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1

Design of minimum drag bodies in incompressible laminar flow  

Microsoft Academic Search

The problem of modifying the shape of a two-dimensional body to reduce its drag while maintaining its section area (volume per unit span) constant is addressed. Two-dimensional, incompressible, laminar flow governed by the steady-state Navier-Stokes equations is assumed about the body. In this study, a set of “adjoint” equations are solved which permits the calculation of the direction and relative

Jianchun Huan; Vijay Modi

1996-01-01

2

Optimum design of minimum drag bodies in incompressible laminar flow using a control theory approach  

Microsoft Academic Search

The problem of modifying the shape of a two-dimensional body to reduce its drag while maintaining its section area (volume per unit span) constant is addressed. Two-dimensional, incompressible, laminar flow governed by the steady-state Navier-Stokes equations is assumed about the body. In this paper, a set of “adjoint” equations is obtained, the solution to which permits the calculation of the

Jianchun Huan; Vijay Modi

1994-01-01

3

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

Microsoft Academic Search

We study the laminar flow of an incompressible Newtonian fluid in a hollow fiber, whose walls are porous. We write the Navier–Stokes\\u000a 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\\u000a condition which accounts for the (possible) slip at the membrane surface. Then, we introduce

Iacopo Borsi; Angiolo Farina; Antonio Fasano

2011-01-01

4

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

SciTech Connect

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 Q2-Q1 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 ([var 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.

Cochran, R.J.

1992-01-01

5

Laminar Validation Cases for the Incompressible Flow Model in ALE3D  

SciTech Connect

To benchmark the incompressible flow model in ALE3D, two test cases are conducted. The first case of two-dimensional flow over a flat plate is selected because it provides a straightforward example to determine whether or not ALE3D can grow a boundary layer by viscous diffusion. The benefit of the flat plate problem is that under certain conditions, the governing Navier-Stokes equations can be simplified and solved with numerical techniques, providing an independent result that can be compared with the solution from ALE3D. The second test case is that of two-dimensional, laminar flow about a circular cylinder. This test case is selected because it provides the complexity of an unsteady bluff-body wake in which vorticity is periodically shed from the surface of the cylinder. Since this canonical flow problem has been studied extensively both experimentally and computationally, the results from ALE3D can be compared with those presented in the literature. The results for the flat plate case demonstrate that the implicit time integration scheme results in an approximate twenty-four-fold reduction of the simulation time over that of the explicit time integration scheme. On the other hand, a problematic trend is observed in the explicit time integration scheme used in the flat plate case. The errors in both the velocity and shear stress are not reduced through grid refinement as one might expect. Another trend that raises concern with the flat plate problem is the sensitivity of the velocity and shear stress to the outlet zero natural boundary condition. In all of the flat plate simulations, at least one of the calculated quantities varies quite noticeably near the outlet of the flow domain. For the case of a circular cylinder in which an explicit time integration scheme is employed, both the drag coefficient and Strouhal number demonstrate trends of converging to a solution that compares favorably with results from other studies in the literature.

Ortega, J

2002-07-16

6

Heat transfer during laminar incompressible flow of fluids in periodic porous media  

NASA Astrophysics Data System (ADS)

Heat transfer during fluid flow through porous media has been of continued interest to researchers due to the increasing pool of application areas. The microscopic heat convection and conduction at pore-scale increases the complexity and difficulty for analyzing such transport phenomena. The main focus of this work is to conduct a systematic study to understand and develop the theory of heat transfer during laminar flow of incompressible fluids through periodic porous media. A new generalized volume-averaged energy balance approach, which relaxes the local thermal equilibrium assumption between the solid and the fluid in the porous media, is developed. Three additional terms are introduced in the macroscopic energy equation by this generalized model. The trivial solution of the generalized model is found as the natural mode for a thermal impulse traveling and spreading in an infinite domain. A link between the macroscopic and microscopic temperature solutions is made by solving the unit cell problem at the microscale with a ``virtual source'' term derived from the macroscale solution. This microscopic temperature solution can be averaged and effective thermal coefficients in the macroscopic energy equation calculated as a function of unit cell geometry, Peclet number and thermo-physical properties of the solid and the fluid. The results agree well with previous experimental data. This methodology could prove useful in studying the micro-transport phenomena in porous media. An application of Liquid Composite Manufacturing (LCM) process is analyzed based on the generalized model. The LCM required the thermosetting resin to saturate the fiber preforms in the heated mold before the resin starts to cure and raise its viscosity to very high value. Our predictions agree with the experimental data. An order of magnitude analysis is presented to explore the possibility for a simplified heat transfer model for LCM process. The justification of the local thermal equilibrium assumption during the LCM process is discussed.

Hsiao, Kuang-Ting

1999-11-01

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

Numerical simulation of incompressible laminar flow in a three-dimensional channel with a cubical open cavity with a bottom wall heated  

NASA Astrophysics Data System (ADS)

A three-dimensional numerical simulation study for both laminar steady and unsteady regimes has been carried out for the mixed convective flow over a three-dimensional cubical open cavity. The cavity is heated from below at constant temperature while the other walls are adiabatic. The numerical simulation has been done using a three-dimensional incompressible finite volume flow solver. The effects over the velocity and temperature distribution of the buoyancy forces acting perpendicular to the mainstream flow are studied for Reynolds numbers (Re) between 100 and 1500; Prandtl number (Pr) is set to 0.7 and Richardson number (Ri) between 10-3 to 101. The phenomenological description of the mixed convection inside and outside the cavity and the combined effects of the natural and forced convection have been obtained. For both high Re and Ri the flow becomes unsteady. The mixed convection effects dominate the flow transport mechanism and push the recirculation zone and the flow further upstream.

Abdelmassih, G.; Vernet, A.; Pallares, J.

2012-11-01

9

A General Method for Calculating Three-Dimensional Incompressible Laminar and Turbulent Boundary Layers. III. Three-Dimensional Flows in Curvilinear Orthogonal Coordinates.  

National Technical Information Service (NTIS)

This report summarizes the third phase of studies conducted on the computation of three-dimensional incompressible laminar and turbulent boundary layers. Solutions of the governing equations in curvilinear orthogonal coordinates are presented for a curved...

T. Cebeci K. Kaups A. Moser

1975-01-01

10

A numerical calculation of three dimensional incompressible laminar, transition and turbulent boundary layers  

Microsoft Academic Search

A method is presented for calculating the 3D boundary layers in incompressible viscous flow, including a differential method for laminar boundary layers, an integral method for turbulent boundary layers, and a numerical solution method for the Orr-Sommerfeld equation in which transition occurs only if the amplification of the disturbance reaches a certain level. These methods are used to calculate a

Jiaxiang Yan; Bin Yu

1991-01-01

11

Supersonic Laminar Flow Control Research.  

National Technical Information Service (NTIS)

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 distr...

C. F. Lo

1994-01-01

12

Supersonic Laminar Flow Control Research.  

National Technical Information Service (NTIS)

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 super laminar flow with distributed...

C. F. Lo

1994-01-01

13

A General Method for Calculating Three-Dimensional Incompressible Laminar and Turbulent Boundary Layers. I. Swept Infinite Cylinders and Small Cross Flow.  

National Technical Information Service (NTIS)

The report presents a general method for solving the laminar and turbulent boundary layer equations for swept infinite cylinders and for small cross flows. In the equations the Reynolds shear stress terms are eliminated by using an eddy viscosity concept....

T. Cebeci G. J. Mosinskis K. Kaups

1972-01-01

14

A numerical calculation of three dimensional incompressible laminar, transition and turbulent boundary layers  

NASA Astrophysics Data System (ADS)

A method is presented for calculating the 3D boundary layers in incompressible viscous flow, including a differential method for laminar boundary layers, an integral method for turbulent boundary layers, and a numerical solution method for the Orr-Sommerfeld equation in which transition occurs only if the amplification of the disturbance reaches a certain level. These methods are used to calculate a swept-wing ONERA M6.

Yan, Jiaxiang; Yu, Bin

1991-06-01

15

Incompressible Flow Along a Corner.  

National Technical Information Service (NTIS)

The incompressible viscous flow along a right-angle corner, formed by the intersection of two semi-infinite flat plates, is considered. The effect of the three-dimensional geometry on the second-order 'boundary layer' flow away from the corner is determin...

S. G. Rubin

1965-01-01

16

The numerical solution of the Navier-Stokes equations for incompressible turbulent flow over airfoils  

Microsoft Academic Search

Numerical solutions are obtained for two-dimensional incompressible turbulent viscous flow over airfoils of arbitrary geometry. An algebraic eddy viscosity turbulence model based on Prandtl's mixing length theory is modified for separated adverse pressure gradient flows. Finite difference methods for solving the inviscid stream function equation and the incompressible laminar Navier-Stokes equations are used. A finite difference method for solving the

H. A. Hegna

1981-01-01

17

Equations of laminar and turbulent flows in general curvilinear coordinates  

Microsoft Academic Search

Recent developments in computational fluid mechanics and grid generation have made it possible to consider complex three dimensional laminar and turbulent flows using nonorthogonal coordinates. However, the necessary equations in generalized nonorthogonal coordinates are not readily available in a single reference. The purpose of this report is to present these equations for an incompressible fluid. Methods of curvilinear tensor analysis

M. C. Richmond; H. C. Chen; V. C. Patel

1986-01-01

18

Flight Experiences with Laminar Flow.  

National Technical Information Service (NTIS)

A review of natural laminar flow (NLF) flight experiences over the period from the 1930's to the present has been given to provide information on the achievability and maintainability of NLF in typical airplane operating environments. Significant effects ...

B. J. Holmes

1986-01-01

19

Laminar Flow in a Two-Dimensional Channel with a Right Angle Corner.  

National Technical Information Service (NTIS)

Laminar, steady, incompressible flow in a two-dimensional channel with a right angle corner was investigated by numerical analysis and experimental measurement. The problem was used as a vehicle to compare a finite differencing method with an upwind diffe...

R. M. Wilson J. A. Owczarek

1973-01-01

20

Incompressible flow simulations without explicit boundary conditions at any open boundary  

NASA Astrophysics Data System (ADS)

Within the context of a pressure-based finite volume method for simulating incompressible flow involving open boundaries, asolution procedure without the need for explicit boundary conditions at any open boundary is proposed. The sole information required in solving the discretized momentum and pressure-linked equations is the flow rate allocated to each of the open boundaries within the solution domain. The methodology isdemonstrated by simulating the laminar flow of an incompressible Newtonian fluid in a duct with a 90 degree branch.

Xue, Shicheng; Barton, Geoffrey

2013-10-01

21

Numerical calculation of fully developed laminar flow in irregular annuli  

Microsoft Academic Search

Purpose – This study seeks to focus on the annular flow between rectangular and equilateral-triangular ducts under all possible arrangements. The aim of this work is to obtain accurate prediction of the friction factor of this flow using high-order finite element method. Design\\/methodology\\/approach – Steady and fully developed laminar flow of incompressible Newtonian fluid in an annulus of variable cross-sectional

O. M. Haddad; M. Q. Al-Odat

2006-01-01

22

Numerical simulation of laminar flow past a circular cylinder  

Microsoft Academic Search

The present paper focuses on the analysis of two- and three-dimensional flow past a circular cylinder in different laminar flow regimes. In this simulation, an implicit pressure-based finite volume method is used for time-accurate computation of incompressible flow using second order accurate convective flux discretisation schemes. The computation results are validated against measurement data for mean surface pressure, skin friction

B. N. Rajani; A. Kandasamy; Sekhar Majumdar

2009-01-01

23

Incompressible boundary layer for longitudinal flow over a cylinder with an applied magnetic field  

Microsoft Academic Search

The flow, heat and mass transfer problem for a steady laminar incompressible boundary layer flow in an electrically conducting fluid over a longitudinal cylinder with an applied magnetic field has been studied. The partial differential equations governing the flow have been solved numerically using an implicit finite-difference scheme. The results are found to be strongly dependent on the magnetic field

B. J. Venkatachala; G. Nath

1980-01-01

24

Laminar free convection heat transfer of a viscous incompressible heat generating fluid-flow past a vertical porous plate in the presence of free-stream oscillations. I  

Microsoft Academic Search

Summary The title problem has been analysed with a view to estimate the effect of the temperature dependent heat sources (sinks) on the oscillatory flow and heat transfer. The governing equations have been reduced to two non-linear ordinary differential equations which have been solved approximately subject to the relevant boundary conditions. The flow- and heat-transfer characteristics have been found to

K. Vajravelu; K. S. Sastri

1978-01-01

25

A general method for calculating three-dimensional incompressible laminar and turbulent boundary layers. 3: Three-dimensional flows in curvilinear orthogonal coordinates  

Microsoft Academic Search

Solutions of the governing equations in curvilinear orthogonal coordinates are presented for a curved rectangular duct. The small-cross-flow methods developed by Cebeci, Kaups, and Mosinskis was applied to compute the boundary layer on a cargo ship hull. The method uses the eddy viscosity concept to model the Reynolds shear-stress terms and uses a very efficient two-point finite difference method to

T. Cebeci; K. Kaups; A. Moser

1975-01-01

26

Investigation of an incompressible flow along a corner by an alternating direction implicit method  

Microsoft Academic Search

The axial corner flow is analyzed for the incompressible laminar boundary layer flow. The governing equations are derived from the Navier-Stokes equations by neglecting second derivative terms of the axial direction. An alternating direction implicit method is used to solve the equations in primitive variables.

G. L. Goglia; D. K. Patel

1977-01-01

27

Approximate factorization for incompressible flow  

Microsoft Academic Search

For computational solution of the incompressible Navier-Stokes equations, the approximate factorization (AF) algorithm is used to solve the vectorized momentum equation in delta form based on the pressure calculated in the previous time step. The newly calculated velocities are substituted into the pressure equation (obtained from a linear combination of the continuity and momentum equation), which is then solved by

R. S. Bernard

1981-01-01

28

An Axisymmetric Incompressible Lattice Boltzmann Model for Pipe Flow  

NASA Astrophysics Data System (ADS)

In this paper an accurate axisymmetric lattice Boltzmann D2Q9 model is proposed to simulate the steady and pulsatile flows in circular pipes. Present model is derived from an incompressible D2Q9 model and some errors in a previous model [Halliday et al., Phys. Rev. E 64, 011208 (2001)] are revised. In the previous model, some terms relative to the radial velocity are missing and would lead to large error for constricted or expanded pipe flows. Present model is validated by cases of laminar steady flow through constricted tubes and 3D Womersley flow. Comparing with the previous model, our model is much more accurate for steady flow in constricted circular pipes. For 3D Womersley flow, it is also observed that the present model can reduce the compressibility effect in previous model.

Lee, T. S.; Huang, Haibo; Shu, C.

29

Dynamic Stall of a NACA 0012 Airfoil in Laminar Flow  

Microsoft Academic Search

The dynamic stall processes of a NACA 0012 airfoil oscillating sinusoidally in pitch and heave in laminar incompressible flow were investigated. The effects of changing the reduced frequency k from 0.6 to 1.2 and the pivot location x_0\\/c from 1\\/4 to 3\\/4 were calculated. The nominal angle of incidence on the airfoil oscillated between 6^circ and 18^circ about a mean

Sasi K. Digavalli

1994-01-01

30

Heat Transfer Study of Two-Dimensional Laminar Incompressible Wall Jet over Backward-Facing Step  

Microsoft Academic Search

A steady-state heat transfer study is carried out for a two-dimensional, laminar, incompressible, plane wall jet over a backward-facing step. An unsteady stream function–vorticity formulation is used to solve the governing equations. The heat transfer characteristics of the jet as functions of Reynolds number (Re), Prandtl number (Pr), and step geometry (step length l and step height s) are reported

P. Rajesh Kanna; Manab Kumar Das

2006-01-01

31

Laminar and Turbulent Flow in Water  

ERIC Educational Resources Information Center

|There are many ways to visualize flow, either for laminar or turbulent flows. A very convincing way to show laminar and turbulent flows is by the perturbations on the surface of a beam of water coming out of a cylindrical tube. Photographs, taken with a flash, show the nature of the flow of water in pipes. They clearly show the difference between…

Riveros, H. G.; Riveros-Rosas, D.

2010-01-01

32

Direct numerical simulation of incompressible axisymmetric flows  

Microsoft Academic Search

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

Patrick Loulou

1994-01-01

33

Application of FCT to Incompressible Flows.  

National Technical Information Service (NTIS)

The flux-corrected transport algorithm (FCT) has been used to solve the Navier-Stokes equation for incompressible flows on colocated grids. In the approach presented here, FCT is used to calculate either the convection terms or to integrate the entire mom...

J. Liu C. R. Kaplan D. R. Mott E. S. Oran

2006-01-01

34

Quadratic finite elements and incompressible viscous flows.  

SciTech Connect

Pressure stabilization methods are applied to higher-order velocity finite elements for application to viscous incompressible flows. Both a standard pressure stabilizing Petrov-Galerkin (PSPG) method and a new polynomial pressure projection stabilization (PPPS) method have been implemented and tested for various quadratic elements in two dimensions. A preconditioner based on relaxing the incompressibility constraint is also tested for the iterative solution of saddle point problems arising from mixed Galerkin finite element approximations to the Navier-Stokes equations. The preconditioner is demonstrated for BB stable elements with discontinuous pressure approximations in two and three dimensions.

Dohrmann, Clark R.; Gartling, David K.

2005-01-01

35

Adaptive remeshing for viscous incompressible flows  

NASA Astrophysics Data System (ADS)

This paper presents an adaptive finite element procedure for solving viscous incompressible flows. The methodology is based on adaptive remeshing for steady state problems. The Navier-Stokes equations for an incompressible fluid are solved in primitive variables by an Uzawa algorithm using a highly accurate element. The efficiency and convergence rate of the adaptive strategy are evaluated by solving problems with known analytical solutions. Finally the methodology is applied to problems of practical interest and predictions are compared with experimental measurements. The use of the proposed adaptive is shown to lead to improved accuracy of the finite element predictions.

Hetu, Jean-Francois; Pelletier, Dominique H.

1990-06-01

36

On a numerical solution of incompressible turbulent boundary layer flow  

NASA Astrophysics Data System (ADS)

The application of the finite element-differential method for turbulent flow problems is considered for a steady two-dimensional incompressible boundary layer flow past a semiinfinite flat plate, in which the boundary layer region is composed of laminar, transitional, and turbulent regimes. The two-layer Cebeci-Smith (1974) closure model was chosen for the eddy viscosity. For the first numerical experiment, a fixed 16-element discretization model is selected with H chosen as 7.0 to cover a large range of local Reynolds numbers. The computed effective eddy profile exhibits oscillatory behavior in the inner region. The next experiment uses an adjustable 15-element model. Finally, a simple adaptive element generation technique for the turbulent flow problem is developed and successfully tested.

Hsu, C.-C.; Chang, T.-H.

37

An Equal-Order Velocity-Pressure Algorithm for Incompressible Thermal Flows, Part 2: Validation  

Microsoft Academic Search

The finite-element algorithm for the solution of two- and three-dimensional incompressible laminar thermal flows described in Part 1 of the article is validated by detailed computational experiments carried out for three typical benchmark problems: flow in lid-driven cavities, natural convection in heated cavities, and stratified flow over backward-facing steps. The numerical simulations concern different values of Reynolds or Rayleigh numbers.

C. Nonino; G. Croce

1997-01-01

38

FULLY DEVELOPED LAMINAR FLOW IN A HELICALLY COILED TUBE OF FINITE PITCH  

Microsoft Academic Search

Solutions for steady, fully developed, laminar flow of an incompressible Newtonian fluid through a helically coiled tube of finite pitch were obtained by finite difference calculations. Prior theoretical solutions have apparently been limited to toroidal flow (with zero pitch). The computed results are consistent with those for this limiting case and with prior experimental data for finite pitch. The behavior

ROMEO L. MANLAPAZ; STUART W. CHURCHILL

1980-01-01

39

Laminar Flow Control at High Speeds  

Microsoft Academic Search

Laminar flow control has always meant controlling the amplitude of linearly unstable waves before transition can occur. In many physical cases, the control of linear Tollmien-Schlichting (T-S) waves is sufficient to prevent transition and many successful demonstrations, including natural laminar flow airfoils, have occurred. Supersonic flight presents another set of challenges that complicates the control process. One has the possibilities

William Saric

2003-01-01

40

Stability criterion of a laminar flow  

Microsoft Academic Search

Conclusions 1.During flow in pipes roughness affects the hydraulic resistance coefficient in the entire laminar region. Relation (8) and other theoretical relations of laminar flow in pipes are valid only for smooth pipes.2.The lower critical value of the Reynolds number varies in wide limits depending on the pipe roughness. Its generally accepted value (1) is not universal and is valid

O. M. Aivazyan

1985-01-01

41

Natural Laminar Flow Nacelle for Transport Aircraft.  

National Technical Information Service (NTIS)

The potential of laminar flow nacelles for reducing installed engine/nacelle drag was studied. The purpose was twofold: to experimentally verify a method for designing laminar flow nacelles and to determine the effect of installation on the extent of lami...

M. Lamb W. K. Abeyounis J. C. Patterson R. J. Re

1986-01-01

42

Nearly incompressible theory and large scale flows  

NASA Astrophysics Data System (ADS)

The nearly incompressible theory of hydrodynamics has been generalized to flows which include a time-independent large-scale inhomogeneous background, such as the solar wind (Hunana, Zank, Shaikh, Phys. Rev. E 74, 026302, 2006). In contrast with the homogeneous case, the expansion of the fully compressible Navier-Stokes equations in powers of sonic Mach number leads at the lowest order to a new system of inhomogeneous equations (referred to as locally incompressible). In this work, we numerically investigate this new inhomogeneous description for two dimensional freely-decaying turbulence. We concentrate on the decay of the power spectrum for density fluctuations with an inhomogeneous density background in one direction that is proportional to 1/r2. Nearly incompressible theory predicts that the density fluctuations ?? behave at the leading order as a passive scalar, with an additional source term produced by coupling to the large-scale inhomogeneous background. In this preliminary work, it is shown that the source term is responsible for a slower power spectrum decay, which has interesting implications for the ``anomalous'' observations of decaying density Voyager spectra described by Bellamy, Cairns, Smith, JGR 110, A10104, 2005.

Hunana, P.; Zank, G. P.; Shaikh, D.; Heerikhuisen, J.

2007-08-01

43

A numerical solution of laminar forced convection in a heated pipe subjected to a reciprocating flow  

Microsoft Academic Search

A numerical solution is presented for laminar forced convection of an incompressible periodically reversing flow in a pipe of finite length at constant wall temperature. It is found that the four parameters that govern the heat transfer characteristics for the problem under consideration are the kinetic Reynolds number Re?, the dimensionless oscillation amplitude Ao, the length to diameter ratio LID,

T. Zhao; P. Cheng

1995-01-01

44

A laminar-flow heat exchanger  

NASA Astrophysics Data System (ADS)

The advantages of designing heat exchangers in the laminar flow regime are discussed from a theoretical standpoint. It is argued that laminar flow designs have the advantages of reducing thermodynamic and hydrodynamic irreversibilities and hence increasing system efficiency. More concretely, laminar flow heat exchangers are free from the turbulence-induced vibration common in conventional heat exchangers and can thus offer longer life and greater reliability. The problems of manufacturing heat exchangers suited to laminar flow are discussed. A method of manufacture which allows compact, modular design is outlined. Experience with this method of manufacture is described, and experimental results are presented. The problems of fouling and flow maldistribution are briefly discussed, and some possible applications are mentioned.

Doty, F. D.; Hosford, G.; Jones, J. D.; Spitzmesser, J. B.

45

Laminar-Flow Wind Tunnel Experiments.  

National Technical Information Service (NTIS)

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 t...

W. D. Harvey C. D. Harris W. G. Sewall J. P. Stack

1989-01-01

46

Research in natural laminar flow and laminar-flow control, part 3  

Microsoft Academic Search

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

J. N. Hefner; F. E. Sabo

1987-01-01

47

Mean flow of turbulent laminar patterns in plane Couette flow  

Microsoft Academic Search

A turbulent-laminar banded pattern in plane Couette flow is studied numerically. This pattern is statistically steady, is oriented obliquely to the streamwise direction, and has a very large wavelength relative to the gap. The mean flow, averaged in time and in the homogeneous direction, is analysed. The flow in the quasi-laminar region is not the linear Couette profile, but results

Dwight Barkley; Laurette S. Tuckerman

2007-01-01

48

Turbulent-Laminar Patterns in Shear Flows  

NASA Astrophysics Data System (ADS)

We study computationally turbulent-laminar patterns in very-large-aspect-ratio plane Couette flow. These states consist of large-scale alternations of turbulent and laminar flow oriented obliquely to the steamwise direction. Such flow patterns are now believed to be typical of many transitional shear flows when observed on long length scales. For a fixed pattern orientation of 24^circ, suggested by experiment, the basic scenario observed in computations as the Reynolds number is decreased is the following: From uniform turbulence there is a transition to intermittent patterns at Re˜420, then to steady, spatially periodic patterns at Re˜390. The wavelength increases as the Reynolds number is decreased until Re˜310, where the flow consists of localized turbulence within a laminar background. This scenario can depend on pattern orientation -- at 90^circ with respect to the flow direction, we observe spatio-temporal intermittency in which turbulent patches that repeatedly disappear abruptly and then re-nucleate gradually. We present an analysis of these flows in terms of mean quantities and discuss the difficulties of determining critical bifurcation parameters for such turbulent-laminar systems.

Barkley, Dwight

2007-03-01

49

Design method for the flow field and drag of bodies of revolution in incompressible flow  

SciTech Connect

A design method has been developed for determining the flow field, pressure distribution, boundary layer separation point, and drag of bodies of revolution at zero angle of attack in incompressible flow. The approach taken is the classical coupling of potential and boundary solutions to obtain the flow field about the body. The potential solution is obtained by modeling the body with an axial distribution of source/sink elements whose strengths vary linearly along their length. The laminar and turbulent boundary layer solutions are obtained from conventional solutions of the momentum integral equation. An approximate method is used to estimate the boundary layer transition point on the body. An empirical base pressure correlation is used to determine the base drag. Body surface pressure distributions and drag predictions are compared with experimental measurements.

Wolfe, W.P.; Oberkampf, W.L.

1982-01-01

50

Pulsating laminar fully developed channel and pipe flows.  

PubMed

Analytical investigations are carried out on pulsating laminar incompressible fully developed channel and pipe flows. An analytical solution of the velocity profile for arbitrary time-periodic pulsations is derived by approximating the pulsating flow variables by a Fourier series. The explicit interdependence between pulsations of velocity, mass-flow rate, pressure gradient, and wall shear stress are shown by using the proper dimensionless parameters that govern the flow. Utilizing the analytical results, the scaling laws for dimensionless pulsation amplitudes of the velocity, mass-flow rate, pressure gradient, and wall shear stress are analyzed as functions of the dimensionless pulsation frequency. Special attention has been given to the scaling laws describing the flow reversal phenomenon occurring in pulsating flows, such as the condition for flow reversal, the dependency of the reversal duration, and the amplitude. It is shown that two reversal locations away from the wall can occur in pulsating flows in pipes and channels and the reversed amount of mass per period reaches a maximum at a certain dimensionless frequency for a given amplitude of mass-flow rate fluctuations. These analyses are numerically conducted for pipe and channel flows over a large frequency range in a comparative manner. PMID:20365456

Haddad, Kais; Ertunç, Ozgür; Mishra, Manoranjan; Delgado, Antonio

2010-01-08

51

CFD analysis of laminar oscillating flows  

SciTech Connect

This paper describes a numerical simulations of oscillating flow in a constricted duct and compares the results with experimental and theoretical data. The numerical simulations were performed using the computational fluid dynamics (CFD) code CFX4.2. The numerical model simulates an experimental oscillating flow facility that was designed to test the properties and characteristics of oscillating flow in tapered ducts, also known as jet pumps. Jet pumps are useful devices in thermoacoustic machinery because they produce a secondary pressure that can counteract an unwanted effect called streaming, and significantly enhance engine efficiency. The simulations revealed that CFX could accurately model velocity, shear stress and pressure variations in laminar oscillating flow. The numerical results were compared to experimental data and theoretical predictions with varying success. The least accurate numerical results were obtained when laminar flow approached transition to turbulent flow.

Booten, C. W. Charles W.); Konecni, S. (Snezana); Smith, B. L. (Barton L.); Martin, R. A. (Richard A.)

2001-01-01

52

The computation of compressible and incompressible recirculating flows by a non-iterative implicit scheme  

NASA Astrophysics Data System (ADS)

In the present study, the PISO algorithm described by Issa (1985), has been implemented in a finite-volume method which employs Euler's implicit temporal difference scheme and a hybrid upwind/centered spatial difference scheme. The developed approach was applied to the circulation of two cases of axisymmetric laminar flow in circular ducts with abrupt enlargement. The first case involved an incompressible fluid with an open duct end, while the second was concerned with a compressible flow and a closed duct end. It is pointed out that the results of the computations verify the findings of the analysis conducted by Issa regarding the accuracy and stability of the algorithm.

Issa, R. I.; Gosman, A. D.; Watkins, A. P.

1986-01-01

53

Passive laminar flow control of crossflow vorticity  

NASA Astrophysics Data System (ADS)

A passive laminar flow crossflow vorticity control system includes an aerodynamic or hydrodynamic surface having geometric perturbations. The perturbations include peaks and valleys having a predetermined spacing and aligned approximately in a streamline direction to force the formation of crossflow vortices. This minimizes amplification and growth of the vortices, thus delaying transition to turbulence and reducing overall drag.

Holmes, Bruce J.

1990-11-01

54

Flight research on natural laminar flow  

Microsoft Academic Search

Five decades of flight experiences with natural laminar flow (NLF) have provided a basis of understanding how this technology can be used for reduction of viscous drag on modern practical aircraft. The effects of cruise unit Reynolds number on NLF achievability and maintainability; compressibility effects on Tollmein-Schlichting growth; flight experiment on the Cessna Citation III business jet; flight instrumentation on

B. J. Holmes; C. C. Croom; E. C. Hastings Jr.; C. J. Obara; C. P. Vandam

1986-01-01

55

Flight Research on Natural Laminar Flow.  

National Technical Information Service (NTIS)

Five decades of flight experiences with natural laminar flow (NLF) have provided a basis of understanding how this technology can be used for reduction of viscous drag on modern practical aircraft. The effects of cruise unit Reynolds number on NLF achieva...

B. J. Holmes C. C. Croom E. C. Hastings C. J. Obara C. P. Vandam

1986-01-01

56

Direct Numerical Simulation of Incompressible Axisymmetric Flows.  

National Technical Information Service (NTIS)

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...

P. Loulou

1994-01-01

57

Incompressible boundary layer transition flight experiments over a nonaxisymmetric fuselage forebody and comparisons with laminar boundary layer stability theory  

Microsoft Academic Search

Analyses of previous boundary-layer transition experiments over axisymmetric bodies indicates a potential for achieving substantial amounts of laminar flow over such shapes. Achievement of natural laminar flow over portions of nonlifting aircraft geometries, such as fuselage to forebodies, tip tanks or engine nacelles, could significantly contribute to the reduction of total aircraft viscous drag. A modern surface-panel method, a streamwise

Paul M. H. W. Vijgen

1990-01-01

58

Statistics of Advective Stretching in Three-dimensional Incompressible Flows  

Microsoft Academic Search

We present a method to quantify kinematic stretching in incompressible, unsteady, isoviscous, three-dimensional flows. We extend the method of Kellogg and Turcotte (J. Geophys. Res. 95:421-432, 1990) to compute the axial stretching\\/thinning experienced by infinitesimal ellipsoidal strain markers in arbitrary three-dimensional incompressible flows and discuss the differences between our method and the computation of Finite Time Lyapunov Exponent (FTLE). We

Natarajan Subramanian; Louise H. Kellogg; Donald L. Turcotte

2009-01-01

59

An approximate projection method for incompressible flow  

NASA Astrophysics Data System (ADS)

This paper presents an approximate projection method for incompressible flows. This method is derived from Galerkin orthogonality conditions using equal-order piecewise linear elements for both velocity and pressure, hereafter Q1Q1. By combining an approximate projection for the velocities with a variational discretization of the continuum pressure Poisson equation, one eliminates the need to filter either the velocity or pressure fields as is often needed with equal-order element formulations. This variational approach extends to multiple types of elements; examples and results for triangular and quadrilateral elements are provided. This method is related to the method of Almgren et al. (SIAM J. Sci. Comput. 2000; 22: 1139-1159) and the PISO method of Issa (J. Comput. Phys. 1985; 62: 40-65). These methods use a combination of two elliptic solves, one to reduce the divergence of the velocities and another to approximate the pressure Poisson equation. Both Q1Q1 and the method of Almgren et al. solve the second Poisson equation with a weak error tolerance to achieve more computational efficiency.A Fourier analysis of Q1Q1 shows that a consistent mass matrix has a positive effect on both accuracy and mass conservation. A numerical comparison with the widely used Q1Q0 (piecewise linear velocities, piecewise constant pressures) on a periodic test case with an analytic solution verifies this analysis. Q1Q1 is shown to have comparable accuracy as Q1Q0 and good agreement with experiment for flow over an isolated cubic obstacle and dispersion of a point source in its wake.

Stevens, David E.; Chan, Stevens T.; Gresho, Phil

2002-12-01

60

Numerical simulation of laminar flow in a curved duct  

NASA Astrophysics Data System (ADS)

This paper describes numerical simulations that were performed to study laminar flow through a square duct with a 900 bend. The purpose of this work was two fold. First, an improved understanding was desired of the flow physics involved in the generation of secondary vortical flows in three-dimensions. Second, adaptive gridding techniques for structured grids in three- dimensions were investigated for the purpose of determining their utility in low Reynolds number, incompressible flows. It was also of interest to validate the commercial computer code CFD-ACE. Velocity predictions for both non-adaptive and adaptive grids are compared with experimental data. Flow visualization was used to examine the characteristics of the flow though the curved duct in order to better understand the viscous flow physics of this problem. Generally, moderate agreement with the experimental data was found but shortcomings in the experiment were demonstrated. The adaptive grids did not produce the same level of accuracy as the non-adaptive grid with a factor of four more grid points.

Lopez, Amalia R.; Oberkampf, William L.

1995-04-01

61

Numerical simulation of incompressible viscous flow in deforming domains  

PubMed Central

We present a second-order accurate finite difference method for numerical solution of the incompressible Navier-Stokes equations in deforming domains. Our approach is a generalization of the Bell-Colella-Glaz predictor–corrector method for incompressible flow. In order to treat the time-dependence and inhomogeneities in the incompressibility constraint introduced by presence of deforming boundaries, we introduce a nontrivial splitting of the velocity field into vortical and potential components to eliminate the inhomogeneous terms in the constraint and a generalization of the Bell-Colella-Glaz algorithm to treat time-dependent constraints. The method is second-order accurate in space and time, has a time step constraint determined by the advective Colella-Friedrichs-Lewy condition, and requires the solution of well behaved linear systems amenable to the use of fast iterative methods. We demonstrate the method on the specific example of viscous incompressible flow in an axisymmetric deforming tube.

Colella, Phillip; Trebotich, David P.

1999-01-01

62

Turning waves and breakdown for incompressible flows  

Microsoft Academic Search

We consider the evolution of an interface generated between two immiscible incompressible and irrotational fluids. Specifically we study the Muskat and water wave problems. We show that starting with a family of initial data given by $(\\\\al,f_0(\\\\al))$, the interface reaches a regime in finite time in which is no longer a graph. Therefore there exists a time $t^*$ where the

A. Castro; D. Cordoba; C. L. Fefferman; F. Gancedo; M. Lopez-Fernandez

2011-01-01

63

Clothing in laminar-flow operating theatres  

Microsoft Academic Search

Bacterial shedding, wound contamination and clinical-infection rates in clean wounds are influenced by operating-theatre dress. The aim of this study was to clarify the relative contribution of hats, masks and clothing to the control of wound contamination in both ultraclean (enclosed vertical laminar-flow) and conventional (plenum ventilated) airflow theatres. Personnel wore varying combinations of dress in both types of theatre.

M. J. Hubble; A. E. Weale; J. V. Perez; K. E. Bowker; A. P. MacGowan; G. C. Bannister

1996-01-01

64

Flight research on natural laminar flow  

NASA Astrophysics Data System (ADS)

Five decades of flight experiences with natural laminar flow (NLF) have provided a basis of understanding how this technology can be used for reduction of viscous drag on modern practical aircraft. The effects of cruise unit Reynolds number on NLF achievability and maintainability; compressibility effects on Tollmein-Schlichting growth; flight experiment on the Cessna Citation III business jet; flight instrumentation on Lear 28/29; OV-I NLF engine nacelle experiments; and viscous drag reduction are examined.

Holmes, B. J.; Croom, C. C.; Hastings, E. C., Jr.; Obara, C. J.; Vandam, C. P.

1986-12-01

65

Incompressible Boundary Layer Transition Flight Experiments Over a Nonaxisymmetric Fuselage Forebody and Comparisons with Laminar Boundary Layer Stability Theory  

Microsoft Academic Search

Analyses of previous boundary-layer transition experiments over axisymmetric bodies indicates a potential for achieving substantial amounts of laminar flow over such shapes. Achievement of natural laminar flow over portions of nonlifting aircraft geometries, such as fuselage forebodies, tip tanks or engine nacelles, could significantly contribute to the reduction of total aircraft viscous drag. A modern surface-panel method, a streamwise boundary-layer

Paul M. H. W. Vijgen

1990-01-01

66

Statistics of Advective Stretching in Three-dimensional Incompressible Flows  

Microsoft Academic Search

We present a method to quantify kinematic stretching in incompressible, unsteady, isoviscous, three-dimensional flows. We\\u000a extend the method of Kellogg and Turcotte (J. Geophys. Res. 95:421–432, 1990) to compute the axial stretching\\/thinning experienced by infinitesimal ellipsoidal strain markers in arbitrary three-dimensional\\u000a incompressible flows and discuss the differences between our method and the computation of Finite Time Lyapunov Exponent (FTLE).\\u000a We use the

Natarajan Subramanian; Louise H. Kellogg; Donald L. Turcotte

2009-01-01

67

Adaptive level set approach for incompressible two-phase flows.  

National Technical Information Service (NTIS)

In Sussman, Smereka and Osher, a numerical method using the level set approach was formulated for solving incompressible two-phase flow with surface tension. In the level set approach, the interface is represented as the zero level set of a smooth functio...

M. Sussman A. S. Almgren J. B. Bell

1997-01-01

68

Spatially Adaptive Techniques for Level Set Methods and Incompressible Flow.  

National Technical Information Service (NTIS)

Since the seminal work of 92 on coupling the level set method of 69 to the equations for two-phase incompressible flow, there has been a great deal of interest in this area. That work demonstrated the most powerful aspects of the level set method, i.e. au...

F. Losasso R. Fedkiw S. Osher

2005-01-01

69

NUMERICAL METHOD FOR SOLVING INCOMPRESSIBLE VISCOUS FLOW PROBLEMS  

Microsoft Academic Search

A numerical method for solving incompressible viscous flow problems is introduced. This method uses the velocities and the (1b) in a domain D in two or three space dimensions, with pressure as variables and is equally applicable to problems in two some appropriate conditions prescribed on the boundary and three space dimensions. The principle of the method lies in the

Alexandre Joel Chorin

1967-01-01

70

An update on projection methods for transient incompressible viscous flow  

SciTech Connect

Introduced in 1990 was the biharmonic equation (for the pressure) and the concomitant biharmonic miracle when transient incompressible viscous flow is solved approximately by a projection method. Herein is introduced the biharmonic catastrophe that sometimes occurs with these same projection methods.

Gresho, P.M.; Chan, S.T.

1995-07-01

71

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

72

A fast adaptive finite element scheme for viscous incompressible flows  

NASA Astrophysics Data System (ADS)

This paper presents an adaptive finite element procedure for solving viscous incompressible flows. The method is based on adaptive remeshing for the solution of the steady-state Navier-Stokes equations for an incompressible fluid. Solutions are obtained in primitive variables by an Uzawa algorithm using a highly accurate element. Two error estimators are presented and compared on a problem with a known analytical solution. The method is then applied to a problem of practical interest and predictions are compared with experimental measurements. The use of the proposed adaptive is shown to lead to improved accuracy of the finite element predictions.

Hetu, Jean-Francois; Pelletier, Dominique H.

73

Lattice Boltzmann model for incompressible flows through porous media  

NASA Astrophysics Data System (ADS)

In this paper a lattice Boltzmann model is proposed for isothermal incompressible flow in porous media. The key point is to include the porosity into the equilibrium distribution, and add a force term to the evolution equation to account for the linear and nonlinear drag forces of the medium (the Darcy's term and the Forcheimer's term). Through the Chapman-Enskog procedure, the generalized Navier-Stokes equations for incompressible flow in porous media are derived from the present lattice Boltzmann model. The generalized two-dimensional Poiseuille flow, Couette flow, and lid-driven cavity flow are simulated using the present model. It is found the numerical results agree well with the analytical and/or the finite-difference solutions.

Guo, Zhaoli; Zhao, T. S.

2002-09-01

74

Lattice Boltzmann model for incompressible flows through porous media.  

PubMed

In this paper a lattice Boltzmann model is proposed for isothermal incompressible flow in porous media. The key point is to include the porosity into the equilibrium distribution, and add a force term to the evolution equation to account for the linear and nonlinear drag forces of the medium (the Darcy's term and the Forcheimer's term). Through the Chapman-Enskog procedure, the generalized Navier-Stokes equations for incompressible flow in porous media are derived from the present lattice Boltzmann model. The generalized two-dimensional Poiseuille flow, Couette flow, and lid-driven cavity flow are simulated using the present model. It is found the numerical results agree well with the analytical and/or the finite-difference solutions. PMID:12366250

Guo, Zhaoli; Zhao, T S

2002-09-17

75

Finite analytic numerical solutions of incompressible flow past inclined axisymmetric bodies  

SciTech Connect

A finite analytic solution for three-dimensional unsteady laminar and turbulent flow is derived on a curvilinear body-fitted coordinate system so that the flow past an arbitrary body shape can be predicted and solved. The general governing equations for turbulent flows are incompressible three-dimensional, ensemble-averaged Navier-Stokes equations. The Reynolds stresses are modeled by the k-epsilon turbulence model with Boussinesq eddy-viscosity assumption. In the numerical solution, the velocity components and pressure are considered as primitive dependent variables and solved explicitly. A numerical program called FANS-3DEF (Finite Analytic Numerical Solution of Three-Dimensional External Flow) is developed. In this program, options are made available for users to select, namely: (1) dimension, (2) grid system, (3) type of flow, and (4) turbulence models. To verify the numerical accuracy and validity of the turbulence models, the finite analytic solution is first obtained for laminar and turbulent flow over a finite flat plate with or without angles of attack at Reynolds number 10/sup 4/, 10/sup 5/ and 2.48 x 10/sup 6/. Then, finite analytic solutions for two axisymmetric bodies without an angle of attack at Reynolds number of 1.2 x 10/sup 6/ and 6.6 x 10/sup 6/ are obtained and compared with available experimental data. Good agreement between the predicted results and experimental data is obtained.

Cheng, W.S.

1986-01-01

76

Numerical simulation for laminar flow and heat transfer of gas in rectanglar micropassages with constant wall heat flux  

Microsoft Academic Search

.   \\u000a Theoretical investigations were performed on the developed laminar flow and convective heat transfer characteristics for incompressible\\u000a gases flow through rectanglar micropassages with constant wall heat flux. Mathematical models were proposed for considering\\u000a the change in viscosity and thermal conductivity of gas in the wall-adjacent region from the kinetic theory. The dimensionless\\u000a velocity distribution and corresponding pressure drop, the

Gang An; Jun-Ming Li; Bu-Xuan Wang

2003-01-01

77

Two-phase laminar boundary layer flow around a wedge  

Microsoft Academic Search

This thesis theoretically presents the phenomena involved in the flow of an incompressible fluid over a wedge with a second incompressible, lighter, and less viscous fluid blown through the surface of the wedge. A method is developed to determine the inner fluid layer thickness, the wall shear stress and the resulting local drag reduction. The results predict substantial drag reduction.

D. Vandord

1982-01-01

78

Roughness and waviness requirements for laminar flow surfaces  

Microsoft Academic Search

Many modern metal and composite airframe manufacturing techniques can provide surface smoothness which is compatible with natural laminar flow (NLF) requirements. An important consideration is manufacturing roughness of the surface in the form of steps and gaps perpendicular to the freestream. The principal challenge to the design and manufacture of laminar flow surfaces today appears to be in the installation

Clifford J. Obara; Bruce J. Holmes

1986-01-01

79

Computational Optimization of a Natural Laminar Flow Experimental Wing Glove.  

National Technical Information Service (NTIS)

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...

F. Hartshom

2012-01-01

80

Design of fuselage shapes for natural laminar flow  

Microsoft Academic Search

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

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

1986-01-01

81

Instability of Steady Flows of an Ideal Incompressible Fluid  

Microsoft Academic Search

\\u000a This article is devoted to recent developments and open questions concerning instabilities in ideal fluid flows. It is argued\\u000a that in some appropriate sense almost all steady flows of an ideal incompressible fluid are unstable. However there are different\\u000a kinds of instability. Many of the instabilities that are described could be termed “slow” and technically they are associated\\u000a with the

Susan Friedlander; Alexander Shnirelman

82

Mean flow of turbulent laminar patterns in plane Couette flow  

NASA Astrophysics Data System (ADS)

A turbulent-laminar banded pattern in plane Couette flow is studied numerically. This pattern is statistically steady, is oriented obliquely to the streamwise direction, and has a very large wavelength relative to the gap. The mean flow, averaged in time and in the homogeneous direction, is analysed. The flow in the quasi-laminar region is not the linear Couette profile, but results from a non-trivial balance between advection and diffusion. This force balance yields a first approximation to the relationship between the Reynolds number, angle, and wavelength of the pattern. Remarkably, the variation of the mean flow along the pattern wavevector is found to be almost exactly harmonic: the flow can be represented via only three cross-channel profiles as U(x,y,z) = U_0(y) + U_c(y) cos(kz) + U_s(y) sin(kz). A model is formulated which relates the cross-channel profiles of the mean flow and of the Reynolds stress. Regimes computed for a full range of angle and Reynolds number in a tilted rectangular periodic computational domain are presented. Observations of regular turbulent-laminar patterns in other shear flows -- Taylor-Couette, rotor-stator, and plane Poiseuille -- are compared.

Barkley, Dwight; Tuckerman, Laurette S.

2007-03-01

83

On Laminar Separation.  

National Technical Information Service (NTIS)

The laminar flow of an incompressible fluid in the vicinity of the separation point on a smooth surface of solid body is investigated. It is shown that the flow separation at large Reynolds number (R) occurs due to the action of large local positive press...

V. V. Sychev

1974-01-01

84

A sharp interface method for incompressible two-phase flows  

Microsoft Academic Search

We present a sharp interface method for computing incompressible immiscible two-phase flows. It couples the level-set and volume-of-fluid techniques and retains their advantages while overcoming their weaknesses. It is stable and robust even for large density and viscosity ratios on the order of 1000 to 1. The numerical method is an extension of the second-order method presented by Sussman [M.

M. Sussman; K. M. Smith; M. Y. Hussaini; M. Ohta; R. Zhi-Wei

2007-01-01

85

Time?dependent incompressible viscous flow past a circular cylinder  

Microsoft Academic Search

In this study, numerical solutions of the equations governing time?dependent, viscous, incompressible fluid flow past a circular cylinder are presented for Reynolds numbers 100, 200, and 500. These solutions are based on the use of body?fitted coordinate systems having a coordinate line coinciding with the body contour regardless of its shape.The implicit solution utilizes vorticity?stream function formulation. All field equations

Robert R. Hwang

1986-01-01

86

An Axisymmetric Incompressible Lattice Boltzmann Model for Pipe Flow  

Microsoft Academic Search

In this paper an accurate axisymmetric lattice Boltzmann D2Q9 model is proposed to simulate the steady and pulsatile flows in circular pipes. Present model is derived from an incompressible D2Q9 model and some errors in a previous model [Halliday et al., Phys. Rev. E 64, 011208 (2001)] are revised. In the previous model, some terms relative to the radial velocity

T. S. Lee; Haibo Huang; C. Shu

2006-01-01

87

Efficient computation of compressible and incompressible flows  

NASA Astrophysics Data System (ADS)

The combination of explicit Runge Kutta time integration with the solution of an implicit system of equations, which in earlier work demonstrated increased efficiency in computing compressible flow on highly stretched meshes, is extended toward conditions where the free stream Mach number approaches zero. Expressing the inviscid flux Jacobians in terms of Mach number, an artificial speed of sound as in low Mach number preconditioning is introduced into the Jacobians, leading to a consistent formulation of the implicit and explicit parts of the discrete equations. Besides extension to low Mach number flows, the augmented Runge Kutta/Implicit method allowed the admissible Courant Friedrichs Lewy number to be increased from O(1 0 0) to O(1 0 0 0). The implicit step introduced into the Runge Kutta framework acts as a preconditioner which now addresses both, the stiffness in the discrete equations associated with highly stretched meshes, and the stiffness in the analytical equations associated with the disparity in the eigenvalues of the inviscid flux Jacobians. Integrated into a multigrid algorithm, the method is applied to efficiently compute different cases of inviscid flow around airfoils at various Mach numbers, and viscous turbulent airfoil flow with varying Mach and Reynolds number. Compared to well tuned conventional methods, computation times are reduced by half an order of magnitude.

Rossow, Cord-Christian

2007-01-01

88

Long-Range LFC (Laminar Flow Control) Transport.  

National Technical Information Service (NTIS)

M = 0.83 Laminar Flow Control (LFC) transports, carrying large percentage payloads over a range of 20000 kilometers at cruise L/D's of 39 appear feasible with large space externally braced wings, external fuel pods, active controls, and 70 percent laminar...

W. Pfenninger

1987-01-01

89

NASA Dryden Fact Sheet - F-16XL Laminar Flow  

NASA Website

F-16XL Laminar Flow Research Aircraft Project Summary Two F-16XL aircraft were used by the Dryden Flight Research Center, Edwards, CA, in a NASA-wide program to improve laminar airflow on aircraft flying at sustained supersonic speeds.

90

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

91

CO-LOCATED EQUAL-ORDER CONTROL-VOLUME FINITE-ELEMENT METHOD FOR MULTIDIMENSIONAL, INCOMPRESSIBLE, FLUID FLOW—PART II: VERIFICATION  

Microsoft Academic Search

This is the second of two companion articles dealing with a co-located equal-order control-volume-based finite-element method (CVFEM) for two- and three-dimensional, incompressible, viscous fluid flow. The formulation of this CVFEM is presented in the first article. In this article, the proposed CVFEM is verified by applying it to four test problems: steady, two-dimensional, laminar flow in a square cavity; steady,

H. J. Saabas; B. R. Baliga

1994-01-01

92

Numerical calculation of heat transfer processes in the case of laminar, free, convection flows in arbitrary, fixed or time-dependent, two-dimensional geometries  

Microsoft Academic Search

The present investigation is concerned with the theoretical study of heat transfer processes in the case of laminar, natural convection flows involving incompressible fluids. A finite difference procedure is proposed for the solution of the equations representing the conservation of mass, momentum, and energy. The formulation of the considered procedure makes it possible to employ arbitrary curvilinear coordinate systems which

H. Rieger

1984-01-01

93

Series solutions for unsteady laminar MHD flow near forward stagnation point of an impulsively rotating and translating sphere in presence of buoyancy forces  

Microsoft Academic Search

The similarity solution for the unsteady laminar incompressible boundary layer flow of a viscous electrically conducting fluid in stagnation point region of an impulsively rotating and translating sphere with a magnetic field and a buoyancy force gives a system of non-linear partial differential equations. These non-linear differential equations are analytically solved by applying a newly developed method, namely the homotopy

Saeed Dinarvand; Ahmad Doosthoseini; Ensiyeh Doosthoseini; Mohammad Mehdi Rashidi

2010-01-01

94

Stability of the laminar boundary layer in an incompressible gas bearing a solid impurity  

Microsoft Academic Search

The article considers the problem of the effect of solid particles suspended in a gas on the stability of the laminar boundary layer with respect to Tollmin-Schlichting waves. An actual scheme for calculating stability is proposed, based on Lin's method. It is shown that, with small values of the concentration of the impurity, s, the critical Reynolds number depends on

I. D. Zheltukhin

1971-01-01

95

Frost Growth and Densification in Laminar Flow Over Flat Surfaces.  

National Technical Information Service (NTIS)

One-dimensional frost growth and densification in laminar flow over flat surfaces has been theoretically investigated. Improved representations of frost density and effective thermal conductivity applicable to a wide range of frost circumstances have been...

M. Kandula

2011-01-01

96

Laminar flow integration: Flight tests status and plans  

Microsoft Academic Search

Under the Aircraft Energy Efficiency - Laminar Flow Control Program, there are currently three flight test programs under way to address critical issues concerning laminar flow technology application to commercial transports. The Leading-Edge Flight Test (LEFT) with a JetStar aircraft is a cooperative effort with the Ames\\/Dryden Flight Research Facility to provide operational experience with candidate leading-edge systems representative of

R. D. Wagner; D. F. Fisher; M. C. Fischer; D. W. Bartlett; R. R. Meyer Jr.

1986-01-01

97

Viscous incompressible flow simulation using penalty finite element method  

NASA Astrophysics Data System (ADS)

Numerical analysis of Navier-Stokes equations in velocity- pressure variables with traction boundary conditions for isothermal incompressible flow is presented. Specific to this study is formulation of boundary conditions on synthetic boundary characterized by traction due to friction and surface tension. The traction and open boundary conditions have been investigated in detail. Navier-Stokes equations are discretized in time using Crank-Nicolson scheme and in space using Galerkin finite element method. Pressure being unknown and is decoupled from the computations. It is determined as post processing of the velocity field. The justification to simulate this class of flow problems is presented through benchmark tests - classical lid-driven cavity flowwidely used by numerous authors due to its simple geometry and complicated flow behavior and squeezed flow between two parallel plates amenable to analytical solution. Results are presented for very low to high Reynolds numbers and compared with the benchmark results.

Sharma, R. L.

2012-04-01

98

Stabilization mechanisms of lifted laminar flames in axisymmetric jet flows  

Microsoft Academic Search

Stabilization mechanisms of lifted laminar propane flames are investigated in an axisymmetric jet flow configuration. Detailed mixing and flow fields upstream of the flame lift-off heights measured by Chung and coworkers [28–30] are calculated on a nonreacting flow basis. The local stoichiometric axial velocity, Ust, and scalar dissipation rate, ?st, are obtained at points that are upstream of the stabilization

Yung-Cheng Chen; Robert W. Bilger

2000-01-01

99

Incompressible and compressible flows through rectangular microorifices entrenched in silicon microchannels  

Microsoft Academic Search

Incompressible and compressible flows through indispensable configurations such as rectangular microorifices entrenched in microchannels have been experimentally investigated. The current endeavor evaluates the effects of microorifice and microchannel size, estimates the discharge coefficients associated with both compressible and incompressible flows, examines the contraction coefficients, probes subsonic and supercritical gas flows, and explores the presence of any anomalous effects such as

Chandan Mishra; Yoav Peles

2005-01-01

100

Banded laminar-turbulent patterns: mean flows, symmetries and statistics  

NASA Astrophysics Data System (ADS)

In large-aspect-ratio plane Couette flow, patterns of oblique bands, alternating between turbulent and laminar flow, are the intermediate regime between uniform turbulence and laminar Couette flow. The mean flows corresponding to these patterns, as well as the Reynolds stress force, are found to be represented almost perfectly by a single trigonometric function along the pattern wavevector, leading to a quantitative description in terms of six ODEs. The Fourier component corresponding to the pattern wavelength provides an order parameter for the transition, which can be described as a bifurcation in its probability distribution function.

Tuckerman, Laurette; Barkley, Dwight

2007-11-01

101

Filter-matrix lattice Boltzmann model for incompressible thermal flows.  

PubMed

In this study, a new filter-matrix lattice Boltzmann (FMLB) model is proposed and extended to include incompressible thermal flows. A new equilibrium solution is found in the improved FMLB model, which is derived from the Hermite expansion. As a result, the velocity-dependent pressure is removed, which is an inherent defect of Somers's FMLB model. In addition, the improved model is extended to include incompressible thermal flows by introducing a class of temperature-distribution function for evaluating the temperature field. Two different temperature-distribution functions are discussed. The improved FMLB model and the temperature-evaluation equation are combined into one coupled model. Numerical simulations are performed on the two-dimensional (2D) lid-driven square cavity flow and the 2D natural convection flow in a square cavity using the improved FMLB model and the two coupled models, respectively. The numerical results of the 2D lid-driven square cavity flow show that the improved FMLB model is superior to the lattice Bhatnagar-Gross-Krook (LBGK) model in terms of both accuracy and stability. When compared with the multi-relaxation-time (MRT) model, the similar accuracy and slightly enhanced stability can be obtained by the improved model. The advantage of the improved model is that it no longer relies on difficult selection of the free parameters requested by the MRT model; in addition, the force term is already included in the collision operator of the improved model. In the case of 2D natural convection flow, the numerical results of the two present models are almost the same, and both exhibit good agreement with the benchmark solution. PMID:22680602

Zhuo, Congshan; Zhong, Chengwen; Cao, Jun

2012-04-11

102

Filter-matrix lattice Boltzmann model for incompressible thermal flows  

NASA Astrophysics Data System (ADS)

In this study, a new filter-matrix lattice Boltzmann (FMLB) model is proposed and extended to include incompressible thermal flows. A new equilibrium solution is found in the improved FMLB model, which is derived from the Hermite expansion. As a result, the velocity-dependent pressure is removed, which is an inherent defect of Somers's FMLB model. In addition, the improved model is extended to include incompressible thermal flows by introducing a class of temperature-distribution function for evaluating the temperature field. Two different temperature-distribution functions are discussed. The improved FMLB model and the temperature-evaluation equation are combined into one coupled model. Numerical simulations are performed on the two-dimensional (2D) lid-driven square cavity flow and the 2D natural convection flow in a square cavity using the improved FMLB model and the two coupled models, respectively. The numerical results of the 2D lid-driven square cavity flow show that the improved FMLB model is superior to the lattice Bhatnagar-Gross-Krook (LBGK) model in terms of both accuracy and stability. When compared with the multi-relaxation-time (MRT) model, the similar accuracy and slightly enhanced stability can be obtained by the improved model. The advantage of the improved model is that it no longer relies on difficult selection of the free parameters requested by the MRT model; in addition, the force term is already included in the collision operator of the improved model. In the case of 2D natural convection flow, the numerical results of the two present models are almost the same, and both exhibit good agreement with the benchmark solution.

Zhuo, Congshan; Zhong, Chengwen; Cao, Jun

2012-04-01

103

[Use of rooms with laminar air flow].  

PubMed

The paper deals with the problem of dependency of the reduction of microbial contamination and of dust pollution of the air mediu min the CAMERA-BOXES with a liminary flux on the aeration degree. It was shown that the degree of aeration in the camera-box constituted from 330 to 1060, with the rate of the air flux at the filter exit of from 0.2 to 0.6 m/sec. Vertical laminar flux provided release of the air from the microbes and dust. The use of the camera-box with a laminar flux for work requiring sterile conditions is recommended. PMID:1266473

Vashkov, V I; Alekseeva, M I; Gol'ts, M V; Morozov, P I; Mal'kov, O S

1976-02-01

104

A SIMPLE based discontinuous Galerkin solver for steady incompressible flows  

NASA Astrophysics Data System (ADS)

In this paper we present how the well-known SIMPLE algorithm can be extended to solve the steady incompressible Navier-Stokes equations discretized by the discontinuous Galerkin method. The convective part is discretized by the local Lax-Friedrichs fluxes and the viscous part by the symmetric interior penalty method. Within the SIMPLE algorithm, the equations are solved in an iterative process. The discretized equations are linearized and an equation for the pressure is derived on the discrete level. The equations obtained for each velocity component and the pressure are decoupled and therefore can be solved sequentially, leading to an efficient solution procedure. The extension of the proposed scheme to the unsteady case is straightforward, where fully implicit time schemes can be used.Various test cases are carried out: the Poiseuille flow, the channel flow with constant transpiration, the Kovasznay flow, the flow into a corner and the backward-facing step flow. Using a mixed-order formulation, i.e. order k for the velocity and order k-1 for the pressure, the scheme is numerically stable for all test cases. Convergence rates of k+1 and k in the L2-norm are observed for velocity and pressure, respectively. A study of the convergence behavior of the SIMPLE algorithm shows that no under-relaxation for the pressure is needed, which is in strong contrast to the application of the SIMPLE algorithm in the context of the finite volume method or the continuous finite element method. We conclude that the proposed scheme is efficient to solve the steady incompressible Navier-Stokes equations in the context of the discontinuous Galerkin method comprising hp-accuracy.

Klein, Benedikt; Kummer, Florian; Oberlack, Martin

2013-03-01

105

An immersed boundary method for complex incompressible flows  

NASA Astrophysics Data System (ADS)

An immersed boundary method for time-dependent, 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 second-order central-differences for the viscous components. Higher-order accuracy achieved by using weighted essentially non-oscillatory (WENO) or total variation diminishing (TVD) schemes. An implicit method based on artificial compressibility and dual-time stepping is used for time advancement. The immersed boundary surfaces are defined as clouds of points, which may be structured or unstructured. Immersed-boundary objects are rendered as level sets in the computational domain, and concepts from computational geometry are used to classify points as being outside, near, or inside the immersed boundary. The velocity field near an immersed surface is determined from separate interpolations of the components tangent and normal to the surface. The tangential velocity near the surface is constructed as a power-law function of the local wall normal distance. Appropriate choices of the power law enable the method to approximate the energizing effects of a turbulent boundary layer for higher Reynolds number flows. Five different flow problems (flow over a circular cylinder, an in-line oscillating cylinder, a NACA0012 airfoil, a sphere, and a stationary mannequin) are simulated using the present immersed boundary method, and the predictions show good agreement with previous computational and experimental results. Finally, the flow induced by realistic human walking motion is simulated as an example of a problem involving multiple moving immersed objects.

Choi, Jung-Il; Oberoi, Roshan C.; Edwards, Jack R.; Rosati, Jacky A.

2007-06-01

106

Discrete Singular Convolution-Finite Subdomain Method for the Solution of Incompressible Viscous Flows  

NASA Astrophysics Data System (ADS)

This paper proposes a discrete singular convolution-finite subdomain method (DSC-FSM) for the analysis of incompressible viscous flows in multiply connected complex geometries. The DSC algorithm has its foundation in the theory of distributions. A block-structured grid of fictitious overlapping interfaces is designed to decompose a complex computational geometry into a finite number of subdomains. In each subdomain, the governing Navier-Stokes equations are discretized by using the DSC algorithm in space and a third-order Runge-Kutta scheme in time. Information exchange between fictitious overlapping zones is realized by using the DSC interpolating algorithm. The Taylor problem, with decaying vortices, could be solved to machine precision, with an excellent comparison against the exact solution. The reliability of the proposed method is tested by simulating the flow in a lid-driven cavity. The utility of the DSC-FSM approach is further illustrated by two other benchmark problems, viz., the flow over a backward-facing step and the laminar flow past a square prism. The present results compare well with the numerical and experimental data available in the literature.

Wan, D. C.; Patnaik, B. S. V.; Wei, G. W.

2002-07-01

107

A continuous Lagrangian sensitivity equation method for incompressible flow  

NASA Astrophysics Data System (ADS)

A continuous Lagrangian sensitivity equation method (CLSEM) is presented as a cost effective alternative to the continuous (Eulerian) sensitivity equation method (CESEM) in the case of shape parameters. Boundary conditions for the CLSEM are simpler than those of the CESEM. However a mapping must be introduced to relate the undeformed and deformed configurations thus making the PDEs more complicated. We propose the use of pseudo-elasticity equations to provide a general framework to generate this mapping for unstructured meshes on complex geometries. The methodology is presented in details for the incompressible Navier-Stokes and sensitivity equations in variational form. The PDEs are solved with an adaptive FEM. Sensitivity data obtained with both approaches for a flow around a NACA 4512 are used to obtain estimates of flows around nearby geometries. Results indicate that the CLSEM produces significant improvements in terms of both accuracy and CPU time.

Charlot, L.; Etienne, S.; Pelletier, D.

2012-07-01

108

Prediction of incompressible flow separation with the approximate factorization technique  

NASA Astrophysics Data System (ADS)

This paper describes an application of the approximate factorization technique to the solution of incompressible steady viscous flow problems in two dimensions. The velocity-pressure formulation of the Navier-Stokes equations written in curvilinear nonorthogonal coordinates is adopted. The continuity equation is replaced with one equation for the pressure by means of the artificial compressibility concept to obtain a system parabolic in time. The resulting equations are discretized in space with centered finite differences, and the steady state solution obtained by a time-marching ADI method requiring to solve 3 x 3 block tridiagonal linear systems. An optimized fourth-order artificial dissipation is introduced to damp the numerical instabilities of the artificial compressibility equation and ensure convergence. The resulting solver is applied to the prediction of a wide variety of internal flows, including both streamlined boundaries and sharp corners, and fast convergence and good results obtained for all the configurations investigated.

Michelassi, V.; Benocci, C.

1987-12-01

109

Laminar flow integration: Flight tests status and plans  

NASA Astrophysics Data System (ADS)

Under the Aircraft Energy Efficiency - Laminar Flow Control Program, there are currently three flight test programs under way to address critical issues concerning laminar flow technology application to commercial transports. The Leading-Edge Flight Test (LEFT) with a JetStar aircraft is a cooperative effort with the Ames/Dryden Flight Research Facility to provide operational experience with candidate leading-edge systems representative of those that might be used on a future transport. In the Variable Sweep Transition Flight Experiment (VSTFE), also a cooperative effort between Langley and Ames/Dryden, basic transition data on an F-14 wing with variable sweep will be obtained to provide a data base for laminar flow wing design. Finally, under contract to the Boeing Company, the acoustic environment on the wing of a 757 aircraft will be measured and the influence of engine noise on laminar flow determined with a natural laminar flow glove on the wing. The status and plans for these programs are reported.

Wagner, R. D.; Fisher, D. F.; Fischer, M. C.; Bartlett, D. W.; Meyer, R. R., Jr.

1986-12-01

110

Immersed interface methods for incompressible flow with moving interfaces  

NASA Astrophysics Data System (ADS)

We introduce a class of immersed interface methods for incompressible Navier-Stokes equations with singular forces. The algorithms are developed using a new hybrid finite volume/finite difference projection method. This projection method uses the high-resolution finite-volume method from CLAWPACK to advect the cell-centered velocity using the divergence-free edge velocity. Then a finite difference method is used for the diffusion and the projection step. This projection method is second-order accurate and is suitable for flow at high Reynolds numbers or problems containing discontinuous conserved quantities. The immersed interface method developed in this thesis is motivated by Peskin's immersed boundary (IB) method, and allows one to model the motion of flexible membranes or other structures immersed in viscous incompressible fluid using a fluid solver on a fixed Cartesian grid. The IB method uses a set of discrete delta functions to spread the entire singular force exerted by the immersed boundary to the nearby fluid grid points. Our method instead incorporates part of this force into jump conditions for the pressure, avoiding discrete dipole terms that adversely affect the accuracy near the immersed boundary. This has been implemented by imposing the correct pressure jump in the course of solving the Poisson problem in the projection step. This gives sharp resolution of the pressure across the interface and better volume conservation than the traditional IB method. A fully implicit method that allows us to model immersed elastic boundaries with mass is also presented.

Lee, Long

111

Rapid preparation of monodispersed droplets with confluent laminar flows  

Microsoft Academic Search

We study the formation of micro droplets in confluent two-phase flows in a microfluidic system. Instability at the interface of two immiscible liquids undergoing laminar flow generates micro droplets of highly uniform size. Under high shear stress the droplets form rapidly, and more than 2000 droplets can be prepared of similar size. Droplet size can be controlled by varying the

Takasi Nisisako; T. Torii; Toshiro Higuchi

2003-01-01

112

NASA Chat: Quest for the Holy Grail of Laminar Flow  

NASA Website

People who love flying are on a quest for aviation's holy grail – laminar flow. It's the absolutely uninterrupted flow of air over a wing and it's something you want but very hard to get. On Wed., March 30, NASA's Ethan Baumann ...

113

Simulation of unsteady incompressible turbulent flows using Galerkin finite element and adaptive grids  

NASA Astrophysics Data System (ADS)

A new procedure for the simulation of unsteady turbulent flows using Galerkin finite element and adaptive grids is presented. The adaptive grids are generated during the simulation using a new mesh generation technique. This technique is fast, produces a quad-dominant mesh while preserving the quality of the elements without the need to move any grid points. The new points are nested to the old mesh to avoid hanging nodes. Interpolation operators are used to map the different variables from one grid to the next one. Refinement zones are defined using the gradient of the vorticity from the previous time step. A Galerkin finite element method is implemented to simulate unsteady incompressible turbulent flows using the primary variables with mixed elements for the velocity components and the pressure. The resulting linearized system is solved using Krylov subspace iterative methods and multigrid. The least-squares commutator is implemented as a preconditioner of the indefinite linear system. The Wilcox k-o turbulence model is implemented and the solver is coupled with the adaptive grid generator in order to produce a new solution resolved grid for every time step. Several application examples are provided to show the strength of this new approach. These applications includes unsteady laminar and turbulent flows over various two-dimensional objects such as cylinders, a NACA0012 airfoil and a multi-element airfoil.

Ebeida, Mohamed S.

114

The Influence of a Magnetic Field on a Laminar Viscous Flow in a Semi-Porous Channel  

NASA Astrophysics Data System (ADS)

In this article, the steady two-dimensional laminar flow of a viscous incompressible fluid in a semi-porous channel in the presence of a transverse magnetic field is considered. The homotopy perturbation method (HPM) and variational iteration method (VIM) are employed to compute an approximation to the solution of the system of differential equations governing on the problem. Velocity profiles, streamlines, and the other parameters of flow are determined. Comparisons are made between the numerical method (NM) and the results of our methods. The results reveal that these methods are very effective, simple, and can be applied to other nonlinear problems.

Ranjbar, A. A.; Domairry, G.; Javadein, M. S.

115

Numerical simulation of incompressible viscous flow past a heaving airfoil  

NASA Astrophysics Data System (ADS)

Numerical simulations of a heaving airfoil undergoing non-sinusoidal motions in an incompressible viscous flow is presented. In particular, asymmetric sinusoidal motions, constant heave rate oscillations, and sinusoidal motions with a quiescent gap, are considered. The wake patterns, thrust force coefficients, and propulsive efficiency at various values of non-dimensional heave velocity are computed. These have been compared with those of corresponding sinusoidal heaving motions of the airfoil. It is shown that for a given non-dimensional heave velocity and reduced frequency of oscillation, asymmetric sinusoidal motions give better thrust and propulsive efficiencies in comparison to pure harmonic motion. On the other hand, constant rate heave motion do not compare favourably with harmonic motion. A train of sinusoidal pulses separated by a quiescent gap compares favourably with a pure sinusoidal motion, but with the notable exception that the quiescent gap induces a discontinuity that induces large impulses to the wake pattern.

Sarkar, Sunetra; Venkatraman, Kartik

2006-05-01

116

A numerical algorithm for viscous incompressible interfacial flows  

NASA Astrophysics Data System (ADS)

We present a new algorithm to numerically simulate two-dimensional viscous incompressible flows with moving interfaces. The motion is updated in time by using the backward difference formula through an iterative procedure. At each iteration, the pseudo-spectral technique is applied in the horizontal direction. The resulting semi-discretized equations constitute a boundary value problem in the vertical coordinate which is solved by decoupling growing and decaying solutions. Numerical tests justify that this method achieves fully second-order accuracy in both the temporal variable and vertical coordinate. As an application of this algorithm, we study the motion of Stokes waves in the presence of viscosity. Our numerical results are consistent with the recently published asymptotic solution for Stokes waves in slightly viscous fluids.

Wang, Jin; Baker, Greg

2009-08-01

117

Roughness and waviness requirements for laminar flow surfaces  

NASA Astrophysics Data System (ADS)

Many modern metal and composite airframe manufacturing techniques can provide surface smoothness which is compatible with natural laminar flow (NLF) requirements. An important consideration is manufacturing roughness of the surface in the form of steps and gaps perpendicular to the freestream. The principal challenge to the design and manufacture of laminar flow surfaces today appears to be in the installation of leading-edge panels on wing, nacelle, and empennage surfaces. A similar challenge is in the installation of access panels, doors, windows, fuselage noses, and engine nacelles. Past work on roughness and waviness manufacturing tolerances and comparisons with more recent experiments are reviewed.

Obara, Clifford J.; Holmes, Bruce J.

1986-12-01

118

Incompressible boundary layer transition flight experiments over a nonaxisymmetric fuselage forebody and comparisons with laminar boundary layer stability theory  

NASA Astrophysics Data System (ADS)

Analyses of previous boundary-layer transition experiments over axisymmetric bodies indicates a potential for achieving substantial amounts of laminar flow over such shapes. Achievement of natural laminar flow over portions of nonlifting aircraft geometries, such as fuselage to forebodies, tip tanks or engine nacelles, could significantly contribute to the reduction of total aircraft viscous drag. A modern surface-panel method, a streamwise boundary-layer analysis method, and streamwise linear stability theory (E(sup n)-method) are used to correlate several previous transition measurements along axisymmetric geometries to study the transition characteristics of a nonaxisymmetric body geometry, a flight investigation was conducted to measure the transition location and analyze the mode of transition over the nonaxisymmetric forebody of an existing light twin-engine propeller-driven airplane. A summary of the inviscid flow field over the forebody of the aircraft at various body angles is presented, indicating the relatively small magnitude of inviscid crossflow along the forebody at typical cruising attitudes. The transition instrumentation installed in the airplane fuselage is described, together with relative surface-waviness measurements along the forebody. The macroscopic location of the transitional front, obtained from arrayed hot-film sensors, is presented for a matrix of flight conditions with various unit-Reynolds numbers, angles of attack and sideslip, and engine power settings.

Vijgen, Paul M. H. W.

1990-11-01

119

Computation of incompressible viscous flows through turbopump components  

NASA Astrophysics Data System (ADS)

Flow through pump components, such as an inducer and an impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudocompressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. the equations are solved in steadily rotating reference frames and the centrifugal force and the Coriolis force are added to the equation of motion. Current computations use a one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside a generic rocket engine pump inducer, a fuel pump impeller, and SSME high pressure fuel turbopump impeller. Numerical results of inducer flow are compared with experimental measurements. In the fuel pump impeller, the effect of downstream boundary conditions is investigated. Flow analyses at 80 percent, 100 percent, and 120 percent of design conditions are presented.

Kiris, Cetin; Chang, Leon

1993-02-01

120

Incompressible Navier-Stokes calculations in pump flows  

NASA Astrophysics Data System (ADS)

Flow through pump components, such as the SSME-HPFTP Impeller and an advanced rocket pump impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. The equations are solved in steadily rotating reference frames and the centrifugal force and the Coriolis force are added to the equation of motion. Current computations use one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside an 11-inch SSME High Pressure Fuel Turbopump impeller, and an advanced rocket pump impeller. Numerical results of SSME-HPFTP impeller flow are compared with experimental measurements. In the advanced pump impeller, the effects of exit and shroud cavities are investigated. Flow analyses at design conditions will be presented.

Kiris, Cetin; Chang, Leon; Kwak, Dochan

1993-07-01

121

A Computational Model for Three-Dimensional Incompressible Small Cross Flow Wall Jets.  

National Technical Information Service (NTIS)

A computational model based on H. Keller's box scheme has been used to characterize turbulent incompressible wall jets in the small cross flow approximation prototypic of flows over upper-surface-blown and augmenter wings. Submerged and coflowing cases ar...

N. D. Malmuth R. K. Szeto

1977-01-01

122

Turbulent-laminar patterns in Couette flow: stripes and spots  

NASA Astrophysics Data System (ADS)

Large-scale turbulent-laminar spirals were first observed in counter-rotating Taylor-Couette flow by Coles (1965). Recently, Prigent and Dauchot (2001) discovered an analogous state in large-aspect-ratio plane Couette flow, consisting of turbulent-laminar bands oriented obliquely to the streamwise direction, while Cros and Le Gal (2002) observed large-scale turbulent spirals between stationary and rotating disks. We study these patterns numerically by extending the minimal flow unit methodology pioneered by Jimenez et al. (1991). Our periodic computational domains are of minimal size in one lateral direction but long (60 gaps) in the other, which can be tilted at any prescribed angle to the streamwise direction. Three types of patterned states are found as Re is decreased from uniform turbulence at Re=400. (1) Intermittent states occur near the turbulent-pattern threshold. (2) Periodic states have a well-defined wavelength which increases with decreasing Re. (3) Localized states are the manifestation in our computations of turbulent spots. This suggests that the basic physics of isolated turbulent spots can be captured without simulating two large lateral directions. Reversion to laminar Couette flow is inevitable when Re? 300. Mean and fluctuating fields for laminar-turbulent patterned flows are presented and shown to be out of phase with one another.

Barkley, Dwight; Tuckerman, Laurette

2004-11-01

123

Natural Laminar-Flow Blades for Vertical-Axis Wind Turbines.  

National Technical Information Service (NTIS)

Natural Laminar Flow (NLF) airfoils are those which can achieve significant extents of laminar flow (greater than 30% of chord) solely through favorable pressure gradients. A number of candidate airfoil sections were defined and then screened in a perform...

P. C. Klimas

1982-01-01

124

Turbulent-Laminar Patterns in Plane Couette Flow  

Microsoft Academic Search

Regular patterns of turbulent and laminar fluid motion arise in plane Couette flow near the lowest Reynolds number for which\\u000a turbulence can be sustained. We study these patterns using an extension of the minimal flow unit approach to simulations of\\u000a channel flows pioneered by Jiménez and Moin. In our case computational domains are of minimal size in only two directions.

Dwight Barkley; Laurette S. Tuckerman

2005-01-01

125

Aerodynamic shape optimization of Airfoils in 2-D incompressible flow  

NASA Astrophysics Data System (ADS)

An optimization framework was developed for maximizing the region of 2-D airfoil immersed in laminar flow with enhanced aerodynamic performance. It uses genetic algorithm over a population of 125, across 1000 generations, to optimize the airfoil. On a stand-alone computer, a run takes about an hour to obtain a converged solution. The airfoil geometry was generated using two Bezier curves; one to represent the thickness and the other the camber of the airfoil. The airfoil profile was generated by adding and subtracting the thickness curve from the camber curve. The coefficient of lift and drag was computed using potential velocity distribution obtained from panel code, and boundary layer transition prediction code was used to predict the location of onset of transition. The objective function of a particular design is evaluated as the weighted-average of aerodynamic characteristics at various angles of attacks. Optimization was carried out for several objective functions and the airfoil designs obtained were analyzed.

Rangasamy, Srinivethan; Upadhyay, Harshal; Somasekaran, Sandeep; Raghunath, Sreekanth

2010-11-01

126

New pressure correction equation for incompressible internal flows  

NASA Astrophysics Data System (ADS)

A space-marching method is employed to integrate the reduced form of the Navier-Stokes equations for steady incompressible viscous fluids for arbitrary three-dimensional internal flow geometries. The Objective of this paper is to present the development of a new pressure correction equation that is used to correct the pressure and then the velocities locally at each marching station. The equation incorporates information from the momentum equations in the form of newly derived variables that are called V-P (velocity-pressure) variables. Although the momentum equations are solved as an uncoupled system, the V-P variables couple the equations indirectly through the solution of the new pressure correction equation. A numerical procedure based on this equation is used to sweep the entire domain in a stationwise manner. At each station one matrix inversion and a two-dimensional Poisson equation are required to satisfy the continuity and the momentum equations at the same time to conserve the volume flow rate. A computer code utilizing this procedure was tested for different geometries. Predictions of the flow through constricted and strongly curved pipes are in good agreement with previous experimental and computational results. As a result of using the V-P variables and the new pressure correction equation, CPU time is reduced.

Mazher, A. K.; Giddens, Don P.

1991-03-01

127

Airborne drug levels in a laminar-flow hood  

Microsoft Academic Search

The airborne levels of fluorouracil and cefazolin sodium injections after manipulation of these drug products inside a horizontal laminar-flow hood were measured. The Biotest RCS Centrifugal Air Sampler, generally used to measure microbial levels in air, was adapted with a paper filter to measure drug levels in air. In each of nine trials, five ampuls of fluorouracil were opened in

M. L. Kleinberg; M. J. Quinn

1981-01-01

128

Wall functions for numerical modeling of laminar MHD flows  

Microsoft Academic Search

A general wall function treatment is presented for the numerical modeling of laminar magnetohydrodynamic (MHD) flows. The wall function expressions are derived analytically from the steady-state momentum and electric potential equations, making use only of local variables of the numerical solution. No assumptions are made regarding the orientation of the magnetic field relative to the wall, nor of the magnitude

Ola Widlund

2003-01-01

129

Numerical simulation of laminar hypersonic flows about an ellipsoid  

Microsoft Academic Search

The laminar hypersonic flow about a double ellipsoid, which idealizes the nose and cockpit of a spacecraft, were numerically simulated. The calculation method solves the three dimensional thin layer Navier-Stokes equations in a conservative formulation on a surface oriented calculation grid using an implicit\\/explicit finite difference technique. The conservative formulation allows the correct calculation of embedded compression shocks, while the

S. Riedelbauch; B. Mueller

1988-01-01

130

Laminar Flow Tube Reactor interface with quadrupole mass spectrometer  

Microsoft Academic Search

Nucleation of supersaturated water vapor was studied using the Laminar Flow Tube Reactor (LFTR) technique. In order to check the presence of contaminants in the freshly nucleated water particles, the LFTR has been connected to a mass spectrometer. Trace amounts contaminants arising from the substances used as a circulating liquid to maintain temperatures of the LFTR have been detected. The

Vladimir B. Mikheev; Nels S. Laulainen; Viktor V. Pervukhin; Stephan E. Barlow

2000-01-01

131

Advanced Nucleation Study Using The Laminar Flow Tube Reactor (LFTR)  

Microsoft Academic Search

Quantitative measurements of homogeneous nucleation rates have been made using the laminar flow tube reactor experimental technique. Thorough computer calculations of the temperature, vapor concentration, supersaturation, and nucleation rate distributions in the reactor tube were made. The nucleation volume as well as the time of nucleation have been determined with high accuracy. The concentration of the particles formed in the

Vladimir Mikheev; Nels Laulainen

1998-01-01

132

Experimental nucleation studies with a laminar flow tube reactor  

Microsoft Academic Search

A Laminar Flow Tube Reactor (LFTR) has been used as a quantitative tool for nucleation measurements. It has been specially designed and constructed in order to minimize the potential experimental inaccuracies. Careful attention has been paid to the temperature conditions inside the LFTR. Other sources of experimental uncertainties, such as initial vapor concentration conditions, calculations of the parameters of the

Vladimir B. Mikheev; Nels S. Laulainen; Stephan E. Barlow

2000-01-01

133

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

134

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

135

Turbulent-laminar patterns in plane Couette flow  

NASA Astrophysics Data System (ADS)

We study turbulent-laminar patterns in large-aspect-ratio plane Couette flow. These states consist of regular alternations of turbulent and laminar flow over large length scales. We simulate these patterns by extending the minimal-flow-unit methodology to computational domains with one long dimension that can be tilted at any prescribed angle to the streamwise direction. At a tilt of 24 degrees, we reproduce experimentally observed oblique patterns. As Re is decreased from 420, uniform turbulence is succeeded by intermittency at Re=410 and then by three well-defined bands at Re=390 which persist to Re=320 and are replaced by two bands at Re=310. Surprisingly, during this entire evolution, the temporally averaged total kinetic energy remains constant. Thus, the turbulence in the bands (which occupy only a portion of the domain) is more intense than the uniform turbulence, in such a way as to compensate for the laminar regions. In a geometry with a long streamwise and a short spanwise direction, turbulent patches repeatedly disappear abruptly and then re-nucleate gradually, for Reynolds numbers as low as 220. When the spanwise direction is long and the streamwise direction short, transition occurs abruptly from uniform turbulence to laminar Couette flow at Re=400.

Tuckerman, Laurette; Barkley, Dwight

2005-11-01

136

Laminar backward-facing step flow using the finite element method  

SciTech Connect

Laminar, incompressible flow over a backward-facing step is calculated using a finite element spatial discretization with a piecewise continuous pressure approximation and an explicit time marching algorithm. The time-accurate evolution to steady state is demonstrated for both two-dimensional (2D) and three-dimensional (3D) simulations. This approach is shown to accurately predict the lengths of the recirculation zone on the top wall and at the step for various meshes and domain lengths, for a Reynolds number of 800 based on the average inlet velocity and twice the inlet channel height. The instantaneous and steady-state results are investigated. The steady-state solutions are evaluated by comparison to published numerical and experimental results.

Kornblum, B.; McCallen, R. [Lawrence Livermore National Lab., CA (United States); Christon, M.A. [Sandia National Labs., Albuquerque, NM (United States); Kollmann, W. [Univ. of California, Davis, CA (United States) Dept. of Mechanical and Aeronautical Engineering] [and others

1995-11-01

137

Computational fluid dynamics methods for low Reynolds number precessing/spinning incompressible flows  

NASA Astrophysics Data System (ADS)

Three dimensional, steady-state, laminar, fully viscous Navier-Stokes simulations were used to predict the behavior of incompressible liquids that were undergoing steady spin and steady precession at a fixed precession angle. These numerical simulations can predict steady viscous and pressure moments. These moments tend to increase the precession angle and reduce the spin rate of the container system. For a completely filled cylinder, liquid-induced roll and side (yaw) moments were computed as functions of cylinder height to diameter.

Nusca, Michael J.

1988-04-01

138

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

2013-06-18

139

Laminar source flow and heat transfer between naturally permeable disks  

NASA Astrophysics Data System (ADS)

Laminar source flow between two infinite parallel naturally permeable, fluid-saturated disks of very small permeability is considered with heat transfer. The solution is obtained by perturbing the source free flow solution and is valid for small values of reduced Reynolds number. Expression for velocity, shear stress, and temperature field are developed and the effects of the permeability on the velocity and the temperature field have been studied and discussed.

Jain, Shalini

2013-09-01

140

Computational Study of Turbulent Laminar Patterns in Couette Flow  

Microsoft Academic Search

Turbulent-laminar patterns near transition are simulated in plane Couette flow using an extension of the minimal-flow-unit methodology. Computational domains are of minimal size in two directions but large in the third. The long direction can be tilted at any prescribed angle to the streamwise direction. Three types of patterned states are found and studied: periodic, localized, and intermittent. These correspond

Dwight Barkley; Laurette S. Tuckerman

2005-01-01

141

Computational Study of Turbulent Laminar Patterns in Couette Flow  

NASA Astrophysics Data System (ADS)

Turbulent-laminar patterns near transition are simulated in plane Couette flow using an extension of the minimal-flow-unit methodology. Computational domains are of minimal size in two directions but large in the third. The long direction can be tilted at any prescribed angle to the streamwise direction. Three types of patterned states are found and studied: periodic, localized, and intermittent. These correspond closely to observations in large-aspect-ratio experiments.

Barkley, Dwight; Tuckerman, Laurette S.

2005-01-01

142

Computational study of turbulent laminar patterns in couette flow.  

PubMed

Turbulent-laminar patterns near transition are simulated in plane Couette flow using an extension of the minimal-flow-unit methodology. Computational domains are of minimal size in two directions but large in the third. The long direction can be tilted at any prescribed angle to the streamwise direction. Three types of patterned states are found and studied: periodic, localized, and intermittent. These correspond closely to observations in large-aspect-ratio experiments. PMID:15698087

Barkley, Dwight; Tuckerman, Laurette S

2005-01-07

143

Particle based flow solvers for incompressible flows in two dimensions: impulsively started flow past a circular cylinder  

Microsoft Academic Search

Vortex methods are effective in providing high-resolution flow solutions for incompressible, viscous fluid flow problems. These methods are grid free and self adaptive by construction. They are typically used for very high-resolution bluff body flow computations. In spite of their simplicity and grid free nature they are not trivial to implement. In this work a sample implementation of a vortex

Prabhu Ramachandran; M. Ramakrishna; S. C. Rajan

144

Laminar-turbulent cycles in inclined lock-exchange flows  

NASA Astrophysics Data System (ADS)

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.

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

2012-06-01

145

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

2012-06-11

146

Heat transfer in all pipe flow regimes: laminar, transitional\\/intermittent, and turbulent  

Microsoft Academic Search

A predictive theory is presented which is capable of providing quantitative results for the heat transfer coefficients in round pipes for the three possible flow regimes: laminar, transitional, and turbulent. The theory is based on a model of laminar-to-turbulent transition which is also viable for purely laminar and purely turbulent flow. Fully developed heat transfer coefficients were predicted for the

J. P. Abraham; E. M. Sparrow; J. C. K. Tong

2009-01-01

147

Newton-Krylov-Schwarz methods for aerodynamics problems: compressible and incompressible flows on unstructured grids.  

National Technical Information Service (NTIS)

We review and extend to the compressible regime an earlier parallelization of an implicit incompressible unstructured Euler code (9), and solve for flow over an M6 wing in subsonic, transonic, and supersonic regimes. While the parallelization philosophy o...

D. K. Kaushik D. E. Keyes B. F. Smith

1999-01-01

148

NACHOS II: A Finite Element Computer Program for Incompressible Flow Problems: Part 1, Theoretical Background.  

National Technical Information Service (NTIS)

The theoretical and numerical background for the finite element computer program, NACHOS II, is presented in detail. The NACHOS II code is designed for the two-dimensional analysis of viscous incompressible fluid flows, including the effects of heat trans...

D. K. Gartling

1987-01-01

149

NACHOS: A Finite Element Computer Program for Incompressible Flow Problems. Part I. Theoretical Background.  

National Technical Information Service (NTIS)

The theoretical background for the finite element computer program, NACHOS, is presented in detail. The NACHOS code is designed for the two-dimensional analysis of viscous incompressible fluid flows, including the effects of heat transfer. A general descr...

D. K. Gartling

1978-01-01

150

Numerische Simulation Laminarer Hyperschall-Stroemungen Um Ellipsoide (Numerical Simulation of Laminar Hypersonic Flows About an Ellipsoid).  

National Technical Information Service (NTIS)

The laminar hypersonic flow about a double ellipsoid, which idealizes the nose and cockpit of a spacecraft, were numerically simulated. The calculation method solves the three dimensional thin layer Navier-Stokes equations in a conservative formulation on...

S. Riedelbauch B. Mueller

1988-01-01

151

Accurate and robust methods for variable density incompressible flows with discontinuities  

SciTech Connect

We are interested in the solution of incompressible flows which are characterized by large density variations, interfacial physics, arbitrary material topologies and strong vortical content. The issues present in constant density incompressible flow are exacerbated by the presence of density discontinuities. A much greater premium requirement is placed the positivity of computed quantities The mechanism of baroclinc vorticity generation exists ({gradient}p x {gradient}p) to further complicate the physics.

Rider, W.J.; Kothe, D.B.; Puckett, E.G.

1996-09-01

152

Turbulent-laminar patterns in Couette flow: parameter dependence  

NASA Astrophysics Data System (ADS)

It now appears that large-scale turbulent-laminar patterns are inevitable intermediate states on the route from turbulent to laminar flow in large-aspect-ratio plane Couette flow. Computations in tilted periodic domains with one long lateral direction can access regimes which are not attainable experimentally. By fixing the pattern angle and wavelength, we determine the boundaries in parameter space within which each pattern can exist. The angle between the pattern and the streamwise direction can vary between 12^rc and 72^rc, a much larger range than has thus far been observed experimentally. The other parameter ranges 300? Re ? 400, 18 ? ? ? 33 (in gap widths) are close to those observed experimentally. When the computational domain is not tilted, i.e. ?=0^rc or 90^rc, we find only uniform turbulence or simple Couette flow. We show that turbulent-laminar transition in a domain with one long direction can occur quite differently from that in a traditional minimal flow unit.

Tuckerman, Laurette; Barkley, Dwight

2004-11-01

153

Laminar Flow Tube Reactor interface with quadrupole mass spectrometer  

NASA Astrophysics Data System (ADS)

Nucleation of supersaturated water vapor was studied using the Laminar Flow Tube Reactor (LFTR) technique. In order to check the presence of contaminants in the freshly nucleated water particles, the LFTR has been connected to a mass spectrometer. Trace amounts contaminants arising from the substances used as a circulating liquid to maintain temperatures of the LFTR have been detected. The results of the mass spectroscopic analysis are in full agreement with the observed values of nucleation rate. .

Mikheev, Vladimir B.; Laulainen, Nels S.; Pervukhin, Viktor V.; Barlow, Stephan E.

2000-08-01

154

Mixing and reaction fronts in laminar flows.  

PubMed

Autocatalytic reaction fronts between unreacted and reacted mixtures in the absence of fluid flow propagate as solitary waves. In the presence of imposed flow, the interplay between diffusion and advection enhances the mixing, leading to Taylor hydrodynamic dispersion. We present asymptotic theories in the two limits of small and large Thiele modulus (slow and fast reaction kinetics, respectively) that incorporate flow, diffusion, and reaction. For the first case, we show that the problem can be handled to leading order by the introduction of the Taylor dispersion replacing the molecular diffusion coefficient by its Taylor counterpart. In the second case, the leading-order behavior satisfies the eikonal equation. Numerical simulations using a lattice gas model show good agreement with the theory. The Taylor model is relevant to microfluidics applications, whereas the eikonal model applies at larger length scales. PMID:15267641

Leconte, M; Martin, J; Rakotomalala, N; Salin, D; Yortsos, Y C

2004-04-22

155

Laminar and turbulent flow over optimal riblets  

NASA Astrophysics Data System (ADS)

In the search for viscous drag reduction, many different techniques have been developed and investigated. One of the more interesting techniques is the drag reduction method involving the use of `riblets'. Riblets are micro-grooves on the bounding surface that are aligned with the mean flow direction; this method is particularly attractive due to its completely passive nature. Riblets have been thoroughly investigated in recent years. A considerable amount of experimental data has been collected regarding the flow over various shapes, sizes, and spacings of riblets in the turbulent regime. It has been found that drag reduction on the order of 8% can be achieved for flow over a flat plate mounted with riblets, if the proper spacings and heights are used. The purpose of the present work is twofold: First, to investigate optimal shapes of riblets, and second to compare our detailed numerical results for triangular riblets with recenly obtained experimental results.

Crawford, C. H.; Chu, D. C.; Karniadakis, G. E.

1992-12-01

156

Laminarization mechanisms in rotating channel flow  

Microsoft Academic Search

The influence of moderate rotation rate on turbulent channel flow is that the turbulence is suppressed on the stable side and augmented on the unstable side because of the Coriolis force. When the rotation increases the turbulent region becomes restricted to an increasingly thin zone near the unstable wall. For a rotation rate, Ro>3 (normalized by bulk velocity and channel

Stefan Wallin; Olof Grundestam; Arne V. Johansson

2008-01-01

157

Laminar and turbulent flow over optimal riblets  

Microsoft Academic Search

In the search for viscous drag reduction, many different techniques have been developed and investigated. One of the more interesting techniques is the drag reduction method involving the use of `riblets'. Riblets are micro-grooves on the bounding surface that are aligned with the mean flow direction; this method is particularly attractive due to its completely passive nature. Riblets have been

C. H. Crawford; D. C. Chu; G. E. Karniadakis

1992-01-01

158

Start-up of laminar pipe flow  

NASA Astrophysics Data System (ADS)

The transient flow in a pipe following the sudden opening of a valve is considered. The axisymmetric Navier-Stokes equations in primitive variables are solved numerically using finite-difference techniques. Predicted variations with time of the axial velocity component and the pressure field are presented for different values of the start-up flow parameter M. The computed velocity profiles for M = 38.25 compare favorably with the measurements of van de Sande et al. (1980). In the long pipe limit M = 0 the numerical solution differs by less than 1 percent from the exact analytic solution due to Szymanksi. For the shorter pipes, it is observed that the start-up time period and the resulting steady-state flow rate are significantly reduced due to the entrance region effects. For M = 0.5, for instance, the start-up time and the ultimate flow rate are reduced by about 55 and 40 percent, respectively, as compared with Szymanski's (1932) infinitely long pipe solution. The time variation of the apparent friction factor is provided for some different cases.

Andersson, H. I.; Kristoffersen, R.

159

Laminar flow of two miscible fluids in a simple network  

NASA Astrophysics Data System (ADS)

When a fluid comprised of multiple phases or constituents flows through a network, nonlinear phenomena such as multiple stable equilibrium states and spontaneous oscillations can occur. Such behavior has been observed or predicted in a number of networks including the flow of blood through the microcirculation, the flow of picoliter droplets through microfluidic devices, the flow of magma through lava tubes, and two-phase flow in refrigeration systems. While the existence of nonlinear phenomena in a network with many inter-connections containing fluids with complex rheology may seem unsurprising, this paper demonstrates that even simple networks containing Newtonian fluids in laminar flow can demonstrate multiple equilibria. The paper describes a theoretical and experimental investigation of the laminar flow of two miscible Newtonian fluids of different density and viscosity through a simple network. The fluids stratify due to gravity and remain as nearly distinct phases with some mixing occurring only by diffusion. This fluid system has the advantage that it is easily controlled and modeled, yet contains the key ingredients for network nonlinearities. Experiments and 3D simulations are first used to explore how phases distribute at a single T-junction. Once the phase separation at a single junction is known, a network model is developed which predicts multiple equilibria in the simplest of networks. The existence of multiple stable equilibria is confirmed experimentally and a criterion for existence is developed. The network results are generic and could be applied to or found in different physical systems.

Karst, Casey M.; Storey, Brian D.; Geddes, John B.

2013-03-01

160

Laminar flow of fine sediment-water mixtures  

NASA Astrophysics Data System (ADS)

Flows of sediment-water mixture (suspensions) are common superficial processes in nature. To investigate the possibility of predicting the behaviour of such flows, we study the free surface flow of a clay-water suspension down a slope, which may represent a simple realistic model for the flow of some concentrated sediment-water mixture in a natural environment. The hydrodynamic lubrication equations governing the flow are derived from the full Navier-Stokes equations, including an appropriate tensorial expression for the constitutive equation of the suspension (a Herschel-Bulkley fluid with a hysteresis in the yield strength). Results have been obtained for the free surface and length of an unsteady, laminar, isothermal flow of the suspension. The theory is in good agreement with laboratory experiments with fine clay suspensions.

Battaglia, M.; Borgia, A.

2000-03-01

161

The shearing effect of vapor flow on laminar liquid flow in capillaries of heat pipes  

Microsoft Academic Search

For heat pipes having open capillaries in the transport section, vapor flow in the tube influences laminar liquid flow in the capillaries in the opposite direction by the shearing action of the vapor at the liquid's surface. The two-dimensional Navier-Stokes equation for liquid flow in rectangular flow in capillaries was solved by a Fourier transformation. The friction factor for liquid

W. Hufschmidt; E. Burck; G. Dicola; H. Hoffman

1975-01-01

162

Development of Micro Rotary Reactor Causing Spiral Laminar Flow Interfaces  

NASA Astrophysics Data System (ADS)

Recently, research and development of the micro-fluidic systems such as ?TAS and Lab-on-chip have been activated in the field of chemical technology and biotechnology. Micro-fluidic systems are realized by micromachine technology and MEMS technology. These are essential elements for miniaturization of chemical analysis reaction systems. Furthermore, micro-fluidic systems can be applied to home medical care system. Micro mixing device is an essential element for a realization of these systems. Normally, mixing of different fluids depends on turbulent flow and diffusion. But it is difficult to generate turbulent flow in minute space. Micro mixer is important to improve reaction efficiency. The aim of this research is a development of a micro rotary reactor which will be built into micro-fluidic systems. The full length and the diameter of this reactor are 59mm and 15mm, respectively. This reactor is driven by an electromagnetic actuator. Therefore, the structure of this reactor becomes very simple and it is easy to miniaturize this reactor. This reactor aims at combing two liquids and forming spiral laminar flow interfaces. Forming spiral laminar flow interfaces increase reaction surface area and reaction distance of two liquids. This paper shows the structure and the characteristics of this reactor.

Furusawa, Hiroaki; Suzumori, Koichi; Kanda, Takefumi; Yamada, Yoshiaki; Sakata, Yusaku; Muto, Akinori

163

Implicit Lower-Upper\\/Approximate-Factorization Schemes for Incompressible Flows  

Microsoft Academic Search

A lower-upper\\/approximate-factorization (LU\\/AF) scheme is developed for the incompressible Euler or Navier–Stokes equations. The LU\\/AF scheme contains an iteration parameter that can be adjusted to improve iterative convergence rate. The LU\\/AF scheme is to be used in conjunction with linearized implicit approximations and artificial compressibility to compute steady solutions, and within sub-iterations to compute unsteady solutions. Formulations based on time

W. Roger Briley; Shyam S. Neerarambam; David L. Whitfield

1996-01-01

164

Experimental nucleation studies with a laminar flow tube reactor  

NASA Astrophysics Data System (ADS)

A Laminar Flow Tube Reactor (LFTR) has been used as a quantitative tool for nucleation measurements. It has been specially designed and constructed in order to minimize the potential experimental inaccuracies. Careful attention has been paid to the temperature conditions inside the LFTR. Other sources of experimental uncertainties, such as initial vapor concentration conditions, calculations of the parameters of the nucleation zone, and particle concentration measurements have been thoroughly analyzed as well. The nucleation rate dependence as a function of supersaturation and temperature has been measured for the dibutyl phthalate, ethylene glycol, and glycerol. The experimental results have been compared with the other experimental data and with the theoretical predictions. .

Mikheev, Vladimir B.; Laulainen, Nels S.; Barlow, Stephan E.

2000-08-01

165

Advanced Nucleation Study Using The Laminar Flow Tube Reactor (LFTR)  

NASA Astrophysics Data System (ADS)

Quantitative measurements of homogeneous nucleation rates have been made using the laminar flow tube reactor experimental technique. Thorough computer calculations of the temperature, vapor concentration, supersaturation, and nucleation rate distributions in the reactor tube were made. The nucleation volume as well as the time of nucleation have been determined with high accuracy. The concentration of the particles formed in the LFTR was measured at the outlet of the reactor tube using the ultrafine CPC TSI-3025A. Comparison of experimental data with theoretical predictions based on SCC-model has been made.

Mikheev, Vladimir; Laulainen, Nels

1998-03-01

166

Development of Quiet-Flow Supersonic Wind Tunnels for Laminar-Turbulent Transition Research.  

National Technical Information Service (NTIS)

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 trans...

S. P. Schneider

1994-01-01

167

On the aeroelastic instability of two-dimensional panels in uniform incompressible flow  

Microsoft Academic Search

A theoretical and experimental study is presented of the aeroelastic instability of a panel with various boundary conditions on its leading and trailing edges, exposed to air flow over its upper surface or on both sides. The flow is incompressible and two-dimensional (no span-wise deformation of the panel). The case of a panel clamped at its leading edge and free

A. Kornecki; E. H. Dowell; J. O'Brien

1976-01-01

168

A front-tracking method for viscous, incompressible, multi-fluid flows  

Microsoft Academic Search

Attention is given to a method to simulate unsteady multifluid flows in which a sharp interface or a front separate incompressible fluids of different density and viscosity. The flow field is discretized by a conservative finite difference approximation on a stationary grid, and the interface is explicitly represented by a separate, unstructured grid that moves through the stationary grid. Since

Salih O. Unverdi; Gretar Tryggvason

1992-01-01

169

A combined PHREEQC-2\\/parallel fracture model for the simulation of laminar\\/non-laminar flow and contaminant transport with reactions  

Microsoft Academic Search

A combination of a parallel fracture model with the PHREEQC-2 geochemical model was developed to simulate sequential flow and chemical transport with reactions in fractured media where both laminar and turbulent flows occur. The integration of non-laminar flow resistances in one model produced relevant effects on water flow velocities, thus improving model prediction capabilities on contaminant transport. The proposed conceptual

Costantino Masciopinto; Angela Volpe; Domenico Palmiotta; Claudia Cherubini

2010-01-01

170

An investigation of Newton-Krylov algorithms for solving incompressible and low Mach number compressible fluid flow and heat transfer problems using finite volume discretization  

SciTech Connect

Fully coupled, Newton-Krylov algorithms are investigated for solving strongly coupled, nonlinear systems of partial differential equations arising in the field of computational fluid dynamics. Primitive variable forms of the steady incompressible and compressible Navier-Stokes and energy equations that describe the flow of a laminar Newtonian fluid in two-dimensions are specifically considered. Numerical solutions are obtained by first integrating over discrete finite volumes that compose the computational mesh. The resulting system of nonlinear algebraic equations are linearized using Newton`s method. Preconditioned Krylov subspace based iterative algorithms then solve these linear systems on each Newton iteration. Selected Krylov algorithms include the Arnoldi-based Generalized Minimal RESidual (GMRES) algorithm, and the Lanczos-based Conjugate Gradients Squared (CGS), Bi-CGSTAB, and Transpose-Free Quasi-Minimal Residual (TFQMR) algorithms. Both Incomplete Lower-Upper (ILU) factorization and domain-based additive and multiplicative Schwarz preconditioning strategies are studied. Numerical techniques such as mesh sequencing, adaptive damping, pseudo-transient relaxation, and parameter continuation are used to improve the solution efficiency, while algorithm implementation is simplified using a numerical Jacobian evaluation. The capabilities of standard Newton-Krylov algorithms are demonstrated via solutions to both incompressible and compressible flow problems. Incompressible flow problems include natural convection in an enclosed cavity, and mixed/forced convection past a backward facing step.

McHugh, P.R.

1995-10-01

171

Multigrid fictitious boundary method for incompressible viscous flows around moving airfoils  

NASA Astrophysics Data System (ADS)

In this paper, an efficient multigrid fictitious boundary method (MFBM) coupled with the FEM solver package FEATFLOW was used for the detailed simulation of incompressible viscous flows around one or more moving NACA0012 airfoils. The calculations were carried on a fixed multigrid finite element mesh on which fluid equations were satisfied everywhere, and the airfoils were allowed to move freely through the mesh. The MFBM was employed to treat interactions between the fluid and the airfoils. The motion of the airfoils was modeled by Newton-Euler equations. Numerical results of experiments verify that this method provides an efficient way to simulate incompressible viscous flows around moving airfoils.

Wan, De-Cheng

2007-06-01

172

Global pressure relaxation for laminar two-dimensional internal flow  

NASA Astrophysics Data System (ADS)

This study extends the reduced Navier-Stokes (RNS) global pressure relaxation procedure developed by Rubin and co-workers for external flow to internal flow applications. The streamwise pressure gradient is split into a backward-differenced or initial value component, as in boundary layer marching, and a forward-differenced or boundary value component that represents the elliptic downstream effects. The streamwise convection terms are upwind-differenced and all other streamwise derivatives are backward-differenced. A standard boundary layer marching technique imbedded in a conventional line relaxation technique is obtained. For compressible flow the pressure iteration determines the interior flow interaction as well as the inlet mass flux that is consistent with the outflow pressure boundary condition. Results have been computed for incompressible flow in both rectangular and curved channels, and for subsonic compressible flow in the simulation of an aerofoil in a wind tunnel. Converged solutions were obtained over a range of Reynolds numbers generating small to moderately large separation bubbles.

Rosenbaum, D.; Rubin, S. G.

1990-05-01

173

Hybrid modeling of convective laminar flow in a permeable tube associated with the cross-flow process  

NASA Astrophysics Data System (ADS)

The confined flows in tubes with permeable surfaces are associated to tangential filtration processes (microfiltration or ultrafiltration). The complexity of the phenomena do not allow for the development of exact analytical solutions, however, approximate solutions are of great interest for the calculation of the transmembrane outflow and estimate of the concentration polarization phenomenon. In the present work, the generalized integral transform technique (GITT) was employed in solving the laminar and permanent flow in permeable tubes of Newtonian and incompressible fluid. The mathematical formulation employed the parabolic differential equation of chemical species conservation (convective diffusive equation). The velocity profiles for the entrance region flow, which are found in the connective terms of the equation, were assessed by solutions obtained from literature. The velocity at the permeable wall was considered uniform, with the concentration at the tube wall regarded as variable with an axial position. A computational methodology using global error control was applied to determine the concentration in the wall and concentration boundary layer thickness. The results obtained for the local transmembrane flux and the concentration boundary layer thickness were compared against others in literature.

Venezuela, A. L.; Pérez-Guerrero, J. S.; Fontes, S. R.

2009-03-01

174

A short note on the discontinuous Galerkin discretization of the pressure projection operator in incompressible flow  

NASA Astrophysics Data System (ADS)

This note reports on the issue of spurious compressibility artifacts that can arise when the popular pressure projection (PP) method is used for unsteady simulations of incompressible flow using the symmetric interior penalty discontinuous Galerkin (SIP-DG) method. Through a spectral analysis of the projection operator's SIP-DG discretization, we demonstrate that the eigenfunctions of the operator do not form a basis that allows for the correct enforcement of the incompressibility constraint. This short-coming can cause numerical instabilities for inviscid, advection-dominated, and density stratified flow simulations, especially for long-time integrations and/or under-resolved situations. To remedy this problem, we propose a local post-processing projection that enforces incompressibility exactly to allow for stable and robust long-time integrations.

Steinmoeller, D. T.; Stastna, M.; Lamb, K. G.

2013-10-01

175

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

176

An experimental study of laminar flow control airfoil with suction through perforated surface at low speed  

Microsoft Academic Search

An experimental study of a laminar flow control airfoil with suction through a perforated surface at low speed was made. The airfoil section was designed to be a natural laminar flow airfoil which can delay the boundary layer transition as far downstream as possible. The effects of suction quantity and position of sucked area on transition delay were examined. It

Yoji Ishida; Masayoshi Noguchi

1988-01-01

177

Optimal product distribution from laminar flow reactors: Newtonian and other power-law fluids  

Microsoft Academic Search

In tubular reactors viscous fluids are in laminar flow. For reactions in series this gives a product distribution different from either plug flow or mixed flow. More importantly, laminar flow depresses the maximum amount of intermediate that can be obtained when compared to plug flow. Here we treat the simple case of an elementary two-step mechanism:(1)[A?R?S]Three special cases of the

Keith L. Levien; Octave Levenspiel

1999-01-01

178

Stability Analysis of Large-Scale Incompressible Flow Calculations on Massively Parallel Computers  

SciTech Connect

A set of linear and nonlinear stability analysis tools have been developed to analyze steady state incompressible flows in 3D geometries. The algorithms have been implemented to be scalable to hundreds of parallel processors. The linear stability of steady state flows are determined by calculating the rightmost eigenvalues of the associated generalize eigenvalue problem. Nonlinear stability is studied by bifurcation analysis techniques. The boundaries between desirable and undesirable operating conditions are determined for buoyant flow in the rotating disk CVD reactor.

LEHOUCQ,RICHARD B.; ROMERO,LOUIS; SALINGER,ANDREW G.

1999-10-25

179

On modified block SSOR iteration methods for linear systems from steady incompressible viscous flow problems  

Microsoft Academic Search

In order to solve the large sparse systems of linear equations arising from numerical solutions of two-dimensional steady incompressible viscous flow problems in primitive variable formulation, we present block SSOR and modified block SSOR iteration methods based on the special structures of the coefficient matrices. In each step of the block SSOR iteration, we employ the block LU factorization to

Yu-Hong Ran; Li Yuan

2010-01-01

180

a Level Set Approach for Computing Solutions to Incompressible Two-Phase Flow  

Microsoft Academic Search

A level set approach for computing solutions to incompressible two-phase flow is presented. The interface between the two fluids is considered to be sharp and is described as the zero level set of a smooth function. A new treatment of the level set method allows us to efficiently maintain the level set function as the signed distance from the interface.

Mark Sussman; Peter Smereka; Stanley Osher

1994-01-01

181

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

NASA Astrophysics Data System (ADS)

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

182

Improved Incompressible Smoothed Particle Hydrodynamics method for simulating flow around bluff bodies  

Microsoft Academic Search

In this article, we present numerical solutions for flow over an airfoil and a square obstacle using Incompressible Smoothed Particle Hydrodynamics (ISPH) method with an improved solid boundary treatment approach, referred to as the Multiple Boundary Tangents (MBT) method. It was shown that the MBT boundary treatment technique is very effective for tackling boundaries of complex shapes. Also, we have

Mostafa Safdari Shadloo; Amir Zainali; Samir H. Sadek; Mehmet Yildiz

2011-01-01

183

A Parallel Second-Order Adaptive Mesh Algorithm for Incompressible Flow in Porous Media  

Microsoft Academic Search

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

George Shu Heng Pau; Ann S. Almgren; John B. Bell; Michael J. Lijewski

2008-01-01

184

Flutter analysis of an airfoil with bounded random parameters in incompressible flow via Gegenbauer polynomial approximation  

Microsoft Academic Search

The effects of parameter uncertainty on the flutter characteristics of a two-dimensional airfoil in an incompressible flow were investigated through Gegenbauer polynomial approximation. The uncertain parameters, such as the linear and cubic pitch stiffness coefficients are modeled as bounded random variables with ?-PDFs (probability density functions). With the aid of Gegenbauer polynomial approximation, the two-dimensional stochastic airfoil system is transformed

Cunli Wu; Huimei Zhang; Tong Fang

2007-01-01

185

An adaptive level set approach for incompressible two-phase flows  

Microsoft Academic Search

In Sussman, Smereka and Osher, a numerical method using the level set approach was formulated for solving incompressible two-phase flow with surface tension. In the level set approach, the interface is represented as the zero level set of a smooth function; this has the effect of replacing the advection of density, which has steep gradients at the interface, with the

M. Sussman; A. S. Almgren; J. B. Bell

1997-01-01

186

An Adaptive Level Set Approach For Incompressible Two-Phase Flows  

Microsoft Academic Search

In Sussman, Smereka and Osher (1994), a numerical method using the level set approachwas formulated for solving incompressible two-phase flow with surface tension. In the levelset approach, the interface is represented as the zero level set of a smooth function; this hasthe effect of replacing the advection of density, which has steep gradients at the interface,with the advection of the

Mark Sussman

1998-01-01

187

Treatment of incompressibility and boundary conditions in 3-D numerical spectral simulations of plane channel flows  

Microsoft Academic Search

A spectral method for numerical computation of 3-D time-dependent incompressible flows between two plane parallel plates is presented. Fourier expansions in the coordinates parallel to the walls and expansions in Chebyshev polynomials in the normal coordinate are used. The time coordinate is discretized with second order finite differences, treating the viscous terms implicitly. An efficient direct solution procedure for the

L. Kleiser; U. Schumann

1980-01-01

188

Finite-Volume Solution Technique for the Navier-Stokes Equations Governing Incompressible Flow.  

National Technical Information Service (NTIS)

A centered finite-volume scheme using explicit Runge-Kutta time integration is formulated for the Navier-Stokes equations governing viscous incompressible flow in two space dimensions. A centered and compact difference scheme is used to obtain the velocit...

J. T. Billdal H. I. Andersson

1989-01-01

189

Structure of velocity and temperature fields in laminar channel flows with longitudinal vortex generators  

NASA Astrophysics Data System (ADS)

Laminar velocity and temperature fields in a rectangular channel with a row of built-in vortex generators in the form of slender delta wings and winglet pairs have been calculated by means of a zonal method consisting of zones of complete and partially parabolized Navier-Stokes and energy equations. A modified version of SOLA for incompressible as well as for variable-density, small-Mach number flows has been used to solve the basic equations. Each wing or winglet pair generates counterrotating longitudinal vortices that, in contrast to similar vortices in an unbounded medium, show an elliptic deformation, a wakelike axial velocity distribution in the core, and an absence of breakdown even at angles of attack as large as 50 deg. The spiraling motion induced by these vortices in the channel can locally enhance the heat transfer coefficient by a factor of 3 compared to its value in a wingless channel. The temperature dependence of density can reduce this enhancement by roughly 10 percent when the ratio of gas-to-wall temperature is 1.3.

Fiegib, M.; Brockmeier, U.; Mitra, N. K.; Guentermann, T.

190

Flowfield-Dependent Variation (FDV) method for compressible, incompressible, viscous, and inviscid flow interactions with FDV adaptive mesh refinements and parallel processing  

NASA Astrophysics Data System (ADS)

A new approach to solution-adaptive grid refinement using the finite element method and Flowfield-Dependent Variation (FDV) theory applied to the Navier-Stokes system of equations is discussed. Flowfield-Dependent Variation (FDV) parameters are introduced into a modified Taylor series expansion of the conservation variables, with the Navier-Stokes system of equations substituted into the Taylor series. The FDV parameters are calculated from the current Fowfield conditions, and automatically adjust the resulting equations from elliptic to parabolic to hyperbolic in type to assure solution accuracy in evolving fluid flowfields that may consist of interactions between regions of compressible and incompressible flow, viscous and inviscid flow, and turbulent and laminar flow. The system of equations is solved using an element-by-element iterative GMRES solver with the elements grouped together to allow the element operations to be performed in parallel. The FDV parameters play many roles in the numerical scheme. One of these roles is to control formations of shock wave discontinuities in high speeds and pressure oscillations in low speeds. To demonstrate these abilities, various example problems are shown, including supersonic flows over a flat plate and a compression corner, and flows involving triple shock waves generated on fin geometries for high speed compressible flows. Furthermore, analysis of low speed incompressible flows is presented in the form of flow in a lid-driven cavity at various Reynolds numbers. Another role of the FDV parameters is their use as error indicators for a solution-adaptive mesh. The finite element grid is refined as dictated by the magnitude of the FDV parameters. Examples of adaptive grids generated using the FDV parameters as error indicators are presented for supersonic flow over flat plate/compression ramp combinations in both two and three dimensions. Grids refined using the FDV parameters as error indicators are comparable to ones refined using primitive variable error indicators, and require less computational time to generate the grids. The use of parallel processing in performing some element operations is shown to reduce the wall clock time approximately forty-five percent in going from one to eight processors. Finally, the algorithm's ability to solve a flowfield containing interactions and transitions between regions of incompressible and compressible, viscous and inviscid, and laminar and turbulent flow is demonstrated by modeling the flowfield generated by supersonic flow over a compression ramp located between two fins. The structure of the resulting systems of shock waves are analyzed and compared with planar laser scattering images obtained experimentally for similar flow structures.

Heard, Gary Wayne

191

Incompressible flow past a circular cylinder: dependence of the computed flow field on the location of the lateral boundaries  

Microsoft Academic Search

The influence of the location of the lateral boundaries on 2D computation of unsteady incompressible flow past a circular cylinder is investigated. The case of Reynolds number 100 is used as a benchmark, and several quantities characterizing the unsteady flow are obtained for a range of lateral boundary locations. The computations are performed with two distinct finite element formulations —

M. Behr; D. Hastreiter; S. Mittal; T. E. Tezduyar

1995-01-01

192

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

193

On the effect of riblets in fully developed laminar channel flows  

NASA Astrophysics Data System (ADS)

The effect of longitudinal riblet surfaces on viscous drag in fully developed laminar channel flows was investigated. Unlike turbulent flows, drag reduction was not obtained in the laminar flows. Results were independent of Reynolds number. Wall-shear rates on most regions of the cross-sectional perimeter of riblets were smaller than that of corresponding plane channel flow even though the net drag was increased.

Choi, Haecheon; Moin, Parviz; Kim, John

1991-08-01

194

Eddy genesis and manipulation in plane laminar shear flow  

NASA Astrophysics Data System (ADS)

Eddy formation and presence in a plane laminar shear flow configuration consisting of two infinitely long plates orientated parallel to each other is investigated theoretically. The upper plate, which is planar, drives the flow; the lower one has a sinusoidal profile and is fixed. The governing equations are solved via a full finite element formulation for the general case and semianalytically at the Stokes flow limit. The effects of varying geometry (involving changes in the mean plate separation or the amplitude and wavelength of the lower plate) and inertia are explored separately. For Stokes flow and varying geometry, excellent agreement between the two methods of solution is found. Of particular interest with regard to the flow structure is the importance of the clearance that exists between the upper plate and the tops of the corrugations forming the lower one. When the clearance is large, an eddy is only present at sufficiently large amplitudes or small wavelengths. However, as the plate clearance is reduced, a critical value is found, which triggers the formation of an eddy in an otherwise fully attached flow for any finite amplitude and arbitrarily large wavelength. This is a precursor to the primary eddy to be expected in the lid-driven cavity flow, which is formed in the limit of zero clearance between the plates. The influence of the flow driving mechanism is assessed by comparison with corresponding solutions for the case of gravity-driven fluid films flowing over an undulating substrate. When inertia is present, the flow generally becomes asymmetrical. However, it is found that for large mean plate separations the flow local to the lower plate becomes effectively decoupled from the inertia dominated overlying flow if the wavelength of the lower plate is sufficiently small. In such cases the local flow retains its symmetry. A local Reynolds number based on the wavelength is shown to be useful in characterizing these large-gap flows. As the mean plate separation is reduced, the form of the asymmetry caused by inertia changes and becomes strongly dependent on the plate separation. For lower plate wavelengths which do not exhibit a kinematically induced secondary eddy, an inertially induced secondary eddy can be created if the mean plate separation is sufficiently small and the global Reynolds number is sufficiently large.

Scholle, M.; Haas, A.; Aksel, N.; Wilson, M. C. T.; Thompson, H. M.; Gaskell, P. H.

2009-07-01

195

On a modification of GLS stabilized FEM for solving incompressible viscous flows  

NASA Astrophysics Data System (ADS)

We deal with 2D flows of incompressible viscous fluids with high Reynolds numbers. Galerkin Least Squares technique of stabilization of the finite element method is studied and its modification is described. We present a number of numerical results obtained by the developed method, showing its contribution to solving flows with high Reynolds numbers. Several recommendations and remarks are included. We are interested in positive as well as negative aspects of stabilization, which cannot be divorced.

Burda, P.; Novotný, J.; Ístek, J.

2006-07-01

196

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

Microsoft Academic Search

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

P. Moin; J. Kim

1980-01-01

197

An Incompressible Three-Dimensional Multiphase Particle-in-Cell Model for Dense Particle Flows  

Microsoft Academic Search

A three-dimensional, incompressible, multiphase particle-in-cell method is presented for dense particle flows. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Difficulties associated with calculating interparticle interactions for dense particle flows with volume fractions above 5% have been eliminated by mapping particle properties to

D. M. Snider

2001-01-01

198

Computation of Two-Dimensional Incompressible Turbulent Boundary Layer Flows with Equilibrium and Nonequilibrium Turbulence Models  

NASA Astrophysics Data System (ADS)

Two-dimensional incompressible turbulent boundary layer flows over a flat plate were predicted using turbulent boundary layer equations. Reynolds stresses were calculated using Cebeci-Smith, Baldwin-Lomax, and Johnson-King eddy viscosity models. Computational results of mean-flow properties based on Cebeci-Smith model and Baldwin-Lomax model are in excellent agreement with experimental data, and, those based on Johnson-King model are not as accurate as the other two models.

Wong, Daniel; Ahmed, Salahuddin

199

Evaluation of integral forces and pressure fields from planar velocimetry data for incompressible and compressible flows  

Microsoft Academic Search

The approach to determine pressure fields and integral loads from planar velocimetry data is discussed, in relation to the\\u000a implementation for incompressible and compressible flows around two-dimensional objects. The method relies upon the application\\u000a of control-volume approaches in combination with the deduction of the pressure field from the experimental data, by making\\u000a use of the flow constitutive equations. In this

B. W. van Oudheusden; F. Scarano; E. W. M. Roosenboom; E. W. F. Casimiri; L. J. Souverein

2007-01-01

200

Moving Grids and Ale-Fem for Incompressible Viscous Flows around Fixed and Moving Cylinders  

NASA Astrophysics Data System (ADS)

In this paper, multigrid fictitious boundary method(MFBM) coupled with arbitrary Lagrangian-Eulerian (ALE) and moving grid techniques is presented to direct numerical simulation of incompressible viscous flows around four fixed, forced oscillating or free moving cylinders to the incoming flow. Numerical results indicate that the present numerical method can capture complex interference and flow-cylinders interaction phenomena including the famous wake galloping effects, in which a cylinder in the wake of another experiences large flow-induced vibration over a wide range of flow velocities.

Wan, Decheng

2010-05-01

201

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

202

Application of laminar flow control to high-bypass-ratio turbofan engine nacelles  

SciTech Connect

Recently, the concept of the application of hybrid laminar flow to modern commercial transport aircraft was successfully flight tested on a Boeing 757 aircraft. In this limited demonstration, in which only part of the upper surface of the swept wing was designed for the attainment of laminar flow, significant local drag reduction was measured. This paper addresses the potential application of this technology to laminarize the external surface of large, modern turbofan engine nacelles which may comprise as much as 5-10 percent of the total wetted area of future commercial transports. A hybrid-laminar-flow-control (HLFC) 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 are presented to determine potential benefits in terms of reduced fuel consumption. 13 refs.

Wie, Y.S.; Collier, F.S. Jr.; Wagner, R.D. (High Technology Corp., Hampton, VA (United States) NASA, Langley Research Center, Hampton, VA (United States))

1991-09-01

203

An Experimental Study of Thermophoretic Deposition of Aerosol Particles in Laminar Tube Flow with Mixed Convection  

Microsoft Academic Search

The thermophoretic deposition of aerosol particles in mixed-convection, laminar tube flow with a cooled wall is considered. The presence of free convection alters the velocity and temperature profiles for laminar tube flow relative to the constant-properties case. Previous modeling results (Walsh, Weimer, and Hrenya, in press), show that the modified flow fields lead to changes in the cumulative deposition-efficiency profiles

J. K. Walsh; A. W. Weimer; C. M. Hrenya

2006-01-01

204

LAMINAR FLOW ELEMENT: ITS USE AS A FLOW STANDARD  

EPA Science Inventory

A standard device to measure flows accurately and precisely was required by the U.S. Environmental Protection Agency (EPA) to establish an air pollution field auditing system capable of generating pollutant concentrations in the parts per million and parts per billion range. he e...

205

Convective-difference scheme using a general curvilinear coordinate grid for incompressible viscous flow problems  

Microsoft Academic Search

A numerical scheme analyzing unsteady two-dimensional incompressible viscous flow using a general curvilinear coordinate grid is proposed. In this scheme, the unsteady Navier-Stokes equations are solved by a convective-difference scheme using a staggered square grid in transformed space and an interpolation formula considering TVD concept, and an elliptic equation of pressure is solved by the iteration scheme. The continuity condition

Yoshihisa Matsumoto; Hisaaki Daiguji

1992-01-01

206

An Accurate Cartesian Grid Method for Viscous Incompressible Flows with Complex Immersed Boundaries  

Microsoft Academic Search

A Cartesian grid method has been developed for simulating two-dimensional unsteady, viscous, incompressible flows with complex immersed boundaries. A finite-volume method based on a second-order accurate central-difference scheme is used in conjunction with a two-step fractional-step procedure. The key aspects that need to be considered in developing such a solver are imposition of boundary conditions on the immersed boundaries and

T. Ye; R. Mittal; H. S. Udaykumar; W. Shyy

1999-01-01

207

MARIAH: A finite-element computer program for incompressible porous flow problems. Theoretical background  

NASA Astrophysics Data System (ADS)

The theoretical background for the finite element computer program MARIAH is presented. The MARIAH code is designed for the analysis of incompressible fluid flow and heat transfer in saturated porous media. A description of the fluid/thermal boundary value problem treated by the program is presented and the finite element method and associated numerical methods used in MARIAH are discussed. Instructions for use of the program are documented in the Sandia National Laboratories report, SAND79-1623.

Gartling, D. K.; Hickox, C. E.

1982-10-01

208

A local adaptive grid procedure for incompressible flows with multigridding and equidistribution concepts  

Microsoft Academic Search

An adaptive-grid solution procedure is developed for incompressible flow problems in which grid refinement based on an equidistribution law is performed in high-error-estimate regions that are flagged from a preliminary coarse-grid solution. Solutions on the locally refined and equidistributed meshes are obtained using boundary conditions interpolated from the preliminary coarse-grid solution, and solutions on both the refined- and coarse-grid regions

F. Moukalled; S. Acharya

1991-01-01

209

ZEPHYR3D: A finite difference computer program for three-dimensional, transient incompressible flow problems  

Microsoft Academic Search

This report describes the finite difference computer code ZEPHYR3D, which is designed to solve three-dimensional, transient incompressible flow problems. ZEPHYR3D includes an energy equation that allows coupled thermal\\/fluid problems to be solved with the limits of the Boussinesq approximation. It also includes an implementation of the Smagorinsky subgrid scale turbulence model, which allows ZEPHYR3D to perform large eddy simulation of

J. A. Schutt

1991-01-01

210

A stabilized MLPG method for steady state incompressible fluid flow simulation  

Microsoft Academic Search

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 Babuška–Brezzi condition. The same stabilization parameter ?(?SUPG=?PSPG) is used in the present method. The circle domain

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

2010-01-01

211

Tracking Rigid Spherical Particles in Incompressible Flows via Dissipative Hydrodynamics  

NASA Astrophysics Data System (ADS)

Solutions for particle trajectories computed using dissipative hydrodynamics (DHD) for rigid spherical particles are discussed. DHD reproduces the many-body hydrodynamics of Stokesian Dynamics (SD), but is more computationally efficient. DHD satisfies the fluctuation-dissipation theorem of Dissipative Particle Dynamics (DPD) and therefore is not hindered by the relaxation-time limitations of Stokesian Dynamics. For a given continuum flow field, the translations and rotations of multiple particles are calculated taking into account both stochastic dissipative effects and deterministic conservative forces. Examples of particle tracking in two-dimensional and three-dimensional flows, computed via spectral element simulations, will be discussed.

Houchens, Brent; Davis, Kenneth; Shi, Yong; Kim, Albert

2010-11-01

212

Unsteady hydromagnetic laminar flow of a conducting dusty fluid between two parallel plates started impulsively from rest  

Microsoft Academic Search

Summary The unsteady laminar motion of an electrically conducting, viscous and incompressible dusty fluid between two infinitely extended non-conducting parallel plates under a uniform transverse magnetic field, fixed relative to the fluid has been considered. The lower and the upper plate are started impulsively from rest and thereafter move with different but uniform velocities. The velocity fields for the conducting

P. Mitra; P. Bhattacharyya

1981-01-01

213

Modeling Bituminous Coal Devolatilization in the Electric Grid and Laminar Entrained Flow Research Reactors.  

National Technical Information Service (NTIS)

Bituminous coal devolatilization data from an electric grid reactor and a laminar entrained flow reactor are modeled using two separate analytical derivations. The analyses are based on the assumption that the reactive volatile component of the pulverized...

K. M. Sprouse

1986-01-01

214

Advanced Natural Laminar Flow Airfoil with High Lift to Drag Ratio.  

National Technical Information Service (NTIS)

An experimental verification of a high performance natural laminar flow (NLF) airfoil for low speed and high Reynolds number applications was completed in the Langley Low Turbulence Pressure Tunnel (LTPT). Theoretical development allowed for the achieveme...

J. K. Viken W. Pfenninger R. J. McGhee

1986-01-01

215

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

216

Investigation of Radiative Interaction in Laminar Flows Using Monte Carlo Simulation.  

National Technical Information Service (NTIS)

The Monte Carlo method (MCM) is employed to study the radiative interactions in fully developed laminar flow between two parallel plates. Taking advantage of the characteristics of easy mathematical treatment of the MCM, a general numerical procedure is d...

J. Liu S. N. Tiwari

1993-01-01

217

Computational Investigation of Wake-Induced AirFoil Flutter in Incompressible Flow and Active Flutter Control.  

National Technical Information Service (NTIS)

In this thesis several incompressible oscillatory flow and flutter problems were investigated. A previously developed unsteady panel code for single airfoil bending torsion flutter analysis was compared to Theodorsen's classical theory. The panel code agr...

M. A. Turner

1994-01-01

218

Incompressibility of impurity flows in low density TJ-II plasmas and comparison with neoclassical theory  

NASA Astrophysics Data System (ADS)

Poloidal and toroidal velocities of fully ionized carbon are measured by means of charge exchange recombination spectroscopy in the TJ-II stellarator. We present a detailed treatment of the 3D geometry and show that flow measurements, performed at different locations of the same flux surface, are compatible with flow incompressibility for the low density plasmas under study (line averaged electron densities \\bar{n}_e\\le 10^{19}\\,m^{-3} ). Furthermore, comparison with neoclassical calculations shows quantitative agreement with the measured radial electric field and ion parallel mass flow in the absence of an external momentum input.

Arévalo, J.; Alonso, J. A.; McCarthy, K. J.; Velasco, J. L.

2013-02-01

219

Hybrid algorithm for modeling of fluid-structure interaction in incompressible, viscous flows  

NASA Astrophysics Data System (ADS)

The objective of this paper is to present and to validate a new hybrid coupling (HC) algorithm for modeling of fluid-structure interaction (FSI) in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled (LC) and tightly coupled (TC) algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible structures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incompressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen's analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical instability issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.

Young, Yin Lu; Chae, Eun Jung; Akcabay, Deniz Tolga

2012-08-01

220

Comparison of linear and nonlinear RNG-based {kappa}-{epsilon} models for incompressible turbulent flows  

SciTech Connect

Linear and nonlinear renormalization group (RNG) {kappa}-{epsilon} models are compared for the prediction of incompressible turbulent flows. The multidimensional finite-volume code KIVA-3 is used to explore the alternative models versus the standard {kappa}-{epsilon} model. Test cases include the classic backward-facing step and the confined co-flow jet flows. The results suggest that the linear RNG {kappa}-{epsilon} model can yield significant improvements over the standard {kappa}-{epsilon} model for recirculatory flows, because of its less dissipative nature. While the nonlinear RNG {kappa}-{epsilon} model can also improve predictions compared to the standard {kappa}-{epsilon} model, its greatly increased cost compared to the linear RNG model renders it less attractive. However, for the case of shear flows, such as for confined co-flow jets, the RNG-based {kappa}-{epsilon} models are in less favorable agreement with experiments compared to the standard {kappa}-{epsilon} model. Overall, it is concluded that combining the claimed universality of the RNG-based {kappa}-{epsilon} model constants with the anisotropies introduced by the nonlinear {kappa}-{epsilon} model cannot enhance predictions of both recirculating and shear incompressible flows.

Papageorgakis, G.C.; Assanis, D.N. [Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Mechanical Engineering and Applied Mechanics

1999-01-01

221

A Riemannian geometric mapping technique for identifying incompressible equivalents to subsonic potential flows  

NASA Astrophysics Data System (ADS)

This research develops a technique for the solution of incompressible equivalents to planar steady subsonic potential flows. Riemannian geometric formalism is used to develop a gauge transformation of the length measure followed by a curvilinear coordinate transformation to map the given subsonic flow into a canonical Laplacian flow with the same boundary conditions. The effect of the transformation is to distort both the immersed profile shape and the domain interior nonuniformly as a function of local flow properties. The method represents the full nonlinear generalization of the classical methods of Prandtl-Glauert and Karman-Tsien. Unlike the classical methods which are "corrections," this method gives exact results in the sense that the inverse mapping produces the subsonic full potential solution over the original airfoil, up to numerical accuracy. The motivation for this research was provided by an observed analogy between linear potential flow and the special theory of relativity that emerges from the invariance of the d'Alembert wave equation under Lorentz transformations. This analogy is well known in an operational sense, being leveraged widely in linear unsteady aerodynamics and acoustics, stemming largely from the work of Kussner. Whereas elements of the special theory can be invoked for compressibility effects that are linear and global in nature, the question posed in this work was whether other mathematical techniques from the realm of relativity theory could be used to similar advantage for effects that are nonlinear and local. This line of thought led to a transformation leveraging Riemannian geometric methods common to the general theory of relativity. A gauge transformation is used to geometrize compressibility through the metric tensor of the underlying space to produce an equivalent incompressible flow that lives not on a plane but on a curved surface. In this sense, forces owing to compressibility can be ascribed to the geometry of space in much the same way that general relativity ascribes gravitational forces to the curvature of space-time. Although the analogy with general relativity is fruitful, it is important not to overstate the similarities between compressibility and the physics of gravity, as the interest for this thesis is primarily in the mathematical framework and not physical phenomenology or epistemology. The thesis presents the philosophy and theory for the transformation method followed by a numerical method for practical solutions of equivalent incompressible flows over arbitrary closed profiles. The numerical method employs an iterative approach involving the solution of the equivalent incompressible flow with a panel method, the calculation of the metric tensor for the gauge transformation, and the solution of the curvilinear coordinate mapping to the canonical flow with a finite difference approach for the elliptic boundary value problem. This method is demonstrated for non-circulatory flow over a circular cylinder and both symmetric and lifting flows over a NACA 0012 profile. Results are validated with accepted subcritical full potential test cases available in the literature. For chord-preserving mapping boundary conditions, the results indicate that the equivalent incompressible profiles thicken with Mach number and develop a leading edge droop with increased angle of attack. Two promising areas of potential applicability of the method have been identified. The first is in airfoil inverse design methods leveraging incompressible flow knowledge including heuristics and empirical data for the potential field effects on viscous phenomena such as boundary layer transition and separation. The second is in aerodynamic testing using distorted similarity-scaled models.

German, Brian Joseph

222

Unsteady lift of thick airfoils in incompressible turbulent flow  

NASA Astrophysics Data System (ADS)

nuThe unsteady lift forces that act on an airfoil in turbulent flow are an undesirable source of vibration and noise in many industrial applications. Methods to predict these forces have traditionally treated the airfoil as a flat plate. At higher frequencies, where the relevant turbulent length scales are comparable to the airfoil thickness, the at plate approximation becomes invalid and results in overprediction of the unsteady force spectrum. This work provides an improved methodology for the prediction of the unsteady lift forces that accounts for the thickness of the airfoil. An analytical model was developed to calculate the response of the airfoil to high frequency gusts. The approach is based on a time-domain calculation with a sharp-edged gust and accounts for the distortion of the gust by the mean flow around the airfoil leading edge. The unsteady lift is calculated from a weighted integration of the gust vorticity, which makes the model relatively straightforward to implement and verify. For routine design calculations of turbulence-induced forces, a closed-form gust response thickness correction factor was developed for NACA 65 series airfoils. The model was then validated by measuring the unsteady lift spectrum using piezoelectric force gages in a water tunnel with grid-generated turbulence. A series of four airfoils with thickness-to-chord ratios ranging from 8 to 16 percent were tested over a wide range of speeds. In addition, the turbulence spectrum was measured using Laser Doppler Velocimetry. The experimental results confirmed that the analytical model accurately predicts the attenuation of the high frequency gust response due to the airfoil thickness.

Lysak, Peter D.

223

Geometry of surfaces with Caputo fractional derivatives and applications to incompressible two-dimensional flows  

NASA Astrophysics Data System (ADS)

Geometric structures of surfaces are formulated based on Caputo fractional derivatives. The Gauss frame of a surface with fractional order is introduced. Then, the non-locality of the fractional derivative characterizes the asymmetric second fundamental form. The mean and Gaussian curvatures of the surface are defined in the case of fractional order. Based on the fractional curvatures, incompressible two-dimensional flows are discussed. The stream functions are obtained from a fractional continuity equation. The asymmetric second fundamental form of stream-function surface is related to the path dependence of flux. Moreover, the fractional curvatures are calculated for the stream-function surfaces of uniform and corner flows. The uniform flow with fractional order is characterized by the non-vanishing mean curvature. The non-locality of corner flow is expressed by the mean and Gaussian curvatures with fractional order. In particular, the fractional order within the stream-function of corner flow determines the change of sign of Gaussian curvature. Therefore, the non-local property of incompressible flows can be investigated by the fractional curvatures.

Yajima, Takahiro; Yamasaki, Kazuhito

2012-02-01

224

Pressure Splitting Applied to the Navier-Stokes Equations for Incompressible Flow  

NASA Astrophysics Data System (ADS)

A finite volume numerical method is presented, in primitive variables, for computing unsteady incompressible flows based on splitting the pressure into overlapping fields. The requirement that these fields should have the same value everywhere provides a constraint that allows for the simultaneous solution of velocities and pressure at each time step. Thus, there is no need to resort to separate methods for solving for the pressure. The method is checked against a test case and applied to the lid-driven cavity flow and the backward facing step and the solutions are compared to others found in the literature.

Haritonidis, Joseph H.

2004-11-01

225

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

226

Two-dimensional MRT LB model for compressible and incompressible flows  

NASA Astrophysics Data System (ADS)

In the paper we extend the Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) model proposed in [Europhys. Lett., 2010, 90: 54003] so that it is suitable also for incompressible flows. To decrease the artificial oscillations, the convection term is discretized by the flux limiter scheme with splitting technique. A new model is validated by some well-known benchmark tests, including Riemann problem and Couette flow, and satisfying agreements are obtained between the simulation results and analytical ones. In order to show the merit of LB model over traditional methods, the non-equilibrium characteristics of system are solved. The simulation results are consistent with the physical analysis.

Chen, Feng; Xu, Ai-Guo; Zhang, Guang-Cai; Wang, Yong-Long

2013-08-01

227

Notes on Newton-Krylov based Incompressible Flow Projection Solver  

SciTech Connect

The purpose of the present document is to formulate Jacobian-free Newton-Krylov algorithm for approximate projection method used in Hydra-TH code. Hydra-TH is developed by Los Alamos National Laboratory (LANL) under the auspices of the Consortium for Advanced Simulation of Light-Water Reactors (CASL) for thermal-hydraulics applications ranging from grid-to-rod fretting (GTRF) to multiphase flow subcooled boiling. Currently, Hydra-TH is based on the semi-implicit projection method, which provides an excellent platform for simulation of transient single-phase thermalhydraulics problems. This algorithm however is not efficient when applied for very slow or steady-state problems, as well as for highly nonlinear multiphase problems relevant to nuclear reactor thermalhydraulics with boiling and condensation. These applications require fully-implicit tightly-coupling algorithms. The major technical contribution of the present report is the formulation of fully-implicit projection algorithm which will fulfill this purpose. This includes the definition of non-linear residuals used for GMRES-based linear iterations, as well as physics-based preconditioning techniques.

Robert Nourgaliev; Mark Christon; J. Bakosi

2012-09-01

228

Variational bounds on energy dissipation in incompressible flows. III. Convection  

SciTech Connect

Building on a method of analysis for the Navier-Stokes equations introduced by Hopf [Math. Ann. {bold 117}, 764 (1941)], a variational principle for upper bounds on the largest possible time averaged convective heat flux is derived from the Boussinesq equations of motion. When supplied with appropriate test background fields satisfying a spectral constraint, reminiscent of an energy stability condition, the variational formulation produces rigorous upper bounds on the Nusselt number (Nu) as a function of the Rayleigh number (Ra). For the case of vertical heat convection between parallel plates in the absence of sidewalls, a simplified (but rigorous) formulation of the optimization problem yields the large Rayleigh number bound Nu{le}0.167 Ra{sup 1/2}{minus}1. Nonlinear Euler-Lagrange equations for the optimal background fields are also derived, which allow us to make contact with the upper bound theory of Howard [J. Fluid Mech. {bold 17}, 405 (1963)] for statistically stationary flows. The structure of solutions of the Euler-Lagrange equations are elucidated from the geometry of the variational constraints, which sheds light on Busse{close_quote}s [J. Fluid Mech. {bold 37}, 457 (1969)] asymptotic analysis of general solutions to Howard{close_quote}s Euler-Lagrange equations. The results of our analysis are discussed in the context of theory, recent experiments, and direct numerical simulations. {copyright} {ital 1996 The American Physical Society.}

Doering, C.R. [Center for Nonlinear Studies, MS-B258, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Constantin, P. [Department of Mathematics, University of Chicago, Chicago, Illinois 60637 (United States)

1996-06-01

229

Method and applications of fiber synthesis using laminar flow  

NASA Astrophysics Data System (ADS)

A Laminar Flow Reactor (LFR) using the principles of hydrodynamic focusing was created and used to fabricate functional composite polymer fibers. These fibers had the ability to conduct or serve as a carrier for singlet oxygen-generating molecules. Critical to the process was designing an easy-to-fabricate, inexpensive device and developing a repeatable method that made efficient use of the materials. The initial designs used a planar layout and hydrodynamically focused in only one dimension while later versions switched to a two-fluid concentric design. Modeling was undertaken and verified for the different device layouts. Three types of conductive particles were embedded in the formed polymer: silver, indium tin oxide (ITO) and polyaniline. The polymer was also used as a carrier to two singlet oxygen generating molecules: Methylene Blue (MB) and perylene. Both were effective in killing Bacillus thuringiensis but MB leached from the fiber into the tested cell suspension. Perylene, which is not water soluble, did not leach out and was just as effective as MB. Research that was performed at ITT is also presented. A critical need exists to detect, identify, quantify, locate, and track virus and toxin aerosols to provide early warning during both light and dark conditions. The solution presented is a remote sensing technology using seeding particles. Seeding particles developed during this program provide specific identification of threat cloud content. When introduced to the threat cloud the seeders will bind specifically to the analyte of interest and upon interrogation from a stand off laser source will fluoresce. The fluorescent signal is detected from a distance using a long-range microscope and collection optics that allow detection of low concentrations of threat aerosols.

Burns, Bradley Justin

230

A numerical study of an unsteady laminar flow in a doubly constricted 3D vessel  

Microsoft Academic Search

Unsteady flow dynamics in doubly constricted 3D vessels have been investigated under pulsatile flow conditions for a full cycle of period T. The coupled non-linear partial differential equations governing the mass and momentum of a viscous incompressible fluid has been numerically analyzed by a time accurate Finite Volume Scheme in an implicit Euler time marching setting. Roe's flux difference splitting

B. V. Rathish Kumar; T. Yamaguchi; H. Liu; R. Himeno

2002-01-01

231

VERIFICATION AND VALIDATION STUDIES FOR LAMINAR HYPERSONIC FLOW OVER A BLUNTED CONE AND A FLAT PLATE  

Microsoft Academic Search

In this paper, verification and validation analysis for laminar hypersonic flow fields is presented. The simulations include a Mach 8 flow of calorically perfect gas over a spherically blunted cone and a Mach 14 flow over a flat plate. Numerical results were obtained using the finite volume method on structured grids. The verification of the numerical solutions was performed by

S. Gokaltun; P. V. Skudarnov; C. X. Lin; Hugh Thornburg

2006-01-01

232

Laminar Flow and Heat Transfer in Power-Law Fluids Flowing in Arbitrary Cross-Sectional Ducts  

Microsoft Academic Search

A numerical method capable of handling three-dimensional transport processes is devised to model the developing steady laminar flow and heat transfer to power-law fluids flowing in ducts of arbitrary but uniform cross section. The governing equations are the general momentum and energy equations parabolized in the axial direction and as such are applicable to flow systems with a predominant flow

Adeniyi Lawal; Arun Mujumdar

1985-01-01

233

A generalized alternating-direction implicit scheme for incompressible magnetohydrodynamic viscous flows at low magnetic Reynolds number  

Microsoft Academic Search

This paper presents numerical simulations of incompressible fluid flows in the presence of a magnetic field at low magnetic Reynolds number. The equations governing the flow are the Navier–Stokes equations of fluid motion coupled with Maxwell’s equations of electromagnetics. The study of fluid flows under the influence of a magnetic field and with no free electric charges or electric fields

Hélio Aparecido Navarro; Luben Cabezas-gómez; Renato César Da Silva; Arlindo Neto Montagnoli

2007-01-01

234

a Segregated Solution Algorithm for Incompressible Flows in General Co-Ordinates  

NASA Astrophysics Data System (ADS)

To analyse an incompressible Navier-Stokes flow problem in a boundary- fitted curvilinear co-ordinate system is definitely not a trivial task. In the primitive variable formulation, choices between working variables and their storage points have to be made judiciously. The present work engages contravariant velocity components and scalar pressure which stagger each other in the mesh to prevent even-odd pressure oscillations from emerging. Now that smoothness of the pressure field is attainable, the remaining task is to ensure a discrete divergence-free velocity field for an incompressible flow simulation. Aside from the flux discretizations, the indispensable metric tensors, Jacobian and Christoffel symbols in the transformed equations should be approximated with care. The guiding idea is to get the property of geometric identity pertaining to these grid-sensitive discretizations. In addition, how to maintain the revertible one-to-one equivalence at the discrete level between primitive and contravariant velocities is another theme in the present staggered formulation. A semi-implicit segregated solution algorithm felicitous for a large-scale flow simulation was utilized to solve the entire set of basic equations iteratively. Also of note is that the present segregated solution algorithm has the virtue of requiring no user-specified relaxation parameters for speeding up the satisfaction of incompressibility in an optimal sense. Three benchmark problems, including an analytic problem, were investigated to justify the capability of the present formulation in handling problems with complex geometry. The test cases considered and the results obtained herein make a useful contribution in solving problems subsuming cells with arbitrary shapes in a boundary-fitted grid system.

Sheu, Tony W. H.; Lee, Shi-Min

1996-03-01

235

Method for the Constrained Design of Natural Laminar Flow Airfoils  

Microsoft Academic Search

An automated iterative design method has been developed by which an airfoil with a substantial amount of natural laminar è ow 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 key features of the method are the compressible

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

1997-01-01

236

Effective equations describing the flow of a viscous incompressible fluid through a long elastic tube  

NASA Astrophysics Data System (ADS)

We study the flow of a viscous incompressible fluid through a long and narrow elastic tube whose walls are modeled by the Navier equations for a curved, linearly elastic membrane. The flow is governed by a given small time dependent pressure drop between the inlet and the outlet boundary, giving rise to creeping flow modeled by the Stokes equations. By employing asymptotic analysis in thin, elastic, domains we obtain the reduced equations which correspond to a Biot type viscoelastic equation for the effective pressure and the effective displacement. The approximation is rigorously justified by obtaining the error estimates for the velocity, pressure and displacement. Applications of the model problem include blood flow in small arteries. We recover the well-known Law of Laplace and provide a new, improved model when shear modulus of the vessel wall is not negligible. To cite this article: S. ?ani?, A. Mikeli?, C. R. Mecanique 330 (2002) 661-666.

?ani?, Sun?ica; Mikeli?, Andro

237

A Modified Streamline-Fractional-Step Finite Element Method for Solving Unsteady Incompressible Viscous Flow  

NASA Astrophysics Data System (ADS)

This paper proposes a numerical method for computing the flows at high Reynolds number (Re). A modified fractional step (FS) finite element method (FEM) is based upon the velocity correction method (VCM) and uses two concepts to conduct intermediate velocity. The first is the streamline method, which provides an accurate multidimensional generalization, and the second is the balancing tensor diffusivity (BTD), which is used as the artificial diffusion for the stabilization techniques. The accuracy of this method for the advection-diffusion equation is demonstrated for the rotating cone problem. The unsteady incompressible viscous flows, such as square cavity flow at Re?10000 and flow past a cylinder at Re?2000, are simulated without any numerical instability.

Morinaga, Eiji

238

Finite-difference method of incompressible flows with rotation and moving boundary in a nonstaggered grid  

SciTech Connect

In this article a finite-difference solution method for simulating incompressible two-dimensional and axisymmetric flow problems with rotation and moving boundary is developed. In this method conservative governing equations are approximated by a vertex-based control-volume discretization in a nonstaggered grid. The solutions for velocity field and pressure are coupled in a similar manner to the SIMPLE family. Moving boundaries are solved step by step from the kinematic boundary condition, and the changing flow domain is fitted by a curvilinear coordinate system with updated grid. To avoid unrealistic distributions of velocity components and pressure, the Rhie-Chow interpolation is employed and the boundary value of pressure on solid surfaces is determined from the local mass conservation. The validation is carried out in simulating two-dimensional lid-driven square cavity flows and rotating coaxial disk flows with and without free surfaces.

Wu, J.; Rath, H.J. (Univ. of Bremen (Germany). Center of Applied Space Technology and Microgravity)

1994-09-01

239

Comparison of pressure correction smoothers for multigrid solution of incompressible flow  

NASA Astrophysics Data System (ADS)

We compare the performance of different pressure correction algorithms used as basic solvers in a multigrid method for the solution of the incompressible Navier-Stokes equations on non-staggered grids. Numerical tests were performed on several cases of lid-driven cavity flow using four different pressure correction schemes, including the traditional SIMPLE and SIMPLEC methods as well as novel variants, and varying combinations of underrelaxation parameters. The results show that three of the four algorithms tested are robust smoothers for the multigrid solver and that one of the new methods converges fastest in most of the tests.

Gjesdal, Thor; Lossius, Magni Elén Hope

1997-08-01

240

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

NASA Astrophysics Data System (ADS)

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 and the associated numerical methods used in the NACHOS 2 code are also outlined. Instructions for use of the program are documented in SAND-86-1817; examples of problems analyzed by the code are provided in SAND-86-1818.

Gartling, D. K.

1987-04-01

241

An Effective Approach to Computation of Forces in Viscous Incompressible Flows  

NASA Astrophysics Data System (ADS)

In the paper we present an effective method to compute forces in external flows of viscous incompressible fluids. It is an extension of the variational approach proposed initially by Quartapelle and Napolitano (1983, AIAA J. 21, 911) and is particularly well adapted to the case where a vortex method is used to solve the hydrodynamic problem. The derived formula involves a harmonic function ? and a convenient method for its determination is also shown. The effectiveness of the presented approach is confirmed by computational examples.

Protas, B.; Styczek, A.; Nowakowski, A.

2000-04-01

242

Energy stable, collocated high order schemes for incompressible flows on distorted grids  

NASA Astrophysics Data System (ADS)

An energy preserving finite difference scheme for incompressible, constant density flows is presented. It is building on the idea of the skew-symmetric rewriting of the non-linear transport term. In contrast to former schemes collocated grids can be used, while exactly preserving the energy conservation and still avoiding the odd-even decoupling of the Laplacian. High order derivatives can be utilized. A formulation for curvilinear grids is discussed and strict skew-symmetry and perfect conservation is found for arbitrary transformations in two dimensions and quite general, but not fully general transformations in three dimensions.

Reiss, Julius

2012-09-01

243

Natural convection flow in a square cavity revisited: Laminar and turbulent models with wall functions  

Microsoft Academic Search

Numerical simulations have been undertaken for the benchmark problem of natural convection flow in a square cavity. The control volume method is used to solve the conservation equations for laminar and turbulent flows for a series of Rayleigh numbers (Ra) reaching values up to 10(exp 10). The k-epsilon model has been used for turbulence modelling with and without logarithmic wall

G. Barakos; E. Mitsoulis; D. Assimacopoulos

1994-01-01

244

Pressure drop coefficient of laminar Newtonian flow in axisymmetric sudden expansions  

Microsoft Academic Search

Laminar flow of a Newtonian fluid in an axisymmetric pipe expansion has been studied numerically by means of the finite-volume approach. Predicted values of some of the overall flow characteristics, such as recirculation length, its strength, and centre location, were compared with available experimental data and correlations, and good agreement was found. The purpose of the work was to evaluate

F. T. Pinho

1997-01-01

245

Heat transfer in laminar tube flow of beef cattle manure slurries  

SciTech Connect

This report describes a concentric-tube heat exchanger and presents the preliminary results of the study of the heat transfer characteristics of the beef cattle manure slurries flowing in laminar region in the inner pipe of the concentric tube heat exchanger with hot water flowing concurrently in the annual space and serving as a heat source.

Chen, Y.R.

1986-01-01

246

Performance Characteristics of Noncircular Bearings in Laminar and Turbulent Flow Regimes  

Microsoft Academic Search

Using linearized turbulent lubrication theory of Ng and Pan, the modified Reynolds equation has been solved by finite element method using Galerkin's technique. Static and dynamic performance characteristics of the noncircular (two-lobe) bearings have been studied, both for laminar and turbulent flow, in terms of load support, oil flow, fluid film stiffness coefficients, damping coefficients, and critical mass for various

S. C. Soni; R. Sinhasan; D. V. Singh

1981-01-01

247

THE LONG TERM CALIBRATION STABILITY OF CRITICAL FLOW NOZZLES AND LAMINAR FLOWMETERS  

Microsoft Academic Search

The National Institute of Standards and Technology (NIST) has performed calibrations of gas flowmeters using piston and bell provers for three decades. Most of the meters calibrated have been either critical flow nozzles or laminar flowmeters since these meter types are generally chosen as the working standards or transfer standards by other flow calibration laboratories. Often the same meters have

John D. Wright

248

A Laminar-Flow, Water-Based Condensation Particle Counter (WCPC)  

Microsoft Academic Search

A new water-based condensation particle counter (WCPC) is presented. The WCPC is a thermally diffusive, laminar flow instrument. Condensational enlargement is achieved through the introduction of a saturated airflow into a “growth tube” with wetted walls held at a temperature higher than that of the entering flow. An unsheathed, 1 L\\/min instrument utilizing this principle has been evaluated with various

Susanne V. Hering; Mark R. Stolzenburg; Frederick R. Quant; Derek R. Oberreit; Patricia B. Keady

2005-01-01

249

Laminar-flow heat transfer in a horizontal tube with internal freezing; Effects of flow acceleration and natural convection  

Microsoft Academic Search

Laminar-flow heat transfer and ice formation phenomena in a horizontal tube with freezing have been examined experimentally. The effect of flow acceleration accompanied by ice growth on local ice thickness was studied, and it was found that the ice thickness can be correlated in terms of a flow acceleration parameter. The effect of natural convection in a horizontal tube with

T. Hirata; C. Hanaoka

1990-01-01

250

PHYSICS REQUIRES A SIMPLE LOW MACH NUMBER FLOW TO BE COMPRESSIBLE  

EPA Science Inventory

Radial, laminar, plane, low velocity flow represents the simplest, non-linear fluid dynamics problem. Ostensibly this apparently trivial flow could be solved using the incompressible Navier-Stokes equations, universally believed to be adequate for such problems. Most researchers ...

251

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

NASA Astrophysics Data System (ADS)

Recently, another approach to study incompressible fluid flow was suggested [S. Ansumali, I. Karlin, and H. Öttinger, 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.

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

2007-12-01

252

An Iterative Numerical Method for the Incompressible Mean Flow over Parabolic Bodies.  

NASA Astrophysics Data System (ADS)

A new numerical method for solving the steady incompressible flow over parabolic bodies is presented. This is motivated by the need for obtaining an accurate solution of the basic flow for use in the solution of the unsteady boundary layer flow for determining leading edge receptivity by the method of Haddad & Corke(J. Fluid Mech.), 368, 1998. The method is a solution of the steady, nonlinear Navier-Stokes equations in streamfunction-vorticity form, in parabolic coordinates. A numerical, finite difference iterative technique was developed which is always stable, always convergent, converges to machine-zero accuracy, is very fast, and always converges to the unique solution regardless of the initial conditions for a given physical case. The method will be demonstrated for a family of parabolic bodies at different angles of attack, and compared to other approaches including ADI used by Davis(J. Fluid Mech.), 51, 3, 1972 for parabolic bodies in parabolic coordinates.

Erturk, E.; Corke, T. C.

1998-11-01

253

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

2007-12-10

254

A Quadrilateral Spectral Multidomain Penalty Method Model For High Reynolds Number Incompressible Stratified Flows  

NASA Astrophysics Data System (ADS)

We present a spectral multidomain penalty method-based incompressible Navier Stokes solver for high Reynolds number stratified turbulent flows in doubly non-periodic domains. Within the solver, time is discretized with a fractional-step method, and, in space, a Gauss-Lobatto-Legendre collocation approach is used in discontinuous quadrilateral subdomains. Stability of the numerical scheme is guaranteed through a penalty scheme and spectral filtering, further buttressed by a overintegration-based dealiasing technique. The efficient iterative solution of the associated discrete pressure Poisson equation is ensured through a Kronecker product based computation of the null vector associated with the global matrix, plus a two-level preconditioner within a GMRES solver. Efficiency and accuracy of the Navier Stokes solver are assessed through the solution of the lid-driven cavity flow, Taylor vortex and double shear layer. The canonical lock exchange problem is also presented to assess the potential of the solver for the study of environmental stratified flows.

Escobar-Vargas, Jorge; Diamessis, Peter

2011-11-01

255

An adaptive level set approach for incompressible two-phase flows  

SciTech Connect

In Sussman, Smereka and Osher, a numerical method using the level set approach was formulated for solving incompressible two-phase flow with surface tension. In the level set approach, the interface is represented as the zero level set of a smooth function; this has the effect of replacing the advection of density, which has steep gradients at the interface, with the advection of the level set function, which is smooth. In addition, the interface can merge or break up with no special treatment. The authors maintain the level set function as the signed distance from the interface in order to robustly compute flows with high density ratios and stiff surface tension effects. In this work, they couple the level set scheme to an adaptive projection method for the incompressible Navier-Stokes equations, in order to achieve higher resolution of the interface with a minimum of additional expense. They present two-dimensional axisymmetric and fully three-dimensional results of air bubble and water drop computations.

Sussman, M.; Almgren, A.S.; Bell, J.B. [and others

1997-04-01

256

Modification of equation of motion of fluid-conveying pipe for laminar and turbulent flow profiles  

NASA Astrophysics Data System (ADS)

Considering the non-uniformity of the flow velocity distribution in fluid-conveying pipes caused by the viscosity of real fluids, the centrifugal force term in the equation of motion of the pipe is modified for laminar and turbulent flow profiles. The flow-profile-modification factors are found to be 1.333, 1.015-1.040 and 1.035-1.055 for laminar flow in circular pipes, turbulent flow in smooth-wall circular pipes and turbulent flow in rough-wall circular pipes, respectively. The critical flow velocities for divergence in the above-mentioned three cases are found to be 13.4%, 0.74-1.9% and 1.7-2.6%, respectively, lower than that with plug flow, while those for flutter are even lower, which could reach 36% for the laminar flow profile. By introducing two new concepts of equivalent flow velocity and equivalent mass, fluid-conveying pipe problems with different flow profiles can be solved with the equation of motion for plug flow.

Guo, C. Q.; Zhang, C. H.; Païdoussis, M. P.

2010-07-01

257

Numerical simulation of pressure-driven startup laminar flows through a planar T-junction channel  

NASA Astrophysics Data System (ADS)

A start-up flow of a viscous incompressible fluid in a T-junction channel is studied numerically. The flow starting from rest is driven by a constant pressure drops suddenly applied between the entries and exits of a planar T-junction channel. The Navier-Stokes equations in primitive variables are solved numerically using finite-volume techniques. Predicted variations with time of the volume flow rates and the flow patterns are presented for several values of pressure drops. It has been shown that a start-up flow can pass through different regimes (or different flow direction) before asymptotically reaching steady state distribution.

Moshkin, N. P.; Yambangwai, D.

2012-03-01

258

A cylinder of arbitrary cross section in a weakly rotational two-parameter flow of an incompressible ideal fluid  

NASA Astrophysics Data System (ADS)

Flow of an incompressible ideal fluid past a circular cylinder is investigated analytically for the case where transverse flow has an arbitrary periodic velocity profile at a large distance upstream. The flow is assumed to be weakly rotational. By using the approach proposed by Shankar (1980), the problem is reduced to two problems that are independent to a first approximation: determining the longitudinal component and the current function of the perturbed flow. A numerical example is presented.

Iarmitskii, A. G.

1989-12-01

259

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

National Technical Information Service (NTIS)

Table of Contents: 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 R...

A. L. Braslow

1999-01-01

260

Flight Test Measurement Techniques for Laminar Flow. Volume 23(Les techniques de mesure en vol des ecoulements laminaires).  

National Technical Information Service (NTIS)

The advantages of laminar flow technology have been well known for decades. Experiments in Germany, the United Kingdom, and the United States date back to the 1930's. One application of some of the early research was the use of a laminar flow airfoil on t...

D. Fisher K. H. Horstmann H. Riedel

2003-01-01

261

Calculation of heat transfer in pipes to gases with variable properties with allowance for the laminar transition of flow  

Microsoft Academic Search

Based on experimental data in the literature, an engineering method for calculating heat transfer in pipes during the heating of turbulent flows of gases with variable properties is developed which allows for the laminar transition of the flow in the region of high thermal loads and moderate and low inlet Reynolds numbers. The effect of the laminar transition is treated

V. A. Kurganov

1987-01-01

262

A fast, high resolution, second-order central scheme for incompressible flows  

PubMed Central

A high resolution, second-order central difference method for incompressible flows is presented. The method is based on a recent second-order extension of the classic Lax–Friedrichs scheme introduced for hyperbolic conservation laws (Nessyahu H. & Tadmor E. (1990) J. Comp. Physics. 87, 408-463; Jiang G.-S. & Tadmor E. (1996) UCLA CAM Report 96-36, SIAM J. Sci. Comput., in press) and augmented by a new discrete Hodge projection. The projection is exact, yet the discrete Laplacian operator retains a compact stencil. The scheme is fast, easy to implement, and readily generalizable. Its performance was tested on the standard periodic double shear-layer problem; no spurious vorticity patterns appear when the flow is underresolved. A short discussion of numerical boundary conditions is also given, along with a numerical example.

Kupferman, Raz; Tadmor, Eitan

1997-01-01

263

A high-order discontinuous Galerkin method for 2D incompressible flows  

SciTech Connect

In this paper the authors introduce a high-order discontinuous Galerkin method for two-dimensional incompressible flow in the vorticity stream-function formulation. The momentum equation is treated explicitly, utilizing the efficiency of the discontinuous Galerkin method. The stream function is obtained by a standard Poisson solver using continuous finite elements. There is a natural matching between these two finite element spaces, since the normal component of the velocity field is continuous across element boundaries. This allows for a correct upwinding gluing in the discontinuous Galerkin framework, while still maintaining total energy conservation with no numerical dissipation and total entropy stability. The method is efficient for inviscid or high Reynolds number flows. Optimal error estimates are proved and verified by numerical experiments.

Liu, J.G.; Shu, C.W.

2000-05-20

264

Spraying Powder Materials by the High-Enthalpy Laminar Plasma Flow  

SciTech Connect

One of the most promising engineering solutions of the problem of spraying powder materials is the proposed method of plasma spraying by the laminar plasma jet. Laminar plasma flow is characterized by small jet angle divergence; the powder particles are penetrated and accelerated mainly in the axial direction. The molten powder particles are transported almost to the surface of a treated work-piece inside the laminar plasma flow in an atmosphere of the plasma-forming gas with the acceleration on the entire transfer area, which leads to an increase in the particles velocity, a decrease of their oxidability, an increase in the powder deposition efficiency, density, adhesion strength with the surface to be coated.

Khutsishvili, M.; Kikvadze, L. [Plasma Spray Laboratory, Georgian Technical University, M. Kostava street 77, Tbilisi 0175 (Georgia)

2008-03-19

265

Acoustic effect on stall hysteresis for low Reynolds number laminar flow  

NASA Astrophysics Data System (ADS)

An experimental investigation was conducted in the Virginia Tech Stability Wind Tunnel to determine the effect of sound waves on the separated laminar boundary layer of a wing at low Reynolds numbers. Also studied was the effect of Reynolds number on the stall hysteresis behavior of the airfoil at Reynolds numbers between 100,000 and 300,000. It was found that increasing the Reynolds number changed the location and magnitude of the maximum lift coefficient. The stall hysteresis loop, a phenomenon that occurs only at low Re, in which the alpha at flow separation and that at reattachment are not identical, was also found to change with increasing Reynolds numbers. It was found that sound could be used to excite turbulence in a separated laminar boundary layer and cause flow reattachment via a laminar bubble. The required sound frequency and level were found to vary with Reynolds number and angle of attack.

Schaefer, C. G., Jr.

266

Spraying Powder Materials by the High-Enthalpy Laminar Plasma Flow  

NASA Astrophysics Data System (ADS)

One of the most promising engineering solutions of the problem of spraying powder materials is the proposed method of plasma spraying by the laminar plasma jet. Laminar plasma flow is characterized by small jet angle divergence; the powder particles are penetrated and accelerated mainly in the axial direction. The molten powder particles are transported almost to the surface of a treated work-piece inside the laminar plasma flow in an atmosphere of the plasma-forming gas with the acceleration on the entire transfer area, which leads to an increase in the particles velocity, a decrease of their oxidability, an increase in the powder deposition efficiency, density, adhesion strength with the surface to be coated.

Khutsishvili, M.; Kikvadze, L.

2008-03-01

267

Statistical analysis of the transition to turbulent-laminar banded patterns in plane Couette flow  

NASA Astrophysics Data System (ADS)

The transition between uniform turbulence in plane Couette flow and turbulent-laminar banded patterns is studied using numerical computations. Timeseries of the velocity along a line in the midplane along the pattern wavevector are Fourier transformed. When averaged in time, these spectra show diffuse maxima corresponding to streaks and longitudinal rolls with a wavelength near 4, and a sharper, higher, maximum corresponding to the turbulent-laminar pattern with wavelength 40. Probability distribution functions are computed for the Fourier component corresponding to wavelength 40. It is shown that this PDF is a Gaussian centered at 0 for a a uniform turbulent flow and that this maximum shifts to a finite value when a turbulent-laminar banded pattern appears.

Tuckerman, Laurette S.; Barkley, Dwight; Dauchot, Olivier

2008-11-01

268

Newton-Krylov-Schwarz methods for aerodynamics problems : compressible and incompressible flows on unstructured grids.  

SciTech Connect

We review and extend to the compressible regime an earlier parallelization of an implicit incompressible unstructured Euler code [9], and solve for flow over an M6 wing in subsonic, transonic, and supersonic regimes. While the parallelization philosophy of the compressible case is identical to the incompressible, we focus here on the nonlinear and linear convergence rates, which vary in different physical regimes, and on comparing the performance of currently important computational platforms. Multiple-scale problems should be marched out at desired accuracy limits, and not held hostage to often more stringent explicit stability limits. In the context of inviscid aerodynamics, this means evolving transient computations on the scale of the convective transit time, rather than the acoustic transit time, or solving steady-state problems with local CFL numbers approaching infinity. Whether time-accurate or steady, we employ Newton's method on each (pseudo-) timestep. The coupling of analysis with design in aerodynamic practice is another motivation for implicitness. Design processes that make use of sensitivity derivatives and the Hessian matrix require operations with the Jacobian matrix of the state constraints (i.e., of the governing PDE system); if the Jacobian is available for design, it may be employed with advantage in a nonlinearly implicit analysis, as well.

Kaushik, D. K.; Keyes, D. E.; Smith, B. F.

1999-02-24

269

New Finite Difference Methods Based on IIM for Inextensible Interfaces in Incompressible Flows  

PubMed Central

In this paper, new finite difference methods based on the augmented immersed interface method (IIM) are proposed for simulating an inextensible moving interface in an incompressible two-dimensional flow. The mathematical models arise from studying the deformation of red blood cells in mathematical biology. The governing equations are incompressible Stokes or Navier-Stokes equations with an unknown surface tension, which should be determined in such a way that the surface divergence of the velocity is zero along the interface. Thus, the area enclosed by the interface and the total length of the interface should be conserved during the evolution process. Because of the nonlinear and coupling nature of the problem, direct discretization by applying the immersed boundary or immersed interface method yields complex nonlinear systems to be solved. In our new methods, we treat the unknown surface tension as an augmented variable so that the augmented IIM can be applied. Since finding the unknown surface tension is essentially an inverse problem that is sensitive to perturbations, our regularization strategy is to introduce a controlled tangential force along the interface, which leads to a least squares problem. For Stokes equations, the forward solver at one time level involves solving three Poisson equations with an interface. For Navier-Stokes equations, we propose a modified projection method that can enforce the pressure jump condition corresponding directly to the unknown surface tension. Several numerical experiments show good agreement with other results in the literature and reveal some interesting phenomena.

Li, Zhilin; Lai, Ming-Chih

2012-01-01

270

Unsteady Laminar Natural Convection from a Non-Isothermal Vertical Cone  

Microsoft Academic Search

Natural convection effects of the numerical solution for unsteady, laminar, free convection flow over an incompressible viscous fluid past a no n-isothermal vertical cone with surface temperature T ' w(x) = T ' ? + ax n varying as power function of distance from the apex (x = 0) is presented here. The dimensionless governing equations of the flow that

B. Pullepu; K. Ekambavanan; A. J. Chamkha

271

A parallel incompressible flow solver package with a parallel mutigrid elliptic kernel  

SciTech Connect

The development and applications of a parallel, time-dependent incompressible Navier-Stokes flow solver and a parallel multigrid elliptic kernel are described. The flow solver is based on a second-order projection method applied to a staggered finite-difference grid. The multigrid algorithms implemented in the parallel elliptic kernel, which is needed by the flow solver, and V-cycle and full V-cycle schemes. A grid-partition strategy is used in the parallel implementations of both the flow solver and the multigrid elliptic kernel on all fine and coarse grids. Numerical experiments and parallel performance tests show the parallel solver package is numerically stable, physically robust, and computationally efficient. Both the multigrid elliptic kernel and the flow solver scale very well to a large number of processors on Intel Paragon and Cray T3D for computations with moderate granularity. The solver package has been carefully designed and coded so that it can be easily adapted to solving a variety of interesting two- and three-dimensional flow problems. The solver package is portable to parallel systems that support MPI, PVM, and NX for interprocessor communications. 13 refs., 23 figs., 3 tabs.

Lou, J.Z.; Ferraro, R. [California Inst. of Technology, Pasadena, CA (United States)

1996-04-01

272

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

PubMed

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

2013-02-13

273

Modelisation des ecoulements compressibles en maillage non structure par extension des methodes numeriques appliquees aux ecoulements incompressibles. (Compressible flow modelling in unstructured mesh topologies using numerical methods developed for incompressible flows).  

National Technical Information Service (NTIS)

The R&D thermal hydraulic codes, notably the finite difference codes Melodie (2D) and ESTET (3D) or the 2D and 3D versions of the finite element code N3S were initially developed for incompressible, possibly dilatable, turbulent flows, i.e. those where de...

A. Caruso N. Mechitoua J. Duplex

1995-01-01

274

A forward-in-time advection scheme and adaptive multilevel flow solver for nearly incompressible atmospheric flow  

SciTech Connect

This paper presents a new forward-in-time advection method for nearly incompressible flow, MU, and its application to an adaptive multilevel flow solver for atmospheric flows. MU is a modification of Leonard et al.`s UTOPIA scheme. MU, like UTOPIA, is based on third-order accurate semi-Lagrangian multidimensional upwinding for constant velocity flows. for varying velocity fields, MU is a second-order conservative method. MU has greater stability and accuracy than UTOPIA and naturally decomposes into a monotone low-order method and a higher-order accurate correction for use with flux limiting. Its stability and accuracy make it a computationally efficient alternative to current finite-difference advection methods. We present a fully second-order accurate flow solver for the anelastic equations, a prototypical low Mach number flow. The flow solver is based on MU which is used for both momentum and scalar transport equations. This flow solver can also be implemented with any forward-in-time advection scheme. The multilevel flow solver conserves discrete global integrals of advected quantities and includes adaptive mesh refinements. Its second-order accuracy is verified using a nonlinear energy conservation integral for the anelastic equations. For a typical geophysical problem in which the flow is most rapidly varying in a small part of the domain, the multilevel flow solver achieves global accuracy comparable to uniform-resolution simulation for 10% of the computational cost. 36 refs., 10 figs.

Stevens, D.E. [Lawrence Berkeley National Lab., CA (United States); Bretherton, S. [Univ. of Washington, Seattle, WA (United States)

1996-12-01

275

Intense destruction of bodies of laminar or granular structure in hypersonic flow  

Microsoft Academic Search

The paper deals with a material granular or laminar structure, composed of alternating radiation transmitting and nontransmitting zones. An expression for the heat exchange efficiency of the material is derived, and the nature of the destruction of the body in a stagnation air flow is examined under the assumption of an optically thin boundary layer. The case of intense destruction,

E. Z. Apshtein

1979-01-01

276

Selective microfabrication of silver electrodes inside a microchannel by multiphase laminar flow with density difference  

Microsoft Academic Search

In this paper, we propose a selective microfabrication technique of metal electrodes in a microchannel. The technique is based on the chemical deposition and the interface rotation of laminar flows among three multiphase fluids. Silver electrodes were patterned by electroless silver deposition only on the wall of the microchannel where the interface between a silver electroless plating solution and a

Seung Ho Paek; Young Ki Choi; Dong Sung Kim

2010-01-01

277

Flocculation kinetics and aggregate structure of kaolinite mixtures in laminar tube flow  

Microsoft Academic Search

Flocculation is commonly used in various solid–liquid separation processes in chemical and mineral industries to separate desired products or to treat waste streams. This paper presents an experimental technique to study flocculation processes in laminar tube flow. This approach allows for more realistic estimation of the shear rate to which an aggregate is exposed, as compared to more complicated shear

R. Sean Sanders; Jacob H. Masliyah

2011-01-01

278

High Reynolds Number Hybrid Laminar Flow Control (HLFC) Flight Experiment, Report 2.  

National Technical Information Service (NTIS)

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 H...

1999-01-01

279

Two-dimensional laminar boundary layer in flow of thermodynamically equilibrated water vapor  

Microsoft Academic Search

This paper examines the boundary problem of a laminar boundary layer in flow of thermodynamically equilibrated water vapor. An approximate method of solution is proposed, based on an approximation for the density and the coefficient of dynamic viscosity across the layer.

R. A. Rakhimzyanov; V. G. Zharinov

1978-01-01

280

Propene pyrolysis and oxidation kinetics in a flow reactor and laminar flames  

Microsoft Academic Search

The pyrolysis and oxidation of propene were studied experimentally in an atmospheric flow reactor. Species profiles were obtained in the intermediate to high temperature range (?1200 K) for lean, stoichiometric, rich, and pyrolytic conditions. Laminar flame speeds of propene\\/air mixtures were also determined over an extensive range of equivalence ratios, at room temperature and atmospheric pressure, using the counterflow twin

S. G. Davis; C. K. Law; H. Wang

1999-01-01

281

Patterning Cells and Their Environments Using Multiple Laminar Fluid Flows in Capillary Networks  

Microsoft Academic Search

This paper describes the use of laminar flow of liquids in capillary systems to pattern the cell culture substrate, to perform patterned cell deposition, and to pattern the cell culture media. We demonstrate the patterning of the cell culture substrate with different proteins, the patterning of different types of cells adjacent to each other, the patterned delivery of chemicals to

Shuichi Takayama; J. Cooper McDonald; Emanuele Ostuni; Michael N. Liang; Paul J. A. Kenis; Rustem F. Ismagilov; George M. Whitesides

1999-01-01

282

The influence of cirrus cloud on drag reduction technologies based on laminar flow  

Microsoft Academic Search

Due the increasing gap between the growth of air tr affic on one side and the requirement to lower its environmental impacts on the other, laminar flow technologies att ract renewed interest as they offer a potential of greater than 10% fuel savings for long-range jet transport aircraft. Further reductions could be achieved if the impact of environmental factors, such

Conny Schmidt; Trevor M. Young; Emmanuel P. Benard; Selcuk Atalay

283

Nacelle/Pylon/Wing Integration on a Transport Model with a Natural Laminar Flow Nacelle.  

National Technical Information Service (NTIS)

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 lo...

M. Lamb W. K. Aabeyounis J. C. Patterson

1985-01-01

284

Laboratory measurement of water nucleation using a laminar flow tube reactor  

Microsoft Academic Search

A Laminar Flow Tube Reactor (LFTR) was used to study the nucleation of water vapor. Computational analysis was carried out to define the operating conditions of the LFTR suitable for water nucleation measurements. An interface between the LFTR and a mass spectrometer was developed to analyze the chemical content of the freshly nucleated water particles. Contaminants were detected in the

Vladimir B. Mikheev; Patricia M. Irving; Nels S. Laulainen; Stephan E. Barlow; Viktor V. Pervukhin

2002-01-01

285

Design and Experimental Results for a Natural-Laminar-Flow Airfoil for General Aviation Applications.  

National Technical Information Service (NTIS)

A natural-laminar-flow airfoil for general aviation applications, the NLF(1)-0416, was designed and analyzed theoretically and verified experimentally in the Langley Low-Turbulence Pressure Tunnel. The basic objective of combining the high maximum lift of...

D. M. Somers

1981-01-01

286

Surface patterning using two-phase laminar flow and in?situ formation of aryldiazonium salts.  

PubMed

In the reaction zone: Reaction of an aryltriazene with acid generates the corresponding aryldiazonium ion. When this reaction takes place in the mixing zone, at the interface between two streams flowing laminarly and in parallel through a 100??m microchannel, a submicrometer line of organic film is grafted at the substrate surface. PMID:23939818

Gross, Andrew J; Nock, Volker; Polson, Matthew I J; Alkaisi, Maan M; Downard, Alison J

2013-08-12

287

Single collector attachment efficiency of colloid capture by a cylindrical collector in laminar overland flow  

Technology Transfer Automated Retrieval System (TEKTRAN)

Little research has been conducted to investigate fate and transport of colloids in surface vegetation in overland flow under unfavorable chemical conditions. In this work, single collector attachment efficiency (a) of colloid capture by a simulated plant stem (i.e. cylindrical collector) in laminar...

288

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...

289

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

290

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

National Technical Information Service (NTIS)

Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft s swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing w...

T. Bui

2013-01-01

291

Thermal radiation and laminar forced convection in a gas pipe flow  

Microsoft Academic Search

The interaction of forced convection and thermal radiation in laminar pipe flow is numerically studied in this paper. An absorbing and emitting gas is considered for the analysis and treated to be a gray medium. The method of moments is used to describe approximately the radiative heat flux in the energy equation. The conservation equations that govern the problem are

A. Campo; C. Schuler

1988-01-01

292

Experimental analysis of colloid capture by a cylindrical collector in laminar overland flow.  

PubMed

Although colloid-facilitated contaminant transport in water flow is a well-known contamination process, little research has been conducted to investigate the transport of colloidal particles through emergent vegetation in overland flow. In this work, a series of laboratory experiments were conducted to measure the single-collector contact efficiency (?(0)) of colloid capture by a simulated plant stem in laminar lateral flow. Fluorescent microspheres of various sizes were used as experimental colloids. The colloid suspensions were applied to a glass cylinder installed in a small size flow chamber at different flow rates. Two cylinder sizes were tested in the experiment and silicone grease was applied to the cylinder surface to make it favorable for colloid deposition. Our results showed that increases in flow rate and collector size reduced the value of ?(0) and a minimum value of ?(0) might exist for a colloid size. The experimental data were compared to theoretical predictions of different single-collector contact efficiency models. The results indicated that existing single-collector contact efficiency models underestimated the ?(0) of colloid capture by the cylinders in laminar overland flow. A regression equation of ?(0) as a function of collector Reynolds number (Re(c)) and Peclet number (N(Pe)) was developed and fit the experimental data very well (R(2) > 0.98). This regression equation can be used to help construct and refine mathematical models of colloid transport and filtration in laminar overland flow on vegetated surfaces. PMID:21809854

Wu, Lei; Gao, Bin; Muñoz-Carpena, Rafael

2011-08-17

293

A coupled pressure-based computational method for incompressible/compressible flows  

NASA Astrophysics Data System (ADS)

Pressure-based flow solvers couple continuity and linearized truncated momentum equations to derive a Poisson type pressure correction equation and use the well known SIMPLE algorithm. Momentum equations and the pressure correction equation are typically solved sequentially. In many cases this method results in slow and often difficult convergence. The current paper proposes a novel computational algorithm, solving for pressure and velocity simultaneously within a pressure-correction coupled solution approach using finite volume method on structured and unstructured meshes. The method can be applied to both incompressible and subsonic compressible flows. For subsonic compressible flows, the energy equation is also coupled with flow field and the density of fluid is obtained by equation of state. The procedure eliminates the pressure correction step, the most expensive component of the SIMPLE-like algorithms. The proposed coupled continuity-momentum-energy equation method can be used to simulate steady state or transient flow problems. The method has been tested on several CFD benchmark cases with excellent results showing dramatically improved numerical convergence and significant reduction in computational time.

Chen, Z. J.; Przekwas, A. J.

2010-12-01

294

A consistent splitting scheme for unsteady incompressible viscous flows I. Dirichlet boundary condition and applications  

NASA Astrophysics Data System (ADS)

A well-recognized approach for handling the incompressibility constraint by operating directly on the discretized Navier-Stokes equations is used to obtain the decoupling of the pressure from the velocity field. By following the current developments by Guermond and Shen, the possibilities of obtaining accurate pressure and reducing boundary-layer effect for the pressure are analysed. The present study mainly reports the numerical solutions of an unsteady Navier-Stokes problem based on the so-called consistent splitting scheme (J. Comput. Phys. 2003; 192:262-276). At the same time the Dirichlet boundary value conditions are considered. The accuracy of the method is carefully examined against the exact solution for an unsteady flow physics problem in a simply connected domain. The effectiveness is illustrated viz. several computations of 2D double lid-driven cavity problems.

Wong, J. C.-F.; Chan, M. K.-H.

2006-06-01

295

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

296

A consistent and stabilized continuous/discontinuous Galerkin method for fourth-order incompressible flow problems  

NASA Astrophysics Data System (ADS)

This paper presents a new consistent and stabilized finite-element formulation for fourth-order incompressible flow problems. The formulation is based on the C0-interior penalty method, the Galerkin least-square (GLS) scheme, which assures that the formulation is weakly coercive for spaces that fail to satisfy the inf-sup condition, and considers discontinuous pressure interpolations. A stability analysis through a lemma establishes that the proposed formulation satisfies the inf-sup condition, thus confirming the robustness of the method. This lemma indicates that, at the element level, there exists an optimal or quasi-optimal GLS stability parameter that depends on the polynomial degree used to interpolate the velocity and pressure fields, the geometry of the finite element, and the fluid viscosity term. Numerical experiments are carried out to illustrate the ability of the formulation to deal with arbitrary interpolations for velocity and pressure, and to stabilize large pressure gradients.

Cruz, A. G. B.; Dutra do Carmo, E. G.; Duda, F. P.

2012-06-01

297

Fractional calculus modelling for unsteady unidirectional flow of incompressible fluids with time-dependent viscosity  

NASA Astrophysics Data System (ADS)

In this note we analyze a model for a unidirectional unsteady flow of a viscous incompressible fluid with time dependent viscosity. A possible way to take into account such behaviour is to introduce a memory formalism, including thus the time dependent viscosity by using an integro-differential term and therefore generalizing the classical equation of a Newtonian viscous fluid. A possible useful choice, in this framework, is to use a rheology based on stress/strain relation generalized by fractional calculus modelling. This is a model that can be used in applied problems, taking into account a power law time variability of the viscosity coefficient. We find analytic solutions of initial value problems in an unbounded and bounded domain. Furthermore, we discuss the explicit solution in a meaningful particular case.

Garra, Roberto; Polito, Federico

2012-12-01

298

A finite volume method to solve the Navier-Stokes equations for incompressible flows on unstructured meshes  

Microsoft Academic Search

A method to solve the Navier-Stokes equations for incompressible viscous flows and the convection and diusion of a scalar is proposed in the present paper. This method is based upon a fractional time step scheme and the finite volume method on unstructured meshes. A recently proposed diusion scheme with interesting theoretical and numerical properties is tested and integrated into the

Sylvain Boivin; Florent Cayré; Jean-Marc Hérard

299

a Finite-Difference Multigrid Algorithm for the Direct Numerical Simulation of Transition and Turbulence in Incompressible Flow  

Microsoft Academic Search

Some of the unresolved issues which arise when using finite-difference spatial discretizations in direct numerical simulations of transition and turbulence are examined in this investigation. The focus of attention is on the development and validation of a finite-difference code for conducting temporal simulations of transition to turbulence in incompressible plane Poiseuille flow. In order to place the present research in

Steven Eric Krist

1993-01-01

300

An efficient, interface-preserving level set redistancing algorithm and its application to interfacial incompressible fluid flow  

Microsoft Academic Search

In Sussman, Smereka, and Osher, a numerical scheme was presented for computing incompressible air-water flows using the level set method. Crucial to the above method was a new iteration method for maintaining the level set function as the signed distance from the zero level set. In this paper the authors implement a constraint along with higher order difference schemes in

Mark Sussman; Emad Fatemi

1999-01-01

301

An implicit algorithm within the arbitrary Lagrangian–Eulerian formulation for solving incompressible fluid flow with large boundary motions  

Microsoft Academic Search

The objective of the paper is to present an implicit algorithm for incompressible fluid flow solution using the arbitrary Lagrangian–Eulerian (ALE) formulation and to investigate solution accuracy and stability of the algorithm. The governing equations of the implicit procedure are derived using isoparametric interpolations for the fluid velocities and pressure. The details suitable for general use are presented in our

Nenad Filipovic; Srboljub Mijailovic; Akira Tsuda; Milos Kojic

2006-01-01

302

Numerical method for calculation of the incompressible flow in general curvilinear co-ordinates with double staggered grid  

Microsoft Academic Search

A solution methodology has been developed for incompressible flow in general curvilinear co-ordinates. Two staggered grids are used to discretize the physical domain. The first grid is a MAC quadrilateral mesh with pressure arranged at the centre and the Cartesian velocity components located at the middle of the sides of the mesh. The second grid is so displaced that its

A. Shklyar; A. Arbel

2003-01-01

303

Experimental and computational study of laminar cavity flows at hypersonic speeds  

NASA Astrophysics Data System (ADS)

This paper presents a combined experimental/computational study of a surface cavity in a low Reynolds number Mach 9 flow. The geometry is based on a body of revolution, which produces highly two-dimensional time-averaged flow for all experimental test cases. A range of cavity length-to-depth ratios, up to a maximum of 8, is investigated. These correspond to ‘closed’ cavity flows, with the free shear layer bridging the entire cavity. For most cases the free shear layer is laminar. However, there is evidence of three-dimensional unsteadiness which is believed to be the consequence of Taylor Görtler-type vortex formation. The effect of this is first detected on the cavity floor but progressively spreads as the cavity length is increased. For the longest cavities the flow is also influenced by the early stages of laminar turbulent transition in the free shear layer.

Jackson, A. P.; Hillier, R.; Soltani, S.

2001-01-01

304

Linear stability of incompressible fluid flow in a cavity using finite element method  

NASA Astrophysics Data System (ADS)

Numerical methods have been applied to theoretical studies of instability and transition to turbulence. In this study an analysis of the linear stability of incompressible flow is undertaken. By means of the finite element method the two-dimensional base flow is computed numerically over a range of Reynolds numbers and is perturbed with three-dimensional disturbances. The partial differential equations governing the evolution of perturbation are obtained from the non-linear Navier-Stokes equations with a slight compressibility by using linear stability and normal mode analysis. In terms of the finite element discretization a non-singular generalized eigenproblem is formulated from these equations whose solution gives the dispersion relation between complex growth rate and wave number. This study presents stability curves to identify the critical Reynolds number and critical wavelength of the neutral mode and discusses the mechanism of instability. The stability of lid-driven cavity flow is examined. Taylor-Göertler-like vortices in the cavity are obtained by means of reconstruction of three-dimensional flows.

Ding, Yan; Kawahara, Mutsuto

1998-01-01

305

A spectral-element discontinuous Galerkin lattice Boltzmann method for incompressible flows.  

SciTech Connect

We present a spectral-element discontinuous Galerkin lattice Boltzmann method for solving nearly incompressible flows. Decoupling the collision step from the streaming step offers numerical stability at high Reynolds numbers. In the streaming step, we employ high-order spectral-element discontinuous Galerkin discretizations using a tensor product basis of one-dimensional Lagrange interpolation polynomials based on Gauss-Lobatto-Legendre grids. Our scheme is cost-effective with a fully diagonal mass matrix, advancing time integration with the fourth-order Runge-Kutta method. We present a consistent treatment for imposing boundary conditions with a numerical flux in the discontinuous Galerkin approach. We show convergence studies for Couette flows and demonstrate two benchmark cases with lid-driven cavity flows for Re = 400-5000 and flows around an impulsively started cylinder for Re = 550-9500. Computational results are compared with those of other theoretical and computational work that used a multigrid method, a vortex method, and a spectral element model.

Min, M.; Lee, T.; Mathematics and Computer Science; City Univ. of New York

2011-01-01

306

A Spalart-Allmaras turbulence model implementation in a discontinuous Galerkin solver for incompressible flows  

NASA Astrophysics Data System (ADS)

In this paper the artificial compressibility flux Discontinuous Galerkin (DG) method for the solution of the incompressible Navier-Stokes equations has been extended to deal with the Reynolds-Averaged Navier-Stokes (RANS) equations coupled with the Spalart-Allmaras (SA) turbulence model. DG implementations of the RANS and SA equations for compressible flows have already been reported in the literature, including the description of limiting or stabilization techniques adopted in order to prevent the turbulent viscosity ?˜ from becoming negative. In this paper we introduce an SA model implementation that deals with negative ?˜ values by modifying the source and diffusion terms in the SA model equation only when the working variable or one of the model closure functions become negative. This results in an efficient high-order implementation where either stabilization terms or even additional equations are avoided. We remark that the proposed implementation is not DG specific and it is well suited for any numerical discretization of the RANS-SA governing equations. The reliability, robustness and accuracy of the proposed implementation have been assessed by computing several high Reynolds number turbulent test cases: the flow over a flat plate (Re=107), the flow past a backward-facing step (Re=37400) and the flow around a NACA 0012 airfoil at different angles of attack (?=0°,10°,15°) and Reynolds numbers (Re=2.88×106,6×106).

Crivellini, Andrea; D'Alessandro, Valerio; Bassi, Francesco

2013-05-01

307

A spectral-element discontinuous Galerkin lattice Boltzmann method for nearly incompressible flows  

NASA Astrophysics Data System (ADS)

We present a spectral-element discontinuous Galerkin lattice Boltzmann method for solving nearly incompressible flows. Decoupling the collision step from the streaming step offers numerical stability at high Reynolds numbers. In the streaming step, we employ high-order spectral-element discontinuous Galerkin discretizations using a tensor product basis of one-dimensional Lagrange interpolation polynomials based on Gauss-Lobatto-Legendre grids. Our scheme is cost-effective with a fully diagonal mass matrix, advancing time integration with the fourth-order Runge-Kutta method. We present a consistent treatment for imposing boundary conditions with a numerical flux in the discontinuous Galerkin approach. We show convergence studies for Couette flows and demonstrate two benchmark cases with lid-driven cavity flows for Re = 400-5000 and flows around an impulsively started cylinder for Re = 550-9500. Computational results are compared with those of other theoretical and computational work that used a multigrid method, a vortex method, and a spectral element model.

Min, Misun; Lee, Taehun

2011-01-01

308

A general method for calculating momentum and heat transfer in laminar and turbulent duct flows  

Microsoft Academic Search

A method for solving boundary-layer equations with boundary conditions corresponding to two-dimensional plane and axisymmetric, laminar and turbulent internal flows is described and results are presented. This method represents an extension of a procedure previously used with considerable success for an extensive range of two- and three-dimensional external flows, and is shown here to be equally successful when applied to

Tuncer Cebeci; K. C. Chang

1978-01-01

309

a General Method for Calculating Momentum and Heat Transfer in Laminar and Turbulent Duct Flows  

Microsoft Academic Search

A method for solving boundary-layer equations with boundary conditions corresponding to two-dimensional plane and axisymmetric, laminar and turbulent internal flows is described and results are presented. This method represents an extension of a procedure previously used with considerable success for an extensive range of two- and three-dimensional external flows, and is shown here to be equally successful when applied to

Tuncer Cebeci; K. C. Chang

1978-01-01

310

Brownian motion and the drift of charged nanoparticles in laminar gas flow in a plane channel  

Microsoft Academic Search

Using two limiting cases (of adsorbing and reflecting channel walls), the influence of Brownian motion on the motion of nanoparticles\\u000a in laminar gas flow under the action of an external electric field has been considered. Similarity criteria making it possible\\u000a to classify experimental situations have been found. Numerical modeling of deposition from the flow has been carried out with\\u000a the

S. P. Fisenko

2009-01-01

311

Studies of pressure-velocity coupling schemes for analysis of incompressible and compressible flows  

NASA Astrophysics Data System (ADS)

Two pressure-velocity coupling schemes, both of which solve the fully implicit discretized equations governing the flow of fluids were examined, and the capability of performing large Reynolds number, low Mach number compressible flow calculations were assessed. The semi-implicit iterative SIMPLE algorithm is extended to handle transient compressible flow calculations. This extension takes into account a strong coupling between the pressure and temperature through a correction procedure, based on the equations of state. Results obtained from the extended SIMPLE algorithm are then compared to similar results obtained from the non-iterative PISO algorithm. Both time-dependent and steady state calculations were performed using an axisymmetric 2:1 pipe expansion geometry and laminar flow conditions corresponding to Reynolds number of 1000 and Mach number of 2.0. For calculations simulating a time-dependent compression/expansion process, both schemes exhibit transient features in excellent agreement with each other, and moreover, the PISO method shows a significant computational time reduction of 60 percent over the SIMPLE scheme, regardless of the time step size or grid size employed. The effects of numerical diffusion are shown to be significant in these calculations. For steady state compressible flows, however, the SIMPLE algorithm displays increasing computational efficiency over the PISO method as the time step sizes employed to reach steady state conditions are decreased.

Burgreen, Gregory Wayne

312

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

313

A direct numerical simulation of laminar and turbulent flow over riblet-mounted surfaces  

NASA Astrophysics Data System (ADS)

Laminar and turbulent flow in a channel with a smooth upper wall and a riblet-mounted lower wall is simulated using a highly efficient spectral element-Fourier method, for a range of Reynolds numbers of 500 to 3500. Steady-state solutions for the entire laminar regime are computed and discussed, and it is shown that the velocity profile in the channel is inflexional inside the riblet valleys. The results for a representative Reynolds number Re = 3500 show that, similar to the laminar solutions, the turbulent mean velocity profile is inflexional in the riblet valleys. However, unlike the case of the laminar regime, where no drag reduction exists, the transitional and turbulent regimes exhibit drag reduction (of about 6 percent at Re = 3500) for the riblet-mounted wall in comparison with the smooth wall of the channel. The accuracy of computations is demonstrated by comparing flow quantities corresponding to the smooth wall with previous experimental results with direct numerical simulation results.

Chu, Douglas C.; Karniadakis, George E.

1993-05-01

314

A Finite-Volume ADI Method for Simulation of Incompressible Flows on Curvilinear Grids  

NASA Astrophysics Data System (ADS)

A second-order accurate finite-volume-based alternating direction implicit (ADI) method is proposed for the solution of incompressible Navier-Stokes equations on structured curvilinear meshes. Numerical accuracy and stability at high Reynolds numbers are achieved with the selection of the discrete operators and solution algorithms which assure discrete kinetic energy conservation in the inviscid limit. Unlike the conventional finite-difference-based ADI schemes, in which the factorization is performed along the transformed generalized-coordinate directions, in the proposed method, the discretized equations are factored along the curvilinear mesh lines without coordinate transformation. The accuracy, stability, and efficiency of the proposed method are assessed in simulations of an unsteady convection-diffusion equation on Cartesian and skewed meshes, and simulations of lid- driven cavity flow, flow over a circular cylinder, and turbulent channel flow. In the proposed method, the computational cost required for the solution of momentum equations is found to be 3 to 5 times smaller than that required when a bi-conjugate gradient stabilized (BCGSTAB) iterative method is employed.

Singh, Satbir; You, Donghyun

2010-11-01

315

Numerical methods for 3-D viscous incompressible flows using velocity/vorticity formulation  

NASA Astrophysics Data System (ADS)

Incompressible Navier-Stokes equations formulated in terms of velocity and vorticity are solved, using finite differences on regular, staggered grids. Both sequential (or segregated) as well as block implicit techniques are used to simulate three-dimensional viscous flows. In the first techniqaue, Poisson's equations for the velocity components are solved separately using a direct inversion procedure while the vorticity transport equations are solved iteratively using a zebra line relaxation. The method is applied to a three-dimensional cavity flow and the solution is in good agreement with results available in literature. The second technique is a generalization of the Alternating Direction Implicit (ADI) method. Approximate factorization of the equations, written in a delta form, requires solutions of two-dimensional like problems in alternating planes. It is shown that this technique is most suitable, particularly if the vorticity equations are written in conservation form. This method can be applied to time dependent problems with second-order accuracy in time and space. No intermediate boundary conditions for the present formulation are required. Preliminary results of a test problem of a three-dimensional flow over a backward facing step are presented.

Dacles, J.; Hafez, M.

1990-01-01

316

Stabilized finite element method for incompressible flows with high Reynolds number  

NASA Astrophysics Data System (ADS)

In the following paper, we discuss the exhaustive use and implementation of stabilization finite element methods for the resolution of the 3D time-dependent incompressible Navier-Stokes equations. The proposed method starts by the use of a finite element variational multiscale (VMS) method, which consists in here of a decomposition for both the velocity and the pressure fields into coarse/resolved scales and fine/unresolved scales. This choice of decomposition is shown to be favorable for simulating flows at high Reynolds number. We explore the behaviour and accuracy of the proposed approximation on three test cases. First, the lid-driven square cavity at Reynolds number up to 50,000 is compared with the highly resolved numerical simulations and second, the lid-driven cubic cavity up to Re = 12,000 is compared with the experimental data. Finally, we study the flow over a 2D backward-facing step at Re = 42,000. Results show that the present implementation is able to exhibit good stability and accuracy properties for high Reynolds number flows with unstructured meshes.

Hachem, E.; Rivaux, B.; Kloczko, T.; Digonnet, H.; Coupez, T.

2010-11-01

317

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 Babuška-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

318

A comparative study of GLS finite elements with velocity and pressure equally interpolated for solving incompressible viscous flows  

Microsoft Academic Search

SUMMARY A comparative study of the bi-linear and bi-quadratic quadrilateral elements and the quadratic triangular element for solving incompressible viscous flows is presented. These elements make use of the stabilized finite element formulation of the Galerkin\\/least-squares method to simulate the flows, with the pressure and velocity fields interpolated with equal orders. The tangent matrices are explicitly derived and the Newton-

Yongtao Wei; Philippe H. Geubelle

2009-01-01

319

Large Data Existence Result for Unsteady Flows of Inhomogeneous Shear-Thickening Heat-Conducting Incompressible Fluids  

Microsoft Academic Search

We consider unsteady flows of inhomogeneous, incompressible, shear-thickening and heat-conducting fluids where the viscosity depends on the density, the temperature and the shear rate, and the heat conductivity depends on the temperature and the density. For any values of initial total mass and initial total energy we establish the long-time existence of weak solution to internal flows inside an arbitrary

Jens Frehse; Josef Málek; Michael R?ži?ka

2010-01-01

320

A parametric study of LES on laminar-turbulent transitional flows past an airfoil  

NASA Astrophysics Data System (ADS)

Low-Reynolds-number aerodynamic performance of small-sized air vehicles is an area of increasing interest. In this study, low-Reynolds-number flows past an SD7003 airfoil are investigated to understand important viscous features of laminar separation and transitional flow followed by the complicated behavior of the flow reattachment process. In order to satisfy the three-dimensional (3D) requirement of the code, a simple “3D wing” is constructed from a two-dimensional (2D) airfoil. A parametric study of large eddy simulation (LES) on the airfoil flows at Re=60,000 is performed. Effects of grid resolution and sub-grid scale (SGS) models are investigated. Although 3D effects cannot be accurately captured owing to the limitation of the grid resolution in the spanwise direction, the preliminary LES calculations do reveal some important flow characteristics such as leading-edge laminar separation and vortex shedding from the primary laminar separation bubble on the low-Reynolds-number airfoil.

Yuan, W.; Xu, H.; Khalid, M.; Radespiel, R.

2006-01-01

321

Laminar, Transitional, and Turbulent Flows in Rotor-Stator Cavities  

NASA Astrophysics Data System (ADS)

This article reviews the range of flows that may be created within thin cylindrical or annular cavities due to the rotation of one of the confining disks. At low Reynolds numbers, the rotation gives rise to an axisymmetric, radially outward motion near the rotor with a return flow along the stationary disk. As the Reynolds number is raised, this base flow gives way to a shear flow populated by discrete vortices, whether of cylindrical or spiral form, near both the rotating and stationary disks. At Reynolds numbers high enough for turbulent flow to occur, in the twentieth century both experimental and computational studies treated the flow as axisymmetric and steady. Recent research has shown, however, that complex organized structures also persist in the turbulent regime.

Launder, Brian; Poncet, Sébastien; Serre, Eric

2010-01-01

322

MP Salsa: a finite element computer program for reacting flow problems. Part 1--theoretical development.  

National Technical Information Service (NTIS)

The theoretical background for the finite element computer program, MPSalsa, is presented in detail. MPSalsa is designed to solve laminar, low Mach number, two- or three-dimensional incompressible and variable density reacting fluid flows on massively par...

J. N. Shadid H. K. Moffat S. A. Hutchinson G. L. Hennigan K. D. Devine

1996-01-01

323

Numerical simulations of flow in a three-dimensional cavity-channel geometry.  

National Technical Information Service (NTIS)

The computational fluid dynamics code FIDAP (Fluid Dynamics International) is used to perform simulations of the steady laminar flow of an incompressible fluid in a three-dimensional rectangular cavity. Although most previous studies have considered a ''l...

J. R. Torczynski T. J. O'Hern

1993-01-01

324

The disappearance of laminar and turbulent wakes in complex flows  

Microsoft Academic Search

The singular effects of steady large-scale external strain on the viscous wake generated by a rigid body and the overall flow field are analysed. In an accelerating flow strained at a positive rate, the vorticity field is annihilated owing to positive and negative vorticity either side of the wake centreline diffusing into one another and the volume flux in the

J. C. R. Hunt; I. Eames

2002-01-01

325

Laminar jet injection in a pipe with co-flow  

NASA Astrophysics Data System (ADS)

Particle Tracking Velocimetry (PTV) was used to investigate confined injection from a generic end-hole catheter within an axial co-flow environment. PTV was carried out in an iterative fashion where an approximate field was calculated from several time instances, and subsequently used as an estimator for hybrid tracking. The influence of momentum ratio on jet expansion, transport, and flow patterns was studied for several velocity ratios (VR = Vjet/Vout) between 0 and 10. The Reynolds number of the outer flow was 150 and that of the inner flow varied from 0 to 260. Flow patterns behind the catheter were dependent upon VR with recirculation regions present for low ratios. A separation bubble was observed behind the catheter for velocity ratios below 0.5 and two counter-rotating vortices were seen for VR = 0. As VR increased, asymmetry in the outer flow resulted in a single vortex behind the catheter with its position skewed toward the low flow side of the vessel and larger entrainment was present on the high flow side of the vessel. As VR increased above 0.5, recirculation was not observed and at VR = 1.0 the jet velocities were mainly in the streamwise direction.

Schmieg, Jaime; Stremler, Mark; Vlachos, Pavlos

2011-11-01

326

The efficiency of alternative pressure-correction formulations for incompressible turbulent flow problems  

NASA Astrophysics Data System (ADS)

Two test cases, one two-dimensional and one three-dimensional, were considered to highlight the convergence characteristics and assess the computational efficiency, of three alternative formulations for the pressure-velocity coupling (viz. SIMPLE, PISO, and AVPI) in the calculation of incompressible turbulent flows. The results from these test cases showed that the use of the more elaborate pressure-velocity algorithm (PISO), requiring more than one pressure-correction equation, did lead to a reduction of the computing time by about 30 percent after careful optimization of the numerical parameters. This relatively small reduction occurred, however, at the expense of an increased memory requirement and the present test cases did not therefore lend strong support to the use of such algorithms. In addition, our results also showed that, in the calculation of at least some turbulent flows, the overall rate of convergence is dominated by the convergence of the turbulence model equations and the influence of the pressure-correction formulation is not significant.

McGuirk, J. J.; Palma, J. M. L. M.

1993-01-01

327

HyPAM: A hybrid continuum-particle model for incompressible free-surface flows  

NASA Astrophysics Data System (ADS)

Three major issues associated with numerical simulations of complex free-surface flows, viz. interface tracking, fragmentation and large physical jumps, are addressed by a new hybrid continuum-particle model (HyPAM). The new model consists of three parts: (1) the Polygonal Area Mapping method [Q. Zhang, P.L.-F. Liu, A new interface tracking method: the polygonal area mapping method, J. Comput. Phys. 227(8) (2008) 4063-4088]; (2) a new algorithm that decomposes the interested (water) phase into a continuum zone, a buffer zone and a particle zone, based on material topology and graph theory; (3) a ‘passive-response’ assumption, in which the air phase is assumed to respond passively to the continuum part of the water phase. The incompressible inviscid Euler equations and the equations describing the free fall of rigid bodies are used as the governing equations for the continuum-buffer zone and the particle zone, respectively, and separately. A number of examples, including water droplet impact, solitary wave propagation, and dam-break problems, are simulated for the illustration and validation of HyPAM. It is shown that HyPAM is more accurate and versatile than a continuum-based Volume-of-Fluid model. One major contribution of this work is the single-phase decomposition algorithm, useful for many other hybrid formulations. Neglecting surface tension, viscosity and particle interactions, HyPAM is currently limited to mildly-fragmented free-surface flows with high Reynolds and Weber numbers.

Zhang, Qinghai; Liu, Philip L.-F.

2009-03-01

328

Entropically damped form of artificial compressibility for explicit simulation of incompressible flow  

NASA Astrophysics Data System (ADS)

An alternative artificial compressibility (AC) scheme is proposed to allow the explicit simulation of the incompressible Navier-Stokes (INS) equations. Traditional AC schemes rely on an artificial equation of state that gives the pressure as a function of the density, which is known to enforce isentropic behavior. This behavior is nonideal, especially in viscously dominated flows. An alternative, the entropically damped artificial compressibility (EDAC) method, is proposed that employs a thermodynamic constraint to damp the pressure oscillations inherent to AC methods. The EDAC method converges to the INS in the low-Mach limit, and is consistent in both the low- and high-Reynolds-number limits, unlike standard AC schemes. The proposed EDAC method is discretized using a simple finite-difference scheme and is compared with traditional AC schemes as well as the lattice-Boltzmann method for steady lid-driven cavity flow and a transient traveling-wave problem. The EDAC method is shown to be beneficial in damping pressure and velocity-divergence oscillations when performing transient simulations. The EDAC method follows a similar derivation to the kinetically reduced local Navier-Stokes (KRLNS) method [Borok , Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.76.066704 76, 066704 (2007)]; however, the EDAC method does not rely on the grand potential as the thermodynamic variable, but instead uses the more common pressure-velocity system. Additionally, a term neglected in the KRLNS is identified that is important for accurately approximating the INS equations.

Clausen, Jonathan R.

2013-01-01

329

Entropically damped form of artificial compressibility for explicit simulation of incompressible flow.  

PubMed

An alternative artificial compressibility (AC) scheme is proposed to allow the explicit simulation of the incompressible Navier-Stokes (INS) equations. Traditional AC schemes rely on an artificial equation of state that gives the pressure as a function of the density, which is known to enforce isentropic behavior. This behavior is nonideal, especially in viscously dominated flows. An alternative, the entropically damped artificial compressibility (EDAC) method, is proposed that employs a thermodynamic constraint to damp the pressure oscillations inherent to AC methods. The EDAC method converges to the INS in the low-Mach limit, and is consistent in both the low- and high-Reynolds-number limits, unlike standard AC schemes. The proposed EDAC method is discretized using a simple finite-difference scheme and is compared with traditional AC schemes as well as the lattice-Boltzmann method for steady lid-driven cavity flow and a transient traveling-wave problem. The EDAC method is shown to be beneficial in damping pressure and velocity-divergence oscillations when performing transient simulations. The EDAC method follows a similar derivation to the kinetically reduced local Navier-Stokes (KRLNS) method [Borok et al., Phys. Rev. E 76, 066704 (2007)]; however, the EDAC method does not rely on the grand potential as the thermodynamic variable, but instead uses the more common pressure-velocity system. Additionally, a term neglected in the KRLNS is identified that is important for accurately approximating the INS equations. PMID:23410462

Clausen, Jonathan R

2013-01-28

330

A numerical investigation of viscous, incompressible flow past an axisymmetric body with and without spin  

NASA Astrophysics Data System (ADS)

This study deals with a preliminary investigation of the effects of spin on the axisymmetric flow past a body of revolution. The study has its genesis larger problem of Magnus forces on spinning bodies at angle of attack. However, the fundamental behavior that arises when a spinning body is placed in a uniform stream is still not well understood; therefore, the problem of axisymmetric flow with spin was undertaken. The body consists of a 3-caliber cant-ogive blunted by a spherical nosecap, a 2-caliber cylindrical section, and a 1-caliber boattail. Numerical solutions of the compressible laminar Navier-Stokes equations are obtained using a modified version of the implicit-explicit method developed by MacCormack in 1981. The benchmark problem is the nonspinning body in uniform flow at a Reynolds number of 1.14. The results show that the modified method performs well and allows time steps that are in order of magnitude greater than those permitted by explicit stability criteria.

Weber, K. F.

1985-12-01

331

Three-dimensional linear stability analysis of incompressible viscous flows using the finite element method  

NASA Astrophysics Data System (ADS)

The linear stability of incompressible flows is investigated on the basis of the finite element method. The two-dimensional base flows computed numerically over a range of Reynolds numbers are perturbed with three-dimensional disturbances. The three-dimensionality in the flow associated with the secondary instability is identified precisely. First, by using linear stability theory and normal mode analysis, the partial differential equations governing the evolution of perturbation are derived from the linearized Navier-Stokes equation with slight compressibility. In terms of the mixed finite element discretization, in which six-node quadratic Lagrange triangular elements with quadratic interpolation for velocities (P2) and three-node linear Lagrange triangular elements for pressure (P1) are employed, a non-singular generalized eigenproblem is formulated from these equations, whose solution gives the dispersion relation between complex growth rate and wave number. Then, the stabilities of two cases, i.e. the lid-driven cavity flow and flow past a circular cylinder, are examined. These studies determine accurately stability curves to identify the critical Reynolds number and the critical wavelength of the neutral mode by means of the Krylov subspace method and discuss the mechanism of instability. For the cavity flow, the estimated critical results are Rec=920.277+/-0.010 for the Reynolds number and kc=7.40+/-0.02 for the wave number. These results are in good agreement with the observation of Aidun et al. and are more accurate than those by the finite difference method. This instability in the cavity is associated with absolute instability [Huerre and Monkewitz, Annu. Rev. Fluid Mech., 22, 473-537 (1990)]. The Taylor-Göertler-like vortices in the cavity are verified by means of the reconstruction of three-dimensional flows. As for the flow past a circular cylinder, the primary instability result shows that the flow has only two-dimensional characteristics at the onset of the von Kármán vortex street, when Re<49. The estimated critical values of primary instability are Rec=46.389+/-0.010 and Stc=0.126 for the Strouhal number. These values are very close to the observation data [Williamson, J. Fluid Mech., 206, 579-627 (1989)] and other stability results [Morzynski and Thiele, Z. Agnew. Math. Mech., 71, T424-T428 (1991); Jackson, J. Fluid Mech., 182, 23-45 (1987)]. This onset of vortex shedding is associated with the symmetry-breaking bifurcation at the Hopf point. Copyright

Ding, Yan; Kawahara, Mutsuto

1999-09-01

332

Supersonic Laminar-Turbulent Gas Flow Past a Circular Cylinder  

Microsoft Academic Search

The flow past a circular cylinder with an isothermal surface at Mach numbers M8=2 and 5 and Reynolds numbers ranging from 104 to 108 is investigated on the basis of the Reynolds equations using a differential two-equation turbulence model. The effect of flow turbulization on the separation point displacement, the separation zone length, the maximum velocity reduction in the separation

V. A. Bashkin; I. V. Egorov; M. V. Egorova; D. V. Ivanov

2000-01-01

333

Influence of Flow and Rotational Oscillations on the Mechanics of Two-Dimensional Laminar Boundary-Layer Flow past Cylinders, Including Uniform Suction or Blowing.  

National Technical Information Service (NTIS)

A theoretical investigation of the influence of flow oscillation, fluctuating circulation and rotational oscillation upon the transfer of momentum, heat and mass in two-dimensional laminar boundary-layer flow past cylinders with or without uniform suction...

W. J. Yang J. A. Clark

1965-01-01

334

A high-order immersed boundary method for unsteady incompressible flow calculations  

NASA Astrophysics Data System (ADS)

A high-order immersed boundary method (IBM) for the computation of unsteady, incompressible fluid flows on two-dimensional, complex domains is proposed, analyzed, developed and validated. In the IBM, the equations of interest are discretized on a fixed Cartesian grid. As a result, domain boundaries do not always conform to the (rectangular) computational domain boundaries. This gives rise to 'immersed boundaries', i.e., boundaries immersed inside the computational domain. A new IBM is proposed to remedy problems in an older existing IBM that had originally been selected for use in numerical flow control investigations. In particular, the older method suffered from considerably reduced accuracy near the immersed boundary surface where sharp jumps in the solution, i.e., jump discontinuities in the function and/or its derivatives, were smeared out over several grid points. To avoid this behavior, a sharp interface method, originally developed by LeVeque & Li (1994) and Wiegmann & Bube (2000) in the context of elliptic PDEs, is introduced where the numerical scheme takes such discontinuities into consideration in its design. By comparing computed solutions to jump-singular PDEs having known analytical solutions, the new IBM is shown to maintain the formal fourth-order accuracy, in both time and space, of the underlying finite-difference scheme. Further validation of the new IBM code was accomplished through its application to several two-dimensional flows, including flow past a circular cylinder, and T-S waves in a flat plate boundary layer. Comparison of results from the new IBM with results available in the literature found good agreement in all cases.

Linnick, Mark N.

335

Problems of the laminar-turbulent boundary layer transition - Physics and prediction  

NASA Astrophysics Data System (ADS)

The paper presents a survey of laminar-turbulent transition problems for 2D and 3D flows, both incompressible and compressible. Receptivity mechanisms and linear and nonlinear stability phenomena are considered. Attention is given to various examples of the application of the exp n method, which provides an estimate of the transition position.

Arnal, D.

336

The conjugate heat transfer from an internal heated small strip in a forced laminar flow  

Microsoft Academic Search

An asymptotic and numerical investigation was conducted for the cooling process, by a forced laminar flow, of a small strip\\u000a with a non-uniform heat source. The nondimensional temperature distribution in the strip has been obtained as a function of\\u000a the following parameters: (a) the intensity and distribution of the internal heat sources, (b) the aspect ratio of the strip,\\u000a (c)

O. Bautista; F. Méndez; C. Treviño

2001-01-01

337

Determination of Kinetic Parameters in Laminar Flow Reactors. II. Experimental Aspects  

Microsoft Academic Search

In the present contribution laser spectroscopic studies are described in which the chemical kinetics of benchmark elementary\\u000a reaction steps in different laminar flow reactors were experimentally investigated along with detailed numerical modeling\\u000a calculations (see the article Carraro\\/Heuveline\\/Rannacher [5] in this vol-ume). Coherent anti-Stokes Raman spectroscopy (CARS) was utilized to study the collisional relaxation and vibrational\\u000a energy transfer of vibrationally excited

A. Hanf; H.-R. Volpp; J. Wolfrum

338

Single-walled carbon nanotube synthesis using ferrocene and iron pentacarbonyl in a laminar flow reactor  

Microsoft Academic Search

A gas-phase process of single-walled carbon nanotube (SWCNT) formation, based on thermal decomposition of iron pentacarbonyl or ferrocene in the presence of carbon monoxide (CO), was investigated in ambient pressure laminar flow reactors in the temperature range of 600–1300°C. Ferrocene was found to be a better catalyst precursor in the studied conditions since iron pentacarbonyl decomposes at lower temperatures resulting

Anna Moisala; Albert G. Nasibulin; David P. Brown; Hua Jiang; Leonid Khriachtchev; Esko I. Kauppinen

2006-01-01

339

Unsteady thermal entrance heat transfer in laminar pipe flows with step change in ambient temperature  

Microsoft Academic Search

A fully implicit upwind finite difference numerical scheme has been proposed to investigate the characteristics of thermal\\u000a entrance heat transfer in laminar pipe flows subject to a step change in ambient temperature. In order to demonstrate the\\u000a results more clearly, a modified Nusselt number is introduced. The unsteady axial variations of modified Nusselt number, bulk\\u000a fluid temperature, and wall temperature

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

1983-01-01

340

Heat transfer properties of nanoparticle-in-fluid dispersions (nanofluids) in laminar flow  

Microsoft Academic Search

The convective heat transfer coefficients of several nanoparticle-in-liquid dispersions (nanofluids) have been measured under laminar flow in a horizontal tube heat exchanger. The nanoparticles used in this research were graphitic in nature, with aspect ratios significantly different from one (l\\/d?0.02). The graphite nanoparticles increased the static thermal conductivities of the fluid significantly at low weight fraction loadings. However, the experimental

Ying Yang; Z. George Zhang; Eric A. Grulke; William B. Anderson; Gefei Wu

2005-01-01

341

Finite volume simulation of viscoelastic laminar flow in a lid-driven cavity  

Microsoft Academic Search

A finite volume technique is presented for the numerical solution of steady laminar flow of Oldroyd-B fluid in a lid-driven square cavity over a wide range of Reynolds and Weissenberg numbers. Second order central difference (CD) scheme is used for the convection part of the momentum equation while first order upwind approximation is employed to handle viscoelastic stresses. A non-uniform

Kerim Yapici; Bulent Karasozen; Yusuf Uludag

2009-01-01

342

Transient study of buoyancy-assisted mixed convection in laminar plane wall jet flow  

Microsoft Academic Search

A numerical investigation of two-dimensional transient buoyancy-assisted laminar plane wall jet flow has been conducted. The governing equations in the stream function-vorticity formulation have been solved by alternating direction implicit (ADI) method. The parameters used are Grashof number 104?107, Prandtl number 0.01, 0.71, 7.1, 10.0 and 15.0 with a constant Reynolds number 400. The plate is considered at a higher

K. Kumar Raja; Manab Kumar Das; P. Rajesh Kanna

2007-01-01

343

Laminar flow heat transfer in pipes including two-dimensional wall and fluid axial conduction  

Microsoft Academic Search

An analysis is made for a conjugate heat transfer problem with thermally developing laminar pipe flow, involving two-dimensional wall and axial fluid conduction. The problem is solved numerically by a finite-difference method for a thick walled, two-regional pipe which has constant outside surface temperatures interfaced by a step change. An exact profile is used to discretize the differential equation in

?ef?k B?l?r

1995-01-01

344

A numerical investigation of laminar and turbulent flow past a cube  

SciTech Connect

Laminar and turbulent flow past a cube is investigated numerically. A vorticity-vector potential approach is used as the basis for a computational algorithm in which semi-implicit finite difference equations are solved iteratively by a vectorizable 8 color SOR algorithm. The calculations are performed on a CRAY X-MP/48 Supercomputers. The laminar calculations are done at a range of Reynolds numbers from 10 to 100. The predicted drag appear to be in good agreement with relevant data including that from a cube drop experiment performed specifically for the present study. An analysis of the flow structure is made which shows it to be in qualitative agreement with similar flows. The turbulent flow calculations are done at Reynolds numbers of 2,000, 14,000 and 170,000 using the Mean Vorticity and Covariance (MVC) closure. The turbulent flow field is computed down to the solid surface without the use of wall functions. The calculated drag is in good agreement with experimental results. A study of the three-dimensional flow structure is carried out with the help of computer graphics. The flow is observed to separate from the side surfaces of the cube. The calculated axial velocity distribution is shown to be in good agreement with that observed experimentally in similar bluff body flows.

Raul, R.

1989-01-01

345

Laminar flow in chevron-type plate heat exchangers: CFD analysis of tortuosity, shape factor and friction factor  

Microsoft Academic Search

Laminar or low Reynolds number flows are usually obtained when liquid foods with high viscosity are processed in plate heat exchangers (PHEs). The tortuosity coefficient is a key parameter used by PHEs manufacturers to estimate Fanning friction factors and convective heat transfer coefficients. Using the finite-element computational fluid dynamics program POLYFLOW®, fully developed laminar flows in double-sine chevron-type PHEs passages

Carla S. Fernandes; Ricardo P. Dias; João M. Nóbrega; João M. Maia

2007-01-01

346

User's guide for the computer code COLTS for calculating the coupled laminar and turbulent flow over a Jovian entry probe  

Microsoft Academic Search

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

A. Kumar; R. A. Graeves

1980-01-01

347

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

Microsoft Academic Search

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

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

1991-01-01

348

Use of laminar flow and unstirred layer models to predict intestinal absorption in the rat.  

PubMed Central

Carbon monoxide (CO) and [14C]warfarin were used to measure the preepithelial diffusion resistance resulting from poor luminal stirring (RL) in the constantly perfused rat jejunum at varying degrees of distension (0.05, 0.1, and 0.2 ml/cm). RL was much greater than epithelial cell resistance, indicating that poor stirring was the limiting factor in absorption and that an appropriate model of stirring should accurately predict absorption. A laminar flow model accurately predicted the absorption rate of both probes at all levels of gut distension, as well as the absorption of glucose when RL was the rate-limiting factor in absorption. In contrast, an unstirred layer model would not have predicted that gut distension would have little influence on absorption, and would have underestimated [14C]warfarin absorption relative to CO. We concluded that in the perfused rat jejunum, laminar flow accurately models luminal stirring and an unstirred layer should be considered to be a unit of resistance in laminar flow, rather than a model of luminal stirring.

Levitt, M D; Kneip, J M; Levitt, D G

1988-01-01

349

O the Sampling of Suspensions in Laminar Flow.  

NASA Astrophysics Data System (ADS)

Dilute suspensions (o = 0.002) of neutrally buoyant, uniform diameter spheres in viscous liquids (eta = 60 mPacdots) are sampled through pores in the wall of a stirred tank. These studies are performed with the intention of investigating screening effects near the sampling orifice which cause samples to be deficient in the dispersed phase. o sbs/o _t, the ratio of sphere concentration in the sample to that of the original suspension, ranges from 0.08 to 1.12. Sample concentration decreases sampling rate, and increasing stirring rates. The objectives of this work are both to obtain experimental relationships and to develop predictive techniques relating flow fields to sample concentration. We attempt to predict o sbs by calculating particle trajectories in the region near the pore and by accounting for steric exclusion. Particle trajectories can differ from fluid streamlines on account of lift forces generated in the flow field. The technique entails numerical computation of the flow field for the fluid alone so that both the ``capture envelope'' and the flow field in the vicinity of the pore can be determined. Next, particle trajectories are determined by calculating lift velocities in the capture envelope using the mathematics recently developed by Schonberg (1989) for the lateral migration of spheres in Poiseuille flow between flat plates. These trajectory calculations permit estimation of the fraction which exit or enter the capture envelope. These estimates constitute {it a priori/} predictions since they do not rely on or introduce any empirical parameters. Predicted values of o_s agree closely with data. Studies are also conducted for sampling through tubes. The same approach as above is taken. Particle trajectories are determined by calculating the lift velocities of the solid particles using the Saffman equation for "unbounded" flow. Predicted values of sample concentration again agree closely with data.

Jones, Francis Joseph

1991-07-01

350

Validation of non-orthogonal three-dimensional laminar flow predictions  

NASA Astrophysics Data System (ADS)

Most of the flow geometries for aeronautical engineering are complex and cannot be discretized using orthogonal coordinates. In addition, some of those flows can only be described in the fully developed form of the Navier-Stokes equations. In this paper the Navier-Stokes equations are solved for three-dimensional complex geometries using a non-orthogonal, non-staggered coordinate system. The strong conservation form of the governing equations for laminar flows is discretized using a finite volume method. A numerical grid generation method is employed in order to easily generate the meshes. The flow through a square diffuser, the flow through a transforming duct of elliptical cross-section, and the flow through a square cross-section S-shaped duct were analyzed. The predictions reveal good agreement with the available data demonstrating the accuracy and generality of the present method. The present solution algorithm can easily be extended to calculate subsonic compressible flows.

Coelho, P. J.; Pereira, J. C. F.

1992-02-01

351

Additional interfacial force in lattice Boltzmann models for incompressible multiphase flows.  

PubMed

The existing lattice Boltzmann models for incompressible multiphase flows are mostly constructed with two distribution functions: one is the order parameter distribution function, which is used to track the interface between different phases, and the other is the pressure distribution function for solving the velocity field. In this paper, it is shown that in these models the recovered momentum equation is inconsistent with the target one: an additional force is included in the recovered momentum equation. The additional force has the following features. First, it is proportional to the macroscopic velocity. Second, it is zero in every single-phase region but is nonzero in the interface. Therefore it can be interpreted as an interfacial force. To investigate the effects of the additional interfacial force, numerical simulations are carried out for the problem of Rayleigh-Taylor instability, droplet splashing on a thin liquid film, and the evolution of a falling droplet under gravity. Numerical results demonstrate that, with the increase of the velocity or the Reynolds number, the additional interfacial force will gradually have an important influence on the interface and affect the numerical accuracy. PMID:22463354

Li, Q; Luo, K H; Gao, Y J; He, Y L

2012-02-16

352

Limit cycle oscillations of rectangular cantilever wings containing cubic nonlinearity in an incompressible flow  

NASA Astrophysics Data System (ADS)

Limit cycle oscillations (LCO) as well as nonlinear aeroelastic analysis of rectangular cantilever wings with a cubic nonlinearity are investigated. Aeroelastic equations of a rectangular cantilever wing with two degrees of freedom in an incompressible potential flow are presented in the time domain. The harmonic balance method is modified to calculate the LCO frequency and amplitude for rectangular wings. In order to verify the derived formulation, flutter boundaries are obtained via a linear analysis of the derived system of equations for five different cases and compared with experimental data. Satisfactory results are gained through this comparison. The problem of finding the LCO frequency and amplitude is solved via applying the two methods discussed for two different cases with hardening cubic nonlinearities. The results from first-, third- and fifth-order harmonic balance methods are compared with the results of an exact numerical solution. A close agreement is obtained between these harmonic balance methods and the exact numerical solution of the governing aeroelastic equations. Finally, the nonlinear aeroelastic analysis of a rectangular cantilever wing with a softening nonlinearity is studied.

Ghadiri, B.; Razi, M.

2007-05-01

353

A parallel second-order adaptive mesh algorithm for incompressible flow in porous media.  

PubMed

In this paper, we present a second-order accurate adaptive algorithm for solving multi-phase, incompressible flow in porous media. We assume a multi-phase 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 are advanced multiple steps to reach the same time as the coarse grids and the data at different 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 behaviour of the method. PMID:19840985

Pau, George S H; Almgren, Ann S; Bell, John B; Lijewski, Michael J

2009-11-28

354

Detached Eddy Simulations (des) of Incompressible Turbulent Flows Using the Finite Element Method  

NASA Astrophysics Data System (ADS)

An explicit Galerkin finite-element (GFEM) formulation of the Spalart-Allmaras (SA) 1-equation turbulent transport model was implemented into an incompressible GFEM code, using both a RANS formulation and a DES formulation. DES is a new technique for simulating/modeling turbulence using a hybrid RANS/LES formulation. The turbulent viscosity is constructed from an intermediate viscosity obtained from the transport equation which is spatially discretized using Q1 elements and integrated in time via forward Euler time integration. Simulations of plane channel flow were conducted to validate the implementation: SA-RANS, SA-DES and Smagorinsky. Preliminary results indicate that the modeling and grid resolution are strongly related, as expected, and that good results can be obtained on the appropriate grid. Using a RANS-grid, very good agreement was observed between the SA-RANS results and theory, namely the Log Law of the Wall (LLW), especially in the viscous sub-layer and, to a lesser extent, in the log- layer. It was observed that near the wall, the SA-DES model behaved as a RANS model, and away from the wall it was more characteristic of an LES model. (This work was performed under the auspices of the U.S. Department of Energy by Lawerence Livermore National Laboratory under Contract W-7405-ENG-48.)

Laskowski, Gregory M.; McCallen, Rose C.; Dunn, Timothy A.; Salari, Kambiz

2001-11-01

355

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

356

A convective-difference scheme using a general curvilinear coordinate grid for steady incompressible viscous flow problems  

Microsoft Academic Search

A numerical scheme for analyzing the steady two-dimensional incompressible viscous flow using a general curvilinear coordinate grid is proposed. In this scheme, the unsteady Navier-Stokes equations are solved by a convective-difference scheme using a staggered square grid in transformed space. An elliptic equation of pressure is solved by the Tchebyscheff SLOR method. The substantial derivative term in the convective-difference scheme

Yoshihisa Matsumoto; Hisaaki Daiguji

1992-01-01

357

Application of AF-preconditioned conjugate gradient-like methods to the computation of unsteady incompressible viscous flows  

Microsoft Academic Search

The preconditioned generalized conjugate residual method, a conjugate gradient-like method, has been applied to the finite difference solution of the unsteady incompressible Navier-Stokes equations in primitive variables. The preconditioner is based on a pseudo-compressible formulation using either incomplete upper\\/lower decomposition or Beam-Warming approximate-factorization. The resulting set of schemes has been successfully tested on the time-dependent flow inside a square cavity

Jack Strigberger; Wagdi G. Habashi

1991-01-01

358

Numerical investigation on a new local preconditioning method for solving the incompressible inviscid, non-cavitating and cavitating flows  

Microsoft Academic Search

A locally power-law preconditioning algorithm is developed. This is applied to compute incompressible inviscid, steady-state, non-cavitating and cavitating flows. The preconditioning parameters are adapted automatically from the pressure of computational domain. This method suggests better convergence rates rather than the standard artificial compressibility and the standard preconditioning method. Single-fluid Euler equations, cast in their conservative form, along with the barotropic

Vahid Esfahanian; Pooria Akbarzadeh

2010-01-01

359

An interface-capturing method for incompressible two-phase flows. Validation and application to bubble dynamics  

Microsoft Academic Search

We report on the development and applications of an interface-capturing method aimed at computing three-dimensional incompressible two-phase flows involving high density and viscosity ratios, together with capillary effects. The numerical approach borrows some features to the Volume of Fluid method (since it is essentially based on the transport of the local volume fraction of the liquid) as well as to

Thomas Bonometti; Jacques Magnaudet

2007-01-01

360

A unified incompressible lattice BGK model and its application to three-dimensional lid-driven cavity flow  

Microsoft Academic Search

A unified lattice Bhatnagar-Gross-Krook (ILBGK) model iDdQq for the incompressible Navier-Stokes equation is presented. To test its efficiency, the lid-driven cavity flow in three-dimensional space for Reynolds number Re=3200 and span aspect ratio SAR=1, 2 and 3 is simulated in detail on a 48×48×(48×SAR) uniform lattice using the model. The test results agree well with those in previous experiments and

Nan-Zhong He; Neng-Chao Wang; Bao-Chang Shi; Zhao-Li Guo

2004-01-01

361

A high-order characteristics upwind FV method for incompressible flow and heat transfer simulation on unstructured grids  

Microsoft Academic Search

This paper presents a new unstructured-grid upwind finite-volume algorithm for accurate numerical simulation of incompressible flows and convection heat transfer on unstructured grids. It is an upwind method at both the differential equation level and discretized equation level, based on the method of characteristics. This is made possible with the introduction of Chorin's (J. Comput. Phys. 2 (1967) 12–26), artificial

Yong Zhao; Baili Zhang

2000-01-01

362

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.

363

Numerical Simulation of Unsteady Incompressible Viscous Flows in Generalized Coordinate Systems.  

National Technical Information Service (NTIS)

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...

M. Rosenfeld D. Kwak

1988-01-01

364

NACHOS: A Finite Element Computer Program for Incompressible Flow Problems. Part II. User's Manual.  

National Technical Information Service (NTIS)

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 trea...

D. K. Gartling

1977-01-01

365

Numerical study of three-dimensional laminar and turbulent flows with system rotation  

NASA Astrophysics Data System (ADS)

The spatial marching analysis is given for economical computation of three-dimensional viscous subsonic flows in rotating geometries. The governing equations are based on a small scalar potential approximation for the vector decomposed secondary flow velocity. No approximation is needed for the streamwise pressure gradient term and this allows strong viscous secondary flows, coordinate curvature and system rotation effects to influence these pressure gradients. This approach is applied to three-dimensional laminar and turbulent flows in rotating 90 degree bends and in rotating straight pipes and ducts. The predicted structure of these flows is consistent with experimental observations and measurements. Computer solutions obtained using 500,000 grid points require only about 15 minutes of CRAY-1S run time. This approach appears promising for further development and application to centrifugal impeller and other turbomachinery flows.

Briley, W. R.; Govindan, T. R.; Levy, R.; McDonald, H.

1986-12-01

366

On the growth of laminar-turbulent patterns in plane Couette flow  

NASA Astrophysics Data System (ADS)

The growth of laminar-turbulent band patterns in plane Couette flow is studied in the vicinity of the global stability threshold Reg below which laminar flow ultimately prevails. Appropriately tailored direct numerical simulations are performed to manage systems extended enough to accommodate several bands. The initial state or germ is an oblique turbulent patch of limited extent. The growth is seen to result from several competing processes: (i) nucleation of turbulent patches close to or at the extremities of already formed band segments, with the same obliquity as the germ or the opposite one, and (ii) turbulence collapse similar to gap formation for band decay. Growth into a labyrinthine pattern is observed as soon as spanwise expansion is effective. An ideally aligned pattern is usually obtained at the end of a long and gradual regularization stage when Re is large enough. Stable isolated bands can be observed slightly above Reg. When growth rates are not large enough, the germ decays at the end of a long transient, similarly to what was observed in experiments. Local continuous growth/decay microscopic mechanisms are seen to compete with large deviations which are the cause of mesoscopic nucleation events (turbulent patches or laminar gaps) controlling the macroscopic behaviour of the system (pattern). The implications of these findings are discussed in the light of Pomeau's proposals based on directed percolation and first-order phase transitions in statistical physics.

Manneville, Paul

2012-06-01

367

Improved laminar predictions using a stabilised time-dependent simple scheme  

NASA Astrophysics Data System (ADS)

A new scheme which can solve unsteady incompressible flows is described in this paper. The scheme is a variant of the SIMPLE methodology. Typically, a scheme of this type tends to suffer from stability problems, which this new scheme overcomes by taking small intermediate steps within a time step. The calculations made in the intermediate steps are damped to enhance the stability of the scheme. The new stabilised scheme is evaluated for laminar flow around a square cylinder, impulsively started laminar flow over a backward-facing step and fluctuating laminar flow over a backward-facing step. Comparisons are made with other numerical predictions and experimental data. In general, good agreement is found, except for the fluctuating laminar flow over a backward-facing step problem. The new scheme is found to have the same level of accuracy, stability and efficiency in comparison with the PISO scheme, but it is easier to code.

Barton, I. E.

1998-10-01

368

Shear stress related blood damage in laminar couette flow.  

PubMed

Artificial organs within the blood stream are generally associated with flow-induced blood damage, particularly hemolysis of red blood cells. These damaging effects are known to be dependent on shear forces and exposure times. The determination of a correlation between these flow-dependent properties and actual hemolysis is the subject of this study. For this purpose, a Couette device has been developed. A fluid seal based on fluorocarbon is used to separate blood from secondary external damage effects. The shear rate within the gap is controlled by the rotational speed of the inner cylinder, and the exposure time by the amount of blood that is axially pumped through the device per given time. Blood damage is quantified by the index of hemolysis (IH), which is calculated from photometric plasma hemoglobin measurements. Experiments are conducted at exposure times from texp=25 - 1250 ms and shear rates ranging from tau=30 up to 450 Pa ensuring Taylor-vortex free flow characteristics. Blood damage is remarkably low over a broad range of shear rates and exposure times. However, a significant increase in blood damage can be observed for shear stresses of tau>or= 425 Pa and exposure times of texp>or= 620 ms. Maximum hemolysis within the investigated range is IH=3.5%. The results indicate generally lower blood damage than reported in earlier studies with comparable devices, and the measurements clearly indicate a rather abrupt (i.e., critical levels of shear stresses and exposure times) than gradual increase in hemolysis, at least for the investigated range of shear rates and exposure times. PMID:12780506

Paul, Reinhard; Apel, Jörn; Klaus, Sebastian; Schügner, Frank; Schwindke, Peter; Reul, Helmut

2003-06-01

369

Laminar flame and acoustic waves in two-dimensional flow  

SciTech Connect

The complete system of fluid dynamics equations describing the development of instability of a reaction front in a two-dimensional flow in reversed time are reduced to a closed system of equations of front dynamics by using Lagrangian variables and integrals of motion. The system can be used to analyze processes behind the front without solving the complete system of fluid dynamics and chemical kinetics equations. It is demonstrated how the gas density disturbances induced by the moving front can be described in the adiabatic approximation.

Zaytsev, M. L., E-mail: mlzaytsev@gmail.com; Akkerman, V. B., E-mail: slava.akkerman@gmail.com [Russian Academy of Sciences, Nuclear Safety Institute (Russian Federation)

2011-03-15

370

Pattern of reaction diffusion fronts in laminar flows.  

PubMed

Autocatalytic reaction between reacted and unreacted species may propagate as solitary waves, namely, at a constant front velocity and with a stationary concentration profile, resulting from a balance between molecular diffusion and chemical reaction. The effect of advective flow on the autocatalytic reaction between iodate and arsenous acid in cylindrical tubes and Hele-Shaw cells is analyzed experimentally and numerically using lattice Bhatnagar-Gross-Krook simulations. We do observe the existence of solitary waves with concentration profiles exhibiting a cusp and we delineate the eikonal and mixing regimes recently predicted. PMID:12688909

Leconte, M; Martin, J; Rakotomalala, N; Salin, D

2003-03-27

371

Hysteretic transition from laminar to vortex shedding flow in soap films  

NASA Astrophysics Data System (ADS)

There are different ways for fluid flow to become turbulent, but usually many instabilities take place before that. Among these instabilities the transition from laminar flow to vortex shedding carries significant practical importance. Here we study a flow, where at high enough flow rates, vortices are generated by a fixed obstacle (cylinder), which penetrates a flowing soap film. We present experimental results that demonstrate that the transition from laminar flow to a periodic von Karman vortex street can be hysteretic, i.e. vortices can survive at velocities lower than the velocity needed to generate themrelated paper. This is an unexpected result since 3D experiments are well described by the Hopf equation, which is incompatible with hysteresis. Beyond that, our data cannot be satisfactorily fitted by the generic model of hysteresis, i.e. the 5th order Landau equation. Evidences are presented that wetting properties of the rod, mechanical instabilities (i.e. vibrations) of the setup, and the effect of the surrounding air are not the cause of the hysteresis. To describe our experimental findings a phenomenological model ("imperfect Hopf bifurcation") will be presented.

Horváth, Viktor; Cressman, Rob; Goldburg, Walter; Wu, Xiao-Lun

1999-11-01

372

MASS TRANSFER TO ROTATING DISKS AND ROTATING RINGS IN LAMINAR, TRANSITION, AND FULLY DEVELOPED TURBULENT FLOW  

SciTech Connect

Experimental data and theoretical calculations are presented for the mass-transfer rate to rotating disks and rotating rings when laminar, transition, and fully developed turbulent flow exist upon different portions of the surface. Good agreement of data and the model is obtained for rotating disks and relatively thick rotating rings. Results of the calculations for thin rings generally exceed the experimental data measured in transition and turbulent flow. A y{sup +{sup 3}} form for the eddy diffusivity is used to fit the data. No improvement is noticed with a form involving both y{sup +{sup 3}} and y{sup +{sup 3}}.

Law Jr., C.G.; Pierini, P.; Newman, J.

1980-07-01

373

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

374

A Numerical Investigation of Controllably Flexible Hydrofoil in Laminar Flows  

NASA Astrophysics Data System (ADS)

Aquatic animals, such as fishes, whales, seals and penguins, are naturally born to be flexible and deformable, which promise their effective locomotion through water. They are able to produce hydrodynamic thrust by active control of their body configurations. That is, the aquatic animals could wiggle their flexible bodies at an appropriate frequency and amplitude suitable to the hydrodynamics surrounding them. However, the mechanism for the active controls has not been adequately understood yet and attracts current research. One obstacle which hinders such investigation is the difficulty in experimental measurements of the flows around the wiggling bodies, and thus numerical simulation is becoming an indispensable alternative. In the paper, an immersed boundary method is developed to simulate the NACA 65-10 hydrofoil. It is observed that a wiggling hydrofoil exhibits a higher thrust while a stationary hydrofoil offers little improvement.

He, G. Y.; Zhang, X.; Zhang, S. G.; He, G. W.

375

Distinct large-scale turbulent-laminar states in transitional pipe flow  

PubMed Central

When fluid flows through a channel, pipe, or duct, there are two basic forms of motion: smooth laminar motion and complex turbulent motion. The discontinuous transition between these states is a fundamental problem that has been studied for more than 100 yr. What has received far less attention is the large-scale nature of the turbulent flows near transition once they are established. We have carried out extensive numerical computations in pipes of variable lengths up to 125 diameters to investigate the nature of transitional turbulence in pipe flow. We show the existence of three fundamentally different turbulent states separated by two distinct Reynolds numbers. Below Re 1 ? 2,300, turbulence takes the form of familiar equilibrium (or longtime transient) puffs that are spatially localized and keep their size independent of pipe length. At Re 1 the flow makes a striking transition to a spatio-temporally intermittent flow that fills the pipe. Irregular alternation of turbulent and laminar regions is inherent and does not result from random disturbances. The fraction of turbulence increases with Re until Re 2 ? 2,600 where there is a continuous transition to a state of uniform turbulence along the pipe. We relate these observations to directed percolation and argue that Re 1 marks the onset of infinite-lifetime turbulence.

Moxey, David; Barkley, Dwight

2010-01-01

376

Distinct large-scale turbulent-laminar states in transitional pipe flow.  

PubMed

When fluid flows through a channel, pipe, or duct, there are two basic forms of motion: smooth laminar motion and complex turbulent motion. The discontinuous transition between these states is a fundamental problem that has been studied for more than 100 yr. What has received far less attention is the large-scale nature of the turbulent flows near transition once they are established. We have carried out extensive numerical computations in pipes of variable lengths up to 125 diameters to investigate the nature of transitional turbulence in pipe flow. We show the existence of three fundamentally different turbulent states separated by two distinct Reynolds numbers. Below Re (1) approximately equal 2,300, turbulence takes the form of familiar equilibrium (or longtime transient) puffs that are spatially localized and keep their size independent of pipe length. At Re (1) the flow makes a striking transition to a spatio-temporally intermittent flow that fills the pipe. Irregular alternation of turbulent and laminar regions is inherent and does not result from random disturbances. The fraction of turbulence increases with Re until Re (2) approximately equal 2,600 where there is a continuous transition to a state of uniform turbulence along the pipe. We relate these observations to directed percolation and argue that Re (1) marks the onset of infinite-lifetime turbulence. PMID:20404193

Moxey, David; Barkley, Dwight

2010-04-19

377

Experiments on densely-loaded non-Newtonian slurries in laminar and turbulent pipe flows  

NASA Astrophysics Data System (ADS)

An experimental description of the flow structure of non-Newtonian slurries in the laminar, transitional, and fully-developed turbulent pipe flow regimes was the primary objective of this research. Experiments were conducted in a large-scale pipe slurry flow facility with an inside diameter of 51 mm (2 inches). Approximately, 550 liters (145 gal) of slurry were necessary in the operation of the loop. Detailed velocity profile measurements by a two-color, two-component laser Doppler anemometer (LDA) were accomplished in a transparent test section with an optically transparent slurry. These velocity measurements were apparently the first ever reported for a non-Newtonian slurry with a yield value. The transparent slurry was formulated for these experiments from silica with a particle size of one to two microns, mineral oil, and Stoddard solvent. From linear regression analysis of concentric-cylinder viscometer data, the slurry exhibited yield-power-law behavior with a yield stress of 100 dynes/cm(sup 2), and an exponent of 0.630 for a solids concentration of 5.65 percent by weight. Good agreement was attained with rheological data derived from the pressure drop data in the flow loop under laminar flow conditions. The rheological properties of the transparent slurry were similar to many industrial slurries, including coal slurries, which have a yield value.

Park, Joel T.; Mannheimer, Richard J.; Grimley, Terrence A.; Morrow, Thomas B.

1989-06-01

378

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

379

Laminar cooling of pseudoplastic fluids flowing through cylindrical horizontal pipes  

NASA Astrophysics Data System (ADS)

We present results concerning heat transfer for pseudoplastic fluids flowing inside cylindrical tubes. The fluids are cooled by an external turbulent counterflow of water. A method is developed to evaluate the values of the local heat exchange coefficients. The variations of the associated Nusselt numbers can be approached using the dimensionless axial abscissa X(sub +) = (2z/D)/Pe. Experimentation shows that the Nusselt numbers remain slightly dependent on the difference between the inlet temperature of the pseudoplastic fluid T(sub e) and the wall temperatures T(sub w)(z). This last phenomenum, attributed to the variations of consistency K and rheological index n with temperature, can be linked to the evolutions of the axial velocity profiles, experimentally determined by laser Doppler anemometry. A very simple correlation Nu(z) = 1.15 ((3n + 1)/4n)(sup 1/3) (1 - 0.008 (T(sub e) - T(sub w)(z))) X(sub +)(sup -0.36) seem to be acceptable in our experimental range. Comparisons with numerical predictions are also proposed.

Azevedo, I.; Lebouche, M.; Devienne, R.

1995-04-01

380

Streamline upwind/Petrov-Galerkin formulations for convection dominated flows with particular emphasis on the incompressible Navier-Stokes equations  

NASA Astrophysics Data System (ADS)

A new finite element formulation for convection dominated flows is developed. The basis of the formulation is the streamline upwind concept, which provides an accurate multidimensional generalization of optimal one-dimensional upwind schemes. When implemented as a consistent Petrov-Galerkin weighted residual method, it is shown that the new formulation is not subject to the artificial diffusion criticisms associated with many classical upwind methods. The accuracy of the streamline upwind/Petrov-Galerkin formulation for the linear advection diffusion equation is demonstrated on several numerical examples. The formulation is extended to the incompressible Navier-Stokes equations. An efficient implicit pressure/explicit velocity transient algorithm is developed which accomodates several treatments of the incompressibility constraint and allows for multiple iterations within a time step. The effectiveness of the algorithm is demonstrated on the problem of vortex shedding from a circular cylinder at a Reynolds number of 100.

Brooks, A. N.; Hughes, T. J. R.

1982-09-01

381

Momentum transport and laminar friction in rough-wall duct flows  

NASA Astrophysics Data System (ADS)

A large number of experiments and numerical simulations have proved that friction factors in laminar channel flows are roughness-dependent provided that the ratios between roughness and channel height (i.e., the relative roughness) exceed some threshold values. However, it is not yet clear what are the causes that lead to this anomalous behaviour. In order to shed light into this issue, this study presents results from two-dimensional Lattice-Boltzmann simulations of laminar flows in channels with rough walls. The Reynolds number, the geometry of the roughness elements and the relative roughness were varied extensively in order to provide a comprehensive set of data. The analysis and interpretation of the data were carried out within the framework of the Spatially Averaged Navier-Stokes equations, which are ideal to investigate momentum transfer mechanisms in flows over rough walls. The results show that for most of the investigated roughness geometries, the pressure gradient driving the flow is balanced by form-drag, viscous drag, and viscous shear stress whereas form-induced stresses remain largely negligible. Furthermore, it was observed that the higher the ratio between the drag acting upon the roughness elements and the total drag, the more friction factors deviate from classical theory. On the basis of these observations, we propose a formula, which predicts the shear stress partitioning and we discuss its relevance within the context of biomedical applications.

Maggiolo, Dario; Manes, Costantino; Marion, Andrea

2013-09-01

382

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

383

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

384

The receptivity of laminar boundary layer flow to leading edge vibrations  

NASA Astrophysics Data System (ADS)

The receptivity of laminar boundary layer flow to leading edge vibrations has been studied experimentally. The experiments reported on in this paper include (1) a stable case and (2) an unstable case. These experiments identify the forcing field imposed by the vibrating leading edge and track the subsequent development of the unstable Tollmien-Schlichting waves. Detailed velocity measurements around the leading edge help in the identification of the source of such unstable boundary layer waves. The near-singular nature of the response of the fluid around the vibrating leading edge is found to be responsible for the generation of unstable boundary layer waves.

Chiu, W. K.; Norton, M. P.

1990-08-01

385

Comparative Analysis of Natural Convection Flows Simulated by both the Conservation and Incompressible Forms of the Navier-Stokes Equations in a Differentially-Heated Square Cavity  

SciTech Connect

This report illustrates a comparative study to analyze the physical differences between numerical simulations obtained with both the conservation and incompressible forms of the Navier-Stokes equations for natural convection flows in simple geometries. The purpose of this study is to quantify how the incompressible flow assumption (which is based upon constant density advection, divergence-free flow, and the Boussinesq gravitational body force approximation) differs from the conservation form (which only assumes that the fluid is a continuum) when solving flows driven by gravity acting upon density variations resulting from local temperature gradients. Driving this study is the common use of the incompressible flow assumption in fluid flow simulations for nuclear power applications in natural convection flows subjected to a high heat flux (large temperature differences). A series of simulations were conducted on two-dimensional, differentially-heated rectangular geometries and modeled with both hydrodynamic formulations. From these simulations, the selected characterization parameters of maximum Nusselt number, average Nusselt number, and normalized pressure reduction were calculated. Comparisons of these parameters were made with available benchmark solutions for air with the ideal gas assumption at both low and high heat fluxes. Additionally, we generated body force, velocity, and divergence of velocity distributions to provide a basis for further analysis. The simulations and analysis were then extended to include helium at the Very High Temperature gas-cooled Reactor (VHTR) normal operating conditions. Our results show that the consequences of incorporating the incompressible flow assumption in high heat flux situations may lead to unrepresentative results. The results question the use of the incompressible flow assumption for simulating fluid flow in an operating nuclear reactor, where large temperature variations are present. The results show that the use of the incompressible flow assumption with the Boussinesq gravitational body force approximation should be restricted to flows where the density change of a fluid particle along a pathline is negligible.

Richard C. Martineau; Ray A. Berry; Aurélia Esteve; Kurt D. Hamman; Dana A. Knoll; Ryosuke Park; William Taitano

2009-01-01

386

Dynamic bioprocessing and microfluidic transport control with smart magnetic nanoparticles in laminar-flow devices.  

PubMed

In the absence of applied forces, the transport of molecules and particulate reagents across laminar flowstreams in microfluidic devices is dominated by the diffusivities of the transported species. While the differential diffusional properties between smaller and larger diagnostic targets and reagents have been exploited for bioseparation and assay applications, there are limitations to methods that depend on these intrinsic size differences. Here a new strategy is described for exploiting the sharply reversible change in size and magnetophoretic mobility of "smart" magnetic nanoparticles (mNPs) to perform bioseparation and target isolation under continuous flow processing conditions. The isolated 5 nm mNPs do not exhibit significant magnetophoretic velocities, but do exhibit high magnetophoretic velocities when aggregated by the action of a pH-responsive polymer coating. A simple external magnet is used to magnetophorese the aggregated mNPs that have captured a diagnostic target from a lower pH laminar flowstream (pH 7.3) to a second higher pH flowstream (pH 8.4) that induces rapid mNP disaggregation. In this second dis-aggregated state and flowstream, the mNPs continue to flow past the magnet rather than being immobilized at the channel surface near the magnet. This stimuli-responsive reagent system has been shown to transfer 81% of a model protein target from an input flowstream to a second flowstream in a continuous flow H-filter device. PMID:19568666

Lai, James J; Nelson, Kjell E; Nash, Michael A; Hoffman, Allan S; Yager, Paul; Stayton, Patrick S

2009-03-16

387

A parallel second-order adaptive mesh algorithm for incompressible flow in porous media  

Microsoft Academic Search

In this paper we present a second-order accurate adaptive algorithm for solving multiphase, incompressible ow 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 uid constituents. In this setting the total velocity, dened to be the sum of

George S. H. Pau; Ann S. Almgren; John B. Bell

2009-01-01

388

A Level Set Formulation of Eulerian Interface Capturing Methods for Incompressible Fluid Flows  

Microsoft Academic Search

A level set formulation is derived for incompressible, immiscible Navier–Stokes equations separated by a free surface. The interface is identified as the zero level set of a smooth function. Eulerian finite difference methods based on this level set formulation are proposed. These methods are robust and efficient and are capable of computing interface singularities such as merging and reconnection. Numerical

Y. C. Chang; T. Y. Hou; B. Merriman; S. Osher

1996-01-01

389

Mathematical derivation of a finite volume formulation for laminar flow in complex geometries  

NASA Astrophysics Data System (ADS)

The mathematical derivation of a finite volume formulation of the Navier-Stokes equation is treated for general nonorthogonal curvilinear coordinates. The covariant velocity components are solved using this formulation, which leads to the pressure-velocity coupling becoming relatively easy to handle at the expense of a more complicated expression of the convective and diffusive fluxes. It is shown that, when using upwind differencing, the use of projected velocities gives better results than when curvature effects are included in the source term. The discretized equations are written in a form which enables the use of the tridiagonal matrix algorithm. The equations can be solved using either the SIMPLEC or PISO procedures. Two examples of laminar flows are given: (1) uniform flow using a cylindrical mesh, and (2) the flow inside a channel with a smooth expansion.

Davidson, Lars; Hedberg, Peter

1989-05-01

390

Finite analytic numerical solutions of laminar and turbulent convective heat transfer for pipe flow past a cavity  

Microsoft Academic Search

Convective heat transfer for laminar and turbulent flow in a pipe through a cylindrical chamber with a sudden expansion and contraction is solved by the finite analytic numeric method. The chamber wall temperature is isothermal and lower than the uniform temperature at the pipe inlet. To predict the turbulent flow and heat transfer, the analysis employs a turbulence model with

Y. H. Yoon

1983-01-01

391

Accelerating incompressible flow computations with a Pthreads-CUDA implementation on small-footprint multi-GPU platforms  

Microsoft Academic Search

Graphics processor units (GPU) that are originally designed for graphics rendering have emerged as massively-parallel “co-processors”\\u000a to the central processing unit (CPU). Small-footprint multi-GPU workstations with hundreds of processing elements can accelerate\\u000a compute-intensive simulation science applications substantially. In this study, we describe the implementation of an incompressible\\u000a flow Navier–Stokes solver for multi-GPU workstation platforms. A shared-memory parallel code with identical numerical

Julien C. Thibault; Inanc Senocak

392

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

393

Optical stimulation and imaging of functional brain circuitry in a segmented laminar flow chamber.  

PubMed

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 Ca(2+) depletion, we provide evidence for Ca(2+)-dependent synaptic transmission. PMID:23044655

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

2013-02-21

394

Numerical analysis of vortex cell efficiency in laminar and turbulent flows past a circular cylinder with embedded rotating bodies  

Microsoft Academic Search

The effect of flow intensification in small-sized vortex cells on the flow pattern in the near wake downstream of a cylinder\\u000a and the cylinder drag in laminar and turbulent flows is analyzed on the basis of a numerical simulation of the two-dimensional\\u000a steady-state flow past a circular cylinder with rotating cylindrical bodies built into the cylinder contour.

S. A. Isaev; Yu. S. Prigorodov; A. G. Sudakov

2000-01-01

395

Finite-difference schemes for incompressible Navier-Stokes equations in general curvilinear coordinates  

Microsoft Academic Search

Explicit and implicit time-marching finite-difference schemes for solving the steady incompressible Navier-Stokes equations are proposed. The schemes are based on the fractional step method for curvilinear coordinate grid. The derivation of the governing equations in curvilinear coordinates is presented. The accuracy of the schemes is verified by calculating the two-dimensional laminar duct flow over a backward-facing step. It is observed

T. Ikohagi; B. R. Shin

1989-01-01

396

Bacteriological evaluation of a mobile laminar cross-flow unit for surgery, under laboratory circumstances.  

PubMed

A mobile laminar cross-flow unit for surgery has been evaluated by the use of an experimental bacterial aerosol of Escherichia coli in different concentrations, generated at several different sites. A separate ventilation system, mounted underneath the table, produced an almost downward directed curtain of sterile air along both sides of the table. When the velocity of the air stream, discharged by the cross-flow unit, was adjusted at 0-50 m./sec. at 2 m. from the filter face (at the head end of the operation table), the surface of the table could be maintained free of bacterial settling even after aerosolization of heavily concentrated suspensions of 10(8) bacteria/ml. at different sites outside the enclosure and underneath the table as well. PMID:1107410

van der Waaij, D; Wiegersma, N; Dankert, J

1976-02-01

397

Flow dynamics stimulated by hairpin-like vortices in initially laminar boundary layers  

NASA Astrophysics Data System (ADS)

Time marching spatial simulations of flow events stimulated by hairpin like vortices in the near wall region of initially laminar boundary layers will be carried out. The behavioral flow characteristics and the underlying physical mechanisms will be elucidated by using three distinct but related methods of analysis. During the current reporting period, the development and improvement of the simulation and analysis tools have been completed. Simulations through the direct solution of time dependent, three dimensional, compressible Navier-Stokes equations are being initiated. The successful completion of this effort will provide more insight into the cyclic turbulence production and transport in turbulent boundary layers. A better understanding of wall turbulence may lead to techniques of turbulence management and control which can impact upon a variety of current important technical problem areas.

Liu, N. S.; Shamroth, S. J.; McDonald, H.

1987-02-01

398

Numerical Simulation of Free Surface Incompressible Liquid Flows surrounded by Compressible Gas  

Microsoft Academic Search

A numerical model for the three-dimensional simulation of liquid-gas o ws with free surfaces is presented. The incompressible Navier-Stokes equations are assumed to hold in the liquid domain. In the gas domain, the velocity is disregarded, the pressure is supposed to be constant in each connected component of the gas domain and follows the ideal gas law. The gas pressure

A. Caboussat; M. Picasso; J. Rappaz

2004-01-01

399

Incompressible Flow and Heat Transfer Computations Using a Continuous Pressure Equation and Nonstaggered Grids  

Microsoft Academic Search

A pressure-based algorithm for incompressible èows is presented. The algorithm employs a énite-volume discretization in general curvilinear coordinates on a nonstaggered mesh. This approach is derived from a é nite-element algorithm, and is here extended to the énite-volume\\/énite-difference context. The algorithm can be classiéed as a SIMPLE-like sequential method, and is validated in two classical test cases: the lid-driven cavity

G. Croce; G. Comini; W. Shyy

2000-01-01

400

Time dependent subscales in the stabilized finite element approximation of incompressible flow problems  

Microsoft Academic Search

In this paper we analyze a stabilized finite element approximation for the incompressible Navier–Stokes equations based on the subgrid-scale concept. The essential point is that we explore the properties of the discrete formulation that results allowing the subgrid-scales to depend on time. This apparently “natural” idea avoids several inconsistencies of previous formulations and also opens the door to generalizations.

Ramon Codina; Javier Principe; Oriol Guasch; Santiago Badia

2007-01-01

401

Applications of the CE/SE Scheme to Incompressible Viscous Flows in Two-Sided Lid-Driven Square Cavities  

NASA Astrophysics Data System (ADS)

The spacetime conservation element-solution element (CE/SE) method is extended to two-dimensional incompressible viscous flow in a two-sided lid-driven square cavity. Based on the SIMPLE method concept, the preconditioned dual-time scheme is introduced for unsteady computations. The CE/SE-based code is validated by simulating one-sided lid-driven cavity flows. The two-sided lid-driven square cavity problem involves several interesting characteristics being successfully predicted, including development of a pair of off-corner vortices and a free shear layer in the case of parallel wall motion, as well as the appearance of corner vortices for lower Reynolds numbers in the case of anti-parallel motion of the walls. It is found that both the Reynolds number and the direction of the moving walls affect the fluid flow in the cavity.

Yang, Duo-Xing; Zhang, De-Liang

2012-08-01

402

Laminar Approximation of Calculating Flow Rate and Wall Shear Stress Distribution in Side and Corner Regions of BN-600 Type Fuel Assembly.  

National Technical Information Service (NTIS)

Briefly presented are programs for mesh generation for the BN-600 fast reactor fuel assembly, for the calculation of laminar flow and for the processing of results. The results are given of finite element calculations of laminar flow rate distribution in ...

I. Smid

1983-01-01

403

Fast Benchtop Fabrication of Laminar Flow Chambers for Advanced Microscopy Techniques  

PubMed Central

Background Fluid handling technology is acquiring an ever more prominent place in laboratory science whether it is in simple buffer exchange systems, perfusion chambers, or advanced microfluidic devices. Many of these applications remain the providence of laboratories at large institutions with a great deal of expertise and specialized equipment. Even with the expansion of these techniques, limitations remain that frequently prevent the coupling of controlled fluid flow with other technologies, such as coupling microfluidics and high-resolution position and force measurements by optical trapping microscopy. Method Here we present a method for fabrication of multiple-input laminar flow devices that are optically clear [glass] on each face, chemically inert, reusable, inexpensive, and can be fabricated on the benchtop in approximately one hour. Further these devices are designed to allow flow regulation by a simple gravity method thus requiring no specialized equipment to drive flow. Here we use these devices to perform total internal reflection fluorescence microscopy measurements as well as position sensitive optical trapping experiments. Significance Flow chamber technology needs to be more accessible to the general scientific community. The method presented here is versatile and robust. These devices use standard slides and coverslips making them compatible with nearly all types and models of light microscopes. These devices meet the needs of groups doing advanced optical trapping experiments, but could also be adapted by nearly any lab that has a function for solution flow coupled with microscopy.

Courson, David S.; Rock, Ronald S.

2009-01-01

404

Parallel Computations of Incompressible Viscous Flow in a Lid-Driven Square Cavity and Program Performance on the NWT Computer System.  

National Technical Information Service (NTIS)

This paper reports parallel computations of incompressible viscous flow in a lid-driven square cavity on the NWT computer system. In order to obtain numerical solutions of this flow, consistent finite-difference approximations on non-staggered grids and f...

S. Hatayama

1998-01-01

405

A parametrized maximum principle preserving flux limiter for finite difference RK-WENO schemes with applications in incompressible flows  

NASA Astrophysics Data System (ADS)

In Xu (2013) [14], a class of parametrized flux limiters is developed for high order finite difference/volume essentially non-oscillatory (ENO) and Weighted ENO (WENO) schemes coupled with total variation diminishing (TVD) Runge-Kutta (RK) temporal integration for solving scalar hyperbolic conservation laws to achieve strict maximum principle preserving (MPP). In this paper, we continue along this line of research, but propose to apply the parametrized MPP flux limiter only to the final stage of any explicit RK method. Compared with the original work (Xu, 2013) [14], the proposed new approach has several advantages: First, the MPP property is preserved with high order accuracy without as much time step restriction; Second, the implementation of the parametrized flux limiters is significantly simplified. Analysis is performed to justify the maintenance of third order spatial/temporal accuracy when the MPP flux limiters are applied to third order finite difference schemes solving general nonlinear problems. We further apply the limiting procedure to the simulation of the incompressible flow: the numerical fluxes of a high order scheme are limited toward that of a first order MPP scheme which was discussed in Levy (2005) [3]. The MPP property is guaranteed, while designed high order of spatial and temporal accuracy for the incompressible flow computation is not affected via extensive numerical experiments. The efficiency and effectiveness of the proposed scheme are demonstrated via several test examples.

Xiong, Tao; Qiu, Jing-Mei; Xu, Zhengfu

2013-11-01

406

Compressible and incompressible fluids  

Microsoft Academic Search

The considered equations of compressible ideal fluid flow in appropriate nondimensional form are a hyperbolic system in four variables, related to density and fluid velocity. The Euler equations of incompressible fluid flow are a distinctly different system of four equations in four unknowns. Qualitative and quantitative properties of a specific limiting process are developed. The new results include more general

S. Klainerman; Andrew Majda

1982-01-01

407

Thermography investigations and numerical analysis of turbulent and laminar flow at light weight structures  

NASA Astrophysics Data System (ADS)

Thermography (IR) allows global visualization of temperature distribution on surfaces with high accuracy. This potential can be used for visualization of fluid mechanics effects at the intersection of laminar and turbulent flows, where temperature jumps appear due to convection and friction i.e. for the optimization in the design of airplane geometries. In civil engineering too it is the aspiration of the modern engineer of light weight structures to meet singular loads like wind peaks rather by intelligent structures and materials than by massive structures. Therefore the "Institute of Conceptual and Structural Design" of the Technical University of Berlin (TUB) is working on the development of adaptive structures, optimized geometry and intelligent microstructures on surfaces of structural elements. The paper shows the potential of modern computational fluid dynamics (CFD) in combination with thermography (IR) to optimize structures by visualization of laminar-tumultuous border layer currents. Therefore CFD simulations and IR wind tunnel experiments will be presented and discussed. For simulations and experiments - artificial and structural elements of the cable-stayed Strelasund Bridge, Germany, are used.

Arndt, Ralf; Gaulke, Alexander

2008-03-01

408

Digital Physics Simulation of Flow Around a Sphere in the Laminar and Transcritical Regimes  

NASA Astrophysics Data System (ADS)

Digital Physics is the name we have given to a new technology for simulating fluid dynamics. The technique is an extension of the particle-based Lattice Gas concept that utilizes elements of the Lattice Boltzmann Single-Time Relaxation Approximation method. Digital Physics removes the disadvantages associated with previously known lattice gas methods which permits practical application of the method. Properties include: 1) Removal of all discreteness artifacts such that the system can be shown to behave statistically like a true continuum fluid; 2) Improved Collision efficiency so that the viscosity can be as small as ? ~ 0.01 in lattice units; 3) Variable resolution grid, free of discretization artifacts; 4) Integer, instead of boolean, occupation values which significantly reduces noise and permits practical measurements of transient quantities; 5) Exact conservation of collisional invariants and non-negativity of particle occupations leads to assured stability; 6) Turbulent Boundary Layer model to allow low resolution access to flows involving large Reynolds numbers. The technique is applied to two spheres, one in the laminar regime, Re=1000, and one in the transcritical, fully-developed turbulent regime. Simulated drags agree with experimental results to within 10%. Location of boundary layer separation is demonstrated to move from pre-equator for the laminar case to post-equator for transcritical. Pressure profiles and wake structures of both are investigated, interpreted, and compared with experiments.

Teixeira, Christopher M.

1996-11-01

409

Motion of cells sedimenting on a solid surface in a laminar shear flow.  

PubMed Central

Cell adhesion often occurs under dynamic conditions, as in flowing blood. A quantitative understanding of this process requires accurate knowledge of the topographical relationships between the cell membrane and potentially adhesive surfaces. This report describes an experimental study made on both the translational and rotational velocities of leukocytes sedimenting of a flat surface under laminar shear flow. The main conclusions are as follows: (a) Cells move close to the wall with constant velocity for several tens of seconds. (b) The numerical values of translational and rotational velocities are inconsistent with Goldman's model of a neutrally buoyant sphere in a laminar shear flow, unless a drag force corresponding to contact friction between cells and the chamber floor is added. The phenomenological friction coefficient was 7.4 millinewton.s/m. (c) Using a modified Goldman's theory, the width of the gap separating cells (6 microns radius) from the chamber floor was estimated at 1.4 micron. (d) It is shown that a high value of the cell-to-substrate gap may be accounted for by the presence of cell surface protrusions of a few micrometer length, in accordance with electron microscope observations performed on the same cell population. (e) In association with previously reported data (Tissot, O., C. Foa, C. Capo, H. Brailly, M. Delaage, and P. Bongrand. 1991. Biocolloids and Biosurfaces. In press), these results are consistent with the possibility that cell-substrate attachment be initiated by the formation of a single molecular bond, which might be considered as the rate limiting step. Images FIGURE 3 FIGURE 8

Tissot, O; Pierres, A; Foa, C; Delaage, M; Bongrand, P

1992-01-01

410

Motion of cells sedimenting on a solid surface in a laminar shear flow.  

PubMed

Cell adhesion often occurs under dynamic conditions, as in flowing blood. A quantitative understanding of this process requires accurate knowledge of the topographical relationships between the cell membrane and potentially adhesive surfaces. This report describes an experimental study made on both the translational and rotational velocities of leukocytes sedimenting of a flat surface under laminar shear flow. The main conclusions are as follows: (a) Cells move close to the wall with constant velocity for several tens of seconds. (b) The numerical values of translational and rotational velocities are inconsistent with Goldman's model of a neutrally buoyant sphere in a laminar shear flow, unless a drag force corresponding to contact friction between cells and the chamber floor is added. The phenomenological friction coefficient was 7.4 millinewton.s/m. (c) Using a modified Goldman's theory, the width of the gap separating cells (6 microns radius) from the chamber floor was estimated at 1.4 micron. (d) It is shown that a high value of the cell-to-substrate gap may be accounted for by the presence of cell surface protrusions of a few micrometer length, in accordance with electron microscope observations performed on the same cell population. (e) In association with previously reported data (Tissot, O., C. Foa, C. Capo, H. Brailly, M. Delaage, and P. Bongrand. 1991. Biocolloids and Biosurfaces. In press), these results are consistent with the possibility that cell-substrate attachment be initiated by the formation of a single molecular bond, which might be considered as the rate limiting step. PMID:1540690

Tissot, O; Pierres, A; Foa, C; Delaage, M; Bongrand, P

1992-01-01

411

Three-dimensional Lagrangian transport phenomena in unsteady laminar flows driven by a rotating sphere  

NASA Astrophysics Data System (ADS)

Magnetic actuation of microscopic beads is a promising technique for enhancement and manipulation of scalar transport in micro-fluidic systems. This implies laminar and essentially three-dimensional (3D) unsteady flow conditions. The present study addresses fundamental transport phenomena in such configurations in terms of 3D coherent structures formed by the Lagrangian fluid trajectories in a 3D time-periodic flow driven by a rotating sphere. The flow field is represented by an exact Stokes solution superimposed by a nonlinear closed-form perturbation. This facilitates systematic ``activation'' and exploration of two fundamental states: (i) invariant spheroidal surfaces accommodating essentially 2D Hamiltonian dynamics; (ii) formation of intricate 3D coherent structures (spheroidal shells interconnected by tubes) and onset to 3D dynamics upon weak perturbation of the former state. Key to the latter state is emergence of isolated periodic points and the particular foliation and interaction of the associated manifolds, which relates intimately to coherent structures of the unperturbed state. The occurrence of such fundamental states and corresponding dynamics is (qualitative) similar to findings on a realistic 3D lid-driven flow subject to weak fluid inertia. This implies, first, a universal response scenario to weak perturbations and, second, an adequate representation of physical effects by the in essence artificial perturbation. The study thus offers important new insights into a class of flow configurations with great practical potential.

Moharana, N. R.; Speetjens, M. F. M.; Trieling, R. R.; Clercx, H. J. H.

2013-09-01

412

A study of laminar flow of polar liquids through circular microtubes  

NASA Astrophysics Data System (ADS)

Recently, the validity of using classical flow theory to describe the laminar flow of polar liquids and electrolytic solutions through microtubes has been questioned for tube diameters as large as 500 ?m [Brutin and Tadrist, Phys. Fluids 15, 653 (2003)]. This potential increase in flow resistance, which has been attributed to electrokinetic effects and enhanced surface roughness effects, is critical to the understanding of certain biofluid systems. We seek to characterize this phenomenon for a variety of capillary/liquid systems. Using a numerical solution to the Poisson-Boltzmann equation, we have calculated the electroviscous effect for the systems under consideration. We have also measured the pressure drop as a function of flow rate across well-characterized stainless steel and polyimide microtubes ranging in diameter from 120 ?m to 440 ?m. Deionized water, tap water, a saline solution, and a variety of glycerol/water mixtures were used. The calculations and measurements suggest that any deviation from Poiseuille flow for tubes larger than 50 microns in diameter is more likely caused by the enhanced importance of surface roughness in microtubes than by electrokinetic effects.

Phares, Denis J.; Smedley, Gregory T.

2004-05-01

413

A global pressure relaxation for high speed laminar and turbulent flows  

NASA Astrophysics Data System (ADS)

The applicability of the Reduced Navier-Stokes (RNS) model is extended to high supersonic flows. The steady-state primitive variable formulation of the RNS equations is employed. The discretization used is a form of flux-difference splitting. The splitting of the streamwise pressure gradient term allows for upstream elliptic influence in subsonic regions through the forward-differenced portion of this term. The finite-difference equations are solved by a streamwise marching line-relaxation procedure developed in previous work. The pressure is the relaxed variable. For some of the flows considered, all shock waves are captured using the conservation form of the governing equations. For flows at higher Mach numbers, the outer bow shock is fitted with the aid of the Rankine-Hugoniot jump conditions. This allows the computational domain to be limited to the region between the outer shock and the body. All embedded shocks in this region are captured. Flows over a number of geometries including cone, aircraft forebody, cone-cylinder-boattail, cone-cylinder-trough, cone-cylinder-cavity, cone-cylinder-flare, cone-cylinder-base, and base flow with and without a centered jet are investigated. The flow over these geometries at high Reynolds number involves strong viscous-inviscid interactions, embedded shocks and moderate to large separation regions. Laminar and turbulent flows are considered for these axisymmetric bodies. Both the Cebeci-Smith and Baldwin-Lomax turbulence models are employed for turbulent flow calculations. Supersonic and high supersonic flow solutions are obtained. Some comparisons with experimental results are made.

Liang, Te

1989-03-01

414

Application of three-level one-stage Runge-Kutta scheme for numerical solution of incompressible flow  

NASA Astrophysics Data System (ADS)

A three-level one-stage Runge-Kutta scheme has been proposed for time integration of the incompressible Navier-Stokes equations. This scheme contains three free parameters and includes the conventional one-stage schemes, forward Euler scheme and Adams-Bashforth scheme, as special cases. The novel feature of the scheme is that the stability region can be extended further than that of the conventional one-stage scheme, and time accuracy can be controlled up to second order by tuning parameters. Numerical solutions for the transient Poiseuille flow and the two-dimensional lid-driven cavity flow are presented and compared with the analytical solution and those of the one-stage schemes. It is shown that the present scheme allows a larger time step and requires less computing cost than does the conventional one-stage scheme.

Miyake, Toshiya; Sakamoto, Yujiro; Tokunaga, Hiroshi; Satofuka, Nobuyuki

1992-01-01

415

Organized modes and the three-dimensional transition to turbulence in the incompressible flow around a NACA0012 wing  

NASA Astrophysics Data System (ADS)

The transition to turbulence in the incompressible flow around a NACA0012 wing at high incidence is studied by DNS in the Reynolds number range 800 10000. Two main routes are identified for the two-dimensional transition mechanisms: that to aperiodicity beyond the von Kármán mode via a period-doubling scenario and the development of a shear-layer instability, forced by the fundamental oscillation of the separation point downstream of the leading edge. The evolution of the global parameters as well as the variation law of the shear-layer instability wavelength are quantified. The history of the three-dimensional transition mechanisms from a nominally two-dimensional flow structure is identified beyond the first bifurcation, as well as the preferred spanwise wavelengths.

Hoarau, Y.; Braza, M.; Ventikos, Y.; Faghani, D.; Tzabiras, G.

2003-12-01

416

THE LAMINAR FLOW TUBULAR REACTOR WITH HOMOGENEOUS AND HETEROGENEOUS REACTIONS I. Integral Equations for Diverse Reaction Rate Regimes  

Microsoft Academic Search

Design equations for non-isothermal Laminar Flow Tubular Reactors (LFTRs) with homogeneous and heterogeneous - at the reactor wall - reactions with arbitrary kinetic equations have been satisfactorily treated transforming the original P.D.E. problem into a system of integral equations. The kernels of the integral operators are related to an eigenvalue problem which does not depend on the kinetic equations; this

RICARDO J. GRAU; MARÍA I. CABRERA; ALBERTO E. CASSANO

2001-01-01

417

The extended Graetz problem with piecewise constant wall heat flux for laminar and turbulent flows inside concentric annuli  

Microsoft Academic Search

In the present paper, the heat transfer characteristics in the thermal entrance region of concentric annuli have been analysed for laminar and turbulent internal flow. Axial heat conduction effects in the fluid have been taken into account. The present paper shows an exact analytical solution for the problem of a piecewise uniform wall heat flux. The obtained analytical solution for

B. Weigand; F. Wrona

2003-01-01

418

Experimental and kinetic modeling study of combustion of JP-8, its surrogates and reference components in laminar nonpremixed flows  

Microsoft Academic Search

Experimental and numerical studies are carried out to construct reliable surrogates that can reproduce aspects of combustion of JP-8 and Jet-A. Surrogate fuels are defined as mixtures of few hydrocarbon compounds with combustion characteristics similar to those of commercial fuels. The combustion characteristics considered here are extinction and autoignition in laminar non premixed flows. The “reference” fuels used as components

S. Humer; A. Frassoldati; S. Granata; T. Faravelli; E. Ranzi; R. Seiser; K. Seshadri

2007-01-01

419

Effect of Working Fluid on Sub2 nm Particle Detection with a Laminar Flow Ultrafine Condensation Particle Counter  

Microsoft Academic Search

The effect of working fluid on size-dependent activation efficiencies with the laminar flow ultrafine condensation particle counter described by Stolzenburg and McMurry (1991) was studied theoretically and experimentally. Criteria considered include tendency to avoid homogeneous nucleation within the condenser and toxicity. The working fluids that were identified have vapor pressures below that of butanol, so particles grow to smaller sizes

Kenjiro Iida; Mark R. Stolzenburg; Peter H. McMurry

2009-01-01

420

Multiple solutions for the laminar flow in a porous pipe with suction at slowly expanding or contracting wall  

Microsoft Academic Search

In this paper, the asymptotic solution for the similarity equation of the laminar flow in a porous pipe with suction at expanding and contracting wall has been obtained using the singular perturbation method. However, this solution neglects exponentially small terms in the matching process. To take into account these exponentially small terms, a method involving the inclusion of exponentially small

Xinhui Si; Liancun Zheng; Xinxin Zhang; Min Li; Jianhong Yang; Ying Chao

2011-01-01

421

The effect of velocity distribution on forced convection laminar flow heat transfer in a pipe at constant wall temperature  

Microsoft Academic Search

In this paper, a theoretical study of heat transfer to a fluid of vanishing viscosity in laminar flow in a pipe is made. The constant wall temperature boundary condition is considered in order to facilitate comparison with other classical solutions. Using velocity profiles of simple geometrical shape, the dependence of the heat transfer on velocity distribution is illustrated. Because of

H. Barrow; J. F. Humphreys

1970-01-01

422

Evaluation of a Long-Endurance-Surveillance Remotely-Piloted Vehicle with and Without Laminar Flow Control.  

National Technical Information Service (NTIS)

Two aircraft were evaluated, using a derated TF34-GE-100 turbofan engine one with laminar flow control (LFC) and one without. The mission of the remotely piloted vehicles (RPV) is one of high-altitude loiter at maximum endurance. With the LFC system maxim...

R. V. Turriziani W. A. Lovell J. E. Prince C. B. Quartero S. F. Washburn

1979-01-01

423

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...

424

Numerical solution of laminar boundary layer flow about a rotating sphere in an axial stream  

NASA Astrophysics Data System (ADS)

A finite-difference scheme is developed for solving the boundary layer equations governing the laminar flow about a rotating sphere which is subjected to a uniform stream in the direction of the axis of rotation. Numerical results are presented for the meridional and azimuthal velocities and for the wall-shear-stress components. Also, the angle at which the meridional velocity gradient normal to the wall vanishes is given at values of the parameter Ta/Re-squared ranged from zero (the stationary sphere case) to 10,000. As compared with the momentum integral technique of Schlichting (1953), the present scheme succeeded in obtaining solutions for very considerably larger values of the parameter Ta/Re-squared.

El-Shaarawi, M. A. I.; El-Refaie, M. F.; El-Bedeawi, S. A.

1985-03-01

425

Laminar flow modelling of a thermosyphon loop at specified wall temperatures  

NASA Astrophysics Data System (ADS)

A thermosyphon loop is analyzed in this study by use of numerical and experimental techniques. A rectangular loop was constructed using copper pipe and the sections which were heated or cooled were designed as concentric tube heat exchangers. Hot or cold water was circulated outside of these sections, and both the surface temperatures and heat transferred to and from the loop were measured. Within the numerical study both the momentum and energy equations were also solved using a SIMPLEX algorithm. Numerical results were obtained for laminar flow within the circuit when there was uniform wall temperature in the vertically heated and cooled sections of the thermosyphon. The two-dimensional numerical model provided results which agree with those found experimentally from the thermosyphon loop. In addition, a simulation model was constructed using a correlation included both the Grashof and Prandtl numbers to evaluate heat transfer through a thermosyphon loop.

Küçüka, Serhan; Ba?aran, Tahsin

2007-10-01

426

Separating Beads and Cells in Multi-channel Microfluidic Devices Using Dielectrophoresis and Laminar Flow  

PubMed Central

Microfluidic devices have advanced cell studies by providing a dynamic fluidic environment on the scale of the cell for studying, manipulating, sorting and counting cells. However, manipulating the cell within the fluidic domain remains a challenge and requires complicated fabrication protocols for forming valves and electrodes, or demands specialty equipment like optical tweezers. Here, we demonstrate that conventional printed circuit boards (PCB) can be used for the non-contact manipulation of cells by employing dielectrophoresis (DEP) for bead and cell manipulation in laminar flow fields for bioactuation, and for cell and bead separation in multichannel microfluidic devices. First, we present the protocol for assembling the DEP electrodes and microfluidic devices, and preparing the cells for DEP. Then, we characterize the DEP operation with polystyrene beads. Lastly, we show representative results of bead and cell separation in a multichannel microfluidic device. In summary, DEP is an effective method for manipulating particles (beads or cells) within microfluidic devices.

Millet, Larry J.; Park, Kidong; Watkins, Nicholas N.; Hsia, K. Jimmy; Bashir, Rashid

2011-01-01

427

Transition from laminar to turbulent drag in flow due to a vibrating quartz fork  

SciTech Connect

Flow due to a commercially available vibrating quartz fork is studied in gaseous helium, He I and He II, over a wide range of temperatures and pressures. On increasing the driving force applied to the fork, the drag changes in character from laminar (characterized by a linear drive vs velocity dependence) to turbulent (characterized by a quadratic drive vs velocity dependence). We characterize this transition by a critical Reynolds number Re{sub cr}{sup {delta}}=U{sub cr}{delta}/{nu}, where U{sub cr} is the critical velocity, {nu} stands for the kinematic viscosity, {delta}={radical}(2{nu}/{omega}) is the viscous penetration depth, and {omega} is the angular frequency of oscillations. We have experimentally verified that the corresponding scaling U{sub cr}{proportional_to}{radical}({nu}{omega}) holds in a classical viscous fluid over two decades of {nu}.

Blazkova, M.; Schmoranzer, D.; Skrbek, L. [Joint Low Temperature Laboratory, Institute of Physics ASCR and Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, 180 00 Prague (Czech Republic)

2007-02-15

428

Separating beads and cells in multi-channel microfluidic devices using dielectrophoresis and laminar flow.  

PubMed

Microfluidic devices have advanced cell studies by providing a dynamic fluidic environment on the scale of the cell for studying, manipulating, sorting and counting cells. However, manipulating the cell within the fluidic domain remains a challenge and requires complicated fabrication protocols for forming valves and electrodes, or demands specialty equipment like optical tweezers. Here, we demonstrate that conventional printed circuit boards (PCB) can be used for the non-contact manipulation of cells by employing dielectrophoresis (DEP) for bead and cell manipulation in laminar flow fields for bioactuation, and for cell and bead separation in multichannel microfluidic devices. First, we present the protocol for assembling the DEP electrodes and microfluidic devices, and preparing the cells for DEP. Then, we characterize the DEP operation with polystyrene beads. Lastly, we show representative results of bead and cell separation in a multichannel microfluidic device. In summary, DEP is an effective method for manipulating particles (beads or cells) within microfluidic devices. PMID:21339720

Millet, Larry J; Park, Kidong; Watkins, Nicholas N; Hsia, K Jimmy; Bashir, Rashid

2011-02-04

429

Patterning cells and their environments using multiple laminar fluid flows in capillary networks  

PubMed Central

This paper describes the use of laminar flow of liquids in capillary systems to pattern the cell culture substrate, to perform patterned cell deposition, and to pattern the cell culture media. We demonstrate the patterning of the cell culture substrate with different proteins, the patterning of different types of cells adjacent to each other, the patterned delivery of chemicals to adhered cells, and performing enzymatic reactions over select cells or over a portion of a cell. This method offers a way to simultaneously control the characteristics of the surface to which cells are attached, the type of cells that are in their vicinity, and the kind of media that cells or part of a cell are exposed to. The method is experimentally simple, highly adaptable, and requires no special equipment except for an elastomeric relief that can be readily prepared by rapid prototyping.

Takayama, Shuichi; McDonald, J. Cooper; Ostuni, Emanuele; Liang, Michael N.; Kenis, Paul J. A.; Ismagilov, Rustem F.; Whitesides, George M.

1999-01-01

430

INCOMPRESSIBLE FLOW PAST A CIRCULAR CYLINDER: DEPENDENCE OF THE COMPUTED FLOW FIELD ON THE LOCATION OF THE LATERAL BOUNDARIESy  

Microsoft Academic Search

The inuence of the location of the lateral boundaries on 2D computation of unsteady incompressible ow past a circular cylinder is investigated. The case of Reynolds number 100 is used as a benchmark, and several quantities characterizing the unsteady ow are obtained for a range of lateral boundary locations. The computations are performed with two distinct nite element formulations {

M. Behr; D. Hastreiter; S. Mittal; T. E. Tezduyar

1994-01-01

431

Artificial compressibility, characteristics-based schemes for variable-density, incompressible, multispecies flows: Part II. Multigrid implementation and numerical tests  

NASA Astrophysics Data System (ADS)

The paper presents an investigation of the accuracy and efficiency of artificial compressibility, characteristics-based (CB) schemes for variable-density incompressible flows. The CB schemes have been implemented in conjunction with a multigrid method for accelerating numerical convergence and a fourth-order, explicit Runge Kutta method for the integration of the governing equations in time. The implementation of the CB schemes is obtained in conjunction with first-, second- and third-order interpolation formulas for calculating the variables at the cell faces of the computational volume. The accuracy and efficiency of the schemes are examined against analytical and experimental results for diffusion broadening in two- and three-dimensional microfluidic channels, a problem that has motivated the development of the present methods. Moreover, unsteady, inviscid simulations have been performed for variable-density mixing layer. The computations revealed that accuracy and efficiency depend on the CB scheme design. The best multigrid convergence rates were exhibited by the conservative CB scheme, which is obtained by the fully conservative formulation of the variable-density, incompressible equations.

Shapiro, Evgeniy; Drikakis, Dimitris

2005-12-01

432

Experiments on densely-loaded non-Newtonian slurries in laminar and turbulent pipe flows  

NASA Astrophysics Data System (ADS)

An experimental description of the flow structure of non-Newtonian slurries in the laminar, transitional, and full turbulent pipe flow regimes is the primary objective of this research. Measurements include rheological characterization of the fluid and local fluid velocity measurements with a Laser Doppler Velocimeter (LDV). Optical access to the flow is gained through a test section and model slurry which are both transparent. The model slurry is formulated from silica gel particles and hydrocarbon liquid mixture whose indices of refraction are matched so that light is not scattered from the particles. Experiments are being conducted in a large-scale pipe slurry. Flow measurements including turbulence quantities such as Reynolds stress were measured with a two-component two-color LDV. The present research indicates that non-Newtonian slurries are possible with concentrations of a few percent by weight of small particles whose sizes are two microns or less. A non-Newtonian slurry from small particles could maintain large particles (one millimeter size) at high concentrations in suspension almost indefinitely. Such a slurry would prevent particle fallout and its associated problems.

Park, J. T.; Mannheimer, R. J.; Grimley, T. A.; Morrow, T. B.

1988-05-01

433

Calibration of a laminar flowmeter  

NASA Astrophysics Data System (ADS)

The parameters needed to describe the flow rate through a laminar flowmeter were investigated. Development of a laminar flow element standard is described, and a theory of laminar flowmeters based on the Poiseuille-Hagan law presented. Application of the theory to the laminar flow element standard is demonstrated. Better than 0.1% precision can be achieved, for short periods (days or longer) of less than six months.

Fain, D. E.

1981-01-01

434

Unsteady separated stagnation-point flow of an incompressible viscous fluid on the surface of a moving porous plate  

NASA Astrophysics Data System (ADS)

Using group-theoretic method, an analysis is presented for a similarity solution of boundary layer equations which represents an unsteady two-dimensional separated stagnation-point (USSP) flow of an incompressible fluid over a porous plate moving in its own plane with speed u0(t). It is observed that the solution to the governing nonlinear ordinary differential equation for the USSP flow admits of two solutions (in contrast with the corresponding steady flow where the solution is unique): one is the attached flow solution (AFS) and the other is the reverse flow solution (RFS). A novel result of the analysis is that in the case of stationary plate (u0(t) = 0), after a certain value of the magnitude of the blowing d (<0) at the plate, only the AFS exists and the solution becomes unique. For a stationary plate (u0(t) = 0), the USSP flow is found to be separated for all values of d in both the cases of AFS and RFS. It is also observed that when u0(t) = 0, in the RFS flow with wall suction d (>0), there are two stagnation-points in the flow but in the presence of blowing d (<0), there is only one stagnation-point in the flow which moves further and further up with increase in |d|. Suction is shown to increase the wall shear stress while blowing has an opposite effect. Streamlines for an USSP flow when u0(t) ? 0 are also plotted. It is found that in this case, the USSP flow is not in general separated.

Dholey, S.; Gupta, A. S.

2013-02-01

435

Laminar flow and heat transfer in power-law fluids flowing in arbitrary cross-sectional ducts  

NASA Astrophysics Data System (ADS)

A numerical method capable of handling three-dimensional transport processes is devised to model the developing steady laminar flow and heat transfer to power-law fluids flowing in ducts of arbitrary but uniform cross section. The governing equations are the general momentum and energy equations parabolized in the axial direction and as such are applicable to flow systems with a predominant flow direction. An orthogonal body-fitted coordinate system is employed to handle complex cross-sectional geometries. The transformed equations are discretized in a finite-difference form, and the resulting algebraic equations are solved by line successive over-relaxation (SOR). For the purpose of testing the algorithms and the computer code, solutions are computed for the well-known case of a Newtonian fluid in a square duct. Excellent agreement with available numerical and experimental results is obtained. The versatility of the code is demonstrated by presentation of flow and heat transfer results for power-law fluids flowing in pentagonal and trapezoidal ducts.

Lawal, A.; Mujumdar, A. S.

436

Experimental development of tubeside heat transfer correlations for laminar flow with and without inserts  

NASA Astrophysics Data System (ADS)

An experimental study of laminar flow heat transfer of an ethylene glycol/water mixture in an electrically heated horizontal tube using wire mesh (HEATEX) and twisted tape inserts was investigated. Twelve thermocouples, inserted in the tube wall at four longitudinal locations, enabled a mean inside experimental heat-transfer coefficient to be accurately measured. A constant wall heat flux boundary condition was placed on the wall by wrapping six 200 W flexible heater tapes tightly around the tube. The ethylene glycol/water mixture provided a coolant Reynolds number between 200-5000 and a Prandtl number between 30-140. Two smooth inside diameters and a roped tube profile were tested with and without the inserts. Heat-transfer correlations for tubes without inserts were developed and compared with theory for both thermally and hydrodynamically developing flow. Correlations were also developed for the two types of inserts. Nusselt numbers for fully developed flow were found to be a function of Reynolds and Prandtl numbers for the wire mesh insert and a function of tape twist ratio, Reynolds and Prandtl numbers for the twisted tape insert. Heat transfer enhancements of over 7 for the wire mesh insert and over 4 for the twisted tape insert at high Reynolds numbers were obtained over the empty tube.

Guido, Joseph D.

1992-09-01

437

Simulations of laminar flow past a superhydrophobic sphere with drag reduction and separation delay  

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces have potential for reducing hydrodynamic drag by combining a structured surface and hydrophobicity to retain a lubricating air layer (plastron) at the surface. In the present contribution, numerical simulations of laminar flow past a superhydrophobic sphere are conducted using a two-phase flow representation. The results show drag reductions in Stokes flow of up to 19% for an air-water system, in agreement with previous analytic work, and demonstrate an increased effect as the Reynolds number is increased to 100. Drag reductions of up to 50% are achieved due to reduction in viscous drag and suppression of separation by the plastron, resulting in a narrower wake. To explore a less idealised model of the plastron, baffles have also been introduced to simulate the support of a plastron by roughness elements. The baffles lead to the attached vortex regime no longer being suppressed, but separation is delayed and drag reductions are evident in comparison to a solid sphere. Increasing the area solid fraction results in a diminished drag reduction due to the plastron, however drag reductions of up to 15% can still be achieved with solid fractions of 10%.

Gruncell, Brian R. K.; Sandham, Neil D.; McHale, Glen

2013-04-01

438

Friction factor correlations for laminar, transition and turbulent flow in smooth pipes  

NASA Astrophysics Data System (ADS)

In this paper we derive an accurate composite friction factor vs. Reynolds number correlation formula for laminar, transition and turbulent flow in smooth pipes. The correlation is given as a rational fraction of rational fractions of power laws which is systematically generated by smoothly connecting linear splines in log-log coordinates with a logistic dose curve algorithm. This kind of correlation seeks the most accurate representation of the data independent of any input from theories arising from the researchers’ ideas about the underlying fluid mechanics. As such, these correlations provide an objective metric against which observations and other theoretical correlations may be applied. Our correlation is as accurate, or more accurate, than other correlations in the range of Reynolds numbers in which the correlations overlap. However, our formula is not restricted to certain ranges of Reynolds numbers but instead applies uniformly to all smooth pipe flow data for which data is available. The properties of the classical logistic dose response curve are reviewed and extended to problems described by multiple branches of power laws. This extended method of fitting which leads to rational fractions of power laws is applied to data of Marusic and Perry (1995) [1] for the velocity profile in a boundary layer on a flat plate with an adverse pressure gradient, to data of Nikuradse (1932) [2] and McKeon et al. (2004) [3] on friction factors for flow in smooth pipes and to the data of Nikuradse [4] for effectively smooth pipes.

Joseph, Daniel D.; Yang, Bobby H.

2010-07-01

439

Prediction of unsteady, separated boundary layer over a blunt body for laminar, turbulent, and transitional flow  

NASA Astrophysics Data System (ADS)

The focus of this paper is to study the ability of unsteady RANS-based CFD to predict separation over a blunt body for a wide range of Reynolds numbers particularly the ability to capture laminar-to-turbulent transition. A perfect test case to demonstrate this point is the cylinder-in-crossflow for which a comparison between experimental results from the open literature and a series of unsteady simulations is made. Reynolds number based on cylinder diameter is varied from 104 to 107 (subcritical through supercritical flow). Two methods are used to account for the turbulence in the simulations: currently available eddy-viscosity models, including standard and realizable forms of the k- model; and a newly developed eddy-viscosity model capable of resolving boundary layer transition, which is absolutely necessary for the type and range of flow under consideration. The new model does not require user input or empirical fixes to force transition. For the first time in the open literature, three distinct flow regimes and the drag crisis due to the downstream shift of the separation point are predicted using an eddy-viscosity based model with transition effects. Discrepancies between experimental and computational results are discussed, and difficulties for CFD prediction are highlighted.

Holloway, D. Scott; Walters, D. Keith; Leylek, James H.

2004-08-01

440

A conservative phase field method for solving incompressible two-phase flows  

NASA Astrophysics Data System (ADS)

In this paper a conservative phase-field method based on the work of Sun and Beckermann [Y. Sun, C. Beckermann, Sharp interface tracking using the phase-field equation, J. Comput. Phys. 220 (2007) 626-653] for solving the two- and three-dimensional two-phase incompressible Navier-Stokes equations is proposed. The present method can preserve the total mass as the Cahn-Hilliard equation, but the calculation and implementation are much simpler than that. The dispersion-relation-preserving schemes are utilized for the advection terms while the Helmholtz smoother is applied to compute the surface-tension force term. To verify the proposed method, several benchmarks are examined and shown to have good agreements with previous results. It also shows that the satisfactions of mass conservations are guaranteed.

Chiu, Pao-Hsiung; Lin, Yan-Ting

2011-01-01

441

Convergence and accuracy of pressure-based finite difference schemes for incompressible viscous flow calculations in a nonorthogonal coordinate system  

NASA Astrophysics Data System (ADS)

The convergence and accuracy of three finite-difference solution schemes (SIMPLE, SIMPLEC and PISO) are tested and evaluated for steady, incompressible, and two-dimensional flows in nonorthogonal body-fitted coordinate systems. When representing the governing equations in a generalized coordinate system, complex cross-derivative pressure terms that involve nodal values on 'corner points' appear. To maximize computational efficiency with a five-point matrix solver, the corner points are generally omitted. However, the neglect of these terms may lead to deterioration in the convergence rate for fairly skewed grids and divergence for highly skewed grids. It is shown in this paper that the PISO solution scheme, with its multicorrector steps, allows the inclusion of the cross-derivative pressure terms and offers a distinct advantage in computational efficiency over the commonly used SIMPLE and SIMPLEC methods.

Hadid, A. H.; Chan, D. C.; Issa, R. I.; Sindir, M. M.

1988-07-01

442

Development of an explicit pressure-based unstructured solver for three-dimensional incompressible flows with graphics hardware acceleration  

NASA Astrophysics Data System (ADS)

In this research, a numerical algorithm was developed to solve the incompressible Navier-Stokes equations using explicit time stepping. The goal of this research was to develop an unsteady SIMPLER based algorithm with lower computational overhead. The new explicit algorithm uses a four stage Runge-Kutta scheme to update the velocities and eliminates the need for the pressure correction equation and sub-iterations. This algorithm was derived for use on unstructured tetrahedral grids and was validated with the lid-driven cavity and unsteady rotor flows. This algorithm proved to be easily parallelized and was implemented in CUDA. As a result, accelerations of over 80x are observed compared to a CPU based implicit SIMPLER algorithm using a standard workstation.

Thistle, Jordan

443

Benchmark Solutions of 2-D Steady Incompressible NS Equations in General Curvilinear Coordinates with NonOrthogonal Grid Mesh; Driven Skewed Cavity Flow  

Microsoft Academic Search

The numerical method presented by Erturk et al. (2005, IJNMF, in Press) is reformulated in its most general form, in general curvilinear coordinates, and tested on non-orthogonal flow problems. The governing 2-D steady incompressible Navier-Stokes equations is solved for the solution of the benchmark problem \\

E. Erturk; B. Dursun

2005-01-01

444

Computational Design for Long-Term Numerical Integration of the Equations of Fluid Motion: Two-Dimensional Incompressible Flow. Part I  

Microsoft Academic Search

The integral constraints on quadratic quantities of physical impor- tance, such as conservation of mean kinetic energy and mean square vorticity, will not be maintained in finite difference analogues of or the equation of motion for two-dimensional incompressible flow, unless the finite difference Jacobian expression for the advection term is restricted to a form which properly represents the interaction ›=

Akio Arakawa

1966-01-01

445

Integral method of calculating friction and heat transfer in the turbulent flow of incompressible media in pipes with a rough permeable wall  

Microsoft Academic Search

A method of calculating friction and heat transfer for a flow of an incompressible liquid over a rough permeable surface is developed on the basis of universal profiles of velocity and temperature in the turbulent boundary layer. A relatively simple transcendental equation is obtained for the friction coefficient c\\/sub f\\/ in the case of uniform injection. This equation can be

B. I. Nigmatulin; Yu. V. Vasilev

1987-01-01

446

Incipient motion of a single particle on regular substrates in laminar shear flow  

NASA Astrophysics Data System (ADS)

We study experimentally the critical conditions for incipient motion of a single spherical particle deposited on a regular substrate under laminar flow conditions. The substrates are triangular and quadratic arrangements of identical glass spheres. For the latter configuration, the distance between the substrate spheres is varied, resulting in different partial shielding of the deposited particle to the shear flow. For the studied particle Reynolds numbers range between 3 × 10-4 and 3, the critical Shields number is independent from the particle density and from the particle Reynolds number but it depends significantly on the geometry of the substrate. Depending on the spacing between the substrate beads and thus on the exposure of the particle to the flow, we have observed an increase of about 50 percent in the critical Shields number. Studying the onset of particle motion as a function of the orientation of the substrate to the flow direction we find that the critical Shields number changes by up to a factor of 2, which is mainly due to the fact that the particle travels through the troughs of the substrate and hence the shear force in travel direction diminishes if not in line with the flow direction. Besides the critical Shields number we study the initial stage of particle motion by detecting the minimum time that is necessary for maintaining a certain Shields number to change the position of a single particle on the regular substrates. In the range studied, the initial stage of motion on the scale of the substrate's periodicity is mainly governed by the equilibrium particle motion.

Agudo, J. R.; Wierschem, A.

2012-09-01

447

Data evaluation of laminar flow diffusion chamber nucleation experiments with different computational methods  

NASA Astrophysics Data System (ADS)

In order to evaluate the experimental data from laminar flow diffusion chamber (LFDC) experiments on homogeneous nucleation, an extensive postmeasurement computational analysis is required. The present work investigates the influence of the used computational methodology on the derived nucleation curves. To this end a reanalysis is made of previous LFDC experiments of 1-butanol nucleation in helium [D. Brus et al., J. Chem. Phys. 122, 214506 (2005)] using two different methods. The first method is based on single fluid heat and vapor transport in the carrier gas ignoring the aerosol processes, as commonly made in LFDC data evaluations. The second method is more comprehensive as is based on multidimensional computational fluid-particle dynamics. The calculations are made under the usual simplification of one-way coupling between fluid flow and particles, which is a valid approximation in most practical aerosols, while full aerosol dynamical effects are accommodated. Similar results were produced by the two methods. This finding corroborates the usual practice of omitting aerosol calculations in LFDC experimental data evaluation.

Mitrakos, D.; Ždímal, V.; Brus, D.; Housiadas, C.

2008-08-01

448

Low Drag Airfoil Design Utilizing Passive Laminar Flow and Coupled Diffusion Control Techniques.  

National Technical Information Service (NTIS)

A two-dimensional high chord Reynolds number passive laminar airfoil was designed for a C sub l = 0.73 at a M at infinity = 0.6 and Re sub c = 4 times 10 to the 7th power providing an extremely high L/D = 240. This laminar airfoil design concept integrate...

R. L. Mask

1980-01-01

449

Heat Transfer in Thermal Entrance Region of Cocurrent Flow Heat Exchangers with Fully Developed Laminar Flow.  

National Technical Information Service (NTIS)

Although the method developed was applied only to cocurrent flow systems, it is believed that a similar approach involving the Duhamel theorem can be used for other multistream problems such as countercurrent flow systems. (Author)

W. N. Gill E. W. Porta R. J. Nunge

1968-01-01

450

Preconditioned pseudo-compressibility methods for incompressible Navier-Stokes equations  

NASA Astrophysics Data System (ADS)

This paper investigates the pseudo-compressibility method for the incompressible Navier-Stokes equations and the preconditioning technique for accelerating the time marching for stiff hyperbolic equations, and derives and presents the eigenvalues and eigenvectors of the Jacobian matrix of the preconditioned pseudo-compressible Navier-Stokes equations in generally cur-vilinear coordinates. Based on the finite difference discretization the cored for efficiently solving incompressible flows numerically is established. The reliability of the procedures is demonstrated by the application to the inviscid flow past a circular cylinder, the laminar flow over a flat plate, and steady low Reynolds number viscous incompressible flows past a circular cylinder. It is found that the solutions to the present algorithm are in good agreement with the exact solutions or experimental data. The effects of the pseudo-compressibility factor and the parameter brought by preconditioning in convergence characteristics of the solution are investigated systematically. The results show that the upwind Roe’s scheme is superior to the second order central scheme, that the convergence rate of the pseudo-compressibility method can be effectively improved by preconditioning and that the self-adaptive pseudo-compressibility factor can modify the numerical convergence rate significantly compared to the constant form, without doing artificial tuning depending on the specific flow conditions. Further validation is also performed by numerical simulations of unsteady low Reynolds number viscous incompressible flows past a circular cylinder. The results are also found in good agreement with the existing numerical results or experimental data.

Qian, Zhansen; Zhang, Jingbai; Li, Chunxuan

2010-11-01

451

Schlieren visualization of the laminar-to-turbulent transition in a shock-tube boundary-layer  

Microsoft Academic Search

The laminar-to-turbulent transition in the flow of a shock-tube boundary layer is measured for shock Mach numbers of 1.06 to 1.5. Schlieren photographs show a pulsation of the boundary-layer thickness in the transition regime. The observed structure of the turbulent boundary layer can be related to the burst phenomena known for incompressible flow. The transition is also measured with hot

K. Bracht; W. Merzkirch

1977-01-01

452

A hybrid vertex-centered finite volume/element method for viscous incompressible flows on non-staggered unstructured meshes  

NASA Astrophysics Data System (ADS)

This paper proposes a hybrid vertex-centered finite volume/finite element method for solution of the two dimensional (2D) incompressible Navier-Stokes equations on unstructured grids. An incremental pressure fractional step method is adopted to handle the velocity-pressure coupling. The velocity and the pressure are collocated at the node of the vertex-centered control volume which is formed by joining the centroid of cells sharing the common vertex. For the temporal integration of the momentum equations, an implicit second-order scheme is utilized to enhance the computational stability and eliminate the time step limit due to the diffusion term. The momentum equations are discretized by the vertex-centered finite volume method (FVM) and the pressure Poisson equation is solved by the Galerkin finite element method (FEM). The momentum interpolation is used to damp out the spurious pressure wiggles. The test case with analytical solutions demonstrates second-order accuracy of the current hybrid scheme in time and space for both velocity and pressure. The classic test cases, the lid-driven cavity flow, the skew cavity flow and the backward-facing step flow, show that numerical results are in good agreement with the published benchmark solutions.

Gao, Wei; Liu, Ru-Xun; Li, Hong

2012-04-01

453

Laminar boundary layer flow of saturated vapor and its condensate over a horizontal tube  

NASA Astrophysics Data System (ADS)

The steady two-dimensional laminar flow of a stream of saturated vapor flowing over a tube that is kept at a uniform temperature, below the saturation temperature, is examined. Owing to the temperature difference between the vapor stream and the solid surface a film of condensate is generated that flows along the surface due to shear, pressure-drop, and gravity. In the limit as the boundary layer and film thickness remain smaller than the radius of curvature of the surface a simplified lubrication-type formulation describes the temperature and flow fields in the film, whereas the usual boundary layer formulation is applied in the vapor boundary layer. The case of flow past a horizontal cylinder of radius R is investigated numerically with the oncoming stream aligned with gravity. The parameters that control momentum and heat transfer in this problem are the viscosity ratio, ?cs/?ss, the density ratio, ?cs/?ss, the Prandtl number, Pr=cpcs?cs/kcs, the Froude number, Fr=U?2/(g?R), and finally the thickness ratio between the condensate and the vapor boundary layer, ?, which is also a measure of the temperature difference between the vapor stream and the tube wall. Then, the Nusselt number and the skin friction coefficient, averaged over the upper half of the cylinder, are calculated for a wide parameter range. When Fr is very small and V relatively large the flow remains attached until the trailing stagnation point of the cylinder. As the effect of adverse pressure drop becomes more pronounced (Fr increases or V decreases) it is shown that the solution exhibits two different types of singularity in the rear part of the cylinder. The first one is a typical Goldstein singularity because it appears at the tube wall and it is associated with vanishing skin friction (wall shear) and rapidly increasing film thickness. The second one takes place near the interface between the vapor stream and the film of condensate in a region where very small velocities prevail in conjunction with vanishing shear rate. The latter has not been reported so far and it is expected to affect the flow locally, as opposed to the Goldstein singularity which is known to lead to massive separation in the case of a cylindrical surface. Upon proper rescaling of Fr and V, Fr'=Fr ?ss/?cs, V'=V6(?ss/?cs)7/2(?cs/?ss)7/2, a critical curve is produced in the (Fr',V') plane that marks the boundary curve separating the two types of singular behavior for most of the numerical data obtained herein for the steam-water system, irrespective of the saturation temperature.

Smyrnaios, D. N.; Pelekasis, N. A.; Tsamopoulos, J. A.

2002-06-01

454

Flow visualization and LDV measurement of fully developed laminar flow in helically coiled tubes  

Microsoft Academic Search

Secondary flow structure in helically coiled tubes is characterized by laser light-sheet flow visualization photographs and laser Doppler velocimetry measured velocity vector field. The torsion-to-curvature ratio and Reynolds number, based on the tube diameter and bulk average axial velocity, were varied from 0.06 to 5.55 and from 35 to 330, respectively, to study their effects on the secondary flow patterns.

T. M. Liou

1992-01-01

455

Algebraic calculation of integral coefficients for the incompressible flow in a labyrinth seal  

NASA Astrophysics Data System (ADS)

Algebraic expressions for the turning moment of rotating disks and cylinders with concentric sheaths are used to derive formulas for the flow field average values of the surrounding flow, the kinetic varying energy, and the latter's dissipation in a labyrinth seal. The calculative results are confirmed by measurements in the flow field. The procedure is suitable for engineering estimations of the flow behavior in similar configurations in labyrinth seals and unsheathed shafts.

Stoff, Horst

1988-01-01

456

Transpired Solar Air Heaters. Volume 3. Effect of Wall Suction on Laminar Entrance Flow with Application to Solar Air Heaters. Final Report.  

National Technical Information Service (NTIS)

Numerical solutions are obtained for hydrodynamically and thermally developing steady-state laminar flow in a long rectangular cavity with uniform suction and one wall and uniform temperature or heat flux independently prescribed at each wall. Fully devel...

S. J. Rhee

1980-01-01

457

The effect of wall friction in single-phase natural circulation stability at the transition between laminar and turbulent flow  

Microsoft Academic Search

The present paper is focused on the prediction of stability of single-phase natural circulation in the range of Reynolds numbers characterizing the transition between laminar and turbulent flow. In particular, the predictions obtained by one-dimensional models making use of different assumptions for evaluating wall friction at this transition are discussed, also in front of experimental information from previous investigations.The starting

W. Ambrosini; N. Forgione; J. C. Ferreri; M. Bucci

2004-01-01

458

Numerical simulation of laminar co-flow methane-oxygen diffusion flames: effect of chemical kinetic mechanisms  

Microsoft Academic Search

Laminar co-flow methane–oxygen flames issuing into the unconfined atmosphere have been studied. A numerical model, which employs different chemical kinetics sub-models, including a skeletal mechanism with 43 reaction steps and 18 species and four global reaction mechanisms (two 2-steps and two 4-steps mechanisms), and an optically thin radiation sub-model, has been employed in the simulations. Numerical model has been validated

Karnam Bhadraiah; Vasudevan Raghavan

2011-01-01

459

Would a Titanium Dioxide Air Cleaner Reduce the Colony-Forming Unit Counts in Laminar Air Flow ORs?  

Microsoft Academic Search

INTRODUCTION: A previous study determined that titanium oxide filters added to standard air ventilation reduced the colony-forming units per cubic meter (CFU\\/m3) in the operating room. Laminar Air Flow has been shown to dramatically reduce CFU\\/m3 in various studies, however, its use depends on room size, configuration, and ventilation requirements to allow for maximum efficiency. From March through May 2003,

A. Schlimm

2004-01-01

460

A High-speed Nature Laminar Flow Airfoil and Its Experimental Study in Wind Tunnel with Nonintrusive Measurement Technique  

Microsoft Academic Search

This article deals with an experimental study on the aerodynamic characteristics of a low-drag high-speed nature laminar flow (NLF) airfoil for business airplanes in the TST27 wind tunnel at Delft University of Technology, the Netherlands. In this experiment, in an attempt to reduce the errors of measurement and improve its accuracy in high-speed flight, some nonintrusive measurement techniques, such as

Zhu Jun; Gao Zhenghong; Zhan Hao; Bai Junqiang

2009-01-01

461

Phase relationship in laminar channel flow controlled by traveling-wave-like blowing or suction  

NASA Astrophysics Data System (ADS)

The phase relationship between the streamwise and the wall-normal velocity disturbances induced by a traveling-wave-like blowing or suction control [T. Min , J. Fluid Mech. 558, 309 (2006)] in a two-dimensional laminar Poiseuille flow is investigated. The investigation is done by solving the linearized Navier-Stokes equation and by using the identity equation between the skin-friction drag and the Reynolds shear stress [K. Fukagata , Phys. Fluids 14, L73 (2002)]. It has been known that a traveling wave creates a nonquadrature between the velocity disturbances and generates the positive phase shift of the streamwise velocity disturbance in the case of a skin-friction drag reduction. The present analysis further reveals that this nonquadrature consists of an inviscid base phase relationship and a near-wall phase shift induced by the viscosity. The analogy between the present control and Stokes’ second problem is discussed. The thickness of the near-wall region in which the viscous phase shift takes place is found to be scaled similarly to the Stokes’ second problem.

Mamori, Hiroya; Fukagata, Koji; Hoepffner, Jerôme

2010-04-01

462

Laboratory Measurement of Water Nucleation Using a Laminar Flow Tube Reactor  

SciTech Connect

A Laminar Flow Tube Reactor (LFTR) was used to study the nucleation of water vapor. Computational analysis was carried out to define the operating conditions of the LFTR suitable for water nucleation measurements. An interface between the LFTR and a mass spectrometer was developed to analyze the chemical content of the freshly nucleated water particles. Presence of contaminants was detected in the initial configuration of the LFTR. As a result, improvements were made to the LFTR to achieve ultra-high purity conditions in the system. The nucleation rate of water vapor as a function of supersaturation was measured over the temperature range 210-250 K. The first measurement of the nucleation rate of water at a temperature of 210 K was obtained. Reasonable agreement with the classical theory predictions is observed for temperatures in the range 230-250 K. However, below 220 K, classical theory begins to overestimate nucleation rates compared to experimental data and the disagreement grows with decreasing temperature. The experimental data obtained provide an excellent benchmark for further nucleation studies of binary, ternary and more complex systems.

Mikheev, Vladimir B. (InnovaTek, Inc); Irving, Patricia M. (InnovaTek); Laulainen, Nels S. (BATTELLE (PACIFIC NW LAB)); Barlow, Stephan E. (BATTELLE (PACIFIC NW LAB)); Pervukhin, Viktor V. (Institute of Inorganic Chemistry of SB RAS, Novosibirsk, Russia)

2002-06-22

463

Laboratory measurement of water nucleation using a laminar flow tube reactor  

NASA Astrophysics Data System (ADS)

A Laminar Flow Tube Reactor (LFTR) was used to study the nucleation of water vapor. Computational analysis was carried out to define the operating conditions of the LFTR suitable for water nucleation measurements. An interface between the LFTR and a mass spectrometer was developed to analyze the chemical content of the freshly nucleated water particles. Contaminants were detected in the initial configuration of the LFTR. As a result, improvements were made to the LFTR to achieve ultrahigh purity conditions in the system. The nucleation rate of water vapor as a function of supersaturation was measured over the temperature range 210-250 K. The first measurement of the nucleation rate of water at a temperature of 210 K was obtained. Reasonable agreement with the classical theory predictions is observed for temperatures in the range 230-250 K. However, below 220 K, classical theory begins to overestimate nucleation rates compared to experimental data and the disagreement grows with decreasing temperature. The experimental data obtained provide an excellent benchmark for further nucleation studies of binary, ternary, and more complex systems.

Mikheev, Vladimir B.; Irving, Patricia M.; Laulainen, Nels S.; Barlow, Stephan E.; Pervukhin, Viktor V.

2002-06-01

464

Prototyping disposable electrophoresis microchips with electrochemical detection using rapid marker masking and laminar flow etching.  

PubMed

Two novel methods are described for the fabrication of components for microchip capillary electrophoresis with electrochemical detection (microchip CEEC) on glass substrates. First, rapid marker masking is introduced as a completely nonphotolithographic method of patterning and fabricating integrated thin-film metal electrodes onto a glass substrate. The process involves applying the pattern directly onto the metal layer with a permanent marker that masks the ensuing chemical etch. The method is characterized, and the performance of the resulting electrode is evaluated using catecholamines. The response compares well with photolithographically defined electrodes and exhibits detection limits of 648 nM and 1.02 microM for dopamine and catechol, respectively. Second, laminar flow etching is introduced as a partially nonphotolithographic method of replicating channel networks onto glass substrates. The replication process involves applying a poly(dimethylsiloxane) (PDMS) mold of the channel network onto a slide coated with a sacrificial metal layer and then pulling solutions of metal etchants through the channels to transfer the pattern onto the sacrificial layer. The method is tested, and prototype channel networks are shown. These methods serve to overcome the time and cost involved in fabricating glass-based microchips, thereby making the goal of a disposable high performance lab-on-a-chip more attainable. PMID:12432536

Manica, Drew P; Ewing, Andrew G

2002-11-01

465

SANDRAG: a computer code for predicting drag of bodies of revolution at zero angle of attack in incompressible flow  

SciTech Connect

A design method is presented for calculating the flow field and drag of bodies of revolution at zero angle of attack in compressible flow. The body pressure distribution, viscous shear stress, and boundary layer separation point are calculated by a combination of a potential flow method and boundary layer techniques. The potential solution is obtained by modeling the body with an axial distribution of source/sink elements whose strengths vary linearly along their length. Both the laminar and turbulent boundary layer solutions use momentum integral techniques which have been modified to account for the effects of surface roughness. An existing technique for estimating the location of transition was also modified to include surface roughness. Empirical correlations are developed to estimate the base pressure coefficient on a wide variety of geometries. Body surface pressure distributions and drag predictions are compared with experimental data for artillery projectiles, conical, and flared bodies. Very good agreement between the present method and experiment is obtained. 30 refs., 31 figs., 6 tabs.

Wolfe, W.P.; Oberkampf, W.L.

1985-04-01

466

Development of Advanced High Lift Leading Edge Technology for Laminar Flow Wings.  

National Technical Information Service (NTIS)

This paper describes the Advanced High Lift Leading Edge (AHLLE) task performed by Northrop Grumman Systems Corporation, Aerospace Systems (NGAS) for the NASA Subsonic Fixed Wing project in an effort to develop enabling high-lift technology for laminar fl...

A. Korntheuer J. C. Lin M. M. Bright S. Komadina

2013-01-01

467

Experimental insights into flow impingement in cerebral aneurysm by stereoscopic particle image velocimetry: transition from a laminar regime.  

PubMed

This study experimentally investigated the instability of flow impingement in a cerebral aneurysm, which was speculated to promote the degradation of aneurysmal wall. A patient-specific, full-scale and elastic-wall replica of cerebral artery was fabricated from transparent silicone rubber. The geometry of the aneurysm corresponded to that found at 9 days before rupture. The flow in a replica was analysed by quantitative flow visualization (stereoscopic particle image velocimetry) in a three-dimensional, high-resolution and time-resolved manner. The mid-systolic and late-diastolic flows with a Reynolds number of 450 and 230 were compared. The temporal and spatial variations of near-wall velocity at flow impingement delineated its inherent instability at a low Reynolds number. Wall shear stress (WSS) at that site exhibited a combination of temporal fluctuation and spatial divergence. The frequency range of fluctuation was found to exceed significantly th