stress in moderately turbulent Taylor-Couette flows by depositing sprayable superhydrophobic microstructures on the inner rotor surface. The magnitude of reduction becomes progressively larger as the Reynolds number increases up to a value of 22% at Re =8.0 ×1 04 . We show that the mean skin friction coefficient Cf in the presence of the superhydrophobic coating can be fitted to a modified Prandtl-von Kármán-type relationship of the form (Cf/2 )-1 /2=M ln (Re (Cf/2 )1 /2) +N +(b /Δ r )Re (Cf/2 )1 /2 from which we extract an effective slip length of b ≈19 μ m . The dimensionless effective slip length b+=b /δν, where δν is the viscous length scale, is the key parameter that governs the drag reduction and is shown to scale as b+˜Re1 /2 in the limit of high Re.
Srinivasan, Siddarth; Kleingartner, Justin A; Gilbert, Jonathan B; Cohen, Robert E; Milne, Andrew J B; McKinley, Gareth H
2015-01-01
We demonstrate a reduction in the measured inner wall shear stress in moderately turbulent Taylor-Couette flows by depositing sprayable superhydrophobic microstructures on the inner rotor surface. The magnitude of reduction becomes progressively larger as the Reynolds number increases up to a value of 22% at Re=8.0×10(4). We show that the mean skin friction coefficient C(f) in the presence of the superhydrophobic coating can be fitted to a modified Prandtl-von Kármán-type relationship of the form (C(f)/2)(-1/2)=Mln (Re(C(f)/2)(1/2))+N+(b/Δr)Re(C(f)/2)(1/2) from which we extract an effective slip length of b≈19 μm. The dimensionless effective slip length b(+)=b/δ(ν), where δ(ν) is the viscous length scale, is the key parameter that governs the drag reduction and is shown to scale as b(+)∼Re(1/2) in the limit of high Re. PMID:25615472
Measurements of wall shear stress in a planar turbulent Couette flow with porous walls
NASA Astrophysics Data System (ADS)
Beuther, Paul
2013-11-01
Measurements of drag on a moving web in a multi-span festoon show a stronger than expected dependency on the porosity of the web. The experiments suggest a wall shear stress 3-4 times larger than non-porous webs or historical Couette flow data for solid walls. Previous DNS studies by Jimenez et al. (JFM Vol 442) of boundary layers with passive porous surfaces predict a much smaller increase in wall shear stress for a porous wall of only 40%. Other DNS studies by Quadrio et al. (JFM Vol 576) of porous walls with periodic transpiration do show a large increase in drag under certain periodic conditions of modest amplitude. Although those results are aligned in magnitude with this study, the exact reason for the observed high drag for porous webs in this present study is not understood because there was no external disturbance applied to the web. It can be hypothesized that natural flutter of the web results in a similar mechanism shown in the periodic DNS study, but when the natural flutter was reduced by increasing web tension, there was only a small decrease of the drag. A key difference in this study is that because of the multiple parallel spans in a festoon, any transpiration in one layer must act in the opposite manner on the adjacent span.
Couette flow of non-Newtonian power-law fluids in narrow eccentric annuli
Yang, L.; Chukwu, G.A.
1995-03-01
The analysis of the steady laminar Couette flow of non-Newtonian power-law fluids in a narrow eccentric cannulus is employed in this study to compute the surge or swab pressure encountered when running or pulling tubular goods in a liquid-filled borehole, respectively. Excessive surge pressure can fracture the formation, while uncontrolled swab pressure can result in well blowout. In this study, the eqs of motion are analytically solved and the solution of these eqs is presented in both dimensionless and graphical forms for a more general application to computing the surge or swab pressure. The family of curves is presented for different pipe/borehole eccentricity ratios and power-law fluid index values which span the range of typical drilling fluids. By employing the computed surge pressures, in combination with the family of curves, the maximum velocity at which the casing can be run in the hole without the danger of fracturing the formation can be obtained. The expected error in surge computation for a narrow concentric annulus represented by a slot, as a result of eccentricity, is evaluated. The results obtained from the these analyses will aid in proper design and optimization of drilling programs, especially in deviated holes.
NASA Astrophysics Data System (ADS)
Power, H.; Soavi, J.; Kantachuvesiri, P.; Nieto, C.
2015-10-01
In this work, a detailed study of the effect of the Thompson and Troian's nonlinear slip condition on the flow behaviour of a Newtonian incompressible fluid between two concentric rotating cylinders (Couette flow) is considered. In Thompson and Troian's nonlinear condition, the slip length on the Navier slip condition is considered to be a function of the tangential shear rate at the solid surface instead of being a constant. The resulting formulation presents an apparent singularity on the slip length when a critical shear rate is approached. By considering this type of nonlinear slip condition, it is possible to predict complex characteristics of the flow field not previously reported in the literature, and to show the effect of nonlinear slip on the inverted velocity profiles previously observed in the linear slip case. Particular attention is given to the behaviour of the flow field near the critical shear rate. In such a limit, it is found that the flow field tends to slip flow with a finite slip length. Consequently, previous critique on the singular behaviour of Thompson and Troian's nonlinear model is not valid in the present case.
Transient growth in Taylor-Couette flow of a Bingham fluid
NASA Astrophysics Data System (ADS)
Chen, Cheng; Wan, Zhen-Hua; Zhang, Wei-Guo
2015-04-01
In this paper we investigate linear transient growth of perturbation energy in Taylor-Couette flow of a Bingham fluid. The effects of yield stress on transient growth and the structure of the optimal perturbation are mainly considered for both the wide-gap case and the narrow-gap case. For this purpose we complement the linear stability of this flow subjected to axisymmetric disturbances, presented by Landry et al. [M. P. Landry, I. A. Frigaard, and D. M. Martinez, J. Fluid Mech. 560, 321 (2006), 10.1017/S0022112006000620], with the transient growth characteristics of both axisymmetric and nonaxisymmetric perturbations. We obtain the variations of the relative amplitude of optimal perturbation with yield stress, analyze the roles played by the Coriolis force and the additional stress in the evolution of meridional perturbations for the axisymmetric modes, and give the explanations for the possible change of the optimal azimuthal mode (featured by the maximum optimal energy growth Gopt) with yield stress. These results might help us in the understanding of the effect of fluid rheology on transient growth mechanism in vortex flows.
Flow regimes in a vertical Taylor-Couette system with a radial thermal gradient
NASA Astrophysics Data System (ADS)
Guillerm, R.; Kang, C.; Savaro, C.; Lepiller, V.; Prigent, A.; Yang, K.-S.; Mutabazi, I.
2015-09-01
A rich variety of flow regimes in a Newtonian fluid inside a vertical large-aspect ratio and a wide-gap Taylor-Couette system with a radial temperature gradient has been determined in experiments and in direct numerical simulations (DNSs). Compared to previous experiments and numerical studies, a wider range of temperature differences (i.e., of the Grashof number Gr) and of the rotation rate (the Taylor number Ta) has been covered. The combined effect of rotation and of the radial temperature gradient is the occurrence of helicoidal vortices or modulated waves at the onset. Stationary axisymmetric vortices are found for very weak temperature differences. A good agreement was found for critical states between results from experiments, linear stability analysis, and DNS. Higher instability modes have been determined for a wide range of parameters and a state diagram of observable flow regimes has been established in the plane spanned by Gr and Ta. Some higher states observed in experiments were retrieved in DNS.
Linear stability of the Couette flow of a vibrationally excited gas. 2. viscous problem
NASA Astrophysics Data System (ADS)
Grigor'ev, Yu. N.; Ershov, I. V.
2016-03-01
Based on the linear theory, stability of viscous disturbances in a supersonic plane Couette flow of a vibrationally excited gas described by a system of linearized equations of two-temperature gas dynamics including shear and bulk viscosity is studied. It is demonstrated that two sets are identified in the spectrum of the problem of stability of plane waves, similar to the case of a perfect gas. One set consists of viscous acoustic modes, which asymptotically converge to even and odd inviscid acoustic modes at high Reynolds numbers. The eigenvalues from the other set have no asymptotic relationship with the inviscid problem and are characterized by large damping decrements. Two most unstable viscous acoustic modes (I and II) are identified; the limits of these modes were considered previously in the inviscid approximation. It is shown that there are domains in the space of parameters for both modes, where the presence of viscosity induces appreciable destabilization of the flow. Moreover, the growth rates of disturbances are appreciably greater than the corresponding values for the inviscid flow, while thermal excitation in the entire considered range of parameters increases the stability of the viscous flow. For a vibrationally excited gas, the critical Reynolds number as a function of the thermal nonequilibrium degree is found to be greater by 12% than for a perfect gas.
Mixing of a stable linear density stratification in Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Oglethorpe, R. L. F.; Caulfield, C. P.; Woods, Andrew W.
2011-11-01
We consider mixing of an initially linear stable salt stratification in turbulent Taylor-Couette flow. The fluid is confined to a cylindrical annulus with a vertical axis. Mixing is caused by rotating the inner cylinder at a constant rate. The outer cylinder is fixed. Experimental measurements show that at high initial bulk Richardson number, defined as Ri0 =N2 /Ω2 , where N is the buoyancy frequency of the initial stratification and Ω is the rotation rate of the inner cylinder, an initially linear salt stratification develops a series of well mixed layers separated by sharp interfaces. The size of these layers appears to depend on Ri0 and the gap width between the cylinders, ΔR. With time, the layers at the top and bottom of the tank evolve in salinity. This leads to entrainment from and eventual mixing with the adjacent layers as the salinity contrast across these interfaces decreases. As a result of successive merger events, eventually the system becomes well mixed. The salinity of the inner layers appears to remain constant, so that salt is transported from the bottom layer to the top layer without changing the structure of the interior. The salt flux through an interface appears to depend only on the rotation rate Ω of the inner cylinder, consistent with our previous study for an initial two-layer salt stratification (Woods et al. (2010) J Fluid Mech. 663, 347-357).
NASA Astrophysics Data System (ADS)
Doi, Toshiyuki
2016-02-01
Transient Couette flow of a rarefied gas between plane parallel walls with different surface properties induced by a sudden start-up of one of the walls is studied based on kinetic theory. The linearized Boltzmann equation for a hard sphere molecular gas is analyzed under the assumptions that one wall is a diffuse reflection boundary and the other wall is a Maxwell-type boundary. The initial and boundary value problem is solved numerically by using a modified hybrid scheme of characteristic coordinate and finite difference methods, to describe the discontinuities in the velocity distribution function correctly. The time evolution of the flow and the approach to the final time-independent state are studied over a wide range of the mean free paths and the accommodation coefficient of the boundary. In the transient process, the shear force acting on the moving wall depends on which wall moves. In contrast, the shear force acting on the wall at rest is independent of which wall moves; this property is a consequence of the symmetric relation of the Boltzmann equation [S. Takata, "Symmetry of the unsteady linearized Boltzmann equation in a fixed bounded domain," J. Stat. Phys. 140, 985 (2010)]. The speed of approach to the time-independent state is fastest at an intermediate value of the mean free path. The behavior of the gas in the final time-independent state, including the heat flow in the isothermal gas, is also discussed.
Drag Measurements over Embedded Cavities in a Low Reynolds Number Couette Flow
NASA Astrophysics Data System (ADS)
Gilmer, Caleb; Lang, Amy; Jones, Robert
2010-11-01
Recent research has revealed that thin-walled, embedded cavities in low Reynolds number flow have the potential to reduce the net viscous drag force acting on the surface. This reduction is due to the formation of embedded vortices allowing the outer flow to pass over the surface via a roller bearing effect. It is also hypothesized that the scales found on butterfly wings may act in a similar manner to cause a net increase in flying efficiency. In this experimental study, rectangular embedded cavities were designed as a means of successfully reducing the net drag across surfaces in a low Reynolds number flow. A Couette flow was generated via a rotating conveyor belt immersed in a tank of high viscosity mineral oil above which the plates with embedded cavities were placed. Drag induced on the plate models was measured using a force gauge and compared directly to measurements acquired over a flat plate. Various cavity aspect ratios and gap heights were tested in order to determine the conditions under which the greatest drag reductions occurred.
Taylor-Couette flow control using the outer cylinder cross-section variation strategy
NASA Astrophysics Data System (ADS)
Oualli, Hamid; Lalaoua, Adel; Hanchi, Samir; Bouabdallah, Ahcene
2013-01-01
A numerical study of a controlled flow evolving in a Taylor-Couette system is presented in this paper. The study is devoted to investigate the effect of the outer cylinder cross-section variation on the flow behavior. It is aimed to make assessment of the flow response in terms of the criticality of the early transitional flow regimes and the accompanying flow topology alterations. The numerical simulations are carried out on the Fluent software package for a three-dimensional incompressible flow. The basic system is characterized by a height H = 200 mm, a ratio of the inner to the outer cylinders radii η = 0.9, an aspect ratio corresponding to the cylinders height reported to the gap length Г = 40 and a ratio of the gap to the radius of the inner cylinder δ = 0.1. The numerical deformation of the outer cylinder is executed using the dynamic mesh program according to a predefined function implemented in a homemade program as an UDF (user defined function). It is established that the first instability mode of transition is retarded from Tac1 = 41.33, corresponding to the first Taylor number critical value, to Tac1 = 70 when the deforming amplitude is equal to 15% the external cylinder diameter value. This flow relaminarization process is accompanied by substantial modifications in the flow behavior and configuration.
Numerical simulations of bubbly Taylor-Couette turbulence in co- and counter rotating regime
NASA Astrophysics Data System (ADS)
Spandan, Vamsi; Verzicco, Roberto; Lohse, Detlef
2015-11-01
Two-phase Taylor-Couette (flow between two co-axial independently rotating cylinders) is simulated using a two-way coupled Euler-Lagrange approach in which the bubbles are treated as point particles with effective forces such as drag, lift, added mass and buoyancy acting on them. The momentum equations for the fluid and the bubbles are solved in the frame of reference of the outer cylinder. While it is already known that when the outer cylinder is stationary, within a certain Taylor number range (Ta ~106 -108) the bubbles disrupt the plume ejection regions and the coherent vortical structures leading to drag reduction, their effect and arrangement in the gap-width when both cylinders are rotating is still unknown. In this study we focus on studying the effect of bubbles on the angular velocity transport for various rotation rates of the cylinders. We find that the net percentage drag reduction persists even with a rotating outer cylinder, but is there a optimum for various rotation rates ? How does the spatial distribution of bubbles vary with in the co- and counter rotating regime ? These are some questions we attempt to answer in this work.
Ultrasonic velocity profiling rheometry based on a widened circular Couette flow
NASA Astrophysics Data System (ADS)
Shiratori, Takahisa; Tasaka, Yuji; Oishi, Yoshihiko; Murai, Yuichi
2015-08-01
We propose a new rheometry for characterizing the rheological properties of fluids. The technique produces flow curves, which represent the relationship between the fluid shear rate and shear stress. Flow curves are obtained by measuring the circumferential velocity distribution of tested fluids in a circular Couette system, using an ultrasonic velocity profiling technique. By adopting a widened gap of concentric cylinders, a designed range of the shear rate is obtained so that velocity profile measurement along a single line directly acquires flow curves. To reduce the effect of ultrasonic noise on resultant flow curves, several fitting functions and variable transforms are examined to best approximate the velocity profile without introducing a priori rheological models. Silicone oil, polyacrylamide solution, and yogurt were used to evaluate the applicability of this technique. These substances are purposely targeted as examples of Newtonian fluids, shear thinning fluids, and opaque fluids with unknown rheological properties, respectively. We find that fourth-order Chebyshev polynomials provide the most accurate representation of flow curves in the context of model-free rheometry enabled by ultrasonic velocity profiling.
NASA Astrophysics Data System (ADS)
Liu, Nansheng; Khomami, Bamin
2011-11-01
Despite tremendous progress in development of numerical techniques and constitutive theories for polymeric fluids in the past decade, Direct Numerical Simulation (DNS) of elastic turbulence has posed tremendous challenges to researchers engaged in developing first principles models and simulations that can accurately and robustly predict the dynamical behavior of polymeric flows. In this presentation, we report the first DNS of elastic turbulence in the Taylor-Couette (TC) flow. Specifically, our computations with prototypical constitutive equations for dilute polymeric solutions, such as the FENE-P model are capable of reproducing the essential features of the experimentally observed elastic turbulence in TC flow of this class of fluids, namely, randomly fluctuating fluid motion excited in a broad range of spatial and temporal scales, and a significant increase of the flow resistance. Moreover, the experimentally measured Power Spectral Density of radial velocity fluctuations, i.e., two contiguous regions of power-law decay, -1.1 at lower frequencies and -2.2 at high-frequencies is accurately computed. We would like to thank NSF through grant CBET-0755269 and NSFC through grant NO. 10972211 for supporting of this work.
A Computational Study of Transient Couette Flow Over an Embedded Cavity Surface
NASA Astrophysics Data System (ADS)
Thompson, Michael; Lang, Amy; Schreiber, Will; Leibenguth, Chase; Palmore, John
2011-11-01
Insect flight has become a topic of increased study due to bio-inspired applications for Micro-Air-Vehicles (MAVs). The complex yet efficient flight mechanism of butterflies relies upon flexible, micro-geometrically surface patterned, scaled wings. Effective vortex control, when flapping as well as low-drag gliding, may result from the wing's texture. This hypothesis was tested by focusing on the formation of embedded vortices between the rows of scales on butterfly wings. To calculate the total surface drag induced on the moving cavity surface a computational fluid dynamics study using FLUENT simulated the flow inside and above the embedded cavities under transient Couette flow conditions with Reynolds numbers varied from 0.01 to 100. The computational model consisted of a single embedded cavity with a periodic boundary condition. Based on SEM pictures of Monarch (Danaus plexippus) butterfly scales, various cavity geometries were tested to deduce drag reduction. Results showed that the embedded vortex size and shape generated within the cavity depended on which surface moved (top, flat wall or bottom, cavity wall) as well as aspect ratio. Surface drag reduction was confirmed over the cavity surfaces when compared to that of a flat plate, and increased with aspect ratio. Funded by REU SITE EEC - 1062611.
NASA Astrophysics Data System (ADS)
Priezzhev, Alexander V.; Khatsevich, Stanislav G.; Lopatin, Vladimir V.
1999-02-01
Asymmetry of light backscattering from a shear flow of 1 mm thick layer of whole blood was measured. The blood samples from different health and diseased individuals were placed in a gap of a cylindrical Couette cell with inner cylinder rotating with variable rates. Probing was performed with a CW He-Ne laser (633 nm). The difference in intensities of backscattered light detected through a transpatent wall of the stationary outer cylinder with a photodetector located at variable distances from the illuminating beam along and opposite to the flow directions depends on the distance between the illuminating and detecting probes, on shear rate, on hematocrit, and on the type of disease. The experiments conducted with blood samples from patients suffering from heart disease, bronchial asthma, and rheumatoid arthritis showed stable and reproducible difference in the amount of asymmetry. This makes the technique potentially applicable for optical biomonitoring and, also, for the study of rheology of concentrated suspensions of large deformable particles, like erythrocytes.
Vortex doubling in a wavy-walled Taylor-Couette apparatus
NASA Astrophysics Data System (ADS)
Staples, Anne; Smits, Alexander
2003-11-01
Flow visualization is done in a Taylor-Couette apparatus with a sinusoidally modulated inner cylinder to determine the basic flow structure. Six combinations of forcing wavelength and amplitude are investigated. For five of the six cases, the flow has a basic state consisting of either one or two vortex pairs per forcing wavelength, which persists through the TTV regime. For the sixth forcing wavelength, equal to approximately four times the gap width (d), the flow is found to change at a Re_crit ≈ 176 from its basic two-pair state to a single vortex pair state. The phenomenon is postulated as resulting from a competition between the two length scales in the problem--the gap width and the forcing wavelength--to set the size of the vortices in the flow. The aspect ratios of the apparatus with the various inner cylinders are all approximately 40, and the radius ratios are approximately 0.9. The forcing wavelengths investigated are λ = d,2d,3d,4d and 5d, all with a forcing amplitude of 0.2d, and one case of λ = 3d with a forcing amplitude of 0.11d.
Transient growth in Taylor-Couette flow of a Bingham fluid.
Chen, Cheng; Wan, Zhen-Hua; Zhang, Wei-Guo
2015-04-01
In this paper we investigate linear transient growth of perturbation energy in Taylor-Couette flow of a Bingham fluid. The effects of yield stress on transient growth and the structure of the optimal perturbation are mainly considered for both the wide-gap case and the narrow-gap case. For this purpose we complement the linear stability of this flow subjected to axisymmetric disturbances, presented by Landry et al. [M. P. Landry, I. A. Frigaard, and D. M. Martinez, J. Fluid Mech. 560, 321 (2006)], with the transient growth characteristics of both axisymmetric and nonaxisymmetric perturbations. We obtain the variations of the relative amplitude of optimal perturbation with yield stress, analyze the roles played by the Coriolis force and the additional stress in the evolution of meridional perturbations for the axisymmetric modes, and give the explanations for the possible change of the optimal azimuthal mode (featured by the maximum optimal energy growth G(opt)) with yield stress. These results might help us in the understanding of the effect of fluid rheology on transient growth mechanism in vortex flows. PMID:25974605
CFD simulation of aggregation and breakage processes in laminar Taylor-Couette flow.
Wang, L; Marchisio, D L; Vigil, R D; Fox, R O
2005-02-15
An experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of approximately 10 microm latex spheres suspended in an aqueous solution undergoing laminar Taylor-Couette flow was carried out according to the following program. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry experiments. Subsequently, the quadrature method of moments (QMOM) was implemented into the CFD code to obtain predictions for mean particle size that account for the effects of local shear rate on the aggregation and breakage. These predictions were then compared with experimental data for latex sphere aggregates (using an in situ optical imaging method) and with predictions using spatial average shear rates. The mean particle size evolution predicted by CFD and QMOM using appropriate kinetic expressions that incorporate information concerning the particle morphology (fractal dimension) and the local fluid viscous effects on aggregation collision efficiency match well with the experimental data. PMID:15589543
NASA Technical Reports Server (NTRS)
Hasiuk, Jan; Hindman, Richard; Iversen, James
1988-01-01
The azimuthal-invariant, three-dimensional cylindrical, incompressible Navier-Stokes equations are solved to steady state for a finite-length, physically realistic model. The numerical method relies on an alternating-direction implicit scheme that is formally second-order accurate in space and first-order accurate in time. The equations are linearized and uncoupled by evaluating variable coefficients at the previous time iteration. Wall grid clustering is provided by a Roberts transformation in radial and axial directions. A vorticity-velocity formulation is found to be preferable to a vorticity-streamfunction approach. Subject to no-slip, Dirichlet boundary conditions, except for the inner cylinder rotation velocity (impulsive start-up) and zero-flow initial conditions, nonturbulent solutions are obtained for sub- and supercritical Reynolds numbers of 100 to 400 for a finite geometry where R(outer)/R(inner) = 1.5, H/R(inner) = 0.73, and H/Delta-R = 1.5. An axially-stretched model solution is shown to asymptotically approach the one-dimensional analytic Couette solution at the cylinder midheight. Flowfield change from laminar to Taylor-vortex flow is discussed as a function of Reynolds number. Three-dimensional velocities, vorticity, and streamfunction are presented via two-dimensional graphs and three-dimensional surface and contour plots.
Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system
NASA Astrophysics Data System (ADS)
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-12-01
We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices.
Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices. PMID:26687638
Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system.
Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng
2015-01-01
We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices. PMID:26687638
Self-sustaining turbulence in a restricted nonlinear model of plane Couette flow
Thomas, Vaughan L.; Gayme, Dennice F.; Lieu, Binh K.; Jovanović, Mihailo R.; Farrell, Brian F.; Ioannou, Petros J.
2014-10-15
This paper demonstrates the maintenance of self-sustaining turbulence in a restricted nonlinear (RNL) model of plane Couette flow. The RNL system is derived directly from the Navier-Stokes equations and permits higher resolution studies of the dynamical system associated with the stochastic structural stability theory (S3T) model, which is a second order approximation of the statistical state dynamics of the flow. The RNL model shares the dynamical restrictions of the S3T model but can be easily implemented by reducing a DNS code so that it retains only the RNL dynamics. Comparisons of turbulence arising from DNS and RNL simulations demonstrate that the RNL system supports self-sustaining turbulence with a mean flow as well as structural and dynamical features that are consistent with DNS. These results demonstrate that the simplified RNL system captures fundamental aspects of fully developed turbulence in wall-bounded shear flows and motivate use of the RNL/S3T framework for further study of wall-turbulence.
Identifying coherent structures and vortex clusters in Taylor-Couette turbulence
NASA Astrophysics Data System (ADS)
Spandan, Vamsi; Ostilla-Monico, Rodolfo; Lohse, Detlef; Verzicco, Roberto
2016-04-01
The nature of the underlying structures in Taylor-Couette (TC) flow, the flow between two co-axial and independently rotating cylinders is investigated by two methods. First, the quadrant analysis technique for identifying structures with intense radial-azimuthal stresses (also referred to as ‘Q’s) of Lozano-Durán et al., (J. Fluid Mech. 694, 100-130) is used to identify the main structures responsible for the transport of angular velocity. Second, the vortex clusters are identified based on the analysis by del Álamo et al., (J. Fluid. Mech., 561, 329-358). In order to test these criteria, two different radius ratios η = ri/ro are considered, where ri and ro are the radii of inner and outer cylinder, respectively: (i) η = 0.5 and (ii) η = 0.909, which correspond to high and low curvature geometries, respectively and have different underlying structures. The Taylor rolls, i.e. the large-scale coherent structures, are effectively captured as ‘Q’s for the low curvature setup and it is observed that curvature plays a dominant role in influencing the size and volumes of these ‘Q’s. On the other hand, the vortex clusters are smaller in size when compared to the ‘Q’ structures. These vortex clusters are found to be taller in the case of η = 0.909, while the distribution of the lengths of these clusters is almost homogenous for both radius ratios.
Magnetic induction and diffusion mechanisms in a liquid sodium spherical Couette experiment
NASA Astrophysics Data System (ADS)
Cabanes, Simon; Schaeffer, Nathanaël; Nataf, Henri-Claude
2014-10-01
We present a reconstruction of the mean axisymmetric azimuthal and meridional flows in the Derviche Tourneur Sodium installation in Grenoble liquid sodium experiment. The experimental device sets a spherical Couette flow enclosed between two concentric spherical shells where the inner sphere holds a strong dipolar magnet, which acts as a magnetic propeller when rotated. Measurements of the mean velocity, mean induced magnetic field, and mean electric potentials have been acquired inside and outside the fluid for an inner sphere rotation rate of 9 Hz (Rm≃28 ). Using the induction equation to relate all measured quantities to the mean flow, we develop a nonlinear least-squares inversion procedure to reconstruct a fully coherent solution of the mean velocity field. We also include in our inversion the response of the fluid layer to the nonaxisymmetric time-dependent magnetic field that results from deviations of the imposed magnetic field from an axial dipole. The mean azimuthal velocity field we obtain shows superrotation in an inner region close to the inner sphere where the Lorentz force dominates, which contrasts with an outer geostrophic region governed by the Coriolis force, but where the magnetic torque remains the driver. The meridional circulation is strongly hindered by the presence of both the Lorentz and the Coriolis forces. Nevertheless, it contributes to a significant part of the induced magnetic energy. Our approach sets the scene for evaluating the contribution of velocity and magnetic fluctuations to the mean magnetic field, a key question for dynamo mechanisms.
Magnetic induction and diffusion mechanisms in a liquid sodium spherical Couette experiment.
Cabanes, Simon; Schaeffer, Nathanaël; Nataf, Henri-Claude
2014-10-01
We present a reconstruction of the mean axisymmetric azimuthal and meridional flows in the Derviche Tourneur Sodium installation in Grenoble liquid sodium experiment. The experimental device sets a spherical Couette flow enclosed between two concentric spherical shells where the inner sphere holds a strong dipolar magnet, which acts as a magnetic propeller when rotated. Measurements of the mean velocity, mean induced magnetic field, and mean electric potentials have been acquired inside and outside the fluid for an inner sphere rotation rate of 9 Hz (Rm≃28). Using the induction equation to relate all measured quantities to the mean flow, we develop a nonlinear least-squares inversion procedure to reconstruct a fully coherent solution of the mean velocity field. We also include in our inversion the response of the fluid layer to the nonaxisymmetric time-dependent magnetic field that results from deviations of the imposed magnetic field from an axial dipole. The mean azimuthal velocity field we obtain shows superrotation in an inner region close to the inner sphere where the Lorentz force dominates, which contrasts with an outer geostrophic region governed by the Coriolis force, but where the magnetic torque remains the driver. The meridional circulation is strongly hindered by the presence of both the Lorentz and the Coriolis forces. Nevertheless, it contributes to a significant part of the induced magnetic energy. Our approach sets the scene for evaluating the contribution of velocity and magnetic fluctuations to the mean magnetic field, a key question for dynamo mechanisms. PMID:25375604
Statistics of turbulent fluctuations in counter-rotating Taylor-Couette flows.
Huisman, Sander G; Lohse, Detlef; Sun, Chao
2013-12-01
The statistics of velocity fluctuations of turbulent Taylor-Couette flow are examined. The rotation rates of the inner and outer cylinders are varied while keeping the Taylor number fixed to 1.49×10(12) [O(Re)=10(6)]. The azimuthal velocity component of the flow is measured using laser Doppler anemometry. For each experiment 5×10(6) data points are acquired and carefully analyzed. Using extended self-similarity [Benzi et al., Phys. Rev. E 48, R29 (1993)] the longitudinal structure function exponents are extracted and are found to weakly depend on the ratio of the rotation rates. For the case where only the inner cylinder rotates the results are in good agreement with results measured by Lewis and Swinney [Phys. Rev. E 59, 5457 (1999)] using hot-film anemometry. The power spectra show clear -5/3 scaling for the intermediate angular velocity ratios -ω(o)/ω(i)∈{0.6,0.8,1.0}, roughly -5/3 scaling for -ω(o)/ω(i)∈{0.2,0.3,0.4,2.0}, and no clear scaling law can be found for -ω(0)/ω(i)=0 (inner cylinder rotation only); the local scaling exponent of the spectra has a strong frequency dependence. We relate these observations to the shape of the probability density function of the azimuthal velocity and the presence of a neutral line. PMID:24483551
Selective interaction between microbubbles and modulating waves in a Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Watamura, Tomoaki; Tasaka, Yuji; Murai, Yuichi
2012-11-01
Modifications of a coherent vortical structure by dispersed microbubbles have been investigated in a vertical Taylor-Couette flow, which is the flow generated between coaxial-rotating double cylinders. Radii of the inner and outer cylinders are 95 mm and 105 mm, respectively. The radius ratio and aspect ratio are 0.905 and 20, respectively. Flow mode in the experiments represents wavy vortex flow and modulated wavy vortex flow. Hydrogen bubbles with 60 μm in the mean diameter were generated by water electrolysis and dispersed from a platinum-wire electrode mounted at the bottom of the fluid layer. Maximum void fraction estimated by input power is smaller than 0.01%. Velocity distribution of microbubbles in a Taylor vortex array is determined by image analysis, and show preferential distribution and motion in the oscillating vortex tube. The fluctuation power of the basic wave was increased by adding microbubbles, while the power of its modulation was decreased. The gradient of the azimuthal velocity in the radial direction, i.e. origin of skin frictional drag acting on the cylinder walls, was decreased. These modifications of flow structure represent the suppression of the flow transition, due to the excitation of the basic wave oscillation and increase of momentum transfer by bubble swarm.
Recent development of hydrodynamic modeling
NASA Astrophysics Data System (ADS)
Hirano, Tetsufumi
2014-09-01
In this talk, I give an overview of recent development in hydrodynamic modeling of high-energy nuclear collisions. First, I briefly discuss about current situation of hydrodynamic modeling by showing results from the integrated dynamical approach in which Monte-Carlo calculation of initial conditions, quark-gluon fluid dynamics and hadronic cascading are combined. In particular, I focus on rescattering effects of strange hadrons on final observables. Next I highlight three topics in recent development in hydrodynamic modeling. These include (1) medium response to jet propagation in di-jet asymmetric events, (2) causal hydrodynamic fluctuation and its application to Bjorken expansion and (3) chiral magnetic wave from anomalous hydrodynamic simulations. (1) Recent CMS data suggest the existence of QGP response to propagation of jets. To investigate this phenomenon, we solve hydrodynamic equations with source term which exhibits deposition of energy and momentum from jets. We find a large number of low momentum particles are emitted at large angle from jet axis. This gives a novel interpretation of the CMS data. (2) It has been claimed that a matter created even in p-p/p-A collisions may behave like a fluid. However, fluctuation effects would be important in such a small system. We formulate relativistic fluctuating hydrodynamics and apply it to Bjorken expansion. We found the final multiplicity fluctuates around the mean value even if initial condition is fixed. This effect is relatively important in peripheral A-A collisions and p-p/p-A collisions. (3) Anomalous transport of the quark-gluon fluid is predicted when extremely high magnetic field is applied. We investigate this possibility by solving anomalous hydrodynamic equations. We found the difference of the elliptic flow parameter between positive and negative particles appears due to the chiral magnetic wave. Finally, I provide some personal perspective of hydrodynamic modeling of high energy nuclear collisions
Constraining relativistic viscous hydrodynamical evolution
Martinez, Mauricio; Strickland, Michael
2009-04-15
We show that by requiring positivity of the longitudinal pressure it is possible to constrain the initial conditions one can use in second-order viscous hydrodynamical simulations of ultrarelativistic heavy-ion collisions. We demonstrate this explicitly for (0+1)-dimensional viscous hydrodynamics and discuss how the constraint extends to higher dimensions. Additionally, we present an analytic approximation to the solution of (0+1)-dimensional second-order viscous hydrodynamical evolution equations appropriate to describe the evolution of matter in an ultrarelativistic heavy-ion collision.
Hydrodynamic resistance of confined cells in rectangular microchannels
NASA Astrophysics Data System (ADS)
Khan, Zeina S.; Vanapalli, Siva A.
2011-03-01
Several microfluidic approaches have been developed to screen suspended cells mechanically in microchannels by exploiting characteristics that are linked to their individual mechanical properties. Typically changes in cell shape due to shear-induced deformation and transit times are reported; while these measurements are qualitative compared to more precise techniques such as atomic force microscopy and micropipette aspiration their advantage lies in throughput, with the ability to screen hundreds to thousands of cells in a minute. We study the potential of a microfluidic cell squeezer to characterize the hydrodynamic resistance of LNCaP prostate cancer cells by measuring dynamical pressure-drop variations along a micrometer-sized channel. The hydrodynamic resistance of the cell introduces an excess pressure drop in the narrow channel which depends on the mechanical stiffness of the cell. We additionally visualize the cell size and assess the influence of cell size on the hydrodynamic resistance of each cell, demonstrating the capability of the microfluidic cell squeezer to yield the hydrodynamic resistance as a mechanical fingerprint of cells.
Hydrodynamics of micropipette aspiration.
Drury, J L; Dembo, M
1999-01-01
The dynamics of human neutrophils during micropipette aspiration are frequently analyzed by approximating these cells as simple slippery droplets of viscous fluid. Here, we present computations that reveal the detailed predictions of the simplest and most idealized case of such a scheme; namely, the case where the fluid of the droplet is homogeneous and Newtonian, and the surface tension of the droplet is constant. We have investigated the behavior of this model as a function of surface tension, droplet radius, viscosity, aspiration pressure, and pipette radius. In addition, we have tabulated a dimensionless factor, M, which can be utilized to calculate the apparent viscosity of the slippery droplet. Computations were carried out using a low Reynolds number hydrodynamics transport code based on the finite-element method. Although idealized and simplistic, we find that the slippery droplet model predicts many observed features of neutrophil aspiration. However, there are certain features that are not observed in neutrophils. In particular, the model predicts dilation of the membrane past the point of being continuous, as well as a reentrant jet at high aspiration pressures. PMID:9876128
Relativistic hydrodynamics on graphic cards
NASA Astrophysics Data System (ADS)
Gerhard, Jochen; Lindenstruth, Volker; Bleicher, Marcus
2013-02-01
We show how to accelerate relativistic hydrodynamics simulations using graphic cards (graphic processing units, GPUs). These improvements are of highest relevance e.g. to the field of high-energetic nucleus-nucleus collisions at RHIC and LHC where (ideal and dissipative) relativistic hydrodynamics is used to calculate the evolution of hot and dense QCD matter. The results reported here are based on the Sharp And Smooth Transport Algorithm (SHASTA), which is employed in many hydrodynamical models and hybrid simulation packages, e.g. the Ultrarelativistic Quantum Molecular Dynamics model (UrQMD). We have redesigned the SHASTA using the OpenCL computing framework to work on accelerators like graphic processing units (GPUs) as well as on multi-core processors. With the redesign of the algorithm the hydrodynamic calculations have been accelerated by a factor 160 allowing for event-by-event calculations and better statistics in hybrid calculations.
Reciprocal relations in dissipationless hydrodynamics
Melnikovsky, L. A.
2014-12-15
Hidden symmetry in dissipationless terms of arbitrary hydrodynamics equations is recognized. We demonstrate that all fluxes are generated by a single function and derive conventional Euler equations using the proposed formalism.
Statistics of turbulent fluctuations in counter-rotating Taylor-Couette flows
NASA Astrophysics Data System (ADS)
Huisman, Sander G.; Lohse, Detlef; Sun, Chao
2013-12-01
The statistics of velocity fluctuations of turbulent Taylor-Couette flow are examined. The rotation rates of the inner and outer cylinders are varied while keeping the Taylor number fixed to 1.49×1012 [O(Re)=106]. The azimuthal velocity component of the flow is measured using laser Doppler anemometry. For each experiment 5×106 data points are acquired and carefully analyzed. Using extended self-similarity [Benzi , Phys. Rev. E1063-651X10.1103/PhysRevE.48.R29 48, R29 (1993)] the longitudinal structure function exponents are extracted and are found to weakly depend on the ratio of the rotation rates. For the case where only the inner cylinder rotates the results are in good agreement with results measured by Lewis and Swinney [Phys. Rev. E1063-651X10.1103/PhysRevE.59.5457 59, 5457 (1999)] using hot-film anemometry. The power spectra show clear -5/3 scaling for the intermediate angular velocity ratios -ωo/ωi∈{0.6,0.8,1.0}, roughly -5/3 scaling for -ωo/ωi∈{0.2,0.3,0.4,2.0}, and no clear scaling law can be found for -ω0/ωi=0 (inner cylinder rotation only); the local scaling exponent of the spectra has a strong frequency dependence. We relate these observations to the shape of the probability density function of the azimuthal velocity and the presence of a neutral line.
Global Hall-MHD simulations of magnetorotational instability in a plasma Couette flow experiment
Ebrahimi, F.; Lefebvre, B.; Bhattacharjee, A.; Forest, C. B.
2011-06-15
Global MHD and Hall-MHD numerical simulations relevant to the Madison plasma Couette flow experiment (MPCX) have been performed using the extended MHD code NIMROD. The MPCX has been constructed to study the magnetorotational instability (MRI) in a plasma. The two-fluid Hall effect, which is relevant to some astrophysical situations such as protostellar disks, is also expected to be important in the MPCX. Here, we first derive the local Hall dispersion relation including viscosity, extending earlier work by Balbus and Terquem [Astrophys. J. 552, 235 (2001)]. The predictions of the local analysis are then compared with nonlocal calculations of linear stability of the MRI for a parameter range relevant to the MPCX. It is found that the MHD stability limit and mode structure are altered by the Hall term, and nonlocal analysis is necessary to obtain quantitatively reliable predictions for MPCX. Two-fluid physics also significantly changes the nonlinear evolution and saturation of the axisymmetric MRI. Both the Reynolds and Maxwell stresses contribute significantly to momentum transport. In the Hall regime, when the magnetic field is parallel to the rotation axis, the Maxwell stress is larger than the Reynolds stress (similar to the MHD regime). However, when the magnetic field is antiparallel to the rotation axis in the Hall regime, the Reynolds stress is much larger than the Maxwell stress. To further study the role of non-axisymmetric modes, we have also carried out fully nonlinear MHD computations. Non-axisymmetric modes play an increasingly important role as the magnetic Reynolds number increases and grow to large amplitudes in a saturated turbulent state.
Nonaxisymmetric MHD Instabilities of Chandrasekhar States in Taylor-Couette Geometry
NASA Astrophysics Data System (ADS)
Gellert, M.; Rüdiger, G.; Schultz, M.; Guseva, A.; Hollerbach, R.
2016-06-01
We consider axially periodic Taylor–Couette geometry with insulating boundary conditions. The imposed basic states are so-called Chandrasekhar states, where the azimuthal flow U ϕ and magnetic field B ϕ have the same radial profiles. Mainly three particular profiles are considered: the Rayleigh limit, quasi-Keplerian, and solid-body rotation. In each case we begin by computing linear instability curves and their dependence on the magnetic Prandtl number {{Pm}}. For the azimuthal wavenumber m = 1 modes, the instability curves always scale with the Reynolds number and the Hartmann number. For sufficiently small {{Pm}} these modes therefore only become unstable for magnetic Mach numbers less than unity, and are thus not relevant for most astrophysical applications. However, modes with m\\gt 1 can behave very differently. For sufficiently flat profiles, they scale with the magnetic Reynolds number and the Lundquist number, thereby allowing instability also for the large magnetic Mach numbers of astrophysical objects. We further compute fully nonlinear, three-dimensional equilibration of these instabilities, and investigate how the energy is distributed among the azimuthal (m) and axial (k) wavenumbers. In comparison spectra become steeper for large m, reflecting the smoothing action of shear. On the other hand kinetic and magnetic energy spectra exhibit similar behavior: if several azimuthal modes are already linearly unstable they are relatively flat, but for the rigidly rotating case where m = 1 is the only unstable mode they are so steep that neither Kolmogorov nor Iroshnikov–Kraichnan spectra fit the results. The total magnetic energy exceeds the kinetic energy only for large magnetic Reynolds numbers {{Rm}}\\gt 100.
Instability modes of a two-layer Newtonian plane Couette flow past a porous medium
NASA Astrophysics Data System (ADS)
Praveen Kumar, A. Ananth; Goyal, Himanshu; Banerjee, Tamal; Bandyopadhyay, Dipankar
2013-06-01
We explore the salient features of the different instability modes of a pressure-driven two-layer plane Couette flow confined between a moving wall and a Darcy-Brinkman porous layer. A linear stability analysis of the conservation laws leads to an Orr-Sommerfeld system, which is solved numerically with appropriate boundary conditions to identify the time and length scales of the instability modes. The study reveals that the movement of the confining wall together with the slippage at the porous-liquid interface originating from the flow inside the porous layer can stimulate a pair of finite-wave-number shear modes in addition to the long-wave interfacial mode of instability. The shear modes dominate the interfacial mode, especially when the frictional influence at the liquid layers is smaller due to the movement of the confining plate or due to the larger slippage at the porous-liquid interface. The shear modes are found to be present under all combinations of the viscosity μr and thickness hr ratios of the liquid layers. This is in stark contrast to the two-layer flow confined between nonporous plates where the interfacial (shear) mode is observed only when μr>hr2 (μr
Boltzmann equation and hydrodynamic fluctuations.
Colangeli, Matteo; Kröger, Martin; Ottinger, Hans Christian
2009-11-01
We apply the method of invariant manifolds to derive equations of generalized hydrodynamics from the linearized Boltzmann equation and determine exact transport coefficients, obeying Green-Kubo formulas. Numerical calculations are performed in the special case of Maxwell molecules. We investigate, through the comparison with experimental data and former approaches, the spectrum of density fluctuations and address the regime of finite Knudsen numbers and finite frequencies hydrodynamics. PMID:20364972
Eightfold Classification of Hydrodynamic Dissipation.
Haehl, Felix M; Loganayagam, R; Rangamani, Mukund
2015-05-22
We provide a complete characterization of hydrodynamic transport consistent with the second law of thermodynamics at arbitrary orders in the gradient expansion. A key ingredient in facilitating this analysis is the notion of adiabatic hydrodynamics, which enables isolation of the genuinely dissipative parts of transport. We demonstrate that most transport is adiabatic. Furthermore, in the dissipative part, only terms at the leading order in gradient expansion are constrained to be sign definite by the second law (as has been derived before). PMID:26047219
Hemodynamics of a hydrodynamic injection
Kanefuji, Tsutomu; Yokoo, Takeshi; Suda, Takeshi; Abe, Hiroyuki; Kamimura, Kenya; Liu, Dexi
2014-01-01
The hemodynamics during a hydrodynamic injection were evaluated using cone beam computed tomography (CBCT) and fluoroscopic imaging. The impacts of hydrodynamic (5 seconds) and slow (60 seconds) injections into the tail veins of mice were compared using 9% body weight of a phase-contrast medium. Hydrodynamically injected solution traveled to the heart and drew back to the hepatic veins (HV), which led to liver expansion and a trace amount of spillover into the portal vein (PV). The liver volumes peaked at 165.6 ± 13.3% and 165.5 ± 11.9% of the original liver volumes in the hydrodynamic and slow injections, respectively. Judging by the intensity of the CBCT images at the PV, HV, right atrium, liver parenchyma (LP), and the inferior vena cava (IVC) distal to the HV conjunction, the slow injection resulted in the higher intensity at PV than at LP. In contrast, a significantly higher intensity was observed in LP after hydrodynamic injection in comparison with that of PV, suggesting that the liver took up the iodine from the blood flow. These results suggest that the enlargement speed of the liver, rather than the expanded volume, primarily determines the efficiency of hydrodynamic delivery to the liver. PMID:26015971
Slurry bubble column hydrodynamics
NASA Astrophysics Data System (ADS)
Rados, Novica
Slurry bubble column reactors are presently used for a wide range of reactions in both chemical and biochemical industry. The successful design and scale up of slurry bubble column reactors require a complete understanding of multiphase fluid dynamics, i.e. phase mixing, heat and mass transport characteristics. The primary objective of this thesis is to improve presently limited understanding of the gas-liquid-solid slurry bubble column hydrodynamics. The effect of superficial gas velocity (8 to 45 cm/s), pressure (0.1 to 1.0 MPa) and solids loading (20 and 35 wt.%) on the time-averaged solids velocity and turbulent parameter profiles has been studied using Computer Automated Radioactive Particle Tracking (CARPT). To accomplish this, CARPT technique has been significantly improved for the measurements in highly attenuating systems, such as high pressure, high solids loading stainless steel slurry bubble column. At a similar set of operational conditions time-averaged gas and solids holdup profiles have been evaluated using the developed Computed Tomography (CT)/Overall gas holdup procedure. This procedure is based on the combination of the CT scans and the overall gas holdup measurements. The procedure assumes constant solids loading in the radial direction and axially invariant cross-sectionally averaged gas holdup. The obtained experimental holdup, velocity and turbulent parameters data are correlated and compared with the existing low superficial gas velocities and atmospheric pressure CARPT/CT gas-liquid and gas-liquid-solid slurry data. The obtained solids axial velocity radial profiles are compared with the predictions of the one dimensional (1-D) liquid/slurry recirculation phenomenological model. The obtained solids loading axial profiles are compared with the predictions of the Sedimentation and Dispersion Model (SDM). The overall gas holdup values, gas holdup radial profiles, solids loading axial profiles, solids axial velocity radial profiles and solids
NASA Astrophysics Data System (ADS)
de Haas, K. H.; van den Ende, D.; Blom, C.; Altena, E. G.; Beukema, G. J.; Mellema, J.
1998-03-01
We describe a new counter-rotating Couette apparatus that has been developed for deformation studies of single sub-millimeter sized particles in shear flow. New features are the adaption to the low viscosities of water-based systems and temperature control of the device. The inner to outer radius ratio of the cylinders used is 0.9785 and the height to width aspect ratio of the gap is 4.0, while the inner radius is 100 mm. Because of the limited particle size a high mechanical accuracy of the Couette geometry is necessary. The swing of the inner cylinder is less than 2 μm and that of the outer cylinder less than 4 μm. We achieved this by carefully choosing the design parameters of the aerostatic bearing and the coupling between cylinder and motor unit. Furthermore, special drive units give a shear rate resolution of 0.018 s-1, while the maximum shear rate is 100 s-1. For a liquid viscosity on the order of 1 mPas the effective maximum shear rate is 30 s-1. We have shown that deformations as small as (L-B)/(L+B)≈0.01 of giant bilayer vesicles (typical radius 10 μm) with length L and width B can be observed with our device.
DSMC-Based Shear-Stress/Velocity-Slip Boundary Condition for Navier-Stokes Couette-Flow Simulations
NASA Astrophysics Data System (ADS)
Torczynski, J. R.; Gallis, M. A.
2011-05-01
Direct Simulation Monte Carlo (DSMC) simulations are used to develop a shear-stress/velocity-slip boundary condition for Navier-Stokes (NS) simulations of low-speed isothermal Couette flow. In this boundary condition, the wall shear stress equals the product of the difference between the gas and wall velocities and a momentum transfer coefficient. This momentum transfer coefficient depends on two dimensionless parameters that determine its behavior in the near-continuum and transitional regimes, respectively. For a given gas, these parameters are determined by comparing the NS Couette-flow shear-stress expression to DSMC shear-stress values for free-molecular to near-continuum pressures with three values of the accommodation coefficient. The parameter values for argon, helium, nitrogen, air, and inverse-power-law (IPL) interactions from hard-sphere to Maxwell lie within narrow ranges. For the hard-sphere interaction, the DSMC-based results are in excellent agreement with previously published analytical approximations.
Sheathless hydrodynamic positioning of buoyant drops and bubbles inside microchannels
NASA Astrophysics Data System (ADS)
Stan, Claudiu A.; Guglielmini, Laura; Ellerbee, Audrey K.; Caviezel, Daniel; Stone, Howard A.; Whitesides, George M.
2011-09-01
Particles, bubbles, and drops carried by a fluid in a confined environment such as a pipe can be subjected to hydrodynamic lift forces, i.e., forces that are perpendicular to the direction of the flow. We investigated the positioning effect of lift forces acting on buoyant drops and bubbles suspended in a carrier fluid and flowing in a horizontal microchannel. We report experiments on drops of water in fluorocarbon liquid, and on bubbles of nitrogen in hydrocarbon liquid and silicone oil, inside microchannels with widths on the order of 0.1-1 mm. Despite their buoyancy, drops and bubbles could travel without contacting with the walls of channels; the most important parameters for reaching this flow regime in our experiments were the viscosity and the velocity of the carrier fluid, and the sizes of drops and bubbles. The dependencies of the transverse position of drops and bubbles on these parameters were investigated. At steady state, the trajectories of drops and bubbles approached the center of the channel for drops and bubbles almost as large as the channel, carried by rapidly flowing viscous liquids; among our experiments, these flow conditions were characterized by larger capillary numbers and smaller Reynolds numbers. Analytical models of lift forces developed for the flow of drops much smaller than the width of the channel failed to predict their transverse position, while computational fluid dynamic simulations of the experiments agreed better with the experimental measurements. The degrees of success of these predictions indicate the importance of confinement on generating strong hydrodynamic lift forces. We conclude that, inside microfluidic channels, it is possible to support and position buoyant drops and bubbles simply by flowing a single-stream (i.e., “sheathless”) carrier liquid that has appropriate velocity and hydrodynamic properties.
Direct numerical simulation of Taylor-Couette flow subjected to a radial temperature gradient
NASA Astrophysics Data System (ADS)
Teng, Hao; Liu, Nansheng; Lu, Xiyun; Khomami, Bamin
2015-12-01
Direct numerical simulations have been performed to study the Taylor-Couette (TC) flow between two rotating, coaxial cylinders in the presence of a radial temperature gradient. Specifically, the influence of the buoyant force and the outer cylinder rotation on the turbulent TC flow system with the radius ratio η = 0.912 was examined. For the co-rotating TC flows with Rei (inner cylinder) =1000 and Reo (outer cylinder) =100, a transition pathway to highly turbulent flows is realized by increasing σ, a parameter signifying the ratio of buoyant to inertial force. This nonlinear flow transition involves four intriguing states that emerge in sequence as chaotic wavy vortex flow for σ = 0, wavy interpenetrating spiral flows for σ = 0.02 and 0.05, intermittent turbulent spirals for σ = 0.1 and 0.2, and turbulent spirals for σ = 0.4. Overall, the fluid motion changes from a centrifugally driven flow regime characterized by large-scale wavy Taylor vortices (TVs) to a buoyancy-dominated flow regime characterized by small-scale turbulent vortices. Commensurate changes in turbulence statistics and heat transfer are seen as a result of the weakening of large-scale TV circulations and enhancement of turbulent motions. Additionally, the influence of variation of the outer cylinder rotation, -500 < Reo < 500 in presence of buoyancy (σ = 0.1) with Rei = 1000, has been considered. Specifically, it is demonstrated that this variation strongly influences the azimuthal and axial mean flows with a weaker influence on the fluctuating fluid motions. Of special interest, here are the turbulent dynamics near the outer wall where a marked decrease of turbulence intensity and a sign inversion of the Reynolds stress Rrz are observed for the strongly counter-rotating regimes (Reo = - 300 and -500). To this end, it has been shown that the underlying flow physics for this drastic modification are associated with the modification of the correlation between the radial and axial fluctuating
Direct numerical simulation of Taylor-Couette flow subjected to a radial temperature gradient
Teng, Hao; Liu, Nansheng Lu, Xiyun; Khomami, Bamin
2015-12-15
Direct numerical simulations have been performed to study the Taylor-Couette (TC) flow between two rotating, coaxial cylinders in the presence of a radial temperature gradient. Specifically, the influence of the buoyant force and the outer cylinder rotation on the turbulent TC flow system with the radius ratio η = 0.912 was examined. For the co-rotating TC flows with Re{sub i} (inner cylinder) =1000 and Re{sub o} (outer cylinder) =100, a transition pathway to highly turbulent flows is realized by increasing σ, a parameter signifying the ratio of buoyant to inertial force. This nonlinear flow transition involves four intriguing states that emerge in sequence as chaotic wavy vortex flow for σ = 0, wavy interpenetrating spiral flows for σ = 0.02 and 0.05, intermittent turbulent spirals for σ = 0.1 and 0.2, and turbulent spirals for σ = 0.4. Overall, the fluid motion changes from a centrifugally driven flow regime characterized by large-scale wavy Taylor vortices (TVs) to a buoyancy-dominated flow regime characterized by small-scale turbulent vortices. Commensurate changes in turbulence statistics and heat transfer are seen as a result of the weakening of large-scale TV circulations and enhancement of turbulent motions. Additionally, the influence of variation of the outer cylinder rotation, −500 < Re{sub o} < 500 in presence of buoyancy (σ = 0.1) with Re{sub i} = 1000, has been considered. Specifically, it is demonstrated that this variation strongly influences the azimuthal and axial mean flows with a weaker influence on the fluctuating fluid motions. Of special interest, here are the turbulent dynamics near the outer wall where a marked decrease of turbulence intensity and a sign inversion of the Reynolds stress R{sub rz} are observed for the strongly counter-rotating regimes (Re{sub o} = − 300 and −500). To this end, it has been shown that the underlying flow physics for this drastic modification are associated with the modification of the correlation
Abnormal pressures as hydrodynamic phenomena
Neuzil, C.E.
1995-01-01
So-called abnormal pressures, subsurface fluid pressures significantly higher or lower than hydrostatic, have excited speculation about their origin since subsurface exploration first encountered them. Two distinct conceptual models for abnormal pressures have gained currency among earth scientists. The static model sees abnormal pressures generally as relict features preserved by a virtual absence of fluid flow over geologic time. The hydrodynamic model instead envisions abnormal pressures as phenomena in which flow usually plays an important role. This paper develops the theoretical framework for abnormal pressures as hydrodynamic phenomena, shows that it explains the manifold occurrences of abnormal pressures, and examines the implications of this approach. -from Author
Hydrodynamic interactions in protein folding
NASA Astrophysics Data System (ADS)
Cieplak, Marek; Niewieczerzał, Szymon
2009-03-01
We incorporate hydrodynamic interactions (HIs) in a coarse-grained and structure-based model of proteins by employing the Rotne-Prager hydrodynamic tensor. We study several small proteins and demonstrate that HIs facilitate folding. We also study HIV-1 protease and show that HIs make the flap closing dynamics faster. The HIs are found to affect time correlation functions in the vicinity of the native state even though they have no impact on same time characteristics of the structure fluctuations around the native state.
Hydrodynamic interactions in protein folding.
Cieplak, Marek; Niewieczerzał, Szymon
2009-03-28
We incorporate hydrodynamic interactions (HIs) in a coarse-grained and structure-based model of proteins by employing the Rotne-Prager hydrodynamic tensor. We study several small proteins and demonstrate that HIs facilitate folding. We also study HIV-1 protease and show that HIs make the flap closing dynamics faster. The HIs are found to affect time correlation functions in the vicinity of the native state even though they have no impact on same time characteristics of the structure fluctuations around the native state. PMID:19334888
Isogeometric analysis of Lagrangian hydrodynamics
NASA Astrophysics Data System (ADS)
Bazilevs, Y.; Akkerman, I.; Benson, D. J.; Scovazzi, G.; Shashkov, M. J.
2013-06-01
Isogeometric analysis of Lagrangian shock hydrodynamics is proposed. The Euler equations of compressible hydrodynamics in the weak form are discretized using Non-Uniform Rational B-Splines (NURBS) in space. The discretization has all the advantages of a higher-order method, with the additional benefits of exact symmetry preservation and better per-degree-of-freedom accuracy. An explicit, second-order accurate time integration procedure, which conserves total energy, is developed and employed to advance the equations in time. The performance of the method is examined on a set of standard 2D and 3D benchmark examples, where good quality of the computational results is attained.
A Microfluidic-based Hydrodynamic Trap for Single Particles
Johnson-Chavarria, Eric M.; Tanyeri, Melikhan; Schroeder, Charles M.
2011-01-01
The ability to confine and manipulate single particles in free solution is a key enabling technology for fundamental and applied science. Methods for particle trapping based on optical, magnetic, electrokinetic, and acoustic techniques have led to major advancements in physics and biology ranging from the molecular to cellular level. In this article, we introduce a new microfluidic-based technique for particle trapping and manipulation based solely on hydrodynamic fluid flow. Using this method, we demonstrate trapping of micro- and nano-scale particles in aqueous solutions for long time scales. The hydrodynamic trap consists of an integrated microfluidic device with a cross-slot channel geometry where two opposing laminar streams converge, thereby generating a planar extensional flow with a fluid stagnation point (zero-velocity point). In this device, particles are confined at the trap center by active control of the flow field to maintain particle position at the fluid stagnation point. In this manner, particles are effectively trapped in free solution using a feedback control algorithm implemented with a custom-built LabVIEW code. The control algorithm consists of image acquisition for a particle in the microfluidic device, followed by particle tracking, determination of particle centroid position, and active adjustment of fluid flow by regulating the pressure applied to an on-chip pneumatic valve using a pressure regulator. In this way, the on-chip dynamic metering valve functions to regulate the relative flow rates in the outlet channels, thereby enabling fine-scale control of stagnation point position and particle trapping. The microfluidic-based hydrodynamic trap exhibits several advantages as a method for particle trapping. Hydrodynamic trapping is possible for any arbitrary particle without specific requirements on the physical or chemical properties of the trapped object. In addition, hydrodynamic trapping enables confinement of a "single" target object in
Multi-resolution flow simulations by smoothed particle hydrodynamics via domain decomposition
NASA Astrophysics Data System (ADS)
Bian, Xin; Li, Zhen; Tang, Yu-Hang; Karniadakis, George
2015-11-01
We present a methodology to concurrently couple particle-based methods via a domain decomposition (DD) technique for simulating viscous flows. In particular, we select two resolutions of the smoothed particle hydrodynamics (SPH) method as demonstration. Within the DD framework, a simulation domain is decomposed into two (or more) overlapping sub-domains, each of which has an individual particle scale determined by the local flow physics. Consistency of the two sub-domains is achieved in the overlap region by matching the two independent simulations based on Lagrangian interpolation of state variables and fluxes. The domain decomposition based SPH method (DD-SPH) employs different spatial and temporal resolutions, and hence, each sub-domain has its own smoothing length and time step. As a consequence, particle refinement and de-refinement are performed asynchronously according to individual time advancement of each sub-domain. The proposed strategy avoids SPH force interactions between different resolutions on purpose, so that coupling, in principle, can go beyond SPH - SPH, and may allow SPH to be coupled with other mesoscopic or microscopic particle methods. The DD-SPH method is validated first for a transient Couette flow, where simulation results base. US DOE Collaboratory on Mathematics for Mesoscopic Modeling of Materials (CM4).
Deformable cells in confined geometries: From hemolysis to hydrodynamic interactions
NASA Astrophysics Data System (ADS)
Abkarian, Manouk; Faivre, Magalie; Stone, Howard A.
2004-11-01
Recent developments in microfluidics allow a wide range of possibilities for studying cellular-scale hydrodynamics. Here we use microfluidic technology to address several open questions in the blood flow literature where cell deformation and hydrodynamic interactions are significant. In particular, we investigate the pressure-driven flow of a dilute suspension in a channel and characterize the transition from steady axisymmetric cell shapes (for which numerical calculations exist) to asymmetric, highly extended shapes, which are precursors to hemolysis (i.e. destruction of the cell). In addition, we examine the influence of geometry on hydrodynamic interactions of deformable cells by contrasting one-dimensional motion of a train of particles in a channel with two-dimensional motions in a Hele-Shaw cell. This study can help to understand flow of cells in microcirculation from the unidirectional flow in capillaries to the two-dimensional flow in the lung alveoli and provides the basic steps to understand certain aspects of microcirculatory deseases like sickle cell anemia for example.
Hydrodynamic slip in silicon nanochannels
NASA Astrophysics Data System (ADS)
Ramos-Alvarado, Bladimir; Kumar, Satish; Peterson, G. P.
2016-03-01
Equilibrium and nonequilibrium molecular dynamics simulations were performed to better understand the hydrodynamic behavior of water flowing through silicon nanochannels. The water-silicon interaction potential was calibrated by means of size-independent molecular dynamics simulations of silicon wettability. The wettability of silicon was found to be dependent on the strength of the water-silicon interaction and the structure of the underlying surface. As a result, the anisotropy was found to be an important factor in the wettability of these types of crystalline solids. Using this premise as a fundamental starting point, the hydrodynamic slip in nanoconfined water was characterized using both equilibrium and nonequilibrium calculations of the slip length under low shear rate operating conditions. As was the case for the wettability analysis, the hydrodynamic slip was found to be dependent on the wetted solid surface atomic structure. Additionally, the interfacial water liquid structure was the most significant parameter to describe the hydrodynamic boundary condition. The calibration of the water-silicon interaction potential performed by matching the experimental contact angle of silicon led to the verification of the no-slip condition, experimentally reported for silicon nanochannels at low shear rates.
Meat Products, Hydrodynamic Pressure Processing
Technology Transfer Automated Retrieval System (TEKTRAN)
The hydrodynamic pressure process (HDP) has been shown to be very effective at improving meat tenderness in a variety of meat cuts. When compared to conventional aging for tenderization, HDP was more effective. The HDP process may offer the meat industry a new alternative for tenderizing meat in add...
Hydrodynamic analysis of time series
NASA Astrophysics Data System (ADS)
Suciu, N.; Vamos, C.; Vereecken, H.; Vanderborght, J.
2003-04-01
It was proved that balance equations for systems with corpuscular structure can be derived if a kinematic description by piece-wise analytic functions is available [1]. For example, the hydrodynamic equations for one-dimensional systems of inelastic particles, derived in [2], were used to prove the inconsistency of the Fourier law of heat with the microscopic structure of the system. The hydrodynamic description is also possible for single particle systems. In this case, averages of physical quantities associated with the particle, over a space-time window, generalizing the usual ``moving averages'' which are performed on time intervals only, were shown to be almost everywhere continuous space-time functions. Moreover, they obey balance partial differential equations (continuity equation for the 'concentration', Navier-Stokes equation, a. s. o.) [3]. Time series can be interpreted as trajectories in the space of the recorded parameter. Their hydrodynamic interpretation is expected to enable deterministic predictions, when closure relations can be obtained for the balance equations. For the time being, a first result is the estimation of the probability density for the occurrence of a given parameter value, by the normalized concentration field from the hydrodynamic description. The method is illustrated by hydrodynamic analysis of three types of time series: white noise, stock prices from financial markets and groundwater levels recorded at Krauthausen experimental field of Forschungszentrum Jülich (Germany). [1] C. Vamoş, A. Georgescu, N. Suciu, I. Turcu, Physica A 227, 81-92, 1996. [2] C. Vamoş, N. Suciu, A. Georgescu, Phys. Rev E 55, 5, 6277-6280, 1997. [3] C. Vamoş, N. Suciu, W. Blaj, Physica A, 287, 461-467, 2000.
NASA Astrophysics Data System (ADS)
Halmstad, Andrew; Olsen, Thomas; Wiener, Richard
2006-11-01
Previously, we have observed a period-doubling cascade to chaos in Modified Taylor-Couette Flow with Hourglass Geometry. Such behavior had been predicted by The Reaction-Diffusion model simulations. The chaotic formation of Taylor-Vortex pair formation was restricted to a very narrow band about the waist of the hourglass. It was suggested that with increasing lengths of systems, the chaotic region would expand. We present a battery of simulations to determine the variation of the size of the chaotic region with length, seeking the transition to spatio- temporal chaos. Richard J. Wiener et al, Phys. Rev. E 55, 5489 (1997). H. Riecke and H.-G. Paap, Europhys. Lett. 14, 1235 (1991).
NASA Astrophysics Data System (ADS)
Mamonov, V. N.; Nazarov, A. D.; Serov, A. F.; Terekhov, V. I.
2016-01-01
The effect of parameters of the multi-ring Couette system with counter rotating coaxial cylinders on the process of thermal energy release in a viscous liquid filling this system is considered with regard to the problem of determining the possibility of creating the high-performance wind heat generator. The multi-cylinder rotor design allows directly conversion of the mechanical power of a device consisting of two "rotor" wind turbines with a common axis normal to the air flow into the thermal energy in a wide range of rotational speed of the cylinders. Experimental results on the measurement of thermal power released in the pilot heat generator at different relative angular speeds of cylinder rotation are presented.
NASA Astrophysics Data System (ADS)
Faranda, D.; Lucarini, V.; Manneville, P.
2012-04-01
Critical transitions are observed in many natural phenomena and it is a scientific challenge to find out whether there are suitable observables to get early warnings of them. Among all the relevant physical problems that exhibit critical transitions, the breakdown of the turbulence in a plane Couette Flow is of great interest as varying the Reynolds number (Re) we observe three different dynamic regimes: if for higher Reynolds number the flow is completely turbulent, when 325< Re<410 plane Couette forms alternately turbulent and laminar oblique bands out of featureless turbulence. Eventually, when Re<325 turbulence is suppressed and a laminar behaviour prevails. We focus on the transition between the intermediate bands regime and the laminar behaviour trying to analyse the fluctuations of the so called perturbation energy. In particular we find that studying extreme fluctuations of the perturbation energy transient through the classical Extreme Value Theory (EVT) helps in understanding the mechanism of the suppression of turbulence: when the Reynolds number is decreased below Re=300, minima fluctuations amplitude increases considerably whereas maxima fluctuations remain about the same. This is compatible with the idea that the system is eventually going to suppress turbulence increasing the probability to observe very low values of turbulent perturbation energy. Although EVT was originally derived in the setting of stochastic variables, the application to fluid dynamics has been made possible by recent progresses on EVT in more general dynamical systems. We believe that testing EVT in an intermediate complexity fluid model could help in understanding what are the real possibilities in applying it to geophysical systems that represent complex real phenomena. Moreover, in the last years a lot of research effort has been directed towards understanding the role of early indicators of critical transitions both as diagnostic or prognostic tool: linking the behaviour of a
3D hydrodynamic focusing microfluidics for emerging sensing technologies.
Daniele, Michael A; Boyd, Darryl A; Mott, David R; Ligler, Frances S
2015-05-15
While the physics behind laminar flows has been studied for 200 years, understanding of how to use parallel flows to augment the capabilities of microfluidic systems has been a subject of study primarily over the last decade. The use of one flow to focus another within a microfluidic channel has graduated from a two-dimensional to a three-dimensional process and the design principles are only now becoming established. This review explores the underlying principles for hydrodynamic focusing in three dimensions (3D) using miscible fluids and the application of these principles for creation of biosensors, separation of cells and particles for sample manipulation, and fabrication of materials that could be used for biosensors. Where sufficient information is available, the practicality of devices implementing fluid flows directed in 3D is evaluated and the advantages and limitations of 3D hydrodynamic focusing for the particular application are highlighted. PMID:25041926
NASA Technical Reports Server (NTRS)
Mceliece, R. J.
1980-01-01
A class of channel models is presented which exhibit varying burst error severity much like channels encountered in practice. An information-theoretic analysis of these channel models is made, and conclusions are drawn that may aid in the design of coded communication systems for realistic noisy channels.
Hydrodynamic simulations with the Godunov smoothed particle hydrodynamics
NASA Astrophysics Data System (ADS)
Murante, G.; Borgani, S.; Brunino, R.; Cha, S.-H.
2011-10-01
We present results based on an implementation of the Godunov smoothed particle hydrodynamics (GSPH), originally developed by Inutsuka, in the GADGET-3 hydrodynamic code. We first review the derivation of the GSPH discretization of the equations of moment and energy conservation, starting from the convolution of these equations with the interpolating kernel. The two most important aspects of the numerical implementation of these equations are (a) the appearance of fluid velocity and pressure obtained from the solution of the Riemann problem between each pair of particles, and (b) the absence of an artificial viscosity term. We carry out three different controlled hydrodynamical three-dimensional tests, namely the Sod shock tube, the development of Kelvin-Helmholtz instabilities in a shear-flow test and the 'blob' test describing the evolution of a cold cloud moving against a hot wind. The results of our tests confirm and extend in a number of aspects those recently obtained by Cha, Inutsuka & Nayakshin: (i) GSPH provides a much improved description of contact discontinuities, with respect to smoothed particle hydrodynamics (SPH), thus avoiding the appearance of spurious pressure forces; (ii) GSPH is able to follow the development of gas-dynamical instabilities, such as the Kevin-Helmholtz and the Rayleigh-Taylor ones; (iii) as a result, GSPH describes the development of curl structures in the shear-flow test and the dissolution of the cold cloud in the 'blob' test. Besides comparing the results of GSPH with those from standard SPH implementations, we also discuss in detail the effect on the performances of GSPH of changing different aspects of its implementation: choice of the number of neighbours, accuracy of the interpolation procedure to locate the interface between two fluid elements (particles) for the solution of the Riemann problem, order of the reconstruction for the assignment of variables at the interface, choice of the limiter to prevent oscillations of
Hydrodynamic interactions in colloidal systems confined to linear geometries with a singular corner
NASA Astrophysics Data System (ADS)
Lin, Binhua; Zarcone, Ryan; Rice, Stuart A.
Here we investigate the question of whether or not the requirement that particles diffuse around a corner affects their hydrodynamic coupling. We report the results of studies of the collective diffusion coefficients of particles in quasi-one-dimensional linear channels of widths 3 and 5um, each with a singular central corner of angle: 60-, 90-, 120-, and 180-degrees. We find that for large angles, the channels are so close in their geometry to 180-degrees that the corner has very little to no effect on the hydrodynamic coupling of particles on opposite sides of the apex. For small angles, the corner's effect is to increase the particle separation at which the maximum hydrodynamic coupling occurs. U Chicago MRSEC (NSF-DMR-1420709), Dreyfus Foundation (Agency Award #: SI-14-014).
Hydrodynamic interactions between rotating helices.
Kim, MunJu; Powers, Thomas R
2004-06-01
Escherichia coli bacteria use rotating helical flagella to swim. At this scale, viscous effects dominate inertia, and there are significant hydrodynamic interactions between nearby helices. These interactions cause the flagella to bundle during the "runs" of bacterial chemotaxis. Here we use slender-body theory to solve for the flow fields generated by rigid helices rotated by stationary motors. We determine how the hydrodynamic forces and torques depend on phase and phase difference, show that rigid helices driven at constant torque do not synchronize, and solve for the flows. We also use symmetry arguments based on kinematic reversibility to show that for two rigid helices rotating with zero phase difference, there is no time-averaged attractive or repulsive force between the helices. PMID:15244620
Hydrodynamic damage to animal cells.
Chisti, Y
2001-01-01
Animal cells are affected by hydrodynamic forces that occur in culture vessel, transfer piping, and recovery operations such as microfiltration. Depending on the type, intensity, and duration of the force, and the specifics of the cell, the force may induce various kinds of responses in the subject cells. Both biochemical and physiological responses are observed, including apoptosis and purely mechanical destruction of the cell. This review examines the kinds of hydrodynamic forces encountered in bioprocessing equipment and the impact of those forces on cells. Methods are given for quantifying the magnitude of the specific forces, and the response thresholds are noted for the common types of cells cultured in free suspension, supported on microcarriers, and anchored to stationary surfaces. PMID:11451047
Brain vascular and hydrodynamic physiology
Tasker, Robert C.
2013-01-01
Protecting the brain in vulnerable infants undergoing surgery is a central aspect of perioperative care. Understanding the link between blood flow, oxygen delivery and oxygen consumption leads to a more informed approach to bedside care. In some cases, we need to consider how high can we let the partial pressure of carbon dioxide go before we have concerns about risk of increased cerebral blood volume and change in intracranial hydrodynamics? Alternatively, in almost all such cases, we have to address the question of how low can we let the blood pressure drop before we should be concerned about brain perfusion? This review, provides a basic understanding of brain bioenergetics, hemodynamics, hydrodynamics, autoregulation and vascular homeostasis to changes in blood gases that is fundamental to our thinking about bedside care and monitoring. PMID:24331089
Generic Conditions for Hydrodynamic Synchronization
NASA Astrophysics Data System (ADS)
Uchida, Nariya; Golestanian, Ramin
2011-02-01
Synchronization of actively oscillating organelles such as cilia and flagella facilitates self-propulsion of cells and pumping fluid in low Reynolds number environments. To understand the key mechanism behind synchronization induced by hydrodynamic interaction, we study a model of rigid-body rotors making fixed trajectories of arbitrary shape under driving forces that are arbitrary functions of the phase. For a wide class of geometries, we obtain the necessary and sufficient conditions for synchronization of a pair of rotors. We also find a novel synchronized pattern with an oscillating phase shift. Our results shed light on the role of hydrodynamic interactions in biological systems, and could help in developing efficient mixing and transport strategies in microfluidic devices.
Algorithm refinement for fluctuating hydrodynamics
Williams, Sarah A.; Bell, John B.; Garcia, Alejandro L.
2007-07-03
This paper introduces an adaptive mesh and algorithmrefinement method for fluctuating hydrodynamics. This particle-continuumhybrid simulates the dynamics of a compressible fluid with thermalfluctuations. The particle algorithm is direct simulation Monte Carlo(DSMC), a molecular-level scheme based on the Boltzmann equation. Thecontinuum algorithm is based on the Landau-Lifshitz Navier-Stokes (LLNS)equations, which incorporate thermal fluctuations into macroscopichydrodynamics by using stochastic fluxes. It uses a recently-developedsolver for LLNS, based on third-order Runge-Kutta. We present numericaltests of systems in and out of equilibrium, including time-dependentsystems, and demonstrate dynamic adaptive refinement by the computationof a moving shock wave. Mean system behavior and second moment statisticsof our simulations match theoretical values and benchmarks well. We findthat particular attention should be paid to the spectrum of the flux atthe interface between the particle and continuum methods, specificallyfor the non-hydrodynamic (kinetic) time scales.
Hydrodynamics from Landau initial conditions
Sen, Abhisek; Gerhard, Jochen; Torrieri, Giorgio; Read jr, Kenneth F.; Wong, Cheuk-Yin
2015-01-01
We investigate ideal hydrodynamic evolution, with Landau initial conditions, both in a semi-analytical 1+1D approach and in a numerical code incorporating event-by-event variation with many events and transverse density inhomogeneities. The object of the calculation is to test how fast would a Landau initial condition transition to a commonly used boost-invariant expansion. We show that the transition to boost-invariant flow occurs too late for realistic setups, with corrections of O (20 - 30%) expected at freezeout for most scenarios. Moreover, the deviation from boost-invariance is correlated with both transverse flow and elliptic flow, with the more highly transversely flowing regions also showing the most violation of boost invariance. Therefore, if longitudinal flow is not fully developed at the early stages of heavy ion collisions, 2+1 dimensional hydrodynamics is inadequate to extract transport coefficients of the quark-gluon plasma. Based on [1, 2
Microscopic derivation of discrete hydrodynamics.
Español, Pep; Anero, Jesús G; Zúñiga, Ignacio
2009-12-28
By using the standard theory of coarse graining based on Zwanzig's projection operator, we derive the dynamic equations for discrete hydrodynamic variables. These hydrodynamic variables are defined in terms of the Delaunay triangulation. The resulting microscopically derived equations can be understood, a posteriori, as a discretization on an arbitrary irregular grid of the Navier-Stokes equations. The microscopic derivation provides a set of discrete equations that exactly conserves mass, momentum, and energy and the dissipative part of the dynamics produces strict entropy increase. In addition, the microscopic derivation provides a practical implementation of thermal fluctuations in a way that the fluctuation-dissipation theorem is satisfied exactly. This paper points toward a close connection between coarse-graining procedures from microscopic dynamics and discretization schemes for partial differential equations. PMID:20059064
Hydrodynamic Forces on Macromolecules Protruding from Lipid Bilayers Due to External Liquid Flows.
Jönsson, Peter; Jönsson, Bengt
2015-11-24
It has previously been observed that an externally applied hydrodynamic shear flow above a fluid lipid bilayer can change the local concentration of macromolecules that are associated with the lipid bilayer. The external liquid flow results in a hydrodynamic force on molecules protruding from the lipid bilayer, causing them to move in the direction of the flow. However, there has been no quantitative study about the magnitude of these forces. We here use finite element simulations to investigate how the magnitude of the external hydrodynamic forces varies with the size and shape of the studied macromolecule. The simulations show that the hydrodynamic force is proportional to the effective hydrodynamic area of the studied molecule, Ahydro, multiplied by the mean hydrodynamic shear stress acting on the membrane surface, σhydro. The parameter Ahydro depends on the size and shape of the studied macromolecule above the lipid bilayer and scales with the cross-sectional area of the molecule. We also investigate how hydrodynamic shielding from other surrounding macromolecules decreases Ahydro when the surface coverage of the shielding macromolecules increases. Experiments where the protein streptavidin is anchored to a supported lipid bilayer on the floor of a microfluidic channel were finally performed at three different surface concentrations, Φ = 1%, 6%, and 10%, where the protein is being moved relative to the lipid bilayer by a liquid flow through the channel. From photobleaching measurements of fluorescently labeled streptavidin we found the experimental drift data to be within good accuracy of the simulated results, less than 12% difference, indicating the validity of the results obtained from the simulations. In addition to giving a deeper insight into how a liquid flow can affect membrane-associated molecules in a lipid bilayer, we also see an interesting potential of using hydrodynamic flow experiments together with the obtained results to study the size and
Interfacial wave behavior in oil-water channel flows: Prospects for a general understanding
McCready, M.J.; Uphold, D.D.; Gifford, K.A.
1997-12-31
Oil-water pressure driven channel flow is examined as a model for general two-layer flows where interfacial disturbances are important. The goal is to develop sufficient understanding of this system so that the utility and limitations of linear and nonlinear theories can be known a priori. Experiments show that sometimes linear stability is useful at predicting the steady or dominant evolving waves. However in other situations there is no agreement between the linearly fastest growing wave and the spectral peak. An interesting preliminary result is that the bifurcation to interfacial waves is supercritical for all conditions that were studied for an oil-water channel flow, gas-liquid channel flow and two-liquid Couette flow. However, three different mechanisms are dominant for each of these three situations.
HYDRODYNAMIC AND MORPHOLOGIC MODELING AT CAPE FEAR INLET, NC
NASA Astrophysics Data System (ADS)
Kashlan, L. R.; Dennis, W. A.; Wutkowski, M. J.
2009-12-01
The Coastal Modeling System (CMS) was applied to compute tidal hydrodynamics, wave transformation, sediment transport and morphology change in the Cape Fear Inlet area. Measured water level, current and wave data in the Cape Fear area were collected from gauges maintained by Wilmington Harbor Monitoring Program. The models were calibrated by comparing simulated and measured water level, current and wave data. Numerical simulations of coupled circulation, wave and sediment transport models were used to estimate the morphology change for a surveyed area during a three month period. The agreement between predicted and measured topographic changes were acceptable. Morphology change analysis will be used in the future to examine different channel alignment scenarios.
Three-dimensional hydrodynamic focusing in a microfluidic Coulter counter
NASA Astrophysics Data System (ADS)
Scott, R.; Sethu, P.; Harnett, C. K.
2008-04-01
Electrical impedance-based particle detection or Coulter counting, offers a lab-on-chip compatible method for flow cytometry. Developments in this area will produce devices with greater portability, lower cost, and lower power requirements than fluorescence-based flow cytometry. Because conventional Coulter apertures are prone to clogging, hydrodynamic focusing improves the device by creating fluid-walled channels with variable width to increase sensitivity without the associated risk of blocking the channel. We describe a device that focuses the sample in three dimensions, creating a narrow sample stream on the floor of the channel for close interaction with sensing electrodes. The key to this design is a stepped outlet channel fabricated in a single layer with soft lithography. In contrast to previous impedance-based designs, the new design requires minimal alignment with the substrate. Three-dimensional focusing maximizes the sensitivity of the device to cell-size particles within much larger channels. Impedance-based particle sensing experiments within this device show an increase in percentage conductivity change by a factor of 2.5 over devices that only focus the sample in the horizontal direction.
Annual Report: Hydrodynamics and Radiative Hydrodynamics with Astrophysical Applications
R. Paul Drake
2005-12-01
We report the ongoing work of our group in hydrodynamics and radiative hydrodynamics with astrophysical applications. During the period of the existing grant, we have carried out two types of experiments at the Omega laser. One set of experiments has studied radiatively collapsing shocks, obtaining high-quality scaling data using a backlit pinhole and obtaining the first (ever, anywhere) Thomson-scattering data from a radiative shock. Other experiments have studied the deeply nonlinear development of the Rayleigh-Taylor (RT) instability from complex initial conditions, obtaining the first (ever, anywhere) dual-axis radiographic data using backlit pinholes and ungated detectors. All these experiments have applications to astrophysics, discussed in the corresponding papers either in print or in preparation. We also have obtained preliminary radiographs of experimental targets using our x-ray source. The targets for the experiments have been assembled at Michigan, where we also prepare many of the simple components. The above activities, in addition to a variety of data analysis and design projects, provide good experience for graduate and undergraduates students. In the process of doing this research we have built a research group that uses such work to train junior scientists.
Forced wetting and hydrodynamic assist
NASA Astrophysics Data System (ADS)
Blake, Terence D.; Fernandez-Toledano, Juan-Carlos; Doyen, Guillaume; De Coninck, Joël
2015-11-01
Wetting is a prerequisite for coating a uniform layer of liquid onto a solid. Wetting failure and air entrainment set the ultimate limit to coating speed. It is well known in the coating art that this limit can be postponed by manipulating the coating flow to generate what has been termed "hydrodynamic assist," but the underlying mechanism is unclear. Experiments have shown that the conditions that postpone air entrainment also reduce the apparent dynamic contact angle, suggesting a direct link, but how the flow might affect the contact angle remains to be established. Here, we use molecular dynamics to compare the outcome of steady forced wetting with previous results for the spontaneous spreading of liquid drops and apply the molecular-kinetic theory of dynamic wetting to rationalize our findings and place them on a quantitative footing. The forced wetting simulations reveal significant slip at the solid-liquid interface and details of the flow immediately adjacent to the moving contact line. Our results confirm that the local, microscopic contact angle is dependent not simply only on the velocity of wetting but also on the nature of the flow that drives it. In particular, they support an earlier suggestion that during forced wetting, an intense shear stress in the vicinity of the contact line can assist surface tension forces in promoting dynamic wetting, thus reducing the velocity-dependence of the contact angle. Hydrodynamic assist then appears as a natural consequence of wetting that emerges when the contact line is driven by a strong and highly confined flow. Our theoretical approach also provides a self-consistent model of molecular slip at the solid-liquid interface that enables its magnitude to be estimated from dynamic contact angle measurements. In addition, the model predicts how hydrodynamic assist and slip may be influenced by liquid viscosity and solid-liquid interactions.
Hydrodynamic loading of tensegrity structures
NASA Astrophysics Data System (ADS)
Wroldsen, Anders S.; Johansen, Vegar; Skelton, Robert E.; Sørensen, Asgeir J.
2006-03-01
This paper introduces hydrodynamic loads for tensegrity structures, to examine their behavior in marine environments. Wave compliant structures are of general interest when considering large marine structures, and we are motivated by the aquaculture industry where new concepts are investigated in order to make offshore installations for seafood production. This paper adds to the existing models and software simulations of tensegrity structures exposed to environmental loading from waves and current. A number of simulations are run to show behavior of the structure as a function of pretension level and string stiffness for a given loading condition.
Flame front as hydrodynamic discontinuity
NASA Astrophysics Data System (ADS)
Fukumoto, Yasuhide; Abarzhi, Snezhana
2012-11-01
We applied generalized Rankine-Hugoniot conditions to study the dynamics of unsteady and curved fronts as a hydrodynamic discontinuity. It is shown that the front is unstable and Landau-Darrieus instability develops only if three conditions are satisfied (1) large-scale vorticity is generated in the fluid bulk; (2) energy flux across the front is imbalanced; (3) the energy imbalance is large. The structure of the solution is studied in details. Flows with and without gravity and thermal diffusion are analyzed. Stabilization mechanisms are identified. NSF 1004330.
Quasi-Static Hydrodynamic Limits
NASA Astrophysics Data System (ADS)
De Masi, Anna; Olla, Stefano
2015-12-01
We consider hydrodynamic limits of interacting particles systems with open boundaries, where the exterior parameters change in a time scale slower than the typical relaxation time scale. The limit deterministic profiles evolve quasi-statically. These limits define rigorously the thermodynamic quasi static transformations also for transitions between non-equilibrium stationary states. We study first the case of the symmetric simple exclusion, where duality can be used, and then we use relative entropy methods to extend to other models like zero range systems. Finally we consider a chain of anharmonic oscillators in contact with a thermal Langevin bath with a temperature gradient and a slowly varying tension applied to one end.
Progress in smooth particle hydrodynamics
Wingate, C.A.; Dilts, G.A.; Mandell, D.A.; Crotzer, L.A.; Knapp, C.E.
1998-07-01
Smooth Particle Hydrodynamics (SPH) is a meshless, Lagrangian numerical method for hydrodynamics calculations where calculational elements are fuzzy particles which move according to the hydrodynamic equations of motion. Each particle carries local values of density, temperature, pressure and other hydrodynamic parameters. A major advantage of SPH is that it is meshless, thus large deformation calculations can be easily done with no connectivity complications. Interface positions are known and there are no problems with advecting quantities through a mesh that typical Eulerian codes have. These underlying SPH features make fracture physics easy and natural and in fact, much of the applications work revolves around simulating fracture. Debris particles from impacts can be easily transported across large voids with SPH. While SPH has considerable promise, there are some problems inherent in the technique that have so far limited its usefulness. The most serious problem is the well known instability in tension leading to particle clumping and numerical fracture. Another problem is that the SPH interpolation is only correct when particles are uniformly spaced a half particle apart leading to incorrect strain rates, accelerations and other quantities for general particle distributions. SPH calculations are also sensitive to particle locations. The standard artificial viscosity treatment in SPH leads to spurious viscosity in shear flows. This paper will demonstrate solutions for these problems that they and others have been developing. The most promising is to replace the SPH interpolant with the moving least squares (MLS) interpolant invented by Lancaster and Salkauskas in 1981. SPH and MLS are closely related with MLS being essentially SPH with corrected particle volumes. When formulated correctly, JLS is conservative, stable in both compression and tension, does not have the SPH boundary problems and is not sensitive to particle placement. The other approach to
Disruptive Innovation in Numerical Hydrodynamics
Waltz, Jacob I.
2012-09-06
We propose the research and development of a high-fidelity hydrodynamic algorithm for tetrahedral meshes that will lead to a disruptive innovation in the numerical modeling of Laboratory problems. Our proposed innovation has the potential to reduce turnaround time by orders of magnitude relative to Advanced Simulation and Computing (ASC) codes; reduce simulation setup costs by millions of dollars per year; and effectively leverage Graphics Processing Unit (GPU) and future Exascale computing hardware. If successful, this work will lead to a dramatic leap forward in the Laboratory's quest for a predictive simulation capability.
Hydrodynamics of a quark droplet
NASA Astrophysics Data System (ADS)
Bjerrum-Bohr, Johan J.; Mishustin, Igor N.; Døssing, Thomas
2012-05-01
We present a simple model of a multi-quark droplet evolution based on the hydrodynamical description. This model includes collective expansion of the droplet, effects of the vacuum pressure and surface tension. The hadron emission from the droplet is described following Weisskopf's statistical model. We have considered evolution of baryon-free droplets which have different initial temperatures and expansion rates. As a typical trend we observe an oscillating behavior of the droplet radius superimposed with a gradual shrinkage due to the hadron emission. The characteristic life time of droplets with radii 1.5-2 fm are about 9-16 fm/c.
Multiplex Particle Focusing via Hydrodynamic Force in Viscoelastic Fluids
NASA Astrophysics Data System (ADS)
Lee, Doo Jin; Brenner, Howard; Youn, Jae Ryoun; Song, Young Seok
2013-11-01
We introduce a multiplex particle focusing phenomenon that arises from the hydrodynamic interaction between the viscoelastic force and the Dean drag force in a microfluidic device. In a confined microchannel, the first normal stress difference of viscoelastic fluids results in a lateral migration of suspended particles. Such a viscoelastic force was harnessed to focus different sized particles in the middle of a microchannel, and spiral channel geometry was also considered in order to take advantage of the counteracting force, Dean drag force that induces particle migration in the outward direction. For theoretical understanding, we performed a numerical analysis of viscoelastic fluids in the spiral microfluidic channel. From these results, a concept of the `Dean-coupled Elasto-inertial Focusing band (DEF)' was proposed. This study provides in-depth physical insight into the multiplex focusing of particles that can open a new venue for microfluidic particle dynamics for a concrete high throughput platform at microscale.
Evidence for hydrodynamic electron flow in PdCoO₂.
Moll, Philip J W; Kushwaha, Pallavi; Nandi, Nabhanila; Schmidt, Burkhard; Mackenzie, Andrew P
2016-03-01
Electron transport is conventionally determined by the momentum-relaxing scattering of electrons by the host solid and its excitations. Hydrodynamic fluid flow through channels, in contrast, is determined partly by the viscosity of the fluid, which is governed by momentum-conserving internal collisions. A long-standing question in the physics of solids has been whether the viscosity of the electron fluid plays an observable role in determining the resistance. We report experimental evidence that the resistance of restricted channels of the ultrapure two-dimensional metal palladium cobaltate (PdCoO2) has a large viscous contribution. Comparison with theory allows an estimate of the electronic viscosity in the range between 6 × 10(-3) kg m(-1) s(-1) and 3 × 10(-4) kg m(-1) s(-1), versus 1 × 10(-3) kg m(-1) s(-1) for water at room temperature. PMID:26912359
Venkatachalam, Kartik; Montell, Craig
2011-01-01
The TRP (Transient Receptor Potential) superfamily of cation channels is remarkable in that it displays greater diversity in activation mechanisms and selectivities than any other group of ion channels. The domain organizations of some TRP proteins are also unusual, as they consist of linked channel and enzyme domains. A unifying theme in this group is that TRP proteins play critical roles in sensory physiology, which include contributions to vision, taste, olfaction, hearing, touch, and thermo- and osmosensation. In addition, TRP channels enable individual cells to sense changes in their local environment. Many TRP channels are activated by a variety of different stimuli and function as signal integrators. The TRP superfamily is divided into seven subfamilies: the five group 1 TRPs (TRPC, TRPV, TRPM, TRPN, and TRPA) and two group 2 subfamilies (TRPP and TRPML). TRP channels are important for human health as mutations in at least four TRP channels underlie disease. PMID:17579562
Microscale hydrodynamics near moving contact lines
NASA Technical Reports Server (NTRS)
Garoff, Stephen; Chen, Q.; Rame, Enrique; Willson, K. R.
1994-01-01
The hydrodynamics governing the fluid motions on a microscopic scale near moving contact lines are different from those governing motion far from the contact line. We explore these unique hydrodynamics by detailed measurement of the shape of a fluid meniscus very close to a moving contact line. The validity of present models of the hydrodynamics near moving contact lines as well as the dynamic wetting characteristics of a family of polymer liquids are discussed.
Averaged implicit hydrodynamic model of semiflexible filaments.
Chandran, Preethi L; Mofrad, Mohammad R K
2010-03-01
We introduce a method to incorporate hydrodynamic interaction in a model of semiflexible filament dynamics. Hydrodynamic screening and other hydrodynamic interaction effects lead to nonuniform drag along even a rigid filament, and cause bending fluctuations in semiflexible filaments, in addition to the nonuniform Brownian forces. We develop our hydrodynamics model from a string-of-beads idealization of filaments, and capture hydrodynamic interaction by Stokes superposition of the solvent flow around beads. However, instead of the commonly used first-order Stokes superposition, we do an equivalent of infinite-order superposition by solving for the true relative velocity or hydrodynamic velocity of the beads implicitly. We also avoid the computational cost of the string-of-beads idealization by assuming a single normal, parallel and angular hydrodynamic velocity over sections of beads, excluding the beads at the filament ends. We do not include the end beads in the averaging and solve for them separately instead, in order to better resolve the drag profiles along the filament. A large part of the hydrodynamic drag is typically concentrated at the filament ends. The averaged implicit hydrodynamics methods can be easily incorporated into a string-of-rods idealization of semiflexible filaments that was developed earlier by the authors. The earlier model was used to solve the Brownian dynamics of semiflexible filaments, but without hydrodynamic interactions incorporated. We validate our current model at each stage of development, and reproduce experimental observations on the mean-squared displacement of fluctuating actin filaments . We also show how hydrodynamic interaction confines a fluctuating actin filament between two stationary lateral filaments. Finally, preliminary examinations suggest that a large part of the observed velocity in the interior segments of a fluctuating filament can be attributed to induced solvent flow or hydrodynamic screening. PMID:20365783
NASA Astrophysics Data System (ADS)
Talmage, Gita; Walker, John S.; Brown, Samuel H.; Sondergaard, Neal A.; Burt, Patricia E.
1990-11-01
Fully developed, viscous liquid-metal velocity profiles and induced magnetic field contours were studied for Hartmann numbers of M=2 and 10 and for different load currents for a particular rectangular channel configuration (two-dimensional Couette flow). The rectangular channel was assumed to have a homogeneous external (axial) magnetic field parallel to the moving, perfectly conducting top wall and the stationary, perfectly conducting bottom wall. The two stationary side walls were also perfect conductors. The small gap between the moving wall and each side wall was an insulating, free surface. The method of weighted residuals was used to obtain truncated series solutions for the variables of interest. The heavy load currents across the channel were obtained by simulating an external potential to the conducting moving wall. The load currents in each case were opposed by the induced electric field. Since there is no pressure gradient, the flow along the channel is driven by the viscous effects of the moving wall and the Lorentz body force and is retarded by the stationary walls. In the case where no load current is applied across the channel, the current circulates in the channel. The circulation is driven by the generator that is due to the axial variation of velocity in an axial magnetic field. The numerical results presented show that the radial gap and the free surface region represent electrical resistances in parallel between the perfectly conducting stationary wall and the perfectly conducting moving wall. The numerical results also show that the resistance of the radial gap increases as M2 while that of the free surface increases by M or M1/2. Thus, as M increases, the division of current shifts to the free surface region and the current density in the radial gap decreases as M-1. The theoretical magnetohydrodynamic model presented here was developed to provide numerical parameters to help in the design of liquid-metal current collectors. Numerical results
Curvilinear grids for sinuous river channels
NASA Technical Reports Server (NTRS)
Tatom, F. B.; Waldrop, W. R.; Smith, S. R.
1980-01-01
In order to effectively analyze the flow in sinuous river channels, a curvilinear grid system was developed for use in the appropriate hydrodynamic code. The CENTERLINE program was designed to generate a two dimensional grid for this purpose. The Cartesian coordinates of a series of points along the boundaries of the sinuous channel represent the primary input to CENTERLINE. The program calculates the location of the river centerline, the distance downstream along the centerline, and both radius of curvature and channel width as a function of such distance downstream. These parameters form the basis for the generation of the curvilinear grid. Based on input values for longitudinal and lateral grid spacing, the corresponding grid system is generated and a file is created containing the appropriate parameters for use in the associated explicit finite difference hydrodynamic programs. Because of the option for a nonuniform grid, grid spacing can be concentrated in areas containing the largest flow gradients.
Direct Numerical Simulation of Turbulent Couette-Poiseuille Flow With Zero Skin Friction
NASA Technical Reports Server (NTRS)
Coleman, Gary N.; Spalart, Philippe R.
2015-01-01
The near-wall scaling of mean velocity U(yw) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to the square root of yw in the region just above the wall at which the mean shear dU=dy = 0.
Collision-dominated nonlinear hydrodynamics in graphene
NASA Astrophysics Data System (ADS)
Briskot, U.; Schütt, M.; Gornyi, I. V.; Titov, M.; Narozhny, B. N.; Mirlin, A. D.
2015-09-01
We present an effective hydrodynamic theory of electronic transport in graphene in the interaction-dominated regime. We derive the emergent hydrodynamic description from the microscopic Boltzmann kinetic equation taking into account dissipation due to Coulomb interaction and find the viscosity of Dirac fermions in graphene for arbitrary densities. The viscous terms have a dramatic effect on transport coefficients in clean samples at high temperatures. Within linear response, we show that viscosity manifests itself in the nonlocal conductivity as well as dispersion of hydrodynamic plasmons. Beyond linear response, we apply the derived nonlinear hydrodynamics to the problem of hot-spot relaxation in graphene.
Thermal transport in a noncommutative hydrodynamics
Geracie, M. Son, D. T.
2015-03-15
We find the hydrodynamic equations of a system of particles constrained to be in the lowest Landau level. We interpret the hydrodynamic theory as a Hamiltonian system with the Poisson brackets between the hydrodynamic variables determined from the noncommutativity of space. We argue that the most general hydrodynamic theory can be obtained from this Hamiltonian system by allowing the Righi-Leduc coefficient to be an arbitrary function of thermodynamic variables. We compute the Righi-Leduc coefficient at high temperatures and show that it satisfies the requirements of particle-hole symmetry, which we outline.
What Controls the Hydrodynamics of the Central Congo River?
NASA Astrophysics Data System (ADS)
O'Loughlin, F.; Bates, P. D.
2014-12-01
Despite being the second largest river basin in the world, with a drainage area greater than 3.7 million square kilometres, little is known about the hydraulics of the Congo River. This lack of knowledge is mainly due to a mixture of conflicts and the difficulty of accessing existing data. We present results of studies which have focused primarily on the middle reach of the Congo River, located between Kisangani and Kinshasa, and its six main tributaries (Kasai, Ubangai, Sangha, Ruki, Lulonga and Lomami rivers). Through a combination of remotely sensed datasets and a hydrodynamic model we investigated what factors control the hydrodynamics of the middle reach. From the analysis of the remotely sensed datasets, we discover that variability in river width of the middle reach of the Congo is large and cannot be represented by empirical equations which relate channel geometry to basin area and discharge. Water surface slopes vary from 3.5 cm/km to 9 cm/km, which is far more than previous studies suggest. The remote datasets indicate that there exist 5 large constrictions in the river width which may result in backwater affecting between 11 and 33 percent of middle reach at low and high water respectively. These results were corroborated by the hydrodynamic model. In fact, when all constrictions caused by a narrowing in width of 1 km or more are considered, water levels along 43 percent of the middle reach change by at least 0.5 m. Using the hydrodynamic model we also investigated the importance of the wetlands to the attenuation of the flood wave through the system. Initial results suggest that for the Congo River, floodplains have far more impact on the peak magnitude than the timing of the flood wave. When the model was run with no floodplain interactions an increase in the magnitude of flood peak was observed, with the timing of the waves being consistent with observed measurements.
Magnetohydrodynamic channel flows with weak transverse magnetic fields.
Rothmayer, A P
2014-07-28
Magnetohydrodynamic flow of an incompressible fluid through a plane channel with slowly varying walls and a magnetic field applied transverse to the channel is investigated in the high Reynolds number limit. It is found that the magnetic field can first influence the hydrodynamic flow when the Hartmann number reaches a sufficiently large value. The magnetic field is found to suppress the steady and unsteady viscous flow near the channel walls unless the wall shapes become large. PMID:24936018
Experimental studies toward the characterization of Inmetro's circulating water channel
NASA Astrophysics Data System (ADS)
Santos, A. M.; Alho, A. T. P.; Garcia, D. A.; Farias, M. H.; Massari, P. L.; Silva, V. V. S.
2016-07-01
Circulating water channels are facilities which can be used for conducting environmental, metrological and engineering studies. The Brazilian National Institute of Metrology-INMETRO has a water channel of innovative design, and the present work deals with the prior experimental investigation of its hydrodynamics performance. By using the optical technique PIV - Particle Image Velocimetry, under certain conditions, the velocity profile behavior in a region inside the channel was analyzed in order to evaluate the scope of applicability of such bench.
Active and driven hydrodynamic crystals.
Desreumaux, N; Florent, N; Lauga, E; Bartolo, D
2012-08-01
Motivated by the experimental ability to produce monodisperse particles in microfluidic devices, we study theoretically the hydrodynamic stability of driven and active crystals. We first recall the theoretical tools allowing to quantify the dynamics of elongated particles in a confined fluid. In this regime hydrodynamic interactions between particles arise from a superposition of potential dipolar singularities. We exploit this feature to derive the equations of motion for the particle positions and orientations. After showing that all five planar Bravais lattices are stationary solutions of the equations of motion, we consider separately the case where the particles are passively driven by an external force, and the situation where they are self-propelling. We first demonstrate that phonon modes propagate in driven crystals, which are always marginally stable. The spatial structures of the eigenmodes depend solely on the symmetries of the lattices, and on the orientation of the driving force. For active crystals, the stability of the particle positions and orientations depends not only on the symmetry of the crystals but also on the perturbation wavelengths and on the crystal density. Unlike unconfined fluids, the stability of active crystals is independent of the nature of the propulsion mechanism at the single-particle level. The square and rectangular lattices are found to be linearly unstable at short wavelengths provided the volume fraction of the crystals is high enough. Differently, hexagonal, oblique, and face-centered crystals are always unstable. Our work provides a theoretical basis for future experimental work on flowing microfluidic crystals. PMID:22864543
The hydrodynamics of lamprey locomotion
NASA Astrophysics Data System (ADS)
Leftwich, Megan C.
The lamprey, an anguilliform swimmer, propels itself by undulating most of its body. This type of swimming produces flow patterns that are highly three-dimensional in nature and not very well understood. However, substantial previous work has been done to understand two-dimensional unsteady propulsion, the possible wake structures and thrust performance. Limited studies of three-dimensional propulsors with simple geometries have displayed the importance of the third dimension in designing unsteady swimmers. Some of the results of those studies, primarily the ways in which vorticity is organized in the wake region, are seen in lamprey swimming as well. In the current work, the third dimension is not the only important factor, but complex geometry and body undulations also contribute to the hydrodynamics. Through dye flow visualization, particle induced velocimetry and pressure measurements, the hydrodynamics of anguilliform swimming are studied using a custom built robotic lamprey. These studies all indicate that the undulations of the body are not producing thrust. Instead, it is the tail which acts to propel the animal. This conclusion led to further investigation of the tail, specifically the role of varying tail flexibility on hydrodymnamics. It is found that by making the tail more flexible, one decreases the coherence of the vorticity in the lamprey's wake. Additional flexibility also yields less thrust.
Web-based hydrodynamics computing
NASA Astrophysics Data System (ADS)
Shimoide, Alan; Lin, Luping; Hong, Tracie-Lynne; Yoon, Ilmi; Aragon, Sergio R.
2005-01-01
Proteins are long chains of amino acids that have a definite 3-d conformation and the shape of each protein is vital to its function. Since proteins are normally in solution, hydrodynamics (describes the movement of solvent around a protein as a function of shape and size of the molecule) can be used to probe the size and shape of proteins compared to those derived from X-ray crystallography. The computation chain needed for these hydrodynamics calculations consists of several separate programs by different authors on various platforms and often requires 3D visualizations of intermediate results. Due to the complexity, tools developed by a particular research group are not readily available for use by other groups, nor even by the non-experts within the same research group. To alleviate this situation, and to foment the easy and wide distribution of computational tools worldwide, we developed a web based interactive computational environment (WICE) including interactive 3D visualization that can be used with any web browser. Java based technologies were used to provide a platform neutral, user-friendly solution. Java Server Pages (JSP), Java Servlets, Java Beans, JOGL (Java bindings for OpenGL), and Java Web Start were used to create a solution that simplifies the computing chain for the user allowing the user to focus on their scientific research. WICE hides complexity from the user and provides robust and sophisticated visualization through a web browser.
Web-based hydrodynamics computing
NASA Astrophysics Data System (ADS)
Shimoide, Alan; Lin, Luping; Hong, Tracie-Lynne; Yoon, Ilmi; Aragon, Sergio R.
2004-12-01
Proteins are long chains of amino acids that have a definite 3-d conformation and the shape of each protein is vital to its function. Since proteins are normally in solution, hydrodynamics (describes the movement of solvent around a protein as a function of shape and size of the molecule) can be used to probe the size and shape of proteins compared to those derived from X-ray crystallography. The computation chain needed for these hydrodynamics calculations consists of several separate programs by different authors on various platforms and often requires 3D visualizations of intermediate results. Due to the complexity, tools developed by a particular research group are not readily available for use by other groups, nor even by the non-experts within the same research group. To alleviate this situation, and to foment the easy and wide distribution of computational tools worldwide, we developed a web based interactive computational environment (WICE) including interactive 3D visualization that can be used with any web browser. Java based technologies were used to provide a platform neutral, user-friendly solution. Java Server Pages (JSP), Java Servlets, Java Beans, JOGL (Java bindings for OpenGL), and Java Web Start were used to create a solution that simplifies the computing chain for the user allowing the user to focus on their scientific research. WICE hides complexity from the user and provides robust and sophisticated visualization through a web browser.
Inducer Hydrodynamic Load Measurement Devices
NASA Technical Reports Server (NTRS)
Skelley, Stephen E.; Zoladz, Thomas F.; Turner, Jim (Technical Monitor)
2002-01-01
Marshall Space Flight Center (MSFC) has demonstrated two measurement devices for sensing and resolving the hydrodynamic loads on fluid machinery. The first - a derivative of the six-component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This rotating balance was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining both the amplitude and frequency content associated with operating in various cavitation modes. The second device - a high frequency response pressure transducer surface mounted on a rotating component - was merely an extension of existing technology for application in water. MSFC has recently completed experimental evaluations of both the rotating balance and surface-mount transducers in a water test loop. The measurement bandwidth of the rotating balance was severely limited by the relative flexibility of the device itself, resulting in an unexpectedly low structural bending mode and invalidating the higher-frequency response data. Despite these limitations, measurements confirmed that the integrated loads on the four-bladed inducer respond to both cavitation intensity and cavitation phenomena. Likewise, the surface-mount pressure transducers were subjected to a range of temperatures and flow conditions in a non-rotating environment to record bias shifts and transfer functions between the transducers and a reference device. The pressure transducer static performance was within manufacturer's specifications and dynamic response accurately followed that of the reference.
Hydrodynamics of Copepods: A Review
NASA Astrophysics Data System (ADS)
Jiang, Houshuo; Osborn, Thomas R.
2004-07-01
This paper reviews the hydrodynamics of copepods, guided by results obtained from recent theoretical and numerical studies of this topic to highlight the key concepts. First, we briefly summarize observational studies of the water flows (e.g., the feeding currents) created by copepods at their body scale. It is noticed that the water flows at individual copepod scale not only determine the net currents going around and through a copepod’s hair-bearing appendages but also set up a laminar flow field around the copepod. This laminar flow field interacts constantly with environmental background flows. Theoretically, we explain the creation of the laminar flow field in terms of the fact that a free-swimming copepod is a self-propelled body. This explanation is able to relate the various flow fields created by copepods to their complex swimming behaviors, and relevant results obtained from numerical simulations are summarized. Finally, we review the role of hydrodynamics in facilitating chemoreception and mechanoreception in copepods. As a conclusion, both past and current research suggests that the fluid mechanical phenomena occurring at copepod body scale play an important role in copepod feeding, sensing, swarming, mating, and predator avoidance.
Hydromechanical transmission with hydrodynamic drive
Orshansky, Jr., deceased, Elias; Weseloh, William E.
1979-01-01
This transmission has a first planetary gear assembly having first input means connected to an input shaft, first output means, and first reaction means, and a second planetary gear assembly having second input means connected to the first input means, second output means, and second reaction means connected directly to the first reaction means by a reaction shaft. First clutch means, when engaged, connect the first output means to an output shaft in a high driving range. A hydrodynamic drive is used; for example, a torque converter, which may or may not have a stationary case, has a pump connected to the second output means, a stator grounded by an overrunning clutch to the case, and a turbine connected to an output member, and may be used in a starting phase. Alternatively, a fluid coupling or other type of hydrodynamic drive may be used. Second clutch means, when engaged, for connecting the output member to the output shaft in a low driving range. A variable-displacement hydraulic unit is mechanically connected to the input shaft, and a fixed-displacement hydraulic unit is mechanically connected to the reaction shaft. The hydraulic units are hydraulically connected together so that when one operates as a pump the other acts as a motor, and vice versa. Both clutch means are connected to the output shaft through a forward-reverse shift arrangement. It is possible to lock out the torque converter after the starting phase is over.
Modeling of Magma Dynamics Based on Two-Fluid Hydrodynamics
NASA Astrophysics Data System (ADS)
Perepechko, Y. V.; Sorokin, K.
2012-12-01
Multi-velocity multi-porous models are often used as a hydrodynamic basis to describe dynamics of fluid-magma systems. These models cover such problems as fast acoustic processes or large-scaled dynamics of magma systems having non-compressible magma. Nonlinear dynamics of magma as multiphase compressible medium has not been studied sufficiently. In this work we study nonlinear thermodynamically consistent two-liquid model of magma system dynamics, based on conservation law method. The model is restricted by short times of local heat balance between phases. Pressure balance between phases is absent. Two-fluid magma model have various rheological properties of the composing phases: viscous liquid and viscoelastic Maxwell medium. The dynamics of magna flows have been studied for two types of magma systems: magma channels and intraplate intermediate magma chambers. Numerical problem of the dynamics for such media is solved using the control volume method ensuring physical correctness of the solution. The solutions are successfully verified for benchmark one-velocity models. In this work we give the results of numerical modeling using CVM for a number of non-stationary problems of nonlinear liquid filtering through granulated medium in magma channels and problems two-liquid system convection in intraplate magma chambers for various parameters. In the last case the convection regimes vary depending on non-dimensional Rayleigh and Darcy numbers and the parameter field, where compressibility effects appear, is located. The given model can be used as a hydrodynamic basis to model the evolution of magma, fluid-magma systems to study thermo-acoustic influence on hydrodynamic flows in such systems. This work was financially supported by the Russian Foundation for Basic Research, Grant #12-05-00625.
Theoretical and numerical study of air layer drag reduction in two-phase Couette-Poiseuille flow
NASA Astrophysics Data System (ADS)
Kim, Dokyun; Moin, Parviz
2008-11-01
The objective of the present study is to predict and understand the air layer drag reduction (ALDR) phenomenon. Recent experiments (Elbing et al. 2008) have shown net drag reductions if air is injected beyond a critical rate next to the wall. The analysis is performed on a two-phase Couette-Poiseuille flow configuration, which mimics the far downstream region of boundary layer flow on a flat plate. Both theoretical and numerical approaches are employed to investigate the stability and mechanisms of ALDR. The linear stability of air-liquid interface is investigated by solving the Orr-Sommerfeld equations. From the stability analysis, the stability of the interface is reduced as the liquid free-stream velocity, Froude number and velocity gradients at the interface are increased, while the stability is enhanced as the gas flow rate and surface tension are increased. The Critical gas flow rates from stability theory are compared with experimental results, showing good agreement. Direct numerical simulations with a Refiend Level Set Grid technique has been performed to investigate the evolution of the interface, the turbulence interaction and nonlinear mechanisms of ALDR. It is observed that the Weber number has significant impact on the characteristics of the interface development.
Combined Effect of Hall and Ion-Slip Currents on Unsteady MHD Couette Flows in a Rotating System
NASA Astrophysics Data System (ADS)
Jha, Basant K.; Apere, Clement A.
2010-10-01
The unsteady MHD Couette flows of a viscous incompressible electrically conducting fluid between two parallel plates in a rotating system are studied taking hall and ion-slip currents into consideration. The relevant equations are solved analytically using the Laplace transform techniques. A unified closed form analytical expressions for the velocity and the skin friction for the cases; when the magnetic lines of force are fixed relative to the fluid or to the moving plate are derived. The solution obtained shows that the inclusion of Hall and ion-slip currents gives some interesting results. It is found that the influence of the Hall and ion slip parameters have a reducing effect on the magnitude of the secondary velocity especially when the magnetic lines of force are fixed relative to the moving plate. It is also interesting to note that the presence of Hall and ion-slip currents led to an increase in the time it took both the primary and the secondary velocities to achieve their steady state values. On the other hand, the resultant skin friction on the moving plate decreases with an increase in both the Hall and ion-slip parameters when the magnetic field is fixed relative to the fluid, while the opposite behaviour is noticed the magnetic field is fixed relative to the moving plate.
NASA Astrophysics Data System (ADS)
Narasimhamurthy, Vagesh D.; Andersson, Helge I.; Pettersen, Bjørnar
2014-03-01
A new flow configuration has been proposed in which a bilateral mixing-layer exists in the junction between co-flowing laminar and turbulent plane Couette flows. Contrary to a classical plane mixing-layer, the present mixing-layer did neither grow in time nor in streamwise direction. However, the mixing zone varied with the distance from the stationary wall. A direct numerical simulation showed that very-large-scale flow structures were found in the turbulent part of the flow with Reynolds number 1300 based on half the velocity U1 of the fastest-moving wall and half of the distance 2h between the walls. The laminar-turbulent interface exhibited a large-scale meandering motion with frequency 0.014U1/h and wavelength about 25h. Large-scale Taylor-Görtler-like roll cells were observed in the nominally laminar flow region with Reynolds number 260. This tailor-made flow is particularly well suited for explorations of momentum transfer and intermittency in the vicinity of the laminar-turbulent interface.
Cylindrical Couette flow of a vapor-gas mixture: Ghost effect and bifurcation in the continuum limit
NASA Astrophysics Data System (ADS)
Yoshida, Hiroaki; Aoki, Kazuo
2006-08-01
A binary mixture of gases is confined in a gap between two coaxial circular cylinders rotating at different angular velocities. One of the component gases is the vapor of the substance that forms the cylinders, so that evaporation or condensation (or sublimation) of the vapor may take place on the surfaces of the cylinders. The other component is a noncondensable gas that neither evaporates nor condenses on the surfaces. Axisymmetric and axially uniform flows (the cylindrical Couette flow) of such a mixture are investigated on the basis of kinetic theory with special interest in the continuum (or fluid-dynamic) limit in which the Knudsen number goes to zero. The fluid-dynamic system that describes the behavior of the mixture is derived by a formal but systematic asymptotic analysis of the Boltzmann system. The resulting system shows some nontrivial phenomena such as the ghost effect and the flow bifurcation. These phenomena are also demonstrated by a Monte Carlo simulation for small Knudsen numbers using the Boltzmann equation.
Alignment of Red Poly[dodecadyin-1,12-diol-bis(4-butoxycarbonyl-methyl-urethane)] in Couette Flow.
Xie, Donglin; Wei, Yalin; Qiao, Greg G; Dunstan, Dave E
2016-09-01
The flow-induced alignment of red poly[dodecadyin-1,12-diol-bis(4-butoxycarbonyl-methyl-urethane)] (poly-4BCMU) in chloroform/toluene solution is reported. Absorption spectra have been measured over a range of shear rates in an optically transparent quartz Couette cell. The measured spectra show that the poly-4BCMU structure stays the same in flow, while the measured absorbance anisotropy is attributed to the flow-induced particle alignment in the red form poly-4BCMU solutions. A limiting orientation at shear rates >50 s(-1) is observed. Numerical simulations show that the spectral changes are consistent with the rodlike poly-4BCMU particle having an aspect ratio of 2.9. The dichroic ratio of 1.9 interpreted from the data indicates that the individual poly-4BCMU chains do not aggregate amorphously in the rodlike conformation, rather they show a preferred orientation along the long axis of the prolate aggregates. PMID:27509310
NASA Astrophysics Data System (ADS)
Kiełczewski, K.; Tuliszka-Sznitko, E.; Bontoux, P.
2014-08-01
In the paper the authors present the results obtained during a numerical investigation (Direct Numerical Simulation/Spectral Vanishing Viscosity method - DNS/SVV) of a flow with heat transfer in rotating cavities (i.e. the flow between two concentric disks and two concentric cylinders). These model flows are useful from numerical and experimental point of view among others because of the simplicity of their geometry. Simultaneously, the flows in rotating cavities appear in numerous industrial installations and machines in the field of mechanics and chemistry, e.g., in ventilation installations, desalination tanks and waste water tanks, in cooling system, in gas turbines and axial compressors. In the paper attention is focused on the laminar-turbulent region in the configuration of the large aspect ratio i.e. Taylor-Couette flow (a Batchelor flow case of small aspect ratio Γ = 0.04 is also presented for comparison). The main purpose of computations is to investigate the influence of different parameters (the aspect ratio, the end-wall boundary conditions and temperature gradient) on the flow structure and flow characteristics. For the non-isothermal flow cases the Nusselt number distributions along cylinders are presented and are correlated with the flow structures. The λ2 method has been used for visualization.
Taylor-Couette flow control by amplitude variation of the inner cylinder cross-section oscillation
NASA Astrophysics Data System (ADS)
Oualli, Hamid; Mekadem, Mahmoud; Lebbi, Mohamed; Bouabdallah, Ahcene
2015-07-01
The hydrodynamic stability of a viscous fluid flow evolving in an annular space between a rotating inner cylinder with a periodically variable radius and an outer fixed cylinder is considered. The basic flow is axis-symmetric with two counter-rotating vortices each wavelength along the whole filled system length. The numerical simulations are implemented on the commercial Fluent software package, a finite-volume CFD code. It is aimed to make investigation of the early flow transition with assessment of the flow response to radial pulsatile motion superimposed to the inner cylinder cross-section as an extension of a previous developed work in Oualli et al. [H. Oualli, A. Lalaoua, S. Hanchi, A. Bouabdallah, Eur. Phys. J. Appl. Phys. 61, 11102 (2013)] where a comparative controlling strategy is applied to the outer cylinder. The same basic system is considered with similar calculating parameters and procedure. In Oualli et al. [H. Oualli, A. Lalaoua, S. Hanchi, A. Bouabdallah, Eur. Phys. J. Appl. Phys. 61, 11102 (2013)], it is concluded that for the actuated outer cylinder and relatively to the non-controlled case, the critical Taylor number, Tac1, characterizing the first instability onset illustrated by the piled Taylor vortices along the gap, increases substantially to reach a growing rate of 70% when the deforming amplitude is ɛ = 15%. Interestingly, when this controlling strategy is applied to the inner cylinder cross-section with a slight modification of the actuating law, this tendency completely inverts and the critical Taylor number decreases sharply from Tac1 = 41.33 to Tac1 = 17.66 for ɛ = 5%, corresponding to a reduction rate of 57%. Fundamentally, this result is interesting and can be interpreted by prematurely triggering instabilities resulting in rapid development of flow turbulence. Practically, important applicative aspects can be met in several industry areas where substantial intensification of transport phenomena (mass, momentum and heat) is
Hydrodynamics, Fungal Physiology, and Morphology.
Serrano-Carreón, L; Galindo, E; Rocha-Valadéz, J A; Holguín-Salas, A; Corkidi, G
2015-01-01
Filamentous cultures, such as fungi and actinomycetes, contribute substantially to the pharmaceutical industry and to enzyme production, with an annual market of about 6 billion dollars. In mechanically stirred reactors, most frequently used in fermentation industry, microbial growth and metabolite productivity depend on complex interactions between hydrodynamics, oxygen transfer, and mycelial morphology. The dissipation of energy through mechanically stirring devices, either flasks or tanks, impacts both microbial growth through shearing forces on the cells and the transfer of mass and energy, improving the contact between phases (i.e., air bubbles and microorganisms) but also causing damage to the cells at high energy dissipation rates. Mechanical-induced signaling in the cells triggers the molecular responses to shear stress; however, the complete mechanism is not known. Volumetric power input and, more importantly, the energy dissipation/circulation function are the main parameters determining mycelial size, a phenomenon that can be explained by the interaction of mycelial aggregates and Kolmogorov eddies. The use of microparticles in fungal cultures is also a strategy to increase process productivity and reproducibility by controlling fungal morphology. In order to rigorously study the effects of hydrodynamics on the physiology of fungal microorganisms, it is necessary to rule out the possible associated effects of dissolved oxygen, something which has been reported scarcely. At the other hand, the processes of phase dispersion (including the suspended solid that is the filamentous biomass) are crucial in order to get an integral knowledge about biological and physicochemical interactions within the bioreactor. Digital image analysis is a powerful tool for getting relevant information in order to establish the mechanisms of mass transfer as well as to evaluate the viability of the mycelia. This review focuses on (a) the main characteristics of the two most
Relativistic Hydrodynamics for Heavy-Ion Collisions
ERIC Educational Resources Information Center
Ollitrault, Jean-Yves
2008-01-01
Relativistic hydrodynamics is essential to our current understanding of nucleus-nucleus collisions at ultrarelativistic energies (current experiments at the Relativistic Heavy Ion Collider, forthcoming experiments at the CERN Large Hadron Collider). This is an introduction to relativistic hydrodynamics for graduate students. It includes a detailed…
Hydrodynamic description for ballistic annihilation systems
Garcia de Soria, Maria Isabel; Trizac, Emmanuel; Maynar, Pablo; Schehr, Gregory; Barrat, Alain
2009-01-21
The problem of the validity of a hydrodynamic description for a system in which there are no collisional invariants is addressed. Hydrodynamic equations have been derived and successfully tested against simulation data for a system where particles annihilate with a probability p, or collide elastically otherwise. The response of the system to a linear perturbation is analyzed as well.
Near-bed turbulence and sediment flux measurements in tidal channels
Wright, S.A.; Whealdon-Haught, D.R.
2012-01-01
Understanding the hydrodynamics and sediment transport dynamics in tidal channels is important for studies of estuary geomorphology, sediment supply to tidal wetlands, aquatic ecology and fish habitat, and dredging and navigation. Hydrodynamic and sediment transport data are essential for calibration and testing of numerical models that may be used to address management questions related to these topics. Herein we report preliminary analyses of near-bed turbulence and sediment flux measurements in the Sacramento-San Joaquin Delta, a large network of tidal channels and wetlands located at the confluence of the Sacramento and San Joaquin Rivers, California, USA (Figure 1). Measurements were made in 6 channels spanning a wide range of size and tidal conditions, from small channels that are primarily fluvial to large channels that are tidally dominated. The results of these measurements are summarized herein and the hydrodynamic and sediment transport characteristics of the channels are compared across this range of size and conditions.
Hydrodynamic model for drying emulsions
NASA Astrophysics Data System (ADS)
Feng, Huanhuan; Sprakel, Joris; van der Gucht, Jasper
2015-08-01
We present a hydrodynamic model for film formation in a dense oil-in-water emulsion under a unidirectional drying stress. Water flow through the plateau borders towards the drying end leads to the buildup of a pressure gradient. When the local pressure exceeds the critical disjoining pressure, the water films between droplets break and the droplets coalesce. We show that, depending on the critical pressure and the evaporation rate, the coalescence can occur in two distinct modes. At low critical pressures and low evaporation rates, coalescence occurs throughout the sample, whereas at high critical pressures and high evaporation rate, coalescence occurs only at the front. In the latter case, an oil layer develops on top of the film, which acts as a diffusive barrier and slows down film formation. Our findings, which are summarized in a state diagram for film formation, are in agreement with recent experimental findings.
Hydrodynamic simulations of recurrent novae
NASA Astrophysics Data System (ADS)
Starrfield, S.; Sparks, W. M.; Truran, J. W.; Sion, E. M.
1984-12-01
Simulations of the 1979 outburst of the recurrent nova U Scorpii using a Lagrangian, hydrodynamic computer code which incorporates accretion in the evolution to the outburst are discussed. Three evolutionary sequences were computed in an attempt to understand the very rapid outburst and short recurrence time of this most unusual nova. It is now possible to reproduce the CNO composition of the ejected material, the light curve, the amount of ejected material, and the kinetic energy of the ejecta. The best sequence studied involved accretion of solar rich material onto a 1.38 solar magnatude white dwarf at a rate of 1.6 x 10 to the minus 8 solar magnatude per year.
Anomalous hydrodynamics kicks neutron stars
NASA Astrophysics Data System (ADS)
Kaminski, Matthias; Uhlemann, Christoph F.; Bleicher, Marcus; Schaffner-Bielich, Jürgen
2016-09-01
Observations show that, at the beginning of their existence, neutron stars are accelerated briskly to velocities of up to a thousand kilometers per second. We argue that this remarkable effect can be explained as a manifestation of quantum anomalies on astrophysical scales. To theoretically describe the early stage in the life of neutron stars we use hydrodynamics as a systematic effective-field-theory framework. Within this framework, anomalies of the Standard Model of particle physics as underlying microscopic theory imply the presence of a particular set of transport terms, whose form is completely fixed by theoretical consistency. The resulting chiral transport effects in proto-neutron stars enhance neutrino emission along the internal magnetic field, and the recoil can explain the order of magnitude of the observed kick velocities.
Hydrodynamics and phases of flocks
Toner, John; Tu Yuhai . E-mail: yuhai@us.ibm.com; Ramaswamy, Sriram
2005-07-01
We review the past decade's theoretical and experimental studies of flocking: the collective, coherent motion of large numbers of self-propelled 'particles' (usually, but not always, living organisms). Like equilibrium condensed matter systems, flocks exhibit distinct 'phases' which can be classified by their symmetries. Indeed, the phases that have been theoretically studied to date each have exactly the same symmetry as some equilibrium phase (e.g., ferromagnets, liquid crystals). This analogy with equilibrium phases of matter continues in that all flocks in the same phase, regardless of their constituents, have the same 'hydrodynamic'-that is, long-length scale and long-time behavior, just as, e.g., all equilibrium fluids are described by the Navier-Stokes equations. Flocks are nonetheless very different from equilibrium systems, due to the intrinsically nonequilibrium self-propulsion of the constituent 'organisms'. This difference between flocks and equilibrium systems is most dramatically manifested in the ability of the simplest phase of a flock, in which all the organisms are, on average moving in the same direction (we call this a 'ferromagnetic' flock; we also use the terms 'vector-ordered' and 'polar-ordered' for this situation) to exist even in two dimensions (i.e., creatures moving on a plane), in defiance of the well-known Mermin-Wagner theorem of equilibrium statistical mechanics, which states that a continuous symmetry (in this case, rotation invariance, or the ability of the flock to fly in any direction) can not be spontaneously broken in a two-dimensional system with only short-ranged interactions. The 'nematic' phase of flocks, in which all the creatures move preferentially, or are simply oriented preferentially, along the same axis, but with equal probability of moving in either direction, also differs dramatically from its equilibrium counterpart (in this case, nematic liquid crystals). Specifically, it shows enormous number fluctuations, which
Radiation hydrodynamics in solar flares
Fisher, G.H.
1985-10-18
Solar flares are rather violent and extremely complicated phenomena, and it should be made clear at the outset that a physically complete picture describing all aspects of flares does not exist. From the wealth of data which is available, it is apparent that many different types of physical processes are involved during flares: energetic particle acceleration, rapid magnetohydrodynamic motion of complex field structures, magnetic reconnection, violent mass motion along magnetic field lines, and the heating of plasma to tens of millions of degrees, to name a few. The goal of this paper is to explore just one aspect of solar flares, namely, the interaction of hydrodynamics and radiation processes in fluid being rapidly heated along closed magnetic field lines. The models discussed are therefore necessarily restrictive, and will address only a few of the observed or observable phenomena. 46 refs., 6 figs.
Hydrodynamic assembly for Fast Ignition
NASA Astrophysics Data System (ADS)
Tabak, Max; Clark, Daniel; Town, Richard; Hatchett, Stephen
2007-11-01
We present directly and indirectly driven implosion designs for Fast Ignition. Directly driven designs using various laser illumination wavelengths are described. We compare these designs with simple hydrodynamic efficiency models. Capsules illuminated with less than 1 MJ of light with perfect zooming at low intensity and low contrast ratio in power can assemble 4 mg of fuel to column density in excess of 3 g/cm^2. We contrast these designs with more optimized designs that lead to Guderley-style self similar implosions. Indirectly driven capsules absorbing 75 kJ of xrays can assemble 0.7 mg to column density 2.7 g/cm^2 in 1D simulations. We describe 2-D simulations including both capsules and attached cones driven by radiation. We describe issues in assembling fuel near the cone tip and cone disruption.
Effect of Surface Roughness on Hydrodynamic Bearings
NASA Technical Reports Server (NTRS)
Majumdar, B. C.; Hamrock, B. J.
1981-01-01
A theoretical analysis on the performance of hydrodynamic oil bearings is made considering surface roughness effect. The hydrodynamic as well as asperity contact load is found. The contact pressure was calculated with the assumption that the surface height distribution was Gaussian. The average Reynolds equation of partially lubricated surface was used to calculate hydrodynamic load. An analytical expression for average gap was found and was introduced to modify the average Reynolds equation. The resulting boundary value problem was then solved numerically by finite difference methods using the method of successive over relaxation. The pressure distribution and hydrodynamic load capacity of plane slider and journal bearings were calculated for various design data. The effects of attitude and roughness of surface on the bearing performance were shown. The results are compared with similar available solution of rough surface bearings. It is shown that: (1) the contribution of contact load is not significant; and (2) the hydrodynamic and contact load increase with surface roughness.
Stellar Explosions: Hydrodynamics and Nucleosynthesis
NASA Astrophysics Data System (ADS)
José, Jordi
2015-12-01
Stars are the main factories of element production in the universe through a suite of complex and intertwined physical processes. Such stellar alchemy is driven by multiple nuclear interactions that through eons have transformed the pristine, metal-poor ashes leftover by the Big Bang into a cosmos with 100 distinct chemical species. The products of stellar nucleosynthesis frequently get mixed inside stars by convective transport or through hydrodynamic instabilities, and a fraction of them is eventually ejected into the interstellar medium, thus polluting the cosmos with gas and dust. The study of the physics of the stars and their role as nucleosynthesis factories owes much to cross-fertilization of different, somehow disconnected fields, ranging from observational astronomy, computational astrophysics, and cosmochemistry to experimental and theoretical nuclear physics. Few books have simultaneously addressed the multidisciplinary nature of this field in an engaging way suitable for students and young scientists. Providing the required multidisciplinary background in a coherent way has been the driving force for Stellar Explosions: Hydrodynamics and Nucleosynthesis. Written by a specialist in stellar astrophysics, this book presents a rigorous but accessible treatment of the physics of stellar explosions from a multidisciplinary perspective at the crossroads of computational astrophysics, observational astronomy, cosmochemistry, and nuclear physics. Basic concepts from all these different fields are applied to the study of classical and recurrent novae, type I and II supernovae, X-ray bursts and superbursts, and stellar mergers. The book shows how a multidisciplinary approach has been instrumental in our understanding of nucleosynthesis in stars, particularly during explosive events.
The hydrodynamics of dolphin drafting
Weihs, Daniel
2004-01-01
Background Drafting in cetaceans is defined as the transfer of forces between individuals without actual physical contact between them. This behavior has long been surmised to explain how young dolphin calves keep up with their rapidly moving mothers. It has recently been observed that a significant number of calves become permanently separated from their mothers during chases by tuna vessels. A study of the hydrodynamics of drafting, initiated in the hope of understanding the mechanisms causing the separation of mothers and calves during fishing-related activities, is reported here. Results Quantitative results are shown for the forces and moments around a pair of unequally sized dolphin-like slender bodies. These include two major effects. First, the so-called Bernoulli suction, which stems from the fact that the local pressure drops in areas of high speed, results in an attractive force between mother and calf. Second is the displacement effect, in which the motion of the mother causes the water in front to move forwards and radially outwards, and water behind the body to move forwards to replace the animal's mass. Thus, the calf can gain a 'free ride' in the forward-moving areas. Utilizing these effects, the neonate can gain up to 90% of the thrust needed to move alongside the mother at speeds of up to 2.4 m/sec. A comparison with observations of eastern spinner dolphins (Stenella longirostris) is presented, showing savings of up to 60% in the thrust that calves require if they are to keep up with their mothers. Conclusions A theoretical analysis, backed by observations of free-swimming dolphin schools, indicates that hydrodynamic interactions with mothers play an important role in enabling dolphin calves to keep up with rapidly moving adult school members. PMID:15132740
Ultrasensitive SERS Flow Detector Using Hydrodynamic Focusing
Negri, Pierre; Jacobs, Kevin T.; Dada, Oluwatosin O.; Schultz, Zachary D.
2013-01-01
Label-free, chemical specific detection in flow is important for high throughput characterization of analytes in applications such as flow injection analysis, electrophoresis, and chromatography. We have developed a surface-enhanced Raman scattering (SERS) flow detector capable of ultrasensitive optical detection on the millisecond time scale. The device employs hydrodynamic focusing to improve SERS detection in a flow channel where a sheath flow confines analyte molecules eluted from a fused silica capillary over a planar SERS-active substrate. Increased analyte interactions with the SERS substrate significantly improve detection sensitivity. The performance of this flow detector was investigated using a combination of finite element simulations, fluorescence imaging, and Raman experiments. Computational fluid dynamics based on finite element analysis was used to optimize the flow conditions. The modeling indicates that a number of factors, such as the capillary dimensions and the ratio of the sheath flow to analyte flow rates, are critical for obtaining optimal results. Sample confinement resulting from the flow dynamics was confirmed using wide-field fluorescence imaging of rhodamine 6G (R6G). Raman experiments at different sheath flow rates showed increased sensitivity compared with the modeling predictions, suggesting increased adsorption. Using a 50-millisecond acquisitions, a sheath flow rate of 180 μL/min, and a sample flow rate of 5 μL/min, a linear dynamic range from nanomolar to micromolar concentrations of R6G with a LOD of 1 nM is observed. At low analyte concentrations, rapid analyte desorption is observed, enabling repeated and high-throughput SERS detection. The flow detector offers substantial advantages over conventional SERS-based assays such as minimal sample volumes and high detection efficiency. PMID:24074461
Khain, Evgeniy; Meerson, Baruch
2006-06-01
We investigate shear-induced crystallization in a very dense flow of monodisperse inelastic hard spheres. We consider a steady plane Couette flow under constant pressure and neglect gravity. We assume that the granular density is greater than the melting point of the equilibrium phase diagram of elastic hard spheres. We employ a Navier-Stokes hydrodynamics with constitutive relations all of which (except the shear viscosity) diverge at the crystal-packing density, while the shear viscosity diverges at a smaller density. The phase diagram of the steady flow is described by three parameters: an effective Mach number, a scaled energy loss parameter, and an integer number m: the number of half-oscillations in a mechanical analogy that appears in this problem. In a steady shear flow the viscous heating is balanced by energy dissipation via inelastic collisions. This balance can have different forms, producing either a uniform shear flow or a variety of more complicated, nonlinear density, velocity, and temperature profiles. In particular, the model predicts a variety of multilayer two-phase steady shear flows with sharp interphase boundaries. Such a flow may include a few zero-shear (solidlike) layers, each of which moving as a whole, separated by fluidlike regions. As we are dealing with a hard sphere model, the granulate is fluidized within the "solid" layers: the granular temperature is nonzero there, and there is energy flow through the boundaries of the solid layers. A linear stability analysis of the uniform steady shear flow is performed, and a plausible bifurcation diagram of the system, for a fixed m, is suggested. The problem of selection of m remains open. PMID:16906816
The hydrodynamic advantages of synchronized swimming in a rectangular pattern.
Daghooghi, Mohsen; Borazjani, Iman
2015-10-01
Fish schooling is a remarkable biological behavior that is thought to provide hydrodynamic advantages. Theoretical models have predicted significant reduction in swimming cost due to two physical mechanisms: vortex hypothesis, which reduces the relative velocity between fish and the flow through the induced velocity of the organized vortex structure of the incoming wake; and the channeling effect, which reduces the relative velocity by enhancing the flow between the swimmers in the direction of swimming. Although experimental observations confirm hydrodynamic advantages, there is still debate regarding the two mechanisms. We provide, to our knowledge, the first three-dimensional simulations at realistic Reynolds numbers to investigate these physical mechanisms. Using large-eddy simulations of self-propelled synchronized swimmers in various rectangular patterns, we find evidence in support of the channeling effect, which enhances the flow velocity between swimmers in the direction of swimming as the lateral distance between swimmers decreases. Our simulations show that the coherent structures, in contrast to the wake of a single swimmer, break down into small, disorganized vortical structures, which have a low chance for constructive vortex interaction. Therefore, the vortex hypothesis, which is relevant for diamond patterns, was not found for rectangular patterns, but needs to be further studied for diamond patterns in the future. Exploiting the channeling mechanism, a fish in a rectangular school swims faster as the lateral distance decreases, while consuming similar amounts of energy. The fish in the rectangular school with the smallest lateral distance (0.3 fish lengths) swims 20% faster than a solitary swimmer while consuming similar amount of energy. PMID:26447493
NASA Astrophysics Data System (ADS)
Pavlov, Yu. M.; Yakovlev, I. V.; Terentiev, Yu. A.; Antipov, V. I.
Results of experimental investigation of transient heat transfer and hydrodynamics of two phase flow in the channel with forced nitrogen circulation under pulse heating conditions are presented. Experimental relationships of channel wall temperature, heat transfer coefficient, pressure in the channel and time of boiling onset and that of crisis of heat transfer from mass flow rate, amplitude of heat pulse and relative channel length are obtained. Experimental results illustrate some regularities of transient heat transfer and hydraulic processes in models of HTSC cable of ICCS type.
Hydrodynamics and Mass Transfer Characteristics of Laminar Bioelectrochemical Systems, a Summary
NASA Astrophysics Data System (ADS)
Cheng, Way Lee; Sadr, Reza
2015-11-01
Hydrodynamics and diffusion characteristics of laminar bioelectrochemical systems (BES) with common micro-channel configuration are summarized. Computational fluid dynamics (CFD) simulations are performed to supplement literature results and to provide a comprehensive summary for the flow and diffusion characteristics in these systems in terms of dimensionless parameters. The results show that decreasing the fluid velocity enhances mixing between the two parallel flow streams with a stronger mixing in the near wall region. Reducing the ratio of channel width to channel height enhances mixing. Changing the angle between the inlet channels, in general, does not have a strong effect on the flow field, except when the angle is larger than about 135°. Furthermore, fluid mixing is substantially different for 60° and 180° angle between the two inlet channels. For the 60° case, the length of mixing zone does not depends on the Reynolds number and it converges asymptotically as channel width-to-height ratio decreases. On the other hand, for the 180° case, this length depends on the flow Reynolds number and decreases monotonically at small ratio of channel width-to-heights ratio. The results show that asymmetric growth of a bio-layer on the channel wall increases shear stress substantially as one side of the channel as its height reduces compare to the other side. Moreover, this asymmetry causes a traverse velocity field that highly skews the mixing zone towards the side of the channel with larger height.
NASA Astrophysics Data System (ADS)
Huisman, Sander G.; van der Veen, Roeland C. A.; Bruggert, Gert-Wim H.; Lohse, Detlef; Sun, Chao
2015-06-01
A new Taylor-Couette system has been designed and constructed with precise temperature control. Two concentric independently rotating cylinders are able to rotate at maximum rates of fi = ± 20 Hz for the inner cylinder and fo = ± 10 Hz for the outer cylinder. The inner cylinder has an outside radius of ri = 75 mm, and the outer cylinder has an inside radius of ro = 105 mm, resulting in a gap of d = 30 mm. The height of the gap is L = 549 mm, giving a volume of V = 9.3 L. The geometric parameters are η = ri/ro = 0.714 and Γ = L/d = 18.3. With water as working fluid at room temperature, the Reynolds numbers that can be achieved are Rei = ωiri(ro - ri)/ν = 2.8 × 105 and Reo = ωoro(ro - ri)/ν = 2 × 105 or a combined Reynolds number of up to Re = (ωiri - ωoro)(ro - ri)/ν = 4.8 × 105. If the working fluid is changed to the fluorinated liquid FC-3284 with kinematic viscosity 0.42 cSt, the combined Reynolds number can reach Re = 1.1 × 106. The apparatus features precise temperature control of the outer and inner cylinders separately and is fully optically accessible from the side and top. The new facility offers the possibility to accurately study the process of boiling inside a turbulent flow and its effect on the flow.
Huisman, Sander G; van der Veen, Roeland C A; Bruggert, Gert-Wim H; Lohse, Detlef; Sun, Chao
2015-06-01
A new Taylor-Couette system has been designed and constructed with precise temperature control. Two concentric independently rotating cylinders are able to rotate at maximum rates of f(i) = ± 20 Hz for the inner cylinder and f(o) = ± 10 Hz for the outer cylinder. The inner cylinder has an outside radius of r(i) = 75 mm, and the outer cylinder has an inside radius of r(o) = 105 mm, resulting in a gap of d = 30 mm. The height of the gap is L = 549 mm, giving a volume of V = 9.3 L. The geometric parameters are η = r(i)/r(o) = 0.714 and Γ = L/d = 18.3. With water as working fluid at room temperature, the Reynolds numbers that can be achieved are Re(i) = ω(i)r(i)(r(o) - r(i))/ν = 2.8 × 10(5) and Re(o) = ω(o)r(o)(r(o) - r(i))/ν = 2 × 10(5) or a combined Reynolds number of up to Re = (ω(i)r(i) - ω(o)r(o))(r(o) - r(i))/ν = 4.8 × 10(5). If the working fluid is changed to the fluorinated liquid FC-3284 with kinematic viscosity 0.42 cSt, the combined Reynolds number can reach Re = 1.1 × 10(6). The apparatus features precise temperature control of the outer and inner cylinders separately and is fully optically accessible from the side and top. The new facility offers the possibility to accurately study the process of boiling inside a turbulent flow and its effect on the flow. PMID:26133874
Drag reduction in numerical two-phase Taylor–Couette turbulence using an Euler–Lagrange approach
NASA Astrophysics Data System (ADS)
Spandan, Vamsi; Ostilla-Mónico, Rodolfo; Verzicco, Roberto; Lohse, Detlef
2016-07-01
Two-phase turbulent Taylor-Couette (TC) flow is simulated using an Euler-Lagrange approach to study the effects of a secondary phase dispersed into a turbulent carrier phase (here bubbles dispersed into water). The dynamics of the carrier phase is computed using Direct Numerical Simulations (DNS) in an Eulerian framework, while the bubbles are tracked in a Lagrangian manner by modelling the effective drag, lift, added mass and buoyancy force acting on them. Two-way coupling is implemented between the dispersed phase and the carrier phase which allows for momentum exchange among both phases and to study the effect of the dispersed phase on the carrier phase dynamics. The radius ratio of the TC setup is fixed to $\\eta=0.833$, and a maximum inner cylinder Reynolds number of $Re_i=8000$ is reached. We vary the Froude number ($Fr$), which is the ratio of the centripetal to the gravitational acceleration of the dispersed phase and study its effect on the net torque required to drive the TC system. For the two-phase TC system, we observe drag reduction, i.e., the torque required to drive the inner cylinder is less compared to that of the single phase system. The net drag reduction decreases with increasing Reynolds number $Re_i$, which is consistent with previous experimental findings (Murai et al. 2005, 2008). The drag reduction is strongly related to the Froude number: for fixed Reynolds number we observe higher drag reduction when $Fr < 1$ than for with$ Fr > 1$. This buoyancy effect is more prominent in low $Re_i$ systems and decreases with increasing Reynolds number $Re_i$. We trace the drag reduction back to the weakening of the angular momentum carrying Taylor rolls by the rising bubbles.
Non abelian hydrodynamics and heavy ion collisions
Calzetta, E.
2014-01-14
The goal of the relativistic heavy ion collisions (RHIC) program is to create a state of matter where color degrees of freedom are deconfined. The dynamics of matter in this state, in spite of the complexities of quantum chromodynamics, is largely determined by the conservation laws of energy momentum and color currents. Therefore it is possible to describe its main features in hydrodynamic terms, the very short color neutralization time notwithstanding. In this lecture we shall give a simple derivation of the hydrodynamics of a color charged fluid, by generalizing the usual derivation of hydrodynamics from kinetic theory to the non abelian case.
Nonlinear waves in second order conformal hydrodynamics
NASA Astrophysics Data System (ADS)
Fogaça, D. A.; Marrochio, H.; Navarra, F. S.; Noronha, J.
2015-02-01
In this work we study wave propagation in dissipative relativistic fluids described by a simplified set of the 2nd order viscous conformal hydrodynamic equations corresponding to Israel-Stewart theory. Small amplitude waves are studied within the linearization approximation while waves with large amplitude are investigated using the reductive perturbation method, which is generalized to the case of 2nd order relativistic hydrodynamics. Our results indicate the presence of a "soliton-like" wave solution in Israel-Stewart hydrodynamics despite the presence of dissipation and relaxation effects.
Molecular dynamics simulations of oscillatory Couette flows with slip boundary conditions
NASA Astrophysics Data System (ADS)
Priezjev, Nikolai
2012-11-01
The effect of interfacial slip on steady-state and time-periodic flows of monatomic liquids is investigated using non-equilibrium molecular dynamics simulations. The simulations were performed in a wide range of oscillation frequencies; namely, when the Stokes boundary layer thickness is smaller than the channel width at the highest frequency, and, on the other hand, at lower frequencies that correspond to quasi-steady flows. It was found that the velocity profiles computed in MD simulations are well described by the continuum solution with the slip length as a fitting parameter that depends on the local shear rate. Interestingly, the shear rate dependence of the slip length obtained in steady-state shear flows is reproduced in oscillatory flows when the slip length is measured as a function of the absolute value of the local shear rate. Finally, for both types of flows, the friction coefficient at the liquid-solid interface correlates well with the structure factor and the contact density of the first fluid layer. Financial support from the National Science Foundation (CBET-1033662) is gratefully acknowledged.
Technology Transfer Automated Retrieval System (TEKTRAN)
This book chapter provides a comprehensive overview of channel catfish aquaculture. Sections include fish biology; commercial culture; culture facilities; production practices; water quality management; nutrition, feeding and feed formulation; infectious diseases; harvesting and processing; and the...
Detonation waves in relativistic hydrodynamics
Cissoko, M. )
1992-02-15
This paper is concerned with an algebraic study of the equations of detonation waves in relativistic hydrodynamics taking into account the pressure and the energy of thermal radiation. A new approach to shock and detonation wavefronts is outlined. The fluid under consideration is assumed to be perfect (nonviscous and nonconducting) and to obey the following equation of state: {ital p}=({gamma}{minus}1){rho} where {ital p}, {rho}, and {gamma} are the pressure, the total energy density, and the adiabatic index, respectively. The solutions of the equations of detonation waves are reduced to the problem of finding physically acceptable roots of a quadratic polynomial {Pi}({ital X}) where {ital X} is the ratio {tau}/{tau}{sub 0} of dynamical volumes behind and ahead of the detonation wave. The existence and the locations of zeros of this polynomial allow it to be shown that if the equation of state of the burnt fluid is known then the variables characterizing the unburnt fluid obey well-defined physical relations.
Hydrodynamic Simulations of Contact Binaries
NASA Astrophysics Data System (ADS)
Kadam, Kundan; Clayton, Geoffrey C.; Frank, Juhan; Marcello, Dominic; Motl, Patrick M.; Staff, Jan E.
2015-01-01
The motivation for our project is the peculiar case of the 'red nova" V1309 Sco which erupted in September 2008. The progenitor was, in fact, a contact binary system. We are developing a simulation of contact binaries, so that their formation, structural, and merger properties could be studied using hydrodynamics codes. The observed transient event was the disruption of the secondary star by the primary, and their subsequent merger into one star; hence to replicate this behavior, we need a core-envelope structure for both the stars. We achieve this using a combination of Self Consistant Field (SCF) technique and composite polytropes, also known as bipolytropes. So far we have been able to generate close binaries with various mass ratios. Another consequence of using bipolytropes is that according to theoretical calculations, the radius of a star should expand when the core mass fraction exceeds a critical value, resulting in interesting consequences in a binary system. We present some initial results of these simulations.
Hydrodynamic Instabilities Produced by Evaporation
NASA Astrophysics Data System (ADS)
Romo-Cruz, Julio Cesar Ruben; Hernandez-Zapata, Sergio; Ruiz-Chavarria, Gerardo
2012-11-01
When a liquid layer (alcohol in the present work) is in an environment where its relative humidity is less than 100 percent evaporation appears. When RH is above a certain threshold the liquid is at rest. If RH decreases below this threshold the flow becomes unstable, and hydrodynamic cells develop. The aim of this work is to understand the formation of those cells and its main features. Firstly, we investigate how the cell size depends on the layer width. We also study how temperature depends on the vertical coordinate when the cells are present. An inverse temperature gradient is found, that is, the bottom of liquid layer is colder than the free surface. This shows that the intuitive idea that the cells are due to a direct temperature gradient, following a Marangoni-like process, does not work. We propose the hypothesis that the evaporation produce a pressure gradient that is responsible of the cell development. On the other hand, using a Schlieren technique we study the topography of the free surface when cells are present. Finally the alcohol vapor layer adjacent to the liquid surface is explored using scattering experiments, giving some insight on the plausibility of the hypothesis described previously. Authors acknowledge support by DGAPA-UNAM under project IN116312 ``Vorticidad y ondas no lineales en fluidos.''
Hydrodynamic repulsion of elastic dumbbells
NASA Astrophysics Data System (ADS)
Ekiel-Jezewska, Maria L.; Bukowicki, Marek; Gruca, Marta
2015-11-01
Dynamics of two identical elastic dumbbells, settling under gravity in a viscous fluid at low Reynolds number are analyzed within the point-particle model. Initially, the dumbbells are vertical, their centers are aligned horizontally, and the springs which connect the dumbbell's beads are at the equilibrium. The motion of the beads is determined numerically with the use of the Runge-Kutta method. After an initial relaxation phase, the system converges to a universal time-dependent solution. The elastic dumbbells tumble while falling, but their relative motion is not periodic (as in case of rigid dumbbells or pairs of separated beads). The elastic constraints break the time-reversal symmetry of the motion. As the result, the horizontal distance between the dumbbells slowly increases - they are hydrodynamically repelled from each other. This effect can be very large even though the elastic forces are always much smaller than gravity. The dynamics described above are equivalent to the motion of a single elastic dumbbell under a constant external force which is parallel to a flat free surface. The dumbbell migrates away from the interface and its tumbling time increases.
Glimm's Method for Relativistic Hydrodynamics
NASA Astrophysics Data System (ADS)
Cannizzo, J. K.; Gehrels, N.; Vishniac, E. T.
2008-06-01
We present the results of standard one-dimensional test problems in relativistic hydrodynamics using Glimm's (random choice) method and compare them to results obtained using finite differencing methods. For problems containing profiles with sharp edges, such as shocks, we find Glimm's method yields global errors ~1-3 orders of magnitude smaller than the traditional techniques. The strongest differences are seen for problems in which a shear field is superposed. For smooth flows, Glimm's method is inferior to standard methods. The location of specific features can be off by up to two grid points with respect to an exact solution in Glimm's method, and furthermore, curved states are not modeled optimally, since the method idealizes solutions as being composed of piecewise constant states. Thus, although Glimm's method is superior at correctly resolving sharp features, especially in the presence of shear, for realistic applications in which one typically finds smooth flows plus strong gradients or discontinuities, standard finite-difference methods yield smaller global errors. Glimm's method may prove useful in certain applications such as GRB afterglow shock propagation into a uniform medium.
Global hydrodynamics of the sun
NASA Astrophysics Data System (ADS)
Monin, A. S.
1980-09-01
A review of studies (1960's-1970's) on solar global hydrodynamics is presented, the main areas discussed being differential rotation and generation of the 11-year solar cycle, which seem to be related. A summary of current knowledge about the sun is given, including dimensions, rotation, radiation, solar atmosphere, and solar interior (neutrinos, convection zone). Solar atmospheric inhomogeneities with relatively short lifetimes are discussed, the most important perturbations being spots, faculae, chromospheric flares, prominences, and coronal streamers and holes. Data on solar rotation are reviewed: Solar differential rotation is accompanied by the expenditure of energy to overcome the viscous forces, and without some mechanism which would replenish this energy, the angular rotation velocities, at various heliographic latitudes, would become equal after a few solar rotations. It is thought that the replenishment mechanism is the meridional and radial transport of angular momentum in the convection zone by giant convection cells and of the parameterized turbulent viscosity. Familiar and undisputed effects of the 11-yr solar cycle include auroras, and magnetic storms. Less familiar effects include variations in the level of atmospheric radioactive carbon, and correlations between solar activity and earth climatic variations.
Hydrodynamic turbulence in quasi-Keplerian rotating flows?
NASA Astrophysics Data System (ADS)
Shi, Liang; Avila, Marc; Hof, Bjoern; Liang Shi Team; Marc Avila Team; Bjoern Hof Team
2013-11-01
The origin of turbulence in astrophysical accretion discs has been under scrutiny for decades and remains still unclear. The velocity profiles of discs (Keplerien profiles) are centrifugally stable and therefore a different instability mechanism is required for turbulence to arise. While in hot discs turbulence can be triggered through magnetorotational instability, cooler discs lack sufficient ionization and it is unclear how turbulence sets in. In analogy to other linearly stable flows like pipe and Couette flow, subcritical transition to turbulence may be the mechanism. Recently, experimental studies of Taylor-Couette flow in quasi-Keplerian regime have given conflicting results and numerical simulations of above experimental flows showed that the top and bottom end-wall leads to strong deviations from the Keplerian velocity profile and drives turbulence. In order to clarify this, we perform direct numerical simulations of incompressible Taylor-Couette flow without end walls in the quasi Keplerian regime for Re up to 200000. Strong transient growth is observed and gives rise to strongly disorted motion, suggesting that for large enough Re this mechanism may lead to turbulence even for Keplerian flows. This work is supported by Deutsche Forschungsgemeinschaft (DFG) under project SFB 963 and Max Planck Society.
Hydrodynamic gradient expansion in gauge theory plasmas.
Heller, Michal P; Janik, Romuald A; Witaszczyk, Przemysław
2013-05-24
We utilize the fluid-gravity duality to investigate the large order behavior of hydrodynamic gradient expansion of the dynamics of a gauge theory plasma system. This corresponds to the inclusion of dissipative terms and transport coefficients of very high order. Using the dual gravity description, we calculate numerically the form of the stress tensor for a boost-invariant flow in a hydrodynamic expansion up to terms with 240 derivatives. We observe a factorial growth of gradient contributions at large orders, which indicates a zero radius of convergence of the hydrodynamic series. Furthermore, we identify the leading singularity in the Borel transform of the hydrodynamic energy density with the lowest nonhydrodynamic excitation corresponding to a 'nonhydrodynamic' quasinormal mode on the gravity side. PMID:23745858
Hydrodynamic phonon transport in suspended graphene.
Lee, Sangyeop; Broido, David; Esfarjani, Keivan; Chen, Gang
2015-01-01
Recent studies of thermal transport in nanomaterials have demonstrated the breakdown of Fourier's law through observations of ballistic transport. Despite its unique features, another instance of the breakdown of Fourier's law, hydrodynamic phonon transport, has drawn less attention because it has been observed only at extremely low temperatures and narrow temperature ranges in bulk materials. Here, we predict on the basis of first-principles calculations that the hydrodynamic phonon transport can occur in suspended graphene at significantly higher temperatures and wider temperature ranges than in bulk materials. The hydrodynamic transport is demonstrated through drift motion of phonons, phonon Poiseuille flow and second sound. The significant hydrodynamic phonon transport in graphene is associated with graphene's two-dimensional features. This work opens a new avenue for understanding and manipulating heat flow in two-dimensional materials. PMID:25693180
NASA Astrophysics Data System (ADS)
Bedrossian, Jacob; Masmoudi, Nader; Vicol, Vlad
2016-03-01
In this work we study the long time inviscid limit of the two dimensional Navier-Stokes equations near the periodic Couette flow. In particular, we confirm at the nonlinear level the qualitative behavior predicted by Kelvin's 1887 linear analysis. At high Reynolds number Re, we prove that the solution behaves qualitatively like two dimensional Euler for times {{t ≲ Re^{1/3}}}, and in particular exhibits inviscid damping (for example the vorticity weakly approaches a shear flow). For times {{t ≳ Re^{1/3}}}, which is sooner than the natural dissipative time scale O( Re), the viscosity becomes dominant and the streamwise dependence of the vorticity is rapidly eliminated by an enhanced dissipation effect. Afterwards, the remaining shear flow decays on very long time scales {{t ≳ Re}} back to the Couette flow. When properly defined, the dissipative length-scale in this setting is {{ℓ_D ˜ Re^{-1/3}}}, larger than the scale {{ℓ_D ˜ Re^{-1/2}}} predicted in classical Batchelor-Kraichnan two dimensional turbulence theory. The class of initial data we study is the sum of a sufficiently smooth function and a small (with respect to Re -1) L 2 function.
Chemo-hydrodynamic patterns in porous media.
De Wit, A
2016-10-13
Chemical reactions can interplay with hydrodynamic flows to generate chemo-hydrodynamic instabilities affecting the spatio-temporal evolution of the concentration of the chemicals. We review here such instabilities for porous media flows. We describe the influence of chemical reactions on viscous fingering, buoyancy-driven fingering in miscible systems, convective dissolution as well as precipitation patterns. Implications for environmental systems are discussed.This article is part of the themed issue 'Energy and the subsurface'. PMID:27597788
Flagellar Synchronization Independent of Hydrodynamic Interactions
NASA Astrophysics Data System (ADS)
Friedrich, Benjamin M.; Jülicher, Frank
2012-09-01
Inspired by the coordinated beating of the flagellar pair of the green algae Chlamydomonas, we study theoretically a simple, mirror-symmetric swimmer, which propels itself at low Reynolds number by a revolving motion of a pair of spheres. We show that perfect synchronization between these two driven spheres can occur due to the motion of the swimmer and local hydrodynamic friction forces. Hydrodynamic interactions, though crucial for net propulsion, contribute little to synchronization for this free-moving swimmer.
A comparison of two finite element models of tidal hydrodynamics using a North Sea data set
Walters, R.A.; Werner, F.E.
1989-01-01
Using the region of the English Channel and the southern bight of the North Sea, we systematically compare the results of two independent finite element models of tidal hydrodynamics. The model intercomparison provides a means for increasing our understanding of the relevant physical processes in the region in question as well as a means for the evaluation of certain algorithmic procedures of the two models. ?? 1989.
Validation of a Global Hydrodynamic Flood Inundation Model
NASA Astrophysics Data System (ADS)
Bates, P. D.; Smith, A.; Sampson, C. C.; Alfieri, L.; Neal, J. C.
2014-12-01
In this work we present first validation results for a hyper-resolution global flood inundation model. We use a true hydrodynamic model (LISFLOOD-FP) to simulate flood inundation at 1km resolution globally and then use downscaling algorithms to determine flood extent and depth at 90m spatial resolution. Terrain data are taken from a custom version of the SRTM data set that has been processed specifically for hydrodynamic modelling. Return periods of flood flows along the entire global river network are determined using: (1) empirical relationships between catchment characteristics and index flood magnitude in different hydroclimatic zones derived from global runoff data; and (2) an index flood growth curve, also empirically derived. Bankful return period flow is then used to set channel width and depth, and flood defence impacts are modelled using empirical relationships between GDP, urbanization and defence standard of protection. The results of these simulations are global flood hazard maps for a number of different return period events from 1 in 5 to 1 in 1000 years. We compare these predictions to flood hazard maps developed by national government agencies in the UK and Germany using similar methods but employing detailed local data, and to observed flood extent at a number of sites including St. Louis, USA and Bangkok in Thailand. Results show that global flood hazard models can have considerable skill given careful treatment to overcome errors in the publicly available data that are used as their input.
Atomistic Hydrodynamics and the Dynamical Hydrophobic Effect in Porous Graphene.
Strong, Steven E; Eaves, Joel D
2016-05-19
Mirroring their role in electrical and optical physics, two-dimensional crystals are emerging as novel platforms for fluid separations and water desalination, which are hydrodynamic processes that occur in nanoscale environments. For numerical simulation to play a predictive and descriptive role, one must have theoretically sound methods that span orders of magnitude in physical scales, from the atomistic motions of particles inside the channels to the large-scale hydrodynamic gradients that drive transport. Here, we use constraint dynamics to derive a nonequilibrium molecular dynamics method for simulating steady-state mass flow of a fluid moving through the nanoscopic spaces of a porous solid. After validating our method on a model system, we use it to study the hydrophobic effect of water moving through pores of electrically doped single-layer graphene. The trend in permeability that we calculate does not follow the hydrophobicity of the membrane but is instead governed by a crossover between two competing molecular transport mechanisms. PMID:27139634
The hydrodynamic focusing effect inside rectangular microchannels
NASA Astrophysics Data System (ADS)
Lee, Gwo-Bin; Chang, Chih-Chang; Huang, Sung-Bin; Yang, Ruey-Jen
2006-05-01
This paper presents a theoretical and experimental investigation into the hydrodynamic focusing effect in rectangular microchannels. Two theoretical models for two-dimensional hydrodynamic focusing are proposed. The first model predicts the width of the focused stream in symmetric hydrodynamic focusing in microchannels of various aspect ratios. The second model predicts the location and the width of the focused stream in asymmetric hydrodynamic focusing in microchannels with a low or high aspect ratio. In both models, the theoretical results are shown to be in good agreement with the experimental data. Hence, the models provide a useful means of performing a theoretical analysis of flow control in microfluidic devices using hydrodynamic focusing effects. The ability of the proposed models to control the focused stream within a micro flow cytometer is verified in a series of experimental trials performed using polystyrene microparticles with a diameter of 20 µm. The experimental data show that the width of the focused stream can be reduced to the same order of magnitude as that of the particle size. Furthermore, it is shown that the microparticles can be successfully hydrodynamically focused and switched to the desired outlet port of the cytometer. Hence, the models presented in this study provide sufficient control to support cell/particle counting and sorting applications.
Hydrodynamic Simulations of Giant Impacts
NASA Astrophysics Data System (ADS)
Reinhardt, Christian; Stadel, Joachim
2013-07-01
We studied the basic numerical aspects of giant impacts using Smoothed Particles Hydrodynamics (SPH), which has been used in most of the prior studies conducted in this area (e.g., Benz, Canup). Our main goal was to modify the massive parallel, multi-stepping code GASOLINE widely used in cosmological simulations so that it can properly simulate the behavior of condensed materials such as granite or iron using the Tillotson equation of state. GASOLINE has been used to simulate hundreds of millions of particles for ideal gas physics so that using several millions of particles in condensed material simulations seems possible. In order to focus our attention of the numerical aspects of the problem we neglected the internal structure of the protoplanets and modelled them as homogenous (isothermal) granite spheres. For the energy balance we only considered PdV work and shock heating of the material during the impact (neglected cooling of the material). Starting at a low resolution of 2048 particles for the target and the impactor we run several simulations for different impact parameters and impact velocities and successfully reproduced the main features of the pioneering work of Benz from 1986. The impact sends a shock wave through both bodies heating the target and disrupting the remaining impactor. As in prior simulations material is ejected from the collision. How much, and whether it leaves the system or survives in an orbit for a longer time, depends on the initial conditions but also on resolution. Increasing the resolution (to 1.2x10⁶ particles) results in both a much clearer shock wave and deformation of the bodies during the impact and a more compact and detailed "arm" like structure of the ejected material. Currently we are investigating some numerical issues we encountered and are implementing differentiated models, making one step closer to more realistic protoplanets in such giant impact simulations.
A two-dimensional hydrodynamic model of a tidal estuary
Walters, Roy A.; Cheng, Ralph T.
1979-01-01
A finite element model is described which is used in the computation of tidal currents in an estuary. This numerical model is patterned after an existing algorithm and has been carefully tested in rectangular and curve-sided channels with constant and variable depth. One of the common uncertainties in this class of two-dimensional hydrodynamic models is the treatment of the lateral boundary conditions. Special attention is paid specifically to addressing this problem. To maintain continuity within the domain of interest, ‘smooth’ curve-sided elements must be used at all shoreline boundaries. The present model uses triangular, isoparametric elements with quadratic basis functions for the two velocity components and a linear basis function for water surface elevation. An implicit time integration is used and the model is unconditionally stable. The resultant governing equations are nonlinear owing to the advective and the bottom friction terms and are solved iteratively at each time step by the Newton-Raphson method. Model test runs have been made in the southern portion of San Francisco Bay, California (South Bay) as well as in the Bay west of Carquinez Strait. Owing to the complex bathymetry, the hydrodynamic characteristics of the Bay system are dictated by the generally shallow basins which contain deep, relict river channels. Great care must be exercised to ensure that the conservation equations remain locally as well as globally accurate. Simulations have been made over several representative tidal cycles using this finite element model, and the results compare favourably with existing data. In particular, the standing wave in South Bay and the progressive wave in the northern reach are well represented.
Two dimensional hydrodynamic modeling of a high latitude braided river
NASA Astrophysics Data System (ADS)
Humphries, E.; Pavelsky, T.; Bates, P. D.
2014-12-01
Rivers are a fundamental resource to physical, ecologic and human systems, yet quantification of river flow in high-latitude environments remains limited due to the prevalence of complex morphologies, remote locations and sparse in situ monitoring equipment. Advances in hydrodynamic modeling and remote sensing technology allow us to address questions such as: How well can two-dimensional models simulate a flood wave in a highly 3-dimensional braided river environment, and how does the structure of such a flood wave differ from flow down a similar-sized single-channel river? Here, we use the raster-based hydrodynamic model LISFLOOD-FP to simulate flood waves, discharge, water surface height, and velocity measurements over a ~70 km reach of the Tanana River in Alaska. In order to use LISFLOOD-FP a digital elevation model (DEM) fused with detailed bathymetric data is required. During summer 2013, we surveyed 220,000 bathymetric points along the study reach using an echo sounder system connected to a high-precision GPS unit. The measurements are interpolated to a smooth bathymetric surface, using Topo to Raster interpolation, and combined with an existing five meter DEM (Alaska IfSAR) to create a seamless river terrain model. Flood waves are simulated using varying complexities in model solvers, then compared to gauge records and water logger data to assess major sources of model uncertainty. Velocity and flow direction maps are also assessed and quantified for detailed analysis of braided channel flow. The most accurate model output occurs with using the full two-dimensional model structure, and major inaccuracies appear to be related to DEM quality and roughness values. Future work will intercompare model outputs with extensive ground measurements and new data from AirSWOT, an airborne analog for the Surface Water and Ocean Topography (SWOT) mission, which aims to provide high-resolution measurements of terrestrial and ocean water surface elevations globally.
Benemei, Silvia; Patacchini, Riccardo; Trevisani, Marcello; Geppetti, Pierangelo
2015-06-01
Evidence is accumulating on the role of transient receptor potential (TRP) channels, namely TRPV1, TRPA1, TRPV4 and TRPM8, expressed by C- and Aδ-fibres primary sensory neurons, in cough mechanism. Selective stimuli for these channels have been proven to provoke and, more rarely, to inhibit cough. More importantly, cough threshold to TRP agonists is increased by proinflammatory conditions, known to favour cough. Off-target effects of various drugs, such as tiotropium or desflurane, seem to produce their protective or detrimental actions on airway irritation and cough via TRPV1 and TRPA1, respectively. Thus, TRPs appear to encode the process that initiates or potentiates cough, activated by exogenous irritants and endogenous proinflammatory mediators. More research on TRP channels may result in innovative cough medicines. PMID:25725213
Hydrodynamic simulations of pulsar glitch recovery
NASA Astrophysics Data System (ADS)
Howitt, G.; Haskell, B.; Melatos, A.
2016-05-01
Glitches are sudden jumps in the spin frequency of pulsars believed to originate in the superfluid interior of neutron stars. Superfluid flow in a model neutron star is simulated by solving the equations of motion of a two-component superfluid consisting of a viscous proton-electron plasma and an inviscid neutron condensate in a spherical Couette geometry. We examine the response of the model to glitches induced in three different ways: by instantaneous changes of the spin frequency of the inner and outer boundaries, and by instantaneous recoupling of the fluid components in the bulk. All simulations are performed with strong and weak mutual friction. It is found that the maximum size of a glitch originating in the bulk decreases as the mutual friction strengthens. It is also found that mutual friction determines the fraction of the frequency jump which is later recovered, a quantity known as the `healing parameter'. These behaviours may explain some of the diversity in observed glitch recoveries.
Hydrodynamic simulations of pulsar glitch recovery
NASA Astrophysics Data System (ADS)
Howitt, G.; Haskell, B.; Melatos, A.
2016-08-01
Glitches are sudden jumps in the spin frequency of pulsars believed to originate in the superfluid interior of neutron stars. Superfluid flow in a model neutron star is simulated by solving the equations of motion of a two-component superfluid consisting of a viscous proton-electron plasma and an inviscid neutron condensate in a spherical Couette geometry. We examine the response of the model to glitches induced in three different ways: by instantaneous changes of the spin frequency of the inner and outer boundaries, and by instantaneous recoupling of the fluid components in the bulk. All simulations are performed with strong and weak mutual friction. It is found that the maximum size of a glitch originating in the bulk decreases as the mutual friction strengthens. It is also found that mutual friction determines the fraction of the frequency jump which is later recovered, a quantity known as the `healing parameter'. These behaviours may explain some of the diversity in observed glitch recoveries.
Hydrodynamics of penguin wing models
NASA Astrophysics Data System (ADS)
Noca, Flavio; Cuong Duong, Nhut; Herpich, Jerome
2010-11-01
The three-dimensional kinematics of penguin wings were obtained from movie footage in aquariums. A 1:1 scale model of the penguin wing (with an identical planform but with a flat section profile and a rigid configuration) was actuated with a robotic arm in a water channel. The experiments were performed at a chord Reynolds number of about 10^4 (an order of magnitude lower than for the observed penguin). The dynamics of the wing were analyzed with force and flowfield measurements. The two main results are: 1. a net thrust on both the upstroke and downstroke movement; 2. the occurence of a leading edge vortex (LEV) along the wing span. The effects of section profile, wing flexibility, and a higher Reynolds number will be investigated in the future.
Instability of streamwise vortices in plane channel flows
NASA Technical Reports Server (NTRS)
Coughlin, K.; Jimenez, J.; Moser, R. D.
1994-01-01
We present analysis and numerical experiments on the instability of streamwise vortices in 'minimal channel' flows and argue that this instability is a key feature in the observed intermittent cycle of formation, break-up, and re-formation of these structures. The base flow is a three-component, two-dimensional pair of counter-rotating rolls with axes aligned along the direction of the mean shear. While it is not a steady solution to the Navier-Stokes equations, we show numerically that this flow is unstable on a fast time scale to a secondary, three-dimensional Floquet mode. The growth of the secondary instability does not saturate in a new equilibrium, but continues until highly unstable local shear layers form and the entire flow breaks down into turbulence. Our analysis is motivated in part by the strong similarities between the intermittent turbulent cycle in minimal channel flows and one studied, both experimentally and in computations, in Couette-Taylor flow.
New formulation of leading order anisotropic hydrodynamics
NASA Astrophysics Data System (ADS)
Tinti, Leonardo
2015-05-01
Anisotropic hydrodynamics is a reorganization of the relativistic hydrodynamics expansion, with the leading order already containing substantial momentum-space anisotropies. The latter are a cause of concern in the traditional viscous hydrodynamics, since large momentum anisotropies generated in ultrarelativistic heavy-ion collisions are not consistent with the hypothesis of small deviations from an isotropic background, i.e., from the local equilibrium distribution. We discuss the leading order of the expansion, presenting a new formulation for the (1+1)- dimensional case, namely, for the longitudinally boost invariant and cylindrically symmetric flow. This new approach is consistent with the well established framework of Israel and Stewart in the close to equilibrium limit (where we expect viscous hydrodynamics to work well). If we consider the (0+1)-dimensional case, that is, transversally homogeneous and longitudinally boost invariant flow, the new form of anisotropic hydrodynamics leads to better agreement with known solutions of the Boltzmann equation than the previous formulations, especially when we consider massive particles.
Hydrodynamic modulation of pluripotent stem cells
2012-01-01
Controlled expansion and differentiation of pluripotent stem cells (PSCs) using reproducible, high-throughput methods could accelerate stem cell research for clinical therapies. Hydrodynamic culture systems for PSCs are increasingly being used for high-throughput studies and scale-up purposes; however, hydrodynamic cultures expose PSCs to complex physical and chemical environments that include spatially and temporally modulated fluid shear stresses and heterogeneous mass transport. Furthermore, the effects of fluid flow on PSCs cannot easily be attributed to any single environmental parameter since the cellular processes regulating self-renewal and differentiation are interconnected and the complex physical and chemical parameters associated with fluid flow are thus difficult to independently isolate. Regardless of the challenges posed by characterizing fluid dynamic properties, hydrodynamic culture systems offer several advantages over traditional static culture, including increased mass transfer and reduced cell handling. This article discusses the challenges and opportunities of hydrodynamic culture environments for the expansion and differentiation of PSCs in microfluidic systems and larger-volume suspension bioreactors. Ultimately, an improved understanding of the effects of hydrodynamics on the self-renewal and differentiation of PSCs could yield improved bioprocessing technologies to attain scalable PSC culture strategies that will probably be requisite for the development of therapeutic and diagnostic applications. PMID:23168068
Hydrodynamic approaches in relativistic heavy ion reactions
NASA Astrophysics Data System (ADS)
Derradi de Souza, R.; Koide, T.; Kodama, T.
2016-01-01
We review several facets of the hydrodynamic description of the relativistic heavy ion collisions, starting from the historical motivation to the present understandings of the observed collective aspects of experimental data, especially those of the most recent RHIC and LHC results. In this report, we particularly focus on the conceptual questions and the physical foundations of the validity of the hydrodynamic approach itself. We also discuss recent efforts to clarify some of the points in this direction, such as the various forms of derivations of relativistic hydrodynamics together with the limitations intrinsic to the traditional approaches, variational approaches, known analytic solutions for special cases, and several new theoretical developments. Throughout this review, we stress the role of course-graining procedure in the hydrodynamic description and discuss its relation to the physical observables through the analysis of a hydrodynamic mapping of a microscopic transport model. Several questions to be answered to clarify the physics of collective phenomena in the relativistic heavy ion collisions are pointed out.
Applications of 3D hydrodynamic and particle tracking models in the San Francisco bay-delta estuary
Smith, P.E.; Donovan, J.M.; Wong, H.F.N.
2005-01-01
Three applications of three-dimensional hydrodynamic and particle-tracking models are currently underway by the United States Geological Survey in the San Francisco Bay-Delta Estuary. The first application is to the San Francisco Bay and a portion of the coastal ocean. The second application is to an important, gated control channel called the Delta Cross Channel, located within the northern portion of the Sacramento-San Joaquin River Delta. The third application is to a reach of the San Joaquin River near Stockton, California where a significant dissolved oxygen problem exists due, in part, to conditions associated with the deep-water ship channel for the Port of Stockton, California. This paper briefly discusses the hydrodynamic and particle tracking models being used and the three applications. Copyright ASCE 2005.
Hydrodynamics of a unitary Bose gas
NASA Astrophysics Data System (ADS)
Man, Jay; Fletcher, Richard; Lopes, Raphael; Navon, Nir; Smith, Rob; Hadzibabic, Zoran
2016-05-01
In general, normal-phase Bose gases are well described by modelling them as ideal gases. In particular, hydrodynamic flow is usually not observed in the expansion dynamics of normal gases, and is more readily observable in Bose-condensed gases. However, by preparing strongly-interacting clouds, we observe hydrodynamic behaviour in normal-phase Bose gases, including the `maximally' hydrodynamic unitary regime. We avoid the atom losses that often hamper experimental access of this regime by using radio-frequency injection, which switches on interactions much faster than trap or loss timescales. At low phase-space densities, we find excellent agreement with a collisional model based on the Boltzmann equation. At higher phase-space densities our results show a deviation from this model in the vicinity of an Efimov resonance, which cannot be accounted for by measured losses.
Dynamo efficiency controlled by hydrodynamic bistability.
Miralles, Sophie; Herault, Johann; Herault, Johann; Fauve, Stephan; Gissinger, Christophe; Pétrélis, François; Daviaud, François; Dubrulle, Bérengère; Boisson, Jean; Bourgoin, Mickaël; Verhille, Gautier; Odier, Philippe; Pinton, Jean-François; Plihon, Nicolas
2014-06-01
Hydrodynamic and magnetic behaviors in a modified experimental setup of the von Kármán sodium flow-where one disk has been replaced by a propeller-are investigated. When the rotation frequencies of the disk and the propeller are different, we show that the fully turbulent hydrodynamic flow undergoes a global bifurcation between two configurations. The bistability of these flow configurations is associated with the dynamics of the central shear layer. The bistable flows are shown to have different dynamo efficiencies; thus for a given rotation rate of the soft-iron disk, two distinct magnetic behaviors are observed depending on the flow configuration. The hydrodynamic transition controls the magnetic field behavior, and bifurcations between high and low magnetic field branches are investigated. PMID:25019895
Hydrodynamic stellar interactions in dense star clusters
NASA Technical Reports Server (NTRS)
Rasio, Frederic A.
1993-01-01
Highly detailed HST observations of globular-cluster cores and galactic nuclei motivate new theoretical studies of the violent dynamical processes which govern the evolution of these very dense stellar systems. These processes include close stellar encounters and direct physical collisions between stars. Such hydrodynamic stellar interactions are thought to explain the large populations of blue stragglers, millisecond pulsars, X-ray binaries, and other peculiar sources observed in globular clusters. Three-dimensional hydrodynamics techniques now make it possible to perform realistic numerical simulations of these interactions. The results, when combined with those of N-body simulations of stellar dynamics, should provide for the first time a realistic description of dense star clusters. Here I review briefly current theoretical work on hydrodynamic stellar interactions, emphasizing its relevance to recent observations.
A hydrodynamic approach to cosmology - Methodology
NASA Technical Reports Server (NTRS)
Cen, Renyue
1992-01-01
The present study describes an accurate and efficient hydrodynamic code for evolving self-gravitating cosmological systems. The hydrodynamic code is a flux-based mesh code originally designed for engineering hydrodynamical applications. A variety of checks were performed which indicate that the resolution of the code is a few cells, providing accuracy for integral energy quantities in the present simulations of 1-3 percent over the whole runs. Six species (H I, H II, He I, He II, He III) are tracked separately, and relevant ionization and recombination processes, as well as line and continuum heating and cooling, are computed. The background radiation field is simultaneously determined in the range 1 eV to 100 keV, allowing for absorption, emission, and cosmological effects. It is shown how the inevitable numerical inaccuracies can be estimated and to some extent overcome.
Hydrodynamics of bacterial colonies: A model
NASA Astrophysics Data System (ADS)
Lega, J.; Passot, T.
2003-03-01
We propose a hydrodynamic model for the evolution of bacterial colonies growing on soft agar plates. This model consists of reaction-diffusion equations for the concentrations of nutrients, water, and bacteria, coupled to a single hydrodynamic equation for the velocity field of the bacteria-water mixture. It captures the dynamics inside the colony as well as on its boundary and allows us to identify a mechanism for collective motion towards fresh nutrients, which, in its modeling aspects, is similar to classical chemotaxis. As shown in numerical simulations, our model reproduces both usual colony shapes and typical hydrodynamic motions, such as the whirls and jets recently observed in wet colonies of Bacillus subtilis. The approach presented here could be extended to different experimental situations and provides a general framework for the use of advection-reaction-diffusion equations in modeling bacterial colonies.
Hydrodynamic instability in warped astrophysical discs
NASA Astrophysics Data System (ADS)
Ogilvie, Gordon I.; Latter, Henrik N.
2013-08-01
Warped astrophysical discs are usually treated as laminar viscous flows, which have anomalous properties when the disc is nearly Keplerian and the viscosity is small: fast horizontal shearing motions and large torques are generated, which cause the warp to evolve rapidly, in some cases at a rate that is inversely proportional to the viscosity. However, these flows are often subject to a linear hydrodynamic instability, which may produce small-scale turbulence and modify the large-scale dynamics of the disc. We use a warped shearing sheet to compute the oscillatory laminar flows in a warped disc and to analyse their linear stability by the Floquet method. We find widespread hydrodynamic instability deriving from the parametric resonance of inertial waves. Even very small, unobservable warps in nearly Keplerian discs of low viscosity can be expected to generate hydrodynamic turbulence, or at least wave activity, by this mechanism.
Toward a Fully Consistent Radiation Hydrodynamics
Castor, J I
2009-07-07
Dimitri Mihalas set the standard for all work in radiation hydrodynamics since 1984. The present contribution builds on 'Foundations of Radiation Hydrodynamics' to explore the relativistic effects that have prevented having a consistent non-relativistic theory. Much of what I have to say is in FRH, but the 3-D development is new. Results are presented for the relativistic radiation transport equation in the frame obtained by a Lorentz boost with the fluid velocity, and the exact momentum-integrated moment equations. The special-relativistic hydrodynamic equations are summarized, including the radiation contributions, and it is shown that exact conservation is obtained, and certain puzzles in the non-relativistic radhydro equations are explained.
Radiation hydrodynamics integrated in the PLUTO code
NASA Astrophysics Data System (ADS)
Kolb, Stefan M.; Stute, Matthias; Kley, Wilhelm; Mignone, Andrea
2013-11-01
Aims: The transport of energy through radiation is very important in many astrophysical phenomena. In dynamical problems the time-dependent equations of radiation hydrodynamics have to be solved. We present a newly developed radiation-hydrodynamics module specifically designed for the versatile magnetohydrodynamic (MHD) code PLUTO. Methods: The solver is based on the flux-limited diffusion approximation in the two-temperature approach. All equations are solved in the co-moving frame in the frequency-independent (gray) approximation. The hydrodynamics is solved by the different Godunov schemes implemented in PLUTO, and for the radiation transport we use a fully implicit scheme. The resulting system of linear equations is solved either using the successive over-relaxation (SOR) method (for testing purposes) or using matrix solvers that are available in the PETSc library. We state in detail the methodology and describe several test cases to verify the correctness of our implementation. The solver works in standard coordinate systems, such as Cartesian, cylindrical, and spherical, and also for non-equidistant grids. Results: We present a new radiation-hydrodynamics solver coupled to the MHD-code PLUTO that is a modern, versatile, and efficient new module for treating complex radiation hydrodynamical problems in astrophysics. As test cases, either purely radiative situations, or full radiation-hydrodynamical setups (including radiative shocks and convection in accretion disks) were successfully studied. The new module scales very well on parallel computers using MPI. For problems in star or planet formation, we added the possibility of irradiation by a central source.
NASA Technical Reports Server (NTRS)
Baker, Victor R.
1988-01-01
The geomorphology of Mars is discussed, focusing on the Martian channels. The great flood channels of Mars, the processes of channel erosion, and dendritic channel networks, are examined. The topography of the Channeled Scabland region of the northwestern U.S. is described and compared to the Martian channels. The importance of water in the evolution of the channel systems is considered.
Hydrodynamics and eutrophication in a mariculture site in the Philippines
NASA Astrophysics Data System (ADS)
Escobar, M. T.; San Diego-McGlone, M. L.; Martin, M.; Villanoy, C.
2014-12-01
Bolinao, Pangasinan in the Philippines is a site for extensive and intensive culture of Chanos chanos. The proliferation of fish farm structures coupled with excessive feeding caused the deterioration of water quality in the area that lead to hypoxic condition (<2mg/L) and fish kills. A hydrodynamic model of the area, developed using DELFT3D, showed a residence time of 5-15 days in the northern channel and 25 to 28 days in the southern end. The complex configuration of the coast, which includes narrow channels that serve as bottlenecks, result to the inefficient flushing of the area. This was further aggravated by the presence of fish farm structures that restricted the natural flow of water. Water quality was monitored in the mariculture site and a nearby seagrass reserve. Nitrate+nitrite concentration ranged from 0.34 - 4.1 µM, 0.13 - 2.7 µM for phosphate, and 1.7 - 8.8 µM for ammonia. Highest nutrient concentrations were seen near the fish farms. Analysis of nutrients, chlorophyll-a and tss for a tidal cycle showed that these substances were inadequately flushed from the coastal waters. Long residence times and high nutrient loading in the area were ideal conditions for the development of hypoxia.
Shadowfax: Moving mesh hydrodynamical integration code
NASA Astrophysics Data System (ADS)
Vandenbroucke, Bert
2016-05-01
Shadowfax simulates galaxy evolution. Written in object-oriented modular C++, it evolves a mixture of gas, subject to the laws of hydrodynamics and gravity, and any collisionless fluid only subject to gravity, such as cold dark matter or stars. For the hydrodynamical integration, it makes use of a (co-) moving Lagrangian mesh. The code has a 2D and 3D version, contains utility programs to generate initial conditions and visualize simulation snapshots, and its input/output is compatible with a number of other simulation codes, e.g. Gadget2 (ascl:0003.001) and GIZMO (ascl:1410.003).
Scaling laws in chiral hydrodynamic turbulence
NASA Astrophysics Data System (ADS)
Yamamoto, Naoki
2016-06-01
We study the turbulent regime of chiral (magneto)hydrodynamics for charged and neutral matter with chirality imbalance. We find that the chiral magnetohydrodynamics for charged plasmas possesses a unique scaling symmetry, only without fluid helicity under the local charge neutrality. We also find a different type of unique scaling symmetry in the chiral hydrodynamics for neutral matter with fluid helicity in the inertial range. We show that these symmetries dictate the self-similar inverse cascade of the magnetic and kinetic energies. Our results imply the possible inverse energy cascade in core-collapse supernovae due to the chiral transport of neutrinos.
The quantum hydrodynamic model for semiconductor devices
NASA Astrophysics Data System (ADS)
Gardner, Carl L.
1995-02-01
Quantum semiconductor devices are playing an increasingly important role in advanced microelectronic applications, including multiple-state logic and memory devices. To model quantum devices, the classical hydrodynamic model for semiconductor devices can be extended to include O(h(2)) quantum corrections. This proposal focused on theoretical and computational investigations of the flow of electrons in semiconductor devices based on the quantum hydrodynamic model. The development of efficient, robots numerical methods for the QHD model in one and two spatial dimensions we also emphasized.
Hydrodynamic Simulations with the Godunov SPH
NASA Astrophysics Data System (ADS)
Borgani, S.; Murante, G.; Brunino, R.; Cha, S.-H.
2012-07-01
We present results based on an implementation of the Godunov Smoothed Particle Hydrodynamics (GSPH). We carry out controlled hydrodynamical three-dimensional tests, namely the Sod shock tube and the development of Kelvin-Helmholtz instabilities in a shear flow test. The results of our tests demonstrate GSPH provides a much improved description of contact discontinuities, with respect to SPH, and is able to follow the development of gas-dynamical instabilities, such as the Kevin-Helmholtz and the Rayleigh-Taylor ones.
Bounce-free spherical hydrodynamic implosion
Kagan, Grigory; Tang Xianzhu; Hsu, Scott C.; Awe, Thomas J.
2011-12-15
In a bounce-free spherical hydrodynamic implosion, the post-stagnation hot core plasma does not expand against the imploding flow. Such an implosion scheme has the advantage of improving the dwell time of the burning fuel, resulting in a higher fusion burn-up fraction. The existence of bounce-free spherical implosions is demonstrated by explicitly constructing a family of self-similar solutions to the spherically symmetric ideal hydrodynamic equations. When applied to a specific example of plasma liner driven magneto-inertial fusion, the bounce-free solution is found to produce at least a factor of four improvement in dwell time and fusion energy gain.
Supernova hydrodynamics experiments using the Nova laser
Remington, B.A.; Glendinning, S.G.; Estabrook, K.; Wallace, R.J.; Rubenchik, A.; Kane, J.; Arnett, D.; Drake, R.P.; McCray, R.
1997-04-01
We are developing experiments using the Nova laser to investigate two areas of physics relevant to core-collapse supernovae (SN): (1) compressible nonlinear hydrodynamic mixing and (2) radiative shock hydrodynamics. In the former, we are examining the differences between the 2D and 3D evolution of the Rayleigh-Taylor instability, an issue critical to the observables emerging from SN in the first year after exploding. In the latter, we are investigating the evolution of a colliding plasma system relevant to the ejecta-stellar wind interactions of the early stages of SN remnant formation. The experiments and astrophysical implications are discussed.
NASA Technical Reports Server (NTRS)
2007-01-01
[figure removed for brevity, see original site] Figure 1
Translucent carbon dioxide ice covers the polar regions of Mars seasonally. It is warmed and sublimates (evaporates) from below, and escaping gas carves a numerous channel morphologies.
In this example (figure 1) the channels form a 'starburst' pattern, radiating out into feathery extensions. The center of the pattern is being buried with dust and new darker dust fans ring the outer edges. This may be an example of an expanding morphology, where new channels are formed as the older ones fill and are no longer efficiently channeling the subliming gas out.
Observation Geometry Image PSP_003443_0980 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 21-Apr-2007. The complete image is centered at -81.8 degrees latitude, 76.2 degrees East longitude. The range to the target site was 247.1 km (154.4 miles). At this distance the image scale is 24.7 cm/pixel (with 1 x 1 binning) so objects 74 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel. The image was taken at a local Mars time of 04:52 PM and the scene is illuminated from the west with a solar incidence angle of 71 degrees, thus the sun was about 19 degrees above the horizon. At a solar longitude of 223.4 degrees, the season on Mars is Northern Autumn.
Modeling the tidal and sub-tidal hydrodynamics in a shallow, micro-tidal estuary
NASA Astrophysics Data System (ADS)
Rayson, Matthew D.; Gross, Edward S.; Fringer, Oliver B.
2015-05-01
The three-dimensional hydrodynamics of Galveston Bay were simulated in two periods of several month duration. The physical setting of Galveston Bay is described by synthesis of long-term observations. Several processes in addition to tidal hydrodynamics and baroclinic circulation processes contribute substantially to the observed variability of currents, water level and salinity. The model was therefore forced with realistic water levels, river discharges, winds, coastal buoyancy currents (due to the Mississippi River plume) and surface heat fluxes. Quantitative metrics were used to evaluate model performance against observations and both spatial and temporal variability in tidal and sub-tidal hydrodynamics were generally well represented by the model. Three different unstructured meshes were tested, a triangular mesh that under-resolved the shipping channel, a triangular mesh that resolved it, and a mixed quadrilateral-triangular grid with approximately equivalent resolution. It is shown that salinity and sub-tidal velocity are better predicted when the important topographic features, such as the shipping channel, are resolved. It was necessary to increase the seabed drag roughness in the mixed quadrilateral-triangular grid simulation to attain similar performance to the equivalent triangular mesh.
(Non)-dissipative hydrodynamics on embedded surfaces
NASA Astrophysics Data System (ADS)
Armas, Jay
2014-09-01
We construct the theory of dissipative hydrodynamics of uncharged fluids living on embedded space-time surfaces to first order in a derivative expansion in the case of codimension-1 surfaces (including fluid membranes) and the theory of non-dissipative hydrodynamics to second order in a derivative expansion in the case of codimension higher than one under the assumption of no angular momenta in transverse directions to the surface. This construction includes the elastic degrees of freedom, and hence the corresponding transport coefficients, that take into account transverse fluctuations of the geometry where the fluid lives. Requiring the second law of thermodynamics to be satisfied leads us to conclude that in the case of codimension-1 surfaces the stress-energy tensor is characterized by 2 hydrodynamic and 1 elastic independent transport coefficient to first order in the expansion while for codimension higher than one, and for non-dissipative flows, the stress-energy tensor is characterized by 7 hydrodynamic and 3 elastic independent transport coefficients to second order in the expansion. Furthermore, the constraints imposed between the stress-energy tensor, the bending moment and the entropy current of the fluid by these extra non-dissipative contributions are fully captured by equilibrium partition functions. This analysis constrains the Young modulus which can be measured from gravity by elastically perturbing black branes.
Boundary conditions in tunneling via quantum hydrodynamics
NASA Technical Reports Server (NTRS)
Nassar, Antonio B.
1993-01-01
Via the hydrodynamical formulation of quantum mechanics, an approach to the problem of tunneling through sharp-edged potential barriers is developed. Above all, it is shown how more general boundary conditions follow from the continuity of mass, momentum, and energy.
Hydrodynamic Issues in PAMS Mandrel Target Fabrication
McQuillan, B M; Paguio, R; Subramanian, P; Takagi, M; Zebib, A
2003-08-27
Imperfections in PAMS mandrels critically govern the quality of final ICF targets. Imperfections in the mandrels can have a wide range of origins. Here, they present observations of 3 types of imperfections, and data to support the proposal that hydrodynamic factors during the curing of the mandrel are potential causes of these imperfections.
HYDRODYNAMIC ISSUES IN PAMS MANDREL TARGET FABRICATION
McQUILLAN,B.W; PAGUIO,R; SUBRAMANIAN,P; TAKAGI,M; ZEBIB,A
2003-09-01
OAK-B135 Imperfections in PAMS mandrels critically govern the quality of final ICF targets. Imperfections in the mandrels can have a wide range of origins. Here, they present observations of 3 types of imperfections, and data to support the proposal that hydrodynamic factors during the curing of the mandrel are potential causes of these imperfections.
An analytical description of hydrodynamic instabilities
NASA Astrophysics Data System (ADS)
Bulanov, S. V.; Sasorov, P. V.
The proper approach to the investigation of the nonlinear stage of hydrodynamic instabilities in a plasma has been discussed. Both the Buneman instability and the beam instability have been considered. A similarity between the nonlinear stage of the beam plasma instability and the process of self-modulation and self-focusing of nonlinear waves is revealed.
Stabilizing geometry for hydrodynamic rotary seals
Dietle, Lannie L.; Schroeder, John E.
2010-08-10
A hydrodynamic sealing assembly including a first component having first and second walls and a peripheral wall defining a seal groove, a second component having a rotatable surface relative to said first component, and a hydrodynamic seal comprising a seal body of generally ring-shaped configuration having a circumference. The seal body includes hydrodynamic and static sealing lips each having a cross-sectional area that substantially vary in time with each other about the circumference. In an uninstalled condition, the seal body has a length defined between first and second seal body ends which varies in time with the hydrodynamic sealing lip cross-sectional area. The first and second ends generally face the first and second walls, respectively. In the uninstalled condition, the first end is angulated relative to the first wall and the second end is angulated relative to the second wall. The seal body has a twist-limiting surface adjacent the static sealing lip. In the uninstalled condition, the twist-limiting surface is angulated relative to the peripheral wall and varies along the circumference. A seal body discontinuity and a first component discontinuity mate to prevent rotation of the seal body relative to the first component.
Chiral Magnetic Effect in Hydrodynamic Approximation
NASA Astrophysics Data System (ADS)
Zakharov, Valentin I.
We review derivations of the chiral magnetic effect (ChME) in hydrodynamic approximation. The reader is assumed to be familiar with the basics of the effect. The main challenge now is to account for the strong interactions between the constituents of the fluid. The main result is that the ChME is not renormalized: in the hydrodynamic approximation it remains the same as for non-interacting chiral fermions moving in an external magnetic field. The key ingredients in the proof are general laws of thermodynamics and the Adler-Bardeen theorem for the chiral anomaly in external electromagnetic fields. The chiral magnetic effect in hydrodynamics represents a macroscopic manifestation of a quantum phenomenon (chiral anomaly). Moreover, one can argue that the current induced by the magnetic field is dissipation free and talk about a kind of "chiral superconductivity". More precise description is a quantum ballistic transport along magnetic field taking place in equilibrium and in absence of a driving force. The basic limitation is the exact chiral limit while temperature—excitingly enough—does not seemingly matter. What is still lacking, is a detailed quantum microscopic picture for the ChME in hydrodynamics. Probably, the chiral currents propagate through lower-dimensional defects, like vortices in superfluid. In case of superfluid, the prediction for the chiral magnetic effect remains unmodified although the emerging dynamical picture differs from the standard one.
Hydrodynamic dispersion of microswimmers in suspension
NASA Astrophysics Data System (ADS)
Martin, Matthieu; Rafaï, Salima; Peyla, Philippe
2014-11-01
In our laboratory, we study hydrodynamics of suspensions of micro-swimmers. These micro-organisms are unicellular algae Chlamydomonas Rheinhardii which are able to swim by using their flagella. The swimming dynamics of these micro-swimmers can be seen as a random walk, in absence of any kind of interaction. In addition, these algae have the property of being phototactic, i.e. they swim towards the light. Combining this property with a hydrodynamic flow, we were able to reversibly separate algae from the rest of the fluid. But for sufficiently high volume fraction, these active particles interact with each other. We are now interested in how the coupling of hydrodynamic interactions between swimmers and phototaxis can modify the swimming dynamics at the scale of the suspension. To this aim, we conduct experiments in microfluidic devices to study the dispersion of the micro-organisms in a the liquid phase as a function of the volume fraction. We show that the dispersion of an assembly of puller type microswimmers is quantitatively affected by hydrodynamics interactions. Phd student.
Hydrodynamically Driven Colloidal Assembly in Dip Coating
NASA Astrophysics Data System (ADS)
Colosqui, Carlos E.; Morris, Jeffrey F.; Stone, Howard A.
2013-05-01
We study the hydrodynamics of dip coating from a suspension and report a mechanism for colloidal assembly and pattern formation on smooth substrates. Below a critical withdrawal speed where the coating film is thinner than the particle diameter, capillary forces induced by deformation of the free surface prevent the convective transport of single particles through the meniscus beneath the film. Capillary-induced forces are balanced by hydrodynamic drag only after a minimum number of particles assemble within the meniscus. The particle assembly can thus enter the thin film where it moves at nearly the withdrawal speed and rapidly separates from the next assembly. The interplay between hydrodynamic and capillary forces produces periodic and regular structures below a critical ratio Ca2/3/Bo<0.7, where Ca and Bo are the capillary and Bond numbers, respectively. An analytical model and numerical simulations are presented for the case of two-dimensional flow with circular particles in suspension. The hydrodynamically driven assembly documented here is consistent with stripe pattern formations observed experimentally in dip coating.
Thermodynamics, Hydrodynamics and Damping in Ultracold Gases
NASA Astrophysics Data System (ADS)
Chafin, Clifford
Ultracold gases have provided experimental systems that span microscopic to macroscopic regimes of behavior and over a range of internal energy scales and interaction strengths that drive behavior from ballistic to hydrodynamic and degenerate to correlated. Here we will examine these systems from several points of view. First, we present a discussion from the standpoint of the evolution of a single many body wavefunction. In support of this picture we examine the longstanding vagueness surrounding measurement and thermalization and show the situation here is significantly better from this point of view than generally presented. The implications for how well defined a temperature can be achieved by various trap manipulation is discussed along with proposed experiments to distinguish these cases. Since hydrodynamic methods have worked well in some cases we then discuss the unitary limit for fermions with contact limited interactions. The scale invariance of the system implies limits on hydrodynamic behavior from which we extract bounds on viscous damping from free expansion and trap oscillation experiments. Linear response theory is used to probe the effect of quantum fluctuations on the viscosity and some nonuniversal contributions are derived. These show that the classical gradient expansion of hydrodynamics breaks down at lower than Burnett order, where problems with the classical expansions typically occur.
Effective hydrodynamics of black D3-branes
NASA Astrophysics Data System (ADS)
Emparan, Roberto; Hubeny, Veronika E.; Rangamani, Mukund
2013-06-01
The long-wavelength effective field theory of world-volume fluctuations of black D3-branes is shown to be a hydrodynamical system to leading order in a gradient expansion. We study the system on a fiducial `cutoff' surface: the fluctuating geometry imprints its dynamics on the surface via an induced stress tensor whose conservation encapsulates the hydrodynamical description. For a generic non-extremal D3-brane, as we move our cutoff surface from the asymptotically flat near-boundary region to the near-horizon region, this hydrodynamical system interpolates between a non-conformal relativistic fluid and a non-relativistic incompressible fluid. We also consider the dependence on the deviation from extremality of the D3-branes. In the near-extremal case we recover the description in terms of a conformal relativistic fluid encountered in the AdS/CFT context. We argue that this system allows us therefore to explore the various connections that have hitherto been suggested relating the dynamics of gravitational systems and fluid dynamics. In particular, we go on to show that the blackfold effective field theory approach allows us to capture this hydrodynamical behaviour and moreover subsumes the constructions encountered in the fluid/gravity correspondence and the black hole membrane paradigm, providing thereby a universal language to explore the effective dynamics of black branes.
Simulating Brownian suspensions with fluctuating hydrodynamics
NASA Astrophysics Data System (ADS)
Delmotte, Blaise; Keaveny, Eric E.
2015-12-01
Fluctuating hydrodynamics has been successfully combined with several computational methods to rapidly compute the correlated random velocities of Brownian particles. In the overdamped limit where both particle and fluid inertia are ignored, one must also account for a Brownian drift term in order to successfully update the particle positions. In this paper, we present an efficient computational method for the dynamic simulation of Brownian suspensions with fluctuating hydrodynamics that handles both computations and provides a similar approximation as Stokesian Dynamics for dilute and semidilute suspensions. This advancement relies on combining the fluctuating force-coupling method (FCM) with a new midpoint time-integration scheme we refer to as the drifter-corrector (DC). The DC resolves the drift term for fluctuating hydrodynamics-based methods at a minimal computational cost when constraints are imposed on the fluid flow to obtain the stresslet corrections to the particle hydrodynamic interactions. With the DC, this constraint needs only to be imposed once per time step, reducing the simulation cost to nearly that of a completely deterministic simulation. By performing a series of simulations, we show that the DC with fluctuating FCM is an effective and versatile approach as it reproduces both the equilibrium distribution and the evolution of particulate suspensions in periodic as well as bounded domains. In addition, we demonstrate that fluctuating FCM coupled with the DC provides an efficient and accurate method for large-scale dynamic simulation of colloidal dispersions and the study of processes such as colloidal gelation.
Simple Waves in Ideal Radiation Hydrodynamics
Johnson, B M
2008-09-03
In the dynamic diffusion limit of radiation hydrodynamics, advection dominates diffusion; the latter primarily affects small scales and has negligible impact on the large scale flow. The radiation can thus be accurately regarded as an ideal fluid, i.e., radiative diffusion can be neglected along with other forms of dissipation. This viewpoint is applied here to an analysis of simple waves in an ideal radiating fluid. It is shown that much of the hydrodynamic analysis carries over by simply replacing the material sound speed, pressure and index with the values appropriate for a radiating fluid. A complete analysis is performed for a centered rarefaction wave, and expressions are provided for the Riemann invariants and characteristic curves of the one-dimensional system of equations. The analytical solution is checked for consistency against a finite difference numerical integration, and the validity of neglecting the diffusion operator is demonstrated. An interesting physical result is that for a material component with a large number of internal degrees of freedom and an internal energy greater than that of the radiation, the sound speed increases as the fluid is rarefied. These solutions are an excellent test for radiation hydrodynamic codes operating in the dynamic diffusion regime. The general approach may be useful in the development of Godunov numerical schemes for radiation hydrodynamics.
Livermore Unstructured Lagrange Explicit Shock Hydrodynamics
Energy Science and Technology Software Center (ESTSC)
2010-09-21
LULESH v1.0 is a 3D unstructured Lagrange hydrodynamics simulation written specifically to solve a standard analytical test problem, known as the Sedov problem. In this problem, a quantum of energy is deposited into a gas and propagates through the gas over time.
Testing different formulations of leading-order anisotropic hydrodynamics
NASA Astrophysics Data System (ADS)
Tinti, Leonardo; Ryblewski, Radoslaw; Florkowski, Wojciech; Strickland, Michael
2016-02-01
A recently obtained set of the equations for leading-order (3+1)D anisotropic hydrodynamics is tested against exact solutions of the Boltzmann equation with the collisional kernel treated in the relaxation time approximation. In order to perform detailed comparisons, the new anisotropic hydrodynamics equations are reduced to the boost-invariant and transversally homogeneous case. The agreement with the exact solutions found using the new anisotropic hydrodynamics equations is similar to that found using previous, less general formulations of anisotropic hydrodynamics. In addition, we find that, when compared to a state-of-the-art second-order viscous hydrodynamics framework, leading-order anisotropic hydrodynamics better reproduces the exact solution for the pressure anisotropy and gives comparable results for the bulk pressure evolution. Finally, we compare the transport coefficients obtained using linearized anisotropic hydrodynamics with results obtained using second-order viscous hydrodynamics.
NASA Astrophysics Data System (ADS)
Rinaldo, Andrea; Rodriguez-Iturbe, Ignacio; Rigon, Riccardo
This review proceeds from Luna Leopold's and Ronald Shreve's lasting accomplishments dealing with the study of random-walk and topologically random channel networks. According to the random perspective, which has had a profound influence on the interpretation of natural landforms, nature's resiliency in producing recurrent networks and landforms was interpreted to be the consequence of chance. In fact, central to models of topologically random networks is the assumption of equal likelihood of any tree-like configuration. However, a general framework of analysis exists that argues that all possible network configurations draining a fixed area are not necessarily equally likely. Rather, a probability P(s) is assigned to a particular spanning tree configuration, say s, which can be generally assumed to obey a Boltzmann distribution: P(s) % e^-H(s)/T, where T is a parameter and H(s) is a global property of the network configuration s related to energetic characters, i.e. its Hamiltonian. One extreme case is the random topology model where all trees are equally likely, i.e. the limit case for T6 4 . The other extreme case is T 6 0, and this corresponds to network configurations that tend to minimize their total energy dissipation to improve their likelihood. Networks obtained in this manner are termed optimal channel networks (OCNs). Observational evidence suggests that the characters of real river networks are reproduced extremely well by OCNs. Scaling properties of energy and entropy of OCNs suggest that large network development is likely to effectively occur at zero temperature (i.e. minimizing its Hamiltonian). We suggest a corollary of dynamic accessibility of a network configuration and speculate towards a thermodynamics of critical self-organization. We thus conclude that both chance and necessity are equally important ingredients for the dynamic origin of channel networks---and perhaps of the geometry of nature.
NASA Astrophysics Data System (ADS)
Durand, Michael; Andreadis, Konstantinos M.; Alsdorf, Douglas E.; Lettenmaier, Dennis P.; Moller, Delwyn; Wilson, Matthew
2008-10-01
The proposed Surface Water and Ocean Topography (SWOT) mission would provide measurements of water surface elevation (WSE) for characterization of storage change and discharge. River channel bathymetry is a significant source of uncertainty in estimating discharge from WSE measurements, however. In this paper, we demonstrate an ensemble-based data assimilation (DA) methodology for estimating bathymetric depth and slope from WSE measurements and the LISFLOOD-FP hydrodynamic model. We performed two proof-of-concept experiments using synthetically generated SWOT measurements. The experiments demonstrated that bathymetric depth and slope can be estimated to within 3.0 microradians or 50 cm, respectively, using SWOT WSE measurements, within the context of our DA and modeling framework. We found that channel bathymetry estimation accuracy is relatively insensitive to SWOT measurement error, because uncertainty in LISFLOOD-FP inputs (such as channel roughness and upstream boundary conditions) is likely to be of greater magnitude than measurement error.
Hydrodynamic comparison between the north and south of Mallorca Island
NASA Astrophysics Data System (ADS)
Amores, Angel; Monserrat, Sebastià
2014-10-01
A hydrodynamic comparison between two zones of fishing interest, one located to the north and the other to the south of Mallorca Island (Balearic Islands, Western Mediterranean) was done. The comparison was conducted using the data from two moorings, one placed in the middle of the Balearic Current, in the Balearic subbasin (herein, Sóller) and the other in the Mallorca Channel, near the Algerian subbasin (called Cabrera). The instruments moored, continuously recorded the temperature, salinity and currents at different depths, for over 15 months. The data analysis suggests that Sóller is hydrodynamically more active than Cabrera, at least during the time of recording the measurements. The mean currents were higher at Sóller than at Cabrera at all depths, also showing greater maximum speeds and variability. In addition, the presence of more mesoscale eddies in Sóller became evident from the altimetry data. These eddies were not only significantly more energetic near the surface, they also generally reached to greater depths, affecting the velocities of the seabed currents. Subsequent to each significant eddy episode, strong changes in temperature and/or salinity were observed, along the entire water column. Spectral analysis revealed the presence of high frequency oscillations with periods of a few hours. One energy peak, with a period around 3.7 h, was observed at both locations, probably related to trapped waves around Mallorca or the Balearic Islands, while others (3 h and 2 h) were reflected only in Sóller, suggesting they could be associated with some standing resonance waves between the Iberian Peninsula and Mallorca.
Scaling supernova hydrodynamics to the laboratory
Kane, J.O.
1999-06-01
Supernova (SN) 1987A focused attention on the critical role of hydrodynamic instabilities in the evolution of supernovae. To test the modeling of these instabilities, we are developing laboratory experiments of hydrodynamic mixing under conditions relevant to supernovae. Initial results were reported in J. Kane et al., Astrophys. J.478, L75 (1997) The Nova laser is used to shock two-layer targets, producing Richtmyer-Meshkov (RM) and Rayleigh-Taylor (RT) instabilities at the interfaces between the layers, analogous to instabilities seen at the interfaces of SN 1987A. Because the hydrodynamics in the laser experiments at intermediate times (3-40 ns) and in SN 1987A at intermediate times (5 s-10{sup 4} s) are well described by the Euler equations, the hydrodynamics scale between the two regimes. The experiments are modeled using the hydrodynamics codes HYADES and CALE, and the supernova code PROMETHEUS, thus serving as a benchmark for PROMETHEUS. Results of the experiments and simulations are presented. Analysis of the spike and bubble velocities in the experiment using potential flow theory and a modified Ott thin shell theory is presented. A numerical study of 2D vs. 3D differences in instability growth at the O-He and He-H interface of SN 1987A, and the design for analogous laser experiments are presented. We discuss further work to incorporate more features of the SN in the experiments, including spherical geometry, multiple layers and density gradients. Past and ongoing work in laboratory and laser astrophysics is reviewed, including experimental work on supernova remnants (SNRs). A numerical study of RM instability in SNRs is presented.
Ulker, Pinar; Meiselman, Herbert J; Baskurt, Oguz K
2008-01-01
Red blood cells (RBC) are exposed to various levels of shear stresses when they are exposed to artificial flow environments, such as extracorporeal flow circuits and hemodialysis equipment. This mechanical trauma affects RBC and the resulting effect is determined by the magnitude of shear forces and exposure time. It has been previously demonstrated that nitric oxide (NO) donors and potassium channel blockers could prevent the sub-hemolytic damage to RBC, when they are exposed to 120 Pa shear stress in a Couette shearing system. This study aimed at testing the effectiveness of NO donor sodium nitroprussid (SNP, 10⁻⁴ M) and non-specific potassium channel blocker tetraethylammonium (TEA, 10⁻⁷ M) in preventing the mechanical damage to RBC in a simple flow system including a roller pump and a glass capillary of 0.12 cm diameter. RBC suspensions were pumped through the capillary by the roller pump at a flow rate that maintains 200 mmHg hydrostatic pressure at the entrance of the capillary. An aliquot of 10 ml of RBC suspension of 0.4 L/L hematocrit was re-circulated through the capillary for 30 minutes. Plasma hemoglobin concentrations were found to be significantly increased (~7 folds compared to control aliquot which was not pumped through the system) and neither SNP nor TEA prevented this hemolysis. Alternatively, RBC deformability assessed by laser diffraction ektacytometry was not altered after 30 min of pumping and both SNP and TEA had no effect on this parameter. The results of this study indicated that, in contrast with the findings in RBC exposed to a well-defined magnitude of shear stress in a Couette shearing system, the mechanical damage induced by a roller pump could not be prevented by NO donor or potassium channel blocker. PMID:19662112
Multi-resolution flow simulations by smoothed particle hydrodynamics via domain decomposition
NASA Astrophysics Data System (ADS)
Bian, Xin; Li, Zhen; Karniadakis, George Em
2015-09-01
We present a methodology to concurrently couple particle-based methods via a domain decomposition (DD) technique for simulating viscous flows. In particular, we select two resolutions of the smoothed particle hydrodynamics (SPH) method as demonstration. Within the DD framework, a simulation domain is decomposed into two (or more) overlapping sub-domains, each of which has an individual particle scale determined by the local flow physics. Consistency of the two sub-domains is achieved in the overlap region by matching the two independent simulations based on Lagrangian interpolation of state variables and fluxes. The domain decomposition based SPH method (DD-SPH) employs different spatial and temporal resolutions, and hence, each sub-domain has its own smoothing length and time step. As a consequence, particle refinement and de-refinement are performed asynchronously according to individual time advancement of each sub-domain. The proposed strategy avoids SPH force interactions between different resolutions on purpose, so that coupling, in principle, can go beyond SPH-SPH, and may allow SPH to be coupled with other mesoscopic or microscopic particle methods. The DD-SPH method is validated first for a transient Couette flow, where simulation results based on proper coupling of spatial-temporal scales agree well with analytical solutions. In particular, we find that the size of the overlap region should be at least rc,1 + 2rc,2, where rc,1 and rc,2 are cut off radii in the two sub-domains with rc,1 ≤rc,2. Subsequently, a perturbation wave is considered traveling either parallel or perpendicular to the hybrid interface. Compressibility is significant if transient behavior at short sonic-time-scale is relevant, while the fluid can be treated as quasi-incompressible at sufficiently long time scale. To this end, we propose a coupling of density fields from the two sub-domains. Finally, a steady Wannier flow is simulated, where a rotating cylinder is placed next to a
78 FR 9907 - Hydrodynamics, Inc.; Notice Denying Late Intervention
Federal Register 2010, 2011, 2012, 2013, 2014
2013-02-12
... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Hydrodynamics, Inc.; Notice Denying Late Intervention On June 24, 2010, Commission staff issued a three-year preliminary permit to Hydrodynamics, Inc. (Hydrodynamics) to study...
Influence of hydrodynamic interactions on mechanical unfolding of proteins
NASA Astrophysics Data System (ADS)
Szymczak, P.; Cieplak, Marek
2007-07-01
We incorporate hydrodynamic interactions in a structure-based model of ubiquitin and demonstrate that the hydrodynamic coupling may reduce the peak force when stretching the protein at constant speed, especially at larger speeds. Hydrodynamic interactions are also shown to facilitate unfolding at constant force and inhibit stretching by fluid flows.
NASA Astrophysics Data System (ADS)
Kałuża, Tomasz; Radecki-Pawlik, Artur; Plesiński, Karol; Walczak, Natalia; Szoszkiewicz, Krzysztof; Radecki-Pawlik, Bartosz
2016-04-01
In the present time integrated water management is directly connected with management and direct works in river channels themselves which are taking into account morphological processes in rivers and improve flow conditions. Our work focused on the hydraulic and hydrodynamic consequences upon the introduction of the concept of the improvement of the hydromorphological conditions of the Flinta River in a given reach following river channel management concept. Based on a comprehensive study of the hydromorphological state of the river, four sections were selected where restoration measures can efficiently improve river habitat conditions in the river. For each section a set of technical and biological measures were proposed and implemented in practice. One of the proposed solutions was to construct plant basket hydraulic structures (PBHS) within the river channel, which are essentially plant barriers working as sediment traps, changing river channel morphology and are in line with concepts of Water Framework Directive. These relatively small structures work as crested weirs and unquestionably change the channel morphology. Along our work we show the results of three-year long (2013-2015) systematic measurements that provided information on the morphological consequences of introducing such structures into a river channel. Our main conclusions are as follows: 1. Plant basket hydraulic structures cause changes in hydrodynamic conditions and result in sediment accumulation and the formation of river backwaters upstream and downstream the obstacle; 2. The introduced plant basket hydraulic structures cause plant debris accumulation which influences the hydrodynamic flow conditions; 3. The installation of plant basket hydraulic structures on the river bed changes flow pattern as well as flow hydrodynamic conditions causing river braiding process; 4. The erosion rate below the plant basket hydraulic structures is due to the hydraulic work conditions of the PBHS and its
Swain, Eric D.; Decker, Jeremy D.; Hughes, Joseph D.
2014-01-01
In this paper, the authors present an analysis of the magnitude of the temporal and spatial acceleration (inertial) terms in the surface-water flow equations and determine the conditions under which these inertial terms have sufficient magnitude to be required in the computations. Data from two South Florida field sites are examined and the relative magnitudes of temporal acceleration, spatial acceleration, and the gravity and friction terms are compared. Parameters are derived by using dimensionless numbers and applied to quantify the significance of the hydrodynamic effects. The time series of the ratio of the inertial and gravity terms from field sites are presented and compared with both a simplified indicator parameter and a more complex parameter called the Hydrodynamic Significance Number (HSN). Two test-case models were developed by using the SWIFT2D hydrodynamic simulator to examine flow behavior with and without the inertial terms and compute the HSN. The first model represented one of the previously-mentioned field sites during gate operations of a structure-managed coastal canal. The second model was a synthetic test case illustrating the drainage of water down a sloped surface from an initial stage while under constant flow. The analyses indicate that the times of substantial hydrodynamic effects are sporadic but significant. The simplified indicator parameter correlates much better with the hydrodynamic effect magnitude for a constant width channel such as Miami Canal than at the non-uniform North River. Higher HSN values indicate flow situations where the inertial terms are large and need to be taken into account.
Preasymptotic hydrodynamic dispersion as a quantitative probe of permeability.
Brosten, Tyler R; Vogt, Sarah J; Seymour, Joseph D; Codd, Sarah L; Maier, Robert S
2012-04-01
We interpret a generalized short-time expansion of stochastic hydrodynamic dispersion dynamics in the case of small Reynolds number flow through macroscopically homogenous permeable porous media to directly determine hydrodynamic permeability. The approach allows determination of hydrodynamic permeability from pulsed field gradient spin-echo nuclear magnetic resonance measurement of the short-time effective hydrodynamic dispersion coefficient. The analytical expansion of asymptotic dynamics agrees with experimental NMR data and lattice Boltzmann simulation of hydrodynamic dispersion in consolidated random sphere pack media. PMID:22680531
Direct characterization of hydrodynamic loading on a microelectromechanical systems microstructure
NASA Astrophysics Data System (ADS)
Mehrnezhad, Ali; Bashir, Rashid; Park, Kidong
2016-03-01
Hydrodynamic loading greatly affects resonant characteristic of microfabricated structures immersed in a viscous fluid. In this letter, we demonstrate a technique to measure hydrodynamic loading on a MEMS resonator in a broad range of actuation frequency. The extracted hydrodynamic loading is in a good agreement with an analytical solution of an oscillating sphere, and a highly accurate model is developed for the hydrodynamic loading of the resonator. The developed technique can directly characterize the hydrodynamic loading of a microstructure with an arbitrary geometry and will facilitate the optimization of MEMS devices and AFM probes operating in a viscous fluid.
Effects of open boundary location on the far-field hydrodynamics of a Severn Barrage
NASA Astrophysics Data System (ADS)
Zhou, Juntao; Pan, Shunqi; Falconer, Roger A.
2014-01-01
The Severn Estuary has the second largest tide range in the world and a barrage across the estuary from Cardiff in South Wales to Weston in South West England has been proposed for over half a century, to extract large amounts of tidal energy from the estuary. To assess the environmental impacts of the proposed tidal barrage requires accurate model predictions of both the near-field and far-field hydrodynamics, which can strongly depend on the model area and the appropriate boundary forcing. In this paper two models, based on the Environmental Fluid Dynamics Code (EFDC) numerical model with a recently-developed Barrage module (EFDC_B), were set up with different computational domains. The Continental Shelf model, which was centred on the Bristol Channel, has its open boundary extended to beyond the Continental Shelf. The Irish Sea model, which was also centred around the Bristol Channel, only has its open boundary extended to the Celtic Sea in the south and the Irish Sea in the north. In order to investigate the effects of the open boundary conditions imposed in the models on the near and far-field hydrodynamics for the case of the Severn Barrage, the Continental Shelf model was first run with and without the operation of the Severn Barrage. The Irish Sea model was then run, also with and without the operation of the Severn Barrage, and with the open boundary conditions provided by the Continental Shelf model. The results from both models were then analysed to study the impact of the tidal barrage on the near-field and far-field hydrodynamics in the Bristol Channel and Irish Sea. Detailed comparisons of the model results indicate that the hydrodynamic conditions along the open boundaries of the Irish Sea model are affected by the tidal barrage and that the open boundary conditions also have noticeable impacts on the far-field hydrodynamics, especially in the Irish Sea, with approximately an average 4-7 cm difference in the maximum water levels predicted in Cardigan
Tentner, A.M.
1994-03-01
A detailed hydrodynamic fuel relocation model has been developed for the analysis of severe accidents in Heavy Water Reactors with multiple-tube Assemblies. This model describes the Fuel Disruption and Relocation inside a nuclear fuel assembly and is designated by the acronym DIANA. DIANA solves the transient hydrodynamic equations for all the moving materials in the core and treats all the relevant flow regimes. The numerical solution techniques and some of the physical models included in DIANA have been developed taking advantage of the extensive experience accumulated in the development and validation of the LEVITATE (1) fuel relocation model of SAS4A [2, 3]. The model is designed to handle the fuel and cladding relocation in both voided and partially voided channels. It is able to treat a wide range of thermal/ hydraulic/neutronic conditions and the presence of various flow regimes at different axial locations within the same hydrodynamic channel.
The Radiation Transport Conundrum in Radiation Hydrodynamics
Castor, J I
2005-03-18
The summary of this paper is: (1) The conundrum in the title is whether to treat radiation in the lab frame or the comoving frame in a radiation-hydrodynamic problem; (2) Several of the difficulties are associated with combining a somewhat relativistic treatment of radiation with a non-relativistic treatment of hydrodynamics; (3) The principal problem is a tradeoff between easily obtaining the correct diffusion limit and describing free-streaming radiation with the correct wave speed; (4) The computational problems of the comoving-frame formulation in more than one dimension, and the difficulty of obtaining both exact conservation and full u/c accuracy argue against this method; (5) As the interest in multi-D increases, as well as the power of computers, the lab-frame method is becoming more attractive; and (6) The Monte Carlo method combines the advantages of both lab-frame and comoving-frame approaches, its only disadvantage being cost.
Hyperbolic metamaterial lens with hydrodynamic nonlocal response.
Yan, Wei; Mortensen, N Asger; Wubs, Martijn
2013-06-17
We investigate the effects of hydrodynamic nonlocal response in hyperbolic metamaterials (HMMs), focusing on the experimentally realizable parameter regime where unit cells are much smaller than an optical wavelength but much larger than the wavelengths of the longitudinal pressure waves of the free-electron plasma in the metal constituents. We derive the nonlocal corrections to the effective material parameters analytically, and illustrate the noticeable nonlocal effects on the dispersion curves numerically. As an application, we find that the focusing characteristics of a HMM lens in the local-response approximation and in the hydrodynamic Drude model can differ considerably. In particular, the optimal frequency for imaging in the nonlocal theory is blueshifted with respect to that in the local theory. Thus, to detect whether nonlocal response is at work in a hyperbolic metamaterial, we propose to measure the near-field distribution of a hyperbolic metamaterial lens. PMID:23787690
Stochastic Hydrodynamic Synchronization in Rotating Energy Landscapes
NASA Astrophysics Data System (ADS)
Koumakis, N.; Di Leonardo, R.
2013-04-01
Hydrodynamic synchronization provides a general mechanism for the spontaneous emergence of coherent beating states in independently driven mesoscopic oscillators. A complete physical picture of those phenomena is of definite importance to the understanding of biological cooperative motions of cilia and flagella. Moreover, it can potentially suggest novel routes to exploit synchronization in technological applications of soft matter. We demonstrate that driving colloidal particles in rotating energy landscapes results in a strong tendency towards synchronization, favoring states where all beads rotate in phase. The resulting dynamics can be described in terms of activated jumps with transition rates that are strongly affected by hydrodynamics leading to an increased probability and lifetime of the synchronous states. Using holographic optical tweezers we quantitatively verify our predictions in a variety of spatial configurations of rotors.
A Hydrodynamical Mechanism for Generating Astrophysical Jets
NASA Astrophysics Data System (ADS)
Hernández, X.; Rendón, P. L.; Rodríguez-Mota, R. G.; Capella, A.
2014-04-01
Whenever in a classical accretion disk the thin disk approximation fails interior to a certain radius, a transition from Keplerian to radial infalling trajectories should occur. We show that this transition is actually expected to occur interior to a certain critical radius, provided surface density profiles are steeper than Sigma(R) ~ R(-1/2) , and further, that it probably corresponds to the observationally inferred phenomena of thick hot walls internally limiting the extent of many stellar accretion disks. Infalling trajectories will lead to the convergent focusing and concentration of matter towards the very central regions, most of which will simply be swallowed by the central object. We show through a perturbative hydrodynamical analysis, that this will naturally develop a well collimated pair of polar jets. A first analytic treatment of the problem described is given, proving the feasibility of purely hydrodynamical mechanisms for astrophysical jet generation.
Structure and hydrodynamics of colloidal systems
NASA Astrophysics Data System (ADS)
Hayter, John B.
1986-02-01
Invited paperColloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to μsec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.
Structure and hydrodynamics of colloidal systems
NASA Astrophysics Data System (ADS)
Hayter, J. B.
1985-07-01
Colloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to (MU) sec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.
Scaling Laws for Hydrodynamically Equivalent Implosions
NASA Astrophysics Data System (ADS)
Murakami, Masakatsu
2001-10-01
The EPOC (equivalent physics of confinement) scenario for the proof of principle of high gain inertial confinement fusion is presented, where the key concept "hydrodynamically equivalent implosions" plays a crucial role. Scaling laws on the target and confinement parameters are derived by applying the Lie group analysis to the PDE (partially differential equations) chain of the hydrodynamic system. It turns out that the conventional scaling law based on adiabatic approximation significantly differs from one which takes such energy transport effect as electron heat conduction into account. Confinement plasma parameters of the hot spot such as the central temperature and the areal mass density at peak compression are obtained with a self-similar solution for spherical implosions.
Modeling Reef Hydrodynamics to Predict Coral Bleaching
NASA Astrophysics Data System (ADS)
Bird, James; Steinberg, Craig; Hardy, Tom
2005-11-01
The aim of this study is to use environmental physics to predict water temperatures around and within coral reefs. Anomalously warm water is the leading cause for mass coral bleaching; thus a clearer understanding of the oceanographic mechanisms that control reef water temperatures will enable better reef management. In March 1998 a major coral bleaching event occurred at Scott Reef, a 40 km-wide lagoon 300 km off the northwest coast of Australia. Meteorological and coral cover observations were collected before, during, and after the event. In this study, two hydrodynamic models are applied to Scott Reef and validated against oceanographic data collected between March and June 2003. The models are then used to hindcast the reef hydrodynamics that led up to the 1998 bleaching event. Results show a positive correlation between poorly mixed regions and bleaching severity.
TORUS: Radiation transport and hydrodynamics code
NASA Astrophysics Data System (ADS)
Harries, Tim
2014-04-01
TORUS is a flexible radiation transfer and radiation-hydrodynamics code. The code has a basic infrastructure that includes the AMR mesh scheme that is used by several physics modules including atomic line transfer in a moving medium, molecular line transfer, photoionization, radiation hydrodynamics and radiative equilibrium. TORUS is useful for a variety of problems, including magnetospheric accretion onto T Tauri stars, spiral nebulae around Wolf-Rayet stars, discs around Herbig AeBe stars, structured winds of O supergiants and Raman-scattered line formation in symbiotic binaries, and dust emission and molecular line formation in star forming clusters. The code is written in Fortran 2003 and is compiled using a standard Gnu makefile. The code is parallelized using both MPI and OMP, and can use these parallel sections either separately or in a hybrid mode.
Hydrodynamic synchronisation of optically driven rotors
NASA Astrophysics Data System (ADS)
Debono, Luke J.; Box, Stuart; Phillips, David B.; Simpson, Stephen H.; Hanna, Simon
2015-08-01
Hydrodynamic coupling is thought to play a role in the coordinated beating of cilia and flagella, and may inform the future design of artificial swimmers and pumps. In this study, optical tweezers are used to investigate the hydrodynamic coupling between a pair of driven oscillators. The theoretical model of Lenz and Ryskin [P. Lenz and A. Ryskin, Phys. Biol. 3, 285{294 (2006)] is experimentally recreated, in which each oscillator consists of a sphere driven in a circular trajectory. The optical trap position is maintained ahead of the sphere to provide a tangential driving force. The trap is also moved radially to harmonically constrain the sphere to the circular trajectory. Analytically, it has been shown that two oscillators of this type are able to synchronise or phase-lock under certain conditions. We explore the interplay between synchronisation mechanisms and find good agreement between experiment, theory and Brownian dynamics simulations.
SPHGR: Smoothed-Particle Hydrodynamics Galaxy Reduction
NASA Astrophysics Data System (ADS)
Thompson, Robert
2015-02-01
SPHGR (Smoothed-Particle Hydrodynamics Galaxy Reduction) is a python based open-source framework for analyzing smoothed-particle hydrodynamic simulations. Its basic form can run a baryonic group finder to identify galaxies and a halo finder to identify dark matter halos; it can also assign said galaxies to their respective halos, calculate halo & galaxy global properties, and iterate through previous time steps to identify the most-massive progenitors of each halo and galaxy. Data about each individual halo and galaxy is collated and easy to access. SPHGR supports a wide range of simulations types including N-body, full cosmological volumes, and zoom-in runs. Support for multiple SPH code outputs is provided by pyGadgetReader (ascl:1411.001), mainly Gadget (ascl:0003.001) and TIPSY (ascl:1111.015).
Hydrodynamics of charge fluctuations and balance functions
NASA Astrophysics Data System (ADS)
Ling, Bo; Springer, Todd; Stephanov, Mikhail
2014-06-01
We apply stochastic hydrodynamics to the study of charge-density fluctuations in QCD matter undergoing Bjorken expansion. We find that the charge-density correlations are given by a time integral over the history of the system, with the dominant contribution coming from the QCD crossover region where the change of susceptibility per entropy, χT /s, is most significant. We study the rapidity and azimuthal angle dependence of the resulting charge balance function using a simple analytic model of heavy-ion collision evolution. Our results are in agreement with experimental measurements, indicating that hydrodynamic fluctuations contribute significantly to the measured charge correlations in high-energy heavy-ion collisions. The sensitivity of the balance function to the value of the charge diffusion coefficient D allows us to estimate the typical value of this coefficient in the crossover region to be rather small, of the order of (2πT)-1, characteristic of a strongly coupled plasma.
Hydrodynamics of ultra-relativistic bubble walls
NASA Astrophysics Data System (ADS)
Leitao, Leonardo; Mégevand, Ariel
2016-04-01
In cosmological first-order phase transitions, gravitational waves are generated by the collisions of bubble walls and by the bulk motions caused in the fluid. A sizeable signal may result from fast-moving walls. In this work we study the hydrodynamics associated to the fastest propagation modes, namely, ultra-relativistic detonations and runaway solutions. We compute the energy injected by the phase transition into the fluid and the energy which accumulates in the bubble walls. We provide analytic approximations and fits as functions of the net force acting on the wall, which can be readily evaluated for specific models. We also study the back-reaction of hydrodynamics on the wall motion, and we discuss the extrapolation of the friction force away from the ultra-relativistic limit. We use these results to estimate the gravitational wave signal from detonations and runaway walls.
Impact of hydrodynamics on oral biofilm strength.
Paramonova, E; Kalmykowa, O J; van der Mei, H C; Busscher, H J; Sharma, P K
2009-10-01
Mechanical removal of oral biofilms is ubiquitously accepted as the best way to prevent caries and periodontal diseases. Removal effectiveness strongly depends on biofilm strength. To investigate the influence of hydrodynamics on oral biofilm strength, we grew single- and multi-species biofilms of Streptococcus oralis J22, Actinomyces naeslundii TV14-J1, and full dental plaque at shear rates ranging from 0.1 to 50 1/sec and measured their compressive strength. Subsequently, biofilm architecture was evaluated by confocal laser scanning microscopy. Multi-species biofilms were stronger than single-species biofilms, with strength values ranging from 6 to 51 Pa and from 5 to 17 Pa, respectively. In response to increased hydrodynamic shear, biofilm strength decreased, and architecture changed from uniform carpet-like to more "fluffy" with higher thickness. S. oralis biofilms grown under variable shear of 7 and 50 1/sec possessed properties intermediate of those measured at the respective single shears. PMID:19783800
Hydrodynamic interaction of bacterial flagella - flagellar bundling
NASA Astrophysics Data System (ADS)
Lim, Sookkyung
2013-11-01
Flagellar bundling is an important aspect of locomotion in bacteria such as Escherichia coli. To study the hydrodynamic behavior of helical flagella, we present a computational model that is based on the geometry of the bacterial flagellar filament at the micrometer scale. We consider two model flagella, each of which has a rotary motor at its base with the rotation rate of the motor set at 100 Hz. Bundling occurs when both flagella are left-handed helices turning counterclockwise (when viewed from the nonmotor end of the flagellum looking back toward the motor) or when both flagella are right-handed helices turning clockwise. Helical flagella of the other combinations of handedness and rotation direction do not bundle. In this work we use the generalized immersed boundary method combined with the unconstrained Kirchhoff rod theory, which allows us to study the complicated hydrodynamics of flagellar behavior. This is a joint work with Charlie Peskin at NYU. NSF
Chemical mixing in smoothed particle hydrodynamics simulations
NASA Astrophysics Data System (ADS)
Greif, Thomas H.; Glover, Simon C. O.; Bromm, Volker; Klessen, Ralf S.
2009-02-01
We introduce a simple and efficient algorithm for diffusion in smoothed particle hydrodynamics (SPH) simulations and apply it to the problem of chemical mixing. Based on the concept of turbulent diffusion, we link the diffusivity of a pollutant to the local physical conditions and can thus resolve mixing in space and time. We apply our prescription to the evolution of an idealized supernova remnant and find that we can model the distribution of heavy elements without having to explicitly resolve hydrodynamic instabilities in the post-shock gas. Instead, the dispersal of the pollutant is implicitly modelled through its dependence on the local velocity dispersion. Our method can thus be used in any SPH simulation that investigates chemical mixing but lacks the necessary resolution on small scales. Potential applications include the enrichment of the interstellar medium in present-day galaxies, as well as the intergalactic medium at high redshifts.
Hydrodynamics with spin in bacterial suspensions
NASA Astrophysics Data System (ADS)
Belovs, M.; CÄ`bers, A.
2016-06-01
We describe a kind of self-propelling motion of bacteria based on the cooperative action of rotating flagella on the surface of bacteria. Describing the ensemble of rotating flagella in the framework of the hydrodynamics with spin, the reciprocal theorem of Stokesian hydrodynamics is generalized accordingly. The velocity of the self-propulsion is expressed in terms of the characteristics of the vector field of flagella orientation and it is shown that the unusually high velocities of Thiovulum majus bacteria may be explained by the cooperative action of the rotating flagella. The expressions obtained enable us to estimate the torque created by the rotary motors of the bacterium and show quantitative agreement with the existing experimental data.
Structure and hydrodynamics of colloidal systems
Hayter, J.B.
1985-07-01
Colloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to ..mu..sec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.
Electro-hydrodynamic synchronization of piezoelectric flags
NASA Astrophysics Data System (ADS)
Xia, Yifan; Doaré, Olivier; Michelin, Sébastien
2016-08-01
Hydrodynamic coupling of flexible flags in axial flows may profoundly influence their flapping dynamics, in particular driving their synchronization. This work investigates the effect of such coupling on the harvesting efficiency of coupled piezoelectric flags, that convert their periodic deformation into an electrical current. Considering two flags connected to a single output circuit, we investigate using numerical simulations the relative importance of hydrodynamic coupling to electrodynamic coupling of the flags through the output circuit due to the inverse piezoelectric effect. It is shown that electrodynamic coupling is dominant beyond a critical distance, and induces a synchronization of the flags' motion resulting in enhanced energy harvesting performance. We further show that this electrodynamic coupling can be strengthened using resonant harvesting circuits.
On the convexity of relativistic hydrodynamics
NASA Astrophysics Data System (ADS)
Ibáñez, José M.; Cordero-Carrión, Isabel; Martí, José M.; Miralles, Juan A.
2013-03-01
The relativistic hydrodynamic system of equations for a perfect fluid obeying a causal equation of state is hyperbolic (Anile 1989 Relativistic Fluids and Magneto-Fluids (Cambridge: Cambridge University Press)). In this report, we derive the conditions for this system to be convex in terms of the fundamental derivative of the equation of state (Menikoff and Plohr1989 Rev. Mod. Phys. 61 75). The classical limit is recovered. Communicated by L Rezzolla
VH-1: Multidimensional ideal compressible hydrodynamics code
NASA Astrophysics Data System (ADS)
Hawley, John; Blondin, John; Lindahl, Greg; Lufkin, Eric
2012-04-01
VH-1 is a multidimensional ideal compressible hydrodynamics code written in FORTRAN for use on any computing platform, from desktop workstations to supercomputers. It uses a Lagrangian remap version of the Piecewise Parabolic Method developed by Paul Woodward and Phil Colella in their 1984 paper. VH-1 comes in a variety of versions, from a simple one-dimensional serial variant to a multi-dimensional version scalable to thousands of processors.
The hydrodynamics of water-walkers
NASA Astrophysics Data System (ADS)
Hu, David L.; Bush, John W. M.
2004-11-01
Legged propulsion on the water surface is accomplished through a variety of means by birds, reptiles and insects. Examples include walking, rowing, hopping and capillary locomotion via deformation of the free surface. We here present experimental observations that yield insight into the scaling of water-walking. Particular attention is given to categorizing water-walking creatures and their modes of propulsion according to the relative magnitudes of the hydrodynamic forces generated by their driving stroke.
Novel techniques for slurry bubble column hydrodynamics
Dudukovic, M.P.
1999-05-14
The objective of this cooperative research effort between Washington University, Ohio State University and Exxon Research Engineering Company was to improve the knowledge base for scale-up and operation of slurry bubble column reactors for syngas conversion and other coal conversion processes by increased reliance on experimentally verified hydrodynamic models. During the first year (July 1, 1995--June 30, 1996) of this three year program novel experimental tools (computer aided radioactive particle tracking (CARPT), particle image velocimetry (PIV), heat probe, optical fiber probe and gamma ray tomography) were developed and tuned for measurement of pertinent hydrodynamic quantities, such as velocity field, holdup distribution, heat transfer and bubble size. The accomplishments were delineated in the First Technical Annual Report. The second year (July, 1996--June 30, 1997) was spent on further development and tuning of the novel experimental tools (e.g., development of Monte Carlo calibration for CARPT, optical probe development), building up the hydrodynamic data base using these tools and comparison of the two techniques (PIV and CARPT) for determination of liquid velocities. A phenomenological model for gas and liquid backmixing was also developed. All accomplishments were summarized in the Second Annual Technical Report. During the third and final year of the program (July 1, 1997--June 30, 1998) and during the nine months no cost extension, the high pressure facility was completed and a set of data was taken at high pressure conditions. Both PIV, CT and CARPT were used. More fundamental hydrodynamic modeling was also undertaken and model predictions were compared to data. The accomplishments for this period are summarized in this report.
The Quantum Hydrodynamic Description of Tunneling
Kendrick, Brian K.
2012-06-15
The quantum hydrodynamic approach is based on the de Broglie-Bohm formulation of quantum mechanics. The resulting fluid-like equations of motion describe the flow of probability and an accurate solution to these equations is equivalent to solving the time-dependent Schroedinger equation. Furthermore, the hydrodynamic approach provides new insight into the mechanisms as well as an alternative computational approach for treating tunneling phenomena. New concepts include well-defined 'quantum trajectories', 'quantum potential', and 'quantum force' all of which have classical analogues. The quantum potential and its associated force give rise to all quantum mechanical effects such as zero point energy, tunneling, and interference. A new numerical approach called the Iterative Finite Difference Method (IFDM) will be discussed. The IFDM is used to solve the set of non-linear coupled hydrodynamic equations. It is 2nd-order accurate in both space and time and exhibits exponential convergence with respect to the iteration count. The stability and computational efficiency of the IFDM is significantly improved by using a 'smart' Eulerian grid which has the same computational advantages as a Lagrangian or Arbitrary Lagrangian Eulerian (ALE) grid. The IFDM is also capable of treating anharmonic potentials. Example calculations using the IFDM will be presented which include: a one-dimensional Gaussian wave packet tunneling through an Eckart barrier, a one-dimensional bound-state Morse oscillator, and a two-dimensional (2D) model collinear reaction using an anharmonic potential energy surface. Approximate treatments of the quantum hydrodynamic equations will also be discussed which could allow scaling of the calculations to hundreds of degrees of freedom which is important for treating tunneling phenomena in condensed phase systems.
Hydrodynamics of spacetime and vacuum viscosity
NASA Astrophysics Data System (ADS)
Eling, Christopher
2008-11-01
It has recently been shown that the Einstein equation can be derived by demanding a non-equilibrium entropy balance law dS = δQ/T+diS hold for all local acceleration horizons through each point in spacetime. The entropy change dS is proportional to the change in horizon area while δQ and T are the energy flux across the horizon and Unruh temperature seen by an accelerating observer just inside the horizon. The internal entropy production term diS is proportional to the squared shear of the horizon and the ratio of the proportionality constant to the area entropy density is hbar/4π. Here we will show that this derivation can be reformulated in the language of hydrodynamics. We postulate that the vacuum thermal state in the Rindler wedge of spacetime obeys the holographic principle. Hydrodynamic perturbations of this state exist and are manifested in the dynamics of a stretched horizon fluid at the horizon boundary. Using the equations of hydrodynamics we derive the entropy balance law and show the Einstein equation is a consequence of vacuum hydrodynamics. This result implies that hbar/4π is the shear viscosity to entropy density ratio of the local vacuum thermal state. The value hbar/4π has attracted much attention as the shear viscosity to entropy density ratio for all gauge theories with an Einstein gravity dual. It has also been conjectured as the universal lower bound on the ratio. We argue that our picture of the vacuum thermal state is consistent with the physics of the gauge/gravity dualities and then consider possible applications to open questions.
Nonlinear phenomena in plasma physics and hydrodynamics
NASA Astrophysics Data System (ADS)
Sagdeev, R. Z.
Advances in the theory of nonlinear phenomena are discussed in individual chapters contributed by Soviet physicists. Topics examined include vortices in plasma and hydrodynamics, oscillations and bifurcations in reversible systems, regular and chaotic dynamics of particles in a magnetic field, and renormalization-group theory and Kolmogorov-Arnold-Moser theory. Consideration is given to nonlinear problems of the turbulent dynamo, strong turbulence and topological solitons, self-oscillations in chemical systems, and autowaves in biologically active media.
Hydrodynamical evolution of coalescing binary neutron stars
NASA Technical Reports Server (NTRS)
Rasio, Frederic A.; Shapiro, Stuart L.
1992-01-01
The hydrodynamics of the final merging of two neutron stars and the corresponding gravitational wave emission is studied in detail. Various test calculations are presented, including the compressible Roche and Darwin problems and the head-on collision of two polytropes. A complete coalescence calculation is presented for the simplest case of two identical neutron stars, represented by Gamma = 2 polytropes, in a circular orbit, with their spins aligned and synchronized with the orbital rotation.
Similitude in hydrodynamic tests involving planing
NASA Technical Reports Server (NTRS)
Gruson, M F
1936-01-01
The problems of using models in planing tests are addressed. If one passes from the model to a hull of linear dimensions n times greater, the speeds are connected by the law of mechanical similitude. The normal forces given by the hydrodynamic equations (perfect fluid) also follow the law of dynamic similitude (Reech's method) and are multiplied by n(exp 3). A series of tests were performed and the actual results were compared to theoretical results.
Hydrodynamics of an Electrochemical Membrane Bioreactor
NASA Astrophysics Data System (ADS)
Wang, Ya-Zhou; Wang, Yun-Kun; He, Chuan-Shu; Yang, Hou-Yun; Sheng, Guo-Ping; Shen, Jin-You; Mu, Yang; Yu, Han-Qing
2015-05-01
An electrochemical membrane bioreactor (EMBR) has recently been developed for energy recovery and wastewater treatment. The hydrodynamics of the EMBR would significantly affect the mass transfers and reaction kinetics, exerting a pronounced effect on reactor performance. However, only scarce information is available to date. In this study, the hydrodynamic characteristics of the EMBR were investigated through various approaches. Tracer tests were adopted to generate residence time distribution curves at various hydraulic residence times, and three hydraulic models were developed to simulate the results of tracer studies. In addition, the detailed flow patterns of the EMBR were acquired from a computational fluid dynamics (CFD) simulation. Compared to the tank-in-series and axial dispersion ones, the Martin model could describe hydraulic performance of the EBMR better. CFD simulation results clearly indicated the existence of a preferential or circuitous flow in the EMBR. Moreover, the possible locations of dead zones in the EMBR were visualized through the CFD simulation. Based on these results, the relationship between the reactor performance and the hydrodynamics of EMBR was further elucidated relative to the current generation. The results of this study would benefit the design, operation and optimization of the EMBR for simultaneous energy recovery and wastewater treatment.
EUNHA: a New Cosmological Hydrodynamic Simulation Code
NASA Astrophysics Data System (ADS)
Shin, Jihye; Kim, Juhan; Kim, Sungsoo S.; Park, Changbom
2014-06-01
We develop a parallel cosmological hydrodynamic simulation code designed for the study of formation and evolution of cosmological structures. The gravitational force is calculated using the TreePM method and the hydrodynamics is implemented based on the smoothed particle hydrodynamics. The initial displacement and velocity of simulation particles are calculated according to second-order Lagrangian perturbation theory using the power spectra of dark matter and baryonic matter. The initial background temperature is given by Recfast and the temperature fluctuations at the initial particle position are assigned according to the adiabatic model. We use a time-limiter scheme over the individual time steps to capture shock-fronts and to ease the time-step tension between the shock and preshock particles. We also include the astrophysical gas processes of radiative heating/cooling, star formation, metal enrichment, and supernova feedback. We test the code in several standard cases such as one-dimensional Riemann problems, Kelvin-Helmholtz, and Sedov blast wave instability. Star formation on the galactic disk is investigated to check whether the Schmidt-Kennicutt relation is properly recovered. We also study global star formation history at different simulation resolutions and compare them with observations.
Hydrodynamics of an electrochemical membrane bioreactor.
Wang, Ya-Zhou; Wang, Yun-Kun; He, Chuan-Shu; Yang, Hou-Yun; Sheng, Guo-Ping; Shen, Jin-You; Mu, Yang; Yu, Han-Qing
2015-01-01
An electrochemical membrane bioreactor (EMBR) has recently been developed for energy recovery and wastewater treatment. The hydrodynamics of the EMBR would significantly affect the mass transfers and reaction kinetics, exerting a pronounced effect on reactor performance. However, only scarce information is available to date. In this study, the hydrodynamic characteristics of the EMBR were investigated through various approaches. Tracer tests were adopted to generate residence time distribution curves at various hydraulic residence times, and three hydraulic models were developed to simulate the results of tracer studies. In addition, the detailed flow patterns of the EMBR were acquired from a computational fluid dynamics (CFD) simulation. Compared to the tank-in-series and axial dispersion ones, the Martin model could describe hydraulic performance of the EBMR better. CFD simulation results clearly indicated the existence of a preferential or circuitous flow in the EMBR. Moreover, the possible locations of dead zones in the EMBR were visualized through the CFD simulation. Based on these results, the relationship between the reactor performance and the hydrodynamics of EMBR was further elucidated relative to the current generation. The results of this study would benefit the design, operation and optimization of the EMBR for simultaneous energy recovery and wastewater treatment. PMID:25997399
Optically controlled hydrodynamic micro-manipulation
NASA Astrophysics Data System (ADS)
Phillips, David B.; Debono, Luke; Simpson, Stephen H.; Padgett, Miles J.
2015-08-01
The ability to precisely manipulate micro- and nano-scale objects has been a major driver in the progression of nanotechnologies. In this proceedings we describe a form of micro-manipulation in which the position of a target object can be controlled via locally generated fluid flow, created by the motion of nearby optically trapped objects. The ability to do this relies on a simple principle: when an object is moved through a fluid, it displaces the surrounding fluid in a predictable manner, resulting in controllable hydrodynamic forces exerted on adjacent objects. Therefore, by moving optically trapped actuators using feedback in response to a target object's current position, the flow-field at the target can be dynamically controlled. Here we investigate the performance of such a system using stochastic Brownian dynamics simulations, which are based on numerical integration of the Langevin equation describing the evolution of the system, using the Rotne-Praga approximation to capture hydrodynamic interactions. We show that optically controlled hydrodynamic micro-manipulation has the potential to hold target objects in place, move them along prescribed trajectories, and damp their Brownian motion, using the indirect forces of the surrounding water alone.
Hydrodynamic Forces on Microbubbles under Ultrasound Excitation
NASA Astrophysics Data System (ADS)
Clark, Alicia; Aliseda, Alberto
2014-11-01
Ultrasound (US) pressure waves exert a force on microbubbles that can be used to steer them in a flow. To control the motion of microbubbles under ultrasonic excitation, the coupling between the volume oscillations induced by the ultrasound pressure and the hydrodynamic forces needs to be well understood. We present experimental results for the motion of small, coated microbubbles, with similar sizes and physico-chemical properties as clinically-available ultrasound contrast agents (UCAs). The size distribution for the bubbles, resulting from the in-house manufacturing process, was characterized by analysis of high magnification microscopic images and determined to be bimodal. More than 99% of the volume is contained in microbubbles less than 10 microns in diameter, the size of a red blood cell. The motion of the microbubbles in a pulsatile flow, at different Reynolds and Womersley numbers, is studied from tracking of high-speed shadowgraphy. The influence of ultrasound forcing, at or near the resonant frequency of the bubbles, on the hydrodynamic forces due to the pulsatile flow is determined from the experimental measurements of the trajectories. Previous evidence of a sign reversal in Saffman lift is the focus of particular attention, as this is frequently the only hydrodynamic force acting in the direction perpendicular to the flow pathlines. Application of the understanding of this physical phenomenon to targeted drug delivery is analyzed in terms of the transport of the microbubbles. NSF GRFP.
Hydrodynamic Instabilities at an Oblique Interface
NASA Astrophysics Data System (ADS)
Kuranz, Carolyn; di Stefano, Carlos; Wan, W. C.; Drake, R. P.; Malamud, G.; Shimony, A.; Shvarts, D.
2015-11-01
Hydrodynamic instabilities are an important phenomenon that have consequences in many high-energy-density systems, including astrophysical systems and inertial confinement fusion experiments. Using the Omega EP laser we have created a sustained shock platform to drive a steady shock wave using a ~ 30 ns laser pulse. Coupled with a Spherical Crystal Imager we have created high-resolution x-ray radiographs to diagnose the evolution of complex hydrodynamic structures. This experiment involves a hydrodynamically unstable interface at an oblique angle so that the Richtmyer-Meshkov and Kelvin-Helmholtz processes are present. A dual-mode perturbation is machined onto the interface and we seek to observe the merging of vertical structures. Preliminary data from recent experiments and simulations results will be shown. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840, and the National Laser User Facility Program, grant number DE-NA0002032 and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-NA0001944.
Hydrodynamics of an Electrochemical Membrane Bioreactor
Wang, Ya-Zhou; Wang, Yun-Kun; He, Chuan-Shu; Yang, Hou-Yun; Sheng, Guo-Ping; Shen, Jin-You; Mu, Yang; Yu, Han-Qing
2015-01-01
An electrochemical membrane bioreactor (EMBR) has recently been developed for energy recovery and wastewater treatment. The hydrodynamics of the EMBR would significantly affect the mass transfers and reaction kinetics, exerting a pronounced effect on reactor performance. However, only scarce information is available to date. In this study, the hydrodynamic characteristics of the EMBR were investigated through various approaches. Tracer tests were adopted to generate residence time distribution curves at various hydraulic residence times, and three hydraulic models were developed to simulate the results of tracer studies. In addition, the detailed flow patterns of the EMBR were acquired from a computational fluid dynamics (CFD) simulation. Compared to the tank-in-series and axial dispersion ones, the Martin model could describe hydraulic performance of the EBMR better. CFD simulation results clearly indicated the existence of a preferential or circuitous flow in the EMBR. Moreover, the possible locations of dead zones in the EMBR were visualized through the CFD simulation. Based on these results, the relationship between the reactor performance and the hydrodynamics of EMBR was further elucidated relative to the current generation. The results of this study would benefit the design, operation and optimization of the EMBR for simultaneous energy recovery and wastewater treatment. PMID:25997399
Testing hydrodynamics schemes in galaxy disc simulations
NASA Astrophysics Data System (ADS)
Few, C. G.; Dobbs, C.; Pettitt, A.; Konstandin, L.
2016-08-01
We examine how three fundamentally different numerical hydrodynamics codes follow the evolution of an isothermal galactic disc with an external spiral potential. We compare an adaptive mesh refinement code (RAMSES), a smoothed particle hydrodynamics code (SPHNG), and a volume-discretized mesh-less code (GIZMO). Using standard refinement criteria, we find that RAMSES produces a disc that is less vertically concentrated and does not reach such high densities as the SPHNG or GIZMO runs. The gas surface density in the spiral arms increases at a lower rate for the RAMSES simulations compared to the other codes. There is also a greater degree of substructure in the SPHNG and GIZMO runs and secondary spiral arms are more pronounced. By resolving the Jeans length with a greater number of grid cells, we achieve more similar results to the Lagrangian codes used in this study. Other alterations to the refinement scheme (adding extra levels of refinement and refining based on local density gradients) are less successful in reducing the disparity between RAMSES and SPHNG/GIZMO. Although more similar, SPHNG displays different density distributions and vertical mass profiles to all modes of GIZMO (including the smoothed particle hydrodynamics version). This suggests differences also arise which are not intrinsic to the particular method but rather due to its implementation. The discrepancies between codes (in particular, the densities reached in the spiral arms) could potentially result in differences in the locations and time-scales for gravitational collapse, and therefore impact star formation activity in more complex galaxy disc simulations.
NASA Astrophysics Data System (ADS)
Sandi, Steven; Rodriguez, Jose F.; Saco, Patricia M.; Riccardi, Gerardo; Wen, Li; Saintilan, Neil
2016-04-01
The Macquarie Marshes is a complex system of marshes, swamps and lagoons interconnected by a network of streams in the semi-arid region in north western NSW, Australia. The low-gradient topography of the site leads to channel breakdown processes where the river network becomes practically non-existent. As a result, the flow extends over large areas of wetland that later re-join and reform channels exiting the system. Vegetation in semiarid wetlands are often water dependent and flood tolerant species that rely on periodical floods in order to maintain healthy conditions. The detrimental state of vegetation in the Macquarie Marshes over the past few decades has been linked to decreasing inundation frequencies. Spatial distribution of flood tolerant overstory species such as River Red Gum and Black Box has not greatly changed since early 1990's, however; the condition of the vegetation patches shows a clear deterioration evidenced by terrestrial species encroachment on the wetland understory. On the other hand, areas of flood dependent species such as Water Couch and Common Reed have undergone complete succession to terrestrial species and dryland. In order to simulate the complex dynamics of the marshes we have developed an ecogeomorphological modelling framework that combines hydrodynamic, vegetation and channel evolution modules and in this presentation we provide an update on the status of the model. The hydrodynamic simulation provides spatially distributed values of inundation extent, duration, depth and recurrence to drive a vegetation model based on species preference to hydraulic conditions. It also provides velocities and shear stresses to assess geomorphological changes. Regular updates of stream network, floodplain surface elevations and vegetation coverage provide feedbacks to the hydrodynamic model. We presents also the development and assessment of transitional rules to determine if the water conditions have been met for different vegetation
Nguyen, Mary-Anne; Srijanto, Bernadeta; Collier, C Patrick; Retterer, Scott T; Sarles, Stephen A
2016-09-21
The droplet interface bilayer (DIB) is a modular technique for assembling planar lipid membranes between water droplets in oil. The DIB method thus provides a unique capability for developing digital, droplet-based membrane platforms for rapid membrane characterization, drug screening and ion channel recordings. This paper demonstrates a new, low-volume microfluidic system that automates droplet generation, sorting, and sequential trapping in designated locations to enable the rapid assembly of arrays of DIBs. The channel layout of the device is guided by an equivalent circuit model, which predicts that a serial arrangement of hydrodynamic DIB traps enables sequential droplet placement and minimizes the hydrodynamic pressure developed across filled traps to prevent squeeze-through of trapped droplets. Furthermore, the incorporation of thin-film electrodes fabricated via evaporation metal deposition onto the glass substrate beneath the channels allows for the first time in situ, simultaneous electrical interrogation of multiple DIBs within a sealed device. Combining electrical measurements with imaging enables measurements of membrane capacitance and resistance and bilayer area, and our data show that DIBs formed in different trap locations within the device exhibit similar sizes and transport properties. Simultaneous, single channel recordings of ion channel gating in multiple membranes are obtained when alamethicin peptides are incorporated into the captured droplets, qualifying the thin-film electrodes as a means for measuring stimuli-responsive functions of membrane-bound biomolecules. This novel microfluidic-electrophysiology platform provides a reproducible, high throughput method for performing electrical measurements to study transmembrane proteins and biomembranes in low-volume, droplet-based membranes. PMID:27513561
Revisiting resolution in hydrodynamic countercurrent chromatography: tubing bore effect.
Berthod, A; Faure, K
2015-04-17
A major challenge in countercurrent chromatography (CCC), the technique that works with a support-free biphasic liquid system, is to retain the liquid stationary phase inside the CCC column (Sf parameter). Two solutions are commercially available: the hydrostatic CCC columns, also called centrifugal partition chromatographs (CPC), with disks of interconnected channels and rotary seals, and the hydrodynamic CCC columns with bobbins of coiled open tube and no rotary seals. It was demonstrated that the amount of liquid stationary phase retained by a coiled tube was higher with larger bore tubing than with small bore tubes. At constant column volume, small bore tubing will be longer producing more efficiency than larger bore tube that will better retain the liquid stationary phase. Since the resolution equation in CCC is depending on both column efficiency and stationary phase retention ratio, the influence of the tubing bore should be studied. This theoretical work showed that there is an optimum tubing bore size depending on solute partition coefficient and mobile phase flow rate. The interesting result of the theoretical study is that larger tubing bores allow for dramatically reduced experiment durations for all solutes: in reversed phase CCC (polar mobile phase), hydrophobic solutes are usually highly retained. These apolar solutes can be separated by the same coil at high flow rates and reduced Sf with similar retention times as polar solutes separated at smaller flow rates and much higher Sf. PMID:25747666
Hydrodynamics of DNA confined in nanoslits and nanochannels
Dorfman, Kevin D.; Gupta, Damini; Jain, Aashish; Muralidhar, Abhiram; Tree, Douglas R.
2014-01-01
Modeling the dynamics of a confined, semi exible polymer is a challenging problem, owing to the complicated interplay between the configurations of the chain, which are strongly affected by the length scale for the confinement relative to the persistence length of the chain, and the polymer-wall hydrodynamic interactions. At the same time, understanding these dynamics are crucial to the advancement of emerging genomic technologies that use confinement to stretch out DNA and “read” a genomic signature. In this mini-review, we begin by considering what is known experimentally and theoretically about the friction of a wormlike chain such as DNA confined in a slit or a channel. We then discuss how to estimate the friction coefficient of such a chain, either with dynamic simulations or via Monte Carlo sampling and the Kirk-wood pre-averaging approximation. We then review our recent work on computing the diffusivity of DNA in nanoslits and nanochannels, and conclude with some promising avenues for future work and caveats about our approach. PMID:25566349
A Nanoscale Hydrodynamical Model for Transport of Water
NASA Astrophysics Data System (ADS)
Bhadauria, Ravi; Sanghi, Tarun; Aluru, N. R.
2015-11-01
We present here a one-dimensional isothermal hydrodynamic transport model for SPC/E water. Two separate mechanisms of flow, viz. viscous and slip are incorporated in the present formulation. Spatially varying viscosity is modeled using the local average density method. Slip velocity is provided as a form of the boundary condition which in turn depends upon the macroscopic interfacial friction coefficient. The friction coefficient bridges the atomistic and continuum descriptions of the problem. The value of this friction coefficient is computed using particle-based wall-fluid force autocorrelations and wall-fluid force-velocity cross correlations, where the particle trajectory is generated using a Generalized Langevin Equation formulation. To test the accuracy of the model, gravity driven flow of SPC/E water confined between graphene and silicon slit shaped nanochannels are considered as examples for low and high friction cases. The proposed model yields good quantitative agreement with the velocity profiles obtained from non-equilibrium molecular dynamics simulations. Furthermore, we demonstrate that the slip length is constant for different channel widths for a fixed thermodynamic state under the linear response regime.
Hydrodynamics of DNA confined in nanoslits and nanochannels
NASA Astrophysics Data System (ADS)
Dorfman, K. D.; Gupta, D.; Jain, A.; Muralidhar, A.; Tree, D. R.
2014-12-01
Modeling the dynamics of a confined, semiflexible polymer is a challenging problem, owing to the complicated interplay between the configurations of the chain, which are strongly affected by the length scale for the confinement relative to the persistence length of the chain, and the polymer-wall hydrodynamic interactions. At the same time, understanding these dynamics are crucial to the advancement of emerging genomic technologies that use confinement to stretch out DNA and "read" a genomic signature. In this mini-review, we begin by considering what is known experimentally and theoretically about the friction of a wormlike chain such as DNA confined in a slit or a channel. We then discuss how to estimate the friction coefficient of such a chain, either with dynamic simulations or via Monte Carlo sampling and the Kirkwood pre-averaging approximation. We then review our recent work on computing the diffusivity of DNA in nanoslits and nanochannels, and conclude with some promising avenues for future work and caveats about our approach.
Accuracy of an estuarine hydrodynamic model using smooth elements
Walters, Roy A.; Cheng, Ralph T.
1980-01-01
A finite element model which uses triangular, isoparametric elements with quadratic basis functions for the two velocity components and linear basis functions for water surface elevation is used in the computation of shallow water wave motions. Specifically addressed are two common uncertainties in this class of two-dimensional hydrodynamic models: the treatment of the boundary conditions at open boundaries and the treatment of lateral boundary conditions. The accuracy of the models is tested with a set of numerical experiments in rectangular and curvilinear channels with constant and variable depth. The results indicate that errors in velocity at the open boundary can be significant when boundary conditions for water surface elevation are specified. Methods are suggested for minimizing these errors. The results also show that continuity is better maintained within the spatial domain of interest when ‘smooth’ curve-sided elements are used at shoreline boundaries than when piecewise linear boundaries are used. Finally, a method for network development is described which is based upon a continuity criterion to gauge accuracy. A finite element network for San Francisco Bay, California, is used as an example.
Optical chromatographic sample separation of hydrodynamically focused mixtures
Terray, A.; Hebert, C. G.; Hart, S. J.
2014-01-01
Optical chromatography relies on the balance between the opposing optical and fluid drag forces acting on a particle. A typical configuration involves a loosely focused laser directly counter to the flow of particle-laden fluid passing through a microfluidic device. This equilibrium depends on the intrinsic properties of the particle, including size, shape, and refractive index. As such, uniquely fine separations are possible using this technique. Here, we demonstrate how matching the diameter of a microfluidic flow channel to that of the focusing laser in concert with a unique microfluidic platform can be used as a method to fractionate closely related particles in a mixed sample. This microfluidic network allows for a monodisperse sample of both polystyrene and poly(methyl methacrylate) spheres to be injected, hydrodynamically focused, and completely separated. To test the limit of separation, a mixed polystyrene sample containing two particles varying in diameter by less than 0.5 μm was run in the system. The analysis of the resulting separation sets the framework for continued work to perform ultra-fine separations. PMID:25553179
Sub-micrometer-precision, three-dimensional (3D) hydrodynamic focusing via “microfluidic drifting”
Nawaz, Ahmad Ahsan; Zhang, Xiangjun; Mao, Xiaole; Rufo, Joseph; Lin, Sz-Chin Steven; Guo, Feng; Zhao, Yanhui; Lapsley, Michael; Li, Peng; McCoy, J. Philip; Levine, Stewart J.; Huang, Tony Jun
2014-01-01
In this article, we demonstrate single-layered, “microfluidic drifting” based three-dimensional (3D) hydrodynamic focusing devices with particle/cell focal positioning approaching submicron precision along both lateral and vertical directions. By systematically optimizing channel geometries and sample/sheath flow rates, a series of “microfluidic drifting” based 3D hydrodynamic focusing devices with different curvature angles are designed and fabricated. Their performances are then evaluated by confocal microscopy, fast camera imaging, and side-view imaging techniques. Using a device with a curvature angle of 180°, we have achieved a standard deviation of ±0.45 µm in particle focal position and a coefficient of variation (CV) of 2.37% in flow cytometric measurements. To the best of our knowledge, this is the best CV that has been achieved by a microfluidic flow cytometry device. Moreover, the device showed the capability to distinguish 8 peaks when subjected to a stringent 8-peak rainbow calibration test, signifying the ability to perform sensitive, accurate tests similar to commercial flow cytometers. We have further tested and validated our device by detection of HEK-293 cells. With its advantages in simple fabrication (i.e., single-layered device), precise 3D hydrodynamic focusing (i.e., submicrometer precision along both lateral and vertical directions), and high detection resolution (i.e., low CV), our method could serve as an important basis for high-performance, mass-producible microfluidic flow cytometry. PMID:24287742
Ley, Mikkel W H; Bruus, Henrik
2016-03-23
A continuum model is established for numerical studies of hydrodynamic particle-particle interactions in microfluidic high-concentration suspensions. A suspension of microparticles placed in a microfluidic channel and influenced by an external force, is described by a continuous particle-concentration field coupled to the continuity and Navier-Stokes equation for the solution. The hydrodynamic interactions are accounted for through the concentration dependence of the suspension viscosity, of the single-particle mobility, and of the momentum transfer from the particles to the suspension. The model is applied on a magnetophoretic and an acoustophoretic system, respectively, and based on the results, we illustrate three main points: (1) for relative particle-to-fluid volume fractions greater than 0.01, the hydrodynamic interaction effects become important through a decreased particle mobility and an increased suspension viscosity. (2) At these high particle concentrations, particle-induced flow rolls occur, which can lead to significant deviations of the advective particle transport relative to that of dilute suspensions. (3) Which interaction mechanism that dominates, depends on the specific flow geometry and the specific external force acting on the particles. PMID:26948344
Sub-micrometer-precision, three-dimensional (3D) hydrodynamic focusing via "microfluidic drifting".
Nawaz, Ahmad Ahsan; Zhang, Xiangjun; Mao, Xiaole; Rufo, Joseph; Lin, Sz-Chin Steven; Guo, Feng; Zhao, Yanhui; Lapsley, Michael; Li, Peng; McCoy, J Philip; Levine, Stewart J; Huang, Tony Jun
2014-01-21
In this article, we demonstrate single-layered, "microfluidic drifting" based three-dimensional (3D) hydrodynamic focusing devices with particle/cell focal positioning approaching submicron precision along both lateral and vertical directions. By systematically optimizing channel geometries and sample/sheath flow rates, a series of "microfluidic drifting" based 3D hydrodynamic focusing devices with different curvature angles are designed and fabricated. Their performances are then evaluated using confocal microscopy, fast camera imaging, and side-view imaging techniques. Using a device with a curvature angle of 180°, we have achieved a standard deviation of ±0.45 μm in particle focal position and a coefficient of variation (CV) of 2.37% in flow cytometric measurements. To the best of our knowledge, this is the best CV that has been achieved using a microfluidic flow cytometry device. Moreover, the device showed the capability to distinguish 8 peaks when subjected to a stringent 8-peak rainbow calibration test, signifying the ability to perform sensitive, accurate tests similar to commercial flow cytometers. We have further tested and validated our device by detection of HEK-293 cells. With its advantages in simple fabrication (i.e., single-layered device), precise 3D hydrodynamic focusing (i.e., submicrometer precision along both lateral and vertical directions), and high detection resolution (i.e., low CV), our method could serve as an important basis for high-performance, mass-producible microfluidic flow cytometry. PMID:24287742
Hydrodynamic interactions of spherical particles in Poiseuille flow between two parallel walls
NASA Astrophysics Data System (ADS)
Bhattacharya, S.; Bławzdziewicz, J.; Wajnryb, E.
2006-05-01
We study hydrodynamic interactions of spherical particles in incident Poiseuille flow in a channel with infinite planar walls. The particles are suspended in a Newtonian fluid, and creeping-flow conditions are assumed. Numerical results, obtained using our highly accurate Cartesian-representation algorithm [Physica A 356, 294 (2005)] are presented for a single sphere, two spheres, and arrays of many spheres. We consider the motion of freely suspended particles as well as the forces and torques acting on particles adsorbed at a wall. We find that the pair hydrodynamic interactions in this wall-bounded system have a complex dependence on the lateral interparticle distance due to the combined effects of the dissipation in the gap between the particle surfaces and the backflow associated with the presence of the walls. For immobile particle pairs we have examined the crossover between several far-field asymptotic regimes corresponding to different relations between the particle separation and the distances of the particles from the walls. We have also shown that the cumulative effect of the far-field flow substantially influences the force distribution in arrays of immobile spheres, and it affects trajectories of suspended particles. Therefore, the far-field contributions should be included in any reliable algorithm for evaluating many-particle hydrodynamic interactions in the parallel-wall geometry.
Hydrodynamics of foam flows for in situ bioremediation of DNAPL-contaminated subsurface
Bouillard, J.X.; Enzien, M.; Peters, R.W.; Frank, J.; Botto, R.E.; Cody, G.
1995-12-31
In situ remediation technologies such as (1) pump-and-treat, (2) soil vacuum extraction, (3) soil flushing/washing, and (4) bioremediation are being promoted for cleanup of contaminated sites. However, these technologies are limited by flow channeling of chemical treatment agents. Argonne National Laboratory (ANL), the Gas Research Institute, and the Institute of Gas Technology are collaboratively investigating a new bioremediation technology using foams. The ability of a foam to block pores and limit flow bypassing makes it ideal for DNAPL remediation. The hydrodynamics of gas/liquid foam flows differ significantly from the hydrodynamics of single and multiphase nonfoaming flows. This is illustrated using a multiphase flow hydrodynamic computer model and a two-dimensional flow visualization cell. A state-of-the-art, nonintrusive, three-dimensional magnetic resonance imaging technique was developed to visualize DNAPL mobilization in three dimensions. Mechanisms to be investigated are in situ DNAPL interactions with the foam, DNAPL emulsification, DNAPL scouring by the foam, and subsequent DNAPL mobilization/redeposition in the porous media.
A hybrid Godunov method for radiation hydrodynamics
NASA Astrophysics Data System (ADS)
Sekora, Michael D.; Stone, James M.
2010-09-01
From a mathematical perspective, radiation hydrodynamics can be thought of as a system of hyperbolic balance laws with dual multiscale behavior (multiscale behavior associated with the hyperbolic wave speeds as well as multiscale behavior associated with source term relaxation). With this outlook in mind, this paper presents a hybrid Godunov method for one-dimensional radiation hydrodynamics that is uniformly well behaved from the photon free streaming (hyperbolic) limit through the weak equilibrium diffusion (parabolic) limit and to the strong equilibrium diffusion (hyperbolic) limit. Moreover, one finds that the technique preserves certain asymptotic limits. The method incorporates a backward Euler upwinding scheme for the radiation energy density Er and flux Fr as well as a modified Godunov scheme for the material density ρ, momentum density m, and energy density E. The backward Euler upwinding scheme is first-order accurate and uses an implicit HLLE flux function to temporally advance the radiation components according to the material flow scale. The modified Godunov scheme is second-order accurate and directly couples stiff source term effects to the hyperbolic structure of the system of balance laws. This Godunov technique is composed of a predictor step that is based on Duhamel's principle and a corrector step that is based on Picard iteration. The Godunov scheme is explicit on the material flow scale but is unsplit and fully couples matter and radiation without invoking a diffusion-type approximation for radiation hydrodynamics. This technique derives from earlier work by Miniati and Colella (2007) [41]. Numerical tests demonstrate that the method is stable, robust, and accurate across various parameter regimes.
Hydrodynamics of helical-shaped bacterial motility
NASA Astrophysics Data System (ADS)
Wada, Hirofumi; Netz, Roland R.
2009-08-01
To reveal the underlying hydrodynamic mechanism for the directed propulsion of the bacterium Spiroplasma, we formulate a coarse-grained elastic polymer model with domains of alternating helicities along the contour. Using hydrodynamic simulations and analytic arguments, we show that the propagation of helical domain walls leads to the directed propulsion of the cell body opposite to the domain-wall traveling direction. Several key features of Spiroplasma motility are reproduced by our model. We in particular show that the helical pitch angle observed for Spiroplasma meliferum, ψ=35° , is optimized for maximal swimming speed and energy-conversion efficiency. Our analytic theory based on the slender-body hydrodynamic approximation agrees very well with our numerical data demonstrating how the chirality switch propagating along the helical cell body is converted to a translational thrust for the cell body itself. We in detail consider thermal effects on the propulsion efficiency in the form of orientational fluctuations and conformational fluctuations of the helix shape. The body length dependence of the cell motility is studied numerically and compared to our approximate analytic theory. For fixed pitch angle ψ=35° , the swimming speed is maximized at a ratio of cell-body length to domain length of about 2-3, which are typical values for real cells. We also propose simple analytic arguments for an enhancement of the swimming velocity with increasing solution viscosity by taking into account the effects of transient confinement of a helical cell body in a polymeric meshwork. Comparison with a generalized theory for the swimming speed of flagellated bacteria in polymeric meshworks shows that the presence of a finite-sized bacterial head gives rise to a maximal swimming speed at a finite solution viscosity, whereas in the absence of a head the swimming speed monotonically increases with increasing viscosity.
Testing hydrodynamics schemes in galaxy disc simulations
NASA Astrophysics Data System (ADS)
Few, C. G.; Dobbs, C.; Pettitt, A.; Konstandin, L.
2016-08-01
We examine how three fundamentally different numerical hydrodynamics codes follow the evolution of an isothermal galactic disc with an external spiral potential. We compare an adaptive mesh refinement code (RAMSES), a smoothed particle hydrodynamics code (sphNG), and a volume-discretised meshless code (GIZMO). Using standard refinement criteria, we find that RAMSES produces a disc that is less vertically concentrated and does not reach such high densities as the sphNG or GIZMO runs. The gas surface density in the spiral arms increases at a lower rate for the RAMSES simulations compared to the other codes. There is also a greater degree of substructure in the sphNG and GIZMO runs and secondary spiral arms are more pronounced. By resolving the Jeans' length with a greater number of grid cells we achieve more similar results to the Lagrangian codes used in this study. Other alterations to the refinement scheme (adding extra levels of refinement and refining based on local density gradients) are less successful in reducing the disparity between RAMSES and sphNG/GIZMO. Although more similar, sphNG displays different density distributions and vertical mass profiles to all modes of GIZMO (including the smoothed particle hydrodynamics version). This suggests differences also arise which are not intrinsic to the particular method but rather due to its implementation. The discrepancies between codes (in particular, the densities reached in the spiral arms) could potentially result in differences in the locations and timescales for gravitational collapse, and therefore impact star formation activity in more complex galaxy disc simulations.
Precipitation patterns during channel flow
NASA Astrophysics Data System (ADS)
Jamtveit, B.; Hawkins, C.; Benning, L. G.; Meier, D.; Hammer, O.; Angheluta, L.
2013-12-01
Mineral precipitation during channelized fluid flow is widespread in a wide variety of geological systems. It is also a common and costly phenomenon in many industrial processes that involve fluid flow in pipelines. It is often referred to as scale formation and encountered in a large number of industries, including paper production, chemical manufacturing, cement operations, food processing, as well as non-renewable (i.e. oil and gas) and renewable (i.e. geothermal) energy production. We have studied the incipient stages of growth of amorphous silica on steel plates emplaced into the central areas of the ca. 1 meter in diameter sized pipelines used at the hydrothermal power plant at Hellisheidi, Iceland (with a capacity of ca 300 MW electricity and 100 MW hot water). Silica precipitation takes place over a period of ca. 2 months at approximately 120°C and a flow rate around 1 m/s. The growth produces asymmetric ca. 1mm high dendritic structures ';leaning' towards the incoming fluid flow. A novel phase-field model combined with the lattice Boltzmann method is introduced to study how the growth morphologies vary under different hydrodynamic conditions, including non-laminar systems with turbulent mixing. The model accurately predicts the observed morphologies and is directly relevant for understanding the more general problem of precipitation influenced by turbulent mixing during flow in channels with rough walls and even for porous flow. Reference: Hawkins, C., Angheluta, L., Hammer, Ø., and Jamtveit, B., Precipitation dendrites in channel flow. Europhysics Letters, 102, 54001
Klein-Gordon Equation in Hydrodynamical Form
Wong, Cheuk-Yin
2010-01-01
We follow and modify the Feshbach-Villars formalism by separating the Klein-Gordon equation into two coupled time-dependent Schroedinger equations for the particle and antiparticle wave functions with positive probability densities. We find that the equation of motion for the probability densities is in the form of relativistic hydrodynamics where various forces have their physical and classical counterparts. An additional element is the presence of the quantum stress tensor that depends on the derivatives of the amplitude of the wave function.
The frontal method in hydrodynamics simulations
Walters, R.A.
1980-01-01
The frontal solution method has proven to be an effective means of solving the matrix equations resulting from the application of the finite element method to a variety of problems. In this study, several versions of the frontal method were compared in efficiency for several hydrodynamics problems. Three basic modifications were shown to be of value: 1. Elimination of equations with boundary conditions beforehand, 2. Modification of the pivoting procedures to allow dynamic management of the equation size, and 3. Storage of the eliminated equations in a vector. These modifications are sufficiently general to be applied to other classes of problems. ?? 1980.
Dynamic coupling of three hydrodynamic models
NASA Astrophysics Data System (ADS)
Hartnack, J. N.; Philip, G. T.; Rungoe, M.; Smith, G.; Johann, G.; Larsen, O.; Gregersen, J.; Butts, M. B.
2008-12-01
The need for integrated modelling is evidently present within the field of flood management and flood forecasting. Engineers, modellers and managers are faced with flood problems which transcend the classical hydrodynamic fields of urban, river and coastal flooding. Historically the modeller has been faced with having to select one hydrodynamic model to cover all the aspects of the potentially complex dynamics occurring in a flooding situation. Such a single hydrodynamic model does not cover all dynamics of flood modelling equally well. Thus the ideal choice may in fact be a combination of models. Models combining two numerical/hydrodynamic models are becoming more standard, typically these models combine a 1D river model with a 2D overland flow model or alternatively a 1D sewer/collection system model with a 2D overland solver. In complex coastal/urban areas the flood dynamics may include rivers/streams, collection/storm water systems along with the overland flow. The dynamics within all three areas is of the same time scale and there is feedback in the system across the couplings. These two aspects dictate a fully dynamic three way coupling as opposed to running the models sequentially. It will be shown that the main challenges of the three way coupling are time step issues related to the difference in numerical schemes used in the three model components and numerical instabilities caused by the linking of the model components. MIKE FLOOD combines the models MIKE 11, MIKE 21 and MOUSE into one modelling framework which makes it possible to couple any combination of river, urban and overland flow fully dynamically. The MIKE FLOOD framework will be presented with an overview of the coupling possibilities. The flood modelling concept will be illustrated through real life cases in Australia and in Germany. The real life cases reflect dynamics and interactions across all three model components which are not possible to reproduce using a two-way coupling alone. The
Effect of geometry on hydrodynamic film thickness
NASA Technical Reports Server (NTRS)
Brewe, D. E.; Hamrock, B. J.; Taylor, C. M.
1978-01-01
The influence of geometry on the isothermal hydrodynamic film separating two rigid solids was investigated. Pressure-viscosity effects were not considered. The minimum film thickness is derived for fully flooded conjunctions by using the Reynolds conditions. It was found that the minimum film thickness had the same speed, viscosity, and load dependence as Kapitza's classical solution. However, the incorporation of Reynolds boundary conditions resulted in an additional geometry effect. Solutions using the parabolic film approximation are compared with those using the exact expression for the film in the analysis. Contour plots are shown that indicate in detail the pressure developed between the solids.
Nonisothermal fluctuating hydrodynamics and Brownian motion.
Falasco, G; Kroy, K
2016-03-01
The classical theory of Brownian dynamics follows from coarse graining the underlying linearized fluctuating hydrodynamics of the solvent. We extend this procedure to globally nonisothermal conditions, requiring only a local thermal equilibration of the solvent. Starting from the conservation laws, we establish the stochastic equations of motion for the fluid momentum fluctuations in the presence of a suspended Brownian particle. These are then contracted to the nonisothermal generalized Langevin description of the suspended particle alone, for which the coupling to stochastic temperature fluctuations is found to be negligible under typical experimental conditions. PMID:27078335
Newtonian hydrodynamics with general relativistic pressure
Hwang, Jai-chan; Noh, Hyerim E-mail: hr@kasi.re.kr
2013-10-01
We present the general relativistic pressure correction terms in Newtonian hydrodynamic equations to the nonlinear order: these are equations (1.1)–(1.3). The derivation is made in the zero-shear gauge based on the fully nonlinear formulation of cosmological perturbation in Einstein's gravity. The correction terms differ from many of the previously suggested forms in the literature based on hand-waving manners. We confirm our results by comparing with (i) the nonlinear perturbation theory, (ii) the first order post-Newtonian approximation, and (iii) the special relativistic limit, and by checking (iv) the consistency with full Einstein's equation.
Consistent Hydrodynamics for Phase Field Crystals.
Heinonen, V; Achim, C V; Kosterlitz, J M; Ying, See-Chen; Lowengrub, J; Ala-Nissila, T
2016-01-15
We use the amplitude expansion in the phase field crystal framework to formulate an approach where the fields describing the microscopic structure of the material are coupled to a hydrodynamic velocity field. The model is shown to reduce to the well-known macroscopic theories in appropriate limits, including compressible Navier-Stokes and wave equations. Moreover, we show that the dynamics proposed allows for long wavelength phonon modes and demonstrate the theory numerically showing that the elastic excitations in the system are relaxed through phonon emission. PMID:26824543
Fast Lattice Boltzmann Solver for Relativistic Hydrodynamics
Mendoza, M.; Herrmann, H. J.; Boghosian, B. M.; Succi, S.
2010-07-02
A lattice Boltzmann formulation for relativistic fluids is presented and numerically validated through quantitative comparison with recent hydrodynamic simulations of relativistic fluids. In order to illustrate its capability to handle complex geometries, the scheme is also applied to the case of a three-dimensional relativistic shock wave, generated by a supernova explosion, impacting on a massive interstellar cloud. This formulation opens up the possibility of exporting the proven advantages of lattice Boltzmann methods, namely, computational efficiency and easy handling of complex geometries, to the context of (mildly) relativistic fluid dynamics at large, from quark-gluon plasmas up to supernovae with relativistic outflows.
Newtonian Hydrodynamics with Arbitrary Volumetric Sources
Lowrie, Robert Byron
2015-11-12
In this note, we derive how to handle mass, momentum, and energy sources for Newtonian hydrodynamics. Much of this is classic, although we’re unaware of a reference that treats mass sources, necessary for certain physics and the method of manufactured solutions. In addition, we felt it important to emphasize that the integral form of the governing equations results in a straightforward treatment of the sources. With the integral form, we’ll demonstrate that there’s no ambiguity between the Lagrangian and Eulerian form of the equations, which is less clear with the differential forms.
Some cautionary remarks about smoothed particle hydrodynamics
NASA Technical Reports Server (NTRS)
Hernquist, Lars
1993-01-01
Potential difficulties with smoothed particle hydrodynamics are discussed. In particular, empirical tests are used to demonstrate that the errors resulting from the use of variable smoothing can be much larger than commonly believed. Fortunately, however, these errors, which are normally small, do not appear to promote instability on small scales, such as fragmentation in self-gravitating fluids. Still, while SPH remains a useful tool for many problems of astrophysical interest, a rigorous formulation of it, which is adaptive but still satisfies conservation properties, is clearly wanting.
Nonisothermal fluctuating hydrodynamics and Brownian motion
NASA Astrophysics Data System (ADS)
Falasco, G.; Kroy, K.
2016-03-01
The classical theory of Brownian dynamics follows from coarse graining the underlying linearized fluctuating hydrodynamics of the solvent. We extend this procedure to globally nonisothermal conditions, requiring only a local thermal equilibration of the solvent. Starting from the conservation laws, we establish the stochastic equations of motion for the fluid momentum fluctuations in the presence of a suspended Brownian particle. These are then contracted to the nonisothermal generalized Langevin description of the suspended particle alone, for which the coupling to stochastic temperature fluctuations is found to be negligible under typical experimental conditions.
Hydrodynamic and Spectral Simulations of HMXB Winds
Mauche, C W; Liedahl, D A; Akiyama, S; Plewa, T
2007-03-30
We describe preliminary results of a global model of the radiatively-driven photoionized wind and accretion flow of the high-mass X-ray binary Vela X-1. The full model combines FLASH hydrodynamic calculations, XSTAR photoionization calculations, HULLAC atomic data, and Monte Carlo radiation transport. We present maps of the density, temperature, velocity, and ionization parameter from a FLASH two-dimensional time-dependent simulation of Vela X-1, as well as maps of the emissivity distributions of the X-ray emission lines.