Autonomous Sensors Powered by Energy Harvesting from von Karman Vortices in Airflow.

PubMed

Demori, Marco; Ferrari, Marco; Bonzanini, Arianna; Poesio, Pietro; Ferrari, Vittorio

2017-09-13

In this paper an energy harvesting system based on a piezoelectric converter to extract energy from airflow and use it to power battery-less sensors is presented. The converter is embedded as a part of a flexure beam that is put into vibrations by von Karman vortices detached from a bluff body placed upstream. The vortex street has been investigated by Computational Fluid Dynamics (CFD) simulations, aiming at assessing the vortex shedding frequency as a function of the flow velocity. From the simulation results the preferred positioning of the beam behind the bluff body has been derived. In the experimental characterization the electrical output from the converter has been measured for different flow velocities and beam orientations. Highest conversion effectiveness is obtained by an optimal orientation of the beam, to exploit the maximum forcing, and for flow velocities where the repetition frequency of the vortices allows to excite the beam resonant frequency at its first flexural mode. The possibility to power battery-less sensors and make them autonomous has been shown by developing an energy management and signal conditioning electronic circuit plus two sensors for measuring temperature and flow velocity and transmitting their values over a RF signal. A harvested power of about 650 μW with retransmission intervals below 2 min have been obtained for the optimal flow velocity of 4 m/s.

Autonomous Sensors Powered by Energy Harvesting from von Karman Vortices in Airflow

PubMed Central

Bonzanini, Arianna; Poesio, Pietro

2017-01-01

In this paper an energy harvesting system based on a piezoelectric converter to extract energy from airflow and use it to power battery-less sensors is presented. The converter is embedded as a part of a flexure beam that is put into vibrations by von Karman vortices detached from a bluff body placed upstream. The vortex street has been investigated by Computational Fluid Dynamics (CFD) simulations, aiming at assessing the vortex shedding frequency as a function of the flow velocity. From the simulation results the preferred positioning of the beam behind the bluff body has been derived. In the experimental characterization the electrical output from the converter has been measured for different flow velocities and beam orientations. Highest conversion effectiveness is obtained by an optimal orientation of the beam, to exploit the maximum forcing, and for flow velocities where the repetition frequency of the vortices allows to excite the beam resonant frequency at its first flexural mode. The possibility to power battery-less sensors and make them autonomous has been shown by developing an energy management and signal conditioning electronic circuit plus two sensors for measuring temperature and flow velocity and transmitting their values over a RF signal. A harvested power of about 650 μW with retransmission intervals below 2 min have been obtained for the optimal flow velocity of 4 m/s. PMID:28902139

Transverse Resonant Vibration of Non-Bearing Structures Caused by Wind

NASA Astrophysics Data System (ADS)

Jendzelovsky, Norbert; Antal, Roland

2017-10-01

Nowadays, there are increasing use of very thin, subtle and light structures in the field of building constructions. We can find such a structures as part of roofs or design facades. By using these lamellas like, non-bearing structures as a part of architectural design of buildings, it is necessary to consider wind effects on these structures. Subtle structures of this type are prone to vibration in the transverse direction of the wind flow. The fact that the vibration occurs depends on wind parameters (wind velocity, direction of an air flow) and it also depends on the properties of lamella (shape, length, mass, natural frequency, support type). The principal idea of this article is to show susceptibility of lamellae-like structures to transverse resonant vibration caused by the phenomenon called Von Karman effect. Comparison of susceptibility to transverse resonance vibration was analysed on the different shapes of lamellas loaded by different wind speed. Analysis was based on usage of empirically derived equations. Von Karman effect arise from wind flow past an object. Turbulence in the form of vortices are formed at the object and shed into the flowing stream intermittently. The potential problem is that this turbulence can induce vibrations into the lamella itself. In terms of this vibration problem, two frequencies are interesting. Von Karman shedding frequency is the frequency at which the vortices are formed and shed at the object. The vortex-shedding frequency increases with the velocity of the wind flow and decreases with the size of the object. Natural frequency of the object depends on the construction of the lamella itself. Parameters of lamella as a shape, mass, length, elasticity modulus of material and support types are directly involved in the calculation of natural frequency. Worst case scenario in the term of transverse resonant vibration occurs when the natural frequency of lamella is equal to the vortex-shedding frequency. In this case vibration rises and structure can be snapped or deformed permanently. In the long term vibration, fatigue stress can be significant. At the conclusion hazardous wind speed and recommendations for different shapes and parameters of lamellas are shown.

Monte Carlo turbulence simulation using rational approximations to von Karman spectra

NASA Technical Reports Server (NTRS)

Campbell, C. W.

1986-01-01

Turbulence simulation is computationally much simpler using rational spectra, but turbulence falls off as f exp -5/3 in frequency ranges of interest to aircraft response and as predicted by von Karman's model. Rational approximations to von Karman spectra should satisfy three requirements: (1) the rational spectra should provide a good approximation to the von Karman spectra in the frequency range of interest; (2) for stability, the resulting rational transfer function should have all its poles in the left half-plane; and (3) at high frequencies, the rational spectra must fall off as an integer power of frequency, and since the -2 power is closest to the -5/3 power, the rational approximation should roll off as the -2 power at high frequencies. Rational approximations to von Karman spectra that satisfy these three criteria are presented, along with spectra from simulated turbulence. Agreement between the spectra of the simulated turbulence and von Karman spectra is excellent.

An approximate analysis of the diffusing flow in a self-controlled heat pipe.

NASA Technical Reports Server (NTRS)

Somogyi, D.; Yen, H. H.

1973-01-01

Constant-density two-dimensional axisymmetric equations are presented for the diffusing flow of a class of self-controlled heat pipes. The analysis is restricted to the vapor space. Condensation of the vapor is related to its mass fraction at the wall by the gas kinetic formula. The Karman-Pohlhausen integral method is applied to obtain approximate solutions. Solutions are presented for a water heat pipe with neon control gas.

On a class of unsteady three-dimensional Navier Stokes solutions relevant to rotating disc flows: Threshold amplitudes and finite time singularities

NASA Technical Reports Server (NTRS)

Hall, Philip; Balakumar, P.

1990-01-01

A class of exact steady and unsteady solutions of the Navier Stokes equations in cylindrical polar coordinates is given. The flows correspond to the motion induced by an infinite disc rotating with constant angular velocity about the z-axis in a fluid occupying a semi-infinite region which, at large distances from the disc, has velocity field proportional to (x,-y,O) with respect to a Cartesian coordinate system. It is shown that when the rate of rotation is large, Karman's exact solution for a disc rotating in an otherwise motionless fluid is recovered. In the limit of zero rotation rate a particular form of Howarth's exact solution for three-dimensional stagnation point flow is obtained. The unsteady form of the partial differential system describing this class of flow may be generalized to time-periodic equilibrium flows. In addition the unsteady equations are shown to describe a strongly nonlinear instability of Karman's rotating disc flow. It is shown that sufficiently large perturbations lead to a finite time breakdown of that flow whilst smaller disturbances decay to zero. If the stagnation point flow at infinity is sufficiently strong, the steady basic states become linearly unstable. In fact there is then a continuous spectrum of unstable eigenvalues of the stability equations but, if the initial value problem is considered, it is found that, at large values of time, the continuous spectrum leads to a velocity field growing exponentially in time with an amplitude decaying algebraically in time.

Aircraft drag prediction and reduction. Addendum 1: Computational drag analyses and minimization; mission impossible?

NASA Technical Reports Server (NTRS)

Slooff, J. W.

1986-01-01

The Special Course on Aircraft Drag Prediction was sponsored by the AGARD Fluid Dynamics Panel and the von Karman Institute and presented at the von Karman Institute, Rhode-Saint-Genese, Belgium, on 20 to 23 May 1985 and at the NASA Langley Research Center, Hampton, Virginia, USA, 5 to 6 August 1985. The course began with a general review of drag reduction technology. Then the possibility of reduction of skin friction through control of laminar flow and through modification of the structure of the turbulence in the boundary layer were discussed. Methods for predicting and reducing the drag of external stores, of nacelles, of fuselage protuberances, and of fuselage afterbodies were then presented followed by discussion of transonic drag rise. The prediction of viscous and wave drag by a method matching inviscid flow calculations and boundary layer integral calculations, and the reduction of transonic drag through boundary layer control are also discussed. This volume comprises Paper No. 9 Computational Drag Analyses and Minimization: Mission Impossible, which was not included in AGARD Report 723 (main volume).

3D Structure of the Inverse Karman Vortex Street in the Wake of a Flapping Foil

NASA Astrophysics Data System (ADS)

Bozkurttas, Meliha; Mittal, Rajat; Dong, Haibo

2004-11-01

Flapping foils are being considered for lift generation and/or propulsion in Micro Aerial Vehicles (MAVs) and Autonomous Underwater Vehicles (AUVs). In the present study, a DNS/LES solver that is capable of simulating these flows in all their complexity will be used. The flow around a NACA 0012 foil undergoing pitch oscillation at a chord Reynolds number of 12600 has been investigated and the comparison of mean thrust coefficient results with the experiment has indicated significant under-prediction of the thrust although good match is observed with a 2D RANS calculation. This discrepancy could be related to the absence of 3D effects in both numerical simulations. Although this conclusion has also been reached in other studies, the details of the physical mechanism that lead to inaccurate prediction of surface pressure and ultimately to thrust force for pitching and heaving flapping foils have not been clarified yet. In this study, the streamwise (secondary) vortical structures in the inverse Karman Vortex Street generated in the wake of a thrust producing flapping foil will be studied.

A Mixing Theory for the Interaction between Dissipative Flows and Nearly-Isentropic Streams

DTIC Science & Technology

1952-01-15

mTVEfOBEE? "- - AEROmUT-IG-AL ENGINEERING i^ORAjPORY i January 15j t--:l A- • *-,- ß» -*- •AbiMÖWEEEGEMSHT - a "I- " Es A- major portion...incident oblique shock, airfoil -chord -_- _ ’ - . - - •airf oil thickness at: -trailing edge •t v:il -:na Es : EeynöiJidG number,. &;^e...von Karman momentum integral for the. dissipatiVe flow region,, where.;, however> this internal flow is treated, as quäai- Que ."uiU4euBi!oncUt

Influence of polymer additives on turbulence in von Karman swirling flow between two disks. II

NASA Astrophysics Data System (ADS)

Burnishev, Yuri; Steinberg, Victor

2016-03-01

We present the experimental studies of the influence of polymer additives on the statistical and scaling properties of the fully developed turbulent regime in a von Karman swirling flow driven either by the smooth or bladed disks using only the global measurements of torque Γ and pressure p fluctuations in water- and water-sugar-based solutions of different viscosities, or elasticity El, and different polymer concentrations ϕ as a function of Re in the same apparatus. There are three highlights achieved and reported in the paper: (i) An observation of turbulent drag reduction (TDR) at both the inertial and viscous flow forcing, in a contradiction to a currently accepted opinion that only the viscous forcing leads to TDR, and the unexpected drastic difference in the transition to the fully developed turbulent and TDR regimes in von Karman swirling flow of water-based polymer solutions depending on the way of the forcing; (ii) a continuous transition to TDR in both the normalized torque drop and the rms pressure fluctuations drop and universality in scaling behavior of Cf in an agreement with theoretical predictions; and (iii) the dramatic differences in the appearance of the frequency power spectra of Γ and in particular p due to the different ways of the forcing are also observed. We discuss and summarize further the results in accordance with these three main achievements. The main message of these studies is that both the inertial forcing and viscous forcing of von Karman swirling flow between two counter-rotating disks lead to TDR in the sharp contrast to the currently accepted opinion [O. Cadot et al., "Turbulent drag reduction in a closed flow system: Boundary layer versus bulk effects," Phys. Fluids 10, 426 (1998); D. Bonn et al., "From scale scales to large scales in three-dimensional turbulence: The effect of diluted polymers," Phys. Rev. E 47, R28 (1993); and D. Bonn et al., "Turbulent drag reduction by polymers," J. Phys.: Condens. Matter 17, S1195 (2005)] that TDR can be observed only at the viscous driving. In this observation, Cadot et al. and Bonn et al., relate to exclusively boundary effect, whereas the existence of TDR in both ways of the flow forcing suggests that both boundary and bulk effects are responsible for TDR. The unexpected result of the striking difference in the transition to the fully developed turbulent and TDR regimes and in their properties in von Karman swirling flow of water-based polymer solutions for the viscous and inertial forcing is reported. For the viscous forcing, just the single turbulent regime is found with the transition values R ec turb = R ec T D R ≃ ( 4 . 8 ± 0 . 2 ) × 1 0 5 independent of polymer concentration ϕ, while for the inertial forcing two turbulent regimes are revealed: fully developed turbulence and the TDR regime with the transition values R ec turb < R ec T D R and both depending on ϕ. Thus in the case of the viscous forcing, the onset to turbulence is not altered by the addition of polymers in the contrast to the inertial forcing, where early turbulence is found. Both regimes differ by the scaling exponents of the fundamental turbulent characteristics, by the dependence of skewness and flatness of probability density functions of p on Re, and by the drastically different frequency power spectra of Γ and p with the different dependencies of their frequency peaks on ϕ. It is also demonstrated that the transition to the TDR state is a continuous one for both Γ ¯ and prms in accord with theoretical arguments and simulations presented in the work of Boffetta et al. ["Drag reduction in the turbulent Kolmogorov flow," Phys. Rev. E 71, 036307 (2005)]. Indeed, Cf presented as a function of R e / R ec T D R for different El show impressive collapse of the data and universal behavior above Rc T D R with the functional dependencies in a full agreement with the prediction from the numerical simulations (Boffetta et al.). Moreover, the crucial issue for the existence of TDR followed from the analysis of stresses in the TDR model is also satisfied in the experiment (Boffetta et al.). As pointed out in the work of Boffetta et al., understanding the reasons of this inequality meaning that the larger effectiveness of the momentum transfer to velocity fluctuations than to elastic stress would reveal the TDR physical mechanism. The power spectra of both Γ and p in the case of the inertial forcing are characterized by the emerging pronounced peaks and their higher harmonics in parallel with up to two orders of magnitude reduction of low frequency fluctuation amplitudes in both the water- and water-sugar-based polymer solutions compared with the power spectra for the Newtonian solvents. The peaks appear at R e ≥ R ec T D R and their normalized peak frequency fp/frot = 0.43 ± 0.02 is independent of El, ϕ, and Re. These observations agree with the numerical results, where the enhancement of the main flow compared to the Newtonian case and the strong reduction of turbulent fluctuations were also observed and quantified. On the other hand, in the case of the viscous forcing, polymers do not alter the appearance of the power spectra of p compared with water, though the scaled peak frequencies fp/frot vary with Re for all ϕ from unity at smaller Re to fp/frot = 0.6 ± 0.02 independent of ϕ and Re in the turbulent regime. Thus the inertial forcing turns out to be much more effective in the pumping energy from turbulent fluctuations into the main vortex due to stronger polymer stretching in the TDR regime that also reveals in more pronounced TDR. We suggest an explanation of the observed effects.

Semiempirical methods for computing turbulent flows

NASA Technical Reports Server (NTRS)

Belov, I. A.; Ginzburg, I. P.

1986-01-01

Two semiempirical theories which provide a basis for determining the turbulent friction and heat exchange near a wall are presented: (1) the Prandtl-Karman theory, and (2) the theory utilizing an equation for the energy of turbulent pulsations. A comparison is made between exact numerical methods and approximate integral methods for computing the turbulent boundary layers in the presence of pressure, blowing, or suction gradients. Using the turbulent flow around a plate as an example, it is shown that, when computing turbulent flows with external turbulence, it is preferable to construct a turbulence model based on the equation for energy of turbulent pulsations.

The Development of a Factorizable Multigrid Algorithm for Subsonic and Transonic Flow

NASA Technical Reports Server (NTRS)

Roberts, Thomas W.

2001-01-01

The factorizable discretization of Sidilkover for the compressible Euler equations previously demonstrated for channel flows has been extended to external flows.The dissipation of the original scheme has been modified to maintain stability for moderately stretched grids. The discrete equations are solved by symmetric collective Gauss-Seidel relaxation and FAS multigrid. Unlike the earlier work ordering the grid vertices in the flow direction has been found to be unnecessary. Solutions for essential incompressible flow (Mach 0.01) and supercritical flows have obtained for a Karman-Trefftz airfoil with it conformally mapped grid,as well as a NACA 0012 on an algebraically generated grid. The current work demonstrates nearly 0(n) convergence for subsonic and slightly transonic flows.

Characterization of the IXV Thermal Protection System in High Enthalphy Plasma Flow

NASA Astrophysics Data System (ADS)

Panerai, F.; Helber, B.; Sakraker, I.; Chazot, O.; Pichon, T.; Barreteau, R.; Tribot, J. P.; Vallee, J. J.; Mareschi, V.; Ferrarella, D.; Rufolo, G.; Mancuso, S.

2011-05-01

An experimental campaign dedicated to the characterization of Intermediate eXperimental Vehicle thermal protection system is performed in the Plasmatron wind tunnel at the von Karman Institute for Fluid Dynamics. Emissivity and catalycity properties for representative ceramic specimens are determined under a wide set of operating conditions in order to reproduce the reentry flight trajectory. Intrusive measurements for flow characterization are used together with optical infrared techniques that provide diagnostic of the test articles surface. Experimental data are postprocessed by means of numerical simulations that allow flow enthalpy rebuilding and characterization of the chemical environment for the different conditions investigated.

Calculations of Laminar Heat Transfer Around Cylinders of Arbitrary Cross Section and Transpiration-Cooled Walls with Application to Turbine Blade Cooling

NASA Technical Reports Server (NTRS)

Eckert, E.R.G.; Livingood, John N.B.

1951-01-01

An approximate method for development of flow and thermal boundary layers in laminar regime on cylinders with arbitrary cross section and transpiration-cooled walls is obtained by use of Karman's integrated momentum equation and an analogous heat-flow equation. Incompressible flow with constant property values throughout boundary layer is assumed. Shape parameters for approximated velocity and temperature profiles and functions necessary for solution of boundary-layer equations are presented as charts, reducing calculations to a minimum. The method is applied to determine local heat-transfer coefficients and surface temperature-cooled turbine blades for a given flow rate. Coolant flow distributions necessary for maintaining uniform blade temperatures are also determined.

Conference on Fluid Machinery, 8th, Budapest, Hungary, Sept. 1987, Proceedings. Volumes 1 & 2

NASA Astrophysics Data System (ADS)

Szabo, A.; Kisbocskoi, L.

The present conference on turbomachine fluid mechanics gives attention to the analysis of labyrinth seals, irrigation turbomachinery, axial-flow fans, poppet valves, the generation of Karman vortices, self-rectifying Wells-type air turbines, computer simulations for water-supply systems, the computation of meridional flow in turbomachines, entrained air effects on vortex pump performance, the three-dimensional potential flow in a draft tube, and hydro powerplant diagnostic methods. Also discussed are a mathematical model for the initiation of cavitation wear, cryogenic flow in ejectors, flow downstream of guide vanes in a Kaplan turbine, unsteady flow in rotating cascades, novel methods for turbomachine vibration monitoring, cavitation breakdown in centrifugal pumps, test results for Banki turbines, centrifugal compressor return-channel flow, performance predictions for regenerative turbomachines, and secondary flows in a centrifugal pump.

Simulation of unsteady flows through stator and rotor blades of a gas turbine using the Chimera method

NASA Technical Reports Server (NTRS)

Nakamura, S.; Scott, J. N.

1993-01-01

A two-dimensional model to solve compressible Navier-Stokes equations for the flow through stator and rotor blades of a turbine is developed. The flow domains for the stator and rotor blades are coupled by the Chimera method that makes grid generation easy and enhances accuracy because the area of the grid that have high turning of grid lines or high skewness can be eliminated from the computational domain after the grids are generated. The results of flow computations show various important features of unsteady flows including the acoustic waves interacting with boundary layers, Karman vortex shedding from the trailing edge of the stator blades, pulsating incoming flow to a rotor blade from passing stator blades, and flow separation from both suction and pressure sides of the rotor blades.

Deformations of a pre-stretched and lubricated finite elastic membrane driven by non-uniform external forcing

NASA Astrophysics Data System (ADS)

Boyko, Evgeniy; Gat, Amir; Bercovici, Moran

2017-11-01

We study viscous-elastic dynamics of a fluid confined between a rigid plate and a finite pre-stretched circular elastic membrane, pinned at its boundaries. The membrane is subjected to forces acting either directly on the membrane or through a pressure distribution in the fluid. Under the assumptions of strong pre-stretching and small deformations of the elastic sheet, and by applying the lubrication approximation for the flow, we derive the Green's function for the resulting linearized 4th order diffusion equation governing the deformation field in cylindrical coordinates. In addition, defining an asymptotic expansion with the ratio of the induced to prescribed tension serving as the small parameter, we reduce the coupled Reynolds and non-linear von-Karman equations to a set of three one-way coupled linear equations. The solutions to these equations provide insight onto the effects of induced tension, and enable simplified prediction of the correction for the deformation field. Funded by the European Research Council (ERC) under the European Union'sHorizon 2020 Research and Innovation Programme, Grant Agreement No. 678734 (MetamorphChip). E.B. is supported by the Adams Fellowship Program.

Preliminary study of the three-dimensional deformation of the vortex in Karman vortex street

NASA Astrophysics Data System (ADS)

Ling, Guocan; Guo, Liang; Wu, Zuobin; Ma, Huiyang

1992-03-01

The mechanism for 3D evolution of the isolated Karman vortex and the thin-vortex filament in a circular cylinder wake is studied numerically using the LIA method. The results show that the vortex motion is unstable for small 3D disturbances in the separated wake of a circular cylinder. Karman vortex in the time-averaged wake flowfield wolves into a horseshoe-spoon-like 3D structure. The thin vortex filament deforms three-dimensionally in the braid and generates streamwise vortex structures which incline to the region maximum-deformation direction of the flowfield.

Properties of the Mean Momentum Balance in Polymer Drag Reduced Channel Flow

NASA Astrophysics Data System (ADS)

White, Christopher; Dubief, Yves; Klewicki, Joseph

2014-11-01

The redistribution of mean momentum and the underlying mechanisms of the redistribution process in polymer drag reduced channel flow are investigated by employing a mean momentum equation based analysis. The work is motivated by recent studies that showed (contrary to long-held views) that polymers modify the von Karman coefficient, κ, at low drag reduction, and at some relatively high drag reduction eradicate the inertially dominated logarithmic region. Since κ is a manifestation of the underlying dynamical behaviors of wall-bounded flow, understanding how polymers modify κ is inherently important to understanding the dynamics of polymer drag reduced flow, and, consequently, the phenomenon of polymer drag reduction. The goal of the present study is to explore and quantify these effects within the framework of a mean momentum based analysis.

The Surface Pressure Response of a NACA 0015 Airfoil Immersed in Grid Turbulence. Volume 1; Characteristics of the Turbulence

NASA Technical Reports Server (NTRS)

Bereketab, Semere; Wang, Hong-Wei; Mish, Patrick; Devenport, William J.

2000-01-01

Two grids have been developed for the Virginia Tech 6 ft x 6 ft Stability wind tunnel for the purpose of generating homogeneous isotropic turbulent flows for the study of unsteady airfoil response. The first, a square bi-planar grid with a 12" mesh size and an open area ratio of 69.4%, was mounted in the wind tunnel contraction. The second grid, a metal weave with a 1.2 in. mesh size and an open area ratio of 68.2% was mounted in the tunnel test section. Detailed statistical and spectral measurements of the turbulence generated by the two grids are presented for wind tunnel free stream speeds of 10, 20, 30 and 40 m/s. These measurements show the flows to be closely homogeneous and isotropic. Both grids produce flows with a turbulence intensity of about 4% at the location planned for the airfoil leading edge. Turbulence produced by the large grid has an integral scale of some 3.2 inches here. Turbulence produced by the small grid is an order of magnitude smaller. For wavenumbers below the upper limit of the inertial subrange, the spectra and correlations measured with both grids at all speeds can be represented using the von Karman interpolation formula with a single velocity and length scale. The spectra maybe accurately represented over the entire wavenumber range by a modification of the von Karman interpolation formula that includes the effects of dissipation. These models are most accurate at the higher speeds (30 and 40 m/s).

Numerical solution of potential flow about arbitrary 2-dimensional multiple bodies

NASA Technical Reports Server (NTRS)

Thompson, J. F.; Thames, F. C.

1982-01-01

A procedure for the finite-difference numerical solution of the lifting potential flow about any number of arbitrarily shaped bodies is given. The solution is based on a technique of automatic numerical generation of a curvilinear coordinate system having coordinate lines coincident with the contours of all bodies in the field, regardless of their shapes and number. The effects of all numerical parameters involved are analyzed and appropriate values are recommended. Comparisons with analytic solutions for single Karman-Trefftz airfoils and a circular cylinder pair show excellent agreement. The technique of application of the boundary-fitted coordinate systems to the numerical solution of partial differential equations is illustrated.

Thermal buoyancy on magneto hydrodynamic flow over a vertical saturated porous surface with viscous dissipation

NASA Astrophysics Data System (ADS)

Nirmala, P. H.; Saila Kumari, A.; Raju, C. S. K.

2018-04-01

In the present article, we studied the magnetohydro dynamic flow induced heat transfer from vertical surface embedded in a saturated porous medium in the presence of viscous dissipation. Appropriate similarity transformations are used to transmute the non-linear governing partial differential equations to non-linear ODE. To solve these ordinary differential equations (ODE) we used the well-known integral method of Von Karman type. A comparison has been done and originates to be in suitable agreement with the previous published results. The tabulated and graphical results are given to consider the physical nature of the problem. From this results we found that the magnetic field parameter depreciate the velocity profiles and improves the heat transfer rate of the flow.

Complex mapping of aerofoils - a different perspective

NASA Astrophysics Data System (ADS)

Matthews, Miccal T.

2012-01-01

In this article an application of conformal mapping to aerofoil theory is studied from a geometric and calculus point of view. The problem is suitable for undergraduate teaching in terms of a project or extended piece of work, and brings together the concepts of geometric mapping, parametric equations, complex numbers and calculus. The Joukowski and Karman-Trefftz aerofoils are studied, and it is shown that the Karman-Trefftz aerofoil is an improvement over the Joukowski aerofoil from a practical point of view. For the most part only a spreadsheet program and pen and paper is required, only for the last portion of the study of the Karman-Trefftz aerofoils a symbolic computer package is employed. Ignoring the concept of a conformal mapping and instead viewing the problem from a parametric point of view, some interesting mappings are obtained. By considering the derivative of the mapped mapping via the chain rule, some new and interesting analytical results are obtained for the Joukowski aerofoil, and numerical results for the Karman-Trefftz aerofoil.

Effects of turbulence, resistivity and boundary conditions on helicoidal flow collimation: Consequences for the Von-Kármán-Sodium dynamo experiment

DOE PAGES

Varela, J.; Oak Ridge National Lab.; Brun, S.; ...

2017-05-01

We present hydrodynamic and magneto-hydrodynamic simulations of a liquid sodium flow using the compressible MHD code PLUTO to investigate the magnetic field regeneration in the Von-Karman-Sodium dynamo experiment. The aim of the study is to analyze influence of the fluid resistivity and turbulence level on the collimation by helicoidal motions of a remnant magnetic field. We use a simplified cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multi-blades impeller inspired by those used in the Von-Karman-Sodium (VKS) experiment. We perform numerical simulations with kinetic Reynolds numbers up to 1000 for magnetic Prandtl numbersmore » between 30 and 0.1. Our study shows that perfect ferromagnetic walls favour enhanced collimation of flow and magnetic fields even if the turbulence degree of the model increases. More specifically the location of the helicoidal coherent vortex in between the blades changes with the impinging velocity. It becomes closer to the upstream blade and impeller base if the flow incident angle is analogous to the TM73 impeller configuration rotating in the unscooping direction. This result is also obtained at higher kinetic Reynolds numbers when the helicoidal vortex undergoes a precessing motion, leading to a reinforced effect in the vortex evolution and in the magnetic field collimation when using again perfect ferromagnetic boundary conditions. Configurations with different materials used for the impeller blades and impeller base confirm a larger enhancement of the magnetic field when perfect ferromagnetic boundary conditions are used compared with the perfect conductor case, although smaller than with a perfect ferromagnetic impeller, as it was observed in the VKS experiment. We further estimate the efficiency of a hypothetical dynamo loop occurring in the vicinity of the impeller and discuss the relevance of our findings in the context of mean field dynamo theory.« less

Effects of turbulence, resistivity and boundary conditions on helicoidal flow collimation: Consequences for the Von-Kármán-Sodium dynamo experiment

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

Varela, J.; Oak Ridge National Lab.; Brun, S.

We present hydrodynamic and magneto-hydrodynamic simulations of a liquid sodium flow using the compressible MHD code PLUTO to investigate the magnetic field regeneration in the Von-Karman-Sodium dynamo experiment. The aim of the study is to analyze influence of the fluid resistivity and turbulence level on the collimation by helicoidal motions of a remnant magnetic field. We use a simplified cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multi-blades impeller inspired by those used in the Von-Karman-Sodium (VKS) experiment. We perform numerical simulations with kinetic Reynolds numbers up to 1000 for magnetic Prandtl numbersmore » between 30 and 0.1. Our study shows that perfect ferromagnetic walls favour enhanced collimation of flow and magnetic fields even if the turbulence degree of the model increases. More specifically the location of the helicoidal coherent vortex in between the blades changes with the impinging velocity. It becomes closer to the upstream blade and impeller base if the flow incident angle is analogous to the TM73 impeller configuration rotating in the unscooping direction. This result is also obtained at higher kinetic Reynolds numbers when the helicoidal vortex undergoes a precessing motion, leading to a reinforced effect in the vortex evolution and in the magnetic field collimation when using again perfect ferromagnetic boundary conditions. Configurations with different materials used for the impeller blades and impeller base confirm a larger enhancement of the magnetic field when perfect ferromagnetic boundary conditions are used compared with the perfect conductor case, although smaller than with a perfect ferromagnetic impeller, as it was observed in the VKS experiment. We further estimate the efficiency of a hypothetical dynamo loop occurring in the vicinity of the impeller and discuss the relevance of our findings in the context of mean field dynamo theory.« less

Volcanic Plume from Mt. Unzen, Dust Cloud, cloud Vortices

NASA Image and Video Library

1991-12-01

Stable, south flowing air over the western Pacific Ocean (26.0N, 131.0E) is disturbed by islands south of Korea, resulting in sinuous clouds known as von Karman vortices. The smoke plume from Japan's Mount Unzen Volcano on Kyushu, is visible just west of the large cloud mass and extending southward. A very large, purple tinged dust pall, originating in Mongolia, can be seen on the Earth's Limb, covering eastern China and extending into the East China Sea.

Modeling of flow-dominated MHD instabilities at WiPPAL using NIMROD

NASA Astrophysics Data System (ADS)

Flanagan, K.; McCollam, K. J.; Milhone, J.; Mirnov, V. V.; Nornberg, M. D.; Peterson, E. E.; Siller, R.; Forest, C. B.

2017-10-01

Using the NIMROD (non-ideal MHD with rotation - open discussion) code developed at UW-Madison, we model two different flow scenarios to study the onset of MHD instabilities in flow-dominated plasmas in the Big Red Ball (BRB) and the Plasma Couette Experiment (PCX). Both flows rely on volumetric current drive, where a large current is drawn through the plasma across a weak magnetic field, injecting J × B torque across the whole volume. The first scenario uses a vertical applied magnetic field and a mostly radial injected current to create Couette-like flows which may excite the magnetorotational instability (MRI). In the other scenario, a quadrupolar field is applied to create counter-rotating von Karman-like flow that demonstrates a dynamo-like instability. For both scenarios, the differences between Hall and MHD Ohm's laws are explored. The implementation of BRB geometry in NIMROD, details of the observed flows, and instability results are shown. This work was funded by DoE and NSF.

Lagrangian Visualization and Real-Time Identification of the Vortex Shedding Time in the Wake of a Circular Cylinder

NASA Astrophysics Data System (ADS)

Rockwood, Matthew P.

The flow around a circular cylinder, a canonical bluff body, has been extensively studied in the literature to determine the mechanisms that cause the formation of vortices in the cylinder wake. Understanding of these mechanisms has led to myriad attempts to control the vortices either to mitigate the oscillating forces they cause, or to augment them in order to enhance mixing in the near-wake. While these flow control techniques have been effective at low Reynolds numbers, they generally lose effectiveness or require excessive power at Reynolds numbers commonly experienced in practical applications. For this reason, new methods for identifying the locations of vortices and their shedding time could increase the effectiveness of the control techniques. In the current work, two-dimensional, two-component velocity data was collected in the wake of a circular cylinder using a planar digital particle image velocimetry (DPIV) measurement system at Reynolds numbers of 9,000 and 19,000. This experimental data, as well as two-dimensional simulation data at a Reynolds number of 150, and three-dimensional simulation data at a Reynolds number of 400, is used to calculate the finite-time Lyapunov exponent (FTLE) field. The locations of Lagrangian saddles, identified as non-parallel intersections of positive and negative time FTLE ridges, are shown to indicate the timing of von Karman vortex shedding in the wake of a circular cylinder. The Lagrangian saddle found upstream of a forming and subsequently shedding vortex is shown to clearly accelerate away from the cylinder surface as the vortex begins to shed. This provides a novel, objective method to determine the timing of vortex shedding. The saddles are impossible to track in real-time, however, since future flow field data is needed for the computation of the FTLE fields. In order to detect the Lagrangian saddle acceleration without direct access to the FTLE, the saddle dynamics are connected to measurable surface quantities on a circular cylinder in crossflow. The acceleration of the Lagrangian saddle occurs simultaneously with a maximum in lift in both numerical cases, and with a minimum in the static pressure at a location slightly upstream of the mean separation location in the numerical cases, as well as the experimental data at a Reynolds number of 19,000. This allows the von Karman vortex shedding time, determined objectively by the acceleration of the Lagrangian saddle away from the circular cylinder, to be detected by a minimum in the static pressure at one location on the cylinder, a quantity that can be measured in real-time using available pressure sensors. These results can be used to place sensors in optimal locations on bluff bodies to inform closed-loop flow control algorithms of the timing of von Karman vortex shedding.

Numerical and Experimental Investigation of Cavitating Characteristics in Centrifugal Pump with Gap Impeller

NASA Astrophysics Data System (ADS)

Zhu, Bing; Chen, Hongxun; Wei, Qun

2014-06-01

This paper is to study the cavitating characteristics in a low specific speed centrifugal pump with gap structure impeller experimentally and numerically. A scalable DES numerical method is proposed and developed by introducing the von Karman scale instead of the local grid scale, which can switch at the RANS and LES region interface smoothly and reasonably. The SDES method can detect and grasp unsteady scale flow structures, which were proved by the flow around a triangular prism and the cavitation flow in a centrifugal pump. Through numerical and experimental research, it's shown that the simulated results match qualitatively with tested cavitation performances and visualization patterns, and we can conclude that the gap structure impeller has a superior feature of cavitation suppression. Its mechanism may be the guiding flow feature of the small vice blade and the pressure auto-balance effect of the gap tunnel.

Turbulence and mechanism of resistance on spheres and cylinders

NASA Technical Reports Server (NTRS)

Ahlborn, FR

1932-01-01

The nature of turbulent flow through pipes and around obstacles is analyzed and illustrated by photographs of turbulence on screens and straighteners. It is shown that the reversal of flow and of the resistance law on spheres is not explainable by Prandtl's turbulence in the boundary layer. The investigation of the analogous phenomena on the cylinder yields a reversal of the total field of flow. The very pronounced changes in pressure distribution connected with it were affirmed by manometric measurements on spheres by Professor O. Krell. The reversal in a homogenous nonvortical flow is brought about by the advance of the stable arrangement of Karman's dead air vortices toward the test object and by the substitution of an alternatingly one-sided or rotating but stable vortex formation in place of the initially symmetrical formation. This also explains the marked variations of the models.

Turbulence and turbulent drag reduction in swirling flow: Inertial versus viscous forcing

NASA Astrophysics Data System (ADS)

Burnishev, Yuri; Steinberg, Victor

2015-08-01

We report unexpected results of a drastic difference in the transition to fully developed turbulent and turbulent drag reduction (TDR) regimes and in their properties in a von Karman swirling flow with counter-rotating disks of water-based polymer solutions for viscous (by smooth disks) as well as inertial (by bladed disks) forcing and by tracking just torque Γ (t ) and pressure p (t ) . For the viscous forcing, just a single TDR regime is found with the transition values of the Reynolds number (Re) Recturb=RecTDR≃(4.8 ±0.2 ) ×105 independent of ϕ , whereas for the inertial forcing two turbulent regimes are revealed. The first transition is to fully developed turbulence, and the second one is to the TDR regime with both Recturb and RecTDR depending on polymer concentration ϕ . Both regimes differ by the values of Cf and Cp, by the scaling exponents of the fundamental turbulent characteristics, by the nonmonotonic dependencies of skewness and flatness of the pressure PDFs on Re, and by the different frequency power spectra of p with the different dependencies of the main vortex peak frequency in the p power spectra on ϕ and Re. Thus our experimental results show the transition to the TDR regime in a von Karman swirling flow for the viscous and inertial forcings in a sharp contrast to the recent experiments [Phys. Fluids 10, 426 (1998), 10.1063/1.869532; Phys. Rev. E 47, R28(R) (1993), 10.1103/PhysRevE.47.R28; and J. Phys.: Condens. Matter 17, S1195 (2005), 10.1088/0953-8984/17/14/008] where the transition to TDR is observed in the same swirling flow with counter-rotating disks only for the viscous forcing. The latter result has led its authors to the wrong conclusion that TDR is a solely boundary effect contrary to the inertial forcing associated with the bulk effect, and this conception is currently rather widely accepted in literature.

Turbulence and turbulent drag reduction in swirling flow: Inertial versus viscous forcing.

PubMed

Burnishev, Yuri; Steinberg, Victor

2015-08-01

We report unexpected results of a drastic difference in the transition to fully developed turbulent and turbulent drag reduction (TDR) regimes and in their properties in a von Karman swirling flow with counter-rotating disks of water-based polymer solutions for viscous (by smooth disks) as well as inertial (by bladed disks) forcing and by tracking just torque Γ(t) and pressure p(t) . For the viscous forcing, just a single TDR regime is found with the transition values of the Reynolds number (Re) Re turb c =Re TDR c ≃(4.8±0.2)×10(5) independent of ϕ , whereas for the inertial forcing two turbulent regimes are revealed. The first transition is to fully developed turbulence, and the second one is to the TDR regime with both Re turb c and Re TDR c depending on polymer concentration ϕ . Both regimes differ by the values of C f and C p , by the scaling exponents of the fundamental turbulent characteristics, by the nonmonotonic dependencies of skewness and flatness of the pressure PDFs on Re, and by the different frequency power spectra of p with the different dependencies of the main vortex peak frequency in the p power spectra on ϕ and Re. Thus our experimental results show the transition to the TDR regime in a von Karman swirling flow for the viscous and inertial forcings in a sharp contrast to the recent experiments [Phys. Fluids 10, 426 (1998); Phys. Rev. E 47, R28(R) (1993); and J. Phys.: Condens. Matter 17, S1195 (2005)] where the transition to TDR is observed in the same swirling flow with counter-rotating disks only for the viscous forcing. The latter result has led its authors to the wrong conclusion that TDR is a solely boundary effect contrary to the inertial forcing associated with the bulk effect, and this conception is currently rather widely accepted in literature.

Drag reducing properties of microalgal exopolymers.

PubMed

Ramus, J; Kenney, B E; Shaughnessy, E J

1989-01-25

Dilute aqueous solutions of polymers released by marine phytoplankton (microalgae) were shown to effectively reduce drag in capillary pipe flow. Tests were performed in a capillary turbulent flow viscometer which extruded small samples under high pressures. In all, 22 species were screened, and the products of one chlorophyte and four rhodophyte species proved especially effective. The viscoelastic polymers produced by these species delayed the transition from laminar to turbulent flow to significantly higher Re. In general, polymeric regime segments come off the maximum drag reduction asymptote at characteristic retro-onset points, and come to lie approximately parallel to, but displaced upwards from the Prandtl-von Karman line. The delay to transition was shown to be dependent on additive polymer concentration, capillary diameter, and temperature. Ionic concentration, ionic composition, or pH had little effect on drag reducing properties.

Equilibrium and stability of flow-dominated Plasmas in the Big Red Ball

NASA Astrophysics Data System (ADS)

Siller, Robert; Flanagan, Kenneth; Peterson, Ethan; Milhone, Jason; Mirnov, Vladimir; Forest, Cary

2017-10-01

The equilibrium and linear stability of flow-dominated plasmas are studied numerically using a spectral techniques to model MRI and dynamo experiments in the Big Red Ball device. The equilibrium code solves for steady-state magnetic fields and plasma flows subject to boundary conditions in a spherical domain. It has been benchmarked with NIMROD (non-ideal MHD with rotation - open discussion), Two different flow scenarios are studied. The first scenario creates a differentially rotating toroidal flow that is peaked at the center. This is done to explore the onset of the magnetorotational instability (MRI) in a spherical geometry. The second scenario creates a counter-rotating von Karman-like flow in the presence of a weak magnetic field. This is done to explore the plasma dynamo instability in the limit of a weak applied field. Both scenarios are numerically modeled as axisymmetric flow to create a steady-state equilibrium solution, the stability and normal modes are studied in the lowest toroidal mode number. The details of the observed flow, and the structure of the fastest growing modes will be shown. DoE, NSF.

Lattice-Gas Automata Fluids on Parallel Supercomputers

DTIC Science & Technology

1993-11-23

Kelvin-Helmholtz shear instabil- ity, and the Von Karman vortex shedding instability. Performance of the two machines in terms of both site update... PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Phillips Laboratory,Hanscom Field,MA,01731 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING...Helmholtz shear instability, and the Von Karman vortex shedding instability. Performance of the two machines in terms of both site update rate and

Unsteady wind loads for TMT: replacing parametric models with CFD

NASA Astrophysics Data System (ADS)

MacMartin, Douglas G.; Vogiatzis, Konstantinos

2014-08-01

Unsteady wind loads due to turbulence inside the telescope enclosure result in image jitter and higher-order image degradation due to M1 segment motion. Advances in computational fluid dynamics (CFD) allow unsteady simulations of the flow around realistic telescope geometry, in order to compute the unsteady forces due to wind turbulence. These simulations can then be used to understand the characteristics of the wind loads. Previous estimates used a parametric model based on a number of assumptions about the wind characteristics, such as a von Karman spectrum and frozen-flow turbulence across M1, and relied on CFD only to estimate parameters such as mean wind speed and turbulent kinetic energy. Using the CFD-computed forces avoids the need for assumptions regarding the flow. We discuss here both the loads on the telescope that lead to image jitter, and the spatially-varying force distribution across the primary mirror, using simulations with the Thirty Meter Telescope (TMT) geometry. The amplitude, temporal spectrum, and spatial distribution of wind disturbances are all estimated; these are then used to compute the resulting image motion and degradation. There are several key differences relative to our earlier parametric model. First, the TMT enclosure provides sufficient wind reduction at the top end (near M2) to render the larger cross-sectional structural areas further inside the enclosure (including M1) significant in determining the overall image jitter. Second, the temporal spectrum is not von Karman as the turbulence is not fully developed; this applies both in predicting image jitter and M1 segment motion. And third, for loads on M1, the spatial characteristics are not consistent with propagating a frozen-flow turbulence screen across the mirror: Frozen flow would result in a relationship between temporal frequency content and spatial frequency content that does not hold in the CFD predictions. Incorporating the new estimates of wind load characteristics into TMT response predictions leads to revised estimates of the response of TMT to wind turbulence, and validates the aerodynamic design of the enclosure.

Calculation of Compressible Flows past Aerodynamic Shapes by Use of the Streamline Curvature

NASA Technical Reports Server (NTRS)

Perl, W

1947-01-01

A simple approximate method is given for the calculation of isentropic irrotational flows past symmetrical airfoils, including mixed subsonic-supersonic flows. The method is based on the choice of suitable values for the streamline curvature in the flow field and the subsequent integration of the equations of motion. The method yields limiting solutions for potential flow. The effect of circulation is considered. A comparison of derived velocity distributions with existing results that are based on calculation to the third order in the thickness ratio indicated satisfactory agreement. The results are also presented in the form of a set of compressibility correction rules that lie between the Prandtl-Glauert rule and the von Karman-Tsien rule (approximately). The different rules correspond to different values of the local shape parameter square root sign YC sub a, in which Y is the ordinate and C sub a is the curvature at a point on an airfoil. Bodies of revolution, completely supersonic flows, and the significance of the limiting solutions for potential flow are also briefly discussed.

Atmospheric Turbulence Modeling for Aerospace Vehicles: Fractional Order Fit

NASA Technical Reports Server (NTRS)

Kopasakis, George (Inventor)

2015-01-01

An improved model for simulating atmospheric disturbances is disclosed. A scale Kolmogorov spectral may be scaled to convert the Kolmogorov spectral into a finite energy von Karman spectral and a fractional order pole-zero transfer function (TF) may be derived from the von Karman spectral. Fractional order atmospheric turbulence may be approximated with an integer order pole-zero TF fit, and the approximation may be stored in memory.

Numerical study of laminar plasma dynamo in cylindrical and spherical geometries

NASA Astrophysics Data System (ADS)

Khalzov, Ivan; Bayliss, Adam; Ebrahimi, Fatima; Forest, Cary; Schnack, Dalton

2009-05-01

We have performed the numerical investigation of possibility of laminar dynamo in two new experiments, Plasma Couette and Plasma Dynamo, which have been designed at the University of Wisconsin-Madison. The plasma is confined by a strong multipole magnetic field localized at the boundary of cylindrical (Plasma Couette) or spherical (Plasma Dynamo) chamber. Electrodes positioned between the magnet rings can be biased with arbitrary potentials so that Lorenz force ExB drives any given toroidal velocity profile at the surface. Using the extended MHD code, NIMROD, we have modeled several types of plasma flows appropriate for dynamo excitation. It is found that for high magnetic Reynolds numbers the counter-rotating von Karman flow (in cylinder) and Dudley-James flow (in sphere) can lead to self-generation of non-axisymmetric magnetic field. This field saturates at certain amplitude corresponding to a new stable equilibrium. The structure of this equilibrium is considered.

Results of aeroheating DFI and ET design-data test on a 0.0175-scale model 60-OTS conducted in the Von Karman Gas Dynamics Facility (VKF) 40" supersonic and the 50" hypersonic wind tunnels A and C

NASA Technical Reports Server (NTRS)

Marroquin, J.; Leef, C. R.

1985-01-01

The 0.0175-scale thin-skin thermocouple Model 60-OTS was tested in the von Karman Gas Facility 40-inch continuous flow supersonic tunnel A and the VKF Tunnel C. Testing was conducted at Mach numbers 2.25 to 4.0, and Reynolds numbers from 0.4 x 10 to the 6th power/ft to 6.6 x 10 to the 6th power/ft. Angle of attack range was from -5.0 to +5.0 degrees, and angle of sideslip range was from -6 to +6 degrees. The primary objective of this test was to provide a valid base for the external tank (ET) and solid rocket booster (SRB) heating prediction methodology for ascent flight by taking heating data at Development Flight Instrumentation (DFI) locations for flight conditions simulating STS-1 through -4. A second objective was to obtain additional aeroheating data to support potential reduction of the thermal protection system (TPS) on the ET. The third phase of the test was funded and conducted by NASA/MSFC for the purpose of establishing confidence in the data base from the lower temperature tunnel A.

Direct Measurements of Skin Friction

NASA Technical Reports Server (NTRS)

Dhawan, Satish

1953-01-01

A device has been developed to measure local skin friction on a flat plate by measuring the force exerted upon a very small movable part of the surface of the flat plate. These forces, which range from about 1 milligram to about 100 milligrams, are measured by means of a reactance device. The apparatus was first applied to measurements in the low-speed range, both for laminar and turbulent boundary layers. The measured skin-friction coefficients show excellent agreement with Blasius' and Von Karman's results. The device was then applied to high-speed subsonic flow and the turbulent-skin-friction coefficients were determined up to a Mach number of about 0.8. A few measurements in supersonic flow were also made. This paper describes the design and construction of the device and the results of the measurements.

Finite element approximation of an optimal control problem for the von Karman equations

NASA Technical Reports Server (NTRS)

Hou, L. Steven; Turner, James C.

1994-01-01

This paper is concerned with optimal control problems for the von Karman equations with distributed controls. We first show that optimal solutions exist. We then show that Lagrange multipliers may be used to enforce the constraints and derive an optimality system from which optimal states and controls may be deduced. Finally we define finite element approximations of solutions for the optimality system and derive error estimates for the approximations.

Numerical investigation of the origin of vortex asymmetry of flows over bodies at large angle of attack

NASA Technical Reports Server (NTRS)

Degani, David

1990-01-01

The occurrence of the flow about a slender body of revolution placed at incidence to an incoming stream is numerically examined for angles of attack ranging from 20 to 80 degrees and a Reynolds number of 200,000 based on maximum body diameter. Over a certain range of Reynolds numbers, the trend of flowfields around slender bodies at incidence can be roughly divided into three main categories: (1) at alpha = 0-30 deg, the flow is steady and symmetric; (2) at alpha = 30-60 deg, the flow under normal conditions is usually asymmetric, but the level of the asymmetry depends on the amount of disturbances present on the tip of the body; and (3) at alpha 60-90 deg, the flow in the wake of the body acts in a fashion similar to that of the Karman vortex shedding behind a two-dimensional circular cylinder. For each of these categories the range of incidence may change by + or - 10 degrees, depending on the quality of flow, or body finish.

Research on conformal dome of Karman-curve shape

NASA Astrophysics Data System (ADS)

Zhang, Yunqiang; Chang, Jun; Niu, Yajun

2018-01-01

Because the conformal optical technology can obviously improve the aerodynamic performance of the infrared guidance missile, it has been studied deeply in recent years. By comparing the performance of the missiles with conformal dome and conventional missiles, the advantages of the conformal optical technology are demonstrated in the maneuverability and stealth of the missile. At present, the study of conformal optical systems focuses on ellipsoid or quadratic curve types. But in actual use, the dome using these curves is not the best choice. In this paper, the influence of different shape of the dome on aerodynamic performance, aerodynamic heating, internal space volume and other properties is discussed. The result shows infrared optical system with conformal dome of Karman-curve shape has a good application prospect, is the future direction of development. Finally, the difficult problems of conformal dome of Karman-curve shape are discussed.

UV reactor flow visualization and mixing quantification using three-dimensional laser-induced fluorescence.

PubMed

Gandhi, Varun; Roberts, Philip J W; Stoesser, Thorsten; Wright, Harold; Kim, Jae-Hong

2011-07-01

Three-dimensional laser-induced fluorescence (3DLIF) was applied to visualize and quantitatively analyze mixing in a lab-scale UV reactor consisting of one lamp sleeve placed perpendicular to flow. The recirculation zone and the von Karman vortex shedding that commonly occur in flows around bluff bodies were successfully visualized. Multiple flow paths were analyzed by injecting the dye at various heights with respect to the lamp sleeve. A major difference in these pathways was the amount of dye that traveled close to the sleeve, i.e., a zone of higher residence time and higher UV exposure. Paths away from the center height had higher velocities and hence minimal influence by the presence of sleeve. Approach length was also characterized in order to increase the probability of microbes entering the region around the UV lamp. The 3DLIF technique developed in this study is expected to provide new insight on UV dose delivery useful for the design and optimization of UV reactors. Copyright © 2011 Elsevier Ltd. All rights reserved.

Holocinematographic velocimeter for measuring time-dependent, three-dimensional flows

NASA Technical Reports Server (NTRS)

Beeler, George B.; Weinstein, Leonard M.

1987-01-01

Two simulatneous, orthogonal-axis holographic movies are made of tracer particles in a low-speed water tunnel to determine the time-dependent, three-dimensional velocity field. This instrument is called a Holocinematographic Velocimeter (HCV). The holographic movies are reduced to the velocity field with an automatic data reduction system. This permits the reduction of large numbers of holograms (time steps) in a reasonable amount of time. The current version of the HCV, built for proof-of-concept tests, uses low-frame rate holographic cameras and a prototype of a new type of water tunnel. This water tunnel is a unique low-disturbance facility which has minimal wall effects on the flow. This paper presents the first flow field examined by the HCV, the two-dimensional von Karman vortex street downstream of an unswept circular cylinder. Key factors in the HCV are flow speed, spatial and temporal resolution required, measurement volume, film transport speed, and laser pulse length. The interactions between these factors are discussed.

Development and application of a particle image velocimeter for high-speed flows

NASA Astrophysics Data System (ADS)

Molezzi, M. J.; Dutton, J. C.

1992-01-01

A particle image velocimetry (PIV) system has been developed for use in high-speed separated air flows. The image acquisition system uses two 550 mJ/pulse Nd:YAG lasers and is fully controlled by a host Macintosh computer. The interrogation system is also Macintosh-based and performs interrogations at approximately 2.3 sec/spot and 4.0 sec/spot when using the Young's fringe and autocorrelation methods, respectively. The system has been proven in preliminary experiments using known-displacement simulated PIV photographs and a simple axisymmetric jet flow. Further results have been obtained in a transonic wind tunnel operating at Mach 0.4 to 0.5 (135 m/s to 170 m/s). PIV experiments were done with an empty test section to provide uniform flow data for comparison with pressure and LDV data, then with a two-dimensional base model, revealing features of the von Karman vortex street wake and underlying small scale turbulence.

Simulations of plasma dynamo in cylindrical and spherical geometries

NASA Astrophysics Data System (ADS)

Khalzov, Ivan; Forest, Cary; Schnack, Dalton; Ebrahimi, Fatima

2010-11-01

We have performed the numerical investigation of plasma flow and possibility of dynamo effect in Madison Plasma Couette Experiment (MPCX) and Madison Plasma Dynamo Experiment (MPDX), which are being installed at the University of Wisconsin- Madison. Using the extended MHD code, NIMROD, we have studied several types of plasma flows appropriate for dynamo excitation. Calculations are done for isothermal compressible plasma model including two-fluid effects (Hall term), which is beyond the standard incompressible MHD picture. It is found that for magnetic Reynolds numbers exceeding the critical one the counter-rotating Von Karman flow (in cylinder) and Dudley- James flow (in sphere) result in self-generation of magnetic field. Depending on geometry and plasma parameters this field can either saturate at certain amplitude corresponding to a new stable equilibrium (laminar dynamo) or lead to turbulent dynamo. It is shown that plasma compressibility results in increase of the critical magnetic Reynolds number while two- fluid effects change the level of saturated dynamo field. The work is supported by NSF.

Turbulent Friction in the Boundary Layer of a Flat Plate in a Two-Dimensional Compressible Flow at High Speeds

NASA Technical Reports Server (NTRS)

Frankl, F.; Voishel, V.

1943-01-01

In the present report an investigation is made on a flat plate in a two-dimensional compressible flow of the effect of compressibility and heating on the turbulent frictional drag coefficient in the boundary layer of an airfoil or wing radiator. The analysis is based on the Prandtl-Karman theory of the turbulent boundary later and the Stodola-Crocco, theorem on the linear relation between the total energy of the flow and its velocity. Formulas are obtained for the velocity distribution and the frictional drag law in a turbulent boundary later with the compressibility effect and heat transfer taken into account. It is found that with increase of compressibility and temperature at full retardation of the flow (the temperature when the velocity of the flow at a given point is reduced to zero in case of an adiabatic process in the gas) at a constant R (sub x), the frictional drag coefficient C (sub f) decreased, both of these factors acting in the same sense.

The effect of chordwise flexibility on flapping foil propulsion in quiescent fluid

NASA Astrophysics Data System (ADS)

Shinde, Sachin; Arakeri, Jaywant

2010-11-01

Motivated to understand the role of wing flexibility of flying creatures during hovering, we experimentally study the effect of chordwise flexibility on the flow generated in quiescent fluid by a sinusoidally pitching rigid symmetrical foil with a flexible flap attached at the trailing edge. This foil produces a narrow, coherent jet containing reverse Karman vortex street, and a corresponding thrust. The thrust and flow is similar to that produced by a hovering bird or insect, however the mechanism seems to be different from known hovering mechanisms. Novelty of the present hovering mechanism is that the thrust generation is due to the coordinated pushing action of rigid foil and flexible flap. We identify the flow and vortex generation mechanism. This foil produces jet flows over a range of flapping frequencies and amplitudes. In contrast, the foil without flap i.e. with rigid trailing edge produces a weak, divergent jet that meanders randomly. Appending a flexible flap to the foil suppresses jet-meandering and strengthens the jet. Flexibility of flap is crucial in determining the flow structure. This study is useful in designing MAVs and thrusters.

Periodic vortex shedding in the supersonic wake of a planar plate

NASA Technical Reports Server (NTRS)

Xing, W. F.; Marenbach, G.

1985-01-01

Vortex sheets in the wake have been mainly studied in incompressible flows and in the transonic region. Heinemann et al. (1976) have shown that for the subsonic region the Strouhal number is nearly independent of the Mach number. Motallebi and Norbury (1981) have observed an increase in the Strouhal number in transonic supersonic flow at Mach numbers up to 1.25. The present investigation is concerned with an extension of the studies of vortex shedding to higher supersonic Mach numbers, taking into account questions regarding the possibility of a generation of stable von Karman vortex paths in the considered Mach number range. It is found that the vortex sheet observed in a supersonic wake behind a rough plate is only stable and reproducible in cases involving a certain surface roughness and certain aspects of trailing edge geometry.

Evaluation of a Multigrid Scheme for the Incompressible Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

Swanson, R. C.

2004-01-01

A fast multigrid solver for the steady, incompressible Navier-Stokes equations is presented. The multigrid solver is based upon a factorizable discrete scheme for the velocity-pressure form of the Navier-Stokes equations. This scheme correctly distinguishes between the advection-diffusion and elliptic parts of the operator, allowing efficient smoothers to be constructed. To evaluate the multigrid algorithm, solutions are computed for flow over a flat plate, parabola, and a Karman-Trefftz airfoil. Both nonlifting and lifting airfoil flows are considered, with a Reynolds number range of 200 to 800. Convergence and accuracy of the algorithm are discussed. Using Gauss-Seidel line relaxation in alternating directions, multigrid convergence behavior approaching that of O(N) methods is achieved. The computational efficiency of the numerical scheme is compared with that of Runge-Kutta and implicit upwind based multigrid methods.

Free-standing thermalized graphene: a hard/soft hybrid

NASA Astrophysics Data System (ADS)

Nelson, David

2015-03-01

Understanding deformations of macroscopic thin plates and shells has a long and rich history, culminating with the Foeppl-von Karman equations in 1904. These highly nonlinear equations are characterized by a dimensionless coupling constant (the ``Foeppl-von Karman number'') that can easily reach vK = 107 in an ordinary sheet of writing paper. Since the late 1980's, it has been clear that thermal fluctuations in microscopically thin elastic membranes fundamentally alter the long wavelength physics, leading to a negative thermal expansion coefficient, and a strongly scale-dependent bending energy and Young's modulus. Recent experiments from the McEuen group at Cornell that twist and bend individual atomically-thin free-standing graphene sheets (with vK = 1013!) call for a theory of the mechanical deformation of thermally excited membranes with large Foeppl-von Karman number. We present here results for the bending and pulling of thermalized graphene ribbons and tabs in the cantilever mode. Work done in collaboration with Andrej Kosmrlj.

Elliptical Instability of Rotating Von Karman Street

NASA Astrophysics Data System (ADS)

Stegner, A.; Pichon, T.; Beunier, M.

Clouds often reveal a meso-scale vortex shedding in the wake of mountainous islands. Unlike the classical bi-dimensional Von-Karman street, these observed vortex street are affected by the earth rot ation and vertical stratification. Theses effects could induce a selective destabilization of anticyclonic vortices. It is well known that inertial instability (also called centrifugal instability) induce a three- dimensional destabilization of anticyclonic structures when the absolute vorticity is larger than the local Coriolis parameter. However, we have shown, by the mean of laboratory experiments, that it is a different type of instability which is mainly responsible for asymmetric rotating Von-Karman street. A serie of experiments were performed to study the wake of a cylinder in a rotating fluid, at medium Reynolds number and order one Rossby number. We have shown that the vertical structure of unstable anticyclonic vortices is characteristic of an elliptical instability. Besides, unlike the inertial instability, the vertical unstable wavelength depends on the Rossby number.

A nonperturbing boundary-layer transition detection

NASA Astrophysics Data System (ADS)

Ohare, J. E.

1985-01-01

A laser interferometer technique is being applied to the characterization of boundary-layer conditions on models in supersonic and hypersonic wind tunnels in the von Karman Facility at Arnold Engineering Development Center (AEDC). The Boundary-Layer Transition Detector (BLTD), based on lateral interferometry, is applicable for determining the turbulence frequency spectrum of boundary layers in compressible flow. The turbulence, in terms of air density fluctuations, is detected by monitoring interferometric fringe phase shifts (in real time) formed by one beam which passes through the boundary layer and a reference beam which is outside the boundary layer. This technique is nonintrusive to the flow field unlike other commonly used methods such as pitot tube probing and hot-wire anemometry. Model boundary-layer data are presented at Mach 8 and compared with data recorded using other methods during boundary-layer transition from laminar to turbulent flow. Spectra from the BLTD reveal the presence of a high-frequency peak during transition, which is characteristic of spectra obtained with hot wires. The BLTD is described along with operational requirements and limitations.

Analysis and calculation by integral methods of laminar compressible boundary-layer with heat transfer and with and without pressure gradient

NASA Technical Reports Server (NTRS)

Morduchow, Morris

1955-01-01

A survey of integral methods in laminar-boundary-layer analysis is first given. A simple and sufficiently accurate method for practical purposes of calculating the properties (including stability) of the laminar compressible boundary layer in an axial pressure gradient with heat transfer at the wall is presented. For flow over a flat plate, the method is applicable for an arbitrarily prescribed distribution of temperature along the surface and for any given constant Prandtl number close to unity. For flow in a pressure gradient, the method is based on a Prandtl number of unity and a uniform wall temperature. A simple and accurate method of determining the separation point in a compressible flow with an adverse pressure gradient over a surface at a given uniform wall temperature is developed. The analysis is based on an extension of the Karman-Pohlhausen method to the momentum and the thermal energy equations in conjunction with fourth- and especially higher degree velocity and stagnation-enthalpy profiles.

Investigation of feasibility of wind turbulence measurement by a pulsed coherent doppler lidar in the atmospheric boundary layer

NASA Astrophysics Data System (ADS)

Smalikho, Igor; Banakh, Viktor

2018-04-01

Feasibilities of determination of the wind turbulence parameters from data measured by the Stream Line coherent Doppler lidar under different atmospheric conditions have been studied experimentally. It has been found that the spatial structure of the turbulence is described well by the von Karman model in the layer of intensive mixing. From the lidar measurements at night under stable conditions the estimation of the outer scale of turbulence with the use of the von Karman model is not possible.

Heat Transfer in a Turbulent Liquid or Gas Stream

NASA Technical Reports Server (NTRS)

Latzko, H.

1944-01-01

The,theory of heat.transfer from a solid body to a liquid stream could he presented previously** only with limiting assumptions about the movement of the fluid (potential flow, laminar frictional flow). (See references 1, 2, and 3). For turbulent flow, the most important practical case, the previous theoretical considerations did not go beyond dimensionless formulas and certain conclusions as to the analogy between the friction factor and the unit thermal conductance, (See references 4, 5, 6, and 7,) In order to obtain numerical results, an experimental treatment of the problem was resorted to, which gave rise to numerous investigations because of the importance of this problem in many branches of technology. However, the results of these investigations frequently deviate from one another. The experimental results are especially dependent upon the overall dimensions and the specific proportions of the equipment. In the present work, the attempt will be made to develop systematically the theory of the heat transfer and of the dependence of the unit thermal conductance upon shape and dimensions, using as a basis the velocity distribution for turbulent flow set up by Prandtl and Von Karman.

On the flow of a compressible fluid by the hodograph method I : unification and extension of present-day results

NASA Technical Reports Server (NTRS)

Garrick, I E; Kaplan, Carl

1944-01-01

Elementary basic solutions of the equations of motion of a compressible fluid in the hodograph variables are developed and used to provide a basis for comparison, in the form of velocity correction formulas, of corresponding compressible and incompressible flows. The known approximate results of Chaplygin, Von Karman and Tsien, Temple and Yarwood, and Prandtl and Glauert are unified by means of the analysis of the present paper. Two new types of approximations, obtained from the basic solutions, are introduced; they possess certain desirable features of the other approximations and appear preferable as a basis for extrapolation into the range of high stream Mach numbers and large disturbances to the main stream. Tables and figures giving velocity and pressure-coefficient correction factors are included in order to facilitate the practical application of the results.

Nonlocal modeling and buckling features of cracked nanobeams with von Karman nonlinearity

NASA Astrophysics Data System (ADS)

Akbarzadeh Khorshidi, Majid; Shaat, Mohamed; Abdelkefi, Abdessattar; Shariati, Mahmoud

2017-01-01

Buckling and postbuckling behaviors of cracked nanobeams made of single-crystalline nanomaterials are investigated. The nonlocal elasticity theory is used to model the nonlocal interatomic effects on the beam's performance accounting for the beam's axial stretching via von Karman nonlinear theory. The crack is then represented as torsional spring where the crack severity factor is derived accounting for the nonlocal features of the beam. By converting the beam into an equivalent infinite long plate with an edge crack subjected to a tensile stress at the far field, the crack energy release rate, intensity factor, and severity factor are derived according to the nonlocal elasticity theory. An analytical solution for the buckling and the postbuckling responses of cracked nonlocal nanobeams accounting for the beam axial stretching according to von Karman nonlinear theory of kinematics is derived. The impacts of the nonlocal parameter on the critical buckling loads and the static nonlinear postbuckling responses of cracked nonlocal nanobeams are studied. The results indicate that the buckling and postbuckling behaviors of cracked nanobeams are strongly affected by the crack location, crack depth, nonlocal parameter, and length-to-thickness ratio.

Three-dimensional modelling of thin liquid films over spinning disks

NASA Astrophysics Data System (ADS)

Zhao, Kun; Wray, Alex; Yang, Junfeng; Matar, Omar

2016-11-01

In this research the dynamics of a thin film flowing over a rapidly spinning, horizontal disk is considered. A set of non-axisymmetric evolution equations for the film thickness, radial and azimuthal flow rates are derived using a boundary-layer approximation in conjunction with the Karman-Polhausen approximation for the velocity distribution in the film. These highly nonlinear partial differential equations are then solved numerically in order to reveal the formation of two and three-dimensional large-amplitude waves that travel from the disk inlet to its periphery. The spatio-temporal profile of film thickness provides us with visualization of flow structures over the entire disk and by varying system parameters(volumetric flow rate of fluid and rotational speed of disk) different wave patterns can be observed, including spiral, concentric, smooth waves and wave break-up in exceptional conditions. Similar types of waves can be found by experimentalists in literature and CFD simulation and our results show good agreement with both experimental and CFD results. Furthermore, the semi-parabolic velocity profile assumed in our model under the waves is directly compared with CFD data in various flow regimes in order to validate our model. EPSRC UK Programme Grant EP/K003976/1.

An Examination of Parameters Affecting Large Eddy Simulations of Flow Past a Square Cylinder

NASA Technical Reports Server (NTRS)

Mankbadi, M. R.; Georgiadis, N. J.

2014-01-01

Separated flow over a bluff body is analyzed via large eddy simulations. The turbulent flow around a square cylinder features a variety of complex flow phenomena such as highly unsteady vortical structures, reverse flow in the near wall region, and wake turbulence. The formation of spanwise vortices is often times artificially suppressed in computations by either insufficient depth or a coarse spanwise resolution. As the resolution is refined and the domain extended, the artificial turbulent energy exchange between spanwise and streamwise turbulence is eliminated within the wake region. A parametric study is performed highlighting the effects of spanwise vortices where the spanwise computational domain's resolution and depth are varied. For Re=22,000, the mean and turbulent statistics computed from the numerical large eddy simulations (NLES) are in good agreement with experimental data. Von-Karman shedding is observed in the wake of the cylinder. Mesh independence is illustrated by comparing a mesh resolution of 2 million to 16 million. Sensitivities to time stepping were minimized and sampling frequency sensitivities were nonpresent. While increasing the spanwise depth and resolution can be costly, this practice was found to be necessary to eliminating the artificial turbulent energy exchange.

Quasi-periodic transverse plasma flow associated with an evolving MHD vortex street in the outer heliosphere

NASA Technical Reports Server (NTRS)

Siregar, Edouard; Roberts, D. A.; Goldstein, Melvyn L.

1993-01-01

We study a transverse plasma flow induced by the evolution of a Karman vortex street using a Chebyshev-Fourier spectral algorithm to solve both the compressible Navier-Stokes and MHD equations. The evolving vortex street is formed by the nonlinear interaction of two vortex sheets initially in equilibrium. We study spatial profiles of the total plasma velocity, the density, the meridional flow angle and the location of sector boundaries and find generally good agreement with Voyager 2 measurements of quasi-periodic transverse flow in the outer heliosphere. The pressure pulses associated with the meridional flows in the simulation are too small, although they are correctly located, and this may be due to the lack of any 'warp' in the current sheet in this model. A strong, flow-aligned magnetic field, such as would occur in the inner heliosphere, is shown to lead to weak effects that would be masked by the background interplanetary turbulence. We also study the plasma and magnetic transport resulting from the meridional flow and find that deficits of magnetic quantities do occur near the ecliptic. While the effect is relatively small, it is in general agreement with the most recent analysis of 'flux deficit' in the outer heliosphere.

Polymer concentration and properties of elastic turbulence in a von Karman swirling flow

NASA Astrophysics Data System (ADS)

Jun, Yonggun; Steinberg, Victor

2017-10-01

We report detailed experimental studies of statistical, scaling, and spectral properties of elastic turbulence (ET) in a von Karman swirling flow between rotating and stationary disks of polymer solutions in a wide, from dilute to semidilute entangled, range of polymer concentrations ϕ . The main message of the investigation is that the variation of ϕ just weakly modifies statistical, scaling, and spectral properties of ET in a swirling flow. The qualitative difference between dilute and semidilute unentangled versus semidilute entangled polymer solutions is found in the dependence of the critical Weissenberg number Wic of the elastic instability threshold on ϕ . The control parameter of the problem, the Weissenberg number Wi, is defined as the ratio of the nonlinear elastic stress to dissipation via linear stress relaxation and quantifies the degree of polymer stretching. The power-law scaling of the friction coefficient on Wi/Wic characterizes the ET regime with the exponent independent of ϕ . The torque Γ and pressure p power spectra show power-law decays with well-defined exponents, which has values independent of Wi and ϕ separately at 100 ≤ϕ ≤900 ppm and 1600 ≤ϕ ≤2300 ppm ranges. Another unexpected observation is the presence of two types of the boundary layers, horizontal and vertical, distinguished by their role in the energy pumping and dissipation, which has width dependence on Wi and ϕ differs drastically. In the case of the vertical boundary layer near the driving disk, wvv is independent of Wi/Wic and linearly decreases with ϕ /ϕ * , while in the case of the horizontal boundary layer wvh its width is independent of ϕ /ϕ * , linearly decreases with Wi/Wic , and is about five times smaller than wvv. Moreover, these Wi and ϕ dependencies of the vertical and horizontal boundary layer widths are found in accordance with the inverse turbulent intensity calculated inside the boundary layers Vθh/Vθh rms and Vθv/Vθv rms , respectively. Specifically, the dependence of Vθv/Vθv rms in the vertical boundary layer on Wi and ϕ agrees with a recent theoretical prediction [S. Belan, A. Chernych, and V. Lebedev, Boundary layer of elastic turbulence (unpublished)].

Experimental characterization of powered Fontan hemodynamics in an idealized total cavopulmonary connection model

NASA Astrophysics Data System (ADS)

Kerlo, Anna-Elodie M.; Delorme, Yann T.; Xu, Duo; Frankel, Steven H.; Giridharan, Guruprasad A.; Rodefeld, Mark D.; Chen, Jun

2013-08-01

A viscous impeller pump (VIP) based on the Von Karman viscous pump is specifically designed to provide cavopulmonary assist in a univentricular Fontan circulation. The technology will make it possible to biventricularize the univentricular Fontan circulation. Ideally, it will reduce the number of surgeries required for Fontan conversion from three to one early in life, while simultaneously improving physiological conditions. Later in life, it will provide a currently unavailable means of chronic support for adolescent and adult patients with failing Fontan circulations. Computational fluid dynamics simulations demonstrate that the VIP can satisfactorily augment cavopulmonary blood flow in an idealized total cavopulmonary connection (TCPC). When the VIP is deployed at the TCPC intersection as a static device, it stabilizes the four-way flow pattern and is not obstructive to the flow. Experimental studies are carried out to assess performance, hemodynamic characteristics, and flow structures of the VIP in an idealized TCPC model. Stereoscopic particle image velocimetry is applied using index-matched blood analog. Results show excellent performance of the VIP without cavitation and with reduction of the energy losses. The non-rotating VIP smoothes and accelerates flow, and decreases stresses and turbulence in the TCPC. The rotating VIP generates the desired low-pressure Fontan flow augmentation (0-10 mmHg) while maintaining acceptable stress thresholds.

Deconvolution of reacting-flow dynamics using proper orthogonal and dynamic mode decompositions

NASA Astrophysics Data System (ADS)

Roy, Sukesh; Hua, Jia-Chen; Barnhill, Will; Gunaratne, Gemunu H.; Gord, James R.

2015-01-01

Analytical and computational studies of reacting flows are extremely challenging due in part to nonlinearities of the underlying system of equations and long-range coupling mediated by heat and pressure fluctuations. However, many dynamical features of the flow can be inferred through low-order models if the flow constituents (e.g., eddies or vortices) and their symmetries, as well as the interactions among constituents, are established. Modal decompositions of high-frequency, high-resolution imaging, such as measurements of species-concentration fields through planar laser-induced florescence and of velocity fields through particle-image velocimetry, are the first step in the process. A methodology is introduced for deducing the flow constituents and their dynamics following modal decomposition. Proper orthogonal (POD) and dynamic mode (DMD) decompositions of two classes of problems are performed and their strengths compared. The first problem involves a cellular state generated in a flat circular flame front through symmetry breaking. The state contains two rings of cells that rotate clockwise at different rates. Both POD and DMD can be used to deconvolve the state into the two rings. In POD the contribution of each mode to the flow is quantified using the energy. Each DMD mode can be associated with an energy as well as a unique complex growth rate. Dynamic modes with the same spatial symmetry but different growth rates are found to be combined into a single POD mode. Thus, a flow can be approximated by a smaller number of POD modes. On the other hand, DMD provides a more detailed resolution of the dynamics. Two classes of reacting flows behind symmetric bluff bodies are also analyzed. In the first, symmetric pairs of vortices are released periodically from the two ends of the bluff body. The second flow contains von Karman vortices also, with a vortex being shed from one end of the bluff body followed by a second shedding from the opposite end. The way in which DMD can be used to deconvolve the second flow into symmetric and von Karman vortices is demonstrated. The analyses performed illustrate two distinct advantages of DMD: (1) Unlike proper orthogonal modes, each dynamic mode is associated with a unique complex growth rate. By comparing DMD spectra from multiple nominally identical experiments, it is possible to identify "reproducible" modes in a flow. We also find that although most high-energy modes are reproducible, some are not common between experimental realizations; in the examples considered, energy fails to differentiate between reproducible and nonreproducible modes. Consequently, it may not be possible to differentiate reproducible and nonreproducible modes in POD. (2) Time-dependent coefficients of dynamic modes are complex. Even in noisy experimental data, the dynamics of the phase of these coefficients (but not their magnitude) are highly regular. The phase represents the angular position of a rotating ring of cells and quantifies the downstream displacement of vortices in reacting flows. Thus, it is suggested that the dynamical characterizations of complex flows are best made through the phase dynamics of reproducible DMD modes.

Landsat 7 Reveals Large-scale Fractal Motion of Clouds

NASA Technical Reports Server (NTRS)

2002-01-01

This Landsat 7 image of clouds off the Chilean coast near the Juan Fernandez Islands (also known as the Robinson Crusoe Islands) on September 15, 1999, shows a unique pattern called a 'von Karman vortex street.' This pattern has long been studied in the laboratory, where the vortices are created by oil flowing past a cylindrical obstacle, making a string of vortices only several tens of centimeters long. Study of this classic 'flow past a circular cylinder' has been very important in the understanding of laminar and turbulent fluid flow that controls a wide variety of phenomena, from the lift under an aircraft wing to Earth's weather. Here, the cylinder is replaced by Alejandro Selkirk Island (named after the true 'Robinson Crusoe,' who was stranded here for many months in the early 1700s). The island is about 1.5 km in diameter, and rises 1.6 km into a layer of marine stratocumulus clouds. This type of cloud is important for its strong cooling of the Earth's surface, partially counteracting the Greenhouse warming. An extended, steady equatorward wind creates vortices with clockwise flow off the eastern edge and counterclockwise flow off the western edge of the island. The vortices grow as they advect hundreds of kilometers downwind, making a street 10,000 times longer than those made in the laboratory. Observing the same phenomenon extended over such a wide range of sizes dramatizes the 'fractal' nature of atmospheric convection and clouds. Fractals are characteristic of fluid flow and other dynamic systems that exhibit 'chaotic' motions. Both clockwise and counter-clockwise vortices are generated by flow around the island. As the flow separates from the island's leeward (away from the source of the wind) side, the vortices 'swallow' some of the clear air over the island. (Much of the island air is cloudless due to a local 'land breeze' circulation set up by the larger heat capacity of the waters surrounding the island.) The 'swallowed' gulps of clear island air get carried along within the vortices, but these are soon mixed into the surrounding clouds. Landsat is unique in its ability to image both the small-scale eddies that mix clear and cloudy air, down to the 30 meter pixel size of Landsat, but also having a wide enough field-of-view, 180 km, to reveal the connection of the turbulence to large-scale flows such as the subtropical oceanic gyres. Landsat 7, with its new onboard digital recorder, has extended this capability away from the few Landsat ground stations to remote areas such as Alejandro Island, and thus is gradually providing a global dynamic picture of evolving human-scale phenomena. (For more details on von Karman vortices, refer to http://climate.gsfc.nasa.gov/cahalan) Image and caption courtesy Bob Cahalan, NASA GSFC

Numerical analysis of MHD Casson Navier's slip nanofluid flow yield by rigid rotating disk

NASA Astrophysics Data System (ADS)

Rehman, Khalil Ur; Malik, M. Y.; Zahri, Mostafa; Tahir, M.

2018-03-01

An exertion is perform to report analysis on Casson liquid equipped above the rigid disk for z bar > 0 as a semi-infinite region. The flow of Casson liquid is achieve through rotation of rigid disk with constant angular frequency Ω bar . Magnetic interaction is consider by applying uniform magnetic field normal to the axial direction. The nanosized particles are suspended in the Casson liquid and rotation of disk is manifested with Navier's slip condition, heat generation/absorption and chemical reaction effects. The obtain flow narrating differential equations subject to MHD Casson nanofluid are transformed into ordinary differential system. For this purpose the Von Karman way of scheme is executed. To achieve accurate trends a computational algorithm is develop rather than to go on with usual build-in scheme. The effects logs of involved parameters, namely magnetic field parameter, Casson fluid parameter, slip parameter, thermophoresis and Brownian motion parameters on radial, tangential velocities, temperature, nanoparticles concentration, Nusselt and Sherwood numbers are provided by means of graphical and tabular structures. It is observed that both tangential and radial velocities are decreasing function of Casson fluid parameter.

Comparative investigation of five nanoparticles in flow of viscous fluid with Joule heating and slip due to rotating disk

NASA Astrophysics Data System (ADS)

Qayyum, Sumaira; Khan, Muhammad Ijaz; Hayat, Tasawar; Alsaedi, Ahmed

2018-04-01

Present article addresses the comparative study for flow of five water based nanofluids. Flow in presence of Joule heating is generated by rotating disk with variable thickness. Nanofluids are suspension of Silver (Ag), Copper (Cu), Copper oxide (CuO), Aluminum oxide or Alumina (Al2O3), Titanium oxide or titania (TiO2) and water. Boundary layer approximation is applied to partial differential equations. Using Von Karman transformations the partial differential equations are converted to ordinary differential equations. Convergent series solutions are obtained. Graphical results are presented to examine the behaviors of axial, radial and tangential velocities, temperature, skin friction and Nusselt number. It is observed that radial, axial and tangential velocities decay for slip parameters. Axial velocity decays for larger nanoparticle volume fraction. Effect of nanofluids on velocities dominant than base material. Temperature rises for larger Eckert number and temperature of silver water nanofluid is more because of its higher thermal conductivity. Surface drag force reduces for higher slip parameters. Transfer of heat is more for larger disk thickness index.

Control of vortical separation on conical bodies

NASA Technical Reports Server (NTRS)

Mourtos, Nikos J.; Roberts, Leonard

1987-01-01

In a variety of aeronautical applications, the flow around conical bodies at incidence is of interest. Such applications include, but are not limited to, highly maneuverable aircraft with delta wings, the aerospace plane and nose portions of spike inlets. The theoretical model used has three parts. First, the single line vortex model is used within the framework of slender body theory, to compute the outer inviscid field for specified separation lines. Next, the three dimensional boundary layer is represented by a momentum equation for the cross flow, analogous to that for a plane boundary layer; a von Karman Pohlhausen approximation is applied to solve this equation. The cross flow separation for both laminar and turbulent layers is determined by matching the pressure at the upper and lower separation points. This iterative procedure yields a unique solution for the separation lines and consequently for the position of the vortices and the vortex lift on the body. Lastly, control of separation is achieved by blowing tangentially from a slot located along a cone generator. It is found that for very small blowing coefficients, the separation can be postponed or suppressedy completely.

Vortex shedding from a blunt trailing edge with equal and unequal external mean velocities

NASA Technical Reports Server (NTRS)

Brinich, P. F.; Boldman, D. R.; Goldstein, M. E.

1975-01-01

A flow visualization study showed that strong Karman vortices are developed behind the blunt trailing edge of a plate when the free stream velocities over both surfaces are equal. These vortices tend to disappear when the surface velocities are unequal. This observation provided an explanation for the occurrence and disappearance of the lip noise often present in coaxial jets. Vortex formation and lip noise occurred at a Strouhal number of about 0.2 based on the lip thickness and the average of the external steady-state velocities. Results from theoretical calculations of the vortex formation, based on an inviscid, incompressible analysis of the motion of point vortices, were in good agreement with the experimental observations.

Wall-layer model for LES with massive separation

NASA Astrophysics Data System (ADS)

Fakhari, Ahmad; Armenio, Vincenzo; Roman, Federico

2016-11-01

Currently, Wall Functions (WF) work well under specific conditions, mostly exhibit drawbacks specially in flows with separation beyond curvatures. In this work, we propose a more general WF which works well in attached and detached flows, in presence and absence of Immersed Boundaries (IB). First we modified an equilibrium stress WF for boundary-fitted geometry making dynamic the computation of the k (von Karman constant) of the log-law; the model was first applied to a periodic open channel flow, and then to the flow over a 2D single hill using uniform coarse grids; the model captured separation with reasonable accuracy. Thereafter IB Method by Roman et al. was improved to avoid momentum loss at the interface between the fluid-solid regions. This required calibration of interfacial eddy viscosity; also a random stochastic forcing was used in wall-normal direction to increase Reynolds stresses and improve mean velocity profile. Finally, to reproduce flow separation, a simplified boundary layer equation was applied to construct velocity at near wall computational nodes. The new scheme was tested on the 2D single hill and periodic hills applying Cartesian and curvilinear grids; good agreement with references was obtained with reduction in cost and complexity. Financial support from project COSMO "CFD open source per opera morta" PAR FSC 2007-2013, Friuli Venezia Giulia.

Investigation of growth features in several hydraulic fractures

NASA Astrophysics Data System (ADS)

Bykov, Alexander; Galybin, Alexander; Evdokimov, Alexander; Zavialova, Natalia; Zavialov, Ivan; Negodiaev, Sergey; Perepechkin, Ilia

2017-04-01

In this paper we simulate the growth of three or more interacting hydraulic fractures in the horizontal well with a cross flow of fluid between them. Calculation of the dynamics of cracks is performed in three dimensional space. The computation of the movement of fracturing fluid with proppant is performed in the two-dimensional space (the flow was averaged along crack aperture). For determining the hydraulic pipe resistance coefficient we used a generalization of the Reynolds number for fluids with power rheology and a generalization of the von Karman equation made by Dodge and Meiner. The calculations showed that the first crack was developing faster than the rest in homogeneous medium. During the steady loading the outer cracks pinch the inner cracks and it was shown that only the first and last fracture develop in extreme case. It is also possible to simulate the parameters at which the two developing outer cracks pinch the central one in the horizontal direction. In this case, the central crack may grow in the vertical direction.

Bending of Rectangular Plates with Large Deflections

NASA Technical Reports Server (NTRS)

Levy, Samuel

1942-01-01

The solution of von Karman's fundamental equations for large deflections of plates is presented for the case of a simply supported rectangular plate under combined edge compression and lateral loading. Numerical solutions are given for square plates and for rectangular plates with a width-span ratio of 3:1. The effective widths under edge compression are compared with effective widths according to von Karman, Bengston, Marguerre, and Cox and with experimental results by Ramberg, McPherson, and Levy. The deflections for a square plate under lateral pressure are compared with experimental and theoretical results by Kaiser. It is found that the effective widths agree closely with Marguerre's formula and with the experimentally observed values and that the deflections agree with the experimental results and with Kaiser's work.

Direct Numerical Simulations of a Full Stationary Wind-Turbine Blade

NASA Astrophysics Data System (ADS)

Qamar, Adnan; Zhang, Wei; Gao, Wei; Samtaney, Ravi

2014-11-01

Direct numerical simulation of flow past a full stationary wind-turbine blade is carried out at Reynolds number, Re = 10,000 placed at 0 and 5 (degree) angle of attack. The study is targeted to create a DNS database for verification of solvers and turbulent models that are utilized in wind-turbine modeling applications. The full blade comprises of a circular cylinder base that is attached to a spanwise varying airfoil cross-section profile (without twist). An overlapping composite grid technique is utilized to perform these DNS computations, which permits block structure in the mapped computational space. Different flow shedding regimes are observed along the blade length. Von-Karman shedding is observed in the cylinder shaft region of the turbine blade. Along the airfoil cross-section of the blade, near body shear layer breakdown is observed. A long tip vortex originates from the blade tip region, which exits the computational plane without being perturbed. Laminar to turbulent flow transition is observed along the blade length. The turbulent fluctuations amplitude decreases along the blade length and the flow remains laminar regime in the vicinity of the blade tip. The Strouhal number is found to decrease monotonously along the blade length. Average lift and drag coefficients are also reported for the cases investigated. Supported by funding under a KAUST OCRF-CRG grant.

Prediction of aerodynamic noise in a ring fan based on wake characteristics

NASA Astrophysics Data System (ADS)

Sasaki, Soichi; Fukuda, Masaharu; Tsujino, Masao; Tsubota, Haruhiro

2011-06-01

A ring fan is a propeller fan that applies an axial-flow impeller with a ring-shaped shroud on the blade tip side. In this study, the entire flow field of the ring fan is simulated using computational fluid dynamics (CFD); the accuracy of the CFD is verified through a comparison with the aerodynamic characteristics of a propeller fan of current model. Moreover, the aerodynamic noise generated by the fan is predicted on the basis of the wake characteristics. The aerodynamic characteristic of the ring fan based on CFD can represent qualitatively the variation in the measured value. The main flow domain of the ring fan is formed at the tip side of the blade because blade tip vortex is not formed at that location. Therefore, the relative velocity of the ring fan is increased by the circumferential velocity. The sound pressure levels of the ring fan within the frequency band of less than 200 Hz are larger than that of the propeller fan. In the analysis of the wake characteristics, it revealed that Karman vortex shedding occurred in the main flow domain in the frequency domain lower than 200 Hz; the aerodynamic noise of the ring fan in the vortex shedding frequency enlarges due to increase in the relative velocity and the velocity fluctuation.

Rolling with the flow: bumblebees flying in unsteady wakes.

PubMed

Ravi, Sridhar; Crall, James D; Fisher, Alex; Combes, Stacey A

2013-11-15

Our understanding of how variable wind in natural environments affects flying insects is limited because most studies of insect flight are conducted in either smooth flow or still air conditions. Here, we investigate the effects of structured, unsteady flow (the von Karman vortex street behind a cylinder) on the flight performance of bumblebees (Bombus impatiens). Bumblebees are 'all-weather' foragers and thus frequently experience variable aerial conditions, ranging from fully mixed, turbulent flow to unsteady, structured vortices near objects such as branches and stems. We examined how bumblebee flight performance differs in unsteady versus smooth flow, as well as how the orientation of unsteady flow structures affects their flight performance, by filming bumblebees flying in a wind tunnel under various flow conditions. The three-dimensional flight trajectories and orientations of bumblebees were quantified in each of three flow conditions: (1) smooth flow, (2) the unsteady wake of a vertical cylinder (inducing strong lateral disturbances) and (3) the unsteady wake of a horizontal cylinder (inducing strong vertical disturbances). In both unsteady conditions, bumblebees attenuated the disturbances induced by the wind quite effectively, but still experienced significant translational and rotational fluctuations as compared with flight in smooth flow. Bees appeared to be most sensitive to disturbance along the lateral axis, displaying large lateral accelerations, translations and rolling motions in response to both unsteady flow conditions, regardless of orientation. Bees also displayed the greatest agility around the roll axis, initiating voluntary casting maneuvers and correcting for lateral disturbances mainly through roll in all flow conditions. Both unsteady flow conditions reduced the upstream flight speed of bees, suggesting an increased cost of flight in unsteady flow, with potential implications for foraging patterns and colony energetics in natural, variable wind environments.

Using resolvent analysis for the design of separation control on a NACA 0012 airfoil

NASA Astrophysics Data System (ADS)

Yeh, Chi-An; Taira, Kunihiko

2017-11-01

A combined effort based on large-eddy simulation and resolvent analysis on the separated flow over a NACA 0012 airfoil is conducted to design active flow control for suppression of separation. This study considers the the airfoil at 6 deg. angle-of-attack and Reynolds number of 23000. The response mode obtained from the resolvent analysis about the baseline turbulent mean flow reveals modal structures that can be categorized into three families when sweeping through the resonant frequency: (1) von Karman wake structure for low frequency; (2) Kelvin-Helmholtz structure in the separation bubble for high frequency; (3) blended structure of (1) and (2) for the intermediate frequency. Leveraging the insights from resolvent analysis, unsteady thermal actuation is introduced to the flow near the leading-edge to examine the use of the frequencies from three families for separation control in LES. As indicated by the resolvent response modes, we find that the use of intermediate frequencies are most effective in suppressing the flow separation, since the shear layer over the separation bubble and the wake are both receptive to the perturbation at the these frequencies. The resolvent-analysis-based control strategy achieves 35% drag reduction and 9% lift increase with effective frequency. This work was supported by Office of Naval Research (N00014-15-R-FO13) and Army Research Office (W911NF-14-1-0224).

Buffeting of NACA 0012 airfoil at high angle of attack

NASA Astrophysics Data System (ADS)

Zhou, Tong; Dowell, Earl

2014-11-01

Buffeting is a fluid instability caused by flow separation or shock wave oscillations in the flow around a bluff body. Typically there is a dominant frequency of these flow oscillations called Strouhal or buffeting frequency. In prior work several researchers at Duke University have noted the analogy between the classic Von Karman Vortex Street behind a bluff body and the flow oscillations that occur for flow around a NACA 0012 airfoil at sufficiently large angle of attack. Lock-in is found for certain combinations of airfoil oscillation (pitching motion) frequencies and amplitudes when the frequency of the airfoil motion is sufficiently close to the buffeting frequency. The goal of this paper is to explore the flow around a static and an oscillating airfoil at high angle of attack by developing a method for computing buffet response. Simulation results are compared with experimental data. Conditions for the onset of buffeting and lock-in of a NACA 0012 airfoil at high angle of attack are determined. Effects of several parameters on lift coefficient and flow response frequency are studied including Reynolds number, angle of attack and blockage ratio of the airfoil size to the wind tunnel dimensions. Also more detailed flow field characteristics are determined. For a static airfoil, a universal Strouhal number scaling has been found for angles of attack from 30° to 90°, where the flow around airfoil is fully separated. For an oscillating airfoil, conditions for lock-in are discussed. Differences between the lock-in case and the unlocked case are also studied. The second affiliation: Duke University.

Link between von-Karman energy decay and reconnection heating in turbulent plasmas

NASA Astrophysics Data System (ADS)

Shay, M. A.; Parashar, T.; Haggerty, C. C.; Matthaeus, W. H.; Phan, T.; Drake, J. F.; Cassak, P.; Wu, P.

2016-12-01

Coherent structures such as current sheets are prevalent in many turbulent plasmas and have been shown to be correlated with dissipation and heating in observations of solar wind turbulence and dissipation in kinetic particle-in-cell (PIC) simulations. However, the role that they play in the dissipation of turbulent energy and ultimately the heating of the plasma are still not well understood. A recent study [1] using kinetic PIC simulations of turbulence found that the total heating in the plasma is consistent with a von-Karman scaling of the cascade rate, and that the proton to electron heating ratio was proportional to the total heating rate and linked to the ratio of gyroperiod to nonlinear turnover time at the ion kinetic scales. We review recent findings regarding the rate of heating in outflow jets during laminar reconnection and apply it to kinetic PIC simulations of turbulence, employing some reasonable assumptions to connect the two theories. The goal is to determine if reconnection is a primary heating mechanism or plays less of a role. Conversely, we also apply the new understanding of the von-Karman cascade to isolated reconnection events to determine if a cascade-like process is controlling the heating rate. [1] W. Matthaeus et al., ApJ Letters, 827, L7, 2016, doi:10.3847/2041-8205/827/1/L7

Works on theory of flapping wing. [considering boundary layer

NASA Technical Reports Server (NTRS)

Golubev, V. V.

1980-01-01

It is shown mathematically that taking account of the boundary layer is the only way to develop a theory of flapping wings without violating the basic observations and mathematics of hydromechanics. A theory of thrust generation by flapping wings can be developed if the conventional downstream velocity discontinuity surface is replaced with the observed Karman type vortex streets behind a flapping wing. Experiments show that the direction of such vortices is the reverse of that of conventional Karman streets. The streets form by breakdown of the boundary layer. Detailed analysis of the movements of certain birds and insects during flight 'in place' is fully consistent with this theory of the lift, thrust and drag of flapping wings. Further directions for research into flight with flapping wings are indicated.

A Powerful Friendship: Theodore von Karman and Hugh L. Dryden

NASA Technical Reports Server (NTRS)

Gorn, Michael

2003-01-01

During their long personal friendship and professional association, Theodore von Karman (1882-1963) and Hugh L. Dryden (1898-1965) exercised a pivotal if somewhat elusive influence over American aeronautics and spaceflight. Both decisive figures in organizing scientists and engineers at home and abroad, both men of undisputed eminence in their technical fields, their range of contacts in government, academia, the armed forces, industry, and professional societies spanned the globe to an extent unparalleled then as now. Moreover, because they coordinated their activities closely, their combined influence far exceeded the sum of each one s individual contributions. This paper illustrates their personal origins as well as the foundations of their friendship, how their relationship became a professional alliance, and their joint impact on the world of aeronautics and astronautics during the twentieth century.

Accuracy of the lattice Boltzmann method for describing the behavior of a gas in the continuum limit.

PubMed

Kataoka, Takeshi; Tsutahara, Michihisa

2010-11-01

The accuracy of the lattice Boltzmann method (LBM) for describing the behavior of a gas in the continuum limit is systematically investigated. The asymptotic analysis for small Knudsen numbers is carried out to derive the corresponding fluid-dynamics-type equations, and the errors of the LBM are estimated by comparing them with the correct fluid-dynamics-type equations. We discuss the following three important cases: (I) the Mach number of the flow is much smaller than the Knudsen number, (II) the Mach number is of the same order as the Knudsen number, and (III) the Mach number is finite. From the von Karman relation, the above three cases correspond to the flows of (I) small Reynolds number, (II) finite Reynolds number, and (III) large Reynolds number, respectively. The analysis is made with the information only of the fundamental properties of the lattice Boltzmann models without stepping into their detailed form. The results are therefore applicable to various lattice Boltzmann models that satisfy the fundamental properties used in the analysis.

The effects of leading-edge serrations on reducing flow unsteadiness about airfoils, an experimental and analytical investigation

NASA Technical Reports Server (NTRS)

Schwind, R. G.; Allen, H. J.

1973-01-01

High frequency surface pressure measurements were obtained from wind-tunnel tests over the Reynolds number range 1.2 times one million to 6.2 times one million on a rectangular wing of NACA 63-009 airfoil section. Measurements were also obtained with a wide selection of leading-edge serrations added to the basic airfoil. Under a two-dimensional laminar bubble very close to the leading edge of the basic airfoil there is a large apatial peak in rms pressure. Frequency analysis of the pressure signals in this region show a large, high-frequency energy peak which is interpreted as an oscillation in size and position of the bubble. The serrations divide the bubble into segments and reduce the peak rms pressures. A low Reynolds number flow visualization test on a hydrofoil in water was also conducted. A von Karman vortex street was found trailing from the rear of the foil. Its frequency is at a much lower Strouhal number than in the high Reynolds number experiment, and is related to the trailing-edge and boundary-layer thicknesses.

The `Henry Problem' of `density-driven' groundwater flow versus Tothian `groundwater flow systems' with variable density: A review of the influential Biscayne aquifer data.

NASA Astrophysics Data System (ADS)

Weyer, K. U.

2017-12-01

Coastal groundwater flow investigations at the Biscayne Bay, south of Miami, Florida, gave rise to the concept of density-driven flow of seawater into coastal aquifers creating a saltwater wedge. Within that wedge, convection-driven return flow of seawater and a dispersion zone were assumed by Cooper et al. (1964) to be the cause of the Biscayne aquifer `sea water wedge'. This conclusion was based on the chloride distribution within the aquifer and on an analytical model concept assuming convection flow within a confined aquifer without taking non-chemical field data into consideration. This concept was later labelled the `Henry Problem', which any numerical variable density flow program must be able to simulate to be considered acceptable. Both, `density-driven flow' and Tothian `groundwater flow systems' (with or without variable density conditions) are driven by gravitation. The difference between the two are the boundary conditions. 'Density-driven flow' occurs under hydrostatic boundary conditions while Tothian `groundwater flow systems' occur under hydrodynamic boundary conditions. Revisiting the Cooper et al. (1964) publication with its record of piezometric field data (heads) showed that the so-called sea water wedge has been caused by discharging deep saline groundwater driven by gravitational flow and not by denser sea water. Density driven flow of seawater into the aquifer was not found reflected in the head measurements for low and high tide conditions which had been taken contemporaneously with the chloride measurements. These head measurements had not been included in the flow interpretation. The very same head measurements indicated a clear dividing line between shallow local fresh groundwater flow and saline deep groundwater flow without the existence of a dispersion zone or a convection cell. The Biscayne situation emphasizes the need for any chemical interpretation of flow pattern to be supported by head data as energy indicators of flow fields. At the Biscayne site density-driven flow of seawater did and does not exist. Instead this site and the Florida coast line in general are the end points of local fresh and regional saline groundwater flow systems driven by gravity forces and not by density differences.

Large-scale Fractal Motion of Clouds

NASA Image and Video Library

2011-04-20

NASA image acquired September 15, 1999 This Landsat 7 image of clouds off the Chilean coast near the Juan Fernandez Islands (also known as the Robinson Crusoe Islands) on September 15, 1999, shows a unique pattern called a “von Karman vortex street.” This pattern has long been studied in the laboratory, where the vortices are created by oil flowing past a cylindrical obstacle, making a string of vortices only several tens of centimeters long. Study of this classic “flow past a circular cylinder” has been very important in the understanding of laminar and turbulent fluid flow that controls a wide variety of phenomena, from the lift under an aircraft wing to Earth’s weather. Here, the cylinder is replaced by Alejandro Selkirk Island (named after the true “Robinson Crusoe,” who was stranded here for many months in the early 1700s). The island is about 1.5 km in diameter, and rises 1.6 km into a layer of marine stratocumulus clouds. This type of cloud is important for its strong cooling of the Earth’s surface, partially counteracting the Greenhouse warming. An extended, steady equatorward wind creates vortices with clockwise flow off the eastern edge and counterclockwise flow off the western edge of the island. The vortices grow as they advect hundreds of kilometers downwind, making a street 10,000 times longer than those made in the laboratory. Observing the same phenomenon extended over such a wide range of sizes dramatizes the “fractal” nature of atmospheric convection and clouds. Fractals are characteristic of fluid flow and other dynamic systems that exhibit “chaotic” motions. Both clockwise and counter-clockwise vortices are generated by flow around the island. As the flow separates from the island’s leeward (away from the source of the wind) side, the vortices “swallow” some of the clear air over the island. (Much of the island air is cloudless due to a local “land breeze” circulation set up by the larger heat capacity of the waters surrounding the island.) The “swallowed” gulps of clear island air get carried along within the vortices, but these are soon mixed into the surrounding clouds. Landsat is unique in its ability to image both the small-scale eddies that mix clear and cloudy air, down to the 30 meter pixel size of Landsat, but also having a wide enough field-of-view, 180 km, to reveal the connection of the turbulence to large-scale flows such as the subtropical oceanic gyres. Landsat 7, with its new onboard digital recorder, has extended this capability away from the few Landsat ground stations to remote areas such as Alejandro Island, and thus is gradually providing a global dynamic picture of evolving human-scale phenomena. For more details on von Karman vortices, refer to climate.gsfc.nasa.gov/~cahalan. Image and caption courtesy Bob Cahalan, NASA GSFC Instrument: Landsat 7 - ETM+ Credit: NASA/GSFC/Landsat NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook

Advanced Space Shuttle simulation model

NASA Technical Reports Server (NTRS)

Tatom, F. B.; Smith, S. R.

1982-01-01

A non-recursive model (based on von Karman spectra) for atmospheric turbulence along the flight path of the shuttle orbiter was developed. It provides for simulation of instantaneous vertical and horizontal gusts at the vehicle center-of-gravity, and also for simulation of instantaneous gusts gradients. Based on this model the time series for both gusts and gust gradients were generated and stored on a series of magnetic tapes, entitled Shuttle Simulation Turbulence Tapes (SSTT). The time series are designed to represent atmospheric turbulence from ground level to an altitude of 120,000 meters. A description of the turbulence generation procedure is provided. The results of validating the simulated turbulence are described. Conclusions and recommendations are presented. One-dimensional von Karman spectra are tabulated, while a discussion of the minimum frequency simulated is provided. The results of spectral and statistical analyses of the SSTT are presented.

Low-Dimensional Model of a Cylinder Wake

NASA Astrophysics Data System (ADS)

Luchtenburg, Mark; Cohen, Kelly; Siegel, Stefan; McLaughlin, Tom

2003-11-01

In a two-dimensional cylinder wake, self-excited oscillations in the form of periodic shedding of vortices are observed above a critical Reynolds number of about 47. These flow-induced non-linear oscillations lead to some undesirable effects associated with unsteady pressures such as fluid-structure interactions. An effective way of suppressing the self-excited flow oscillations is by the incorporation of closed-loop flow control. In this effort, a low dimensional, proper orthogonal decomposition (POD) model is based on data obtained from direct numerical simulations of the Navier Stokes equations for the two dimensional circular cylinder wake at a Reynolds number of 100. Three different conditions are examined, namely, the unforced wake experiencing steady-state vortex shedding, the transient behavior of the unforced wake at the startup of the simulation, and transient response to open-loop harmonic forcing by translation. We discuss POD mode selection and the number of modes that need to be included in the low-dimensional model. It is found that the transient dynamics need to be represented by a coupled system that includes an aperiodic mean-flow mode, an aperiodic shift mode and the periodic von Karman modes. Finally, a least squares mapping method is introduced to develop the non-linear state equations. The predictive capability of the state equations demonstrates the ability of the above approach to model the transient dynamics of the wake.

Analysis of the two-point velocity correlations in turbulent boundary layer flows

NASA Technical Reports Server (NTRS)

Oberlack, M.

1995-01-01

The general objective of the present work is to explore the use of Rapid Distortion Theory (RDT) in analysis of the two-point statistics of the log-layer. RDT is applicable only to unsteady flows where the non-linear turbulence-turbulence interaction can be neglected in comparison to linear turbulence-mean interactions. Here we propose to use RDT to examine the structure of the large energy-containing scales and their interaction with the mean flow in the log-region. The contents of the work are twofold: First, two-point analysis methods will be used to derive the law-of-the-wall for the special case of zero mean pressure gradient. The basic assumptions needed are one-dimensionality in the mean flow and homogeneity of the fluctuations. It will be shown that a formal solution of the two-point correlation equation can be obtained as a power series in the von Karman constant, known to be on the order of 0.4. In the second part, a detailed analysis of the two-point correlation function in the log-layer will be given. The fundamental set of equations and a functional relation for the two-point correlation function will be derived. An asymptotic expansion procedure will be used in the log-layer to match Kolmogorov's universal range and the one-point correlations to the inviscid outer region valid for large correlation distances.

Vortex shedding in bileaflet heart valve prostheses.

PubMed

Gross, J M; Shermer, C D; Hwang, N H

1988-01-01

A dynamic study of two geometrically similar bileaflet heart valve prostheses (HVP) was performed using a physiologic mock circulatory flow loop. The HVPs studied were the 25 mm St. Jude Medical (SJM) and the 25 mm Carbomedics (CMI) in the aortic position and the 27 mm SJM and 27 mm CMI in the mitral position. All data were collected at a heart rate of 70 beats/min and a cardiac output of 5.0 L/min. Flow visualization was conducted in the transparent flow chambers of the pulsatile mock circulatory flow loop using a 15 mW He-Ne laser light source. A cylindrical lens and optics system converted the incident laser beam into a thin parallel light plane, and 420 microns tracer particles were suspended in the testing fluid to illuminate the flow field at selected planes. Frame-by-frame analysis of the 16 mm high-speed cine provides detailed phasic flow patterns in the vicinity of the HVP. A series of still photographs of flow patterns, taken at approximately 22.5 degrees phase intervals, are sequentially presented for each HVP. In the aortic position, a Karman-like vortex pattern appears downstream of the SJM at the end of the ejection phase. The CMI exhibits a rather symmetrical ejection flow pattern that turns into random motion immediately after the onset of ejection. In the mitral position, the SJM again exhibits a strong core flow during ventricular filling, whereas the CMI produces a more diffuse pattern during the same period. A pair of vortices shed from both the SJM and CMI are clearly visible toward the end of the ventricular filling phase. The vortex mechanisms are discussed in light of leaflet boundary layer formation.

Systematic characterization of degas-driven flow for poly(dimethylsiloxane) microfluidic devices

DOE PAGES

Liang, David Y.; Tentori, Augusto M.; Dimov, Ivan K.; ...

2011-01-01

Degas-driven flow is a novel phenomenon used to propel fluids in poly(dimethylsiloxane) (PDMS)-based microfluidic devices without requiring any external power. This method takes advantage of the inherently high porosity and air solubility of PDMS by removing air molecules from the bulk PDMS before initiating the flow. The dynamics of degas-driven flow are dependent on the channel and device geometries and are highly sensitive to temporal parameters. These dependencies have not been fully characterized, hindering broad use of degas-driven flow as a microfluidic pumping mechanism. Here, we characterize, for the first time, the effect of various parameters on the dynamics ofmore » degas-driven flow, including channel geometry, PDMS thickness, PDMS exposure area, vacuum degassing time, and idle time at atmospheric pressure before loading. We investigate the effect of these parameters on flow velocity as well as channel fill time for the degas-driven flow process. Using our devices, we achieved reproducible flow with a standard deviation of less than 8% for flow velocity, as well as maximum flow rates of up to 3 nL/s and mean flow rates of approximately 1-1.5 nL/s. Parameters such as channel surface area and PDMS chip exposure area were found to have negligible impact on degas-driven flow dynamics, whereas channel cross-sectional area, degas time, PDMS thickness, and idle time were found to have a larger impact. In addition, we develop a physical model that can predict mean flow velocities within 6% of experimental values and can be used as a tool for future design of PDMS-based microfluidic devices that utilize degas-driven flow.« less

The effect of porosity and flexibility on the hydrodynamics behind a mangrove-like root model

NASA Astrophysics Data System (ADS)

Kazemi, Amirkhosro; Parry, Samantha; van de Riet, Keith; Curet, Oscar

2015-11-01

Mangroves play a prominent role in coastal areas in subtropics regions. Mangrove forests are of special interest to protect shorelines against storm surges, hurricane winds, sea-level rise and tsunamis. In addition, mangroves play a critical role in filtering water and providing habitat to different organisms. In this work we study the complex interaction of water flow and mangrove roots which were modeled with a circular array of cylinders with different spacing between them as well as different configurations. In addition, we modeled the flexibility of the roots by attaching rigid cylinders to torsional connectors. The models were tested in a water tunnel for a range of Reynolds number from 2200 to 12000. In a series of experiments we measured the drag force, instant and mean velocity behind the models. We also performed 2D flow visualization for the models in a flowing soap film setup. The results show that the minimum velocity of the wake is highly dependent on the porosity and flexibility of the roots. We observed that there is a small-scale turbulent region. This turbulence is recombined downstream in a larger vortex structure eventually forming a von Karman vortex street wake. We compare the results from rigid cylinder and the flexible counterpart.

Experimental And Numerical Investigation Of Aerothermal Characteristics Of The IXV Hypersonic Vehicle

NASA Astrophysics Data System (ADS)

Paris, S.; Charbonnier, D.; Tran, D.

2011-05-01

The main results of the aerothermodynamic hypersonic characterization of Intermediate eXperimental Vehicle (IXV), by means of both CFD simulations and wind tunnel measurements, have been reported and analyzed. In the framework of ESA FLPP Program, the VKI (Von Karman Institute) was in charge of an experimental test campaign for the consolidation of the aerothermal database in cold hypersonic regime. The tests campaign has been carried out at VKI Free Piston Longshot wind tunnel at mach 14. The numerical simulations have been performed for VKI wind tunnel conditions by CFSE with the in-house NSMB flow solver (Navier-Stokes Multi-Blocks 3D), the goal being to support the procedure of extrapolation-to-flight of the measurements and the general aerothermal characterization. Laminar, transitional and fully turbulent flows have been computed, with air considered as an ideal gas, for the wind tunnel tests numerical rebuilding. A detailed comparison of all measured and predicted hypersonic relevant phenomena and parameters (surface pressure and heat flux) is reported in the paper, together with a detailed description of configuration, freestream conditions, model attitude effects and flap deflection effect. The detailed analyze of the experimental and numerical data gives information on the nature of the flow on the body and on the flaps for the most critical configuration

Shape change of Galileo probe models in free-flight tests

NASA Technical Reports Server (NTRS)

Park, C.; Derose, C. F.

1980-01-01

Scale models of the Galileo Probe made of polycarbonate, AXF5Q graphite, carbon-carbon composite, and carbon-phenolic were flown in a free flight range in an ambient gas of air, krypton, or xenon. Mach numbers varied between 14 and 24, Reynolds numbers between 300,000 and 1,000,000, stagnation pressures between 31 and 200 atm, and stagnation point heat transfer rates between 10 and 1,000 kW/sq cm. Shadowgraphs indicate gouging ablation of the aft portion of the frustum; the gouging was moderate in air and severe in the noble gases. The graphite models break in the same region. An explanation of the phenomena is offered in terms of the strong compression and shear caused by the reattachment of a turbulent separated flow. Conditions are calculated for similar tests appropriate for Von Karman Facility of the Arnold Engineering Development Center in which a larger model can be flown in argon.

An approximate theoretical method for modeling the static thrust performance of non-axisymmetric two-dimensional convergent-divergent nozzles. M.S. Thesis - George Washington Univ.

NASA Technical Reports Server (NTRS)

Hunter, Craig A.

1995-01-01

An analytical/numerical method has been developed to predict the static thrust performance of non-axisymmetric, two-dimensional convergent-divergent exhaust nozzles. Thermodynamic nozzle performance effects due to over- and underexpansion are modeled using one-dimensional compressible flow theory. Boundary layer development and skin friction losses are calculated using an approximate integral momentum method based on the classic karman-Polhausen solution. Angularity effects are included with these two models in a computational Nozzle Performance Analysis Code, NPAC. In four different case studies, results from NPAC are compared to experimental data obtained from subscale nozzle testing to demonstrate the capabilities and limitations of the NPAC method. In several cases, the NPAC prediction matched experimental gross thrust efficiency data to within 0.1 percent at a design NPR, and to within 0.5 percent at off-design conditions.

Modeling the Exo-Brake and the Development of Strategies for De-Orbit Drag Modulation

NASA Technical Reports Server (NTRS)

Murbach, M. S.; Papadopoulos, P.; Glass, C.; Dwyer-Cianciolo, A.; Powell, R. W.; Dutta, S.; Guarneros-Luna, A.; Tanner, F. A.; Dono, A.

2016-01-01

The Exo-Brake is a simple, non-propulsive means of de-orbiting small payloads from orbital platforms such as the International Space Station (ISS). Two de-orbiting experiments with fixed surface area Exo-Brakes have been successfully conducted in the last two years on the TechEdSat-3 and -4 nano-satellite missions. The development of the free molecular flow aerodynamic data-base is presented in terms of angle of attack, projected front surface area variation, and altitude. Altitudes are considered ranging from the 400km ISS jettison altitude to 90km. Trajectory tools are then used to predict de-orbit/entry corridors with the inclusion of the key atmospheric and geomagnetic uncertainties. Control system strategies are discussed which will be applied to the next two planned TechEdSat-5 and -6 nano-satellite missions - thus increasing the targeting accuracy at the Von Karman altitude through the proposed drag modulation technique.

Analyses and assessments of span wise gust gradient data from NASA B-57B aircraft

NASA Technical Reports Server (NTRS)

Frost, Walter; Chang, Ho-Pen; Ringnes, Erik A.

1987-01-01

Analysis of turbulence measured across the airfoil of a Cambera B-57 aircraft is reported. The aircraft is instrumented with probes for measuring wind at both wing tips and at the nose. Statistical properties of the turbulence are reported. These consist of the standard deviations of turbulence measured by each individual probe, standard deviations and probability distribution of differences in turbulence measured between probes and auto- and two-point spatial correlations and spectra. Procedures associated with calculations of two-point spatial correlations and spectra utilizing data were addressed. Methods and correction procedures for assuring the accuracy of aircraft measured winds are also described. Results are found, in general, to agree with correlations existing in the literature. The velocity spatial differences fit a Gaussian/Bessel type probability distribution. The turbulence agrees with the von Karman turbulence correlation and with two-point spatial correlations developed from the von Karman correlation.

Insights into asthenospheric anisotropy and deformation in Mainland China

NASA Astrophysics Data System (ADS)

Zhu, Tao

2018-03-01

Seismic anisotropy can provide direct constraints on asthenospheric deformation which also can be induced by the inherent mantle flow within our planet. Mantle flow calculations thus have been an effective tool to probe asthenospheric anisotropy. To explore the source of seismic anisotropy, asthenospheric deformation and the effects of mantle flow on seismic anisotropy in Mainland China, mantle flow models driven by plate motion (plate-driven) and by a combination of plate motion and mantle density heterogeneity (plate-density-driven) are used to predict the fast polarization direction of shear wave splitting. Our results indicate that: (1) plate-driven or plate-density-driven mantle flow significantly affects the predicted fast polarization direction when compared with simple asthenospheric flow commonly used in interpreting the asthenospheric source of seismic anisotropy, and thus new insights are presented; (2) plate-driven flow controls the fast polarization direction while thermal mantle flow affects asthenospheric deformation rate and local deformation direction significantly; (3) asthenospheric flow is an assignable contributor to seismic anisotropy, and the asthenosphere is undergoing low, large or moderate shear deformation controlled by the strain model, the flow plane/flow direction model or both in most regions of central and eastern China; and (4) the asthenosphere is under more rapid extension deformation in eastern China than in western China.

Stability investigations of airfoil flow by global analysis

NASA Technical Reports Server (NTRS)

Morzynski, Marek; Thiele, Frank

1992-01-01

As the result of global, non-parallel flow stability analysis the single value of the disturbance growth-rate and respective frequency is obtained. This complex value characterizes the stability of the whole flow configuration and is not referred to any particular flow pattern. The global analysis assures that all the flow elements (wake, boundary and shear layer) are taken into account. The physical phenomena connected with the wake instability are properly reproduced by the global analysis. This enhances the investigations of instability of any 2-D flows, including ones in which the boundary layer instability effects are known to be of dominating importance. Assuming fully 2-D disturbance form, the global linear stability problem is formulated. The system of partial differential equations is solved for the eigenvalues and eigenvectors. The equations, written in the pure stream function formulation, are discretized via FDM using a curvilinear coordinate system. The complex eigenvalues and corresponding eigenvectors are evaluated by an iterative method. The investigations performed for various Reynolds numbers emphasize that the wake instability develops into the Karman vortex street. This phenomenon is shown to be connected with the first mode obtained from the non-parallel flow stability analysis. The higher modes are reflecting different physical phenomena as for example Tollmien-Schlichting waves, originating in the boundary layer and having the tendency to emerge as instabilities for the growing Reynolds number. The investigations are carried out for a circular cylinder, oblong ellipsis and airfoil. It is shown that the onset of the wake instability, the waves in the boundary layer, the shear layer instability are different solutions of the same eigenvalue problem, formulated using the non-parallel theory. The analysis offers large potential possibilities as the generalization of methods used till now for the stability analysis.

Measurements of Heat-Transfer and Friction Coefficients for Helium Flowing in a Tube at Surface Temperatures up to 5900 Deg R

NASA Technical Reports Server (NTRS)

Taylor, Maynard F.; Kirchgessner, Thomas A.

1959-01-01

Measurements of average heat transfer and friction coefficients and local heat transfer coefficients were made with helium flowing through electrically heated smooth tubes with length-diameter ratios of 60 and 92 for the following range of conditions: Average surface temperature from 1457 to 4533 R, Reynolds numbe r from 3230 to 60,000, heat flux up to 583,200 Btu per hr per ft2 of heat transfer area, and exit Mach numbe r up to 1.0. The results indicate that, in the turbulent range of Reynolds number, good correlation of the local heat transfer coefficients is obtained when the physical properties and density of helium are evaluated at the surface temperature. The average heat transfer coefficients are best correlated on the basis that the coefficient varies with [1 + (L/D))(sup -0,7)] and that the physical properties and density are evaluated at the surface temperature. The average friction coefficients for the tests with no heat addition are in complete agreement with the Karman-Nikuradse line. The average friction coefficients for heat addition are in poor agreement with the accepted line.

Yield Hardening of Electrorheological Fluids in Channel Flow

NASA Astrophysics Data System (ADS)

Helal, Ahmed; Qian, Bian; McKinley, Gareth H.; Hosoi, A. E.

2016-06-01

Electrorheological fluids offer potential for developing rapidly actuated hydraulic devices where shear forces or pressure-driven flow are present. In this study, the Bingham yield stress of electrorheological fluids with different particle volume fractions is investigated experimentally in wall-driven and pressure-driven flow modes using measurements in a parallel-plate rheometer and a microfluidic channel, respectively. A modified Krieger-Dougherty model can be used to describe the effects of the particle volume fraction on the yield stress and is in good agreement with the viscometric data. However, significant yield hardening in pressure-driven channel flow is observed and attributed to an increase and eventual saturation of the particle volume fraction in the channel. A phenomenological physical model linking the densification and consequent microstructure to the ratio of the particle aggregation time scale compared to the convective time scale is presented and used to predict the enhancement in yield stress in channel flow, enabling us to reconcile discrepancies in the literature between wall-driven and pressure-driven flows.

Electrokinetic effects on motion of submicron particles in microchannel

NASA Astrophysics Data System (ADS)

Sato, Yohei; Hishida, Koichi

2006-11-01

Two-fluid mixing utilizing electrokinetically driven flow in a micro-channel is investigated by micron-resolution particle image velocimetry and an image processing technique. Submicron particles are transported and mixed with deionized water by electrophoresis. The particle electrophoretic velocity that is proportional to an applied electric field is measured in a closed cell, which is used to calculate the electroosmotic flow velocity. At a constant electric field, addition of pressure-driven flow to electrokinetically driven flow in a T-shaped micro-channel enhances two-fluid mixing because the momentum flux is increased. On the other hand, on application of an alternative sinusoidal electric field, the velocity difference between pressure-driven and electroosmotic flows has a significant effect on increasing the length of interface formed between two fluids. It is concluded from the present experiments that the transport and mixing process in the micro-channel will be enhanced by accurate flow-rate control of both pressure-driven and electroosmotic flows.

Hydrodynamic investigation of a self-propelled robotic fish based on a force-feedback control method.

PubMed

Wen, L; Wang, T M; Wu, G H; Liang, J H

2012-09-01

We implement a mackerel (Scomber scombrus) body-shaped robot, programmed to display the three most typical body/caudal fin undulatory kinematics (i.e. anguilliform, carangiform and thunniform), in order to biomimetically investigate hydrodynamic issues not easily tackled experimentally with live fish. The robotic mackerel, mounted on a servo towing system and initially at rest, can determine its self-propelled speed by measuring the external force acting upon it and allowing for the simultaneous measurement of power, flow field and self-propelled speed. Experimental results showed that the robotic swimmer with thunniform kinematics achieved a faster final swimming speed (St = 0.424) relative to those with carangiform (St = 0.43) and anguilliform kinematics (St = 0.55). The thrust efficiency, estimated from a digital particle image velocimetry (DPIV) flow field, showed that the robotic swimmer with thunniform kinematics is more efficient (47.3%) than those with carangiform (31.4%) and anguilliform kinematics (26.6%). Furthermore, the DPIV measurements illustrate that the large-scale characteristics of the flow pattern generated by the robotic swimmer with both anguilliform and carangiform kinematics were wedge-like, double-row wake structures. Additionally, a typical single-row reverse Karman vortex was produced by the robotic swimmer using thunniform kinematics. Finally, we discuss this novel force-feedback-controlled experimental method, and review the relative self-propelled hydrodynamic results of the robot when utilizing the three types of undulatory kinematics.

Effect of boundary representation on viscous, separated flows in a discontinuous-Galerkin Navier-Stokes solver

NASA Astrophysics Data System (ADS)

Nelson, Daniel A.; Jacobs, Gustaaf B.; Kopriva, David A.

2016-08-01

The effect of curved-boundary representation on the physics of the separated flow over a NACA 65(1)-412 airfoil is thoroughly investigated. A method is presented to approximate curved boundaries with a high-order discontinuous-Galerkin spectral element method for the solution of the Navier-Stokes equations. Multiblock quadrilateral element meshes are constructed with the grid generation software GridPro. The boundary of a NACA 65(1)-412 airfoil, defined by a cubic natural spline, is piecewise-approximated by isoparametric polynomial interpolants that represent the edges of boundary-fitted elements. Direct numerical simulation of the airfoil is performed on a coarse mesh and fine mesh with polynomial orders ranging from four to twelve. The accuracy of the curve fitting is investigated by comparing the flows computed on curved-sided meshes with those given by straight-sided meshes. Straight-sided meshes yield irregular wakes, whereas curved-sided meshes produce a regular Karman street wake. Straight-sided meshes also produce lower lift and higher viscous drag as compared with curved-sided meshes. When the mesh is refined by reducing the sizes of the elements, the lift decrease and viscous drag increase are less pronounced. The differences in the aerodynamic performance between the straight-sided meshes and the curved-sided meshes are concluded to be the result of artificial surface roughness introduced by the piecewise-linear boundary approximation provided by the straight-sided meshes.

Space shuttle simulation model

NASA Technical Reports Server (NTRS)

Tatom, F. B.; Smith, S. R.

1980-01-01

The effects of atmospheric turbulence in both horizontal and near horizontal flight, during the return of the space shuttle, are important for determining design, control, and 'pilot-in-the-loop' effects. A nonrecursive model (based on von Karman spectra) for atmospheric turbulence along the flight path of the shuttle orbiter was developed which provides for simulation of instantaneous vertical and horizontal gusts at the vehicle center-of-gravity, and also for simulation of instantaneous gust gradients. Based on this model, the time series for both gusts and gust gradients were generated and stored on a series of magnetic tapes which are entitled shuttle simulation turbulence tapes (SSTT). The time series are designed to represent atmospheric turbulence from ground level to an altitude of 10,000 meters. The turbulence generation procedure is described as well as the results of validating the simulated turbulence. Conclusions and recommendations are presented and references cited. The tabulated one dimensional von Karman spectra and the results of spectral and statistical analyses of the SSTT are contained in the appendix.

Development and validation of a turbulent-mix model for variable-density and compressible flows.

PubMed

Banerjee, Arindam; Gore, Robert A; Andrews, Malcolm J

2010-10-01

The modeling of buoyancy driven turbulent flows is considered in conjunction with an advanced statistical turbulence model referred to as the BHR (Besnard-Harlow-Rauenzahn) k-S-a model. The BHR k-S-a model is focused on variable-density and compressible flows such as Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) driven mixing. The BHR k-S-a turbulence mix model has been implemented in the RAGE hydro-code, and model constants are evaluated based on analytical self-similar solutions of the model equations. The results are then compared with a large test database available from experiments and direct numerical simulations (DNS) of RT, RM, and KH driven mixing. Furthermore, we describe research to understand how the BHR k-S-a turbulence model operates over a range of moderate to high Reynolds number buoyancy driven flows, with a goal of placing the modeling of buoyancy driven turbulent flows at the same level of development as that of single phase shear flows.

Ground Test Investigation on a Thermal Protection System Junction

NASA Astrophysics Data System (ADS)

Panerai, F.; Thoemel, J.; Chazot, O.

2009-01-01

During the atmospheric reentry of a spacecraft, the dissociated flow around its Thermal Protection System (TPS) could travel from a low cat- alytic to a high catalytic surface. In this situation a peak of heat flux is experienced at the junction between the two materials. A safe vehicle design cannot preclude investigations on such a phenomenon, since the consequent heating could be harmful for the integrity of TPS. The present work finds its framework on the EXPERT (Eu- ropean eXPErimental Re-entry Testbed) project. The EXPERT vehicle TPS is composed of a C/SiC nose and a PM1000 skirt, so that a catalytic transition occurs in correspondence of their junction. Experiments on wall catalysis phenomena over Thermal Protection Materials (TPM) are performed in this project, using the von Karman Institute (VKI) induction-coupled plasma generator (Plasmatron), under operating conditions representative for real flight situation. In- frared thermography and pyrometry temperature measurements are performed in order to experimentally prove and quantify the transition.

Finite dimensional approximation of a class of constrained nonlinear optimal control problems

NASA Technical Reports Server (NTRS)

Gunzburger, Max D.; Hou, L. S.

1994-01-01

An abstract framework for the analysis and approximation of a class of nonlinear optimal control and optimization problems is constructed. Nonlinearities occur in both the objective functional and in the constraints. The framework includes an abstract nonlinear optimization problem posed on infinite dimensional spaces, and approximate problem posed on finite dimensional spaces, together with a number of hypotheses concerning the two problems. The framework is used to show that optimal solutions exist, to show that Lagrange multipliers may be used to enforce the constraints, to derive an optimality system from which optimal states and controls may be deduced, and to derive existence results and error estimates for solutions of the approximate problem. The abstract framework and the results derived from that framework are then applied to three concrete control or optimization problems and their approximation by finite element methods. The first involves the von Karman plate equations of nonlinear elasticity, the second, the Ginzburg-Landau equations of superconductivity, and the third, the Navier-Stokes equations for incompressible, viscous flows.

Heat Transfer on a Flat Plate with Uniform and Step Temperature Distributions

NASA Technical Reports Server (NTRS)

Bahrami, Parviz A.

2005-01-01

Heat transfer associated with turbulent flow on a step-heated or cooled section of a flat plate at zero angle of attack with an insulated starting section was computationally modeled using the GASP Navier-Stokes code. The algebraic eddy viscosity model of Baldwin-Lomax and the turbulent two-equation models, the K- model and the Shear Stress Turbulent model (SST), were employed. The variations from uniformity of the imposed experimental temperature profile were incorporated in the computations. The computations yielded satisfactory agreement with the experimental results for all three models. The Baldwin- Lomax model showed the closest agreement in heat transfer, whereas the SST model was higher and the K-omega model was yet higher than the experiments. In addition to the step temperature distribution case, computations were also carried out for a uniformly heated or cooled plate. The SST model showed the closest agreement with the Von Karman analogy, whereas the K-omega model was higher and the Baldwin-Lomax was lower.

Revising the `Henry Problem' of density-driven groundwater flow: A review of historic Biscayne aquifer data.

NASA Astrophysics Data System (ADS)

Weyer, K. U.

2016-12-01

Coastal groundwater flow investigations at the Cutler site of the Biscayne Bay south of Miami, Florida, gave rise to the dominating concept of density-driven flow of sea water into coastal aquifers indicated as a saltwater wedge. Within that wedge convection type return flow of seawater and a dispersion zone were concluded by Cooper et al. (1964, USGS Water Supply Paper 1613-C) to be the cause of the Biscayne aquifer `sea water wedge'. This conclusion was merely based on the chloride distribution within the aquifer and on an analytical model concept assuming convection flow within a confined aquifer without taking non-chemical field data into consideration. This concept was later labelled the `Henry Problem', which any numerical variable density flow program has to be able to simulate to be considered acceptable. Revisiting the above summarizing publication with its record of piezometric field data (heads) showed that the so-called sea water wedge was actually caused by discharging deep saline groundwater driven by gravitational flow and not by denser sea water. Density driven flow of seawater into the aquifer was not found reflected in the head measurements for low and high tide conditions which had been taken contemporaneously with the chloride measurements. These head measurements had not been included in the flow interpretation. The very same head measurements indicated a clear dividing line between shallow local fresh groundwater flow and saline deep groundwater flow without the existence of a dispersion zone or a convection cell. The Biscayne situation emphasizes the need for any chemical interpretation of flow pattern to be backed up by head data as energy indicators of flow fields. At the Biscayne site density driven flow of seawater did and does not exist. Instead this site and the Florida coast line in general are the end points of local fresh and regional saline groundwater flow systems driven by gravity forces and not by density differences.

Analysis of low altitude atmospheric turbulence data measured in flight

NASA Technical Reports Server (NTRS)

Ganzer, V. M.; Joppa, R. G.; Vanderwees, G.

1977-01-01

All three components of turbulence were measured simultaneously in flight at each wing tip of a Beech D-18 aircraft. The flights were conducted at low altitude, 30.5 - 61.0 meters (100-200 ft.), over water in the presence of wind driven turbulence. Statistical properties of flight measured turbulence were compared with Gaussian and non-Gaussian turbulence models. Spatial characteristics of the turbulence were analyzed using the data from flight perpendicular and parallel to the wind. The probability density distributions of the vertical gusts show distinctly non-Gaussian characteristics. The distributions of the longitudinal and lateral gusts are generally Gaussian. The power spectra compare in the inertial subrange at some points better with the Dryden spectrum, while at other points the von Karman spectrum is a better approximation. In the low frequency range the data show peaks or dips in the power spectral density. The cross between vertical gusts in the direction of the mean wind were compared with a matched non-Gaussian model. The real component of the cross spectrum is in general close to the non-Gaussian model. The imaginary component, however, indicated a larger phase shift between these two gust components than was found in previous research.

Jet Propulsion Laboratory's Space Explorations. Part 1; History of JPL

NASA Technical Reports Server (NTRS)

Chau, Savio

2005-01-01

This slide presentation briefly reviews the history of the Jet Propulsion Laboratory from its founding by Dr von Karman in 1936 for research in rocketry through the post-Sputnik shift to unmanned space exploration in 1957. The presentation also reviews the major JPL missions with views of the spacecraft.

Structural Influence of Dynamics of Bottom Loads

DTIC Science & Technology

2014-02-10

using the Numerette research craft, are underway. Early analytic research on slamming was done by von Karman [5] using a momentum approach, and by...pressure q{x,t) as two constant pressures, qi and qj, traveling at a constant speed c. Using the Euler- Bernoulli beam assumptions the governing

An extended theory of thin airfoils and its application to the biplane problem

NASA Technical Reports Server (NTRS)

Millikan, Clark B

1931-01-01

The report presents a new treatment, due essentially to von Karman, of the problem of the thin airfoil. The standard formulae for the angle of zero lift and zero moment are first developed and the analysis is then extended to give the effect of disturbing or interference velocities, corresponding to an arbitrary potential flow, which are superimposed on a normal rectilinear flow over the airfoil. An approximate method is presented for obtaining the velocities induced by a 2-dimensional airfoil at a point some distance away. In certain cases this method has considerable advantage over the simple "lifting line" procedure usually adopted. The interference effects for a 2-dimensional biplane are considered in the light of the previous analysis. The results of the earlier sections are then applied to the general problem of the interference effects for a 3-dimensional biplane, and formulae and charts are given which permit the characteristics of the individual wings of an arbitrary biplane without sweepback or dihedral to be calculated. In the final section the conclusions drawn from the application of the theory to a considerable number of special cases are discussed, and curves are given illustrating certain of these conclusions and serving as examples to indicate the nature of the agreement between the theory and experiment.

Wind influence on a coastal buoyant outflow

NASA Astrophysics Data System (ADS)

Whitney, Michael M.; Garvine, Richard W.

2005-03-01

This paper investigates the interplay between river discharge and winds in forcing coastal buoyant outflows. During light winds a plume influenced by the Earth's rotation will flow down shelf (in the direction of Kelvin wave propagation) as a slender buoyancy-driven coastal current. Downwelling favorable winds augment this down-shelf flow, narrow the plume, and mix the water column. Upwelling favorable winds drive currents that counter the buoyancy-driven flow, spread plume waters offshore, and rapidly mix buoyant waters. Two criteria are developed to assess the wind influence on a buoyant outflow. The wind strength index (Ws) determines whether a plume's along-shelf flow is in a wind-driven or buoyancy-driven state. Ws is the ratio of the wind-driven and buoyancy-driven along-shelf velocities. Wind influence on across-shelf plume structure is rated with a timescale (ttilt) for the isopycnal tilting caused by wind-driven Ekman circulation. These criteria are used to characterize wind influence on the Delaware Coastal Current and can be applied to other coastal buoyant outflows. The Delaware buoyant outflow is simulated for springtime high-river discharge conditions. Simulation results and Ws values reveal that the coastal current is buoyancy-driven most of the time (∣Ws∣ < 1 on average). Wind events, however, overwhelm the buoyancy-driven flow (∣Ws∣ > 1) several times during the high-discharge period. Strong upwelling events reverse the buoyant outflow; they constitute an important mechanism for transporting fresh water up shelf. Across-shelf plume structure is more sensitive to wind influence than the along-shelf flow. Values of ttilt indicate that moderate or strong winds persisting throughout a day can modify plume width significantly. Plume widening during upwelling events is accompanied by mixing that can erase the buoyant outflow.

Flutter Phenomenon in Flow Driven Energy Harvester–A Unified Theoretical Model for “Stiff” and “Flexible” Materials

PubMed Central

Chen, Yu; Mu, Xiaojing; Wang, Tao; Ren, Weiwei; Yang, Ya; Wang, Zhong Lin; Sun, Chengliang; Gu, Alex Yuandong

2016-01-01

Here, we report a stable and predictable aero-elastic motion in the flow-driven energy harvester, which is different from flapping and vortex-induced-vibration (VIV). A unified theoretical frame work that describes the flutter phenomenon observed in both “stiff” and “flexible” materials for flow driven energy harvester was presented in this work. We prove flutter in both types of materials is the results of the coupled effects of torsional and bending modes. Compared to “stiff” materials, which has a flow velocity-independent flutter frequency, flexible material presents a flutter frequency that almost linearly scales with the flow velocity. Specific to “flexible” materials, pre-stress modulates the frequency range in which flutter occurs. It is experimentally observed that a double-clamped “flexible” piezoelectric P(VDF-TrFE) thin belt, when driven into the flutter state, yields a 1,000 times increase in the output voltage compared to that of the non-fluttered state. At a fixed flow velocity, increase in pre-stress level of the P(VDF-TrFE) thin belt up-shifts the flutter frequency. In addition, this work allows the rational design of flexible piezoelectric devices, including flow-driven energy harvester, triboelectric energy harvester, and self-powered wireless flow speed sensor. PMID:27739484

Flutter Phenomenon in Flow Driven Energy Harvester-A Unified Theoretical Model for "Stiff" and "Flexible" Materials.

PubMed

Chen, Yu; Mu, Xiaojing; Wang, Tao; Ren, Weiwei; Yang, Ya; Wang, Zhong Lin; Sun, Chengliang; Gu, Alex Yuandong

2016-10-14

Here, we report a stable and predictable aero-elastic motion in the flow-driven energy harvester, which is different from flapping and vortex-induced-vibration (VIV). A unified theoretical frame work that describes the flutter phenomenon observed in both "stiff" and "flexible" materials for flow driven energy harvester was presented in this work. We prove flutter in both types of materials is the results of the coupled effects of torsional and bending modes. Compared to "stiff" materials, which has a flow velocity-independent flutter frequency, flexible material presents a flutter frequency that almost linearly scales with the flow velocity. Specific to "flexible" materials, pre-stress modulates the frequency range in which flutter occurs. It is experimentally observed that a double-clamped "flexible" piezoelectric P(VDF-TrFE) thin belt, when driven into the flutter state, yields a 1,000 times increase in the output voltage compared to that of the non-fluttered state. At a fixed flow velocity, increase in pre-stress level of the P(VDF-TrFE) thin belt up-shifts the flutter frequency. In addition, this work allows the rational design of flexible piezoelectric devices, including flow-driven energy harvester, triboelectric energy harvester, and self-powered wireless flow speed sensor.

A numerical study of the laminar necklace vortex system and its effect on the wake for a circular cylinder

NASA Astrophysics Data System (ADS)

Kirkil, Gokhan; Constantinescu, George

2012-07-01

Large eddy simulation (LES) is used to investigate the structure of the laminar horseshoe vortex (HV) system and the dynamics of the necklace vortices as they fold around the base of a circular cylinder mounted on the flat bed of an open channel for Reynolds numbers defined with the cylinder diameter, D, smaller than 4460. The study concentrates on the analysis of the structure of the HV system in the periodic breakaway sub-regime, which is characterized by the formation of three main necklace vortices. Over one oscillation cycle of the previously observed breakaway sub-regime, the corner vortex and the primary vortex merge (amalgamate) and a developing vortex separates from the incoming laminar boundary layer (BL) to become the new primary vortex. Results show that while the classical breakaway sub-regime, in which one amalgamation event occurs per oscillation cycle, is present when the nondimensional displacement thickness of the incoming BL at the location of the cylinder is relatively large (δ*/D > 0.1), a new type of breakaway sub-regime is present for low values of δ*/D. This sub-regime, which we call the double-breakaway sub-regime, is characterized by the occurrence of two amalgamation events over one full oscillation cycle. LES results show that when the HV system is in one of the breakaway sub-regimes, the interactions between the highly coherent necklace vortices and the eddies shed inside the separated shear layers (SSLs) are very strong. For the relatively shallow flow conditions considered in this study (H/D ≅ 1, H is the channel depth), at times, the disturbances induced by the legs of the necklace vortices do not allow the SSLs on the two sides of the cylinder to interact in a way that allows the vorticity redistribution mechanism to lead to the formation of a new wake roller. As a result, the shedding of large-scale rollers in the turbulent wake is suppressed for relatively large periods of time. Simulation results show that the wake structure changes randomly between time intervals when large-scale rollers are forming and are convected in the wake (von Karman regime), and time intervals when the rollers do not form. When the wake is in the von Karman regime, the shedding frequency of the rollers is close to that observed for flow past infinitely long cylinders.

Features of the Kaiser effect in coal specimens at different stages of the triaxial axisymmetric deformation

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

Shkuratnik, V.L.; Filimonov, Y.L.; Kuchurin, S.V.

2007-01-15

The experimental data are presented for the features of formation and manifestation of the acoustic-emission and deformation memory effects in specimens of anthracite at different stages of the triaxial cyclic deformation by the Karman scheme in the pre-limiting and post-limiting zones.

Acoustic-emissive memory effect in coal samples under triaxial axial-symmetric compression

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

Shkuratnik, V.L.; Filimonov, Y.L.; Kuchurin, S.V.

2006-05-15

The experimental data are presented for production and manifestation of the Kaiser effect in coal samples subjected to triaxial loading by the Karman scheme in the first cycle and to various loading modes in the second cycle. The Kaiser effect is identified with the help of a deformation memory effect.

Atmospheric turbulence simulation for Shuttle orbiter

NASA Technical Reports Server (NTRS)

Tatom, F. B.; Smith, S. R.

1979-01-01

An improved non-recursive model for atmospheric turbulence along the flight path of the Shuttle Orbiter is developed which provides for simulation of instantaneous vertical and horizontal gusts at the vehicle center-of-gravity, and also for simulation of instantaneous gust gradients. Based on this model the time series for both gusts and gust gradients are generated and stored on a series of magnetic tapes. Section 2 provides a description of the various technical considerations associated with the turbulence simulation model. Included in this section are descriptions of the digital filter simulation model, the von Karman spectra with finite upper limits, and the final non recursive turbulence simulation model which was used to generate the time series. Section 2 provides a description of the various technical considerations associated with the turbulence simulation model. Included in this section are descriptions of the digial filter simulation model, the von Karman spectra with finite upper limits, and the final non recursive turbulence simulation model which was used to generate the time series. Section 3 provides a description of the time series as currently recorded on magnetic tape. Conclusions and recommendations are presented in Section 4.

Comparison of wing-span averaging effects on lift, rolling moment, and bending moment for two span load distributions and for two turbulence representations

NASA Technical Reports Server (NTRS)

Lichtenstein, J. H.

1978-01-01

An analytical method of computing the averaging effect of wing-span size on the loading of a wing induced by random turbulence was adapted for use on a digital electronic computer. The turbulence input was assumed to have a Dryden power spectral density. The computations were made for lift, rolling moment, and bending moment for two span load distributions, rectangular and elliptic. Data are presented to show the wing-span averaging effect for wing-span ratios encompassing current airplane sizes. The rectangular wing-span loading showed a slightly greater averaging effect than did the elliptic loading. In the frequency range most bothersome to airplane passengers, the wing-span averaging effect can reduce the normal lift load, and thus the acceleration, by about 7 percent for a typical medium-sized transport. Some calculations were made to evaluate the effect of using a Von Karman turbulence representation. These results showed that using the Von Karman representation generally resulted in a span averaging effect about 3 percent larger.

The Value of GRACE Data in Improving, Assessing and Evaluating Land Surface and Climate Models

NASA Astrophysics Data System (ADS)

Yang, Z.

2011-12-01

I will review how the Gravity Recovery and Climate Experiment (GRACE) satellite measurements have improved land surface models that are developed for weather, climate, and hydrological studies. GRACE-derived terrestrial water storage (TWS) changes have been successfully used to assess and evaluate the improved representations of land-surface hydrological processes such as groundwater-soil moisture interaction, frozen soil and infiltration, and the topographic control on runoff production, as evident in the simulations from the latest Noah-MP, the Community Land Model, and the Community Climate System Model. GRACE data sets have made it possible to estimate key terrestrial water storage components (snow mass, surface water, groundwater or water table depth), biomass, and surface water fluxes (evapotranspiration, solid precipitation, melt of snow/ice). Many of the examples will draw from my Land, Environment and Atmosphere Dynamics group's work on land surface model developments, snow mass retrieval, and multi-sensor snow data assimilation using the ensemble Karman filter and the ensemble Karman smoother. Finally, I will briefly outline some future directions in using GRACE in land surface modeling.

Flow-Driven Waves and Phase-Locked Self-Organization in Quasi-One-Dimensional Colonies of Dictyostelium discoideum

NASA Astrophysics Data System (ADS)

Gholami, A.; Steinbock, O.; Zykov, V.; Bodenschatz, E.

2015-01-01

We report experiments on flow-driven waves in a microfluidic channel containing the signaling slime mold Dictyostelium discoideum. The observed cyclic adenosine monophosphate (cAMP) wave trains developed spontaneously in the presence of flow and propagated with the velocity proportional to the imposed flow velocity. The period of the wave trains was independent of the flow velocity. Perturbations of flow-driven waves via external periodic pulses of the signaling agent cAMP induced 1 ∶1 , 2 ∶1 , 3 ∶1 , and 1 ∶2 frequency responses, reminiscent of Arnold tongues in forced oscillatory systems. We expect our observations to be generic to active media governed by reaction-diffusion-advection dynamics, where spatially bound autocatalytic processes occur under flow conditions.

Characterization of an induced pressure pumping force for microfluidics

NASA Astrophysics Data System (ADS)

Jiang, Hai; Fan, Na; Peng, Bei; Weng, Xuan

2017-05-01

The electro-osmotic pumping and pressure-driven manipulation of fluids are considered as the most common strategies in microfluidic devices. However, both of them exhibit major disadvantages such as hard integration and high reagent consumption, and they are destructive methods for detection and photo bleaching. In this paper, an electric field-effect flow control approach, combining the electro-osmotic pumping force and the pressure-driven pumping force, was developed to generate the induced pressure-driven flow in a T-shaped microfluidic chip. Electro-osmotic flow between the T-intersection and two reservoirs was demonstrated, and it provided a stable, continuous, and electric field-free flow in the section of the microchannel without the electrodes. The velocity of the induced pressure-driven flow was linearly proportional to the applied voltages. Both numerical and experimental investigations were conducted to prove the concept, and the experimental results showed good agreement with the numerical simulations. In comparison to other induced pressure pumping methods, this approach can induce a high and controllable pressure drop in the electric field-free segment, subsequently causing an induced pressure-driven flow for transporting particles or biological cells. In addition, the generation of bubbles and the blocking of the microchannel are avoided.

Regulation of electron temperature gradient turbulence by zonal flows driven by trapped electron modes

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

Asahi, Y., E-mail: y.asahi@nr.titech.ac.jp; Tsutsui, H.; Tsuji-Iio, S.

2014-05-15

Turbulent transport caused by electron temperature gradient (ETG) modes was investigated by means of gyrokinetic simulations. It was found that the ETG turbulence can be regulated by meso-scale zonal flows driven by trapped electron modes (TEMs), which are excited with much smaller growth rates than those of ETG modes. The zonal flows of which radial wavelengths are in between the ion and the electron banana widths are not shielded by trapped ions nor electrons, and hence they are effectively driven by the TEMs. It was also shown that an E × B shearing rate of the TEM-driven zonal flows is larger thanmore » or comparable to the growth rates of long-wavelength ETG modes and TEMs, which make a main contribution to the turbulent transport before excitation of the zonal flows.« less

Kinetic instability of electrostatic ion cyclotron waves in inter-penetrating plasmas

NASA Astrophysics Data System (ADS)

Bashir, M. F.; Ilie, R.; Murtaza, G.

2018-05-01

The Electrostatic Ion Cyclotron (EIC) instability that includes the effect of wave-particle interaction is studied owing to the free energy source through the flowing velocity of the inter-penetrating plasmas. It is shown that the origin of this current-less instability is different from the classical current driven EIC instability. The threshold conditions applicable to a wide range of plasma parameters and the estimate of the growth rate are determined as a function of the normalized flowing velocity ( u0/vt f e ), the temperature ( Tf/Ts ) and the density ratios ( nf 0/ns 0 ) of flowing component to static one. The EIC instability is driven by either flowing electrons or flowing ions, depending upon the different Doppler shifted frequency domains. It is found that the growth rate for electron-driven instability is higher than the ion-driven one. However, in both cases, the denser (hotter) is the flowing plasma, the lesser (greater) is the growth rate. The possible applications related to the terrestrial solar plasma environment are also discussed.

Enhanced Forced Convection Heat Transfer using Small Scale Vorticity Concentrations Effected by Flow Driven, Aeroelastically Vibrating Reeds

DTIC Science & Technology

2016-08-03

insulated from behind (using an air gap) as shown in figure III.3-1c. Each of the heated side walls are instrumented with seven equally-spaced T-Type...AFRL-AFOSR-VA-TR-2016-0339 Enhanced convection heat transfer using small-scale vorticity concentrations effected by flow-driven, aeroelastically...public release. Enhanced Forced Convection Heat Transfer using Small-Scale Vorticity Concentrations Effected by Flow-Driven, Aeroelastically Vibrating

Thermally Driven Josephson Effect

NASA Technical Reports Server (NTRS)

Penanen, Konstantin; Chui, Talso

2008-01-01

A concept is proposed of the thermally driven Josephson effect in superfluid helium. Heretofore, the Josephson effect in a superfluid has been recognized as an oscillatory flow that arises in response to a steady pressure difference between two superfluid reservoirs separated by an array of submicron-sized orifices, which act in unison as a single Josephson junction. Analogously, the thermally driven Josephson effect is an oscillatory flow that arises in response to a steady temperature difference. The thermally driven Josephson effect is partly a consequence of a quantum- mechanical effect known as the fountain effect, in which a temperature difference in a superfluid is accompanied by a pressure difference. The thermally driven Josephson effect may have significance for the development of a high-resolution gyroscope based on the Josephson effect in a superfluid: If the pressure-driven Josephson effect were used, then the fluid on the high-pressure side would become depleted, necessitating periodic interruption of operation to reverse the pressure difference. If the thermally driven Josephson effect were used, there would be no net flow and so the oscillatory flow could be maintained indefinitely by maintaining the required slightly different temperatures on both sides of the junction.

Analysis of non-equilibrium phenomena in inductively coupled plasma generators

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

Zhang, W.; Panesi, M., E-mail: mpanesi@illinois.edu; Lani, A.

This work addresses the modeling of non-equilibrium phenomena in inductively coupled plasma discharges. In the proposed computational model, the electromagnetic induction equation is solved together with the set of Navier-Stokes equations in order to compute the electromagnetic and flow fields, accounting for their mutual interaction. Semi-classical statistical thermodynamics is used to determine the plasma thermodynamic properties, while transport properties are obtained from kinetic principles, with the method of Chapman and Enskog. Particle ambipolar diffusive fluxes are found by solving the Stefan-Maxwell equations with a simple iterative method. Two physico-mathematical formulations are used to model the chemical reaction processes: (1) Amore » Local Thermodynamics Equilibrium (LTE) formulation and (2) a thermo-chemical non-equilibrium (TCNEQ) formulation. In the TCNEQ model, thermal non-equilibrium between the translational energy mode of the gas and the vibrational energy mode of individual molecules is accounted for. The electronic states of the chemical species are assumed in equilibrium with the vibrational temperature, whereas the rotational energy mode is assumed to be equilibrated with translation. Three different physical models are used to account for the coupling of chemistry and energy transfer processes. Numerical simulations obtained with the LTE and TCNEQ formulations are used to characterize the extent of non-equilibrium of the flow inside the Plasmatron facility at the von Karman Institute. Each model was tested using different kinetic mechanisms to assess the sensitivity of the results to variations in the reaction parameters. A comparison of temperatures and composition profiles at the outlet of the torch demonstrates that the flow is in non-equilibrium for operating conditions characterized by pressures below 30 000 Pa, frequency 0.37 MHz, input power 80 kW, and mass flow 8 g/s.« less

Analysis of non-equilibrium phenomena in inductively coupled plasma generators

NASA Astrophysics Data System (ADS)

Zhang, W.; Lani, A.; Panesi, M.

2016-07-01

This work addresses the modeling of non-equilibrium phenomena in inductively coupled plasma discharges. In the proposed computational model, the electromagnetic induction equation is solved together with the set of Navier-Stokes equations in order to compute the electromagnetic and flow fields, accounting for their mutual interaction. Semi-classical statistical thermodynamics is used to determine the plasma thermodynamic properties, while transport properties are obtained from kinetic principles, with the method of Chapman and Enskog. Particle ambipolar diffusive fluxes are found by solving the Stefan-Maxwell equations with a simple iterative method. Two physico-mathematical formulations are used to model the chemical reaction processes: (1) A Local Thermodynamics Equilibrium (LTE) formulation and (2) a thermo-chemical non-equilibrium (TCNEQ) formulation. In the TCNEQ model, thermal non-equilibrium between the translational energy mode of the gas and the vibrational energy mode of individual molecules is accounted for. The electronic states of the chemical species are assumed in equilibrium with the vibrational temperature, whereas the rotational energy mode is assumed to be equilibrated with translation. Three different physical models are used to account for the coupling of chemistry and energy transfer processes. Numerical simulations obtained with the LTE and TCNEQ formulations are used to characterize the extent of non-equilibrium of the flow inside the Plasmatron facility at the von Karman Institute. Each model was tested using different kinetic mechanisms to assess the sensitivity of the results to variations in the reaction parameters. A comparison of temperatures and composition profiles at the outlet of the torch demonstrates that the flow is in non-equilibrium for operating conditions characterized by pressures below 30 000 Pa, frequency 0.37 MHz, input power 80 kW, and mass flow 8 g/s.

Dynamic simulations of under-rib convection-driven flow-field configurations and comparison with experiment in polymer electrolyte membrane fuel cells

NASA Astrophysics Data System (ADS)

Duy, Vinh Nguyen; Lee, Jungkoo; Kim, Kyungcheol; Ahn, Jiwoong; Park, Seongho; Kim, Taeeun; Kim, Hyung-Man

2015-10-01

The under-rib convection-driven flow-field design for the uniform distribution of reacting gas and the generation of produced water generates broad scientific interest, especially among those who study the performance of polymer electrolyte membrane fuel cells (PEMFCs). In this study, we simulate the effects of an under-rib convection-driven serpentine flow-field with sub-channel and by-pass (SFFSB) and a conventional advanced serpentine flow-field (CASFF) on single cell performance, and we compare the simulation results with experimental measurements. In the under-rib convection-driven flow-field configuration with SFFSB, the pressure drop is decreased because of the greater cross-sectional area for gas flow, and the decreased pressure drop results in the reduction of the parasitic loss. The anode liquid water mass fraction increases with increasing channel height because of increased back diffusion, while the cathode liquid water mass fraction does not depend upon the sub-channels but is ascribed mainly to the electro-osmotic drag. Simulation results verify that the maximum current and the power densities of the SFFSB are increased by 18.85% and 23.74%, respectively, due to the promotion of under-rib convection. The findings in this work may enable the optimization of the design of under-rib convection-driven flow-fields for efficient PEMFCs.

Second Order Non-Linear Optical Polyphosphazenes. Proceedings of Symposium on Non-Linear Optics, ACS Meeting, Held in Boston, Massachusetts 1990

DTIC Science & Technology

1990-03-23

Paciorek Dr. William B. Moniz Ultrasystems Defense and Space, Inc. Code 6120 16775 Von Karman Avenue Naval Research Laboratory Irvine, CA 92714 Washington...413h004 Dr. Les H. Sperling Dr. Richard S. Stein Materials Research Center #32 Polymer Research Institute Lehigh University University of Massachusetts

Grid generation using classical techniques

NASA Technical Reports Server (NTRS)

Moretti, G.

1980-01-01

A brief historical review of conformal mapping and its applications to problems in fluid mechanics and electromagnetism is presented. The use of conformal mapping as a grid generator is described. The philosophy of the 'closed form' approach and its application to a Neumann problem is discussed. Karman-Trefftz mappings and grids for ablated, three dimensional bodies are also discussed.

Hydrodynamic bifurcation in electro-osmotically driven periodic flows

NASA Astrophysics Data System (ADS)

Morozov, Alexander; Marenduzzo, Davide; Larson, Ronald G.

2018-06-01

In this paper, we report an inertial instability that occurs in electro-osmotically driven channel flows. We assume that the charge motion under the influence of an externally applied electric field is confined to a small vicinity of the channel walls that, effectively, drives a bulk flow through a prescribed slip velocity at the boundaries. Here, we study spatially periodic wall velocity modulations in a two-dimensional straight channel numerically. At low slip velocities, the bulk flow consists of a set of vortices along each wall that are left-right symmetric, while at sufficiently high slip velocities, this flow loses its stability through a supercritical bifurcation. Surprisingly, the flow state that bifurcates from a left-right symmetric base flow has a rather strong mean component along the channel, which is similar to pressure-driven velocity profiles. The instability sets in at rather small Reynolds numbers of about 20-30, and we discuss its potential applications in microfluidic devices.

Role of large-scale velocity fluctuations in a two-vortex kinematic dynamo.

PubMed

Kaplan, E J; Brown, B P; Rahbarnia, K; Forest, C B

2012-06-01

This paper presents an analysis of the Dudley-James two-vortex flow, which inspired several laboratory-scale liquid-metal experiments, in order to better demonstrate its relation to astrophysical dynamos. A coordinate transformation splits the flow into components that are axisymmetric and nonaxisymmetric relative to the induced magnetic dipole moment. The reformulation gives the flow the same dynamo ingredients as are present in more complicated convection-driven dynamo simulations. These ingredients are currents driven by the mean flow and currents driven by correlations between fluctuations in the flow and fluctuations in the magnetic field. The simple model allows us to isolate the dynamics of the growing eigenvector and trace them back to individual three-wave couplings between the magnetic field and the flow. This simple model demonstrates the necessity of poloidal advection in sustaining the dynamo and points to the effect of large-scale flow fluctuations in exciting a dynamo magnetic field.

Design of pressure-driven microfluidic networks using electric circuit analogy.

PubMed

Oh, Kwang W; Lee, Kangsun; Ahn, Byungwook; Furlani, Edward P

2012-02-07

This article reviews the application of electric circuit methods for the analysis of pressure-driven microfluidic networks with an emphasis on concentration- and flow-dependent systems. The application of circuit methods to microfluidics is based on the analogous behaviour of hydraulic and electric circuits with correlations of pressure to voltage, volumetric flow rate to current, and hydraulic to electric resistance. Circuit analysis enables rapid predictions of pressure-driven laminar flow in microchannels and is very useful for designing complex microfluidic networks in advance of fabrication. This article provides a comprehensive overview of the physics of pressure-driven laminar flow, the formal analogy between electric and hydraulic circuits, applications of circuit theory to microfluidic network-based devices, recent development and applications of concentration- and flow-dependent microfluidic networks, and promising future applications. The lab-on-a-chip (LOC) and microfluidics community will gain insightful ideas and practical design strategies for developing unique microfluidic network-based devices to address a broad range of biological, chemical, pharmaceutical, and other scientific and technical challenges.

Electroviscous effect and electrokinetic energy conversion in time periodic pressure-driven flow through a parallel-plate nanochannel with surface charge-dependent slip

NASA Astrophysics Data System (ADS)

Buren, Mandula; Jian, Yongjun; Zhao, Yingchun; Chang, Long

2018-05-01

In this paper we analytically investigate the electroviscous effect and electrokinetic energy conversion in the time periodic pressure-driven flow of an incompressible viscous Newtonian liquid through a parallel-plate nanochannel with surface charge-dependent slip. Analytical and semi-analytical solutions for electric potential, velocity and streaming electric field are obtained and are utilized to compute electrokinetic energy conversion efficiency. The results show that velocity amplitude and energy conversion efficiency are reduced when the effect of surface charge on slip length is considered. The surface charge effect increases with zeta potential and ionic concentration. In addition, the energy conversion efficiency is large when the ratio of channel half-height to the electric double layer thickness is small. The boundary slip results in a large increase in energy conversion. Higher values of the frequency of pressure pulsation lead to higher values of the energy conversion efficiency. We also obtain the energy conversion efficiency in constant pressure-driven flow and find that the energy conversion efficiency in periodical pressure-driven flow becomes larger than that in constant pressure-driven flow when the frequency is large enough.

Surface tension driven flow in glass melts and model fluids

NASA Technical Reports Server (NTRS)

Mcneil, T. J.; Cole, R.; Subramanian, R. S.

1982-01-01

Surface tension driven flow has been investigated analytically and experimentally using an apparatus where a free column of molten glass or model fluids was supported at its top and bottom faces by solid surfaces. The glass used in the experiments was sodium diborate, and the model fluids were silicone oils. In both the model fluid and glass melt experiments, conclusive evidence was obtained to prove that the observed flow was driven primarily by surface tension forces. The experimental observations are in qualitative agreement with predictions from the theoretical model.

Finite micro-tab system for load control on a wind turbine

NASA Astrophysics Data System (ADS)

Bach, A. B.; Lennie, M.; Pechlivanoglou, G.; Nayeri, C. N.; Paschereit, C. O.

2014-06-01

Finite micro-tabs have been investigated experimentally to evaluate the potential for load control on wind turbines. Two dimensional full span, as well as multiple finite tabs of various aspect ratios have been studied on an AH93W174 airfoil at different chord wise positions. A force balance was used to measure the aerodynamic loads. Furthermore, the wake vortex system consisting of the Karman vortex street as well as the tab tip vortices was analyzed with a 12-hole probe and hot wire anemometry. Finally, conventional oil paint as well as a quantitative digital flow analysis technique called SMARTviz were used to visualize the flow around the finite tab configurations. Results have shown that the devices are an effective solution to alleviate the airfoils overall load. The influence of the tab height, tab position as well as the finite tab aspect ratio on the lift and lift to drag ratio have been evaluated. It could be shown, that the lift difference can either be varied by changing the tab height as well as by altering the aspect ratio of the finite tabs. The drag of a two-dimensional flap is directly associated with the vortex street, while in the case of the finite tab, the solidity ratio of the tabs has the strongest effect on the drag. Therefore, the application of a finite tab system showed to improve the lift to drag ratio.

Development of the wake behind a circular cylinder impulsively started into rotatory and rectilinear motion: Intermediate rotation rates

NASA Technical Reports Server (NTRS)

Chen, Yen-Ming; Ou, Yuh-Roung; Pearlstein, Arne J.

1991-01-01

The temporal development of two-dimensional viscous incompressible flow generated by a circular cylinder started impulsively into steady rotatory and rectilinear motion is studied by integration of a velocity/vorticity formulation of the governing equations, using an explicit finite-difference/pseudo-spectral technique and an implementation of the Biot-Savart law. Results are presented for a Reynolds number of 200 (based on the cylinder diameter 2a and the magnitude U of the rectilinear velocity) for several values of the angular/rectilinear speed ratio alpha = (omega x a)/U (where omega is the angular speed) up to 3.25. Several aspects of the kinematics and dynamics of the flow not considered earlier are discussed. For higher values of alpha, the results indicate that for Re = 200, vortex shedding does indeed occur for alpha = 3.25. The shedding process is; however, very different from that which gives rise to the usual Karman vortex street for alpha = 0. In particular, consecutive vortices shed by the body can be shed from the same side and be of the same sense, in contrast to the nonrotating case, in which mirror-image vortices of opposite sense are shed alternately on opposite sides of the body. The implications of the results are discussed in relation to the possibility of suppressing vortex shedding by open or closed-loop control of the rotation rate.

Passive Endwall Treatments for Enhancing Stability

NASA Technical Reports Server (NTRS)

Hathaway, Michael D.

2007-01-01

These lecture notes were presented at the von Karman Institutes lecture series on Advances in Axial Compressor Aerodynamics, May 2006. They provide a fairly extensive overview of what's been learned from numerous investigations of various passive casing endwall technologies that have been proposed for alleviating the stall limiting physics associated with the compressor endwall flow field. The lecture notes are organized to give an appreciation for the inventiveness and understanding of the earliest compressor technologists and to provide a coherent thread of understanding that has arisen out of the early investigations. As such the lecture notes begin with a historical overview of casing treatments from their infancy through the earliest proposed concepts involving blowing, suction and flow recirculation. A summary of lessons learned from these early investigations is provided at the end of this section. The lecture notes then provide a somewhat more in-depth overview of recent advancements in the development of passive casing treatments from the late 1990's through 2006, including advancements in understanding the flow mechanism of circumferential groove casing treatments, and the development of discrete tip injection and self-recirculating casing treatments. At the conclusion of the lecture notes a final summary of lessons learned throughout the history of the development of passive casing treatments is provided. Finally, a list of future needs is given. It is hoped that these lecture notes will be a useful reference for future research endeavors to improve our understanding of the fluid physics of passive casing treatments and how they act to enhance compressor stability, and that they will perhaps provide a springboard for future research activities in this area of interest

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

Sasaki, Kazuki; Suzuki, Naoya; Saito, Hiroki

Vortex shedding from an obstacle potential moving in a Bose-Einstein condensate is investigated. Long-lived alternately aligned vortex pairs are found to form in the wake, which is similar to the Benard-von Karman vortex street in classical viscous fluids. Various patterns of vortex shedding are systematically studied and the drag force on the obstacle is calculated. It is shown that the phenomenon can be observed in a trapped system.

Continuous particle separation using pressure-driven flow-induced miniaturizing free-flow electrophoresis (PDF-induced μ-FFE).

PubMed

Jeon, Hyungkook; Kim, Youngkyu; Lim, Geunbae

2016-01-28

In this paper, we introduce pressure-driven flow-induced miniaturizing free-flow electrophoresis (PDF-induced μ-FFE), a novel continuous separation method. In our separation system, the external flow and electric field are applied to particles, such that particle movement is affected by pressure-driven flow, electroosmosis, and electrophoresis. We then analyzed the hydrodynamic drag force and electrophoretic force applied to the particles in opposite directions. Based on this analysis, micro- and nano-sized particles were separated according to their electrophoretic mobilities with high separation efficiency. Because the separation can be achieved in a simple T-shaped microchannel, without the use of internal electrodes, it offers the advantages of low-cost, simple device fabrication and bubble-free operation, compared with conventional μ-FFE methods. Therefore, we expect the proposed separation method to have a wide range of filtering/separation applications in biochemical analysis.

Continuous particle separation using pressure-driven flow-induced miniaturizing free-flow electrophoresis (PDF-induced μ-FFE)

PubMed Central

Jeon, Hyungkook; Kim, Youngkyu; Lim, Geunbae

2016-01-01

In this paper, we introduce pressure-driven flow-induced miniaturizing free-flow electrophoresis (PDF-induced μ-FFE), a novel continuous separation method. In our separation system, the external flow and electric field are applied to particles, such that particle movement is affected by pressure-driven flow, electroosmosis, and electrophoresis. We then analyzed the hydrodynamic drag force and electrophoretic force applied to the particles in opposite directions. Based on this analysis, micro- and nano-sized particles were separated according to their electrophoretic mobilities with high separation efficiency. Because the separation can be achieved in a simple T-shaped microchannel, without the use of internal electrodes, it offers the advantages of low-cost, simple device fabrication and bubble-free operation, compared with conventional μ-FFE methods. Therefore, we expect the proposed separation method to have a wide range of filtering/separation applications in biochemical analysis. PMID:26819221

Preliminary research on flow rate and free surface of the accelerator driven subcritical system gravity-driven dense granular-flow target

PubMed Central

Li, Xiaodong; Wan, Jiangfeng; Zhang, Sheng; Lin, Ping; Zhang, Yanshi; Yang, Guanghui; Wang, Mengke; Duan, Wenshan; Sun, Jian’an

2017-01-01

A spallation target is one of the three core parts of the accelerator driven subcritical system (ADS), which has already been investigated for decades. Recently, a gravity-driven Dense Granular-flow Target (DGT) is proposed, which consists of a cylindrical hopper and an internal coaxial cylindrical beam pipe. The research on the flow rate and free surface are important for the design of the target whether in Heavy Liquid Metal (HLM) targets or the DGT. In this paper, the relations of flow rate and the geometry of the DGT are investigated. Simulations based on the discrete element method (DEM) implementing on Graphics Processing Units (GPUs) and experiments are both performed. It is found that the existence of an internal pipe doesn’t influence the flow rate when the distance from the bottom of the pipe to orifice is large enough even in a larger system. Meanwhile, snapshots of the free surface formed just below the beam pipe are given. It is observed that the free surface is stable over time. The entire research is meaningful for the design of DGT. PMID:29095910

Preliminary research on flow rate and free surface of the accelerator driven subcritical system gravity-driven dense granular-flow target.

PubMed

Li, Xiaodong; Wan, Jiangfeng; Zhang, Sheng; Lin, Ping; Zhang, Yanshi; Yang, Guanghui; Wang, Mengke; Duan, Wenshan; Sun, Jian'an; Yang, Lei

2017-01-01

A spallation target is one of the three core parts of the accelerator driven subcritical system (ADS), which has already been investigated for decades. Recently, a gravity-driven Dense Granular-flow Target (DGT) is proposed, which consists of a cylindrical hopper and an internal coaxial cylindrical beam pipe. The research on the flow rate and free surface are important for the design of the target whether in Heavy Liquid Metal (HLM) targets or the DGT. In this paper, the relations of flow rate and the geometry of the DGT are investigated. Simulations based on the discrete element method (DEM) implementing on Graphics Processing Units (GPUs) and experiments are both performed. It is found that the existence of an internal pipe doesn't influence the flow rate when the distance from the bottom of the pipe to orifice is large enough even in a larger system. Meanwhile, snapshots of the free surface formed just below the beam pipe are given. It is observed that the free surface is stable over time. The entire research is meaningful for the design of DGT.

Analytics of crystal growth in space

NASA Technical Reports Server (NTRS)

Chang, C. E.; Lefever, R. A.; Wilcox, W. R.

1975-01-01

The variation of radial impurity distribution induced by surface tension driven flow increases as the zone length decreases in silicon crystals grown by floating zone melting. In combined buoyancy driven and surface tension driven convection at the gravity of earth, the buoyancy contribution becomes relatively smaller as the zone diameter decreases and eventually convection is dominated by the surface tension driven flow (in the case of silicon, for zones of less than about 0.8 cm in diameter). Preliminary calculations for sapphire suggest the presence of an oscillatory surface tension driven convection as a result of an unstable melt surface temperature that results when the zone is heated by a radiation heater.

Excitation of vertical coronal loop oscillations by impulsively driven flows

NASA Astrophysics Data System (ADS)

Kohutova, P.; Verwichte, E.

2018-05-01

Context. Flows of plasma along a coronal loop caused by the pressure difference between loop footpoints are common in the solar corona. Aims: We aim to investigate the possibility of excitation of loop oscillations by an impulsively driven flow triggered by an enhanced pressure in one of the loop footpoints. Methods: We carry out 2.5D magnetohydrodynamic (MHD) simulations of a coronal loop with an impulsively driven flow and investigate the properties and evolution of the resulting oscillatory motion of the loop. Results: The action of the centrifugal force associated with plasma moving at high speeds along the curved axis of the loop is found to excite the fundamental harmonic of a vertically polarised kink mode. We analyse the dependence of the resulting oscillations on the speed and kinetic energy of the flow. Conclusions: We find that flows with realistic speeds of less than 100 km s-1 are sufficient to excite oscillations with observable amplitudes. We therefore propose plasma flows as a possible excitation mechanism for observed transverse loop oscillations.

On solving the compressible Navier-Stokes equations for unsteady flows at very low Mach numbers

NASA Technical Reports Server (NTRS)

Pletcher, R. H.; Chen, K.-H.

1993-01-01

The properties of a preconditioned, coupled, strongly implicit finite difference scheme for solving the compressible Navier-Stokes equations in primitive variables are investigated for two unsteady flows at low speeds, namely the impulsively started driven cavity and the startup of pipe flow. For the shear-driven cavity flow, the computational effort was observed to be nearly independent of Mach number, especially at the low end of the range considered. This Mach number independence was also observed for steady pipe flow calculations; however, rather different conclusions were drawn for the unsteady calculations. In the pressure-driven pipe startup problem, the compressibility of the fluid began to significantly influence the physics of the flow development at quite low Mach numbers. The present scheme was observed to produce the expected characteristics of completely incompressible flow when the Mach number was set at very low values. Good agreement with incompressible results available in the literature was observed.

Laboratory modelling of resonant wave-current interaction in the vicinity wind farm masts

NASA Astrophysics Data System (ADS)

Gunnoo, Hans; Abcha, Nizar; Garcia-Hermosa, Maria-Isabel; Ezersky, Alexander

2015-04-01

In the nearest future, by 2020, about 4% of electricity in Europe will be supplied by sea stations operating from renewable sources: ocean thermal energy, wave and tidal energy, wind farms. By now the wind stations located in the coastal zone, provide the most part of electricity in different European countries. Meanwhile, effects of wind farms on the environment are not sufficiently studied. We report results of laboratory simulations aimed at investigation of hydrodynamic fields arising in the vicinity of wind farm masts under the action of currents and surface waves. The main attention is paid to modeling the resonance effects when the amplitude of velocity pulsations in the vicinity of the masts under the joint action of currents and harmonic waves demonstrate significant growth. This resonance can lead to an increase in Reynolds stress on the bottom, intensification of sediment transport and sound generation. The experiments are performed in the 17 meters hydrodynamical channel of laboratory Morphodynamique Continentale et Côtière UMR CNRS 6143. Mast are modeled by vertical cylinder placed in a steady flow. Behind the cylinder turbulent Karman vortex street occurs. Results are obtained in interval of Reynolds numbers Re=103 - 104(Re=Ud/v, where U is the velocity of the flow, d is diameter of the cylinder, ν is cinematic viscosity). Harmonic surface waves of small amplitude propagating upstream are excited by computer controlled wave maker. In the absence of surface waves, turbulent Karman street with averaged frequency f is observed. It is revealed experimentally that harmonic surface waves with a frequencies closed to 2f can synchronize vortex shedding and increase the amplitude of velocity fluctuations in the wake of the cylinder. Map of regimes is found on the parameter plane amplitude of the surface wave - wave frequency. In order to distinguish the synchronization regimes, we defined phase of oscillations using the Hilbert transform technique. We investigate effect of hydrodynamic turbulence on synchronization of hydrodynamic wake by surface waves. To change the level of turbulence we used honeycombs. Measuring the velocity upstream the cylinder, we found that under our experimental conditions honeycombs can reduce the level of hydrodynamic turbulence in two times. It is found that intensity of turbulence determines the amplitude threshold of synchronization in the wake behind cylinder. The physical mechanisms of synchronization, its impact to the Reynolds stress and the possibility of such a resonance in the vicinity of masts located in the coastal zone are discussed. This work was supported by the OFELIA (Offshore Foundations Environmental Impact Assessments) project in the frame of the European cross-border cooperation programme INTERREG IV A France (Channel) - England, co-funded by the ERDF.

Multiblock High Order Large Eddy Simulation of Powered Fontan Hemodynamics: Towards Computational Surgery

PubMed Central

Delorme, Yann T.; Rodefeld, Mark D.; Frankel, Steven H.

2016-01-01

Children born with only one functional ventricle must typically undergo a series of three surgeries to obtain the so-called Fontan circulation in which the blood coming from the body passively flows from the Vena Cavae (VCs) to the Pulmonary Arteries (PAs) through the Total Cavopulmonary Connection (TCPC). The circulation is inherently inefficient due to the lack of a subpulmonary ventricle. Survivors face the risk of circulatory sequelae and eventual failure for the duration of their lives. Current efforts are focused on improving the outcomes of Fontan palliation, either passively by optimizing the TCPC, or actively by using mechanical support. We are working on a chronic implant that would be placed at the junction of the TCPC, and would provide the necessary pressure augmentation to re-establish a circulation that recapitulates a normal two-ventricle circulation. This implant is based on the Von Karman viscous pump and consists of a vaned impeller that rotates inside the TCPC. To evaluate the performance of such a device, and to study the flow features induced by the presence of the pump, Computational Fluid Dynamics (CFD) is used. CFD has become an important tool to understand hemodynamics owing to the possibility of simulating quickly a large number of designs and flow conditions without any harm for patients. The transitional and unsteady nature of the flow can make accurate simulations challenging. We developed and in-house high order Large Eddy Simulation (LES) solver coupled to a recent Immersed Boundary Method (IBM) to handle complex geometries. Multiblock capability is added to the solver to allow for efficient simulations of complex patient specific geometries. Blood simulations are performed in a complex patient specific TCPC geometry. In this study, simulations without mechanical assist are performed, as well as after virtual implantation of the temporary and chronic implants being developed. Instantaneous flow structures, hepatic factor distribution, and statistical data are presented for all three cases. PMID:28649147

Numerical simulations of current generation and dynamo excitation in a mechanically forced turbulent flow.

PubMed

Bayliss, R A; Forest, C B; Nornberg, M D; Spence, E J; Terry, P W

2007-02-01

The role of turbulence in current generation and self-excitation of magnetic fields has been studied in the geometry of a mechanically driven, spherical dynamo experiment, using a three-dimensional numerical computation. A simple impeller model drives a flow that can generate a growing magnetic field, depending on the magnetic Reynolds number Rm=micro0sigmaVa and the fluid Reynolds number Re=Vanu of the flow. For Re<420, the flow is laminar and the dynamo transition is governed by a threshold of Rmcrit=100, above which a growing magnetic eigenmode is observed that is primarily a dipole field transverse to the axis of symmetry of the flow. In saturation, the Lorentz force slows the flow such that the magnetic eigenmode becomes marginally stable. For Re>420 and Rm approximately 100 the flow becomes turbulent and the dynamo eigenmode is suppressed. The mechanism of suppression is a combination of a time varying large-scale field and the presence of fluctuation driven currents (such as those predicted by the mean-field theory), which effectively enhance the magnetic diffusivity. For higher Rm, a dynamo reappears; however, the structure of the magnetic field is often different from the laminar dynamo. It is dominated by a dipolar magnetic field aligned with the axis of symmetry of the mean-flow, which is apparently generated by fluctuation-driven currents. The magnitude and structure of the fluctuation-driven currents have been studied by applying a weak, axisymmetric seed magnetic field to laminar and turbulent flows. An Ohm's law analysis of the axisymmetric currents allows the fluctuation-driven currents to be identified. The magnetic fields generated by the fluctuations are significant: a dipole moment aligned with the symmetry axis of the mean-flow is generated similar to those observed in the experiment, and both toroidal and poloidal flux expulsion are observed.

Thermal Performance of Surface Wick Structures.

NASA Astrophysics Data System (ADS)

Chen, Yongkang; Tavan, Noel; Baker, John; Melvin, Lawrence; Weislogel, Mark

2010-03-01

Microscale surface wick structures that exploit capillary driven flow in interior corners have been designed. In this study we examine the interplay between capillary flow and evaporative heat transfer that effectively reduces the surface temperature. The tests are performed by raising the surface temperature to various levels before the flow is introduced to the surfaces. Certainly heat transfer weakens the capillary driven flow. It is observed, however, the surface temperature can be reduced significantly. The effects of geometric parameters and interconnectivity are to be characterized to identify optimal configurations.

Mantle flow tectonics - The influence of a ductile lower crust and implications for the formation of topographic uplands on Venus

NASA Technical Reports Server (NTRS)

Bindschadler, Duane L.; Parmentier, E. Marc

1990-01-01

The crust and mantle of Venus can be represented by a model of a layered structure stratified in both density and viscosity. This structure consists of a brittle-elastic upper crustal layer; a ductile weaker crustal layer; a strong upper mantle layer, about 10 percent denser than the crust; and a weaker substrate, representing the portion of the mantle in which convective flow occurs which is a primary source of large-scale topographic and tectonic features. This paper examines the interactions between these four layers and the mantle flow driven by thermal or compositional variations. Solutions are found for a flow driven by a buoyancy-force distribution within the mantle and by relief at the surface and crust-mantle boundary. It is shown that changes in crustal thickness are driven by vertical normal stresses due to mantle flow and by shear coupling of horizontal mantle flow into the crust.

Large eddy simulations of time-dependent and buoyancy-driven channel flows

NASA Technical Reports Server (NTRS)

Cabot, William H.

1993-01-01

The primary goal of this work has been to assess the performance of the dynamic SGS model in the large eddy simulation (LES) of channel flows in a variety of situations, viz., in temporal development of channel flow turned by a transverse pressure gradient and especially in buoyancy-driven turbulent flows such as Rayleigh-Benard and internally heated channel convection. For buoyancy-driven flows, there are additional buoyant terms that are possible in the base models, and one objective has been to determine if the dynamic SGS model results are sensitive to such terms. The ultimate goal is to determine the minimal base model needed in the dynamic SGS model to provide accurate results in flows with more complicated physical features. In addition, a program of direct numerical simulation (DNS) of fully compressible channel convection has been undertaken to determine stratification and compressibility effects. These simulations are intended to provide a comparative base for performing the LES of compressible (or highly stratified, pseudo-compressible) convection at high Reynolds number in the future.

Nonlinear optimal control policies for buoyancy-driven flows in the built environment

NASA Astrophysics Data System (ADS)

Nabi, Saleh; Grover, Piyush; Caulfield, Colm

2017-11-01

We consider optimal control of turbulent buoyancy-driven flows in the built environment, focusing on a model test case of displacement ventilation with a time-varying heat source. The flow is modeled using the unsteady Reynolds-averaged equations (URANS). To understand the stratification dynamics better, we derive a low-order partial-mixing ODE model extending the buoyancy-driven emptying filling box problem to the case of where both the heat source and the (controlled) inlet flow are time-varying. In the limit of a single step-change in the heat source strength, our model is consistent with that of Bower et al.. Our model considers the dynamics of both `filling' and `intruding' added layers due to a time-varying source and inlet flow. A nonlinear direct-adjoint-looping optimal control formulation yields time-varying values of temperature and velocity of the inlet flow that lead to `optimal' time-averaged temperature relative to appropriate objective functionals in a region of interest.

Numerical study of the transient flow in the driven tube and the nozzle section of a shock tunnel

NASA Technical Reports Server (NTRS)

Tokarcik-Polsky, Susan; Cambier, Jean-Luc

1993-01-01

The initial flow in a shock tunnel was examined numerically using computational fluid dynamics (CFD). A finite-volume total variation diminishing (TVD) scheme was used to calculate the transient flow in a shock tunnel. Both viscous and inviscid, chemically nonreacting flows were studied. The study consisted of two parts, the first dealt with the transient flow in the driven-tube/nozzle interface region (inviscid calculations). The effects of varying the geometry in this region was examined. The second part of the study examined the transient flow in the nozzle (viscous calculations). The results were compared to experimental data.

Two-fluid flowing equilibria of spherical torus sustained by coaxial helicity injection

NASA Astrophysics Data System (ADS)

Kanki, Takashi; Steinhauer, Loren; Nagata, Masayoshi

2007-11-01

Two-dimensional equilibria in helicity-driven systems using two-fluid model were previously computed, showing the existence of an ultra-low-q spherical torus (ST) configuration with diamagnetism and higher beta. However, this computation assumed purely toroidal ion flow and uniform density. The purpose of the present study is to apply the two-fluid model to the two-dimensional equilibria of helicity-driven ST with non-uniform density and both toroidal and poloidal flows for each species by means of the nearby-fluids procedure, and to explore their properties. We focus our attention on the equilibria relevant to the HIST device, which are characterized by either driven or decaying λ profiles. The equilibrium for the driven λ profile has a diamagnetic toroidal field, high-β (βt = 32%), and centrally broad density. By contrast, the decaying equilibrium has a paramagnetic toroidal field, low-β (βt = 10%), and centrally peaked density with a steep gradient in the outer edge region. In the driven case, the toroidal ion and electron flows are in the same direction, and two-fluid effects are less important since the ExB drift is dominant. In the decaying case, the toroidal ion and electron flows are opposite in the outer edge region, and two-fluid effects are significant locally in the edge due to the ion diamagnetic drift.

Lagrangian chaos in three- dimensional steady buoyancy-driven flows

NASA Astrophysics Data System (ADS)

Contreras, Sebastian; Speetjens, Michel; Clercx, Herman

2016-11-01

Natural convection plays a key role in fluid dynamics owing to its ubiquitous presence in nature and industry. Buoyancy-driven flows are prototypical systems in the study of thermal instabilities and pattern formation. The differentially heated cavity problem has been widely studied for the investigation of buoyancy-induced oscillatory flow. However, far less attention has been devoted to the three-dimensional Lagrangian transport properties in such flows. This study seeks to address this by investigating Lagrangian transport in the steady flow inside a cubic cavity differentially-heated from the side. The theoretical and numerical analysis expands on previously reported similarities between the current flow and lid-driven flows. The Lagrangian dynamics are controlled by the Péclet number (Pe) and the Prandtl number (Pr). Pe controls the behaviour qualitatively in that growing Pe progressively perturbs the integable state (Pe =0), thus paving the way to chaotic dynamics. Pr plays an entirely quantitative role in that Pr<1 and Pr>1 amplifies and diminishes, respectively, the perturbative effect of non-zero Pe. S.C. acknowledges financial support from Consejo Nacional de Ciencia y Tecnología (CONACYT).

Studies of Radiation-Driven and Buoyancy-Driven Fluid Flows and Transport

NASA Technical Reports Server (NTRS)

Ronney, Paul D.; Fortmeyer, Justin M.

1994-01-01

It is well known that radiative heat transport influences many types of buoyant flows due to its effect on the temperature and thus density field in the fluid medium. It is of interest to study gaseous flows driven solely by radiation in the absence of buoyancy, particularly because of its application to astrophysical flows that are well known from astronomical observations and numerical simulation. However, no laboratory-scale experiments of this phenomenon have ever been conducted. To study the possibility of obtaining such flows in the laboratory, an apparatus was built to produce large temperature differences (Delta T) up to 300 K in a gas confined between flat parallel plates. SF6 was used as the radiatively-active gas because its Planck absorption length is much shorter than that of any other common non-reactive gas. The NASA-Lewis 2.2 second drop tower was used to obtain reduced gravity in order to suppress buoyancy effects. To image the resulting flows, a laser shearing interferometer was employed. Initial results indicate the presence of flow that does not appear to be attributable to the residual flow resulting from buoyancy influences before the drop. For Delta T greater than 70 K, slight deformations in the interferometer fringes seen at lower Delta T became large unsteady swirls. Such behavior did not occur for radiatively-inactive gases, suggesting that a flow driven solely by radiation was obtained in SF6 and to a lesser extent in CO2 This was more pronounced at higher pressures and plate spacings, consistent with our scaling predictions.

Studies of Radiation-Driven and Buoyancy-Driven Fluid Flows and Transport

NASA Technical Reports Server (NTRS)

Ronney, Paul D.; Fortmeyer, Justin M.

1996-01-01

It is well known that radiative heat transport influences many types of buoyant flows due to its effect on the temperature and thus density field in the fluid medium. It is of interest to study gaseous flows driven solely by radiation in the absence of buoyancy, particularly because of its application to astrophysical flows that are well known from astronomical observations and numerical simulation. However, no laboratory-scale experiments of this phenomenon have ever been conducted. To study the possibility of obtaining such flows in the laboratory, an apparatus was built to produce large temperature differences (Delta (T)) up to 300 K in a gas confined between flat parallel plates. SF6 was used as the radiatively-active gas because its Planck absorption length is much shorter than that of any other common non-reactive gas. The NASA-Lewis 2.2 second drop tower was used to obtain reduced gravity in order to suppress buoyancy effects. To image the resulting flows, a laser shearing interferometer was employed. Initial results indicate the presence of flow that does not appear to be attributable to the residual flow resulting from buoyancy influences before the drop. For Delta(T) greater than 70 K, slight deformations in the interferometer fringes seen at lower Delta(T) became large unsteady swirls. Such behavior did not occur for radiatively-inactive gases, suggesting that a flow driven solely by radiation was obtained in SF6 and to a lesser extent in CO2. This was more pronounced at higher pressures and plate spacings, consistent with our scaling predictions.

Quantification and visualization of injury and regeneration to the ciliated epithelium using quantitative flow imaging and speckle variance optical coherence tomography (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gamm, Ute A.; Huang, Brendan K.; Mis, Emily K.; Khokha, Mustafa K.; Choma, Michael A.

2017-04-01

Mucociliary flow is an important defense mechanism in the lung to remove inhaled pathogens and pollutants. A disruption of ciliary flow can lead to respiratory infections. Even though patients in the intensive care unit (ICU) either have or are very susceptible to respiratory infections, mucociliary flow is not well understood in the ICU setting. We recently demonstrated that hyperoxia, a consequence of administering supplemental oxygen to a patient in respiratory failure, can lead to a significant reduction of cilia-driven fluid flow in mouse trachea. There are other factors that are relevant to ICU medicine that can damage the ciliated tracheal epithelium, including inhalation injury and endotracheal tube placement. In this study we use two animal models, Xenopus embryo and ex vivo mouse trachea, to analyze flow defects in the injured ciliated epithelium. Injury is generated either mechanically with a scalpel or chemically by calcium chloride (CaCl2) shock, which efficiently but reversibly deciliates the embryo skin. In this study we used optical coherence tomography (OCT) and particle tracking velocimetry (PTV) to quantify cilia driven fluid flow over the surface of the Xenopus embryo. We additionally visualized damage to the ciliated epithelium by capturing 3D speckle variance images that highlight beating cilia. Mechanical injury disrupted cilia-driven fluid flow over the injured site, which led to a reduction in cilia-driven fluid flow over the whole surface of the embryo (n=7). The calcium chloride shock protocol proved to be highly effective in deciliating embryos (n=6). 3D speckle variance images visualized a loss of cilia and cilia-driven flow was halted immediately after application. We also applied CaCl2-shock to cultured ex vivo mouse trachea (n=8) and found, similarly to effects in Xenopus embryo, an extensive loss of cilia with resulting cessation of flow. We investigated the regeneration of the ciliated epithelium after an 8 day incubation period, and found that cilia had regrown and flow was completely restored. In conclusion, OCT is a valuable tool to visualize injury of the ciliated epithelium and to quantify reduction of generated flow. This method allows for systematic investigation of focal and diffuse injury of the ciliated epithelium and the assessment of mechanisms to compensate for loss of flow.

Predicting Explosion-Generated SN and LG Coda Using Syntheic Seismograms

DTIC Science & Technology

2008-09-01

velocities in the upper crust are based on borehole data, geologic and gravity data, refraction studies and seismic experiments (McLaughlin et al. 1983...realizations of random media. We have estimated the heterogeneity parameters for the NTS using available seismic and geologic data. Lateral correlation...variance and coherence measures between seismic traces are estimated from clusters of nuclear explosions and well- log data. The horizontal von Karman

Flapping Wing Flight Dynamic Modeling

DTIC Science & Technology

2011-08-22

cases. Pesavento and Wang [24] solved the two dimensional Navier-Stokes equations in relation to a piece of free falling paper at Reynolds number near...von Karman, T. and Burgers, J. M., Gerneral Aerodynamic Theory - Perfect Fluids , Vol. II, Julius Springer, Berlin, 1935. [24] Pesavento , U. and Wang...2004, pp. 14. [25] Andersen, A., Pesavento , U., and Wang, Z. J., Unsteady aerodynamics of uttering and tumbling plates, Journal of Fluid Mechanics

Numerical simulation of the nonlinear response of composite plates under combined thermal and acoustic loading

NASA Technical Reports Server (NTRS)

Mei, Chuh; Moorthy, Jayashree

1995-01-01

A time-domain study of the random response of a laminated plate subjected to combined acoustic and thermal loads is carried out. The features of this problem also include given uniform static inplane forces. The formulation takes into consideration a possible initial imperfection in the flatness of the plate. High decibel sound pressure levels along with high thermal gradients across thickness drive the plate response into nonlinear regimes. This calls for the analysis to use von Karman large deflection strain-displacement relationships. A finite element model that combines the von Karman strains with the first-order shear deformation plate theory is developed. The development of the analytical model can accommodate an anisotropic composite laminate built up of uniformly thick layers of orthotropic, linearly elastic laminae. The global system of finite element equations is then reduced to a modal system of equations. Numerical simulation using a single-step algorithm in the time-domain is then carried out to solve for the modal coordinates. Nonlinear algebraic equations within each time-step are solved by the Newton-Raphson method. The random gaussian filtered white noise load is generated using Monte Carlo simulation. The acoustic pressure distribution over the plate is capable of accounting for a grazing incidence wavefront. Numerical results are presented to study a variety of cases.

An Experimental Study of Continuous Plasma Flows Driven by a Confined Arc in a Transverse Magnetic Field

NASA Technical Reports Server (NTRS)

Barger, R. L.; Brooks, J. D.; Beasley, W. D.

1961-01-01

A crossed-field, continuous-flow plasma accelerator has been built and operated. The highest measured velocity of the flow, which was driven by the interaction of the electric and magnetic fields, was about 500 meters per second. Some of the problems discussed are ion slip, stability and uniformity of the discharge, effect of the magnetic field on electron emission, use of preionization, and electrode contamination.

Model Scramjet Inlet Unstart Induced by Mass Addition and Heat Release

NASA Astrophysics Data System (ADS)

Im, Seong-Kyun; Baccarella, Damiano; McGann, Brendan; Liu, Qili; Wermer, Lydiy; Do, Hyungrok

2015-11-01

The inlet unstart phenomena in a model scramjet are investigated at an arc-heated hypersonic wind tunnel. The unstart induced by nitrogen or ethylene jets at low or high enthalpy Mach 4.5 freestream flow conditions are compared. The jet injection pressurizes the downstream flow by mass addition and flow blockage. In case of the ethylene jet injection, heat release from combustion increases the backpressure further. Time-resolved schlieren imaging is performed at the jet and the lip of the model inlet to visualize the flow features during unstart. High frequency pressure measurements are used to provide information on pressure fluctuation at the scramjet wall. In both of the mass and heat release driven unstart cases, it is observed that there are similar flow transient and quasi-steady behaviors of unstart shockwave system during the unstart processes. Combustion driven unstart induces severe oscillatory flow motions of the jet and the unstart shock at the lip of the scramjet inlet after the completion of the unstart process, while the unstarted flow induced by solely mass addition remains relatively steady. The discrepancies between the processes of mass and heat release driven unstart are explained by flow choking mechanism.

BRIEF COMMUNICATION: On the drift kinetic equation driven by plasma flows

NASA Astrophysics Data System (ADS)

Shaing, K. C.

2010-07-01

A drift kinetic equation that is driven by plasma flows has previously been derived by Shaing and Spong 1990 (Phys. Fluids B 2 1190). The terms that are driven by particle speed that is parallel to the magnetic field B have been neglected. Here, such terms are discussed to examine their importance to the equation and to show that these terms do not contribute to the calculations of plasma viscosity in large aspect ratio toroidal plasmas, e.g. tokamaks and stellarators.

Hydrodynamic Capture of Particles by Micro-swimmers under Hele-Shaw Flows

NASA Astrophysics Data System (ADS)

Mishler, Grant; Tsang, Alan Cheng Hou; Pak, On Shun

2017-11-01

We explore a hydrodynamic capture mechanism of a driven particle by a micro-swimmer in confined microfluidic environments with an idealized model. The capture is mediated by the hydrodynamic interactions between the micro-swimmer, the driven particle, and the background flow. This capture mechanism relies on the existence of attractive stable equilibrium configurations between the driven particle and the micro-swimmer, which occurs when the background flow is larger than a certain critical threshold. Dynamics and stability of capture and non-capture events will be discussed. This study may have potential applications in the study of capture and delivery of therapeutic payloads by micro-swimmers as well as particle self-assembly under confinements.

Flow Rate Driven by Peristaltic Movement in Plasmodial Tube of Physarum Polycephalum

NASA Astrophysics Data System (ADS)

Yamada, Hiroyasu; Nakagaki, Toshiyuki

2008-07-01

We report a theoretical analysis of protoplasmic streaming driven by peristaltic movement in an elastic tube of an amoeba-like organism. The Plasmodium of Physarum polycephalum, a true slime mold, is a large amoeboid organism that adopts a sheet-like form with a tubular network. The network extends throughout the Plasmodium and enables the transport and circulation of chemical signals and nutrients. This tubular flow is driven by periodically propagating waves of active contraction of the tube cortex, a process known as peristaltic movement. We derive the relationship between the phase velocity of the contraction wave and the flow rate, and we discuss the physiological implications of this relationship.

Reduced order modeling of fluid/structure interaction.

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

Barone, Matthew Franklin; Kalashnikova, Irina; Segalman, Daniel Joseph

2009-11-01

This report describes work performed from October 2007 through September 2009 under the Sandia Laboratory Directed Research and Development project titled 'Reduced Order Modeling of Fluid/Structure Interaction.' This project addresses fundamental aspects of techniques for construction of predictive Reduced Order Models (ROMs). A ROM is defined as a model, derived from a sequence of high-fidelity simulations, that preserves the essential physics and predictive capability of the original simulations but at a much lower computational cost. Techniques are developed for construction of provably stable linear Galerkin projection ROMs for compressible fluid flow, including a method for enforcing boundary conditions that preservesmore » numerical stability. A convergence proof and error estimates are given for this class of ROM, and the method is demonstrated on a series of model problems. A reduced order method, based on the method of quadratic components, for solving the von Karman nonlinear plate equations is developed and tested. This method is applied to the problem of nonlinear limit cycle oscillations encountered when the plate interacts with an adjacent supersonic flow. A stability-preserving method for coupling the linear fluid ROM with the structural dynamics model for the elastic plate is constructed and tested. Methods for constructing efficient ROMs for nonlinear fluid equations are developed and tested on a one-dimensional convection-diffusion-reaction equation. These methods are combined with a symmetrization approach to construct a ROM technique for application to the compressible Navier-Stokes equations.« less

Forced free-shear layer measurements

NASA Technical Reports Server (NTRS)

Leboeuf, Richard L.

1994-01-01

Detailed three-dimensional three-component phase averaged measurements of the spanwise and streamwise vorticity formation and evolution in acoustically forced plane free-shear flows have been obtained. For the first time, phase-averaged measurements of all three velocity components have been obtained in both a mixing layer and a wake on three-dimensional grids, yielding the spanwise and streamwise vorticity distributions without invoking Taylor's hypothesis. Initially, two-frequency forcing was used to phase-lock the roll-up and first pairing of the spanwise vortical structures in a plane mixing layer. The objective of this study was to measure the near-field vortical structure morphology in a mixing layer with 'natural' laminar initial boundary layers. For the second experiment the second and third subharmonics of the fundamental roll-up frequency were added to the previous two-frequency forcing in order to phase-lock the roll-up and first three pairings of the spanwise rollers in the mixing layer. The objective of this study was to determine the details of spanwise scale changes observed in previous time-averaged measurements and flow visualization of unforced mixing layers. For the final experiment, single-frequency forcing was used to phase-lock the Karman vortex street in a plane wake developing from nominally two-dimensional laminar initial boundary layers. The objective of this study was to compare measurements of the three-dimensional structure in a wake developing from 'natural' initial boundary layers to existing models of wake vortical structure.

Quantification and visualization of injury and regeneration in the developing ciliated epithelium using quantitative flow imaging and speckle variance optical coherence tomography (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gamm, Ute A.; Huang, Brendan K.; Mis, Emily K.; Khokha, Mustafa K.; Choma, Michael A.

2017-02-01

Premature infants are at a high risk for respiratory diseases owing to an underdeveloped respiratory system that is very susceptible to infection and inflammation. One aspect of respiratory health is the state of the ciliated respiratory epithelium which lines the trachea and bronchi. The ciliated epithelium is responsible for trapping and removing pathogens and pollutants from the lungs and an impairment of ciliary functionality can lead to recurring respiratory infections and subsequent lung damage. Mechanisms of cilia-driven fluid flow itself but also factors influenced by development like ciliary density and flow generation are incompletely understood. Furthermore, medical interventions like intubation and accidental aspiration can lead to focal or diffuse loss of cilia and disruption of flow. In this study we use two animal models, Xenopus embryo and ex vivo mouse trachea, to analyze flow defects in the injured ciliated epithelium. Injury is generated either mechanically with a scalpel or chemically by calcium chloride (CaCl2) shock, which efficiently but reversibly deciliates the embryo skin. In this study we used optical coherence tomography (OCT) and particle tracking velocimetry (PTV) to quantify cilia driven fluid flow over the surface of the Xenopus embryo. We additionally visualized damage to the ciliated epithelium by capturing 3D speckle variance images that highlight beating cilia. Mechanical injury disrupted cilia-driven fluid flow over the injured site, which led to a reduction in cilia-driven fluid flow over the whole surface of the embryo (n=7). The calcium chloride shock protocol proved to be highly effective in deciliating embryos (n=6). 3D speckle variance images visualized a loss of cilia and cilia-driven flow was halted immediately after application. We also applied CaCl2-shock to cultured ex vivo mouse trachea (n=8) and found, similarly to effects in Xenopus embryo, an extensive loss of cilia with resulting cessation of flow. We investigated the regeneration of the ciliated epithelium after an 8 day incubation period, and found that cilia had regrown and flow was completely restored. In conclusion, OCT is a valuable tool to visualize injury of the ciliated epithelium and to quantify reduction of generated flow. This method allows for systematic investigation of focal and diffuse injury of the ciliated epithelium and the assessment of mechanisms to compensate for loss of flow.

Retrospective cost adaptive Reynolds-averaged Navier-Stokes k-ω model for data-driven unsteady turbulent simulations

NASA Astrophysics Data System (ADS)

Li, Zhiyong; Hoagg, Jesse B.; Martin, Alexandre; Bailey, Sean C. C.

2018-03-01

This paper presents a data-driven computational model for simulating unsteady turbulent flows, where sparse measurement data is available. The model uses the retrospective cost adaptation (RCA) algorithm to automatically adjust the closure coefficients of the Reynolds-averaged Navier-Stokes (RANS) k- ω turbulence equations to improve agreement between the simulated flow and the measurements. The RCA-RANS k- ω model is verified for steady flow using a pipe-flow test case and for unsteady flow using a surface-mounted-cube test case. Measurements used for adaptation of the verification cases are obtained from baseline simulations with known closure coefficients. These verification test cases demonstrate that the RCA-RANS k- ω model can successfully adapt the closure coefficients to improve agreement between the simulated flow field and a set of sparse flow-field measurements. Furthermore, the RCA-RANS k- ω model improves agreement between the simulated flow and the baseline flow at locations at which measurements do not exist. The RCA-RANS k- ω model is also validated with experimental data from 2 test cases: steady pipe flow, and unsteady flow past a square cylinder. In both test cases, the adaptation improves agreement with experimental data in comparison to the results from a non-adaptive RANS k- ω model that uses the standard values of the k- ω closure coefficients. For the steady pipe flow, adaptation is driven by mean stream-wise velocity measurements at 24 locations along the pipe radius. The RCA-RANS k- ω model reduces the average velocity error at these locations by over 35%. For the unsteady flow over a square cylinder, adaptation is driven by time-varying surface pressure measurements at 2 locations on the square cylinder. The RCA-RANS k- ω model reduces the average surface-pressure error at these locations by 88.8%.

Neuroimaging and Neuroenergetics: Brain Activations as Information-Driven Reorganization of Energy Flows

ERIC Educational Resources Information Center

Strelnikov, Kuzma

2010-01-01

There is increasing focus on the neurophysiological underpinnings of brain activations, giving birth to an emerging branch of neuroscience--neuroenergetics. However, no common definition of "brain activation" exists thus far. In this article, we define brain activation as the information-driven reorganization of energy flows in a population of…

Flow-driven rotor simulation of vertical axis tidal turbines: A comparison of helical and straight blades

NASA Astrophysics Data System (ADS)

Le, Tuyen Quang; Lee, Kwang-Soo; Park, Jin-Soon; Ko, Jin Hwan

2014-06-01

In this study, flow-driven rotor simulations with a given load are conducted to analyze the operational characteristics of a vertical-axis Darrieus turbine, specifically its self-starting capability and fluctuations in its torque as well as the RPM. These characteristics are typically observed in experiments, though they cannot be acquired in simulations with a given tip speed ratio (TSR). First, it is shown that a flow-driven rotor simulation with a two-dimensional (2D) turbine model obtains power coefficients with curves similar to those obtained in a simulation with a given TSR. 3D flowdriven rotor simulations with an optimal geometry then show that a helical-bladed turbine has the following prominent advantages over a straight-bladed turbine of the same size: an improvement of its self-starting capabilities and reduced fluctuations in its torque and RPM curves as well as an increase in its power coefficient from 33% to 42%. Therefore, it is clear that a flow-driven rotor simulation provides more information for the design of a Darrieus turbine than a simulation with a given TSR before experiments.

Influence of fracture network physical properties on stability criteria of density-driven flow in a dual-porosity system

NASA Astrophysics Data System (ADS)

Hassanzadeh, H.; Jafari Raad, S. M.

2017-12-01

Linear stability analysis is conducted to study the onset of buoyancy-driven convection involved in solubility trapping of CO2 into deep fractured aquifers. In this study, the effect of fracture network physical properties on the stability criteria in a brine-rich fractured porous layer is investigated using dual porosity concept for both single and variable matrix block size distributions. Linear stability analysis results show that both fracture interporosity flow and fracture storativity factors play an important role in the stability behavior of the system. It is shown that a diffusive boundary layer under the gravity field in a fractured rock with lower fracture storativity and/or higher fracture interporosity flow coefficient is more stable. We present scaling relations that relate the onset of convective instability in fractured aquifers. These findings improve our understanding of buoyancy driven flow in fractured aquifers and are particularly important in estimation of potential storage capacity, risk assessment, and storage sites characterization and screening.Keywords: CO2 sequestration; fractured rock; buoyancy-driven convection; stability analysis

Density-driven vertical transport of saltwater through the freshwater lens on the island of Baltrum (Germany) following the 1962 storm flood

NASA Astrophysics Data System (ADS)

Post, Vincent E. A.; Houben, Georg J.

2017-08-01

Due to the growing vulnerability of low-lying coastal zones to flooding by seawater, there is a current need for studies of the impact of such inundations on fresh groundwater resources. The knowledge from the literature is biased towards tropical atoll environments, and only few studies specifically investigated the effect of density-driven downward flow, even though its importance is widely acknowledged. The present study is based on previously unpublished hydrochemical data collected on the island of Baltrum following a devastating storm in 1962, which uniquely show the impact of seawater inundation on a freshwater lens in a siliciclastic aquifer. The field data show that about 3 kg of Cl per m2 of inundated land area, or 18 cm of seawater, infiltrated, and that elevated salinities persisted at the measurement depths of 4 and 6 m for at least 4 years, and at least for 6 years at greater depths. Numerical models support the assertion that the shape of the measured salinographs, i.e. an initial sharp rise in the salt concentration with time, followed by a continually-slowing decrease, must be attributed to density-driven salt fingering. Models that did not consider density effects fail to simulate the observed patterns. Transient recharge, model dimension and lateral flow modify the details of the simulation results, but in all models density-driven vertical flow dominates the overall system behaviour. The diminishing importance of density-driven flow at greater depths, however, in combination with slow recharge-driven flow rates prolongs flushing times, and enhances the risk of brackish-water up-coning when pumping is resumed too soon.

Stability of a jet in confined pressure-driven biphasic flows at low reynolds numbers.

PubMed

Guillot, Pierre; Colin, Annie; Utada, Andrew S; Ajdari, Armand

2007-09-07

Motivated by its importance for microfluidic applications, we study the stability of jets formed by pressure-driven concentric biphasic flows in cylindrical capillaries. The specificity of this variant of the classical Rayleigh-Plateau instability is the role of the geometry which imposes confinement and Poiseuille flow profiles. We experimentally evidence a transition between situations where the flow takes the form of a jet and regimes where drops are produced. We describe this as the transition from convective to absolute instability, within a simple linear analysis using lubrication theory for flows at low Reynolds number, and reach remarkable agreement with the data.

Observation of the L-H confinement bifurcation triggered by a turbulence-driven shear flow in a tokamak plasma.

PubMed

Yan, Z; McKee, G R; Fonck, R; Gohil, P; Groebner, R J; Osborne, T H

2014-03-28

Comprehensive 2D turbulence and eddy flow velocity measurements on DIII-D demonstrate a rapidly increasing turbulence-driven shear flow that develops ∼100  μs prior to the low-confinement (L mode) to high-confinement (H mode) transition and appears to trigger it. These changes are localized to a narrow layer 1-2 cm inside the magnetic boundary. Increasing heating power increases the Reynolds stress, the energy transfer from turbulence to the poloidal flow, and the edge flow shearing rate that then exceeds the decorrelation rate, suppressing turbulence and triggering the transition.

A flux monitoring method for easy and accurate flow rate measurement in pressure-driven flows.

PubMed

Siria, Alessandro; Biance, Anne-Laure; Ybert, Christophe; Bocquet, Lydéric

2012-03-07

We propose a low-cost and versatile method to measure flow rate in microfluidic channels under pressure-driven flows, thereby providing a simple characterization of the hydrodynamic permeability of the system. The technique is inspired by the current monitoring method usually employed to characterize electro-osmotic flows, and makes use of the measurement of the time-dependent electric resistance inside the channel associated with a moving salt front. We have successfully tested the method in a micrometer-size channel, as well as in a complex microfluidic channel with a varying cross-section, demonstrating its ability in detecting internal shape variations.

Driven waves in a two-fluid plasma

NASA Astrophysics Data System (ADS)

Roberge, W. G.; Ciolek, Glenn E.

2007-12-01

We study the physics of wave propagation in a weakly ionized plasma, as it applies to the formation of multifluid, magnetohydrodynamics (MHD) shock waves. We model the plasma as separate charged and neutral fluids which are coupled by ion-neutral friction. At times much less than the ion-neutral drag time, the fluids are decoupled and so evolve independently. At later times, the evolution is determined by the large inertial mismatch between the charged and neutral particles. The neutral flow continues to evolve independently; the charged flow is driven by and slaved to the neutral flow by friction. We calculate this driven flow analytically by considering the special but realistic case where the charged fluid obeys linearized equations of motion. We carry out an extensive analysis of linear, driven, MHD waves. The physics of driven MHD waves is embodied in certain Green functions which describe wave propagation on short time-scales, ambipolar diffusion on long time-scales and transitional behaviour at intermediate times. By way of illustration, we give an approximate solution for the formation of a multifluid shock during the collision of two identical interstellar clouds. The collision produces forward and reverse J shocks in the neutral fluid and a transient in the charged fluid. The latter rapidly evolves into a pair of magnetic precursors on the J shocks, wherein the ions undergo force-free motion and the magnetic field grows monotonically with time. The flow appears to be self-similar at the time when linear analysis ceases to be valid.

The Dynamics of Small-Scale Turbulence Driven Flows

NASA Astrophysics Data System (ADS)

Beer, M. A.; Hammett, G. W.

1997-11-01

The dynamics of small-scale fluctuation driven flows are of great interest for micro-instability driven turbulence, since nonlinear toroidal simulations have shown that these flows play an important role in the regulation of the turbulence and transport levels. The gyrofluid treatment of these flows was shown to be accurate for times shorter than a bounce time.(Beer, M. A., Ph. D. thesis, Princeton University (1995).) Since the decorrelation times of the turbulence are generally shorter than a bounce time, our original hypothesis was that this description was adequate. Recent work(Hinton, F. L., Rosenbluth, M. N., and Waltz, R. E., International Sherwood Fusion Theory Conference (1997).) pointed out possible problems with this hypothesis, emphasizing the existence of a linearly undamped component of the flow which could build up in time and lower the final turbulence level. While our original gyrofluid model reproduces some aspects of the linear flow, there are differences between the long time gyrofluid and kinetic linear results in some cases. On the other hand, if the long time behavior of these flows is dominated by nonlinear damping (which seems reasonable), then the existing nonlinear gyrofluid simulations may be sufficiently accurate. We test these possibilities by modifying the gyrofluid description of these flows and diagnosing the flow evolution in nonlinear simulations.

Clogging and transport of driven particles in asymmetric funnel arrays

NASA Astrophysics Data System (ADS)

Reichhardt, C. J. O.; Reichhardt, C.

2018-06-01

We numerically examine the flow and clogging of particles driven through asymmetric funnel arrays when the commensurability ratio of the number of particles per plaquette is varied. The particle–particle interactions are modeled with a soft repulsive potential that could represent vortex flow in type-II superconductors or driven charged colloids. The velocity-force curves for driving in the easy flow direction of the funnels exhibit a single depinning threshold; however, for driving in the hard flow direction, we find that there can be both negative mobility where the velocity decreases with increasing driving force as well as a reentrant pinning effect in which the particles flow at low drives but become pinned at intermediate drives. This reentrant pinning is associated with a transition from smooth 1D flow at low drives to a clogged state at higher drives that occurs when the particles cluster in a small number of plaquettes and block the flow. When the drive is further increased, particle rearrangements occur that cause the clog to break apart. We map out the regimes in which the pinned, flowing, and clogged states appear as a function of plaquette filling and drive. The clogged states remain robust at finite temperatures but develop intermittent bursts of flow in which a clog temporarily breaks apart but quickly reforms.

Nonlinear effects in the bounded dust-vortex flow in plasma

NASA Astrophysics Data System (ADS)

Laishram, Modhuchandra; Sharma, Devendra; Chattopdhyay, Prabal K.; Kaw, Predhiman K.

2017-03-01

The vortex structures in a cloud of electrically suspended dust in a streaming plasma constitutes a driven system with a rich nonlinear flow regime. Experimentally recovered toroidal formations of this system have motivated study of its volumetrically driven-dissipative vortex flow dynamics using two-dimensional hydrodynamics in the incompressible Navier-Stokes regime. Nonlinear equilibrium solutions are obtained for this system where a nonuniformly driven two-dimensional dust flow exhibits distinct regions of localized accelerations and strong friction caused by stationary fluids at the confining boundaries resisting the dust flow. In agreement with observations in experiments, it is demonstrated that the nonlinear effects appear in the limit of small viscosity, where the primary vortices form scaling with the most dominant spatial scales of the domain topology and develop separated virtual boundaries along their periphery. This separation is triggered beyond a critical dust viscosity that signifies a structural bifurcation. Emergence of uniform vorticity core and secondary vortices with a newer level of identical dynamics highlights the applicability of the studied dynamics to gigantic vortex flows, such as the Jovian great red spot, to microscopic biophysical intracellular activity.

Onset of nanoscale dissipation in superfluid 4He at zero temperature: Role of vortex shedding and cavitation

NASA Astrophysics Data System (ADS)

Ancilotto, Francesco; Barranco, Manuel; Eloranta, Jussi; Pi, Martí

2017-08-01

Two-dimensional flow past an infinitely long cylinder of nanoscopic radius in superfluid 4He at zero temperature is studied using time-dependent density-functional theory. The calculations reveal two distinct critical phenomena for the onset of dissipation: (i) vortex-antivortex pair shedding from the periphery of the moving cylinder, and (ii) the appearance of cavitation in the wake, which possesses similar geometry to that observed experimentally for fast-moving micrometer-scale particles in superfluid 4He. The formation of cavitation bubbles behind the cylinder is accompanied by a sudden jump in the drag exerted on the moving cylinder by the fluid. Vortex pairs with the same circulation are occasionally emitted in the form of dimers, which constitute the building blocks for the Benard-von Karman vortex street structure observed in classical turbulent fluids and Bose-Einstein condensates. The cavitation-induced dissipation mechanism should be common to all superfluids that are self-bound and have a finite surface tension, which include the recently discovered self-bound droplets in ultracold Bose gases. These systems would provide an ideal testing ground for further exploration of this mechanism experimentally.

Investigation of wall-bounded turbulence over regularly distributed roughness

NASA Astrophysics Data System (ADS)

Placidi, Marco; Ganapathisubramani, Bharathram

2012-11-01

The effects of regularly distributed roughness elements on the structure of a turbulent boundary layer are examined by performing a series of Planar (high resolution l+ ~ 30) and Stereoscopic Particle Image Velocimetry (PIV) experiments in a wind tunnel. An adequate description of how to best characterise a rough wall, especially one where the density of roughness elements is sparse, is yet to be developed. In this study, rough surfaces consisting of regularly and uniformly distributed LEGO® blocks are used. Twelve different patterns are adopted in order to systematically examine the effects of frontal solidity (λf, frontal area of the roughness elements per unit wall-parallel area) and plan solidity (λp, plan area of roughness elements per unit wall-parallel area), on the turbulence structure. The Karman number, Reτ , is approximately 4000 across the different cases. Spanwise 3D vector fields at two different wall-normal locations (top of the canopy and within the log-region) are also compared to examine the spanwise homogeneity of the flow across different surfaces. In the talk, a detailed analysis of mean and rms velocity profiles, Reynolds stresses, and quadrant decomposition for the different patterns will be presented.

Control of Flowing Liquid Films By Electrostatic Fields in Space

NASA Technical Reports Server (NTRS)

Bankoff, S. George; Miksis, Michael J.; Kim, Hyo

1996-01-01

A novel type of lightweight space radiator has been proposed which employs internal electrostatic fields to stop coolant leaks from punctures caused by micrometeorites or space debris. Extensive calculations have indicated the feasibility of leak stoppage without film destabilization for both stationary and rotating designs. Solutions of the evolution equation for a liquid-metal film on an inclined plate, using lubrication theory for low Reynolds numbers, Karman-Pohlhausen quadratic velocity profiles for higher Reynolds numbers, and a direct numerical solution are shown. For verification an earth-based falling-film experiment on a precisely-vertical wall with controllable vacuum on either side of a small puncture is proposed. The pressure difference required to start and to stop the leak, in the presence and absence of a strong electric field, will be measured and compared with calculations. Various parameters, such as field strength, film Reynolds number, contact angle, and hole diameter will be examined. A theoretical analysis will be made of the case where the electrode is close enough to the film surface that the electric field equation and the surface dynamics equations are coupled. Preflight design calculations will be made in order to transfer the modified equipment to a flight experiment.

Ares I and Ares I-X Stage Separation Aerodynamic Testing

NASA Technical Reports Server (NTRS)

Pinier, Jeremy T.; Niskey, Charles J.

2011-01-01

The aerodynamics of the Ares I crew launch vehicle (CLV) and Ares I-X flight test vehicle (FTV) during stage separation was characterized by testing 1%-scale models at the Arnold Engineering Development Center s (AEDC) von Karman Gas Dynamics Facility (VKF) Tunnel A at Mach numbers of 4.5 and 5.5. To fill a large matrix of data points in an efficient manner, an injection system supported the upper stage and a captive trajectory system (CTS) was utilized as a support system for the first stage located downstream of the upper stage. In an overall extremely successful test, this complex experimental setup associated with advanced postprocessing of the wind tunnel data has enabled the construction of a multi-dimensional aerodynamic database for the analysis and simulation of the critical phase of stage separation at high supersonic Mach numbers. Additionally, an extensive set of data from repeated wind tunnel runs was gathered purposefully to ensure that the experimental uncertainty would be accurately quantified in this type of flow where few historical data is available for comparison on this type of vehicle and where Reynolds-averaged Navier-Stokes (RANS) computational simulations remain far from being a reliable source of static aerodynamic data.

HEAT TRANSFER FROM SURFACES OF NON-UNIFORM TEMPERATURE DISTRIBUTION. PART II. TURBULENT TRANSFER FROM ISOTHERMAL SPANWISE STRIPS ON A FLAT PLATE

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

Sogin, H.H.; Goldstein, R.J.

1960-02-01

Experiments were performed on mass transfer by forced convection from naphthalene strips on a flat plate to an air stream at ordinary temperature and pressure. Turbulence was induced in the boundary layer by means of a wire strip. In all cases there was a hydrodynamic starting length upstream of the strips. The ratio of this inert length to the total length was varied from about 0.80 to 0.96. The flow was practically incompressible with Reynolds number, based on the total length, varying from 175,000 to 486,000. The Schmidt number was 2.5. The experimental results fell in proximity to the Sebanmore » step function factor when they were reduced after the massmomentum analysis of Deissler and Loeffler for a surface of uniform vapor pressure. When Karman's formulation of the mass- momentum analogy was assumed, the data fell between the values predicted by the Seban and by the Rubesin expression for the step function factor. The results were well correlated by the Colburn analogy in conjunction with the Rubesin step function factor. (auth)« less

Dilatation-dissipation corrections for advanced turbulence models

NASA Technical Reports Server (NTRS)

Wilcox, David C.

1992-01-01

This paper analyzes dilatation-dissipation based compressibility corrections for advanced turbulence models. Numerical computations verify that the dilatation-dissipation corrections devised by Sarkar and Zeman greatly improve both the k-omega and k-epsilon model predicted effect of Mach number on spreading rate. However, computations with the k-gamma model also show that the Sarkar/Zeman terms cause an undesired reduction in skin friction for the compressible flat-plate boundary layer. A perturbation solution for the compressible wall layer shows that the Sarkar and Zeman terms reduce the effective von Karman constant in the law of the wall. This is the source of the inaccurate k-gamma model skin-friction predictions for the flat-plate boundary layer. The perturbation solution also shows that the k-epsilon model has an inherent flaw for compressible boundary layers that is not compensated for by the dilatation-dissipation corrections. A compressibility modification for k-gamma and k-epsilon models is proposed that is similar to those of Sarkar and Zeman. The new compressibility term permits accurate predictions for the compressible mixing layer, flat-plate boundary layer, and a shock separated flow with the same values for all closure coefficients.

Onset of turbulence in accelerated high-Reynolds-number flow

NASA Astrophysics Data System (ADS)

Zhou, Ye; Robey, Harry F.; Buckingham, Alfred C.

2003-05-01

A new criterion, flow drive time, is identified here as a necessary condition for transition to turbulence in accelerated, unsteady flows. Compressible, high-Reynolds-number flows initiated, for example, in shock tubes, supersonic wind tunnels with practical limitations on dimensions or reservoir capacity, and high energy density pulsed laser target vaporization experimental facilities may not provide flow duration adequate for turbulence development. In addition, for critical periods of the overall flow development, the driving background flow is often unsteady in the experiments as well as in the physical flow situations they are designed to mimic. In these situations transition to fully developed turbulence may not be realized despite achievement of flow Reynolds numbers associated with or exceeding stationary flow transitional criteria. Basically our transitional criterion and prediction procedure extends to accelerated, unsteady background flow situations the remarkably universal mixing transition criterion proposed by Dimotakis [P. E. Dimotakis, J. Fluid Mech. 409, 69 (2000)] for stationary flows. This provides a basis for the requisite space and time scaling. The emphasis here is placed on variable density flow instabilities initiated by constant acceleration Rayleigh-Taylor instability (RTI) or impulsive (shock) acceleration Richtmyer-Meshkov instability (RMI) or combinations of both. The significant influences of compressibility on these developing transitional flows are discussed with their implications on the procedural model development. A fresh perspective for predictive modeling and design of experiments for the instability growth and turbulent mixing transitional interval is provided using an analogy between the well-established buoyancy-drag model with applications of a hierarchy of single point turbulent transport closure models. Experimental comparisons with the procedural results are presented where use is made of three distinctly different types of acceleration driven instability experiments: (1) classical, relatively low speed, constant acceleration RTI experiments; (2) shock tube, shockwave driven RMI flow mixing experiments; (3) laser target vaporization RTI and RMI mixing experiments driven at very high energy density. These last named experiments are of special interest as they provide scaleable flow conditions simulating those of astrophysical magnitude such as shock-driven hydrodynamic mixing in supernova evolution research.

Large-eddy simulation of a bluff-body stabilised turbulent premixed flame using the transported flame surface density approach

NASA Astrophysics Data System (ADS)

Lee, Chin Yik; Cant, Stewart

2017-07-01

A premixed propane-air flame stabilised on a triangular bluff body in a model jet-engine afterburner configuration is investigated using large-eddy simulation (LES). The reaction rate source term for turbulent premixed combustion is closed using the transported flame surface density (TFSD) model. In this approach, there is no need to assume local equilibrium between the generation and destruction of subgrid FSD, as commonly done in simple algebraic closure models. Instead, the key processes that create and destroy FSD are accounted for explicitly. This allows the model to capture large-scale unsteady flame propagation in the presence of combustion instabilities, or in situations where the flame encounters progressive wrinkling with time. In this study, comprehensive validation of the numerical method is carried out. For the non-reacting flow, good agreement for both the time-averaged and root-mean-square velocity fields are obtained, and the Karman type vortex shedding behaviour seen in the experiment is well represented. For the reacting flow, two mesh configurations are used to investigate the sensitivity of the LES results to the numerical resolution. Profiles for the velocity and temperature fields exhibit good agreement with the experimental data for both the coarse and dense mesh. This demonstrates the capability of LES coupled with the TFSD approach in representing the highly unsteady premixed combustion observed in this configuration. The instantaneous flow pattern and turbulent flame behaviour are discussed, and the differences between the non-reacting and reacting flow are described through visualisation of vortical structures and their interaction with the flame. Lastly, the generation and destruction of FSD are evaluated by examining the individual terms in the FSD transport equation. Localised regions where straining, curvature and propagation are each dominant are observed, highlighting the importance of non-equilibrium effects of FSD generation and destruction in the model afterburner.

Perspectives on continuum flow models for force-driven nano-channel liquid flows

NASA Astrophysics Data System (ADS)

Beskok, Ali; Ghorbanian, Jafar; Celebi, Alper

2017-11-01

A phenomenological continuum model is developed using systematic molecular dynamics (MD) simulations of force-driven liquid argon flows confined in gold nano-channels at a fixed thermodynamic state. Well known density layering near the walls leads to the definition of an effective channel height and a density deficit parameter. While the former defines the slip-plane, the latter parameter relates channel averaged density with the desired thermodynamic state value. Definitions of these new parameters require a single MD simulation performed for a specific liquid-solid pair at the desired thermodynamic state and used for calibration of model parameters. Combined with our observations of constant slip-length and kinematic viscosity, the model accurately predicts the velocity distribution and volumetric and mass flow rates for force-driven liquid flows in different height nano-channels. Model is verified for liquid argon flow at distinct thermodynamic states and using various argon-gold interaction strengths. Further verification is performed for water flow in silica and gold nano-channels, exhibiting slip lengths of 1.2 nm and 15.5 nm, respectively. Excellent agreements between the model and the MD simulations are reported for channel heights as small as 3 nm for various liquid-solid pairs.

Electrically driving large magnetic Reynolds number flows on the Madison plasma dynamo experiment

NASA Astrophysics Data System (ADS)

Weisberg, David; Wallace, John; Peterson, Ethan; Endrezzi, Douglass; Forest, Cary B.; Desangles, Victor

2015-11-01

Electrically-driven plasma flows, predicted to excite a large-scale dynamo instability, have been generated in the Madison plasma dynamo experiment (MPDX), at the Wisconsin Plasma Astrophysics Laboratory. Numerical simulations show that certain topologies of these simply-connected flows may be optimal for creating a plasma dynamo and predict critical thresholds as low as Rmcrit =μ0 σLV = 250 . MPDX plasmas are shown to exceed this critical Rm , generating large (L = 1 . 4 m), warm (Te > 10 eV), unmagnetized (MA > 1) plasmas where Rm < 600 . Plasma flow is driven using ten thermally emissive LaB6 cathodes which generate a J × B torque in Helium plasmas. Detailed Mach probe measurements of plasma velocity for two flow topologies will be presented: edge-localized drive using the multi-cusp boundary field, and volumetric drive using an axial Helmholtz field. Radial velocity profiles show that edge-driven flow is established via ion viscosity but is limited by a volumetric neutral drag force (χ ~ 1 / (ντin)), and measurements of velocity shear compare favorably to Braginskii transport theory. Volumetric flow drive is shown to produce stronger velocity shear, and is characterized by the radial potential gradient as determined by global charge balance.

A synchronized particle image velocimetry and infrared thermography technique applied to convective mass transfer in champagne glasses

NASA Astrophysics Data System (ADS)

Beaumont, Fabien; Liger-Belair, Gérard; Bailly, Yannick; Polidori, Guillaume

2016-05-01

In champagne glasses, it was recently suggested that ascending bubble-driven flow patterns should be involved in the release of gaseous carbon dioxide (CO2) and volatile organic compounds. A key assumption was that the higher the velocity of the upward bubble-driven flow patterns in the liquid phase, the higher the volume fluxes of gaseous CO2 desorbing from the supersaturated liquid phase. In the present work, simultaneous monitoring of bubble-driven flow patterns within champagne glasses and gaseous CO2 escaping above the champagne surface was performed, through particle image velocimetry and infrared thermography techniques. Two quite emblematic types of champagne drinking vessels were investigated, namely a long-stemmed flute and a wide coupe. The synchronized use of both techniques proved that the cloud of gaseous CO2 escaping above champagne glasses strongly depends on the mixing flow patterns found in the liquid phase below.

Pre-X Experimental Re-Entry Lifting Body: Design of Flight Test Experiments for Critical Aerothermal Phenomena

DTIC Science & Technology

2007-06-01

the CNES proposal to perform in-flight experimentation mainly on reusable thermal protections, aero-thermo-dynamics and guidance to secure the second...the vehicle. A preliminary in-flight experimentation and measurement plan has been assessed defining the main objectives in terms of reusable Thermal ...Energy Management THEFA Thermographie Face Arrière TPS Thermal Protection System VKI Von Karman Institute WRT With Respect To WTT Wind

Crystallographic interpretation of Galois symmetries for magnetic pentagonal ring

NASA Astrophysics Data System (ADS)

Milewski, J.; Lulek, T.; Łabuz, M.

2017-03-01

Galois symmetry of exact Bethe Ansatz eigenstates for the magnetic pentagonal ring within the XXX model are investigated by a comparison with crystallographic constructions of space groups. It follows that the arithmetic symmetry of Bethe parameters for the interior of the Brillouin zone admits crystallographic interpretation, in terms of the periodic square Z2 ×Z2 , that is the two-dimensional crystal lattice with Born-Karman period two in both directions.

Zeus++ - A GUI-Based Flowfield Analysis Tool, Version 1.0, User’s Manual

DTIC Science & Technology

1999-02-01

A.B. and Priolo, F.J., Personal Communication and unpublished documentation. 9 . Tecplot v7.0 Plotting Package, Amtec Engineering, 1998. lO.Hymer... 9 . SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 5. FUNDING NUMBERS 8. PERFORMING ORGANIZATION REPORT NUMBER NSWCDD/TR-98/147 10...12 7 VON KARMAN OGIVE PARAMETERS 13 HAACK SERIES NOSE PARAMETERS 13 9 POWER SERIES NOSE PARAMETERS 14 10 MISCELLANEOUS OPTIONS 15 11

Heat of transport of air in clay.

PubMed

Minkin, Leonid; Shapovalov, Alexander S

2007-01-01

By measuring the thermomolecular pressure difference and using principles of irreversible thermodynamics, heat of transport of air in clay and its coefficient of diffusion are found. A comparison of thermotranspiration and pressure driven gas fluxes through concrete slab in homes is examined. It is shown that thermotranspiration air/radon flow may greatly exceed diffusion (pressure driven) flow in homes.

Fluid flows and forces in development: functions, features and biophysical principles

PubMed Central

Freund, Jonathan B.; Goetz, Jacky G.; Hill, Kent L.; Vermot, Julien

2012-01-01

Throughout morphogenesis, cells experience intracellular tensile and contractile forces on microscopic scales. Cells also experience extracellular forces, such as static forces mediated by the extracellular matrix and forces resulting from microscopic fluid flow. Although the biological ramifications of static forces have received much attention, little is known about the roles of fluid flows and forces during embryogenesis. Here, we focus on the microfluidic forces generated by cilia-driven fluid flow and heart-driven hemodynamics, as well as on the signaling pathways involved in flow sensing. We discuss recent studies that describe the functions and the biomechanical features of these fluid flows. These insights suggest that biological flow determines many aspects of cell behavior and identity through a specific set of physical stimuli and signaling pathways. PMID:22395739

Demonstration of the role of turbulence-driven poloidal flow generation in the L-H transition

NASA Astrophysics Data System (ADS)

Yu, C. X.; Xu, Y. H.; Luo, J. R.; Mao, J. S.; Liu, B. H.; Li, J. G.; Wan, B. N.; Wan, Y. X.

2000-05-01

This paper presents the evidence for the role of turbulence-driven poloidal flow generation in the L-H transition induced by a turbulent heating pulse on the HT-6M tokamak. It is found that the poloidal flow υθ plays a key role in developing the electric field Er and triggering the transition. The acceleration of υθ across the transition is clearly correlated with the enhancement of the Reynolds stress gradient.

Fluid Flow and Mass Transfer in Micro/Nano-Channels

NASA Astrophysics Data System (ADS)

Conlisk, A. T.; McFerran, Jennifer; Hansford, Derek; Zheng, Zhi

2001-11-01

In this work the fluid flow and mass transfer due to the presence of an electric field in a rectangular channel is examined. We consider a mixture of water or other neutral solvent and a salt compound such as sodium chloride for which the ionic species are entirely dissociated. Results are produced for the case where the channel height is much greater than the electric double layer(EDL)(microchannel) and for the case where the channel height is of the order or somewhat greater than the width of the EDL(nanochannel). For the electroosmotic flow so induced, the velocity field and the potential are similar. The fluid is assumed to behave as a continuum and the Boltzmann distribution for the mole fractions of the ions emerges from the classical dilute mass transfer equation in the limiting case where the EDL thickness is much less than the channel height. Depending on the relative magnitude of the mole fractions at the walls of the channel, both forward and reversed flow may occur. The volume flow rate is observed to vary linearly with channel height for electrically driven flow in contrast to pressure driven flow which varies as height cubed. This means that power requirements for small channels are much greater for pressure driven flow. Supported by DARPA

Moving Computational Domain Method and Its Application to Flow Around a High-Speed Car Passing Through a Hairpin Curve

NASA Astrophysics Data System (ADS)

Watanabe, Koji; Matsuno, Kenichi

This paper presents a new method for simulating flows driven by a body traveling with neither restriction on motion nor a limit of a region size. In the present method named 'Moving Computational Domain Method', the whole of the computational domain including bodies inside moves in the physical space without the limit of region size. Since the whole of the grid of the computational domain moves according to the movement of the body, a flow solver of the method has to be constructed on the moving grid system and it is important for the flow solver to satisfy physical and geometric conservation laws simultaneously on moving grid. For this issue, the Moving-Grid Finite-Volume Method is employed as the flow solver. The present Moving Computational Domain Method makes it possible to simulate flow driven by any kind of motion of the body in any size of the region with satisfying physical and geometric conservation laws simultaneously. In this paper, the method is applied to the flow around a high-speed car passing through a hairpin curve. The distinctive flow field driven by the car at the hairpin curve has been demonstrated in detail. The results show the promising feature of the method.

Electro-osmotically driven liquid delivery method and apparatus

DOEpatents

Rakestraw, David J.; Anex, Deon S.; Yan, Chao; Dadoo, Rajeev; Zare, Richard N.

1999-01-01

Method and apparatus for controlling precisely the composition and delivery of liquid at sub-.mu.L/min flow rate. One embodiment of such a delivery system is an electro-osmotically driven gradient flow delivery system that generates dynamic gradient flows with sub-.mu.L/min flow rates by merging a plurality of electro-osmotic flows. These flows are delivered by a plurality of delivery arms attached to a mixing connector, where they mix and then flow into a receiving means, preferably a column. Each inlet of the plurality of delivery arms is placed in a corresponding solution reservoir. A plurality of independent programmable high-voltage power supplies is used to apply a voltage program to each of the plurality of solution reservoirs to regulate the electro-osmotic flow in each delivery arm. The electro-osmotic flow rates in the delivery arms are changed with time according to each voltage program to deliver the required gradient profile to the column.

Large-Eddy Simulations of Fully Developed Turbulent Channel and Pipe Flows with Smooth and Rough Walls

NASA Astrophysics Data System (ADS)

Saito, Namiko

Studies in turbulence often focus on two flow conditions, both of which occur frequently in real-world flows and are sought-after for their value in advancing turbulence theory. These are the high Reynolds number regime and the effect of wall surface roughness. In this dissertation, a Large-Eddy Simulation (LES) recreates both conditions over a wide range of Reynolds numbers Retau = O(102) - O(108) and accounts for roughness by locally modeling the statistical effects of near-wall anisotropic fine scales in a thin layer immediately above the rough surface. A subgrid, roughness-corrected wall model is introduced to dynamically transmit this modeled information from the wall to the outer LES, which uses a stretched-vortex subgrid-scale model operating in the bulk of the flow. Of primary interest is the Reynolds number and roughness dependence of these flows in terms of first and second order statistics. The LES is first applied to a fully turbulent uniformly-smooth/rough channel flow to capture the flow dynamics over smooth, transitionally rough and fully rough regimes. Results include a Moody-like diagram for the wall averaged friction factor, believed to be the first of its kind obtained from LES. Confirmation is found for experimentally observed logarithmic behavior in the normalized stream-wise turbulent intensities. Tight logarithmic collapse, scaled on the wall friction velocity, is found for smooth-wall flows when Re tau ≥ O(106) and in fully rough cases. Since the wall model operates locally and dynamically, the framework is used to investigate non-uniform roughness distribution cases in a channel, where the flow adjustments to sudden surface changes are investigated. Recovery of mean quantities and turbulent statistics after transitions are discussed qualitatively and quantitatively at various roughness and Reynolds number levels. The internal boundary layer, which is defined as the border between the flow affected by the new surface condition and the unaffected part, is computed, and a collapse of the profiles on a length scale containing the logarithm of friction Reynolds number is presented. Finally, we turn to the possibility of expanding the present framework to accommodate more general geometries. As a first step, the whole LES framework is modified for use in the curvilinear geometry of a fully-developed turbulent pipe flow, with implementation carried out in a spectral element solver capable of handling complex wall profiles. The friction factors have shown favorable agreement with the superpipe data, and the LES estimates of the Karman constant and additive constant of the log-law closely match values obtained from experiment.

Stability of magnetohydrodynamic Dean Flow as applied to centrifugally confined plasmas

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

Hassam, A.B.

1999-10-01

Dean Flow is the azimuthal flow of fluid between static concentric cylinders. In a magnetized plasma, there may also be radial stratification of the pressure. The ideal magnetohydrodynamic stability of such a flow in the presence of a strong axial magnetic field and an added radial gravitational force is examined. It is shown that both the Kelvin{endash}Helmholtz instability and pressure-gradient-driven interchanges can be stabilized if the flow is driven by a unidirectional external force and if the plasma annulus is sufficiently thin (large aspect ratio). These results find application in schemes using centrifugal confinement of plasma for fusion. {copyright} {italmore » 1999 American Institute of Physics.}« less

Topographically driven crustal flow and its implication to the development of pinned oroclines

NASA Technical Reports Server (NTRS)

Hsui, Albert T.; Wilkerson, M. Scott; Marshak, Stephen

1990-01-01

Pinned oroclines, a type of curved orogen which results from lateral pinning of a growing fold-thrust belt, tend to resemble parabolic Newtonian curvature modified by different degrees of flattening at the flow front. It is proposed that such curves can be generated by Newtonian crustal flow driven by topographic variations. In this model, regional topographic differences create a regional flow which produces a parabolic flow front on interaction with lateral bounding obstacles. Local topographic variations modify the parabolic curves and yield more flat-crested, non-Newtonian-type curvatures. A finite-difference thin-skin tectonic simulation demonstrates that both Newtonian and non-Newtonian curved orogens can be produced within a Newtonian crust.

A three-dimensional turbulent separated flow and related mesurements

NASA Technical Reports Server (NTRS)

Pierce, F. J.

1985-01-01

The applicability of and the limits on the applicability of 11 near wall similarity laws characterizing three-dimensional turbulent boundary layer flows were determined. A direct force sensing local wall shear stress meter was used in both pressure-driven and shear-driven three-dimensional turbulent boundary layers, together with extensive mean velocity field and wall pressure field data. This resulted in a relatively large number of graphical comparisons of the predictive ability of 10 of these 11 similarity models relative to measured data over a wide range of flow conditions. Documentation of a complex, separated three-dimensional turbulent flow as a standard test case for evaluating the predictive ability of numerical codes solving such flows is presented.

Analytical study of mixed electroosmotic-pressure-driven flow in rectangular micro-channels

NASA Astrophysics Data System (ADS)

Movahed, Saeid; Kamali, Reza; Eghtesad, Mohammad; Khosravifard, Amir

2013-09-01

Operational state of many miniaturized devices deals with flow field in microchannels. Pressure-driven flow (PDF) and electroosmotic flow (EOF) can be recognized as the two most important types of the flow field in such channels. EOF has many advantages in comparison with PDF, such as being vibration free and not requiring any external mechanical pumps or moving parts. However, the disadvantages of this type of flow such as Joule heating, electrophoresis demixing, and not being suitable for mobile devices must be taken into consideration carefully. By using mixed electroosmotic/pressure-driven flow, the role of EOF in producing desired velocity profile will be reduced. In this way, the advantages of EOF can be exploited, and its disadvantages can be prevented. Induced pressure gradient can be utilized in order to control the separation in the system. Furthermore, in many complicated geometries such as T-shape microchannels, turns may induce pressure gradient to the electroosmotic velocity. While analytical formulas are completely essential for analysis and control of any industrial and laboratory microdevices, lack of such formulas in the literature for solving Poisson-Boltzmann equation and predicting electroosmotic velocity field in rectangular domains is evident. In the present study, first a novel method is proposed to solve Poisson-Boltzmann equation (PBE). Subsequently, this solution is utilized to find the electroosmotic and the mixed electroosmotic/pressure-driven velocity profile in a rectangular domain of the microchannels. To demonstrate the accuracy of the presented analytical method in solving PBE and finding electroosmotic velocity, a general nondimensional example is analyzed, and the results are compared with the solution of boundary element method. Additionally, the effects of different nondimensional parameters and also aspect ratio of channels on the electroosmotic part of the flow field will be investigated.

Spectral element simulation of precession driven flows in the outer cores of spheroidal planets

NASA Astrophysics Data System (ADS)

Vormann, Jan; Hansen, Ulrich

2015-04-01

A common feature of the planets in the solar system is the precession of the rotation axes, driven by the gravitational influence of another body (e.g. the Earth's moon). In a precessing body, the rotation axis itself is rotating around another axis, describing a cone during one precession period. Similar to the coriolis and centrifugal force appearing from the transformation to a rotating system, the addition of precession adds another term to the Navier-Stokes equation, the so called Poincaré force. The main geophysical motivation in studying precession driven flows comes from their ability to act as magnetohydrodynamic dynamos in planets and moons. Precession may either act as the only driving force or operate together with other forces such as thermochemical convection. One of the challenges in direct numerical simulations of such flows lies in the spheroidal shape of the fluid volume, which should not be neglected since it contributes an additional forcing trough pressure torques. Codes developed for the simulation of flows in spheres mostly use efficient global spectral algorithms that converge fast, but lack geometric flexibility, while local methods are usable in more complex shapes, but often lack high accuracy. We therefore adapted the spectral element code Nek5000, developed at Argonne National Laboratory, to the problem. The spectral element method is capable of solving for the flow in arbitrary geometries while still offering spectral convergence. We present first results for the simulation of a purely hydrodynamic, precession-driven flow in a spheroid with no-slip boundaries and an inner core. The driving by the Poincaré force is in a range where theoretical work predicts multiple solutions for a laminar flow. Our simulations indicate a transition to turbulent flows for Ekman numbers of 10-6 and lower.

Clogging and transport of driven particles in asymmetric funnel arrays

DOE PAGES

Olson Reichhardt, Cynthia J.; Reichhardt, Charles

2018-05-03

In this paper, we numerically examine the flow and clogging of particles driven through asymmetric funnel arrays when the commensurability ratio of the number of particles per plaquette is varied. The particle-particle interactions are modeled with a soft repulsive potential that could represent vortex flow in type-II superconductors or driven charged colloids. The velocity-force curves for driving in the easy flow direction of the funnels exhibit a single depinning threshold; however, for driving in the hard flow direction, we find that there can be both negative mobility where the velocity decreases with increasing driving force as well as a reentrantmore » pinning effect in which the particles flow at low drives but become pinned at intermediate drives. This reentrant pinning is associated with a transition from smooth one-dimensional flow at low drives to a clogged state at higher drives that occurs when the particles cluster in a small number of plaquettes and block the flow. When the drive is further increased, particle rearrangements occur that cause the clog to break apart. We map out the regimes in which the pinned, flowing, and clogged states appear as a function of plaquette filling and drive. Finally, the clogged states remain robust at finite temperatures but develop intermittent bursts of flow in which a clog temporarily breaks apart but quickly reforms.« less

Clogging and transport of driven particles in asymmetric funnel arrays

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

Olson Reichhardt, Cynthia J.; Reichhardt, Charles

In this paper, we numerically examine the flow and clogging of particles driven through asymmetric funnel arrays when the commensurability ratio of the number of particles per plaquette is varied. The particle-particle interactions are modeled with a soft repulsive potential that could represent vortex flow in type-II superconductors or driven charged colloids. The velocity-force curves for driving in the easy flow direction of the funnels exhibit a single depinning threshold; however, for driving in the hard flow direction, we find that there can be both negative mobility where the velocity decreases with increasing driving force as well as a reentrantmore » pinning effect in which the particles flow at low drives but become pinned at intermediate drives. This reentrant pinning is associated with a transition from smooth one-dimensional flow at low drives to a clogged state at higher drives that occurs when the particles cluster in a small number of plaquettes and block the flow. When the drive is further increased, particle rearrangements occur that cause the clog to break apart. We map out the regimes in which the pinned, flowing, and clogged states appear as a function of plaquette filling and drive. Finally, the clogged states remain robust at finite temperatures but develop intermittent bursts of flow in which a clog temporarily breaks apart but quickly reforms.« less

The dynamic behavior of chemically "stiffened" red blood cells in microchannel flows.

PubMed

Forsyth, Alison M; Wan, Jiandi; Ristenpart, William D; Stone, Howard A

2010-07-01

The rigidity of red blood cells (RBCs) plays an important role in whole blood viscosity and is correlated with several cardiovascular diseases. Two chemical agents that are commonly used to study cell deformation are diamide and glutaraldehyde. Despite diamide's common usage, there are discrepancies in the literature surrounding diamide's effect on the deformation of RBCs in shear and pressure-driven flows; in particular, shear flow experiments have shown that diamide stiffens cells, while pressure-driven flow in capillaries did not give this result. We performed pressure-driven flow experiments with RBCs in a microfluidic constriction and quantified the cell dynamics using high-speed imaging. Diamide, which affects RBCs by cross-linking spectrin skeletal membrane proteins, did not reduce deformation and showed an unchanged effective strain rate when compared to healthy cells. In contrast, glutaraldehyde, which is a non-specific fixative that acts on all components of the cell, did reduce deformation and showed increased instances of tumbling, both of which are characteristic features of stiffened, or rigidified, cells. Because glutaraldehyde increases the effective viscosity of the cytoplasm and lipid membrane while diamide does not, one possible explanation for our results is that viscous effects in the cytoplasm and/or lipid membrane are a dominant factor in dictating dynamic responses of RBCs in pressure-driven flows. Finally, literature on the use of diamide as a stiffening agent is summarized, and provides supporting evidence for our conclusions. Copyright 2010 Elsevier Inc. All rights reserved.

Subtidal circulation patterns in a shallow, highly stratified estuary: Mobile Bay, Alabama

USGS Publications Warehouse

Noble, M.A.; Schroeder, W.W.; Wiseman, W.J.; Ryan, H.F.; Gelfenbaum, G.

1996-01-01

Mobile Bay is a wide (25-50 km), shallow (3 m), highly stratified estuary on the Gulf coast of the United States. In May 1991 a series of instruments that measure near-surface and near-bed current, temperature, salinity, and middepth pressure were deployed for a year-long study of the bay. A full set of measurements were obtained at one site in the lower bay; all but current measurements were obtained at a midbay site. These observations show that the subtidal currents in the lower bay are highly sheared, despite the shallow depth of the estuary. The sheared flow patterns are partly caused by differential forcing from wind stress and river discharge. Two wind-driven flow patterns actually exist in lower Mobile Bay. A barotropic response develops when the difference between near-surface and near-bottom salinity is less than 5 parts per thousand. For stronger salinity gradients the wind-driven currents are larger and the response resembles a baroclinic flow pattern. Currents driven by river flows are sheared and also have a nonlinear response pattern. Only near-surface currents are driven seaward by discharges below 3000 m3/s. At higher discharge rates, surface current variability uncouples from the river flow and the increased discharge rates drive near-bed current seaward. This change in the river-forced flow pattern may be associated with a hydraulic jump in the mouth of the estuary. Copyright 1996 by the American Geophysical Union.

Nonlinear MHD simulation of magnetic relaxation during DC helicity injection in spherical torus plasmas

NASA Astrophysics Data System (ADS)

Kanki, Takashi; Nagata, Masayoshi; Kagei, Yasuhiro

2009-11-01

Recently, the intermittent plasma flow has been observed to be correlated with the fluctuations of the toroidal current It and n=1 mode in the HIST spherical torus device. During the partially driven phase mixed with a resistive decay, the toroidal ion flow velocity (˜ 40 km/s) in the opposite direction of It is driven in the central open flux region, and the oscillations in n=1 mode occur there, while during the resistive decay phase, this flow velocity reverses and results in the same as that of It, and the oscillations in n=1 mode disappear there. The purpose of the present study is to investigate the plasma flow reversal process and the relevant MHD relaxation by using the 3-D nonlinear MHD simulations. The numerical results exhibit that during the driven phase, the toroidal flow velocity (˜ 37 km/s) is in the opposite direction to It, but in the same direction as the ExB rotation induced by an applied voltage. This flow is driven by the magnetic reconnection occurring at the X-point during the repetitive process of the non-axisymmetric magnetized plasmoid ejection from the helicity injector. The oscillations of poloidal flux ψp are out of phase with those of toroidal flux ψt and magnetic energy for the dominant n=1 mode, indicating the flux conversion from ψt to ψp. The effect of the vacuum toroidal field strength on the plasma dynamics is discussed.

On-Chip Pressure Generation for Driving Liquid Phase Separations in Nanochannels.

PubMed

Xia, Ling; Choi, Chiwoong; Kothekar, Shrinivas C; Dutta, Debashis

2016-01-05

In this Article, we describe the generation of pressure gradients on-chip for driving liquid phase separations in submicrometer deep channels. The reported pressure-generation capability was realized by applying an electrical voltage across the interface of two glass channel segments with different depths. A mismatch in the electroosmotic flow rate at this junction led to the generation of pressure-driven flow in our device, a fraction of which was then directed to an analysis channel to carry out the desired separation. Experiments showed the reported strategy to be particularly conducive for miniaturization of pressure-driven separations yielding flow velocities in the separation channel that were nearly unaffected upon scaling down the depth of the entire fluidic network. Moreover, the small dead volume in our system allowed for high dynamic control over this pressure gradient, which otherwise was challenging to accomplish during the sample injection process using external pumps. Pressure-driven velocities up to 3.1 mm/s were realized in separation ducts as shallow as 300 nm using our current design for a maximum applied voltage of 3 kV. The functionality of this integrated device was demonstrated by implementing a pressure-driven ion chromatographic analysis that relied on analyte interaction with the nanochannel surface charges to yield a nonuniform solute concentration across the channel depth. Upon coupling such analyte distribution to the parabolic pressure-driven flow profile in the separation duct, a mixture of amino acids could be resolved. The reported assay yielded a higher separation resolution compared to its electrically driven counterpart in which sample migration was realized using electroosmosis/electrophoresis.

Comment on "Heat transfer and fluid flow in microchannels and nanochannels at high Knudsen number using thermal lattice-Boltzmann method".

PubMed

Luo, Li-Shi

2011-10-01

In this Comment we reveal the falsehood of the claim that the lattice Bhatnagar-Gross-Krook (BGK) model "is capable of modeling shear-driven, pressure-driven, and mixed shear-pressure-driven rarified [sic] flows and heat transfer up to Kn=1 in the transitional regime" made in a recent paper [Ghazanfarian and Abbassi, Phys. Rev. E 82, 026307 (2010)]. In particular, we demonstrate that the so-called "Knudsen effects" described are merely numerical artifacts of the lattice BGK model and they are unphysical. Specifically, we show that the erroneous results for the pressure-driven flow in a microchannel imply the false and unphysical condition that 6σKn<-1, where Kn is the Knudsen number σ=(2-σ(v))/σ(v) and σ(v)∈(0,1] is the tangential momentum accommodation coefficient. We also show explicitly that the defects of the lattice BGK model can be completely removed by using the multiple-relaxation-time collision model.

Heat Transfer Characteristics of Mixed Electroosmotic and Pressure Driven Micro-Flows

NASA Astrophysics Data System (ADS)

Horiuchi, Keisuke; Dutta, Prashanta

We analyze heat transfer characteristics of steady electroosmotic flows with an arbitrary pressure gradient in two-dimensional straight microchannels considering the effects of Joule heating in electroosmotic pumping. Both the temperature distribution and local Nusselt number are mathematically derived in this study. The thermal analysis takes into consideration of the interaction among advective, diffusive, and Joule heating terms to obtain the thermally developing behavior. Unlike macro-scale pipes, axial conduction in micro-scale cannot be negligible, and the governing energy equation is not separable. Thus, a method that considers an extended Graetz problem is introduced. Analytical results show that the Nusselt number of pure electrooosmotic flow is higher than that of plane Poiseulle flow. Moreover, when the electroosmotic flow and pressure driven flow coexist, it is found that adverse pressure gradient to the electroosmotic flow makes the thermal entrance length smaller and the heat transfer ability stronger than pure electroosmotic flow case.

The least-squares finite element method for low-mach-number compressible viscous flows

NASA Technical Reports Server (NTRS)

Yu, Sheng-Tao

1994-01-01

The present paper reports the development of the Least-Squares Finite Element Method (LSFEM) for simulating compressible viscous flows at low Mach numbers in which the incompressible flows pose as an extreme. Conventional approach requires special treatments for low-speed flows calculations: finite difference and finite volume methods are based on the use of the staggered grid or the preconditioning technique; and, finite element methods rely on the mixed method and the operator-splitting method. In this paper, however, we show that such difficulty does not exist for the LSFEM and no special treatment is needed. The LSFEM always leads to a symmetric, positive-definite matrix through which the compressible flow equations can be effectively solved. Two numerical examples are included to demonstrate the method: first, driven cavity flows at various Reynolds numbers; and, buoyancy-driven flows with significant density variation. Both examples are calculated by using full compressible flow equations.

Quantitative optical coherence tomography imaging of intermediate flow defect phenotypes in ciliary physiology and pathophysiology

NASA Astrophysics Data System (ADS)

Huang, Brendan K.; Gamm, Ute A.; Jonas, Stephan; Khokha, Mustafa K.; Choma, Michael A.

2015-03-01

Cilia-driven fluid flow is a critical yet poorly understood aspect of pulmonary physiology. Here, we demonstrate that optical coherence tomography-based particle tracking velocimetry can be used to quantify subtle variability in cilia-driven flow performance in Xenopus, an important animal model of ciliary biology. Changes in flow performance were quantified in the setting of normal development, as well as in response to three types of perturbations: mechanical (increased fluid viscosity), pharmacological (disrupted serotonin signaling), and genetic (diminished ciliary motor protein expression). Of note, we demonstrate decreased flow secondary to gene knockdown of kif3a, a protein involved in ciliogenesis, as well as a dose-response decrease in flow secondary to knockdown of dnah9, an important ciliary motor protein.

The effect of power-law body forces on a thermally driven flow between concentric rotating spheres

NASA Technical Reports Server (NTRS)

Macaraeg, M. G.

1986-01-01

A numerical study is conducted to determine the effect of power-law body forces on a thermally-driven axisymmetric flow field confined between concentric co-rotating spheres. This study is motivated by Spacelab geophysical fluid-flow experiments, which use an electrostatic force on a dielectric fluid to simulate gravity; this force exhibits a (1/r)sup 5 distribution. Meridional velocity is found to increase when the electrostatic body force is imposed, relative to when the body force is uniform. Correlation among flow fields with uniform, inverse-square, and inverse-quintic force fields is obtained using a modified Grashof number.

The effect of power law body forces on a thermally-driven flow between concentric rotating spheres

NASA Technical Reports Server (NTRS)

Macaraeg, M. G.

1985-01-01

A numerical study is conducted to determine the effect of power-law body forces on a thermally-driven axisymmetric flow field confined between concentric co-rotating spheres. This study is motivated by Spacelab geophysical fluid-flow experiments, which use an electrostatic force on a dielectric fluid to simulate gravity; this force exhibits a (1/r)sup 5 distribution. Meridional velocity is found to increase when the electrostatic body force is imposed, relative to when the body force is uniform. Correlation among flow fields with uniform, inverse-square, and inverse-quintic force fields is obtained using a modified Grashof number.

A phenomenological continuum model for force-driven nano-channel liquid flows

NASA Astrophysics Data System (ADS)

Ghorbanian, Jafar; Celebi, Alper T.; Beskok, Ali

2016-11-01

A phenomenological continuum model is developed using systematic molecular dynamics (MD) simulations of force-driven liquid argon flows confined in gold nano-channels at a fixed thermodynamic state. Well known density layering near the walls leads to the definition of an effective channel height and a density deficit parameter. While the former defines the slip-plane, the latter parameter relates channel averaged density with the desired thermodynamic state value. Definitions of these new parameters require a single MD simulation performed for a specific liquid-solid pair at the desired thermodynamic state and used for calibration of model parameters. Combined with our observations of constant slip-length and kinematic viscosity, the model accurately predicts the velocity distribution and volumetric and mass flow rates for force-driven liquid flows in different height nano-channels. Model is verified for liquid argon flow at distinct thermodynamic states and using various argon-gold interaction strengths. Further verification is performed for water flow in silica and gold nano-channels, exhibiting slip lengths of 1.2 nm and 15.5 nm, respectively. Excellent agreements between the model and the MD simulations are reported for channel heights as small as 3 nm for various liquid-solid pairs.

Plasma Wind Tunnel Testing of Electron Transpiration Cooling Concept

DTIC Science & Technology

2017-02-28

AFRL-AFOSR-UK-TR-2017-0012 Plasma Wind Tunnel Testing of Electron Transpiration Cooling Concept Olivier Chazot INSTITUT VON KARMAN DE DYNAMIQUE DES...28-02-2017 2. REPORT TYPE Final 3. DATES COVERED (From - To) 01 Dec 2015 to 30 Nov 2016 4. TITLE AND SUBTITLE Plasma Wind Tunnel Testing of Electron ...Aeronautics and Aerospace Department B-1640 Rhode Saint Genèse Belgium Internal Ref: ARR 1605 February 2017 Plasma Wind Tunnel Testing of Electron

Effect of von Karman Vortex Shedding on Regular and Open-slit V-gutter Stabilized Turbulent Premixed Flames

DTIC Science & Technology

2012-04-01

Both flame lengths shrink and large scale disruptions occur downstream with vortex shedding carrying reaction zones. Flames in both flameholders...9) the flame structure changes dramatically for both regular and open-slit V-gutter. Both flame lengths shrink and large scale disruptions occur...reduces the flame length . However, qualitatively the open-slit V-gutter appears to be more sensitive than the regular V-gutter. Both flames remain

Final Environmental Assessment: Base-Wide Building Demolition Arnold Air Force Base, Tennessee

DTIC Science & Technology

2006-02-01

Building • Engine Test Facility ( ETF )-B Exhauster • ETF -A Airside • ETF -A Exhauster • ETF -A Reefer • CE Facility • Rocket Storage • Von Karman Gas...Executive Order ESA Endangered Species Act ETF Engine Test Facility FamCamp Family Camping Area P:\\ARNOLDAFB\\333402DO42COMPLIANCE\\DEMOLITION...Fabrication Shop • Natural Resources Building • Salt Storage Building • Administration Building • Engine Test Facility ( ETF )-B Exhauster • ETF -A

Turbulence simulation mechanization for Space Shuttle Orbiter dynamics and control studies

NASA Technical Reports Server (NTRS)

Tatom, F. B.; King, R. L.

1977-01-01

The current version of the NASA turbulent simulation model in the form of a digital computer program, TBMOD, is described. The logic of the program is discussed and all inputs and outputs are defined. An alternate method of shear simulation suitable for incorporation into the model is presented. The simulation is based on a von Karman spectrum and the assumption of isotropy. The resulting spectral density functions for the shear model are included.

Seismic Pulse Broadening Associated with Fracture Damage Caused by Explosions in Crystalline Rock

DTIC Science & Technology

1989-08-30

1/ 3 ’)I 3/ 2 -C2(() - 1 +) 3D °2/ 3 D 1 - D 1/ - (I -C, X) 1+ 2/3)-)o _ I C4)L( oj and for loading at constant a3 43 D 02𔃽 (D )?/3 31 (28) where S...U3, 103-112. Von Karman, T. (1911). Festigkeitswversuche unter allseiRgim druck , Z. Ver. Dt. Ing., 51, 1749-1757. Wawersik, W.R., and C. Fairhurst

JPRS Report, Science & Technology, Japan

DTIC Science & Technology

1990-10-22

34 Particularly, details of the "Comparison with Other Countries" have been described in a series of this journal since the first edition. Also, the...transportation. Comparison of energy efficiency between different means of transportation was done by von Karman 2 but, for walking, he referred to living things...Federation Lecture Meeting, 1988, pp 333-334. 6. Kumar, V.R. and Waldron,. K.J,.. ""Force Distribution in Cl6sed’Kinematics Chains," IEEE J. ROBOTICS AND

[Modern techniques for terminating pregnancy].

PubMed

Palmer, R; Brunerie, J; Henrion, R; Newton, J; De Watteville; Wijnberg, B

1974-01-01

This panel presentation consists of detailed technical descriptions of Karman aspiration and of hypertonic saline injection, a list of legal indications for abortion in France, a brief summary of how abortions are conducted in England, and a question and answer period, all following an introduction published in this journal (ibid. 1(1): 21-22, 1973.). The Karman aspiration is done only until 8 weeks of amenorrhea, with premedication only, using a polyethylene cannula and either a 50 cc syringe, a hand pump or a mechanical pump (.5-1 atmosphere vacuum). Pro fuse details of technique, treatment and complications are given, since the procedure is new to French physicians, and is currently done "semi-clandestinely." Most of the text on midtrimester abortions concerns indications and dilatation of the cervix; the hypertonic saline technique was shown in a film. The accepted indications at the Port Royal Maternity are: chromosomal or metabolic genetic defects demonstruated by amniocentesis and culture, probably severe congenital d efect indicated by elevated alpha-feto-protein, infection by German measles shown by presence of IgM in maternal serum. Every precaution is taken in such cases to guarantee the possibility of a healthy living infant in the future. Second trimester abortions in King's College Hospital, London, are usually by intraamniotic prostaglandins and iv oxytocin, and an IUD is inserted immediately. The questions concerned mainly where abortions can be performed, where techniques can be learned , and early abortion clinics in Holland.

Intensity and angle-of-arrival spectra of laser light propagating through axially homogeneous buoyancy-driven turbulence.

PubMed

Pawar, Shashikant S; Arakeri, Jaywant H

2016-08-01

Frequency spectra obtained from the measurements of light intensity and angle of arrival (AOA) of parallel laser light propagating through the axially homogeneous, axisymmetric buoyancy-driven turbulent flow at high Rayleigh numbers in a long (length-to-diameter ratio of about 10) vertical tube are reported. The flow is driven by an unstable density difference created across the tube ends using brine and fresh water. The highest Rayleigh number is about 8×10⁹. The aim of the present work is to find whether the conventional Obukhov-Corrsin scaling or Bolgiano-Obukhov (BO) scaling is obtained for the intensity and AOA spectra in the case of light propagation in a buoyancy-driven turbulent medium. Theoretical relations for the frequency spectra of log amplitude and AOA fluctuations developed for homogeneous isotropic turbulent media are modified for the buoyancy-driven flow in the present case to obtain the asymptotic scalings for the high and low frequency ranges. For low frequencies, the spectra of intensity and vertical AOA fluctuations obtained from measurements follow BO scaling, while scaling for the spectra of horizontal AOA fluctuations shows a small departure from BO scaling.

Wind effect on diurnal thermally driven flow in vegetated nearshore of a lake

NASA Astrophysics Data System (ADS)

Lin, Y. T.

2014-12-01

In this study, a highly idealized model is developed to discuss the interplay of diurnal heating/cooling induced buoyancy and wind stress on thermally driven flow over a vegetated slope. Since the model is linear, the horizontal velocity components can be broken into buoyancy-driven and surface wind-driven parts. Due to the presence of rooted emergent vegetation, the circulation strength even under the surface wind condition is still significantly reduced, and the transient (adjustment) stage for the initial conditions is shorter than that without vegetation. The flow in shallows is dominated by a viscosity/buoyancy balance as the case without wind, while the effect of wind stress is limited to the upper layer in deep water. In the lower layer of deep regions, vegetative drag is prevailing except the near bottom regions, where viscosity dominates. Under the unidirectional wind condition, a critical dimensionless shear stress to stop the induced flow can be found and is a function of horizontal location . For the periodic wind condition, if the two forcing mechanisms work in concert, the circulation magnitude can be increased. For the case where buoyancy and wind shear stress act against each other, the circulation strength is reduced and its structure becomes more complex. However, the flow magnitudes near the bottom for and are comparable because surface wind almost has no influence.

Flow-driven waves and sink-driven oscillations during aggregation of Dictyostelium discoideum

NASA Astrophysics Data System (ADS)

Gholami, Azam; Zykov, Vladimir; Steinbock, Oliver; Bodenschatz, Eberhard

The slime mold Dictyostelium discoideum (D.d) is a well-known model system for the study of biological pattern formation. Under starvation, D.d. cells aggregate chemotactically towards cAMP signals emitted periodically from an aggregation center. In the natural environment, D.d cells may experience fluid flows that can profoundly change the underlying wave generation process. We investigate spatial-temporal dynamics of a uniformly distributed population of D.d. cells in a flow-through narrow microfluidic channel with a cell-free inlet area. We show that flow can significantly influence the dynamics of the system and lead to a flow- driven instability that initiate downstream traveling cAMP waves. We also show that cell-free boundary regions have a significant effect on the observed patterns and can lead to a new kind of instability. Since there are no cells in the inlet to produce cAMP, the points in the vicinity of the inlet lose cAMP due to advection or diffusion and gain only a little from the upstream of the channel (inlet). In other words, there is a large negative flux of cAMP in the neighborhood close to the inlet, which can be considered as a sink. This negative flux close to the inlet drives a new kind of instability called sink-driven oscillations. Financial support of the MaxSynBio Consortium is acknowledged.

Topographically driven groundwater flow and the San Andreas heat flow paradox revisited

USGS Publications Warehouse

Saffer, D.M.; Bekins, B.A.; Hickman, S.

2003-01-01

Evidence for a weak San Andreas Fault includes (1) borehole heat flow measurements that show no evidence for a frictionally generated heat flow anomaly and (2) the inferred orientation of ??1 nearly perpendicular to the fault trace. Interpretations of the stress orientation data remain controversial, at least in close proximity to the fault, leading some researchers to hypothesize that the San Andreas Fault is, in fact, strong and that its thermal signature may be removed or redistributed by topographically driven groundwater flow in areas of rugged topography, such as typify the San Andreas Fault system. To evaluate this scenario, we use a steady state, two-dimensional model of coupled heat and fluid flow within cross sections oriented perpendicular to the fault and to the primary regional topography. Our results show that existing heat flow data near Parkfield, California, do not readily discriminate between the expected thermal signature of a strong fault and that of a weak fault. In contrast, for a wide range of groundwater flow scenarios in the Mojave Desert, models that include frictional heat generation along a strong fault are inconsistent with existing heat flow data, suggesting that the San Andreas Fault at this location is indeed weak. In both areas, comparison of modeling results and heat flow data suggest that advective redistribution of heat is minimal. The robust results for the Mojave region demonstrate that topographically driven groundwater flow, at least in two dimensions, is inadequate to obscure the frictionally generated heat flow anomaly from a strong fault. However, our results do not preclude the possibility of transient advective heat transport associated with earthquakes.

Granular avalanches down inclined and vibrated planes

NASA Astrophysics Data System (ADS)

Gaudel, Naïma; Kiesgen de Richter, Sébastien; Louvet, Nicolas; Jenny, Mathieu; Skali-Lami, Salaheddine

2016-09-01

In this article, we study granular avalanches when external mechanical vibrations are applied. We identify conditions of flow arrest and compare with the ones classically observed for nonvibrating granular flows down inclines [Phys. Fluids 11, 542 (1999), 10.1063/1.869928]. We propose an empirical law to describe the thickness of the deposits with the inclination angle and the vibration intensity. The link between the surface velocity and the depth of the flow highlights a competition between gravity and vibrations induced flows. We identify two distinct regimes: (a) gravity-driven flows at large angles where vibrations do not modify dynamical properties but the deposits (scaling laws in this regime are in agreement with the literature for nonvibrating granular flows) and (b) vibrations-driven flows at small angles where no flow is possible without applied vibrations (in this last regime, the flow behavior can be properly described by a vibration induced activated process). We show, in this study, that granular flows down inclined planes can be finely tuned by external mechanical vibrations.

The effect of sheared toroidal rotation on pressure driven magnetic islands in toroidal plasmas

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

Hegna, C. C.

2016-05-15

The impact of sheared toroidal rotation on the evolution of pressure driven magnetic islands in tokamak plasmas is investigated using a resistive magnetohydrodynamics model augmented by a neoclassical Ohm's law. Particular attention is paid to the asymptotic matching data as the Mercier indices are altered in the presence of sheared flow. Analysis of the nonlinear island Grad-Shafranov equation shows that sheared flows tend to amplify the stabilizing pressure/curvature contribution to pressure driven islands in toroidal tokamaks relative to the island bootstrap current contribution. As such, sheared toroidal rotation tends to reduce saturated magnetic island widths.

Light-Driven Transport of a Liquid Marble with and against Surface Flows.

PubMed

Kavokine, Nikita; Anyfantakis, Manos; Morel, Mathieu; Rudiuk, Sergii; Bickel, Thomas; Baigl, Damien

2016-09-05

Liquid marbles, that is, liquid drops coated by a hydrophobic powder, do not wet any solid or liquid substrate, making their transport and manipulation both highly desirable and challenging. Herein, we describe the light-driven transport of floating liquid marbles and emphasize a surprising motion behavior. Liquid marbles are deposited on a water solution containing photosensitive surfactants. Irradiation of the solution generates photoreversible Marangoni flows that transport the liquid marbles toward UV light and away from blue light when the thickness of the liquid substrate is large enough (Marangoni regime). Below a critical thickness, the liquid marbles move in the opposite direction to that of the surface flow at a speed increasing with decreasing liquid thickness (anti-Marangoni). We demonstrate that the anti-Marangoni motion is driven by the free surface deformation, which propels the non-wetting marble against the surface flow. We call this behavior "slide effect". © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pressure-driven occlusive flow of a confined red blood cell.

PubMed

Savin, Thierry; Bandi, M M; Mahadevan, L

2016-01-14

When red blood cells (RBCs) move through narrow capillaries in the microcirculation, they deform as they flow. In pathophysiological processes such as sickle cell disease and malaria, RBC motion and flow are severely restricted. To understand this threshold of occlusion, we use a combination of experiment and theory to study the motion of a single swollen RBC through a narrow glass capillary of varying inner diameter. By tracking the movement of the squeezed cell as it is driven by a controlled pressure drop, we measure the RBC velocity as a function of the pressure gradient as well as the local capillary diameter, and find that the effective blood viscosity in this regime increases with both decreasing RBC velocity and tube radius by following a power-law that depends upon the length of the confined cell. Our observations are consistent with a simple elasto-hydrodynamic model and highlight the role of lateral confinement in the occluded pressure-driven slow flow of soft confined objects.

Open-ocean boundary conditions from interior data: Local and remote forcing of Massachusetts Bay

USGS Publications Warehouse

Bogden, P.S.; Malanotte-Rizzoli, P.; Signell, R.

1996-01-01

Massachusetts and Cape Cod Bays form a semienclosed coastal basin that opens onto the much larger Gulf of Maine. Subtidal circulation in the bay is driven by local winds and remotely driven flows from the gulf. The local-wind forced flow is estimated with a regional shallow water model driven by wind measurements. The model uses a gravity wave radiation condition along the open-ocean boundary. Results compare reasonably well with observed currents near the coast. In some offshore regions however, modeled flows are an order of magnitude less energetic than the data. Strong flows are observed even during periods of weak local wind forcing. Poor model-data comparisons are attributable, at least in part, to open-ocean boundary conditions that neglect the effects of remote forcing. Velocity measurements from within Massachusetts Bay are used to estimate the remotely forced component of the flow. The data are combined with shallow water dynamics in an inverse-model formulation that follows the theory of Bennett and McIntosh [1982], who considered tides. We extend their analysis to consider the subtidal response to transient forcing. The inverse model adjusts the a priori open-ocean boundary condition, thereby minimizing a combined measure of model-data misfit and boundary condition adjustment. A "consistency criterion" determines the optimal trade-off between the two. The criterion is based on a measure of plausibility for the inverse solution. The "consistent" inverse solution reproduces 56% of the average squared variation in the data. The local-wind-driven flow alone accounts for half of the model skill. The other half is attributable to remotely forced flows from the Gulf of Maine. The unexplained 44% comes from measurement errors and model errors that are not accounted for in the analysis. 

Efficacy and safety of strategies to preserve stable extracorporeal life support flow during simulated hypovolemia.

PubMed

Simons, A P; Lindelauf, A A M A; Ganushchak, Y M; Maessen, J G; Weerwind, P W

2014-01-01

Without volume-buffering capacity in extracorporeal life support (ELS) systems, hypovolemia can acutely reduce support flow. This study aims at evaluating efficacy and safety of strategies for preserving stable ELS during hypovolemia. Flow and/or pressure-guided servo pump control, a reserve-driven control strategy and a volume buffer capacity (VBC) device were evaluated with respect to pump flow, venous line pressure and arterial gaseous microemboli (GME) during simulated normovolemia and hypovolemia. Normovolemia resulted in a GME-free pump flow of 3.1 ± 0.0 L/min and a venous line pressure of -10 ± 1 mmHg. Hypovolemia without servo pump control resulted in a GME-loaded flow of 2.3 ± 0.4 L/min with a venous line pressure of -114 ± 52 mmHg. Servo control resulted in an unstable and GME-loaded flow of 1.5 ± 1.2 L/min. With and without servo pump control, the VBC device stabilised flow (SD = 0.2 and 0.0 L/min, respectively) and venous line pressure (SD=51 and 4 mmHg, respectively) with near-absent GME activity. Reserve-driven pump control combined with a VBC device restored a near GME-free flow of 2.7 ± 0.0 L/min with a venous line pressure of -9 ± 0 mmHg. In contrast to a reserve-driven pump control strategy combined with a VBC device, flow and pressure servo control for ELS show evident deficits in preserving stable and safe ELS flow during hypovolemia.

Microfluidic converging/diverging channels optimised for homogeneous extensional deformation.

PubMed

Zografos, K; Pimenta, F; Alves, M A; Oliveira, M S N

2016-07-01

In this work, we optimise microfluidic converging/diverging geometries in order to produce constant strain-rates along the centreline of the flow, for performing studies under homogeneous extension. The design is examined for both two-dimensional and three-dimensional flows where the effects of aspect ratio and dimensionless contraction length are investigated. Initially, pressure driven flows of Newtonian fluids under creeping flow conditions are considered, which is a reasonable approximation in microfluidics, and the limits of the applicability of the design in terms of Reynolds numbers are investigated. The optimised geometry is then used for studying the flow of viscoelastic fluids and the practical limitations in terms of Weissenberg number are reported. Furthermore, the optimisation strategy is also applied for electro-osmotic driven flows, where the development of a plug-like velocity profile allows for a wider region of homogeneous extensional deformation in the flow field.

Microfluidic converging/diverging channels optimised for homogeneous extensional deformation

PubMed Central

Zografos, K.; Oliveira, M. S. N.

2016-01-01

In this work, we optimise microfluidic converging/diverging geometries in order to produce constant strain-rates along the centreline of the flow, for performing studies under homogeneous extension. The design is examined for both two-dimensional and three-dimensional flows where the effects of aspect ratio and dimensionless contraction length are investigated. Initially, pressure driven flows of Newtonian fluids under creeping flow conditions are considered, which is a reasonable approximation in microfluidics, and the limits of the applicability of the design in terms of Reynolds numbers are investigated. The optimised geometry is then used for studying the flow of viscoelastic fluids and the practical limitations in terms of Weissenberg number are reported. Furthermore, the optimisation strategy is also applied for electro-osmotic driven flows, where the development of a plug-like velocity profile allows for a wider region of homogeneous extensional deformation in the flow field. PMID:27478523

Mechanistic basis of otolith formation during teleost inner ear development

PubMed Central

Wu, David; Freund, Jonathan B.; Fraser, Scott E.; Vermot, Julien

2011-01-01

Otoliths, which are connected to stereociliary bundles in the inner ear, serve as inertial sensors for balance. In teleostei, otolith development is critically dependant on flow forces generated by beating cilia; however, the mechanism by which flow controls otolith formation remains unclear. Here, we have developed a non-invasive flow probe using optical tweezers and a viscous flow model in order to demonstrate how the observed hydrodynamics influence otolith assembly. We show that rotational flow stirs and suppresses precursor agglomeration in the core of the cilia-driven vortex. The velocity field correlates with the shape of the otolith and we provide evidence that hydrodynamics is actively involved in controlling otolith morphogenesis. An implication of this hydrodynamic effect is that otolith self-assembly is mediated by the balance between Brownian motion and cilia-driven flow. More generally, this flow feature highlights an alternative biological strategy for controlling particle localization in solution. PMID:21316594

Glory, Vortex Street off Baja California

NASA Technical Reports Server (NTRS)

2007-01-01

On June 19, 2007, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured both a vortex street and a glory visible amid the lattice of clouds over the Pacific Ocean off Baja California. In this image, the swirling clouds known as vortex streets appear along the left edge of the image, stretching southward from Isla Guadalupe. Another NASA satellite captured an earlier example of vortex streets in June 2000. These atmospheric vortices, known as Von Karman vortex streets, often occur in the wake of an obstacle to air flow, such as an island. Stratocumulus clouds--low-lying, sheets of puffy clouds-- over the ocean show the impact of the island on air flow visible though their alternating pattern of clockwise and counter-clockwise swirls. Southeast of the vortex street, a glory, which resembles a rainbow, hovers above the cloud cover. The glory is faint but large, 200 to 300 kilometers long, along a north-south orientation. This phenomenon can occur when the satellite passes directly between the Sun and a bank of clouds below. (People also observe them while looking down on clouds from airplanes.) Not just any kind of cloud can produce a glory; only clouds composed entirely of water droplets (as opposed to ice crystals) can make them. The droplets that form glories generally have diameters of less than 50 micrometers (a micrometers is a millionth of a meter). The water droplets bend the light, showing its different wavelengths, or colors. In this glory, reds and oranges are most visible. NASA image by Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center.

Pulsating Flows in a Tube with Expandable Wall

NASA Astrophysics Data System (ADS)

Raguso, Frank; Goushcha, Oleg

2017-11-01

A mean axial fluid flow inside a cardiovascular system has a periodic behavior driven by a heart. In one period, the flow through aorta is accelerated to a Reynolds number associated with turbulent flow and decelerated to nearly stagnant condition. The cyclic pressure in the aorta also exerts time-dependent forces on the walls of the cardiovascular system. Since walls are not rigid, they can expand under fluidic pressure. It is of interest to examine the effect of expandable walls on the flow regime transition. To achieve this, an experimental apparatus has been set up. The periodic mean axial flow inside the tubes is driven by a motor-controlled piston programmed to induce a periodic flow. A time-resolved particle image velocimetry method has been used to calculate the flow velocity field in two tubes: (1) a rigid tube and (2) a flexible tube with expandable walls. The velocity fields from two tubes were comparted to identify any differences in flow transition mechanisms.

Electro-osmotically driven liquid delivery method and apparatus

DOEpatents

Rakestraw, D.J.; Anex, D.S.; Yan, C.; Dadoo, R.; Zare, R.N.

1999-08-24

Method and apparatus are disclosed for controlling precisely the composition and delivery of liquid at sub-{micro}L/min flow rate. One embodiment of such a delivery system is an electro-osmotically driven gradient flow delivery system that generates dynamic gradient flows with sub-{micro}L/min flow rates by merging a plurality of electro-osmotic flows. These flows are delivered by a plurality of delivery arms attached to a mixing connector, where they mix and then flow into a receiving means, preferably a column. Each inlet of the plurality of delivery arms is placed in a corresponding solution reservoir. A plurality of independent programmable high-voltage power supplies is used to apply a voltage program to each of the plurality of solution reservoirs to regulate the electro-osmotic flow in each delivery arm. The electro-osmotic flow rates in the delivery arms are changed with time according to each voltage program to deliver the required gradient profile to the column. 4 figs.

Contraction driven flow in the extended vein networks of Physarum polycephalum

NASA Astrophysics Data System (ADS)

Alim, Karen; Amselem, Gabriel; Peaudecerf, Francois; Pringle, Anne; Brenner, Michael P.

2011-11-01

The true slime mold Physarum polycephalum is a basal organism that forms an extended network of veins to forage for food. P. polycephalum is renown for its adaptive changes of vein structure and morphology in response to food sources. These rearrangements presumably occur to establish an efficient transport and mixing of resources throughout the networks thus presenting a prototype to design transport networks under the constraints of laminar flow. The physical flows of cytoplasmic fluid enclosed by the veins exhibit an oscillatory flow termed ``shuttle streaming.'' The flow exceed by far the volume required for growth at the margins suggesting that the additional energy cost for generating the flow is spent for efficient and/or targeted redistribution of resources. We show that the viscous shuttle flow is driven by the radial contractions of the veins that accompany the streaming. We present a model for the fluid flow and resource dispersion arising due to radial contractions. The transport and mixing properties of the flow are discussed.

Natural convection in melt crystal growth - The influence of flow pattern on solute segregation

NASA Technical Reports Server (NTRS)

Brown, R. A.; Yamaguchi, Y.; Chang, C. J.

1982-01-01

The results of two lines of research aimed at calculating the structure of the flows driven by buoyancy in small-scale crystal growth systems and at understanding the coupling between these flows, the shape of the solidification interface, and dopant segregation in the crystal are reviewed. First, finite-element methods are combined with computer-aided methods for detecting multiple steady solutions to analyze the structure of the buoyancy-driven axisymmetric flows in a vertical cylinder heated from below. This system exhibits onset of convection, multiple steady flows, and loss of the primary stable flow beyond a critical value of the Rayleigh number. Second, results are presented for calculations of convection, melt/solid interface shape, and dopant segregation within a vertical ampoule with thermal boundary conditions that represent a prototype of the vertical Bridgman growth system.

Spatio-temporal organization of dynamics in a two-dimensional periodically driven vortex flow: A Lagrangian flow network perspective.

PubMed

Lindner, Michael; Donner, Reik V

2017-03-01

We study the Lagrangian dynamics of passive tracers in a simple model of a driven two-dimensional vortex resembling real-world geophysical flow patterns. Using a discrete approximation of the system's transfer operator, we construct a directed network that describes the exchange of mass between distinct regions of the flow domain. By studying different measures characterizing flow network connectivity at different time-scales, we are able to identify the location of dynamically invariant structures and regions of maximum dispersion. Specifically, our approach allows us to delimit co-existing flow regimes with different dynamics. To validate our findings, we compare several network characteristics to the well-established finite-time Lyapunov exponents and apply a receiver operating characteristic analysis to identify network measures that are particularly useful for unveiling the skeleton of Lagrangian chaos.

Medication and volume delivery by gravity-driven micro-drip intravenous infusion: potential variations during "wide-open" flow.

PubMed

Pierce, Eric T; Kumar, Vikram; Zheng, Hui; Peterfreund, Robert A

2013-03-01

Gravity-driven micro-drip infusion sets allow control of medication dose delivery by adjusting drops per minute. When the roller clamp is fully open, flow in the drip chamber can be a continuous fluid column rather than discrete, countable, drops. We hypothesized that during this "wide-open" state, drug delivery becomes dependent on factors extrinsic to the micro-drip set and is therefore difficult to predict. We conducted laboratory experiments to characterize volume delivery under various clinically relevant conditions of wide-open flow in an in vitro laboratory model. A micro-drip infusion set, plugged into a bag of normal saline, was connected to a high-flow stopcock at the distal end. Vertically oriented IV catheters (gauges 14-22) were connected to the stopcock. The fluid meniscus height in the bag was fixed (60-120 cm) above the outflow point. The roller clamp on the infusion set was in fully open position for all experiments resulting in a continuous column of fluid in the drip chamber. Fluid volume delivered in 1 minute was measured 4 times with each condition. To model resistive effects of carrier flow, volumetric infusion pumps were used to deliver various flow rates of normal saline through a carrier IV set into which a micro-drip infusion was "piggybacked." We also compared delivery by micro-drip infusion sets from 3 manufacturers. The volume of fluid delivered by gravity-driven infusion under wide-open conditions (continuous fluid column in drip chamber) varied 2.9-fold (95% confidence interval, 2.84-2.96) depending on catheter size and fluid column height. Total model resistance of the micro-drip with stopcock and catheter varied with flow rate. Volume delivered by the piggybacked micro-drip decreased up to 29.7% ± 0.8% (mean ± SE) as the carrier flow increased from 0 to 1998 mL/min. Delivery characteristics of the micro-drip infusion sets from 3 different manufacturers were similar. Laboratory simulation of clinical situations with gravity-driven micro-drip infusion sets under wide-open flow conditions revealed that infusion rate (drug and/or volume delivery) can vary widely depending on extrinsic factors including catheter size, fluid column height, and carrier flow. The variable resistance implies nonlaminar flow in the micro-drip model that cannot be easily predicted mathematically. These findings support the use of mechanical pumps instead of gravity-driven micro-drips to enhance the precision and safety of IV infusions, especially for vasoactive drugs.

Microgravity Segregation in Binary Mixtures of Inelastic Spheres Driven by Velocity Fluctuation Gradients

NASA Technical Reports Server (NTRS)

Jenkins, James T.; Louge, Michel Y.

1996-01-01

We are interested in collisional granular flows of dry materials in reduced gravity. Because the particles interact through collisions, the energy of the particle velocity fluctuations plays an important role in the physics. Here we focus on the separation of grains by properties - size, for example - that is driven by spatial gradients in the fluctuation energy of the grains. The segregation of grains by size is commonly observed in geophysical flows and industrial processes. Segregation of flowing grains can also take place based on other properties, e.g. shape, mass, friction, and coefficient of restitution. Many mechanisms may be responsible for segregation; most of these are strongly influenced by gravity. Here, we outline a mechanism that is independent of gravity. This mechanism may be important but is often obscured in terrestrial grain flows. It is driven by gradients in fluctuation energy. In microgravity, the separation of grains by property will proceed slowly enough to permit flight observations to provide an unambiguous measurement of the transport coefficients associated with the segregation. In this context, we are planning a microgravity shear cell experiment that contains a mixture of two types of spherical grains. The grains will be driven to interact with two different types of boundaries on either sides of the cell. The resulting separation will be observed visually.

Pressure-Driven Poiseuille Flow: A Major Component of the Torque-Balance Governing Pacific Plate Motion

NASA Astrophysics Data System (ADS)

Stotz, I. L.; Iaffaldano, G.; Davies, D. R.

2018-01-01

The Pacific Plate is thought to be driven mainly by slab pull, associated with subduction along the Aleutians-Japan, Marianas-Izu-Bonin, and Tonga-Kermadec trenches. This implies that viscous flow within the sub-Pacific asthenosphere is mainly generated by overlying plate motion (i.e., Couette flow) and that the associated shear stresses at the lithosphere's base are resisting such motion. Recent studies on glacial isostatic adjustment and lithosphere dynamics provide tighter constraints on the viscosity and thickness of Earth's asthenosphere and, therefore, on the amount of shear stress that asthenosphere and lithosphere mutually exchange, by virtue of Newton's third law of motion. In light of these constraints, the notion that subduction is the main driver of present-day Pacific Plate motion becomes somewhat unviable, as the pulling force that would be required by slabs exceeds the maximum available from their negative buoyancy. Here we use coupled global models of mantle and lithosphere dynamics to show that the sub-Pacific asthenosphere features a significant component of pressure-driven (i.e., Poiseuille) flow and that this has driven at least 50% of the Pacific Plate motion since, at least, 15 Ma. A corollary of our models is that a sublithospheric pressure difference as high as ±50 MPa is required across the Pacific domain.

Aerodynamic and Thermal Performance Characteristics of Supersonic-X Type Decelerators at Mach Number 8

DTIC Science & Technology

1977-02-01

SUPERSONIC -X TYPE DECELERATORS AT MACH NUMBER 8 t’z.r I # I JJ’, o,. VON KARMAN GAS DYNAMICS FACILITY ARNOLD ENGINEERING DEVELOPMENT CENTER AIR FORCE...AERODYNAMIC AND THERMAL PERFORMANCE CHARACTERISTICS OF SUPERSONIC - X TYPE DECELERATORS AT MACH NUMBER 8 ’ 7 AU THORCs,: p ; J . D. Corce , ARO, Inc...pe r fo rmance cha rac t e r i s t i c s of model nylon, Kevlar 29, and Bisbenzimidazobenzophenanthroline Supersonic -X type parachutes behind a

Large amplitude vibrations of laminated hybrid composite plates

NASA Astrophysics Data System (ADS)

Sarma, M. S.; Venkateshwar Rao, A.; Pillai, S. R. R.; Nageswara Rao, B.

1992-12-01

A general equation of motion for the nonlinear vibration of a rectangular plate is formulated using Kirchhoff's hypothesis and von Karman type strain-displacement relations. The formulation includes in-plane deformations and neglects the corresponding inertia terms. The amplitudes are written under assumption that mode shapes are approximately the fundamental modes which satisfy the boundary conditions of the problem. It is shown that the method can be used to easily calculate an excellent aproximation to the periodic solutions of the nonlinear antisymmetric quadratic oscillator.

Vortex-Airfoil Interaction and Application of Methods for Digital Fringe Analysis.

DTIC Science & Technology

1986-03-15

angles of attack. Different kinds of bluff bodies are used as vortex generators. Their wake is a Karman vortex street consisting of strong vortices of...Table of Contents 1. Introduction 1 2. A model for vortex paths around a profile and the sound generated by vortex -profile interaction 2"-- 3...I’ S.TTE(d~,t. TYPE OF PIrPORT a PERID COWERED ’. * Vortex -airfoil interaction and application of *methods for digital fringe analysis . 1 6

Earth Observation

NASA Image and Video Library

2014-06-20

ISS040-E-016422 (20 June 2014) --- One of the Expedition 40 crew members aboard the International Space Station used a 28mm focal length to record this long stretch of California's Pacific Coast on June 20, 2014. Guadalupe Island and the surrounding von Karman cloud vortices over the Pacific can be seen just above frame center. San Diego is visible in upper left and the Los Angeles Basin is just to the left of center frame. Much of the Mojave Desert is visible in bottom frame.

MIT Lincoln Laboratory: Technology in Support of National Security

DTIC Science & Technology

2011-01-01

not display a currently valid OMB control number. 1. REPORT DATE 2011 2. REPORT TYPE 3. DATES COVERED 00-00-2011 to 00-00-2011 4. TITLE AND...in a letter dated October 3, 1960, from Brigadier General Charles Terhune, Jr., U.S. Air Force, to Carl Overhage, director of Lincoln Laboratory...Karman asked Valley to put his concerns in writing, and Valley did in a letter dated November 8, 1949. In a key paragraph, he wrote: “I therefore

Nonlinear dynamics and control of a vibrating rectangular plate

NASA Technical Reports Server (NTRS)

Shebalin, J. V.

1983-01-01

The von Karman equations of nonlinear elasticity are solved for the case of a vibrating rectangular plate by meams of a Fourier spectral transform method. The amplification of a particular Fourier mode by nonlinear transfer of energy is demonstrated for this conservative system. The multi-mode system is reduced to a minimal (two mode) system, retaining the qualitative features of the multi-mode system. The effect of a modal control law on the dynamics of this minimal nonlinear elastic system is examined.

The Unsteady Temperature Field in a Turbine Blade Cooling Channel

DTIC Science & Technology

2003-03-01

SYB) 39-1 The Unsteady Temperature Field in a Turbine Blade Cooling Channel T . Arts Von Karman Institute for Fluid Dynamics 72, chausse de Waterloo...wall coordinates (y+ and T +) are used for this purpose: ν = − ρ−= τ+τ + uyy q TT uCT wall wall p (1) (SYB) 39...poor performance of the Baldwin-Lomax model and, up to some extent, of the standard k-ε model (Fig. 5). 0 5 10 15 20 25 1 10 100 1000 10000 Y+ T

The transport of vorticity through fluids in turbulent motion : in the light of the Prandtl and Taylor theories

NASA Technical Reports Server (NTRS)

Ferrari, C

1936-01-01

The report studies the problem of the transport of vorticity or of momentum in light of the Taylor and Prandtl theories which are briefly reviewed. It also show how the formulas of Prandtl could be brought into agreement with experimental results in those cases where they agree with the principle of statistic similitude of Karman, and particularly in the problem of the distribution of velocity and temperature in the wake of a heated cylindrical obstacle.

Scramjet Thermal Management (Tenue thermique des superstatoreacteurs)

DTIC Science & Technology

2010-09-01

RTO-EN-AVT-185 13 - 1 Scramjet Thermal Management (Tenue thermique des superstatoréacteurs) Marc BOUCHEZ MBDA France Rond-point Marcel...SPEED PROPULSION: ENGINE DESIGN – INTEGRATION AND THERMAL MANAGEMENT” fut donné à l’Institut Von Karman en septembre 2010 et à l’Université Wright de ...Dayton (Ohio, USA) en décembre 2010. Le présent cours aborde la tenue thermique. Il est basé sur des informations publiées, et des détails

Aeroelasticity - Frontiers and beyond /von Karman Lecture/

NASA Technical Reports Server (NTRS)

Garrick, I. E.

1976-01-01

The lecture aims at giving a broad survey of the current reaches of aeroelasticity with some narrower views for the specialist. After a short historical review of concepts for orientation, several topics are briefly presented. These touch on current flight vehicles having special points of aeroelastic interest; recent developments in the active control of aeroelastic response including control of flutter; remarks on the unsteady aerodynamics of arbitrary configurations; problems of the space shuttle related to aeroelasticity; and aeroelastic response in flight.

Entry-probe studies of the atmospheres of earth, Mars, and Venus - A review (Von Karman Lecture)

NASA Technical Reports Server (NTRS)

Seiff, Alvin

1990-01-01

This paper overviews the history (since 1963) of the exploration of planetary atmospheres by use of entry probes. The techniques used to measure the compositions of the atmospheres of the earth, Mars, and Venus are described together with the key results obtained. Attention is also given to the atmosphere-structure experiment aboard the Galileo Mission, launched on October 17, 1989 and now under way on its 6-yr trip to Jupiter, and to future experiments.

The USAF Scientific Advisory Board: Its First Twenty Years. 1944-1964

DTIC Science & Technology

1967-02-01

responsibility for substantive rather than administrative matters.൒ In early 1963, with the chore of reducing board membership out of the way , SAB...humor. Before the war, a near-disastrous gulf had opened between American men of arms and science at ;. the top levels. This was Arnold’s way ...von Karman and the other distinguished civilian scientists who answered Arnold’s call opened the way to an enduring partner- •> ship. [’• k The

TopoDrive and ParticleFlow--Two Computer Models for Simulation and Visualization of Ground-Water Flow and Transport of Fluid Particles in Two Dimensions

USGS Publications Warehouse

Hsieh, Paul A.

2001-01-01

This report serves as a user?s guide for two computer models: TopoDrive and ParticleFlow. These two-dimensional models are designed to simulate two ground-water processes: topography-driven flow and advective transport of fluid particles. To simulate topography-driven flow, the user may specify the shape of the water table, which bounds the top of the vertical flow section. To simulate transport of fluid particles, the model domain is a rectangle with overall flow from left to right. In both cases, the flow is under steady state, and the distribution of hydraulic conductivity may be specified by the user. The models compute hydraulic head, ground-water flow paths, and the movement of fluid particles. An interactive visual interface enables the user to easily and quickly explore model behavior, and thereby better understand ground-water flow processes. In this regard, TopoDrive and ParticleFlow are not intended to be comprehensive modeling tools, but are designed for modeling at the exploratory or conceptual level, for visual demonstration, and for educational purposes.

Unstart phenomena induced by flow choking in scramjet inlet-isolators

NASA Astrophysics Data System (ADS)

Im, Seong-kyun; Do, Hyungrok

2018-02-01

A review of recent research outcomes in downstream flow choking-driven unstart is presented. Unstart is a flow phenomenon at the inlet that severely reduces the air mass flow rate through the engine, causing a loss of thrust and considerable transient mechanical loading. Therefore, unstart in a scramjet engine crucially affects the design and the operation range of hypersonic vehicles. Downstream flow choking is known to be one of the major mechanisms inducing inlet unstart, as confirmed by recent scramjet-powered flight tests. The current paper examines recent research progress in identifying flow choking mechanisms that trigger unstart. Three different flow choking mechanisms are discussed: flow blockage, mass addition, and heat release from combustion reactions. Current research outcomes on the characteristic of unstarting flows, such as transient and quasi-steady motions, are reviewed for each flow choking mechanism. The characteristics of unstarted flows are described including Buzzing phenomena and oscillatory motions of unstarted shockwaves. Then, the state-of-the-art methods to predict, detect, and control unstart are presented. The review suggests that further investigations with high-enthalpy ground facilities will aid understanding of heat release-driven unstart.

Disruption of a cyclonic eddy circulation by wind stress in Prince William Sound, Alaska

NASA Astrophysics Data System (ADS)

Halverson, Mark J.; Carter Ohlmann, J.; Johnson, Mark A.; Scott Pegau, W.

2013-07-01

Oceanographic observations made during the Sound Predictions 2009 field experiment in Prince William Sound, Alaska, have documented rapid changes in the upper water column (0-40m) circulation. An assortment of drifting buoys, sampling four different depths, and HF radar surface current mapping, revealed three modes of circulation: anticyclonic, open cyclonic, and closed cyclonic. Each mode was observed at least once within an 18-day window, and the transition between them took as little as a day. Time-resolved hydrographic measurements show that the mass field was variable, but generally arranged such that the surface geostrophic flow should be in a closed-core cyclonic eddy configuration. Observations show that the mass field was likely influenced by relatively low salinity water flowing into Prince William Sound from the shelf, and from local freshwater input. We quantitatively examine why a closed-core circulation was not always observed by focusing on the transition between the closed and open cyclonic flow patterns. The western region of the central sound is a key area for this transition. Here, the high-frequency radar revealed that the closed circulation was established when the net flow shifted direction from northward to southward. A detailed comparison of the meridional geostrophic and wind-driven flows, using measured winds and hydrographic data from CTD profiles and two autonomous vehicles, shows that the geostrophic flow was mostly southward while the wind-driven flow was mostly northward. A net southward flow can be caused by a decrease in the northward wind-driven flow or an increase in the southward geostrophic flow.

Space-based laser-driven MHD generator: Feasibility study

NASA Technical Reports Server (NTRS)

Choi, S. H.

1986-01-01

The feasibility of a laser-driven MHD generator, as a candidate receiver for a space-based laser power transmission system, was investigated. On the basis of reasonable parameters obtained in the literature, a model of the laser-driven MHD generator was developed with the assumptions of a steady, turbulent, two-dimensional flow. These assumptions were based on the continuous and steady generation of plasmas by the exposure of the continuous wave laser beam thus inducing a steady back pressure that enables the medium to flow steadily. The model considered here took the turbulent nature of plasmas into account in the two-dimensional geometry of the generator. For these conditions with the plasma parameters defining the thermal conductivity, viscosity, electrical conductivity for the plasma flow, a generator efficiency of 53.3% was calculated. If turbulent effects and nonequilibrium ionization are taken into account, the efficiency is 43.2%. The study shows that the laser-driven MHD system has potential as a laser power receiver for space applications because of its high energy conversion efficiency, high energy density and relatively simple mechanism as compared to other energy conversion cycles.

Vibration isolation in a free-piston driven expansion tube facility

NASA Astrophysics Data System (ADS)

Gildfind, D. E.; Jacobs, P. A.; Morgan, R. G.

2013-09-01

The stress waves produced by rapid piston deceleration are a fundamental feature of free-piston driven expansion tubes, and wave propagation has to be considered in the design process. For lower enthalpy test conditions, these waves can traverse the tube ahead of critical flow processes, severely interfering with static pressure measurements of the passing flow. This paper details a new device which decouples the driven tube from the free-piston driver, and thus prevents transmission of stress waves. Following successful incorporation of the concept in the smaller X2 facility, it has now been applied to the larger X3 facility, and results for both facilities are presented.

Grouping of optic flow stimuli during binocular rivalry is driven by monocular information.

PubMed

Holten, Vivian; Stuit, Sjoerd M; Verstraten, Frans A J; van der Smagt, Maarten J

2016-10-01

During binocular rivalry, perception alternates between two dissimilar images, presented dichoptically. Although binocular rivalry is thought to result from competition at a local level, neighboring image parts with similar features tend to be perceived together for longer durations than image parts with dissimilar features. This simultaneous dominance of two image parts is called grouping during rivalry. Previous studies have shown that this grouping depends on a shared eye-of-origin to a much larger extent than on image content, irrespective of the complexity of a static image. In the current study, we examine whether grouping of dynamic optic flow patterns is also primarily driven by monocular (eye-of-origin) information. In addition, we examine whether image parameters, such as optic flow direction, and partial versus full visibility of the optic flow pattern, affect grouping durations during rivalry. The results show that grouping of optic flow is, as is known for static images, primarily affected by its eye-of-origin. Furthermore, global motion can affect grouping durations, but only under specific conditions. Namely, only when the two full optic flow patterns were presented locally. These results suggest that grouping during rivalry is primarily driven by monocular information even for motion stimuli thought to rely on higher-level motion areas. Copyright © 2016 Elsevier Ltd. All rights reserved.

Multiphase groundwater flow near cooling plutons

USGS Publications Warehouse

Hayba, D.O.; Ingebritsen, S.E.

1997-01-01

We investigate groundwater flow near cooling plutons with a computer program that can model multiphase flow, temperatures up to 1200??C, thermal pressurization, and temperature-dependent rock properties. A series of experiments examines the effects of host-rock permeability, size and depth of pluton emplacement, single versus multiple intrusions, the influence of a caprock, and the impact of topographically driven groundwater flow. We also reproduce and evaluate some of the pioneering numerical experiments on flow around plutons. Host-rock permeability is the principal factor influencing fluid circulation and heat transfer in hydrothermal systems. The hottest and most steam-rich systems develop where permeability is of the order of 10-15 m2. Temperatures and life spans of systems decrease with increasing permeability. Conduction-dominated systems, in which permeabilities are ???10-16m2, persist longer but exhibit relatively modest increases in near-surface temperatures relative to ambient conditions. Pluton size, emplacement depth, and initial thermal conditions have less influence on hydrothermal circulation patterns but affect the extent of boiling and duration of hydrothermal systems. Topographically driven groundwater flow can significantly alter hydrothermal circulation; however, a low-permeability caprock effectively decouples the topographically and density-driven systems and stabilizes the mixing interface between them thereby defining a likely ore-forming environment.

Understanding L-H transition in tokamak fusion plasmas

NASA Astrophysics Data System (ADS)

Xu, Guosheng; Wu, Xingquan

2017-03-01

This paper reviews the current state of understanding of the L-H transition phenomenon in tokamak plasmas with a focus on two central issues: (a) the mechanism for turbulence quick suppression at the L-H transition; (b) the mechanism for subsequent generation of sheared flow. We briefly review recent advances in the understanding of the fast suppression of edge turbulence across the L-H transition. We uncover a comprehensive physical picture of the L-H transition by piecing together a number of recent experimental observations and insights obtained from 1D and 2D simulation models. Different roles played by diamagnetic mean flow, neoclassical-driven mean flow, turbulence-driven mean flow, and turbulence-driven zonal flows are discussed and clarified. It is found that the L-H transition occurs spontaneously mediated by a shift in the radial wavenumber spectrum of edge turbulence, which provides a critical evidence for the theory of turbulence quench by the flow shear. Remaining questions and some key directions for future investigations are proposed. This work was supported by National Magnetic Confinement Fusion Science Program of China under Contracts No. 2015GB101000, No. 2013GB106000, and No. 2013GB107000 and National Natural Science Foundation of China under Contracts No. 11575235 and No. 11422546.

Rapid and efficient mixing in a slip-driven three-dimensional flow in a rectangular channel

NASA Astrophysics Data System (ADS)

Pacheco, J. Rafael; Ping Chen, Kang; Hayes, Mark A.

2006-08-01

A method for generating mixing in an electroosmotic flow of an electrolytic solution in a three-dimensional channel is proposed. When the width-to-height aspect ratio of the channel cross-section is large, mixing of a blob of a solute in a slip-driven three-dimensional flow in a rectangular channel can be used to model and assess the effectiveness of this method. It is demonstrated through numerical simulations that under certain operating conditions, rapid and efficient mixing can be achieved. Future investigation will include the solution of the exact equations and experimentation.

Validity of thermally-driven small-scale ventilated filling box models

NASA Astrophysics Data System (ADS)

Partridge, Jamie L.; Linden, P. F.

2013-11-01

The majority of previous work studying building ventilation flows at laboratory scale have used saline plumes in water. The production of buoyancy forces using salinity variations in water allows dynamic similarity between the small-scale models and the full-scale flows. However, in some situations, such as including the effects of non-adiabatic boundaries, the use of a thermal plume is desirable. The efficacy of using temperature differences to produce buoyancy-driven flows representing natural ventilation of a building in a small-scale model is examined here, with comparison between previous theoretical and new, heat-based, experiments.

Scaling laws in granular flow and pedestrian flow

NASA Astrophysics Data System (ADS)

Chen, Shumiao; Alonso-Marroquin, Fernando; Busch, Jonathan; Hidalgo, Raúl Cruz; Sathianandan, Charmila; Ramírez-Gómez, Álvaro; Mora, Peter

2013-06-01

We use particle-based simulations to examine the flow of particles through an exit. Simulations involve both gravity-driven particles (representing granular material) and velocity-driven particles (mimicking pedestrian dynamics). Contact forces between particles include elastic, viscous, and frictional forces; and simulations use bunker geometry. Power laws are observed in the relation between flow rate and exit width. Simulations of granular flow showed that the power law has little dependence on the coefficient of friction. Polydisperse granular systems produced higher flow rates than those produced by monodisperse ones. We extend the particle model to include the main features of pedestrian dynamics: thoracic shape, shoulder rotation, and desired velocity oriented towards the exit. Higher desired velocity resulted in higher flow rate. Granular simulations always give higher flow rate than pedestrian simulations, despite the values of aspect ratio of the particles. In terms of force distribution, pedestrians and granulates share similar properties with the non-democratic distribution of forces that poses high risks of injuries in a bottleneck situation.

Force Evaluation in the Lattice Boltzmann Method Involving Curved Geometry

NASA Technical Reports Server (NTRS)

Mei, Renwei; Yu, Dazhi; Shyy, Wei; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)

2002-01-01

The present work investigates two approaches for force evaluation in the lattice Boltzmann equation: the momentum- exchange method and the stress-integration method on the surface of a body. The boundary condition for the particle distribution functions on curved geometries is handled with second order accuracy based on our recent works. The stress-integration method is computationally laborious for two-dimensional flows and in general difficult to implement for three-dimensional flows, while the momentum-exchange method is reliable, accurate, and easy to implement for both two-dimensional and three-dimensional flows. Several test cases are selected to evaluate the present methods, including: (i) two-dimensional pressure-driven channel flow; (ii) two-dimensional uniform flow past a column of cylinders; (iii) two-dimensional flow past a cylinder asymmetrically placed in a channel (with vortex shedding); (iv) three-dimensional pressure-driven flow in a circular pipe; and (v) three-dimensional flow past a sphere. The drag evaluated by using the momentum-exchange method agrees well with the exact or other published results.

Re-evaluation of heat flow data near Parkfield, CA: Evidence for a weak San Andreas Fault

USGS Publications Warehouse

Fulton, P.M.; Saffer, D.M.; Harris, Reid N.; Bekins, B.A.

2004-01-01

Improved interpretations of the strength of the San Andreas Fault near Parkfield, CA based on thermal data require quantification of processes causing significant scatter and uncertainty in existing heat flow data. These effects include topographic refraction, heat advection by topographically-driven groundwater flow, and uncertainty in thermal conductivity. Here, we re-evaluate the heat flow data in this area by correcting for full 3-D terrain effects. We then investigate the potential role of groundwater flow in redistributing fault-generated heat, using numerical models of coupled heat and fluid flow for a wide range of hydrologic scenarios. We find that a large degree of the scatter in the data can be accounted for by 3-D terrain effects, and that for plausible groundwater flow scenarios frictional heat generated along a strong fault is unlikely to be redistributed by topographically-driven groundwater flow in a manner consistent with the 3-D corrected data. Copyright 2004 by the American Geophysical Union.

Flow enhancement of deformable self-driven objects by countercurrent

NASA Astrophysics Data System (ADS)

Mashiko, Takashi; Fujiwara, Takashi

2016-10-01

We report numerical simulations of the mixed flows of two groups of deformable self-driven objects. The objects belonging to the group A (B) have drift coefficient D =DA (DB), where a positive (negative) value of D denotes the rightward (leftward) driving force. For co-current flows (DA ,DB > 0), the result is rather intuitive: the net flow of one group (QA) increases if the driving force of the other group is stronger than its own driving force (i.e., DB >DA), and decreases otherwise (DB

Microfluidic diffusion diluter: bulging of PDMS microchannels under pressure-driven flow

NASA Astrophysics Data System (ADS)

Holden, Matthew A.; Kumar, Saurabh; Beskok, Ali; Cremer, Paul S.

2003-05-01

The bulging of microfluidic systems during pressure-driven flow is potentially a major consideration for polydimethylsiloxane (PDMS)-based devices. Microchannel cross-sectional areas can change drastically as a function of flow rate and downstream microchannel position. Such geometrical flexibility leads to difficulties in predicting convective/diffusive transport for these systems. We have previously introduced a non-dimensional parameter, kappa, for characterizing convection and diffusion behavior for pressure-driven flow in rigid all-glass systems. This paper describes a modification of that concept for application to non-rigid systems, which is accomplished by incorporating an experimental step to account for the bulging in PDMS/glass microsystems. Specifically, an experimental measurement of channel height by fluorescence microscopy is combined with the aforementioned theory to characterize convective/diffusive behavior at a single location in the device. This allowed the parameter kappa to be determined at that point and applied to predict fluid flow in the subsequent portion of the PDMS microsystem. This procedure was applied to a PDMS/glass microfluidic diffusion dilution (muDD) device designed for generating concentration gradients. Theoretically predicted and experimentally measured distributions of concentrations within the microsystem matched well.

Computational Fluid Dynamics Simulation of Flows in an Oxidation Ditch Driven by a New Surface Aerator.

PubMed

Huang, Weidong; Li, Kun; Wang, Gan; Wang, Yingzhe

2013-11-01

In this article, we present a newly designed inverse umbrella surface aerator, and tested its performance in driving flow of an oxidation ditch. Results show that it has a better performance in driving the oxidation ditch than the original one with higher average velocity and more uniform flow field. We also present a computational fluid dynamics model for predicting the flow field in an oxidation ditch driven by a surface aerator. The improved momentum source term approach to simulate the flow field of the oxidation ditch driven by an inverse umbrella surface aerator was developed and validated through experiments. Four kinds of turbulent models were investigated with the approach, including the standard k - ɛ model, RNG k - ɛ model, realizable k - ɛ model, and Reynolds stress model, and the predicted data were compared with those calculated with the multiple rotating reference frame approach (MRF) and sliding mesh approach (SM). Results of the momentum source term approach are in good agreement with the experimental data, and its prediction accuracy is better than MRF, close to SM. It is also found that the momentum source term approach has lower computational expenses, is simpler to preprocess, and is easier to use.

On plane submerged laminar jets

NASA Astrophysics Data System (ADS)

Coenen, Wilfried; Sanchez, Antonio L.

2016-11-01

We address the laminar flow generated when a developed stream of liquid of kinematic viscosity ν flowing along channel of width 2 h discharges into an open space bounded by two symmetric plane walls departing from the channel rim with an angle α 1 . Attention is focused on values of the jet volume flux 2 Q such that the associated Reynolds number Re = Qh / ν is of order unity. The formulation requires specification of the boundary conditions far from the channel exit. If the flow is driven by the volume flux, then the far-field solution corresponds to Jeffery-Hamel self-similar flow. However, as noted by Fraenkel (1962), such solutions exist only for α <129o in a limited range of Reynolds numbers 0 <=Re <=Rec (α) (e.g. Rec = 1 . 43 for α = π / 2). It is reasoned that an alternative solution, driven by a fraction of the momentum flux of the feed stream, may also exist for all values of Re and α, including a near-centerline Bickley jet, a surrounding Taylor potential flow driven by the jet entrainment, and a Falkner-Skan near-wall boundary layer. Numerical integrations of the Navier-Stokes equations are used to ascertain the existence of these different solutions.

Shear-flow trapped-ion-mode interaction revisited. II. Intermittent transport associated with low-frequency zonal flow dynamics

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

Ghizzo, A., E-mail: alain.ghizzo@univ-lorraine.fr; Palermo, F.

We address the mechanisms underlying low-frequency zonal flow generation in turbulent system and the associated intermittent regime of ion-temperature-gradient (ITG) turbulence. This model is in connection with the recent observation of quasi periodic zonal flow oscillation at a frequency close to 2 kHz, at the low-high transition, observed in the ASDEX Upgrade [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)] and EAST tokamak [Xu et al., Phys. Rev. Lett 107, 125001 (2011)]. Turbulent bursts caused by the coupling of Kelvin-Helmholtz (KH) driven shear flows with trapped ion modes (TIMs) were investigated by means of reduced gyrokinetic simulations. It was foundmore » that ITG turbulence can be regulated by low-frequency meso-scale zonal flows driven by resonant collisionless trapped ion modes (CTIMs), through parametric-type scattering, a process in competition with the usual KH instability.« less

Intermittent gravity-driven flow of grains through narrow pipes

NASA Astrophysics Data System (ADS)

Alvarez, Carlos A.; de Moraes Franklin, Erick

2017-01-01

Grain flows through pipes are frequently found in various settings, such as in pharmaceutical, chemical, petroleum, mining and food industries. In the case of size-constrained gravitational flows, density waves consisting of alternating high- and low-compactness regions may appear. This study investigates experimentally the dynamics of density waves that appear in gravitational flows of fine grains through vertical and slightly inclined pipes. The experimental device consisted of a transparent glass pipe through which different populations of glass spheres flowed driven by gravity. Our experiments were performed under controlled ambient temperature and relative humidity, and the granular flow was filmed with a high-speed camera. Experimental results concerning the length scales and celerities of density waves are presented, together with a one-dimensional model and a linear stability analysis. The analysis exhibits the presence of a long-wavelength instability, with the most unstable mode and a cut-off wavenumber whose values are in agreement with the experimental results.

Unsteady Specific Work and Isentropic Efficiency of a Radial Turbine Driven by Pulsed Detonations

DTIC Science & Technology

2012-06-14

iv AFIT/DS/ENY/12-25 Abstract There has been longstanding government and industry interest in pressure-gain combustion for use in Brayton cycle...10 III.A. Unsteady Flow in Conventional Brayton Cycle Turbines ........................10 III.B. Unsteady Flow in Pulsed Detonation Driven...Szpynda and Nalim 2007) 114 Figure 69. Heiser and Pratt comparison of ideal PDE, Humphrey, and Brayton cycles on a temperature-entropy diagram (Heiser

Flow-driven triboelectric generator for directly powering a wireless sensor node.

PubMed

Wang, Shuhua; Mu, Xiaojing; Yang, Ya; Sun, Chengliang; Gu, Alex Yuandong; Wang, Zhong Lin

2015-01-14

A triboelectric generator (TEG) for scavenging flow-driven mechanical -energy to directly power a wireless sensor node is demonstrated for the first time. The output performances of TEGs with different dimensions are systematically investigated, indicating that a largest output power of about 3.7 mW for one TEG can be achieved under an external load of 3 MΩ. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Flux-driven simulations of turbulence collapse

DOE PAGES

Park, G. Y.; Kim, S. S.; Jhang, Hogun; ...

2015-03-12

In this study, using self-consistent three-dimensional nonlinear simulations of tokamak turbulence, we show that an edge transport barrier (ETB) forms naturally due to mean E x B shear feedback through evolving pressure gradient once input power exceeds a threshold value. The temporal evolution and development of the transition are elucidated. Profiles, turbulence-driven flows and neoclassical coefficients are evolved self-consistently. A slow power ramp-up simulation shows that ETB transition is triggered by the turbulence-driven flows via an intermediate phase which involves coherent oscillation of turbulence intensity and E x B flow shear. A novel observation of the evolution is that themore » turbulence collapses and the ETB transition begins when R T > 1 at t = t R (R T : normalized Reynolds power), while the conventional transition criterion (ω E x B > γlin) is satisfied only after t = t C (> t R), when the mean ow shear grows due to positive feedback.« less

Onset of density-driven instabilities in fractured aquifers

NASA Astrophysics Data System (ADS)

Jafari Raad, Seyed Mostafa; Hassanzadeh, Hassan

2018-04-01

Linear stability analysis is conducted to study the onset of density-driven convection involved in solubility trapping of C O2 in fractured aquifers. The effect of physical properties of a fracture network on the stability of a diffusive boundary layer in a saturated fractured porous media is investigated using the dual porosity concept. Linear stability analysis results show that both fracture interporosity flow and fracture storativity play an important role in the stability behavior of the system. It is shown that a diffusive boundary layer under the gravity field in fractured porous media with lower fracture storativity and/or higher fracture interporosity flow coefficient is more stable. We present scaling relations for the onset of convective instability in fractured aquifers with single and variable matrix block size distribution. These findings improve our understanding of density-driven flow in fractured aquifers and are important in the estimation of potential storage capacity, risk assessment, and storage site characterization and screening.

A pressure-driven flow analysis of gas trapping behavior in nanocomposite thermite films

NASA Astrophysics Data System (ADS)

Sullivan, K. T.; Bastea, S.; Kuntz, J. D.; Gash, A. E.

2013-10-01

This article is in direct response to a recently published article entitled Electrophoretic deposition and mechanistic studies of nano-Al/CuO thermites (K. T. Sullivan et al., J. Appl. Phys., 112(2), 2012), in which we introduced a non-dimensional parameter as the ratio of gas production to gas escape within a thin porous thermite film. In our original analysis, we had treated the problem as Fickian diffusion of gases through the porous network. However, we believe a more physical representation of the problem is to treat this as pressure-driven flow of gases in a porous medium. We offer a new derivation of the non-dimensional parameter which calculates gas velocity using the well-known Poiseuille's Law for pressure-driven flow in a pipe. This updated analysis incorporates the porosity, gas viscosity, and pressure gradient into the equation.

In situ insights into shock-driven reactive flow

NASA Astrophysics Data System (ADS)

Dattelbaum, Dana

2017-06-01

Shock-driven reactions are commonplace. Examples include the detonation of high explosives, shock-driven dissociation of polymers, and transformation of carbon from graphite to diamond phases. The study of shock-driven chemical reactions is important for understanding reaction thresholds, their mechanisms and rates, and associated state sensitivities under the extreme conditions generated by shock compression. Reactions are distinguished by their thermicity - e.g. the volume and enthalpy changes along the reaction coordinate. A survey of the hallmarks of shock-driven reactivity for a variety of simple molecules and polymers will be presented, including benzene, acetylenes and nitriles, and formic acid. Many of the examples will illustrate the nature of the reactive flow through particle velocity wave profiles measured by in situ electromagnetic gauging in gas gun-driven plate impact experiments. General trends will be presented linking molecular moieties, shock temperatures, and reaction state sensitivities. Progress in applying bond-specific diagnostics will also be presented, including time-resolved Raman spectroscopy, and recent results of in situ x-ray diffraction of carbon at the Linac Coherent Light Souce (LCLS) free electron laser.

A numerical study of the laminar necklace vortex system and its effect on the wake for a circular cylinder

NASA Astrophysics Data System (ADS)

Kirkil, Gokhan; Constantinescu, George

2014-11-01

Large Eddy Simulation is used to investigate the structure of the laminar horseshoe vortex (HV) system and the dynamics of the necklace vortices as they fold around the base of a circular cylinder mounted on the flat bed of an open channel for Reynolds numbers defined with the cylinder diameter, D, smaller than 4,460. The study concentrates on the analysis of the structure of the HV system in the periodic breakaway sub-regime which is characterized by the formation of three main necklace vortices. For the relatively shallow flow conditions considered in this study (H/D 1, H is the channel depth), at times, the disturbances induced by the legs of the necklace vortices do not allow the SSLs on the two sides of the cylinder to interact in a way that allows the vorticity redistribution mechanism to lead to the formation of a new wake roller. As a result, the shedding of large scale rollers in the turbulent wake is suppressed for relatively large periods of time. Simulation results show that the wake structure changes randomly between time intervals when large-scale rollers are forming and are convected in the wake (von Karman regime), and time intervals when the rollers do not form.

Counter-rotating type tidal stream power unit boarded on pillar (performances and flow conditions of tandem propellers)

NASA Astrophysics Data System (ADS)

Usui, Yuta; Kanemoto, Toshiaki; Hiraki, Koju

2013-12-01

The authors have invented the unique counter-rotating type tidal stream power unit composed of the tandem propellers and the double rotational armature type peculiar generator without the traditional stator. The front and the rear propellers counter-drive the inner and the outer armatures of the peculiar generator, respectively. The unit has the fruitful advantages that not only the output is sufficiently higher without supplementary equipment such as a gearbox, but also the rotational moment hardly act on the pillar because the rotational torque of both propellers/armatures are counter-balanced in the unit. This paper discusses experimentally the performances of the power unit and the effects of the propeller rotation on the sea surface. The axial force acting on the pillar increases naturally with the increase of not only the stream velocity but also the drag of the tandem propellers. Besides, the force vertical to the stream also acts on the pillar, which is induced from the Karman vortex street and the dominant frequencies appear owing to the front and the rear propeller rotations. The propeller rotating in close to the sea surface brings the abnormal wave and the amplitude increases as the stream velocity is faster and/or the drag is stronger.

Idealized debris flow in flume with bed driven by a conveyor belt

USGS Publications Warehouse

Ling, Chi-Hai; Chen, Cheng-lung

1989-01-01

The generalized viscoplastic fluid (GVF) model is used to derive the theoretical expressions of two-dimensional velocities and surface profile for debris flow established in a flume with bed driven by a conveyor belt. The rheological parameters of the GVF model are evaluated through the comparison of theoretical results with measured data. A slip velocity of the established (steady) nonuniform flow on the moving bed (i.e., the conveyor belt) is observed, and a relation between the slip velocity and the velocity gradient at the bed is derived. Two belts, one rough and the other smooth, were tested. The flow profile in the flume is found to be linear and dependent on the roughness of the belt, but not much on its speed.

Driven magnetic reconnection in three dimensions - Energy conversion and field-aligned current generation

NASA Technical Reports Server (NTRS)

Sato, T.; Walker, R. J.; Ashour-Abdalla, M.

1984-01-01

The energy conversion processes occurring in three-dimensional driven reconnection is analyzed. In particular, the energy conversion processes during localized reconnection in a taillike magnetic configuration are studied. It is found that three-dimensional driven reconnection is a powerful energy converter which transforms magnetic energy into plasma bulk flow and thermal energy. Three-dimensional driven reconnection is an even more powerful energy converter than two-dimensional reconnection, because in the three-dimensional case, plasmas were drawn into the reconnection region from the sides as well as from the top and bottom. Field-aligned currents are generated by three-dimensional driven reconnection. The physical mechanism responsible for these currents which flow from the tail toward the ionosphere on the dawnside of the reconnection region and from the ionosphere toward the tail on the duskside is identified. The field-aligned currents form as the neutral sheet current is diverted through the slow shocks which form on the outer edge of the reconnected field lines (outer edge of the plasma sheet).

Wall Driven Cavity Approach to Slug Flow Modeling In a Micro channel

NASA Astrophysics Data System (ADS)

Sahu, Avinash; Kulkarni, Shekhar; Pushpavanam, Subramaniam; Pushpavanam Research League Team, Prof.

2014-03-01

Slug flow is a commonly observed stable regime and occurs at relatively low flow rates of the fluids. Wettability of channel decides continuous and discrete phases. In these types of biphasic flows, the fluid - fluid interface acts as a barrier that prohibits species movement across the interface. The flow inside a slug is qualitatively similar to the well known shallow cavity flow. In shallow cavities the flow mimics the ``fully developed'' internal circulation in slug flows. Another approach to slug flow modeling can be in a moving reference frame. Here the wall boundary moves in the direction opposite to that of the flow, hence induces circulations within the phases which is analogous to the well known Lid Driven Cavity. The two parallel walls are moved in the opposite directions which generate circulation patterns, equivalent to the ones regularly observed in slug flow in micro channels. A fourth order stream function equation is solved using finite difference approach. The flow field obtained using the two approaches will be used to analyze the effect on mass transfer and chemical reactions in the micro channel. The internal circulations and the performance of these systems will be validated experimentally.

Stability analysis of wall driven nanofluid flow through a tube

NASA Astrophysics Data System (ADS)

Hossain, M. Mainul; Khan, M. A. H.

2017-06-01

Wall driven incompressible viscous fluid flow with nanoparticles through a tube is considered where two different nanofluids (Cu-water, SiO2-water) are used separately. Flow becomes gradually unstable due to movement of wall and existence of nanoparticles. However, Reynolds number, volume fraction and density ratio are responsible for flow instability. The mathematical model of the problem is constructed and solved by means of series solution method. Special type Hermite-Padé approximation method is used to improve the series solution. The critical point for Reynolds number, volume fraction and density ratio are determined and described using approximation technique and bifurcation diagram for both nanofluids. Moreover, Interaction between these three numbers and their effect on velocity profile are discussed. To indicate the nanofluid which is more effective for flow stability is our major concerned.

Wave-driven winds from cool stars. I - Some effects of magnetic field geometry

NASA Technical Reports Server (NTRS)

Hartmann, L.; Macgregor, K. B.

1982-01-01

The wave-driven wind theory of Hartmann and MacGregor (1980) is extended to include effects due to non-radial divergence of the flow. Specifically, isothermal expansion within a flow tube whose cross-sectional area increases outward faster than the square of the radius near the stellar surface is considered. It is found that the qualitative conclusions of Hartmann and MacGregor concerning the physical properties of Alfven wave-driven winds are largely unaffected. In particular, mass fluxes of similar magnitude are obtained, and wave dissipation is still necessary to produce acceptably small terminal velocities. Increasingly divergent flow geometries generally lead to higher initial wind speeds and slightly lower terminal velocities. For some cases of extremely rapid flow tube divergence, steady supersonic wind solutions which extend to infinity with vanishing gas pressure cannot be obtained. In addition, departures from spherical symmetry can cause the relative Alfven wave amplitude delta-B/B to become approximately greater than 1 within several stellar radii of the base of the wind, suggesting that nonlinear processes may contribute to the wave dissipation required by the theory.

Interactions Between Raindrop Impact and Shallow Interrill Flow Under Wind-Driven Rain

USDA-ARS?s Scientific Manuscript database

Raindrops impacting shallow interrill flow create hydraulic friction in overland flow, and the roughness caused by raindrops against the shallow flow is generally explained by the Darcy-Weisbach friction coefficient, which is calculated as a function of rainfall intensity along with bed roughness. H...

Interactions between raindrop impact and shallow interrill flow under wind-driven rain (WDR)

USDA-ARS?s Scientific Manuscript database

Raindrops impacting shallow interrill flow create hydraulic friction in overland flow, and the roughness caused by raindrops against the shallow flow is generally explained by the Darcy-Weisbach friction coefficient, which is calculated as a function of rainfall intensity along with bed roughness. H...

Flow Velocity Profiles in Actively-Driven 2D Nozzle Experiments using Freely-Suspended Smectic Liquid Crystal Films

NASA Astrophysics Data System (ADS)

Dutch, Evan; Briggs, Corrina; Ferguson, Kyle; Green, Adam; Park, Cheol; Glaser, Matt; Maclennan, Joe; Clark, Noel

Freely-suspended smectic A liquid crystal films have been used to explore a large range of interesting flow phenomena. Passive microrheology experiments have confirmed previously that such films are ideal systems with which to investigate two-dimensional (2D) hydrodynamics. Here we describe an experiment that uses smectic films to study actively-driven 2D flows. Flow excited by blowing air over a film of smectic liquid crystal material containing small inclusions is captured using digital video microscopy. The flow fields are extracted using particle imaging velocimetry. We have measured the velocity field generated by flow through a thin nozzle into a large rectangular reservoir and compared this to a theoretical model based on 2D complex potential flows. The observations confirm that there is parabolic flow in straight channels, and that the theory accurately models the film velocity flow field in the reservoir. This work was supported by NASA Grant No. NNX-13AQ81G, and NSF MRSEC Grants No. DMR-0820579 and DMR-1420736.

Statistical properties of gravity-driven granular discharge flow under the influence of an obstacle

NASA Astrophysics Data System (ADS)

Endo, Keita; Katsuragi, Hiroaki

2017-06-01

Two-dimensional granular discharge flow driven by gravity under the influence of an obstacle is experimentally investigated. A horizontal exit of width W is opened at the bottom of vertical Hele-Shaw cell filled with stainless-steel particles to start the discharge flow. In this experiment, a circular obstacle is placed in front of the exit. Thus, the distance between the exit and obstacle L is also an important parameter. During the discharge, granular-flow state is acquired by a high-speed camera. The bulk discharge-flow rate is also measured by load cell sensors. The obtained high-speed-image data are analyzed to clarify the particle-level granular-flow dynamics. Using the measured data, we find that the obstacle above the exit affects the granular- flow field. Specifically, the existence of obstacle results in large horizontal granular temperature and small packing fraction. This tendency becomes significant when L is smaller than approximately 6Dg when W ≃ 4Dg, where Dg is diameter of particles.

Calculations of separated 3-D flows with a pressure-staggered Navier-Stokes equations solver

NASA Technical Reports Server (NTRS)

Kim, S.-W.

1991-01-01

A Navier-Stokes equations solver based on a pressure correction method with a pressure-staggered mesh and calculations of separated three-dimensional flows are presented. It is shown that the velocity pressure decoupling, which occurs when various pressure correction algorithms are used for pressure-staggered meshes, is caused by the ill-conditioned discrete pressure correction equation. The use of a partial differential equation for the incremental pressure eliminates the velocity pressure decoupling mechanism by itself and yields accurate numerical results. Example flows considered are a three-dimensional lid driven cavity flow and a laminar flow through a 90 degree bend square duct. For the lid driven cavity flow, the present numerical results compare more favorably with the measured data than those obtained using a formally third order accurate quadratic upwind interpolation scheme. For the curved duct flow, the present numerical method yields a grid independent solution with a very small number of grid points. The calculated velocity profiles are in good agreement with the measured data.

Application of Pressure Sensitive Paint in Hypersonic Flows

NASA Technical Reports Server (NTRS)

Jules, Kenol; Carbonaro, Mario; Zemsch, Stephan

1995-01-01

It is well known in the aerodynamic field that pressure distribution measurement over the surface of an aircraft model is a problem in experimental aerodynamics. For one thing, a continuous pressure map can not be obtained with the current experimental methods since they are discrete. Therefore, interpolation or CFD methods must be used for a more complete picture of the phenomenon under study. For this study, a new technique was investigated which would provide a continuous pressure distribution over the surface under consideration. The new method is pressure sensitive paint. When pressure sensitive paint is applied to an aerodynamic surface and placed in an operating wind-tunnel under appropriate lighting, the molecules luminesce as a function of the local pressure of oxygen over the surface of interest during aerodynamic flow. The resulting image will be brightest in the areas of low pressure (low oxygen concentration), and less intense in the areas of high pressure (where oxygen is most abundant on the surface). The objective of this investigation was to use pressure sensitive paint samples from McDonnell Douglas (MDD) for calibration purpose in order to assess the response of the paint under appropriate lighting and to use the samples over a flat plate/conical fin mounted at 75 degrees from the center of the plate in order to study the shock/boundary layer interaction at Mach 6 in the Von Karman wind-tunnel. From the result obtained it was concluded that temperature significantly affects the response of the paint and should be given the uppermost attention in the case of hypersonic flows. Also, it was found that past a certain temperature threshold, the paint intensity degradation became irreversible. The comparison between the pressure tap measurement and the pressure sensitive paint showed the right trend. However, there exists a shift when it comes to the actual value. Therefore, further investigation is under way to find the cause of the shift.

Pattern Formation in Diffusion Flames Embedded in von Karman Swirling Flows

NASA Technical Reports Server (NTRS)

Nayagam, Vedha

2006-01-01

Pattern formation is observed in nature in many so-called excitable systems that can support wave propagation. It is well-known in the field of combustion that premixed flames can exhibit patterns through differential diffusion mechanism between heat and mass. However, in the case of diffusion flames where fuel and oxidizer are separated initially there have been only a few observations of pattern formation. It is generally perceived that since diffusion flames do not possess an inherent propagation speed they are static and do not form patterns. But in diffusion flames close to their extinction local quenching can occur and produce flame edges which can propagate along stoichiometric surfaces. Recently, we reported experimental observations of rotating spiral flame edges during near-limit combustion of a downward-facing polymethylmethacrylate disk spinning in quiescent air. These spiral flames, though short-lived, exhibited many similarities to patterns commonly found in quiescent excitable media including compound tip meandering motion. Flame disks that grow or shrink with time depending on the rotational speed and in-depth heat loss history of the fuel disk have also been reported. One of the limitations of studying flame patterns with solid fuels is that steady-state conditions cannot be achieved in air at normal atmospheric pressure for experimentally reasonable fuel thickness. As a means to reproduce the flame patterns observed earlier with solid fuels, but under steady-state conditions, we have designed and built a rotating, porous-disk burner through which gaseous fuels can be injected and burned as diffusion flames. The rotating porous disk generates a flow of air toward the disk by a viscous pumping action, generating what is called the von K rm n boundary layer which is of constant thickness over the entire burner disk. In this note we present a map of the various dynamic flame patterns observed during the combustion of methane in air as a function of fuel flow rate and the burner rotational speed.

Cerebral pressure–flow relationship in lowlanders and natives at high altitude

PubMed Central

Smirl, Jonathan D; Lucas, Samuel J E; Lewis, Nia C S; duManior, Gregory R; Smith, Kurt J; Bakker, Akke; Basnyat, Aperna S; Ainslie, Philip N

2014-01-01

We investigated if dynamic cerebral pressure–flow relationships in lowlanders are altered at high altitude (HA), differ in HA natives and after return to sea level (SL). Lowlanders were tested at SL (n=16), arrival to 5,050 m, after 2-week acclimatization (with and without end-tidal PO2 normalization), and upon SL return. High-altitude natives (n=16) were tested at 5,050 m. Testing sessions involved resting spontaneous and driven (squat–stand maneuvers at very low (VLF, 0.05 Hz) and low (LF, 0.10 Hz) frequencies) measures to maximize blood pressure (BP) variability and improve assessment of the pressure–flow relationship using transfer function analysis (TFA). Blood flow velocity was assessed in the middle (MCAv) and posterior (PCAv) cerebral arteries. Spontaneous VLF and LF phases were reduced and coherence was elevated with acclimatization to HA (P<0.05), indicating impaired pressure–flow coupling. However, when BP was driven, both the frequency- and time-domain metrics were unaltered and comparable with HA natives. Acute mountain sickness was unrelated to TFA metrics. In conclusion, the driven cerebral pressure–flow relationship (in both frequency and time domains) is unaltered at 5,050 m in lowlanders and HA natives. Our findings indicate that spontaneous changes in TFA metrics do not necessarily reflect physiologically important alterations in the capacity of the brain to regulate BP. PMID:24169852

Cerebral pressure-flow relationship in lowlanders and natives at high altitude.

PubMed

Smirl, Jonathan D; Lucas, Samuel J E; Lewis, Nia C S; duManoir, Gregory R; Dumanior, Gregory R; Smith, Kurt J; Bakker, Akke; Basnyat, Aperna S; Ainslie, Philip N

2014-02-01

We investigated if dynamic cerebral pressure-flow relationships in lowlanders are altered at high altitude (HA), differ in HA natives and after return to sea level (SL). Lowlanders were tested at SL (n=16), arrival to 5,050 m, after 2-week acclimatization (with and without end-tidal PO2 normalization), and upon SL return. High-altitude natives (n=16) were tested at 5,050 m. Testing sessions involved resting spontaneous and driven (squat-stand maneuvers at very low (VLF, 0.05 Hz) and low (LF, 0.10 Hz) frequencies) measures to maximize blood pressure (BP) variability and improve assessment of the pressure-flow relationship using transfer function analysis (TFA). Blood flow velocity was assessed in the middle (MCAv) and posterior (PCAv) cerebral arteries. Spontaneous VLF and LF phases were reduced and coherence was elevated with acclimatization to HA (P<0.05), indicating impaired pressure-flow coupling. However, when BP was driven, both the frequency- and time-domain metrics were unaltered and comparable with HA natives. Acute mountain sickness was unrelated to TFA metrics. In conclusion, the driven cerebral pressure-flow relationship (in both frequency and time domains) is unaltered at 5,050 m in lowlanders and HA natives. Our findings indicate that spontaneous changes in TFA metrics do not necessarily reflect physiologically important alterations in the capacity of the brain to regulate BP.

Tidally driven pore water exchange within offshore intertidal sandbanks: Part II numerical simulations

NASA Astrophysics Data System (ADS)

Gibbes, B.; Robinson, C.; Li, L.; Lockington, D.; Li, H.

2008-12-01

Field measurements presented by [Gibbes, B., Robinson, C., Li, L., Lockington, D.A., Carey, H., 2008. Tidally driven pore water exchange within offshore intertidal sandbanks: Part I Field measurements. Estuarine, Coastal and Shelf Science 79, pp. 121-132.] revealed a tidally driven pore water flow system within an offshore intertidal sandbank in Moreton Bay, Australia. The field data suggested that this flow system might be capable of delivering nutrients, and in particular bio-available iron, across the sediment-water interface. Bio-available iron has been implicated as a key nutrient in the growth of the toxic marine cyanobacteria Lyngbya majuscula and therefore this pore water exchange process is of interest at sites where L. majuscula blooms have been observed. In this study two-dimensional numerical simulations were used in conjunction with hydraulic data from field measurements to further investigate the tidally induced pore water flow patterns. Simulation results generally showed good agreement with the field data and revealed a more complex residual pore water flow system in the sandbank than shown by the field data. The flow system, strongly influenced by the geometry of the sandbank, was characterized by two circulation cells which resulted in pore water discharge at the bank edge and also to a permanently ponded area within the sandbank interior. Simulated discharge volumes in these two zones were in the order of 0.813 m 3 and 0.143 m 3 per meter width (along shore) of sandbank per tidal cycle at the bank edge and sandbank interior respectively. Transit times of pore water circulating through these cells were found to range from ≈ 17 days to > 60 years with an average time of 780 days. The results suggest that the tidally driven flow systems might provide a mechanism for transport of bio-available iron across the sediment-water interface. This flow could constitute a previously unrecognized source of bio-available iron for L. majuscula blooms in the Bay.

One-way coupling of an integrated assessment model and a water resources model: evaluation and implications of future changes over the US Midwest

NASA Astrophysics Data System (ADS)

Voisin, N.; Liu, L.; Hejazi, M.; Tesfa, T.; Li, H.; Huang, M.; Liu, Y.; Leung, L. R.

2013-11-01

An integrated model is being developed to advance our understanding of the interactions between human activities, terrestrial system and water cycle, and to evaluate how system interactions will be affected by a changing climate at the regional scale. As a first step towards that goal, a global integrated assessment model, which includes a water-demand model driven by socioeconomics at regional and global scales, is coupled in a one-way fashion with a land surface hydrology-routing-water resources management model. To reconcile the scale differences between the models, a spatial and temporal disaggregation approach is developed to downscale the annual regional water demand simulations into a daily time step and subbasin representation. The model demonstrates reasonable ability to represent the historical flow regulation and water supply over the US Midwest (Missouri, Upper Mississippi, and Ohio river basins). Implications for future flow regulation, water supply, and supply deficit are investigated using climate change projections with the B1 and A2 emission scenarios, which affect both natural flow and water demand. Although natural flow is projected to increase under climate change in both the B1 and A2 scenarios, there is larger uncertainty in the changes of the regulated flow. Over the Ohio and Upper Mississippi river basins, changes in flow regulation are driven by the change in natural flow due to the limited storage capacity. However, both changes in flow and demand have effects on the Missouri River Basin summer regulated flow. Changes in demand are driven by socioeconomic factors, energy and food demands, global markets and prices with rainfed crop demand handled directly by the land surface modeling component. Even though most of the changes in supply deficit (unmet demand) and the actual supply (met demand) are driven primarily by the change in natural flow over the entire region, the integrated framework shows that supply deficit over the Missouri River Basin sees an increasing sensitivity to changes in demand in future periods. It further shows that the supply deficit is six times as sensitive as the actual supply to changes in flow and demand. A spatial analysis of the supply deficit demonstrates vulnerabilities of urban areas located along mainstream with limited storage.

A simulation of dielectrophoresis force actuated liquid lens

NASA Astrophysics Data System (ADS)

Yao, Xiaoyin; Xia, Jun

2009-11-01

Dielectrophoresis (DEP) and electrowetting on dielectric (EWOD) are based on the electrokinetic mechanisms which have great potential in microfluidic manipulation. DEP dominate the movement of particles induced by polarization effects in nonuniform electric field ,while EWOD has become one of the most widely used tools for manipulating tiny amounts of liquids on solid surfaces. Liquid lens driven by EWOD have been well studied and developed. But liquid lens driven by DEP has not been studied adequately. This paper focuses on modeling liquid lens driven by DEP force. A simulation of DEP driven droplet dynamics was performed by coupling of the electrostatic field and the two-phase flow field. Two incompressible and dielectric liquids with different permittivity were chosen in the two-phase flow field. The DEP force density, in direct proportion to gradient of the square of the electric field intensity, was used as a body force density in Navier-Stokes equation. When voltage applied, the liquid with high permittivity flowed to the place where the gradient of the square of the electric field intensity was higher, and thus change the curvature of interface between two immiscible liquid. The differences between DEP and EWOD liquid lens were also presented.

Electrically Driven Liquid Film Boiling Experiment

NASA Technical Reports Server (NTRS)

Didion, Jeffrey R.

2016-01-01

This presentation presents the science background and ground based results that form the basis of the Electrically Driven Liquid Film Boiling Experiment. This is an ISS experiment that is manifested for 2021. Objective: Characterize the effects of gravity on the interaction of electric and flow fields in the presence of phase change specifically pertaining to: a) The effects of microgravity on the electrically generated two-phase flow. b) The effects of microgravity on electrically driven liquid film boiling (includes extreme heat fluxes). Electro-wetting of the boiling section will repel the bubbles away from the heated surface in microgravity environment. Relevance/Impact: Provides phenomenological foundation for the development of electric field based two-phase thermal management systems leveraging EHD, permitting optimization of heat transfer surface area to volume ratios as well as achievement of high heat transfer coefficients thus resulting in system mass and volume savings. EHD replaces buoyancy or flow driven bubble removal from heated surface. Development Approach: Conduct preliminary experiments in low gravity and ground-based facilities to refine technique and obtain preliminary data for model development. ISS environment required to characterize electro-wetting effect on nucleate boiling and CHF in the absence of gravity. Will operate in the FIR - designed for autonomous operation.

Observations and a model of undertow over the inner continental shelf

USGS Publications Warehouse

Lentz, Steven J.; Fewings, Melanie; Howd, Peter; Fredericks, Janet; Hathaway, Kent

2008-01-01

Onshore volume transport (Stokes drift) due to surface gravity waves propagating toward the beach can result in a compensating Eulerian offshore flow in the surf zone referred to as undertow. Observed offshore flows indicate that wave-driven undertow extends well offshore of the surf zone, over the inner shelves of Martha’s Vineyard, Massachusetts, and North Carolina. Theoretical estimates of the wave-driven offshore transport from linear wave theory and observed wave characteristics account for 50% or more of the observed offshore transport variance in water depths between 5 and 12 m, and reproduce the observed dependence on wave height and water depth.During weak winds, wave-driven cross-shelf velocity profiles over the inner shelf have maximum offshore flow (1–6 cm s−1) and vertical shear near the surface and weak flow and shear in the lower half of the water column. The observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the surf zone. Instead, the vertical structure is similar to the Stokes drift velocity profile but with the opposite direction. This vertical structure is consistent with a dynamical balance between the Coriolis force associated with the offshore flow and an along-shelf “Hasselmann wave stress” due to the influence of the earth’s rotation on surface gravity waves. The close agreement between the observed and modeled profiles provides compelling evidence for the importance of the Hasselmann wave stress in forcing oceanic flows. Summer profiles are more vertically sheared than either winter profiles or model profiles, for reasons that remain unclear.

The steady state solutions of radiatively driven stellar winds for a non-Sobolev, pure absorption model

NASA Technical Reports Server (NTRS)

Poe, C. H.; Owocki, S. P.; Castor, J. I.

1990-01-01

The steady state solution topology for absorption line-driven flows is investigated for the condition that the Sobolev approximation is not used to compute the line force. The solution topology near the sonic point is of the nodal type with two positive slope solutions. The shallower of these slopes applies to reasonable lower boundary conditions and realistic ion thermal speed v(th) and to the Sobolev limit of zero of the usual Castor, Abbott, and Klein model. At finite v(th), this solution consists of a family of very similar solutions converging on the sonic point. It is concluded that a non-Sobolev, absorption line-driven flow with a realistic values of v(th) has no uniquely defined steady state. To the extent that a pure absorption model of the outflow of stellar winds is applicable, radiatively driven winds should be intrinsically variable.

Improved Merge Valve

NASA Technical Reports Server (NTRS)

George-Falvy, Dez

1992-01-01

Circumferential design combines compactness and efficiency. In remotely controlled valve, flow in tributary duct along circumference of primary duct merged with flow in primary duct. Flow in tributary duct regulated by variable throat nuzzle driven by worm gear. Design leak-proof, and most components easily fabricated on lathe.

Centrifuge in space fluid flow visualization experiment

NASA Technical Reports Server (NTRS)

Arnold, William A.; Wilcox, William R.; Regel, Liya L.; Dunbar, Bonnie J.

1993-01-01

A prototype flow visualization system is constructed to examine buoyancy driven flows during centrifugation in space. An axial density gradient is formed by imposing a thermal gradient between the two ends of the test cell. Numerical computations for this geometry showed that the Prandtl number plays a limited part in determining the flow.

Deriving Process-Driven Collaborative Editing Pattern from Collaborative Learning Flow Patterns

ERIC Educational Resources Information Center

Marjanovic, Olivera; Skaf-Molli, Hala; Molli, Pascal; Godart, Claude

2007-01-01

Collaborative Learning Flow Patterns (CLFPs) have recently emerged as a new method to formulate best practices in structuring the flow of activities within various collaborative learning scenarios. The term "learning flow" is used to describe coordination and sequencing of learning tasks. This paper adopts the existing concept of CLFP and argues…

Induced charge electroosmosis micropumps using arrays of Janus micropillars.

PubMed

Paustian, Joel S; Pascall, Andrew J; Wilson, Neil M; Squires, Todd M

2014-09-07

We report on a microfluidic AC-driven electrokinetic pump that uses Induced Charge Electro-Osmosis (ICEO) to generate on-chip pressures. ICEO flows occur when a bulk electric field polarizes a metal object to induce double layer formation, then drives electroosmotic flow. A microfabricated array of metal-dielectric Janus micropillars breaks the symmetry of ICEO flow, so that an AC electric field applied across the array drives ICEO flow along the length of the pump. When pumping against an external load, a pressure gradient forms along the pump length. The design was analyzed theoretically with the reciprocal theorem. The analysis reveals a maximum pressure and flow rate that depend on the ICEO slip velocity and micropillar geometry. We then fabricate and test the pump, validating our design concept by demonstrating non-local pressure driven flow using local ICEO slip flows. We varied the voltage, frequency, and electrolyte composition, measuring pump pressures of 15-150 Pa. We use the pump to drive flows through a high-resistance microfluidic channel. We conclude by discussing optimization routes suggested by our theoretical analysis to enhance the pump pressure.

Flow path oscillations in transient ground-water simulations of large peatland systems

USGS Publications Warehouse

Reeve, A.S.; Evensen, R.; Glaser, P.H.; Siegel, D.I.; Rosenberry, D.

2006-01-01

Transient numerical simulations of the Glacial Lake Agassiz Peatland near the Red Lakes in Northern Minnesota were constructed to evaluate observed reversals in vertical ground-water flow. Seasonal weather changes were introduced to a ground-water flow model by varying evapotranspiration and recharge over time. Vertical hydraulic reversals, driven by changes in recharge and evapotranspiration were produced in the simulated peat layer. These simulations indicate that the high specific storage associated with the peat is an important control on hydraulic reversals. Seasonally driven vertical flow is on the order of centimeters in the deep peat, suggesting that seasonal vertical advective fluxes are not significant and that ground-water flow into the deep peat likely occurs on decadal or longer time scales. Particles tracked within the ground-water flow model oscillate over time, suggesting that seasonal flow reversals will enhance vertical mixing in the peat column. The amplitude of flow path oscillations increased with increasing peat storativity, with amplitudes of about 5 cm occurring when peat specific storativity was set to about 0.05 m-1. ?? 2005 Elsevier B.V. All rights reserved.

Computational Fluid Dynamics Simulation of Flows in an Oxidation Ditch Driven by a New Surface Aerator

PubMed Central

Huang, Weidong; Li, Kun; Wang, Gan; Wang, Yingzhe

2013-01-01

Abstract In this article, we present a newly designed inverse umbrella surface aerator, and tested its performance in driving flow of an oxidation ditch. Results show that it has a better performance in driving the oxidation ditch than the original one with higher average velocity and more uniform flow field. We also present a computational fluid dynamics model for predicting the flow field in an oxidation ditch driven by a surface aerator. The improved momentum source term approach to simulate the flow field of the oxidation ditch driven by an inverse umbrella surface aerator was developed and validated through experiments. Four kinds of turbulent models were investigated with the approach, including the standard k−ɛ model, RNG k−ɛ model, realizable k−ɛ model, and Reynolds stress model, and the predicted data were compared with those calculated with the multiple rotating reference frame approach (MRF) and sliding mesh approach (SM). Results of the momentum source term approach are in good agreement with the experimental data, and its prediction accuracy is better than MRF, close to SM. It is also found that the momentum source term approach has lower computational expenses, is simpler to preprocess, and is easier to use. PMID:24302850

Rethinking the process of detrainment: jets in obstructed natural flows

NASA Astrophysics Data System (ADS)

Mossa, Michele; de Serio, Francesca

2016-12-01

A thorough understanding of the mixing and diffusion of turbulent jets released in porous obstructions is still lacking in literature. This issue is undoubtedly of interest because it is not strictly limited to vegetated flows, but also includes outflows which come from different sources and which spread among oyster or wind farms, as well as aerial pesticide treatments sprayed onto orchards. The aim of the present research is to analyze this process from a theoretical point of view. Specifically, by examining the entrainment coefficient, it is deduced that the presence of a canopy prevents a momentum jet from having an entrainment process, but rather promotes its detrainment. In nature, detrainment is usually associated with buoyancy-driven flows, such as plumes or density currents flowing in a stratified environment. The present study proves that detrainment occurs also when a momentum-driven jet is issued in a not-stratified obstructed current, such as a vegetated flow.

Statistical parameters of thermally driven turbulent anabatic flow

NASA Astrophysics Data System (ADS)

Hilel, Roni; Liberzon, Dan

2016-11-01

Field measurements of thermally driven turbulent anabatic flow over a moderate slope are reported. A collocated hot-films-sonic anemometer (Combo) obtained the finer scales of the flow by implementing a Neural Networks based in-situ calibration technique. Eight days of continuous measurements of the wind and temperature fluctuations reviled a diurnal pattern of unstable stratification that forced development of highly turbulent unidirectional up slope flow. Empirical fits of important turbulence statistics were obtained from velocity fluctuations' time series alongside fully resolved spectra of velocity field components and characteristic length scales. TKE and TI showed linear dependence on Re, while velocity derivative skewness and dissipation rates indicated the anisotropic nature of the flow. Empirical fits of normalized velocity fluctuations power density spectra were derived as spectral shapes exhibited high level of similarity. Bursting phenomenon was detected at 15% of the total time. Frequency of occurrence, spectral characteristics and possible generation mechanism are discussed. BSF Grant #2014075.

Microscopic phenomena and a modern approach to turbulence. [using arc driven shock tubes to support the kinetic theory of turbulence

NASA Technical Reports Server (NTRS)

Johnson, J. A., III; Chen, S.; I, L.; Jones, W.; Ramaiah, R.; Santiago, J.

1979-01-01

The use of an arc driven shock tube as a technique in the study of turbulence and evidence to support a kinetic theory of turbulence are described. Topics covered include: (1) reaction rate distortion in turbulent flow; (2) turbulent bursts in a shock tube; (3) driver gas flow with fluctuations; (4) improving the Mach number capabilities of arc driver shock tubes; and (5) resonant absorption in an argon plasma at thermal equilibrium.

Surface-tension-driven flow in a glass melt

NASA Technical Reports Server (NTRS)

Mcneil, Thomas J.; Cole, Robert; Shankar Subramanian, R.

1985-01-01

Motion driven by surface tension gradients was observed in a vertical capillary liquid bridge geometry in a sodium borate melt. The surface tension gradients were introduced by maintaining a temperature gradient on the free melt surface. The flow velocities at the free surface of the melt, which were measured using a tracer technique, were found to be proportional to the applied temperature difference and inversely proportional to the melt viscosity. The experimentally observed velocities were in reasonable accord with predictions from a theoretical model of the system.

Magnetic Heat Pump Containing Flow Diverters

NASA Technical Reports Server (NTRS)

Howard, Frank S.

1995-01-01

Proposed magnetic heat pump contains flow diverters for suppression of undesired flows. If left unchecked, undesired flows mix substantial amounts of partially heated and partially cooled portions of working fluid, effectively causing leakage of heat from heated side to cooled side. By reducing leakage of heat, flow diverters increase energy efficiency of magnetic heat pump, potentially offering efficiency greater than compressor-driven refrigerator.

A hydrogeologic model of stratiform copper mineralization in the Midcontinent Rift System, Northern Michigan, USA

USGS Publications Warehouse

Swenson, J.B.; Person, M.; Raffensperger, Jeff P.; Cannon, W.F.; Woodruff, L.G.; Berndt, M.E.

2004-01-01

This paper presents a suite of two-dimensional mathematical models of basin-scale groundwater flow and heat transfer for the middle Proterozoic Midcontinent Rift System. The models were used to assess the hydrodynamic driving mechanisms responsible for main-stage stratiform copper mineralization of the basal Nonesuch Formation during the post-volcanic/pre-compressional phase of basin evolution. Results suggest that compaction of the basal aquifer (Copper Harbor Formation), in response to mechanical loading during deposition of the overlying Freda Sandstone, generated a pulse of marginward-directed, compaction-driven discharge of cupriferous brines from within the basal aquifer. The timing of this pulse is consistent with the radiometric dates for the timing of mineralization. Thinning of the basal aquifer near White Pine, Michigan, enhanced stratiform copper mineralization. Focused upward leakage of copper-laden brines into the lowermost facies of the pyrite-rich Nonesuch Formation resulted in copper sulfide mineralization in response to a change in oxidation state. Economic-grade mineralization within the White Pine ore district is a consequence of intense focusing of compaction-driven discharge, and corresponding amplification of leakage into the basal Nonesuch Formation, where the basal aquifer thins dramatically atop the Porcupine Mountains volcanic structure. Equilibrium geochemical modeling and mass-balance calculations support this conclusion. We also assessed whether topography and density-driven flow systems could have caused ore genesis at White Pine. Topography-driven flow associated with the Ottawan orogeny was discounted because it post-dates main-stage ore genesis and because recent seismic interpretations of basin inversion indicates that basin geometry would not be conductive to ore genesis. Density-driven flow systems did not produce focused discharge in the vicinity of the White Pine ore district.

TURBULENCE AND PROTON–ELECTRON HEATING IN KINETIC PLASMA

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

Matthaeus, William H; Parashar, Tulasi N; Wu, P.

2016-08-10

Analysis of particle-in-cell simulations of kinetic plasma turbulence reveals a connection between the strength of cascade, the total heating rate, and the partitioning of dissipated energy into proton heating and electron heating. A von Karman scaling of the cascade rate explains the total heating across several families of simulations. The proton to electron heating ratio increases in proportion to total heating. We argue that the ratio of gyroperiod to nonlinear turnover time at the ion kinetic scales controls the ratio of proton and electron heating. The proposed scaling is consistent with simulations.

Analytical results for post-buckling behaviour of plates in compression and in shear

NASA Technical Reports Server (NTRS)

Stein, M.

1985-01-01

The postbuckling behavior of long rectangular isotropic and orthotropic plates is determined. By assuming trigonometric functions in one direction, the nonlinear partial differential equations of von Karman large deflection plate theory are converted into nonlinear ordinary differential equations. The ordinary differential equations are solved numerically using an available boundary value problem solver which makes use of Newton's method. Results for longitudinal compression show different postbuckling behavior between isotropic and orthotropic plates. Results for shear show that change in inplane edge constraints can cause large change in postbuckling stiffness.

RFB research and development in WIG vehicles

NASA Astrophysics Data System (ADS)

Fischer, Hanno

An account is given of the development history of wing-in-ground (WIG) effect aircraft at a major West German aircraft manufacturer since 1964; these efforts have encompassed the development of the X113 and X114 'airfoilboat' WIG seaplanes. Attention is given to the aerodynamic efficiency and operational economy trends that result from up-scaling of WIG craft configurations to takeoff gross weights of the order of 300 tons. Also noted is the illustration of comparative efficiency among types of transportation, including WIG vehicles, given by the von Karman-Gabrielli diagram.

Statistics of some atmospheric turbulence records relevant to aircraft response calculations

NASA Technical Reports Server (NTRS)

Mark, W. D.; Fischer, R. W.

1981-01-01

Methods for characterizing atmospheric turbulence are described. The methods illustrated include maximum likelihood estimation of the integral scale and intensity of records obeying the von Karman transverse power spectral form, constrained least-squares estimation of the parameters of a parametric representation of autocorrelation functions, estimation of the power spectra density of the instantaneous variance of a record with temporally fluctuating variance, and estimation of the probability density functions of various turbulence components. Descriptions of the computer programs used in the computations are given, and a full listing of these programs is included.

On the sensitivity of mesoscale models to surface-layer parameterization constants

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Pielke, R. A.

1989-09-01

The Colorado State University standard mesoscale model is used to evaluate the sensitivity of one-dimensional (1D) and two-dimensional (2D) fields to differences in surface-layer parameterization “constants”. Such differences reflect the range in the published values of the von Karman constant, Monin-Obukhov stability functions and the temperature roughness length at the surface. The sensitivity of 1D boundary-layer structure, and 2D sea-breeze intensity, is generally less than that found in published comparisons related to turbulence closure schemes generally.

Advanced technology and the Space Shuttle /10th Von Karman Lecture/.

NASA Technical Reports Server (NTRS)

Love, E. S.

1973-01-01

Selected topics in technology advancement related to the space shuttle are examined. Contributions from long-range research prior to the advent of the 'shuttle-focused technology program' of the past 3 years are considered together with highlights from the latter. Attention is confined to three of the shuttle's seven principal technology areas: aerothermodynamics/configurations, dynamics/aeroelasticity, and structures/materials. Some observations are presented on the shuttle's origin, the need to sustain advanced research, and future systems that could emerge from a combination of shuttle and non-shuttle technology advancements.

Analysis of data from NASA B-57B gust gradient program

NASA Technical Reports Server (NTRS)

Frost, W.; Lin, M. C.; Chang, H. P.; Ringnes, E.

1985-01-01

Statistical analysis of the turbulence measured in flight 6 of the NASA B-57B over Denver, Colorado, from July 7 to July 23, 1982 included the calculations of average turbulence parameters, integral length scales, probability density functions, single point autocorrelation coefficients, two point autocorrelation coefficients, normalized autospectra, normalized two point autospectra, and two point cross sectra for gust velocities. The single point autocorrelation coefficients were compared with the theoretical model developed by von Karman. Theoretical analyses were developed which address the effects spanwise gust distributions, using two point spatial turbulence correlations.

Some Recent Contributions to the Study of Transition and Turbulent Boundary Layers

NASA Technical Reports Server (NTRS)

Dryden, Hugh L

1947-01-01

The first part of this paper reviews the present state of the problem of the instability of laminar boundary layers which has formed an important part of the general lectures by von Karman at the first and fourth Congresses and by Taylor at the fifth Congress. This problem may now be considered as essentially solved as the result of work completed since 1938. When the velocity fluctuations of the free-stream flow are less than 0.1 percent of the mean speed, instability occurs as described by the well-known Tollmien-Schlichting theory. The Tollmien-Schlichting waves were first observed experimentally by Schubauer and Skramstad in 1940. They devised methods of introducing controlled small disturbances and obtained measured values of frequency, damping, and wave length at various Reynolds numbers which agreed well with the theoretical results. Their experimental results were confirmed by Liepmann. Much theoretical work was done in Germany in extending the Tol1mien-Schlichting theory to other boundary conditions, in particular to flow along a porous wall to which suction is applied for removing part of the boundary layer. The second part of this paper summarizes the present state of knowledge of the mechanics of turbulent boundary layers, and of the methods now being used for fundamental studies of the turbulent fluctuations in turbulent boundary layers. A brief review is given of the semi-empirical method of approach as developed by Buri, Gruschwitz, Fediaevsky, and Kalikhman. In recent years the National Advisory.Commsittee for Aeronautics has sponsored a detailed study at the National Bureau of Standards of the turbulent fluctuations in a turbulent boundary layer under adverse pressure gradient sufficient to produce separation. The aims of this investigation and its present status are described.

Development and validation of an improved mechanical thorax for simulating cardiopulmonary resuscitation with adjustable chest stiffness and simulated blood flow.

PubMed

Eichhorn, Stefan; Spindler, Johannes; Polski, Marcin; Mendoza, Alejandro; Schreiber, Ulrich; Heller, Michael; Deutsch, Marcus Andre; Braun, Christian; Lange, Rüdiger; Krane, Markus

2017-05-01

Investigations of compressive frequency, duty cycle, or waveform during CPR are typically rooted in animal research or computer simulations. Our goal was to generate a mechanical model incorporating alternate stiffness settings and an integrated blood flow system, enabling defined, reproducible comparisons of CPR efficacy. Based on thoracic stiffness data measured in human cadavers, such a model was constructed using valve-controlled pneumatic pistons and an artificial heart. This model offers two realistic levels of chest elasticity, with a blood flow apparatus that reflects compressive depth and waveform changes. We conducted CPR at opposing levels of physiologic stiffness, using a LUCAS device, a motor-driven plunger, and a group of volunteers. In high-stiffness mode, blood flow generated by volunteers was significantly less after just 2min of CPR, whereas flow generated by LUCAS device was superior by comparison. Optimal blood flow was obtained via motor-driven plunger, with trapezoidal waveform. Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.

Instability in extensional microflow of aqueous gel

NASA Astrophysics Data System (ADS)

Bryce, Robert; Freeman, Mark

2007-03-01

Microfluidic devices are typically characterized by laminar flows, often leading to diffusion limited mixing. Recently it has been demonstrated that the addition of polymer to fluids can lead to elastic instabilities and, under some conditions, turbulence at arbitrarily low Reynolds numbers in mechanically driven flows [1]. We investigated electroosmotic driven extensional flow of an aqueous polymer gel. Microchannels with 100 micron width and 20 micron depth with the characteristic ``D'' chemical etch cross section were formed in glass. A Y-channel geometry with two input channels and a single output created extensional flow at the channel intersection. Instabilities where observed in the extensional region by fluorescently tagging one input stream. Instabilities were characterized by 1/f spectra in laser induced fluorescent brightness profiles. Due to the simple geometry of extensional flow and the importance of electroosmotic flows for integrated applications and in scaling, this is of interest for device applications. [1] A. Groisman and V. Steinberg, Nature 405, 53-55, 2000.

From convection rolls to finger convection in double-diffusive turbulence

PubMed Central

Verzicco, Roberto; Lohse, Detlef

2016-01-01

Double-diffusive convection (DDC), which is the buoyancy-driven flow with fluid density depending on two scalar components, is ubiquitous in many natural and engineering environments. Of great interests are scalars' transfer rate and flow structures. Here we systematically investigate DDC flow between two horizontal plates, driven by an unstable salinity gradient and stabilized by a temperature gradient. Counterintuitively, when increasing the stabilizing temperature gradient, the salinity flux first increases, even though the velocity monotonically decreases, before it finally breaks down to the purely diffusive value. The enhanced salinity transport is traced back to a transition in the overall flow pattern, namely from large-scale convection rolls to well-organized vertically oriented salt fingers. We also show and explain that the unifying theory of thermal convection originally developed by Grossmann and Lohse for Rayleigh–Bénard convection can be directly applied to DDC flow for a wide range of control parameters (Lewis number and density ratio), including those which cover the common values relevant for ocean flows. PMID:26699474

Solutal Marangoni flows of miscible liquids drive transport without surface contamination

NASA Astrophysics Data System (ADS)

Kim, Hyoungsoo; Muller, Koen; Shardt, Orest; Afkhami, Shahriar; Stone, Howard A.

2017-11-01

Mixing and spreading of different liquids are omnipresent in nature, life and technology, such as oil pollution on the sea, estuaries, food processing, cosmetic and beverage industries, lab-on-a-chip devices, and polymer processing. However, the mixing and spreading mechanisms for miscible liquids remain poorly characterized. Here, we show that a fully soluble liquid drop deposited on a liquid surface remains as a static lens without immediately spreading and mixing, and simultaneously a Marangoni-driven convective flow is generated, which are counterintuitive results when two liquids have different surface tensions. To understand the dynamics, we develop a theoretical model to predict the finite spreading time and length scales, the Marangoni-driven convection flow speed, and the finite timescale to establish the quasi-steady state for the Marangoni flow. The fundamental understanding of this solutal Marangoni flow may enable driving bulk flows and constructing an effective drug delivery and surface cleaning approach without causing surface contamination by immiscible chemical species.

Flow-driven instabilities during pattern formation of Dictyostelium discoideum

NASA Astrophysics Data System (ADS)

Gholami, A.; Steinbock, O.; Zykov, V.; Bodenschatz, E.

2015-06-01

The slime mold Dictyostelium discoideum is a well known model system for the study of biological pattern formation. In the natural environment, aggregating populations of starving Dictyostelium discoideum cells may experience fluid flows that can profoundly change the underlying wave generation process. Here we study the effect of advection on the pattern formation in a colony of homogeneously distributed Dictyostelium discoideum cells described by the standard Martiel-Goldbeter model. The external flow advects the signaling molecule cyclic adenosine monophosphate (cAMP) downstream, while the chemotactic cells attached to the solid substrate are not transported with the flow. The evolution of small perturbations in cAMP concentrations is studied analytically in the linear regime and by corresponding numerical simulations. We show that flow can significantly influence the dynamics of the system and lead to a flow-driven instability that initiate downstream traveling cAMP waves. We also show that boundary conditions have a significant effect on the observed patterns and can lead to a new kind of instability.

Cerebrospinal fluid bulk flow is driven by the cardiac cycle

NASA Astrophysics Data System (ADS)

Tithof, Jeffrey; Mestre, Humberto; Thomas, John; Nedergaard, Maiken; Kelley, Douglas

2017-11-01

Recent discoveries have uncovered a cerebrospinal fluid (CSF) transport system in the perivascular spaces (PVS) of the mammalian brain which clears excess extracellular fluid and protein waste products. The oscillatory pattern of CSF flow has long been attributed to arterial pulsations due to cardiac contractility but limitations in imaging techniques have impeded quantitative measurement of flow rates within the PVS. In this talk, we describe quantitative measurements from the first ever direct imaging of CSF flow in the PVS of a mouse brain. We perform particle tracking velocimetry to obtain time-resolved velocity measurements. To identify the cardiac and/or respiratory dependence of the flow, while imaging, we simultaneously record the mouse's electrocardiogram and respiration. Our measurements conclusively indicate that CSF pulsatility in the arterial PVS is directly driven by the cardiac cycle and not by the respiratory cycle or cerebral vasomotion. These results offer a substantial step forward in understanding bulk flow of CSF in the mammalian brain and may have important implications related to neurodegenerative diseases.

The temporal evolution of the resistive pressure-gradient-driven turbulence and anomalous transport in shear flow across the magnetic field

NASA Astrophysics Data System (ADS)

Lee, Hae June; Mikhailenko, Vladmir; Mikhailenko, Vladimir

2017-10-01

The temporal evolution of the resistive pressure-gradient-driven mode in the sheared flow is investigated by employing the shearing modes approach. It reveals an essential difference in the processes, which occur in the case of the flows with velocity shearing rate less than the growth rate of the instability in the steady plasmas, and in the case of the flows with velocity shear larger than the instability growth rate in steady plasmas. It displays the physical content of the empirical ``quench rule'' which predicts the suppression of the turbulence in the sheared flows when the velocity shearing rate becomes larger than the maximum growth rate of the possible instability. We found that the distortion of the perturbations by the sheared flow with such velocity shear introduces the time dependencies into the governing equations, which prohibits the application of the eigenmodes formalism and requires the solution of the initial value problem.

Length and time for development of laminar flow in tubes following a step increase of volume flux

NASA Astrophysics Data System (ADS)

Chaudhury, Rafeed A.; Herrmann, Marcus; Frakes, David H.; Adrian, Ronald J.

2015-01-01

Laminar flows starting up from rest in round tubes are relevant to numerous industrial and biomedical applications. The two most common types are flows driven by an abruptly imposed constant pressure gradient or by an abruptly imposed constant volume flux. Analytical solutions are available for transient, fully developed flows, wherein streamwise development over the entrance length is absent (Szymanski in J de Mathématiques Pures et Appliquées 11:67-107, 1932; Andersson and Tiseth in Chem Eng Commun 112(1):121-133, 1992, respectively). They represent the transient responses of flows in tubes that are very long compared with the entrance length, a condition that is seldom satisfied in biomedical tube networks. This study establishes the entrance (development) length and development time of starting laminar flow in a round tube of finite length driven by a piston pump that produces a step change from zero flow to a constant volume flux for Reynolds numbers between 500 and 3,000. The flows are examined experimentally, using stereographic particle image velocimetry and computationally using computational fluid dynamics, and are then compared with the known analytical solutions for fully developed flow conditions in infinitely long tubes. Results show that step function volume flux start-up flows reach steady state and fully developed flow five times more quickly than those driven by a step function pressure gradient, a 500 % change when compared with existing estimates. Based on these results, we present new, simple guidelines for achieving experimental flows that are fully developed in space and time in realistic (finite) tube geometries. To a first approximation, the time to achieve steady spatially developing flow is nearly equal to the time needed to achieve steady, fully developed flow. Conversely, the entrance length needed to achieve fully developed transient flow is approximately equal to the length needed to achieve fully developed steady flow. Beyond this level of description, the numerical results reveal interaction between the effects of space and time development and nonlinear Reynolds number effects.

Turbulent Flow Enhancement by Polyelectrolyte Additives: Mechanistic Implications for Drag Reduction.

NASA Astrophysics Data System (ADS)

Wagger, David Leonard

1992-01-01

The drag reduction phenomenon was experimentally studied in two pipes, of diameters 1.46 and 1.02 cm, using seven polyelectrolytic HPAM additives, with molecular weights from 1 to 20 times 10^6 g/mole and degree of backbone hydrolysis from 8 to 60%, at concentrations from 1 to 1000 wppm, in saline solutions containing from 0.3 to 0.00001 N NaCl. Both laminar and turbulent flow behavior were greatly influenced by salinity-induced changes in the initial conformation of the HPAM additives. Initially collapsed, random-coiling conformations exhibited Newtonian laminar flow and Type-A turbulent drag reduction, while initially extended conformations exhibited shear-thinning in laminar flow and Type-B turbulent drag reduction. The gross-flow physics of Type-B drag reduction were delineated. A characteristic "ladder" structure prevailed, with polymeric regime segments that were roughly parallel to, but shifted upward from, the Prandtl-Karman line. In the polymeric regime, both Type-A fan and Type -B ladder structures were essentially independent of pipe diameter, and were scaled by the wall shear stress. The wall shear stress also scaled degradation during drag reduction. New onset and slope increment correlations were presented for Type-A drag reduction by HPAM additives. In Type-B drag reduction, flow enhancement was found proportional to additive concentration, and the intrinsic slip, Sigma = S^'/(c/M _{rm w}), varied roughly as the third power of backbone chain links N_ {rm bb}. New intrinsic slip and retro-onset correlations were presented for Type-B drag reduction by HPAM additives. Analysis of Type-B literature revealed a wide range of additive efficacies, with specific slips S^'/c from 0.0001 to 4. For the most effective additives, HPAM and asbestos fibers, the additive-pervaded volume fraction per unit flow enhancement, X_{rm v} /S^' ~ 3000, implied that these additives align during drag reduction. The slip ratio R_{rm sc}, which is the relative flow enhancement induced in Type-A and Type-B drag reduction at constant additive concentration, was found to be a universal function of the normalized turbulent flow strength (Re_ {rm s}sqrtf/Re_ {rm s}sqrtf*). The extension of initially collapsed, random-coiling, HPAM macromolecules by the turbulent flow field thus seems independent of additive parameters and absolute wall shear stress levels. Gross flow additive equivalence was detected at iso-slip points, where different polymer solutions induced equal flow enhancements. At numerous such points, the collapsed to extended slip ratio at constant concentration, R_{rm sc}, was essentially equal to the extended to collapsed concentration ratio at constant slip, R _{rm cs}. Thus, for fixed total additive concentration, the R_{ rm sc} observed at any Re_ {rm s}sqrtf simply represents the fraction of originally collapsed macromolecules that have become extended in the flow, and thence effective in drag reduction. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).

Energy Exchange in Driven Open Quantum Systems at Strong Coupling

NASA Astrophysics Data System (ADS)

Carrega, Matteo; Solinas, Paolo; Sassetti, Maura; Weiss, Ulrich

2016-06-01

The time-dependent energy transfer in a driven quantum system strongly coupled to a heat bath is studied within an influence functional approach. Exact formal expressions for the statistics of energy dissipation into the different channels are derived. The general method is applied to the driven dissipative two-state system. It is shown that the energy flows obey a balance relation, and that, for strong coupling, the interaction may constitute the major dissipative channel. Results in analytic form are presented for the particular value K =1/2 of strong Ohmic dissipation. The energy flows show interesting behaviors including driving-induced coherences and quantum stochastic resonances. It is found that the general characteristics persists for K near 1/2 .

Computational And Experimental Studies Of Three-Dimensional Flame Spread Over Liquid Fuel Pools

NASA Technical Reports Server (NTRS)

Ross, Howard D. (Technical Monitor); Cai, Jinsheng; Liu, Feng; Sirignano, William A.; Miller, Fletcher J.

2003-01-01

Schiller, Ross, and Sirignano (1996) studied ignition and flame spread above liquid fuels initially below the flashpoint temperature by using a two-dimensional computational fluid dynamics code that solves the coupled equations of both the gas and the liquid phases. Pulsating flame spread was attributed to the establishment of a gas-phase recirculation cell that forms just ahead of the flame leading edge because of the opposing effect of buoyancy-driven flow in the gas phase and the thermocapillary-driven flow in the liquid phase. Schiller and Sirignano (1996) extended the same study to include flame spread with forced opposed flow in the gas phase. A transitional flow velocity was found above which an originally uniform spreading flame pulsates. The same type of gas-phase recirculation cell caused by the combination of forced opposed flow, buoyancy-driven flow, and thermocapillary-driven concurrent flow was responsible for the pulsating flame spread. Ross and Miller (1998) and Miller and Ross (1998) performed experimental work that corroborates the computational findings of Schiller, Ross, and Sirignano (1996) and Schiller and Sirignano (1996). Cai, Liu, and Sirignano (2002) developed a more comprehensive three-dimensional model and computer code for the flame spread problem. Many improvements in modeling and numerical algorithms were incorporated in the three-dimensional model. Pools of finite width and length were studied in air channels of prescribed height and width. Significant three-dimensional effects around and along the pool edge were observed. The same three-dimensional code is used to study the detailed effects of pool depth, pool width, opposed air flow velocity, and different levels of air oxygen concentration (Cai, Liu, and Sirignano, 2003). Significant three-dimensional effects showing an unsteady wavy flame front for cases of wide pool width are found for the first time in computation, after being noted previously by experimental observers (Ross and Miller, 1999). Regions of uniform and pulsating flame spread are mapped for the flow conditions of pool depth, opposed flow velocity, initial pool temperature, and air oxygen concentration under both normal and microgravity conditions. Details can be found in Cai et al. (2002, 2003). Experimental results recently performed at NASA Glenn of flame spread across a wide, shallow pool as a function of liquid temperature are also presented here.

Reflection of a Year Long Model-Driven Business and UI Modeling Development Project

NASA Astrophysics Data System (ADS)

Sukaviriya, Noi; Mani, Senthil; Sinha, Vibha

Model-driven software development enables users to specify an application at a high level - a level that better matches problem domain. It also promises the users with better analysis and automation. Our work embarks on two collaborating domains - business process and human interactions - to build an application. Business modeling expresses business operations and flows then creates business flow implementation. Human interaction modeling expresses a UI design, its relationship with business data, logic, and flow, and can generate working UI. This double modeling approach automates the production of a working system with UI and business logic connected. This paper discusses the human aspects of this modeling approach after a year long of building a procurement outsourcing contract application using the approach - the result of which was deployed in December 2008. The paper discusses in multiple areas the happy endings and some heartache. We end with insights on how a model-driven approach could do better for humans in the process.

Fluid-driven reciprocating apparatus and valving for controlling same

DOEpatents

Whitehead, John C.; Toews, Hans G.

1993-01-01

A control valve assembly for alternately actuating a pair of fluid-driven free-piston devices by using fluid pressure communication therebetween. Each control valve is switched by a pressure signal depending on the state of its counterpart's piston. The communication logic is arranged to provide overlap of the forward strokes of the pistons, so that at least one of the pair will always be pressurized. Thus, uninterrupted pumping of liquid is made possible from a pair of free-piston pumps. In addition, the speed and frequency of piston stroking is entirely dependent on the mechanical power load applied. In the case of a pair of pumps, this enables liquid delivery at a substantially constant pressure over the full range of flow rates, from zero to maximum flow. One embodiment of the invention utilized two pairs of fluid-driven free-piston devices whereby a bipropellant liquid propulsion system may be operated, so as to provide continuous flow of both fuel and oxidizer liquids when used in rocket applications, for example.

A frictionally and hydraulically constrained model of the convectively driven mean flow in partially enclosed seas

NASA Astrophysics Data System (ADS)

Maxworthy, T.

1997-08-01

A simple three-layer model of the dynamics of partially enclosed seas, driven by a surface buoyancy flux, is presented. It contains two major elements, a hydraulic constraint at the exit contraction and friction in the interior of the main body of the sea; both together determine the vertical structure and magnitudes of the interior flow variables, i.e. velocity and density. Application of the model to the large-scale dynamics of the Red Sea gives results that are not in disagreement with observation once the model is applied, also, to predict the dense outflow from the Gulf of Suez. The latter appears to be the agent responsible for the formation of dense bottom water in this system. Also, the model is reasonably successful in predicting the density of the outflow from the Persian Gulf, and can be applied to any number of other examples of convectively driven flow in long, narrow channels, with or without sills and constrictions at their exits.

Axisymmetric flows from fluid injection into a confined porous medium

NASA Astrophysics Data System (ADS)

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

2016-02-01

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

Thermocapillary effect on the dynamics of viscous beads on vertical fiber

NASA Astrophysics Data System (ADS)

Liu, Rong; Liu, Qiu Sheng

2014-09-01

The gravity-driven flow of a thin liquid film down a uniformly heated vertical fiber is considered. This is an unstable open flow that exhibits rich dynamics including the formation of droplets, or beads, driven by a Rayleigh-Plateau mechanism modified by the presence of gravity as well as the variation of surface tension induced by temperature disturbance at the interface. A linear stability analysis and a nonlinear simulation are performed to investigate the dynamic of axisymmetric disturbances. The results showed that the Marangoni instability and the Rayleigh-Plateau instability reinforce each other. With the increase of the thermocapillary effect, the fiber flow has a tendency to break up into smaller droplets.

Ion sound instability driven by the ion flows

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

Koshkarov, O., E-mail: koshkarov.alexandr@usask.ca; Smolyakov, A. I.; National Research Centre

2015-05-15

Ion sound instabilities driven by the ion flow in a system of a finite length are considered by analytical and numerical methods. The ion sound waves are modified by the presence of stationary ion flow resulting in negative and positive energy modes. The instability develops due to coupling of negative and positive energy modes mediated by reflections from the boundary. It is shown that the wave dispersion due to deviation from quasineutrality is crucial for the stability. In finite length system, the dispersion is characterized by the length of the system measured in units of the Debye length. The instabilitymore » is studied analytically and the results are compared with direct, initial value numerical simulations.« less

Air-Flow-Driven Triboelectric Nanogenerators for Self-Powered Real-Time Respiratory Monitoring.

PubMed

Wang, Meng; Zhang, Jiahao; Tang, Yingjie; Li, Jun; Zhang, Baosen; Liang, Erjun; Mao, Yanchao; Wang, Xudong

2018-06-04

Respiration is one of the most important vital signs of humans, and respiratory monitoring plays an important role in physical health management. A low-cost and convenient real-time respiratory monitoring system is extremely desirable. In this work, we demonstrated an air-flow-driven triboelectric nanogenerator (TENG) for self-powered real-time respiratory monitoring by converting mechanical energy of human respiration into electric output signals. The operation of the TENG was based on the air-flow-driven vibration of a flexible nanostructured polytetrafluoroethylene (n-PTFE) thin film in an acrylic tube. This TENG can generate distinct real-time electric signals when exposed to the air flow from different breath behaviors. It was also found that the accumulative charge transferred in breath sensing corresponds well to the total volume of air exchanged during the respiration process. Based on this TENG device, an intelligent wireless respiratory monitoring and alert system was further developed, which used the TENG signal to directly trigger a wireless alarm or dial a cell phone to provide timely alerts in response to breath behavior changes. This research offers a promising solution for developing self-powered real-time respiratory monitoring devices.

Numerical Study of the Buoyancy-Driven Flow in a Four-Electrode Rectangular Electrochemical Cell

NASA Astrophysics Data System (ADS)

Sun, Zhanyu; Agafonov, Vadim; Rice, Catherine; Bindler, Jacob

2009-11-01

Two-dimensional numerical simulation is done on the buoyancy-driven flow in a four-electrode rectangular electrochemical cell. Two kinds of electrode layouts, the anode-cathode-cathode-anode (ACCA) and the cathode-anode-anode-cathode (CAAC) layouts, are studied. In the ACCA layout, the two anodes are placed close to the channel outlets while the two cathodes are located between the two anodes. The CAAC layout can be converted from the ACCA layout by applying higher electric potential on the two middle electrodes. Density gradient was generated by the electrodic reaction I3^-+2e^- =3I^-. When the electrochemical cell is accelerated axially, buoyancy-driven flow occurs. In our model, electro-neutrality is assumed except at the electrodes. The Navier-Stokes equations with the Boussinesq approximation and the Nernst-Planck equations are employed to model the momentum and mass transports, respectively. It is found that under a given axial acceleration, the electrolyte density between the two middle electrodes determines the bulk flow through the electrochemical cell. The cathodic current difference is found to be able to measure the applied acceleration. Other important electro-hydrodynamic characteristics are also discussed.

Experimental Investigations on the Surface-Driven Capillary Flow of Aqueous Microparticle Suspensions in the Microfluidic Laboratory-On Systems

NASA Astrophysics Data System (ADS)

Mukhopadhyay, Subhadeep

In this work, total 1592 individual leakage-free polymethylmethacrylate (PMMA) microfluidic devices as laboratory-on-a-chip systems are fabricated by maskless lithography, hot embossing lithography, and direct bonding technique. Total 1094 individual Audio Video Interleave Files as experimental outputs related to the surface-driven capillary flow have been recorded and analyzed. The influence of effective viscosity, effect of surface wettability, effect of channel aspect ratio, and effect of centrifugal force on the surface-driven microfluidic flow of aqueous microparticle suspensions have been successfully and individually investigated in these laboratory-on-a-chip systems. Also, 5 micron polystyrene particles have been separated from the aqueous microparticle suspensions in the microfluidic lab-on-a-chip systems of modified design with 98% separation efficiency, and 10 micron polystyrene particles have been separated with 100% separation efficiency. About the novelty of this work, the experimental investigations have been performed on the surface-driven microfluidic flow of aqueous microparticle suspensions with the investigations on the separation time in particle-size based separation mechanism to control these suspensions in the microfluidic lab-on-a-chip systems. This research work contains a total of 10,112 individual experimental outputs obtained using total 30 individual instruments by author’s own hands-on completely during more than three years continuously. Author has performed the experimental investigations on both the fluid statics and fluid dynamics to develop an automated fluid machine.

Comparing two models for post-wildfire debris flow susceptibility mapping

NASA Astrophysics Data System (ADS)

Cramer, J.; Bursik, M. I.; Legorreta Paulin, G.

2017-12-01

Traditionally, probabilistic post-fire debris flow susceptibility mapping has been performed based on the typical method of failure for debris flows/landslides, where slip occurs along a basal shear zone as a result of rainfall infiltration. Recent studies have argued that post-fire debris flows are fundamentally different in their method of initiation, which is not infiltration-driven, but surface runoff-driven. We test these competing models by comparing the accuracy of the susceptibility maps produced by each initiation method. Debris flow susceptibility maps are generated according to each initiation method for a mountainous region of Southern California that recently experienced wildfire and subsequent debris flows. A multiple logistic regression (MLR), which uses the occurrence of past debris flows and the values of environmental parameters, was used to determine the probability of future debris flow occurrence. The independent variables used in the MLR are dependent on the initiation method; for example, depth to slip plane, and shear strength of soil are relevant to the infiltration initiation, but not surface runoff. A post-fire debris flow inventory serves as the standard to compare the two susceptibility maps, and was generated by LiDAR analysis and field based ground-truthing. The amount of overlap between the true locations where debris flow erosion can be documented, and where the MLR predicts high probability of debris flow initiation was statistically quantified. The Figure of Merit in Space (FMS) was used to compare the two models, and the results of the FMS comparison suggest that surface runoff-driven initiation better explains debris flow occurrence. Wildfire can breed conditions that induce debris flows in areas that normally would not be prone to them. Because of this, nearby communities at risk may not be equipped to protect themselves against debris flows. In California, there are just a few months between wildland fire season and the wet season to assess a community's risk and prepare. It is important, therefore, that researchers have a way to quickly and accurately assess the susceptibility for debris flows in recently burned areas.

Strong wave/mean-flow coupling in baroclinic acoustic streaming

NASA Astrophysics Data System (ADS)

Chini, Greg; Michel, Guillaume

2017-11-01

Recently, Chini et al. demonstrated the potential for large-amplitude acoustic streaming in compressible channel flows subjected to strong background cross-channel density variations. In contrast with classic Rayleigh streaming, standing acoustic waves of O (ɛ) amplitude acquire vorticity owing to baroclinic torques acting throughout the domain rather than via viscous torques acting in Stokes boundary layers. More significantly, these baroclinically-driven streaming flows have a magnitude that also is O (ɛ) , i.e. comparable to that of the sound waves. In the present study, the consequent potential for fully two-way coupling between the waves and streaming flows is investigated using a novel WKBJ analysis. The analysis confirms that the wave-driven streaming flows are sufficiently strong to modify the background density gradient, thereby modifying the leading-order acoustic wave structure. Simulations of the wave/mean-flow system enabled by the WKBJ analysis are performed to illustrate the nature of the two-way coupling, which contrasts sharply with classic Rayleigh streaming, for which the waves can first be determined and the streaming flows subsequently computed.

Magnetism of toroidal field in two-fluid equilibrium of CHI driven spherical torus

NASA Astrophysics Data System (ADS)

Kanki, T.; Nagata, M.

2016-10-01

Double-pulsing CHI (D-CHI) experiment has been conducted in the HIST device to achieve a quasi-steady sustainment and good confinement of spherical torus (ST) plasmas. The feature of CHI driven ST such as diamagnetic toroidal field in the central open flux column (OFC) region and strong poloidal flow shear around the separatrix in the high field side suggests the two-fluid effect. The relationship between the magnetism of the toroidal field and the poloidal flow velocity is investigated by modelling the D-CHI (mainly driving the poloidal electron flow along the open flux) in the two-fluid equilibrium calculations. The poloidal component of Ampere's law leads that the toroidal field is related to the difference between the stream functions of ion ψi and electron ψe for the poloidal flow, indicating that the toroidal field with ψe >ψi results in a diamagnetic profile, while that with ψe <ψi results in a paramagnetic one. The gradient of the stream function determines the polarity and the strength of the poloidal flow velocity. It is found that the two-fluid equilibrium of CHI driven ST satisfies ψe > 0 and ψi < 0 in the OFC region, and ψe < 0 and ψi < 0 in the closed flux region. The toroidal field is a diamagnetic profile in the OFC region due to ψe >ψi and |uez | > |uiz | , where uez and uiz denote the poloidal electron and ion flow velocities, respectively. It becomes from a diamagnetic to a paramagnetic profile in the closed flux region, because ψe (uez) approaches ψi (uiz) around the magnetic axis. The poloidal ion flow shear is enhanced in the OFC region due to the ion inertial effect through the toroidal ion flow velocity.

Tidally-driven Surface Flow in a Georgia Estuarine Saltmarsh

NASA Astrophysics Data System (ADS)

Young, D.; Bruder, B. L.; Haas, K. A.; Webster, D. R.

2016-02-01

Estuarine saltmarshes are diverse, valuable, and productive ecosystems. Vegetation dampens wave and current energy, thereby allowing the estuaries to serve as a nursery habitat for shellfish and fish species. Tidally-driven flow transports nutrients into and out of the estuary, nourishing inshore and offshore vegetation and animals. The effects of vegetation on the marsh hydrodynamics and on the estuary creek and channel flow are, unfortunately, poorly understood, and the knowledge that does exist primarily originates from modeling studies. Field studies addressing marsh surface flows are limited due to the difficulty of accurately measuring the water surface elevation and acquiring concurrent velocity measurements in the dense marsh vegetation. This study partially bridges the gap between the model observations of marsh flow driven by water surface elevation gradients and flume studies of flow through vegetation. Three current meters and three pressure transducers were deployed for three days along a transect perpendicular to the main channel (Little Ogeechee River) in a saltmarsh adjacent to Rose Dhu Island (Savannah, Georgia, USA). The pressure transducer locations were surveyed daily with static GPS yielding highly accurate water surface elevation data. During flood and ebb tide, water surface elevation differences between the marsh and Little Ogeechee River were observed up to 15 cm and pressure gradients were observed up to 0.0017 m of water surface elevation drop per m of linear distance. The resulting channel-to-saltmarsh pressure gradients substantially affected tidal currents at all current meters. At one current meter, the velocity was nearly perpendicular to the Little Ogeechee River bank. The velocity at this location was effectively modeled as a balance between the pressure gradient and marsh vegetation-induced drag force using the Darcy-Weisbach/Lindner's equations developed for flow-through-vegetation analysis in open channel flow.

Steady Capillary Driven Flow

NASA Technical Reports Server (NTRS)

Weislogel, Mark M.

1996-01-01

A steady capillary driven flow is developed for a liquid index in a circular tube which is partially coated with a surface modifier to produce a discontinuous wetting condition from one side of the tube to the other. The bulk flow is novel in that it is truly steady, and controlled solely by the physics associated with dynamic wetting. The influence of gravity on the flow is minimized through the use of small diameter tubes approximately O(1 mm) tested horizontally in a laboratory and larger tubes approximately O(10 mm) tested in the low gravity environment of a drop tower. Average steady velocities are predicted and compared against a large experimental data set which includes the effects of tube dimensions and fluid properties. The sensitivity of the velocity to surface cleanliness is dramatic and the advantages of experimentation in a microgravity environment are discussed.

Numerical simulations of bistable flows in precessing spheroidal shells

NASA Astrophysics Data System (ADS)

Vormann, J.; Hansen, U.

2018-05-01

Precession of the rotation axis is an often neglected mechanical driving mechanism for flows in planetary interiors, through viscous coupling at the boundaries and topographic forcing in non-spherical geometries. We investigate precession-driven flows in spheroidal shells over a wide range of parameters and test the results against theoretical predictions. For Ekman numbers down to 8.0 × 10-7, we see a good accordance with the work of Busse, who assumed the precession-driven flow to be dominated by a rigid rotation component that is tilted to the main rotation axis. The velocity fields show localized small-scale structures for lower Ekman numbers and clear signals of inertial waves for some parameters. For the case of moderate viscosity and strong deformation, we report the realization of multiple solutions at the same parameter combination, depending on the initial condition.

Pressure driven flow of superfluid 4He through a nanopipe

NASA Astrophysics Data System (ADS)

Botimer, Jeffrey; Taborek, Peter

2016-09-01

Pressure driven flow of superfluid helium through single high-aspect-ratio glass nanopipes into a vacuum has been studied for a wide range of pressure drop (0-30 bars), reservoir temperature (0.8-2.5 K), pipe lengths (1-30 mm), and pipe radii (131 and 230 nm). As a function of pressure drop we observe two distinct flow regimes above and below a critical pressure drop Pc. For P

Theory of ion Bernstein wave induced shear suppression of turbulence

NASA Astrophysics Data System (ADS)

Craddock, G. G.; Diamond, P. H.; Ono, M.; Biglari, H.

1994-06-01

The theory of radio frequency induced ion Bernstein wave- (IBW) driven shear flow in the edge is examined, with the goal of application of shear suppression of fluctuations. This work is motivated by the observed confinement improvement on IBW heated tokamaks [Phys. Fluids B 5, 241 (1993)], and by previous low-frequency work on RF-driven shear flows [Phys. Rev. Lett. 67, 1535 (1991)]. It is found that the poloidal shear flow is driven electrostatically by both Reynolds stress and a direct ion momentum source, analogous to the concepts of helicity injection and electron momentum input in current drive, respectively. Flow drive by the former does not necessarily require momentum input to the plasma to induce a shear flow. For IBW, the direct ion momentum can be represented by direct electron momentum input, and a charge separation induced stress that imparts little momentum to the plasma. The derived Er profile due to IBW predominantly points inward, with little possibility of direction change, unlike low-frequency Alfvénic RF drive. The profile scale is set by the edge density gradient and electron dissipation. Due to the electrostatic nature of ion Bernstein waves, the poloidal flow contribution dominates in Er. Finally, the necessary edge power absorbed for shear suppression on Princeton Beta Experiment-Modified (PBX-M) [9th Topical Conference on Radio Frequency Power in Plasmas, Charleston, SC, 1991 (American Institute of Physics, New York, 1991), p. 129] is estimated to be 100 kW distributed over 5 cm.

Slow Magnetosonic Waves and Fast Flows in Active Region Loops

NASA Technical Reports Server (NTRS)

Ofman, L.; Wang, T. J.; Davila, J. M.

2012-01-01

Recent extreme ultraviolet spectroscopic observations indicate that slow magnetosonic waves are present in active region (AR) loops. Some of the spectral data were also interpreted as evidence of fast (approx 100-300 km/s) quasiperiodic flows. We have performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar AR that contains impulsively generated waves and flows in coronal loops. The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with an upflow-driven steadily or periodically in localized regions at the footpoints of magnetic loops. The resulting flows along the magnetic field lines of the AR produce higher density loops compared to the surrounding plasma by injection of material into the flux tubes and the establishment of siphon flow.We find that the impulsive onset of flows with subsonic speeds result in the excitation of damped slow magnetosonic waves that propagate along the loops and coupled nonlinearly driven fast-mode waves. The phase speed of the slow magnetosonic waves is close to the coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock-like wave trains are produced. When the upflows are driven periodically, undamped oscillations are produced with periods determined by the periodicity of the upflows. Based on the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and persistent upflows may be produced by the same impulsive events at the bases of ARs.

Energy flow and functional compensation in Great Basin small mammals under natural and anthropogenic environmental change

PubMed Central

Terry, Rebecca C.; Rowe, Rebecca J.

2015-01-01

Research on the ecological impacts of environmental change has primarily focused at the species level, leaving the responses of ecosystem-level properties like energy flow poorly understood. This is especially so over millennial timescales inaccessible to direct observation. Here we examine how energy flow within a Great Basin small mammal community responded to climate-driven environmental change during the past 12,800 y, and use this baseline to evaluate responses observed during the past century. Our analyses reveal marked stability in energy flow during rapid climatic warming at the terminal Pleistocene despite dramatic turnover in the distribution of mammalian body sizes and habitat-associated functional groups. Functional group turnover was strongly correlated with climate-driven changes in regional vegetation, with climate and vegetation change preceding energetic shifts in the small mammal community. In contrast, the past century has witnessed a substantial reduction in energy flow caused by an increase in energetic dominance of small-bodied species with an affinity for closed grass habitats. This suggests that modern changes in land cover caused by anthropogenic activities—particularly the spread of nonnative annual grasslands—has led to a breakdown in the compensatory dynamics of energy flow. Human activities are thus modifying the small mammal community in ways that differ from climate-driven expectations, resulting in an energetically novel ecosystem. Our study illustrates the need to integrate across ecological and temporal scales to provide robust insights for long-term conservation and management. PMID:26170294

Vascular structure determines pulmonary blood flow distribution

NASA Technical Reports Server (NTRS)

Hlastala, M. P.; Glenny, R. W.

1999-01-01

Scientific knowledge develops through the evolution of new concepts. This process is usually driven by new methodologies that provide observations not previously available. Understanding of pulmonary blood flow determinants advanced significantly in the 1960s and is now changing rapidly again, because of increased spatial resolution of regional pulmonary blood flow measurements.

Experimental investigation of certain internal condensing and boiling flows: Their sensitivity to pressure fluctuations and heat transfer enhancements

NASA Astrophysics Data System (ADS)

Kivisalu, Michael Toomas

Space-based (satellite, scientific probe, space station, etc.) and millimeter -- to -- micro-scale (such as are used in high power electronics cooling, weapons cooling in aircraft, etc.) condensers and boilers are shear/pressure driven. They are of increasing interest to system engineers for thermal management because flow boilers and flow condensers offer both high fluid flow-rate-specific heat transfer capacity and very low thermal resistance between the fluid and the heat exchange surface, so large amounts of heat may be removed using reasonably-sized devices without the need for excessive temperature differences. However, flow stability issues and degredation of performance of shear/pressure driven condensers and boilers due to non-desireable flow morphology over large portions of their lengths have mostly prevented their use in these applications. This research is part of an ongoing investigation seeking to close the gap between science and engineering by analyzing two key innovations which could help address these problems. First, it is recommended that the condenser and boiler be operated in an innovative flow configuration which provides a non-participating core vapor stream to stabilize the annular flow regime throughout the device length, accomplished in an energy-efficient manner by means of ducted vapor re-circulation. This is demonstrated experimentally.. Second, suitable pulsations applied to the vapor entering the condenser or boiler (from the re-circulating vapor stream) greatly reduce the thermal resistance of the already effective annular flow regime. For experiments reported here, application of pulsations increased time-averaged heat-flux up to 900 % at a location within the flow condenser and up to 200 % at a location within the flow boiler, measured at the heat-exchange surface. Traditional fully condensing flows, reported here for comparison purposes, show similar heat-flux enhancements due to imposed pulsations over a range of frequencies. Shear/pressure driven condensing and boiling flow experiments are carried out in horizontal mm-scale channels with heat exchange through the bottom surface. The sides and top of the flow channel are insulated. The fluid is FC-72 from 3M Corporation.

Solar Dynamo Driven by Periodic Flow Oscillation

NASA Technical Reports Server (NTRS)

Mayr, Hans G.; Hartle, Richard E.; Einaudi, Franco (Technical Monitor)

2001-01-01

We have proposed that the periodicity of the solar magnetic cycle is determined by wave mean flow interactions analogous to those driving the Quasi Biennial Oscillation in the Earth's atmosphere. Upward propagating gravity waves would produce oscillating flows near the top of the radiation zone that in turn would drive a kinematic dynamo to generate the 22-year solar magnetic cycle. The dynamo we propose is built on a given time independent magnetic field B, which allows us to estimate the time dependent, oscillating components of the magnetic field, (Delta)B. The toroidal magnetic field (Delta)B(sub phi) is directly driven by zonal flow and is relatively large in the source region, (Delta)(sub phi)/B(sub Theta) much greater than 1. Consistent with observations, this field peaks at low latitudes and has opposite polarities in both hemispheres. The oscillating poloidal magnetic field component, (Delta)B(sub Theta), is driven by the meridional circulation, which is difficult to assess without a numerical model that properly accounts for the solar atmosphere dynamics. Scale-analysis suggests that (Delta)B(sub Theta) is small compared to B(sub Theta) in the dynamo region. Relative to B(sub Theta), however, the oscillating magnetic field perturbations are expected to be transported more rapidly upwards in the convection zone to the solar surface. As a result, (Delta)B(sub Theta) (and (Delta)B(sub phi)) should grow relative to B(sub Theta), so that the magnetic fields reverse at the surface as observed. Since the meridional and zonai flow oscillations are out of phase, the poloidal magnetic field peaks during times when the toroidal field reverses direction, which is observed. With the proposed wave driven flow oscillation, the magnitude of the oscillating poloidal magnetic field increases with the mean rotation rate of the fluid. This is consistent with the Bode-Blackett empirical scaling law, which reveals that in massive astrophysical bodies the magnetic moment tends to increase with the angular momentum of the fluid.

The variance of angle-of-arrival fluctuation of partially coherent Gaussian-Schell Model beam propagations in slant atmospheric turbulence

NASA Astrophysics Data System (ADS)

Tan, Zhenkun; Ke, Xizheng

2017-10-01

The variance of angle-of-arrival fluctuation of the partially coherent Gaussian-Schell Model (GSM) beam propagations in the slant path, based on the extended Huygens-Fresnel principle and the model of atmospheric refraction index structural constant proposed by the international telecommunication union-radio (ITU-R), has been investigated under the modified Hill turbulence model. The expression of that has been obtained. Firstly, the effects of optical wavelength, the inner-and-outer scale of the turbulence and turbulence intensity on the variance of angle-of-arrival fluctuation have been analyzed by comparing with the partially coherent GSM beam and the completely coherent Gaussian beam. Secondly, the variance of angle-of-arrival fluctuation has been compared with the von Karman spectrum and the modified Hill spectrum under the partially coherent GSM beam. Finally, the effects of beam waist radius and partial coherence length on the variance of angle-of-arrival of the collimated (focused) beam have been analyzed under the modified Hill turbulence model. The results show that the influence of the variance of angle-of-arrival fluctuation for the inner scale effect is larger than that of the outer scale effect. The variance of angle-of-arrival fluctuation under the modified Hill spectrum is larger than that of the von Karman spectrum. The influence of the waist radius on the variance of angle-of-arrival for the collimated beam is less than focused the beam. This study will provide a necessary theoretical basis for the experiments of partially coherent GSM beam propagation through atmosphere turbulence.

Simulations of material mixing in laser-driven reshock experiments

NASA Astrophysics Data System (ADS)

Haines, Brian M.; Grinstein, Fernando F.; Welser-Sherrill, Leslie; Fincke, James R.

2013-02-01

We perform simulations of a laser-driven reshock experiment [Welser-Sherrill et al., High Energy Density Phys. (unpublished)] in the strong-shock high energy-density regime to better understand material mixing driven by the Richtmyer-Meshkov instability. Validation of the simulations is based on direct comparison of simulation and radiographic data. Simulations are also compared with published direct numerical simulation and the theory of homogeneous isotropic turbulence. Despite the fact that the flow is neither homogeneous, isotropic nor fully turbulent, there are local regions in which the flow demonstrates characteristics of homogeneous isotropic turbulence. We identify and isolate these regions by the presence of high levels of turbulent kinetic energy (TKE) and vorticity. After reshock, our analysis shows characteristics consistent with those of incompressible isotropic turbulence. Self-similarity and effective Reynolds number assessments suggest that the results are reasonably converged at the finest resolution. Our results show that in shock-driven transitional flows, turbulent features such as self-similarity and isotropy only fully develop once de-correlation, characteristic vorticity distributions, and integrated TKE, have decayed significantly. Finally, we use three-dimensional simulation results to test the performance of two-dimensional Reynolds-averaged Navier-Stokes simulations. In this context, we also test a presumed probability density function turbulent mixing model extensively used in combustion applications.

A data-driven approach for modeling post-fire debris-flow volumes and their uncertainty

USGS Publications Warehouse

Friedel, Michael J.

2011-01-01

This study demonstrates the novel application of genetic programming to evolve nonlinear post-fire debris-flow volume equations from variables associated with a data-driven conceptual model of the western United States. The search space is constrained using a multi-component objective function that simultaneously minimizes root-mean squared and unit errors for the evolution of fittest equations. An optimization technique is then used to estimate the limits of nonlinear prediction uncertainty associated with the debris-flow equations. In contrast to a published multiple linear regression three-variable equation, linking basin area with slopes greater or equal to 30 percent, burn severity characterized as area burned moderate plus high, and total storm rainfall, the data-driven approach discovers many nonlinear and several dimensionally consistent equations that are unbiased and have less prediction uncertainty. Of the nonlinear equations, the best performance (lowest prediction uncertainty) is achieved when using three variables: average basin slope, total burned area, and total storm rainfall. Further reduction in uncertainty is possible for the nonlinear equations when dimensional consistency is not a priority and by subsequently applying a gradient solver to the fittest solutions. The data-driven modeling approach can be applied to nonlinear multivariate problems in all fields of study.

Passive injection control for microfluidic systems

DOEpatents

Paul, Phillip H.; Arnold, Don W.; Neyer, David W.

2004-12-21

Apparatus for eliminating siphoning, "dead" regions, and fluid concentration gradients in microscale analytical devices. In its most basic embodiment, the present invention affords passive injection control for both electric field-driven and pressure-driven systems by providing additional fluid flow channels or auxiliary channels disposed on either side of a sample separation column. The auxiliary channels are sized such that volumetric fluid flow rate through these channels, while sufficient to move the sample away from the sample injection region in a timely fashion, is less than that through the sample separation channel or chromatograph.

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

NASA Technical Reports Server (NTRS)

Haj-Hariri, Hossein; Borhan, A.

1996-01-01

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

Study of Magnetic Damping Effect on Convection and Solidification Under G-Jitter Conditions

NASA Technical Reports Server (NTRS)

Li, Ben Q.; deGroh, H. C., III

1999-01-01

As shown by NASA resources dedicated to measuring residual gravity (SAMS and OARE systems), g-jitter is a critical issue affecting space experiments on solidification processing of materials. This study aims to provide, through extensive numerical simulations and ground based experiments, an assessment of the use of magnetic fields in combination with microgravity to reduce the g-jitter induced convective flows in space processing systems. We have so far completed asymptotic analyses based on the analytical solutions for g-jitter driven flow and magnetic field damping effects for a simple one-dimensional parallel plate configuration, and developed both 2-D and 3-D numerical models for g-jitter driven flows in simple solidification systems with and without presence of an applied magnetic field. Numerical models have been checked with the analytical solutions and have been applied to simulate the convective flows and mass transfer using both synthetic g-jitter functions and the g-jitter data taken from space flight. Some useful findings have been obtained from the analyses and the modeling results. Some key points may be summarized as follows: (1) the amplitude of the oscillating velocity decreases at a rate inversely proportional to the g-jitter frequency and with an increase in the applied magnetic field; (2) the induced flow approximately oscillates at the same frequency as the affecting g-jitter, but out of a phase angle; (3) the phase angle is a complicated function of geometry, applied magnetic field, temperature gradient and frequency; (4) g-jitter driven flows exhibit a complex fluid flow pattern evolving in time; (5) the damping effect is more effective for low frequency flows; and (6) the applied magnetic field helps to reduce the variation of solutal distribution along the solid-liquid interface. Work in progress includes numerical simulations and ground-based measurements. Both 2-D and 3-D numerical simulations are being continued to obtain further information on g-jitter driven flows and magnetic field effects. A physical model for ground-based measurements is completed and some measurements of the oscillating convection are being taken on the physical model. The comparison of the measurements with numerical simulations is in progress. Additional work planned in the project will also involve extending the 2-D numerical model to include the solidification phenomena with the presence of both g-jitter and magnetic fields.

Turbidity current with a roof: Direct numerical simulation of self-stratified turbulent channel flow driven by suspended sediment

NASA Astrophysics Data System (ADS)

Cantero, Mariano I.; Balachandar, S.; Cantelli, Alessandro; Pirmez, Carlos; Parker, Gary

2009-03-01

In this work we present direct numerical simulations (DNS) of sediment-laden channel flows. In contrast to previous studies, where the flow has been driven by a constant, uniform pressure gradient, our flows are driven by the excess density imposed by suspended sediment. This configuration provides a simplified model of a turbidity current and is thus called the turbidity current with a roof configuration. Our calculations elucidate with DNS for the first time several fascinating features of sediment-laden flows, which may be summarized as follows. First, the presence of sediment breaks the symmetry of the flow because of a tendency to self-stratify. More specifically, this self-stratification is manifested in terms of a Reynolds-averaged suspended sediment concentration that declines in the upward normal direction and a Reynolds-averaged velocity profile with a maximum that is below the channel centerline. Second, this self-stratification damps the turbulence, particularly near the bottom wall. Two regimes are observed, one in which the flow remains turbulent but the level of turbulence is reduced and another in which the flow relaminarizes in a region near the bottom wall, i.e., bed. Third, the analysis allows the determination of a criterion for the break between these two regimes in terms of an appropriately defined dimensionless settling velocity. The results provide guidance for the improvement of Reynolds-averaged closures for turbulent flow in regard to stratification effects. Although the analysis reported here is not performed at the scale of large oceanic turbidity currents, which have sufficiently large Reynolds numbers to be inaccessible via DNS at this time, the implication of flow relaminarization is of considerable importance. Even a swift oceanic turbidity current which at some point crosses the threshold into the regime of relaminarization may lose the capacity to reentrain sediment that settles on the bed and thus may quickly die as it loses its driving force.

Building Integrated Active Flow Control: Improving the Aerodynamic Performance of Tall Buildings Using Fluid-Based Aerodynamic Modification

NASA Astrophysics Data System (ADS)

Menicovich, David

By 2050 an estimated 9 billion people will inhabit planet earth and almost all the growth in the next 40 years will be in urban areas putting tremendous pressure on creating sustainable cities. The rapid increase in population, rise in land value and decrease in plot sizes in cities around the world positions tall or more importantly slender buildings as the best suited building typology to address the increasingly critical demand for space in this pressing urbanization trend. However, the majority of new tall building urban developments have not followed principles of environmental and/or sustainable design and incentives to innovate, both technological and economic, are urgently required. The biggest climatic challenge to the design, construction and performance of tall buildings is wind sensitivity. This challenge is further emphasized seeing two market driven trends: on one hand as urban population grows, land value rises while plot sizes decrease; on the other, more cost effective modular construction techniques are introducing much lighter tall building structures. The combination of the two suggests a potential increase in the slenderness ratio of tall buildings (typically less than 6:1 but stretching to 20:1 in the near future) where not-so-tall but much lighter buildings will be the bulk of new construction in densely populated cities, providing affordable housing in the face of fast urbanization but also introducing wind sensitivity which was previously the problem of a very limited number of super tall buildings to a much larger number of buildings and communities. The proposed research aims to investigate a novel approach to the interaction between tall buildings and their environment. Through this approach the research proposes a new relationship between buildings and the flows around, through and inside them, where buildings could adapt to better control and manage the air flow around them, and consequently produce significant opportunities to reduce material and energy consumption profiles of tall building. To date, the increasing use of light-weight and high-strength materials in tall buildings, with greater flexibility and reduced damping, has increased susceptibility to dynamic wind load effects that limit the gains afforded by incorporating these new materials. Wind, particularly fluctuating wind and its interaction with buildings induces two main responses; alongwind - in the direction of the flow and crosswind - perpendicular to the flow. The main risk associated with this vulnerability is resonant oscillations induced by von-Karman-like vortex shedding at or near the natural frequency of the structure caused by flow separation. Dynamic wind loading effects often increase with a power of wind speed greater than 3, thus increasingly, tall buildings pay a significant price in material to increase the natural frequency and/or the damping to overcome this response. In particular, crosswind response often governs serviceability (human habitability) design criteria of slender buildings. Currently, reducing crosswind response relies on a Solid-based Aerodynamic Modification (SAM), either by changing structural or geometric characteristics such as the tower shape or through the addition of damping systems. While this approach has merit it has two major drawbacks: firstly, the loss of valuable rentable areas and high construction costs due to increased structural requirements for mass and stiffness, further contributing towards the high consumption of non-renewable resources by the commercial building sector. For example, in order to insure human comfort within an acceptable range of crosswind response induced accelerations at the top of a building, an aerodynamically efficient plan shape comes at the expense of floor area. To compensate for the loss of valuable area compensatory stories are required, resulting in an increase in wind loads and construction costs. Secondly, a limited, if at all, ability to adaptively respond to fluctuating environmental conditions such as changes in wind direction or velocity over the height of building which could be of consequence if the conditions for which the building was designed for change due to, for example, changes in the built environment surrounding it. Fluidic-based Aerodynamic Modification (FAM) is a fundamentally different approach; instead of adjusting the solid material to improve the aerodynamic 'shape' of the structure, fluid-based flow control is used to manipulate the boundary layer characteristics. The local flow field is modified to 'view' the solid as a different shape, and thus, that solid will experience reduced loads.

Initial conditions and modeling for simulations of shock driven turbulent material mixing

DOE PAGES

Grinstein, Fernando F.

2016-11-17

Here, we focus on the simulation of shock-driven material mixing driven by flow instabilities and initial conditions (IC). Beyond complex multi-scale resolution issues of shocks and variable density turbulence, me must address the equally difficult problem of predicting flow transition promoted by energy deposited at the material interfacial layer during the shock interface interactions. Transition involves unsteady large-scale coherent-structure dynamics capturable by a large eddy simulation (LES) strategy, but not by an unsteady Reynolds-Averaged Navier–Stokes (URANS) approach based on developed equilibrium turbulence assumptions and single-point-closure modeling. On the engineering end of computations, such URANS with reduced 1D/2D dimensionality and coarsermore » grids, tend to be preferred for faster turnaround in full-scale configurations.« less

The Feasibility of Applying AC Driven Low-Temperature Plasma for Multi-Cycle Detonation Initiation

NASA Astrophysics Data System (ADS)

Zheng, Dianfeng

2016-11-01

Ignition is a key system in pulse detonation engines (PDE). As advanced ignition methods, nanosecond pulse discharge low-temperature plasma ignition is used in some combustion systems, and continuous alternating current (AC) driven low-temperature plasma using dielectric barrier discharge (DBD) is used for the combustion assistant. However, continuous AC driven plasmas cannot be used for ignition in pulse detonation engines. In this paper, experimental and numerical studies of pneumatic valve PDE using an AC driven low-temperature plasma igniter were described. The pneumatic valve was jointly designed with the low-temperature plasma igniter, and the numerical simulation of the cold-state flow field in the pneumatic valve showed that a complex flow in the discharge area, along with low speed, was beneficial for successful ignition. In the experiments ethylene was used as the fuel and air as oxidizing agent, ignition by an AC driven low-temperature plasma achieved multi-cycle intermittent detonation combustion on a PDE, the working frequency of the PDE reached 15 Hz and the peak pressure of the detonation wave was approximately 2.0 MPa. The experimental verifications of the feasibility in PDE ignition expanded the application field of AC driven low-temperature plasma. supported by National Natural Science Foundation of China (No. 51176001)

Pulsatile flow and mass transport over an array of cylinders: gas transfer in a cardiac-driven artificial lung.

PubMed

Chan, Kit Yan; Fujioka, Hideki; Bartlett, Robert H; Hirschl, Ronald B; Grotberg, James B

2006-02-01

The pulsatile flow and gas transport of a Newtonian passive fluid across an array of cylindrical microfibers are numerically investigated. It is related to an implantable, artificial lung where the blood flow is driven by the right heart. The fibers are modeled as either squared or staggered arrays. The pulsatile flow inputs considered in this study are a steady flow with a sinusoidal perturbation and a cardiac flow. The aims of this study are twofold: identifying favorable array geometry/spacing and system conditions that enhance gas transport; and providing pressure drop data that indicate the degree of flow resistance or the demand on the right heart in driving the flow through the fiber bundle. The results show that pulsatile flow improves the gas transfer to the fluid compared to steady flow. The degree of enhancement is found to be significant when the oscillation frequency is large, when the void fraction of the fiber bundle is decreased, and when the Reynolds number is increased; the use of a cardiac flow input can also improve gas transfer. In terms of array geometry, the staggered array gives both a better gas transfer per fiber (for relatively large void fraction) and a smaller pressure drop (for all cases). For most cases shown, an increase in gas transfer is accompanied by a higher pressure drop required to power the flow through the device.

Implementation of density-based solver for all speeds in the framework of OpenFOAM

NASA Astrophysics Data System (ADS)

Shen, Chun; Sun, Fengxian; Xia, Xinlin

2014-10-01

In the framework of open source CFD code OpenFOAM, a density-based solver for all speeds flow field is developed. In this solver the preconditioned all speeds AUSM+(P) scheme is adopted and the dual time scheme is implemented to complete the unsteady process. Parallel computation could be implemented to accelerate the solving process. Different interface reconstruction algorithms are implemented, and their accuracy with respect to convection is compared. Three benchmark tests of lid-driven cavity flow, flow crossing over a bump, and flow over a forward-facing step are presented to show the accuracy of the AUSM+(P) solver for low-speed incompressible flow, transonic flow, and supersonic/hypersonic flow. Firstly, for the lid driven cavity flow, the computational results obtained by different interface reconstruction algorithms are compared. It is indicated that the one dimensional reconstruction scheme adopted in this solver possesses high accuracy and the solver developed in this paper can effectively catch the features of low incompressible flow. Then via the test cases regarding the flow crossing over bump and over forward step, the ability to capture characteristics of the transonic and supersonic/hypersonic flows are confirmed. The forward-facing step proves to be the most challenging for the preconditioned solvers with and without the dual time scheme. Nonetheless, the solvers described in this paper reproduce the main features of this flow, including the evolution of the initial transient.

The formation and dissipation of electrostatic shock waves: the role of ion–ion acoustic instabilities

NASA Astrophysics Data System (ADS)

Zhang, Wen-shuai; Cai, Hong-bo; Zhu, Shao-ping

2018-05-01

The role of ion–ion acoustic instabilities in the formation and dissipation of collisionless electrostatic shock waves driven by counter-streaming supersonic plasma flows has been investigated via two-dimensional particle-in-cell simulations. The nonlinear evolution of unstable waves and ion velocity distributions has been analyzed in detail. It is found that for electrostatic shocks driven by moderate-velocity flows, longitudinal and oblique ion–ion acoustic instabilities can be excited in the downstream and upstream regions, which lead to thermalization of the transmitted and reflected ions, respectively. For high-velocity flows, oblique ion–ion acoustic instabilities can develop in the overlap layer during the shock formation process and impede the shock formation.

Multiple independent autonomous hydraulic oscillators driven by a common gravity head.

PubMed

Kim, Sung-Jin; Yokokawa, Ryuji; Lesher-Perez, Sasha Cai; Takayama, Shuichi

2015-06-15

Self-switching microfluidic circuits that are able to perform biochemical experiments in a parallel and autonomous manner, similar to instruction-embedded electronics, are rarely implemented. Here, we present design principles and demonstrations for gravity-driven, integrated, microfluidic pulsatile flow circuits. With a common gravity head as the only driving force, these fluidic oscillator arrays realize a wide range of periods (0.4 s-2 h) and flow rates (0.10-63 μl min(-1)) with completely independent timing between the multiple oscillator sub-circuits connected in parallel. As a model application, we perform systematic, parallel analysis of endothelial cell elongation response to different fluidic shearing patterns generated by the autonomous microfluidic pulsed flow generation system.

Experiments on two- and three-dimensional vortex flows in lid-driven cavities

NASA Astrophysics Data System (ADS)

Siegmann-Hegerfeld, Tanja; Albensoeder, Stefan; Kuhlmann, Hendrik C.

2009-11-01

Vortex flows in one-sided lid-driven cavities with different cross-sectional aspect ratios (γ = 0.26 up to γ = 6.3) are investigated experimentally. In all cases the spanwise aspect ratio λ>>γ is very large and much larger than most previous experiments. Flow-structure visualizations will be presented together with quantitative LDA and PIV measurements. The experimental results are in good agreement with the critical data from numerical stability analyses and with nonlinear simulations. Experimentally, we find four different three-dimensional instabilities. Particular attention is paid to the so-called C4 mode which arises at large cross-sectional aspect ratios. When the spanwise aspect ratio is small the first bifurcation of the C4 mode is strongly imperfect.

What Drives Saline Circulation Cells in Coastal Aquifers? An Energy Balance for Density-Driven Groundwater Systems

NASA Astrophysics Data System (ADS)

Harvey, C. F.; Michael, H. A.

2017-12-01

We formulate the energy balance for coastal groundwater systems and apply it to: (1) Explain the energy driving offshore saline circulation cells, and; (2) Assess the accuracy of numerical simulations of coastal groundwater systems. The flow of fresh groundwater to the ocean is driven by the loss of potential energy as groundwater drops from the elevation of the inland watertable, where recharge occurs, to discharge at sea level. This freshwater flow creates an underlying circulation cell of seawater, drawn into coastal aquifers offshore and discharging near shore, that adds to total submarine groundwater discharge. The saline water in the circulation cell enters and exits the aquifer through the sea floor at the same hydraulic potential. Existing theory explains that the saline circulation cell is driven by mixing of fresh and saline without any additional source of potential or mechanical power. This explanation raises a basic thermodynamic question: what is the source of energy that drives the saline circulation cell? Here, we resolve this question by building upon Hubbert's conception of hydraulic potential to formulate an energy balance for density-dependent flow and salt transport through an aquifer. We show that, because local energy dissipation within the aquifer is proportional to the square of the groundwater velocity, more groundwater flow may be driven through an aquifer for a given energy input if local variations in velocity are smoothed. Our numerical simulations of coastal groundwater systems show that dispersion of salt across the fresh-saline interface spreads flow over larger volumes of the aquifer, smoothing the velocity field, and increasing total flow and submarine groundwater discharge without consuming more power. The energy balance also provides a criterion, in addition to conventional mass balances, for judging the accuracy of numerical solutions of non-linear density-dependent flow problems. Our results show that some numerical simulations of saline circulation converge to excellent balances of both mass and energy, but that other simulations may poorly balance energy even after converging to a good mass balance. Thus, the energy balance can be used to identify incorrect simulations that pass convential mass balance criteria for accuracy.

The evolution of sensory divergence in the context of limited gene flow in the bumblebee bat

PubMed Central

Puechmaille, Sébastien J.; Gouilh, Meriadeg Ar; Piyapan, Piyathip; Yokubol, Medhi; Mie, Khin Mie; Bates, Paul J.; Satasook, Chutamas; Nwe, Tin; Bu, Si Si Hla; Mackie, Iain J.; Petit, Eric J.; Teeling, Emma C.

2011-01-01

The sensory drive theory of speciation predicts that populations of the same species inhabiting different environments can differ in sensory traits, and that this sensory difference can ultimately drive speciation. However, even in the best-known examples of sensory ecology driven speciation, it is uncertain whether the variation in sensory traits is the cause or the consequence of a reduction in levels of gene flow. Here we show strong genetic differentiation, no gene flow and large echolocation differences between the allopatric Myanmar and Thai populations of the world's smallest mammal, Craseonycteris thonglongyai, and suggest that geographic isolation most likely preceded sensory divergence. Within the geographically continuous Thai population, we show that geographic distance has a primary role in limiting gene flow rather than echolocation divergence. In line with sensory-driven speciation models, we suggest that in C. thonglongyai, limited gene flow creates the suitable conditions that favour the evolution of sensory divergence via local adaptation. PMID:22146392

GPU accelerated simulations of three-dimensional flow of power-law fluids in a driven cube

NASA Astrophysics Data System (ADS)

Jin, K.; Vanka, S. P.; Agarwal, R. K.; Thomas, B. G.

2017-01-01

Newtonian fluid flow in two- and three-dimensional cavities with a moving wall has been studied extensively in a number of previous works. However, relatively a fewer number of studies have considered the motion of non-Newtonian fluids such as shear thinning and shear thickening power law fluids. In this paper, we have simulated the three-dimensional, non-Newtonian flow of a power law fluid in a cubic cavity driven by shear from the top wall. We have used an in-house developed fractional step code, implemented on a Graphics Processor Unit. Three Reynolds numbers have been studied with power law index set to 0.5, 1.0 and 1.5. The flow patterns, viscosity distributions and velocity profiles are presented for Reynolds numbers of 100, 400 and 1000. All three Reynolds numbers are found to yield steady state flows. Tabulated values of velocity are given for the nine cases studied, including the Newtonian cases.

Realistic Data-Driven Traffic Flow Animation Using Texture Synthesis.

PubMed

Chao, Qianwen; Deng, Zhigang; Ren, Jiaping; Ye, Qianqian; Jin, Xiaogang

2018-02-01

We present a novel data-driven approach to populate virtual road networks with realistic traffic flows. Specifically, given a limited set of vehicle trajectories as the input samples, our approach first synthesizes a large set of vehicle trajectories. By taking the spatio-temporal information of traffic flows as a 2D texture, the generation of new traffic flows can be formulated as a texture synthesis process, which is solved by minimizing a newly developed traffic texture energy. The synthesized output captures the spatio-temporal dynamics of the input traffic flows, and the vehicle interactions in it strictly follow traffic rules. After that, we position the synthesized vehicle trajectory data to virtual road networks using a cage-based registration scheme, where a few traffic-specific constraints are enforced to maintain each vehicle's original spatial location and synchronize its motion in concert with its neighboring vehicles. Our approach is intuitive to control and scalable to the complexity of virtual road networks. We validated our approach through many experiments and paired comparison user studies.

Cast-to-shape electrokinetic trapping medium

DOEpatents

Shepodd, Timothy J.; Franklin, Elizabeth; Prickett, Zane T.; Artau, Alexander

2004-08-03

A three-dimensional microporous polymer network material, or monolith, cast-to-shape in a microchannel. The polymer monolith, produced by a phase separation process, is capable of trapping and retaining charged protein species from a mixture of charged and uncharged species under the influence of an applied electric field. The retained charged protein species are released from the porous polymer monolith by a pressure driven flow in the substantial absence of the electric field. The pressure driven flow is independent of direction and thus neither means to reverse fluid flow nor a multi-directional flow field is required, a single flow through the porous polymer monolith can be employed, in contrast to prior art systems. The monolithic polymer material produced by the invention can function as a chromatographic medium. Moreover, by virtue of its ability to retain charged protein species and quantitatively release the retained species the porous polymer monolith can serve as a means for concentrating charged protein species from, for example, a dilute solution.

Cast-to-shape electrokinetic trapping medium

DOEpatents

Shepodd, Timothy J [Livermore, CA; Franklin, Elizabeth [Rolla, MO; Prickett, Zane T [Golden, CO; Artau, Alexander [Pleasanton, CA

2006-05-30

A three-dimensional microporous polymer network material, or monolith, cast-to-shape in a microchannel. The polymer monolith, produced by a phase separation process, is capable of trapping and retaining charged protein species from a mixture of charged and uncharged species under the influence of an applied electric field. The retained charged protein species are released from the porous polymer monolith by a pressure driven flow in the substantial absence of the electric field. The pressure driven flow is independent of direction and thus neither means to reverse fluid flow nor a multi-directional flow field is required, a single flow through the porous polymer monolith can be employed, in contrast to prior art systems. The monolithic polymer material produced by the invention can function as a chromatographic medium. Moreover, by virtue of its ability to retain charged protein species and quantitatively release the retained species the porous polymer monolith can serve as a means for concentrating charged protein species from, for example, a dilute solution.

Foam relaxation in fractures and narrow channels

NASA Astrophysics Data System (ADS)

Lai, Ching-Yao; Rallabandi, Bhargav; Perazzo, Antonio; Stone, Howard A.

2017-11-01

Various applications, from foam manufacturing to hydraulic fracturing with foams, involve pressure-driven flow of foams in narrow channels. We report a combined experimental and theoretical study of this problem accounting for the compressible nature of the foam. In particular, in our experiments the foam is initially compressed in one channel and then upon flow into a second channel the compressed foam relaxes as it moves. A plug flow is observed in the tube and the pressure at the entrance of the tube is higher than the exit. We measure the volume collected at the exit of the tube, V, as a function of injection flow rate, tube length and diameter. Two scaling behaviors for V as a function of time are observed depending on whether foam compression is important or not. Our work may relate to foam fracturing, which saves water usage in hydraulic fracturing, more efficient enhanced oil recovery via foam injection, and various materials manufacturing processes involving pressure-driven flow foams.

Scaling of mean inertia and theoretical basis for a log law in turbulent boundary layers

NASA Astrophysics Data System (ADS)

Philip, Jimmy; Morrill-Winter, Caleb; Klewicki, Joseph

2017-11-01

Log law in the mean streamwise velocity (U) for pipes/channels is well accepted based on the derivation from the mean momentum balance (MMB) equation and support from experimental data. For flat plate turbulent boundary layers (TBLs), however, there is only empirical evidence and a theoretical underpinning of the kind available for pipes/channels in lacking. The main difficultly is the mean inertia (MI) term in the MMB equation, which, unlike in pipes/channels, is not a constant in TBLs. We present results from our paper (JFM `` 2017, Vol 813, pp 594-617), where the MI term for TBL is transformed so as to render it invariant in the outer region, corroborated with high Re (δ+) data from Melbourne Wind Tunnel and New Hampshire Flow Physics Facility. The transformation is possible because the MI term in the TBL has a `shape' which becomes invariant with increasing δ+ and a `magnitude' which is proportional to 1 /δ+ . The transformed equation is then employed to derive a log law for U with κ an order one (von-Karman) constant. We also show that the log law begins at y+ =C1√{δ+} , and the peak location of the Reynolds shear stress, ym+ =C2√{δ+} , where, C1 3.6 and C2 2.17 are from high Re data. Australian Research Council and the US National Science Foundation.

Finite Element Analysis of Magnetic Damping Effects on G-Jitter Induced Fluid Flow

NASA Technical Reports Server (NTRS)

Pan, Bo; Li, Ben Q.; deGroh, Henry C., III

1997-01-01

This paper reports some interim results on numerical modeling and analyses of magnetic damping of g-jitter driven fluid flow in microgravity. A finite element model is developed to represent the fluid flow, thermal and solute transport phenomena in a 2-D cavity under g-jitter conditions with and without an applied magnetic field. The numerical model is checked by comparing with analytical solutions obtained for a simple parallel plate channel flow driven by g-jitter in a transverse magnetic field. The model is then applied to study the effect of steady state g-jitter induced oscillation and on the solute redistribution in the liquid that bears direct relevance to the Bridgman-Stockbarger single crystal growth processes. A selection of computed results is presented and the results indicate that an applied magnetic field can effectively damp the velocity caused by g-jitter and help to reduce the time variation of solute redistribution.

The cryogenic wind tunnel for high Reynolds number testing. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Kilgore, R. A.

1974-01-01

Experiments performed at the NASA Langley Research Center in a cryogenic low-speed continuous-flow tunnel and in a cryogenic transonic continuous-flow pressure tunnel have demonstrated the predicted changes in Reynolds number, drive power, and fan speed with temperature, while operating with nitrogen as the test gas. The experiments have also demonstrated that cooling to cryogenic temperatures by spraying liquid nitrogen directly into the tunnel circuit is practical and that tunnel temperature can be controlled within very close limits. Whereas most types of wind tunnel could operate with advantage at cryogenic temperatures, the continuous-flow fan-driven tunnel is particularly well suited to take full advantage of operating at these temperatures. A continuous-flow fan-driven cryogenic tunnel to satisfy current requirements for test Reynolds number can be constructed and operated using existing techniques. Both capital and operating costs appear acceptable.

Calculation of turbulence-driven secondary motion in ducts with arbitrary cross section

NASA Technical Reports Server (NTRS)

Demuren, A. O.

1989-01-01

Calculation methods for turbulent duct flows are generalized for ducts with arbitrary cross-sections. The irregular physical geometry is transformed into a regular one in computational space, and the flow equations are solved with a finite-volume numerical procedure. The turbulent stresses are calculated with an algebraic stress model derived by simplifying model transport equations for the individual Reynolds stresses. Two variants of such a model are considered. These procedures enable the prediction of both the turbulence-driven secondary flow and the anisotropy of the Reynolds stresses, in contrast to some of the earlier calculation methods. Model predictions are compared to experimental data for developed flow in triangular duct, trapezoidal duct and a rod-bundle geometry. The correct trends are predicted, and the quantitative agreement is mostly fair. The simpler variant of the algebraic stress model procured better agreement with the measured data.

Electrokinetically driven microfluidic mixing with patchwise surface heterogeneity and AC applied electric field

NASA Astrophysics Data System (ADS)

Luo, Win-Jet; Yue, Cheng-Feng

2004-12-01

This paper investigates two-dimensional, time-dependent electroosmotic flows driven by an AC electric field via patchwise surface heterogeneities distributed along the microchannel walls. The time-dependent flow fields through the microchannel are simulated for various patchwise heterogeneous surface patterns using the backwards-Euler time stepping numerical method. Different heterogeneous surface patterns are found to create significantly different electrokinetic transport phenomena. It is shown that the presence of oppositely charged surface heterogeneities on the microchannel walls results in the formation of localized flow circulations within the bulk flow. These circulation regions grow and decay periodically in accordance with the applied periodic AC electric field intensity. The circulations provide an effective means of enhancing species mixing in the microchannel. A suitable design of the patchwise heterogeneous surface pattern permits the mixing channel length and the retention time required to attain a homogeneous solution to be reduced significantly.

A dilation-driven vortex flow in sheared granular materials explains a rheometric anomaly.

PubMed

Krishnaraj, K P; Nott, Prabhu R

2016-02-11

Granular flows occur widely in nature and industry, yet a continuum description that captures their important features is yet not at hand. Recent experiments on granular materials sheared in a cylindrical Couette device revealed a puzzling anomaly, wherein all components of the stress rise nearly exponentially with depth. Here we show, using particle dynamics simulations and imaging experiments, that the stress anomaly arises from a remarkable vortex flow. For the entire range of fill heights explored, we observe a single toroidal vortex that spans the entire Couette cell and whose sense is opposite to the uppermost Taylor vortex in a fluid. We show that the vortex is driven by a combination of shear-induced dilation, a phenomenon that has no analogue in fluids, and gravity flow. Dilatancy is an important feature of granular mechanics, but not adequately incorporated in existing models.

Ultra-sensitive flow measurement in individual nanopores through pressure--driven particle translocation.

PubMed

Gadaleta, Alessandro; Biance, Anne-Laure; Siria, Alessandro; Bocquet, Lyderic

2015-05-07

A challenge for the development of nanofluidics is to develop new instrumentation tools, able to probe the extremely small mass transport across individual nanochannels. Such tools are a prerequisite for the fundamental exploration of the breakdown of continuum transport in nanometric confinement. In this letter, we propose a novel method for the measurement of the hydrodynamic permeability of nanometric pores, by diverting the classical technique of Coulter counting to characterize a pressure-driven flow across an individual nanopore. Both the analysis of the translocation rate, as well as the detailed statistics of the dwell time of nanoparticles flowing across a single nanopore, allow us to evaluate the permeability of the system. We reach a sensitivity for the water flow down to a few femtoliters per second, which is more than two orders of magnitude better than state-of-the-art alternative methods.

Influence of Reservoirs on Pressure Driven Gas Flow in a Microchannel

NASA Astrophysics Data System (ADS)

Shterev, K. S.; Stefanov, S. K.

2011-11-01

Rapidly emerging micro-electro-mechanical devices create new potential microfluidic applications. A simulation of an internal and external gas flows with accurate boundary conditions for these devices is important for their design. In this paper we study influence of reservoirs used at the microchannel inlet and outlet on the characteristics of the gas flow in the microchannel. The problem is solved by using finite volume method SIMPLE-TS (continuum approach), which is validated using Direct Simulation Monte Carlo (molecular approach). We investigate two cases: a microchannels with reservoirs and without reservoirs. We compare the microchannels with different aspect ratios A = Lch/Hch = 10,15,20,30,40 and 50, where Lch is the channel length, Hch is the channel height. Comparisons of results obtained by using continuum approach for pressure driven flow in a microchannel with and without reservoirs at the channel ends are presented.

Effects of Initial Conditions on Shock Driven Flows

NASA Astrophysics Data System (ADS)

Martinez, Adam A.; Mula, Swathi M.; Charonko, John; Prestridge, Kathy

2017-11-01

The spatial and temporal evolution of shock-driven, variable density flows, such as the Richtmyer Meshkov (RM) instability, are strongly influenced by the initial conditions (IC's) of the flow at the time of interaction with shockwave. We study the effects of the IC's on the Vertical Shock Tube (VST) and on flows from Mach =1.2 to Mach =9. Experiments at the VST are of an Air-SF6 (At =0.6) multimode interface. Perturbations are generated using a shear layer with a flapper plate. Planar Laser Induced Fluorescence (PLIF) is used to characterize the IC's. New experiments are occurring using the Powder Gun driver at LANL Proton Radiography (pRad) facility. Mach number up to M =9 accelerate a Xenon-Helium (At =0.94) interface that is perturbed using a membrane supported by different sized grids. This presentation focuses on how to design and characterize different types of initial conditions for experiments.

A Process Dynamics and Control Experiment for the Undergraduate Laboratory

ERIC Educational Resources Information Center

Spencer, Jordan L.

2009-01-01

This paper describes a process control experiment. The apparatus includes a three-vessel glass flow system with a variable flow configuration, means for feeding dye solution controlled by a stepper-motor driven valve, and a flow spectrophotometer. Students use impulse response data and nonlinear regression to estimate three parameters of a model…

A Theory For The Variability of The Baroclinic Quasi-geostrophic Winnd Driven Circulation.

NASA Astrophysics Data System (ADS)

Ben Jelloul, M.; Huck, T.

We propose a theory of the wind driven circulation based on the large scale (i.e. small Burger number) quasi-geostrophic assumptions retained in the Rhines and Young (1982) classical study of the steady baroclinic flow. We therefore use multiple time scale and asymptotic expansions to separate steady and the time dependent component of the flow. The barotropic flow is given by the Sverdrup balance. At first order in Burger number, the baroclinic flow can be decom- posed in two parts. A steady contribution ensures no flow in the deep layer which is at rest in absence of dissipative processes. Since the baroclinic instability is inhibited at large scale a spectrum of neutral modes also arises. These are of three type, classical Rossby basin modes deformed through advection by the barotropic flow, recirculating modes localized in the recirculation gyre and blocked modes corresponding to closed potential vorticity contours. At next order in Burger number, amplitude equations for baroclinic modes are derived. If dissipative processes are included at this order, the system adjusts towards Rhines and Young solution with a homogenized potential vorticity pool.

The Relationship of Magnetotail Flow Bursts and Ground Onset Signatures

NASA Technical Reports Server (NTRS)

Kepko, Larry; Spanswick, Emma; Angelopoulos, Vassilis; Donovan, Eric

2010-01-01

It has been known for decades that auroral substorm onset occurs on (or at least near) the most equatorward auroral arc, which is thought to map to the near geosynchronous region. The lack of auroral signatures poleward of this arc prior to onset has been a major criticism of flow-burst driven models of substorm onset. The combined THEMIS 5 spacecraft in-situ and ground array measurements provide an unprecedented opportunity to examine the causal relationship between midtail plasma flows, aurora, and ground magnetic signatures. I first present an event from 2008 using multi-spectral all sky imager data from Gillam and in-situ data from THEMIS. The multispectral data indicate an equatorward moving auroral form prior to substorm onset. When this forms reaches the most equatorward arc, the arc brightens and an auroral substorm begins. The THEMIS data show fast Earthward flows prior to onset as well. I discuss further the association of flow bursts and Pi2 pulsations, in the con text of the directly-driven Pi2 model. This model directly links flows and Pi2 pulsations, providing an important constraint on substorm onset theories.

SPH with dynamical smoothing length adjustment based on the local flow kinematics

NASA Astrophysics Data System (ADS)

Olejnik, Michał; Szewc, Kamil; Pozorski, Jacek

2017-11-01

Due to the Lagrangian nature of Smoothed Particle Hydrodynamics (SPH), the adaptive resolution remains a challenging task. In this work, we first analyse the influence of the simulation parameters and the smoothing length on solution accuracy, in particular in high strain regions. Based on this analysis we develop a novel approach to dynamically adjust the kernel range for each SPH particle separately, accounting for the local flow kinematics. We use the Okubo-Weiss parameter that distinguishes the strain and vorticity dominated regions in the flow domain. The proposed development is relatively simple and implies only a moderate computational overhead. We validate the modified SPH algorithm for a selection of two-dimensional test cases: the Taylor-Green flow, the vortex spin-down, the lid-driven cavity and the dam-break flow against a sharp-edged obstacle. The simulation results show good agreement with the reference data and improvement of the long-term accuracy for unsteady flows. For the lid-driven cavity case, the proposed dynamical adjustment remedies the problem of tensile instability (particle clustering).

Lateral, Vertical, and Longitudinal Source Area Connectivity Drive Runoff and Carbon Export Across Watershed Scales

NASA Astrophysics Data System (ADS)

Zimmer, Margaret A.; McGlynn, Brian L.

2018-03-01

Watersheds are three-dimensional hydrologic systems where the longitudinal expansion/contraction of stream networks, vertical connection/disconnection between shallow and deep groundwater systems, and lateral connectivity of these water sources to streams mediate runoff production and nutrient export. The connectivity of runoff source areas during both baseflow and stormflow conditions and their combined influence on biogeochemical fluxes remain poorly understood. Here we focused on a set of 3.3 and 48.4 ha nested watersheds (North Carolina, USA). These watersheds comprise ephemeral and intermittent runoff-producing headwaters and perennial runoff-producing lowlands. Within these landscape elements, we characterized the timing and magnitude of precipitation, runoff, and runoff-generating flow paths. The active surface drainage network (ASDN) reflected connectivity to, and contributions from, source areas that differed under baseflow and stormflow conditions. The baseflow-associated ASDN expanded and contracted seasonally, driven by the rise and fall of the seasonal water table. Superimposed on this were event-activated source area contributions driven by connectivity to surficial and shallow subsurface flow paths. Frequently activated shallow flow paths also caused increased in-stream dissolved organic carbon (DOC) concentrations with increases in runoff across both watershed scales. The spread and variability within this DOC-runoff relationship was driven by a seasonal depletion of DOC from continual shallow subsurface flow path activation and subsequent replenishment from autumn litterfall. Our findings suggest that hydrobiogeochemical signals at larger watershed outlets can be driven by the expansion, contraction, and connection of lateral, longitudinal, and vertical source areas with distinct runoff generation processes.

Precessionally driven dynamos in ellipsoidal geometry

NASA Astrophysics Data System (ADS)

Ernst-Hullermann, J.; Harder, H.; Hansen, U.

2013-12-01

Precession was suggested as an alternative driving mechanism for Earth's and planetary magnetic fields by Bullard in 1949. Recent estimates of the thermal and electrical conductivity of Earth's core even show that the energy budget for buoyancy driven dynamos might be very tight. Therefore it seems worth to consider precession at least as an additional if not the only source of energy for the geodynamo. We are going to investigate precessionally driven dynamos by the use of a Finite Volume code. As precession drives a flow only due to the movement of the boundaries the shape of the container is essential for the character of the flow. In planets, it is much more effective to drive a precessional flow by the pressure differences induced by the topography of the precessing body rather than by viscous coupling to the walls. Numerical simulations are the only method offering the possibility to investigate the influence of the topography since laboratory experiments normally are constrained by the predetermined geometry of the vessel. We discuss how ellipticity of the planets can be included in our simulations by the use of a non-orthogonal grid. We will show that even laminar precession-driven flows are capable to generate a magnetic field. Most of the magnetic energy of this dynamos resides in the outer viscous boundary layer. While at lower Ekman number the kinematic dynamos also have magnetic fields located in the bulk, these diminish in the full magneto-hydrodynamic case. The laminar dynamos may not scale to Earth-like parameters. Nevertheless, with our new method we have the possibility to explore the parameter space much more systematically.

In Situ Measurement of Ground-Surface Flow Resistivity

NASA Technical Reports Server (NTRS)

Zuckerwar, A. J.

1984-01-01

New instrument allows in situ measurement of flow resistivity on Earth's ground surface. Nonintrusive instrument includes specimen holder inserted into ground. Flow resistivity measured by monitoring compressed air passing through flow-meters; pressure gages record pressure at ground surface. Specimen holder with knife-edged inner and outer cylinders easily driven into ground. Air-stream used in measuring flow resistivity of ground enters through quick-connect fitting and exits through screen and venthole.

Time and flow-direction responses of shear-styress-sensitive liquid crystal coatings

NASA Technical Reports Server (NTRS)

Reda, Daniel C.; Muraqtore, J. J.; Heinick, James T.

1994-01-01

Time and flow-direction responses of shear-stress liquid crystal coatings were exploresd experimentally. For the time-response experiments, coatings were exposed to transient, compressible flows created during the startup and off-design operation of an injector-driven supersonic wind tunnel. Flow transients were visualized with a focusing schlieren system and recorded with a 100 frame/s color video camera.

Competition of Perpendicular and Parallel Flows in a Straight Magnetic Field

NASA Astrophysics Data System (ADS)

Li, Jiacong; Diamond, Patrick; Hong, Rongjie; Tynan, George

2017-10-01

In tokamaks, intrinsic rotations in both toroidal and poloidal directions are important for the stability and confinement. Since they compete for energy from background turbulence, the coupling of them is the key to understanding the physics of turbulent state and transport bifurcations, e.g. L-H transition. V⊥ can affect the parallel Reynolds stress via cross phase and energetics, and thus regulates the parallel flow generation. In return, the turbulence driven V∥ plays a role in the mean vorticity flux, influencing the generation of V⊥. Also, competition of intrinsic azimuthal and axial flows is observed in CSDX-a linear plasma device with straight magnetic fields. CSDX is a well diagnosed venue to study the basic physics of turbulence-flow interactions in straight magnetic fields. Here, we study the turbulent energy branching between the turbulence driven parallel flow and perpendicular flow. Specifically, the ratio between parallel and perpendicular Reynolds power decreases when the mean perpendicular flow increases. As the mean parallel flow increases, this ratio first increases and then decreases before the parallel flow shear hits the parallel shear flow instability threshold. We seek to understand the flow states and compare with CSDX experiments. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, under Award Number DE-FG02-04ER54738.

Wind tunnel tests of Space Shuttle external tank insulation material in the aerothermal tunnel at elevated (1440 deg F) total temperatures

NASA Technical Reports Server (NTRS)

Hartman, A. S.; Nutt, K. W.

1982-01-01

Tests of the space shuttle external tank foam insulation were conducted in the von Karman Gas Dynamics Facility Tunnel C. For these tests, Tunnel C was run at Mach 4 with a total temperature of 1440 F and a total pressure which varied from 30-100 psia. Cold wall heating rates were changed by varying the test article support wedge angle and by adding and removing a shock generator or a cylindrical protuberance. Selected results are presented to illustrate the test techniques and typical data obtained.

Quasi-Static Analysis of Round LaRC THUNDER Actuators

NASA Technical Reports Server (NTRS)

Campbell, Joel F.

2007-01-01

An analytic approach is developed to predict the shape and displacement with voltage in the quasi-static limit of round LaRC Thunder Actuators. The problem is treated with classical lamination theory and Von Karman non-linear analysis. In the case of classical lamination theory exact analytic solutions are found. It is shown that classical lamination theory is insufficient to describe the physical situation for large actuators but is sufficient for very small actuators. Numerical results are presented for the non-linear analysis and compared with experimental measurements. Snap-through behavior, bifurcation, and stability are presented and discussed.

Quasi-Static Analysis of LaRC THUNDER Actuators

NASA Technical Reports Server (NTRS)

Campbell, Joel F.

2007-01-01

An analytic approach is developed to predict the shape and displacement with voltage in the quasi-static limit of LaRC Thunder Actuators. The problem is treated with classical lamination theory and Von Karman non-linear analysis. In the case of classical lamination theory exact analytic solutions are found. It is shown that classical lamination theory is insufficient to describe the physical situation for large actuators but is sufficient for very small actuators. Numerical results are presented for the non-linear analysis and compared with experimental measurements. Snap-through behavior, bifurcation, and stability are presented and discussed.

Orbital ATK CRS-7 "What's on Board" Science Briefing

NASA Image and Video Library

2017-04-17

Henry Martin, left, external payloads coordinator with NanoRacks, and Davide Massuti, QB50 CubeSats at Von Karman Institute, talk to NASA Social participants during a science briefing at the agency's Kennedy Space Center in Florida. The briefing was for Orbital ATK's commercial resupply services mission, CRS-7, to the International Space Station. Orbital ATK's Cygnus pressurized cargo module is set to launch on the United Launch Alliance Atlas V rocket from Space Launch Complex 41 at Cape Canaveral Air Force Station on April 18. Liftoff is scheduled for 11:11 a.m. EDT.

Loads and Deformations of Buckled Rectangular Plates. Degree awarded by Virginia Polytechnic Inst., Jun. 1958

NASA Technical Reports Server (NTRS)

Stein, Manuel

1959-01-01

The nonlinear large-deflection equations of von Karman for plates are converted into a set of linear equations by expanding the displacements Into a power series in terms of an arbitrary parameter. The postbuckling behavior of simply supported rectangular plates subjected to longitudinal compression and subject to a uniform temperature rise is investigated in detail by solving the first few of the equations. Experimental data are presented for the compression problem. Comparisons are made for total shortening and local strains and deflections which indicate good agreement between experimental and theoretical results.

A dispersion relationship governing incompressible wall turbulence

NASA Technical Reports Server (NTRS)

Tsuge, S.

1978-01-01

The method of separation of variables is shown to make turbulent correlation equations of Karman-Howarth type tractable for shear turbulence as well under the condition of neglected triple correlation. The separated dependent variable obeys an Orr-Sommerfeld equation. A new analytical method is developed using a scaling law different from the classical one due to Heisenberg and Lin and more appropriate for wall turbulent profiles. A dispersion relationship between the wave number and the separation constant which has the dimension of a frequency is derived in support of experimental observations of wave or coherent structure of wall turbulence.

Thermoviscoplastic response of thin plates subjected to intense local heating

NASA Technical Reports Server (NTRS)

Byrom, Ted G.; Allen, David H.; Thornton, Earl A.

1992-01-01

A finite element method is employed to investigate the thermoviscoplastic response of a half-cylinder to intense localized transient heating. Thermoviscoplastic material behavior is characterized by the Bodner-Partom constitutive model. Structure geometry is modeled with a three-dimensional assembly of CST-DKT plate elements incorporating the large deflection von Karman assumptions. The paper compares the results of a dynamic analysis with a quasi-static analysis for the half-cylinder structure with a step-function transient temperature loading similar to that which may be encountered with shock wave interference on a hypersonic leading edge.

Airplane wing vibrations due to atmospheric turbulence

NASA Technical Reports Server (NTRS)

Pastel, R. L.; Caruthers, J. E.; Frost, W.

1981-01-01

The magnitude of error introduced due to wing vibration when measuring atmospheric turbulence with a wind probe mounted at the wing tip was studied. It was also determined whether accelerometers mounted on the wing tip are needed to correct this error. A spectrum analysis approach is used to determine the error. Estimates of the B-57 wing characteristics are used to simulate the airplane wing, and von Karman's cross spectrum function is used to simulate atmospheric turbulence. It was found that wing vibration introduces large error in measured spectra of turbulence in the frequency's range close to the natural frequencies of the wing.

A perspective on the status of measurement of atmospheric turbulence in the US

NASA Technical Reports Server (NTRS)

Murrow, H. N.

1985-01-01

A perspective on status of measurement of atmospheric turbulence is presented. Details are given for turbulence characteristics measured in four distinct meteorological conditions. The emphasis is on identifying appropriate values of L, the integral scale value in the von Karman expression. On-going activity to measure spanwise gradients of turbulence at low altitudes is described. A resume of the NASA VGH program is given, as well as on-going utilization of flight recorder data on wide-body transports to reconstruct special turbulence encounters. Reference is made to some other activities regarding sensing, measurement, modeling, and alleviation.

Quantifying the Contribution of Thermally Driven Recirculation to a High-Ozone Event Along the Colorado Front Range Using Lidar

NASA Technical Reports Server (NTRS)

Sullivan, John T.; McGee, Thomas J.; Langford, Andrew O.; Alvarez, Raul J., II; Senff, Christoph; Reddy, Patrick J.; Thompson, Anne M.; Twigg, Laurence W.; Sumnicht, Grant K.; Lee, Pius;

Density-driven transport process following the seawater indundation of the freshwater lens of the island of Baltrum, Germany

NASA Astrophysics Data System (ADS)

Post, Vincent E. A.; Houben, Georg J.

2017-04-01

Due to the growing vulnerability of low-lying coastal zones to flooding by seawater, there is a need for more studies of the impact of inundations on fresh groundwater resources. We present previously unpublished data collected on the island of Baltrum following a devastating storm in 1962, which uniquely show the impact of seawater inundation on a freshwater lens in a siliciclastic aquifer. The field data show that elevated salinities persisted for at least 4 years at the measurement depths of 4 and 6 m, and at least for 6 years at greater depths. Numerical models confirm the importance of density-driven salt fingering. Models that did not consider density effects failed to simulate the observed breakthrough curves. Transient recharge, model dimension and lateral flow modify the details of the simulation results, but in all models density-driven flow dominates the overall system behaviour. The sequestration of intruded seawater into the deeper parts of the flow system, prolongs recovery and enhances the risk of upconing when pumping is resumed too early.

Radiation Pressure-Driven Magnetic Disk Winds in Broad Absorption Line Quasi-Stellar Objects

NASA Technical Reports Server (NTRS)

DeKool, Martin; Begelman, Mitchell C.

1995-01-01

We explore a model in which QSO broad absorption lines (BALS) are formed in a radiation pressure-driven wind emerging from a magnetized accretion disk. The magnetic field threading the disk material is dragged by the flow and is compressed by the radiation pressure until it is dynamically important and strong enough to contribute to the confinement of the BAL clouds. We construct a simple self-similar model for such radiatively driven magnetized disk winds, in order to explore their properties. It is found that solutions exist for which the entire magnetized flow is confined to a thin wedge over the surface of the disk. For reasonable values of the mass-loss rate, a typical magnetic field strength such that the magnetic pressure is comparable to the inferred gas pressure in BAL clouds, and a moderate amount of internal soft X-ray absorption, we find that the opening angle of the flow is approximately 0.1 rad, in good agreement with the observed covering factor of the broad absorption line region.

A comparative study of artificial neural network, adaptive neuro fuzzy inference system and support vector machine for forecasting river flow in the semiarid mountain region

NASA Astrophysics Data System (ADS)

He, Zhibin; Wen, Xiaohu; Liu, Hu; Du, Jun

2014-02-01

Data driven models are very useful for river flow forecasting when the underlying physical relationships are not fully understand, but it is not clear whether these data driven models still have a good performance in the small river basin of semiarid mountain regions where have complicated topography. In this study, the potential of three different data driven methods, artificial neural network (ANN), adaptive neuro fuzzy inference system (ANFIS) and support vector machine (SVM) were used for forecasting river flow in the semiarid mountain region, northwestern China. The models analyzed different combinations of antecedent river flow values and the appropriate input vector has been selected based on the analysis of residuals. The performance of the ANN, ANFIS and SVM models in training and validation sets are compared with the observed data. The model which consists of three antecedent values of flow has been selected as the best fit model for river flow forecasting. To get more accurate evaluation of the results of ANN, ANFIS and SVM models, the four quantitative standard statistical performance evaluation measures, the coefficient of correlation (R), root mean squared error (RMSE), Nash-Sutcliffe efficiency coefficient (NS) and mean absolute relative error (MARE), were employed to evaluate the performances of various models developed. The results indicate that the performance obtained by ANN, ANFIS and SVM in terms of different evaluation criteria during the training and validation period does not vary substantially; the performance of the ANN, ANFIS and SVM models in river flow forecasting was satisfactory. A detailed comparison of the overall performance indicated that the SVM model performed better than ANN and ANFIS in river flow forecasting for the validation data sets. The results also suggest that ANN, ANFIS and SVM method can be successfully applied to establish river flow with complicated topography forecasting models in the semiarid mountain regions.

Lagrangian transport in a class of three-dimensional buoyancy-driven flows

NASA Astrophysics Data System (ADS)

Contreras, Sebastian; Speetjens, Michel; Clercx, Herman

2017-11-01

The study concerns the Lagrangian dynamics of three-dimensional (3D) buoyancy-driven cavity flows under steady and laminar conditions due to a global temperature gradient imposed via an opposite hot and cold sidewall. This serves as archetypal configuration for natural-convection flows in which gravity is perpendicular to the global temperature gradient. Limited insight into the Lagrangian properties of this class of flows motivates this study. The 3D Lagrangian dynamics are investigated in terms of the generic structure of the Lagrangian flow topology that is described in terms of the Grashof number (Gr) and the Prandtl number (Pr). Gr is the principal control parameter for the flow topology: vanishing Gr yields a state of closed streamlines (integrable state); increasing Gr causes the formation of toroidal coherent structures embedded in chaotic streamlines governed by Hamiltonian mechanisms. Fluid inertia prevails for ``smaller'' Gr. A buoyancy-induced bifurcation of the flow topology occurs for ``larger'' Gr and underlies the emergence of ``secondary rolls'' and secondary tori for ``larger'' Pr. Stagnation points and corresponding manifold interactions are key to the dynamics. S.C. acknowledges financial support from Consejo Nacional de Ciencia y Tecnología (CONACYT).

Experiments in a flighted conveyor comparing shear rates in compressed versus free surface flows

NASA Astrophysics Data System (ADS)

Pohlman, Nicholas; Higgins, Hannah; Krupiarz, Kamila; O'Connor, Ryan

2017-11-01

Uniformity of granular flow rate is critical in industry. Experiments in a flighted conveyor system aim to fill a gap in knowledge of achieving steady mass flow rate by correlating velocity profile data with mass flow rate measurements. High speed images were collected for uniformly-shaped particles in a bottom-driven flow conveyor belt system from which the velocity profiles can be generated. The correlation of mass flow rates from the velocity profiles to the time-dependent mass measurements will determine energy dissipation rates as a function of operating conditions. The velocity profiles as a function of the size of the particles, speed of the belt, and outlet size, will be compared to shear rate relationships found in past experiments that focused on gravity-driven systems. The dimension of the linear shear and type of decaying transition to the stationary bed may appear different due to the compression versus dilation space in open flows. The application of this research can serve to validate simulations in discrete element modeling and physically demonstrate a process that can be further developed and customized for industry applications, such as feeding a biomass conversion reactor. Sponsored by NIU's Office of Student Engagement and Experiential Learning.

Application of boundary element method to Stokes flows over a striped superhydrophobic surface with trapped gas bubbles

NASA Astrophysics Data System (ADS)

Ageev, A. I.; Golubkina, I. V.; Osiptsov, A. N.

2018-01-01

A slow steady flow of a viscous fluid over a superhydrophobic surface with a periodic striped system of 2D rectangular microcavities is considered. The microcavities contain small gas bubbles on the curved surface of which the shear stress vanishes. The general case is analyzed when the bubble occupies only a part of the cavity, and the flow velocity far from the surface is directed at an arbitrary angle to the cavity edge. Due to the linearity of the Stokes flow problem, the solution is split into two parts, corresponding to the flows perpendicular and along the cavities. Two variants of a boundary element method are developed and used to construct numerical solutions on the scale of a single cavity with periodic boundary conditions. By averaging these solutions, the average slip velocity and the slip length tensor components are calculated over a wide range of variation of governing parameters for the cases of a shear-driven flow and a pressure-driven channel flow. For a sufficiently high pressure drop in a microchannel of finite length, the variation of the bubble surface shift into the cavities induced by the streamwise pressure variation is estimated from numerical calculations.

Skeletal adaptation to intramedullary pressure-induced interstitial fluid flow is enhanced in mice subjected to targeted osteocyte ablation.

PubMed

Kwon, Ronald Y; Meays, Diana R; Meilan, Alexander S; Jones, Jeremiah; Miramontes, Rosa; Kardos, Natalie; Yeh, Jiunn-Chern; Frangos, John A

2012-01-01

Interstitial fluid flow (IFF) is a potent regulatory signal in bone. During mechanical loading, IFF is generated through two distinct mechanisms that result in spatially distinct flow profiles: poroelastic interactions within the lacunar-canalicular system, and intramedullary pressurization. While the former generates IFF primarily within the lacunar-canalicular network, the latter generates significant flow at the endosteal surface as well as within the tissue. This gives rise to the intriguing possibility that loading-induced IFF may differentially activate osteocytes or surface-residing cells depending on the generating mechanism, and that sensation of IFF generated via intramedullary pressurization may be mediated by a non-osteocytic bone cell population. To begin to explore this possibility, we used the Dmp1-HBEGF inducible osteocyte ablation mouse model and a microfluidic system for modulating intramedullary pressure (ImP) to assess whether structural adaptation to ImP-driven IFF is altered by partial osteocyte depletion. Canalicular convective velocities during pressurization were estimated through the use of fluorescence recovery after photobleaching and computational modeling. Following osteocyte ablation, transgenic mice exhibited severe losses in bone structure and altered responses to hindlimb suspension in a compartment-specific manner. In pressure-loaded limbs, transgenic mice displayed similar or significantly enhanced structural adaptation to Imp-driven IFF, particularly in the trabecular compartment, despite up to ∼50% of trabecular lacunae being uninhabited following ablation. Interestingly, regression analysis revealed relative gains in bone structure in pressure-loaded limbs were correlated with reductions in bone structure in unpressurized control limbs, suggesting that adaptation to ImP-driven IFF was potentiated by increases in osteoclastic activity and/or reductions in osteoblastic activity incurred independently of pressure loading. Collectively, these studies indicate that structural adaptation to ImP-driven IFF can proceed unimpeded following a significant depletion in osteocytes, consistent with the potential existence of a non-osteocytic bone cell population that senses ImP-driven IFF independently and potentially parallel to osteocytic sensation of poroelasticity-derived IFF.

POWER GENERATION USING MEGNETOHYDRODYNAMIC GENERATOR WITH A CIRCULATION FLOW DRIVEN BY SOLAR-HEAT-INDUCED NATURAL CONVECTION

EPA Science Inventory

The project team has theoretically studied the mechanism of magnetohydrodynamic generator, the coupling of heat transfer and buoyancy-driven free convection, and radiation heat transfer. A number of ideas for the projects have been brainstormed in the team. The underline physi...

Raindrop and flow interactions for interrill erosion with wind-driven rain

USDA-ARS?s Scientific Manuscript database

Wind-driven rain (WDR) experiments were conducted to evaluate interrill component of the Water Erosion Prediction Project (WEPP) model with two-dimensional experimental set-up in wind tunnel. Synchronized wind and rain simulations were applied to soil surfaces on windward and leeward slopes of 7, 15...

Transition from steady to periodic liquid-metal magnetohydrodynamic flow in a sliding electrical contact

NASA Astrophysics Data System (ADS)

Talmage, Gita; Walker, John S.; Brown, Samuel H.; Sondergaard, Neal A.

1993-09-01

In homopolar motors and generators, large dc electric currents pass through the sliding electrical contacts between rotating copper disks (rotors) and static copper surfaces shrouding the rotor tips (stators). A liquid metal in the small radial gap between the rotor tip and concentric stator surface can provide a low-resistance, low-drag electrical contact. Since there is a strong magnetic field in the region of the electrical contacts, there are large electromagnetic body forces on the liquid metal. The primary, azimuthal motion consists of simple Couette flow, plus an electromagnetically driven flow with large extremes of the azimuthal velocity near the rotor corners. The secondary flow involves the radial and axial velocity components, is driven by the centrifugal force associated with the primary flow, and is opposed by the electromagnetic body force, so that the circulation varies inversely as the square of the magnetic-field strength. Three flow regimes are identified as the angular velocity Ω of the rotor is increased. For small Ω, the primary flow is decoupled from the secondary flow. As Ω increases, the secondary flow begins to convect the azimuthal-velocity peaks radially outward, which in turn changes the centrifugal force driving the secondary flow. At some critical value of Ω, the flow becomes periodic through the coupling of the primary and secondary flows. The azimuthal-velocity peaks begin to move radially in and out with an accompanying oscillation in the secondary-flow strength.

The Influence of Chordwise Flexibility on the Flow Structure and Streamwise Force of a Sinusoidally Pitching Airfoil

NASA Astrophysics Data System (ADS)

Olson, David Arthur

Many natural flyers and swimmers need to exploit unsteady mechanisms in order to generate sufficient aerodynamic forces for sustained flight and propulsion. This is, in part, due to the low speed and length scales at which they typically operate. In this low Reynolds number regime, there are many unanswered questions on how existing aerodynamic theory for both steady and unsteady flows can be applied. Additionally, most of these natural flyers and swimmers have deformable wing/fin structures, three dimensional wing planforms, and exhibit complex kinematics during motion. While some biologically-inspired studies seek to replicate these complex structures and kinematics in the laboratory or in numerical simulations, it becomes difficult to draw explicit connections to the existing knowledge base of classical unsteady aerodynamic theory due to the complexity of the problems. In this experimental study, wing kinematics, structure, and planform are greatly simplified to investigate the effect of chordwise flexibility on the streamwise force (thrust) and wake behavior of a sinusoidally pitching airfoil. The study of flexibility in the literature has typically utilized flat plates with varying thicknesses or lengths to change their chordwise flexibility. This choice introduces additional complexities when comparing to the wealth of knowledge originally developed on streamlined aerodynamic shapes. The current study capitalizes on the recent developments in 3D printer technology to create accurate shapes out of materials with varying degrees of flexibility by creating two standard NACA 0009 airfoils: one rigid and one flexible. Each of the two airfoils are sinusoidally pitched about the quarter chord over a range of oscillation amplitudes and frequencies while monitoring the deformation of the airfoil. The oscillation amplitude is selected to be small enough such that leading edge vortices do not form, and the vortical structures in the wake are formed from the trailing edge. Two-component Molecular Tagging Velocimetry (MTV) is employed to measure the vortical flowfield over the first chord length behind the airfoil. A control volume method is used to estimate the mean thrust of the airfoil based on the mean and fluctuating velocity profiles from the MTV results. The mean thrust results show chordwise flexibility increases the thrust produced by the airfoil over the range of motion parameters and the flexibility considered in this study. The flexible airfoil is also seen to experience the drag-to-thrust crossover at a lower oscillation frequency than its rigid counterpart. The relative change in thrust due to flexibility decreases with increasing amplitude. The increase in thrust can, however, be captured as an amplitude effect when the Strouhal number based on the actual trailing edge displacement, Stte, is used for scaling. Scaling based strictly on the prescribed motion, typically employed in the literature, is not sufficient for the data to collapse. Motion trajectories which produced a classical von Karman vortex street or a reverse von Karman vortex street (depending on the arrangement of the vortices), are considered for further study. The vortices in the wake are characterized in terms of their strength, size, and spacing using phase-averaged MTV results. The circulation of the vortices are shown to collapse for both rigid and flexible airfoils when plotted against Stte. The actual trailing edge displacement is used as a length scale to normalize the transverse and streamwise spacing, and the vortex core size. These measurements also now collapse when plotted against Stte across oscillation amplitude for both the rigid and flexible airfoils.

Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Brebrick, R. F.; Burger, A.; Dudley, M.; Ramachandran, N.

2003-01-01

The objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the crystals grown by vapor transport as results of buoyance-driven convection and growth interface fluctuations caused by irregular fluid-flows. ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, were grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals were characterized extensively to correlate the grown crystal properties with the growth conditions.

Convection-driven tectonics on Venus

NASA Astrophysics Data System (ADS)

Phillips, R. J.

1990-02-01

An analysis is presented of convective stress coupling to an elastic lithosphere as applied to Venus. Theoretical solutions are introduced for the response of a mathematically thick elastic plate overlying a Newtonian viscous medium with an exponential depth dependence of viscosity, and a Green's function solution is obtained for the viscous flow driven by a harmonic density distribution at a specified depth. An elastic-plastic analysis is carried out for the deformation of a model Venus lithosphere. The results predict that dynamic uplift of Venusian topography must be accompanied by extensive brittle failure and viscous flow in the lithosphere.

Flow pumping system for physiological waveforms.

PubMed

Tsai, William; Savaş, Omer

2010-02-01

A pulsatile flow pumping system is developed to replicate flow waveforms with reasonable accuracy for experiments simulating physiological blood flows at numerous points in the body. The system divides the task of flow waveform generation between two pumps: a gear pump generates the mean component and a piston pump generates the oscillatory component. The system is driven by two programmable servo controllers. The frequency response of the system is used to characterize its operation. The system has been successfully tested in vascular flow experiments where sinusoidal, carotid, and coronary flow waveforms are replicated.

Extension of a System Level Tool for Component Level Analysis

NASA Technical Reports Server (NTRS)

Majumdar, Alok; Schallhorn, Paul

2002-01-01

This paper presents an extension of a numerical algorithm for network flow analysis code to perform multi-dimensional flow calculation. The one dimensional momentum equation in network flow analysis code has been extended to include momentum transport due to shear stress and transverse component of velocity. Both laminar and turbulent flows are considered. Turbulence is represented by Prandtl's mixing length hypothesis. Three classical examples (Poiseuille flow, Couette flow and shear driven flow in a rectangular cavity) are presented as benchmark for the verification of the numerical scheme.

Extension of a System Level Tool for Component Level Analysis

NASA Technical Reports Server (NTRS)

Majumdar, Alok; Schallhorn, Paul; McConnaughey, Paul K. (Technical Monitor)

2001-01-01

This paper presents an extension of a numerical algorithm for network flow analysis code to perform multi-dimensional flow calculation. The one dimensional momentum equation in network flow analysis code has been extended to include momentum transport due to shear stress and transverse component of velocity. Both laminar and turbulent flows are considered. Turbulence is represented by Prandtl's mixing length hypothesis. Three classical examples (Poiseuille flow, Couette flow, and shear driven flow in a rectangular cavity) are presented as benchmark for the verification of the numerical scheme.

Intensification of abamectin pesticide degradation using the combination of ultrasonic cavitation and visible-light driven photocatalytic process: Synergistic effect and optimization study.

PubMed

Mosleh, Soleiman; Rahimi, Mahmood Reza

2017-03-01

Degradation of abamectin pesticide was carried out using visible light driven Cu 2 (OH)PO 4 -HKUST-1 MOF photocatalyst through the sonophotocatalytic technique. Cu 2 (OH)PO 4 -HKUST-1 MOF as a visible-light driven photocatalyst, was synthesized and characterized by XRD, SEM, EDS and DRS. The direct bang gaps of HKUST-1 MOF and Cu 2 (OH)PO 4 -HKUST-1 MOF were estimated about 2.63 and 2.59eV, respectively, which reveals that these photocatalysts can be activated under blue light illumination. All sonophotodegradation experiments were performed using a continuous flow-loop reactor. The central composite design (CCD) methodology was applied for modeling, optimization and investigation of influence of operational parameters, i.e. irradiation time, pH, solution flow rate, oxygen flow rate, initial concentration and photocatalyst dosage on the sonophotocatalytic degradation of abamectin. The maximum degradation efficiency of 99.93% was found at optimal values as 20min, 4, 90mL/min, 0.2mL/min, 30mg/L and 0.4g/L, for irradiation time, pH, solution flow rate, oxygen flow rate, initial concentration and photocatalyst dosage, respectively. Evaluation of the synergism in the combination of ultrasonic and photocatalysis lead to a synergistic index of 2.19, which reveals that coupling of ultrasonic and photocatalysis has a greater efficiency than the sum of individual procedures for degradation of abamectin. Copyright © 2016 Elsevier B.V. All rights reserved.

Magnetohydrodynamic stability of stochastically driven accretion flows.

PubMed

Nath, Sujit Kumar; Mukhopadhyay, Banibrata; Chattopadhyay, Amit K

2013-07-01

We investigate the evolution of magnetohydrodynamic (or hydromagnetic as coined by Chandrasekhar) perturbations in the presence of stochastic noise in rotating shear flows. The particular emphasis is the flows whose angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows, however, are Rayleigh stable but must be turbulent in order to explain astrophysical observed data and, hence, reveal a mismatch between the linear theory and observations and experiments. The mismatch seems to have been resolved, at least in certain regimes, in the presence of a weak magnetic field, revealing magnetorotational instability. The present work explores the effects of stochastic noise on such magnetohydrodynamic flows, in order to resolve the above mismatch generically for the hot flows. We essentially concentrate on a small section of such a flow which is nothing but a plane shear flow supplemented by the Coriolis effect, mimicking a small section of an astrophysical accretion disk around a compact object. It is found that such stochastically driven flows exhibit large temporal and spatial autocorrelations and cross-correlations of perturbation and, hence, large energy dissipations of perturbation, which generate instability. Interestingly, autocorrelations and cross-correlations appear independent of background angular velocity profiles, which are Rayleigh stable, indicating their universality. This work initiates our attempt to understand the evolution of three-dimensional hydromagnetic perturbations in rotating shear flows in the presence of stochastic noise.

Instabilities and spin-up behaviour of a rotating magnetic field driven flow in a rectangular cavity

NASA Astrophysics Data System (ADS)

Galindo, V.; Nauber, R.; Räbiger, D.; Franke, S.; Beyer, H.; Büttner, L.; Czarske, J.; Eckert, S.

2017-11-01

This study presents numerical simulations and experiments considering the flow of an electrically conducting fluid inside a cube driven by a rotating magnetic field (RMF). The investigations are focused on the spin-up, where a liquid metal (GaInSn) is suddenly exposed to an azimuthal body force generated by the RMF and the subsequent flow development. The numerical simulations rely on a semi-analytical expression for the induced electromagnetic force density in an electrically conducting medium inside a cuboid container with insulating walls. Velocity distributions in two perpendicular planes are measured using a novel dual-plane, two-component ultrasound array Doppler velocimeter with continuous data streaming, enabling long term measurements for investigating transient flows. This approach allows identifying the main emerging flow modes during the transition from stable to unstable flow regimes with exponentially growing velocity oscillations using the Proper Orthogonal Decomposition method. Characteristic frequencies in the oscillating flow regimes are determined in the super critical range above the critical magnetic Taylor number T ac≈1.26 ×1 05, where the transition from the steady double vortex structure of the secondary flow to an unstable regime with exponentially growing oscillations is detected. The mean flow structures and the temporal evolution of the flow predicted by the numerical simulations and observed in experiments are in very good agreement.

Marine Propulsion Load Emulation.

DTIC Science & Technology

1985-06-01

single-entry centrifugal compressor mechanically coupled to a single-stage axial - flow turbine , two cross- connected can type combustion chambers, and...an accessory- drive section. The power output section incorporates a second axial - flow turbine , reduction gears and output shaft, and is driven by the... Flow .... ............. ... 36 4.7 Load Valve Characteristics ... ............. .38 4.8 Photograph of Turbine Test gell .......... 39, * 4.9

Active Learning in Fluid Mechanics: Youtube Tube Flow and Puzzling Fluids Questions

ERIC Educational Resources Information Center

Hrenya, Christine M.

2011-01-01

Active-learning exercises appropriate for a course in undergraduate fluid mechanics are presented. The first exercise involves an experiment in gravity-driven tube flow, with small groups of students partaking in a contest to predict the experimental flow rates using the mechanical energy balance. The second exercise takes the form of an…

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

Juanes, Ruben

The overarching goal of this project was to develop a new continuum theory of multiphase flow in porous media. The theory follows a phase-field modeling approach, and therefore has a sound thermodynamical basis. It is a phenomenological theory in the sense that its formulation is driven by macroscopic phenomena, such as viscous instabilities during multifluid displacement. The research agenda was organized around a set of hypothesis on hitherto unexplained behavior of multiphase flow. All these hypothesis are nontrivial, and testable. Indeed, a central aspect of the project was testing each hypothesis by means of carefully-designed laboratory experiments, therefore probing themore » validity of the proposed theory. The proposed research places an emphasis on the fundamentals of flow physics, but is motivated by important energy-driven applications in earth sciences, as well as microfluidic technology.« less

Distribution-Agnostic Stochastic Optimal Power Flow for Distribution Grids: Preprint

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

Baker, Kyri; Dall'Anese, Emiliano; Summers, Tyler

2016-09-01

This paper outlines a data-driven, distributionally robust approach to solve chance-constrained AC optimal power flow problems in distribution networks. Uncertain forecasts for loads and power generated by photovoltaic (PV) systems are considered, with the goal of minimizing PV curtailment while meeting power flow and voltage regulation constraints. A data- driven approach is utilized to develop a distributionally robust conservative convex approximation of the chance-constraints; particularly, the mean and covariance matrix of the forecast errors are updated online, and leveraged to enforce voltage regulation with predetermined probability via Chebyshev-based bounds. By combining an accurate linear approximation of the AC power flowmore » equations with the distributionally robust chance constraint reformulation, the resulting optimization problem becomes convex and computationally tractable.« less

First-order particle acceleration in magnetically driven flows

DOE PAGES

Beresnyak, Andrey; Li, Hui

2016-03-02

In this study, we demonstrate that particles are regularly accelerated while experiencing curvature drift in flows driven by magnetic tension. Some examples of such flows include spontaneous turbulent reconnection and decaying magnetohydrodynamic turbulence, where a magnetic field relaxes to a lower-energy configuration and transfers part of its energy to kinetic motions of the fluid. We show that this energy transfer, which normally causes turbulent cascade and heating of the fluid, also results in a first-order acceleration of non-thermal particles. Since it is generic, this acceleration mechanism is likely to play a role in the production of non-thermal particle distribution inmore » magnetically dominant environments such as the solar chromosphere, pulsar magnetospheres, jets from supermassive black holes, and γ-ray bursts.« less

Analysis of microfluidic flow driven by electrokinetic and pressure forces

NASA Astrophysics Data System (ADS)

Chen, Chien-Hsin

2011-12-01

This work presents an analysis of microfluidic flow introduced by mixed electrokinetic force and pressure gradient. Analytical solutions are presented for the case of constant surface heat flux, taking the Joule heating effect into account. The present problem is governed by two scale ratios and the dimensionless source term. The two important ratios are the length scale ratio e (the ratio of Debye length to the tube radius R) and the velocity scale ratio Γ (the ratio of the pressuredriven velocity scale for Poiseuille flow to Helmholtz-Smoluchowski velocity for electroosmotic flow). For mixed electroosmotic and pressure-driven flow, the resulting velocity profile is the superimposed effect of both electroosmotic and Poiseuille flow phenomena. It is found that the velocity profile decreases as e increases and the normalized temperature profiles across the tube increases monotonously form the core to the wall. The maximum dimensionless temperature is observed at the wall and the wall temperature increases with increasing Joule heating. Also, the temperature is increased with increasing the value of ɛ . The fully developed Nusselt number takes the maximum value at the limiting case of ɛ --> 0 , and then decreases with increasing ɛ . Moreover, the Nusselt number decreases with Γ and then goes asymptotically to the limit of Poiseuille flow as Γ --> ∞ , where the flow is dominated by the pressure force.

The Debye-Huckel Approximation in Electroosmotic Flow in Micro- and Nano-channels

NASA Astrophysics Data System (ADS)

Conlisk, A. Terrence

2002-11-01

In this work we consider the electroosmotic flow in a rectangular channel. We consider a mixture of water or other neutral solvent and a salt compound such as sodium chloride and other buffers for which the ionic species are entirely dissociated. Results are produced for the case where the channel height is much greater than the electric double layer(EDL)(microchannel) and for the case where the channel height is of the order or slightly greater than the width of the EDL(nanochannel). At small cation, anion concentration differences the Debye-Huckel approximation is appropriate; at larger concentration differences, the Gouy-Chapman picture of the electric double emerges naturally. In the symmetric case for the electroosmotic flow so induced, the velocity field and the potential are similar. We specifically focus in this paper on the limits of the Debye-Huckel approximation for a simplified version of a phosphate buffered saline(PBS) mixture. The fluid is assumed to behave as a continuum and the volume flow rate is observed to vary linearly with channel height for electrically driven flow in contrast to pressure driven flow which varies as height cubed. This means that very large pressure drops are required to drive flows in small channels. However, useful volume flow rates may be obtained at a very low driving voltage.

Transitioning from a single-phase fluid to a porous medium: a boundary layer approach

NASA Astrophysics Data System (ADS)

Dalwadi, Mohit P.; Chapman, S. Jon; Oliver, James M.; Waters, Sarah L.

2014-11-01

Pressure-driven laminar channel flow is a classic problem in fluid mechanics, and the resultant Poiseuille flow is one of the few exact solutions to the Navier-Stokes equations. If the channel interior is a porous medium (governed by Darcy's law) rather than a single-phase fluid, the resultant behaviour is plug flow. But what happens when these two flow regions are coupled, as is the case for industrial membrane filtration systems or biological tissue engineering problems? How does one flow transition to the other? We use asymptotic methods to investigate pressure-driven flow through a long channel completely blocked by a finite-length porous obstacle. We analytically solve for the flow at both small and large Reynolds number (whilst remaining within the laminar regime). The boundary layer structure is surprisingly intricate for large Reynolds number. In that limit, the structure is markedly different depending on whether there is inflow or outflow through the porous medium, there being six asymptotic regions for inflow and three for outflow. We have extended this result to a wide class of 3D porous obstacles within a Hele-Shaw cell. We obtain general boundary conditions to couple the outer flows, and find that these conditions are far from obvious at higher order.

Turbulence, transport, and zonal flows in the Madison symmetric torus reversed-field pinch

NASA Astrophysics Data System (ADS)

Williams, Z. R.; Pueschel, M. J.; Terry, P. W.; Hauff, T.

2017-12-01

The robustness and the effect of zonal flows in trapped electron mode (TEM) turbulence and Ion Temperature Gradient (ITG) turbulence in the reversed-field pinch (RFP) are investigated from numerical solutions of the gyrokinetic equations with and without magnetic external perturbations introduced to model tearing modes. For simulations without external magnetic field perturbations, zonal flows produce a much larger reduction of transport for the density-gradient-driven TEM turbulence than they do for the ITG turbulence. Zonal flows are studied in detail to understand the nature of their strong excitation in the RFP and to gain insight into the key differences between the TEM- and ITG-driven regimes. The zonal flow residuals are significantly larger in the RFP than in tokamak geometry due to the low safety factor. Collisionality is seen to play a significant role in the TEM zonal flow regulation through the different responses of the linear growth rate and the size of the Dimits shift to collisionality, while affecting the ITG only minimally. A secondary instability analysis reveals that the TEM turbulence drives zonal flows at a rate that is twice that of the ITG turbulence. In addition to interfering with zonal flows, the magnetic perturbations are found to obviate an energy scaling relation for fast particles.

Groundwater flow and its effect on salt dissolution in Gypsum Canyon watershed, Paradox Basin, southeast Utah, USA

NASA Astrophysics Data System (ADS)

Reitman, Nadine G.; Ge, Shemin; Mueller, Karl

2014-09-01

Groundwater flow is an important control on subsurface evaporite (salt) dissolution. Salt dissolution can drive faulting and associated subsidence on the land surface and increase salinity in groundwater. This study aims to understand the groundwater flow system of Gypsum Canyon watershed in the Paradox Basin, Utah, USA, and whether or not groundwater-driven dissolution affects surface deformation. The work characterizes the groundwater flow and solute transport systems of the watershed using a three-dimensional (3D) finite element flow and transport model, SUTRA. Spring samples were analyzed for stable isotopes of water and total dissolved solids. Spring water and hydraulic conductivity data provide constraints for model parameters. Model results indicate that regional groundwater flow is to the northwest towards the Colorado River, and shallow flow systems are influenced by topography. The low permeability obtained from laboratory tests is inconsistent with field observed discharges, supporting the notion that fracture permeability plays a significant role in controlling groundwater flow. Model output implies that groundwater-driven dissolution is small on average, and cannot account for volume changes in the evaporite deposits that could cause surface deformation, but it is speculated that dissolution may be highly localized and/or weaken evaporite deposits, and could lead to surface deformation over time.

Effect of Unsaturated Flow Modes on Partitioning Dynamics of Gravity-Driven Flow at a Simple Fracture Intersection: Laboratory Study and Three-Dimensional Smoothed Particle Hydrodynamics Simulations

NASA Astrophysics Data System (ADS)

Kordilla, Jannes; Noffz, Torsten; Dentz, Marco; Geyer, Tobias; Tartakovsky, Alexandre M.

2017-11-01

In this work, we study gravity-driven flow of water in the presence of air on a synthetic surface intersected by a horizontal fracture and investigate the importance of droplet and rivulet flow modes on the partitioning behavior at the fracture intersection. We present laboratory experiments, three-dimensional smoothed particle hydrodynamics (SPH) simulations using a heavily parallelized code, and a theoretical analysis. The flow-rate-dependent mode switching from droplets to rivulets is observed in experiments and reproduced by the SPH model, and the transition ranges agree in SPH simulations and laboratory experiments. We show that flow modes heavily influence the "bypass" behavior of water flowing along a fracture junction. Flows favoring the formation of droplets exhibit a much stronger bypass capacity compared to rivulet flows, where nearly the whole fluid mass is initially stored within the horizontal fracture. The effect of fluid buffering within the horizontal fracture is presented in terms of dimensionless fracture inflow so that characteristic scaling regimes can be recovered. For both cases (rivulets and droplets), the flow within the horizontal fracture transitions into a Washburn regime until a critical threshold is reached and the bypass efficiency increases. For rivulet flows, the initial filling of the horizontal fracture is described by classical plug flow. Meanwhile, for droplet flows, a size-dependent partitioning behavior is observed, and the filling of the fracture takes longer. For the case of rivulet flow, we provide an analytical solution that demonstrates the existence of classical Washburn flow within the horizontal fracture.

Magnetically Driven Flows of Suspensions of Rods to Deliver Clot-Busting Drugs to Dead-End Arteries

NASA Astrophysics Data System (ADS)

Bonnecaze, Roger; Clements, Michael

2014-11-01

Suspensions of iron particles in the presence of a magnetic field create flows that could significantly increase the delivery of drugs to dissolve clots in stroke victims. An explanation of this flow rests on the foundation of the seminal works by Prof. Acrivos and his students on effective magnetic permittivity of suspensions of rods, hydrodynamic diffusion of particles, and the flow of suspensions. Intravenous administration of the clot dissolving tissue plasminogen activator (tPA) is the most used therapy for stroke. This therapy is often unsuccessful because the tPA delivery is diffusion-limited and too slow to be effective. Observations show that added iron particles in a rotating magnetic field form rotating rods along the wall of the occluded vessel, creating a convective flow that can carry tPA much faster than diffusion. We present a proposed mechanism for this magnetically driven flow in the form of coupled particle-scale and vessel-scale flow models. At the particle-scale, particles chain up to form rods that rotate, diffuse and translate in the presence of the flow and magnetic fields. Localized vorticity created by the rotating particles drives a macroscopic convective flow in the vessel. Suspension transport equations describe the flow at the vessel-scale. The flow affects the convection and diffusion of the suspension of particles, linking the two scales. The model equations are solved asymptotically and numerically to understand how to create convective flows in dead-end or blocked vessels.

The oceanic boundary layer driven by wave breaking with stochastic variability. Part 1. Direct numerical simulations

NASA Astrophysics Data System (ADS)

Sullivan, Peter P.; McWilliams, James C.; Melville, W. Kendall

2004-05-01

We devise a stochastic model for the effects of breaking waves and fit its distribution functions to laboratory and field data. This is used to represent the space time structure of momentum and energy forcing of the oceanic boundary layer in turbulence-resolving simulations. The aptness of this breaker model is evaluated in a direct numerical simulation (DNS) of an otherwise quiescent fluid driven by an isolated breaking wave, and the results are in good agreement with laboratory measurements. The breaker model faithfully reproduces the bulk features of a breaking event: the mean kinetic energy decays at a rate approaching t(-1) , and a long-lived vortex (eddy) is generated close to the water surface. The long lifetime of this vortex (more than 50 wave periods) makes it effective in energizing the surface region of oceanic boundary layers. Next, a comparison of several different DNS of idealized oceanic boundary layers driven by different surface forcing (i.e. constant current (as in Couette flow), constant stress, or a mixture of constant stress plus stochastic breakers) elucidates the importance of intermittent stress transmission to the underlying currents. A small amount of active breaking, about 1.6% of the total water surface area at any instant in time, significantly alters the instantaneous flow patterns as well as the ensemble statistics. Near the water surface a vigorous downwelling upwelling pattern develops at the head and tail of each three-dimensional breaker. This enhances the vertical velocity variance and generates both negative- and positive-signed vertical momentum flux. Analysis of the mean velocity and scalar profiles shows that breaking effectively increases the surface roughness z_o by more than a factor of 30; for our simulations z_o/lambda {≈} 0.04 to 0.06, where lambda is the wavelength of the breaking wave. Compared to a flow driven by a constant current, the extra mixing from breakers increases the mean eddy viscosity by more than a factor of 10 near the water surface. Breaking waves alter the usual balance of production and dissipation in the turbulent kinetic energy (TKE) budget; turbulent and pressure transports and breaker work are important sources and sinks in the budget. We also show that turbulent boundary layers driven by constant current and constant stress (i.e. with no breaking) differ in fundamental ways. The additional freedom provided by a constant-stress boundary condition permits finite velocity variances at the water surface, so that flows driven by constant stress mimic flows with weakly and statistically homogeneous breaking waves.

Fluid Physics and Macromolecular Crystal Growth in Microgravity

NASA Technical Reports Server (NTRS)

Pusey, M.; Snell, E.; Judge, R.; Chayen, N.; Boggon, T.

2000-01-01

The molecular structure of biological macromolecules is important in understanding how these molecules work and has direct application to rational drug design for new medicines and for the improvement and development of industrial enzymes. In order to obtain the molecular structure, large, well formed, single macromolecule crystals are required. The growth of macromolecule crystals is a difficult task and is often hampered on the ground by fluid flows that result from the interaction of gravity with the crystal growth process. One such effect is the bulk movement of the crystal through the fluid due to sedimentation. A second is buoyancy driven convection close to the crystal surface. On the ground the crystallization process itself induces both of these flows. Buoyancy driven convection results from density differences between the bulk solution and fluid close to the crystal surface which has been depleted of macromolecules due to crystal growth. Schlieren photograph of a growing lysozyme crystal illustrating a 'growth plume' resulting from buoyancy driven convection. Both sedimentation and buoyancy driven convection have a negative effect on crystal growth and microgravity is seen as a way to both greatly reduce sedimentation and provide greater stability for 'depletion zones' around growing crystals. Some current crystal growth hardware however such as those based on a vapor diffusion techniques, may also be introducing unwanted Marangoni convection which becomes more pronounced in microgravity. Negative effects of g-jitter on crystal growth have also been observed. To study the magnitude of fluid flows around growing crystals we have attached a number of different fluorescent probes to lysozyme molecules. At low concentrations, less than 40% of the total protein, the probes do not appear to effect the crystal growth process. By using these probes we expect to determine not only the effect of induced flows due to crystal growth hardware design but also hope to optimize crystallization hardware so that destructive flows are minimized both on the ground and in microgravity.

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

Murphy, Gareth C.; Pessah, Martin E., E-mail: gmurphy@nbi.dk, E-mail: mpessah@nbi.dk

The magnetorotational instability (MRI) is thought to play an important role in enabling accretion in sufficiently ionized astrophysical disks. The rate at which MRI-driven turbulence transports angular momentum is intimately related to both the strength of the amplitudes of the fluctuations on various scales and the degree of anisotropy of the underlying turbulence. This has motivated several studies to characterize the distribution of turbulent power in spectral space. In this paper we investigate the anisotropic nature of MRI-driven turbulence using a pseudo-spectral code and introduce novel ways for providing a robust characterization of the underlying turbulence. We study the growth ofmore » the MRI and the subsequent transition to turbulence via parasitic instabilities, identifying their potential signature in the late linear stage. We show that the general flow properties vary in a quasi-periodic way on timescales comparable to ∼10 inverse angular frequencies, motivating the temporal analysis of its anisotropy. We introduce a 3D tensor invariant analysis to quantify and classify the evolution of the anisotropy of the turbulent flow. This analysis shows a continuous high level of anisotropy, with brief sporadic transitions toward two- and three-component isotropic turbulent flow. This temporal-dependent anisotropy renders standard shell averaging especially when used simultaneously with long temporal averages, inadequate for characterizing MRI-driven turbulence. We propose an alternative way to extract spectral information from the turbulent magnetized flow, whose anisotropic character depends strongly on time. This consists of stacking 1D Fourier spectra along three orthogonal directions that exhibit maximum anisotropy in Fourier space. The resulting averaged spectra show that the power along each of the three independent directions differs by several orders of magnitude over most scales, except the largest ones. Our results suggest that a first-principles theory to describe fully developed MRI-driven turbulence will likely have to consider the anisotropic nature of the flow at a fundamental level.« less

Stability of Buoyancy-Driven Gas Flow: Visualization of Coherent and Incoherent Gas Flow Patterns and Capillary Trapping

NASA Astrophysics Data System (ADS)

Geistlinger, H. W.; Samani, S.; Pohlert, M.; Jia, R.; Lazik, D.

2009-12-01

There are several mechanisms by which the CO2 can be stored: (1) In hydrodynamic trapping, the buoyant CO2 remains as a mobile fluid but is prevented from flowing back to the surface by an impermeable cap rock. (2) In solution trapping, CO2 dissolves into the brine, possibly enhanced by gravity instabilities due to the larger density of the brine-CO2 liquid mixture. (3) In mineral trapping, geochemical binding to the rock due to mineral precipitation. (4) In capillary trapping, the CO2 phase is disconnected into a coherent, mobile phase and an incoherent, immobile (trapped) phase. Recent analytical and numerical investigations [Juanes et al., 2006, 2009; Hesse et al., 2007 ] of buoyant-driven CO2-plume along a sloped aquifer are based on the following conceptual process model: (1) During the injection period, the less wetting CO2 displaces the more wetting brine in a drainage-like process. It is assumed that no capillary trapping occurs and that the CO2-network is coherent and driven both by the injection pressure and the buoyant pressure. Because of this coherence assumption a generalized Darcy-law can be used for the dynamics of the mobile, gaseous CO2-phase. (2) After injection the buoyant CO2 migrates laterally and upward, and water displaces CO2 at the trailing edge of the plume in an imbibition-like process. During this process, there are several physical mechanisms by which the water can displace the CO2 [Lenormand et al., 1983]. In addition to piston-type displacement, core-annular flow (also called: cooperative pore-body filling) may occur, i.e. the wetting phase moves along the walls and under certain conditions the CO2-core flow becomes unstable (snap-off). For water wet rocks, snap-off is the dominant mechanism [Al-Futaisi and Patzek, 2003; Valvatne and Blunt, 2004]. There seems to be consensus that the capillary trapping mechanism has a huge impact on the migration and distribution of CO2 which, in turn, affects the effectiveness of the other sequestration mechanisms. In order to investigate the stability of buoyancy-driven gas flow and the transition between coherent flow, incoherent flow, and their correlation to capillary trapping, we conducted high-resolution optical bench scale experiments. We observed a grain-size (dk) - and flow-rate (Q) dependent transition from incoherent to coherent flow. Based on core-annular flow (= cooperative pore-body filling), we propose a dynamic stability criterion that could describe our experimental results. Our experimental results for vertical gas flow support the experimental results by Lenormand et al. [1983] obtained for horizontal flow, if one takes into account that gravity leads to more unstable flow conditions. Our main results, which are in strong contradiction to the accepted conceptual model of the sloped aquifer, are: (1) Capillary Trapping can already occur during injection and at the front of the plume [Lazik et al., 2008] (2) Gas clusters or bubbles can be mobile (incoherent gas flow) and immobile (capillary trapping), and (3) Incoherent gas flow can not be described by a generalized Darcy law [Geistlinger et al., 2006, 2009].

Calculation of three-dimensional (3-D) internal flow by means of the velocity-vorticity formulation on a staggered grid

NASA Technical Reports Server (NTRS)

Stremel, Paul M.

1995-01-01

A method has been developed to accurately compute the viscous flow in three-dimensional (3-D) enclosures. This method is the 3-D extension of a two-dimensional (2-D) method developed for the calculation of flow over airfoils. The 2-D method has been tested extensively and has been shown to accurately reproduce experimental results. As in the 2-D method, the 3-D method provides for the non-iterative solution of the incompressible Navier-Stokes equations by means of a fully coupled implicit technique. The solution is calculated on a body fitted computational mesh incorporating a staggered grid methodology. In the staggered grid method, the three components of vorticity are defined at the centers of the computational cell sides, while the velocity components are defined as normal vectors at the centers of the computational cell faces. The staggered grid orientation provides for the accurate definition of the vorticity components at the vorticity locations, the divergence of vorticity at the mesh cell nodes and the conservation of mass at the mesh cell centers. The solution is obtained by utilizing a fractional step solution technique in the three coordinate directions. The boundary conditions for the vorticity and velocity are calculated implicitly as part of the solution. The method provides for the non-iterative solution of the flow field and satisfies the conservation of mass and divergence of vorticity to machine zero at each time step. To test the method, the calculation of simple driven cavity flows have been computed. The driven cavity flow is defined as the flow in an enclosure driven by a moving upper plate at the top of the enclosure. To demonstrate the ability of the method to predict the flow in arbitrary cavities, results will he shown for both cubic and curved cavities.

Direct numerical simulation of turbulence in injection-driven plane channel flows

NASA Astrophysics Data System (ADS)

Venugopal, Prem; Moser, Robert D.; Najjar, Fady M.

2008-10-01

Compressible turbulent flow in a periodic plane channel with mass injecting walls is studied as a simplified model for core flow in a solid-propellant rocket motor with homogeneous propellant and other injection-driven internal flows. In this model problem, the streamwise direction was asymptotically homogenized by assuming that at large distances from the closed end, both the mean and rms of turbulent fluctuations evolve slowly in the streamwise direction when compared to the turbulent fluctuations themselves. The Navier-Stokes equations were then modified to account for this slow growth. A direct numerical simulation of the homogenized compressible injection-driven turbulent flow was then conducted for conditions occurring at a streamwise location situated 40 channel half-widths from the closed off end and at an injection Reynolds number of approximately 190. The turbulence in this model flow was found to be only weakly compressible, although significant compressibility existed in the mean flow. As in nontranspired channels, turbulence resulted in increased near-wall shear for the mean streamwise velocity. When normalized by the average rate of turbulence production, the magnitudes of near-wall velocity fluctuations were similar to those in the log region of nontranspired wall-bounded turbulence. However, the sharp peak in streamwise velocity fluctuations observed in nontranspired channels was absent. While streaks and inclined vortices were observed in the near-wall region, their structure was very similar to those observed in the log region of nontranspired channels. These differences are attributed to the absence of a viscous sublayer in the transpired case which in turn is the result of the fact that the no-slip condition for the transpired case is an inviscid boundary condition. That is, unlike nontranspired walls, with transpiration, zero tangential velocity boundary conditions can be imposed at the wall for the Euler (inviscid) equations. The results of this study have important implications on the ability of turbulence models to predict this flow.

Experimental Evaluation of an Isolated Synthetic Jet IN Crossflow

NASA Technical Reports Server (NTRS)

Schaeffler, Norman W.; Jenkins, Luther N.; Hepner, Timothy E.

2007-01-01

The second case for this workshop builds upon the isolated synthetic jet of Case 1 by adding a crossflow, with no streamwise pressure gradient, for the developing jet to interact with. Formally, Case 2 examines the interaction of a single, isolated, synthetic jet and a fully turbulent zero-pressure gradient boundary layer. The resulting flow has many of the characteristics that need to be modeled with fidelity if the results of the calculations are to serve as the basis for research and design with active flow control devices. These include the turbulence in the boundary layer, the time-evolution of the large vortical structure emanating from the jet orifice and its subsequent interaction with and distortion by the boundary layer turbulence, and the effect of the suction cycle on the boundary layer flow. In a synthetic jet, the flow through the orifice and out into the outer flowfield alternates between an exhaust and a suction cycle, driven by the contraction and expansion of a cavity internal to the actuator. In the present experiment, the volume changes in the internal cavity are accomplished by replacing one of the rigid walls of the cavity, the wall opposite the orifice exit, with a deformable wall. This flexible wall is driven by a bottom-mounted moveable piston. The piston is driven electro-mechanically. The synthetic jet issues into the external flow through a circular orifice. In the present experiment, this orifice has a diameter of 0.250 inches (6.35 mm). The flow is conceptually similar to that documented in Schaeffler [1]. To document the flow, several measurement techniques were utilized. The upstream boundary conditions (in-flow conditions), and several key phase-averaged velocity profiles were measured with a 3-component laser-Doppler velocimetry system. Phase-averaged velocity field measurements were made with both stereo digital particle image velocimetry and 2-D digital particle image velocimetry as the primary measurement system. Surface pressure measurements were made utilizing an electronically scanned pressure system.

Tidally driven pore water exchange in offshore intertidal sandbanks: Part I. Field measurements

NASA Astrophysics Data System (ADS)

Gibbes, B.; Robinson, C.; Carey, H.; Li, L.; Lockington, D.

2008-08-01

In recent years blooms of the toxic marine cyanobacteria Lyngbya majuscula have been frequently observed in a system of offshore intertidal sandbanks in Moreton Bay, Australia. Past research suggests that these blooms are linked to the presence of bio-available forms of iron. Using hydraulic and pore water chemistry data collected from a shore normal transect at an offshore bloom site, the role of tidally driven exchange as a potential mechanism for delivery of bio-available iron across the sediment-water interface was examined. Field data revealed a residual pore water flow system in the sandbank, with seawater entering the upper sandbank platform and discharging through the bank edge. Upward flow and elevated near-surface dissolved Fe(II) concentrations (>20 μM Fe(II) at -0.05 m depth) were measured simultaneously in the discharge zones at the sandbank edge. The measured concentrations were more than four times greater than concentrations previously shown to stimulate L. majuscula growth. These results suggest that the tidally driven exchange mechanism might be capable of delivering dissolved Fe(II) to sites within offshore intertidal sandbanks where blooms of L. majuscula have been observed. While the source of the iron was not identified, potential candidates are discussed. These findings have implications for the current conceptual model for L. majuscula blooms in offshore intertidal sandbanks within Moreton Bay. Further investigations are required to fully understand the role of tidally driven exchange in controlling the export of bio-available iron to coastal waters at the field site. In particular there is a need to better assess the link between the pore water flows and the geochemical reactions that might occur along the flow path.

Magnetic Control of Solutal Buoyancy Driven Convection

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Leslie, F. W.

2003-01-01

Volumetric forces resulting from local density variations and gravitational acceleration cause buoyancy induced convective motion in melts and solutions. Solutal buoyancy is a result of concentration differences in an otherwise isothermal fluid. If the fluid also exhibits variations in magnetic susceptibility with concentration then convection control by external magnetic fields can be hypothesized. Magnetic control of thermal buoyancy induced convection in ferrofluids (dispersions of ferromagnetic particles in a carrier fluid) and paramagnetic fluids have been demonstrated. Here we show the nature of magnetic control of solutal buoyancy driven convection of a paramagnetic fluid, an aqueous solution of Manganese Chloride hydrate. We predict the critical magnetic field required for balancing gravitational solutal buoyancy driven convection and validate it through a simple experiment. We demonstrate that gravity driven flow can be completely reversed by a magnetic field but the exact cancellation of the flow is not possible. This is because the phenomenon is unstable. The technique can be applied to crystal growth processes in order to reduce convection and to heat exchanger devices for enhancing convection. The method can also be applied to impose a desired g-level in reduced gravity applications.

Elementary Hemodynamic Principles Based on Modified Bernoulli's Equation.

ERIC Educational Resources Information Center

Badeer, Henry S.

1985-01-01

Develops and expands basic concepts of Bernoulli's equation as it applies to vascular hemodynamics. Simple models are used to illustrate gravitational potential energy, steady nonturbulent flow, pump-driven streamline flow, and other areas. Relationships to the circulatory system are also discussed. (DH)

Development of a Computational Framework for Big Data-Driven Prediction of Long-Term Bridge Performance and Traffic Flow

DOT National Transportation Integrated Search

2018-04-01

Consistent efforts with dense sensor deployment and data gathering processes for bridge big data have accumulated profound information regarding bridge performance, associated environments, and traffic flows. However, direct applications of bridge bi...

Controlling flows in microchannels with patterned surface charge and topography.

PubMed

Stroock, Abraham D; Whitesides, George M

2003-08-01

This Account reviews two procedures for controlling the flow of fluids in microchannels. The first procedure involves patterning the density of charge on the inner surfaces of a channel. These patterns generate recirculating electroosmotic flows in the presence of a steady electric field. The second procedure involves patterning topography on an inner surface of a channel. These patterns generate recirculation in the cross-section of steady, pressure-driven flows. This Account summarizes applications of these flow to mixing and to controlling dispersion (band broadening).

Simulation of 2D Granular Hopper Flow

NASA Astrophysics Data System (ADS)

Li, Zhusong; Shattuck, Mark

2012-02-01

Jamming and intermittent granular flow are big problems in industry, and the vertical hopper is a canonical example of these difficulties. We simulate gravity driven flow and jamming of 2D disks in a vertical hopper and compare with identical companion experiments presented in this session. We measure and compare the flow rate and probability for jamming as a function of particle properties and geometry. We evaluate the ability of standard Hertz-Mindlin contact mode to quantitatively predict the experimental flow.

Electroosmotic Flow Driven by DC and AC Electric Fields in Curved Microchannels

NASA Astrophysics Data System (ADS)

Chen, Jia-Kun; Luo, Win-Jet; Yang, Ruey-Jen

2006-10-01

The purpose of this study is to investigate electroosmotic flows driven by externally applied DC and AC electric fields in curved microchannels. For the DC electric driving field, the velocity distribution and secondary flow patterns are investigated in microchannels with various curvature ratios. We use the Dean number to describe the curvature effect of the flow field in DC electric field. The result implies that the effect of curvatures and the strength of the secondary flows become get stronger when the curvature ratio of C/A (where C is the radius of curvature of the microchannel and A is the half-height of rectangular curved tube.) is smaller. For the AC electric field, the velocity distribution and secondary flow patterns are investigated for driving frequencies in the range of 2.0 kHz (\\mathit{Wo}=0.71) to 11 kHz (\\mathit{Wo}=1.66). The numerical results reveal that the velocity at the center of the microchannel becomes lower at higher frequencies of the AC electric field and the strength of the secondary flow decreases. When the applied frequency exceeds 3.0 kHz (\\mathit{Wo}=0.87), vortices are no longer observed at the corners of the microchannel. Therefore, it can be concluded that the secondary flow induced at higher AC electric field frequencies has virtually no effect on the axial flow field in the microchannel.

Granular flow through an aperture: influence of the packing fraction.

PubMed

Aguirre, M A; De Schant, R; Géminard, J-C

2014-07-01

For the last 50 years, the flow of a granular material through an aperture has been intensely studied in gravity-driven vertical systems (e.g., silos and hoppers). Nevertheless, in many industrial applications, grains are horizontally transported at constant velocity, lying on conveyor belts or floating on the surface of flowing liquids. Unlike fluid flows, that are controlled by the pressure, granular flow is not sensitive to the local pressure but rather to the local velocity of the grains at the outlet. We can also expect the flow rate to depend on the local density of the grains. Indeed, vertical systems are packed in dense configurations by gravity, but, in contrast, in horizontal systems the density can take a large range of values, potentially very small, which may significantly alter the flow rate. In the present article, we study, for different initial packing fractions, the discharge through an orifice of monodisperse grains driven at constant velocity by a horizontal conveyor belt. We report how, during the discharge, the packing fraction is modified by the presence of the outlet, and we analyze how changes in the packing fraction induce variations in the flow rate. We observe that variations of packing fraction do not affect the velocity of the grains at the outlet, and, therefore, we establish that flow-rate variations are directly related to changes in the packing fraction.

Granular flow through an aperture: Influence of the packing fraction

NASA Astrophysics Data System (ADS)

Aguirre, M. A.; De Schant, R.; Géminard, J.-C.

2014-07-01

For the last 50 years, the flow of a granular material through an aperture has been intensely studied in gravity-driven vertical systems (e.g., silos and hoppers). Nevertheless, in many industrial applications, grains are horizontally transported at constant velocity, lying on conveyor belts or floating on the surface of flowing liquids. Unlike fluid flows, that are controlled by the pressure, granular flow is not sensitive to the local pressure but rather to the local velocity of the grains at the outlet. We can also expect the flow rate to depend on the local density of the grains. Indeed, vertical systems are packed in dense configurations by gravity, but, in contrast, in horizontal systems the density can take a large range of values, potentially very small, which may significantly alter the flow rate. In the present article, we study, for different initial packing fractions, the discharge through an orifice of monodisperse grains driven at constant velocity by a horizontal conveyor belt. We report how, during the discharge, the packing fraction is modified by the presence of the outlet, and we analyze how changes in the packing fraction induce variations in the flow rate. We observe that variations of packing fraction do not affect the velocity of the grains at the outlet, and, therefore, we establish that flow-rate variations are directly related to changes in the packing fraction.

Three-dimensional Cascaded Lattice Boltzmann Model for Thermal Convective Flows

NASA Astrophysics Data System (ADS)

Hajabdollahi, Farzaneh; Premnath, Kannan

2017-11-01

Fluid motion driven by thermal effects, such as due to buoyancy in differentially heated enclosures arise in several natural and industrial settings, whose understanding can be achieved via numerical simulations. Lattice Boltzmann (LB) methods are efficient kinetic computational approaches for coupled flow physics problems. In this study, we develop three-dimensional (3D) LB models based on central moments and multiple relaxation times for D3Q7 and D3Q15 lattices to solve the energy transport equations in a double distribution function approach. Their collision operators lead to a cascaded structure involving higher order terms resulting in improved stability. This is coupled to a central moment based LB flow solver with source terms. The new 3D cascaded LB models for the convective flows are first validated for natural convection of air driven thermally on two vertically opposite faces in a cubic cavity at different Rayleigh numbers against prior numerical and experimental data, which show good quantitative agreement. Then, the detailed structure of the 3D flow and thermal fields and the heat transfer rates at different Rayleigh numbers are analyzed and interpreted.

From flying wheel to square flow: Dynamics of a flow driven by acoustic forcing

NASA Astrophysics Data System (ADS)

Cambonie, Tristan; Moudjed, Brahim; Botton, Valéry; Henry, Daniel; Ben Hadid, Hamda

2017-12-01

Acoustic streaming designates the ability to drive quasisteady flows by acoustic propagation in dissipative fluids and results from an acoustohydrodynamics coupling. It is a noninvasive way of putting a fluid into motion using the volumetric acoustic force and can be used for different applications such as mixing purposes. We present an experimental investigation of a kind of square flow driven by acoustic streaming, with the use of beam reflections, in a water tank. Time-resolved experiments using particle image velocimetry have been performed to investigate the velocity field in the reference plane of the experiments for six powers: 0.5, 1, 2, 4, 6, and 8 W. The evolution of the flow regime from almost steady to strongly unsteady states is characterized using different tools: the plot of time-averaged and instantaneous velocity fields, the calculation of presence density maps for vortex positions and for the maximal velocity and vorticity crest lines, and the use of spatiotemporal maps of the waving observed on the jets created by acoustic streaming. A transition is observed between two regimes at moderate and high acoustic forcing.

Numerical study of enhanced mixing in pressure-driven flows in microchannels using a spatially periodic electric field

NASA Astrophysics Data System (ADS)

Krishnaveni, T.; Renganathan, T.; Picardo, J. R.; Pushpavanam, S.

2017-09-01

We propose an innovative mechanism for enhancing mixing in steady pressure driven flow of an electrolytic solution in a straight rectangular microchannel. A transverse electric field is used to generate an electroosmotic flow across the cross-section. The resulting flow field consists of a pair of helical vortices that transport fluid elements along the channel. We show, through numerical simulations, that chaotic advection may be induced by periodically varying the direction of the applied electric field along the channel length. This periodic electric field generates a longitudinally varying, three-dimensional steady flow, such that the streamlines in the first half of the repeating unit cell intersect those in the second half, when projected onto the cross-section. Mixing is qualitatively characterized by tracking passive particles and obtaining Poincaré maps. For quantification of the extent of mixing, Shannon entropy is calculated using particle advection of a binary mixture. The convection diffusion equation is also used to track the evolution of a scalar species and quantify the mixing efficiency as a function of the Péclet number.

Numerical study of enhanced mixing in pressure-driven flows in microchannels using a spatially periodic electric field.

PubMed

Krishnaveni, T; Renganathan, T; Picardo, J R; Pushpavanam, S

2017-09-01

We propose an innovative mechanism for enhancing mixing in steady pressure driven flow of an electrolytic solution in a straight rectangular microchannel. A transverse electric field is used to generate an electroosmotic flow across the cross-section. The resulting flow field consists of a pair of helical vortices that transport fluid elements along the channel. We show, through numerical simulations, that chaotic advection may be induced by periodically varying the direction of the applied electric field along the channel length. This periodic electric field generates a longitudinally varying, three-dimensional steady flow, such that the streamlines in the first half of the repeating unit cell intersect those in the second half, when projected onto the cross-section. Mixing is qualitatively characterized by tracking passive particles and obtaining Poincaré maps. For quantification of the extent of mixing, Shannon entropy is calculated using particle advection of a binary mixture. The convection diffusion equation is also used to track the evolution of a scalar species and quantify the mixing efficiency as a function of the Péclet number.

Behavior of neutral solutes in pressurized flow driven electrochromatography using a mixed stationary phase of ODS and anion-exchange.

PubMed

Kitagawa, Shinya; Tsuda, Takao

2003-05-02

The behavior of neutral sample solutes in pressurized flow driven electrochromatography using a mixed stationary phase, which consisted of ODS and anion-exchange (ODS-SAX), was studied. Applications of both positive and negative voltage on a column induced increases in retention factors of sample solutes. The direction of an electroosmotic flow under applications of positive and negative voltage were the same, therefore, the sign of the surface charge density under positive and negative voltage was opposite. We proposed a new equation for the relationship between applied voltage and surface charge density, and the practical electroosmotic flow conformed to this equation. Studying the electroosmotic flow using our proposed equation revealed that the applied negative voltage accelerates the protonation of the quaternary ammonium group and dissociation of the silanol group on packing materials. The retention behavior of a neutral solute was affected by the existence of the charged functional groups. We propose that this phenomenon is applicable to the control of the retention behavior of a sample solute using an electric field.

Characterization of a membrane-based, electrochemically driven pumping system using aqueous electrolyte solutions.

PubMed

Norman, Mya A; Evans, Christine E; Fuoco, Anthony R; Noble, Richard D; Koval, Carl A

2005-10-01

Electrokinetic flow provides a mechanism for a variety of fluid pumping schemes. The design and characterization of an electrochemically driven pump that utilizes porous carbon electrodes, iodide/triiodide redox electrolytes, and Nafion membranes is described. Fluid pumping by the cell is reversible and controlled by the cell current. Chronopotentiometry experiments indicate that the total available fluid that can be pumped in a single electrolysis without gas evolution is determined solely by the initial concentration of electrolyte and the applied current. The magnitude of the fluid flow at a given current is determined by the nature of the cation in the electrolyte and by the water absorption properties of the Nafion membrane. For 1 M aqueous electrolytes, pumping rates ranging from 1 to 14 microL/min were obtained for current densities of 10-30 mA/cm2 of membrane area. Molar volume changes for the I3-/I- redox couple and for the alkali cation migration contribute little to the observed volumetric flow rates; the magnitude of the flow is dominated by the migration-induced flow of water.

Hydraulic transport across hydrophilic and hydrophobic nanopores: Flow experiments with water and n-hexane.

PubMed

Gruener, Simon; Wallacher, Dirk; Greulich, Stefanie; Busch, Mark; Huber, Patrick

2016-01-01

We experimentally explore pressure-driven flow of water and n-hexane across nanoporous silica (Vycor glass monoliths with 7- or 10-nm pore diameters, respectively) as a function of temperature and surface functionalization (native and silanized glass surfaces). Hydraulic flow rates are measured by applying hydrostatic pressures via inert gases (argon and helium, pressurized up to 70 bar) on the upstream side in a capacitor-based membrane permeability setup. For the native, hydrophilic silica walls, the measured hydraulic permeabilities can be quantitatively accounted for by bulk fluidity provided we assume a sticking boundary layer, i.e., a negative velocity slip length of molecular dimensions. The thickness of this boundary layer is discussed with regard to previous capillarity-driven flow experiments (spontaneous imbibition) and with regard to velocity slippage at the pore walls resulting from dissolved gas. Water flow across the silanized, hydrophobic nanopores is blocked up to a hydrostatic pressure of at least 70 bar. The absence of a sticking boundary layer quantitatively accounts for an enhanced n-hexane permeability in the hydrophobic compared to the hydrophilic nanopores.

Generalized two-temperature model for coupled phonon-magnon diffusion.

PubMed

Liao, Bolin; Zhou, Jiawei; Chen, Gang

2014-07-11

We generalize the two-temperature model [Sanders and Walton, Phys. Rev. B 15, 1489 (1977)] for coupled phonon-magnon diffusion to include the effect of the concurrent magnetization flow, with a particular emphasis on the thermal consequence of the magnon flow driven by a nonuniform magnetic field. Working within the framework of the Boltzmann transport equation, we derive the constitutive equations for coupled phonon-magnon transport driven by gradients of both temperature and external magnetic fields, and the corresponding conservation laws. Our equations reduce to the original Sanders-Walton two-temperature model under a uniform external field, but predict a new magnon cooling effect driven by a nonuniform magnetic field in a homogeneous single-domain ferromagnet. We estimate the magnitude of the cooling effect in an yttrium iron garnet, and show it is within current experimental reach. With properly optimized materials, the predicted cooling effect can potentially supplement the conventional magnetocaloric effect in cryogenic applications in the future.

Experimental characterization of 3-dimensional gravity-driven fingering in a porous medium

NASA Astrophysics Data System (ADS)

Dalbe, Marie-Julie; Juanes, Ruben

2017-11-01

When water infiltrates a dry porous media, a gravity-driven instability can be observed. Water will penetrate the porous media along preferential paths, called fingers. This gravity-driven unstable multiphase flow has important implications for natural phenomena such as rainwater infiltration in soil and secondary oil migration in reservoir rocks. While several experimental and numerical studies have described the instability in 2-dimensional (2D) settings, fundamental questions remain on the morphodynamics of gravity fingering in 3D. We developed a 3D experimental set-up based on planar laser-induced fluorescence of index-matched fluids that allows us to image this phenomenon dynamically. We study the impact of some crucial parameters such as rainfall rate or grain size on the finger size and velocity. In addition, experiments in stratified media reveal interesting dynamics of finger flow across material interfaces, an essential aspect towards the understanding of water infiltration in soils.

Hybrid finite-difference/lattice Boltzmann simulations of microchannel and nanochannel acoustic streaming driven by surface acoustic waves

NASA Astrophysics Data System (ADS)

Tan, Ming K.; Yeo, Leslie Y.

2018-04-01

A two-dimensional hybrid numerical method that allows full coupling of the elastic motion in a piezoelectric solid (modeled using a finite-difference time-domain technique) with the resultant compressional flow in a fluid (simulated using a lattice Boltzmann scheme) is developed to study the acoustic streaming that arises in both microchannels and nanochannels under surface acoustic wave (SAW) excitation. In addition to verifying the model through a comparison of the simulations with results from experimental and numerical studies of microchannel and nanochannel flows driven by both standing and traveling SAWs in the literature, we highlight salient features of the flow field that arise and discuss the underlying mechanisms responsible for the flow. In microchannels, boundary layer streaming is the dominant mechanism when the channel height is below the sound wavelength in the liquid, whereas Eckart streaming—arising as a consequence of the attenuation of the sound wave in the liquid—dominates in the form of periodic vortices for larger channel heights. The absence of Eckart streaming and the overlapping of boundary layers in nanochannels with heights below the boundary layer thickness, on the other hand, give rise to a time-averaged dynamic acoustic pressure that results in an inertial-dominant flow, which paradoxically possesses a parabolic-like velocity profile resembling pressure-driven laminar flow. In contrast, if the nanochannel were to be filled instead with air, the significantly lower fluid density leads to a considerable reduction in the dynamic acoustic pressure and hence inertial forcing such that boundary layer streaming once again dominates, asymptotically imposing a slip condition along the channel surface that results in a negative pluglike velocity profile.

Time-dependent particle migration and margination in the pressure-driven channel flow of blood

NASA Astrophysics Data System (ADS)

Qi, Qin M.; Shaqfeh, Eric S. G.

2018-03-01

We present a theory to describe the time evolution of the red blood cell (RBC) and platelet concentration distributions in pressure-driven flow through a straight channel. This model is based on our previous theory for the steady-state distributions [Qi and Shaqfeh, Phys. Rev. Fluids 2, 093102 (2017), 10.1103/PhysRevFluids.2.093102] and captures the flow-induced nonuniformity of the concentrations of RBCs and platelets in the cross-flow direction. Starting with a uniform concentration, RBCs migrate away from the channel walls due to a shear-induced lift force and eventually reach steady state due to shear-induced diffusion, i.e., hydrodynamic "collisions" with other RBCs. On the other hand, platelets exit the cell-laden region due to RBC-platelet interactions and enter the cell-free layer, resulting in margination. To validate the theory, we also perform boundary integral simulations of blood flow in microchannels and directly compare various measureables between theory and simulation. The timescales associated with RBC migration and platelet margination are discussed in the context of the simulation and theory, and their importance in the function of microfluidic devices as well as the vascular network are elucidated. Due to the varying shear rate in pressure-driven flow and the wall-induced RBC lift, we report a separation of timescales for the transport in the near-wall region and in the bulk region. We also relate the transient problem to the axial variation of migration and margination, and we demonstrate how the relevant timescales can be used to predict corresponding entrance lengths. Our theory can serve as a fast and convenient alternative to large-scale simulations of these phenomena.

The precession dynamo experiment at HZDR

NASA Astrophysics Data System (ADS)

Giesecke, A.; Gundrum, T.; Herault, J.; Stefani, F.; Gerbeth, G.

2015-12-01

In a next generation dynamo experiment currently under development atthe Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a fluid flow of liquidsodium, solely driven by precession, will be considered as a possiblesource for magnetic field generation. The experiment is mainlymotivated by alternative concepts for astrophysical dynamos that arebased on mechanical flow driving. For example, it has long beendiscussed whether precession may be a complementary power source forthe geodynamo (Malkus, Science 1968) or for the ancient lunar dynamodue to the Earth-driven precession of the lunar spin axis (Dwyer, Nature 2011).We will present the current state of development of the dynamoexperiment together with results from non-linear hydrodynamicsimulations with moderate precessional forcing. Our simulations reveala non-axisymmetric forced mode with an amplitude of up to one fourthof the rotation velocity of the cylindrical container confirming thatprecession provides a rather efficient flow driving mechanism even atmoderate precession rates.More relevant for dynamo action might be free Kelvin modes (thenatural flow eigenmodes in a rotating cylinder) with higher azimuthalwave number. These modes may become relevant when constituting atriadic resonance with the fundamental forced mode, i.e., when theheight of the container matches their axial wave lengths. We findtriadic resonances at aspect ratios close to those predicted by thelinear theory except around the primary resonance of the forcedmode. In that regime we still identify free Kelvin modes propagatingin retrograde direction but none of them can be assigned to a triade.Our results will enter into the development of flow models that willbe used in kinematic simulations of the electromagnetic inductionequation in order to determine whether a precession driven flow willbe capable to drive a dynamo at all and to limit the parameter spacewithin which the occurrence of dynamo action is most promising.

High-resolution seismic constraints on flow dynamics in the oceanic asthenosphere.

PubMed

Lin, Pei-Ying Patty; Gaherty, James B; Jin, Ge; Collins, John A; Lizarralde, Daniel; Evans, Rob L; Hirth, Greg

2016-07-28

Convective flow in the mantle and the motions of tectonic plates produce deformation of Earth's interior, and the rock fabric produced by this deformation can be discerned using the anisotropy of the seismic wave speed. This deformation is commonly inferred close to lithospheric boundaries beneath the ocean in the uppermost mantle, including near seafloor-spreading centres as new plates are formed via corner flow, and within a weak asthenosphere that lubricates large-scale plate-driven flow and accommodates smaller scale convection. Seismic models of oceanic upper mantle differ as to the relative importance of these deformation processes: seafloor spreading fabric is very strong just beneath the crust-mantle boundary (the Mohorovičić discontinuity, or Moho) at relatively local scales, but at the global and ocean-basin scales, oceanic lithosphere typically appears weakly anisotropic when compared to the asthenosphere. Here we use Rayleigh waves, recorded across an ocean-bottom seismograph array in the central Pacific Ocean (the NoMelt Experiment), to provide unique localized constraints on seismic anisotropy within the oceanic lithosphere-asthenosphere system in the middle of a plate. We find that azimuthal anisotropy is strongest within the high-seismic-velocity lid, with the fast direction coincident with seafloor spreading. A minimum in the magnitude of azimuthal anisotropy occurs within the middle of the seismic low-velocity zone, and then increases with depth below the weakest portion of the asthenosphere. At no depth does the fast direction correlate with the apparent plate motion. Our results suggest that the highest strain deformation in the shallow oceanic mantle occurs during corner flow at the ridge axis, and via pressure-driven or buoyancy-driven flow within the asthenosphere. Shear associated with motion of the plate over the underlying asthenosphere, if present, is weak compared to these other processes.

Multiphase flow in geometrically simple fracture intersections

USGS Publications Warehouse

Basagaoglu, H.; Meakin, P.; Green, C.T.; Mathew, M.; ,

2006-01-01

A two-dimensional lattice Boltzmann (LB) model with fluid-fluid and solid-fluid interaction potentials was used to study gravity-driven flow in geometrically simple fracture intersections. Simulated scenarios included fluid dripping from a fracture aperture, two-phase flow through intersecting fractures and thin-film flow on smooth and undulating solid surfaces. Qualitative comparisons with recently published experimental findings indicate that for these scenarios the LB model captured the underlying physics reasonably well.

Observation of turbulent-driven shear flow in a cylindrical laboratory plasma device.

PubMed

Holland, C; Yu, J H; James, A; Nishijima, D; Shimada, M; Taheri, N; Tynan, G R

2006-05-19

An azimuthally symmetric radially sheared plasma fluid flow is observed to spontaneously form in a cylindrical magnetized helicon plasma device with no external sources of momentum input. A turbulent momentum conservation analysis shows that this shear flow is sustained by the Reynolds stress generated by collisional drift turbulence in the device. The results provide direct experimental support for the basic theoretical picture of drift-wave-shear-flow interactions.

Roles of type II myosin and a tropomyosin isoform in retrograde actin flow in budding yeast

PubMed Central

Huckaba, Thomas M.; Lipkin, Thomas; Pon, Liza A.

2006-01-01

Retrograde flow of cortical actin networks and bundles is essential for cell motility and retrograde intracellular movement, and for the formation and maintenance of microvilli, stereocilia, and filopodia. Actin cables, which are F-actin bundles that serve as tracks for anterograde and retrograde cargo movement in budding yeast, undergo retrograde flow that is driven, in part, by actin polymerization and assembly. We find that the actin cable retrograde flow rate is reduced by deletion or delocalization of the type II myosin Myo1p, and by deletion or conditional mutation of the Myo1p motor domain. Deletion of the tropomyosin isoform Tpm2p, but not the Tpm1p isoform, increases the rate of actin cable retrograde flow. Pretreatment of F-actin with Tpm2p, but not Tpm1p, inhibits Myo1p binding to F-actin and Myo1p-dependent F-actin gliding. These data support novel, opposing roles of Myo1p and Tpm2 in regulating retrograde actin flow in budding yeast and an isoform-specific function of Tpm1p in promoting actin cable function in myosin-driven anterograde cargo transport. PMID:17178912

Multiple buoyancy driven flows in a vertical cylinder heated from below

NASA Technical Reports Server (NTRS)

Yamaguchi, Y.; Chang, C. J.; Brown, R. A.

1983-01-01

The structure of axisymmetric buoyancy-driven convection in a vertical cylinder heated from below is probed by finite element solution of the Boussinesq equations coupled with computed-implemented perturbation techniques for detecting and tracking multiple flows and for determining flow stability. Results are reported for fluids with Prandtl number of one and for cylinders with aspect ratio (Lambda) (defined as the height to radius of the cylinder) between 0.5 and 2.25. Extensive calculations of the neutral stability curve for the static solution and of the nonlinear motions along the bifurcating flow families show a continuous evolution of the primary cellular motion from a single toroidal cell to two and three cells nested radially in the cylinder, instead of the sharp transitions found for a cylinder with shear-free sidewalls. The smooth transitions in flow structure with Rayleigh number and lambda are explained by nonlinear connectivity between the first two bifurcating flow families formed either by a secondary bifurcation point for Lambda or = Lambda * approximately 0.80 or by a limit point for Lambda Lambda *. The transition between these two modes may be described by the theory of multiple limit point bifurcation.