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1

Radiative interactions in laminar incompressible and compressible internal flows  

NASA Technical Reports Server (NTRS)

Analyses and numerical procedures are presented to investigate the radiative interactions of gray and nongray absorbing-emitting species between two parallel plates and in a circular tube. Laminar fully developed incompressible as well as entrance region subsonic flows are considered. The participating species considered are OH, CO, CO2, CH4, and H2O. Results obtained for different flow conditions indicate that the radiative interactions can be quite significant in fully developed incompressible flows. For subsonic flows, however, the flowfield is not changed significantly due to radiative interactions.

Tiwari, S. N.; Singh, D. J.; Trivedi, P. A.

1990-01-01

2

Two-dimensional laminar incompressible separated flow past airfoils  

NASA Technical Reports Server (NTRS)

A method is proposed to treat the problem of steady, two-dimensional, laminar, incompressible high Reynolds number separated flow past thin airfoils. An integral form of the boundary layer equations with interaction is used and the interaction between the inviscid and viscous flow fields is provided for by use of a thin-airfoil integral. Documentation of the attempts at obtaining a solution is presented. A survey of the current state-of-the-art of problems involving viscous-inviscid interactions in flow fields with separation is given.

Plotkin, A.

1973-01-01

3

Transient radiative energy transfer in incompressible laminar flows  

NASA Technical Reports Server (NTRS)

Analysis and numerical procedures are presented to investigate the transient radiative interactions of nongray absorbing-emitting species in laminar fully-developed flows between two parallel plates. The particular species considered are OH, CO, CO2, and H2O and different mixtures of these. Transient and steady-state results are obtained for the temperaure distribution and bulk temperature for different plate spacings, wall temperatures, and pressures. Results, in general, indicate that the rate of radiative heating can be quite high during earlier times. This information is useful in designing thermal protection systems for transient operations.

Tiwari, S. N.; Singh, D. J.

1987-01-01

4

Theoretical investigation of maintaining the boundary layer of revolution laminar using suction slits in incompressible flow  

NASA Technical Reports Server (NTRS)

The transition of the laminar boundary layer into the turbulent state, which results in an increased drag, can be avoided by sucking of the boundary layer particles near the wall. The technically-interesting case of sucking the particles using individual slits is investigated for bodies of revolution in incompressible flow. The results of the variational calculations show that there is an optimum suction height, where the slot separations are maximum. Combined with favorable shaping of the body, it is possible to keep the boundary layer over bodies of revolution laminar at high Reynolds numbers using relatively few suction slits and small amounts of suction flow.

Thiede, P.

1978-01-01

5

Numerical analysis of laminar and turbulent incompressible flows using the finite element Fluid Dynamics Analysis Package (FIDAP)  

NASA Technical Reports Server (NTRS)

The purpose of the study is the evaluation of the numerical accuracy of FIDAP (Fluid Dynamics Analysis Package). Accordingly, four test problems in laminar and turbulent incompressible flows are selected and the computational results of these problems compared with other numerical solutions and/or experimental data. These problems include: (1) 2-D laminar flow inside a wall-driven cavity; (2) 2-D laminar flow over a backward-facing step; (3) 2-D turbulent flow over a backward-facing step; and (4) 2-D turbulent flow through a turn-around duct.

Sohn, Jeong L.

1988-01-01

6

Laminar and turbulent incompressible fluid flow analysis with heat transfer by the finite element method  

NASA Astrophysics Data System (ADS)

A study of the finite element method applied to two-dimensional incompressible fluid flow analysis with heat transfer is performed using a mixed Galerkin finite element method with the primitive variable form of the model equations. Four biquadratic, quadrilateral elements are compared in this study--the serendipity biquadratic element with bilinear continuous pressure interpolation (Q2(8)-Q1) and the Lagrangian biquadratic element with bilinear continuous pressure interpolation (Q2-Q1) of the Taylor-Hood form. A modified form of the Q-2Q1 element is also studied. The pressure interpolation is augmented by a discontinuous constant shape function for pressure (Q2-Q1+). The discontinuous pressure element formulation makes use of biquadratic shape functions and a discontinuous linear interpolation of the pressure (Q2-P1(3)). Laminar flow solutions, with heat transfer, are compared to analytical and computational benchmarks for flat channel, backward-facing step and buoyancy driven flow in a square cavity. It is shown that the discontinuous pressure elements provide superior solution characteristics over the continuous pressure elements. Highly accurate heat transfer solutions are obtained and the Q2-P1(3) element is chosen for extension to turbulent flow simulations. Turbulent flow solutions are presented for both low turbulence Reynolds number and high Reynolds number formulations of two equation turbulence models. The following three forms of the length scale transport equation are studied: the turbulence energy dissipation rate (epsilon), the turbulence frequency (omega) and the turbulence time scale (tau). It is shown that the low turbulence Reynolds number model consisting of the k-tau transport equations, coupled with the damping functions of Shih and Hsu, provides an optimal combination of numerical stability and solution accuracy for the flat channel flow. Attempts to extend the formulation beyond the flat channel were not successful due to oscillatory behavior of the solutions. It is shown that the Streamline-Upwind/Petrov-Galerkin (SUPG) formulation provides stable solutions for the advection diffusion equation with biquadratic elements. However, when coupled with the Newton-Raphson linearization method, convergence behavior is reduced to less than first order, leading to unattainable computer time requirements. The high Reynolds number form of the k-epsilon and k-omega turbulence models are applied to flat channel and backward-facing step flows using a wall function element. This biquadratic element has continuous law-of-the-wall shape functions normal to the wall. It is shown that the k-epsilon and k-omega models work well for the flat channel flow. The k-epsilon model gave acceptable results for the backward-facing step flow, while the k-omega model gave erroneous results. flow can be achieved.

Cochran, Robert James

7

Incompressible laminar flow through hollow fibers: a general study by means of a two-scale approach  

NASA Astrophysics Data System (ADS)

We study the laminar flow of an incompressible Newtonian fluid in a hollow fiber, whose walls are porous. We write the Navier-Stokes equations for the flow in the inner channel and Darcy's law for the flow in the fiber, coupling them by means of the Beavers-Joseph condition which accounts for the (possible) slip at the membrane surface. Then, we introduce a small parameter {\\varepsilon ? 1} (the ratio between the radius and the length of the fiber) and expand all relevant quantities in powers of ?. Averaging over the fiber cross section, we find the velocity profiles for the longitudinal flow and for the cross-flow, and eventually, we determine the explicit expression of the permeability of the system. This work is also preliminary to the study of more complex systems comprising a large number of identical fibers (e.g., ultrafiltration modules and dialysis).

Borsi, Iacopo; Farina, Angiolo; Fasano, Antonio

2011-08-01

8

Natural laminar flow and laminar flow control  

NASA Technical Reports Server (NTRS)

The present volume discusses the development history and basic concepts of laminar flow control, laminar flow flight experiments, subsonic laminar-flow airfoils, and a design philosophy for long-range laminar flow-control commercial transports with advanced supercritical airfoils. Also discussed are the relationship of wave-interaction theory to laminar flow control, supersonic laminar flow control, and the NASA-Langley 8-ft Transonic Pressure Tunnel.

Barnwell, R. W. (editor); Hussaini, M. Y. (editor)

1992-01-01

9

Laminar Flow Aircraft Certification  

NASA Technical Reports Server (NTRS)

Various topics telative to laminar flow aircraft certification are discussed. Boundary layer stability, flaps for laminar flow airfoils, computational wing design studies, manufacturing requirements, windtunnel tests, and flow visualization are among the topics covered.

Williams, Louis J. (compiler)

1986-01-01

10

Navier-Stokes solutions for laminar incompressible flow over a NACA 0012 airfoil and a backward facing step  

NASA Astrophysics Data System (ADS)

For the solution of the incompressible Navier-Stokes equation, an explicit Runge-Kutta finite-volume solver was created. The gradients due to the viscous terms were approximated in the cells by surface integrals along the cell boundaries. A stability analysis for the condition of the local time step for the Runge-Kutta scheme was performed. Results for external and internal flow in two dimensions are presented. The code was verified for the external flow over a NACA 0012 airfoil at different Reynolds numbers and angles of attack, and the results were compared to corresponding compressible cases and to experiments. The code was also applied for the internal flow over a backward facing step for different Reynolds numbers, for which experimental data and numerical results are available. The results agree with other numerical results and with experimental data.

Eliasson, Peter

1987-08-01

11

Aircraft Laminar Flow Control  

NASA Technical Reports Server (NTRS)

Aircraft laminar flow control (LFC) from the 1930's through the 1990's is reviewed and the current status of the technology is assessed. Examples are provided to demonstrate the benefits of LFC for subsonic and supersonic aircraft. Early studies related to the laminar boundary-layer flow physics, manufacturing tolerances for laminar flow, and insect-contamination avoidance are discussed. LFC concept studies in wind-tunnel and flight experiments are the major focus of the paper. LFC design tools are briefly outlined for completeness.

Joslin, Ronald D.

1998-01-01

12

Supersonic laminar flow control research  

NASA Technical Reports Server (NTRS)

The objective of the research is to understand supersonic laminar flow stability, transition, and active control. Some prediction techniques will be developed or modified to analyze laminar flow stability. The effects of supersonic laminar flow with distributed heating and cooling on active control will be studied. The primary tasks of the research applying to the NASA/Ames Proof of Concept (POC) Supersonic Wind Tunnel and Laminar Flow Supersonic Wind Tunnel (LFSWT) nozzle design with laminar flow control are as follows: (1) predictions of supersonic laminar boundary layer stability and transition, (2) effects of wall heating and cooling for supersonic laminar flow control, and (3) performance evaluation of POC and LFSWT nozzles design with wall heating and cooling effects applying at different locations and various length.

Lo, Ching F.

1994-01-01

13

Compressible laminar flow in a channel  

NASA Astrophysics Data System (ADS)

Laminar flow of a compressible Newtonian fluid in a channel is analyzed. An analytic solution to the vorticity-stream function form of the hydrodynamics equations is found for weakly compressible flow using a regular perturbation method. In contrast with previous studies, the present analysis does not invoke the lubrication approximation and, consequently, predicts both a nonzero transverse velocity and a nonzero transverse pressure gradient. Predicted velocity and pressure fields from the perturbation solution are compared with previously published analytical and numerical solutions. Expressions for pressure drop are also given for compressible laminar flow in a channel that display significant deviations from the incompressible case. In addition, experimental data from the literature for the flow of gases in microchannels are analyzed and compared with predictions from the analytical solution. We find that a commonly used method for analyzing microchannel flow experiments obscures a rather simple dependence of pressure drop on the same dimensionless parameter used in the perturbation solution.

Venerus, D. C.; Bugajsky, D. J.

2010-04-01

14

Unified approach for incompressible flows  

NASA Technical Reports Server (NTRS)

A unified approach for solving incompressible flows has been investigated in this study. The numerical CTVD (Centered Total Variation Diminishing) scheme used in this study was successfully developed by Sanders and Li for compressible flows, especially for the high speed. The CTVD scheme possesses better mathematical properties to damp out the spurious oscillations while providing high-order accuracy for high speed flows. It leads us to believe that the CTVD scheme can equally well apply to solve incompressible flows. Because of the mathematical difference between the governing equations for incompressible and compressible flows, the scheme can not directly apply to the incompressible flows. However, if one can modify the continuity equation for incompressible flows by introducing pseudo-compressibility, the governing equations for incompressible flows would have the same mathematical characters as compressible flows. The application of the algorithm to incompressible flows thus becomes feasible. In this study, the governing equations for incompressible flows comprise continuity equation and momentum equations. The continuity equation is modified by adding a time-derivative of the pressure term containing the artificial compressibility. The modified continuity equation together with the unsteady momentum equations forms a hyperbolic-parabolic type of time-dependent system of equations. Thus, the CTVD schemes can be implemented. In addition, the physical and numerical boundary conditions are properly implemented by the characteristic boundary conditions. Accordingly, a CFD code has been developed for this research and is currently under testing. Flow past a circular cylinder was chosen for numerical experiments to determine the accuracy and efficiency of the code. The code has shown some promising results.

Chang, Tyne-Hsien

1995-01-01

15

Overview of Laminar Flow Control  

NASA Technical Reports Server (NTRS)

The history of Laminar Flow Control (LFC) from the 1930s through the 1990s is reviewed and the current status of the technology is assessed. Early studies related to the natural laminar boundary-layer flow physics, manufacturing tolerances for laminar flow, and insect-contamination avoidance are discussed. Although most of this publication is about slot-, porous-, and perforated-suction LFC concept studies in wind tunnel and flight experiments, some mention is made of thermal LFC. Theoretical and computational tools to describe the LFC aerodynamics are included for completeness.

Joslin, Ronald D.

1998-01-01

16

Improved Algorithm Computes Incompressible Flow  

NASA Technical Reports Server (NTRS)

Algorithm numerically integrates Navier-Stokes equations of time-dependent or steady flow of incompressible, viscous fluid. Simulates realistic three-dimensional flows bounded by stationary or moving surface(s) of complicated shape(s). Only two arbitrary parameters specified by user. Algorithm described in "Numerical Simulation Of Flow Through An Artificial Heart" (ARC-12478). Algorithm tested by application to number of steady and unsteady flows, including flow in artificial heart discussed in noted prior article.

Rogers, Stuart E.

1993-01-01

17

A Power-Law Formulation of Laminar Flow in Short Pipes Max Sherman  

E-print Network

A Power-Law Formulation of Laminar Flow in Short Pipes Max Sherman Indoor Environment Program-law representation between the air flow and applied pressure for laminar flow in short pipes. It is found that short of interest. The system studied herein is the flow of an incompressible, viscous fluid through a short pipe

18

Laminar flow control is maturing  

NASA Technical Reports Server (NTRS)

Recent research demonstrates that laminar flow (LF) can be reliable in flight and that the support system need not be complex. Shaping produces favorable pressure gradients for maintaining natural laminar flow (NLF), and laminar flow control (LFC) techniques such as full chord suction promise a fuel-saving payoff of up to 30 percent on long-range missions. For large aircraft, current research is concentrated on hybrid LFC concepts which combine suction and pressure-gradient control. At NASA Ames, an F-14 with variable wing sweep has been flight tested with smooth surface gloves on the wings; preliminary results indicate high transition Reynolds numbers to sweep angles as large as 25 deg. In addition, a 757 was flight tested with an NLF glove on the right wing just outboard of the engine pylon; and the LF was found to be suprisingly robust.

Wagner, Richard D.; Bartlett, Dennis W.; Maddalon, Dal V.

1988-01-01

19

Incompressible flow around small obstacles  

NASA Astrophysics Data System (ADS)

In recent years, the author and his research team have obtained several results concerning the limiting behavior of incompressible flow around small obstacles, both in the inviscid and viscous cases. These results showcase the difficulties and mathematical issues surrounding the description of fluid-solid interaction at large Reynolds number. In this talk, we will present the main results obtained, focusing especially of the joint small viscosity/small obstacle limit, see [1], ongoing research on homogenization, and open problems. [4pt] [1] Iftimie, D., Lopes Filho, M.C. and Nussenzveig Lopes, H.J., Incompressible flow around a small obstacle and the vanishing viscosity limit, Commun. Math. Phys. V. 287 (2009), 99-115

Lopes Filho, Milton

2010-11-01

20

Laminar-flow flight experiments  

NASA Technical Reports Server (NTRS)

The flight testing conducted over the past 10 years in the NASA laminar-flow control (LFC) will be reviewed. The LFC program was directed towards the most challenging technology application, the high supersonic speed transport. To place these recent experiences in perspective, earlier important flight tests will first be reviewed to recall the lessons learned at that time.

Wagner, Richard D.; Maddalon, Dal V.; Bartlett, D. W.; Collier, F. S., Jr.; Braslow, A. L.

1989-01-01

21

Radiative interactions in laminar duct flows  

NASA Technical Reports Server (NTRS)

Analyses and numerical procedures are presented for infrared radiative energy transfer in gases when other modes of energy transfer occur simultaneously. Two types of geometries are considered, a parallel plate duct and a circular duct. Fully developed laminar incompressible flows of absorbing-emitting species in black surfaced ducts are considered under the conditions of uniform wall heat flux. The participating species considered are OH, CO, CO2, and H2O. Nongray as well as gray formulations are developed for both geometries. Appropriate limiting solutions of the governing equations are obtained and conduction-radiation interaction parameters are evaluated. Tien and Lowder's wide band model correlation was used in nongray formulation. Numerical procedures are presented to solve the integro-differential equations for both geometries. The range of physical variables considered are 300 to 2000 K for temperature, 0.1 to 100.0 atm for pressure, and 0.1 to 100 cm spacings between plates/radius of the tube. An extensive parametric study based on nongray formulation is presented. Results obtained for different flow conditions indicate that the radiative interactions can be quite significant in fully developed incompressible flows.

Trivedi, P. A.; Tiwari, S. N.

1990-01-01

22

Operational considerations for laminar flow aircraft  

NASA Technical Reports Server (NTRS)

Considerable progress has been made in the development of laminar flow technology for commercial transports during the NASA Aircraft Energy Efficiency (ACEE) laminar flow program. Practical, operational laminar flow control (LFC) systems have been designed, fabricated, and are undergoing flight testing. New materials, fabrication methods, analysis techniques, and design concepts were developed and show much promise. The laminar flow control systems now being flight tested on the NASA Jetstar aircraft are complemented by natural laminar flow flight tests to be accomplished with the F-14 variable-sweep transition flight experiment. An overview of some operational aspects of this exciting program is given.

Maddalon, Dal V.; Wagner, Richard D.

1986-01-01

23

Computational Challenges of Viscous Incompressible Flows  

NASA Technical Reports Server (NTRS)

Over the past thirty years, numerical methods and simulation tools for incompressible flows have been advanced as a subset of the computational fluid dynamics (CFD) discipline. Although incompressible flows are encountered in many areas of engineering, simulation of compressible flow has been the major driver for developing computational algorithms and tools. This is probably due to the rather stringent requirements for predicting aerodynamic performance characteristics of flight vehicles, while flow devices involving low-speed or incompressible flow could be reasonably well designed without resorting to accurate numerical simulations. As flow devices are required to be more sophisticated and highly efficient CFD took become increasingly important in fluid engineering for incompressible and low-speed flow. This paper reviews some of the successes made possible by advances in computational technologies during the same period, and discusses some of the current challenges faced in computing incompressible flows.

Kwak, Dochan; Kiris, Cetin; Kim, Chang Sung

2004-01-01

24

Viscous Laminar Flow  

Microsoft Academic Search

\\u000a As briefly discussed in Chapter 4, the motion of Newtonian fluids is described by the Navier-Stokes equations. Due to the\\u000a non-linear nature of these equations and the general complexity of the flow geometry, analytical solutions of Navier-Stoke’s\\u000a equations has been exhibiting a major problem in fluid mechanics. The continuous development in the area of computer technology\\u000a and the introduction of

Meinhard T. Schobeiri

25

Faster Algorithm For Computation Of Incompressible Flow  

NASA Technical Reports Server (NTRS)

Improved algorithm yields faster numerical solutions of Navier-Stokes equations of steady or unsteady three-dimensional flow of incompressible fluid. In artificial-compressibility method, unsteady flow treated as incompressible in advancing from one time step to next, but at each time step (or in steady state), fluid treated as having variable compressibility enabling propagation of flow field, and subiterations performed in increments of pseudotime until effects of compressibility subside. Directly couples pressure and velocity fields at same time step and converts elliptic incompressible Navier-Stokes equations to hyperbolic form more amenable to numerical integration.

Rogers, S. E.; Kwak, D.; Kiris, C.

1991-01-01

26

Nonlinear flows in nearly incompressible hydrodynamic fluids.  

PubMed

Nearly incompressible viscous hydrodynamic fluids are investigated using nonlinear fluid simulations. Nearly incompressible fluids possess acoustic modes through high frequency fluctuations associated with the subsonic fluid Mach number. These modes, in combination with the fluid modes, drive linearly unstable modes and nonlinearly excite flows. The nonlinear flows damp the long wavelengths in our simulations, and are dissipated resonantly when certain nonlinear conditions are satisfied. In agreement with our analytic analysis, the nonlinearly saturated flows in nearly incompressible fluids are generated through the action of the Reynolds stress forces. PMID:15244728

Dastgeer, S; Zank, G P

2004-06-01

27

Laminar-flow wind tunnel experiments  

NASA Technical Reports Server (NTRS)

Although most of the laminar flow airfoils recently developed at the NASA Langley Research Center were intended for general aviation applications, low-drag airfoils were designed for transonic speeds and wind tunnel performance tested. The objective was to extend the technology of laminar flow to higher Mach and Reynolds numbers and to swept leading edge wings representative of transport aircraft to achieve lower drag and significantly improved operation costs. This research involves stabilizing the laminar boundary layer through geometric shaping (Natural Laminar Flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (Laminar-Flow Control, LFC), either through discrete slots or perforated surface. Results show that extensive regions of laminar flow with large reductions in skin friction drag can be maintained through the application of passive NLF boundary-layer control technologies to unswept transonic wings. At even greater extent of laminar flow and reduction in the total drag level can be obtained on a swept supercritical airfoil with active boundary layer-control.

Harvey, William D.; Harris, Charles D.; Sewall, William G.; Stack, John P.

1989-01-01

28

Laminar Motion of the Incompressible Fluids in Self-Acting Thrust Bearings with Spiral Grooves  

PubMed Central

We analyze the laminar motion of incompressible fluids in self-acting thrust bearings with spiral grooves with inner or external pumping. The purpose of the study is to find some mathematical relations useful to approach the theoretical functionality of these bearings having magnetic controllable fluids as incompressible fluids, in the presence of a controllable magnetic field. This theoretical study approaches the permanent motion regime. To validate the theoretical results, we compare them to some experimental results presented in previous papers. The laminar motion of incompressible fluids in bearings is described by the fundamental equations of fluid dynamics. We developed and particularized these equations by taking into consideration the geometrical and functional characteristics of these hydrodynamic bearings. Through the integration of the differential equation, we determined the pressure and speed distributions in bearings with length in the “pumping” direction. These pressure and speed distributions offer important information, both quantitative (concerning the bearing performances) and qualitative (evidence of the viscous-inertial effects, the fluid compressibility, etc.), for the laminar and permanent motion regime. PMID:24526896

Velescu, Cornel; Popa, Nicolae Calin

2014-01-01

29

Laminar motion of the incompressible fluids in self-acting thrust bearings with spiral grooves.  

PubMed

We analyze the laminar motion of incompressible fluids in self-acting thrust bearings with spiral grooves with inner or external pumping. The purpose of the study is to find some mathematical relations useful to approach the theoretical functionality of these bearings having magnetic controllable fluids as incompressible fluids, in the presence of a controllable magnetic field. This theoretical study approaches the permanent motion regime. To validate the theoretical results, we compare them to some experimental results presented in previous papers. The laminar motion of incompressible fluids in bearings is described by the fundamental equations of fluid dynamics. We developed and particularized these equations by taking into consideration the geometrical and functional characteristics of these hydrodynamic bearings. Through the integration of the differential equation, we determined the pressure and speed distributions in bearings with length in the "pumping" direction. These pressure and speed distributions offer important information, both quantitative (concerning the bearing performances) and qualitative (evidence of the viscous-inertial effects, the fluid compressibility, etc.), for the laminar and permanent motion regime. PMID:24526896

Velescu, Cornel; Popa, Nicolae Calin

2014-01-01

30

The elliptic calculation of viscous incompressible turbomachinery flows  

NASA Astrophysics Data System (ADS)

A new pressure based method was developed to solve the incompressible Navier-Stokes equations for turbomachinery flows. The new method solves for the pressure implicitly; no explicit correction is necessary within the iteration scheme. This new method was found to have better convergence than the pressure correction method. For two dimensional flows, the effects of turbulence are simulated by a low Reynolds number version of the two equation turbulence model. The validity of the turbulence model was extended by the prediction of two dimensional flow over a compressor blade profile. Turbine blade heat transfer was also computed and compared to experimental results. The three dimensional version of the code is validated with the prediction laminar internal flows. Finally, the complex three dimensional turbulent flow through a turbine end wall cascade was computed, and most physical phenomena were adequately resolved.

Hobson, Garth Victor

31

A faster 'transition' to laminar flow  

NASA Technical Reports Server (NTRS)

A discussion is given of the ongoing research related to laminar flow airfoils, nacelles, and wings where the laminar flow is maintained by a favorable pressure gradient, surface suction or a combination of the two. Design methologies for natural laminar flow airfoil sections and wings for both low and high speed applications are outlined. Tests of a 7-foot chord, 23-deg sweep laminar flow-control airfoil at high subsonic Mach numbers are described, along with the associated stability theory used to design the suction system. The state-of-the-art of stability theory is simply stated and a typical calculation illustrated. In addition, recent computer simulations of transition using the time dependent Navier-Stokes equations are briefly described. Advances in wind tunnel capabilities and instrumentation will be reviewed, followed by the presentation of a few results from both wind tunnels and flight. Finally, some suggestions for future work will complete the paper.

Bobbitt, P. J.; Waggoner, E. G.; Harvey, W. D.; Dagenhart, J. R.

1985-01-01

32

Efficient solutions of two-dimensional incompressible steady viscous flows  

NASA Technical Reports Server (NTRS)

A simple, efficient, and robust numerical technique is provided for solving two dimensional incompressible steady viscous flows at moderate to high Reynolds numbers. The proposed approach employs an incremental multigrid method and an extrapolation procedure based on minimum residual concepts to accelerate the convergence rate of a robust block-line-Gauss-Seidel solver for the vorticity-stream function Navier-Stokes equations. Results are presented for the driven cavity flow problem using uniform and nonuniform grids and for the flow past a backward facing step in a channel. For this second problem, mesh refinement and Richardson extrapolation are used to obtain useful benchmark solutions in the full range of Reynolds numbers at which steady laminar flow is established.

Morrison, J. H.; Napolitano, M.

1988-01-01

33

Efficient solutions of two-dimensional incompressible steady viscous flows  

NASA Technical Reports Server (NTRS)

A simple, efficient, and robust numerical technique is provided for solving two dimensional incompressible steady viscous flows at moderate to high Reynolds numbers. The proposed approach employs an incremental multigrid method and an extrapolation procedure based on minimum residual concepts to accelerate the convergence rate of a robust block-line-Gauss-Seidel solver for the vorticity-stream function Navier-Stokes equations. Results are presented for the driven cavity flow problem using uniform and nonuniform grids and for the flow past a backward facing step in a channel. For this second problem, mesh refinement and Richardson extrapolation are used to obtain useful benchmark solutions in the full range of Reynolds numbers at which steady laminar flow is established.

Morrison, J. H.; Napolitano, M.

1986-01-01

34

Research in Natural Laminar Flow and Laminar-Flow Control, part 3  

NASA Technical Reports Server (NTRS)

Part 3 of the Symposium proceedings contains papers addressing advanced airfoil development, flight research experiments, and supersonic transition/laminar flow control research. Specific topics include the design and testing of natural laminar flow (NLF) airfoils, NLF wing gloves, and NLF nacelles; laminar boundary-layer stability over fuselage forebodies; the design of low noise supersonic/hypersonic wind tunnels; and boundary layer instability mechanisms on swept leading edges at supersonic speeds.

Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)

1987-01-01

35

An acoustic analogy applied to the laminar upstream flow over an open 2D cavity  

NASA Astrophysics Data System (ADS)

In this work a modified version of the Lighthill-Curle's analogy is applied to study the near field acoustics of an upstream laminar flow past an open cavity. Three incompressible cases have been computed and are compared against the corresponding compressible results. The three incompressible cases are carried out with different time-step sizes, distances from the cavity trailing edge to the outlet and spatial resolution in the streamwise direction. The aim of the work is to study the differences in compressible and incompressible sources in Lighthill-Curle's equation and their influence on the sound radiated. To cite this article: J. Ask, L. Davidson, C. R. Mecanique 333 (2005).

Ask, Jonas; Davidson, Lars

2005-09-01

36

The NASA Langley laminar-flow-control experiment on a swept, supercritical airfoil: Suction coefficient analysis  

NASA Technical Reports Server (NTRS)

A swept supercritical wing incorporating laminar flow control at transonic flow conditions was designed and tested. The definition of an experimental suction coefficient and a derivation of the compressible and incompressible formulas for the computation of the coefficient from measurable quantities is presented. The suction flow coefficient in the highest velocity nozzles is shown to be overpredicted by as much as 12 percent through the use of an incompressible formula. However, the overprediction on the computed value of suction drag when some of the suction nozzles were operating in the compressible flow regime is evaluated and found to be at most 6 percent at design conditions.

Brooks, Cuyler W., Jr.; Harris, Charles D.; Harvey, William D.

1991-01-01

37

Optical flow for incompressible turbulence motion estimation  

NASA Astrophysics Data System (ADS)

We propose in this paper a new formulation of optical flow dedicated to 2D incompressible turbulent flows. It consists in minimizing an objective function constituted by an observation term and a regularization one. The observation term is based on the transport equation of the passive scalar field. For non-fully resolved scalar images, we propose to use the mixed model in large eddy simulation to determine the interaction between large scales and unresolved ones. The regularization term is based on the continuity equation of 2D incompressible flows. Compared to prototypical method, this regularizer preserves more vortex structures by eliminating constraints over the vorticity field. The evaluation of the proposed formulation is done over synthetic and experimental images, and the improvements in term of estimation are discussed.

Chen, Xu; Zillé, Pascal; Shao, Liang; Corpetti, Thomas

2015-01-01

38

A Numerical Method for Simulation of Incompressible Three-Dimensional Newtonian and Non-Newtonian Flows  

Microsoft Academic Search

Three-dimensional Newtonian and non-Newtonian flows are found in numerous engineering applications. Simulation of this class of problems requires robust mathematical and computational modeling. The main goal of this article is to propose a unified numerical methodology for solving three-dimensional, laminar, incompressible Newtonian and non-Newtonian steady flows. A second-order, fully implicit finite-difference approximation is used to discretize the governing equations in

P. S. B. Zdanski; M. Vaz Jr.

2011-01-01

39

Incompressible viscous flow in tubes with occlusions  

NASA Astrophysics Data System (ADS)

Viscous, incompressible flow in tubes with partial occlusion is investigated using numerical and experimental procedures. The study is related to the problem of atherosclerosis, one of the most common diseases of the circulatory system. One of the computational difficulties in solving the incompressible Navier-Stokes equations is the lack of pressure or vorticity boundary conditions. A finite difference approach, referred to as the interior constraint (IC) method, is proposed to resolve this difficulty. As a general numerical method, it is formulated for both the stream function-vorticity and primitive (physical) variable formulations. The procedure is explained using a one dimensional model with extensive numerical tests presented for two dimensional cases, including flow in a driven cavity and flow over a backward facing step. Results are obtained with second-order accuracy. Next, the IC method is applied to flow in a tube with an occlusion, which is used as the model for blood flow in stenosed arteries in the study of the pathology of atherosclerosis. Numerical results are obtained for both steady and pulsatile flows. Results are compared with those of SIMPLE, one of the commercially available numerical algorithms. The pulsatile flow study revealed several interesting new features. It suggested that the high shear stress is not likely to initiate atherosclerosis lesions. The recirculation region, which is a prominent feature of the unsteady flow, is more likely to cause the initiation and development of the disease. Experimental measurements for steady flow complement the numerical study and show qualitative agreement.

Huang, Huaxiong

40

High-End Computing for Incompressible Flows  

NASA Technical Reports Server (NTRS)

The objective of the First MIT Conference on Computational Fluid and Solid Mechanics (June 12-14, 2001) is to bring together industry and academia (and government) to nurture the next generation in computational mechanics. The objective of the current talk, 'High-End Computing for Incompressible Flows', is to discuss some of the current issues in large scale computing for mission-oriented tasks.

Kwak, Dochan; Kiris, Cetin

2001-01-01

41

Class II (laminar flow) biological safety cabinet  

Microsoft Academic Search

A microbiological survey of the effectiveness of class II (laminar flow) 'safety' cabinets found in the UK in the last six years is recorded. Only two of the nine units tested approached the containment of aerosols achieved by a good class I (exhaust protective) cabinet. The others were potentially hazardous if used with pathogenic material. The National Sanitation Foundation and

S W Newsom

1979-01-01

42

Laminar Entrained Flow Reactor (Fact Sheet)  

SciTech Connect

The Laminar Entrained Flow Reactor (LEFR) is a modular, lab scale, single-user reactor for the study of catalytic fast pyrolysis (CFP). This system can be employed to study a variety of reactor conditions for both in situ and ex situ CFP.

Not Available

2014-02-01

43

Research in Natural Laminar Flow and Laminar-Flow Control, part 1  

NASA Technical Reports Server (NTRS)

Since the mid 1970's, NASA, industry, and universities have worked together to conduct important research focused at developing laminar flow technology that could reduce fuel consumption for general aviation, commuter, and transport aircraft by as much as 40 to 50 percent. The symposium was planned in view of the recent accomplishments within the areas of laminar flow control and natural laminar flow, and the potential benefits of laminar flow technology to the civil and military aircraft communities in the United States. Included were technical sessions on advanced theory and design tool development; wind tunnel and flight research; transition measurement and detection techniques; low and high Reynolds number research; and subsonic and supersonic research.

Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)

1987-01-01

44

Laminar Flow in the Ocean Ekman Layer  

NASA Astrophysics Data System (ADS)

INTRODUCTION THE EFFECT OF A STABLE DENSITY GRADIENT THE FATAL FLAW FLOW VISUALIZATION THE DISCOVERY OF LAMINAR FLOW FINE STRUCTURE WAVE-INDUCED SHEAR INSTABILITY BILLOW TURBULENCE REVERSE TRANSITION REVISED PARADIGM ONE-DIMENSIONAL MODELLING OF THE UPPER OCEAN DIURNAL VARIATION BUOYANT CONVECTION BILLOW TURBULENCE IN THE DIURNAL THERMOCLINE CONSEQUENCES FOR THE EKMAN CURRENT PROFILE SOLAR RADIATION APPLICATIONS Slippery Seas of Acapulco Pollution Afternoon Effect in Sonar Patchiness Fisheries Climate DISCUSSION CONCLUSION REFERENCES

Woods, J. T. H.

45

Insect contamination protection for laminar flow surfaces  

NASA Technical Reports Server (NTRS)

The ability of modern aircraft surfaces to achieve laminar flow was well-accepted in recent years. Obtaining the maximum benefit of laminar flow for aircraft drag reduction requires maintaining minimum leading-edge contamination. Previously proposed insect contamination prevention methods have proved impractical due to cost, weight, or inconvenience. Past work has shown that insects will not adhere to water-wetted surfaces, but the large volumes of water required for protection rendered such a system impractical. The results of a flight experiment conducted by NASA to evaluate the performance of a porous leading-edge fluid discharge ice protection system operated as an insect contamination protections system are presented. In addition, these flights explored the environmental and atmospheric conditions most suitable for insect accumulation.

Croom, Cynthia C.; Holmes, Bruce J.

1986-01-01

46

Simulation Of Unsteady, Viscous, Incompressible Flow  

NASA Technical Reports Server (NTRS)

Method for numerical solution of Navier-Stokes equations of viscous, incompressible flow developed based on use of fractional-step procedure. Accurate to second order in both space and time. Attempt made to minimize Poisson-equation difficulties by choosing pressures at centers and volume fluxes across faces of computational cells as dependent variables instead of familiar Cartesian components of velocity. Choice ensures satisfaction of discrete equation of conservation of mass to within round-off errors in any coordinate system and has favorable effects on convergence properties.

Rosenfeld, Moshe; Kwak, Dochan

1990-01-01

47

Laminar Flow Control Flight Experiment Design  

E-print Network

at the surface of the Earth GIIB Gulfstream IIB aircraft GIII Gulfstream III aircraft h altitude H0 null hypothesis H1 alternate hypothesis 1 H2 alternate hypothesis 2 in inches IR infrared wavelength of light k DRE height K Kelvin xvii kg kilogram... reduction associated with a natural laminar flow wing glove at wing sweep, ? = 20?, Figure 8. Jetstar LFC aircraft [19] 16 as well as gathered data for computational validation [25]. Infrared (IR) cameras were used to measure transition location...

Tucker, Aaron 1975-

2012-11-29

48

Research in Natural Laminar Flow and Laminar-Flow Control, part 2  

NASA Technical Reports Server (NTRS)

Part 2 of the Symposium proceedings includes papers addressing various topics in basic wind tunnel research/techniques and computational transitional research. Specific topics include: advanced measurement techniques; laminar flow control; Tollmien-Schlichting wave characteristics; boundary layer transition; flow visualization; wind tunnel tests; flight tests; boundary layer equations; swept wings; and skin friction.

Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)

1987-01-01

49

Adjoint operator approach to shape design for internal incompressible flows  

NASA Technical Reports Server (NTRS)

The problem of determining the profile of a channel or duct that provides the maximum static pressure rise is solved. Incompressible, laminar flow governed by the steady state Navier-Stokes equations is assumed. Recent advances in computational resources and algorithms have made it possible to solve the direct problem of determining such a flow through a body of known geometry. It is possible to obtain a set of adjoint equations, the solution to which permits the calculation of the direction and relative magnitude of change in the diffuser profile that leads to a higher pressure rise. The solution to the adjoint problem can be shown to represent an artificially constructed flow. This interpretation provides a means to construct numerical solutions to the adjoint equations that do not compromise the fully viscous nature of the problem. The algorithmic and computational aspects of solving the adjoint equations are addressed. The form of these set of equations is similar but not identical to the Navier-Stokes equations. In particular some issues related to boundary conditions and stability are discussed.

Cabuk, H.; Sung, C.-H.; Modi, V.

1991-01-01

50

Supercomputing Aspects for Simulating Incompressible Flow  

NASA Technical Reports Server (NTRS)

The primary objective of this research is to support the design of liquid rocket systems for the Advanced Space Transportation System. Since the space launch systems in the near future are likely to rely on liquid rocket engines, increasing the efficiency and reliability of the engine components is an important task. One of the major problems in the liquid rocket engine is to understand fluid dynamics of fuel and oxidizer flows from the fuel tank to plume. Understanding the flow through the entire turbo-pump geometry through numerical simulation will be of significant value toward design. One of the milestones of this effort is to develop, apply and demonstrate the capability and accuracy of 3D CFD methods as efficient design analysis tools on high performance computer platforms. The development of the Message Passage Interface (MPI) and Multi Level Parallel (MLP) versions of the INS3D code is currently underway. The serial version of INS3D code is a multidimensional incompressible Navier-Stokes solver based on overset grid technology, INS3D-MPI is based on the explicit massage-passing interface across processors and is primarily suited for distributed memory systems. INS3D-MLP is based on multi-level parallel method and is suitable for distributed-shared memory systems. For the entire turbo-pump simulations, moving boundary capability and efficient time-accurate integration methods are built in the flow solver, To handle the geometric complexity and moving boundary problems, an overset grid scheme is incorporated with the solver so that new connectivity data will be obtained at each time step. The Chimera overlapped grid scheme allows subdomains move relative to each other, and provides a great flexibility when the boundary movement creates large displacements. Two numerical procedures, one based on artificial compressibility method and the other pressure projection method, are outlined for obtaining time-accurate solutions of the incompressible Navier-Stokes equations. The performance of the two methods is compared by obtaining unsteady solutions for the evolution of twin vortices behind a flat plate. Calculated results are compared with experimental and other numerical results. For an unsteady flow, which requires small physical time step, the pressure projection method was found to be computationally efficient since it does not require any subiteration procedure. It was observed that the artificial compressibility method requires a fast convergence scheme at each physical time step in order to satisfy the incompressibility condition. This was obtained by using a GMRES-ILU(0) solver in present computations. When a line-relaxation scheme was used, the time accuracy was degraded and time-accurate computations became very expensive.

Kwak, Dochan; Kris, Cetin C.

2000-01-01

51

Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames  

NASA Technical Reports Server (NTRS)

This is the final report of a research program considering interactions between flow and soot properties within laminar diffusion flames. Laminar diffusion flames were considered because they provide model flame systems that are far more tractable for theoretical and experimental studies than more practical turbulent diffusion flames. In particular, understanding the transport and chemical reaction processes of laminar flames is a necessary precursor to understanding these processes in practical turbulent flames and many aspects of laminar diffusion flames have direct relevance to turbulent diffusion flames through application of the widely recognized laminar flamelet concept of turbulent diffusion flames. The investigation was divided into three phases, considering the shapes of nonbuoyant round laminar jet diffusion flames in still air, the shapes of nonbuoyant round laminar jet diffusion flames in coflowing air, and the hydrodynamic suppression of soot formation in laminar diffusion flames.

Dai, Z.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.

2002-01-01

52

A co-located finite volume method for solving the Navier-Stokes equations for incompressible and compressible flows in turbomachinery - Results and applications  

NASA Astrophysics Data System (ADS)

A robust, efficient, and accurate CFD technology has been developed and implemented in computer codes for two- and three-dimensional viscous flow in turbomachinery. The method can model incompressible to supersonic flows and can solve laminar or turbulent (k-epsilon model) flows. The paper briefly describes some of the details of the method and presents results for benchmark application problems.

Raw, M. R.; Galpin, P. F.; Hutchinson, B. R.

1989-12-01

53

Class II (laminar flow) biological safety cabinet.  

PubMed

A microbiological survey of the effectiveness of class II (laminar flow) 'safety' cabinets found in the UK in the last six years is recorded. Only two of the nine units tested approached the containment of aerosols achieved by a good class I (exhaust protective) cabinet. The others were potentially hazardous if used with pathogenic material. The National Sanitation Foundation and the British Standards Institute have now laid down adequate specifications based on biological containment, and hopefully the conforming cabinets will be much better; even so, the purchase of a cabinet must be undertaken with care, and the cabinet requires frequent monitoring during use and after servicing. PMID:469008

Newsom, S W

1979-05-01

54

Direct numerical simulation of incompressible axisymmetric flows  

NASA Technical Reports Server (NTRS)

In the present work, we propose to conduct direct numerical simulations (DNS) of incompressible turbulent axisymmetric jets and wakes. The objectives of the study are to understand the fundamental behavior of axisymmetric jets and wakes, which are perhaps the most technologically relevant free shear flows (e.g. combuster injectors, propulsion jet). Among the data to be generated are various statistical quantities of importance in turbulence modeling, like the mean velocity, turbulent stresses, and all the terms in the Reynolds-stress balance equations. In addition, we will be interested in the evolution of large-scale structures that are common in free shear flow. The axisymmetric jet or wake is also a good problem in which to try the newly developed b-spline numerical method. Using b-splines as interpolating functions in the non-periodic direction offers many advantages. B-splines have local support, which leads to sparse matrices that can be efficiently stored and solved. Also, they offer spectral-like accuracy that are C(exp O-1) continuous, where O is the order of the spline used; this means that derivatives of the velocity such as the vorticity are smoothly and accurately represented. For purposes of validation against existing results, the present code will also be able to simulate internal flows (ones that require a no-slip boundary condition). Implementation of no-slip boundary condition is trivial in the context of the b-splines.

Loulou, Patrick

1994-01-01

55

Modified laminar flow biological safety cabinet.  

PubMed

Tests are reported on a modified laminar flow biological safety cabinet in which the return air plenum that conducts air from the work area to the high efficiency particulate air filters is under negative pressure. Freon gas released inside the cabinet could not be detected outside by a freon gas detection method capable of detecting 10(-6) cc/s. When T3 bacteriophage was aerosolized 5 cm outside the front opening in 11 tests, no phage could be detected inside the cabinet with the motor-filter unit in operation. An average of 2.8 x 10(5) plaque-forming units (PFU)/ft(3) (ca. 0.028 m(3)) were detected with the motor-filter unit not in operation, a penetration of 0.0%. Aerosolization 5 cm inside the cabinet yielded an average of 10 PFU/ft(3) outside the cabinet with the motor-filter unit in operation and an average of 4.1 x 10(5) PFU/ft(3) with the motor-filter unit not in operation, a penetration of 0.002%. These values are the same order of effectiveness as the positive-pressure laminar flow biological safety cabinets previously tested. The advantages of the negative-pressure return plenum design include: (i) assurance that if cracks or leaks develop in the plenum it will not lead to discharge of contaminated air into the laboratory; and (ii) the price is lower due to reduced manufacturing costs. PMID:4420479

McGarrity, G J; Coriell, L L

1974-10-01

56

AN IMMERSED BOUNDARY METHOD FOR COMPLEX INCOMPRESSIBLE FLOWS  

EPA Science Inventory

An immersed boundary method for time-dependant, three- dimensional, incompressible flows is presented in this paper. The incompressible Navier-Stokes equations are discretized using a low-diffusion flux splitting method for the inviscid fluxes and a second order central differenc...

57

Simplex finite element analysis of viscous incompressible flow with penalty function formulation  

NASA Technical Reports Server (NTRS)

Viscous flow calculations are important for the determination of separated flows, recirculating flows, secondary flows and so on. This paper presents a penalty function approach for the finite element analysis of steady incompressible viscous flow. A simplex element is used with linear velocity and constant pressure in contrast to other works which usually employ higher order elements. Simplex elements yield analytical expressions for the element matrices which in turn lead to efficient solutions. Earlier works have partially indicated how constraint and lock-up problems might be avoided for simplex elements. This paper extends the earlier works by indicating the approach in detail and verifying that it is successful for several applications not discussed in the literature so far. Solution times and accuracy considerations are discussed for Couette flow, plane Poiseuille flow, a driven cavity problem, and laminar and turbulent flow over a step.

Allaire, P. E.; Rosen, M. C.; Rice, J. G.

1985-01-01

58

Stability of the laminar flow on a body of revolution at incidence  

NASA Astrophysics Data System (ADS)

An asymmetric incompressible gas flow past a body of revolution was studied in a subsonic wind tunnel. Characteristics of the velocity field at the stern of the experimental model, where a laminar boundary-layer separation and concomitant destabilization of the flow occur under axisymmetric conditions, were determined. Declination of the axis of symmetry of the body within several angular degrees results in a radical change of the time-average velocity field, the amplitude distribution of growing hydrodynamic disturbances, and their spectral distribution.

Dovgal, A. V.; Zanin, B. Yu.; Sorokin, A. M.

2014-08-01

59

Laminar flow control perforated wing panel development  

NASA Technical Reports Server (NTRS)

Many structural concepts for a wing leading edge laminar flow control hybrid panel were analytically investigated. After many small, medium, and large tests, the selected design was verified. New analytic methods were developed to combine porous titanium sheet bonded to a substructure of fiberglass and carbon/epoxy cloth. At -65 and +160 F test conditions, the critical bond of the porous titanium to the composite failed at lower than anticipated test loads. New cure cycles, design improvements, and test improvements significantly improved the strength and reduced the deflections from thermal and lateral loadings. The wave tolerance limits for turbulence were not exceeded. Consideration of the beam column midbay deflections from the combinations of the axial and lateral loadings and thermal bowing at -65 F, room temperature, and +160 F were included. Many lap shear tests were performed at several cure cycles. Results indicate that sufficient verification was obtained to fabricate a demonstration vehicle.

Fischler, J. E.

1986-01-01

60

Implicit runge-kutta methods to simulate unsteady incompressible flows  

E-print Network

A numerical method (SIMPLE DIRK Method) for unsteady incompressible viscous flow simulation is presented. The proposed method can be used to achieve arbitrarily high order of accuracy in time-discretization which is otherwise limited to second order...

Ijaz, Muhammad

2009-05-15

61

Inductively coupled plasma torch with laminar flow cooling  

DOEpatents

An improved inductively coupled gas plasma torch. The torch includes inner and outer quartz sleeves and tubular insert snugly fitted between the sleeves. The insert includes outwardly opening longitudinal channels. Gas flowing through the channels of the insert emerges in a laminar flow along the inside surface of the outer sleeve, in the zone of plasma heating. The laminar flow cools the outer sleeve and enables the torch to operate at lower electrical power and gas consumption levels additionally, the laminar flow reduces noise levels in spectroscopic measurements of the gaseous plasma.

Rayson, Gary D. (Las Cruces, NM); Shen, Yang (Las Cruces, NM)

1991-04-30

62

Finite element analysis of incompressible viscous flow around multi-element aerofoils  

NASA Astrophysics Data System (ADS)

The Navier-Stokes equation was solved by the finite element method to simulate the laminar flow around airfoils. The concept of the penalty function method was introduced in the finite element method to simplify the implication of the incompressibility constraint. The streamline upwind/Petrov-Galerkin (SU/PG) method was also incorporated to avoid the numerical oscillation in the velocity field, which is known to appear when a simple finite element formulation is applied to flow problems in high Reynolds number region. Three examples were chosen to test the usability of the formulation developed. These are a flow around a symmetric airfoil with zero angle of attack, a flow around an airfoil which is known to show the laminar leading edge separation when the Reynolds number is fairly low, and a flow around an airfoil with flap. All flows obtained showed separation. The separated region of all examples experienced unsteady periodic shedding of vortices except the one on the symmetric airfoil with low Reynolds number, therefore the time marching follows of phenomena became necessary. The theta-method was used to integrate equations with respect to time, with theta between 0.5 and 0.55. The calculated result shows reasonably good agreement with the measured result which accompanies the laminar separation. Even if the airfoil is multi-elemented, there are no particular difficulties in application of this formulation in comparison with the case when the airfoil is single-elemented.

Shigemi, Masashi

1987-11-01

63

Distributed parallel calculation method of incompressible viscous flow in cylindrical passage  

NASA Astrophysics Data System (ADS)

The method was used to solve the incompressible viscous laminar flow in a cylindrical passage. The idea is that all the calculated area is divided into some subranges by the strip range split method with overlapping, then the momentum and pressure correction equations are distributively and parallelly solved in each subrange respectively; the block correction method is used to quicken the convergence speed of linear algebraic equations for the pressure correction equation. The calculation was carried out on the IBM-386 microcomputer outfitting TRANSPUTER boards, and the calculated examples show that the parallel calculation method has a good prospect.

Zhou, Xu; He, Hongqing; Cai, Timin

1994-12-01

64

General Equation Set Solver for Compressible and Incompressible Turbomachinery Flows  

NASA Technical Reports Server (NTRS)

Turbomachines for propulsion applications operate with many different working fluids and flow conditions. The flow may be incompressible, such as in the liquid hydrogen pump in a rocket engine, or supersonic, such as in the turbine which may drive the hydrogen pump. Separate codes have traditionally been used for incompressible and compressible flow solvers. The General Equation Set (GES) method can be used to solve both incompressible and compressible flows, and it is not restricted to perfect gases, as are many compressible-flow turbomachinery solvers. An unsteady GES turbomachinery flow solver has been developed and applied to both air and water flows through turbines. It has been shown to be an excellent alternative to maintaining two separate codes.

Sondak, Douglas L.; Dorney, Daniel J.

2002-01-01

65

F-111 TACT natural laminar flow glove flight results  

NASA Technical Reports Server (NTRS)

Improvements in cruise efficiency on the order of 15 to 40% are obtained by increasing the extent of laminar flow over lifting surfaces. Two methods of achieving laminar flow are being considered, natural laminar flow and laminar flow control. Natural laminar flow (NLF) relies primarily on airfoil shape while laminar flow control involves boundary layer suction or blowing with mechanical devices. The extent of natural laminar flow that could be achieved with consistency in a real flight environment at chord Reynolds numbers in the range of 30 x 10(6) power was evaluated. Nineteen flights were conducted on the F-111 TACT airplane having a NLF airfoil glove section. The section consists of a supercritical airfoil providing favorable pressure gradients over extensive portions of the upper and lower surfaces of the wing. Boundary layer measurements were obtained over a range of wing leading edge sweep angles at Mach numbers from 0.80 to 0.85. Data were obtained for natural transition and for a range of forced transition locations over the test airfoil.

Montoya, L. C.; Steers, L. L.; Trujillo, B.

1981-01-01

66

Statistical theory of turbulent incompressible multimaterial flow  

SciTech Connect

Interpenetrating motion of incompressible materials is considered. ''Turbulence'' is defined as any deviation from the mean motion. Accordingly a nominally stationary fluid will exhibit turbulent fluctuations due to a single, slowly moving sphere. Mean conservation equations for interpenetrating materials in arbitrary proportions are derived using an ensemble averaging procedure, beginning with the exact equations of motion. The result is a set of conservation equations for the mean mass, momentum and fluctuational kinetic energy of each material. The equation system is at first unclosed due to integral terms involving unknown one-point and two-point probability distribution functions. In the mean momentum equation, the unclosed terms are clearly identified as representing two physical processes. One is transport of momentum by multimaterial Reynolds stresses, and the other is momentum exchange due to pressure fluctuations and viscous stress at material interfaces. Closure is approached by combining careful examination of multipoint statistical correlations with the traditional physical technique of kappa-epsilon modeling for single-material turbulence. This involves representing the multimaterial Reynolds stress for each material as a turbulent viscosity times the rate of strain based on the mean velocity of that material. The multimaterial turbulent viscosity is related to the fluctuational kinetic energy kappa, and the rate of fluctuational energy dissipation epsilon, for each material. Hence a set of kappa and epsilon equations must be solved, together with mean mass and momentum conservation equations, for each material. Both kappa and the turbulent viscosities enter into the momentum exchange force. The theory is applied to (a) calculation of the drag force on a sphere fixed in a uniform flow, (b) calculation of the settling rate in a suspension and (c) calculation of velocity profiles in the pneumatic transport of solid particles in a pipe.

Kashiwa, B.

1987-10-01

67

Natural laminar flow airfoil analysis and trade studies  

NASA Technical Reports Server (NTRS)

An analysis of an airfoil for a large commercial transport cruising at Mach 0.8 and the use of advanced computer techniques to perform the analysis are described. Incorporation of the airfoil into a natural laminar flow transport configuration is addressed and a comparison of fuel requirements and operating costs between the natural laminar flow transport and an equivalent turbulent flow transport is addressed.

1979-01-01

68

A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for high Reynolds number laminar flows  

NASA Technical Reports Server (NTRS)

A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for the Navier-Stokes equations is presented. In the method, the velocity variables were interpolated using complete quadratic shape functions and the pressure was interpolated using linear shape functions. For the two dimensional case, the pressure is defined on a triangular element which is contained inside the complete biquadratic element for velocity variables; and for the three dimensional case, the pressure is defined on a tetrahedral element which is again contained inside the complete tri-quadratic element. Thus the pressure is discontinuous across the element boundaries. Example problems considered include: a cavity flow for Reynolds number of 400 through 10,000; a laminar backward facing step flow; and a laminar flow in a square duct of strong curvature. The computational results compared favorable with those of the finite difference methods as well as experimental data available. A finite elememt computer program for incompressible, laminar flows is presented.

Kim, Sang-Wook

1988-01-01

69

Laminar Flow Control Leading Edge Systems in Simulated Airline Service  

NASA Technical Reports Server (NTRS)

Achieving laminar flow on the wings of a commercial transport involves difficult problems associated with the wing leading edge. The NASA Leading Edge Flight Test Program has made major progress toward the solution of these problems. The effectiveness and practicality of candidate laminar flow leading edge systems were proven under representative airline service conditions. This was accomplished in a series of simulated airline service flights by modifying a JetStar aircraft with laminar flow leading edge systems and operating it out of three commercial airports in the United States. The aircraft was operated as an airliner would under actual air traffic conditions, in bad weather, and in insect infested environments.

Wagner, R. D.; Maddalon, D. V.; Fisher, D. F.

1988-01-01

70

FORMATION OF ROLL WAVES IN LAMINAR SHEET FLOW  

E-print Network

functions of the Froude number #12;I. INTRODUCTION Sheet flow is classified as "wide" open channel flow because channel walls do not affect the flow pattern. Wide open channel flow exists when the ratioFORMATION OF ROLL WAVES IN LAMINAR SHEET FLOW by Pierre Y. Julien and David M. Hartley January 1985

Julien, Pierre Y.

71

A Hermite finite element method for incompressible fluid flow  

Microsoft Academic Search

SUMMARY We describe some Hermite stream function and velocity finite elements and a divergence-free finite element method for the computation of incompressible flow. Divergence-free velocity bases defined on (but not limited to) rectangles are presented, which produce pointwise divergence-free flow fields ( ?· uh ? 0). The discrete velocity satisfies a flow equation which does not involve pressure. The pressure

J. T. Holdeman

2009-01-01

72

Application of natural laminar flow to a supersonic transport concept  

NASA Technical Reports Server (NTRS)

Results are presented of a preliminary investigation into an application of supersonic natural laminar flow (NLF) technology for a high speed civil transport (HSCT) configuration. This study focuses on natural laminar flow without regard to suction devices which are required for laminar flow control (LFC) or hybrid laminar flow control (HLFC). An HSCT design is presented with a 70 deg inboard leading-edge sweep and a 20 deg leading-edge outboard crank to obtain NLF over the outboard crank section. This configuration takes advantage of improved subsonic performance and NLF on the low-sweep portion of the wing while minimizing the wave drag and induced drag penalties associated with low-sweep supersonic cruise aircraft. In order to assess the benefits of increasing natural laminar flow wetted area, the outboard low-sweep wing area is parametrically increased. Using a range of supersonic natural laminar flow transition Reynolds numbers, these aircraft are then optimized and sized for minimum take-off gross weight (TOGW) subject to mission constraints. Results from this study indicate reductions in TOGW for the NLF concepts, due mainly to reductions in wing area and total wing weight. Furthermore, significant reductions in block fuel are calculated throughout the range of transition Reynolds numbers considered. Observations are made on the benefits of unsweeping the wingtips with all turbulent flow.

Fuhrmann, Henri D.

1993-01-01

73

Comparison of Implicit Multigrid Schemes for Three-Dimensional Incompressible Flows  

NASA Astrophysics Data System (ADS)

To develop a robust and efficient computational flow simulation tool for incompressible flow applications, a number of different implicit multigrid schemes for solving the three-dimensional incompressible Navier-Stokes equations are compared in the current study. These schemes consist of a common full approximation storage (FAS) multigrid algorithm implemented in conjunction with three different implicit schemes, which include a modified point Gauss relaxation, a standard Gauss-Seidel line relaxation, and the Beam-Warming alternating direction implicit (ADI) scheme. The flow solver used in the study is based on artificial compressibility and uses a third-order upwind difference for the convective terms and a second-order central difference for the viscous terms. The efficiency of each implicit multigrid scheme is assessed in terms of the computing time required for two laminar flow problems: the entry flow through a 90° bent square duct, and the steady-state and unsteady flows past a prolate spheroid at incidence with an axis ratio of 4 : 1. It is found that implementation of Neumann boundary conditions on the coarse grid in terms of the flow variable correction rather than the flow variable itself is essential for obtaining good convergence in the collocated finite difference discretization. The results of steady-state flow computations show that all the implicit multigrid schemes yield more than 50% computational time savings over their single grid counterparts, and the point or line relaxation multigrid scheme outperforms the ADI multigrid scheme by at least a factor of 2. However, in unsteady flow computations, the computational time saving of the multigrid scheme is less than that in steady-state cases. The current study concludes that the FAS multigrid algorithm implemented with the modified point Gauss relaxation scheme is preferable for simulating both steady-state and time-dependent incompressible flows.

Yuan, Li

2002-03-01

74

On the characteristics-based ACM for incompressible flows  

NASA Astrophysics Data System (ADS)

In this paper, the revised characteristics-based (CB) method for incompressible flows recently derived by Neofytou [P. Neofytou, Revision of the characteristic-based scheme for incompressible flows, J. Comput. Phys. 222 (2007) 475-484] has been further investigated. We have derived all the formulas for pressure and velocities from this revised CB method, which is based on the artificial compressibility method (ACM) [A.J. Chorin, A numerical solution for solving incompressible viscous flow problems, J. Comput. Phys. 2 (1967) 12]. Then we analyze the formulations of the original CB method [D. Drikakis, P.A. Govatsos, D.E. Papatonis, A characteristic based method for incompressible flows, Int. J. Numer. Meth. Fluids 19 (1994) 667-685; E. Shapiro, D. Drikakis, Non-conservative and conservative formulations of characteristics numerical reconstructions for incompressible flows, Int. J. Numer. Meth. Eng. 66 (2006) 1466-1482; D. Drikakis, P.K. Smolarkiewicz, On spurious vortical structures, J. Comput. Phys. 172 (2001) 309-325; F. Mallinger, D. Drikakis, Instability in three-dimensional, unsteady stenotic flows, Int. J. Heat Fluid Flow 23 (2002) 657-663; E. Shapiro, D. Drikakis, Artificial compressibility, characteristics-based schemes for variable density, incompressible, multi-species flows. Parts I. Derivation of different formulations and constant density limit, J. Comput. Phys. 210 (2005) 584-607; Y. Zhao, B. Zhang, A high-order characteristics upwind FV method for incompressible flow and heat transfer simulation on unstructured grids, Comput. Meth. Appl. Mech. Eng. 190 (5-7) (2000) 733-756] to investigate their consistency with the governing flow equations after convergence has been achieved. Furthermore we have implemented both formulations in an unstructured-grid finite volume solver [Y. Zhao, B. Zhang, A high-order characteristics upwind FV method for incompressible flow and heat transfer simulation on unstructured grids, Comput. Meth. Appl. Mech. Eng. 190 (5-7) (2000) 733-756]. Detailed numerical experiments show that both methods give almost identical solutions and convergence rates. Both can generate solutions which agree well with published results and experimental measurements. We thus conclude that both methods, being upwind schemes designed for the ACM, have the same performances in terms of accuracy and convergence speed, even though the revised method is more complex with less stringent assumptions made, while the original CB method is simpler due to the use of extra simplifying assumptions.

Su, Xiaohui; Zhao, Yong; Huang, Xiaoyang

2007-11-01

75

Selected experiments in laminar flow: An annotated bibliography  

NASA Technical Reports Server (NTRS)

Since the 1930s, there have been attempts to reduce drag on airplanes by delaying laminar to turbulent boundary layer transition. Experiments conducted during the 1940's, while successful in delaying transition, were discouraging because of the careful surface preparation necessary to meet roughness and waviness requirements. The resulting lull in research lasted nearly 30 years. By the late 1970s, airframe construction techniques had advanced sufficiently that the high surface quality required for natural laminar flow (NLF) and laminar flow control (LFC) appeared possible on production aircraft. As a result, NLF and LFC research became widespread. This report is an overview of that research. The experiments summarized herein were selected for their applicability to small transonic aircraft. Both flight and wind tunnel tests are included. The description of each experiment is followed by corresponding references. Part One summarizes NLF experiments; Part Two deals with LFC and hybrid laminar flow control (HLFC) experiments.

Drake, Aaron; Kennelly, Robert A., Jr.

1992-01-01

76

Design of fuselage shapes for natural laminar flow  

NASA Technical Reports Server (NTRS)

Recent technological advances in airplane construction techniques and materials allow for the production of aerodynamic surfaces without significant waviness and roughness, permitting long runs of natural laminar flow (NLF). The present research effort seeks to refine and validate computational design tools for use in the design of axisymmetric and nonaxisymmetric natural-laminar-flow bodies. The principal task of the investigation involves fuselage body shaping using a computational design procedure. Analytical methods were refined and exploratory calculations conducted to predict laminar boundary-layer on selected body shapes. Using a low-order surface-singularity aerodynamic analysis program, pressure distribution, boundary-layer development, transition location and drag coefficient have been obtained for a number of body shapes including a representative business-aircraft fuselage. Extensive runs of laminar flow were predicted in regions of favorable pressure gradient on smooth body surfaces. A computational design procedure was developed to obtain a body shape with minimum drag having large extent of NLF.

Dodbele, S. S.; Vandam, C. P.; Vijgen, P. M. H. W.

1986-01-01

77

Finite element analysis of incompressible viscous flows around single and multi-element aerofoils in high Reynolds number region  

NASA Astrophysics Data System (ADS)

Incompressible viscous flows around aerofoils are solved by a finite element method. This finite element method makes use of the penalty function method as well as the streamline-upwind Petrov-Galerkin (SUPG) method and, therefore, it can be applied to the computations of the flow at a high Reynolds number. In unsteady formulations, pressure distributions are evaluated by solving Poisson's equation with regard to pressure, rather than by direct application of the penalty function equation, since the latter tends to introduce violent oscillations in the solution. Though the present computation assumes that the flows are laminar, good agreement is obtained with experimentally measured results, particularly when the flow shows laminar separation. It is shown that this method can be applied to problems of flow around complicated geometries, and it is stated that the extension of the method to three-dimensional problems is promising.

Shigemi, Masashi

1988-12-01

78

Laminar and intermittent flow in a tilted heat pipe.  

PubMed

Heat transfer measurements performed by Riedinger et al. (Phys. Fluids, 25, 015117 (2013)) showed that in an inclined channel, heated from below and cooled from above with adiabatic walls, the flow is laminar or intermittent (local bursts can occur in the laminar flow) when the inclination angle is sufficiently high and the applied power sufficiently low. In this case, gravity plays a crucial role in the characteristics of the flow. In this paper, we present velocity measurements, and their derived tensors, obtained with Particle Image Velocimetry inside the channel. We, also, propose a model derived from a jet interpretation of the flow. Comparison between experiment and model shows a fair agreement. PMID:24464137

Rusaouen, E; Riedinger, X; Tisserand, J-C; Seychelles, F; Salort, J; Castaing, B; Chillà, F

2014-01-01

79

Solution techniques for incompressible flow problems  

NASA Astrophysics Data System (ADS)

A three-step Petrov-Galerkin (PG)/operator spliting scheme for the time-dependent incompressible Navier-Stokes equations is proposed. Each time step is split into two Stokes problems and one nonlinear convection-diffusion problem. Using a PG technique on the two outer Stokes problems ensures a stable scheme despite equal-order interpolation, while using a streamline upwind PG scheme on the inner convection-diffusion problem ensures a numerically stable solution at high Reynolds numbers. Numerical tests of this method have been carried out.

Tezduyar, T. E.; Liou, J.; Ganjoo, D. K.; Glowinski, R.

80

Solution techniques for incompressible flow problems  

NASA Technical Reports Server (NTRS)

A three-step Petrov-Galerkin (PG)/operator spliting scheme for the time-dependent incompressible Navier-Stokes equations is proposed. Each time step is split into two Stokes problems and one nonlinear convection-diffusion problem. Using a PG technique on the two outer Stokes problems ensures a stable scheme despite equal-order interpolation, while using a streamline upwind PG scheme on the inner convection-diffusion problem ensures a numerically stable solution at high Reynolds numbers. Numerical tests of this method have been carried out.

Tezduyar, T. E.; Liou, J.; Ganjoo, D. K.; Glowinski, R.

1989-01-01

81

Finite volume and finite element methods applied to 3D laminar and turbulent channel flows  

NASA Astrophysics Data System (ADS)

The work deals with numerical simulations of incompressible flow in channels with rectangular cross section. The rectangular cross section itself leads to development of various secondary flow patterns, where accuracy of simulation is influenced by numerical viscosity of the scheme and by turbulence modeling. In this work some developments of stabilized finite element method are presented. Its results are compared with those of an implicit finite volume method also described, in laminar and turbulent flows. It is shown that numerical viscosity can cause errors of same magnitude as different turbulence models. The finite volume method is also applied to 3D turbulent flow around backward facing step and good agreement with 3D experimental results is obtained.

Louda, Petr; Svá?ek, Petr; Kozel, Karel; P?íhoda, Jaromír

2014-12-01

82

Comparison of measured and calculated velocity profiles of a laminar incompressible free jet at low Reynolds numbers  

NASA Technical Reports Server (NTRS)

A comparison of the measured and calculated velocity profiles of a laminar, incompressible, low Reynolds number jet is presented. The experimental jet was produced by a nozzle which consists of a porous metal plate covering the end of a pipe. This nozzle produces a uniform exit velocity profile at Reynolds numbers well below those at which conventional contoured nozzles are completely filled by the boundary layer. A jet mixing analysis based on the boundary-layer equations accurately predicted the velocity field for each test condition. The Reynolds number based on nozzle diameter ranged from 50 to 1000 with jet exit velocity either 30 or 61 m/s (100 or 200 ft/sec).

Greene, G. C.

1974-01-01

83

Lockheed laminar-flow control systems development and applications  

NASA Technical Reports Server (NTRS)

Progress is summarized from 1974 to the present in the practical application of laminar-flow control (LFC) to subsonic transport aircraft. Those efforts included preliminary design system studies of commercial and military transports and experimental investigations leading to the development of the leading-edge flight test article installed on the NASA JetStar flight test aircraft. The benefits of LFC on drag, fuel efficiency, lift-to-drag ratio, and operating costs are compared with those for turbulent flow aircraft. The current activities in the NASA Industry Laminar-Flow Enabling Technologies Development contract include summaries of activities in the Task 1 development of a slotted-surface structural concept using advanced aluminum materials and the Task 2 preliminary conceptual design study of global-range military hybrid laminar flow control (HLFC) to obtain data at high Reynolds numbers and at Mach numbers representative of long-range subsonic transport aircraft operation.

Lange, Roy H.

1987-01-01

84

Lecture Series "Boundary Layer Theory". Part I - Laminar Flows. Part 1; Laminar Flows  

NASA Technical Reports Server (NTRS)

In the lecture series starting today author want to give a survey of a field of aerodynamics which has for a number of years been attracting an ever growing interest. The subject is the theory of flows with friction, and, within that field, particularly the theory of friction layers, or boundary layers. A great many considerations of aerodynamics are based on the ideal fluid, that is the frictionless incompressibility and fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid, (potential theory) has been made possible. Actual liquids and gases satisfy the condition of incomressibility rather well if the velocities are not extremely high or, more accurately, if they are small in comparison with sonic velocity. For air, for instance, the change in volume due to compressibility amounts to about 1 percent for a velocity of 60 meters per second. The hypothesis of absence of friction is not satisfied by any actual fluid; however, it is true that most technically important fluids, for instance air and water, have a very small friction coefficient and therefore behave in many cases almost like the ideal frictionless fluid. Many flow phenomena, in particular most cases of lift, can be treated satisfactorily, - that is, the calculations are in good agreement with the test results, -under the assumption of frictionless fluid. However, the calculations with frictionless flow show a very serious deficiency; namely, the fact, known as d'Alembert's paradox, that in frictionless flow each body has zero drag whereas in actual flow each body experiences a drag of greater or smaller magnitude. For a long time the theory has been unable to bridge this gap between the theory of frictionless flow and the experimental findings about actual flow. The cause of this fundamental discrepancy is the viscosity which is neglected in the theory of ideal fluid; however, in spite of its extraordinary smallness it is decisive for the course of the flow phenomena.

Schlichting, H.

1949-01-01

85

Computational Analysis of the G-III Laminar Flow Glove  

NASA Technical Reports Server (NTRS)

Under NASA's Environmentally Responsible Aviation Project, flight experiments are planned with the primary objective of demonstrating the Discrete Roughness Elements (DRE) technology for passive laminar flow control at chord Reynolds numbers relevant to transport aircraft. In this paper, we present a preliminary computational assessment of the Gulfstream-III (G-III) aircraft wing-glove designed to attain natural laminar flow for the leading-edge sweep angle of 34.6deg. Analysis for a flight Mach number of 0.75 shows that it should be possible to achieve natural laminar flow for twice the transition Reynolds number ever achieved at this sweep angle. However, the wing-glove needs to be redesigned to effectively demonstrate passive laminar flow control using DREs. As a by-product of the computational assessment, effect of surface curvature on stationary crossflow disturbances is found to be strongly stabilizing for the current design, and it is suggested that convex surface curvature could be used as a control parameter for natural laminar flow design, provided transition occurs via stationary crossflow disturbances.

Malik, Mujeeb R.; Liao, Wei; Lee-Rausch, Elizabeth M.; Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan

2011-01-01

86

Brief history of laminar flow clean room systems  

SciTech Connect

This paper reviews the development and evolution of laminar flow clean rooms and hoods and describes the underlying principles and rationales associated with development of this type of clean room system and Federal Standard No. 209. By the mid 1970's, over a thousand hospitals in the US had installed laminar flow equipment in operating rooms. During the past several years a great deal of attention has been focused on conserving energy in clean rooms. Some gains in energy conservation have been achieved by improved design, off hours shutdown, and closer evaluation of requirements for clean rooms. By the early 1970's, the laminar flow principle had been carried from the Laboratory and applied to production hardware to create a mature industry producing and marketing a variety of laminar flow equipment in less than 10 years time. This achievement was made possible by literally dozens of persons in industry, government, military, and private individuals who developed hardware, added numerous innovations, and had the foresight to apply the technology to many fields other than industrial clean rooms. Now, with laminar flow devices available, class 100 levels are readily achievable and maintained, and at the same time require fewer operating restrictions than previously possible.

Whitfield, W J

1981-01-01

87

Simplified thermal lattice Boltzmann model for incompressible thermal flows  

Microsoft Academic Search

Considering the fact that the compression work done by the pressure and the viscous heat dissipation can be neglected for the incompressible flow, and its relationship with the gradient term in the evolution equation for the temperature in the thermal energy distribution model, a simplified thermal energy distribution model is proposed. This thermal model does not have any gradient term

Y. Peng; C. Shu; Y. T. Chew

2003-01-01

88

An unconstrained Hamiltonian formulation for incompressible fluid flow  

Microsoft Academic Search

The equations governing the time evolution of an ideal fluid in material coordinates are expressed as an unconstrained canonical Hamiltonian system. The incompressibility of the flow is consequent upon certain first integrals of the motion. The variable conjugate to the configuration field is not the usual linear momentum, but is instead a quantity that is related to linear momentum through

John H. Maddocks; Robert L. Pego

1995-01-01

89

Blow up criterion for incompressible nematic liquid crystal flows  

E-print Network

In this paper, we consider the short time classical solution to a simplified hydrodynamic flow modeling incompressible, nematic liquid crystal materials in dimension three. We establish a criterion for possible breakdown of such solutions at a finite time. More precisely, if $(u,d)$ is smooth up to time $T$ provided that $\\int_0^T|\

Guochun Wu

2012-10-27

90

Numerical Method for Incompressible Vortical Flows with Two Unbounded Directions  

Microsoft Academic Search

A new, efficient, and accurate method has been developed for computing unsteady, incompressible, viscous flows in a domain where two dimensions are unbounded, the third dimension is periodic and the vorticity is rapidly decaying in the unbounded directions. We use the term unbounded to mean doubly infinite (no boundaries of any kind). This is an extension of the methods described

Steven C. Rennich; Sanjiva K. Lele

1997-01-01

91

Computation of trailing edge noise from an incompressible flow calculation  

Microsoft Academic Search

A new methodology for calculating low Mach number trailing edge noise is developed and tested. The input to this methodology is the fluctuating surface pressure obtained from an incompressible, turbulent flow calculation. The surface pressure is used to calculate an intermediate incident pressure. This pressure in conjunction with the sound-hard boundary condition yields the scattered pressure which accounts for the

Assad A. Oberaiy; M. Wang

92

Finite element analysis of viscous, incompressible fluid flow  

Microsoft Academic Search

A numerical procedure was developed for the analysis of general two dimensional flows of viscous incompressible fluids using the finite element method. The partial differential equations describing the continuum motion of the fluid were discretized using a Galerkin procedure in conjunction with the finite element approximation. The isoparametric families of quadrilateral and triangular finite elements were used to represent the

D. K. Gartling; E. B. Becker

1975-01-01

93

Numerical studies of incompressible viscous flow in a driven cavity  

NASA Technical Reports Server (NTRS)

A series of project papers is presented in computational fluid dynamics. The work was performed during the 1973-74 academic year at Old Dominion University. Each paper briefly examines a numerical method(s) that can be applied to the Navier-Stokes equations governing incompressible flow in a driven cavity. Solutions obtained with a cubic spline procedure are also included.

1975-01-01

94

A computer code for three-dimensional incompressible flows using nonorthogonal body-fitted coordinate systems  

NASA Technical Reports Server (NTRS)

In this report, a numerical method for solving the equations of motion of three-dimensional incompressible flows in nonorthogonal body-fitted coordinate (BFC) systems has been developed. The equations of motion are transformed to a generalized curvilinear coordinate system from which the transformed equations are discretized using finite difference approximations in the transformed domain. The hybrid scheme is used to approximate the convection terms in the governing equations. Solutions of the finite difference equations are obtained iteratively by using a pressure-velocity correction algorithm (SIMPLE-C). Numerical examples of two- and three-dimensional, laminar and turbulent flow problems are employed to evaluate the accuracy and efficiency of the present computer code. The user's guide and computer program listing of the present code are also included.

Chen, Y. S.

1986-01-01

95

Numerical study of incompressible flow about fixed cylinder pairs  

NASA Astrophysics Data System (ADS)

A comprehensive numerical investigation of incompressible flow about fixed cylinder pairs is performed. Cylinder arrangements include tandem, side-by-side, and staggered and Reynolds numbers of 80 and 1000 are considered. A second order Streamline Upwind Petrov-Galerkin projection scheme is used along with routines for interactive steering and dynamic meshing to solve the 2-D incompressible Navier-Stokes equations efficiently on a large number of different configurations. Qualitative and quantitative comparisons with published experimental data are made which show the ability of the present numerical method to capture complex, unsteady flow features. Experimentally observed flow physics such as hysteresis effects in tandem arrangements and bistable biased gap flow in tandem arrangements have been reproduced by the present numerical method. Furthermore, an extensive series of staggered simulations in experimentally classified interference regimes has been performed.

Jester, W.; Kallinderis, Y.

2003-03-01

96

Stability of axisymmetric swirl flows of viscous incompressible fluid  

NASA Astrophysics Data System (ADS)

A new method of solution to the problem of stability of the swirl flow of viscous incompressible fluid is developed. The method based on expansion of the required function into power series of radial coordinate allows an avoidance of difficulties related to numerical integration of the system of differential equations with a singular point. Stability of the Poiseuille flow in a rotating pipe is considered as an example.

Aktershev, S. P.; Kuibin, P. A.

2013-09-01

97

Computational Optimization of a Natural Laminar Flow Experimental Wing Glove  

NASA Technical Reports Server (NTRS)

Computational optimization of a natural laminar flow experimental wing glove that is mounted on a business jet is presented and discussed. The process of designing a laminar flow wing glove starts with creating a two-dimensional optimized airfoil and then lofting it into a three-dimensional wing glove section. The airfoil design process does not consider the three dimensional flow effects such as cross flow due wing sweep as well as engine and body interference. Therefore, once an initial glove geometry is created from the airfoil, the three dimensional wing glove has to be optimized to ensure that the desired extent of laminar flow is maintained over the entire glove. TRANAIR, a non-linear full potential solver with a coupled boundary layer code was used as the main tool in the design and optimization process of the three-dimensional glove shape. The optimization process uses the Class-Shape-Transformation method to perturb the geometry with geometric constraints that allow for a 2-in clearance from the main wing. The three-dimensional glove shape was optimized with the objective of having a spanwise uniform pressure distribution that matches the optimized two-dimensional pressure distribution as closely as possible. Results show that with the appropriate inputs, the optimizer is able to match the two dimensional pressure distributions practically across the entire span of the wing glove. This allows for the experiment to have a much higher probability of having a large extent of natural laminar flow in flight.

Hartshom, Fletcher

2012-01-01

98

Conservative properties of finite difference schemes for incompressible flow  

NASA Technical Reports Server (NTRS)

The purpose of this research is to construct accurate finite difference schemes for incompressible unsteady flow simulations such as LES (large-eddy simulation) or DNS (direct numerical simulation). In this report, conservation properties of the continuity, momentum, and kinetic energy equations for incompressible flow are specified as analytical requirements for a proper set of discretized equations. Existing finite difference schemes in staggered grid systems are checked for satisfaction of the requirements. Proper higher order accurate finite difference schemes in a staggered grid system are then proposed. Plane channel flow is simulated using the proposed fourth order accurate finite difference scheme and the results compared with those of the second order accurate Harlow and Welch algorithm.

Morinishi, Youhei

1995-01-01

99

Design of a hybrid laminar flow control nacelle  

NASA Technical Reports Server (NTRS)

Consideration is given to the potential application of hybrid-laminar-flow control to the external surface of a modern, high-bypass-ratio (HBR) turbofan engine nacelle. With the advent of advanced ultra-HBR fans (with bypass ratios of 10-15), the wetted areas of these nacelles approach 10 percent of the total wetted area of future commercial transports. A hybrid-laminar-flow-control pressure distribution is specified and the corresponding nacelle geometry is computed utilizing a predictor/corrector design method. Linear stability calculations are conducted to provide predictions of the extent of the laminar boundary layer. Performance studies on an advanced twin-engine transport configuration are presented to determine potential benefits in terms of reduced fuel consumption.

Wie, Yong-Sun; Collier, Fayette S., Jr.; Wagner, Richard D.; Viken, Jeffery K.; Pfenninger, Werner

1992-01-01

100

Laminar/turbulent oscillating flow in circular pipes  

NASA Technical Reports Server (NTRS)

A two-dimensional oscillating flow analysis was conducted simulating the gas flow inside Stirling engine heat exchangers. Both laminar and turbulent oscillating pipe flow were investigated numerically for Re(max) = 1920 (Va = 80), 10,800 (Va = 272), 19,300 (Va = 272), and 60,800 (Va = 126). The results are compared with experimental results of previous investigators. Predictions of the flow regime are also checked by comparing velocity amplitudes and phase difference with those from laminar theory and quasi-steady profile. A high Reynolds number k-epsilon turbulence model was used for turbulent oscillating pipe flow. Finally, the performance of the k-epsilon model was evaluated to explore the applicability of quasi-steady turbulent models to unsteady oscillating flow analysis.

Ahn, Kyung H.; Ibrahim, Mounir B.

1992-01-01

101

A finite element method for turbulent incompressible flow  

NASA Astrophysics Data System (ADS)

In the scope of the 1990-04 lecture series on computational fluid dynamics, the solution of incompressible Navier-Stokes equation is presented. A computational code, named N sub 3 S, was developed for solving internal flows, turbomachinery flows, thermal hydraulics, external flows and flows in tube bundles. The main features and the experience acquired in the field of numerical analysis by developing the N sub 3 S code are summarized. The equations to be solved and the modelization necessary to take into account turbulence are presented. The variational formulation and the finite element discretization are discussed. The resolution of linear systems and the methods employed are included.

Chabard, J.-P.

102

NUMERICAL SIMULATION OF INCOMPRESSIBLE FLOWS IN ...  

E-print Network

canonical rotating flows which will help us to isolate generic mechanisms which lead to transitions to turbulence in rotating flows and to design corresponding dynamic .... The Reynolds number is Re = ?R2/?, where ? is the kinematic viscosity. ..... The linear Floquet analysis in [12] shows that for Rea ? 70 and ? ? 30, the.

103

Theory of laminar viscous jets  

NASA Astrophysics Data System (ADS)

Results of recent theoretical studies of laminar jet flows of a viscous incompressible fluid are reviewed. In particular, attention is given to plane, fan-shaped, axisymmetric, and swirling jet flows; jet flows behind bodies; and slipstream jet flows. The discussion also covers dissipation of mechanical energy in jet flows, jet flows with a zero excess momentum, and asymptotic series expansions in the theory of jet flows.

Martynenko, O. G.; Korovkin, V. N.; Sokovishin, Iu. A.

104

THE BERNOULLI EQUATION AND COMPRESSIBLE FLOW THEORIES  

EPA Science Inventory

The incompressible Bernoulli equation is an analytical relationship between pressure, kinetic energy, and potential energy. As perhaps the simplest and most useful statement for describing laminar flow, it buttresses numerous incompressible flow models that have been developed ...

105

A numerical method for the solution of three dimensional, incompressible, viscous flows over slender bodies  

NASA Technical Reports Server (NTRS)

A marching iterative method for the solution of the three dimensional, incompressibhle, steady and parabolized Navier-Stokes equations is described. The equations are written in primitive variables and discretized in general axisymmetric orthogonal coordinate systems. The coupled set of finite-difference equations are solved without any splitting or factorization errors. Moreover, the continuity equation and the two crossflow momentum equations are exactly satisfied at every step of the iterative process. The solution scheme is equivalent to the solution of one Poisson equation by the Successive Plane Over Relaxation method and has good convergence properties. Other existing solution methods resemble a Jacobi-type iterative scheme and therefore are less efficient. Numerical experiments include the laminar, incompressible flow over prolate spheroids at incidence.

Rosenfeld, Moshe; Israeli, Moshe; Wolfshtein, Micha

1987-01-01

106

The Beltrami spectrum for incompressible fluid flows  

NASA Astrophysics Data System (ADS)

Recently V. Yakhot, S. Orszag, and their co-workers have suggested that turbulent flows in various regions of space organize into a coherent hierarchy of weakly interacting superimposed approximate Beltrami flows. A mathematical framework is developed here to study organized Beltrami hierarchies in a systematic fashion. This framework is applied to several important classes of examples with universal Beltrami hierarchies. An analysis of the persistence of such Beltrami hierarchies is also presented for general solutions of the Navier-Stokes equations.

Constantin, Peter; Majda, Andrew

1988-09-01

107

Electrostatic quadrupole focused particle accelerating assembly with laminar flow beam  

DOEpatents

A charged particle accelerating assembly provided with a predetermined ratio of parametric structural characteristics and with related operating voltages applied to each of its linearly spaced focusing and accelerating quadrupoles, thereby to maintain a particle beam traversing the electrostatic fields of the quadrupoles in the assembly in an essentially laminar flow through the assembly.

Maschke, A.W.

1984-04-16

108

Application of laminar flow control to supersonic transport configurations  

NASA Technical Reports Server (NTRS)

The feasibility and impact of implementing a laminar flow control system on a supersonic transport configuration were investigated. A hybrid laminar flow control scheme consisting of suction controlled and natural laminar flow was developed for a double-delta type wing planform. The required suction flow rates were determined from boundary layer stability analyses using representative wing pressure distributions. A preliminary design of structural modifications needed to accommodate suction through a perforated titanium skin was carried out together with the ducting and systems needed to collect, compress and discharge the suction air. The benefits of reduced aerodynamic drag were weighed against the weight, volume and power requirement penalties of suction system installation in a mission performance and sizing program to assess the net benefits. The study showed a feasibility of achieving significant laminarization of the wing surface by use of a hybrid scheme, leading to an 8.2 percent reduction in the cruise drag. This resulted in an 8.5 percent reduction in the maximum takeoff weight and a 12 percent reduction in the fuel burn after the inclusion of the LFC system installation penalties. Several research needs were identified for a resolution of aerodynamics, structural and systems issues before these potential benefits could be realized in a practical system.

Parikh, P. G.; Nagel, A. L.

1990-01-01

109

Electrostatic quadrupole focused particle accelerating assembly with laminar flow beam  

DOEpatents

A charged particle accelerating assembly provided with a predetermined ratio of parametric structural characteristics and with related operating voltages applied to each of its linearly spaced focusing and accelerating quadrupoles, thereby to maintain a particle beam traversing the electrostatic fields of the quadrupoles in the assembly in an essentially laminar flow throughout the assembly.

Maschke, Alfred W. (East Moriches, NY)

1985-01-01

110

Mathematical aspects of finite element methods for incompressible viscous flows  

NASA Technical Reports Server (NTRS)

Mathematical aspects of finite element methods are surveyed for incompressible viscous flows, concentrating on the steady primitive variable formulation. The discretization of a weak formulation of the Navier-Stokes equations are addressed, then the stability condition is considered, the satisfaction of which insures the stability of the approximation. Specific choices of finite element spaces for the velocity and pressure are then discussed. Finally, the connection between different weak formulations and a variety of boundary conditions is explored.

Gunzburger, M. D.

1986-01-01

111

Numerical simulation of multiply connected axisymmetric discontinuous incompressible potential flows  

NASA Astrophysics Data System (ADS)

The ascend and evolution of an axisymmetric gas bubble are studied numerically using an inviscid incompressible potential flow model. The volume of the gas bubble varies adiabatically. The transition from a simply connected bubble to a doubly connected toroidal one and its interaction with the free surface are simulated. The change in connectedness is accompanied by a nonzero velocity circulation and a discontinuous velocity potential occurring over an arbitrary toroidal liquid surface enclosing the bubble.

Bubenchikov, A. M.; Korobitsyn, V. A.; Korobitsyn, D. V.; Kotov, P. P.; Shokin, Yu. I.

2014-07-01

112

Incompressible, Viscous Flow About An Ogive/Cylinder  

NASA Technical Reports Server (NTRS)

Theoretical predictions and observations of incompressible viscous flow about body of revolution at angle of attack compared in report. Body consists of solid circular cylinder at downstream end and tapered in ogive of revolution to point on axis at upstream end. Study was test of modern numerical methods for solution of equations of fluid dynamics, conducted as step toward future work on more difficult problems.

Zilliac, Gregory G.

1991-01-01

113

Incompressible viscous flow simulations of the NFAC wind tunnel  

NASA Technical Reports Server (NTRS)

The capabilities of an existing 3-D incompressible Navier-Stokes flow solver, INS3D, are extended and improved to solve turbulent flows through the incorporation of zero- and two-equation turbulence models. The two-equation model equations are solved in their high Reynolds number form and utilize wall functions in the treatment of solid wall boundary conditions. The implicit approximate factorization scheme is modified to improve the stability of the two-equation solver. Applications to the 3-D viscous flow inside the 80 by 120 feet open return wind tunnel of the National Full Scale Aerodynamics Complex (NFAC) are discussed and described.

Champney, Joelle Milene

1986-01-01

114

Dominated splitting and zero volume for incompressible three flows  

NASA Astrophysics Data System (ADS)

We prove that there exists an open and dense subset of the incompressible 3-flows of class C2 such that, if a flow in this set has a positive volume regular invariant subset with dominated splitting for the linear Poincaré flow, then it must be an Anosov flow. With this result we are able to extend the dichotomies of Bochi-Mañé (see Bessa 2007 Ergod. Theory Dyn. Syst. 27 1445-72, Bochi 2002 Ergod. Theory Dyn. Syst. 22 1667-96, Mañé 1996 Int. Conf. on Dynamical Systems (Montevideo, Uruguay, 1995) (Harlow: Longman) pp 110-9) and of Newhouse (see Newhouse 1977 Am. J. Math. 99 1061-87, Bessa and Duarte 2007 Dyn. Syst. Int. J. submitted Preprint 0709.0700) for flows with singularities. That is, we obtain for a residual subset of the C1 incompressible flows on 3-manifolds that: (i) either all Lyapunov exponents are zero or the flow is Anosov and (ii) either the flow is Anosov or else the elliptic periodic points are dense in the manifold.

Araujo, Vitor; Bessa, Mário

2008-07-01

115

On Nonhydrostatic Twolayer Models of Incompressible Flow  

E-print Network

of the flow. The well­known shallow water equations describe such a model. This is in fact the simplest member of the variation of the vertical component of the velocity vector. To derive the usual shallow water model ideas. In particular, the use of stacked layers of shallow water have proven useful in modeling basin

116

Nature of laminar-turbulence intermittency in shear flows.  

PubMed

In pipe, channel, and boundary layer flows turbulence first occurs intermittently in space and time: at moderate Reynolds numbers domains of disordered turbulent motion are separated by quiescent laminar regions. Based on direct numerical simulations of pipe flow we argue here that the spatial intermittency has its origin in a nearest neighbor interaction between turbulent regions. We further show that in this regime turbulent flows are intrinsically intermittent with a well-defined equilibrium turbulent fraction but without ever assuming a steady pattern. This transition scenario is analogous to that found in simple models such as coupled map lattices. The scaling observed implies that laminar intermissions of the turbulent flow will persist to arbitrarily large Reynolds numbers. PMID:23848777

Avila, M; Hof, B

2013-06-01

117

Laminar Flow Supersonic Wind Tunnel primary air injector  

NASA Technical Reports Server (NTRS)

This paper describes the requirements, design, and prototype testing of the flex-section and hinge seals for the Laminar Flow Supersonic Wind Tunnel Primary Injector. The supersonic atmospheric primary injector operates between Mach 1.8 and Mach 2.2 with mass-flow rates of 62 to 128 lbm/s providing the necessary pressure reduction to operate the tunnel in the desired Reynolds number (Re) range.

Smith, Brooke Edward

1993-01-01

118

Violation of the incompressibility of liquid by simple shear flow.  

PubMed

In standard fluid dynamics, the density change associated with flow is often assumed to be negligible, implying that the fluid is incompressible. For example, this has been established for simple shear flows, where no pressure change is associated with flow: there is no volume deformation due to viscous stress and inertial effects can be neglected. Accordingly, any flow-induced instabilities (such as cavitation) are unexpected for simple shear flows. Here we demonstrate that the incompressibility condition can be violated even for simple shear flows, by taking into account the coupling between the flow and density fluctuations, which arises owing to the density dependence of the viscosity. We show that a liquid can become mechanically unstable above a critical shear rate that is given by the inverse of the derivative of viscosity with respect to pressure. Our model predicts that, for very viscous liquids, this shear-induced instability should occur at moderate shear rates that are experimentally accessible. Our results explain the unusual shear-induced instability observed in viscous lubricants, and may illuminate other poorly understood phenomena associated with mechanical instability of liquids at low Reynolds number; for example, shear-induced cavitation and bubble growth, and shear-banding of very viscous liquids such as metallic glasses and the Earth's mantle. PMID:17006510

Furukawa, Akira; Tanaka, Hajime

2006-09-28

119

Preliminary aerodynamic design considerations for advanced laminar flow aircraft configurations  

NASA Technical Reports Server (NTRS)

Modern composite manufacturing methods have provided the opportunity for smooth surfaces that can sustain large regions of natural laminar flow (NLF) boundary layer behavior and have stimulated interest in developing advanced NLF airfoils and improved aircraft designs. Some of the preliminary results obtained in exploratory research investigations on advanced aircraft configurations at the NASA Langley Research Center are discussed. Results of the initial studies have shown that the aerodynamic effects of configuration variables such as canard/wing arrangements, airfoils, and pusher-type and tractor-type propeller installations can be particularly significant at high angles of attack. Flow field interactions between aircraft components were shown to produce undesirable aerodynamic effects on a wing behind a heavily loaded canard, and the use of properly designed wing leading-edge modifications, such as a leading-edge droop, offset the undesirable aerodynamic effects by delaying wing stall and providing increased stall/spin resistance with minimum degradation of laminar flow behavior.

Johnson, Joseph L., Jr.; Yip, Long P.; Jordan, Frank L., Jr.

1986-01-01

120

Laminar-turbulent cycles in inclined lock-exchange flows.  

PubMed

We consider strongly confined, stably stratified shear flows generated as a lock exchange in a tube inclined at an angle of ?=45(?). This paper focuses on a transitional regime, in which the flow alternates between two distinct states: laminar, parallel shear flow and intense transverse motion characteristic of turbulence. Laminar-turbulent cycles were captured at Atwood numbers At?(?(2)-?(1))/(?(1)+?(2)) ranging from 2.45×10(-3) to 4.0×10(-3), where (?(1),?(2)) are the initial densities of the two fluids, with multiple cycles observed at At=2.55×10(-3). The evolution of the density and velocity fields in these flows was measured simultaneously using laser-induced fluorescence and particle image velocimetry. During each laminar-turbulent cycle, the axial velocity exhibits a distinctive ramp-cliff pattern, indicating that the flow accelerates as it relaminarizes, then decelerates rapidly as the Kelvin-Helmholtz billows break down. Within the range of experimental conditions, transverse stratification does not directly determine the onset of instability. Instead, the data suggest that a necessary criterion for the onset of instability is for the local Reynolds number to exceed 2200, with only a weak dependence on the Richardson number. PMID:23005207

Tanino, Yukie; Moisy, Frédéric; Hulin, Jean-Pierre

2012-06-01

121

Computational Evaluation of a Transonic Laminar-Flow Wing Glove Design  

E-print Network

The aerodynamic benefits of laminar flow have long made it a sought-after attribute in aircraft design. By laminarizing portions of an aircraft, such as the wing or empennage, significant reductions in drag could be achieved, reducing fuel burn...

Roberts, Matthew William

2012-07-16

122

Spiral Laminar Flow: A revolution in understanding?  

E-print Network

30 40 50 60 70 80 Minimal Moderate Severe spiral non-spiral #12;Leonardo da Vinci Spirals in art: (1) the drawings of Leonardo da Vinci from Vindzone Library showing spiral flows in the heart cavity. La Bockeria

Greenaway, Alan

123

Self-pumping suction/propulsion for laminar flow bodies  

NASA Astrophysics Data System (ADS)

An analysis is presented to investigate the feasibility of a self-pumping suction system for a very low drag suction laminar flow control (SLFC) underwater test body. The nose and afterbody of a torpedo-like body are contoured such that a prominent low-pressure region in the aft part of the body can serve as a suction pump to suck the boundary layer fluid through the circumferential surface-slots and thus laminarize the entire body length forward of the aft low-pressure peak. The results indicate that it is feasible to laminarize a test body in this fashion at a design speed, such as 40 knots; but that the laminarization of a particular configuration is limited to a band of speeds at and near the design speed. If an SLFC test body with a wide range of speed capability is desired, then a controllable-speed suction pump and controllable suction distribution along the body are indicated. The analysis includes a suction system design calculation example and should be a useful reference for future development of undersea SLFC vehicles.

Rogers, K. H.; King, D. A.

1984-06-01

124

Gyrotactic trapping in laminar and turbulent Kolmogorov flow  

NASA Astrophysics Data System (ADS)

Phytoplankton patchiness, namely the heterogeneous distribution of microalgae over multiple spatial scales, dramatically impacts marine ecology. A spectacular example of such heterogeneity occurs in thin phytoplankton layers (TPLs), where large numbers of photosynthetic microorganisms are found within a small depth interval. Some species of motile phytoplankton can form TPLs by gyrotactic trapping due to the interplay of their particular swimming style (directed motion biased against gravity) and the transport by a flow with shear along the direction of gravity. Here we consider gyrotactic swimmers in numerical simulations of the Kolmogorov shear flow, both in laminar and turbulent regimes. In the laminar case, we show that the swimmer motion is integrable and the formation of TPLs can be fully characterized by means of dynamical systems tools. We then study the effects of rotational Brownian motion or turbulent fluctuations (appearing when the Reynolds number is large enough) on TPLs. In both cases, we show that TPLs become transient, and we characterize their persistence.

Santamaria, Francesco; De Lillo, Filippo; Cencini, Massimo; Boffetta, Guido

2014-11-01

125

Development of laminar flow control wing surface porous structure  

NASA Technical Reports Server (NTRS)

It was concluded that the chordwise air collection method, which actually combines chordwise and spanwise air collection, is the best of the designs conceived up to this time for full chord laminar flow control (LFC). Its shallower ducting improved structural efficiency of the main wing box resulting in a reduction in wing weight, and it provided continuous support of the chordwise panel joints, better matching of suction and clearing airflow requirements, and simplified duct to suction source minifolding. Laminar flow control on both the upper and lower surfaces was previously reduced to LFC suction on the upper surface only, back to 85 percent chord. The study concludes that, in addition to reduced wing area and other practical advantages, this system would be lighter because of the increase in effective structural wing thickness.

Klotzsche, M.; Pearce, W.; Anderson, C.; Thelander, J.; Boronow, W.; Gallimore, F.; Brown, W.; Matsuo, T.; Christensen, J.; Primavera, G.

1984-01-01

126

Nonlinear spectral dynamics of hypersonic laminar boundary layer flow  

NASA Astrophysics Data System (ADS)

The nonlinear interactions of the instability modes in a hypersonic laminar boundary layer undergoing natural transition are examined using bispectral analysis. The data are from an experiment of a boundary layer flow on a cooled-wall cone in a low-level free-stream disturbance hypersonic wind tunnel, and thus, the bispectral measurements are a good representation of the natural transition processes. The bispectral analysis shows that in the initial stages of transition the dominant nonlinear interaction is forcing by the fundamental to generate a harmonic. Subsequently, mutual forcing of the fundamental and harmonic yield a second harmonic. Difference interactions within the band of unstable disturbances centered on the fundamental and harmonic also generate a low frequency nonlinear interaction. At high amplitudes of the fundamental and harmonic a nonlinear interaction characterized by a low frequency modulation of the fundamental and harmonic then follows. This nonlinear interaction is then the most dominant and precedes the breakdown of the laminar flow.

Chokani, Ndaona

1999-12-01

127

Adaptive Solutions for Unsteady Laminar Flows on Unstructured Grids  

NASA Astrophysics Data System (ADS)

An adaptive finite volume method for the simulation of time-dependent, viscous flow is presented. The Navier-Stokes equations are discretized by central schemes on unstructured grids and solved by an explicit Runge-Kutta method. The essential topics of the present study are a new concept for a local Runge-Kutta time-stepping scheme, called multisequence Runge-Kutta, which reduces the severe stability restriction in unsteady problems, a common grid generation and adaptation procedure and the application of dynamic grids for capturing moving flow structures. Results are presented for laminar, separated flow around an aerofoil with a flap.

Vilsmeier, R.; Hänel, D.

1996-01-01

128

Laminar flow efficiency of stratified chilled-water storage tanks  

Microsoft Academic Search

This paper presents results for the efficiency of a stratified chilled-water storage tank with one inlet and one outlet. Numerical solutions for the two-dimensional, unsteady, laminar flow during stably stratified tank filling are compared with a one-dimensional model involving only conductive heat transfer across the thermocline separating the entering cold water and the exiting warm water. This one-dimensional model represents

K. O. Homan; S. L. Soo

1998-01-01

129

Ground vibration test of the laminar flow control JStar airplane  

NASA Technical Reports Server (NTRS)

A ground vibration test was conducted on a Lockheed JetStar airplane that had been modified for the purpose of conducting laminar flow control experiments. The test was performed prior to initial flight flutter tests. Both sine-dwell and single-point-random excitation methods were used. The data presented include frequency response functions and a comparison of mode frequencies and mode shapes from both methods.

Kehoe, M. W.; Cazier, F. W., Jr.; Ellison, J. F.

1985-01-01

130

Preconditioning and the limit to the incompressible flow equations  

NASA Technical Reports Server (NTRS)

The use of preconditioning methods to accelerate the convergence to a steady state for both the incompressible and compressible fluid dynamic equations are considered. The relation between them for both the continuous problem and the finite difference approximation is also considered. The analysis relies on the inviscid equations. The preconditioning consists of a matrix multiplying the time derivatives. Hence, the steady state of the preconditioned system is the same as the steady state of the original system. For finite difference methods the preconditioning can change and improve the steady state solutions. An application to flow around an airfoil is presented.

Turkel, E.; Fiterman, A.; Vanleer, B.

1993-01-01

131

Pseudo-compressibility methods for the incompressible flow equations  

NASA Technical Reports Server (NTRS)

Preconditioning methods to accelerate convergence to a steady state for the incompressible fluid dynamics equations are considered. The analysis relies on the inviscid equations. The preconditioning consists of a matrix multiplying the time derivatives. Thus the steady state of the preconditioned system is the same as the steady state of the original system. The method is compared to other types of pseudo-compressibility. For finite difference methods preconditioning can change and improve the steady state solutions. An application to viscous flow around a cascade with a non-periodic mesh is presented.

Turkel, Eli; Arnone, A.

1993-01-01

132

A Fractional-Step Method Of Computing Incompressible Flow  

NASA Technical Reports Server (NTRS)

Method of computing time-dependent flow of incompressible, viscous fluid involves numerical solution of Navier-Stokes equations on two- or three-dimensional computational grid based on generalized curvilinear coordinates. Equations of method derived in primitive-variable formulation. Dependent variables are pressure at center of each cell of computational grid and volume fluxes across faces of each cell. Volume fluxes replace Cartesian components of velocity; these fluxes correspond to contravariant components of velocity multiplied by volume of computational cell, in staggered grid. Choice of dependent variables enables simple extension of previously developed staggered-grid approach to generalized curvilinear coordinates and facilitates enforcement of conservation of mass.

Kwak, Dochan; Rosenfeld, Moshe; Vinokur, Marcel

1993-01-01

133

A correction function method to solve incompressible fluid flows to high accuracy with immersed geometries  

E-print Network

Numerical simulations of incompressible viscous flows in realistic configurations are increasingly important in many scientific and engineering fields. In Aeronautics, for instance, relatively cheap numerical computations ...

Marques, Alexandre Noll

2012-01-01

134

Study of two-dimensional laminar flow in a polar cavity by Ansys Fluent  

NASA Astrophysics Data System (ADS)

Study of 2-D cavity flow becomes more popular among Engineering and Science researchers. Flow investigation using experimental and analytical method, numerical methods and software (Ansys Fluent) to study the physical properties of the flow inside the cavity are very common. For computation simplicity, 2D laminar incompressible viscous fluid flow is assumed. It is further assumed that the fluid is uniformly filled the cavity and he walls are at uniform temperature. The working fluid is air and it shall be assumed as idle gas and other mechanical and thermal properties of fluid are constant with respect to temperature and pressure. Cavity walls such as inner radial (lower curve) and side walls are kept in stationary, while outer-radial boundary is in circumferential movement. The dimensionless radius, R kept as a constant, while Reynolds numbers, Re and polar cavity angles, ? varies. The fluid motion phenomena are studied using Fluent software. The study is focused to discover the flow of physicals properties in different Reynolds numbers and different angles (30°, 60° and 90°). The flow in polar cavity is expected to change dramatically as angles and Re are varied.

VilaVandran, Alfred Sagayam; Darus, A. N.

2012-06-01

135

Natural laminar flow experiments on modern airplane surfaces  

NASA Technical Reports Server (NTRS)

Flight and wind-tunnel natural laminar flow experiments have been conducted on various lifting and nonlifting surfaces of several airplanes at unit Reynolds numbers between 0.63 x 10 to the 6th power/ft and 3.08 x 10 to the 6th power/ft, at Mach numbers from 0.1 to 0.7, and at lifting surface leading-edge sweep angles from 0 deg to 63 deg. The airplanes tested were selected to provide relatively stiff skin conditions, free from significant roughness and waviness, on smooth modern production-type airframes. The observed transition locations typically occurred downstream of the measured or calculated pressure peak locations for the test conditions involved. No discernible effects on transition due to surface waviness were observed on any of the surfaces tested. None of the measured heights of surface waviness exceeded the empirically predicted allowable surface waviness. Experimental results consistent with spanwise contamination criteria were observed. Large changes in flight-measured performance and stability and control resulted from loss of laminar flow by forced transition. Rain effects on the laminar boundary layer caused stick-fixed nose-down pitch-trim changes in two of the airplanes tested. No effect on transition was observed for flight through low-altitude liquid-phase clouds. These observations indicate the importance of fixed-transition tests as a standard flight testing procedure for modern smooth airframes.

Holmes, B. J.; Obara, C. J.; Yip, L. P.

1984-01-01

136

Laminar flow transition: A large-eddy simulation approach  

NASA Technical Reports Server (NTRS)

A vectorized, semi-implicit code was developed for the solution of the time-dependent, three dimensional equations of motion in plane Poiseuille flow by the large-eddy simulation technique. The code is tested by comparing results with those obtained from the solutions of the Orr-Sommerfeld equation. Comparisons indicate that finite-differences employed along the cross-stream direction act as an implicit filter. This removes the necessity of explicit filtering along this direction (where a nonhomogeneous mesh is used) for the simulation of laminar flow transition into turbulence in which small scale turbulence will be accounted for by a subgrid scale turbulence model.

Biringen, S.

1982-01-01

137

Polymer Effects on Heat Transport in Laminar Boundary Layer Flow  

E-print Network

We consider a laminar Blasius boundary-layer flow above a slightly heated horizontal plate and study the effect of polymer additives on the heat transport. We show that the action of the polymers can be understood as a space-dependent effective viscosity that first increases from the zero-shear value then decreases exponentially back to the zero-shear value as one moves away from the boundary. We find that with such an effective viscosity, both the horizontal and vertical velocities near the plate are decreased thus leading to an increase in the friction drag and a decrease in the heat transport in the flow.

Roberto Benzi; Emily S. C. Ching; Vivien W. S. Chu

2011-04-21

138

On three-dimensionality and control of incompressible cavity flow  

NASA Astrophysics Data System (ADS)

The incompressible large eddy simulation technique, coupled with the Lighthill-Curle acoustic analogy, is used to investigate the oscillation mechanism and sound source of a two-dimensional cavity with a length-to-depth ratio of L /D=4 and Reynolds number of ReD=5000. It is demonstrated that the development of the three-dimensional flow field, initiated by the introduction of a random inflow disturbance, is eventually accompanied by transition from the wake to the shear layer oscillation mode, regardless of the amplitude and shape of the inflow disturbance. Once the transition to the shear layer mode is accomplished, the amplitude and frequency of oscillations are not very sensitive to the particular shape of the inflow disturbance. The effectiveness of controlling the flow oscillations by applying simultaneous steady injection and suction through the front and rear cavity walls, respectively, is demonstrated. The results show that, for injection levels exceeding a certain threshold value, the oscillations are quenched, and for levels below that value, the oscillation process is virtually unaffected. The major difference between the averaged uncontrolled and controlled velocity fields is the amount of reverse flow in the rear part of the cavity. With the aid of linear stability analysis, it is demonstrated that for injection levels leading to the quenching of the oscillations the mean velocity profiles in the cavity region are only convectively unstable, whereas for the uncontrolled case there is an absolutely unstable region. This suggests that, at least for incompressible flow, the reduction of the reverse flow inside the cavity can reduce or eliminate the oscillation process.

Suponitsky, Victoria; Avital, Eldad; Gaster, Mike

2005-10-01

139

Experimental investigation of flow instabilities in a laminar separation bubble  

NASA Astrophysics Data System (ADS)

The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large scale coherent structures generated as a consequence of the Kelvin-Helmholtz instability process. Measurements have been performed along a flat plate installed within a double contoured test section, designed to produce an adverse pressure gradient typical of Ultra-High-Lift turbine blade profiles, which induces the formation of a laminar separation bubble at low Reynolds number condition. Measurements have been carried out by means of complementary techniques: hot-wire (HW) anemometry, Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV). The high accuracy 2-dimensional LDV results allow investigating reverse flow magnitude and both Reynolds normal and shear stress distributions along the separated flow region, while the high frequency response of the HW anemometer allows analyzing the amplification process of flow oscillations induced by instability mechanisms. PIV results complement the flow field analysis providing information on the generation and evolution of the large scale coherent structures shed as a consequence of the separated shear layer roll-up, through instantaneous velocity vector maps. The simultaneous analysis of the data obtained by means of the different measuring techniques allows an in depth view of the instability mechanisms involved in the transition/reattachment processes of the separated shear layer.

Simoni, D.; Ubaldi, M.; Zunino, P.

2014-06-01

140

Analysis of developing laminar flows in circular pipes using a higher-order finite-difference technique  

NASA Technical Reports Server (NTRS)

A higher-order finite-difference technique is developed to calculate the developing-flow field of steady incompressible laminar flows in the entrance regions of circular pipes. Navier-Stokes equations governing the motion of such a flow field are solved by using this new finite-difference scheme. This new technique can increase the accuracy of the finite-difference approximation, while also providing the option of using unevenly spaced clustered nodes for computation such that relatively fine grids can be adopted for regions with large velocity gradients. The velocity profile at the entrance of the pipe is assumed to be uniform for the computation. The velocity distribution and the surface pressure drop of the developing flow then are calculated and compared to existing experimental measurements reported in the literature. Computational results obtained are found to be in good agreement with existing experimental correlations and therefore, the reliability of the new technique has been successfully tested.

Gladden, Herbert J.; Ko, Ching L.; Boddy, Douglas E.

1995-01-01

141

Interaction of transient radiation in fully developed laminar flows  

NASA Technical Reports Server (NTRS)

The transient radiative interactions of nongray absorbing-emitting species in laminar fully-developed flows between two parallel plates are investigated analytically and numerically. The particular species considered are OH, CO, CO2, and H2O and different mixtures of these species. Transient and steady-state results are obtained for the temperature distribution and bulk temperature for different plate spacings, wall temperatures, and pressures. Results, in general, indicate that the rate of radiative heating can be quite high during earlier times. This information is useful in designing thermal protection systems for transient operations.

Tiwari, S. N.; Singh, D. J.

1987-01-01

142

Aircraft energy efficiency laminar flow control wing design study  

NASA Technical Reports Server (NTRS)

An engineering design study was performed in which laminar flow control (LFC) was integrated into the wing of a commercial passenger transport aircraft. A baseline aircraft configuration was selected and the wing geometry was defined. The LFC system, with suction slots, ducting, and suction pumps was integrated with the wing structure. The use of standard aluminum technology and advanced superplastic formed diffusion bonded titanium technology was evaluated. The results of the design study show that the LFC system can be integrated with the wing structure to provide a structurally and aerodynamically efficient wing for a commercial transport aircraft.

Bonner, T. F., Jr.; Pride, J. D., Jr.; Fernald, W. W.

1977-01-01

143

Heat Transfer Effects on Laminar Velocity Profiles in Pipe Flow  

NASA Astrophysics Data System (ADS)

Heat Transfer Effects on Laminar Velocity Profiles in Pipe Flow. Robert L. Powell, Thomas P. Jenkins Department of Chemical Engineering & Materials Science University of California, Davis, CA 95616 Using laser Doppler velocimetry, we have measured the axial velocity profiles for steady, pressure driven, laminar flow of water in a circular tube. The flow was established in a one inch diameter seamless glass tube. The entry length prior to the measuring section was over one hundred diameters. Reynolds numbers in the range 500-2000 were used. Under conditions where the temperature difference between the fluid and the surroundings differed by as little as 0.2C, we found significant asymmetries in the velocity profiles. This asymmetry was most pronounced in the vertical plane. Varying the temperature difference moved the velocity maximum either above or below the centerline depending upon whether the fluid was warmer or cooler than the room. These results compare well to existing calculations. Using the available theory and our experiments it is possible to identify parameter ranges where non-ideal conditions(not parabolic velocity profiles) will be found. Supported by the EMSP Program of DOE.

Powell, Robert; Jenkins, Thomas

1998-11-01

144

Combination of integrated thermal flow and capacitive pressure sensors for high sensitivity flow measurements in both laminar and turbulent regions  

Microsoft Academic Search

A combination of a silicon thermal flow and two capacitive pressure sensors placed in a specially designed housing, is proposed for high sensitivity flow measurements in both laminar and turbulent flows. The system of these sensors can determine the transition point between laminar and turbulent region with sufficient accuracy. The pressure distribution in the flow tube was studied in detail

G. Kaltsas; D. Goustouridis; A. G. Nassiopoulou; D. Tsoukalas

2005-01-01

145

Laminar-flow fluid mixer for fast fluorescence kinetics studies.  

PubMed

The ability to mix aqueous liquids on microsecond time scales, while consuming minimal amounts of sample and maintaining UV-visible optical access to the mixing region, is highly desirable for a range of biophysical studies of fast protein and nucleic acid interactions and folding. We have constructed a laminar coaxial jet mixer that allows the measurement of UV-excited fluorescence from nanoliter and microliter quantities of material, mixed at microsecond rates. The mixer injects a narrow cylindrical stream (radius a < 1 microm) of fluorescent sample into a larger flow of diluting buffer that moves through a capillary (100 microm i.d.) at a speed approximately 20 cm/s, under laminar flow conditions (Re approximately equal to 14). Construction from a fused silica capillary allows the laser excitation (at 266 nm) and detection (at 350 nm) of tryptophan fluorescence at reasonably low working concentrations, without interference from background fluorescence. Using this mixer we have measured sub-millisecond fluorescence quenching kinetics while consuming fluorescent sample at rates no greater than 6 nl/s. Consumption of the diluting buffer is also very modest (approximately 1-3 microl/s) in comparison with other rapid mixer designs. PMID:12414719

Pabit, Suzette A; Hagen, Stephen J

2002-11-01

146

Low temperature high current ion beams and laminar flows  

NASA Astrophysics Data System (ADS)

Self-consistent Vlasov-Poisson equilibria for the extraction of ions with low temperature Ti are discussed, with comparison to the laminar flow case Ti = 0, in two dimensional diodes. Curvilinear coordinates aligned with laminar beam flow lines are extended to the low ion temperature case, with a reduced current density jd, expressed with cathode integrals. This generalizes one-dimensional interpolation between rays along the cathode coordinate to multidimensional integrations, including also the momentum components, so that jd is free from the granularity defect and noise, typical of standard ray tracing approach. A robust numerical solution procedure is developed, which allows studying current saturated extraction and drift tube effects. A discussion of particle initial conditions determines the emission angles and shows that temperature effect at beam edge is partly balanced by the focus electrode inclination. Results for a typical diode are described, with detail about normalized emittance, here taken strictly proportional to the x - px phase space area, for a beam with non uniform velocities. Contribution to the Topical Issue "Theory and Applications of the Vlasov Equation", edited by Francesco Pegoraro, Francesco Califano, Giovanni Manfredi and Philip J. Morrison.

Cavenago, Marco

2014-07-01

147

Exploring Roughness Effect on Laminar Internal Flow–Are We Ready for Change?  

Microsoft Academic Search

Laminar flow is often encountered in the channels of microdevices as a result of the small hydraulic diameters. The roughness introduced on the walls of these channels through various fabrication techniques, such as etching, micromachining, laser drilling, etc., results in a high value of relative roughness (defined as the wall surface roughness to channel hydraulic diameter ratio). Laminar flow in

Satish G. Kandlikar

2008-01-01

148

Laminar flow control leading edge glove flight test article development  

NASA Technical Reports Server (NTRS)

A laminar flow control (LFC) flight test article was designed and fabricated to fit into the right leading edge of a JetStar aircraft. The article was designed to attach to the front spar and fill in approx. 70 inches of the leading edge that are normally occupied by the large slipper fuel tank. The outer contour of the test article was constrained to align with an external fairing aft of the front spar which provided a surface pressure distribution over the test region representative of an LFC airfoil. LFC is achieved by applying suction through a finely perforated surface, which removes a small fraction of the boundary layer. The LFC test article has a retractable high lift shield to protect the laminar surface from contamination by airborne debris during takeoff and low altitude operation. The shield is designed to intercept insects and other particles that could otherwise impact the leading edge. Because the shield will intercept freezing rain and ice, a oozing glycol ice protection system is installed on the shield leading edge. In addition to the shield, a liquid freezing point depressant can be sprayed on the back of the shield.

Pearce, W. E.; Mcnay, D. E.; Thelander, J. A.

1984-01-01

149

Numerical simulation of rarefied laminar flow past a circular cylinder  

NASA Astrophysics Data System (ADS)

Numerical simulations have been obtained for two-dimensional laminar flows past a circular cylinder in the transitional regime. Computations are performed using the direct simulation Monte Carlo method for Knudsen numbers of 0.02 and 0.2 and Mach numbers of 0.102 and 0.4. For these conditions, Reynolds number ranges from 0.626 to 24.63 and the flows are steady. Results show that separation occurs in the wake region for the flow with Mach number of 0.4 and Knudsen number of 0.02, but for the other cases flows are attached. The effects of flow speed, rarefaction, domain size and the outflow boundary conditions are investigated. Results show sensitivity to the domain size and the outflow boundary conditions in the low Mach number calculations, but as the speed increases the sensitivity decreases. Although no experimental data are available for direct comparison, the present calculations are found to be in very good agreement with the findings of other researchers.

?elenligil, M. Cevdet

2014-12-01

150

Postfragmentation density function for bacterial aggregates in laminar flow  

NASA Astrophysics Data System (ADS)

The postfragmentation probability density of daughter flocs is one of the least well-understood aspects of modeling flocculation. We use three-dimensional positional data of Klebsiella pneumoniae bacterial flocs in suspension and the knowledge of hydrodynamic properties of a laminar flow field to construct a probability density function of floc volumes after a fragmentation event. We provide computational results which predict that the primary fragmentation mechanism for large flocs is erosion. The postfragmentation probability density function has a strong dependence on the size of the original floc and indicates that most fragmentation events result in clumps of one to three bacteria eroding from the original floc. We also provide numerical evidence that exhaustive fragmentation yields a limiting density inconsistent with the log-normal density predicted in the literature, most likely due to the heterogeneous nature of K. pneumoniae flocs. To support our conclusions, artificial flocs were generated and display similar postfragmentation density and exhaustive fragmentation.

Byrne, Erin; Bortz, David M.; Dzul, Steve; Solomon, Michael; Younger, John

2011-04-01

151

Computational wing design studies relating to natural laminar flow  

NASA Technical Reports Server (NTRS)

Two research studies are described which directly relate to the application of natural laminar flow (NLF) technology to transonic transport-type wing planforms. Each involved using state-of-the-art computational methods to design three-dimensional wing contours which generate significant runs of favorable pressure gradients. The first study supported the Variable Sweep Transition Flight Experiment and involves design of a full-span glove which extends from the leading edge to the spoiler hinge line on the upper surface of an F-14 outer wing panel. A wing was designed computationally for a corporate transport aircraft in the second study. The resulting wing design generated favorable pressure gradients from the leading edge aft to the mid-chord on both upper and lower surfaces at the cruise design point. Detailed descriptions of the computational design approach are presented along with the various constraints imposed on each of the designs.

Waggoner, Edgar G.

1986-01-01

152

Characteristics of laminar flow past a sphere in uniform shear  

NASA Astrophysics Data System (ADS)

Numerical simulations are performed to investigate the characteristics of laminar flow past a sphere in uniform shear. The Reynolds numbers considered are Re =300, 425, and 480 based on the inlet center velocity uc and sphere diameter d. The nondimensional shear rate K of inlet uniform shear is varied from 0 to 0.15, where K =??u?d/uc (??u?) and ??u? is the shear rate at inlet. For all Reynolds numbers investigated, the head of the hairpin vortex loop is always located on the high-velocity side in uniform shear. The flow maintains planar symmetry at Re =300. At Re =425 and 480, the temporal variation in the azimuthal angle of the hairpin vortex formation appearing in the uniform inlet flow is greatly reduced in uniform shear, but the flows still keep asymmetry for most inlet shear rates. However, in the cases of K =0.075 and 0.1, at Re =425, the flows become planar symmetric and their characteristics of formation and evolution of the hairpin vortex loops are different from those of asymmetric flows. In most cases, except the instances showing planar symmetry at Re =425, the Strouhal number and time-averaged drag and lift coefficients increase with increasing inlet shear rate. On the other hand, for K =0.075 and 0.1, showing planar symmetry at Re =425, three different vortices are shed in the wake, resulting in three distinct peak frequencies. Finally, a hysteresis phenomenon switching from planar symmetry to asymmetry (or vice versa) depending on the initial condition is observed at Re =425 and 450, implying that small variations in the flow or initial conditions change the flow field at these Reynolds numbers.

Kim, Dongjoo; Choi, Hyungseok; Choi, Haecheon

2005-10-01

153

Progress Toward Efficient Laminar Flow Analysis and Design  

NASA Technical Reports Server (NTRS)

A multi-fidelity system of computer codes for the analysis and design of vehicles having extensive areas of laminar flow is under development at the NASA Langley Research Center. The overall approach consists of the loose coupling of a flow solver, a transition prediction method and a design module using shell scripts, along with interface modules to prepare the input for each method. This approach allows the user to select the flow solver and transition prediction module, as well as run mode for each code, based on the fidelity most compatible with the problem and available resources. The design module can be any method that designs to a specified target pressure distribution. In addition to the interface modules, two new components have been developed: 1) an efficient, empirical transition prediction module (MATTC) that provides n-factor growth distributions without requiring boundary layer information; and 2) an automated target pressure generation code (ATPG) that develops a target pressure distribution that meets a variety of flow and geometry constraints. The ATPG code also includes empirical estimates of several drag components to allow the optimization of the target pressure distribution. The current system has been developed for the design of subsonic and transonic airfoils and wings, but may be extendable to other speed ranges and components. Several analysis and design examples are included to demonstrate the current capabilities of the system.

Campbell, Richard L.; Campbell, Matthew L.; Streit, Thomas

2011-01-01

154

Drag Measurements in Laminar Flows over Superhydrophobic Porous Membranes  

NASA Astrophysics Data System (ADS)

An anomalous hydrodynamic response has recently been observed in oscillating flows on mesh-like porous superhydrophobic membranes.ootnotetextS. Rajauria, O. Ozsun, J. Lawall, V. Yakhot, and K. L. Ekinci, Phys. Rev. Lett. 107, 174501 (2011) This effect was attributed to a stable Knudsen layer of gas at the solid-liquid interface. In this study, we investigate laminar channel flow over these porous superhydrophobic membranes. We have fabricated surfaces with solid area fraction ?s, which can maintain intimate contact with both air and water reservoirs on either side. Typical structures have linear dimensions of 1.5 mm x 15 mm x 1 ?m and pore area of 10 ?m x 10 ?m. The surfaces are enclosed with precisely machined plastic microchannels, where pressure driven flow of DI water is generated. Pressure drop across the microchannels is measured as a function of flow rate. Slip lengths are inferred from the Poiseuille relation as a function of ?s and compared to that of similar standard superhydrophobic surfaces, which lack intimate contact with an air reservoir.

Ozsun, Ozgur; Yakhot, Victor; Ekinci, Kamil L.

2012-02-01

155

Laminar flow around corners triggers the formation of biofilm streamers  

PubMed Central

Bacterial biofilms have an enormous impact on medicine, industry and ecology. These microbial communities are generally considered to adhere to surfaces or interfaces. Nevertheless, suspended filamentous biofilms, or streamers, are frequently observed in natural ecosystems where they play crucial roles by enhancing transport of nutrients and retention of suspended particles. Recent studies in streamside flumes and laboratory flow cells have hypothesized a link with a turbulent flow environment. However, the coupling between the hydrodynamics and complex biofilm structures remains poorly understood. Here, we report the formation of biofilm streamers suspended in the middle plane of curved microchannels under conditions of laminar flow. Experiments with different mutant strains allow us to identify a link between the accumulation of extracellular matrix and the development of these structures. Numerical simulations of the flow in curved channels highlight the presence of a secondary vortical motion in the proximity of the corners, which suggests an underlying hydrodynamic mechanism responsible for the formation of the streamers. Our findings should be relevant to the design of all liquid-carrying systems where biofilms are potentially present and provide new insights on the origins of microbial streamers in natural and industrial environments. PMID:20356880

Rusconi, Roberto; Lecuyer, Sigolene; Guglielmini, Laura; Stone, Howard A.

2010-01-01

156

Field descriptions for a developing laminar tube flow with and without a concentrically located spherical obstacle  

E-print Network

in developing laminar flows at any Reynolds number, and second, no complete pressure fields have been computed using numerical 22 techniques. Blood flow through artificial devices is one example of partic- ulate flows where destruction of the particles...FIELD DESCRIPTIONS FOR A DEVELOPING LAMINAR TUBE FLOW WITH AND WITHOUT A CONCENTRICALLY LOCATED SPHERICAL OBSTACLE A Thesis by CLARK DOUGLAS MIKKELSEN Submitted to the Graduate College of Texas ASM University in partial fulfillment...

Mikkelsen, Clark Douglas

2012-06-07

157

Section 9: Laminar flows and transition 1 Section 9: Laminar flows and transition  

E-print Network

wind tunnel testing and flight tests, CFD simulation based on RANS solvers has become a standard design and detects transition due to Tollmien- Schlichting or cross flow instabilities. The stability code, which of the transition points, uses a frequency esti- mator for the detection of the relevant regions of amplified

Kohlenbach, Ulrich

158

On plane laminar two-phase jet flow with full expansion  

NASA Astrophysics Data System (ADS)

Laminar mixing of a two-dimensional jet of particulate suspension in an incompressible carrier fluid with a free stream moving in direction of the jet axis has been considered. The basic equations are of the boundary layer type and include the diffusion equation for the solid particles. The governing equations have been linearized by employing perturbation method and they have been solved by finite difference technique. It is found that the effect of increase in the parameter K, which is the ratio between the Reynolds number of the fluid flow and the particle relaxation parameter, is to quicken the attainment of the particle velocity to that of the carrier fluid. The parameter epsilon, the ratio of particle diffusion coefficient and the kinematic viscosity of the carrier fluid, has both damping and spreading effects on the jet. The effect of increasing the concentration of dust particles is to widen the mixing region. It is also found that the migration of the finer particles away from the jet axis is greater than that of the coarse particles.

Datta, N.; Mishra, S. K.

1984-04-01

159

Predictions and observations of the flow field induced by laminar flow control microperforations  

Microsoft Academic Search

Hybrid laminar flow control (HLFC) aims to reduce aircraft skin friction drag by controlling the boundary-layer characteristics through a combination of surface suction and surface profile shaping. Suction is applied through an array of microperforations in the surface; and, to enable HLFC design criteria to be established with confidence, a full understanding of how these suction perforations affect the boundary

David G. MacManus; John A. Eaton

1996-01-01

160

Feasibility study of applying laminar flow control to an lta vehicle. Final report. [Lighter than air vehicles  

SciTech Connect

The feasibility of applying laminar boundary-layer control with body shaping to a high altitude, Lighter-Than-Air vehicle was investigated. Solar-radiation-induced surface heating was shown to have a destablizing effect on laminar flow and caused the laminar flow to break down on regions of the vehicle surface exposed to high levels of solar radiation. Aerodynamic drag estimates were made for the vehicle. Surface waviness and roughness criteria for achieving laminar flow were determined.

Warner, D.J.; Ozgur, S.A.; Haigh, W.W.

1980-04-01

161

A general integral form of the boundary-layer equation for incompressible flow with an application to the calculation of the separation point of turbulent boundary layers  

NASA Technical Reports Server (NTRS)

A general integral form of the boundary-layer equation, valid for either laminar or turbulent incompressible boundary-layer flow, is derived. By using the experimental finding that all velocity profiles of the turbulent boundary layer form essentially a single-parameter family, the general equation is changed to an equation for the space rate of change of the velocity-profile shape parameter. The lack of precise knowledge concerning the surface shear and the distribution of the shearing stress across turbulent boundary layers prevented the attainment of a reliable method for calculating the behavior of turbulent boundary layers.

Tetervin, Neal; Lin, Chia Chiao

1951-01-01

162

A characteristic based method for the calculation of three-dimensional incompressible, turbulent and steady flows in hydraulic turbomachines and installations  

NASA Astrophysics Data System (ADS)

The present algorithm is developed to calculate three-dimensional incompressible, turbulent and steady flows in hydraulic turbomachines and installations. The code is based on a characteristic based method for the solution of the incompressible Navier-Stokes equations, coupling the continuity and momentum equations after the introduction of the artificial compressibility formulation. The primitive variables, pressure and velocity components are defined as functions of their values on the characteristics. The primitive variables on the characteristics are calculated by an upwind differencing scheme based on the sign of the local eigenvalue of the Jacobian matrix of the convective fluxes. The upwind scheme uses interpolation formulas of third-order accuracy. The standard k- model is applied for the description of turbulence effects. The time discretization is obtained by the explicit Runge-Kutta method. For faster convergences to the steady state solution, a local time stepping and a mesh-sequencing scheme are used. Validation of the algorithm is performed on many two- and three-dimensional laminar and turbulent flow cases, while in the present work, the three-dimensional flow (laminar and turbulent) through a square duct with a 90° bend is presented. Finally, the code is applied for the prediction of the relative flow through the impeller of the Societe Hydrotechnique de France (SHF) water pump. The numerical results are compared with the corresponding experimental measurements. Copyright

Govatsos, P. A.; Papantonis, D. E.

2000-09-01

163

Laminar boundary layer flow of a nanofluid along a wedge in the presence of suction/injection  

NASA Astrophysics Data System (ADS)

The behavior of an incompressible laminar boundary layer flow over a wedge in a nanofluid with suction or injection has been investigated. The model used for the nanofluid integrates the effects of the Brownian motion and thermophoresis parameters. The governing partial differential equations of this problem, subjected to their boundary conditions, are solved by the Runge-Kutta-Gill technique with the shooting method for finding the skin friction and the rate of heat and mass transfer. The result are presented in the form of velocity, temperature, and volume fraction profiles for different values of the suction/injection parameter, Brownian motion parameter, thermophoresis parameter, pressure gradient parameter, Prandtl number, and Lewis number. The conclusion is drawn that these parameters significantly affect the temperature and volume fraction profiles, but their influence on the velocity profile is comparatively smaller.

Kasmani, R. Md.; Muhaimin, I.; Kandasamy, R.

2013-05-01

164

Summary of past experience in natural laminar flow and experimental program for resilient leading edge  

NASA Technical Reports Server (NTRS)

The potential of natural laminar flow for significant drag reduction and improved efficiency for aircraft is assessed. Past experience with natural laminar flow as reported in published and unpublished data and personal observations of various researchers is summarized. Aspects discussed include surface contour, waviness, and smoothness requirements; noise and vibration effects on boundary layer transition, boundary layer stability criteria; flight experience with natural laminar flow and suction stabilized boundary layers; and propeller slipstream, rain, frost, ice and insect contamination effects on boundary layer transition. The resilient leading edge appears to be a very promising method to prevent leading edge insect contamination.

Carmichael, B. H.

1979-01-01

165

Aircraft energy efficiency laminar flow control glove flight conceptual design study  

NASA Technical Reports Server (NTRS)

A laminar flow control glove applied to the wing of a short to medium range jet transport with aft mounted engines was designed. A slotted aluminum glove concept and a woven stainless steel mesh porous glove concept suction surfaces were studied. The laminar flow control glove and a dummy glove with a modified supercritical airfoil, ducting, modified wing leading and trailing edges, modified flaps, and an LFC trim tab were applied to the wing after slot spacing suction parameters, and compression power were determined. The results show that a laminar flow control glove can be applied to the wing of a jet transport with an appropriate suction system installed.

Wright, A. S.

1979-01-01

166

Erosion of a granular bed driven by laminar fluid flow  

E-print Network

Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed driven by a laminar fluid to give us new insights into the relationship between hydrodynamic stress and surface granular flow. A closed cell of rectangular cross-section is partially filled with glass beads and a constant fluid flux $Q$ flows through the cell. The refractive indices of the fluid and the glass beads are matched and the cell is illuminated with a laser sheet, allowing us to image individual beads. The bed erodes to a rest height $h_r$ which depends on $Q$. The Shields threshold criterion assumes that the non-dimensional ratio $\\theta$ of the viscous stress on the bed to the hydrostatic pressure difference across a grain is sufficient to predict the granular flux. Furthermore, the Shields criterion states that the granular flux is non-zero only for $\\theta >\\theta_c$. We find that the Shields criterion describes the observed relationship $h_r \\propto Q^{1/2}$ when the bed height is offset by approximately half a grain diameter. Introducing this offset in the estimation of $\\theta$ yields a collapse of the measured Einstein number $q^*$ to a power-law function of $\\theta - \\theta_c$ with exponent $1.75 \\pm 0.25$. The dynamics of the bed height relaxation are well described by the power law relationship between the granular flux and the bed stress.

A. E. Lobkovsky; A. V. Orpe; R. Molloy; A. Kudrolli; D. H. Rothman

2008-05-01

167

Global response of laminar flow separation to local flow perturbations ( review)  

NASA Astrophysics Data System (ADS)

In the present paper, we summarize our experimental data on flow separation control on wings at low subsonic velocities. The focus is on the reduction of the separation region by stationary and nonstationary controlled flow perturbations. Wind-tunnel data obtained for test models of different aspect ratios prove that the entire separated flow can be modified by forcing its narrow parts much smaller in size than the transverse extent of the separation region. Such an approach to flow control at laminar separation comes from non-local interaction of the large-scale flow structure with spatially concentrated disturbances.

Dovgal, A. V.; Zanin, B. Yu.; Kozlov, V. V.

2012-03-01

168

Young Measures Generated by Ideal Incompressible Fluid Flows  

NASA Astrophysics Data System (ADS)

In their seminal paper, D iP erna and M ajda (Commun Math Phys 108(4):667-689, 1987) introduced the notion of a measure-valued solution for the incompressible Euler equations in order to capture complex phenomena present in limits of approximate solutions, such as persistence of oscillation and development of concentrations. Furthermore, they gave several explicit examples exhibiting such phenomena. In this paper we show that any measure-valued solution can be generated by a sequence of exact weak solutions. In particular this gives rise to a very large, arguably too large, set of weak solutions of the incompressible Euler equations.

Székelyhidi, László; Wiedemann, Emil

2012-10-01

169

Unique encoding for streamline topologies of incompressible and inviscid flows in multiply connected domains  

NASA Astrophysics Data System (ADS)

This study considers the flow of incompressible and inviscid fluid in two-dimensional multiply connected domains. For such flows, encoding algorithms to assign a unique sequence of words to any structurally stable streamline topology based on the theory presented by Yokoyama and Sakajo (2013 Proc. R. Soc. A 469 20120558) are proposed. As an application, we utilize the algorithms to characterize the evolution of an incompressible and viscid flow around a flat plate inclined to the uniform flow in terms of the change of the word representations for their instantaneous streamline topologies.

Sakajo, T.; Sawamura, Y.; Yokoyama, T.

2014-06-01

170

Design and operation of a laminar-flow electrostatic-quadrupole-focused acceleration column  

SciTech Connect

This report deals with the design principles involved in the design of a laminar-flow electrostatic-quadrupole-focused acceleration column. In particular, attention will be paid to making the parameters suitable for incorporation into a DC MEQALAC design.

Maschke, A.W.

1983-06-20

171

Fabrication of a graphite/epoxy composite leading edge for laminar flow control  

NASA Technical Reports Server (NTRS)

Lockheed, under NASA contract, has recently completed the first phase of a program to evaluate laminar flow control concepts for transport aircraft. Achievement of laminar flow over a wing surface requires a system of slots, metering holes, ducts and pumps to be used to remove the turbulent air adjacent to the surface. This requirement poses severe restrictions on conventional metallic structure. Graphite/epoxy composite with its unique properties appears to be the material that might solve the very complex structural problems associated with a laminar flow control aircraft. A six-foot span graphite/epoxy test article incorporating provisions for leading edge cleaning, deicing and laminar flow control was designed, fabricated and tested.

Beall, R. T.

1980-01-01

172

Laminar boundary layer in conditions of natural transition to turbulent flow  

NASA Technical Reports Server (NTRS)

Results of experimental study of regularities of a natural transition of a laminar boundary layer to a turbulent layer at low subsonic air flow velocities are presented, analyzed and compared with theory and model experiments.

Polyakov, N. F.

1986-01-01

173

A flight test of laminar flow control leading-edge systems  

NASA Technical Reports Server (NTRS)

NASA's program for development of a laminar flow technology base for application to commercial transports has made significant progress since its inception in 1976. Current efforts are focused on development of practical reliable systems for the leading-edge region where the most difficult problems in applying laminar flow exist. Practical solutions to these problems will remove many concerns about the ultimate practicality of laminar flow. To address these issues, two contractors performed studies, conducted development tests, and designed and fabricated fully functional leading-edge test articles for installation on the NASA JetStar aircraft. Systems evaluation and performance testing will be conducted to thoroughly evaluate all system capabilities and characteristics. A simulated airline service flight test program will be performed to obtain the operational sensitivity, maintenance, and reliability data needed to establish that practical solutions exist for the difficult leading-edge area of a future commercial transport employing laminar flow control.

Fischer, M. C.; Wright, A. S., Jr.; Wagner, R. D.

1983-01-01

174

Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove  

NASA Technical Reports Server (NTRS)

This is the presentation related to the paper of the same name describing Reynolds Averaged Navier Stokes (RANS) computational Fluid Dynamics (CFD) analysis of low speed stall aerodynamics of a swept wing with a laminar flow wing glove.

Bui, Trong

2013-01-01

175

Distributed acoustic receptivity in laminar flow control configurations  

NASA Technical Reports Server (NTRS)

A model problem related to distributed receptivity to free-stream acoustic waves in laminar flow control (LFC) configurations is studied, within the Orr-Sommerfield framework, by a suitable extension of the Goldstein-Ruban theory for receptivity due to localized disturbances on the airfoil surface. The results, thus, complement the earlier work on the receptivity produced by local variations in the surface suction and/or surface admittance. In particular, we show that the cumulative effect of the distributed receptivity can be substantially larger than that of a single, isolated suction strip or slot. Furthermore, even if the receptivity is spread out over very large distances, the most effective contributions come from a relatively short region in vicinity of the lower branch of the neutral stability curve. The length scale of this region is intermediate to that of the mean of these two length scales. Finally, it is found that the receptivity is effectively dominated by a narrow band of Fourier components from the wall-suction and admittance distributions, roughly corresponding to a detuning of less than ten percent with respect to the neutral instability wavenumber at the frequency under consideration. The results suggest that the drop-off in receptivity magnitudes away from the resonant wavenumber is nearly independent of the frequency parameter.

Choudhari, Meelan

1992-01-01

176

A perspective of laminar-flow control. [aircraft energy efficiency program  

NASA Technical Reports Server (NTRS)

A historical review of the development of laminar flow control technology is presented with reference to active laminar boundary-layer control through suction, the use of multiple suction slots, wind-tunnel tests, continuous suction, and spanwise contamination. The ACEE laminar flow control program is outlined noting the development of three-dimensional boundary-layer codes, cruise-noise prediction techniques, airfoil development, and leading-edge region cleaning. Attention is given to glove flight tests and the fabrication and testing of wing box designs.

Braslow, A. L.; Muraca, R. J.

1978-01-01

177

A preliminary design study on an acoustic muffler for the laminar flow transition research apparatus  

NASA Technical Reports Server (NTRS)

An acoustic muffler design of a research tool for studying laminar flow and the mechanisms of transition, the Laminar Flow and Transition Research Apparatus (LFTRA) is investigated. Since the presence of acoustic pressure fluctuations is known to affect transition, low background noise levels in the test section of the LFTRA are mandatory. The difficulties and tradeoffs of various muffler design concepts are discussed and the most promising candidates are emphasized.

Abrahamson, A. L.

1984-01-01

178

Numerical methods for incompressible viscous flows with engineering applications  

NASA Technical Reports Server (NTRS)

A numerical scheme has been developed to solve the incompressible, 3-D Navier-Stokes equations using velocity-vorticity variables. This report summarizes the development of the numerical approximation schemes for the divergence and curl of the velocity vector fields and the development of compact schemes for handling boundary and initial boundary value problems.

Rose, M. E.; Ash, R. L.

1988-01-01

179

Observations and implications of natural laminar flow on practical airplane surfaces  

NASA Technical Reports Server (NTRS)

The results of natural laminar flow (NLF) experiments conducted by NASA to determine if modern aircraft structures can benefit from NLF as do sailplanes are presented. Seven aircraft, ranging from a Cessna 210 to a Learjet 28/29, with relatively stiff skins were flown in production configurations with no modifications. Measurements were made of the boundary-layer laminar to turbulent transition locations on various aerodynamic surfaces, the effect of a total loss of laminar flow, the effect of the propeller slipstream on the wing boundary-layer transition and the boundary-layer profiles, the wing section profile drag, the effect of flight through clouds, and insect debris contamination effects. Favorable pressure gradients for NLF were concluded to be feasible up to a transition Reynolds number of 11 million. Laminar flows were observed in propeller slipstreams, and insects were found to cause transition 1/4 of the time.

Holmes, B. J.; Obara, C. J.

1982-01-01

180

An Approach to the Constrained Design of Natural Laminar Flow Airfoils  

NASA Technical Reports Server (NTRS)

A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integral turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the laminar flow toward the desired amount. An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.

Green, Bradford E.

1997-01-01

181

A generalized implicit finite difference method for transient analysis of compressible and incompressible fluid flows  

NASA Astrophysics Data System (ADS)

The Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm for engineering heat transfer and fluid flow problems is presently modified for use in the transient analysis of high speed (compressible) and low speed (incompressible) fluid flows. The modification expresses the density variation in terms of both pressure variation and the speed of sound. The applicability and validity of the SIMPLE algorithm, using the modifications discussed, are tested in the cases of two problems involving one-dimensional transient flow. One case is compressible, the other incompressible. Good agreement is obtained with earlier solutions.

Han, S. M.

182

A Moving Particle Method with Embedded Pressure Mesh (MPPM) for Incompressible Flow Calculations  

Microsoft Academic Search

An accurate moving particle method for incompressible flow calculations is presented in this article. The major distinctive feature in this proposition is the insertion of a pressure mesh within the particle cloud to handle the continuity constraint. It is motivated by the thought that pressure should be a field variable rather than a material one moving with fluid flow. Both

Yao-Hsin Hwang

2011-01-01

183

Front Speed Enhancement by Incompressible Flows in Three or Higher Dimensions  

NASA Astrophysics Data System (ADS)

We study, in dimensions N ? 3, the family of first integrals of an incompressible flow: these are functions whose level surfaces are tangential to the streamlines of the advective incompressible field. One main motivation for this study comes from earlier results proving that the existence of nontrivial first integrals of an incompressible flow q is the main key that leads to a "linear speed up" by a large advection of pulsating traveling fronts solving a reaction-advection-diffusion equation in a periodic heterogeneous framework. The family of first integrals is not well understood in dimensions N ? 3 due to the randomness of the trajectories of q and this is in contrast with the case N = 2. By looking at the domain of propagation as a union of different components produced by the advective field, we provide more information about first integrals and we give a class of incompressible flows which exhibit "ergodic components" of positive Lebesgue measure (and hence are not shear flows) and which, under certain sharp geometric conditions, speed up the KPP fronts linearly with respect to the large amplitude. In the proofs, we establish a link between incompressibility, ergodicity, first integrals and the dimension to give a sharp condition about the asymptotic behavior of the minimal KPP speed in terms of the configuration of ergodic components.

El Smaily, Mohammad; Kirsch, Stéphane

2014-07-01

184

Heat transfer of laminar flow over a 2-D backward facing step with isotropic porous floor segments  

SciTech Connect

Forced convection due to fluid flow over a backward facing step has been studied extensively. Flow through porous media occurs in a wide range of engineering applications such as the flow through insulation material, grain storage, and water movement through a geothermal reservoir. Control of the heat transfer characteristics is desirable, and the control mechanism can be either active or passive. Here, the incompressible laminar (Re{sub H} = 100) reattaching flow over a 2-D backward facing step with different length porous floor segments was solved numerically using the finite element method. The focus of this study is the change in the forced convection heat transfer characteristics of the flow field due to the addition of porous floor segments. Several isotropic porous floor segment configurations with different lengths and depths were studied. The porosity of the segments was varied over a wide range by changing the value of the pressure loss coefficient (KP = 10{sup {minus}2}--10{sup 6}). The changes in the local and overall Nusselt number are reported and discussed. Depending on the configuration, axial variation of the local Nusselt number could be altered. For all configurations, the overall Nusselt number decreased by as much as 16% while the maximum local Nusselt number increased by as much as 170%, both relative to their respective values for the reference case of solid floor.

Abu-Hijleh, B.A.K

1997-07-01

185

Laminar cold-flow model for the internal gas dynamics of a slab rocket motor  

Microsoft Academic Search

This paper considers the internal fluid dynamics of the slab rocket motor based on a laminar cold-flow model. An idealization process applicable to nonreacting flows leads to a mathematical solution for both steady and unsteady flow variables. Results are compared to the circular-port solution. This brings into focus the effect of a motor's radius of curvature. By comparison to a

Joseph Majdalani; William K. Van Moorhemb

2001-01-01

186

Multi-material incompressible flow simulation using the moment-of-fluid method  

SciTech Connect

The Moment-of-Fluid interface reconstruction technique is implemented in a second order accurate, unstructured finite element variable density incompressible Navier-Stokes solver. For flows with multiple materials, MOF significantly outperforms existing first and second order interface reconstruction techniques. For two material flows, the performance of MOF is similar to other interface reconstruction techniques. For strongly driven bouyant flows, the errors in the flow solution dominate and all the interface reconstruction techniques perform similarly.

Garimella, R V [Los Alamos National Laboratory; Schofield, S P [Los Alamos National Laboratory; Lowrie, R B [Los Alamos National Laboratory; Swartz, B K [Los Alamos National Laboratory; Christon, M A [SIMULIA; Dyadechko, V [EXXON-MOBIL

2009-01-01

187

Three-dimensional incompressible Navier-Stokes computations of internal flows  

NASA Technical Reports Server (NTRS)

Several incompressible Navier-Stokes solution methods for obtaining steady and unsteady solutions are discussed. Special attention is given to internal flows which involve distinctly different features from external flows. The characterisitcs of the flow solvers employing the method of pseudocompressibility and a fractional step method are briefly described. This discussion is limited to a primitive variable formulation in generalized curvilinear coordinates. Computed results include simple test cases and internal flow in the Space Shuttle main engine hot-gas manifold.

Kwak, D.; Chang, J. L. C.; Rogers, S. E.; Rosenfeld, M.; Kwak, D.

1988-01-01

188

Numerical simulation methods of incompressible flows and an application to the space shuttle main engine  

Microsoft Academic Search

Incompressible Navier-Stokes solution methods are discussed with an emphasis on the pseudocompressibility method. A steady-state flow solver based on the pseudocompressibility approach is then described. This flow-solver code was used to analyze the internal flow in the Space Shuttle main engine hot-gas manifold. Salient features associated with this three-dimensional realistic flow simulation are discussed. Numerical solutions relevant to the current

J. L. C. Chang; D. Kwak; S. E. Rogers; R.-J. Yang

1988-01-01

189

Numerical simulation methods of incompressible flows and an application to the Space Shuttle main engine  

Microsoft Academic Search

This paper discusses incompressible Navier-Stokes solution methods with an emphasis on the pseudocompressibility method. A steady-state flow solver based on the pseudocompressibility approach is then described. This flow solver code has been used to analyze the internal flow in the Space Shuttle main engine hot-gas manifold. Salient features associated with this three-dimensional realistic flow simulation are discussed. Numerical solutions relevant

J. L. C. Chang; D. Kwak; S. E. Rogers; R.-J. Yang

1988-01-01

190

Application of superplastically formed and diffusion bonded aluminum to a laminar flow control leading edge  

NASA Technical Reports Server (NTRS)

NASA sponsored the Aircraft Energy Efficiency (ACEE) program in 1976 to develop technologies to improve fuel efficiency. Laminar flow control was one such technology. Two approaches for achieving laminar flow were designed and manufactured under NASA sponsored programs: the perforated skin concept used at McDonnell Douglas and the slotted design used at Lockheed-Georgia. Both achieved laminar flow, with the slotted design to a lesser degree (JetStar flight test program). The latter design had several fabrication problems concerning springback and adhesive flow clogging the air flow passages. The Lockheed-Georgia Company accomplishments is documented in designing and fabricating a small section of a leading edge article addressing a simpler fabrication method to overcome the previous program's manufacturing problems, i.e., design and fabrication using advanced technologies such as diffusion bonding of aluminum, which has not been used on aerospace structures to date, and the superplastic forming of aluminum.

Goodyear, M. D.

1987-01-01

191

Numerical investigation of pressure drop and heat transfer in developing laminar and turbulent nanofluid flows  

NASA Astrophysics Data System (ADS)

This paper concerns the study of laminar and turbulent force convection heat transfer and pressure drop between horizontal parallel plates with a nanofluid composed of Al2O3 and water. A set of governing equations are solved using a non-staggered SIMPLE procedure for the velocity-pressure coupling. For the convection-diffusion terms a power-law scheme is employed. A modified k-? model with a two-layer technique for the near-wall region has been used to predict the turbulent viscosity. The effects of nanoparticle volume fraction in the base fluid on laminar and turbulent flow variables are presented and discussed. The velocity and temperature profiles, friction factor, pressure coefficient and Nusselt number at different Reynolds numbers in the entrance region for both the laminar and turbulent flow regimes are reported under different thermal boundary conditions. The results show that the effect of the presence of nanoparticles in the base fluid on hydraulic and thermal parameters for the turbulent flow is not very significant, while the rate of heat transfer for the laminar flow with nanoparticles is greater than that of the base liquid. Furthermore, the thermal boundary layer and consequently the Nusselt number more quickly reach their fully developed values by increasing the percentage of nanoparticles in the base fluid for the laminar flow regime, while no changes in the trend are observed for the turbulent flow.

Ziaei-Rad, Masoud

2013-07-01

192

Discrete unified gas kinetic scheme with force term for incompressible fluid flows  

E-print Network

The discrete unified gas kinetic scheme (DUGKS) is a finite-volume scheme with discretization of particle velocity space, which combines the advantages of both lattice Boltzmann equation (LBE) method and unified gas kinetic scheme (UGKS) method, such as the simplified flux evaluation scheme, flexible mesh adaption and the asymptotic preserving properties. However, DUGKS is proposed for near incompressible fluid flows, the existing compressible effect may cause some serious errors in simulating incompressible problems. To diminish the compressible effect, in this paper a novel DUGKS model with external force is developed for incompressible fluid flows by modifying the approximation of Maxwellian distribution. Meanwhile, due to the pressure boundary scheme, which is wildly used in many applications, has not been constructed for DUGKS, the non-equilibrium extrapolation (NEQ) scheme for both velocity and pressure boundary conditions is introduced. To illustrate the potential of the proposed model, numerical simul...

Wu, Chen; Chai, Zhenhua; Wang, Peng

2014-01-01

193

Flow in a mechanical bileaflet heart valve at laminar and near-peak systole flow rates: CFD simulations and experiments.  

PubMed

Time-accurate, fully 3D numerical simulations and particle image velocity laboratory experiments are carried out for flow through a fully open bileaflet mechanical heart valve under steady (nonpulsatile) inflow conditions. Flows at two different Reynolds numbers, one in the laminar regime and the other turbulent (near-peak systole flow rate), are investigated. A direct numerical simulation is carried out for the laminar flow case while the turbulent flow is investigated with two different unsteady statistical turbulence modeling approaches, unsteady Reynolds-averaged Navier-Stokes (URANS) and detached-eddy simulation (DES) approach. For both the laminar and turbulent cases the computed mean velocity profiles are in good overall agreement with the measurements. For the turbulent simulations, however, the comparisons with the measurements demonstrate clearly the superiority of the DES approach and underscore its potential as a powerful modeling tool of cardiovascular flows at physiological conditions. The study reveals numerous previously unknown features of the flow. PMID:16248308

Ge, Liang; Leo, Hwa-Liang; Sotiropoulos, Fotis; Yoganathan, Ajit P

2005-10-01

194

History of Suction-Type Laminar-Flow Control with Emphasis on Flight Resrearch: Monographs in Aerospace History Number 13  

NASA Technical Reports Server (NTRS)

The paper contains the following sections: Foreword; Preface; Laminar-Flow Control Concepts and Scope of Monograph; Early Research on Suction-Type Laminar-Flow Control (Research from the 1930s through the War Years; Research from after World War II to the Mid-1960s); Post X-21 Research on Suction-Type Laminar-Flow Control; Status of Laminar-Flow Control Technology in the Mid-1990s; Glossary; Document 1-Aeronautics Panel, AACB, R&D Review, Report of the Subpanel on Aeronautic Energy Conservation/Fuels; Document 2-Report of Review Group on X-21A Laminar Flow Control Program; Document 3-Langley Research Center Announcement, Establishment of Laminar Flow Control Working Group; Document 4-Intercenter Agreement for Laminar Flow Control Leading Edge Glove Flights, LaRC and DFRC; Document 5-Flight Report NLF-144, of AFTIF-111 Aircraft with the TACT Wing Modified by a Natural Laminar Flow Glove; Document 6-Flight Record, F-16XL Supersonic Laminar Flow Control Aircraft; Index; and About the Author.

Braslow, A. L.

1999-01-01

195

A coarse-grid projection method for accelerating incompressible flow computations  

NASA Astrophysics Data System (ADS)

We present a coarse-grid projection (CGP) method for accelerating incompressible flow computations, which is applicable to methods involving Poisson equations as incompressibility constraints. The CGP methodology is a modular approach that facilitates data transfer with simple interpolations and uses black-box solvers for the Poisson and advection-diffusion equations in the flow solver. After solving the Poisson equation on a coarsened grid, an interpolation scheme is used to obtain the fine data for subsequent time stepping on the full grid. A particular version of the method is applied here to the vorticity-stream function, primitive variable, and vorticity-velocity formulations of incompressible Navier-Stokes equations. We compute several benchmark flow problems on two-dimensional Cartesian and non-Cartesian grids, as well as a three-dimensional flow problem. The method is found to accelerate these computations while retaining a level of accuracy close to that of the fine resolution field, which is significantly better than the accuracy obtained for a similar computation performed solely using a coarse grid. A linear acceleration rate is obtained for all the cases we consider due to the linear-cost elliptic Poisson solver used, with reduction factors in computational time between 2 and 42. The computational savings are larger when a suboptimal Poisson solver is used. We also find that the computational savings increase with increasing distortion ratio on non-Cartesian grids, making the CGP method a useful tool for accelerating generalized curvilinear incompressible flow solvers.

San, Omer; Staples, Anne E.

2013-01-01

196

A History of Suction-Type Laminar Flow Control with Emphasis on Flight Research  

NASA Technical Reports Server (NTRS)

Laminar-flow control is an area of aeronautical research that has a long history at NASA's Langley Research Center, Dryden Flight Research Center, their predecessor organizations, and elsewhere. In this monograph, the author, who spent much of his career at Langley working with this research, presents a history of that portion of laminar-flow technology known as active laminar-flow control, which employs suction of a small quantity of air through airplane surfaces. This important technique offers the potential for significant reduction in drag and, thereby, for large increases in range or reductions in fuel usage for aircraft. For transport aircraft, the reductions in fuel consumed as a result of laminar-flow control may equal 30 percent of present consumption. Given such potential, it is obvious that active laminar-flow control with suction is an important technology. In this study, the author covers the early history of the subject and brings the story all the way to the mid-1990s with an emphasis on flight research, much of which has occurred at Dryden. This is an important monograph that not only encapsulates a lot of history in a brief compass but also does so in language that is accessible to non-technical readers. NASA is publishing it in a format that will enable it to reach the wide audience the subject deserves.

Braslow, Albert L.

1999-01-01

197

Boundary-Layer Transition Results from the F-16XL-2 Supersonic Laminar Flow Control Experiment  

NASA Technical Reports Server (NTRS)

A variable-porosity suction glove has been flown on the F-16XL-2 aircraft to demonstrate the feasibility of this technology for the proposed High-Speed Civil Transport (HSCT). Boundary-layer transition data have been obtained on the titanium glove primarily at Mach 2.0 and altitudes of 53,000-55,000 ft. The objectives of this supersonic laminar flow control flight experiment have been to achieve 50- to 60-percent-chord laminar flow on a highly swept wing at supersonic speeds and to provide data to validate codes and suction design. The most successful laminar flow results have not been obtained at the glove design point (Mach 1.9 at an altitude of 50,000 ft). At Mach 2.0 and an altitude of 53,000 ft, which corresponds to a Reynolds number of 22.7 X 10(exp 6), optimum suction levels have allowed long runs of a minimum of 46-percent-chord laminar flow to be achieved. This paper discusses research variables that directly impact the ability to obtain laminar flow and techniques to correct for these variables.

Marshall, Laurie A.

1999-01-01

198

Design of a laminar-flow-control supercritical airfoil for a swept wing  

NASA Technical Reports Server (NTRS)

An airfoil was analytically designed and analyzed for a combination of supercritical flow and laminar flow control (LFC) by boundary layer suction. A shockless inverse method was used to design an airfoil and an analysis method was used in lower surface redesign work. The laminar flow pressure distributions were computed without a boundary layer under the assumption that the laminar boundary layer would be kept thin by suction. Inviscid calculations showed that this 13.5 percent thick airfoil has shockless flows for conditions at and below the design normal Mach number of 0.73 and the design section lift coefficient of 0.60, and that the maximum local normal Mach number is 1.12 at the design point. The laminar boundary layer instabilities can be controlled with suction but the undercut leading edge of the airfoil provides a low velocity, constant pressure coefficients region which is conducive to laminar flow without suction. The airfoil was designed to be capable of lift recovery with no suction by the deflection of a small trailing edge flap.

Allison, D. O.; Dagenhart, J. R.

1978-01-01

199

A Numerical Study of Displacement Body and Curvature Effects on Incompressible and Compressible Laminar Boundary Layers. Ph.D. Thesis - Va. Polytechnic Inst.  

NASA Technical Reports Server (NTRS)

This technique has been applied to study such effects on incompressible flow around cylinders at moderate to low Reynolds numbers and for compression ramps at hypersonic Mach numbers by employing a finite difference method to obtain numerical solutions. The results indicate that the technique can be applied successfully in both regimes and does predict the correct trend in regions of large curvature and displacement body effects. It was concluded that curvature corrections should only be attempted in cases where all displacement effects can be fully accounted for.

Wornom, S. F.

1971-01-01

200

A finite volume unstructured multigrid method for efficient computation of unsteady incompressible viscous flows  

Microsoft Academic Search

An unstructured non-nested multigrid method is presented for efficient simulation of unsteady incompressible Navier-Stokes flows. The Navier-Stokes solver is based on the artificial compressibility approach and a higher-order characteristics-based finite-volume scheme on unstructured grids. Unsteady flow is calculated with an implicit dual time stepping scheme. For efficient computation of unsteady viscous flows over complex geometries, an unstructured multigrid method is

Chin Hoe Tai; Yong Zhao

2004-01-01

201

Laminar flow and heat transfer in plate-fin triangular ducts in thermally developing entry region  

Microsoft Academic Search

Laminar forced flow and heat transfer in plate-fin isosceles triangular ducts encountered in compact heat exchangers is investigated. The flow is hydrodynamically fully developed, but developing thermally under uniform temperature conditions. Heat conduction in the fin of finite conductance and convection in the fluid are analyzed simultaneously as a conjugate problem. The study covers a wide range of apex angles

Li-Zhi Zhang

2007-01-01

202

Development of advanced stability theory suction prediction techniques for laminar flow control. [on swept wings  

NASA Technical Reports Server (NTRS)

The problem of obtaining accurate estimates of suction requirements on swept laminar flow control wings was discussed. A fast accurate computer code developed to predict suction requirements by integrating disturbance amplification rates was described. Assumptions and approximations used in the present computer code are examined in light of flow conditions on the swept wing which may limit their validity.

Srokowski, A. J.

1978-01-01

203

Transient thermal entrance heat transfer in laminar pipe flows with step change in pumping pressure  

Microsoft Academic Search

Analysis is made for the transient heat transfer phenomena in the thermal entrance region of laminar pipe flows. The transient results from both the change in flow field, a step change in pressure gradient from zero to a fixed value, and the change in thermal field, a step change in the inlet temperature. An exponential scheme has been employed to

T. F. Lin; K. H. Hawks; W. Leidenfrost

1983-01-01

204

On the efficiency of a numerical method with periodic time strides for solving incompressible flows  

Microsoft Academic Search

An explicit numerical method to solve the unsteady incompressible flow equations consisting on N small time steps ?t between each two much larger time steps (?t)1 is considered. The stability and efficiency of the method is first analyzed using the one-dimensional diffusion equation. It is shown that the use of a time step ?t slightly smaller than the critical one

E. Sanmiguel-Rojas; J. Ortega-Casanova; R. Fernandez-Feria

2003-01-01

205

On the efficiency of an explicit numerical method with periodic time strides for solving incompressible flows  

Microsoft Academic Search

An explicit numerical method to solve the unsteady incompressible flow equations consisting on N small time steps Delta t between each two much larger time steps (Delta t)1 is considered. The stability and efficiency of the method is first analyzed using the one dimensional diffusion equation. It is shown that the use of a time step Delta t slightly smaller

Ramon Fernandez-Feria; Enrique Sanmiguel-Rojas; Joaquin Ortega-Casanova

2001-01-01

206

Time accuracy and spurious transients of projection methods for viscous incompressible flows  

E-print Network

Time accuracy and spurious transients of projection methods for viscous incompressible flows considered result from algebraically splitting the linear system corresponding to each time step of first, second and third order in the time step size t are obtained, depending on the method. The methods

Buscaglia, Gustavo C.

207

NACHOS 2: A finite element computer program for incompressible flow problems. Part 1: Theoretical background  

Microsoft Academic Search

The theoretical and numerical background for the finite element computer program, NACHOS 2, is presented in detail. The NACHOS 2 code is designed for the two-dimensional analysis of viscous incompressible fluid flows, including the effects of heat transfer and\\/or other transport processes. A general description of the boundary value problems treated by the program is presented. The finite element formulations

D. K. Gartling

1987-01-01

208

NACHOS: A finite element computer program for incompressible flow problems. Part 1: Theoretical background  

Microsoft Academic Search

The NACHOS code designed for the two-dimensional analysis of viscous incompressible fluid flows, including the effects of heat transfer, is described as well as the fluid\\/thermal boundary value problems treated by the program. The finite element method and the associated numerical methods used are also presented.

D. K. Gartling

1978-01-01

209

Progress in incompressible Navier-Stokes computations for propulsion flows and its dual-use applications  

NASA Technical Reports Server (NTRS)

Development of an incompressible Navier-Stokes solution procedure was performed for the analysis of a liquid rocket engine pump components and for the mechanical heart assist devices. The solution procedure for the propulsion systems is applicable to incompressible Navier-Stokes flows in a steadily rotating frame of reference for any general complex configurations. The computer codes were tested on different complex configurations such as liquid rocket engine inducer and impellers. As a spin-off technology from the turbopump component simulations, the flow analysis for an axial heart pump was conducted. The baseline Left Ventricular Assist Device (LVAD) design was improved by adding an inducer geometry by adapting from the liquid rocket engine pump. The time-accurate mode of the incompressible Navier-Stokes code was validated with flapping foil experiment by using different domain decomposition methods. In the flapping foil experiment, two upstream NACA 0025 foils perform high-frequency synchronized motion and generate unsteady flow conditions for a downstream larger stationary foil. Fairly good agreement was obtained between unsteady experimental data and numerical results from two different moving boundary procedures. Incompressible Navier-Stokes code (INS3D) has been extended for heat transfer applications. The temperature equation was written for both forced and natural convection phenomena. Flow in a square duct case was used for the validation of the code in both natural and forced convection.

Kiris, Cetin

1995-01-01

210

Low-Disturbance Flow Characteristics of the NASA-Ames Laminar Flow Supersonic Wind Tunnel  

NASA Technical Reports Server (NTRS)

A unique, low-disturbance (quiet) supersonic wind tunnel has been commissioned at the NASA-Ames Fluid Mechanics Laboratory (FML) to support Supersonic Laminar Flow Control (SLFC) research. Known as the Laminar Flow Supersonic Wind Tunnel (LFSWT), this tunnel is designed to operate at potential cruise Mach numbers and unit Reynolds numbers (Re) of the High Speed Civil Transport (HSCT). The need to better understand the receptivity of the transition phenomena on swept (HSCT) wings to attachment-line contamination and cross-flows has provided the impetus for building the LFSWT. Low-disturbance or "quiet" wind tunnels are known to be an essential part of any meaningful boundary layer transition research. In particular, the receptivity of supersonic boundary layers to wind tunnel disturbances can significantly alter the transition phenomena under investigation on a test model. Consequently, considerable effort has gone into the design of the LFSWT to provide quiet flow. The paper describes efforts to quantify the low-disturbance flows in the LFSWT operating at Mach 1.6, as a precursor to transition research on wing models. The research includes: (1) Flow measurements in both the test section and settling chamber of the LFSWT, using a full range of measurement techniques; (2) Study of the state of the test section boundary layer so far by using a single hot-wire mounted above the floor centerline, with and without boundary layer trips fitted at the test section entrance; (3) The effect of flow quality of unsteady supersonic diffuser flow, joint steps and gaps, and wall vibration.

Wolf, Stephen W. D.; Laub, James A.; Davis, Sanford S. (Technical Monitor)

1994-01-01

211

Summary of Transition Results From the F-16XL-2 Supersonic Laminar Flow Control Experiment  

NASA Technical Reports Server (NTRS)

A variable-porosity suction glove has been flown on the F-16XL-2 aircraft to demonstrate the feasibility of this technology for the proposed High-Speed Civil Transport. Boundary-layer transition data on the titanium glove primarily have been obtained at speeds of Mach 2.0 and altitudes of 15,240-16,764 m (50,000-55,000 ft). The objectives of this flight experiment have been to achieve 0.50-0.60 chord laminar flow on a highly swept wing at supersonic speeds and to provide data to validate codes and suction design. The most successful laminar flow results have not been obtained at the glove design point, a speed of Mach 1.9 at an altitude of 15,240 m (50,000 ft); but rather at a speed of Mach 2.0 and an altitude of 16,154 m (53,000 ft). Laminar flow has been obtained to more than 0.46 wing chord at a Reynolds number of 22.7 x 10(exp 6). A turbulence diverter has been used to initially obtain a laminar boundary layer at the attachment line. A lower-surface shock fence was required to block an inlet shock from the wing leading edge. This paper discusses research variables that directly impact the ability to obtain laminar flow and techniques to correct for these variables.

Marshall, Laurie A.

2000-01-01

212

An approach to the constrained design of natural laminar flow airfoils  

NASA Technical Reports Server (NTRS)

A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integml turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the larninar flow toward the desired amounl An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.

Green, Bradford Earl

1995-01-01

213

High Reynolds Number Hybrid Laminar Flow Control (HLFC) Flight Experiment. Report 2; Aerodynamic Design  

NASA Technical Reports Server (NTRS)

This document describes the aerodynamic design of an experimental hybrid laminar flow control (HLFC) wing panel intended for use on a Boeing 757 airplane to provide a facility for flight research on high Reynolds number HLFC and to demonstrate practical HLFC operation on a full-scale commercial transport airplane. The design consists of revised wing leading edge contour designed to produce a pressure distribution favorable to laminar flow, definition of suction flow requirements to laminarize the boundary layer, provisions at the inboard end of the test panel to prevent attachment-line boundary layer transition, and a Krueger leading edge flap that serves both as a high lift device and as a shield to prevent insect accretion on the leading edge when the airplane is taking off or landing.

1999-01-01

214

An approach to aerodynamic sound prediction based on incompressible-flow pressure  

NASA Astrophysics Data System (ADS)

Curle's analogy provides a solution to Lighthill's equation to predict flow-generated sound in the presence of rigid boundaries. Nevertheless, Curle's solution requires the flow pressure, including its acoustic component, to be known in the source region. If the pressure corresponds to an incompressible-flow description instead and the surface is not acoustically compact, significant errors can arise in the acoustic prediction. In this work, it is argued that flow wall pressure can be used to define appropriate boundary conditions of an equivalent acoustic boundary value problem for an arbitrary geometry, and a formulation of a boundary condition based on incompressible-flow pressure is proposed. The theoretical analysis suggests that if the flow is incompressible, the error has the leading order of a dipole plus a quadrupole for Curle's analogy and of just a quadrupole for the proposed alternative approach, thus making the latter more accurate when dipole sources are dominant. A numerical test case is presented as a proof of concept, consisting of a trailing edge noise problem due to the flow past a slender body.

Martínez-Lera, P.; Schram, C.; Bériot, H.; Hallez, R.

2014-01-01

215

Laminar flow studies of a low-temperature space radiator model using D-shaped tubes  

NASA Technical Reports Server (NTRS)

Test results of a low-temperature space radiator model are presented. Radiator performance is evaluated with a low-thermal-conductivity fluid in laminar flow in D-shaped cross-section tubes. The test covered a Reynolds number range from 50 to 4500 and a fluid temperature range from 294 to 414 K (70 to 286 F). For low-temperature radiators, the fluid-to-surface temperature differential was predominately influenced by fluid temperature in laminar flow. Heat transfer and pressure drop for the radiator tube could be predicted within engineering accuracy from existing correlations.

Cintula, T. C.; Prok, G. M.; Johnston, D. B.

1972-01-01

216

Start of fluidization of a bulk granular material in laminar flow  

SciTech Connect

This report examines the usage and transformation of an equation of the form Re/sub cr/=Ar(1400+5.22/Ar) which is used in design calculations for determination of the velocity of the start of fluidization of a granular material bearing initial voidage e/sub o/=0.4. Variations of the Reynold's number corresponding to the Critical Fluidization velocity at various voidages of the granular bed and different values of the Archimedes number in laminar flow are presented. Results indicate that the equation cannot be recommended for use even for rough estimates of the bulk materials in laminar flow.

Rozhdestvenskii, O.I.; Bednyakov, G.E.; Zayats, E.I.; Kirillov, I.N.; Serebryakova, T.V.

1982-04-20

217

Incompressible viscous flow computations for the pump components and the artificial heart  

NASA Technical Reports Server (NTRS)

A finite-difference, three-dimensional incompressible Navier-Stokes formulation to calculate the flow through turbopump components is utilized. The solution method is based on the pseudocompressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. Both steady and unsteady flow calculations can be performed using the current algorithm. In this work, the equations are solved in steadily rotating reference frames by using the steady-state formulation in order to simulate the flow through a turbopump inducer. Eddy viscosity is computed by using an algebraic mixing-length turbulence model. Numerical results are compared with experimental measurements and a good agreement is found between the two. Included in the appendix is a paper on incompressible viscous flow through artificial heart devices with moving boundaries. Time-accurate calculations, such as impeller and diffusor interaction, will be reported in future work.

Kiris, Cetin

1992-01-01

218

Incompressible turbulent flow calculation in body-fitted coordinates using block-implicit finite difference method  

Microsoft Academic Search

The block-implicit finite-difference method is used to calculate 3D incompressible turbulent flows in the body-fitted coordinate system. In the numerical discretization the hybrid difference scheme is used to treat Reynolds-averaged Navier-Stokes equations. The iterative solution of velocities and pressure on the flow field is obtained by solving simultaneously the Reynolds-averaged N-S equations and continuity equation for each cell. In the

Zeming Hu; Xuechun Chen; Yulin Wu

1991-01-01

219

Aerodynamic design of a midsized vertical-axis wind turbine using natural laminar-flow blade elements  

Microsoft Academic Search

Natural laminar-flow (NLF) airfoils are those which can achieve significant extents of laminar flow (greater than or equal to 30% chord) solely through favorable pressure gradients. Studies have shown that vertical-axis wind turbines (VAWTs) using NLF sections as blade elements have the potential of producing energy at a significantly lower cost (approx. =20%) than turbines of current design. Sandia National

P. C. Klimas; D. E. Berg

1983-01-01

220

Direct pore-level modeling of incompressible fluid flow in porous media  

NASA Astrophysics Data System (ADS)

We present a dynamic particle-based model for direct pore-level modeling of incompressible viscous fluid flow in disordered porous media. The model is capable of simulating flow directly in three-dimensional high-resolution micro-CT images of rock samples. It is based on moving particle semi-implicit (MPS) method. We modify this technique in order to improve its stability for flow in porous media problems. Using the micro-CT image of a rock sample, the entire medium, i.e., solid and fluid, is discretized into particles. The incompressible Navier-Stokes equations are then solved for each particle using the MPS summations. The model handles highly irregular fluid-solid boundaries effectively. An algorithm to split and merge fluid particles is also introduced. To handle the computational load, we present a parallel version of the model that runs on distributed memory computer clusters. The accuracy of the model is validated against the analytical, numerical, and experimental data available in the literature. The validated model is then used to simulate both unsteady- and steady-state flow of an incompressible fluid directly in a representative elementary volume (REV) size micro-CT image of a naturally-occurring sandstone with 3.398 ?m resolution. We analyze the quality and consistency of the predicted flow behavior and calculate absolute permeability using the steady-state flow rate.

Ovaysi, Saeed; Piri, Mohammad

2010-09-01

221

Direct pore-level modeling of incompressible fluid flow in porous media  

SciTech Connect

We present a dynamic particle-based model for direct pore-level modeling of incompressible viscous fluid flow in disordered porous media. The model is capable of simulating flow directly in three-dimensional high-resolution micro-CT images of rock samples. It is based on moving particle semi-implicit (MPS) method. We modify this technique in order to improve its stability for flow in porous media problems. Using the micro-CT image of a rock sample, the entire medium, i.e., solid and fluid, is discretized into particles. The incompressible Navier-Stokes equations are then solved for each particle using the MPS summations. The model handles highly irregular fluid-solid boundaries effectively. An algorithm to split and merge fluid particles is also introduced. To handle the computational load, we present a parallel version of the model that runs on distributed memory computer clusters. The accuracy of the model is validated against the analytical, numerical, and experimental data available in the literature. The validated model is then used to simulate both unsteady- and steady-state flow of an incompressible fluid directly in a representative elementary volume (REV) size micro-CT image of a naturally-occurring sandstone with 3.398 {mu}m resolution. We analyze the quality and consistency of the predicted flow behavior and calculate absolute permeability using the steady-state flow rate.

Ovaysi, Saeed, E-mail: sovaysi@uwyo.ed [Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, WY 82071-2000 (United States); Piri, Mohammad, E-mail: mpiri@uwyo.ed [Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, WY 82071-2000 (United States)

2010-09-20

222

Feasibility and benefits of laminar flow control on supersonic cruise airplanes  

NASA Technical Reports Server (NTRS)

An evaluation was made of the applicability and benefits of laminar flow control (LFC) technology to supersonic cruise airplanes. Ancillary objectives were to identify the technical issues critical to supersonic LFC application, and to determine how those issues can be addressed through flight and wind-tunnel testing. Vehicle types studied include a Mach 2.2 supersonic transport configuration, a Mach 4.0 transport, and two Mach 2-class fighter concepts. Laminar flow control methodologies developed for subsonic and transonic wing laminarization were extended and applied. No intractible aerodynamic problems were found in applying LFC to airplanes of the Mach 2 class, even ones of large size. Improvements of 12 to 17 percent in lift-drag ratios were found. Several key technical issues, such as contamination avoidance and excresence criteria were identified. Recommendations are made for their resolution. A need for an inverse supersonic wing design methodology is indicated.

Powell, A. G.; Agrawal, S.; Lacey, T. R.

1989-01-01

223

Dispersion of swimming algae in laminar and turbulent channel flows: theory and simulations  

E-print Network

Algal swimming is often biased by environmental cues, e.g. gravitational and viscous torques drive cells towards downwelling fluid (gyrotaxis). In view of biotechnological applications, it is important to understand how such biased swimming affects cell dispersion in a flow. Here, we study the dispersion of gyrotactic swimming algae in laminar and turbulent channel flows. By direct numerical simulation (DNS) of cell motion within upwelling and downwelling channel flows, we evaluate time-dependent measures of dispersion for increasing values of the flow Peclet (Reynolds) numbers, Pe (Re). Furthermore, we derive an analytical `swimming Taylor-Aris dispersion' theory, using flow-dependent transport parameters given by existing microscopic models. In the laminar regime, DNS results and analytical predictions compare very well, providing the first confirmation that cells' response to flow is best described by the generalized-Taylor-dispersion microscopic model. We predict that cells drift along a channel faster th...

Croze, O A; Ahmed, M; Bees, M A; Brandt, L

2012-01-01

224

Nacelle/pylon/wing integration on a transport model with a natural laminar flow nacelle  

NASA Technical Reports Server (NTRS)

Tests were conducted in the Langley 16-Foot Transonic Tunnel at free-stream Mach numbers from 0.70 to 0.82 and angles of attack from -2.5 deg to 4.0 deg to determine if nacelle/pylon/wing integration affects the achievement of natural laminar flow on a long-duct flow-through nacelle for a high-wing transonic transport configuration. In order to fully assess the integration effect on a nacelle designed to achieve laminar flow, the effects of fixed and free nacelle transitions as well as nacelle longitudinal position and pylon contouring were obtained. The results indicate that the ability to achieve laminar flow on the nacelle is not significantly altered by nacelle/pylon/wing integration. The increment in installed drag between free and fixed transition for the nacelles on symmetrical pylons is essentially the calculated differences between turbulent and laminar flow on the nacelles. The installed drag of the contoured pylon is less than that of the symmetrical pylon. The installed drag for the nacelles in a rearward position is greater than that for the nacelles in a forward position.

Lamb, M.; Aabeyounis, W. K.; Patterson, J. C., Jr.

1985-01-01

225

Effect of varied air flow on flame structure of laminar inverse diffusion flames  

Microsoft Academic Search

The structure of laminar inverse diffusion flames (IDFs) of methane and ethylene was studied using a cylindrical co-flowing burner. Several flames of the same fuel flow-rate yet various air flow-rates were examined. Heights of visible flames were obtained using measurements of hydroxyl (OH) laser-induced fluorescence (LIF) and visible images. Polycyclic aromatic hydrocarbon (PAH) LIF and soot laser-induced incandescence (LII) were

Christopher R. Shaddix; Timothy C. Williams; Linda Gail Blevins; Mark A. Mikofski

2004-01-01

226

DNS of a Laminar Separation Bubble in the Presence of Oscillating External Flow  

Microsoft Academic Search

A three-dimensional Direct Numerical Simulation (DNS) of a laminar separation bubble in the presence of oscillating flow is\\u000a performed. The oscillating flow induces a streamwise pressure gradient varying in time. The special shape of the upper boundary\\u000a of the computational domain, together with the oscillating pressure gradient causes the boundary layer flow to alternately\\u000a separate and re-attach. When the inflow

J. G. Wissink; W. Rodi

2003-01-01

227

A theoretical method for the analysis and design of axisymmetric bodies. [flow distribution and incompressible fluids  

NASA Technical Reports Server (NTRS)

A theoretical method is presented for the computation of the flow field about an axisymmetric body operating in a viscous, incompressible fluid. A potential flow method was used to determine the inviscid flow field and to yield the boundary conditions for the boundary layer solutions. Boundary layer effects in the forces of displacement thickness and empirically modeled separation streamlines are accounted for in subsequent potential flow solutions. This procedure is repeated until the solutions converge. An empirical method was used to determine base drag allowing configuration drag to be computed.

Beatty, T. D.

1975-01-01

228

Dispersion of swimming algae in laminar and turbulent channel flows: consequences for photobioreactors  

PubMed Central

Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary to understand how such biases affect algal dispersion in natural and industrial flows, especially in view of growing interest in algal photobioreactors. Motivated by this, we here study the dispersion of gyrotactic algae in laminar and turbulent channel flows using direct numerical simulation (DNS) and a previously published analytical swimming dispersion theory. Time-resolved dispersion measures are evaluated as functions of the Péclet and Reynolds numbers in upwelling and downwelling flows. For laminar flows, DNS results are compared with theory using competing descriptions of biased swimming cells in shear flow. Excellent agreement is found for predictions that employ generalized Taylor dispersion. The results highlight peculiarities of gyrotactic swimmer dispersion relative to passive tracers. In laminar downwelling flow the cell distribution drifts in excess of the mean flow, increasing in magnitude with Péclet number. The cell effective axial diffusivity increases and decreases with Péclet number (for tracers it merely increases). In turbulent flows, gyrotactic effects are weaker, but discernable and manifested as non-zero drift. These results should have a significant impact on photobioreactor design. PMID:23407572

Croze, Ottavio A.; Sardina, Gaetano; Ahmed, Mansoor; Bees, Martin A.; Brandt, Luca

2013-01-01

229

Some Rotational Flows of an Incompressible Fluid of Variable Viscosity  

Microsoft Academic Search

f is a function, ? the stream function, () 0 a ? and b are the arbitrary constants. In three, out of four cases, the function ( ) x f is arbitrary, and the solutions are the solutions of the flow equations for all the flows characterized by the equation ( ) b a x f y + ? +

Rana Khalid Naeem; Waseem Ahmed Khan; Muhammad Akhtar; Asif Mansoor

2009-01-01

230

FINITE ELEMENT METHODS FOR THE SIMULATION OF INCOMPRESSIBLE POWDER FLOW  

E-print Network

with high numerical efficiency. The results of several computational experiments for realistic flow. The flowing of powders brings a new challenging and interesting problem to the CFD community: at very high concentrations and low rate-of-strain, grains are in permanent contact, rolling on each other. Therefore

Hron, Jaroslav

231

A fast Multigrid method for 3-D turbulent incompressible flows  

Microsoft Academic Search

The averaged Navier-Stokes and the k-epsilon turbulence model equations are used to simulate turbulent flows in some internal flow cases. The discrete equations are solved by different variants of Multigrid methods. These include both steady state as well as time dependent solvers. Local grid refinements are possible in all cases. The Multigrid schemes result in fast convergence rate, whereas local

X. S. Bai; L. Fuchs

1991-01-01

232

Formation of Two-Dimensional Sand Ripples under Laminar Shear Flow Vincent Langlois and Alexandre Valance  

E-print Network

Formation of Two-Dimensional Sand Ripples under Laminar Shear Flow Vincent Langlois and Alexandre 20 June 2005) The process of ripple formation on a two-dimensional sand bed sheared by a viscous fluid is investigated theoretically. The sand transport is described taking into account both the local

233

Two-fluid modeling of aerosol transport in laminar and turbulent flows  

Microsoft Academic Search

The two-fluid model has been adapted to dilute dispersions of dense inclusions (i.e. particles) carried by laminar or turbulent flows where an exchange of momentum takes place between particles and fluid. It is assumed that the medium is isothermal and free of phase change. The model is used to simulate different experimental applications and the simulations are compared to the

P. Armand; D. Boulaud; M. Pourprix; J. Vendel

1998-01-01

234

AIR-BREATHING LAMINAR FLOW BASED MICROFLUIDIC FUEL CELL Ranga S. Jayashree1  

E-print Network

bipolar plate purchased from Fuel Cell Stores.com) was cleaned by sonication in large portions of Milli of the laminar flow-based microfluidic fuel cell. A 5-mm thick graphite plate (anode, fuel cell grade graphite. The catalyst ink was added drop wise onto the exposed area of the graphite plate, between the second inlet

Kenis, Paul J. A.

235

Excitation of bioluminescence by laminar fluid shear associated with simple Couette flow  

Microsoft Academic Search

The effect of fluid motion on the excitation of bioluminescence was examined for cultured dinoflagellates and plankton samples subjected to steady state laminar shear associated with simple Couette flow estab- lished in the gap between concentric cylinders with only the outer cylinder rotating. The excitation threshold for the thecate dinoflagellate, Gonyaulax polyedra, occurred at a shear stress of 1 dyn

MICHAEL I. LATZ; JAMES F. CASE; ROBERT L. GRAN

1994-01-01

236

EXPERIMENTS WITH HEAVY GAS JETS IN LAMINAR AND TURBULENT CROSS-FLOWS  

EPA Science Inventory

A wind tunnel study was performed to determine the dispersion characteristics of gas jets with densities heavier than that of air. he experiments were done in a laminar cross-flow and then repeated in a turbulent boundary layer. ll major boundary-layer characteristics were measur...

237

An experimental investigation of the flow of a laminar boundary layer into a suction slot  

Microsoft Academic Search

The problem of the flow of a laminar boundary layer into a suction slot has been examined experimentally in a low turbulence water channel. A dimensional analysis is used to determine the variables that are important to the problem and these are found to be the slot Reynolds number and a new parameter that is introduced to describe the mean

A. S. W. Thomas; K. C. Cornelius

1981-01-01

238

Laminar Forced Convection Heat Transfer From Isothermal Bodies With Unity Aspect Ratio in Coaxial Air Flow  

Microsoft Academic Search

In this article a semianalytical approach is employed to obtain dimensionless heat transfer correlations for forced convection over three geometries—sphere, cone, and cylinder with unity aspect ratio in laminar axial air flow. The comparison of the present results for a sphere with the previous work shows very good agreement. For example, the average difference between the results of the present

Yaser Hadad; Khosrow Jafarpur

2012-01-01

239

Heat transfer optimization in internally finned tubes under laminar flow conditions  

Microsoft Academic Search

In the present work the problem of optimizing the geometry of internally finned tubes in order to enhance the heat transfer under laminar flow conditions is studied. The velocity and temperature distributions on the finned tube cross-section are determined with the help of a finite element model, and a global heat transfer coefficient is calculated. A polynomial lateral profile is

Giampietro Fabbri

1998-01-01

240

Second Law Analysis of Laminar Flow In A Channel Filled With Saturated Porous Media  

Microsoft Academic Search

The entropy generation rate in a laminar flow through a channel filled with saturated porous media is investigated. The upper surface of the channel is adiabatic and the lower wall is assumed to have a constant heat flux. The Brinkman model is employed. Velocity and temperature profiles are obtained for large Darcy number (Da) and used to obtain the entropy

O. D. Makinde; E. Osalusi

2005-01-01

241

Simultaneous wall and fluid axial conduction in laminar pipe-flow heat transfer  

Microsoft Academic Search

Consideration is given to a laminar pipe flow in which the upstream portion of the wall is externally insulated while the downstream portion of the wall is uniformly heated. An analysis of the problem is performed whose special feature is the accounting of axial conduction in both the tube wall and in the fluid. This conjugate heat transfer problem is

M. Faghri; E. M. Sparrow

1980-01-01

242

Heat transfer enhancement in laminar slurry pipe flows with power law thermal conductivities  

Microsoft Academic Search

Generalized theoretical results for heat transfer in laminar pipe flow with power law varying thermal conductivities are presented. The study is motivated by experimental observations that above a threshold shear rate the effective thermal conductivity for disperse two-phase mixtures increases with shear rate. Using a relatively general three parameter power law model for conductivity as a function of shear rate,

C. W. Sohn; M. M. Chen

1984-01-01

243

CFD Investigations of a Transonic Swept-Wing Laminar Flow Control Flight Experiment  

E-print Network

of a swept-wing typical of a transport aircraft represents a promising technique able to control crossflow and delay transition to accomplish the goal of increased laminar flow. Recently, the Flight Research Laboratory at Texas A&M University conducted...

Neale, Tyler P.

2011-08-08

244

LABORATORY AND NUMERICAL INVESTIGATIONS OF RESIDENCE TIME DISTRIBUTION OF FLUIDS IN LAMINAR FLOW STIRRED ANNULAR PHOTOREACTOR  

EPA Science Inventory

Laboratory and Numerical Investigations of Residence Time Distribution of Fluids in Laminar Flow Stirred Annular Photoreactor E. Sahle-Demessie1, Siefu Bekele2, U. R. Pillai1 1U.S. EPA, National Risk Management Research Laboratory Sustainable Technology Division,...

245

The use of laminar flow for obtaining germ-free mice.  

PubMed

Hysterectomy in a laminar-flow cabinet affords greater economy of time and effort in obtaining germ-free mice than other methods. No contamination has occurred during the surgical procedure or in the subsequent transfer of the neonates into germ-free isolators. PMID:1207038

Taylor, D M

1975-10-01

246

Operating Room Environment Control. Part A: a Valve Cannister System for Anesthetic Gas Adsorption. Part B: a State-of-the-art Survey of Laminar Flow Operating Rooms. Part C: Three Laminar Flow Experiments  

NASA Technical Reports Server (NTRS)

An anesthetic gas flow pop-off valve canister is described that is airtight and permits the patient to breath freely. Once its release mechanism is activated, the exhaust gases are collected at a hose adapter and passed through activated coal for adsorption. A survey of laminar air flow clean rooms is presented and the installation of laminar cross flow air systems in operating rooms is recommended. Laminar flow ventilation experiments determine drying period evaporation rates for chicken intestines, sponges, and sections of pig stomach.

Meyer, J. S.; Kosovich, J.

1973-01-01

247

Preliminary Investigation of Certain Laminar-Flow Airfoils for Application at High Speeds and Reynolds Numbers  

NASA Technical Reports Server (NTRS)

In order to extend the useful range of Reynolds numbers of airfoils designed to take advantage of the extensive laminar boundary layers possible in an air stream of low turbulence, tests were made of the NACA 2412-34 and 1412-34 sections in the NACA low-turbulence tunnel. Although the possible extent of the laminar boundary layer on these airfoils is not so great as for specially designed laminar-flow airfoils, it is greater than that for conventional airfoils, and is sufficiently extensive so that at Reynolds numbers above 11,000,000 the laminar region is expected to be limited by the permissible 'Reynolds number run' and not by laminar separation as is the case with conventional airfoils. Drag measurements by the wake-survey method and pressure-distribution measurements were made at several lift coefficients through a range of Reynolds numbers up to 11,400,000. The drag scale-effect curve for the NACA 1412-34 is extrapolated to a Reynolds number of 30,000,000 on the basis of theoretical calculations of the skin friction. Comparable skin-friction calculations were made for the NACA 23012. The results indicate that, for certain applications at moderate values of the Reynolds number, the NACA 1412-34 and 2412-34 airfoils offer some advantages over such conventional airfoils as the NACA 23012. The possibility of maintaining a more extensive laminar boundary layer on these airfoils should result in a small drag reduction, and the absence of pressure peaks allows higher speeds to be reached before the compressibility burble is encountered. At lower Reynold numbers, below about 10,000,000, these airfoils have higher drags than airfoils designed to operate with very extensive laminar boundary layers.

Jacobs, E.N.; Abbott, Ira H.; von Doenhoff, A.E.

1939-01-01

248

Laminar and turbulent nozzle-jet flows and their acoustic near-field  

NASA Astrophysics Data System (ADS)

We investigate numerically the effects of nozzle-exit flow conditions on the jet-flow development and the near-field sound at a diameter-based Reynolds number of ReD = 18 100 and Mach number Ma = 0.9. Our computational setup features the inclusion of a cylindrical nozzle which allows to establish a physical nozzle-exit flow and therefore well-defined initial jet-flow conditions. Within the nozzle, the flow is modeled by a potential flow core and a laminar, transitional, or developing turbulent boundary layer. The goal is to document and to compare the effects of the different jet inflows on the jet flow development and the sound radiation. For laminar and transitional boundary layers, transition to turbulence in the jet shear layer is governed by the development of Kelvin-Helmholtz instabilities. With the turbulent nozzle boundary layer, the jet flow development is characterized by a rapid changeover to a turbulent free shear layer within about one nozzle diameter. Sound pressure levels are strongly enhanced for laminar and transitional exit conditions compared to the turbulent case. However, a frequency and frequency-wavenumber analysis of the near-field pressure indicates that the dominant sound radiation characteristics remain largely unaffected. By applying a recently developed scaling procedure, we obtain a close match of the scaled near-field sound spectra for all nozzle-exit turbulence levels and also a reasonable agreement with experimental far-field data.

Bühler, Stefan; Obrist, Dominik; Kleiser, Leonhard

2014-08-01

249

Novel features of a fully developed mixing-layer between co-flowing laminar and turbulent Couette flows  

NASA Astrophysics Data System (ADS)

A new flow configuration has been proposed in which a bilateral mixing-layer exists in the junction between co-flowing laminar and turbulent plane Couette flows. Contrary to a classical plane mixing-layer, the present mixing-layer did neither grow in time nor in streamwise direction. However, the mixing zone varied with the distance from the stationary wall. A direct numerical simulation showed that very-large-scale flow structures were found in the turbulent part of the flow with Reynolds number 1300 based on half the velocity U1 of the fastest-moving wall and half of the distance 2h between the walls. The laminar-turbulent interface exhibited a large-scale meandering motion with frequency 0.014U1/h and wavelength about 25h. Large-scale Taylor-Görtler-like roll cells were observed in the nominally laminar flow region with Reynolds number 260. This tailor-made flow is particularly well suited for explorations of momentum transfer and intermittency in the vicinity of the laminar-turbulent interface.

Narasimhamurthy, Vagesh D.; Andersson, Helge I.; Pettersen, Bjørnar

2014-03-01

250

Computing three-dimensional incompressible flows with vortex elements  

NASA Technical Reports Server (NTRS)

The techniques, capabilities and applicability of numerical models of three-dimensional, unsteady vortical flows with high Re are assessed. Vorticity is calculated only in appropriate regions and the velocity field is derived from the boundary conditions. Vorticity is assumed to take the shape of tubes with uniform core structures in the case of turbulence. The efforts being made to simplify equations for dense collections of vortex filaments in order to make them tractable to computer simulations are described. The effectiveness of vorticity arrow representations for accurately describing vorticity fields near surfaces is discussed, along with Lagrangian vortex elements, which may be of use in modelling the rotational part of flows around bluff bodies, nonuniform density flows and chemically reacting flows.

Leonard, A.

1985-01-01

251

Analysis and evaluation of an integrated laminar flow control propulsion system  

NASA Technical Reports Server (NTRS)

Reduction of drag has been a major goal of the aircraft industry as no other single quantity influences the operating costs of transport aircraft more than aerodynamic drag. It has been estimated that even modest reduction of frictional drag could reduce fuel costs by anywhere from 2 to 5 percent. Current research on boundary layer drag reduction deals with various approaches to reduce turbulent skin friction drag as a means of improving aircraft performance. One of the techniques belonging to this category is laminar flow control in which extensive regions of laminar flow are maintained over aircraft surfaces by delaying transition to turbulence through the ingestion of boundary layer air. While problems of laminar flow control have been studied in some detail, the prospect of improving the propulsion system of an aircraft by the use of ingested boundary layer air has received very little attention. An initial study for the purpose of reducing propulsion system requirements by utilizing the kinetic energy of boundary layer air was performed in the mid-1970's at LeRC. This study which was based on ingesting the boundary layer air at a single location, did not yield any significant overall propulsion benefits; therefore, the concept was not pursued further. However, since then it has been proposed that if the boundary layer air were ingested at various locations on the aircraft surface instead of just at one site, an improvement in the propulsion system might be realized. The present report provides a review of laminar flow control by suction and focuses on the problems of reducing skin friction drag by maintaining extensive regions of laminar flow over the aircraft surfaces. In addition, it includes an evaluation of an aircraft propulsion system that is augmented by ingested boundary layer air.

Keith, Theo G., Jr.; Dewitt, Kenneth J.

1993-01-01

252

Higher-Order Compact Schemes for Numerical Simulation of Incompressible Flows  

NASA Technical Reports Server (NTRS)

A higher order accurate numerical procedure has been developed for solving incompressible Navier-Stokes equations for 2D or 3D fluid flow problems. It is based on low-storage Runge-Kutta schemes for temporal discretization and fourth and sixth order compact finite-difference schemes for spatial discretization. The particular difficulty of satisfying the divergence-free velocity field required in incompressible fluid flow is resolved by solving a Poisson equation for pressure. It is demonstrated that for consistent global accuracy, it is necessary to employ the same order of accuracy in the discretization of the Poisson equation. Special care is also required to achieve the formal temporal accuracy of the Runge-Kutta schemes. The accuracy of the present procedure is demonstrated by application to several pertinent benchmark problems.

Wilson, Robert V.; Demuren, Ayodeji O.; Carpenter, Mark

1998-01-01

253

Correlation of Water Frost Porosity in Laminar Flow over Flat Surfaces  

NASA Technical Reports Server (NTRS)

A dimensionless correlation has been proposed for water frost porosity expressing its dependence on frost surface temperature and Reynolds number for laminar forced flow over a flat surface. The correlation is presented in terms of a dimensionless frost surface temperature scaled with the cold plate temperature, and the freezing temperature. The flow Reynolds number is scaled with reference to the critical Reynolds number for laminar-turbulent transition. The proposed correlation agrees satisfactorily with the simultaneous measurements of frost density and frost surface temperature covering a range of plate temperature, ambient air velocity, humidity, and temperature. It is revealed that the frost porosity depends primarily on the frost surface and the plate temperatures and the flow Reynolds number, and is only weakly dependent on the relative humidity. The results also point out the general character of frost porosity displaying a decrease with an increase in flow Reynolds number.

Kandula, Max

2011-01-01

254

An advanced meshless LBIE\\/RBF method for solving two-dimensional incompressible fluid flows  

Microsoft Academic Search

The present work presents a meshless local boundary integral equation (LBIE) method for the solution of two-dimensional incompressible\\u000a fluid flow problems governed by the Navier–Stokes equations. The method uses, for its meshless implementation, nodal points\\u000a spread over the analyzed domain and employs in an efficient way the radial basis functions (RBF) for the interpolation of\\u000a the interior and boundary variables.

Euripides J. Sellountos; Adélia Sequeira

2008-01-01

255

A p-version finite element method for steady incompressible fluid flow and convective heat transfer  

NASA Technical Reports Server (NTRS)

A new p-version finite element formulation for steady, incompressible fluid flow and convective heat transfer problems is presented. The steady-state residual equations are obtained by considering a limiting case of the least-squares formulation for the transient problem. The method circumvents the Babuska-Brezzi condition, permitting the use of equal-order interpolation for velocity and pressure, without requiring the use of arbitrary parameters. Numerical results are presented to demonstrate the accuracy and generality of the method.

Winterscheidt, Daniel L.

1993-01-01

256

Time-Accurate Computation of Viscous Incompressible Flow Around Deforming Bodies Using Overset Grids  

Microsoft Academic Search

We solve the incompressible Navier-Stokes equations on moving overset grids. Near dynamically deforming boundaries we use thin, body-fitted grids and cover most of the computational domain with fixed Cartesian grids. Large scale deformation of the flow boundaries can be handled efficiently without global regridding. We'll discuss a velocity-pressure formulation of the Navier-Stokes equations for domains with elastic boundaries. Time permitting,

Petri Fast

2001-01-01

257

Study on transient local entropy generation in pulsating fully developed laminar flow through an externally heated pipe  

Microsoft Academic Search

This study presents the investigation of transient local entropy generation rate in pulsating fully developed laminar flow through an externally heated pipe. The flow inlet to the pipe is considered as pulsating at a constant period and amplitude (only the velocity oscillates). The simulations are extended to include different pulsating flow cases (sinusoidal flow, step flow, and saw-down flow). To

Hüseyin Yapici; Nesrin Kayatas; Gamze Bastürk; Nafiz Kahraman

2006-01-01

258

Developing laminar flow in curved pipe and bifurcation in fully developed region  

NASA Astrophysics Data System (ADS)

Parabolized Navier-Stokes solutions are given for laminar developing and fully developed flow in a curved pipe. Two inlet velocity conditions of uniform or parabolic profiles are considered, and fully-developed flow solutions by a truncated version of the computer-code are also reported. The predicted friction factors, axial velocity developments, and pressure difference between outside and inside wall are in good agreement with available experimental data.

Ishigaki, Hiroshi; Ueda, Shuichi

259

Inverse co-flow approach to sooting laminar diffusion flames  

Microsoft Academic Search

Normal and inverse diffusion flames (NDFs and IDFs) were used to study flame pyrolysis and soot formation processes. In an IDF, the reactant flows are reversed from the NDF configuration, that is, the oxidizer flows through the central tube into a surrounding co-flowing fuel stream. Soot formation processes are more effectively separated from oxidation processes in the IDF, which also

Sidebotham

1988-01-01

260

Fully consistent CFD methods for incompressible flow computations  

NASA Astrophysics Data System (ADS)

Nowadays collocated grid based CFD methods are one of the most efficient tools for computations of the flows past wind turbines. To ensure the robustness of the methods they require special attention to the well-known problem of pressure-velocity coupling. Many commercial codes to ensure the pressure-velocity coupling on collocated grids use the so-called momentum interpolation method of Rhie and Chow [1]. As known, the method and some of its widely spread modifications result in solutions, which are dependent of time step at convergence. In this paper the magnitude of the dependence is shown to contribute about 0.5% into the total error in a typical turbulent flow computation. Nevertheless if coarse grids are used, the standard interpolation methods result in much higher non-consistent behavior. To overcome the problem, a recently developed interpolation method, which is independent of time step, is used. It is shown that in comparison to other time step independent method, the method may enhance the convergence rate of the SIMPLEC algorithm up to 25 %. The method is verified using turbulent flow computations around a NACA 64618 airfoil and the roll-up of a shear layer, which may appear in wind turbine wake.

Kolmogorov, D. K.; Shen, W. Z.; Sørensen, N. N.; Sørensen, J. N.

2014-06-01

261

A Method for the Constrained Design of Natural Laminar Flow Airfoils  

NASA Technical Reports Server (NTRS)

A fully automated iterative design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. Drag reductions have been realized using the design method over a range of Mach numbers, Reynolds numbers and airfoil thicknesses. The thrusts of the method are its ability to calculate a target N-Factor distribution that forces the flow to undergo transition at the desired location; the target-pressure-N-Factor relationship that is used to reduce the N-Factors in order to prolong transition; and its ability to design airfoils to meet lift, pitching moment, thickness and leading-edge radius constraints while also being able to meet the natural laminar flow constraint. The method uses several existing CFD codes and can design a new airfoil in only a few days using a Silicon Graphics IRIS workstation.

Green, Bradford E.; Whitesides, John L.; Campbell, Richard L.; Mineck, Raymond E.

1996-01-01

262

Simulated-airline-service flight tests of laminar-flow control with perforated-surface suction system  

NASA Technical Reports Server (NTRS)

The effectiveness and practicality of candidate leading edge systems for suction laminar flow control transport airplanes were investigated in a flight test program utilizing a modified JetStar airplane. The leading edge region imposes the most severe conditions on systems required for any type of laminar flow control. Tests of the leading edge systems, therefore, provided definitive results as to the feasibility of active laminar flow control on airplanes. The test airplane was operated under commercial transport operating procedures from various commercial airports and at various seasons of the year.

Maddalon, Dal V.; Braslow, Albert L.

1990-01-01

263

Large eddy simulation of incompressible turbulent channel flow  

NASA Technical Reports Server (NTRS)

The three-dimensional, time-dependent primitive equations of motion were numerically integrated for the case of turbulent channel flow. A partially implicit numerical method was developed. An important feature of this scheme is that the equation of continuity is solved directly. The residual field motions were simulated through an eddy viscosity model, while the large-scale field was obtained directly from the solution of the governing equations. An important portion of the initial velocity field was obtained from the solution of the linearized Navier-Stokes equations. The pseudospectral method was used for numerical differentiation in the horizontal directions, and second-order finite-difference schemes were used in the direction normal to the walls. The large eddy simulation technique is capable of reproducing some of the important features of wall-bounded turbulent flows. The resolvable portions of the root-mean square wall pressure fluctuations, pressure velocity-gradient correlations, and velocity pressure-gradient correlations are documented.

Moin, P.; Reynolds, W. C.; Ferziger, J. H.

1978-01-01

264

Finite element computation of unsteady incompressible flows involving moving boundaries and interfaces and iterative solution strategies  

NASA Astrophysics Data System (ADS)

In these lecture notes we review some of the recent progress on stabilized finite element formulation used in computation of incompressible flows. The stabilization techniques emphasized in these lecture notes are the Galerkin/least-squares, streamline-upwind/Petrov-Galerkin, and pressure-stabilizing/Petrov-Galerkin formulations. Most of the examples considered are unsteady flow problems, with emphasis on moving boundaries and interfaces, such as free surface flows, liquid drops, flow past an oscillating cylinder, and flow past an oscillating airfoil. Also reviewed are the iteration strategies employed to solve the implicit equation systems resulting from the finite element discretization of these flow problems, including space-time formulations. The lecture notes also describe a new mixed clustered-element-by-element (CEBE/CC) preconditioning method for finite element computations.

Tezduyar, Tayfun E.

1992-05-01

265

Stochastic finite difference lattice Boltzmann method for steady incompressible viscous flows  

NASA Astrophysics Data System (ADS)

With the advent of state-of-the-art computers and their rapid availability, the time is ripe for the development of efficient uncertainty quantification (UQ) methods to reduce the complexity of numerical models used to simulate complicated systems with incomplete knowledge and data. The spectral stochastic finite element method (SSFEM) which is one of the widely used UQ methods, regards uncertainty as generating a new dimension and the solution as dependent on this dimension. A convergent expansion along the new dimension is then sought in terms of the polynomial chaos system, and the coefficients in this representation are determined through a Galerkin approach. This approach provides an accurate representation even when only a small number of terms are used in the spectral expansion; consequently, saving in computational resource can be realized compared to the Monte Carlo (MC) scheme. Recent development of a finite difference lattice Boltzmann method (FDLBM) that provides a convenient algorithm for setting the boundary condition allows the flow of Newtonian and non-Newtonian fluids, with and without external body forces to be simulated with ease. Also, the inherent compressibility effect in the conventional lattice Boltzmann method, which might produce significant errors in some incompressible flow simulations, is eliminated. As such, the FDLBM together with an efficient UQ method can be used to treat incompressible flows with built in uncertainty, such as blood flow in stenosed arteries. The objective of this paper is to develop a stochastic numerical solver for steady incompressible viscous flows by combining the FDLBM with a SSFEM. Validation against MC solutions of channel/Couette, driven cavity, and sudden expansion flows are carried out.

Fu, S. C.; So, R. M. C.; Leung, W. W. F.

2010-08-01

266

A Quantitative Comparison of Leading-edge Vortices in Incompressible and Supersonic Flows  

NASA Technical Reports Server (NTRS)

When requiring quantitative data on delta-wing vortices for design purposes, low-speed results have often been extrapolated to configurations intended for supersonic operation. This practice stems from a lack of database owing to difficulties that plague measurement techniques in high-speed flows. In the present paper an attempt is made to examine this practice by comparing quantitative data on the nearwake properties of such vortices in incompressible and supersonic flows. The incompressible flow data are obtained in experiments conducted in a low-speed wind tunnel. Detailed flow-field properties, including vorticity and turbulence characteristics, obtained by hot-wire and pressure probe surveys are documented. These data are compared, wherever possible, with available data from a past work for a Mach 2.49 flow for the same wing geometry and angles-of-attack. The results indicate that quantitative similarities exist in the distributions of total pressure and swirl velocity. However, the streamwise velocity of the core exhibits different trends. The axial flow characteristics of the vortices in the two regimes are examined, and a candidate theory is discussed.

Wang, F. Y.; Milanovic, I. M.; Zaman, K. B. M. Q.

2002-01-01

267

Incompressible spatially-developing free-shear flows  

NASA Technical Reports Server (NTRS)

The first goal of this research is to understand the dynamics of three dimensional vortical structures, especially the interaction of the ribs and two dimensional rollers. Because of vortex stretching effects, this requires accurate and well resolved simulations. Another goal is to distinguish temporally- and spatially-growing shear layers in terms of the dynamics and observed vortical structures. This is important since the former is much easier to compute, but the error incurred in using temporal results for certain applications is unknown. The third goal is to investigate the effects of asymmetry on passive scalar mixing and fast-chemistry product formation. In this report a brief summary of a new numerical method is presented, followed by results for mixing layers and wake flows.

Buell, J. C.

1990-01-01

268

Oscillating aerodynamics and flutter of an aerodynamically detuned cascade in an incompressible flow  

NASA Technical Reports Server (NTRS)

A mathematical model is developed and utilized to demonstrate the enhanced torsion mode stability associated with alternate blade circumferential aerodynamic detuning of a rotor operating in an incompressible flow field. The oscillating cascade aerodynamics, including steady loading effects, are determined by developing a complete first order unsteady aerodynamic analysis. An unsteady aerodynamic influence coefficient technique is then utilized, thereby enabling the stability of both conventional uniformly spaced rotors and detuned nonuniform circumferentially spaced rotors to be determined. To demonstrate the enhanced flutter aeroelastic stability associated with this aerodynamic detuning mechanism, this model is applied to a baseline unstable rotor with a Gostelow flow geometry.

Chiang, Hsiao-Wei D.; Fleeter, Sanford

1989-01-01

269

A pressure based method for the solution of viscous incompressible turbomachinery flows  

NASA Technical Reports Server (NTRS)

A new technique was developed for the solution of the incompressible Navier-Stokes equations. The numerical technique, derived from a pressure substitution method (PSM), overcomes many of the deficiencies of the pressure correction method. This technique allows for the direct solution of the actual pressure in the form of a Poisson equation which is derived from the pressure weighted substitution of the full momentum equations into the continuity equation. Two dimensional internal flows are computed with this method. The prediction of cascade performance is presented. The extention of the pressure correction method for the solution of three dimensional flows is also presented.

Hobson, Garth Victor; Lakshminarayana, B.

1991-01-01

270

Finite element methods for viscous incompressible flow with interface pressure jumps  

NASA Astrophysics Data System (ADS)

Surface tension in multi-phase fluid flow engender pressure discontinuities on phase interfaces. In this work we present two finite element methods to solve viscous incompressible flows problems, especially designed to cope with such a situation. Taking as a model the two-dimensional Stokes system, we consider stable solution methods based on piecewise linear approximations of both the velocity and pressure, with either velocity bubble or divergence free penalty enrichment. However a modification of the pressure space is employed in order to represent interface discontinuities. A priori error analyses point to optimal convergence rates for both approaches, which justify observations from plentiful numerical experiments.

Buscaglia, G.; Ruas, V.

2013-10-01

271

Time-accurate incompressible flow computations with quadrilateral velocity-pressure elements  

NASA Astrophysics Data System (ADS)

Quadrilateral velocity-pressure elements with constant and linear pressure interpolations are examined in the context of time-accurate finite element computation of unsteady incompressible flows. These elements involve streamline-upwind/Petrov-Galerkin stabilization and are implemented in conjunction with the one-step and multi-step temporal integration of the Navier-Stokes equations. The two test cases chosen for the performance evaluation of the formulations are the standing vortex problem and flow past a circular cylinder at Reynolds number 100.

Tezduyar, T. E.; Mittal, S.; Shih, R.

1991-06-01

272

Time-accurate incompressible flow computations with quadrilateral velocity-pressure elements  

NASA Technical Reports Server (NTRS)

Quadrilateral velocity-pressure elements with constant and linear pressure interpolations are examined in the context of time-accurate finite element computation of unsteady incompressible flows. These elements involve streamline-upwind/Petrov-Galerkin stabilization and are implemented in conjunction with the one-step and multi-step temporal integration of the Navier-Stokes equations. The two test cases chosen for the performance evaluation of the formulations are the standing vortex problem and flow past a circular cylinder at Reynolds number 100.

Tezduyar, T. E.; Mittal, S.; Shih, R.

1991-01-01

273

On the numerical solution of time-dependent viscous incompressible fluid flows involving solid boundaries  

NASA Technical Reports Server (NTRS)

An inherent numerical problem associated with the fully explicit pseudospectral numerical simulation of the incompressible Navier-Stokes equation for viscous flows with no-slip walls is described. A semi-implicit scheme which circumvents this numerical difficulty is presented. In this algorithm the equation of continuity rather than the Poisson equation for pressure is solved directly. Pseudospectral formulation of the channel flow problem using Fourier series and Chebyshev polynomials expansions is given for this scheme. An example demonstrating the applicability of the method is given.

Moin, P.; Kim, J.

1980-01-01

274

Microtube liquid single-phase heat transfer in laminar flow  

Microsoft Academic Search

One of the main applications of microscale flow is miniature, high-efficiency heat transfer. The most simple and immediate solution to the problem of concentrated heat exchange is the use of small diameter channels with single-phase water flow, but there is a lack of publicised knowledge about the heat transfer performance in these conditions. In this article, an experimental investigation is

G. P. Celata; M. Cumo; V. Marconi; S. J. McPhail; G. Zummo

2006-01-01

275

Handling of temperature dependence of viscosity in problems of incompressible medium flow around a cylinder  

NASA Astrophysics Data System (ADS)

The viscous incompressible medium (water, air) flow past a circular cylinder is considered with regard for the temperature T dependent viscosity v. The influence of different boundary conditions for temperature on flow structure, the drag coefficient and its components due to the pressure and viscosity is investigated in the problem of the flow past a cylinder at rest for the (diameter-based) Reynolds number ReD = 40. A relation between the viscosity gradient along a normal to the body surface and the integral vorticity flux from the body surface into the boundary layer is discussed. Unlike the constant viscosity case the vorticity flux may be different from zero, which must lead because of the integral conservation law for the vorticity to an alteration of the far-field boundary conditions for the velocity. In the same connection, the problem is analysed on the heat spot entry into the computational region under consideration for the flow past a circular cylinder. The examples of the symmetrization of separated flow past a cylinder performing rotation oscillations in a uniform free stream (the Taneda problem) are considered. A comparison with flow computations for low Mach numbers M « 1 for the flow of a medium past a cylinder at rest is carried out. At the computation of the equation for heat transfer under the assumption of incompressibility of such media as air, it is proposed to retain the pressure derivative, which is typical of gases. In this case, a better agreement with the computations of compressible flows (for M « 1) is achieved, for example, at the determination of the sizes of a symmetric zone of flow separation past a circular cylinder. An unsteady flow in the neighborhood of the point of joining the zero streamline bounding a closed region of separated flow (the cavity) in a wake of the cylinder at rest is obtained by a numerical simulation at the Reynolds number equal to 40.

Zakharenkov, M. N.

2007-12-01

276

A parallel overset-curvilinear-immersed boundary framework for simulating complex 3D incompressible flows.  

PubMed

We develop an overset-curvilinear immersed boundary (overset-CURVIB) method in a general non-inertial frame of reference to simulate a wide range of challenging biological flow problems. The method incorporates overset-curvilinear grids to efficiently handle multi-connected geometries and increase the resolution locally near immersed boundaries. Complex bodies undergoing arbitrarily large deformations may be embedded within the overset-curvilinear background grid and treated as sharp interfaces using the curvilinear immersed boundary (CURVIB) method (Ge and Sotiropoulos, Journal of Computational Physics, 2007). The incompressible flow equations are formulated in a general non-inertial frame of reference to enhance the overall versatility and efficiency of the numerical approach. Efficient search algorithms to identify areas requiring blanking, donor cells, and interpolation coefficients for constructing the boundary conditions at grid interfaces of the overset grid are developed and implemented using efficient parallel computing communication strategies to transfer information among sub-domains. The governing equations are discretized using a second-order accurate finite-volume approach and integrated in time via an efficient fractional-step method. Various strategies for ensuring globally conservative interpolation at grid interfaces suitable for incompressible flow fractional step methods are implemented and evaluated. The method is verified and validated against experimental data, and its capabilities are demonstrated by simulating the flow past multiple aquatic swimmers and the systolic flow in an anatomic left ventricle with a mechanical heart valve implanted in the aortic position. PMID:23833331

Borazjani, Iman; Ge, Liang; Le, Trung; Sotiropoulos, Fotis

2013-04-01

277

Sound generated in laminar flow past a two-dimensional rectangular cylinder  

Microsoft Academic Search

The far-field sound generated from low Mach number flow past a two-dimensional rectangular cylinder is studied by using a two-step aeroacoustic prediction method. In the first step, the incompressible Navier–Stokes equations are solved numerically. This allows the time-dependent acoustic source to be determined from Powell's vortex sound theory. Using this information, in the second step, the inhomogeneous wave equation is

Y. S. K. Liow; B. T. Tan; M. C. Thompson; K. Hourigan

2006-01-01

278

The Stability of Particulate Ladden Laminar Boundary-Layer Flows  

NASA Technical Reports Server (NTRS)

During the course of this investigation, the following two topics were studied theoretically: (1) forced convection and sedimentation past a flat plate, and (2) the effect of rain on airfoil performance. The prototype of the first topic is that of air flowing past the wing section of an aircraft under heavy rain and high windshear. The long-range objective of this project was to identify the various factors determining the dynamics of the flow and then to develop a theoretical framework for modeling such systems. The second topic focused on the idea that the presence of the gas-liquid interface (being the air flow around the airfoil and the thin liquid film created by the rain) accelerates flow separation and thus induces performance losses.

Acrivos, Andreas

1996-01-01

279

On Analysis of Stationary Viscous Incompressible Flow Through a Radial Blade Machine  

NASA Astrophysics Data System (ADS)

The paper is concerned with the analysis of the two dimensional model of incompressible, viscous, stationary flow through a radial blade machine. This type of turbine is sometimes called Kaplan's turbine. In the technical area the use is either to force some regular characteristic to the flow of the medium going through the turbine (flow of melted iron, air conditioning) or to gain some energy from the flowing medium (water). The inflow and outflow part of boundary are in general a concentric circles. The larger one represents an inflow part of boundary the smaller one the outflow part of boundary. Between them are regularly spaced the blades of the machine. We study the existence of the weak solution in the case of nonlinear boundary condition of the "do-nothing" type. The model is interesting for study the behavior of the flow when the boundary is formed by mutually disjoint and separated parts.

Neustupa, Tomáš

2010-09-01

280

Pressure and kinetic energy transport across the mouth of laminar cavity flows.  

NASA Astrophysics Data System (ADS)

The nature of the separated recirculating cavity flow depends upon the Reynolds number (Re), the upstream flow regime, as well as the cavity aspect ratio. Here we use DNS to investigate the pressure (-pv) and kinetic energy (Kv) transport in shallow cavities in a channel, in the laminar regime varying Re (here based on the channel height). In recirculating flows the pressure-velocity correlation plays an increasingly important role in the energy balance. This is in contrast to parallel flows, such as boundary layers or channel flows, where mean shear is high, and the flow is dominated by the convective transport. This was highlighted by Yoshizawa (PoF 2002) and confirmed with the results of shearless inhomogeneous turbulent mixing Tordella et al. (PRE 2008). The cavity flow lies between these two extremes. We have shown that this trend can also be seen in laminar flows. Observing the transport properties at the cavity mouth, for Re 50-2000, Kv reaches a peak at Re=200, whereas --pv peaks at Re=700. As Re is increased from these values, and the cavity flow moves from closed to open, Kv becomes less significant, with --pv having a greater importance beyond Re=500.

Bailey, Peter; Abba', Antonella; Tordella, Daniela

2008-11-01

281

Analytical solutions for laminar fully developed flows in double-sine shaped ducts  

Microsoft Academic Search

Fully developed, constant property, laminar flows in double-sine shaped ducts are considered. This cross section represents a limiting inter-plate channel geometry in plate heat exchangers. Accurate analytical solutions based on the Galerkin integral method are presented. Heat transfer with both T and H1 thermal boundary conditions is analyzed; they simulate the most fundamental practical heating\\/cooling applications. Velocity and temperature distributions,

J. Ding; R. M. Manglik

1996-01-01

282

Unsteady entrance heat transfer in laminar pipe flows with convection from the ambient  

Microsoft Academic Search

The characteristics of unsteady entrance heat transfer in the combined entrance heat transfer region of laminar pipe flows resulting from time-varying inlet temperature are numerically investigated. Three non-dimensional parameters,Nu0, a*, andf are identified in the study. Also, their effects on the non-dimensional duct wall temperature, fluid bulk temperature, and duct wall heat flux are discussed in great detail. Comparisons are

W.-M. Yan; T.-F. Lin

1988-01-01

283

A three-dimensional incompressible flow simulation method and its application to the Space Shuttle main engine. II Turbulent flow  

Microsoft Academic Search

An implicit finite difference code cast in general curvilinear coordinates is further developed for three-dimensional incompressible turbulent flows. The code is based on the method of pseudocompressibility and utilizes the Beam and Warming implicit approximate factorization algorithm to achieve computational efficiency. A multiple-zone method is further extended to include composite-grids to overcome the excessive computer memory required for solving turbulent

J. L. C. Chang; R. Rosen; S. C. Dao; D. Kwak

1985-01-01

284

An efficient and robust algorithm for two dimensional time dependent incompressible Navier-Stokes equations: High Reynolds number flows  

NASA Technical Reports Server (NTRS)

An algorithm is presented for unsteady two-dimensional incompressible Navier-Stokes calculations. This algorithm is based on the fourth order partial differential equation for incompressible fluid flow which uses the streamfunction as the only dependent variable. The algorithm is second order accurate in both time and space. It uses a multigrid solver at each time step. It is extremely efficient with respect to the use of both CPU time and physical memory. It is extremely robust with respect to Reynolds number.

Goodrich, John W.

1991-01-01

285

CONVEC: A computer program for transient incompressible fluid flow based on quadratic finite elements. Part 1: Theoretical aspects  

Microsoft Academic Search

The theoretical and numerical aspects of the finite element computer code CONVEC designed for the transient analysis of two-dimensional plane or three-dimensional axisymmetric incompressible flows including the effects of heat transfer are described. The governing equations are the time-dependent incompressible Navier-Stokes equations and the thermal energy equation. The finite element method (FEM) is employed as a basic spatial discretization technique.

H. Laval

1981-01-01

286

F-111 natural laminar flow glove flight test data analysis and boundary layer stability analysis  

NASA Technical Reports Server (NTRS)

An analysis of 34 selected flight test data cases from a NASA flight program incorporating a natural laminar flow airfoil into partial wing gloves on the F-111 TACT airplane is given. This analysis determined the measured location of transition from laminar to turbulent flow. The report also contains the results of a boundary layer stability analysis of 25 of the selected cases in which the crossflow (C-F) and Tollmien-Schlichting (T-S) disturbance amplification factors are correlated with the measured transition location. The chord Reynolds numbers for these cases ranges from about 23 million to 29 million, the Mach numbers ranged from 0.80 to 0.85, and the glove leading-edge sweep angles ranged from 9 deg to 25 deg. Results indicate that the maximum extent of laminar flow varies from 56% chord to 9-deg sweep on the upper surface, and from 51% chord at 16-deg sweep to 6% chord at 25-deg sweep on the lower. The results of the boundary layer stability analysis indicate that when both C-F and T-S disturbances are amplified, an interaction takes place which reduces the maximum amplification factor of either type of disturbance that can be tolerated without causing transition.

Runyan, L. J.; Navran, B. H.; Rozendaal, R. A.

1984-01-01

287

The least-squares meshfree method for the steady incompressible viscous flow  

NASA Astrophysics Data System (ADS)

A least-squares meshfree method (LSMFM) based on the first-order velocity-pressure-vorticity formulation for two-dimensional steady incompressible viscous flow is presented. The discretization of all governing equations is implemented by the least-squares method. The equal-order moving least-squares (MLS) approximation is employed. Gauss quadrature is used in the background cells constructed by the quadtree algorithm and the boundary conditions are enforced by the penalty method. The matrix-free element-by-element Jacobi preconditioned conjugate method is applied to solve the discretized linear systems. A numerical example with analytical solution for the Stokes problem is devised to analyze the error estimates of the LSMFM. Also, cavity-driven flow for the Stokes problem and the flow past a circular cylinder at low Reynolds numbers for the steady incompressible viscous flow are solved. Through the comparisons of the LSMFM's results with other experimental and numerical results, the numerical features of the presented LSMFM are investigated and discussed.

Zhang, Xiang Kun; Kwon, Kie-Chan; Youn, Sung-Kie

2005-06-01

288

Cauchy's almost forgotten Lagrangian formulation of the Euler equation for 3D incompressible flow  

NASA Astrophysics Data System (ADS)

Two prized papers, one by Augustin Cauchy in 1815, presented to the French Academy and the other by Hermann Hankel in 1861, presented to Göttingen University, contain major discoveries on vorticity dynamics whose impact is now quickly increasing. Cauchy found a Lagrangian formulation of 3D ideal incompressible flow in terms of three invariants that generalize to three dimensions the now well-known law of conservation of vorticity along fluid particle trajectories for two-dimensional flow. This has very recently been used to prove analyticity in time of fluid particle trajectories for 3D incompressible Euler flow and can be extended to compressible flow, in particular to cosmological dark matter. Hankel showed that Cauchy's formulation gives a very simple Lagrangian derivation of the Helmholtz vorticity-flux invariants and, in the middle of the proof, derived an intermediate result which is the conservation of the circulation of the velocity around a closed contour moving with the fluid. This circulation theorem was to be rediscovered independently by William Thomson (Kelvin) in 1869. Cauchy's invariants were only occasionally cited in the 19th century - besides Hankel, foremost by George Stokes and Maurice Lévy - and even less so in the 20th until they were rediscovered via Emmy Noether's theorem in the late 1960, but reattributed to Cauchy only at the end of the 20th century by Russian scientists.

Frisch, Uriel; Villone, Barbara

2014-09-01

289

Developing laminar flow characteristics in elliptic ducts using Mathieu functions  

Microsoft Academic Search

The study of flow through elliptic ducts is important in view of its application in compact heat exchangers. The governing differential equations in the entrance region of elliptic ducts are solved using Langhaar's linearization technique and the developing velocity solutions are expressed in terms of Fourier and Bessel product type Mathieu functions. Based on these solutions, the details of the

T. R. Jagadeesh; J. S. R. Murthy

1980-01-01

290

Laminar flow effects in the coil planet centrifuge  

Microsoft Academic Search

The coil planet centrifuge designed by Ito employs flow of a single liquid phase, through a rotating coiled tube in a centrifugal force field, to provide a separation of particles based on sedimentation rates. Mathematical solutions are derived for the linear differential equations governing particle behavior in the coil planet centrifuge device. These solutions are then applied as the basis

F. T. Herrmann

1984-01-01

291

Pressure Drop of Fully Developed, Laminar Flow in Rough Microtubes  

E-print Network

at the interface of a heat-generating component and heat sink is eliminated. This feature leads to lower substrate ASME J. R. Culham1 Associate Professor Mem. ASME Microelectronics Heat Transfer Laboratory, Department of microscale heat transfer and fluid flow. Microchannel heat ex- changers can dissipate high heat fluxes which

Bahrami, Majid

292

Multifluid laminar flow in a microchannel (Kenis et al. 1999)  

E-print Network

reactions, e.g., jet engine and power generation gas turbines, internal combustion engines, furnaces: Micro/biofluidics, multiphase flows, turbulent combustion, CFD. Softwares : We develop and use our in research, we specialize in fluid mechanics, combustion and scientific computing. We're primarily concerned

Muradoglu, Metin

293

Laminar entrace region flow of the Bingham fluid  

Microsoft Academic Search

Summary The chief purpose of this paper is to solve numerically the entrance region flow of the Bingham fluid by omitting the necessity of pre-assuming the form of velocity profile within the boundary layer, as it has been done elsewhere [2]. By employing the macroscopic mass and momentum balances the changes in velocity profile and pressure gradient with increasing distance

Z. Nowak; B. Gajdeczko

1983-01-01

294

Application of the vorticity redistribution method to LES of incompressible flow*  

NASA Astrophysics Data System (ADS)

Efficient computation of noise generation by shearflows is achieved using a model that employs the vortex element method(VEM)to reproduce the unsteady incompressible flow dynamics and the expansion aboutincompressible flow(EIF) technique to capture the acoustic field. Severalstrategies in coupling the VEM with the EIF approach are proposed. The VEM-EIF model is demonstrated by computing the sound generation due to aforced as well as an unforced planar shear layer. Results for the forced casecompare favourably with previous computational evidence. They exhibit apreferential directivity for the subharmonic frequency of the mostunstable flow frequency in the region just below the streamwise coordinate axis.The unforced flow results exhibit a qualitatively similar behaviour, suggestingthat the beaming of subharmonic noise is not an artifact of the forcing.

Gharakhani, Adrin

2003-02-01

295

Incompressible turbulent flow calculation in body-fitted coordinates using block-implicit finite difference method  

NASA Astrophysics Data System (ADS)

The block-implicit finite-difference method is used to calculate 3D incompressible turbulent flows in the body-fitted coordinate system. In the numerical discretization the hybrid difference scheme is used to treat Reynolds-averaged Navier-Stokes equations. The iterative solution of velocities and pressure on the flow field is obtained by solving simultaneously the Reynolds-averaged N-S equations and continuity equation for each cell. In the iterative process the Gauss-Seidel method is used to solve nonlinear algebraic equations. The turbulent flow is simulated by the k-epsilon turbulence modeling in conjunction with Reynolds equations. The turbulent flow of a curved duct with square cross sections is treated in detail.

Hu, Zeming; Chen, Xuechun; Wu, Yulin

296

Mimicking Natural Laminar to Turbulent Flow Transition: A Systematic CFD Study Using PAB3D  

NASA Technical Reports Server (NTRS)

For applied aerodynamic computations using a general purpose Navier-Stokes code, the common practice of treating laminar to turbulent flow transition over a non-slip surface is somewhat arbitrary by either treating the entire flow as turbulent or forcing the flow to undergo transition at given trip locations in the computational domain. In this study, the possibility of using the PAB3D code, standard k-epsilon turbulence model, and the Girimaji explicit algebraic stresses model to mimic natural laminar to turbulent flow transition was explored. The sensitivity of flow transition with respect to two limiters in the standard k-epsilon turbulence model was examined using a flat plate and a 6:1 aspect ratio prolate spheroid for our computations. For the flat plate, a systematic dependence of transition Reynolds number on background turbulence intensity was found. For the prolate spheroid, the transition patterns in the three-dimensional boundary layer at different flow conditions were sensitive to the free stream turbulence viscosity limit, the reference Reynolds number and the angle of attack, but not to background turbulence intensity below a certain threshold value. The computed results showed encouraging agreements with the experimental measurements at the corresponding geometry and flow conditions.

Pao, S. Paul; Abdol-Hamid, Khaled S.

2005-01-01

297

Laminar and turbulent flows over spherically blunted cone and hyperboloid with massive surface blowing  

NASA Technical Reports Server (NTRS)

Numerical solutions are presented for the flow over a spherically blunted cone and hyperboloid with massive surface blowing. Time-dependent viscous shock-layer equations are used to describe the flow field. The boundary conditions on the body surface include a prescribed blowing-rate distribution. The governing equations are solved by a time-asymptotic finite-difference method. Results presented here are only for a perfect gas-type flow at zero angle of attack. Both laminar and turbulent flow solutions are obtained. It is found that the effect of the surface blowing on the laminar flow field is to smooth out the curvature discontinuity at the sphere-cone juncture point, which results in a positive pressure gradient over the body. The shock slope increases on the downstream portion of the body as the surface blowing rate is increased. The turbulent flow with surface blowing is found to redevelop a boundary-layer-like region near the surface. The effects of this boundary-layer region on the flow field and heating rates are discussed.

Kumar, A.; Twari, S. N.

1979-01-01

298

Laminar flow effects in the coil planet centrifuge  

NASA Technical Reports Server (NTRS)

The coil planet centrifuge designed by Ito employs flow of a single liquid phase, through a rotating coiled tube in a centrifugal force field, to provide a separation of particles based on sedimentation rates. Mathematical solutions are derived for the linear differential equations governing particle behavior in the coil planet centrifuge device. These solutions are then applied as the basis of a model for optimizing particle separations.

Herrmann, F. T.

1984-01-01

299

Laminar flow effects in the coil planet centrifuge  

NASA Astrophysics Data System (ADS)

The coil planet centrifuge designed by Ito employs flow of a single liquid phase, through a rotating coiled tube in a centrifugal force field, to provide a separation of particles based on sedimentation rates. Mathematical solutions are derived for the linear differential equations governing particle behavior in the coil planet centrifuge device. These solutions are then applied as the basis of a model for optimizing particle separations.

Herrmann, F. T.

300

Analytic solutions for three dimensional swirling strength in compressible and incompressible flows  

NASA Astrophysics Data System (ADS)

Eigenvalues of the 3D critical point equation (?u)? = ?? are normally computed numerically. In the letter, we present analytic solutions for 3D swirling strength in both compressible and incompressible flows. The solutions expose functional dependencies that cannot be seen in numerical solutions. To illustrate, we study the difference between using fluctuating and total velocity gradient tensors for vortex identification. Results show that mean shear influences vortex detection and that distortion can occur, depending on the strength of mean shear relative to the vorticity at the vortex center.

Chen, Huai; Adrian, Ronald J.; Zhong, Qiang; Wang, Xingkui

2014-08-01

301

Wave Number Selection for Incompressible Parallel Jet Flows Periodic in Space  

NASA Technical Reports Server (NTRS)

The temporal instability of a spatially periodic parallel flow of an incompressible inviscid fluid for various jet velocity profiles is studied numerically using Floquet Analysis. The transition matrix at the end of a period is evaluated by direct numerical integration. For verification, a method based on approximating a continuous function by a series of step functions was used. Unstable solutions were found only over a limited range of wave numbers and have a band type structure. The results obtained are analogous to the behavior observed in systems exhibiting complexity at the edge of order and chaos.

Miles, Jeffrey Hilton

1997-01-01

302

Laminar Flow About a Rotating Body of Revolution in an Axial Airstream  

NASA Technical Reports Server (NTRS)

We have set ourselves the problem of calculating the laminar flow on a body of revolution in an axial flow which simultaneously rotates about its axis. The problem mentioned above, the flow about a rotating disk in a flow, which we solved some time ago, represents the first step in the calculation of the flow on the rotating body of revolution in a flow insofar as, in the case of a round nose, a small region about the front stagnation point of the body of revolution may be replaced by its tangential plane. In our problem regarding the rotating body of revolution in a flow, for laminar flow, one of the limiting cases is known: that of the body which is in an axial approach flow but does not rotate. The other limiting case, namely the flow in the neighborhood of a body which rotates but is not subjected to a flow is known only for the rotating circular cylinder, aside from the rotating disk. In the case of the cylinder one deals with a distribution of the circumferential velocity according to the law v = omega R(exp 2)/r where R signifies the cylinder radius, r the distance from the center, and omega the angular velocity of the rotation. The velocity distribution as it is produced here by the friction effect is therefore the same as in the neighborhood of a potential vortex. When we treat, in what follows, the general case of the rotating body of revolution in a flow according to the calculation methods of Prandtl's boundary-layer theory, we must keep in mind that this solution cannot contain the limiting case of the body of revolution which only rotates but is not subjected to a flow. However, this is no essential limitation since this case is not of particular importance for practical purposes.

Schlichting, H.

1956-01-01

303

Inverse co-flow approach to sooting laminar diffusion flames  

SciTech Connect

Normal and inverse diffusion flames (NDFs and IDFs) were used to study flame pyrolysis and soot formation processes. In an IDF, the reactant flows are reversed from the NDF configuration, that is, the oxidizer flows through the central tube into a surrounding co-flowing fuel stream. Soot formation processes are more effectively separated from oxidation processes in the IDF, which also tend to soot less. Temperature-controlled smoke height tests were applied to allene, 1,3-butadiene, several cyclic hydrocarbons, and branched aliphatic fuels. As found in previous studies, pyrolysis chemistry governs soot formation. Thermocouples and microprobe sampling were then used to measure thermal and chemical fields of NDF and IDF pyrolysis zones. First, NDF pyrolysis zones were probed using fuels with high sooting tendency, namely allene, 1,3-butadiene and benzene. The results support the growing consensus that aromatic ring formation is a controlling step in soot formation. The particular aromatic formation mechanism depends on flame type, fuel structure and local temperature. Next, the transition from near to slightly-sooting IDFs was examined using methane, ethene, propene and 1-butene as fuels. Soot inception occurred for the olefins when: (1) the temperature exceeded approximately 1300K in a predominantly pyrolytic regions; and (2) the location was sufficiently close to the main oxidation zone (where radicals are generated). Methane required higher temperatures to induce inception because it does not readily form acetylene. While these conditions determine whether inception will occur, the aromatic content, which scaled with the fuel's sooting tendency, affects the ultimate soot loading once inception has occurred.

Sidebotham, G.W.

1988-01-01

304

MRI of retinal and choroidal blood flow with laminar resolution  

PubMed Central

The retina is nourished by two distinct circulations: the retinal vessels within the inner retina and the choroidal vessels behind the neural retina. The outer nuclear layer and the inner and outer segments of the photoreceptors in between are avascular. The aim of this study was to determine whether arterial spin labeling MRI could provide sufficient resolution to differentiate between quantitative retinal blood flow (rBF) and choroidal blood flow (chBF), and whether this technique is sufficiently sensitive to detect vascular-specific blood flow (BF) changes modulated by anesthetics. Arterial spin labeling MRI was performed at 42 × 42 × 400 µm3 in the mouse retina at 7 T, and was used to investigate the effects of isoflurane and ketamine/xylazine anesthesia on rBF and chBF. MRI yielded unambiguous differentiation of rBF, chBF and the avascular layer in between. Under isoflurane, chBF was 7.7 ± 2.1 mL/g/min and rBF was 1.3 ± 0.44 mL/g/min (mean ± SD, n = 7, p < 0.01). Under ketamine/xylazine anesthesia in the same animals, chBF was 4.3 ± 1.9 mL/g/min and rBF was 0.88 ± 0.22 mL/g/min (p < 0.01). Under ketamine/xylazine anesthesia, rBF was lower by 29% (P < 0.01) and chBF by 42% (P < 0.01) relative to isoflurane. This study demonstrates, for the first time, the quantitative imaging of rBF and chBF in vivo, providing a new method to study basal values and alterations of rBF and chBF. PMID:20821409

Muir, Eric R.; Duong, Timothy Q.

2010-01-01

305

Effects of Pulsatility on the Laminar Mixing Surface in Converging Microchannel Flows  

NASA Astrophysics Data System (ADS)

Continuing developments in MEMS based fluidic systems require innovative approaches to the problem of microscale mixing. Owing to the low Reynolds number characteristic of these flows, non-traditional strategies have been proposed. In this work, we investigate the effects of flow pulsatility on the laminar mixing surface formed between two converging flows. The basic motivation is drawn from blood flow, with governing parameters adapted to a MEMS setting. Parametric studies involving flow-ratio, viscosity-ratio, frequency-ratio and the flow geometry will be reported. Our results have indicated complex interfacial distortions at high frequency pulsations ( 1kHz). The extent of mixing will also be quantified in terms of the interfacial distortion achieved by the pulsatile inlets.

Prabhu, R. D.; Hitt, Darren L.

2001-11-01

306

A microfluidic chip for generating reactive plasma at gas–gas interface formed in laminar flow  

NASA Astrophysics Data System (ADS)

A gas–gas interface is used for generating a localized reactive plasma flow at an atmospheric pressure. A microfluidic chip is fabricated as the reactor integrating a small plasma source located upstream. Within a Y-shaped microchannel, a discharging gas flows with a chemical gas. Owing to the small width of the microchannel, the gas flow is stabilized in a laminar flow. The resultant gas–gas interface is formed in the area where two gases flow facing each other activating the chemical gas through the energetic species in the discharging gas. A characteristic stream pattern is observed as the etching profile of a carbon film with a sub-µm sharp step change that can be explained by the spatial distribution of the reactive oxygen. This etching profile is different from that obtained when plasma discharging occurs near the channel exit being affected by the turbulent flow.

Hashimoto, Masahiro; Tsukasaki, Katsuki; Kumagai, Shinya; Sasaki, Minoru

2015-01-01

307

Entropy Generation in Laminar Fluid Flow through a Circular Pipe  

NASA Astrophysics Data System (ADS)

A numerical solution to the entropy generation in a circular pipe is made. Radial and axial variations are considered. Navier-Stokes equations in cylindrical coordinates are used to solve the velocity and temperature fields. Uniform wall heat flux is considered as the thermal boundary condition. The distribution of the entropy generation rate is investigated throughout the volume of the fluid as it flows through the pipe. Engine oil is selected as the working fluid. In addition, water and Freon are used in a parametric study. The total entropy generation rate is calculated by integration over the various cross-sections as well as over the entire volume.

Sahin, Ahmet Z.; Ben-Mansour, Rached

2003-12-01

308

A space-time hybridizable discontinuous Galerkin method for incompressible flows on deforming domains  

NASA Astrophysics Data System (ADS)

We present the first space-time hybridizable discontinuous Galerkin (HDG) finite element method for the incompressible Navier-Stokes and Oseen equations. Major advantages of a space-time formulation are its excellent capabilities of dealing with moving and deforming domains and grids and its ability to achieve higher-order accurate approximations in both time and space by simply increasing the order of polynomial approximation in the space-time elements. Our formulation is related to the HDG formulation for incompressible flows introduced recently in, e.g., [N.C. Nguyen, J. Peraire, B. Cockburn, A hybridizable discontinuous Galerkin method for Stokes flow, Comput. Methods Appl. Mech. Eng. 199 (2010) 582-597]. However, ours is inspired in typical DG formulations for compressible flows which allow for a more straightforward implementation. Another difference is the use of polynomials of fixed total degree with space-time hexahedral and quadrilateral elements, instead of simplicial elements. We present numerical experiments in order to assess the quality of the performance of the methods on deforming domains and to experimentally investigate the behavior of the convergence rates of each component of the solution with respect to the polynomial degree of the approximations in both space and time.

Rhebergen, Sander; Cockburn, Bernardo

2012-06-01

309

A coarse-grid projection method for accelerating incompressible flow computations  

NASA Astrophysics Data System (ADS)

We present a coarse-grid projection (CGP) algorithm for accelerating incompressible flow computations, which is applicable to methods involving Poisson equations as incompressibility constraints. CGP methodology is a modular approach that facilitates data transfer with simple interpolations and uses black-box solvers for the Poisson and advection-diffusion equations in the flow solver. Here, we investigate a particular CGP method for the vorticity-stream function formulation that uses the full weighting operation for mapping from fine to coarse grids, the third-order Runge-Kutta method for time stepping, and finite differences for the spatial discretization. After solving the Poisson equation on a coarsened grid, bilinear interpolation is used to obtain the fine data for consequent time stepping on the full grid. We compute several benchmark flows: the Taylor-Green vortex, a vortex pair merging, a double shear layer, decaying turbulence and the Taylor-Green vortex on a distorted grid. In all cases we use either FFT-based or V-cycle multigrid linear-cost Poisson solvers. Reducing the number of degrees of freedom of the Poisson solver by powers of two accelerates these computations while, for the first level of coarsening, retaining the same level of accuracy in the fine resolution vorticity field.

San, Omer; Staples, Anne

2011-11-01

310

Development of technology for the fabrication of reliable laminar flow control panels on subsonic transports  

NASA Technical Reports Server (NTRS)

The feasibility of using porous composite materials (Kevlar, Doweave, and Leno Weave) as lightweight, efficient laminar flow control (LFC) surface materials is compared to the metallic 319L stainless Dynapore surfaces and electron beam drilled composite surfaces. Areas investigated include: (1) selection of the LFC-suitable surface materials, structural materials, and fabrication techniques for the LFC aircraft skins; (2) aerodynamic static air flow test results in terms of pressure drop through the LFC panel and the corresponding effective porosity; (3) structural design definition and analyses of the panels, and (4) contamination effects on static drop and effective porosity. Conclusions are presented and discussed.

1976-01-01

311

Laminar-Turbulent Transition: The Change of the Flow State Temperature with the Reynolds Number  

NASA Astrophysics Data System (ADS)

Representing the fluid flow as a collection of coherent structures of various size, the statistical temperature of the flow state is determined as a function of the Reynolds number. It is shown that at small Reynolds numbers, associated with laminar states, the temperature is positive, while at large Reynolds numbers, associated with turbulent states, it is negative. At intermediate Reynolds numbers, the temperature changes from positive to negative as the size of the coherent structures increases, similar to what was predicted by Onsager for a system of parallel point-vortices in an inviscid fluid. It is also shown that in the range of intermediate Reynolds numbers the temperature exhibits a critical divergence.

Chekmarev, Sergei F.

2014-12-01

312

Numerical Solution of Supersonic Laminar Flow Over an Inclined Body of Revolution  

NASA Technical Reports Server (NTRS)

A mixed explicit-implicit scheme is used to solve the time-dependent thin-layer approximation of the Navier-Stokes equations for a supersonic laminar flow over an inclined body of revolution. Test cases for Mach 2.8 flow over a cylinder with 15-deg flare angle at angles of attack of 0,1, and 4 deg are calculated. Good agreement is obtained between the present computed results and experimental measurements of surface pressure. A pair of vortices on the leeward and a peak in the normal force distribution near the flared juncture are predicted; the role of circumferential communication is discussed.

Hung, C. M.

1980-01-01

313

Numerical solution of supersonic laminar flow over an inclined body of revolution  

NASA Technical Reports Server (NTRS)

A mixed explicit-implicit scheme is used to solve the time-dependent thin-layer approximation of the Navier-Stokes equations for a supersonic laminar flow over an inclined body of revolution. Test cases for Mach 2.8 flow over a cylinder with 15 deg flare angle at angles of attack of 0, 1, and 4 deg are calculated. Good agreement is obtained between the present computed results and experimental measurements of surface pressure. A pair of vortices on the leeward and a peak in the normal force distribution near the flared juncture are predicted; the role of circumferential communication is discussed.

Hung, C. M.

1979-01-01

314

Numerical simulation of laminar reacting flows with complex chemistry  

SciTech Connect

We present an adaptive algorithm for low Mach number reacting flows with complex chemistry. Our approach uses a form of the low Mach number equations that discretely conserves both mass and energy. The discretization methodology is based on a robust projection formulation that accommodates large density contrasts. The algorithm uses an operator-split treatment of stiff reaction terms and includes effects of differential diffusion. The basic computational approach is embedded in an adaptive projection framework that uses structured hierarchical grids with subcycling in time that preserves the discrete conservation properties of the underlying single-grid algorithm. We present numerical examples illustrating the performance of the method on both premixed and non-premixed flames.

Day, Marcus S.; Bell, John B.

1999-12-01

315

Heat transport by laminar boundary layer flow with polymers  

E-print Network

Motivated by recent experimental observations, we consider a steady-state Prandtl-Blasius boundary layer flow with polymers above a slightly heated horizontal plate and study how the heat transport might be affected by the polymers. We discuss how a set of equations can be derived for the problem and how these equations can be solved numerically by an iterative scheme. By carrying out such a scheme, we find that the effect of the polymers is equivalent to producing a space-dependent effective viscosity that first increases from the zero-shear value at the plate then decreases rapidly back to the zero-shear value far from the plate. We further show that such an effective viscosity leads to an enhancement in the drag, which in turn leads to a reduction in heat transport.

Roberto Benzi; Emily S. C. Ching.; Vivien W. S. Chu

2011-04-23

316

Helmholtz decomposition revisited: Vorticity generation and trailing edge condition. I - Incompressible flows  

NASA Technical Reports Server (NTRS)

Using the decomposition for the infinite-space, the issue of the nonuniqueness of the Helmholtz decomposition for the problem of the three-dimensional unsteady incompressible flow around a body is considered. A representation for the velocity that is valid for both the fluid region and the region inside the boundary surface is employed, and the motion of the boundary is described as the limiting case of a sequence of impulsive accelerations. At each instant of velocity discontinuity, vorticity is shown to be generated by the boundary condition on the normal component of the velocity, for both inviscid and viscous flows. In viscous flows, the vorticity is shown to diffuse into the surroundings, and the no-slip conditions are automatically satisfied. A trailing edge condition must be satisfied for the solution to the Euler equations to be the limit of the solution of the Navier-Stokes equations.

Morino, L.

1986-01-01

317

A numerical resolution study of high order essentially non-oscillatory schemes applied to incompressible flow  

NASA Technical Reports Server (NTRS)

High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth-order central differences through fast Fourier transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large scale features, such as the total circulation around the roll-up region, are adequately resolved.

Weinan, E.; Shu, Chi-Wang

1994-01-01

318

A numerical resolution study of high order essentially non-oscillatory schemes applied to incompressible flow  

NASA Technical Reports Server (NTRS)

High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth order central differences through Fast Fourier Transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large-scale features, such as the total circulation around the roll-up region, are adequately resolved.

Weinan, E.; Shu, Chi-Wang

1992-01-01

319

Kinetically reduced local Navier-Stokes equations for simulation of incompressible viscous flows.  

PubMed

Recently, another approach to study incompressible fluid flow was suggested [S. Ansumali, I. Karlin, and H. Ottinger, Phys. Rev. Lett. 94, 080602 (2005)]-the kinetically reduced local Navier-Stokes (KRLNS) equations. We consider a simplified two-dimensional KRLNS system and compare it with Chorin's artificial compressibility method. A comparison of the two methods for steady state computation of the flow in a lid-driven cavity at various Reynolds numbers shows that the results from both methods are in good agreement with each other. However, in the transient flow, it is demonstrated that the KRLNS equations correctly describe the time evolution of the velocity and of the pressure, unlike the artificial compressibility method. PMID:18233940

Borok, S; Ansumali, S; Karlin, I V

2007-12-01

320

Viscid-inviscid interaction associated with incompressible flow past wedges at high Reynolds number  

NASA Technical Reports Server (NTRS)

An analytical method is suggested for the study of the viscid inviscid interaction associated with incompressible flow past wedges with arbitrary angles. It is shown that the determination of the nearly constant pressure (base pressure) prevailing within the near wake is really the heart of the problem, and the pressure can only be established from these interactive considerations. The basic free streamline flow field is established through two discrete parameters which adequately describe the inviscid flow around the body and the wake. The viscous flow processes such as the boundary layer buildup, turbulent jet mixing, and recompression are individually analyzed and attached to the inviscid flow in the sense of the boundary layer concept. The interaction between the viscous and inviscid streams is properly displayed by the fact that the aforementioned discrete parameters needed for the inviscid flow are determined by the viscous flow condition at the point of reattachment. It is found that the reattachment point behaves as a saddle point singularity for the system of equations describing the recompressive viscous flow processes, and this behavior is exploited for the establishment of the overall flow field. Detailed results such as the base pressure, pressure distributions on the wedge, and the geometry of the wake are determined as functions of the wedge angle.

Warpinski, N. R.; Chow, W. L.

1977-01-01

321

Computations of three-dimensional steady and unsteady viscous incompressible flows  

NASA Technical Reports Server (NTRS)

The INS3D family of computational fluid dynamics computer codes is presented. These codes are used to as tools in developing and assessing algorithms for solving the incompressible Navier-Stokes equations for steady-state and unsteady flow problems. This work involves applying the codes to real-world problems involving complex three-dimensional geometries. The algorithms utilized include the method of pseudocompressibility including both central and upwind differencing, several types of artificial dissipation schemes, approximate factorization, and an implicit line-relaxation scheme. These codes have been validated using a wide range of problems including flow over a backward-facing step, driven cavity flow, flow through various types of ducts, and steady and unsteady flow over a circular cylinder. Many diverse flow applications have been solved using these codes including parts of the Space Shuttle Main Engine, problems in naval hydrodynamics, low-speed aerodynamics, and biomedical fluid flows. The presentation details several of these, including the flow through a Space Shuttle Main Engine inducer, vortex shedding behind a circular cylinder, and flow through an artificial heart.

Kwak, Dochan; Rogers, Stuart E.; Yoon, Seokkwan; Rosenfeld, Moshe; Chang, Leon

1989-01-01

322

Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames  

NASA Technical Reports Server (NTRS)

Nonpremixed (diffusion) flames are attractive for practical applications because they avoid the stability, autoignition, flashback, etc. problems of premixed flames. Unfortunately, soot formation in practical hydrocarbon-fueled diffusion flames reduces their attractiveness due to widely-recognized public health and combustor durability problems of soot emissions. For example, more deaths are attributed to the emission of soot (15,000-60,000 deaths annually in the U.S. alone) than any other combustion-generated pollutant. In addition, continuum radiation from soot-containing flames is the principle heat load to combustor components and is mainly responsible for engine durability problems of aircraft and gas turbine engines. As a result, there is considerable interest in controlling both soot concentrations within flames and soot emissions from flames. Thus, the objective of the present investigation is to study ways to control soot formation in diffusion flames by manipulating the mixing process between the fuel and oxidant streams. In order to prevent the intrusion of gravity from masking flow properties that reduce soot formation in practical flames (where effects of gravity are small), methods developed during past work will be exploited to minimize effects of buoyant motion.

Dai, Z.; Faeth, G. M.

1999-01-01

323

Bacteriological testing of a modified laminar flow microbiological safety cabinet.  

PubMed

A modified microbiological safety cabinet which can be used as a class II and a class III safety cabinet has been bacteriologically tested. This cabinet makes use of a high-speed down-flow air curtain in the front opening to minimize the amount of air escaping over the arms of the operator. By using artificial aerosols and a dummy or a test person placing his arms into the working opening of the cabinet, a transfer from the inside to the environment was detected only when the highest concentration of the test aerosol was used. Since the number of bacteria detected was very low, this is considered to be acceptable. When the cabinet was used as a class III type, with a glove panel mounted in the front opening, leakage from the environment occurred. This could be completely prevented by fixing tape over the hinge of the front panel. The conclusion is drawn that this type of biohazard hood can be safely used as a class II and a class III microbiological safety cabinet, provided the construction of the hinge of the front panel will be adapted to prevent transfer from the environment to the working area. PMID:7149701

Heidt, P J

1982-01-01

324

Computational Analysis of a Laminar Jet in a Cross-Flow  

NASA Technical Reports Server (NTRS)

A jet in cross-flow (JIFC) consists of a jet exhausting at a large angle into a freestream flow. It is a flow field which is relevant to a wide variety of technologies and applications. Despite the nearly 65 years of JIFC research there are few results available for laminar hypersonic flows, a combination which will be encountered by re-entry and high altitude vehicles over some portion of their flight path. This research consists of developing a numerical model to investigate the interaction of a normal sonic jet exhausting into a hypersonic cross-flow. The model was validated by comparing experimental measurements with corresponding numerical results generated by the model.

Jeffries, Damon K.; Krishnamurthy, R.; Chandra, S.

1998-01-01

325

The response of a laminar boundary layer in supersonic flow to small amplitude progressive waves  

NASA Technical Reports Server (NTRS)

The effect of a small amplitude progressive wave on the laminar boundary layer on a semi-infinite flat plate, due to a uniform supersonic freestream flow, is considered. The perturbation to the flow divides into two streamwise zones. In the first, relatively close to the leading edge of the plate, on a transverse scale comparable to the boundary layer thickness, the perturbation flow is described by a form of the unsteady linearized compressible boundary layer equations. In the freestream, this component of flow is governed by the wave equation, the solution of which provides the outer velocity conditions for the boundary layer. This system is solved numerically, and also the asymptotic structure in the far downstream limit is studied. This reveals a breakdown and a subsequent second streamwise zone, where the flow disturbance is predominantly inviscid. The two zones are shown to match in a proper asymptotic sense.

Duck, Peter W.

1989-01-01

326

Laminar, turbulent, and inertial shear-thickening regimes in channel flow of neutrally buoyant particle suspensions.  

PubMed

The aim of this Letter is to characterize the flow regimes of suspensions of finite-size rigid particles in a viscous fluid at finite inertia. We explore the system behavior as a function of the particle volume fraction and the Reynolds number (the ratio of flow and particle inertia to viscous forces). Unlike single-phase flows, where a clear distinction exists between the laminar and the turbulent states, three different regimes can be identified in the presence of a particulate phase, with smooth transitions between them. At low volume fractions, the flow becomes turbulent when increasing the Reynolds number, transitioning from the laminar regime dominated by viscous forces to the turbulent regime characterized by enhanced momentum transport by turbulent eddies. At larger volume fractions, we identify a new regime characterized by an even larger increase of the wall friction. The wall friction increases with the Reynolds number (inertial effects) while the turbulent transport is weakly affected, as in a state of intense inertial shear thickening. This state may prevent the transition to a fully turbulent regime at arbitrary high speed of the flow. PMID:25554885

Lashgari, Iman; Picano, Francesco; Breugem, Wim-Paul; Brandt, Luca

2014-12-19

327

Development of quiet-flow supersonic wind tunnels for laminar-turbulent transition research  

NASA Technical Reports Server (NTRS)

This grant supported research into quiet-flow supersonic wind-tunnels, between May 1990 and December 1994. Quiet-flow nozzles operate with laminar nozzle-wall boundary layers, in order to provide low-disturbance flow for studies of laminar-turbulent transition under conditions comparable to flight. Major accomplishments include: (1) the design, fabrication, and performance-evaluation of a new kind of quiet tunnel, a quiet-flow Ludweig tube; (2) the integration of preexisting codes for nozzle design, 2D boundary-layer computation, and transition-estimation into a single user-friendly package for quiet-nozzle design; and (3) the design and preliminary evaluation of supersonic nozzles with square cross-section, as an alternative to conventional quiet-flow nozzles. After a brief summary of (1), a description of (2) is presented. Published work describing (3) is then summarized. The report concludes with a description of recent results for the Tollmien-Schlichting and Gortler instability in one of the square nozzles previously analyzed.

Schneider, Steven P.

1994-01-01

328

Laminar, Turbulent, and Inertial Shear-Thickening Regimes in Channel Flow of Neutrally Buoyant Particle Suspensions  

NASA Astrophysics Data System (ADS)

The aim of this Letter is to characterize the flow regimes of suspensions of finite-size rigid particles in a viscous fluid at finite inertia. We explore the system behavior as a function of the particle volume fraction and the Reynolds number (the ratio of flow and particle inertia to viscous forces). Unlike single-phase flows, where a clear distinction exists between the laminar and the turbulent states, three different regimes can be identified in the presence of a particulate phase, with smooth transitions between them. At low volume fractions, the flow becomes turbulent when increasing the Reynolds number, transitioning from the laminar regime dominated by viscous forces to the turbulent regime characterized by enhanced momentum transport by turbulent eddies. At larger volume fractions, we identify a new regime characterized by an even larger increase of the wall friction. The wall friction increases with the Reynolds number (inertial effects) while the turbulent transport is weakly affected, as in a state of intense inertial shear thickening. This state may prevent the transition to a fully turbulent regime at arbitrary high speed of the flow.

Lashgari, Iman; Picano, Francesco; Breugem, Wim-Paul; Brandt, Luca

2014-12-01

329

Identification of whistling ability of a single hole orifice from an incompressible flow simulation  

SciTech Connect

Pure tone noise from orifices in pipe result from vortex shedding with lock-in. Acoustic amplification at the orifice is coupled to resonant condition to create self-sustained oscillations. One key feature of this phenomenon is hence the ability of an orifice to amplify acoustic waves in a given range of frequencies. Here a numerical investigation of the linear response of an orifice is undertaken, with the support of experimental data for validation. The study deals with a sharp edge orifice. Its diameter equals to 0.015 m and its thickness to 0.005 m. The pipe diameter is 0.030 m. An air flow with a Mach number 0.026 and a Reynolds number 18000 in the main pipe is present. At such a low Mach number; the fluid behavior can reasonably be described as locally incompressible. The incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved with the help of a finite volume fluid mechanics software. The orifice is submitted to an average flow velocity, with superimposed small harmonic perturbations. The harmonic response of the orifice is the difference between the upstream and downstream pressures, and a straightforward calculation brings out the acoustic impedance of the orifice. Comparison with experiments shows that the main physical features of the whistling phenomenon are reasonably reproduced. (authors)

Lacombe, Romain; Moussou, Pierre [LaMSID - UMR EDF/CNRS/CEA, DEN-DM2S, 8193 EDF R et D, 1 avenue du General de Gaulle, 92141 Clamart Cedex (France); Auregan, Yves [Universite du Maine, Le Mans, (France)

2012-07-01

330

Large-scale computation of incompressible viscous flow by least-squares finite element method  

NASA Technical Reports Server (NTRS)

The least-squares finite element method (LSFEM) based on the velocity-pressure-vorticity formulation is applied to large-scale/three-dimensional steady incompressible Navier-Stokes problems. This method can accommodate equal-order interpolations and results in symmetric, positive definite algebraic system which can be solved effectively by simple iterative methods. The first-order velocity-Bernoulli function-vorticity formulation for incompressible viscous flows is also tested. For three-dimensional cases, an additional compatibility equation, i.e., the divergence of the vorticity vector should be zero, is included to make the first-order system elliptic. The simple substitution of the Newton's method is employed to linearize the partial differential equations, the LSFEM is used to obtain discretized equations, and the system of algebraic equations is solved using the Jacobi preconditioned conjugate gradient method which avoids formation of either element or global matrices (matrix-free) to achieve high efficiency. To show the validity of this scheme for large-scale computation, we give numerical results for 2D driven cavity problem at Re = 10000 with 408 x 400 bilinear elements. The flow in a 3D cavity is calculated at Re = 100, 400, and 1,000 with 50 x 50 x 50 trilinear elements. The Taylor-Goertler-like vortices are observed for Re = 1,000.

Jiang, Bo-Nan; Lin, T. L.; Povinelli, Louis A.

1993-01-01

331

Stability of the laminar boundary-layer flow behind a roughness element  

NASA Astrophysics Data System (ADS)

Roughness elements in laminar boundary layers generate both high shear layers and streaky structures. Because these phenomena interact, it is difficult to precisely ascertain the dominant instability mechanisms. With the goal of explicating such interactions, we study the stability of a laminar boundary layer subject to a single roughness element at a Reynolds number subcritical of bypass transition. Our work involves two parts: bi-global linear stability theory (LST) analysis and corroborating experimental measurements. Linear stability analysis of a flat-plate boundary layer perturbed by streamwise streaks reveals the presence of several unstable modes. Of the dominant two modes, one exhibits spanwise symmetry and the other is antisymmetric. These modes are termed `varicose' and `sinuous,' respectively. Corroborating experiments were conducted in the laminar water channel of the University of Stuttgart. By simultaneously traversing two hot-film probes, we are able to confirm the presence of both eigenmodes predicted by LST and to extract relevant data for each: eigenvalues, eigenfunctions, growth rates and phase distributions. The main part of the experiments has been performed under `natural' conditions, i.e., in the absence of external forcing. As the amplitude of the sinuous part of the results is much smaller than the varicose one and hence affected by measurement noise, a case with asymmetric external forcing is presented as well. Despite some deficiencies of the setup, it is possible to enhance the sinuous mode with respect to the unforced case and to confirm its existence as an eigenmode of the flow.

Shin, Yong-su; Rist, Ulrich; Krämer, Ewald

2015-01-01

332

Parallel-plate Flow Chamber and Continuous Flow Circuit to Evaluate Endothelial Progenitor Cells under Laminar Flow Shear Stress  

PubMed Central

The overall goal of this method is to describe a technique to subject adherent cells to laminar flow conditions and evaluate their response to well quantifiable fluid shear stresses1. Our flow chamber design and flow circuit (Fig. 1) contains a transparent viewing region that enables testing of cell adhesion and imaging of cell morphology immediately before flow (Fig. 11A, B), at various time points during flow (Fig. 11C), and after flow (Fig. 11D). These experiments are illustrated with human umbilical cord blood-derived endothelial progenitor cells (EPCs) and porcine EPCs2,3. This method is also applicable to other adherent cell types, e.g. smooth muscle cells (SMCs) or fibroblasts. The chamber and all parts of the circuit are easily sterilized with steam autoclaving. In contrast to other chambers, e.g. microfluidic chambers, large numbers of cells (> 1 million depending on cell size) can be recovered after the flow experiment under sterile conditions for cell culture or other experiments, e.g. DNA or RNA extraction, or immunohistochemistry (Fig. 11E), or scanning electron microscopy5. The shear stress can be adjusted by varying the flow rate of the perfusate, the fluid viscosity, or the channel height and width. The latter can reduce fluid volume or cell needs while ensuring that one-dimensional flow is maintained. It is not necessary to measure chamber height between experiments, since the chamber height does not depend on the use of gaskets, which greatly increases the ease of multiple experiments. Furthermore, the circuit design easily enables the collection of perfusate samples for analysis and/or quantification of metabolites secreted by cells under fluid shear stress exposure, e.g. nitric oxide (Fig. 12)6. PMID:22297325

Lane, Whitney O.; Jantzen, Alexandra E.; Carlon, Tim A.; Jamiolkowski, Ryan M.; Grenet, Justin E.; Ley, Melissa M.; Haseltine, Justin M.; Galinat, Lauren J.; Lin, Fu-Hsiung; Allen, Jason D.; Truskey, George A.; Achneck, Hardean E.

2012-01-01

333

Phenomenon of concentrical spiral separation of microparticles in laminar vortical blood flow.  

PubMed

1. Previously unknown phenomenon of a stable ordered laminar vortical blood flow of opposite direction has been discovered in the systemic and pulmonary circulations consisting in the fact that in the circulation system there exists a rotative, twisted, spiral-like blood movement due to (a) special organization of intracavitary architectonics of heart and blood vessels in the form of funnel-like cavities with tangential inflow into the heart, outflow from the heart and blood vessel branching, (b) twisting character of contraction of spiral-oriented muscular elements creating the ejection effect of the vortical blood jet. 2. Previously unknown phenomenon of concentrical spiral separation of blood microparticles has been discovered consisting in the fact that in moving blood there exists a layered distribution of microparticles on flow radius according to their size and mass due tot the stable ordered laminar vortical blood flow of opposite direction in the systemic and pulmonary circulations, the largest and heaviest microparticles constituting the axial nucleus of the flow and the smallest and lightest microparticles constituting parietal layers. PMID:8522566

Zakharov, V N

1995-10-01

334

Development of a compact laminar flow heat exchanger with stainless steel micro-tubes  

NASA Astrophysics Data System (ADS)

The present paper describes the design concept and manufacturing of a new compact laminar flow heat exchanger with stainless-steel micro-tubes for helium refrigerators. In the temperature range of less than 20 K, aluminum plate fin type heat exchangers exhibit a remarkable fall of performance characteristics as a compact heat exchanger. We presented in a previous paper that some compact heat exchangers with good performance in the temperature range of less than 4 K are required for a subcooled He II refrigerator cycle to be worked with 3He turbo-compressors (F. Doty, et al., A new look at the closed brayton cycle, Proceedings, IECEC-90 Reno, NV, 1991, p. 116). For this requirement, we developed a micro-tube strip counter flow type heat exchanger, which consists of 12 elements with a total of 4800 stainless steel micro-tubes. Each element is formed with 400 tubes and a newly developed vacuum brazing method was applied for the bonding to the side plate. Each tube has an inner diameter of 0.5 mm, an outer diameter of 0.7 mm and is 310 mm long. We developed a cladding plate with two layers of gold brazing sheet sandwiched inside. In aerodynamic and thermal design of the element, the laminar flow conditions were adopted for the flows of inner and outer tubes to keep a high heat transfer rate and a low pressure loss.

Saji, N.; Nagai, S.; Tsuchiya, K.; Asakura, H.; Obata, M.

2001-05-01

335

Moderated, Water-Based, Condensational Particle Growth in a Laminar Flow  

PubMed Central

Presented is a new approach for laminar-flow water condensation that produces saturations above 1.5 while maintaining temperatures of less than 30°C in the majority of the flow and providing an exiting dew point below 15°C. With the original laminar flow water condensation method, the particle activation and growth occurs in a region with warm, wetted walls throughout, which has the side-effect of heating the flow. The “moderated” approach presented here replaces this warm region with a two sections – a short, warm, wet-walled “initiator”, followed by a cool-walled “moderator”. The initiator provides the water vapor that creates the supersaturation, while the moderator provides the time for particle growth. The combined length of the initiator and moderator sections is the same as that of the original, warm-walled growth section. Model results show that this new approach reduces the added heat and water vapor while achieving the same peak supersaturation and similar droplet growth. Experimental measurements confirm the trends predicted by the modeling. PMID:24839342

Hering, Susanne V.; Spielman, Steven R.; Lewis, Gregory S.

2014-01-01

336

Laminar flow mediated continuous single-cell analysis on a novel poly(dimethylsiloxane) microfluidic chip.  

PubMed

A novel microfluidic chip with simple design, easy fabrication and low cost, coupled with high-sensitive laser induced fluorescence detection, was developed to provide continuous single-cell analysis based on dynamic cell manipulation in flowing streams. Making use of laminar flows, which formed in microchannels, single cells were aligned and continuously introduced into the sample channel and then detection channel in the chip. In order to rapidly lyse the moving cells and completely transport cellular contents into the detection channel, the angle of the side-flow channels, the asymmetric design of the channels, and the number, shape and layout of micro-obstacles were optimized for effectively redistributing and mixing the laminar flows of single cells suspension, cell lysing reagent and detection buffer. The optimized microfluidic chip was an asymmetric structure of three microchannels, with three microcylinders at the proper positions in the intersections of channels. The microchip was evaluated by detection of anticancer drug doxorubicin (DOX) uptake and membrane surface P-glycoprotein (P-gp) expression in single leukemia K562 cells. An average throughput of 6-8 cells min(-1) was achieved. The detection results showed the cellular heterogeneity in DOX uptake and surface P-gp expression within K562 cells. Our researches demonstrated the feasibility and simplicity of the newly developed microfluidic chip for chemical single-cell analysis. PMID:24745743

Deng, Bin; Tian, Yu; Yu, Xu; Song, Jian; Guo, Feng; Xiao, Yuxiu; Zhang, Zhiling

2014-04-11

337

Flutter control of incompressible flow turbomachine blade rows by splitter blades  

NASA Technical Reports Server (NTRS)

Splitter blades as a passive flutter control technique is investigated by developing a mathematical model to predict the stability of an aerodynamically loaded splittered-rotor operating in an incompressible flow field. The splitter blades, positioned circumferentially in the flow passage between two principal blades, introduce aerodynamic and/or combined aerodynamic-structural detuning into the rotor. The two-dimensional oscillating cascade unsteady aerodynamics, including steady loading effects, are determined by developing a complete first-order unsteady aerodynamic analysis together with an unsteady aerodynamic influence coefficient technique. The torsion mode flutter of both uniformly spaced tuned rotors and detuned rotors are predicted by incorporating the unsteady aerodyamic influence coefficients into a single-degree-of-freedom aeroelastic model. This model is then utilized to demonstrate that incorporating splitters into unstable rotor configurations results in stable splittered-rotor configurations.

Chiang, Hsiao-Wei D.; Fleeter, Sanford

1991-01-01

338

Parallel solution of high-order numerical schemes for solving incompressible flows  

NASA Technical Reports Server (NTRS)

A new parallel numerical scheme for solving incompressible steady-state flows is presented. The algorithm uses a finite-difference approach to solving the Navier-Stokes equations. The algorithms are scalable and expandable. They may be used with only two processors or with as many processors as are available. The code is general and expandable. Any size grid may be used. Four processors of the NASA LeRC Hypercluster were used to solve for steady-state flow in a driven square cavity. The Hypercluster was configured in a distributed-memory, hypercube-like architecture. By using a 50-by-50 finite-difference solution grid, an efficiency of 74 percent (a speedup of 2.96) was obtained.

Milner, Edward J.; Lin, Avi; Liou, May-Fun; Blech, Richard A.

1993-01-01

339

Frequency-selection mechanism in incompressible open-cavity flows via reflected instability waves  

NASA Astrophysics Data System (ADS)

We present an alternative perspective on nonharmonic mode coexistence, commonly found in the shear layer spectrum of open-cavity flows. Modes obtained by a local linear stability analysis of perturbations to a two-dimensional, incompressible, and inviscid sheared flow over a cavity of finite length and depth were conditioned by a so-called coincidence condition first proposed by Kulikowskii [J. Appl. Math. Mech. 30, 180 (1966), 10.1016/0021-8928(66)90066-9] which takes into account instability wave reflection within the cavity. The analysis yields a set of discrete, nonharmonic frequencies, which compare well with experimental results [Phys. Fluids 20, 114101 (2008), 10.1063/1.3005435; Exp. Fluids 50, 905 (2010), 10.1007/s00348-010-0942-9].

Tuerke, F.; Sciamarella, D.; Pastur, L. R.; Lusseyran, F.; Artana, G.

2015-01-01

340

Stationary MHD waves modified by Hall current coupling -- 2: Incompressible flow  

NASA Astrophysics Data System (ADS)

In this paper we consider the incompressible limit of the general development presented in Woodward and McKenzie (1994), who analyze the system of stationary waves generated by a point source current immersed in a flowing magnetoplasma including Hall current effects. There are two wave modes present in this limit, namely the fast and slow modes, both of which are semi-field-aligned, and the slow mode experiences a resonance at the proton gyrofrequency. In contrast to the compressible situation, the magnetic pressure perturbation displays a Laplacian decay in addition to the characteristics of the fast and slow modes. Furthermore in the very sub-Alfvenic flow limit, the parallel current and magnetic pressure disturbances together with the associated electric potential perturbation are predominantly of fast mode character.

Woodward, T. I.; McKenzie, J. F.

1994-06-01

341

Numerical simulation of unsteady incompressible viscous flows in generalized coordinate systems  

NASA Technical Reports Server (NTRS)

Several numerical solutions of the three dimensional unsteady incompressible Navier-Stokes equations in generalized coordinate systems are presented. The governing equations are discretized by finite volumes with special care to the accurate approximation of the geometric quantities. The unknowns are the pressure and the volume fluxes over the computational cell faces. This formulation results in a robust fractional step solution method for solving discrete equations. Although this method is formulated for the three dimensional case, only two dimensional unsteady results are given. Results are presented for a lid driven two dimensional cavity flow at Reynolds number of 10,000, and for the flow over a circular cylinder with vortex shedding for several Reynolds numbers in the range 100 less than Re less than 1000.

Rosenfeld, Moshe; Kwak, Dochan

1988-01-01

342

A lattice kinetic scheme for incompressible viscous flows with heat transfer.  

PubMed

A lattice kinetic scheme for incompressible viscous flows with heat transfer is developed based on the lattice Boltzmann method. In the new scheme, macroscopic variables are calculated without velocity distribution functions. Thus, the scheme can save computer memory because there is no need to store the velocity distribution functions. Governing equations for the macroscopic variables are obtained by applying the asymptotic theory. The continuity equation, the Navier-Stokes equations, and the convection-diffusion equation for fluid temperature are obtained with relative errors of O(epsilon2), where epsilon is a small parameter that is of the same order as a lattice spacing and is related to a relaxation parameter. In order to verify the accuracy of the scheme, natural convection flows in a square cavity are simulated, and the calculated results are in good agreement with available standard results. PMID:16210191

Inamuro, Takaji

2002-03-15

343

Effect of varied air flow on flame structure of laminar inverse diffusion flames.  

SciTech Connect

The structure of laminar inverse diffusion flames (IDFs) of methane and ethylene was studied using a cylindrical co-flowing burner. Several flames of the same fuel flow-rate yet various air flow-rates were examined. Heights of visible flames were obtained using measurements of hydroxyl (OH) laser-induced fluorescence (LIF) and visible images. Polycyclic aromatic hydrocarbon (PAH) LIF and soot laser-induced incandescence (LII) were also measured. In visible images, radiating soot masks the blue region typically associated with the flame height in normal diffusion flames (NDFs). Increased air flow-rates resulted in longer flames. PAH LIF and soot LII indicated that PAh and soot are present on the fuel side of the flame and that soot is located closer to the reaction zone than PAH. Ethylene flames produced significantly higher PAH LIF and soot LII signals than methane flames, which is consistent with the sooting propensity of ethylene.

Shaddix, Christopher R.; Williams, Timothy C.; Blevins, Linda Gail; Mikofski, Mark A. (University of California Berkeley)

2004-03-01

344

Experimental Study of Saddle Point of Attachment in Laminar Juncture Flow  

NASA Technical Reports Server (NTRS)

An experimental study of laminar horseshoe vortex flows upstream of a cylinder/flat plate juncture has been conducted to verify the existence of saddle-point-of-attachment topologies. In the classical depiction of this flowfield, a saddle point of separation exists on the flat plate upstream of the cylinder, and the boundary layer separates from the surface. Recent computations have indicated that the topology may actually involve a saddle point of attachment on the surface and additional singular points in the flow. Laser light sheet flow visualizations have been performed on the symmetry plane and crossflow planes to identify the saddle-point-of-attachment flowfields. The visualizations reveal that saddle-point-of-attachment topologies occur over a range of Reynolds numbers in both single and multiple vortex regimes. An analysis of the flow topologies is presented that describes the existence and evolution of the singular points in the flowfield.

Coon, Michael D.; Tobak, Murray

1995-01-01

345

Active control of instabilities in laminar boundary-layer flow. Part 1: An overview  

NASA Technical Reports Server (NTRS)

This paper (the first in a series) focuses on using active-control methods to maintain laminar flow in a region of the flow in which the natural instabilities, if left unattended, lead to turbulent flow. The authors review previous studies that examine wave cancellation (currently the most prominent method) and solve the unsteady, nonlinear Navier-Stokes equations to evaluate this method of controlling instabilities. It is definitely shown that instabilities are controlled by the linear summation of waves (i.e., wave cancellation). Although a mathematically complete method for controlling arbitrary instabilities has been developed (but not yet tested), the review, duplication, and physical explanation of previous studies are important steps for providing an independent verification of those studies, for establishing a framework for subsequent work which will involve automated transition control, and for detailing the phenomena by which the automated studies can be used to expand knowledge of flow control.

Joslin, Ronald D.; Erlebacher, Gordon; Hussaini, M. Yousuff

1994-01-01

346

The NASA Langley Laminar-Flow-Control (LFC) experiment on a swept, supercritical airfoil: Design overview  

NASA Technical Reports Server (NTRS)

A large-chord, swept, supercritical, laminar-flow-control (LFC) airfoil was designed and constructed and is currently undergoing tests in the Langley 8 ft Transonic Pressure Tunnel. The experiment was directed toward evaluating the compatibility of LFC and supercritical airfoils, validating prediction techniques, and generating a data base for future transport airfoil design as part of NASA's ongoing research program to significantly reduce drag and increase aircraft efficiency. Unique features of the airfoil included a high design Mach number with shock free flow and boundary layer control by suction. Special requirements for the experiment included modifications to the wind tunnel to achieve the necessary flow quality and contouring of the test section walls to simulate free air flow about a swept model at transonic speeds. Design of the airfoil with a slotted suction surface, the suction system, and modifications to the tunnel to meet test requirements are discussed.

Harris, Charles D.; Harvey, William D.; Brooks, Cuyler W., Jr.

1988-01-01

347

An a-posteriori finite element error estimator for adaptive grid computation of viscous incompressible flows  

NASA Astrophysics Data System (ADS)

In this thesis, an a-posteriori error estimator is presented and employed for solving viscous incompressible flow problems. In an effort to detect local flow features, such as vortices and separation, and to resolve flow details precisely, a velocity angle error estimator e theta which is based on the spatial derivative of velocity direction fields is designed and constructed. The a-posteriori error estimator corresponds to the antisymmetric part of the deformation-rate-tensor, and it is sensitive to the second derivative of the velocity angle field. Rationality discussions reveal that the velocity angle error estimator is a curvature error estimator, and its value reflects the accuracy of streamline curves. It is also found that the velocity angle error estimator contains the nonlinear convective term of the Navier-Stokes equations, and it identifies and computes the direction difference when the convective acceleration direction and the flow velocity direction have a disparity. Through benchmarking computed variables with the analytic solution of Kovasznay flow or the finest grid of cavity flow, it is demonstrated that the velocity angle error estimator has a better performance than the strain error estimator. The benchmarking work also shows that the computed profile obtained by using etheta can achieve the best matching outcome with the true theta field, and that it is asymptotic to the true theta variation field, with a promise of fewer unknowns. Unstructured grids are adapted by employing local cell division as well as unrefinement of transition cells. Using element class and node class can efficiently construct a hierarchical data structure which provides cell and node inter-reference at each adaptive level. Employing element pointers and node pointers can dynamically maintain the connection of adjacent elements and adjacent nodes, and thus avoids time-consuming search processes. The adaptive scheme is applied to viscous incompressible flow at different Reynolds numbers. It is found that the velocity angle error estimator can detect most flow characteristics and produce dense grids in the regions where flow velocity directions have abrupt changes. In addition, the e theta estimator makes the derivative error dilutely distribute in the whole computational domain and also allows the refinement to be conducted at regions of high error. Through comparison of the velocity angle error across the interface with neighbouring cells, it is verified that the adaptive scheme in using etheta provides an optimum mesh which can clearly resolve local flow features in a precise way. The adaptive results justify the applicability of the etheta estimator and prove that this error estimator is a valuable adaptive indicator for the automatic refinement of unstructured grids.

Wu, Heng

2000-10-01

348

Multiphase lattice Boltzmann flux solver for incompressible multiphase flows with large density ratio  

NASA Astrophysics Data System (ADS)

A multiphase lattice Boltzmann flux solver (MLBFS) is proposed in this paper for incompressible multiphase flows with low- and large-density-ratios. In the solver, the flow variables at cell centers are given from the solution of macroscopic governing differential equations (Navier-Stokes equations recovered by multiphase lattice Boltzmann (LB) model) by the finite volume method. At each cell interface, the viscous and inviscid fluxes are evaluated simultaneously by local reconstruction of solution for the standard lattice Boltzmann equation (LBE). The forcing terms in the governing equations are directly treated by the finite volume discretization. The phase interfaces are captured by solving the phase-field Cahn-Hilliard equation with a fifth order upwind scheme. Unlike the conventional multiphase LB models, which restrict their applications on uniform grids with fixed time step, the MLBFS has the capability and advantage to simulate multiphase flows on non-uniform grids. The proposed solver is validated by several benchmark problems, such as two-phase co-current flow, Taylor-Couette flow in an annulus, Rayleigh-Taylor instability, and droplet splashing on a thin film at density ratio of 1000 with Reynolds numbers ranging from 20 to 1000. Numerical results show the reliability of the proposed solver for multiphase flows with high density ratio and high Reynolds number.

Wang, Y.; Shu, C.; Huang, H. B.; Teo, C. J.

2015-01-01

349

Flight evaluation of an insect contamination protection system for laminar flow wings  

NASA Technical Reports Server (NTRS)

The maintenance of minimum wing leading edge contamination is critical to the preservation of drag-reducing laminar flow; previous methods for the prevention of leading edge contamination by insects have, however, been rendered impractical by their excessive weight, cost, or inconvenience. Attention is presently given to the results of a NASA flight experiment which evaluated the performance of a porous leading edge fluid-discharge ice protection system in the novel role of insect contamination removal; high insect contamination conditions were also noted in the experiment. Very small amounts of the fluid are found to be sufficient for insect contamination protection.

Croom, C. C.; Holmes, B. J.

1985-01-01

350

Natural laminar flow flight experiments on a swept-wing business jet  

NASA Technical Reports Server (NTRS)

Flight test experiments have been conducted to measure the extent and nature of laminar flow on a smoothed test region of a swept-wing business jet. Surface hot film anemometers and sublimating chemicals were used for transition detection. Surface pressure distributions were measured using pressure belts. Instrumentation techniques and problems are presented. Correlation was obtained between the hot film and sublimating chemicals for transition detection. Taylor-Goertler vortices were observed for some flight conditions. Boundary layer stability analysis is being conducted using measured pressure distributions to determine the correlation possible for transition prediction on swept wings.

Wentz, W. H., Jr.; Nyenhuis, R.; Ahmed, A.

1984-01-01

351

An Exploratory Investigation of a Slotted, Natural-Laminar-Flow Airfoil  

NASA Technical Reports Server (NTRS)

A 15-percent-thick, slotted, natural-laminar-flow (SNLF) airfoil, the S103, for general aviation applications has been designed and analyzed theoretically and verified experimentally in the Langley Low-Turbulence Pressure Tunnel. The two primary objectives of high maximum lift and low profile drag have been achieved. The constraints on the pitching moment and the airfoil thickness have been satisfied. The airfoil exhibits a rapid stall, which does not meet the design goal. Comparisons of the theoretical and experimental results show good agreement. Comparison with the baseline, NASA NLF(1)-0215F airfoil confirms the achievement of the objectives.

Somers, Dan M.

2012-01-01

352

Evaluation of laminar flow control systems concepts for subsonic commercial transport aircraft  

NASA Technical Reports Server (NTRS)

An evaluation was made of laminar flow control (LFC) system concepts for subsonic commercial transport aircraft. Configuration design studies, performance analyses, fabrication development, structural testing, wind tunnel testing, and contamination-avoidance techniques were included. As a result of trade studies, a configuration with LFC on the upper wing surface only, utilizing an electron beam-perforated suction surface, and employing a retractable high-lift shield for contamination avoidance, was selected as the most practical LFC system. The LFC aircraft was then compared with an advanced turbulent aircraft designed for the same mission. This comparison indicated significant fuel savings and reduced direct operating cost benefits would result from using LFC.

Pearce, W. E.

1983-01-01

353

Effects of an aft facing step on the surface of a laminar flow glider wing  

NASA Technical Reports Server (NTRS)

A motor glider was used to perform a flight test study on the effects of aft facing steps in a laminar boundary layer. This study focuses on two dimensional aft facing steps oriented spanwise to the flow. The size and location of the aft facing steps were varied in order to determine the critical size that will force premature transition. Transition over a step was found to be primarily a function of Reynolds number based on step height. Both of the step height Reynolds numbers for premature and full transition were determined. A hot film anemometry system was used to detect transition.

Sandlin, Doral R.; Saiki, Neal

1993-01-01

354

Unique laminar-flow stability limit based shallow-water theory  

USGS Publications Warehouse

Two approaches are generally taken in deriving the stability limit for the Froude member (Fs) for laminar sheet flow. The first approach used the Orr-Sommerfeld equation, while the second uses the cross-section-averaged equations of continuity and motion. Because both approaches are based on shallow-water theory, the values of Fs obtained from both approaches should be identical, yet in the literature they are not. This suggests that a defect exists in at least one of the two approaches. After examining the governing equations used in both approaches, one finds that the existing cross-section -averaged equation of motion is dependent on the frame of reference.

Chen, Cheng-lung

1993-01-01

355

Natural laminar flow airfoil design considerations for winglets on low-speed airplanes  

NASA Technical Reports Server (NTRS)

Winglet airfoil section characteristics which significantly influence cruise performance and handling qualities of an airplane are discussed. A good winglet design requires an airfoil section with a low cruise drag coefficient, a high maximum lift coefficient, and a gradual and steady movement of the boundary layer transition location with angle of attack. The first design requirement provides a low crossover lift coefficient of airplane drag polars with winglets off and on. The other requirements prevent nonlinear changes in airplane lateral/directional stability and control characteristics. These requirements are considered in the design of a natural laminar flow airfoil section for winglet applications and chord Reynolds number of 1 to 4 million.

Vandam, C. P.

1984-01-01

356

Design and experimental results for a flapped natural-laminar-flow airfoil for general aviation applications  

NASA Technical Reports Server (NTRS)

A flapped natural laminar flow airfoil for general aviation applications, the NLF(1)-0215F, has been designed and analyzed theoretically and verified experimentally in the Langley Low Turbulence Pressure Tunnel. The basic objective of combining the high maximum lift of the NASA low speed airfoils with the low cruise drag of the NACA 6 series airfoils has been achieved. The safety requirement that the maximum lift coefficient not be significantly affected with transition fixed near the leading edge has also been met. Comparisons of the theoretical and experimental results show generally good agreement.

Somers, D. M.

1981-01-01

357

Laminar mixed convection heat transfer in axial flow-through cylinders  

SciTech Connect

Laminar heat transfer in combined forced- and natural-convective axial flow of fluid through closely packed triangular and square arrays of cylinders with a uniform wall temperature are investigated experimentally. Experiments are conducted for cooling a liquid (ethylene glycol) flowing vertically upward and vertically downward in heat-transfer ducts of the same cross sections formed by both arrays of contacting cylinders, and the boundary condition of uniform temperature at the cylinder wall is substantially achieved. By comparing the experimental results with the authors' previous numerical results, semi-empirical equations suitable for predicting the logarithmic-mean Nusselt number are derived for closely packed cylinders with the pitch-to-diameter ratios of 1 to 1.1 and 1 to 1.2 for triangular and square arrays, respectively. In the case of laminar heat transfer in forced-convective axial fluid flow through a triangular array of cylinders with a uniform wall heat flux, the experimental results of the multipoint arithmetic-mean Nusselt number obtained by Kim et al. are found to be less in agreement with the authors' previous numerical results. the discrepancy between the two results is seen to be primarily due to the overestimation of the transitional Reynolds number.

Miyatake, Osamu; Omori, Hiromi

1993-10-01

358

Petrov-Galerkin finite element stabilization for two-phase flows  

NASA Astrophysics Data System (ADS)

A finite element model for incompressible laminar two-phase flows is presented. A two-fluid model, describing the laminar non-equilibrium flow of two incompressible phases, is discretized by means of a properly designed streamline upwind Petrov-Galerkin (SUPG) finite element procedure. Such a procedure is consistent with a continuous pressure equation. The design and the implementation of the algorithm are presented together with its validation throughout a comparison with simulations available in the literature.

Giordano, Michele; Magi, Vinicio

2006-07-01

359

Finite-difference solution of the Navier-Stokes equations for incompressible three-dimensional internal flows  

Microsoft Academic Search

An {nte9ration technique is presented for solving the Navier-Stokes equations of an incompressible homogeneous fluid flow through vessels with time- and space-dependent cross-sections. Interest in such problems is motivated by blood flow and diffusion problems in cardiovascular and bronchial systems. The entire flow field is split into several domains of integration. The coordinates are oriented along the major axes of

Nan-suey Liu

360

Simulations of granular bed erosion due to laminar shear flow near the critical Shields number  

NASA Astrophysics Data System (ADS)

Direct numerical simulations of granular beds consisting of uniformly sized spherical particles being eroded by a shear flow of Newtonian liquid have been performed. The lattice-Boltzmann method has been used for resolving the flow of the interstitial liquid. Fluid and solid dynamics are fully coupled with the particles having finite size and undergoing hard-sphere collisions. Only laminar flow has been considered with particle-based Reynolds numbers in the range 0.02 to 0.6. The parameter range of the simulations covers the transition between static and mobilized beds. The transition occurs for 0.10

Derksen, J. J.

2011-11-01

361

Application of Hybrid Laminar Flow Control to Global Range Military Transport Aircraft  

NASA Technical Reports Server (NTRS)

A study was conducted to evaluate the application of hybrid laminar flow control (HLFC) to global range military transport aircraft. The global mission included the capability to transport 132,500 pounds of payload 6500 nautical miles, land and deliver the payload and without refueling return 6500 nautical miles to a friendly airbase. The preliminary design studies show significant performance benefits obtained for the HLFC aircraft as compared to counterpart turbulent flow aircraft. The study results at M=0.77 show that the largest benefits of HLFC are obtained with a high wing with engines on the wing configuration. As compared with the turbulent flow baseline aircraft, the high wing HLFC aircraft shows 17 percent reduction in fuel burned, 19.2 percent increase in lift-to-drag ratio, an insignificant increase in operating weight, and a 7.4 percent reduction in gross weight.

Lange, Roy H.

1988-01-01

362

Laminar boundary layer on cone in supersonic flow at large angle of attack  

NASA Technical Reports Server (NTRS)

The laminar boundary-layer flow about a circular cone at large angles of attack to a supersonic stream has been analyzed in the plane of symmetry by a method applicable in general to the flow about conical bodies. At the bottom of the cone, velocity profiles were obtained showing the expected tendency of the boundary layer to become thinner on the under side of the cone as the angle of attack is increased. At the top of the cone, the analysis failed to yield unique solutions except for small angles of attack. Beyond a certain critical angle of attack, boundary-layer flow does not exist in the plane of symmetry, thus indicating separation. This critical angle is presented as a function of Mach number and cone vertex angle.

Moore, Franklin K

1953-01-01

363

Three-Dimensional Vortex Simulation of Time Dependent Incompressible Internal Viscous Flows  

NASA Astrophysics Data System (ADS)

A hybrid random vortex-boundary element method is developed for the solution of time-dependent incompressible three-dimensional internal flow problems. The numerical scheme is grid-free within the flow domain and is based on a combination of the Lagrangian vortex method to capture the convection and stretch of the vortical field, the random walk method to describe the diffusion process, and the boundary element method to superimpose a potential flow on the vortical field such that the normal flux boundary condition is satisfied. The no-slip boundary condition is satisfied by generating vorticity tiles on solid boundaries, which are subsequently diffused and convected into the flow interior. Additionally, a boundary condition is devised for the application of fully developed flow properties at the exit plane. In this paper, the formulation and the numerical scheme are presented, followed by a parametric study of the accuracy of the method using the model problem of the flow in a duct with square cross section at R e= 100. We show that the method converges to the analytical solution of the problem as the resolution of the time integration and the discretization are improved, and we discuss the impact of each resolution parameter on the accuracy. In addition, selected results from the simulation of an impulsively started flow over a cube at R e= 100 are presented. We use the results of this test case to demonstrate that the method captures the effect of sharp edges, parallel and normal to the streamwise flow direction, on the flow dynamics.

Gharakhani, Adrin; Ghoniem, Ahmed F.

1997-06-01

364

Direct Numerical Simulation of Incompressible Pipe Flow Using a B-Spline Spectral Method  

NASA Technical Reports Server (NTRS)

A numerical method based on b-spline polynomials was developed to study incompressible flows in cylindrical geometries. A b-spline method has the advantages of possessing spectral accuracy and the flexibility of standard finite element methods. Using this method it was possible to ensure regularity of the solution near the origin, i.e. smoothness and boundedness. Because b-splines have compact support, it is also possible to remove b-splines near the center to alleviate the constraint placed on the time step by an overly fine grid. Using the natural periodicity in the azimuthal direction and approximating the streamwise direction as periodic, so-called time evolving flow, greatly reduced the cost and complexity of the computations. A direct numerical simulation of pipe flow was carried out using the method described above at a Reynolds number of 5600 based on diameter and bulk velocity. General knowledge of pipe flow and the availability of experimental measurements make pipe flow the ideal test case with which to validate the numerical method. Results indicated that high flatness levels of the radial component of velocity in the near wall region are physical; regions of high radial velocity were detected and appear to be related to high speed streaks in the boundary layer. Budgets of Reynolds stress transport equations showed close similarity with those of channel flow. However contrary to channel flow, the log layer of pipe flow is not homogeneous for the present Reynolds number. A topological method based on a classification of the invariants of the velocity gradient tensor was used. Plotting iso-surfaces of the discriminant of the invariants proved to be a good method for identifying vortical eddies in the flow field.

Loulou, Patrick; Moser, Robert D.; Mansour, Nagi N.; Cantwell, Brian J.

1997-01-01

365

Effectiveness of micro synthetic jet actuator enhanced by flow instability in controlling laminar separation caused by adverse pressure gradient  

Microsoft Academic Search

This paper aims to understand how a micro synthetic jet actuator works effectively to prevent the boundary layer flow from laminar separation caused by adverse pressure gradient. Experimental results showed that synthetic jets were effective when the forcing frequency was a lower frequency of the Tollmien–Schlichting (T–S) wave, which received amplification from the base flow. They demonstrated the feasibility of

Guang Hong

2006-01-01

366

Laminar flow in a microchannel with superhydrophobic walls exhibiting transverse ribs  

NASA Astrophysics Data System (ADS)

One approach recently proposed for reducing the frictional resistance to liquid flow in microchannels is the patterning of microribs and cavities on the channel walls. When treated with a hydrophobic coating, the liquid flowing in the microchannel wets only the surfaces of the ribs, and does not penetrate the cavities, provided the pressure is not too high. The net result is a reduction in the surface contact area between channel walls and the flowing liquid. For microribs and cavities that are aligned normal to the channel axis (principal flow direction), these micropatterns form a repeating, periodic structure. This paper presents results of a study exploring the momentum transport in a parallel-plate microchannel with such microengineered walls. The investigation explored the entire laminar flow Reynolds number range and characterized the influence of the vapor cavity depth on the overall flow field. The liquid-vapor interface (meniscus) in the cavity regions is treated as flat in the numerical analysis and two conditions are explored with regard to the cavity region: (1) The liquid flow at the liquid-vapor interface is treated as shear-free (vanishing viscosity in the vapor region), and (2) the liquid flow in the microchannel core and the vapor flow within the cavity are coupled by matching the velocity and shear stress at the interface. Regions of slip and no-slip behavior exist and the velocity field shows distinct variations from classical laminar flow in a parallel-plate channel. The local streamwise velocity profiles, interfacial velocity distributions, and maximum interfacial velocities are presented for a number of scenarios and provide a sound understanding of the local flow physics. The predictions and accompanying measurements reveal that significant reductions in the frictional pressure drop (enhancement in effective fluid slip at the channel walls) can be achieved relative to the classical smooth-channel Stokes flow. Reductions in the friction factor and enhancements in the fluid slip are greater as the cavity-to-rib length ratio is increased (increasing shear-free fraction) and as the channel hydraulic diameter is decreased. The results also show that the slip length and average friction factor-Reynolds number product exhibit a flow Reynolds dependence. Furthermore, the predictions reveal the global impact of the vapor cavity depth on the overall frictional resistance.

Davies, J.; Maynes, D.; Webb, B. W.; Woolford, B.

2006-08-01

367

An explicit Runge-Kutta method for 3D turbulent incompressible flows  

NASA Technical Reports Server (NTRS)

A computer code has been developed to solve for the steady-state solution of the 3D incompressible Reynolds-averaged Navier-Stokes equations. The approach is based on the cell-center, central-difference, finite-volume formulation and an explicit one-step, multistage Runge-Kutta time-stepping scheme. The Baldwin-Lomax turbulence model is used. Techniques to accelerate the rate of convergence to a steady-state solution include the preconditioned method, the local time stepping, and the implicit residual smoothing. Improvements in computational efficiency have been demonstrated in several areas. This numerical procedure has been used to simulate the turbulent horseshoe vortex flow around an airfoil/flat-plate juncture.

Sung, Chao-Ho; Lin, Cheng-Wen; Hung, C. M.

1988-01-01

368

A vortex point method for calculating inviscid incompressible flows around rotary wings  

NASA Astrophysics Data System (ADS)

An integral method is presented for calculating incompressible inviscid unsteady flow around thin bodies in arbitrary motion, i.e., rotor blades in motion with respect to one another. Because an integral method is used, discretization is limited to the solid boundaries and the vortices. Boundary conditions are treated in terms of equation for the slipstream on the walls, the vorticity vector, a volume integral for the vorticity and a first-order Fredholm integral. The Helmholtz equation governs the evolution of vorticity, which forms a sheet of doublets. The pressure jumps on the blades are covered by the unsteady Bernoulli equation. Applications of the method to helicopter rotors, medium- and high-aspect ratio propellers and low-aspect ratio nautical propellers are demonstrated.

Canatloube, B.; Huberson, S.

1985-05-01

369

Effects of mistuning on bending-torsion flutter and response of a cascade in incompressible flow  

SciTech Connect

An investigation of the effects of blade mistuning on the aeroelastic stability and response of a cascade in incompressible flow is reported. The aerodynamic, inertial, and structural coupling between the bending and torsional motions of each blade and the aerodynamic coupling between the blades are included in the formulation. A digital computer program was developed to conduct parametric studies. Results indicate that the mistuning has a beneficial effect on the coupled bending-torsion and uncoupled torsion flutter. The effect of mistuning on forced response, however, may be either beneficial or adverse, depending on the engine order of the forcing function. Additionally, the results illustrate that it may be feasible to utilize mistuning as a passive control to increase flutter speed while maintaining forced response at an acceptable level.

Kaza, K.R.V.; Kielb, R.E.

1981-01-01

370

Solution techniques for the vorticity-streamfunction formulation of two-dimensional unsteady incompressible flows  

NASA Astrophysics Data System (ADS)

A review of the solution techniques of Tezduyar et al. (1988 and 1989) for the vorticity-streamfunction formulation of two-dimensional incompressible flows is presented. While both the viscous and inviscid cases are considered, the derivation of the proper finite-element formulations for multiply connected domains is emphasized. In all formulations associated with the vorticity transport equation, the streamline upwind/Petrov-Galerkin method is used. The adaptive implicit-explicit and grouped element-by-element solution strategies are employed to maximize the computational efficiency. The solutions obtained in all test cases compare well with solutions from previously published investigations. The convergence and benchmark studies performed in this paper show that the solution techniques presented are accurate, reliable, and efficient.

Tezduyar, T. E.; Liou, J.; Ganjoo, D. K.; Behr, M.

1990-10-01

371

Solution techniques for the vorticity-streamfunction formulation of two-dimensional unsteady incompressible flows  

NASA Technical Reports Server (NTRS)

A review of the solution techniques of Tezduyar et al. (1988 and 1989) for the vorticity-streamfunction formulation of two-dimensional incompressible flows is presented. While both the viscous and inviscid cases are considered, the derivation of the proper finite-element formulations for multiply connected domains is emphasized. In all formulations associated with the vorticity transport equation, the streamline upwind/Petrov-Galerkin method is used. The adaptive implicit-explicit and grouped element-by-element solution strategies are employed to maximize the computational efficiency. The solutions obtained in all test cases compare well with solutions from previously published investigations. The convergence and benchmark studies performed in this paper show that the solution techniques presented are accurate, reliable, and efficient.

Tezduyar, T. E.; Liou, J.; Ganjoo, D. K.; Behr, M.

1990-01-01

372

Numerical investigation of the onset of separation of an incompressible viscous flow from objects in ducts  

NASA Technical Reports Server (NTRS)

Simulation has been used to investigate the phenomenon of separation of a steady flow of an incompressible viscous fluid from a symmetric object in a duct. Two essentially two-dimensional problems were studied: (1) an elliptical cylinder located between two parallel plates, and (2) a sphere placed on the axis of a cylindrical pipe. The steady-state vorticity transport equation and the second order differential equation relating vorticity and the stream function were iterated using the method of overrelaxation to obtain a solution for each set of initial conditions. The relationship between the Reynolds number corresponding to the onset of separation and the size of the object relative to the duct was found to be linear over a wide range.

Winchester, L. W., Jr.; Nimitz, K. S.

1980-01-01

373

Simulation of Unsteady Incompressible Viscous Flow using Higher-Order Implicit Runge-Kutta Methods - Staggered Grid  

Microsoft Academic Search

A numerical method (SIMPLE DIRK method) for transient incompressible viscous flow simulation is presented. The proposed method can be used to achieve arbitrarily high order of accuracy in time discretization, which is otherwise limited to second order in the majority of currently available simulation techniques. A special class of implicit Runge-Kutta methods is used for time discretization in conjunction with

Muhammad Ijaz; N. K. Anand

2007-01-01

374

On the Use of Two-Dimensional Incompressible Flow to Study Secondary Eyewall Formation in Tropical Cyclones  

E-print Network

Cyclones YUMIN MOON, DAVID S. NOLAN, AND MOHAMED ISKANDARANI Rosenstiel School of Marine and Atmospheric eyewall formation in tropical cyclones by using two-dimensional incompressible flow. Those studies as the tropical cyclone core or as purely asymmetric vorticity perturbations that are an order of magnitude weaker

Miami, University of

375

Analysis for the application of hybrid laminar flow control to a long-range subsonic transport aircraft  

NASA Technical Reports Server (NTRS)

The FLOPS aircraft conceptual design/analysis code has been used to evaluate the effects of incorporating hybrid laminar flow control (HLFC) in a 300-passenger, 6500 n. mi. range, twin-engine subsonic transport aircraft. The baseline configuration was sized to account for 50 percent chord laminar flow on the wing upper surface as well as both surfaces of the empennage airfoils. Attention is given to the additional benefits of achieving various degrees of laminar flow on the engine nacelles, and the horsepower extraction and initial weight and cost increments entailed by the HLFC system. The sensitivity of the results obtained to fuel-price and off-design range are also noted.

Arcara, P. C., Jr.; Bartlett, D. W.; Mccullers, L. A.

1991-01-01

376

A novel micropreconcentrator employing a laminar flow patterned heater for micro gas chromatography  

NASA Astrophysics Data System (ADS)

A simple micromachined process based on one photomask is developed for a novel micropreconcentrator (µPCT) used in a micro gas chromatograph (µGC). Unique thick silver heating microstructures with a high surface area for microheater of µPCT are fabricated by combining the microfluidic laminar flow technique and the Tollens’ reaction within a microchannel. Silver deposition using this laminar flow patterning technique provides a higher deposition rate and easier microfabrication compared to conventional micromachined technologies for thick metal microstructures (>200 µm). An amorphous and porous carbon film that functions as an adsorbent is grown on microheaters inside the microchannel. The µPCT can be heated to >300 °C rapidly by applying a constant electrical power of ˜1 W with a heating rate of 10 °C s-1. Four volatile organic compounds, acetone, benzene, toluene and xylene, are collected through the proposed novel µPCTs and separated successfully using a 17 m long gas chromatography column. The peak widths at half height (PWHHs) of the four compounds are relatively narrow (<6 s), and the minimum PWHH of 3.75 s is obtained for acetone. The preconcentration factors are >38 000 for benzene and toluene.

Tian, W.-C.; Wu, T. H.; Lu, C.-J.; Chen, W. R.; Sheen, H. J.

2012-06-01

377

Optical Stimulation and Imaging of Functional Brain Circuitry in a Segmented Laminar Flow Chamber  

PubMed Central

Microfluidic technology is emerging as a useful tool for the study of brain slices, offering precise delivery of chemical factors along with robust oxygen and nutrient transport. However, continued reliance upon electrode-based physiological recording poses inherent limitations in terms of physical access as well as the number of sites that can be sampled simultaneously. In the present study, we combine a microfluidic laminar flow chamber with fast voltage-sensitive dye imaging and laser photostimulation via caged glutamate to map neural network activity across large cortical regions in living brain slices. We find that the closed microfluidic chamber results in greatly improved signal-to-noise performance for optical measurements of neural signaling. These optical tools are also leveraged to characterize laminar flow interfaces within the device, demonstrating a functional boundary width of less than 100 ?m. Finally, we utilize this integrated platform to investigate the mechanism of signal propagation for spontaneous neural activity in the developing mouse hippocampus. Through the use of localized Ca2+ depletion, we provide evidence for Ca2+-dependent synaptic transmission. PMID:23044655

Ahrar, Siavash; Nguyen, Transon V.; Shi, Yulin; Ikrar, Taruna; Xu, Xiangmin; Hui, Elliot E.

2012-01-01

378

A fast pressure-correction method for incompressible two-fluid flows  

NASA Astrophysics Data System (ADS)

We have developed a new pressure-correction method for simulating incompressible two-fluid flows with large density and viscosity ratios. The method's main advantage is that the variable coefficient Poisson equation that arises in solving the incompressible Navier-Stokes equations for two-fluid flows is reduced to a constant coefficient equation, which can be solved with an FFT-based, fast Poisson solver. This reduction is achieved by splitting the variable density pressure gradient term in the governing equations. The validity of this splitting is demonstrated from our numerical tests, and it is explained from a physical viewpoint. In this paper, the new pressure-correction method is coupled with a mass-conserving volume-of-fluid method to capture the motion of the interface between the two fluids but, in general, it could be coupled with other interface advection methods such as level-set, phase-field, or front-tracking. First, we verified the new pressure-correction method using the capillary wave test-case up to density and viscosity ratios of 10,000. Then, we validated the method by simulating the motion of a falling water droplet in air and comparing the droplet terminal velocity with an experimental value. Next, the method is shown to be second-order accurate in space and time independent of the VoF method, and it conserves mass, momentum, and kinetic energy in the inviscid limit. Also, we show that for solving the two-fluid Navier-Stokes equations, the method is 10-40 times faster than the standard pressure-correction method, which uses multigrid to solve the variable coefficient Poisson equation. Finally, we show that the method is capable of performing fully-resolved direct numerical simulation (DNS) of droplet-laden isotropic turbulence with thousands of droplets using a computational mesh of 10243 points.

Dodd, Michael S.; Ferrante, Antonino

2014-09-01

379

Stability analysis of a class of unsteady nonparallel incompressible flows via separation of variables  

NASA Astrophysics Data System (ADS)

Stability of some unsteady three-dimensional flows (exact solutions of the viscous incompressible Navier-Stokes equations in cylindrical coordinates) is studied via separation of variables in the linearized equations for the flow perturbations. The flows in an expanding rotating porous cylinder and in a gap between two coaxial rotating cylinders are considered. Converting the stability equations to the new variables allows perturbation forms (counterparts of normal modes of the steady state parallel flow stability problem) such that the linear stability problems are exactly reduced to eigenvalue problems of ordinary differential equations. The eigenvalue problems are solved numerically with the help of the spectral collocation method based on Chebyshev polynomials. The results showing dependence of the stability threshold on the parameters of the problems and a spatial structure of the unstable perturbation modes are presented. For some classes of perturbations, exact analytical solutions of the eigenvalue problems are available. A combination of analytical and numerical solutions can provide useful testing for numerical methods used in the hydrodynamic stability studies. It may also provide a basis for a well-grounded discussion of some problematic points of (numerical) stability analysis. In particular, in the present paper, a problem of formulation of the boundary conditions for perturbations at the axis r =0 is discussed on the basis of the solutions obtained.

Burde, Georgy I.; Nasibullayev, Ildar Sh.; Zhalij, Alexander

2007-11-01

380

A versatile sharp interface immersed boundary method for incompressible flows with complex boundaries  

NASA Astrophysics Data System (ADS)

A sharp interface immersed boundary method for simulating incompressible viscous flow past three-dimensional immersed bodies is described. The method employs a multi-dimensional ghost-cell methodology to satisfy the boundary conditions on the immersed boundary and the method is designed to handle highly complex three-dimensional, stationary, moving and/or deforming bodies. The complex immersed surfaces are represented by grids consisting of unstructured triangular elements; while the flow is computed on non-uniform Cartesian grids. The paper describes the salient features of the methodology with special emphasis on the immersed boundary treatment for stationary and moving boundaries. Simulations of a number of canonical two- and three-dimensional flows are used to verify the accuracy and fidelity of the solver over a range of Reynolds numbers. Flow past suddenly accelerated bodies are used to validate the solver for moving boundary problems. Finally two cases inspired from biology with highly complex three-dimensional bodies are simulated in order to demonstrate the versatility of the method.

Mittal, R.; Dong, H.; Bozkurttas, M.; Najjar, F. M.; Vargas, A.; von Loebbecke, A.

2008-05-01

381

A VERSATILE SHARP INTERFACE IMMERSED BOUNDARY METHOD FOR INCOMPRESSIBLE FLOWS WITH COMPLEX BOUNDARIES.  

PubMed

A sharp interface immersed boundary method for simulating incompressible viscous flow past three-dimensional immersed bodies is described. The method employs a multi-dimensional ghost-cell methodology to satisfy the boundary conditions on the immersed boundary and the method is designed to handle highly complex three-dimensional, stationary, moving and/or deforming bodies. The complex immersed surfaces are represented by grids consisting of unstructured triangular elements; while the flow is computed on non-uniform Cartesian grids. The paper describes the salient features of the methodology with special emphasis on the immersed boundary treatment for stationary and moving boundaries. Simulations of a number of canonical two- and three-dimensional flows are used to verify the accuracy and fidelity of the solver over a range of Reynolds numbers. Flow past suddenly accelerated bodies are used to validate the solver for moving boundary problems. Finally two cases inspired from biology with highly complex three-dimensional bodies are simulated in order to demonstrate the versatility of the method. PMID:20216919

Mittal, R; Dong, H; Bozkurttas, M; Najjar, F M; Vargas, A; von Loebbecke, A

2008-01-01

382

The theoretical research of basic function method in incompressible viscous flow and its simulations in three-dimensional aneurysms  

NASA Astrophysics Data System (ADS)

Basic function method is developed to treat the incompressible viscous flow. Artificial compressibility coefficient, the technique of flux splitting method and the combination of central and upwind schemes are applied to construct the basic function scheme of trigonometric function type for solving three-dimensional incompressible Navier-Stokes equations numerically. To prove the method, flows in finite-length-pipe are calculated, the velocity and pressure distribution of which solved by our method quite coincide with the exact solutions of Poiseuille flow except in the areas of entrance and exit. After the method is proved elementary, the hemodynamics in two- and three-dimensional aneurysms is researched numerically by using the basic function method of trigonometric function type and unstructured grids generation technique. The distributions of velocity, pressure and shear force in steady flow of aneurysms are calculated, and the influence of the shape of the aneurysms on the hemodynamics is studied.

Shen, Fang; Wu, Wangyi

2009-06-01

383

A new high-order method for the simulation of incompressible wall-bounded turbulent flows  

NASA Astrophysics Data System (ADS)

A new high-order method for the accurate simulation of incompressible wall-bounded flows is presented. In the stream- and spanwise directions the discretisation is performed by standard Fourier series, while in the wall-normal direction the method combines high-order collocated compact finite differences with the influence matrix method to calculate the pressure boundary conditions that render the velocity field exactly divergence-free. The main advantage over Chebyshev collocation is that in wall-normal direction, the grid can be chosen freely and thus excessive clustering near the wall is avoided. This can be done while maintaining the high-order approximation as offered by compact finite differences. The discrete Poisson equation is solved in a novel way that avoids any full matrices and thus improves numerical efficiency. Both explicit and implicit discretisations of the viscous terms are described, with the implicit method being more complex, but also having a wider range of applications. The method is validated by simulating two-dimensional Tollmien-Schlichting waves, forced transition in turbulent channel flow, and fully turbulent channel flow at friction Reynolds number Re?=395, and comparing our data with analytical and existing numerical results. In all cases, the results show excellent agreement showing that the method simulates all physical processes correctly.

Lenaers, Peter; Schlatter, Philipp; Brethouwer, Geert; Johansson, Arne V.

2014-09-01

384

A stabilized MLPG method for steady state incompressible fluid flow simulation  

NASA Astrophysics Data System (ADS)

In this paper, the meshless local Petrov-Galerkin (MLPG) method is extended to solve the incompressible fluid flow problems. The streamline upwind Petrov-Galerkin (SUPG) method is applied to overcome oscillations in convection-dominated problems, and the pressure-stabilizing Petrov-Galerkin (PSPG) method is applied to satisfy the so-called Babu\\vska-Brezzi condition. The same stabilization parameter ?( ?SUPG = ?PSPG) is used in the present method. The circle domain of support, linear basis, and fourth-order spline weight function are applied to compute the shape function, and Bubnov-Galerkin method is applied to discretize the PDEs. The lid-driven cavity flow, backward facing step flow and natural convection in the square cavity are applied to validate the accuracy and feasibility of the present method. The results show that the stability of the present method is very good and convergent solutions can be obtained at high Reynolds number. The results of the present method are in good agreement with the classical results. It also seems that the present method (which is a truly meshless) is very promising in dealing with the convection- dominated problems.

Wu, Xue-Hong; Tao, Wen-Quan; Shen, Sheng-Ping; Zhu, Xing-Wang

2010-11-01

385

MEMBRANELESS FUEL CELL BASED ON LAMINAR FLOW Eric R. Choban, Piotr Waszczuk, Larry J. Markoski, Andrzej Wieckowski, and Paul J.A. Kenis*  

E-print Network

MEMBRANELESS FUEL CELL BASED ON LAMINAR FLOW Eric R. Choban, Piotr Waszczuk, Larry J. Markoski in this area focus on downscaling of existing fuel cell technology such as the well-known proton exchange membrane (PEM) fuel cells. Here we study a novel concept for fuel cells: the use of laminar flow instead

Kenis, Paul J. A.

386

Large-eddy Simulation of Incompressible Flow Around a Sphere with Trip Wire at Re = 50 000  

Microsoft Academic Search

In this work the large-eddy simulation (LES) is used to investigate incompressible flow around a sphere with trip wire. The\\u000a sphere is located in a channel with square cross-section, and the bulk Reynolds number is Re = 50 000. The computational effort implied by demands for sufficient spatial and temporal resolution of the flow structures\\u000a requires parallel runs on a

M. Torlak; G. Jensen; I. Hadži?

387

CONVEC: A computer program for transient incompressible fluid flow based on quadratic finite elements. Part 2: User's manual  

Microsoft Academic Search

The computer code CONVEC is a general computer program designed for the solution of transient two-dimensional incompressible fluid flow problems. The solution procedure is based on the finite element method. The class of problems treated by the present version of CONVEC are those described by the time-dependent, two-dimensional (plane or axisymmetric) form of the Navier-Stokes equations. The flow field is

H. Laval

1981-01-01

388

An extended pressure finite element space for two-phase incompressible flows with surface tension  

NASA Astrophysics Data System (ADS)

We consider a standard model for incompressible two-phase flows in which a localized force at the interface describes the effect of surface tension. If a level set (or VOF) method is applied then the interface, which is implicitly given by the zero level of the level set function, is in general not aligned with the triangulation that is used in the discretization of the flow problem. This non-alignment causes severe difficulties w.r.t. the discretization of the localized surface tension force and the discretization of the flow variables. In cases with large surface tension forces the pressure has a large jump across the interface. In standard finite element spaces, due to the non-alignment, the functions are continuous across the interface and thus not appropriate for the approximation of the discontinuous pressure. In many simulations these effects cause large oscillations of the velocity close to the interface, so-called spurious velocities. In this paper, for a simplified model problem, we give an analysis that explains why known (standard) methods for discretization of the localized force term and for discretization of the pressure variable often yield large spurious velocities. In the paper [S. Groß, A. Reusken, Finite element discretization error analysis of a surface tension force in two-phase incompressible flows, Preprint 262, IGPM, RWTH Aachen, SIAM J. Numer. Anal. (accepted for publication)], we introduce a new and accurate method for approximation of the surface tension force. In the present paper, we use the extended finite element space (XFEM), presented in [N. Moes, J. Dolbow, T. Belytschko, A finite element method for crack growth without remeshing, Int. J. Numer. Meth. Eng. 46 (1999) 131-150; T. Belytschko, N. Moes, S. Usui, C. Parimi, Arbitrary discontinuities in finite elements, Int. J. Numer. Meth. Eng. 50 (2001) 993-1013], for the discretization of the pressure. We show that the size of spurious velocities is reduced substantially, provided we use both the new treatment of the surface tension force and the extended pressure finite element space.

Groß, Sven; Reusken, Arnold

2007-05-01

389

Dimensioning of ducts for maximal volumetric heat transfer taking both laminar and turbulent flow possibilities into consideration  

NASA Astrophysics Data System (ADS)

It is intended to design compact heat exchangers which can transfer high heat flow for a given volume and temperature difference with high efficiency. This work presents the optimal design of heat exchangers for a given length or hydraulic diameter with a constraint of a certain pressure loss and constant wall temperature. Both volumetric heat transfer and heat transfer efficiency are taken into consideration for the design in laminar or turbulent flow regions. Equations are derived which easily enable optimal design for all shapes of ducts and for all Pr numbers. It is found that optimum conditions for turbulent flow is possible for all duct hydraulic diameters; however, it is possible to have optimum conditions till a certain dimensionless duct hydraulic diameter for laminar flow. Besides maximal volumetric heat flow, heat transfer efficiency should be taken into consideration in turbulent flow for optimum design.

Yilmaz, Alper

2014-09-01

390

The effect of neutrally buoyant finite-size particles on channel flows in the laminar-turbulent transition regime  

NASA Astrophysics Data System (ADS)

The presence of finite-size particles in a channel flow close to the laminar-turbulent transition is simulated with the Force Coupling Method which allows two-way coupling with the flow dynamics. Spherical particles with channel height-to-particle diameter ratio of 16 are initially randomly seeded in a fluctuating flow above the critical Reynolds number corresponding to single phase flow relaminarization. When steady-state is reached, the particle volume fraction is homogeneously distributed in the channel cross-section (? ? 5%) except in the near-wall region where it is larger due to inertia-driven migration. Turbulence statistics (intensity of velocity fluctuations, small-scale vortical structures, wall shear stress) calculated in the fully coupled two-phase flow simulations are compared to single-phase flow data in the transition regime. It is observed that particles increase the transverse r.m.s. flow velocity fluctuations and they break down the flow coherent structures into smaller, more numerous and sustained eddies, preventing the flow to relaminarize at the single-phase critical Reynolds number. When the Reynolds number is further decreased and the suspension flow becomes laminar, the wall friction coefficient recovers the evolution of the laminar single-phase law provided that the suspension viscosity is used in the Reynolds number definition. The residual velocity fluctuations in the suspension correspond to a regime of particulate shear-induced agitation.

Loisel, Vincent; Abbas, Micheline; Masbernat, Olivier; Climent, Eric

2013-12-01

391

Front propagation in a laminar cellular flow: shapes, velocities, and least time criterion.  

PubMed

We experimentally investigate the propagation of chemical fronts in steady laminar cellular flows at large Péclet numbers and large Damköhler numbers. Fronts are generated in an aqueous solution by an autocatalytic oxydoreduction reaction. They propagate in a channel in which a chain of counter-rotative parallel vortices is induced by electroconvection. We first accurately determine the form, the dynamics and the mean velocity of these fronts in the whole Hele-Shaw regime of the flow. We then address the modeling of the evolution of their mean velocity with the flow amplitude. The structure of the front wakes yields us to reject an effective reaction-diffusion wave as a relevant model for large-scale front propagation. On the other hand, analysis of the role of front heads brings us to introduce a kinematic model at the vortex scale for uncovering the front dynamics. This model addresses the propagation of the front leading point in a chain of vortices whose field is modeled by a two-dimensional solid rotation complemented by a boundary layer. Interestingly, it sensitively relies on the effective trajectory followed by the front leading point. To account for this, a competition is worked out among a one-parameter family of potential trajectories. The actual trajectory is then selected as the fastest one with quite a good agreement with measurements and observations. In particular, the measured effective front velocities are well recovered from the model, including their intrinsic dependence on the boundary layer width. Accordingly, effective front propagation in a laminar steadily stirred medium is thus understood from an optimization principle similar to the Fermat principle of ray propagation in heterogeneous media. PMID:18517508

Pocheau, A; Harambat, F

2008-03-01

392

Convective heat transfer in foams under laminar flow in pipes and tube bundles  

PubMed Central

The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux.

Attia, Joseph A.; McKinley, Ian M.; Moreno-Magana, David; Pilon, Laurent

2014-01-01

393

NACHOS: A finite element computer program for incompressible flow problems. Part 2: Users manual  

Microsoft Academic Search

The NACHOS computer code is a general purpose computer program designed for the solution of two dimensional, incompressible fluid dynamics problems. The solution method used in NACHOS is based on the finite element method. The class of problems treated by the present version of NACHOS were those described by the two dimensional, incompressible form of the Navier-Stokes equations. An energy

D. K. Gartling

1977-01-01

394

NACHOS: a finite element computer program for incompressible flow problems. Part II. User's manual  

Microsoft Academic Search

The NACHOS computer code is a general purpose computer program designed for the solution of two dimensional, incompressible fluid dynamics problems. The solution method used in NACHOS is based on the finite element method (FEM). The class of problems treated by the present version of NACHOS are those described by the two dimensional (plane or axisymmetric), incompressible form of the

Gartling

1977-01-01

395

A consistent projection-based SUPG/PSPG XFEM for incompressible two-phase flows  

NASA Astrophysics Data System (ADS)

In this paper, a consistent projection-based streamline upwind/pressure stabilizing Petrov-Galerkin (SUPG/PSPG) extended finite element method (XFEM) is presented to model incompressible immiscible two-phase flows. As the application of linear elements in SUPG/PSPG schemes gives rise to inconsistency in stabilization terms due to the inability to regenerate the diffusive term from viscous stresses, the numerical accuracy would deteriorate dramatically. To address this issue, projections of convection and pressure gradient terms are constructed and incorporated into the stabilization formulation in our method. This would substantially recover the consistency and free the practitioner from burdensome computations of most items in the residual. Moreover, the XFEM is employed to consider in a convenient way the fluid properties that have interfacial jumps leading to discontinuities in the velocity and pressure fields as well as the projections. A number of numerical examples are analyzed to demonstrate the complete recovery of consistency, the reproduction of interfacial discontinuities and the ability of the proposed projection-based SUPG/PSPG XFEM to model two-phase flows with open and closed interfaces.

Liao, Jian-Hui; Zhuang, Zhuo

2012-10-01

396

Unsteady three-dimensional incompressible flow interaction in multiple-blade-row turbomachinery  

NASA Astrophysics Data System (ADS)

Marine propulsors operate in an inherently unsteady flowfield. To design a propulsor that meets the conditions imposed by hydrodynamic and hydroacoustic requirements, knowledge of component interactions and unsteady flow patterns throughout the propulsor is essential. At the present time, the effect of the unsteady flow on the performance of the propulsor is not thoroughly understood. The goal of this work is to use computational fluid dynamics (CFD) coupled with measurements and analytic methods to provide some insight into the physics associated with unsteady propulsor flows. The unsteady, incompressible Reynolds-Averaged Navier Stokes (RANS) code developed at Mississippi State University has been extended for use in analyzing the unsteady flow interaction between blade rows in relative motion. The approach used to model the dynamic interface between the blade rows is the localized grid distortion technique of Janus. The spatial and temporal discretizations result in third order spatial accuracy and second order (implicit) temporal accuracy. To validate the dynamic grid capabilities, computed results for the unsteady flow around a two-dimensional hydrofoil undergoing a high, reduced-frequency gust loading are compared with measured data. The unsteady gusts are generated by a pair of oscillating foils (flappers) upstream of the hydrofoil. A dynamic grid is used around the oscillating foils. The results from a parametric study indicate that 500 time steps per flapper period with three subiterations at each time step are sufficient to capture the time-accurate behavior of both the inviscid and viscous flow fields. The algorithm is then used to compute the unsteady flow through a three-dimensional, high Reynolds number pump consisting of 13 stator blades and 7 rotor blades. A detailed analysis of the primary, secondary and unsteady flow effects is presented along with an investigation of the effects of sub-iterations on the time-accuracy on the solution. The unsteady interaction between the blade rows is apparent in both the stator and rotor blade rows. The computations verify that the potential flow interaction leads to unsteady pressures on the stators and the wake interaction leads to unsteady loadings on the rotor.

Busby, Judy Ann

397

Membraneless Vanadium Redox Fuel Cell Using Laminar Flow Rosaria Ferrigno, Abraham D. Stroock, Thomas D. Clark, Michael Mayer, and  

E-print Network

). At this interface, some redox species are inevitably lost by diffusive mixing and reaction. A good approximationMembraneless Vanadium Redox Fuel Cell Using Laminar Flow Rosaria Ferrigno, Abraham D. Stroock This communication describes a small redox fuel cell fabricated using a design that omits the membrane normally used

Prentiss, Mara

398

Survey and bibliography on attainment of laminar flow control in air using pressure gradient and suction, volume 1  

NASA Technical Reports Server (NTRS)

A survey was conducted and a bibliography compiled on attainment of laminar flow in air through the use of favorable pressure gradient and suction. This report contains the survey, summaries of data for both ground and flight experiments, and abstracts of referenced reports. Much early information is also included which may be of some immediate use as background material for LFC applications.

Bushnell, D. M.; Tuttle, M. H.

1979-01-01

399

Laminar Forced Convection Heat Transfer from Isothermal Bodies with Unity Aspect Ratio in Co-Axial Air Flow  

Microsoft Academic Search

In this article a semi—analytical approach is employed to obtain dimensionless heat transfer correlations for forced convection over three geometries sphere, cone and cylinder with unity aspect ratio in laminar axial air flow. The comparison of the present results for sphere with the previous works shows a very good agreement. For example, the average difference between the results of the

YASER HADAD; KHOSROW JAFARPUR

2011-01-01

400

Analysis of viscous dissipation effect on thermal entrance heat transfer in laminar pipe flows with convective boundary conditions  

Microsoft Academic Search

Consideration is given to the influence of viscous dissipation on the thermal entrance region laminar pipe flow heat transfer with convective boundary condition. The Eigenfunction series expansion technique is employed to solve the governing energy equation. The results for axial distributions of dimensionless bulk and wall temperatures, local Nusselt number as well as modified local Nusselt number are presented graphically

T. F. Lin; K. H. Hawks; W. Leidenfrost

1983-01-01

401

AEROSOL NUCLEATION AND GROWTH DURING LAMINAR TUBE FLOW: MAXIMUM SATURATIONS AND NUCLEATION RATES. (R827354C008)  

EPA Science Inventory

An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...

402

Interacting boundary-layer solutions for laminar separated flow past airfoils  

NASA Technical Reports Server (NTRS)

Numerical solutions of the interacting laminar boundary layer equations are presented for two symmetric airfoils at zero incidence: the NACA 0012 and the NACA 66 sub 3-108 airfoils. The potential flow was computed using Carlson's code, and viscous interaction was treated following a Hilbert integral scheme due to Veldman. Effects of various grid parameters are studied, and pressure and skin friction distributions are compared at several Reynolds numbers. For the NACA 0012 airfoil, Reynolds number is varied from a value just below separation (R sub N = 3000) to a value for which extensive separation occurs (R sub N = 100,000). For the 66 sub 3-018 airfoil, results are given at intermediate values (R sub N - 10,000 and 40,000). The method fails to converge for greater values of Reynolds number, corresponding to the development of very thin well separated shear layers where transition to turbulence would occur naturally.

Burggraf, O. R.

1984-01-01

403

Evaluation of laminar flow control system concepts for subsonic commercial transport aircraft  

NASA Technical Reports Server (NTRS)

A two-year study conducted to establish a basis for industry decisions on the application of laminar flow control (LFC) to future commercial transports was presented. Areas of investigation included: (1) mission definition and baseline selection; (2) concepts evaluations; and (3) LFC transport configuration selection and component design. The development and evaluation of competing design concepts was conducted in the areas of aerodynamics, structures and materials, and systems. The results of supporting wind tunnel and laboratory testing on a full-scale LFC wing panel, suction surface opening concepts and structural samples were included. A final LFC transport was configured in incorporating the results of concept evaluation studies and potential performance improvements were assessed. Remaining problems together with recommendations for future research are discussed.

1978-01-01

404

Evaluation of Laminar Flow Control System Concepts for Subsonic Commercial Transport Aircraft  

NASA Technical Reports Server (NTRS)

Alternatives in the design of laminar flow control (LFC) subsonic commerical transport aircraft for opeation in the 1980's period were studied. Analyses were conducted to select mission parameters and define optimum aircraft configurational parameters for the selected mission, defined by a passenger payload of 400 and a design range of 12, 038 km (6500 n mi). The baseline aircraft developed for this mission was used as a vehicle for the evaluation and development of alternative LFC system concepts. Alternatices in the areas of aerodynamics, structures and materials, LFC systems, leading-edge region cleaning, and integration of auxiliary systems were studied. Relative to a similarly-optimized advanced technology turbulent transport, the final LFC configuration is approximately equal in DOC but provides descreases of 8.2% in gross weight and 21.7% in fuel consumption.

Sturgeon, R. F.

1980-01-01

405

Laminar flow of a gas in a tube with large temperature differences  

NASA Astrophysics Data System (ADS)

The laminar low Mach number flow of a gas in a tube is analyzed for very small and very large values of the inlet-to-wall temperature ratio. When this ratio tends to zero, pressure forces confine the cold gas to a thin core around the axis of the tube. This core is neatly bounded by an ablation front that consumes it at a finite distance from the tube inlet. When the temperature ratio tends to infinity, the temperature of the gas increases smoothly from the wall to the axis of the tube and the shear stress and heat flux are positive at the wall despite the fact that the viscosity and thermal conductivity of the gas scaled with their inlet values tend to zero at the wall.

Higuera, F. J.

2011-12-01

406

Steady laminar flow of liquid-liquid jets at high Reynolds numbers*  

NASA Astrophysics Data System (ADS)

The axisymmetric steady-state laminar flow of a Newtonian liquid jet injected vertically into another immiscible Newtonian liquid is investigated for various Reynolds numbers. The steady-state solution was calculated by solving the axisymmetric transient equations of motion and continuity using a numerical scheme based on the volume of fluid (VOF) method combined with the new continuum surface force (CSF) algorithm. The analysis takes into account pressure, viscous, inertial, gravitational, and surface tension forces. Comparison with previous experimental measurements, performed on a xylene/water system, under conditions where all of these forces are important, shows good agreement over the entire range of conditions studied. Comparisons of the present numerical method with the numerical results of previous boundary-layer methods help establish their range of validity.

Richards, John R.; Beris, Antony N.; Lenhoff, Abraham M.

1993-07-01

407

Heat transfer optimization in finned annular ducts under laminar-flow conditions  

SciTech Connect

In the present work the problem of optimizing the lateral profile of longitudinal fins in annular ducts in order to enhance the heat transfer under laminar coolant flow conditions is studied. The velocity and temperature distributions on the annular duct cross section are determined with the help of a finite-element model, and a global heat transfer coefficient is calculated. A polynomial lateral profile is proposed for the fins, and the geometry is optimized in order to make the transferred heat as high as possible for a given amount of material and for a given hydraulic resistance. Lastly, the optimum fin profiles obtained for different situations by means of a genetic algorithm are shown.

Fabbri, G. [Univ. degli Studi di Bologna (Italy). Dipt. di Ingegneria Energetica, Nucleare e del Controllo Ambientale

1998-10-01

408

A laminar-flow chamber assay for measuring bacterial adhesion under shear stress.  

PubMed

Shear stress levels generated by circulating blood have a strong impact on biological processes taking place in the vasculature. It is therefore important to take them into account when studying infectious agents targeting the endothelium. Here we describe a protocol using disposable laminar-flow chambers and video microcopy to study bacterial infections in an environment that mimics the bloodstream. We initially focused on the interaction of Neisseria meningitidis with human endothelial cells and determined that shear stress is an important factor for the pathogen's initial adhesion and for the formation of micro-colonies. The experimental set-up can be used to investigate other pathogens that interact with the endothelium as well as with other sites where shear stress is present. PMID:21993647

Soyer, Magali; Duménil, Guillaume

2012-01-01

409

Some Aspects of Bifurcation Structure of Laminar Flow in Curved Ducts  

NASA Technical Reports Server (NTRS)

A bifurcation study is made of laminar flow in curved ducts. The problem is formulated in a curvilinear coordinate system, and the governing equations, after orthogonal mapping is applied, are solved numerically by an iterative finite-difference method. Many computer runs were made with various duct cross-sections ranging from a circle to a square, to learn the transition of bifurcation structure with this change in cross-section and to reconcile the differences between them. In addition, a simpler technique is proposed to generate symmetric four-cell solutions in a circular pipe and a means is put forward to stabilize four-vortex structures in a complete cross-section.

Kao, Hsiao C.

1992-01-01

410

Designing a Hybrid Laminar-Flow Control Experiment: The CFD-Experiment Connection  

NASA Technical Reports Server (NTRS)

The NASA/Boeing hybrid laminar flow control (HLFC) experiment, designed during 1993-1994 and conducted in the NASA LaRC 8-foot Transonic Pressure Tunnel in 1995, utilized computational fluid dynamics and numerical simulation of complex fluid mechanics to an unprecedented extent for the design of the test article and measurement equipment. CFD was used in: the design of the test wing, which was carried from definition of desired disturbance growth characteristics, through to the final airfoil shape that would produce those growth characteristics; the design of the suction-surface perforation pattern that produced enhanced crossflow-disturbance growth: and in the design of the hot-wire traverse system that produced minimal influence on measured disturbance growth. These and other aspects of the design of the test are discussed, after the historical and technical context of the experiment is described.

Streett, C. L.

2003-01-01

411

Multifractal Analysis of Taylor-Couette Flow with Hourglass Geometry in both Laminar and Turbulent Regimes  

NASA Astrophysics Data System (ADS)

Previously we have presented Correlation Dimension and Kaplan-Yorke Dimension analyses of the irregular generation of new Taylor Vortex Pairs in both laminar and turbulent Taylor-Couette flow with hourglass geometry could be characterized as low dimensional chaosootnotetextA. Kowalski, T. Olsen, & R. Wiener, Bull. Am. Phys. Soc. 50-9, P1.00030 (2006).. We now present a multifractal analysisootnotetextJ. A. Glazier & A. Libchaber, IEEE Trans. On Circuits and Systems 35-7, 790 (1988).^,ootnotetextT. Halsey, M. H. Jensen, L. P. Kadanoff, I. Procaccia, & B. I. Shraiman, Phys. Rev. A 33, 1141 (1986). of the same data. We comment on the additional insights into the physical process provided.

Kowalski, Adam; Olsen, Thomas; Wiener, Richard

2007-11-01

412

An outflow boundary condition and algorithm for incompressible two-phase flows with phase field approach  

NASA Astrophysics Data System (ADS)

We present an effective outflow boundary condition, and an associated numerical algorithm, within the phase-field framework for dealing with two-phase outflows or open boundaries. The set of two-phase outflow boundary conditions for the phase-field and flow variables are designed to prevent the un-controlled growth in the total energy of the two-phase system, even in situations where strong backflows or vortices may be present at the outflow boundaries. We also present an additional boundary condition for the phase field function, which together with the usual Dirichlet condition can work effectively as the phase-field inflow conditions. The numerical algorithm for dealing with these boundary conditions is developed on top of a strategy for de-coupling the computations of all flow variables and for overcoming the performance bottleneck caused by variable coefficient matrices associated with variable density/viscosity. The algorithm contains special constructions, for treating the variable dynamic viscosity in the outflow boundary condition, and for preventing a numerical locking at the outflow boundaries for time-dependent problems. Extensive numerical tests with incompressible two-phase flows involving inflow and outflow boundaries demonstrate that, the two-phase outflow boundary conditions and the numerical algorithm developed herein allow for the fluid interface and the two-phase flow to pass through the outflow or open boundaries in a smooth and seamless fashion, and that our method produces stable simulations when large density ratios and large viscosity ratios are involved and when strong backflows are present at the outflow boundaries.

Dong, S.

2014-06-01

413

Experimental design studies and flow visualization of proportional laminar-flow fluidic amplifiers  

NASA Technical Reports Server (NTRS)

The effects of certain parameter variations on the performance characteristics of laminar, proportional, jet-deflection fluidic amplifiers were studied. The matching and staging of amplifiers to obtain high pressure gain was included, but dynamic effects were not. The parameter variations considered were aspect ratio, setback, control length, splitter distance, receiver-duct width, width of center-vent duct, and bias pressure. Usable pressure gains of 19 per stage were achieved, and 5 amplifier stages were integrated to yield an overall pressure gain of 2,000,000.

Hellbaum, R. F.; Mcdermon, J. N.

1977-01-01

414

Numerical evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes  

PubMed Central

Convective heat transfer can be enhanced by changing flow geometry and/or by enhancing thermal conductivity of the fluid. This study proposes simultaneous passive heat transfer enhancement by combining the geometry effect utilizing nanofluids inflow in coils. The two nanofluid suspensions examined in this study are: water-Al2O3 and water-CuO. The flow behavior and heat transfer performance of these nanofluid suspensions in various configurations of coiled square tubes, e.g., conical spiral, in-plane spiral, and helical spiral, are investigated and compared with those for water flowing in a straight tube. Laminar flow of a Newtonian nanofluid in coils made of square cross section tubes is simulated using computational fluid dynamics (CFD)approach, where the nanofluid properties are treated as functions of particle volumetric concentration and temperature. The results indicate that addition of small amounts of nanoparticles up to 1% improves significantly the heat transfer performance; however, further addition tends to deteriorate heat transfer performance. PMID:21711901

2011-01-01

415

Fatigue response of perforated titanium for application in laminar flow control  

NASA Technical Reports Server (NTRS)

The room temperature tensile and fatigue response of non-perforated and perforated titanium for laminar flow control application was investigated both experimentally and analytically. Results showed that multiple perforations did not affect the tensile response, but did reduce the fatigue life. A two dimensional finite element stress analysis was used to determine that the stress fields from adjacent perforations did not influence one another. The stress fields around the holes did not overlap one another, allowing the materials to be modeled as a plate with a center hole. Fatigue life was predicted using an equivalent MW flow size approach to relate the experimental results to microstructural features of the titanium. Predictions using flaw sizes ranging from 1 to 15 microns correlated within a factor of 2 with the experimental results by using a flow stress of 260 MPa. By using two different flow stresses in the crack closure model and correcting for plasticity, the experimental results were bounded by the predictions for high applied stresses. Further analysis of the complex geometry of the perforations and the local material chemistry is needed to further understand the fatigue behavior of the perforated titanium.

Johnson, W. Steven; Miller, Jennifer L.; Newman, Jr., James

1996-01-01

416

Unsteady incompressible flow analysis using C-type grid with a curved branch cut  

NASA Astrophysics Data System (ADS)

For an unsteady viscous flow simulation on a two-dimensional body at high angle of attack, the calculation of unsteady aerodynamic forces acting on the body is influenced not only by the unsteady separated flow near the body but also by the unsteady wake behind the body. To resolve the wake flow behind the trailing edge, an orthogonal C-grid topology with a curved branch cut aligned with the inviscid stagnation streamline is generated using a conformal mapping technique. This permits the desired grid clustering in the wake region and leads to better flow results in that region. The conformal mapping technique also provides analytical Jacobian metrics for the coordinate transformation and an inviscid solution which is useful in initiating the viscous flow of the impulsively started motion. The use of analytical metric coefficients facilitates the direct determination of part of the coefficients in the governing equations without introducing numerical errors. The unsteady two-dimensional incompressible Navier-Stokes equations in generalized orthogonal coordinates are solved using a vorticity-stream function formulation. The analysis also requires coupling of flow circulation in the far field. As a result, the vorticity-stream function formulation introduced in the present study contains the spatially elliptic equation for the disturbance stream function coupled with the temporally parabolic vorticity transport equation. An efficient direct Block-Gaussian Elimination (BGE) technique is used to solve the stream function Poisson problem subject to Neumann and Dirichlet boundary conditions. The vorticity transport equation is solved using the Alternating Direct Implicit (ADI) method. In addition, the Jacobian at the grid points along the curved branch cut is multi-valued and the metric coefficients are found to be discontinuous across the branch cut. Hence, a special finite element interpolation is implemented in the governing equations at those points in order to overcome this discontinuity. To achieve the objective stated above, the unsteady flow over a stationary NACA 0015 airfoil at various angles of attack is selected in the present study.

Fang, Kuan-Chieh

2000-08-01

417

Local transfer and spectra of a diffusive field advected by large-scale incompressible flows.  

PubMed

This study revisits the problem of advective transfer and spectra of a diffusive scalar field in large-scale incompressible flows in the presence of a (large-scale) source. By "large scale" it is meant that the spectral support of the flows is confined to the wave-number region kflows mediate couplings between neighboring wave numbers within kd of each other only. It is found that the spectral rate of transport (flux) of scalar variance across a high wave number k>kd is bounded from above by UkdkTheta(k,t) , where U denotes the maximum fluid velocity and Theta(k,t) is the spectrum of the scalar variance, defined as its average over the shell (k-kd,k+kd) . For a given flux, say vartheta>0 , across k>kd , this bound requires Theta(k,t)> or =(varthetaUkd)k(-1) . This is consistent with recent numerical studies and with Batchelor's theory that predicts a k(-1) spectrum (with a slightly different proportionality constant) for the viscous-convective range, which could be identified with (kd,kkappa) . Thus, Batchelor's formula for the variance spectrum is recovered by the present method in the form of a critical lower bound. The present result applies to a broad range of large-scale advection problems in space dimensions > or =2 , including some filter models of turbulence, for which the turbulent velocity field is advected by a smoothed version of itself. For this case, Theta(k,t) and vartheta are the kinetic energy spectrum and flux, respectively. PMID:18851146

Tran, Chuong V

2008-09-01

418

A Parallel Second-Order Adaptive Mesh Algorithm for Incompressible Flow in Porous Media  

SciTech Connect

In this paper we present a second-order accurate adaptive algorithm for solving multiphase, incompressible flows in porous media. We assume a multiphase form of Darcy's law with relative permeabilities given as a function of the phase saturation. The remaining equations express conservation of mass for the fluid constituents. In this setting the total velocity, defined to be the sum of the phase velocities, is divergence-free. The basic integration method is based on a total-velocity splitting approach in which we solve a second-order elliptic pressure equation to obtain a total velocity. This total velocity is then used to recast component conservation equations as nonlinear hyperbolic equations. Our approach to adaptive refinement uses a nested hierarchy of logically rectangular grids with simultaneous refinement of the grids in both space and time. The integration algorithm on the grid hierarchy is a recursive procedure in which coarse grids are advanced in time, fine grids areadvanced multiple steps to reach the same time as the coarse grids and the data atdifferent levels are then synchronized. The single grid algorithm is described briefly,but the emphasis here is on the time-stepping procedure for the adaptive hierarchy. Numerical examples are presented to demonstrate the algorithm's accuracy and convergence properties and to illustrate the behavior of the method.

Pau, George Shu Heng; Almgren, Ann S.; Bell, John B.; Lijewski, Michael J.

2008-04-01

419

Strong Solutions to Non-Stationary Channel Flows of Heat-Conducting Viscous Incompressible Fluids with Dissipative Heating  

E-print Network

We study an initial-boundary-value problem for time-dependent flows of heat-conducting viscous incompressible fluids in channel-like domains on a time interval $(0,T)$. For the parabolic system with strong nonlinearities and including the artificial (the so called "do nothing") boundary conditions, we prove the local in time existence, global uniqueness and smoothness of the solution on a time interval $(0,T^*)$, where $0< T^* \\leq T$.

Michal Beneš

2011-08-08

420

A comparative study of sound generation by laminar, combusting and non-combusting jet flows  

NASA Astrophysics Data System (ADS)

Sound production by two-dimensional, laminar jet flows with and without combustion is studied numerically and theoretically. The compressible Navier-Stokes, energy and progress variable equations are solved by resolving both the near field and the acoustics. The combusting jet flows are compared to non-combusting jets of the same jet Mach number, with the non-combusting, non-isothermal jets having the same steady temperature difference as the combusting jets. This infers that the magnitude of entropic and density disturbances is similar in some of the combusting and non-combusting cases. The flows are perturbed by a sinusoidal inlet velocity fluctuation at different Strouhal numbers. The computational domain is resolved to the far field in all cases, allowing direct examination of the sound radiated and its sources. Lighthill's acoustic analogy is then solved numerically using Green's functions. The radiated sound calculated using Lighthill's equation is in good agreement with that from the simulations for all cases, validating the numerical solution of Lighthill's equation. The contribution of the source terms in Dowling's reformulation of Lighthill's equation is then investigated. It is shown that the source term relating to changes in the momentum of density inhomogeneities is the dominant source term for all non-reacting, non-isothermal cases. Further, this source term has similar magnitude in the combusting cases and is one of the several source terms that have similar magnitude to the source term involving fluctuations in the heat release rate.

Talei, Mohsen; Brear, Michael J.; Hawkes, Evatt R.

2014-08-01

421

A numerical study on distributions during cryoprotectant loading caused by laminar flow in a microchannel.  

PubMed

In this work, we conduct a computational study on the loading of cryoprotective agents into cells in preparation for cryopreservation. The advantages of microfluidics in cryopreserving cells include control of fluid flow parameters for reliable cryoprotectant loading and reproducible streamlined processing of samples. A 0.25?m long, three inlet T-junction microchannel serves as an idealized environment for this process. The flow field and concentration distribution are determined from a computational fluid dynamics study and cells are tracked as inert particles in a Lagrangian frame. These particles are not confined to streamlines but can migrate laterally due to the Segre-Sildeberg effect for particles in a shear flow. During this tracking, the local concentration field surrounding the cell is monitored. This data are used as input into the Kedem-Katchalsky equations to numerically study passive solute transport across the cell membrane. As a result of the laminar flow, each cell has a unique pathline in the flow field resulting in different residence times and a unique external concentration field along its path. However, in most previous studies, the effect of a spatially varying concentration field on the transport across the cell membrane is ignored. The dynamics of this process are investigated for a population of cells released from the inlet. Using dimensional analysis, we find a governing parameter ?, which is the ratio of the time scale for membrane transport to the average residence time in the channel. For [Formula: see text], cryoprotectant loading is completed to within 5% of the target concentration for all of the cells. However, for [Formula: see text], we find the population of cells does not achieve complete loading and there is a distribution of intracellular cryoprotective agent concentration amongst the population. Further increasing ? beyond a value of 2 leads to negligible cryoprotectant loading. These simulations on populations of cells may lead to improved microfluidic cryopreservation protocols where more consistent cryoprotective agent loading and freezing can be achieved, thus increasing cell survival. PMID:24404009

Scherr, T; Pursley, S; Monroe, W T; Nandakumar, K

2013-01-01

422

A numerical study on distributions during cryoprotectant loading caused by laminar flow in a microchannel  

PubMed Central

In this work, we conduct a computational study on the loading of cryoprotective agents into cells in preparation for cryopreservation. The advantages of microfluidics in cryopreserving cells include control of fluid flow parameters for reliable cryoprotectant loading and reproducible streamlined processing of samples. A 0.25?m long, three inlet T-junction microchannel serves as an idealized environment for this process. The flow field and concentration distribution are determined from a computational fluid dynamics study and cells are tracked as inert particles in a Lagrangian frame. These particles are not confined to streamlines but can migrate laterally due to the Segre-Sildeberg effect for particles in a shear flow. During this tracking, the local concentration field surrounding the cell is monitored. This data are used as input into the Kedem-Katchalsky equations to numerically study passive solute transport across the cell membrane. As a result of the laminar flow, each cell has a unique pathline in the flow field resulting in different residence times and a unique external concentration field along its path. However, in most previous studies, the effect of a spatially varying concentration field on the transport across the cell membrane is ignored. The dynamics of this process are investigated for a population of cells released from the inlet. Using dimensional analysis, we find a governing parameter ?, which is the ratio of the time scale for membrane transport to the average residence time in the channel. For ?<=0.224, cryoprotectant loading is completed to within 5% of the target concentration for all of the cells. However, for ?>0.224, we find the population of cells does not achieve complete loading and there is a distribution of intracellular cryoprotective agent concentration amongst the population. Further increasing ? beyond a value of 2 leads to negligible cryoprotectant loading. These simulations on populations of cells may lead to improved microfluidic cryopreservation protocols where more consistent cryoprotective agent loading and freezing can be achieved, thus increasing cell survival. PMID:24404009

Scherr, T.; Pursley, S.; Monroe, W. T.; Nandakumar, K.

2013-01-01

423

Laser Doppler flowmetry for measurement of laminar capillary blood flow in the horse  

NASA Astrophysics Data System (ADS)

Current methods for in vivo evaluation of digital hemodynamics in the horse include angiography, scintigraphy, Doppler ultrasound, electromagnetic flow and isolated extracorporeal pump perfused digit preparations. These techniques are either non-quantifiable, do not allow for continuous measurement, require destruction of the horse orare invasive, inducing non- physiologic variables. In vitro techniques have also been reported for the evaluation of the effects of vasoactive agents on the digital vessels. The in vitro techniques are non-physiologic and have evaluated the vasculature proximal to the coronary band. Lastly, many of these techniques require general anesthesia or euthanasia of the animal. Laser Doppler flowmetry is a non-invasive, continuous measure of capillary blood flow. Laser Doppler flowmetry has been used to measure capillary blood flow in many tissues. The principle of this method is to measure the Doppler shift, that is, the frequency change that light undergoes when reflected by moving objects, such as red blood cells. Laser Doppler flowmetry records a continuous measurement of the red cell motion in the outer layer of the tissue under study, with little or no influence on physiologic blood flow. This output value constitutes the flux of red cells and is reported as capillary perfusion units. No direct information concerning oxygen, nutrient or waste metabolite exchange in the surrounding tissue is obtained. The relationship between the flowmeter output signal and the flux of red blood cells is linear. The principles of laser Doppler flowmetry will be discussed and the technique for laminar capillary blood flow measurements will be presented.

Adair, Henry S., III

1998-07-01

424

Reynolds number dependence of the drag coefficient for laminar flow through fine-scale screens  

NASA Astrophysics Data System (ADS)

The laminar flow downstream of fine mesh screens is studied experimentally and numerically. Two different screen types are examined experimentally, both with open areas greater than 50 percent and wire dimensions less than 100 micro-m. Such screens produce flow disturbances of much smaller scale than those examined in most previous studies of flow conditioning screens and grid generated turbulence. Instead of using standard woven wire screens, high uniformity screens are used which are fabricated by photo-etching holes into 50.8 micro-m thick Inconel sheets. The holes thus produced are square with rounded corners, arranged to form a square array, with a minimum wire thickness (located halfway between wire crossings) of D = 50.8 micro-m. A flow facility has been constructed for experiments with these screens. Air at 85 kPa and 295 K is passed through each screen at upstream velocities of 1 to 12 m/s, yielding Reynolds numbers Re(sub D) = (rho)UD/mu in the range 2 less than or equal to Re(sub D) less than or equal to 35. Pressure drops across the screens are measured at these conditions using pressure transducers and manometers. From these data, the Reynolds number dependence of the drag coefficient c(sub D) is determined. Three dimensional flow simulations are performed using the spectral element code NEKTON. The geometry of the photo-etched screens is simulated by a similar geometry with the same open area and minimum wire thickness. The drag coefficients are determined from the computed pressure differences across the screens and are in reasonable agreement with the experimental values, although the agreement degrades slightly with increasing Reynolds number. Such correlations are applicable for the present screens so long as the correct choices for screen open area fraction O and minimum wire thickness D are used in correlation.

Ohern, T. J.; Torczynski, J. R.

425

Numerical simulation for flux change in laminar flow under oscillating boundary condition with Lattice Boltzmann method  

NASA Astrophysics Data System (ADS)

Since the amount of oil production in the world is decreasing recently, it is of importance to seek the technological development for enhanced oil recovery (EOR). Seismic stimulation is known as one of the methods for EOR. Numerous observations show that seismic stimulation could improve oil production and therefore is called as the seismic EOR. However, in order to use seismic EOR more efficiently, we need to understand the mechanisms in Eulerian specifications in flow analyses. In this study, we attempt to evaluate the flux change in viscous laminar flow under a boundary condition oscillating with various frequencies and amplitudes for modeling of interstitial flow. In this study, we use Lattice Boltzmann method (LBM) described by Boltzmann equation. We discuss the difference between the effect of wall oscillation and the pressure disturbance. Then we consider seven major characteristics which would have influences on the flux change: i.e. the amplitudes of wall oscillation, the frequencies, the incident angles, the aspect ratios of pore length to pore width, the thermal effect and interfacial tension. The pressure disturbance has little effect to improve flow and wall oscillation may have large effect to improve flow. In wall oscillation, all characteristics are possibly related with the amount of flux change, but have not been elucidated their mechanisms in detail. In our simulation, the flux of a single-phase flow could increase with large amplitude, high frequency, large angle of incident to the wall, large aspect ratio or large scale. Considering thermal effect, the flux could increase more then not considering that, because wall oscillation generates periodic velocity change and a little temperature increase. In this simulation, the flux of two phase flow could increase with large amplitude, low frequency. On the other hand, the vertically oscillating wall has smaller effect or flux reduction effect even if the other characteristics satisfy the condition to cause the flux increment in the case of horizontal oscillation. Considering flux change under single-phase flow and multi-phase, we found that seismic EOR has the possibility of flux change under the wide frequency range. Our numerical results imply that the flow resistance increases by the velocity difference between the wall and the center of flow. It is also suggested that the fluid extrusion is generated by partial pressure gradient near the wall, and the oscillating boundary may cause pressure loss. The purpose of this study The condition for this simulation

Ueda, R.; Mikada, H.; Goto, T.; Takekawa, J.

2013-12-01

426

Flow and heat transfer characteristics of laminar mixed convection of water with sub-millimeter bubbles in a vertical channel  

NASA Astrophysics Data System (ADS)

Laminar mixed-convection heat transfer is widely seen in compact heat exchangers. Injection of sub-millimeter bubbles is considered as one of the efficient techniques for enhancing laminar mixed-convection heat transfer for liquids. However, the effects of sub-millimeter-bubble injection on the laminar mixed-convection heat transfer are poorly understood. In this study, we experimentally investigate flow and heat transfer characteristics of the laminar mixed-convection of water with sub-millimeter bubbles in a vertical channel. The thermocouples and a PTV (Particle Tracking Velocimetry) technique are used for the temperature and velocity measurements, respectively. Tap water is used for working fluid and hydrogen bubbles generated by electrolysis of water are used as the sub-millimeter bubbles. The Reynolds number of the main flow ranges from 100 to 150. Our results show that the ratio of the heat transfer coefficient with sub-millimeter-bubble injection to that without injection decreases as the Reynolds number increases. It is found from the liquid velocity measurements that this decrease is mainly due to a decrease in the "bubble advection effect".

Kitagawa, A.; Kimura, K.; Endo, H.; Hagiwara, Y.

2009-02-01

427

A free surface model for incompressible pipe and open channel flow. Universite de Toulon, IMATH, EA 2134, 83957 La Garde, France.  

E-print Network

A free surface model for incompressible pipe and open channel flow. M. Ersoy 1 1 Universit´e de in the general framework of unsteady mixed flows in closed water pipes and is largely used by the engineers channel or pipe as well as pressurized flow (when considering pipe flow) plays an important role in many

Paris-Sud XI, Université de

428

Structural development of laminar flow control aircraft chordwise wing joint designs  

NASA Technical Reports Server (NTRS)

For laminar flow to be achieved, any protuberances on the surface must be small enough to avoid transition to turbulent flow. However, the surface must have joints between the structural components to allow assembly or replacement of damaged parts, although large continuous surfaces can be utilized to minimize the number the number of joints. Aircraft structural joints usually have many countersunk bolts or rivets on the outer surface. To maintain no mismatch on outer surfaces, it is desirable to attach the components from the inner surface. It is also desirable for the panels to be interchangeable, without the need for shims at the joint, to avoid surface discontinuities that could cause turbulence. Fabricating components while pressing their outer surfaces against an accurate mold helps to ensure surface smoothness and continuity at joints. These items were considered in evaluating the advantages and disadvantages of the joint design concepts. After evaluating six design concepts, two of the leading candidates were fabricated and tested using many small test panels. One joint concept was also built and tested using large panels. The small and large test panel deflections for the leading candidate designs at load factors up to +1.5 g's were well within the step and waviness requirements for avoiding transition.The small panels were designed and tested for compression and tension at -65 F, at ambient conditions, and at 160 F. The small panel results for the three-rib and the sliding-joint concepts indicated that they were both acceptable. The three-rib concept, with tapered splice plates, was considered to be the most practical. A modified three-rib joint that combined the best attributes of previous candidates was designed, developed, and tested. This improved joint met all of the structural strength, surface smoothness, and waviness criteria for laminar flow control (LFC). The design eliminated all disadvantages of the initial three-rib concept except for unavoidable eccentricity, which was reduced and reacted satisfactorily by the rib supports. It should also result in a relatively simple low-cost installation, and makes it easy to replace any panels damaged in the field.

Fischler, J. E.; Jerstad, N. M.; Gallimore, F. H., Jr.; Pollard, T. J.

1989-01-01

429

User's guide for the computer code COLTS for calculating the coupled laminar and turbulent flow over a Jovian entry probe  

NASA Technical Reports Server (NTRS)

A user's guide for a computer code 'COLTS' (Coupled Laminar and Turbulent Solutions) is provided which calculates the laminar and turbulent hypersonic flows with radiation and coupled ablation injection past a Jovian entry probe. Time-dependent viscous-shock-layer equations are used to describe the flow field. These equations are solved by an explicit, two-step, time-asymptotic finite-difference method. Eddy viscosity in the turbulent flow is approximated by a two-layer model. In all, 19 chemical species are used to describe the injection of carbon-phenolic ablator in the hydrogen-helium gas mixture. The equilibrium composition of the mixture is determined by a free-energy minimization technique. A detailed frequency dependence of the absorption coefficient for various species is considered to obtain the radiative flux. The code is written for a CDC-CYBER-203 computer and is capable of providing solutions for ablated probe shapes also.

Kumar, A.; Graeves, R. A.

1980-01-01

430

Performance evaluation on an air-cooled heat exchanger for alumina nanofluid under laminar flow  

PubMed Central

This study analyzes the characteristics of alumina (Al2O3)/water nanofluid to determine the feasibility of its application in an air-cooled heat exchanger for heat dissipation for PEMFC or electronic chip cooling. The experimental sample was Al2O3/water nanofluid produced by the direct synthesis method at three different concentrations (0.5, 1.0, and 1.5 wt.%). The experiments in this study measured the thermal conductivity and viscosity of nanofluid with weight fractions and sample temperatures (20-60°C), and then used the nanofluid in an actual air-cooled heat exchanger to assess its heat exchange capacity and pressure drop under laminar flow. Experimental results show that the nanofluid has a higher heat exchange capacity than water, and a higher concentration of nanoparticles provides an even better ratio of the heat exchange. The maximum enhanced ratio of heat exchange and pressure drop for all the experimental parameters in this study was about 39% and 5.6%, respectively. In addition to nanoparticle concentration, the temperature and mass flow rates of the working fluid can affect the enhanced ratio of heat exchange and pressure drop of nanofluid. The cross-section aspect ratio of tube in the heat exchanger is another important factor to be taken into consideration. PMID:21827644

2011-01-01

431

Natural laminar flow flight experiments on a swept wing business jet-boundary layer stability analyses  

NASA Technical Reports Server (NTRS)

The linear boundary layer stability analyses and their correlation with data of 18 cases from a natural laminar flow (NLF) flight test program using a Cessna Citation 3 business jet are described. The transition point varied from 5% to 35% chord for these conditions, and both upper and lower wing surfaces were included. Altitude varied from 10,000 to 43,000 ft and Mach number from 0.3 to 0.8. Four cases were at nonzero sideslip. Although there was much scatter in the results, the analyses of boundary layer stability at the 18 conditions led to the conclusion that crossflow instability was the primary cause of transition. However, the sideslip cases did show some interaction of crossflow and Tollmien-Schlichting disturbances. The lower surface showed much lower Tollmien-Schlichting amplification at transition than the upper surface, but similar crossflow amplifications. No relationship between Mach number and disturbance amplification at transition could be found. The quality of these results is open to question from questionable wing surface quality, inadequate density of transition sensors on the wing upper surface, and an unresolved pressure shift in the wing pressure data. The results of this study show the need for careful preparation for transition experiments. Preparation should include flow analyses of the test surface, boundary layer disturbance amplification analyses, and assurance of adequate surface quality in the test area. The placement of necessary instruments and usefulness of the resulting data could largely be determined during the pretest phase.

Rozendaal, R. A.

1986-01-01

432

Effect of wall suction on laminar entrance flow with application to solar air heaters  

NASA Astrophysics Data System (ADS)

Numerical solutions are obtained for hydrodynamically and thermally developing steady-state laminar flow in a long rectangular cavity with uniform suction on one wall and uniform temperature or heat flux independently prescribed at each wal. Collection efficiencies for several solar air heaters are predicted by performing a system analysis. A two dimensional thermal system model is considered, where temperature variation along the direction of flow is allowed in each system element. Five selective black metal plate experimental solar air heaters with and without transpiration were designed, fabricated, and tested to compare their technical merits and to prove how well the theoretical results and system analysis predict performance of actual solar collectors. Discussion of the design of a full-scale selective black metal plate solar air heater with transpiration through slots is presented. Discussed are: (1) The number of teflon films for cover glazing assembly; (2) the spacing between glazing elements; (3) the spacing between the absorber plate and the inner glazing; and (4) the design of inlet and outlet manifolds.

Rhee, S. J.

1980-12-01

433

Analysis of a laminar-flow diffusional mixer for directed self-assembly of liposomes.  

PubMed

The present work describes the operation and simulation of a microfluidic laminar-flow mixer. Diffusive mixing takes place between a core solution containing lipids in ethanol and a sheath solution containing aqueous buffer, leading to self assembly of liposomes. Present device architecture hydrodynamically focuses the lipid solution into a cylindrical core positioned at the center of a microfluidic channel of 125?×?125-?m(2) cross-section. Use of the device produces liposomes in the size range of 100-300?nm, with larger liposomes forming at greater ionic strength in the sheath solution and at lower lipid concentration in the core solution. Finite element simulations compute the concentration distributions of solutes at axial distances of greater than 100 channel widths. These simulations reduce computation time and enable computation at long axial distances by utilizing long hexahedral elements in the axial flow region and fine tetrahedral elements in the hydrodynamic focusing region. Present meshing technique is generally useful for simulation of long microfluidic channels and is fully implementable using comsol Multiphysics. Confocal microscopy provides experimental validation of the simulations using fluorescent solutions containing fluorescein or enhanced green fluorescent protein. PMID:24348890

Kennedy, Matthew J; Ladouceur, Harold D; Moeller, Tiffany; Kirui, Dickson; Batt, Carl A

2012-01-01

434

Heat transfer enhancement of laminar nanofluids flow in a triangular duct using vortex generator  

NASA Astrophysics Data System (ADS)

In this work, two dimensional laminar flow of different nanofluids flow inside a triangular duct with the existence of vortex generator is numerically investigated. The governing equations of mass, momentum and energy were solved using the finite volume method (FVM). The effects of type of the nanoparticles, particle concentrations, and Reynolds number on the heat transfer coefficient and pressure drop of nanofluids are examined. Reynolds number is ranged from 100 to 800. A constant surface temperature is assumed to be the thermal condition for the upper and lower heated walls. In the present work, three nanofluids are examined which are Al2O3, CuO and SiO2 suspended in the base fluid of ethylene glycol with nanoparticles concentrations ranged from 1 to 6%. The results show that for the case of SiO2-EG, at ? = 6% and Re = 800, it is found that the average Nusselt number is about 50.0% higher than the case of Re = 100.

Ahmed, H. E.; Mohammed, H. A.; Yusoff, M. Z.

2012-09-01

435

Constrained large-eddy simulation of laminar-turbulent transition in channel flow  

NASA Astrophysics Data System (ADS)

A constrained large-eddy simulation (CLES) of a laminar-turbulent transition in a temporally developing channel flow is performed. First, we confirm the capability of CLES to simulate this transition problem using the a priori Reynolds stress estimated from a direct numerical simulation. Based on the analysis of the Reynolds stress during the transition process, an intermittency factor is introduced in the Reynolds-averaged Navier-Stokes equation (RANS) model to account for the transition property. Two simple approaches are used to construct the intermittency factor. One is based on the shape factor, and the other is based on the coefficients of Smagorinsky models. The CLES results using the intermittency modified RANS model can accurately predict the onset of the transition and the basic transition process, in a manner similar to a large eddy simulation with dynamics Smagorinsky model (LES-DSM). Meanwhile, CLES preserves its advantage over LES-DSM in the turbulent state. The present work illustrates that CLES can be used to simulate transitional flows.

Zhao, Yaomin; Xia, Zhenhua; Shi, Yipeng; Xiao, Zuoli; Chen, Shiyi

2014-09-01

436

Analysis of a laminar-flow diffusional mixer for directed self-assembly of liposomes  

PubMed Central

The present work describes the operation and simulation of a microfluidic laminar-flow mixer. Diffusive mixing takes place between a core solution containing lipids in ethanol and a sheath solution containing aqueous buffer, leading to self assembly of liposomes. Present device architecture hydrodynamically focuses the lipid solution into a cylindrical core positioned at the center of a microfluidic channel of 125?×?125-?m2 cross-section. Use of the device produces liposomes in the size range of 100–300?nm, with larger liposomes forming at greater ionic strength in the sheath solution and at lower lipid concentration in the core solution. Finite element simulations compute the concentration distributions of solutes at axial distances of greater than 100 channel widths. These simulations reduce computation time and enable computation at long axial distances by utilizing long hexahedral elements in the axial flow region and fine tetrahedral elements in the hydrodynamic focusing region. Present meshing technique is generally useful for simulation of long microfluidic channels and is fully implementable using comsol Multiphysics. Confocal microscopy provides experimental validation of the simulations using fluorescent solutions containing fluorescein or enhanced green fluorescent protein. PMID:24348890

Kennedy, Matthew J.; Ladouceur, Harold D.; Moeller, Tiffany; Kirui, Dickson; Batt, Carl A.

2012-01-01

437

A two element laminar flow airfoil optimized for cruise. M.S. Thesis  

NASA Technical Reports Server (NTRS)

Numerical and experimental results are presented for a new two-element, fixed-geometry natural laminar flow airfoil optimized for cruise Reynolds numbers on the order of three million. The airfoil design consists of a primary element and an independent secondary element with a primary to secondary chord ratio of three to one. The airfoil was designed to improve the cruise lift-to-drag ratio while maintaining an appropriate landing capability when compared to conventional airfoils. The airfoil was numerically developed utilizing the NASA Langley Multi-Component Airfoil Analysis computer code running on a personal computer. Numerical results show a nearly 11.75 percent decrease in overall wing drag with no increase in stall speed at sailplane cruise conditions when compared to a wing based on an efficient single element airfoil. Section surface pressure, wake survey, transition location, and flow visualization results were obtained in the Texas A&M University Low Speed Wind Tunnel. Comparisons between the numerical and experimental data, the effects of the relative position and angle of the two elements, and Reynolds number variations from 8 x 10(exp 5) to 3 x 10(exp 6) for the optimum geometry case are presented.

Steen, Gregory Glen

1994-01-01

438

Transient Analysis of Slip Flow and Heat Transfer in Microchannels  

Microsoft Academic Search

Hybrid analytical-numerical solutions for transient flow and transient convective heat transfer within microchannels are presented. Analytical solutions for flow transients in microchannels are obtained by making use of the integral transform approach. The proposed model involves the transient fully developed flow equation for laminar regime and incompressible flow with slip at the walls in simple channel geometries. The solution is

F. V. Castellões; C. R. Cardoso; P. Couto; R. M. Cotta

2007-01-01

439

A general panel method for the analysis and design of arbitrary configurations in incompressible flows. [boundary value problem  

NASA Technical Reports Server (NTRS)

A method for solving the linear integral equations of incompressible potential flow in three dimensions is presented. Both analysis (Neumann) and design (Dirichlet) boundary conditions are treated in a unified approach to the general flow problem. The method is an influence coefficient scheme which employs source and doublet panels as boundary surfaces. Curved panels possessing singularity strengths, which vary as polynomials are used, and all influence coefficients are derived in closed form. These and other features combine to produce an efficient scheme which is not only versatile but eminently suited to the practical realities of a user-oriented environment. A wide variety of numerical results demonstrating the method is presented.

Johnson, F. T.

1980-01-01

440

On a Regularized Family of Models for Homogeneous Incompressible Two-Phase Flows  

NASA Astrophysics Data System (ADS)

We consider a general family of regularized models for incompressible two-phase flows based on the Allen-Cahn formulation in -dimensional compact Riemannian manifolds for . The system we consider consists of a regularized family of Navier-Stokes equations (including the Navier-Stokes--like model, the Leray- model, the modified Leray- model, the simplified Bardina model, the Navier-Stokes-Voight model, and the Navier-Stokes model) for the fluid velocity suitably coupled with a convective Allen-Cahn equation for the order (phase) parameter . We give a unified analysis of the entire three-parameter family of two-phase models using only abstract mapping properties of the principal dissipation and smoothing operators and then use assumptions about the specific form of the parameterizations, leading to specific models, only when necessary to obtain the sharpest results. We establish existence, stability, and regularity results and some results for singular perturbations, which as special cases include the inviscid limit of viscous models and the limit in models. Then we show the existence of a global attractor and exponential attractor for our general model and establish precise conditions under which each trajectory converges to a single equilibrium by means of a Lojasiewicz-Simon inequality. We also derive new results on the existence of global and exponential attractors for the regularized family of Navier-Stokes equations and magnetohydrodynamics models that improve and complement the results of Holst et al. (J Nonlinear Sci 20(5):523-567, 2010). Finally, our analysis is applied to certain regularized Ericksen-Leslie models for the hydrodynamics of liquid crystals in -dimensional compact Riemannian manifolds.

Gal, Ciprian G.; Medjo, T. Tachim

2014-12-01

441

Wind tunnel results for a high-speed, natural laminar-flow airfoil designed for general aviation aircraft  

NASA Technical Reports Server (NTRS)

Two dimensional wind tunnel tests were conducted on a high speed natural laminar flow airfoil in both the Langley 6 x 28 inch Transonic Tunnel and the Langley Low Turbulence Pressure Tunnel. The test conditions consisted of Mach numbers ranging from 0.10 to 0.77 and Reynolds numbers ranging from 3 x 1 million to 11 x 1 million. The airfoil was designed for a lift coefficient of 0.20 at a Mach number of 0.70 and Reynolds number of 11 x 1 million. At these conditions, laminar flow would extend back to 50 percent chord of the upper surface and 70 percent chord of the lower surface. Low speed results were also obtained with a 0.20 chord trailing edge split flap deflected 60 deg.

Sewall, William G.; Mcghee, Robert J.; Viken, Jeffery K.; Waggoner, Edgar G.; Walker, Betty S.; Millard, Betty F.

1985-01-01

442

Computer program for solving compressible nonsimilar-boundary-layer equations for laminar, transitional, or turbulent flows of a perfect gas  

NASA Technical Reports Server (NTRS)

A computer program is described which solves the compressible laminar, transitional, or turbulent boundary-layer equations for planar or axisymmetric flows. Three-point implicit difference relations are used to reduce the momentum and energy equations to finite-difference form. These equations are solved simultaneously without iteration. Turbulent flow is treated by the inclusion of either a two-layer eddy-viscosity model or a mixing-length formulation. The eddy conductivity is related to the eddy viscosity through a static turbulent Prandtl number which may be an arbitrary function of the distance from the wall boundary. The transitional boundary layer is treated by the inclusion of an intermittency function which modifies the fully turbulent model. The laminar-boundary-layer equations are recovered when the intermittency is zero, and the fully turbulent equations are solved when the intermittency is unity.

Price, J. M.; Harris, J. F.

1972-01-01

443

A new universal series for the calculation of laminar boundary layer flows  

NASA Astrophysics Data System (ADS)

A new universal series for calculating two-dimensional steady incompressible boundary layer flow is presented. Second derivatives of the universal coefficient functions needed for determining the wall shear stress of a symmetric cylinder with a blunt leading edge are calculated. The wall shear stress of Curle's boundary layer and the boundary layer over the circular cylinder are determined as examples. It is found that the rate of convergence of the new series is apparently faster than that of old ones, especially in the region near the separation point. After two or three terms, all the remaining terms on the new infinite series can be accurately approximated by a so-called 'common term method'. The first two terms of the new series for boundary layers with different outer velocity distributions are all the same, provided that the leading edge conditions are the same, and hence the two known terms alone may be used to give a practical approximation in a certain portion of the boundary layer.

Liu, Yu

1985-07-01

444

On the existence of solutions of an equation arising in the theory of laminar flow in a uniformly porous channel with injection  

NASA Technical Reports Server (NTRS)

The existence of concave solutions of Berman's equation which describes the laminar flow in channels with injection through porous walls is established. It was found that the (unique) concave solutions exist for all injection Reynolds numbers R less than 0.

Shih, Ke-Gang

1987-01-01

445

CFD simulation of the laminar flow in stirred tanks generated by double helical ribbons and double helical screw ribbons impellers  

Microsoft Academic Search

In this paper, the mixing performance of double helical ribbons and double helical screw ribbons impellers mounted on stirred\\u000a tanks is numerical investigated. The computer simulations are conducted within a specific computational fluid dynamic (CFD)\\u000a code, based on resolution of the Naviers-Stokes equations in the laminar flow with a finite volume discretization. The field\\u000a velocity and the viscous dissipation rate

Zied Driss; Sarhan Karray; Hedi Kchaou; Mohamed Salah Abid

2011-01-01

446

Multigrid acceleration for recirculating laminar and turbulent flows computed with a non-orthogonal, collocated finite-volume scheme  

Microsoft Academic Search

A study has been undertaken of multigrid convergence acceleration in iterative calculations of recirculating laminar and turbulent flows. The basic numerical platform is a 2D\\/3D non-orthogonal, collocated finite-volume algorithm in which convection is approximated, optionally, by a non-monotonic upstream-weighted third-order scheme or by a monotonic second-order MUSCL\\/TVD formulation, and which iterates the solution towards the steady state by way of

F. S. Lien; M. A. Leschziner

1994-01-01

447

Computational wing design in support of an NLF variable sweep transition flight experiment. [Natural Laminar Flow  

NASA Technical Reports Server (NTRS)

A natural laminar flow outer panel wing glove has been designed for a variable sweep fighter aircraft using state-of-the-art computational techniques. Testing of the design will yield wing pressure and boundary-layer data under actual flight conditions and environment. These data will be used to enhance the understanding of the interaction between crossflow and Tollmien-Schlichting disturbances on boundary-layer transition. The outer wing panel was contoured such that a wide range of favorable pressure gradients could be obtained on the wing upper surface. Extensive computations were performed to support the design effort which relied on two- and three-dimensional transonic design and analysis techniques. A detailed description of the design procedure that evolved during this study is presented. Results on intermediate designs at various stages in the design process demonstrate how the various physical and aerodynamic constraints were integrated into the design. Final results of the glove design analyzed as part of the complete aircraft configuration with a full-potential wing/body analysis code indicate that the aerodynamic design objectives were met.

Waggoner, E. G.; Campbell, R. L.; Phillips, P. S.

1985-01-01

448

Self similar growth of a 1D granular fan under laminar flow near threshold  

NASA Astrophysics Data System (ADS)

Alluvial fans are major sedimentary bodies that make the transition between the reliefs and the sedimentary basins. They are found at the outlet of some drainages catchments, where rivers are free to diverge and avulse, and to depose part of their sedimentary load. Understanding their dynamics of formation and evolution is a great problem of sediment transport. Rivers and fan profiles are usually described as diffusive systems but this is only true if the shear stress exerted on the bed is high compared to the critical shear stress. This might be the case for sand bed rivers, but not for gravel bed rivers, for which it is known that the shear stress is only slightly higher than the critical one. This is why we need to develop a new model to describe the evolution of alluvial fans built by gravel bed rivers. To do this analytically, we work in 1D, with a laminar flow and one grain-size in order to be able to describe both the fluid and the sediment transport. In addition, the conditions of the experiments insured that the boundary shear stress is near the critical value for motion inception of the granular material. Using Taylor expansion, we show that for asymptotically long times, the fan growth is self-similar and can be decomposed into a triangular ``threshold" shape plus a small quadratic deviation. We performed experiments with glass beads and glycerol to test and successfully validate this theory.

Guerit, Laure; Métivier, François; Devauchelle, Olivier; Lajeunesse, Eric; Barrier, Laurie

2014-05-01

449

Hybrid laminar flow control experiments in the NASA - Ames, 11-foot tunnel  

NASA Technical Reports Server (NTRS)

It was proposed to design and conduct experiments in the NASA-Ames Research Center, 11-foot wind tunnel, that would assess the role of freestream turbulence and surface roughness on swept-wing transition to turbulence. The work was to be a cooperative effort that had direct application to hybrid laminar flow control (HLFC) airfoils. The first part of the proposed work, initiated in FY92 and continued into FY93, concentrated on the design of such an experiment whose results may be compared with results obtained in other wind-tunnel facilities. At the same time, concurrent work in the Arizona State University (ASU) Unsteady Wind Tunnel would be conducted on the effects of surface roughness. The second part of the work, which was to be initiated in FY94, would have consisted of experiments conducted in both the 11-foot tunnel at NASA-Ames and the ASU Unsteady Wind Tunnel. However, this work was not continued. This report summarizes the experimental design considerations and some preliminary experiments that made up the first part of the work.

Saric, William S.

1995-01-01

450