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1

Laminar flow of a viscous incompressible fluid in a long porous wavy channel  

Microsoft Academic Search

The linearization technique is used to study viscous incompressible fluid laminar flows in a long, porous, wavy channel, through the simplification and solution of the governing equations of motion under the assumption that the fluid velocity consists of a primary mean flow, perturbed flows, and a secondary mean flow. Long wave approximations are used in obtaining the solution for the

C. N. B. Rao

1981-01-01

2

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

NASA Technical Reports Server (NTRS)

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

Thiede, P.

1978-01-01

3

Split, Characteristic Based Semi-Implicit Algorithm for Laminar/turbulent Incompressible Flows  

NASA Astrophysics Data System (ADS)

In an earlier paper, Zienkiewicz and Codina (Int. j. numer. methods fluids, 20, 869-885 (1995)) presented a general algorithm for the solution of both compressible and incompressible Navier-Stokes equations. The algorithm, based on operator splitting, permits arbitrary interpolation functions to be used while avoiding the Babska-Brezzi restriction. In addition, its characteristic based approach introduces a form of rational dissipation. Zienkiewicz et al. (Int. j. numer. methods fluids, 20, 887-913 (1995)) presented the application of this algorithm in its fully explicit form to various inviscid compressible flow problems. They also presented two incompressible flow problems solved by the fully explicit form, employing a pseudo compressibility. The present work deals with the application of the above algorithm it its semi-implicit form to some incompressible flow benchmark problems. Further, it extends the methodology to turbulent flows by employing both one, and two equation turbulence models. A comparison of results with earlier investigations is presented. Other issues addressed in this study include the effect of additional diffusion terms present in the scheme for both laminar and turbulent flow problems and some practical difficulties associated with local time stepping.

Zienkiewicz, O. C.; Sai, B. V. K. Satya; Morgan, K.; Codina, R.

1996-10-01

4

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

NASA Technical Reports Server (NTRS)

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

Sohn, Jeong L.

1988-01-01

5

Proposal for Numerical Benchmarking of Fluid-Structure Interaction between an Elastic Object and Laminar Incompressible Flow  

Microsoft Academic Search

We describe new benchmark settings for the rigorous evaluation of different methods for fluid-structure interaction problems.\\u000a The configurations consist of laminar incompressible channel flow around an elastic object which results in self-induced oscillations\\u000a of the structure. Moreover, characteristic flow quantities and corresponding plots are provided for a quantitative comparison.

Stefan Turek; Jaroslav Hron

6

Transitions and interactions of inviscid/viscous, compressible/incompressible and laminar/turbulent flows  

NASA Astrophysics Data System (ADS)

This paper addresses the flow field-dependent variation (FDV) methods in which complex physical phenomena are taken into account in the final form of partial differential equations to be solved so that finite difference methods (FDM) or finite element methods (FEM) themselves will not dictate the physics, but rather they are no more than simply the options how to discretize between adjacent nodal points or within an element. The variation parameters introduced in the formulation are calculated from the current flow field based on changes of Mach numbers, Reynolds numbers, Peclet numbers and Damkohler numbers between adjacent nodal points, which play many significant roles, such as adjusting the governing equations (hyperbolic, parabolic and/or elliptic), resolving various physical phenomena and controlling the accuracy and stability of the numerical solution. The theory is verified by a number of example problems addressing the physical implications of the variation parameters, which resemble the flow field itself, shock capturing mechanism, transitions and interactions between inviscid/viscous, compressibility/incompressibility and laminar/turbulent flows. Copyright

Chung, T. J.

1999-09-01

7

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

8

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

NASA Astrophysics Data System (ADS)

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

Cochran, Robert James

9

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

10

Laminar flow control laminarization  

NASA Technical Reports Server (NTRS)

A practical aerodynamically and structurally reasonably efficient laminar flow control (LFC) suction method, removing the slowest boundary layer particles through many closed spaced fine slots, was developed and subsequently applied to a second F94 LFC wing glove in flight: 100 percent laminar flow was observed up to the F94 test limit. Laminar flow on LFC wings in flight is thus possible at a much higher Reynold's number than even in the best low turbulence tunnels as a result of the negligible influence of the atmospheric microscale turbulence on transition. The F94 LFC glove comparison experiments, with suction starting at 0.03c and 0.4c, verified the theoretically predicted boundary layer stabilization by suction starting at 0.08c, thus maintaining laminar flow at substantially higher C sub L numbers as compared to boundary layer stabilization by flow acceleration; i.e., geometry alone without suction upstream of 0.4c.

Pfeminger, W.

1977-01-01

11

On Possible Similarity Solutions for Three-Dimensional Incompressible Laminar Boundary-Layer Flows Over Developable Surfaces and with Proportional Mainstream Velocity Components  

NASA Technical Reports Server (NTRS)

Analysis is presented on the possible similarity solutions of the three-dimensional, laminar, incompressible, boundary-layer equations referred to orthogonal, curvilinear coordinate systems. Requirements of the existence of similarity solutions are obtained for the following: flow over developable surface and flow over non-developable surfaces with proportional mainstream velocity components.

Hansen, Arthur G.

1958-01-01

12

Second law analysis of the 2D laminar flow of two-immiscible, incompressible viscous fluids in a channel  

NASA Astrophysics Data System (ADS)

The laminar and fully developed flows of two immiscible fluids confined in a thin slit of constant wall heat fluxes are analyzed in terms of entropy generations due to irreversibility of forced convection heat transfer. The governing equations are analytically derived using expressions for velocity distributions. The derived equation for the dimensionless entropy generation number is used to interpret the relative importance of frictions to conduction by varying irreversibility distribution ratio ?. It is found that the minimum entropy generation takes place at the dimensionless half transverse distance (?) of 0.3 for values of ? higher than zero. The entropy generation near the plate increases more rapidly in fluid I than in fluid II as viscous dissipation effects becomes more important. The velocity profiles are found to be in agreement with the distributions of the dimensionless entropy generation number ( N S ) for two-immiscible incompressible flows in the slit.

Kam??l?, Fethi; Öztop, Hakan F.

2008-04-01

13

Numerical simulations of incompressible laminar flows using viscous-inviscid interaction procedures  

NASA Astrophysics Data System (ADS)

The present method is based on Helmholtz velocity decomposition where velocity is written as a sum of irrotational (gradient of a potential) and rotational (correction due to vorticity) components. Substitution of the velocity decomposition into the continuity equation yields an equation for the potential, while substitution into the momentum equations yields equations for the velocity corrections. A continuation approach is used to relate the pressure to the gradient of the potential through a modified Bernoulli's law, which allows the elimination of the pressure variable from the momentum equations. The present work considers steady and unsteady two-dimensional incompressible flows over an infinite cylinder and NACA 0012 airfoil shape. The numerical results are compared against standard methods (stream function-vorticity and SMAC methods) and data available in literature. The results demonstrate that the proposed formulation leads to a good approximation with some possible benefits compared to the available formulations. The method is not restricted to two-dimensional flows and can be used for viscous-inviscid domain decomposition calculations.

Shatalov, Alexander V.

14

Study of the development of natural instabilities in a laminar boundary layer in incompressible flow  

NASA Technical Reports Server (NTRS)

Natural instabilities which are created in a laminar boundary layer and which consist of intermittent wave trains were studied. The spectral analysis of these fluctuations makes it possible to localize them in terms of frequency and to isolate their spectrum of amplitude modulation. The variation in terms of abscissa value and ordinate value of these instabilities is compared with the results derived from the solution of the Orr-Sommerfeld equation.

Burnel, S.; Gougat, P.

1981-01-01

15

Transitions and interactions of inviscid\\/viscous, compressible\\/incompressible and laminar\\/turbulent flows  

Microsoft Academic Search

This paper addresses the flow field-dependent variation (FDV) methods in which complex physical phenomena are taken into account in the final form of partial differential equations to be solved so that finite difference methods (FDM) or finite element methods (FEM) themselves will not dictate the physics, but rather they are no more than simply the options how to discretize between

T. J. Chung

1999-01-01

16

Laminar Flow Aircraft Certification  

NASA Technical Reports Server (NTRS)

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

Williams, Louis J. (compiler)

1986-01-01

17

Unified approach for incompressible flows  

NASA Technical Reports Server (NTRS)

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

Chang, Tyne-Hsien

1995-01-01

18

Unified approach for incompressible flows  

NASA Technical Reports Server (NTRS)

An unified approach for solving both compressible and incompressible flows was investigated in this study. The difference in CFD code development between incompressible and compressible flows is due to the mathematical characteristics. However, if one can modify the continuity equation for incompressible flows by introducing pseudocompressibility, the governing equations for incompressible flows would have the same mathematical characters as compressible flows. The application of a compressible flow code to solve incompressible flows becomes feasible. Among numerical algorithms developed for compressible flows, the Centered Total Variation Diminishing (CTVD) schemes possess better mathematical properties to damp out the spurious oscillations while providing high-order accuracy for high speed flows. It leads us to believe that CTVD schemes can equally well solve incompressible flows. In this study, the governing equations for incompressible flows include the continuity equation and momentum equations. The continuity equation is modified by adding a time-derivative of the pressure term containing the artificial compressibility. The modified continuity equation together with the unsteady momentum equations forms a hyperbolic-parabolic type of time-dependent system of equations. The continuity equation is modified by adding a time-derivative of the pressure term containing the artificial compressibility. The modified continuity equation together with the unsteady momentum equations forms a hyperbolic-parabolic type of time-dependent system of equations. Thus, the CTVD schemes can be implemented. In addition, the boundary conditions including physical and numerical boundary conditions must be properly specified to obtain accurate solution. The CFD code for this research is currently in progress. Flow past a circular cylinder will be used for numerical experiments to determine the accuracy and efficiency of the code before applying this code to more specific applications.

Chang, Tyne-Hsien

1993-01-01

19

Triangular spectral elements for incompressible fluid flow  

NASA Technical Reports Server (NTRS)

We discuss the use of triangular elements in the spectral element method for direct simulation of incompressible flow. Triangles provide much greater geometric flexibility than quadrilateral elements and are better conditioned and more accurate when small angles arise. We employ a family of tensor product algorithms for triangles, allowing triangular elements to be handled with comparable arithmetic complexity to quadrilateral elements. The triangular discretizations are applied and validated on the Poisson equation. These discretizations are then applied to the incompressible Navier-Stokes equations and a laminar channel flow solution is given. These new triangular spectral elements can be combined with standard quadrilateral elements, yielding a general and flexible high order method for complex geometries in two dimensions.

Mavriplis, C.; Vanrosendale, John

1993-01-01

20

Triangular spectral elements for incompressible fluid flow  

NASA Technical Reports Server (NTRS)

We discuss the use of triangular elements in the spectral element method for direct simulation of incompressible flow. Triangles provide much greater geometric flexibility and are better conditioned and more accurate than quadrilateral elements when small angles arise. We employ a family of tensor product algorithms for triangles, allowing triangular elements to be handled with comparable arithmetic complexity to quadrilateral elements. The triangular discretizations are applied to the Poisson equation and are validated. The triangular discretizations are then applied to the incompressible Navier-Stokes equations, and a laminar channel flow solution is given. The new triangular spectral elements can be combined with standard quadrilateral elements, yielding a general and flexible high order method for complex geometries in two dimensions.

Mavriplis, Catherine; Van Rosendale, John

1993-01-01

21

Computation of viscous incompressible flows  

NASA Technical Reports Server (NTRS)

Incompressible Navier-Stokes solution methods and their applications to three-dimensional flows are discussed. A brief review of existing methods is given followed by a detailed description of recent progress on development of three-dimensional generalized flow solvers. Emphasis is placed on primitive variable formulations which are most promising and flexible for general three-dimensional computations of viscous incompressible flows. Both steady- and unsteady-solution algorithms and their salient features are discussed. Finally, examples of real world applications of these flow solvers are given.

Kwak, Dochan

1989-01-01

22

Supersonic laminar flow control research  

NASA Technical Reports Server (NTRS)

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

Lo, Ching F.

1994-01-01

23

Preconditioners for incompressible flows  

NASA Astrophysics Data System (ADS)

We consider solution methods for large systems of linear equations that arise from the finite element discretization of the incompressible Navier-Stokes equations. These systems are of the so-called saddle point type, which means that there is a large block of zeros on the main diagonal. To solve these type of systems efficiently, several block preconditioners have been published. We propose a new block preconditioner MSIMPLER which is a modified version of the SIMPLER solver proposed by Patankar. We compare the performance of the block preconditioners: pressure convection diffusion (PCD), least squares commutator (LSC), and augmented Lagrangian based (AL) preconditioners with the MSIMPLER preconditioner. These preconditioners are first compared for academic problems generated by the IFISS package. Thereafter, we compare the best preconditioners for industrial problems using the SEPRAN FEM package. It appears that the MSIMPLER preconditioner is in general the best method. Finally we also consider the solution of the Stokes problem with variable viscosity. We consider smoothly varying viscosity and jumps in the viscosity. It appears that a special preconditioner is independent of the grid-size and independent of the viscosity variation. Applications from geophysics are used to illustrate the performance.

Vuik, Cornelis; Rehman, Mehfooz Ur; Segal, Guus

2009-11-01

24

Incompressible flow around small obstacles  

NASA Astrophysics Data System (ADS)

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

Lopes Filho, Milton

2010-11-01

25

On Hydrodynamic Stability of Two-Dimensional Unsteady Incompressible Laminar Boundary Layers.  

National Technical Information Service (NTIS)

A linearized hydrodynamic stability theory for unsteady incompressible laminar boundary layers over arbitrary cylinders is described. Criteria based on the instantaneous rate of change of the disturbance energy are introduced. In order to apply these crit...

K. T. Yang M. D. Kelleher

1964-01-01

26

Overview of Laminar Flow Control  

NASA Technical Reports Server (NTRS)

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

Joslin, Ronald D.

1998-01-01

27

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

28

Direct Energy Conversion Systems. Supplement 1. Heat and Mass Transfer from the Surface of a Cylinder with Discontinuous Boundary Conditions to an Incompressible Laminar Flow.  

National Technical Information Service (NTIS)

Heat and mass transfer studies for flow over a cylinder having a longitudinal-strip source of hear or mass, are presented. A theory for the two asymptotic cases of Pr6 approaches infinity and Pr approaches 0 is developed, giving the temperature profile an...

Z. Rotem D. M. Mason

1964-01-01

29

Accurate solution algorithms for incompressible multiphase flows  

SciTech Connect

A number of advances in modeling multiphase incompressible flow are described. These advances include high-order Godunov projection methods, piecewise linear interface reconstruction and tracking and the continuum surface force model. Examples are given.

Rider, W.J.; Kothe, D.B.; Mosso, S.J.; Cerutti, J.H. [Los Alamos National Lab., NM (United States); Hochstein, J.I. [Memphis State Univ., TN (United States). Dept. of Mechanical Engineering

1994-10-19

30

Laminar-flow flight experiments  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

31

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

PubMed Central

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

Velescu, Cornel; Popa, Nicolae Calin

2014-01-01

32

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

33

Incompressible viscous flows on adaptive, multi-block grids  

NASA Technical Reports Server (NTRS)

Adaptive, multi-block grid solutions to incompressible viscous flows using a pseudocompressibility approach in generalized three-dimensional coordinates are presented. The multi-block approach described in this paper allows the user to compute flows in arbitrary geometries without the necessity of ad hoc modifications to the flow code. Complete grid continuity at block interfaces is assumed and block-to-block connectivity in a domain, including all boundary conditions, is specified by user input through the NAMELIST utility. Therefore, solution continuity across block interfaces is achieved through automatic communication among adjacent blocks. Also, adaptive grid generation is employed to enhance grid quality in response to the evolving solution in order to better resolve the flow field. Several two- and three-dimensional solutions are compared with equivalent non-adaptive solutions and available experimental data to validate the present method for both laminar and turbulent cases.

Kim, Young-Mog; Gatlin, Boyd

1993-01-01

34

Efficient solutions of two-dimensional incompressible steady viscous flows  

NASA Technical Reports Server (NTRS)

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

Morrison, J. H.; Napolitano, M.

1986-01-01

35

Combination Of Techniques For Computing Incompressible Flow  

NASA Technical Reports Server (NTRS)

Pseudocompressibility, upwind differencing, and other techniques used to solve Navier-Stokes equations. Scheme for finite-difference numerical solution of two-dimensional Navier-Stokes equations of incompressible flow combines several recently developed methods, each developed to increase speed and/or accuracy of computations of this kind.

Kwak, D.; Rogers, S. E.

1990-01-01

36

Maximal mixing by incompressible fluid flows  

NASA Astrophysics Data System (ADS)

We consider a model for mixing binary viscous fluids under an incompressible flow. We prove the impossibility of perfect mixing in finite time for flows with finite viscous dissipation. As measures of mixedness we consider a Monge-Kantorovich-Rubinstein transportation distance and, more classically, the H-1 norm. We derive rigorous a priori lower bounds on these mixing norms which show that mixing cannot proceed faster than exponentially in time. The rate of the exponential decay is uniform in the initial data.

Seis, Christian

2013-12-01

37

A computational model for three-dimensional incompressible wall jets with large cross flow  

NASA Technical Reports Server (NTRS)

A computational model for the flow field of three dimensional incompressible wall jets prototypic of thrust augmenting ejectors with large cross flow is presented. The formulation employs boundary layer equations in an orthogonal curvilinear coordinate system. Simulation of laminar as well as turbulen wall jets is reported. Quantification of jet spreading, jet growth, nominal separation, and jet shrink effects due to corss flow are discussed.

Murphy, W. D.; Shankar, V.; Malmuth, N. D.

1979-01-01

38

A combustion model for incompressible flows  

SciTech Connect

Flow of a pre-mixed, reactive, incompressible, viscous fluid was studied using a combination of vortex methods and a flame propagation algorithm based on Huygens principle. The random vortex methods are lagrangian methods used to resolve the motion of incompressible fluids regulated by the Navier-Stokes equations. They are best suited for flows at high Reynolds numbers. Detailed description of the vortex blobs, and vortex sheets methods is given together with the presentation of a hybrid vortex method that relates the two. The combustion part of the problem is modeled by a variation of the SLIC (Simple Line Interface Calculation) algorithm, that involves the use of a flame dictionary which contains flame speeds and preheat thicknesses. The combined algorithms are tested on a cold flat plate with different free stream velocities. The numerical results show the effects of cold boundaries, turbulence, and exothermicity on the burning process.

Calzada, M.E.

1991-01-01

39

a Combustion Model for Incompressible Flows  

NASA Astrophysics Data System (ADS)

We study the flow of a pre-mixed, reactive, incompressible, viscous fluid, using a combination of vortex methods and a flame propagation algorithm based on Huyghens' principle. The random vortex methods are lagrangian methods used to resolve the motion of incompressible fluids regulated by the Navier -Stokes equations. They are best suited for flows at high Reynolds numbers. Detailed description of the vortex blobs, and vortex sheets methods is given together with the presentation of a hybrid vortex method that relates the two. The combustion part of the problem is modeled by a variation of the SLIC (Simple Line Interface Calculation) algorithm, that involves the use of a flame dictionary which contains flame speeds and preheat thicknesses. The combined algorithms are tested on a cold flat late with different free stream velocities. The numerical results show the effects of cold boundaries, turbulence, and exothermicity on the burning process.

Calzada, Maria Eugenia

40

Laminar-flow wind tunnel experiments  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

41

High-End Computing for Incompressible Flows  

NASA Technical Reports Server (NTRS)

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

Kwak, Dochan; Kiris, Cetin

2001-01-01

42

Flow Solver for Incompressible Rectangular Domains  

NASA Technical Reports Server (NTRS)

This is an extension of the Flow Solver for Incompressible 2-D Drive Cavity software described in the preceding article. It solves the Navier-Stokes equations for incompressible flow using finite differencing on a uniform, staggered grid. There is a runtime choice of either central differencing or modified upwinding for the convective term. The domain must be rectangular, but may have a rectangular walled region within it. Currently, the position of the interior region and exterior boundary conditions are changed by modifying parameters in the code and recompiling. These features make it possible to solve a variety of classical fluid flow problems such as an L-shaped cavity, channel flow, or wake flow past a square cylinder. The code uses fourth-order Runge-Kutta time-stepping and overall second-order spatial accuracy. This software permits the walled region to be positioned such that flow past a square cylinder, an L-shaped cavity, and the flow over a back-facing step can all be solved by reconfiguration. Also, this extension has an automatic detection of periodicity, as well as use of specialized data structure for ease of configuring domain decomposition and computing convergence in overlap regions.

Kalb, Virginia L.

2008-01-01

43

A flow network formulation for compressible and incompressible flow  

Microsoft Academic Search

Purpose – One-dimensional pipe network flow analysis can be used in many applications to satisfactorily solve various engineering problems. The paper aims to focus on this. Design\\/methodology\\/approach – A hybrid nodal method is detailed, which solves the pressure field prior to the elemental flows, and models both compressible gas and incompressible liquid and gas flows. Findings – The results obtained

J. J. Pretorius; A. G. Malan; J. A. Visser

2008-01-01

44

Penalty function finite element analysis of steady viscous incompressible flow in rotating coordinates  

NASA Technical Reports Server (NTRS)

Finite element methods for incompressible viscous flow in turbomachines have not been presented in the literature previously. This paper develops a penalty function primitive variable method including Coriolis and centrifugal force terms for steady flow in a rotating coordinate system. Simplex elements are used with the result of solution times comparable to equivalent finite different solutions. Example cases considered are Couette flow, Poiseuile flow, flow over a step and flow in a rotating channel. Both laminar and turbulent flows are discussed. The accuracy of computed solutions compares well with theoretical solutions and experimenal measurements.

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

1984-01-01

45

Physical effects in laminar microconvection due to variations in incompressible fluid properties  

Microsoft Academic Search

In this investigation we report the identification of laminar microconvection physical effects due to the variation of viscosity and thermal-conductivity of liquid. Viscosity variation significantly distorts the axial velocity profile and varies this distortion along the microflow, thereby inducing radial flow due to flow continuity. The resulting induced radial heat convection can be a significant percentage of the axial heat

S. P. Mahulikar; H. Herwig

2006-01-01

46

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

47

Laminar fully developed flow and heat transfer of Robertson-Stiff fluids in a rectangular duct  

Microsoft Academic Search

The laminar fully developed flow and heat transfer through a rectangular duct of a viscous incompressible Robertson-Stiff fluid is investigated. Robertson-Stiff fluids are time independent non-Newtonian materials possessing a yield value. The governing momentum and energy equations are solved numerically using finite-difference approximations. We consider two cases of thermal boundary conditions: H-1 the \\

M. E. Sayed-Ahmed; A. S. El-Yazal

2005-01-01

48

Skin-Friction Measurements in Incompressible Flow  

NASA Technical Reports Server (NTRS)

Experiments have been conducted to measure the local surface-shear stress and the average skin-friction coefficient in Incompressible flow for a turbulent boundary layer on a smooth flat plate having zero pressure gradient. Data were obtained for a range of Reynolds numbers from 1 million to 45 million. The local surface-shear stress was measured by a floating-element skin-friction balance and also by a calibrated total head tube located on the surface of the test wall. The average skin-friction coefficient was obtained from boundary-layer velocity profiles.

Smith, Donald W.; Walker, John H.

1959-01-01

49

Multigrid Approach to Incompressible Viscous Cavity Flows  

NASA Technical Reports Server (NTRS)

Two-dimensional incompressible viscous driven-cavity flows are computed for Reynolds numbers on the range 100-20,000 using a loosely coupled, implicit, second-order centrally-different scheme. Mesh sequencing and three-level V-cycle multigrid error smoothing are incorporated into the symmetric Gauss-Seidel time-integration algorithm. Parametrics on the numerical parameters are performed, achieving reductions in solution times by more than 60 percent with the full multigrid approach. Details of the circulation patterns are investigated in cavities of 2-to-1, 1-to-1, and 1-to-2 depth to width ratios.

Wood, William A.

1996-01-01

50

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

51

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

52

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

SciTech Connect

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

Hefner, J.N.; Sabo, F.E.

1987-12-01

53

Supercomputing Aspects for Simulating Incompressible Flow  

NASA Technical Reports Server (NTRS)

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

Kwak, Dochan; Kris, Cetin C.

2000-01-01

54

Method for the evaluation of minor losses in pulsatile laminar fluid flow  

NASA Astrophysics Data System (ADS)

This article focuses on description and evaluation of the size of the minor losses in pulsatile laminar flow. It describes a method for determination of minor losses with respect to the phase delay between pressure waveforms and flow waveforms. The whole evaluation method is presented on the example of minor loss in the sharp 90° bend in the channel with constant square cross-section in pulsatile laminar flow of an incompressible Newtonian fluid. For this example, the minor loss coefficient is expressed depending on the dimensionless flow parameters. Total minor loss was calculated numerically. An analytical solution was used for quantification of the head loss in the developed laminar flow in the straight channel. Unsteady flow conditions were controlled by the sinusoidal flow.

Net?ebská, H.; Mat?cha, J.; Schmirler, M.; Manoch, L.; Adamec, J.

2014-03-01

55

Wing Leading Edge Joint Laminar Flow Tests  

NASA Technical Reports Server (NTRS)

An F-104G aircraft at NASA's Dryden Flight Research Center has been equipped with a specially designed and instrumented test fixture to simulate surface imperfections of the type likely to be present near the leading edge on the wings of some laminar flow aircraft. The simulated imperfections consisted of five combinations of spanwise steps and gaps of various sizes. The unswept fixture yielded a pressure distribution similar to that of some laminar flow airfoils. The experiment was conducted at cruise conditions typical for business-jets and light transports: Mach numbers were in the range 0.5-0.8, and unit Reynolds numbers were 1.5-2.5 million per foot. Skin friction measurements indicated that laminar flow was often maintained for some distance downstream of the surface imperfections. Further work is needed to more precisely define transition location and to extend the experiments to swept-wing conditions and a broader range of imperfection geometries.

Drake, Aaron; Westphal, Russell V.; Zuniga, Fanny A.; Kennelly, Robert A., Jr.; Koga, Dennis J.

1996-01-01

56

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

57

Simulation of laminar flow inside ducts of irregular geometry using integral transforms  

NASA Astrophysics Data System (ADS)

The Generalized Integral Transform Technique is employed in the hybrid numerical-analytical solution of the steady two-dimensional Navier-Stokes equations, defined within arbitrarily shaped domains, for incompressible laminar channel flow. The formalism is illustrated for the classical test-case of laminar flow in a gradual expansion duct. Numerical results with automatic global accuracy control are obtained for suggested values of Reynolds numbers in the literature, and critically compared against previously reported benchmark solutions for the same problem. The relative merits of the proposed approach are then pointed out.

Pérez Guerrero, J. S.; Quaresma, J. N. N.; Cotta, R. M.

58

AN IMMERSED BOUNDARY METHOD FOR COMPLEX INCOMPRESSIBLE FLOWS  

EPA Science Inventory

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

59

A parallel implicit incompressible flow solver using unstructured meshes  

NASA Astrophysics Data System (ADS)

An incompressible flow solver based on unstructured grids is implemented on a parallel distributed memory computer architecture. An important phase in the flow solver is the solution of the elliptic equations for the velocities and pressure. This elliptic solver is parallelized and incorporated into both the explicit and implicit versions of the incompressible flow solver. Performance and scalability studies are carried out on both Intel iPSC 860 and the Intel Delta prototype, and show that the code is scalable. A parallelizable load balancing algorithm is developed to be used in conjunction with the incompressible flow solver. Steady and unsteady flows over a tri-element airfoil and NACA0012 airfoil are computed using the parallel incompressible flow solver.

Raniamurti, Ravi; Lohner, Rainald

1993-01-01

60

Laminar Flow in the Ocean Ekman Layer  

NASA Astrophysics Data System (ADS)

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

Woods, J. T. H.

61

Investigation of a Laminar Flow Leading Edge  

NASA Technical Reports Server (NTRS)

The recent resurgence of interest in utilizing laminar flow on aircraft surfaces for reduction in skin friction drag has generated a considerable amount of research in natural laminar flow (NLF) and hybrid laminar flow control (HLFC) on transonic aircraft wings. This research has focused primarily on airfoil design and understanding transition behavior with little concern for the surface imperfections and manufacturing variations inherent to most production aircraft. In order for laminar flow to find wide-spread use on production aircraft, techniques for constructing the wings must be found such that the large surface imperfections present in the leading edge region of current aircraft do not occur. Toward this end, a modification to existing leading edge construction techniques was devised such that the resulting surface did not contain large gaps and steps as are common on current production aircraft of this class. A lowspeed experiment was first conducted on a simulation of the surface that would result from this construction technique. Preston tube measurements of the boundary layer downstream of the simulated joint and flow visualization using sublimation chemicals validated the literature on the effects of steps on a laminar boundary layer. These results also indicated that the construction technique was indeed compatible with laminar flow. In order to fully validate the compatibility of this construction technique with laminar flow, thus proving that it is possible to build wings that are smooth enough to be used on business jets and light transports in a manner compatible with laminar flow, a flight experiment is being conducted. In this experiment Mach number and Reynolds number will be matched in a real flight environment. The experiment is being conducted using the NASA Dryden F-104 Flight Test Fixture (FTF). The FTF is a low aspect ratio ventral fin mounted beneath an F-104G research aircraft. A new nose shape was designed and constructed for this experiment. This nose shape provides an accelerating pressure gradient in the leading edge region. By flying the aircraft at appropriate Mach numbers and altitudes, this nose shape simulates the leading edge region of a laminar flow wing for a business jet or light transport. Manufactured into the nose shape is a spanwise slot located approximately four inches downstream of the leading edge. The slot, which is an inch wide and one-eighth of an inch deep allows the simulation of surface imperfections, such as gaps and steps at skin joints, which will occur on aircraft using this new construction technique. By placing strips of aluminum of various sizes and shapes in the slot, the effect on the boundary layer of different sizes and shapes of steps and gaps will be examined. It is planned to use five different configurations, differing primarily in the size and number of gaps. Downstream of the slot, the state of the boundary layer is determined using hot film gages and Stanton gages. Agreement between these two very different techniques of measuring boundary layer properties is considered important to being able to state with confidence the effects on the boundary layer of the simulated manufacturing imperfections. To date, the aircraft has not flown. First flights of the aircraft are on schedule to begin October 4, 1993. Low-speed, preliminary experiments at matching Reynolds numbers have been completed.

Drake, Aaron; Kennelly, Robert A., Jr.; Koga, Dennis J.; Westphal, Russell V.; Zuniga, Fanny

1994-01-01

62

Spatially adaptive techniques for level set methods and incompressible flow  

Microsoft Academic Search

Since the seminal work of [Sussman, M, Smereka P, Osher S. A level set approach for computing solutions to incompressible two-phase flow. J Comput Phys 1994;114:146–59] on coupling the level set method of [Osher S, Sethian J. Fronts propagating with curvature-dependent speed: algorithms based on Hamilton–Jacobi formulations. J Comput Phys 1988;79:12–49] to the equations for two-phase incompressible flow, there has

Frank Losasso; Ronald Fedkiw; Stanley Osher

2006-01-01

63

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

64

Laminar Flow Through Circular Tubes with Side Inlets  

NASA Astrophysics Data System (ADS)

We discuss experimental results on steady axisymmetric flow of a Newtonian incompressible fluid through circular pipes with side inlets. Circular tubes with a set of holes along their sidewalls are used in a number of medical procedures as straight catheters to transfer fluid into or out of the human body. For example, because of the small size of the incision required, they are commonly used in peritoneal dialysis. The internal diameter and the diameter of the side holes are often 1 mm and less, and as a result, the fluid flow is laminar in a typical medical procedure. An understanding of the flow inside the catheter tube in terms of its geometric parameters will be key in designing new catheters with optimal clinical performance for specific applications. In the experiments, water is withdrawn from a smooth tube with side holes and the local axial pressure and flow rates through the side holes are measured for different flow conditions. A nondimensionalization of the data shows a power-law behavior in only some cases. Using numerical simulations, it is shown how the interaction of the axial flow with the impinging jets from the side holes can change the overall behavior of the flow for a given suction pressure.

Abedian, Behrouz; Muhlanger, Eric

2004-11-01

65

Statistical theory of turbulent incompressible multimaterial flow  

SciTech Connect

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

Kashiwa, B.

1987-10-01

66

Hydrodynamic and heat transfer characteristics of laminar flow past a parabolic cylinder with constant heat flux  

Microsoft Academic Search

Steady, two-dimensional, symmetric, laminar and incompressible flow past parabolic bodies in a uniform stream with constant heat flux is investigated numerically. The full Navier-Stokes and energy equations in parabolic coordinates with stream function, vorticity and temperature as dependent variables were solved. These equations were solved using a second order accurate finite difference scheme on a non-uniform grid. The leading edge

M. Abu-Qudais; O. M. Haddad; A. M. Maqableh

2001-01-01

67

Hydrodynamic and heat transfer characteristics of laminar flow past a parabolic cylinder with constant heat flux  

Microsoft Academic Search

Steady, two-dimensional, symmetric, laminar and incompressible flow past parabolic bodies in a uniform stream with constant\\u000a heat flux is investigated numerically. The full Navier–Stokes and energy equations in parabolic coordinates with stream function,\\u000a vorticity and temperature as dependent variables were solved. These equations were solved using a second order accurate finite\\u000a difference scheme on a non-uniform grid. The leading edge

M. Abu-Qudais; O. M. Haddad; A. M. Maqableh

2001-01-01

68

Comparison of Pressure-Based and Artificial Compressibility Methods for Solving 3D Steady Incompressible Viscous Flows  

Microsoft Academic Search

Pressure-based and artificial compressibility methods for calculating three-dimensional, steady, incompressible viscous flows are compared in this work. Each method is applied to the prediction of three-dimensional, laminar flows in strongly curved ducts of square and circular cross sections. Numerical predictions from each method are compared with available experimental data and previously reported predictions using a multigrid numerical method. The accuracy,

Panos Tamamidis; Guoqing Zhang; Dennis N. Assanis

1996-01-01

69

General Equation Set Solver for Compressible and Incompressible Turbomachinery Flows  

NASA Technical Reports Server (NTRS)

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

Sondak, Douglas L.; Dorney, Daniel J.

2002-01-01

70

Insect contamination protection for laminar flow surfaces  

NASA Technical Reports Server (NTRS)

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

Croom, Cynthia C.; Holmes, Bruce J.

1986-01-01

71

Laminar Flow Control at High Speeds  

NASA Astrophysics Data System (ADS)

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 of T-S waves, Goertler vortices, crossflow vortices, and attachment-line contamination. Choices range from using 2-D wings instead of 3-D wings, subsonic or supersonic leading edges, and passive or active control methods. Goertler and crossflow vortices exhibit early nonlinear growth and saturation and require solutions outside of the usual linear stability analysis. As a result, one brings to bear coordinated wind-tunnel tests, flight tests, DNS, and nonlinear PSE. All of these efforts are reviewed with special attention paid to the use of distributed roughness to modulate the nonlinear growth of crossflow waves.

Saric, William

2003-11-01

72

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

73

Laminar nanofluid flow in microheat-sinks  

Microsoft Academic Search

In response to the ever increasing demand for smaller and lighter high-performance cooling devices, steady laminar liquid nanofluid flow in microchannels is simulated and analyzed. Considering two types of nanofluids, i.e., copper-oxide nanospheres at low volume concentrations in water or ethylene glycol, the conjugated heat transfer problem for microheat-sinks has been numerically solved. Employing new models for the effective thermal

J. Koo; C. Kleinstreuer

2005-01-01

74

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

75

A Poisson equation formulation for pressure calculations in penalty finite element models for viscous incompressible flows  

NASA Technical Reports Server (NTRS)

The calculation of pressures when the penalty-function approximation is used in finite-element solutions of laminar incompressible flows is addressed. A Poisson equation for the pressure is formulated that involves third derivatives of the velocity field. The second derivatives appearing in the weak formulation of the Poisson equation are calculated from the C0 velocity approximation using a least-squares method. The present scheme is shown to be efficient, free of spurious oscillations, and accurate. Examples of applications are given and compared with results obtained using mixed formulations.

Sohn, J. L.; Heinrich, J. C.

1990-01-01

76

Calculation of incompressible fluid flow through cambered blades  

NASA Technical Reports Server (NTRS)

Conformal mapping technique yields linear, approximate solutions for calculating flow of an incompressible fluid through staggered array of cambered blades for the cases of flow with partial cavitation and supercavitation. Lift and drag coefficients, cavitation number, cavity shape, and exit flow conditions can be determined.

Hsu, C. C.

1970-01-01

77

Boundary Layer Theory. Part 1; Laminar Flows  

NASA Technical Reports Server (NTRS)

The purpose of this presentation is to give you a survey of a field of aerodynamics which has for a number of years been attracting an ever growing interest. The subject is the theory of flows with friction, and, within that field, particularly the theory of friction layers, or boundary layers. As you know, a great many considerations of aerodynamics are based on the so-called ideal fluid, that is, the frictionless incompressible fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid (potential theory) has been made possible.

Schlichting, H.

1949-01-01

78

ENHANCEMENTS OF THE SIMPLE METHOD FOR PREDICTING INCOMPRESSIBLE FLUID FLOWS  

Microsoft Academic Search

Variations of the SIMPLE method of Patankar and Spalding have been widely used over the past decade to obtain numerical solutions to problems involving incompressible flows. The present paper shows several modifications to the method which both simplify its implementation and reduce solution costs. The performances of SIMPLE, SIMPLER, and SIMPLEC (the present method) are compared for two recirculating flow

J. P. Van Doormaal; G. D. Raithby

1984-01-01

79

Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

80

A Numerical Method for Incompressible Flow with Heat Transfer  

NASA Technical Reports Server (NTRS)

A numerical method for the convective heat transfer problem is developed for low speed flow at mild temperatures. A simplified energy equation is added to the incompressible Navier-Stokes formulation by using Boussinesq approximation to account for the buoyancy force. A pseudocompressibility method is used to solve the resulting set of equations for steady-state solutions in conjunction with an approximate factorization scheme. A Neumann-type pressure boundary condition is devised to account for the interaction between pressure and temperature terms, especially near a heated or cooled solid boundary. It is shown that the present method is capable of predicting the temperature field in an incompressible flow.

Sa, Jong-Youb; Kwak, Dochan

1997-01-01

81

Microphone Detects Waves In Laminar Boundary-Layer Flow  

NASA Technical Reports Server (NTRS)

Simple noninvasive acoustical technique effective in measurement of instability waves, which precede onset of turbulence in laminar boundary layer flows. Microphone mounted below surface detects pressure waves indicative of instabilities in laminar flow. Relatively insensitive to long-wavelength background noise. Such measurements important in research on aerodynamic flows and potential applications in control of turbulence (with consequent reduction of drag) on aircraft.

Kendall, James M.

1990-01-01

82

A monolithic mass tracking formulation for bubbles in incompressible flow  

SciTech Connect

We devise a novel method for treating bubbles in incompressible flow that relies on the conservative advection of bubble mass and an associated equation of state in order to determine pressure boundary conditions inside each bubble. We show that executing this algorithm in a traditional manner leads to stability issues similar to those seen for partitioned methods for solid–fluid coupling. Therefore, we reformulate the problem monolithically. This is accomplished by first proposing a new fully monolithic approach to coupling incompressible flow to fully nonlinear compressible flow including the effects of shocks and rarefactions, and then subsequently making a number of simplifying assumptions on the air flow removing not only the nonlinearities but also the spatial variations of both the density and the pressure. The resulting algorithm is quite robust, has been shown to converge to known solutions for test problems, and has been shown to be quite effective on more realistic problems including those with multiple bubbles, merging and pinching, etc. Notably, this approach departs from a standard two-phase incompressible flow model where the air flow preserves its volume despite potentially large forces and pressure differentials in the surrounding incompressible fluid that should change its volume. Our bubbles readily change volume according to an isothermal equation of state.

Aanjaneya, Mridul, E-mail: aanjneya@cs.stanford.edu; Patkar, Saket, E-mail: patkar@cs.stanford.edu; Fedkiw, Ronald, E-mail: fedkiw@cs.stanford.edu

2013-08-15

83

Base pressure in laminar supersonic flow.  

NASA Technical Reports Server (NTRS)

An asymptotic description is proposed for supersonic laminar flow over a wedge or a backward-facing step, for large Reynolds number and for a base or step height which is small compared with the boundary-layer length. The analysis is carried out for adiabatic wall conditions and a viscosity coefficient proportional to temperature. In a particular limit corresponding to a very thick boundary layer, a similarity law is obtained for the base pressure. For a thinner boundary layer an asymptotic form for the base pressure is obtained which shows the dependence on the parameters explicitly and which permits good agreement with experiment. This latter result is based on an inviscid-flow approximation for the corner expansion and for reattachment with viscous forces important primarily in a thin sublayer about the dividing streamline. A prediction of the pressure distribution at reattachment is given and the result is compared with experimental pressure distributions.

Messiter, A. F.; Hough, G. R.; Feo, A.

1973-01-01

84

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

85

A stabilised nonconforming finite element method for steady incompressible flows  

Microsoft Academic Search

A stabilised nonconforming finite element method for the steady incompressible flow problem with damping based on local Gauss integration is considered in this article. The method combines the nonconforming finite element method with the stabilised strategy. Moreover, the stability and error estimates are analysed. Finally, numerical results are shown to support the developed theory analysis. Compared with some classical, closely

Pengzhan Huang; Xinlong Feng; Demin Liu

2012-01-01

86

Steady incompressible flow past a row of circular cylinders  

Microsoft Academic Search

Numerical solutions are presented for steady two-dimensional incompressible flow past an infinite row of cylinders (of unit radii, with distances W between their centers). The calculations cover R below 700 for cylinder separations from 5 to infinity and also R = 800 for between 5 and 100 (where R denotes the Reynolds number based on the cylinder diameters). The recirculation

Bengt Fornberg

1991-01-01

87

Laminar flow control perforated wing panel development  

NASA Technical Reports Server (NTRS)

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

Fischler, J. E.

1986-01-01

88

Stability of axisymmetric swirl flows of viscous incompressible fluid  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

89

Gliding Swifts Attain Laminar Flow over Rough Wings  

PubMed Central

Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1–2% of chord length on the upper surface—10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n?=?3; std 13%) of their total area during glides that maximize flight distance and duration—similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance.

Lentink, David; de Kat, Roeland

2014-01-01

90

Gliding Swifts Attain Laminar Flow over Rough Wings.  

PubMed

Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1-2% of chord length on the upper surface-10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n?=?3; std 13%) of their total area during glides that maximize flight distance and duration-similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. PMID:24964089

Lentink, David; de Kat, Roeland

2014-01-01

91

Perfect and Incompressible Fluid Flow in Turbomachines.  

National Technical Information Service (NTIS)

A method for calculating flow through an airfoil cascade drawn on a surface of revolution is discussed. The three-dimensional flow was assumed to be represented by part-channels of varying width. The basic equations are the equation of continuity and the ...

L. R. Eremeef

1974-01-01

92

Conservative properties of finite difference schemes for incompressible flow  

NASA Technical Reports Server (NTRS)

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

Morinishi, Youhei

1995-01-01

93

Inductively coupled plasma torch with laminar flow cooling  

DOEpatents

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

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

1991-04-30

94

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

NASA Technical Reports Server (NTRS)

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

Chen, Y. S.

1986-01-01

95

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

NASA Technical Reports Server (NTRS)

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

Kim, Sang-Wook

1988-01-01

96

A finite element method for turbulent incompressible flow  

NASA Astrophysics Data System (ADS)

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

Chabard, J.-P.

97

Numerical study of laminar and turbulent flows inside a turnaround duct with and without guide vanes  

NASA Technical Reports Server (NTRS)

The purpose of this study is to examine in detail incompressible laminar and turbulent flows inside a turnaround duct with and without guide vanes and to investigate the effects of vanes on the flow characteristics. To perform this study, an implicit finite difference code cast in general curvilinear coordinates is further developed. The code is based on the method of pseudo-compressibility and utilize ADI or implicit approximate factorization algorithm to achieve computational efficiency. Method of segmental sweeping is developed to overcome the multiple-zone problem due to imposition of guide vanes. In the present study, several test cases have been computed. These test cases include laminar and turbulent flows inside a turnaround duct without and with two or three guide vanes. The study reveals that: (1) there exists large recirculation zones inside the duct if no vanes are present; (2) properly shaped and positional guide vanes are effective in eliminating flow separation; and (3) laminar and turbulent flows have similar flow features. But turbulent flow has less total pressure drop.

Lin, S.-J.; Chang, James L. C.

1987-01-01

98

Windtunnel as a Tool for Laminar Flow Research.  

National Technical Information Service (NTIS)

Testing laminar airfoils or wings in the wind tunnel, entails some specific experimental problems. These problems are discussed in the paper using the (limited) experience of laminar flow tests made in the High Speed Wind Tunnel HST of NLR. Special measur...

A. Elsenaar

1990-01-01

99

Incompressible Turbulent Wing-Body Junction Flow  

NASA Technical Reports Server (NTRS)

The overall objective of this study is to contribute to the optimized design of fan bypass systems in advanced turbofan engines. Increasing the engine bypass ratios have provided a major boost in engine performance improvement over the last fifty years. An engine with high bypass ratio (11-16:1) such as the Advanced Ducted Propulsion (ADP) is being developed and is expected to provide an additional 25% improvement in overall efficiency over the early turbofans. Such significant improvements in overall efficiency would reduce the cost per seat mile, which is a major government and Industry challenge for the 21th century. The research is part of the Advanced Subsonic Technology (AST) program that involves a NASA, U.S. Industry and FAA partnership with the goal of a safe and highly productive global air transportation system. The immediate objective of the study is to perform numerical simulation of duct-strut interactions to elucidate the loss mechanisms associated with this configuration that is typical of advanced turbofan engines such as ADP. However, at present experimental data for a duct-strut configuration are not available. Thus, as a first step a wing-body junction flow would be studied and is the specific objective of the present study. At the outset it is to be recognized that while duct-strut interaction flow is similar to that of wing-body junction flows, there are some differences owing to the presence of a wall at both ends of the strut. Likewise, some differences are due to the sheared inflow (as opposed to a uniform inflow) velocity profile. It is however expected that some features of a wing-body junction flow would persist. Next, some of the salient aspects of the complex flow near a wing-body junction, as revealed by various studies reported in the literature will be reviewed. One of the principle characteristics of the juncture flow, is the presence of the mean flow components in a plane perpendicular to the direction of the oncoming free-stream flow. The lateral curvature of the wing/strat causes the oncoming turbulent layer to skew about am axis (x-axis) parallel to the plane (xz-plane) of the mean shear. This is the principle mechanism for the generation of secondary flow. Such skew-induced secondary flows are slow to be attenuated by Reynolds stresses. Additional contribution to the generation of secondary flow comes from anisotropies in Reynolds stresses. Upstream of the strut, the mean-vorticity is directed span wise (along the y-direction). The presence of secondary flow in the vicinity of the strut causes the vorticity to stretch around the obstacle in a horse-shoe shape, with each leg having a vorticity of the opposite sense. The blockage effect of the strut imposes a severe adverse pressure gradient on the oncoming turbulent shear layer, causing boundary layer separation ahead of the leading edge, resulting in a vortex that rolls up and flows downstream into the juncture region. The separation vortices trailing in the wake of the wing can alter the lift or drag characteristics of the surfaces downstream of the wing-body juncture. Likewise, on submarines, the wake flow behind the appendage can degrade the performance of the propeller located downstream. The complex nature of this flow is caused by the presence of all six components of Reynolds stresses. Devenport and Simpson report that in the vicinity of the horse-shoe vortex there is intense recirculation with turbulent stresses being much larger than those normally observed in turbulent flows. These features contribute to making this flow a challenge to predict numerically. Some of the past studies provide useful insights into this flow that would guide our numerical efforts. In measurements reported by Shabaka and Bradshaw, the eddy viscosity tensor is seen to be non-isotropic and has negative components in certain regions. In an effort to evaluate the closure assumptions of various turbulence models, Devenport and Simpson used their own extensive measurements in juncture flows around the nose of a wing-body junction. Measured values of me

Krishnamurthy, R.; Cagle, Corey D.; Chandra, S.

1998-01-01

100

Natural laminar flow airfoil analysis and trade studies  

NASA Technical Reports Server (NTRS)

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

1979-01-01

101

Current Laminar Flow Control Experiments at NASA Dryden  

NASA Technical Reports Server (NTRS)

An experiment to demonstrate laminar flow over the swept wing of a subsonic transport is being developed. Discrete Roughness Elements are being used to maintain laminar flow over a substantial portion of a wing glove. This passive laminar flow technology has only come to be recognized as a significant player in airliner drag reduction in the last few years. NASA is implementing this experiment and is planning to demonstrate this technology at full-scale Bight cruise conditions of a small-to-medium airliner.

Bowers, Al

2010-01-01

102

Laminar Flow Control Leading Edge Systems in Simulated Airline Service  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

103

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

104

Aeroelastic instability of aircraft composite wings in an incompressible flow  

Microsoft Academic Search

The aeroelastic stability of an aircraft wing modeled as an anisotropic composite thin-walled beam in an incompressible flow is investigated. The wing is built-up as a single-cell box beam whose central point is noncoincident with the mid-chord of the profile. The effects of material anisotropy, transverse shear, warping inhibition, nonuniform torsional model and rotary inertia are considered in the structural

H. Haddadpour; M. A. Kouchakzadeh; F. Shadmehri

2008-01-01

105

Mathematical aspects of finite element methods for incompressible viscous flows  

NASA Technical Reports Server (NTRS)

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

Gunzburger, M. D.

1986-01-01

106

Error estimation and adaptivity in Navier-Stokes incompressible flows  

NASA Astrophysics Data System (ADS)

An adaptive remeshing procedure for solving Navier-Stokes incompressible fluid flow problems is presented in this paper. This procedure has been implemented using the error estimator developed by Zienkiewicz and Zhu (1987, 1989) and a semi-implicit time-marching scheme for Navier-Stokes flow problems (Zienkiewicz et al. 1990). Numerical examples are presented, showing that the error estimation and adaptive procedure are capable of monitoring the flow field, updating the mesh when necessary, and providing nearly optimal meshes throughout the calculation, thus making the solution reliable and the computation economical and efficient.

Wu, J.; Zhu, J. Z.; Szmelter, J.; Zienkiewicz, O. C.

1990-07-01

107

RIPPLE: A new model for incompressible flows with free surfaces  

SciTech Connect

A new free surface flow model, RIPPLE, is summarized. RIPPLE obtains finite difference solutions for incompressible flow problems having strong surface tension forces at free surfaces of arbitrarily complex topology. The key innovation is the Continuum Surface Force (CSF) model which represents surface tension as a (strongly) localized volume force. Other features include a high-order momentum advection model, a volume-of-fluid free surface treatment, and an efficient two-step projection solution method. RIPPLE'S unique capabilities are illustrated with two example problems: low-gravity jet-induced tank flow, and the collision and coalescence of two cylindrical rods. 17 refs., 7 figs.

Kothe, D.B.; Mjolsness, R.C.

1991-01-01

108

Assessment of the National Transonic Facility for Laminar Flow Testing  

NASA Technical Reports Server (NTRS)

A transonic wing, designed to accentuate key transition physics, is tested at cryogenic conditions at the National Transonic Facility at NASA Langley. The collaborative test between Boeing and NASA is aimed at assessing the facility for high-Reynolds number testing of configurations with significant regions of laminar flow. The test shows a unit Reynolds number upper limit of 26 M/ft for achieving natural transition. At higher Reynolds numbers turbulent wedges emanating from the leading edge bypass the natural transition process and destroy the laminar flow. At lower Reynolds numbers, the transition location is well correlated with the Tollmien-Schlichting-wave N-factor. The low-Reynolds number results suggest that the flow quality is acceptable for laminar flow testing if the loss of laminar flow due to bypass transition can be avoided.

Crouch, Jeffrey D.; Sutanto, Mary I.; Witkowski, David P.; Watkins, A. Neal; Rivers, Melissa B.; Campbell, Richard L.

2010-01-01

109

Supersonic laminar flow development in a square duct  

NASA Technical Reports Server (NTRS)

Supersonic laminar flow development in a constant-area square duct exhibits as one of its distinguishing features the formation of two contrarotating secondary flow vortices centered about the corner bisector. This phenomenon does not occur in unbounded corner flow. The secondary flow causes an outward bulging of total pressure contours in the vicinity of the corner bisector for wholly attached flow conditions.

Davis, D. O.; Gessner, F. B.; Kerlick, G. D.

1987-01-01

110

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

111

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

NASA Technical Reports Server (NTRS)

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

Rosenfeld, Moshe; Israeli, Moshe; Wolfshtein, Micha

1987-01-01

112

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

113

A model for predicting laminar gas flow through micropassages  

NASA Astrophysics Data System (ADS)

An theoretical investigation was conducted to detect the gas-solid interface effect on laminar flow characteristics for gas flowing through micropassages. In the wall-adjacent region, the change in viscosity of fluid vs the distance from the wall surface, as derived from the kinetic theory of gases result in significant influence on the flow characteristics in micropassages. A model was proposed to account for the wall effect. Analytical expressions for velocity profiles and pressure drop were derived, respectively, for laminar flow of gases in microtubes and in extremely narrow parallel plates. The Knudsen number, Kn, as a criterion, that the flow can be treated reasonably as flow in macrochannels, is discussed.

Li, Jun-Ming; Wang, Bu-Xuan; Peng, Xiao-Feng

1997-12-01

114

Design of fuselage shapes for natural laminar flow  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

115

Viscous Incompressible Flow Computations for 3-D Steady and Unsteady Flows  

NASA Technical Reports Server (NTRS)

This viewgraph presentation gives an overview of viscous incompressible flow computations for three-dimensional steady and unsteady flows. Details are given on the use of computational fluid dynamics (CFD) as an engineering tool, solution methods for incompressible Navier-Stokes equations, numerical and physical characteristics of the primitive variable approach, and the role of CFD in the past and in current engineering and research applications.

Kwak, Dochan

2001-01-01

116

A divergence preserving Adaptive Mesh Refinement strategy for viscous incompressible flows  

NASA Astrophysics Data System (ADS)

Structured adaptive mesh refinement (S-AMR) concentrates computational resources (i.e. grid points) in high-gradient regions of the flow, while maintaining most of the desirable properties of structured Cartesian solvers. Whenever the computational grid is locally refined/derefined the flow variables in S-AMR calculations need to maintain certain conservation properties during restriction or prolongation operations. Restriction refers to the transfer of a flow variable from a grid at a fine level of refinement to an underlying grid at a coarser level, while prolongation is the data transfer in the inverse direction. Of particular interest in S- AMR applications in viscous incompressible flows are divergence-preserving prolongation operators of a vector field. When the mesh refinement-derefinement procedure is applied after the predictor step of the fractional step integration scheme, divergence preservation for prolongation is crucial to avoid spurious pressure oscillations and additional errors on the computed flow field. In this work we propose method for divergence-preserving prolongation applicable to nested grids that differ by a factor of two in terms of resolution. The accuracy of the method is evaluated on prototypical laminar flows, like the Taylor-Green vortex problem and flow around a cylinder.

Vanella, M.; Balaras, E.

2009-11-01

117

Simulation of two-dimensional fully developed laminar flow for a magneto-hydrodynamic (MHD) pump.  

PubMed

MHD micro-pumps circumvent the wear and fatigue caused by high pressure-drop across the check valves of mechanical micro-pumps in micro-fluidic systems. Early analyses of the fluid flow for MHD micro-pumps were mostly made possible by the Poiseuille flow theory; however, this conventional laminar approach cannot illustrate the effects of various channel sizes and shapes. This paper, therefore, presents a simplified MHD flow model based upon steady state, incompressible and fully developed laminar flow theory to investigate the characteristics of a MHD pump. Inside the pump, flowing along the channel is the electrically conducting fluid flowing driven by the Lorentz forces in the direction perpendicular to both dc magnetic field and applied electric currents. The Lorentz forces were converted into a hydrostatic pressure gradient in the momentum equations of the MHD channel flow model. The numerical simulations conducted with the explicit finite difference method show that the channel dimensions and the induced Lorentz forces have significant influences on the flow velocity profile. Furthermore, the simulation results agree well with the experimental results published by other researchers. PMID:15142583

Wang, Pei-Jen; Chang, Chia-Yuan; Chang, Ming-Lang

2004-07-30

118

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

119

Visualization tools for vorticity transport analysis in incompressible flow.  

PubMed

Vortices are undesirable in many applications while indispensable in others. It is therefore of common interest to understand their mechanisms of creation. This paper aims at analyzing the transport of vorticity inside incompressible flow. The analysis is based on the vorticity equation and is performed along pathlines which are typically started in upstream direction from vortex regions. Different methods for the quantitative and explorative analysis of vorticity transport are presented and applied to CFD simulations of water turbines. Simulation quality is accounted for by including the errors of meshing and convergence into analysis and visualization. The obtained results are discussed and interpretations with respect to engineering questions are given. PMID:17080821

Sadlo, Filip; Peikert, Ronald; Sick, Mirjam

2006-01-01

120

NASA-VOF3D. Incompressible Flows Free Surfaces  

SciTech Connect

NASA-VOF3D is a three-dimensional, transient, free surface, incompressible fluid dynamics program. It is specifically designed to calculate confined flows in a low gravity environment in which surface physics must be accurately treated. It allows multiple free surfaces with surface tension and wall adhesion and includes a partial cell treatment that allows curved boundaries and internal obstacles. Variable mesh spacing is permitted in all three coordinate directions. Boundary conditions available are rigid free-slip wall, rigid no-slip wall, continuative, periodic, and specified pressure outflow boundary.

Torrey, M.D. [Los Alamos National Laboratory, NM (United States)

1992-03-16

121

Flow Solver for Incompressible 2-D Drive Cavity  

NASA Technical Reports Server (NTRS)

This software solves the Navier-Stokes equations for the incompressible driven cavity flow problem. The code uses second-order finite differencing on a staggered grid using the Chorin projection method. The resulting intermediate Poisson equation is efficiently solved using the fast Fourier transform. Time stepping is done using fourth-order Runge-Kutta for stability at high Reynolds numbers. Features include check-pointing, periodic field snapshots, ongoing reporting of kinetic energy and changes between time steps, time histories at selected points, and optional streakline generation.

Kalb, Virginia L.

2008-01-01

122

Fully elliptic incompressible flow calculations on regular grid by a new pressure substitution method  

NASA Technical Reports Server (NTRS)

A new method is presented for the solution of incompressible flow in generalized coordinates. This method is based on the substitution of the pressure weighted form of the momentum equations into the continuity equation. The algorithm is rigorously derived and a Fourier analysis is used to assess its suitability to act as an error smoother. Linear stability analysis results indicate that the performance of the new pressure substitution method (PSM) and the pressure correction method (PCM) is about the same at low Reynolds numbers, with no significant pressure gradient. At high Reynolds numbers the PSM shows much faster convergence. Likewise prediction of various flows indicate that the PSM has better accuracy for high Reynolds number flows with significant pressure gradients. Since most practical aerodynamic flows have significant pressure gradients, the PSM seems to be attractive for such flows. Solutions for both laminar and turbulent flow are compared with the experimental data. A two-equation low Reynolds number turbulence model is used to resolve the turbulent flowfield.

Hobson, G. V.; Lakshminarayana, B.

1990-01-01

123

Axial Flow in Laminar Trailing Vortices.  

National Technical Information Service (NTIS)

The structure of laminar trailing vortices behind a lifting wing is considered. The inviscid roll up of the trailing vortex sheet is examined, and the nature of the singularity at the centre of the spiral is determined. It is shown that viscosity removes ...

D. W. Moore P. G. Saffman

1972-01-01

124

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 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^{rm 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. Comparison of predicted and measured longitudinal and circumferential surface-pressure distributions along the forebody show good agreement in regions not affected by surface waviness and the propeller flow field. The macroscopic location of the transition 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. The measured axial extent of laminar flow (maximum of 4.9 ft along the side) demonstrates the achievability of laminar flow on the smoothed nonaxisymmetric fuselage forebody of a typical twin-engine light airplane in the presence of engine acoustic disturbances and surface waviness. Spectral analysis of measured hot-film signals revealed amplified disturbances in the range of predicted Tollmien-Schlichting (T-S) instabilities. The computed logarithmic T-S amplitude ratios ("n-factors") using the axisymmetric-analogue e^{rm n }-method are found to be generally lower than from the axisymmetric transition correlations. The relatively low "n-factors" on both the side and the top of the forebody may result from the waviness of the test surface. The proximity of the propeller-propulsion system appears to have affected the location of transition onset along the side of the fuselage forebody in some flight conditions. The flow visualization did not reveal evidence of transition caused by crossflow-vorticity instability on the forebody side; however, neither the axisymmetric-analogue method predicts possible crossflow-instability growth along the forebody.

Vijgen, Paul M. H. W.

125

Laminar flow control, 1976 - 1982: A selected annotated bibliography  

NASA Technical Reports Server (NTRS)

Laminar Flow Control technology development has undergone tremendous progress in recent years as focused research efforts in materials, aerodynamics, systems, and structures have begun to pay off. A virtual explosion in the number of research papers published on this subject has occurred since interest was first stimulated by the 1976 introduction of NASA's Aircraft Energy Efficiency Laminar Flow Control Program. The purpose of this selected bibliography is to list available, unclassified laminar flow (both controlled and natural) research completed from about 1975 to mid 1982. Some earlier pertinent reports are included but listed separately in the Appendix. Reports listed herein emphasize aerodynamics and systems studies, but some structures work is also summarized. Aerodynamic work is mainly limited to the subsonic and transonic sped regimes. Because wind-tunnel flow qualities, such as free stream disturbance level, play such an important role in boundary-layer transition, much recent research has been done in this area and it is also included.

Tuttle, M. H.; Maddalon, D. V.

1982-01-01

126

Lockheed laminar-flow control systems development and applications  

NASA Technical Reports Server (NTRS)

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

Lange, Roy H.

1987-01-01

127

Computational Analysis of the G-III Laminar Flow Glove  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

128

Laminar flow integration: Flight tests status and plans  

NASA Technical Reports Server (NTRS)

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.

1986-01-01

129

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

130

Numerical solution of the Navier-Stokes equations for high Reynolds number incompressible turbulent flow  

Microsoft Academic Search

The full Navier-Stokes equations for incompressible turbulent flow must be solved to accurately represent all flow phenomena which occur in a high Reynolds number incompressible flow. A two layer algebraic eddy viscosity turbulence model is used to represent the Reynolds stress in the primitive variable formulation. The development of the boundary-fitted coordinate systems makes the numerical solution of these equations

D. S. Thompson

1980-01-01

131

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

132

Experimental investigation of nanofluids in confined laminar radial flows  

Microsoft Academic Search

This paper presents an experimental investigation of heat transfer enhancement capabilities of coolants with suspended nanoparticles (Al2O3 dispersed in water) inside a radial flow cooling device. Steady, laminar radial flow of a nanofluid between a heated disk and a flat plate with axial coolant injection has been considered. An experimental test rig was built. Results show that heat transfer enhancements

Iulian Gherasim; Gilles Roy; Cong Tam Nguyen; Dinh Vo-Ngoc

2009-01-01

133

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

134

Pressure boundary conditions for computing incompressible flows with SPH  

NASA Astrophysics Data System (ADS)

In Smoothed Particle Hydrodynamics (SPH) methods for fluid flow, incompressibility may be imposed by a projection method with an artificial homogeneous Neumann boundary condition for the pressure Poisson equation. This is often inconsistent with physical conditions at solid walls and inflow and outflow boundaries. For this reason open-boundary flows have rarely been computed using SPH. In this work, we demonstrate that the artificial pressure boundary condition produces a numerical boundary layer that compromises the solution near boundaries. We resolve this problem by utilizing a "rotational pressure-correction scheme" with a consistent pressure boundary condition that relates the normal pressure gradient to the local vorticity. We show that this scheme computes the pressure and velocity accurately near open boundaries and solid objects, and extends the scope of SPH simulation beyond the usual periodic boundary conditions.

Hosseini, S. Majid; Feng, James J.

2011-08-01

135

The critical Reynolds number of a laminar incompressible mixing layer from minimal composite theory  

NASA Astrophysics Data System (ADS)

According to parallel-flow theory based on the Orr Sommerfeld equation, a mixing layer is unstable at all Reynolds numbers. However this is untenable from energy considerations, which demand that there exist a non-zero Reynolds number below which disturbances cannot extract net energy from the mean flow. It is shown here that a linear stability analysis of similarity solutions of the plane mixing layer, including the effects of flow non-parallelism using the minimal composite theory and the properties of adjoints, following Govindarajan & Narasimha (Theor. Comput. Fluid Dyn. vol. 19, 2005, p. 229) resolves the issue by yielding a non-zero critical Reynolds number for co-flowing streams of any velocity ratio. The critical Reynolds number for the total disturbance kinetic energy is found to be close to 30 for all velocity ratios in the range from zero to unity.

Bhattacharya, Pinaki; Manoharan, M. P.; Govindarajan, Rama; Narasimha, R.

2006-10-01

136

Multidimensional upwinding for incompressible flows based on characteristics  

NASA Astrophysics Data System (ADS)

In this paper, the multidimensional characteristic based upwind scheme (MCB) which has been recently introduced by the authors is applied to two another benchmark problems namely flow in a channel with a backward facing step and two-dimensional steady and unsteady flows past a circular cylinder. Extension of MCB scheme for calculating convective fluxes on non-Cartesian grids is presented here. For the flow over backward facing step, obtained results were compared against well-known experimental data and the results show high accuracy of MCB scheme and faster convergence rate with respect to conventional CB scheme. In the case of flow over circular cylinder, the flow at steady and transient regimes is investigated by MCB scheme. Again, the results obtained by MCB are compared to the other results in the literature and show good agreement with them. Also, rapid convergence rate of MCB was observed in this case too. It is concluded that, the genuinely multidimensional characteristic based (MCB) scheme, has been introduced earlier by the authors, is a robust and powerful scheme for modeling incompressible viscous flows for achieving the high accuracy and remarkable advantage in convergence rate with respect to conventional characteristic based schemes.

Zamzamian, Kamiar; Razavi, Seyed Esmail

2008-10-01

137

Conforming Chebyshev spectral collocation methods for the solution of laminar flow in a constricted channel  

NASA Technical Reports Server (NTRS)

The numerical simulation of steady planar two-dimensional, laminar flow of an incompressible fluid through an abruptly contracting channel using spectral domain decomposition methods is described. The key features of the method are the decomposition of the flow region into a number of rectangular subregions and spectral approximations which are pointwise C(1) continuous across subregion interfaces. Spectral approximations to the solution are obtained for Reynolds numbers in the range 0 to 500. The size of the salient corner vortex decreases as the Reynolds number increases from 0 to around 45. As the Reynolds number is increased further the vortex grows slowly. A vortex is detected downstream of the contraction at a Reynolds number of around 175 that continues to grow as the Reynolds number is increased further.

Karageorghis, Andreas; Phillips, Timothy N.

1990-01-01

138

Computational Optimization of a Natural Laminar Flow Experimental Wing Glove  

NASA Technical Reports Server (NTRS)

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

Hartshom, Fletcher

2012-01-01

139

Flight Tests of a Supersonic Natural Laminar Flow Airfoil  

NASA Technical Reports Server (NTRS)

A flight test campaign of a supersonic natural laminar flow airfoil has been recently completed. The test surface was an 80-inch (203 cm) chord and 40-inch (102 cm) span article mounted on the centerline store location of an F-15B airplane. The wing was designed with a leading edge sweep of effectively 0 deg to minimize boundary layer crossflow. The test article surface was coated with an insulating material to avoid significant heat transfer to and from the test article structure to maintain a quasi-adiabatic wall. An aircraft-mounted infrared camera system was used to determine boundary layer transition and the extent of laminar flow. The tests were flown up to Mach 2.0 and chord Reynolds numbers in excess of 30 million. The objectives of the tests were to determine the extent of laminar flow at high Reynolds numbers and to determine the sensitivity of the flow to disturbances. Both discrete (trip dots) and 2-D disturbances (forward-facing steps) were tested. A series of oblique shocks, of yet unknown origin, appeared on the surface, which generated sufficient crossflow to affect transition. Despite the unwanted crossflow, the airfoil performed well. The results indicate the sensitivity of the flow to the disturbances, which can translate into manufacturing tolerances, were similar to that of subsonic natural laminar flow wings.

Frederick, M. A.; Banks, D. W.; Garzon, G. A.; Matisheck, J. R.

2014-01-01

140

Method and apparatus for detecting laminar flow separation and reattachment  

NASA Technical Reports Server (NTRS)

The invention is a method and apparatus for detecting laminar flow separation and flow reattachment of a fluid stream by simultaneously sensing and comparing a plurality of output signals, each representing the dynamic shear stress at one of an equal number of sensors spaced along a straight line on the surface of an airfoil or the like that extends parallel to the fluid stream. The output signals are concurrently compared to detect the sensors across which a reversal in phase of said output signal occurs, said detected sensors being in the region of laminar separation or reattachment. The novelty in this invention is the discovery and use of the phase reversal phenomena to detect laminar separation and attachment of a fluid stream from any surface such as an airfoil supported therein.

Stack, John P. (inventor); Mangalam, Sivaramakrishnan M. (inventor)

1989-01-01

141

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.

142

Laminar/turbulent oscillating flow in circular pipes  

NASA Technical Reports Server (NTRS)

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

Ahn, Kyung H.; Ibrahim, Mounir B.

1992-01-01

143

Laminar/turbulent oscillating flow in circular pipes  

NASA Astrophysics Data System (ADS)

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

Ahn, Kyung H.; Ibrahim, Mounir B.

1992-12-01

144

Some observations regarding steady laminar flows past bluff bodies.  

PubMed

Steady laminar flows past simple objects, such as a cylinder or a sphere, have been studied for well over a century. Theoretical, experimental and numerical methods have all contributed fundamentally towards our understanding of the resulting flows. This article focuses on developments during the past few decades, when mostly numerical and asymptotical advances have provided insights also for steady, although unstable, high-Reynolds-numbers flow regimes. PMID:24936017

Fornberg, Bengt; Elcrat, Alan R

2014-07-28

145

Drag reduction in laminar and turbulent flows past superhydrophobic surfaces  

NASA Astrophysics Data System (ADS)

A series of experiments and direct numerical simulations (DNS) will be presented which demonstrate significant drag reduction for both laminar and turbulent flows of water through channels using superhydrophobic surfaces with well-defined micron-sized surface roughness. The surfaces are fabricated from PDMS to incorporate precise patterns of ridges or posts that can support a shear-free air-water interface. A flow cell is used to measure the pressure drop and velocity profile as a function of the flow rate for a series of channel geometries and superhydrophobic surface designs. DNS are performed for flow past superhydrophobic surfaces which both complement and extend the range of geometries and Reynolds number obtained in the experiments. We will show that drag reductions up to 75% and slip lengths up to 150?m can be obtained in turbulent flows past superhydrophobic surfaces. Additionally, we will show that slip along the air water interface forestalls the transition from laminar to turbulent flow. The drag reduction is found to increases with increasing post/ridge spacing and the fraction of air-water interface. In turbulent flows, the drag reduction increases with Reynolds number before eventually reaching a plateau. These results suggest that in turbulent flows, the drag reduction scales with the thickness of the viscous sublayer and not the overall channel height as in laminar flows.

Rothstein, Jonathan P.

2009-11-01

146

Pseudo-divergence-free element free Galerkin method for incompressible fluid flow  

Microsoft Academic Search

Incompressible modeling in finite elements has been a major concern since its early developments and has been extensively studied. However, incompressibility in mesh-free methods is still an open topic. Thus, instabilities or locking can preclude the use of mesh-free approximations in such problems. Here, a novel mesh-free formulation is proposed for incompressible flow. It is based on defining a pseudo-divergence-free

Antonio Huerta; Yolanda Vidal; Pierre Villon

2004-01-01

147

Application of porous materials for laminar flow control  

NASA Technical Reports Server (NTRS)

Fairly smooth porous materials were elected for study Doweave; Fibermetal; Dynapore; and perforated titanium sheet. Factors examined include: surface smoothness; suction characteristics; porosity; surface impact resistance; and strain compatibility. A laminar flow control suction glove arrangement was identified with material combinations compatible with thermal expansion and structural strain.

Pearce, W. E.

1978-01-01

148

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

149

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

150

Laminar flow in a porous tube with uniform mass injection  

Microsoft Academic Search

Laminar flows in a cylindrical porous tube with uniform mass injection through the porous wall are studies. The full Navier-Stokes equations are solved numerically by employing some finite-difference schemes. Solutions for velocity profiles and frictional pressure drops are obtained by the use of vorticity and stream function approach. The results indicate: 1) The fully developed velocity profiles do exist after

J. Ku; W. Leidenfrost

1981-01-01

151

Theory for Aerosol Generation in Laminar Flow Condensers  

Microsoft Academic Search

Generation of aerosols in laminar flow condensers is investigated theoretically. A model is developed for simultaneous heat and vapor mass transfer, aerosol nucleation, condensation, coagulation, thermophoresis, and diffusion representing the aerosol size distribution by a lognormal function throughout the process. The importance of the above physical phenomena and the effect of process parameters (reheater and boiler temperature, seed nuclei concentration)

Gautam M. Phanse; Sotiris E. Pratsinis

1989-01-01

152

Application of laminar flow control to supersonic transport configurations  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

153

F-16XL-2 Supersonic Laminar Flow Control Flight Test Experiment  

NASA Technical Reports Server (NTRS)

The F-16XL-2 Supersonic Laminar Flow Control Flight Test Experiment was part of the NASA High-Speed Research Program. The goal of the experiment was to demonstrate extensive laminar flow, to validate computational fluid dynamics (CFD) codes and design methodology, and to establish laminar flow control design criteria. Topics include the flight test hardware and design, airplane modification, the pressure and suction distributions achieved, the laminar flow achieved, and the data analysis and code correlation.

Anders, Scott G.; Fischer, Michael C.

1999-01-01

154

Transition-Sensitized Turbulence Models for Compressible and Incompressible Flows  

NASA Technical Reports Server (NTRS)

During the grant period from January 1,2002 to December 31,2002 work was carried out on three projects to extend the range of applicability of advanced turbulence models. First, a new transition-sensitized turbulence model was tested and refined. Second, the influence of compressibility on the pressure-strain rate correlation was studied. Third, the relationship between time-filtered large eddy simulation (TLES) and Reynolds-averaged Navier Stokes (RANS) modeling was investigated leading to submission of the article. The transition-sensitized turbulence model encompasses the early-stage transition and turbulent flow regimes describing the evolution of the ensemble mean disturbance energy and dissipation rate. It is founded on a consistent mathematical description of the laminar regime with its linear disturbances and the fully turbulent regime with its stochastic fluctuations. The unified description is provided by the ensemble viewpoint.

Thacker, William D.

2003-01-01

155

Numerical Simulation of Incompressible Flows within Simple Boundaries. I. Galerkin (Spectral) Representations.  

National Technical Information Service (NTIS)

Galerkin (spectral) methods are explored for the numerical simulation of incompressible flows within simple boundaries. A major consideration is development of transform methods for simulation of flows in box geometries with periodic and free-slip boundar...

S. A. Orszag

1971-01-01

156

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

157

Laminar fully developed flow and heat transfer of Robertson-Stiff fluids in a rectangular duct  

NASA Astrophysics Data System (ADS)

The laminar fully developed flow and heat transfer through a rectangular duct of a viscous incompressible Robertson-Stiff fluid is investigated. Robertson-Stiff fluids are time independent non-Newtonian materials possessing a yield value. The governing momentum and energy equations are solved numerically using finite-difference approximations. We consider two cases of thermal boundary conditions: H-1 the "circumferentially constant wall temperature and axially constant wall heat flux" and H-2 the "circumferentially and axially constant wall heat flux". The velocity, temperature, the average friction factor and Nusselt numbers for the two cases are computed for various values of the physical parameters. The present results have been compared with the known solutions for Newtonian and power-law fluids and are found to be in good agreement.

Sayed-Ahmed, M. E.; El-Yazal, A. S.

2005-02-01

158

Drag reduction in laminar and turbulent flows past superhydrophobic surfaces  

Microsoft Academic Search

A series of experiments and direct numerical simulations (DNS) will be presented which demonstrate significant drag reduction for both laminar and turbulent flows of water through channels using superhydrophobic surfaces with well-defined micron-sized surface roughness. The surfaces are fabricated from PDMS to incorporate precise patterns of ridges or posts that can support a shear-free air-water interface. A flow cell is

Jonathan P. Rothstein

2009-01-01

159

Laminar flow past a sphere rotating in the transverse direction  

Microsoft Academic Search

Laminar flow past a sphere rotating in the transverse direction is numerically investigated in order to understand the effect\\u000a of the rotation on the characteristics of flow over the sphere. Numerical simulations are performed at Re = 100, 250 and 300,\\u000a where the Reynolds number is based on the free-stream velocity and the sphere diameter. The rotational speeds considered are

Dongjoo Kim

2009-01-01

160

Finite Element Simulation of Two-Dimensional Incompressible Magnetohydrodynamic Flows  

NASA Astrophysics Data System (ADS)

A new finite element code has been developed for simulation of the dynamics of two-dimensional incompressible magnetohydrodynamic flows. The solution scheme used in spatial discretization is the Galerkin weighted-residual finite-element method, incorporating the mixed interpolation technique, and a combination of the penalty and pseudocompressibility methods for implementing the incompressibility constraint. An implicit and stable theta-weighting finite difference scheme is used for integration in time, and a non-iterative time-level averaging method is employed for treatment of nonlinear terms. The code has been extensively benchmarked against known analytical solutions in magnetohydrodynamics and has been found to produce highly accurate results. The tearing-mode instability of a magnetic-field-reversing current sheet in the presence of coplanar stagnation-point flow, in which the unperturbed equilibrium state is an exact solution of the steady-state dissipative MHD equations, has been examined by use of the code. Simulation results indicate stability for sufficiently small values of the viscous Lundquist number, S_nu, or the resistive Lundquist number, S_eta : a curve in the S_nu -S_eta plane separating the stable and unstable regions has been found. In the unstable regime, the results show occurrence of multiple x-line reconnection along the center of the current sheet at x = 0. Small-scale structures of vorticity and current density near the x-point reconnection sites are observed and are found to be consistent with results obtained by Matthaeus (1982). Average linear growth rates are estimated for modest values of S_eta. In the range S_eta<=500, the number of magnetic islands is found to be independent of Seta, which implies that there exists a single dominant wavelength of the tearing-mode in this range. The stretching of magnetic islands which is present in this configuration but not in the perpendicular flow and field configuration examined by Phan and Sonnerup (1991), caused a substantial decrease in linear growth rate relative to that obtained by those authors. It is of particular interest that, unlike most simulations of the tearing-mode, no symmetry conditions are imposed on the perturbations; nevertheless they develop in an anti -symmetric manner.

Ip, Justin Tsz Ching

161

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

Microsoft Academic Search

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

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

1999-01-01

162

A Numerical Method for Two-Phase Flow Consisting of Separate Compressible and Incompressible Regions  

Microsoft Academic Search

We propose a numerical method for modeling two-phase flow consisting of separate compressible and incompressible regions. This is of interest, for example, when the combustion of fuel droplets or the shock-induced mixing of liquids is numerically modeled. We use the level set method to track the interface between the compressible and incompressible regions, as well as the Ghost Fluid Method

Rachel Caiden; Ronald P. Fedkiw; Chris Anderson

2001-01-01

163

Implicit lower-upper/approximate-factorization schemes for incompressible flows  

SciTech Connect

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 linearization with and without sub-iteration and on Newton linearization are developed using spatial difference operators. The spatial approximation used includes upwind differencing based on Roe`s approximate Riemann solver and van Leer`s MUSCL scheme, with numerically computed implicit flux linearizations. Simple one-dimensional diffusion and advection/diffusion problems are first studied analytically to provide insight for development of the Navier-Stokes algorithm. The optimal values of both time step and LU/AF parameter are determined for a test problem consisting of two-dimensional flow past a NACA 0012 airfoil, with a highly stretched grid. The optimal parameter provides a consistent improvement in convergence rate for four test cases having different grids and Reynolds numbers and, also, for an inviscid case. The scheme can be easily extended to three dimensions and adapted for compressible flows. 24 refs., 11 figs., 2 tabs.

Briley, W.R.; Neerarambam, S.S.; Whitfield, D.L. [Mississippi State Univ., MS (United States)] [Mississippi State Univ., MS (United States)

1996-10-01

164

Hydrodynamic Fluctuations in Laminar Fluid Flow. II. Fluctuating Squire Equation  

NASA Astrophysics Data System (ADS)

We use fluctuating hydrodynamics to evaluate the enhancement of thermally excited fluctuations in laminar fluid flow using plane Couette flow as a representative example. In a previous publication (J. Stat. Phys. 144:774, 2011) we derived the energy amplification arising from thermally excited wall-normal fluctuations by solving a fluctuating Orr-Sommerfeld equation. In the present paper we derive the energy amplification arising from wall-normal vorticity fluctuation by solving a fluctuating Squire equation. The thermally excited wall-normal vorticity fluctuations turn out to yield the dominant contribution to the energy amplification. In addition, we show that thermally excited streaks, even in the absence of any externally imposed perturbations, are present in laminar fluid flow.

Ortiz de Zárate, José M.; Sengers, Jan V.

2013-02-01

165

Preliminary aerodynamic design considerations for advanced laminar flow aircraft configurations  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

166

Enhanced mixing in laminar flows with ultrahydrophobic surfaces  

NASA Astrophysics Data System (ADS)

Ultrahydrophobic surfaces have recently been shown to produce significant drag reduction in laminar flows. In this presentation, we will talk about current research aimed at engineering these ultrahydrophobic surfaces to produce mixing enhancement in laminar flows. Our research utilizes the slip velocity along the shear-free air-water interface formed between the surface structures to produce secondary flows which stretch and fold fluid elements to produce enhanced mixing. The surfaces are fabricated with PDMS casted from silicon mold with hydrophobic patterns of microridges in different spacing and at various angles to the flow direction. The effectiveness of the surfaces is tested in micro mixing flow cell using a confocal microscope to track fluorescent die. At the inlet, to streams of fluid are brought together at a y-junction, one stream is tagged with fluorescent die. The normalized fluorescence intensity is used in experiments to calculate the degree of mixing and compared directly to the mixing predictions from numerical simulations. The kinematical mechanism of this laminar mixing enhancement method is studied though both experimental and simulations. The mixing length is shown to be dramatically reduced when compared to smooth channels and can be optimized through the design of the microridges.

Ou, Jia; Moss, Geoffrey; Rothstein, Jonathan

2006-11-01

167

Oblique laminar-turbulent interfaces in plane shear flows.  

PubMed

Localized structures such as turbulent stripes and turbulent spots are typical features of transitional wall-bounded flows in the subcritical regime. Based on an assumption for scale separation between large and small scales, we show analytically that the corresponding laminar-turbulent interfaces are always oblique with respect to the mean direction of the flow. In the case of plane Couette flow, the mismatch between the streamwise flow rates near the boundaries of the turbulence patch generates a large-scale flow with a nonzero spanwise component. Advection of the small-scale turbulent fluctuations (streaks) by the corresponding large-scale flow distorts the shape of the turbulence patch and is responsible for its oblique growth. This mechanism can be easily extended to other subcritical flows such as plane Poiseuille flow or Taylor-Couette flow. PMID:23373928

Duguet, Yohann; Schlatter, Philipp

2013-01-18

168

The exact calculation of quadrupole sources for some incompressible flows  

NASA Technical Reports Server (NTRS)

This paper is concerned with the application of the acoustic analogy of Lighthill to the acoustic and aerodynamic problems associated with moving bodies. The Ffowcs Williams-Hawkings equation, which is an interpretation of the acoustic analogy for sound generation by moving bodies, manipulates the source terms into surface and volume sources. Quite often in practice the volume sources, or quadrupoles, are neglected for various reasons. Recently, Farassat, Long and others have attempted to use the FW-H equation with the quadrupole source and neglected to solve for the surface pressure on the body. The purpose of this paper is to examine the contribution of the quadrupole source to the acoustic pressure and body surface pressure for some problems for which the exact solution is known. The inviscid, incompressible, 2-D flow, calculated using the velocity potential, is used to calculate the individual contributions of the various surface and volume source terms in the FW-H equation. The relative importance of each of the sources is then assessed.

Brentner, Kenneth S.

1988-01-01

169

A massively parallel fractional step solver for incompressible flows  

SciTech Connect

This paper presents a parallel implementation of fractional solvers for the incompressible Navier-Stokes equations using an algebraic approach. Under this framework, predictor-corrector and incremental projection schemes are seen as sub-classes of the same class, making apparent its differences and similarities. An additional advantage of this approach is to set a common basis for a parallelization strategy, which can be extended to other split techniques or to compressible flows. The predictor-corrector scheme consists in solving the momentum equation and a modified 'continuity' equation (namely a simple iteration for the pressure Schur complement) consecutively in order to converge to the monolithic solution, thus avoiding fractional errors. On the other hand, the incremental projection scheme solves only one iteration of the predictor-corrector per time step and adds a correction equation to fulfill the mass conservation. As shown in the paper, these two schemes are very well suited for massively parallel implementation. In fact, when compared with monolithic schemes, simpler solvers and preconditioners can be used to solve the non-symmetric momentum equations (GMRES, Bi-CGSTAB) and to solve the symmetric continuity equation (CG, Deflated CG). This gives good speedup properties of the algorithm. The implementation of the mesh partitioning technique is presented, as well as the parallel performances and speedups for thousands of processors.

Houzeaux, G. [Barcelona Supercomputing Center (BSC-CNS), Edificio NEXUS I, Campus Nord UPC, Gran Capitan 2-4, 08034 Barcelona (Spain)], E-mail: guillaume.houzeaux@bsc.es; Vazquez, M. [Barcelona Supercomputing Center (BSC-CNS), Edificio NEXUS I, Campus Nord UPC, Gran Capitan 2-4, 08034 Barcelona (Spain)], E-mail: mariano.vazquez@bsc.es; Aubry, R. [Barcelona Supercomputing Center (BSC-CNS), Edificio NEXUS I, Campus Nord UPC, Gran Capitan 2-4, 08034 Barcelona (Spain)], E-mail: romain.aubry@bsc.es; Cela, J.M. [Barcelona Supercomputing Center (BSC-CNS), Edificio NEXUS I, Campus Nord UPC, Gran Capitan 2-4, 08034 Barcelona (Spain)

2009-09-20

170

Implicit Runge-Kutta methods to simulate unsteady incompressible flows  

NASA Astrophysics Data System (ADS)

A numerical method (SIMPLE DIRK Method) for unsteady incompressible viscous flow simulation is presented. The proposed method can be used to achieve arbitrarily high order of accuracy in time-discretization which is otherwise limited to second order in majority of the currently used simulation techniques. A special class of implicit Runge-Kutta methods is used for time discretization in conjunction with finite volume based SIMPLE algorithm. The algorithm was tested by solving for velocity field in a lid-driven square cavity. In the test case calculations, power law scheme was used in spatial discretization and time discretization was performed using a second-order implicit Runge-Kutta method. Time evolution of velocity profile along the cavity centerline was obtained from the proposed method and compared with that obtained from a commercial computational fluid dynamics software program, FLUENT 6.2.16. Also, steady state solution from the present method was compared with the numerical solution of Ghia, Ghia, and Shin and that of Erturk, Corke, and Gookcol. Good agreement of the solution of the proposed method with the solutions of FLUENT; Ghia, Ghia, and Shin; and Erturk, Corke, and Gookcol establishes the feasibility of the proposed method.

Ijaz, Muhammad

171

Numerical Simulation of an Aortic Flow Based on a HLLC Type Incompressible Flow Solver  

Microsoft Academic Search

In this study, a three-dimensional artificial compressibility solver based on the average-state Harten-Lax-van Leer-Contact (HLLC) (13) type Riemann solution is first proposed and developed to solve the time-dependent incompressible flow equa- tions. To implement unsteady flow calculations, a dual time stepping strategy in- cluding the LU decomposition method is used in the pseudo-time iteration and the second-order accurate backward difference

Yang-Yao Niu; Chih-Hung Chang; Wen-Yih I. Tseng; Hsu-Hsia Peng; Hsi-Yu Yu

2009-01-01

172

Experimental investigation of oxide nanofluids laminar flow convective heat transfer  

Microsoft Academic Search

In the present investigation nanofluids containing CuO and Al2O3 oxide nanoparticles in water as base fluid in different concentrations produced and the laminar flow convective heat transfer through circular tube with constant wall temperature boundary condition were examined. The experimental results emphasize that the single phase correlation with nanofluids properties (Homogeneous Model) is not able to predict heat transfer coefficient

S. Zeinali Heris; S. Gh. Etemad; M. Nasr Esfahany

2006-01-01

173

Ground vibration test of the laminar flow control JStar airplane  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

174

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

NASA Astrophysics Data System (ADS)

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

VilaVandran, Alfred Sagayam; Darus, A. N.

2012-06-01

175

Co-laminar flow cells for electrochemical energy conversion  

NASA Astrophysics Data System (ADS)

In this review, we present the major developments in the evolution of ‘membraneless’ microfluidic electrochemical cells which utilize co-laminar flow to minimize reactant mixing while producing electrical power in a compact form. Categorization of devices according to reactant phases is suggested, with further differentiation being subject to fabrication method and function, namely multi-layer sandwich structures for medium-power cell stacks and single-layer monolithic cells for low-power on-chip applications. Power density metrics reveal that recent co-laminar flow cells compare favourably with conventional membrane-based electrochemical cells and that further optimization of device architecture could be expedited through standardized testing. Current research trends indicate that co-laminar flow cell technology for power generation is growing rapidly and finding additional use as an analytical and education tool. Practical directions and recommendations for further research are provided, with the intention to guide scientific advances and technology development toward ultimate pairing with commercial applications.

Goulet, Marc-Antoni; Kjeang, Erik

176

Unsteady Pressure Measurements in Rotor Blade Tips with Incidence in Incompressible Flow.  

National Technical Information Service (NTIS)

The measurement of unsteady pressure on harmonically oscillating rotor blade tips, in incompressible subsonic flow is dealt with. The measurements were made in a subsonic wind tunnel. The pressure was measured in five sections, allowing the three-dimensio...

H. Triebstein

1977-01-01

177

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

178

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

179

Three-layer interactive method for computing supersonic laminar separated flows  

NASA Technical Reports Server (NTRS)

An interactive model for numerical computation of complicated two-dimensional flowfields including regions of reversed flow is proposed. The present approach is one of dividing the flowfield into three regions, in each of which a simplified mathematical model is applied: (1) outer, supersonic flow for which the full potential equation (hyperbolic) is used; (2) viscous, laminar layer in which the compressible boundary-layer model (parabolic) is used; and (3) recirculating flow modeled by the incompressible Navier-Stokes equations (elliptic). For matching of the numerical solutions in the three layers, two interaction models are developed: one for pressure interaction, the other for interaction between the shear layer and the recirculating flow. The uniform solution for the whole flowfield is then obtained by iteration of the local solutions under the constraints imposed by matching. The three-layer interactive model is used for solution of the flowfield past an asymmetric cavity. The method is shown to be capable of dealing with backflow without encountering problems at separation, characteristic to the boundary-layer approach.

Brandeis, J.; Rom, J.

1980-01-01

180

Experimental investigation of flow instabilities in a laminar separation bubble  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

181

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

182

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

Microsoft Academic Search

In this thesis, an a-posteriori error estimator is presented and employed for solving viscous incompressible flow problems. In an effort to detect local flow features, such as vortices and separation, and to resolve flow details precisely, a velocity angle error estimator e theta which is based on the spatial derivative of velocity direction fields is designed and constructed. The a-posteriori

Heng Wu

2000-01-01

183

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

Microsoft Academic Search

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

Brian Joseph German

2007-01-01

184

Proper Orthogonal Decomposition and Incompressible Flow: An Application to Particle Modeling  

Microsoft Academic Search

The Proper Orthogonal Decomposition (POD) is a reduced-order modeling tech- nique that is used to compactly represent unsteady flows. In this paper, we use the POD to capture the parametric variation of a flow with Reynolds number. We study incompressible, axisymmetric, steady flow over spherical particles at various Reynolds numbers in order to give an alternative to correlation-based approaches for

B. J. O'Donnell; B. T. Helenbrook

2006-01-01

185

Aircraft energy efficiency laminar flow control wing design study  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

186

Manufacturing tolerances for natural laminar flow airframe surfaces  

NASA Technical Reports Server (NTRS)

Published aircraft surface waviness and boundary layer transition measurements imply that currently achievable low levels of surface waviness are compatible with the natural laminar flow (NLF) requirements of business and commuter aircraft, in the cases of both metallic and composite material airframes. The primary challenge to the manufacture of NLF-compatible surfaces is two-dimensional roughness in the form of steps and gaps at structural joints. Attention is presently given to recent NASA investigations of manufacturing tolerance requirements for NLF surfaces, including flight experiment results.

Holmes, B. J.; Obara, C. J.; Martin, G. L.; Domack, C. S.

1985-01-01

187

Hybrid laminar flow control applied to advanced turbofan engine nacelles  

NASA Technical Reports Server (NTRS)

The potential application of hybrid laminar flow control (HLFC) to the external surface of an advanced, high bypass ratio turbofan engine nacelle with a wetted area that approaches 15 percent of the wing total wetted area of future commercial transports is presented. A pressure distribution compatible with HLFC is specified and the corresponding nacelle geometry is computed employing a predictor/corrector design technique. Performance evaluations on an advanced twin-engine transport configuration are discussed to determine potential benefits in terms of reduced fuel consumption.

Collier, F. S., Jr.; Arcara, P. C., Jr.; Wie, Y. S.

1992-01-01

188

Airborne drug levels in a laminar-flow hood  

SciTech Connect

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 the hood and transferred to empty vials. Likewise, in each of nine trials, 50 vials of cefazolin sodium 1 g were reconstituted and transferred to small-volume i.v. solutions. Drug manipulations were performed between the hood's filter and the Biotest, which was placed inside the hood. Drug collected on the filter in the Biotest was assayed with ultraviolet spectrophotometry after extraction. The range of fluorouracil collected by the Biotest was from 0 to 14 microgram, corresponding to 0-0.07 microgram/liter of sample air. Recovered cefazolin sodium ranged from 28 to 131 microgram, or 0.02-0.11 microgram/liter of sampled air. Following routine manipulation of drug products in a laminar-flow hood, the drug can contaminate, the air flowing over the product.

Kleinberg, M.L.; Quinn, M.J.

1981-09-01

189

Transport Coefficients for Laminar and Turbulent Flow Through a Four-Cusp Channel.  

National Technical Information Service (NTIS)

The heat transfer coefficients for laminar and turbulent flow in a four-cusp channel were determined. A numerical solution was developed for laminar flow an and experimental study for turbulent flow was carried out. Systematic variations of the Reynolds n...

A. Souza Dutra J. A. R. Parise P. R. Souza Mendes

1986-01-01

190

Spatial distribution of laminar flow-assisted dendritic amplification.  

PubMed

In this paper, we report spatial distribution of laminar flow-assisted dendritic amplification (LFDA) product. LFDA is a recently invented signal amplification method dedicated to biomolecular binding events on microchannel walls. Onto the bound biomolecule, a dendritic structure is constructed by supplying two building blocks from laminar streams produced by a Y-shaped microchannel. In view of the extension of LFDA to simultaneous amplification of multiple binding spots, we have investigated the distribution of the LFDA product across and along the microchannel with the course of time. We fabricated a Y-shaped microchannel with a cross section of 110 microm x 22 microm using poly(dimethylsiloxane). As the LFDA building blocks, FITC-labeled streptavidin and biotinylated anti-streptavidin were injected from the two inlets of the microchannel at a mean flow velocity of 6.2 mm s(-1) (after the confluence). Nonspecific adsorption of the building blocks formed the seed layer of LFDA. The progress of LFDA was monitored with a fluorescence microscope up to 10.1 mm of microchannel length. After 5 min or later, the fluorescence intensity profile across the microchannel showed a peak at the center of the channel. With the course of time, the peak height grew exponentially except for slight saturation, but the peak width was almost constant. Along the microchannel, the peak height decreased almost linearly with the increasing logarithm of the distance, and the peak width was broadened in accordance with the 1/3 power law. PMID:19156297

Hosokawa, Kazuo; Maeda, Mizuo

2009-02-01

191

Global pressure relaxation for laminar two-dimensional internal flow  

NASA Technical Reports Server (NTRS)

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.

1990-01-01

192

Front Speed Enhancement by Incompressible Flows in Three or Higher Dimensions  

NASA Astrophysics Data System (ADS)

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

El Smaily, Mohammad; Kirsch, Stéphane

2014-07-01

193

Linear Stability of Incompressible Flow Using a Mixed Finite Element Method  

Microsoft Academic Search

We analyzed the linear stability for incompressible flow using the mixed finite element method. First, by means of the fractional step finite element method, the two-dimensional base flows were numerically computed over a range of Reynolds numbers, and then they were perturbed with three-dimensional disturbances. By using linear stability and normal mode analysis, we obtained the partial differential equations governing

Yan Ding; Mutsuto Kawahara

1998-01-01

194

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

195

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

Microsoft Academic Search

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

Yao-Hsin Hwang

2011-01-01

196

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

197

Investigation B: Laminar confined coaxial entrance flow with heat generation  

NASA Technical Reports Server (NTRS)

The results of a parametric study on the entrance flow region in a gas core nuclear reactor are presented. The physical system is modeled as laminar confined, coaxial flow with heat generation in the inner fluid. The governing equations include the boundary layer approximations and the assumptions of only radial radiative transport of energy represented as an energy diffusion term. The Von Mises transformation and a zeta transformation are used to transform the equations into nonlinear nonhomogeneous convective-diffusion equations. A unique combination of forward and backward difference equations which yields accurate results at moderate computational times, is used in the numerical method. Results show that the rapidly accelerating, heat generating inner stream actually shrinks in radius as it expands axially.

Bobba, G. K. M.; Weinstein, H.

1975-01-01

198

High-flaps for natural laminar flow airfoils  

NASA Technical Reports Server (NTRS)

A review of the NACA and NASA low-drag airfoil research is presented with particular emphasis given to the development of mechanical high-lift flap systems and their application to general aviation aircraft. These flap systems include split, plain, single-slotted, and double-slotted trailing-edge flaps plus slat and Krueger leading-edge devices. The recently developed continuous variable-camber high-lift mechanism is also described. The state-of-the-art of theoretical methods for the design and analysis of multi-component airfoils in two-dimensional subsonic flow is discussed, and a detailed description of the Langley MCARF (Multi-Component Airfoil Analysis Program) computer code is presented. The results of a recent effort to design a single- and double-slotted flap system for the NASA high speed natural laminar flow (HSNLF) (1)-0213 airfoil using the MCARF code are presented to demonstrate the capabilities and limitations of the code.

Morgan, Harry L.

1986-01-01

199

Stability theory applications to laminar-flow control  

NASA Technical Reports Server (NTRS)

In order to design Laminar Flow Control (LFC) configurations, reliable methods are needed for boundary-layer transition predictions. Among the available methods, there are correlations based upon R sub e, shape factors, Goertler number and crossflow Reynolds number. The most advanced transition prediction method is based upon linear stability theory in the form of the e sup N method which has proven to be successful in predicting transition in two- and three-dimensional boundary layers. When transition occurs in a low disturbance environment, the e sup N method provides a viable design tool for transition prediction and LFC in both 2-D and 3-D subsonic/supersonic flows. This is true for transition dominated by either TS, crossflow, or Goertler instability. If Goertler/TS or crossflow/TS interaction is present, the e sup N will fail to predict transition. However, there is no evidence of such interaction at low amplitudes of Goertler and crossflow vortices.

Malik, Mujeeb R.

1987-01-01

200

Semidirect computation of three-dimensional viscous flows over suction holes in laminar flow control surfaces  

NASA Technical Reports Server (NTRS)

A summary is given of the attempts made to apply semidirect methods to the calculation of three-dimensional viscous flows over suction holes in laminar flow control surfaces. The attempts were all unsuccessful, due to either (1) lack of resolution capability, (2) lack of computer efficiency, or (3) instability.

Roache, P. J.

1979-01-01

201

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

202

Laminar flow control leading edge glove flight test article development  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

203

Three-dimensional incompressible Navier-Stokes computations of internal flows  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

204

Numerical solutions for laminar and turbulent viscous flow over single and multi-element airfoils using body-fitted coordinate systems  

NASA Technical Reports Server (NTRS)

The technique of body-fitted coordinate systems is applied in numerical solutions of the complete time-dependent compressible and incompressible Navier-Stokes equations for laminar flow and to the time-dependent mean turbulent equations closed by modified Kolmogorov hypotheses for turbulent flow. Coordinate lines are automatically concentrated near to the bodies at higher Reynolds number so that accurate resolution of the large gradients near the solid boundaries is achieved. Two-dimensional bodies of arbitrary shapes are treated, the body contour(s) being simply input to the program. The complication of the body shape is thus removed from the problem.

Thompson, J. F.; Warsi, Z. U. A.; Amlicke, B. B.

1976-01-01

205

A Novel Microfluidic Platform for Continuous DNA Extraction and Purification using Laminar Flow Magnetophoresis  

Microsoft Academic Search

We present a novel microfluidic platform using laminar-flow magnetophoresis for combined continuous extraction and purification of DNA. All essential unit operations (DNA binding, sample washing and DNA elution) are integrated on one single chip. The key function is the motion of magnetic beads given by the interplay of laminar flow and time-varying magnetic field. The time for extraction was 1

M. Karle; J. Miwa; G. Roth; R. Zengerle; F. von Stetten

2009-01-01

206

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

Microsoft Academic Search

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

Y. S. Wie; F. S. Jr. Collier; R. D. Wagner

1991-01-01

207

Aerodynamic design of a natural laminar flow nacelle and the design validation by flight testing  

Microsoft Academic Search

The laminar flow technology is one of the key technologies in aeronautics offering substantial improvements in the areas of economy and ecology. This paper describes the aerodynamic design methodology for a natural laminar flow (NLF) nacelle and the subsequent verification of the design quality by flight tests with a subsonic transport aircraft. The aerodynamic design was a contribution within the

H. Riedel; K.-H. Horstmann; A. Ronzheimer; M. Sitzmann

1998-01-01

208

The Effects of Axial Conduction in the Wall on Heat Transfer with Laminar Flow.  

National Technical Information Service (NTIS)

Wall conduction effects on steady-state laminar flow heat-transfer experiments are examined, and an analysis of heat transfer with axial conduction in the wall bounding a fluid in laminar flow is developed to determine the effects of the conduction in the...

E. J. Davis W. N. Gill

1969-01-01

209

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

Microsoft Academic Search

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

Satish G. Kandlikar

2008-01-01

210

Combustion characteristics of the end burning hybrid rockets in laminar flow  

Microsoft Academic Search

In this study, we aim to clarify the blowoff mechanism for flame spreading in an opposed laminar flow in narrow solid fuel ducts. To clarify this mechanism we conducted two experiments. First, we observed the changes of the flame spread rate at various oxygen velocities, ambient pressures, and port diameters. For flame spreading in laminar flow, combustion modes could be

Tsuneyoshi Matsuoka; Harunori Nagata

2011-01-01

211

Computational wing design studies relating to natural laminar flow  

NASA Technical Reports Server (NTRS)

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

Waggoner, Edgar G.

1986-01-01

212

Analysis and Optimization Laminar Viscous Flow Through a Channel  

NASA Astrophysics Data System (ADS)

Optimizing of laminar viscous flow through a pipe by two dimensionless values is investigated analytically. Dimensionless entropy generation and pumping power to heat transfer rate ratio are used as basis for constant viscous and the temperature dependence on the viscosity. For this matter we calculate entropy generation and pumping power for a fully developed in a pipe subjected to constant wall temperature for either constant viscosity and the variable viscosity. The variation entropy generation increase along the pipe length for viscous fluid is drawn, either the variation summation dimensionless entropy generation and the pumping power to heat transfer rate ratio are varying the fluid inlet temperature for fixed pipe length and are varying pipe length for fixed fluid inlet temperature are drawn. For low heat transfer conditions the entropy generation due to viscosity friction becomes dominant and the dependence of viscosity with the temperature becomes essentially important to be considered.

Langeroudi, H. G.; Aghanajafi, C.

2006-12-01

213

F-16XL Ship #2 Laminar Flow Glove mounting  

NASA Technical Reports Server (NTRS)

NASA's two-seat F-16XL research aircraft is shown in the modification hangar at NASA's Dryden Flight Research Center, Edwards, California, during installation of a titanium 'glove' on the upper surface of its modified left wing. The aircraft subsequently carried out a 13-month-long, 45-flight research program which investigated drawing off a small part of the boundary-layer air in order to provide laminar--or smooth--flow over a major portion of a wing flying at supersonic speeds. A turbo-compressor in the aircraft's fuselage provided suction to draw air through more than 10 million tiny laser-drilled holes in the glove via a manifold system employing 20 valves. Data obtained during the program could assist designers of future aircraft in developing a more efficient high-speed civil transport.

1995-01-01

214

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

215

Laminar air flow versus barrier nursing in marrow transplant recipients.  

PubMed

Forty-eight patients with acute leukaemia in relapse (n = 14), acute leukaemia in complete remission (n = 19), chronic myeloid leukaemia (n = 8) or severe aplastic anaemia (n = 7) received a marrow transplant. The first 26 patients were nursed in laminar-air-flow plastic isolators while the next 22 patients were treated in barrier nursing rooms. Gnotobiotic parameters and morbidity in the 2 groups are compared. Good decontamination of the gastro-intestinal tract was obtained using either of the 2 isolation techniques. The incidence of bacterial and mycotic infections, as well as the supportive care required by the patients was almost equal in both groups. Our results also suggest that the incidence of graft versus host disease may decrease with efficient decontamination of the patients. PMID:6388667

Mahmoud, H K; Schaefer, U W; Schüning, F; Schmidt, C G; Bamberg, M; Haralambie, E; Linzenmeier, G; Hantschke, D; Grosse-Wilde, H; Luboldt, W

1984-11-01

216

An Improved Lattice Kinetic Scheme for Incompressible Viscous Fluid Flows  

NASA Astrophysics Data System (ADS)

The lattice Boltzmann method (LBM) is an explicit numerical scheme for the incompressible Navier-Stokes equations (INSE) without integrating the Poisson equation for the pressure. In spite of its merit, the LBM has some drawbacks in accuracy. First, we review drawbacks for three numerical methods based on the LBM. The three methods are the LBM with the Bhatnagar-Gross-Krook model (LBGK), the lattice kinetic scheme (LKS) and the link-wise artificial compressibility method (LWACM). Second, in order to remedy the drawbacks, we propose an improved LKS. The present method incorporates (i) the scheme used in the LWACM for determining the kinematic viscosity, (ii) an iterative calculation of the pressure and (iii) a semi-implicit algorithm, while preserving the simplicity of the algorithm of the original LKS. Finally, in simulations of test problems, we find that the improved LKS eliminates the drawbacks and gives more accurate and stable results than LBGK, LKS and LWACM.

Suzuki, Kosuke; Inamuro, Takaji

2014-01-01

217

Progress Toward Efficient Laminar Flow Analysis and Design  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

218

Calculation of Incompressible Viscous Flows by an Unconditionally Stable Projection FEM  

Microsoft Academic Search

This paper investigates the numerical performance of a finite element implementation of a new incremental fractional-step method to compute steady and unsteady incompressible viscous flows under general boundary conditions and using unstructured meshes. A variational framework is adopted which accommodates two different spaces for representing and approximating the velocity fields calculated respectively in the viscous and inviscid phases of the

J.-L. Guermond; L. Quartapelle

1997-01-01

219

Unified edge-oriented stabilization of nonconforming finite element methods for incompressible flow problems  

Microsoft Academic Search

Summary. This paper deals with various aspects of edge-oriented stabilization techniques for nonconforming finite element methods for the numerical solution of incompressible flow problems. We discuss two separate classes of problems which require appropriate stabilization techniques: First, the lack of coercivity for nonconforming low order approximations for treating problems with the symmetric deformation tensor instead of the gradient formulation in

Abderrahim Ouazzi; Stefan Turek

220

Application of a posteriori error estimation to finite element simulation of incompressible Navier–Stokes flow  

Microsoft Academic Search

The main goal of this paper is to study adaptive mesh techniques, using a posteriori error estimates, for the finite element solution of the Navier–Stokes equations modeling steady and unsteady flows of an incompressible viscous fluid. Among existing operator splitting techniques, the ?-scheme is used for time integration of the Navier–Stokes equations. Then, a posteriori error estimates, based on the

Jun Cao

2005-01-01

221

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

Microsoft Academic Search

We consider a standard model for incompressible two-phase flows in which a localized force at the interface describes the effect of surface tension. If a level set (or VOF) method is applied then the interface, which is implicitly given by the zero level of the level set function, is in general not aligned with the triangulation that is used in

Arnold Reusken

2006-01-01

222

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

223

An Adaptive Level Set Approach for Incompressible Two-Phase Flows  

Microsoft Academic Search

We present a numerical method using the level set approach for solving incompressible two-phase flow with surface tension. In the level set approach, the free surface 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 free surface, with the advection of the

Mark Sussman; Ann S Almgren; John B Bell; Phillip Colella; Louis H Howell; Michael L Welcome

1999-01-01

224

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

225

A One-Cell Local Multigrid Method for Solving Unsteady Incompressible Multiphase Flows  

Microsoft Academic Search

An original local multigrid method for solving incompressible two-phase flow with surface tension is described. The dynamics of the interface are resolved on a hierarchy of structured and uniform grids (orthogonal Cartesian meshes). A new type of composite boundary condition is proposed to solve the dynamics of the multigrid calculation domains. The interface tracking is described by a TVD VOF

Stéphane Vincent; Jean-Paul Caltagirone

2000-01-01

226

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

227

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

NASA Technical Reports Server (NTRS)

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

Kiris, Cetin

1995-01-01

228

Incompressible Navier-Stokes algorithm for flow and heat transfer over rough surfaces  

NASA Astrophysics Data System (ADS)

The development of a computer model for simulation of incompressible turbulent flow and heat transfer over rough surfaces using the discrete element method is presented. The discrete element roughness model is implemented into an existing incompressible Navier-Stokes algorithm. This algorithm is a finite volume, incompressible Navier-Stokes solver which uses artificial compressibility and the Roe approximate Riemann solver, also referred to as the flux difference split method. The equations solved in this code were modified to include surface roughness effects in the flow. Details of the roughness effects on the flow are modeled empirically instead of being resolved in the computational geometry. The roughness element from drag and heat transfer are treated as volumetric sink and source terms, respectively. Cases were treated for flow and convective heat transfer over smooth and rough flat plates with different free stream velocities and roughness distributions. Also, flow computations were performed for an axisymmetric body with an inflected curved stern and a NACA-0012 airfoil. The rough flow prediction model was observed to simulate the effects of surface roughness accurately; in one case flow separation was indicated. In all cases the computed effects of surface roughness were observed to yield higher skin friction than the equivalent flow over a smooth surface. For the case of computed heat transfer over the flat plate, roughness increased heat transfer.

Fleming, Kenton Ridgeway

229

An anisotropic flow law for incompressible polycrystalline materials  

NASA Astrophysics Data System (ADS)

New and explicit anisotropic constitutive equations between the stretching and deviatoric stress tensors for the two- and three-dimensional cases of incompressible polycrystalline materials are presented. The anisotropy is assumed to be driven by an Orientation Distribution Function (ODF). The polycrystal is composed of transversally isotropic crystallites, the lattice orientation of which can be characterized by a single unit vector. The proposed constitutive equations are valid for any frame of reference and for every state of deformation. The basic assumption of this method is that the principle directions of the stretching and of the stress deviator are the same in the isotropic as well as in the anisotropic case. This means that the proposed constitutive laws are able to model the effects of anisotropy only via a change of the fluidity due to a change of the ODF. Such an assumption is justified to guarantee that, besides knowledge of the parameters involved in the isotropic constitutive equation, the anisotropic material response is completely characterized by only one additional parameter, a type of enhancement factor. Explicit comparisons with experimental data are conducted for Ih ice.

Placidi, Luca; Hutter, Kolumban

2005-11-01

230

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

231

Numerical methods in laminar and turbulent flow; Proceedings of the 7th International Conference, Stanford Univ., CA, July 15-19, 1991. Vol. 7, pts. 1 & 2  

NASA Technical Reports Server (NTRS)

Consideration is given to the impulse response of a laminar boundary layer and receptivity; numerical transition to turbulence in plane Poiseuille flow; large eddy simulation of turbulent wake flow; a viscous model and loss calculation of a multisplitter cascade; vortex initiation during dynamic stall of an airfoil; a numerical analysis of isothermal flow in a combustion chamber; and compressible flow calculations with a two-equation turbulence model and unstructured grids. Attention is also given to a 2D calculation of a buoyant flow around a burning sphere, a fast multigrid method for 3D turbulent incompressible flows, a streaming flow induced by an oscillating cascade of circular cylinders, an algebraic multigrid scheme for solving the Navier-Stokes equations on unstructured meshes; and nonlinear coupled multigrid solutions to thermal problems employing different nodal grid arrangements and convective transport approximations.

Taylor, C. (editor); Chin, J. H. (editor); Homsy, G. M. (editor)

1991-01-01

232

Numerical methods in laminar and turbulent flow; Proceedings of the 7th International Conference, Stanford Univ., CA, July 15-19, 1991. Vol. 7, pts. 1 & 2  

NASA Astrophysics Data System (ADS)

Consideration is given to the impulse response of a laminar boundary layer and receptivity; numerical transition to turbulence in plane Poiseuille flow; large eddy simulation of turbulent wake flow; a viscous model and loss calculation of a multisplitter cascade; vortex initiation during dynamic stall of an airfoil; a numerical analysis of isothermal flow in a combustion chamber; and compressible flow calculations with a two-equation turbulence model and unstructured grids. Attention is also given to a 2D calculation of a buoyant flow around a burning sphere, a fast multigrid method for 3D turbulent incompressible flows, a streaming flow induced by an oscillating cascade of circular cylinders, an algebraic multigrid scheme for solving the Navier-Stokes equations on unstructured meshes; and nonlinear coupled multigrid solutions to thermal problems employing different nodal grid arrangements and convective transport approximations.

Taylor, C.; Chin, J. H.; Homsy, G. M.

233

Missing Boundary Conditions with Unsteady Incompressible Navier-Stokes Flows.  

National Technical Information Service (NTIS)

An unsteady viscous flow problem where good boundary conditions are available on only part of the boundary is investigated. This problem appears when the flow phenomena of interest are concentrated in a part of the flow region and, for reasons of computat...

F. K. Hebeker, P. Wilde

1990-01-01

234

Measurements of laminar and turbulent flow in a curved duct with thin inlet boundary layers  

NASA Technical Reports Server (NTRS)

Laser Doppler velocimetry was used to measure the laminar and turbulent flow in a 90 deg square bend of strong curvature. The boundary layers at the inlet to the bend were approximately 25 percent and 15 percent of the hydraulic diameter for the laminar and turbulent flows, respectively. The development of the pressure driven secondary motion is more rapid for laminar flow: the maximum cross stream component measured was 60 percent of the bulk velocity in contrast to 40 percent for turbulent flow. The streamwise isotachs show that, for laminar flow, large velocities are found progressively nearer to the outer radius of the bend and along the sidewalls. For turbulent flow, the isotachs move towards the inner radius until about 60 deg around the bend where strong secondary motion results in a similar redistribution. Turbulence level and shear stress measurements are also presented.

Taylor, A. M. K. P.; Whitelaw, J. H.; Yianneskis, M.

1981-01-01

235

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

236

Three-dimensional finite-volume method for incompressible flows with complex boundaries  

Microsoft Academic Search

A finite-volume method is presented for calculating incompressible 3D flows with curved irregular boundaries. The method employs structured nonorthogonal grids, cell-centered variable arrangement, and Cartesian velocity components. A special interpolation procedure for evaluating the mass fluxes at the cell-faces is used to avoid the nonphysical oscillation of flow variables usually encountered with the cell-centered arrangement. The SIMPLE algorithm is used

S. Majumdar; W. Rodi; J. Zhu

1992-01-01

237

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

NASA Technical Reports Server (NTRS)

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

Carmichael, B. H.

1979-01-01

238

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

NASA Technical Reports Server (NTRS)

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

Wornom, S. F.

1971-01-01

239

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...

240

Laminar flow and heat transfer in confined channel flow past square bars arranged side by side  

Microsoft Academic Search

.   \\u000a A numerical investigation was conducted to analyze the unsteady laminar flow field and heat transfer characteristics in a\\u000a plane channel with two square bars mounted side by side to the approaching flow. A finite volume technique is applied with\\u000a a fine grid and time resolution. The transverse separation distance between the bars (G\\/d) is varied from 0 to

Alvaro Valencia; Ronald Paredes

2003-01-01

241

Laminarization of minimal plane Couette flow: Going beyond the basin of attraction of turbulence  

NASA Astrophysics Data System (ADS)

Laminarization of minimal plane Couette turbulence is achieved numerically through short-time imposition of weak spanwise system rotation. A laminarization strategy presented in this Letter is inspired by investigation of the phase-space structure in the vicinity of a recently found unstable periodic orbit [G. Kawahara and S. Kida, ``Periodic motion embedded in plane Couette turbulence: regeneration cycle and burst,'' J. Fluid Mech. 449, 291 (2001)]. The periodic orbit, which a turbulent state occasionally approaches, and its local stable manifold are found to form the separatrix between the basin of attraction of turbulent and laminar flows. The introduction of the slight rotation during its approach to the periodic orbit enables the state to go beyond the basin of attraction of the turbulence toward the laminar flow. The global stabilization of the unstable periodic orbit by the method of controlling chaos is also performed to accomplish the laminarization without waiting until the natural approach.

Kawahara, Genta

2005-04-01

242

Numerical solution of the Navier-Stokes equations for high Reynolds number incompressible turbulent flow  

NASA Astrophysics Data System (ADS)

The full Navier-Stokes equations for incompressible turbulent flow must be solved to accurately represent all flow phenomena which occur in a high Reynolds number incompressible flow. A two layer algebraic eddy viscosity turbulence model is used to represent the Reynolds stress in the primitive variable formulation. The development of the boundary-fitted coordinate systems makes the numerical solution of these equations feasible for arbitrarily shaped bodies. The nondimensional time averaged Navier-Stokes equations, including the turbulence mode, are represented by finite difference approximations in the transformed plane. The resulting coupled system of nonlinear algebraic equations is solved using a point successive over relaxation iteration. The test case considered was a NACA 64A010 airfoil section at an angle of attack of two degrees and a Reynolds number of 2,000,000.

Thompson, D. S.

1980-05-01

243

SALLY LEVEL II- COMPUTE AND INTEGRATE DISTURBANCE AMPLIFICATION RATES ON SWEPT AND TAPERED LAMINAR FLOW CONTROL WINGS WITH SUCTION  

NASA Technical Reports Server (NTRS)

The computer program SALLY was developed to compute the incompressible linear stability characteristics and integrate the amplification rates of boundary layer disturbances on swept and tapered wings. For some wing designs, boundary layer disturbance can significantly alter the wing performance characteristics. This is particularly true for swept and tapered laminar flow control wings which incorporate suction to prevent boundary layer separation. SALLY should prove to be a useful tool in the analysis of these wing performance characteristics. The first step in calculating the disturbance amplification rates is to numerically solve the compressible laminar boundary-layer equation with suction for the swept and tapered wing. A two-point finite-difference method is used to solve the governing continuity, momentum, and energy equations. A similarity transformation is used to remove the wall normal velocity as a boundary condition and place it into the governing equations as a parameter. Thus the awkward nonlinear boundary condition is avoided. The resulting compressible boundary layer data is used by SALLY to compute the incompressible linear stability characteristics. The local disturbance growth is obtained from temporal stability theory and converted into a local growth rate for integration. The direction of the local group velocity is taken as the direction of integration. The amplification rate, or logarithmic disturbance amplitude ratio, is obtained by integration of the local disturbance growth over distance. The amplification rate serves as a measure of the growth of linear disturbances within the boundary layer and can serve as a guide in transition prediction. This program is written in FORTRAN IV and ASSEMBLER for batch execution and has been implemented on a CDC CYBER 70 series computer with a central memory requirement of approximately 67K (octal) of 60 bit words. SALLY was developed in 1979.

Srokowski, A. J.

1994-01-01

244

Computing three-dimensional incompressible flows with vortex elements  

NASA Technical Reports Server (NTRS)

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

Leonard, A.

1985-01-01

245

Distributed acoustic receptivity in laminar flow control configurations  

NASA Technical Reports Server (NTRS)

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

Choudhari, Meelan

1992-01-01

246

Development of laminar flow control wing surface composite structures  

NASA Technical Reports Server (NTRS)

The dramatic increases in fuel costs and the potential for periods of limited fuel availability provided the impetus to explore technologies to reduce transport aircraft fuel consumption. NASA sponsored the Aircraft Energy Efficiency (ACEE) program beginning in 1976 to develop technologies to improve fuel efficiency. This report documents the Lockheed-Georgia Company accomplishments under NAS1-16235 LFC Laminar-Flow-Control Wing Panel Structural Design And Development (WSSD); Design, manufacturing, and testing activities. An in-depth preliminary design of the baseline 1993 LFC wing was accomplished. A surface panel using the Lockheed graphite/epoxy integrated LFC wing box structural concept was designed. The concept was shown by analysis to be structurally efficient and cost effective. Critical details of the surface and surface joints were demonstrated by fabricating and testing complex, concept selection specimens. Cost of the baseline LFC aircraft was estimated and compared to the turbulent aircraft. The mission fuel weight was 21.7 percent lower for the LFC aircraft. The calculation shows that the lower fuel costs for LFC offset the higher incremental costs of LFC in less than six months.

Lineberger, L. B.

1984-01-01

247

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

NASA Technical Reports Server (NTRS)

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

Beatty, T. D.

1975-01-01

248

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

NASA Technical Reports Server (NTRS)

Incompressible Navier-Stokes solution methods are discussed with an emphasis on the pseudocompressibility method. A steady-state flow solver based on the pseudocompressibility approach is then described. This flow-solver code was used to analyze the internal flow in the Space Shuttle main engine hot-gas manifold. Salient features associated with this three-dimensional realistic flow simulation are discussed. Numerical solutions relevant to the current engine analysis and the redesign effort are discussed along with experimental results. This example demonstrates the potential of computational fluid dynamics as a design tool for aerospace applications.

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

1988-01-01

249

Laminar flow control research at TsAGI: Past and present  

NASA Astrophysics Data System (ADS)

This paper presents a brief review of activities in laminar flow control being performed at the Central Aerohydrodynamic Institute named after Prof. N.E. Zhukovsky (TsAGI). These efforts are focused on the improvement of the existing laminar flow control methods and on the development of new ones. The investigations have demonstrated the effectiveness of aircraft surface laminarization applications with the aim of friction drag reduction. The opportunity of considerable delaying of laminar-turbulent transition due to special wing profile geometry and using boundary layer suction and surface cooling has been verified at sub- and supersonic speeds through various wind tunnel testing at TsAGI and during flying laboratory experiments at the Flight Research Institute (LII). The investigations on using hybrid laminar flow control systems for friction drag reduction were also carried out. New techniques of laminar flow control were proposed, in particular, the method of local heating of the wing leading edge, boundary layer laminarization by means of receptivity control, and electrohydrodynamic methods of boundary layer stability control.

Chernyshev, S. L.; Kiselev, A. Ph.; Kuryachii, A. P.

2011-04-01

250

Development of Technology for the Fabrication of Reliable Laminar Flow Control Panels on Subsonic Transports.  

National Technical Information Service (NTIS)

The feasibility of using porous composite materials (Kevlar, Doweave, and Leno Weave) as lightweight, efficient laminar flow control (LFC) surface materials is compared to the metallic 319L stainless Dynapore surfaces and electron beam drilled composite s...

1976-01-01

251

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

National Technical Information Service (NTIS)

Laminar-flow control is an area of aeronautical research that has a long history at NASA's Langley Research Center, Dryden Flight Research Center, their predecessor organizations, and elsewhere. In this monograph, the author, who spent much of his career ...

A. L. Braslow

1999-01-01

252

Laminar boundary layer in conditions of natural transition to turbulent flow  

NASA Technical Reports Server (NTRS)

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

Polyakov, N. F.

1986-01-01

253

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

254

Laminar Flow Cyclone Development Program. Quarterly Technical Progress Report, April 1-June 30, 1979.  

National Technical Information Service (NTIS)

The objective of this program is to develop a laminar flow cyclone concept which could have a marked reduction in collection cut size, improved efficiency, increased throughput per unit volume, and potentially low capital cost relative to more conventiona...

W. B. Giles K. L. Bekofske

1979-01-01

255

Natural laminar flow flight experiments on a turbine engine nacelle fairing  

NASA Technical Reports Server (NTRS)

Flight experiments are being conducted with the objective to investigate the interactions between acoustic disturbances and laminar flow in the flight environment. In the experiments, the laminar boundary layer on the nacelles will be exposed to discrete and broadband external noises, and the effect of varying noise levels and frequencies on the stability of the laminar flow will be studied. The present paper provides an overview of the complete project and a status report on the results which have been obtained. The flight experiment is conducted with the aid of a modified research aircraft. The phase I flight tests are concerned with a quick and simple determination of natural laminar flow (NLF) behavior on an engine nacelle. Attention is given to instrumentation, the acoustic noise source, flow visualization, and the test results.

Obara, C. J.; Hastings, E. C.; Schoenster, J. A.; Parrott, T. L.; Holmes, B. J.

1986-01-01

256

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

257

F-16XL Supersonic Laminar Flow Test Flight  

NASA Video Gallery

An F-16XL aircraft was used by the Dryden Flight Research Center, Edwards, California, in a NASA-wide program to improve laminar airflow on aircraft flying at sustained supersonic speeds. It was th...

258

Turbulence in nearly incompressible fluids: density spectrum, flows, correlations and implication to the interstellar medium  

NASA Astrophysics Data System (ADS)

Interstellar scintillation and angular radio wave broadening measurements show that interstellar and solar wind (electron) density fluctuations exhibit a Kolmogorov-like k-5/3 power spectrum extending over many decades in wavenumber space. The ubiquity of the Kolmogorov-like interstellar medium (ISM) density spectrum led to an explanation based on coupling incompressible magnetohydrodynamic (MHD) fluctuations to density fluctuations through a "pseudosound" relation within the context of "nearly incompressible" (NI) hydrodynamics (HD) and MHD models. The NI theory provides a fundamentally different explanation for the observed ISM density spectrum in that the density fluctuations can be a consequence of passive scalar convection due to background incompressible fluctuations. The theory further predicts generation of long-scale structures and various correlations between the density, temperature and the (magneto) acoustic as well as convective pressure fluctuations in the compressible ISM fluids in different thermal regimes that are determined purely by the thermal fluctuation level. In this paper, we present the results of our two dimensional nonlinear fluid simulations, exploring various nonlinear aspects that lead to inertial range ISM turbulence within the context of a NI hydrodymanics model. In qualitative agreement with the NI predictions and the in-situ observations, we find that i) the density fluctuations exhibit a Kolmogorov-like spectrum via a passive convection in the field of the background incompressible fluctuations, ii) the compressible ISM fluctuations form long scale flows and structures, and iii) the density and the temperature fluctuations are anti-correlated.

Dastgeer, S.; Zank, G. P.

2005-01-01

259

NUMERICAL SIMULATION OF LAMINAR SOLID-LIQUID TWO-PHASE FLOW IN STIRRED TANKS  

Microsoft Academic Search

Laminar flow of solid-liquid suspension has been rarely reported in the literature. In this article, the laminar solid-liquid two-phase flow in a lab-scale stirred tank is measured with digital particle image velocimetry (DPIV) and numerically simulated with the improved inner-outer iterative method. The simulation results show good agreement with the present data. In the range of low solid volume concentration

Long Fan; Zai-Sha Mao; Chao Yang; Yundong Wang

2007-01-01

260

Simulation of contaminated groundwater migration in fractured rock by a laminar pipe-flow model  

Microsoft Academic Search

In this paper, the ability of a laminar pipe-flow model to reproduce the hydrodynamic transport of contaminated groundwater in fractured rock is investigated. It is assumed that the cross-section areas are circular and that the flow is laminar. The molecular diffusion is neglected as well as the impact of variations in velocity over the cross-section area. It is assumed that

Peter Dahlblom

1992-01-01

261

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

Microsoft Academic Search

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

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

2012-01-01

262

Higher-Order Compact Schemes for Numerical Simulation of Incompressible Flows  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

263

On a two-level element-free Galerkin method for incompressible fluid flow  

Microsoft Academic Search

In this paper, a new element-free Galerkin method called the two-level element-free Galerkin method is presented for incompressible fluid flow. This method consists of two parts: One at the global level and the other at the local level. The new method is based on the Hughes' variational multiscale formulation, and arises from a decomposition of the unknown variables into coarse\\/resolved

Lin Zhang; Jie Ouyang; Xiao-Hua Zhang

2009-01-01

264

The coupling of element-free Galerkin method and molecular dynamics for the incompressible flow problems  

Microsoft Academic Search

The coupling between the macro-scale numerical method and the molecular dynamics (MD) simulation is developed for simulating\\u000a the micro- and nano-scale incompressible flow problems. The proposed coupling schemes are based on the technique of “domain\\u000a decomposition” in which the MD simulation is used in the region where molecular details are important, while the macro-scale\\u000a numerical method is used in the

Lin ZhangJie; Jie Ouyang; Xiaohua Zhang

2011-01-01

265

Application of Meshless Local Petrov-Galerkin (MLPG) Approach to Simulation of Incompressible Flow  

Microsoft Academic Search

The meshless local Petrov-Galerkin (MLPG) method is an effective local mesh-free method for solving partial differential equations using moving least-squares (MLS) approximation and local weak form. In this article, the MLPG formulation is used with some modifications to simulate the incompressible flow within an irregular domain with scattered nodal distribution. The governing equations are taken in terms of vorticity–stream functions.

Y. L. Wu; G. R. Liu; Y. T. Gu

2005-01-01

266

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

267

Level Set Calculations for Incompressible Two-Phase Flows on a Dynamically Adaptive Grid  

Microsoft Academic Search

We present a coupled moving mesh and level set method for computing incom- pressible two-phase flow with surface tension. This work extends a recent work of Di et al. ((2005). SIAM J. Sci. Comput. 26, 1036-1056) where a moving mesh strategy was proposed to solve the incompressible Navier-Stokes equa- tions. With the involvement of the level set function and the

Yana Di; Ruo Li; Tao Tang; Pingwen Zhang

2007-01-01

268

Parallel finite element simulation of 3D incompressible flows: Fluid-structure interactions  

Microsoft Academic Search

SUMMARY Massively parallel finite element computations of 3D, unsteady incompressible flows, including those involving fluid-structure interactions, are presented. The computations with time-varying spatial domains are based on the deforming spatial domain\\/stabilized space-time (DSD\\/SST) finite element formulation. The capability to solve 3D problems involving fluid-structure interactions is demonstrated by investigating the dynamics of a fle~ible cantilevered pipe conveying fluid. Computations of

S. Mittal; T. E. Tezduyar

1995-01-01

269

On the stability and extension of reduced-order Galerkin models in incompressible flows  

Microsoft Academic Search

Proper orthogonal decomposition (POD) has been used to develop a reduced-order model of the hydrodynamic forces acting on\\u000a a circular cylinder. Direct numerical simulations of the incompressible Navier–Stokes equations have been performed using\\u000a a parallel computational fluid dynamics (CFD) code to simulate the flow past a circular cylinder. Snapshots of the velocity\\u000a and pressure fields are used to calculate the

Imran Akhtar; Ali H. Nayfeh; Calvin J. Ribbens

2009-01-01

270

A coarse-constrained multiscale method for accelerating incompressible flow computations  

Microsoft Academic Search

We present a coarse-constrained multiscale (CCM) method for accelerating incompressible flow computations. Reducing the number of degrees of freedom of the Poisson solver by powers of two in the primitive variable fractional-step method, or the vorticity-stream function formulation of the problem accelerates these computations while, for the first level of coarsening, retaining the same level of accuracy in the fine-resolution

Omer San; Anne E. Staples

271

Numerical Convergence Study of Nearly Incompressible, Inviscid Taylor-Green Vortex Flow  

Microsoft Academic Search

A spectral method and a fifth-order weighted essentially non-oscillatory method were used to examine the consequences of filtering in the numerical simulation of the three-dimensional evolution of nearly-incompressible, in- viscid Taylor-Green vortex flow. It was found that numerical filtering using the high-order exponential filter and low-pass filter with sharp high mode cutoff applied in the spectral simulations significantly affects the

Chi-wang Shu; Wai-sun Don; David I. Gottlieb; Oleg Schilling; Leland Jameson

2005-01-01

272

A Multigrid Accelerated High-Order Compact Fractional Step Method for Unsteady Incompressible Viscous Flows  

Microsoft Academic Search

An efficient high-order compact scheme is presented for computing unsteady incompressible viscous flows. The scheme is constructed on a staggered Cartesian grid. Using the fractional step framework, the Navier-Stokes equations are advanced in time with the second-order Adams-Bashforth method without considering the pressure terms in the predictor step. The velocity field is then corrected so that the continuity equation is

Omer San; Anne Staples

2009-01-01

273

a Level Set Method for Incompressible Two-Fluid Flows with Immersed Solid Boundaries  

Microsoft Academic Search

A numerical method is presented for computing incompressible gas–liquid (or two-fluid) flows with immersed solid boundaries on fixed Cartesian meshes. A level set technique for tracking the gas–liquid interface is modified to treat the contact angle condition at the gas–liquid–solid interline as well as the no-slip condition at the fluid–solid interface. The no-slip condition is imposed by introducing another level

Gihun Son

2005-01-01

274

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

NASA Technical Reports Server (NTRS)

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

Winterscheidt, Daniel L.

1993-01-01

275

Incompressible moving boundary flows with the finite volume particle method  

Microsoft Academic Search

Mesh-free methods offer the potential for greatly simplified modeling of flow with moving walls and phase interfaces. The finite volume particle method (FVPM) is a mesh-free technique based on interparticle fluxes which are exactly analogous to intercell fluxes in the mesh-based finite volume method. Consequently, the method inherits many of the desirable properties of the classical finite volume method, including

Ruairi M. Nestor; Nathan J. Quinlan

2010-01-01

276

Spontaneous singularity in three-dimensional, inviscid, incompressible flow  

Microsoft Academic Search

In the present paper, evidence in support of the conjecture that vortex lines may be stretched an infinite amount in a finite time is obtained by applying series-analysis techniques to the time evolution of the inviscid Taylor-Green vortex (1937). The resulting power-series expansions are analyzed, using techniques developed for studying singularities in critical phenomena. The flow is the solution of

R. H. Morf; S. A. Orszag; U. Frisch

1980-01-01

277

An Approach to the Constrained Design of Natural Laminar Flow Airfoils  

NASA Technical Reports Server (NTRS)

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

Green, Bradford E.

1997-01-01

278

Multigrid Computations of 3-D Incompressible Internal and External Viscous Rotating Flows  

NASA Technical Reports Server (NTRS)

This report presents multigrid methods for solving the 3-D incompressible viscous rotating flows in a NASA low-speed centrifugal compressor and a marine propeller 4119. Numerical formulations are given in both the rotating reference frame and the absolute frame. Comparisons are made for the accuracy, efficiency, and robustness between the steady-state scheme and the time-accurate scheme for simulating viscous rotating flows for complex internal and external flow applications. Prospects for further increase in efficiency and accuracy of unsteady time-accurate computations are discussed.

Sheng, Chunhua; Taylor, Lafayette K.; Chen, Jen-Ping; Jiang, Min-Yee; Whitfield, David L.

1996-01-01

279

Flow visualization of supersonic laminar flow over a backward-facing step via NPLS  

NASA Astrophysics Data System (ADS)

An experimental study on a supersonic laminar flow over a backward-facing step of 5 mm height was undertaken in a low-noise indraft wind tunnel. To investigate the fine structures of Ma = 3.0 and 3.8 laminar flow over a backward-facing step, nanotracer planar laser scattering was adopted for flow visualization. Flow structures, including supersonic laminar boundary layer, separation, reattachment, redeveloping turbulent boundary layer, expansion wave fan and reattachment shock, were revealed in the transient flow fields. In the Ma = 3.0 BFS (backward-facing step) flow, by measuring four typical regions, it could be found that the emergence of weak shock waves was related to the K-H (Kelvin-Helmholtz) vortex which appeared in the free shear layer and that the convergence of these waves into a reattachment shock was distinct. Based on large numbers of measurements, the structure of time-averaging flow field could be gained. Reattachment occurred at the location downstream from the step, about 7-7.5 h distance. After reattachment, the recovery boundary layer developed into turbulence quickly and its thickness increased at an angle of 4.6°. At the location of X = 14 h, the redeveloping boundary layer was about ten times thicker than its original thickness, but it still had not changed into fully developed turbulence. However, in the Ma = 3.8 flow, the emergence of weak shock waves could be seen seldom, due to the decrease of expansion. The reattachment point was thought to be near X = 15 h according to the averaging result. The reattachment shock was not legible, which meant the expansion and compression effects were not intensive.

Chen, Z.; Yi, S. H.; Tian, L. F.; He, L.; Zhu, Y. Z.

2013-07-01

280

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

281

A multiple-scale turbulence model for incompressible flow  

NASA Technical Reports Server (NTRS)

A multiple-scale eddy viscosity model is described. This model splits the energy spectrum into a high wave number regime and a low wave number regime. Dividing the energy spectrum into multiple regimes simplistically emulates the cascade of energy through the turbulence spectrum. The constraints on the model coefficients are determined by examining decaying turbulence and homogeneous turbulence. A direct link between the partitioned energies and the energy transfer process is established through the coefficients. This new model was calibrated and tested for boundary-free turbulent shear flows. Calculations of mean and turbulent properties show good agreement with experimental data for two mixing layers, a plane jet and a round jet.

Duncan, B. S.; Liou, W. W.; Shih, T. H.

1993-01-01

282

Actuator disk theory for incompressible highly rotating flows.  

NASA Technical Reports Server (NTRS)

A solution has been obtained for a stator-rotor pair operating in an annulus with constant hub and tip radii. The stator and rotor are represented as actuator discs, and perfect fluid flow is assumed. The solutions are exact within these limitations, no linearization being required. The forms of blade loadings considered allow the introduction of large vorticity by either the rotor or stator. As a result, the rotor may be a ?nonconstant-work' row. The solutions obtained are of summational form, but many of the summations are obtained in closed form, the resultant formulas allowing rapid calculation of desired examples. An example numerical result is included.

Oates, G. C.

1971-01-01

283

Laminar flow reduces cases of surgical site infections in vascular patients  

PubMed Central

Introduction Numerous strategies are employed routinely in an effort to lower rates of surgical site infections (SSIs). A laminar flow theatre environment is generally used during orthopaedic surgery to reduce rates of SSIs. Its role in vascular surgery, especially when arterial bypass grafts are used, is unknown. Methods A retrospective review of a prospectively maintained database was undertaken for all vascular procedures performed by a single consultant over a one-year period. Cases were performed, via random allocation, in either a laminar or non-laminar flow theatre environment. Demographic data, operative data and evidence of postoperative SSIs were noted. A separate subgroup analysis was undertaken for patients requiring an arterial bypass graft. Univariate and multivariate logistical regression was undertaken to identify significant factors associated with SSIs. Results Overall, 170 procedures were analysed. Presence of a groin incision, insertion of an arterial graft and a non-laminar flow theatre were shown to be predictive of SSIs in this cohort. In the subgroup receiving arterial grafts, only a non-laminar flow theatre environment was shown to be predictive of an SSI. Conclusions This study suggests that laminar flow may reduce incidences of SSI, especially in the subgroup of patients receiving arterial grafts.

Bosanquet, DC; Jones, CN; Gill, N; Jarvis, P

2013-01-01

284

Large eddy simulation of incompressible turbulent channel flow  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

285

A fundamental study of suction for Laminar Flow Control (LFC)  

NASA Technical Reports Server (NTRS)

This report covers the period forming the first year of the project. The aim is to experimentally investigate the effects of suction as a technique for Laminar Flow Control. Experiments are to be performed which require substantial modifications to be made to the experimental facility. Considerable effort has been spent developing new high performance constant temperature hot-wire anemometers for general purpose use in the Fluid Mechanics Laboratory. Twenty instruments have been delivered. An important feature of the facility is that it is totally automated under computer control. Unprecedently large quantities of data can be acquired and the results examined using the visualization tools developed specifically for studying the results of numerical simulations on graphics works stations. The experiment must be run for periods of up to a month at a time since the data is collected on a point-by-point basis. Several techniques were implemented to reduce the experimental run-time by a significant factor. Extra probes have been constructed and modifications have been made to the traverse hardware and to the real-time experimental code to enable multiple probes to be used. This will reduce the experimental run-time by the appropriate factor. Hot-wire calibration drift has been a frustrating problem owing to the large range of ambient temperatures experienced in the laboratory. The solution has been to repeat the calibrations at frequent intervals. However the calibration process has consumed up to 40 percent of the run-time. A new method of correcting the drift is very nearly finalized and when implemented it will also lead to a significant reduction in the experimental run-time.

Watmuff, Jonathan H.

1992-01-01

286

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

287

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.

288

Product selectivity control induced by using liquid-liquid parallel laminar flow in a microreactor.  

PubMed

Product selectivity control based on a liquid-liquid parallel laminar flow has been successfully demonstrated by using a microreactor. Our electrochemical microreactor system enables regioselective cross-coupling reaction of aldehyde with allylic chloride via chemoselective cathodic reduction of substrate by the combined use of suitable flow mode and corresponding cathode material. The formation of liquid-liquid parallel laminar flow in the microreactor was supported by the estimation of benzaldehyde diffusion coefficient and computational fluid dynamics simulation. The diffusion coefficient for benzaldehyde in Bu(4)NClO(4)-HMPA medium was determined to be 1.32 × 10(-7) cm(2) s(-1) by electrochemical measurements, and the flow simulation using this value revealed the formation of clear concentration gradient of benzaldehyde in the microreactor channel over a specific channel length. In addition, the necessity of the liquid-liquid parallel laminar flow was confirmed by flow mode experiments. PMID:21483942

Amemiya, Fumihiro; Matsumoto, Hideyuki; Fuse, Keishi; Kashiwagi, Tsuneo; Kuroda, Chiaki; Fuchigami, Toshio; Atobe, Mahito

2011-06-01

289

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

290

Method and apparatus for detecting laminar flow separation and reattachment  

NASA Technical Reports Server (NTRS)

The invention is a method and apparatus for simultaneously detecting laminar separation and reattachment of a fluid stream such as an airstream from and to the upper surface of an airfoil by simultaneously sensing and comparing a plurality of output signals. Each signal represents the dynamic shear stress at one of an equal number of sensors spaced along a straight line on the surface of the airfoil that extends parallel to the airstream. The output signals are simultaneously compared to detect the sensors across which a reversal in phase of said output signal occurs, said detected sensors being in the region of laminar separation or reattachment.

Stack, John P. (inventor); Mangalam, Sivaramakrishnan M. (inventor)

1990-01-01

291

Stability of relativistic laminar flow equilibria for electrons drifting in crossed fields  

Microsoft Academic Search

Planar, relativistic laminar flow states in which electric charge is taken to be constant across the flow and lie in the range between zero and one are derived. The equilibrium state is discussed, and the linear electromagnetic instability of transverse magnetic waves propagating along the direction of electron flow is presented. The results and conclusions are similar to those for

John Swegle

1983-01-01

292

Effect of laminar unsteady fluid flows on mass transfer in electrochemical systems  

Microsoft Academic Search

A numerical study of mass transfer in steady as well as unsteady two-dimensional laminar channel flows is investigated. When a circular cylinder is suspended in a steady flow stream, the flow becomes unsteady and oscillates periodically for Reynolds numbers, Re, between 200 and 800 (where Re is based on the channel height) due to the formation of the Karman vortex

Ahmed Kamal Shehata

1999-01-01

293

Viscosity induced non-uniform flow in laminar flow heat exchangers  

NASA Astrophysics Data System (ADS)

Laminar flow heat exchangers which cool oil in noninterconnected parallel passages can experience nonuniform flows and a reduction in the effective heat exchanger coefficient in a range of Reynolds number which varies with tube length and diameter, tube wall temperature and fluid inlet temperature. The method of predicting the reduction in effective heat transfer coefficient and the range of Reynolds number over which these instabilities exist is presented for a particular oil, Mobil aviation oil 120. Included, also, is the prediction of the effect of radial viscosity variation on the constant property magnitudes of friction and heat transfer coefficient.

Putnam, G. R.; Rohsenow, W. M.

1985-05-01

294

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

295

The convergence of a mixed finite element method for steady convective incompressible viscous flow  

NASA Astrophysics Data System (ADS)

Some results on the convergence of the “assumed deviatoric stress-pressure-velocity” mixed finite element method for steady, convective, incompressible, viscous flow are given. An abstract error estimate is proved, which shows that the same LBB conditions for hybrid finite element method for Stokes flow are also applicable to the present method. An unusual term appears in the estimate, the rate of convergence for this term is examined. To make our idea clear, the same finite element method is applied to single elliptic equations first.

Ying, L.-A.

1987-03-01

296

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

NASA Technical Reports Server (NTRS)

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

Hobson, Garth Victor; Lakshminarayana, B.

1991-01-01

297

Treatment of branch cut lines in the computation of incompressible flows with C-grids  

NASA Astrophysics Data System (ADS)

It is well recognised that C-grids are ideally suited for computing flows about bodies with a rounded leading edge like aerofoils. A branch cut line is an essential feature of such a grid and is usually treated as one of the boundaries. However, when one computes an incompressible flow using a pressure correction method, the presence of such a feature can be problematic in achieving a stable convergence. This paper describes a novel way of handling the branch cut line which ensures convergence of solution when using SIMPLEC type pressure correction procedures.

Mellen, C. P.; Srinivas, K.

298

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

NASA Technical Reports Server (NTRS)

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

Goodyear, M. D.

1987-01-01

299

Experimental Studies on Laminar Level and Curved Flows Experimentelle Untersuchungen von Stroemungen in Ebenen und Gekruemmten Lamellen.  

National Technical Information Service (NTIS)

Experiments to determine the characteristics and structure of laminar air flow were conducted using various flow visualization techniques. The flow pattern around bodies of revolution of various configurations are illustrated. The apparatus used for flow ...

P. E. M. Schneider

1974-01-01

300

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

NASA Astrophysics Data System (ADS)

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

Ziaei-Rad, Masoud

2013-07-01

301

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

NASA Technical Reports Server (NTRS)

An implicit finite difference code cast in general curvilinear coordinates is further developed for three-dimensional incompressible turbulent flows. The code is based on the method of pseudocompressibility and utilizes the Beam and Warming implicit approximate factorization algorithm to achieve computational efficiency. A multiple-zone method is further extended to include composite-grids to overcome the excessive computer memory required for solving turbulent flows in complex three-dimensional geometries. A simple turbulence model is proposed for internal flows. The code is being used for the Space Shuttle Main Engine (SSME) internal flow analyses.

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

1985-01-01

302

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

NASA Astrophysics Data System (ADS)

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

Zakharenkov, M. N.

2007-12-01

303

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

PubMed Central

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

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

2013-01-01

304

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

PubMed

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

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

2005-10-01

305

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

NASA Technical Reports Server (NTRS)

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

Marshall, Laurie A.

1999-01-01

306

Effect of temperature on turbulent and laminar flow efficacy analysis of nanofluids  

NASA Astrophysics Data System (ADS)

The present study investigates the temperature-dependent efficacy analysis of nanofluids for both laminar and turbulent flow applications. Characterizations for the thermo-physical properties of nanofluids are carried out at different temperatures for the viability analysis. Thermal conductivity of yttria nanofluids shows strong temperature dependence compared to copper nanofluids with an increase of 7.5% to 21% for a temperature range of 25 °C to 85 °C. Moreover, the effective viscosity of yttria nanofluids is found to decrease gradually with temperatures in spite of copper nanofluid insensitivity. A theoretical study is carried out to compute the efficacy of yttria and copper nanofluids for laminar and turbulent flow regimes over a range of temperatures with the help of their thermo-physical properties. Yttria nanofluids are found viable for both laminar and turbulent flow for temperatures above 37 °C and 45 °C, respectively. On the other hand, copper nanofluids are found applicable only in laminar flow condition for temperatures above 75 °C. The stability and superior figure of merit for yttria nanofluids with temperature make it a potential coolant for higher-temperature convective cooling systems working on both laminar and turbulent flows.

Tesfai, Waka; Singh, Pawan K.; Masharqa, Salim J. S.; Chiesa, Matteo; Shatilla, Youssef

2012-03-01

307

Parallel computation of unsteady incompressible viscous flows around moving rigid bodies using an immersed object method with overlapping grids  

Microsoft Academic Search

A novel immersed object method is developed for simulating two-dimensional unsteady incompressible viscous flows around arbitrarily moving rigid bodies. It has been implemented in a parallel unstructured finite volume incompressible Navier–Stokes solver, based on the artificial compressibility (AC) approach using a higher-order characteristics-based upwind scheme and matrix-free implicit dual time-stepping. In the immersed object method, an object is immersed in

C. H. Tai; Yong Zhao; K. M. Liew

2005-01-01

308

Parallel computation of unsteady incompressible viscous flows around moving rigid bodies using an immersed object method with overlapping grids  

Microsoft Academic Search

A novel immersed object method is developed for simulating two-dimensional unsteady incompressible viscous flows around arbitrarily moving rigid bodies. It has been implemented in a parallel unstructured finite volume incompressible Navier Stokes solver, based on the artificial compressibility (AC) approach using a higher-order characteristics-based upwind scheme and matrix-free implicit dual time-stepping. In the immersed object method, an object is immersed

C. H. Tai; Y. Zhao; K. M. Liew

2005-01-01

309

Method for calculation of laminar heat transfer in air flow around cylinders of arbitrary cross section (including large temperature differences and transpiration cooling)  

NASA Technical Reports Server (NTRS)

The solution of heat-transfer problems has become vital for many aeronautical applications. The shapes of objects to be cooled can often be approximated by cylinders of various cross sections with flow normal to the axis as, for instance heat transfer on gas-turbine blades and on air foils heated for deicing purposes. A laminar region always exists near the stagnation point of such objects. A method previously presented by E. R. G. Eckert permits the calculation of local heat transfer around the periphery of cylinders of arbitrary cross section in the laminar region for flow of a fluid with constant property values with an accuracy sufficient for engineering purposes. The method is based on exact solutions of the boundary-layer equations for incompressible wedge-type flow and on the postulate that at any point on the cylinder the boundary-layer growth is the same as that on a wedge with comparable flow conditions. This method is extended herein to take into account the influence of large temperature differences between the cylinder wall and the flow as well as the influence of transpiration cooling when the same medium as the outside flow is used as coolant.

Eckert, E R; Livingood, John N B

1953-01-01

310

Implicit/Multigrid Algorithms for Incompressible Turbulent Flows on Unstructured Grids  

NASA Technical Reports Server (NTRS)

An implicit code for computing inviscid and viscous incompressible flows on unstructured grids is described. The foundation of the code is a backward Euler time discretization for which the linear system is approximately solved at each time step with either a point implicit method or a preconditioned Generalized Minimal Residual (GMRES) technique. For the GMRES calculations, several techniques are investigated for forming the matrix-vector product. Convergence acceleration is achieved through a multigrid scheme that uses non-nested coarse grids that are generated using a technique described in the present paper. Convergence characteristics are investigated and results are compared with an exact solution for the inviscid flow over a four-element airfoil. Viscous results, which are compared with experimental data, include the turbulent flow over a NACA 4412 airfoil, a three-element airfoil for which Mach number effects are investigated, and three-dimensional flow over a wing with a partial-span flap.

Anderson, W. Kyle; Rausch, Russ D.; Bonhaus, Daryl L.

1997-01-01

311

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

NASA Technical Reports Server (NTRS)

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

Srokowski, A. J.

1978-01-01

312

Pressure Drop Characteristics in Continuum-Based Laminar Compressible Microconvective Flow  

Microsoft Academic Search

Pressure drop (?p) in microconvective flows is of basic importance in several applications in which fluid flows through micropassages for heat removal. This investigation studies the effects of variations in air properties due to convective heat transfer on basic laminar microflow parameters: wall shear stress, Fanning friction factor, pressure drop, and Darcy friction factor. These effects are classified as direct

Shripad P. Mahulikar; N. P. Gulhane; S. D. Pradhan; K. Hrisheekesh; S. V. Prabhu

2012-01-01

313

Instrumentation requirements for laminar flow research in the NLR high speed wind tunnel HST  

Microsoft Academic Search

It is noted that the testing of laminar flow airfoils and wings in wind tunnels imposes very stringent requirements on the wind tunnel and the measurement techniques. Starting from experience obtained in the high-speed tunnel (HST) of the NLR, typical aspects such as scale effects, flow quality, and model contamination are discussed. Different techniques of transition detection are reviewed, and

A. Elsenaar; P. B. Rohne; D. Rozendal; R. Poestkoke

1989-01-01

314

Conjugate heat transfer in fully developed laminar pipe flow and thermally induced stresses  

Microsoft Academic Search

Thermal stresses developed in pipes due to conjugate heat transfer are important in engineering applications. In the present study, fully developed laminar flow through a pipe is considered. Uniform heat flux from the external surface of the pipe is introduced. The thermal stresses developed due to conjugate heating are analyzed. The governing flow and energy equations are solved numerically using

I. T Al-Zaharnah; B. S Yilbas; M. S. J Hashmi

2000-01-01

315

Re-Design of ARL/HLF (Heated Laminar Flow) Body Nose Region.  

National Technical Information Service (NTIS)

The ARL (Penn State Univ.'s Applied Research Lab.) Heated Laminar flow (HLF) body is a streamlined body with a pointed nose. One of the experimental objectives for the ARL/HLF body is to provide for limited (low flow) stagnation point fluid ejection. Beca...

G. C. Lauchle S. L. Giner

1984-01-01

316

Combined convection and radiation heat transfer to thermally developing laminar droplet flow in concentric annuli  

Microsoft Academic Search

This paper presents numerical results for combined convection and radiation heat transfer to a laminar mist flow in the thermal entrance region of a concentric annulus with a heated core at constant wall temperature and an insulated outer wall. The saturated droplets in the mist flow are considered as equivalent heat sinks distributed in the superheated vapor stream. Numerical calculations

T. H. Hwang; J. K. Lin

1992-01-01

317

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

318

Dirichlet and Neumann boundary conditions for the pressure Poisson equation of incompressible flow  

NASA Astrophysics Data System (ADS)

Numerical solution techniques for the pressure Poisson equation (which plays two distinct roles in the formulation of the incompressible Navier-Stokes equations) are investigated analytically, with a focus on the influence of the boundary conditions adopted. Solutions obtained for two cases of the inviscid stagnation problem of point flow using Dirichlet boundary conditions are presented in graphs and compared with solutions obtained using Neumann boundary conditions and a consistent finite-difference procedure on staggered grids: these solutions are shown to be identical, confirming the result of Gresho and Sani (1987).

Abdallah, S.; Dreyer, J.

1988-09-01

319

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

320

Preconditioned upwind methods to solve 3-D incompressible Navier-Stokes equations for viscous flows  

NASA Technical Reports Server (NTRS)

A computational method for calculating low-speed viscous flowfields is developed. The method uses the implicit upwind-relaxation finite-difference algorithm with a nonsingular eigensystem to solve the preconditioned, three-dimensional, incompressible Navier-Stokes equations in curvilinear coordinates. The technique of local time stepping is incorporated to accelerate the rate of convergence to a steady-state solution. An extensive study of optimizing the preconditioned system is carried out for two viscous flow problems. Computed results are compared with analytical solutions and experimental data.

Hsu, C.-H.; Chen, Y.-M.; Liu, C. H.

1990-01-01

321

A general explicit or semi-explicit algorithm for compressible and incompressible flows  

NASA Technical Reports Server (NTRS)

A unified finite element algorithm is developed which is applicable to a wide range of problems of fluid mechanics without recourse to artificial, empirically determined factors. In its explicit form, the algorithm is similar to the Taylor-Galerkin scheme and is easily adopted to standard codes. The scheme proposed here possesses sufficient natural balancing diffusion and thus reduces and sometimes eliminates the need for special 'shock capturing' diffusion. The efficiency of the algorithm is demonstrated using several examples ranging from incompressible through transonic regions to supersonic flows.

Zienkiewicz, O. C.; Wu, J.

1992-01-01

322

Wave Number Selection for Incompressible Parallel Jet Flows Periodic in Space  

NASA Technical Reports Server (NTRS)

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

Miles, Jeffrey Hilton

1997-01-01

323

Heat and mass transfer in two-phase flow - A mathematical model for laminar film flow and its experimental validation  

NASA Astrophysics Data System (ADS)

A mathematical model is presented for the vaporisation of liquid from a laminar film flowing down the inside surface of a smooth tube into a countercurrent laminar flow of gas. The partial differential equations that describe temperature and composition distributions are integrated across the tube to give a set of four coupled ordinary differential equations. A numerical method for the solution of the equations is proposed and examined; the method is posed to solve the transient response for heat and mass transfer. A satisfactory solution is found for a range of space and time intervals. The mathematical model has been validated by experimental measurements on a falling film evaporator with evaporation occurring at sub-boiling temperatures from a laminar liquid film into a laminar gas stream. The performance of the evaporator is assessed.

Conder, J. R.; Gunn, D. J.; Shaikh, M. A.

1982-08-01

324

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

NASA Technical Reports Server (NTRS)

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

1999-01-01

325

Parametric study on laminar flow for finite wings at supersonic speeds  

NASA Technical Reports Server (NTRS)

Laminar flow control has been identified as a key element in the development of the next generation of High Speed Transports. Extending the amount of laminar flow over an aircraft will increase range, payload, and altitude capabilities as well as lower fuel requirements, skin temperature, and therefore the overall cost. A parametric study to predict the extent of laminar flow for finite wings at supersonic speeds was conducted using a computational fluid dynamics (CFD) code coupled with a boundary layer stability code. The parameters investigated in this study were Reynolds number, angle of attack, and sweep. The results showed that an increase in angle of attack for specific Reynolds numbers can actually delay transition. Therefore, higher lift capability, caused by the increased angle of attack, as well as a reduction in viscous drag, due to the delay in transition, can be expected simultaneously. This results in larger payload and range.

Garcia, Joseph Avila

1994-01-01

326

Natural Laminar-Flow blades for vertical-axis wind turbines  

SciTech Connect

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 performance simulation. The section selected for fabrication and test was one which supported a 47% chord laminar flow. A comparison of lift and drag coefficients is made. A two-blade set was extruded for a 5-m diameter vertical axis wind turbine. A test series was then conducted at a turbine rotational speed of 175 rpm and a corresponding equatorial Reynolds number of 360,000. Field and wind tunnel tests have been and will be conducted. (LEW)

Klimas, P.C.

1982-01-01

327

An approach to the constrained design of natural laminar flow airfoils  

NASA Technical Reports Server (NTRS)

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

Green, Bradford Earl

1995-01-01

328

A coarse-grid projection method for accelerating incompressible flow computations  

NASA Astrophysics Data System (ADS)

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

San, Omer; Staples, Anne

2011-11-01

329

The numerical study of separated laminar and turbulent flows past bluff bodies of arbitrary shape  

Microsoft Academic Search

The flow motion and heat transfer of separated laminar and turbulent flows past an arbitrarily shaped bluff body is numerically investigated. The turbulent flows are characterized using time-averaged Reynolds equations and a two-equation. The computational approach uses a body-fitted coordinate system to account for irregularities in the flow domain. The modified strongly implicit (MSI) iteration method is applied to solve

Shih-Shan Wei; Selcuk I. Guceri

1987-01-01

330

Digital data acquisition and preliminary instrumentation study for the F-16 laminar flow control vehicle  

NASA Technical Reports Server (NTRS)

Preliminary studies have shown that maintenance of laminar flow through active boundary-layer control is viable. Current research activity at NASA Langley and NASA Dryden is utilizing the F-16XL-1 research vehicle fitted with a laminar-flow suction glove that is connected to a vacuum manifold in order to create and control laminar flow at supersonic flight speeds. This experimental program has been designed to establish the feasibility of obtaining laminar flow at supersonic speeds with highly swept wing and to provide data for computational fluid dynamics (CFD) code calibration. Flight experiments conducted as supersonic speeds have indicated that it is possible to achieve laminar flow under controlled suction at flight Mach numbers greater than 1. Currently this glove is fitted with a series of pressure belts and flush mounted hot film sensors for the purpose of determining the pressure distributions and the extent of laminar flow region past the stagnation point. The present mode of data acquisition relies on out-dated on board multi-channel FM analogue tape recorder system. At the end of each flight, the analogue data is digitized through a long laborious process and then analyzed. It is proposed to replace this outdated system with an on board state-of-the-art digital data acquisition system capable of a through put rate of up to 1 MegaHertz. The purpose of this study was three-fold: (1) to develop a simple algorithm for acquiring data via 2 analogue-to-digital convertor boards simultaneously (total of 32 channels); (2) to interface hot-film/wire anemometry instrumentation with a PCAT type computer; and (3) to characterize the frequency response of a flush mounted film sensor. A brief description of each of the above tasks along with recommendations are given.

Ostowari, Cyrus

1992-01-01

331

Exact Calculation of Laminar Boundary Layer in Longitudinal Flow over a Flat Plate with Homogeneous Suction  

NASA Technical Reports Server (NTRS)

Lately it has been proposed to reduce the friction drag of a body in a flow for the technically important large Reynolds numbers by the following expedient: the boundary layer, normally turbulent, is artificially kept laminar up to high Reynolds numbers by suction. The reduction in friction drag thus obtained is of the order of magnitude of 60 to 80 percent of the turbulent friction drag, since the latter, for large Reynolds numbers, is several times the laminar friction drag. In considering the idea mentioned one has first to consider whether suction is a possible means of keeping the boundary layer laminar. This question can be answered by a theoretical investigation of the stability of the laminar boundary layer with suction. A knowledge, as accurate as possible, of the velocity distribution in the laminar boundary layer with suction forms the starting point for the stability investigation. E. Schlichting recently gave a survey of the present state of calculation of the laminar boundary layer with suction.

Iglisch, Rudolf

1949-01-01

332

Accuracy and convergence of a finite element algorithm for laminar boundary layer flow  

NASA Technical Reports Server (NTRS)

The Galerkin-weighted residuals formulation is employed to derive an implicit finite element solution algorithm for a generally non-linear initial-boundary value problem. Solution accuracy and convergence with discretization refinement are quantized in several error norms, for the non-linear parabolic partial differential equation system governing laminar boundary layer flow, using linear, quadratic and cubic functions. Richardson extrapolation is used to isolate integration truncation error in all norms, and Newton iteration is employed for all equation solutions performed in double-precision. The mathematical theory supporting accuracy and convergence concepts for linear elliptic equations appears extensible to the non-linear equations characteristic of laminar boundary layer flow.

Soliman, M. O.; Baker, A. J.

1981-01-01

333

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

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

334

Start of fluidization of a bulk granular material in laminar flow  

SciTech Connect

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

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

1982-04-20

335

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

336

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

337

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

338

Efficient simulation of incompressible viscous flow over multi-element airfoils  

NASA Technical Reports Server (NTRS)

The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The solution algorithm employs the method of pseudo compressibility and utilizes an upwind differencing scheme for the convective fluxes, and an implicit line-relaxation scheme. The motivation for this work includes interest in studying high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack up to stall is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared; a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time on a CRAY YMP per element in the airfoil configuration.

Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan

1993-01-01

339

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

340

Efficient simulation of incompressible viscous flow over multi-element airfoils  

NASA Technical Reports Server (NTRS)

The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The computer code uses the method of pseudo-compressibility with an upwind-differencing scheme for the convective fluxes and an implicit line-relaxation solution algorithm. The motivation for this work includes interest in studying the high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack, up to stall, is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared: a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time (on a CRAY YMP) per element in the airfoil configuration.

Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan

1992-01-01

341

Efficient simulation of incompressible viscous flow over single and multi-element airfoils  

NASA Technical Reports Server (NTRS)

Incompressible viscous turbulent flows over single- and multiple-element airfoils are numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The solution algorithm uses the method of pseudocompressibility with an upwind-differencing scheme for the convective fluxes and an implicit line-relaxation scheme to study high-lift take-off and landing configurations and to compute lift and drag at various angles of attack up to stall. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil. The approach used for multiple-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared: a patched system of grids and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface-pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time on a CRAY YMP per element in the airfoil configuration.

Rogers, Stuart E.; Wiltberger, N. L.; Kwak, Dochan

1992-01-01

342

Feasibility and benefits of laminar flow control on supersonic cruise airplanes  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

343

DRE-Enhanced Swept-Wing Natural Laminar Flow at High Reynolds Numbers  

NASA Technical Reports Server (NTRS)

Nonlinear parabolized stability equations and secondary instability analyses are used to provide a computational assessment of the potential use of the discrete roughness elements (DRE) technology for extending swept-wing natural laminar flow at chord Reynolds numbers relevant to transport aircraft. Computations performed for the boundary layer on a natural laminar flow airfoil with a leading-edge sweep angle of 34.6deg, free-stream Mach number of 0.75 and chord Reynolds numbers of 17 x 10(exp 6), 24 x 10(exp 6) and 30 x 10(exp 6) suggest that DRE could delay laminar-turbulent transition by about 20% when transition is caused by stationary crossflow disturbances. Computations show that the introduction of small wavelength stationary crossflow disturbances (i.e., DRE) also suppresses the growth of most amplified traveling crossflow disturbances.

Malik, Mujeeb; Liao, Wei; Li, Fe; Choudhari, Meelan

2013-01-01

344

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

345

Experimental study of mixed convection and pressure drop in helically dimpled tubes for laminar and transition flow  

Microsoft Academic Search

This paper presents the experimental results carried out in dimpled tubes for laminar and transition flows and completes a previous work of the authors focused on the turbulent region. It was observed that laminar flow heat transfer through horizontal dimpled tubes is produced in mixed convection, where Nusselt number depends on both the natural convection and the entry region. Employing

Pedro G. Vicente; Alberto Garc??a; Antonio Viedma

2002-01-01

346

A Numerical Method for Multiphase Incompressible Thermal Flows with Solid-Liquid and Liquid-Vapor Phase Transformations  

Microsoft Academic Search

A numerical method for multiphase incompressible thermal flows with solid–liquid and liquid–vapor phase transformations is presented. The flow is mainly driven by thermocapillary force and vaporization. Based on the level set method and mixture continuum model, a set of governing equations valid for solid, liquid, and vapor phases is derived, considering phase boundary conditions as source terms in the transport

Hyungson Ki; Pravansu S. Mohanty; Jyoti Mazumder

2005-01-01

347

A Lattice Boltzmann Scheme for Incompressible Multiphase Flow and Its Application in Simulation of Rayleigh–Taylor Instability  

Microsoft Academic Search

In this paper, we propose a new lattice Boltzmann scheme for simulation of multiphase flow in the nearly incompressible limit. The new scheme simulates fluid flows based on distribution functions. The interfacial dynamics, such as phase segregation and surface tension, are modeled by incorporating molecular interactions. The lattice Boltzmann equations are derived from the continuous Boltzmann equation with appropriate approximations

Xiaoyi He; Shiyi Chen; Raoyang Zhang

1999-01-01

348

Biomimetic structures for fluid drag reduction in laminar and turbulent flows  

NASA Astrophysics Data System (ADS)

Biomimetics allows one to mimic nature to develop materials and devices of commercial interest for engineers. Drag reduction in fluid flow is one of the examples found in nature. In this study, nano, micro, and hierarchical structures found in lotus plant surfaces, as well as shark skin replica and a rib patterned surface to simulate shark skin structure were fabricated. Drag reduction efficiency studies on the surfaces were systematically carried out using water flow. An experimental flow channel was used to measure the pressure drop in laminar and turbulent flows, and the trends were explained in terms of the measured and predicted values by using fluid dynamics models. The slip length for various surfaces in laminar flow was also investigated based on the measured pressure drop. For comparison, the pressure drop for various surfaces was also measured using air flow.

Jung, Yong Chae; Bhushan, Bharat

2010-01-01

349

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

350

Laminar gas micro-flow convection characteristics due to steep density gradients  

Microsoft Academic Search

We report numerical simulation of pure continuum-based laminar gas micro-flow convection with steep density gradients, which cause, for the case of heated air, flattening and rate of flattening of axial velocity profile. This flattening is similar to the characteristics in constant-properties slip flow, and high rate of flattening can cause hydrodynamic undevelopment of flow---the reverse process of hydrodynamic development. By

S. P. Mahulikar; H. Herwig; O. Hausner; F. Kock

2004-01-01

351

Heat transfer solutions in laminar co-current flow of immiscible liquids  

Microsoft Academic Search

Thermal entry region solutions are analytically determined for horizontal, co-current laminar flow of immiscible liquids in direct contact, inside circular tubes and parallel plate channels. The related eigenvalue problem for such a composite media is readily solved by extending the ideas in the recently advanced sign-count method. It is assumed a core-annular flow configuration for circular tubes and sheat-core flow

E. Nogueira; R. M. Cotta

1990-01-01

352

Higher-order finite element discretizations in a benchmark problem for incompressible flows  

NASA Astrophysics Data System (ADS)

We present a numerical study of several finite element discretizations applied to a benchmark problem for the two-dimensional steady state incompressible Navier-Stokes equations defined in Schäfer and Turek (The benchmark problem Flow around a cylinder. In Flow Simulation with High-Performance Computers II. Notes on Numerical Fluid Mechanics, vol. 52, Hirschel EH (ed.). Vieweg: Wiesbaden, 1996; 547-566). The discretizations are compared with respect to the accuracy of the computed benchmark parameters. Higher-order isoparametric finite element discretizations turned out to be by far the most accurate. The discrete systems obtained with higher-order discretizations are solved with a modified coupled multigrid method whose behaviour within the benchmark problem is also studied numerically. Copyright

John, Volker; Matthies, Gunar

2001-12-01

353

Performance of under-resolved two-dimensional incompressible flow simulations, II  

SciTech Connect

This paper presents a study of the behavior of several difference approximations for the incompressible Navier-Stokes equations as a function of the computational mesh resolution. In particular, the under-resolved case is considered. The methods considered include a Godunov projection method, a primitive variable ENO method, an upwind vorticity stream-function method, centered difference methods of both a pressure-Poisson and vorticity stream-function formulation. and a pseudospectral method. It is demonstrated that all these methods produce spurious, nonphysical vortices of the type described by Brown and Minion for a Godunov projection method when the flow is sufficiently under-resolved. The occurrence of these artifacts appears to be due to a nonlinear effect in which the truncation error of the difference method initiates a vortex instability in the computed flow. The implications of this study for adaptive mesh refinement strategies are also discussed. 29 refs., 14 figs., 2 tabs.

Minion, M.L. [Univ. of North Carolina, Chapel Hill, NC (United States)] [Univ. of North Carolina, Chapel Hill, NC (United States); Brown, D.L. [Los Alamos National Lab., NM (United States)] [Los Alamos National Lab., NM (United States)

1997-12-01

354

A two pressure-velocity approach for immersed boundary methods in three dimensional incompressible flows  

NASA Astrophysics Data System (ADS)

This paper describes an innovative method for computing fluid solid interaction using Immersed boundary methods with two stage pressure-velocity corrections. The algorithm calculates the interactions between incompressible viscous flows and a solid shape in three-dimensional domain. The fractional step method is used to solve the Navier-Stokes equations in finite difference schemes. Most of IBMs are concern about exchange of the momentum between the Eulerian variables (fluid) and the Lagrangian nodes (solid). To address that concern, a new algorithm to correct the pressure and the velocity using Simplified Marker and Cell method is added. This scheme is applied on staggered grid to simulate the flow past a circular cylinder and study the effect of the new stage on calculations cost. To evaluate the accuracy of the computations the results are compared with the previous software results. The paper confirms the capacity of new algorithm for accurate and robust simulation of Fluid Solid Interaction with respect to pressure field.

Sabir, O.; Ya, T. M. Y. S. Tuan; Ahmad, Norhafizan; Nukman, Y.

2013-12-01

355

A Multigrid Accelerated High-Order Compact Fractional Step Method for Unsteady Incompressible Viscous Flows  

NASA Astrophysics Data System (ADS)

An efficient high-order compact scheme is presented for computing unsteady incompressible viscous flows. The scheme is constructed on a staggered Cartesian grid. Using the fractional step framework, the Navier-Stokes equations are advanced in time with the second-order Adams-Bashforth method without considering the pressure terms in the predictor step. The velocity field is then corrected so that the continuity equation is satisfied through a pressure Poisson equation. Since the efficiency of the fractional step method depends on the Poisson solver, a Mehrstellen-based V-cycle multigrid acceleration is implemented in the solution of the Poisson equation to enhance the computational efficiency. The method is validated by simulating a decaying Taylor-Green vortex. The results show that the method has high resolving efficiency, drastically reduced computational time, and high-order accuracy, making it applicable for the simulation of complex turbulent flows.

San, Omer; Staples, Anne

2009-11-01

356

A High Order Discontinuous Galerkin Method for 2D Incompressible Flows  

NASA Technical Reports Server (NTRS)

In this paper we introduce a high order discontinuous Galerkin method for two dimensional incompressible flow in vorticity streamfunction formulation. The momentum equation is treated explicitly, utilizing the efficiency of the discontinuous Galerkin method The streamfunction 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 enstrophy stability The method is suitable for inviscid or high Reynolds number flows. Optimal error estimates are proven and verified by numerical experiments.

Liu, Jia-Guo; Shu, Chi-Wang

1999-01-01

357

Near field vortex dynamics in axially forced, laminar, co-flowing jets: a descriptive study of the flow configurations  

Microsoft Academic Search

An experimental study is presented of the vortex structures that appear in the shear layer of laminar, co-flowing air jets subjected to strong axial forcing. A set of flow visualisation experiments has been performed to elucidate the nature of the different structures and the mechanisms leading to their appearance and further interactions. The axial forcing sets the axisymmetric instability to

Pedro Rodr??guez-Aumente; Ulpiano Ruiz-Rivas; Antonio Lecuona

2001-01-01

358

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

2013-04-01

359

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

360

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

361

Performance of laminar-flow leading-edge test articles in cloud encounters  

NASA Technical Reports Server (NTRS)

An extensive data bank of concurrent measurements of laminar flow (LF), particle concentration, and aircraft charging state was gathered for the first time. From this data bank, 13 flights in the simulated airline service (SAS) portion were analyzed to date. A total of 6.86 hours of data at one-second resolution were analyzed. An extensive statistical analysis, for both leading-edge test articles, shows that there is a significant effect of cloud and haze particles on the extent of laminar flow obtained. Approximately 93 percent of data points simulating LFC flight were obtained in clear air conditions; approximately 7 percent were obtained in cloud and haze. These percentages are consistent with earlier USAF and NASA estimates and results. The Hall laminar flow loss criteria was verified qualitatively. Larger particles and higher particle concentrations have a more marked effect on LF than do small particles. A particle spectrometer of a charging patch are both acceptable as diagnostic indicators of the presence of particles detrimental to laminar flow.

Davis, Richard E.; Maddalon, Dal V.; Wagner, Richard D.

1987-01-01

362

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

EPA Science Inventory

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

363

Chaotic mixing and mass transfer enhancement bypulsatile laminar flow in an axisymmetric wavy channel  

Microsoft Academic Search

Mass transfer enhancement by a pulsatile laminar flow in an axisymmetric wavy channel has been investigated numerically for the range of 50 ? Re ? 250 and 0.1 ? St ? 10. The optimal Strouhal number has been determined as a function of the Reynolds number and the wavelength of the channel. It is found that the optimal Strouhal number

B. S. Lee; I. S. Kang; H. C. Lim

1999-01-01

364

THE SOLUTION OF THE HEAT TRANSFER EQUATION FOR LAMINAR FLOW IN AN ANNULUS  

Microsoft Academic Search

The solution of the heat transfer equation for the case of fully ; developed laminar flow through an annular space is given in the form of a series ; of eigenfunctions with the corresponding eigenvalues. The problem is solved for ; a specified diameter ratio for the case of inner wall of the annulus kept at ; constant temperature and

Eldor

1962-01-01

365

Heat transfer in laminar flows of extended modified power law fluids in rectangular ducts  

Microsoft Academic Search

This paper reports the results of a numerical study of the Nusselt number for the H1 and T boundary conditions in laminar, fully-developed flows of pseudoplastic and dilatant fluids in rectangular ducts. Equations for the apparent viscosity that span the entire shear rate range were utilized and the Nusselt numbers were calculated as a function of a shear rate parameter

Massimo Capobianchi; Darcy Wagner

2010-01-01

366

Design of a Slotted, Natural-Laminar-Flow Airfoil for Business-Jet Applications  

NASA Technical Reports Server (NTRS)

A 14-percent-thick, slotted, natural-laminar-flow airfoil, the S204, for light business-jet applications has been designed and analyzed theoretically. The two primary objectives of high maximum lift, relatively insensitive to roughness, and low profile drag have been achieved. The drag-divergence Mach number is predicted to be greater than 0.70.

Somers, Dan M.

2012-01-01

367

HEAT TRANSFER PROPERTIES OF NANODIAMOND-ENGINE OIL NANOFLUID IN LAMINAR FLOW  

Microsoft Academic Search

The present study investigates the effects of utilizing nanodiamond as an additive to engine oil on the heat transfer enhancement in laminar pipe flow. A plain tube with internal diameter of 6 mm was used as the test section and heated by an electrical coil heater to produce a constant heat flux thermal boundary condition. Thermal conductivity, specific heat and

M. Ghazvini; M. A. Akhavan-Behabadi; E. Rasouli; M. Raisee

2011-01-01

368

Heat Transfer Properties of Nanodiamond–Engine Oil Nanofluid in Laminar Flow  

Microsoft Academic Search

This study investigates the effects of utilizing nanodiamond as an additive to engine oil on the heat transfer enhancement in laminar pipe flow. A plain tube with internal diameter of 6 mm was used as the test section and heated by an electrical coil heater to produce a constant heat flux thermal boundary condition. Thermal conductivity, specific heat, and viscosity

M. Ghazvini; M. A. Akhavan-Behabadi; E. Rasouli; M. Raisee

2012-01-01

369

Experiments on Laminar Flow Control at Mach 2.4 using Distributed Roughness  

Microsoft Academic Search

A new technique for the passive laminar flow control, in the supersonic regime, over highly swept wings beyond the characteristic Mach angle is here studied. A series of previous low-speed experiments at Arizona State University has demonstrated the possibility to control stationary crossflow waves by distributed roughness near the attachment line, provided the roughness spacing is below a critical value.

Simone Zuccher; Lloyd McNeil; Elizabeth Bennett; William Saric; Helen Reed

2002-01-01

370

A new look at the laminar flow of power law fluids through granular beds  

Microsoft Academic Search

Summary The paper deals with laminar flow of power law fluids through granular beds. A critical review of the assumptions concerning the capillary model of the bed, applied by various authors, led us to the conclusion that the derivation of the correlation eq. [13] given byChristopher andMiddleman was based on a too simplified model of the granular bed. Taking advantage

Z. Kemblowski; M. Michniewicz

1979-01-01

371

Interacting Boundary-Layer Solutions for Laminar Separated Flow past Airfoils.  

National Technical Information Service (NTIS)

Numerical solutions of the interacting laminar boundary layer equations are presented for two symmetric airfoils at zero incidence: the NACA 0012 and the NACA 66 sub 3-108 airfoils. The potential flow was computed using Carlson's code, and viscous interac...

O. R. Burggraf

1984-01-01

372

Interaction Between a Laminar Flame and Its Self-Generated Flow.  

National Technical Information Service (NTIS)

The interaction between a premixed laminar flame and its self-generated flow is experimentally studied in a closed duct. A laser Doppler anemometer measures two components of the enclosed gas velocity during the flame propagation. High-speed schlieren cin...

D. Dunn-Rankin

1985-01-01

373

Experimental Development of Tubeside Heat Transfer Correlations for Laminar Flow with and without Inserts.  

National Technical Information Service (NTIS)

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 l...

J. D. Guido

1992-01-01

374

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

375

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

376

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

2011-09-15

377

Theoretical investigations on keeping laminar the compressible boundary layer by means of slit suction  

Microsoft Academic Search

On the basis of former investigations of incompressible flows, this paper deals with the problem of keeping the compressible boundary layer laminar on two-dimensional and axisymmetric body shapes using slot suction. The new values of the boundary layer behind a slot are approximately determined according to Walz's amputation principle extended to compressible flows, whose reliability is backed up by boundary

P. Thiede; F. Otte

1975-01-01

378

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

379

A numerical scheme for time-accurate solutions of incompressible flow equations  

NASA Astrophysics Data System (ADS)

A numerical scheme to compute time-accurate solutions of incompressible flow problems is developed. Flow equations in primitive variables and in fully coupled form are used. The divergence-free velocity condition is achieved by using a dual time-stepping approach. The flow equations, cast in a pseudotime, tau, are integrated in tau until convergence for each physical time step. Three-dimensional time-accurate solutions of the flow through a marine propeller operating in a wake-dominated flow-field were obtained. Convective flux derivatives are evaluated using third-order accurate upwind-biased flux-split differencing. The implicit operators generated using upwind fluxes are diagonally dominant and have good stability and convergence characteristics. In multidimensional problems, inversion of the operators is done by using an implicit lower-upper (L-U) factorization. Stability of the overall integration procedure is carefully analyzed using a Fourier transform method in vector form. The pseudotime-integration procedure is found to be unconditionally stable in all spatial dimensions, and for all pseudo-time steps. Boundary conditions for inviscid flow problems are enforced using the method of characteristics (MOC) in implicit form. A variety of one- and two-dimensional flow problems are computed. Fast convergence rates are obtained in one- and two-dimesional problems: typically 4 to 11 iterations per physical time step are found sufficient. In three-dimensional flows, the accuracy is verified by comparing the finite difference solutions with velocity potential and other numerical solutions. Time-dependent flow through a marine propeller operating in a wake-influenced flow field is computed as an engineering application. For these calculations 4 to 7 iterations are required per time step.

Athavale, Mahesh Madhukar

380

Correlation of Water Frost Porosity in Laminar Flow over Flat Surfaces  

NASA Technical Reports Server (NTRS)

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

Kandula, Max

2011-01-01

381

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

1996-12-01

382

Active unsteady aerodynamic suppression of rotating stall in an incompressible flow centrifugal compressor with vaned diffuser  

NASA Technical Reports Server (NTRS)

A mathematical model is developed to analyze the suppression of rotating stall in an incompressible flow centrifugal compressor with a vaned diffuser, thereby addressing the important need for centrifugal compressor rotating stall and surge control. In this model, the precursor to to instability is a weak rotating potential velocity perturbation in the inlet flow field that eventually develops into a finite disturbance. To suppress the growth of this potential disturbance, a rotating control vortical velocity disturbance is introduced into the impeller inlet flow. The effectiveness of this control is analyzed by matching the perturbation pressure in the compressor inlet and exit flow fields with a model for the unsteady behavior of the compressor. To demonstrate instability control, this model is then used to predict the control effectiveness for centrifugal compressor geometries based on a low speed research centrifugal compressor. These results indicate that reductions of 10 to 15 percent in the mean inlet flow coefficient at instability are possible with control waveforms of half the magnitude of the total disturbance at the inlet.

Lawless, Patrick B.; Fleeter, Sanford

1991-01-01

383

Internal Laminar Flow and Heat Transfer with Wall Mass Transfer.  

National Technical Information Service (NTIS)

Developed velocity profiles, for flows with mass addition or withdrawal through the boundary, are reported for both circular tube and two-dimensional rectangular duct geometries. For flow in a two dimensional duct, a new solution was found, which suggests...

G. D. Raithby

1972-01-01

384

A study on the stability of laminar open-channel flow over a sandy rippled bed  

Microsoft Academic Search

The bed of a river often features some kinds of bedform, such as sand ripples, dunes, and so on. Even if the bed is smooth\\u000a initially, disturbances arising from the bed or other external sources will cause the laminar flow in an open channel to become\\u000a unstable as soon as the flow develops, thereby leading to the formation of sand

Yuchuan Bai; Haijue Xu

2005-01-01

385

Non-Newtonian fluid laminar flow and forced convection heat transfer in rectangular ducts  

Microsoft Academic Search

Numerical solutions for fully developed laminar flow forced convection heat transfer of a power law non-Newtonian fluid in rectangular ducts are presented in this paper. Finite difference methods are developed for the governing equations to obtain the velocity and temperature distributions. Friction factor results are given for flow through rectangular ducts of aspect ratios of 0.2, 0.5 and 1.0 with

S. X. Gao; J. P. Hartnett

1992-01-01

386

Heat transfer to non-Newtonian fluids in laminar flow through rectangular ducts  

Microsoft Academic Search

Heat transfer to non-newtonian fluids flowing laminarly through rectangular ducts is examined. The conservation equations of mass, momentum, and energy are solved numerically with the aid of a finite volume technique. The viscoelastic behavior of the fluid is represented by the Criminale-Ericksen-Filbey (CEF) constitutive equation. Secondary flows occur due to the elastic behavior of the fluid, and, consequently, heat transfer

Mônica F. Naccache; Paulo R. Souza Mendes

1996-01-01

387

Experimental investigation into convective heat transfer of nanofluids at the entrance region under laminar flow conditions  

Microsoft Academic Search

This paper reports an experimental work on the convective heat transfer of nanofluids, made of ?-Al2O3 nanoparticles and de-ionized water, flowing through a copper tube in the laminar flow regime. The results showed considerable enhancement of convective heat transfer using the nanofluids. The enhancement was particularly significant in the entrance region, and was much higher than that solely due to

Dongsheng Wen; Yulong Ding

2004-01-01

388

Secondary cells and separation in developing laminar curved-pipe flows  

Microsoft Academic Search

Laminar flows through 180° curved bends of circular cross section are investigated numerically. For small curvature ratio, a, defined as pipe radius over mean bend radius, the governing equations could be parabolized. The equations are solved for an a range of from 0.04 to 0.143, a Dean number (De) range of from 277.5 to 1360, and for a uniform flow,

R. M. C. So; H. S. Zhang; Y. G. Lai

1991-01-01

389

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

390

Stabilized finite element schemes with LBB-stable elements for incompressible flows  

NASA Astrophysics Data System (ADS)

We study stabilized FE approximations of SUPG type to the incompressible Navier-Stokes problem. Revisiting the analysis for the linearized model, we show that for conforming LBB-stable elements the design of the stabilization parameters for many practical flows differs from that commonly suggested in literature and initially designed for the case of equal-order approximation. Then we analyze a reduced SUPG scheme often used in practice for LBB-stable elements. To provide the reduced scheme with appropriate stability estimates we introduce a modified LBB condition which is proved for a family of FE approximations. The analysis is given for the linearized equations. Numerical experiments for some linear and nonlinear benchmark problems support the theoretical results.

Gelhard, Tobias; Lube, Gert; Olshanskii, Maxim A.; Starcke, Jan-Hendrik

2005-05-01

391

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

392

Lower bounds on the mix norm of passive scalars advected by incompressible enstrophy-constrained flows  

NASA Astrophysics Data System (ADS)

Consider a diffusion-free passive scalar ? being mixed by an incompressible flow u on the torus { T}^d . Our aim is to study how well this scalar can be mixed under an enstrophy constraint on the advecting velocity field. Our main result shows that the mix-norm ({\\Vert}{\\theta(t)}{\\Vert}_{H^{-1}}) is bounded below by an exponential function of time. The exponential decay rate we obtain is not universal and depends on the size of the support of the initial data. We also perform numerical simulations and confirm that the numerically observed decay rate scales similarly to the rigorous lower bound, at least for a significant initial period of time. The main idea behind our proof is to use the recent work of Crippa and De Lellis (2008 J. Reine Angew. Math. 616 15–46) making progress towards the resolution of Bressan's rearrangement cost conjecture.

Iyer, Gautam; Kiselev, Alexander; Xu, Xiaoqian

2014-05-01

393

Preconditioned High-order WENO Scheme for Incompressible Viscous Flows Simulation  

NASA Astrophysics Data System (ADS)

A high-order accurate and highly-efficient finite difference algorithm for numerical simulation of the incompressible viscous flows has been developed. This algorithm is based on the pseudo-compressibility formulation, which combines the preconditioning technique for accelerating the time marching for stiff hyperbolic equations. Third-, fifth- and seventh-order accurate WENO schemes are used to discrete the inviscid fluxes and fourth- and sixth-order central schemes are employed for the viscous fluxes and metric terms. Implicit lower-upper symmetric Gauss-Seidel (LU-SGS) time marching procedure is performed for temporal discretization. The accuracy and the efficiency of the proposed method are demonstrated for several numerical test cases.

Qian, Z. S.; Zhang, J. B.; Li, C. X.

2011-09-01

394

A computational study of heat transfer for laminar hypervelocity flows  

NASA Technical Reports Server (NTRS)

Computational Fluid Dynamics (CFD) codes are routinely used to predict the flowfield and the heating environment around complex reentry configurations. At hypervelocities, where the velocity is greater than 3 km/sec, the AFWAL version of the blunt body code predicts the correct surface pressure distributions but underpredicts laminar wall heat fluxes. This study was performed to determine the reasons for the underprediction. The computer code chosen solves thin-layer Navier-Stokes equations in a time-asymptotic manner and assumes a constant isentropic exponent. Flowfields around a spherical configuration at various entry velocities are computed. The computed pressure distributions agree well with the tabulated, inviscid results of Lyubimov and Rusanov for entry velocities ranging from 0.6 to 5.92 km/sec. At hypervelocities, the calculated stagnation point heat transfer rates were lower by roughly fifty percent when compared to engineering correlations available in the literature. Good comparisons between heat transfer rates are obtained at hypervelocity entry conditions provided the CFD code is modified to include equilibrium air properties.

Balakrishnan, A.; Chaussee, D. S.

1988-01-01

395

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

396

Topology Optimization of Flow Problems Modeled by the Incompressible Navier-Stokes Equations  

NASA Astrophysics Data System (ADS)

This work is concerned with topology optimization of incompressible flow problems. While size and shape optimization methods are limited to modifying existing boundaries, topology optimization allows for merging boundaries as well as creating new ones. Since topology optimization methods do not require a good initial guess, they are powerful tools for finding new and non-intuitive designs. The latter is particularly beneficial for flow problems which are typically nonlinear as well as transient. Depending on the complexity of the flow problem, predicting a solution may be challenging. Determining an improved or optimized design for complex flow problems is an even greater challenge as it not only requires a solution to the flow problem for a given design, but also a prediction on how a design change will affect the flow. Fluid topology optimization commonly uses a material interpolation approach for describing the geometry during the optimization process: solid material is modeled via an artificial porosity that penalizes the flow velocities. While this approach works well for simple steady-state problems aiming to minimize the dissipated energy, the current study shows that using the porosity approach may cause issues for more complex problems such as coupled fluid-structure-interaction (FSI) systems, unsteady flow problems or problems aiming to match a target performance. To overcome these issues a geometric boundary description based on level sets is developed. This geometric boundary description is applied to both, a steady-state hydrodynamic lattice Boltzmann formulation and a stabilized finite element formulation of the steady-state Navier-Stokes equations. The enforcement of the no-slip condition along the fluid-solid interface is handled via an immersed boundary technique in case of the lattice Boltzmann method, while the Navier-Stokes formulation uses an extended finite element method (XFEM). Through the research conducted in this work, the spectrum of flow problems that can be solved by topology optimization techniques has been broadened significantly.

Kreissl, Sebastian

397

A laminar flow unit for the care of critically ill newborn infants  

PubMed Central

Introduction Medical and nursing care of newborns is predicated on the delicate control and balance of several vital parameters. Closed incubators and open radiant warmers are the most widely used devices for the care of neonates in intensive care; however, several well-known limitations of these devises have not been resolved. The use of laminar flow is widely used in many fields of medicine, and may have applications in neonatal care. Objective To describe the neonatal laminar flow unit, a new equipment we designed for care of ill newborns. Methods The idea, design, and development of this device was completed in Sao Paulo, Brazil. The unit is an open mobile bed designed with the objective of maintaining the advantages of the incubator and radiant warmer, while overcoming some of their inherent shortcomings; these shortcomings include noise, magnetic fields and acrylic barriers in incubators, and lack of isolation and water loss through skin in radiant warmers. The unit has a pump that aspirates environmental air which is warmed by electrical resistance and decontaminated with High Efficiency Particulate Air Filter (HEPA) filters (laminar flow). The flow is directed by an air flow directioner. The unit has an embedded humidifier to increase humidity in the infant’s microenvironment and a servo control mechanism for regulation of skin temperature. Results The laminar flow unit is open and facilitates access of care providers and family, which is not the case in incubators. It provides warming by convection at an air velocity of 0.45 m/s, much faster than an incubator (0.1 m/s). The system provides isolation 1000 class (less than 1,000 particles higher than 0.3 micron per cubic feet at all times). This is much more protection than an incubator provides and more than radiant warmers, which have no isolation whatsoever. Additionally, it provides humidification of the newborn’s microenvironment (about 60% relative humidity), which is impossible with a radiant warmer, which produces high water body loss. It has no mechanical barriers like acrylic walls, its magnetic field is lower than an incubator (0.25 ?t versus 1.2 ?t), and the noise is minimal compared to incubators. The unit is also able to provide controlled total body hypothermia, which is not possible with either of the other two units. Conclusion The laminar flow unit for neonatal care is a novel device which we recently developed. The introduction of laminar flow technology represents a real innovation in the neonatal field. We have described the various components of the unit and the potential advantages for management of ill neonates. This will hopefully lead to improved clinical outcomes and more effective neonatal management and safety.

Perez, Jose MR; Golombek, Sergio G; Fajardo, Carlos; Sola, Augusto

2013-01-01

398

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

NASA Astrophysics Data System (ADS)

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

Dodd, Michael S.; Ferrante, Antonino

2014-09-01

399

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

400

An exponentially fitted finite volume method for the numerical soulution of 2D unsteady incompressible flow problems  

Microsoft Academic Search

In this paper we develop and test an exponentially fitted finite volume method for the numerical solution of the Navier-Stokes equations describing 2D incompressible flows. The method is based on an unstructured Delaunay mesh and its dual Dirichlet tessellation, combined with a locally constant approximation to the flux. This yields a piecewise exponential approximation to the exact solution. Numerical tests

J. J. H. Miller; Song Wang

1994-01-01

401

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 diffusion 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 diffusion scheme with interesting theoretical and numerical properties is tested and integrated into the

Sylvain Boivin; Florent Cayré; Jean-Marc Hérard

2000-01-01

402

On the stability and extension of reduced-order Galerkin models in incompressible flows. A numerical study of vortex shedding  

Microsoft Academic Search

Proper orthogonal decomposition (POD) has been used to develop a reduced-order model of the hydrodynamic forces acting on a circular cylinder. Direct numerical simulations of the incompressible Navier-Stokes equations have been performed using a parallel computational fluid dynamics (CFD) code to simulate the flow past a circular cylinder. Snapshots of the velocity and pressure fields are used to calculate the

Imran Akhtar; Ali H. Nayfeh; Calvin J. Ribbens

2009-01-01

403

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

404

Grid-refinement study of hypersonic laminar flow over a 2-D ramp  

NASA Technical Reports Server (NTRS)

Computations were made for those test cases of Problem 3 which were designated as laminar flows, viz., test cases 3.1, 3.2, 3.4, and 3.5. These test cases corresponded to flows over a flat plate and a compression ramp at high Mach number and at high Reynolds number. The computations over the compression ramps indicate a substantial streamwise extent of separation. Based on previous experience with separated laminar flows at high Mach numbers which indicated a substantial effect with spatial grid refinement, a series of computations with different grid sizes were performed. Also, for the flat plate, comparisons of the results for two different algorithms were made.

Thomas, James L.; Rudy, David H.; Kumar, Ajay; Van Leer, Bram

1991-01-01

405

A Method for the Constrained Design of Natural Laminar Flow Airfoils  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

406

Secondary flow patterns and mixing in laminar pulsating flow through a curved pipe  

NASA Astrophysics Data System (ADS)

Mixing by secondary flow is studied by particle image velocimetry (PIV) in a developing laminar pulsating flow through a circular curved pipe. The pipe curvature ratio is ? = r 0/ r c = 0.09, and the curvature angle is 90°. Different secondary flow patterns are formed during an oscillation period due to competition among the centrifugal, inertial, and viscous forces. These different secondary-flow structures lead to different transverse-mixing schemes in the flow. Here, transverse mixing enhancement is investigated by imposing different pulsating conditions (Dean number, velocity ratio, and frequency parameter); favorable pulsating conditions for mixing are introduced. To obviate light-refraction effects during PIV measurements, a T-shaped structure is installed downstream of the curved pipe. Experiments are carried out for the Reynolds numbers range 420 ? Rest ? 1,000 (Dean numbers 126.6 ? Dn ? 301.5) corresponding to non-oscillating flow, velocity component ratios 1 ? (? = U max,osc/ U m,st) ? 4 (the ratio of velocity amplitude of oscillations to the mean velocity without oscillations), and frequency parameters 8.37 < (? = r 0(?/?)0.5) < 24.5, where ?2 is the ratio of viscous diffusion time over the pipe radius to the characteristic oscillation time. The variations in cross-sectional average values of absolute axial vorticity (|?|) and transverse strain rate (|?|) are analyzed in order to quantify mixing. The effects of each parameter (Rest, ?, and ?) on transverse mixing are discussed by comparing the dimensionless vorticities (|? P |/|? S |) and dimensionless transverse strain rates (|? P |/|? S |) during a complete oscillation period.

Jarrahi, Mojtaba; Castelain, Cathy; Peerhossaini, Hassan

2011-06-01

407

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

408

Stability analysis for laminar flow control, part 1  

NASA Technical Reports Server (NTRS)

The basic equations for the stability analysis of flow over three dimensional swept wings are developed and numerical methods for their solution are surveyed. The equations for nonlinear stability analysis of three dimensional disturbances in compressible, three dimensional, nonparallel flows are given. Efficient and accurate numerical methods for the solution of the equations of stability theory were surveyed and analyzed.

Benney, D. J.; Orszag, S. A.

1977-01-01

409

CONTROL OF LAMINAR AND TURBULENT SHEAR FLOWS USING PLASMA ACTUATORS  

Microsoft Academic Search

The use of AC discharge plasma actuators in flow control applications is experimentally investigated using PIV. Exper- imental observations include actuators in quiescent flow, a flat plate boundary layer, and a low pressure turbine blade cascade. The actuators are shown to generate a high ve- locity region near the wall downstream of the interface with large fluctuating components. Even in

Jamey D. Jacob; Karthik Ramakumar; Rich Anthony; Richard B. Rivir

410

Microtube liquid single-phase heat transfer in laminar flow  

Microsoft Academic Search

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

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

2006-01-01

411

A monolithic FEM-multigrid solver for non-isothermal incompressible flow on general meshes  

NASA Astrophysics Data System (ADS)

We present special numerical simulation methods for non-isothermal incompressible viscous fluids which are based on LBB-stable FEM discretization techniques together with monolithic multigrid solvers. For time discretization, we apply the fully implicit Crank-Nicolson scheme of 2nd order accuracy while we utilize the high order Q2P1 finite element pair for discretization in space which can be applied on general meshes together with local grid refinement strategies including hanging nodes. To treat the nonlinearities in each time step as well as for direct steady approaches, the resulting discrete systems are solved via a Newton method based on divided differences to calculate explicitly the Jacobian matrices. In each nonlinear step, the coupled linear subproblems are solved simultaneously for all quantities by means of a monolithic multigrid method with local multilevel pressure Schur complement smoothers of Vanka type. For validation and evaluation of the presented methodology, we perform the MIT benchmark 2001 [M.A. Christon, P.M. Gresho, S.B. Sutton, Computational predictability of natural convection flows in enclosures, in: First MIT Conference on Computational Fluid and Solid Mechanics, vol. 40, Elsevier, 2001, pp. 1465-1468] of natural convection flow in enclosures to compare our results with respect to accuracy and efficiency. Additionally, we simulate problems with temperature and shear dependent viscosity and analyze the effect of an additional dissipation term inside the energy equation. Moreover, we discuss how these FEM-multigrid techniques can be extended to monolithic approaches for viscoelastic flow problems.

Damanik, H.; Hron, J.; Ouazzi, A.; Turek, S.

2009-06-01

412

A stabilized MLPG method for steady state incompressible fluid flow simulation  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

413

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

414

The Stability of Particulate Ladden Laminar Boundary-Layer Flows  

NASA Technical Reports Server (NTRS)

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

Acrivos, Andreas

1996-01-01

415

Re-design of ARL/HLF (Heated Laminar Flow) body nose region  

NASA Astrophysics Data System (ADS)

The ARL (Penn State Univ.'s Applied Research Lab.) Heated Laminar Flow (HLF) body is a streamlined body with a pointed nose. One of the experimental objectives for the ARL/HLF body is to provide for limited (low flow) stagnation point fluid ejection. Because fluid ejection can, in many instances, create laminar instabilities farther downstream, it is important to have a stagnation region geometry that helps minimize the enhancement of these instabilities. This is best achieved by using a geometry that supports a very favorable pressure gradient in the ejection region. Such a geometry has been specified for the ARL/HLF body. This report presents the important analytical results which led to this re-designed nose region. The results include potential flow pressure distributions, boundary layer development, and disturbance amplification ratios, for both the original and modified nose geometry. In the absence of fluid ejection, it is concluded that the laminar flow performance of the modified body will be the same as that of the original body.

Lauchle, G. C.; Giner, S. L.

1984-11-01

416

A Second-Order Time-Accurate Finite Volume Method for Unsteady Incompressible Flow on Hybrid Unstructured Grids  

Microsoft Academic Search

A new second-order time-accurate fractional-step method for solving unsteady incompressible Navier–Stokes equations on hybrid unstructured grids is presented. The nonstaggered grid method, originally developed by Rhie and Chow (1983, AIAA J.21, 1525) for steady flow and further extended by Zang et al. (1994, J. Comput. Phys.114, 18) to unsteady flow on structured grids, is employed in the present study to

Dongjoo Kim; Haecheon Choi

2000-01-01

417

Experimental Investigation of a Synthetic Jet Array in a Laminar Channel Flow  

NASA Astrophysics Data System (ADS)

The paper deals with an impinging synthetic jet, namely on the case of a synthetic jet array interacting with a laminar channel flow. This arrangement can be useful in many micro-scale applications, such as cooling of micro-electronics. The flow regime in micro-scale is usually laminar with very small Reynolds numbers; therefore synthetic jet array can be used for the profile disturbance and heat transfer enhancement. The paper focuses on the low Reynolds number (in order 102). The working fluid is water and a piezoceramic transducer is used as a moving membrane in the synthetic jet actuator. Experiments are performed with four experimental methods (tin ion visualization, hot wire anemometry in constant temperature mode, laser Doppler vibrometry and particle image velocimetry) in three laboratories (at the Eindhoven University of Technology, Netherlands, at the Institute of Thermodynamics CAS, v.v.i. and Technical University of Liberec, both Czech Republic).

Dan?ová, P.; Trávní?ek, Z.; Vít, T.

2013-04-01

418

Experimental Results for a Flapped Natural-Laminar-Flow Airfoil with High Lift/Drag Ratio  

NASA Technical Reports Server (NTRS)

Experimental results have been obtained for a flapped natural-laminar-flow airfoil, NLF(1)-0414F, in the Langley Low-Turbulence Pressure Tunnel. The tests were conducted over a Mach number range from 0.05 to 0.40 and a chord Reynolds number range from about 3.0 x 10(6) to 22.0 x 10(6). The airfoil was designed for 0.70 chord laminar flow on both surfaces at a lift coefficient of 0.40, a Reynolds number of 10.0 x 10(6), and a Mach number of 0.40. A 0.125 chord simple flap was incorporated in the design to increase the low-drag, lift-coefficient range. Results were also obtained for a 0.20 chord split-flap deflected 60 deg.

Mcghee, R. J.; Viken, J. K.; Pfenninger, W.; Beasley, W. D.; Harvey, W. D.

1984-01-01

419

Design aspects of long range supersonic LFC airplanes with highly swept wings. [laminar flow control  

NASA Technical Reports Server (NTRS)

Studies on supersonic long-range LFC (laminar flow control) aircraft were performed with the aim of maximizing L/D and alleviating sonic boom during supersonic cruise. It is found that configurations with highly swept LFC wings of very high structural aspect ratio, with the sweep increasing toward the wing root and braced externally by wide chord laminarized struts, appear especially promising. In the supersonic cruise design condition the wing upper surface isobars are swept such that the flow in the direction normal to them is transonic with embedded supersonic zones and practically shock-free over most of the span, with M-perpendicular equal to the two-dimensional design values of advanced SC LFC airfoils, e.g., of the X-787 or X-6 type.

Pfenninger, W.; Vemuru, C. S.

1990-01-01

420

A parametric study of supersonic laminar flow for swept wings using linear stability analysis  

NASA Technical Reports Server (NTRS)

A parametric study to predict the extent of laminar flow on the upper surface of a generic swept-back wing (NACA 64A010 airfoil section) at supersonic speeds was conducted. The results were obtained by using surface pressure predictions from an Euler/Navier-Stokes computational fluid dynamics code coupled with a boundary layer code, which predicts detailed boundary layer profiles, and finally with a linear stability code to determine the extent of laminar flow. The parameters addressed are Reynolds number, angle of attack, and leading-edge wing sweep. The results of this study show that an increase in angle of attack, for specific Reynolds numbers, can actually delay transition. Therefore, higher lift capability, caused by the increased angle of attack, as well as a reduction in viscous drag due to the delay in transition is possible for certain flight conditions.

Cummings, Russell M.; Garcia, Joseph A.; Tu, Eugene L.

1995-01-01

421

A unified approach for numerical simulation of viscous compressible and incompressible flows over adiabatic and isothermal walls  

NASA Technical Reports Server (NTRS)

A new formulation (including the choice of variables, their non-dimensionalization, and the form of the artificial viscosity) is proposed for the numerical solution of the full Navier-Stokes equations for compressible and incompressible flows with heat transfer. With the present approach, the same code can be used for constant as well as variable density flows. The changes of the density due to pressure and temperature variations are identified and it is shown that the low Mach number approximation is a special case. At zero Mach number, the density changes due to the temperature variation are accounted for, mainly through a body force term in the momentum equation. It is also shown that the Boussinesq approximation of the buoyancy effects in an incompressible flow is a special case. To demonstrate the new capability, three examples are tested. Flows in driven cavities with adiabatic and isothermal walls are simulated with the same code as well as incompressible and supersonic flows over a wall with and without a groove. Finally, viscous flow simulations of an oblique shock reflection from a flat plate are shown to be in good agreement with the solutions available in literature.

Hafez, M.; Soliman, M.; White, S.

1992-01-01

422

Numerical investigation of effective parameters in convective heat transfer of nanofluids flowing under a laminar flow regime  

Microsoft Academic Search

This article presents a numerical investigation on heat transfer performance and pressure drop of nanofluids flows through a straight circular pipe in a laminar flow regime and constant heat flux boundary condition. Al2O3, CuO, carbon nanotube (CNT) and titanate nanotube (TNT) nanoparticles dispersed in water and ethylene glycol\\/water with particle concentrations ranging between 0 and 6vol.% were used as working

Ehsan Ebrahimnia-Bajestan; Hamid Niazmand; Weerapun Duangthongsuk; Somchai Wongwises

2011-01-01

423

Phase separation of parallel laminar flow for aqueous two phase systems in branched microchannel  

Microsoft Academic Search

Aqueous two phase systems (ATPSs) have good biocompatibility and special selectivity. Their phase equilibrium and applications\\u000a in biological analysis have received much attention. Herein, parallel laminar flow (PLF) in the microchannel can provide an\\u000a effective platform to enhance mass transfer and preserve separate phases simultaneously. As fundamentals in feasible and convenient\\u000a sampling of PLF for ATPS, the phase separation methods

Yangcheng LuYang; Yang Xia; Guangsheng Luo

2011-01-01

424

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

425

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

Microsoft Academic Search

The present paper describes the design concept and manufacturing of a new compact laminar flow heat exchanger with stainless-steel micro-tubes for helium refrigerators. In the temperature range of less than 20 K, aluminum plate fin type heat exchangers exhibit a remarkable fall of performance characteristics as a compact heat exchanger.We presented in a previous paper that some compact heat exchangers

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

2001-01-01

426

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

427

Note on heat conduction in liquid metals. A comparison of laminar and turbulent flow effects  

NASA Astrophysics Data System (ADS)

The difference between heat transfer in liquid metals with electric currents and magnetic fields on the one hand and heat transfer in electrically insulating fluids and in conducting solids on the other is pointed out. Laminar and turbulent flow effects in liquid metal sliding electric contacts for homopolar machines are considered. Large temperature gradients can develop within a small region of liquid metal. A model of a liquid-metal sliding electrical contact is developed and analyzed.

Talmage, G.

1994-05-01

428

Enhanced laminar-flow heat transfer at fiber-flocked surfaces  

Microsoft Academic Search

High-conductivity carbon fibers have been “flocked”, or perpendicularly attached onto surfaces, thus enabling heat transfer enhancement for such fiber-flocked surfaces. Here, an analysis is performed for fully developed laminar flow and heat transfer in plane and cylindrical ducts with fiber-covered walls. The fiber volumetric packing density is sparse such that single-cylinder correlations are applied for the drag and heat transfer

Kurt O. Lund; Timothy R. Knowles

2001-01-01

429

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

430

Design and Test of the UW5006 Transonic Natural-Laminar-Flow Wing  

Microsoft Academic Search

A transonic natural-laminar-flow wing design procedure has been set up, integrating a parametric geometry model with several analysis tools. A direct design strategy has been applied and three levels of aerodynamic analysis have been used: a full-potential method (with which to rapidly iterate to obtain the target pressure distribution), an Euler solution coupled with a boundary-layer solver and a semi-empirical

Ubaldo Cella; Domenico Quagliarella; Raffaele Donelli; Biagio Imperatore

2010-01-01

431

Effects of axial conduction in laminar tube flow with convective boundaries  

NASA Astrophysics Data System (ADS)

Heat transfer in laminar tube flow with convective boundary conditions and axial heat conduction in the fluid is solved exactly. The effects of the external Biot numbers and the axial conduction in fluid on the temperature distribution and the local Nusselt number are determined for both the upstream and the downstream regions. In order to illustrate the effects of velocity profile, the results for the slug flow and the parabolic velocity profiles are plotted simultaneously. The heat transfer characteristics of the flow are found to be rather sensitive to the Peclet number, the external Biot numbers and the velocity profile in the thermal entrance region.

Vick, B.; Ozisik, M. N.; Ullrich, D. F.

1983-08-01

432

Penalty finite element method for transient free convective laminar flow  

Microsoft Academic Search

The influence of the penalty parameter,grid size and relaxation parameter in the penalty finite element method is studied for Rayleigh number between 103 and 108. The relaxation parameter is shown to exert a pronunced influence on convergence and values near unity are required for Rayleigh numbers exceeding 106. The flow currents and temperature distributions are shown to be dominated by

K. Ravi; K. Ramamurthi

1995-01-01

433

Sedimentation speed of inertial particles in laminar and turbulent flows  

Microsoft Academic Search

We consider passive inertial particles settling under the combined action of gravity and a Stokes drag in two-dimensional velocity fields with increasing complexity. The average settling speed is studied in simple steady and time-dependent cellular and in turbulent flows. Different regimes are identified in relation to the physical properties and complexity of the fields. While for steady and slowly varying

F. DeLillo; F. Cecconi; G. Lacorata; A. Vulpiani

2008-01-01

434

Heat transfer enhancement with laminar liquid-gas slug flows  

Microsoft Academic Search

This paper investigates a two-phase non-boiling slug flow regime for the purposes of enhancing heat transfer in microchannel heat sinks or compact heat exchangers. The primary focus is upon understanding the mechanisms leading to enhanced heat transfer and also the effect of utilizing different Prandtl number fluids. Experiments were conducted using Infrared thermography and results presented in terms of Nusselt

James A. Howard; Patrick A. Walsh; Edmond J. Walsh; Yu. S. Muzychka

2010-01-01

435

Russian Laminar Flow Airfoils 3rd Part: Measurements on the Profile No. 2315 BIS with Ava-Nose Flap  

NASA Technical Reports Server (NTRS)

The tests on the Russian airfoil 2315 Bis were continued. This airfoil shows, according to Moscow tests, good laminar flow characteristics. Several tests were prepared in the large wind tunnel at Gottingen; partial results were obtained.

Riegels, F.

1947-01-01

436

Simulated-Airline-Service Flight Tests of Laminar-Flow Control with Perforated-Surface Suction System.  

National Technical Information Service (NTIS)

The effectiveness and practicality of candidate leading edge systems for suction laminar flow control transport airplanes were investigated in a flight test program utilizing a modified JetStar airplane. The leading edge region imposes the most severe con...

D. V. Maddalon A. L. Braslow

1990-01-01

437

NASA Langley Laminar-Flow-Control Experiment on a Swept, Supercritical Airfoil: Evaluation of Initial Perforated Configuration.  

National Technical Information Service (NTIS)

The initial evaluation of a large-chord, swept, supercritical airfoil incorporating an active laminar-flow-control (LFC) suction system with a perforated upper surface is documented in a chronological manner, and the deficiencies in the suction capability...

C. D. Harris C. W. Brooks P. G. Clukey J. P. Stack

1992-01-01

438

High Reynolds Number Hybrid Laminar Flow Control (HLFC) Flight Experiment. 3; Leading Edge Design, Fabrication, and Installation  

NASA Technical Reports Server (NTRS)

This document describes the design, fabrication, and installation of the suction panel and the required support structure, ducting, valving, and high-lift system (Krueger flaps) for flight demonstration of hybrid laminar flow control on the Boeing 757 airplane.

1999-01-01

439

Parallel finite element simulations of incompressible viscous fluid flow by domain decomposition with Lagrange multipliers  

NASA Astrophysics Data System (ADS)

A parallel approach to solve three-dimensional viscous incompressible fluid flow problems using discontinuous pressure finite elements and a Lagrange multiplier technique is presented. The strategy is based on non-overlapping domain decomposition methods, and Lagrange multipliers are used to enforce continuity at the boundaries between subdomains. The novelty of the work is the coupled approach for solving the velocity-pressure-Lagrange multiplier algebraic system of the discrete Navier-Stokes equations by a distributed memory parallel ILU (0) preconditioned Krylov method. A penalty function on the interface constraints equations is introduced to avoid the failure of the ILU factorization algorithm. To ensure portability of the code, a message based memory distributed model with MPI is employed. The method has been tested over different benchmark cases such as the lid-driven cavity and pipe flow with unstructured tetrahedral grids. It is found that the partition algorithm and the order of the physical variables are central to parallelization performance. A speed-up in the range of 5-13 is obtained with 16 processors. Finally, the algorithm is tested over an industrial case using up to 128 processors. In considering the literature, the obtained speed-ups on distributed and shared memory computers are found very competitive.

Rivera, Christian A.; Heniche, Mourad; Glowinski, Roland; Tanguy, Philippe A.

2010-07-01

440

Benchmark Comparison of Finite Element Adaptive Estimators in the Solution of Viscous Incompressible Flows  

NASA Astrophysics Data System (ADS)

A novel analytic solution is used to benchmark finite element adaptive error estimators for solving viscous incompressible flows. We construct a well-defined analytic flowfield to evaluate error estimators for the grid refinement. Benchmark comparison includes: Zienkiewicz and Zhu estimator, rotation estimator (antisymmetric part of the deformation-rate-tensor), pressure estimator, and velocity angle estimator. Usually, critical flow features such as stagnation points and wakes are often embedded in a small region where velocity magnitude is small. We find that the velocity angle estimator can detect the critical regions such as separation zone and circulation zone where other three estimators fail to sense those refinement regions. Also, the error computation for uniform and adaptive cells obtained by integrating over the area of the element of interest makes effectivity indices closer to unity than the traditional methods. The numerical results on the square cavity flo! w and the backward-facing step flo w illustrate the accuracy and efficiency of the present adaptive finite element method.

Wu, H.; Currie, I. G.

1996-11-01

441

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

NASA Astrophysics Data System (ADS)

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

Liao, Jian-Hui; Zhuang, Zhuo

2012-10-01

442

Transonic flight test of a laminar flow leading edge with surface excrescences  

NASA Technical Reports Server (NTRS)

A flight experiment, conducted at NASA Dryden Flight Research Center, investigated the effects of surface excrescences, specifically gaps and steps, on boundary-layer transition in the vicinity of a leading edge at transonic flight conditions. A natural laminar flow leading-edge model was designed for this experiment with a spanwise slot manufactured into the leading-edge model to simulate gaps and steps like those present at skin joints of small transonic aircraft wings. The leading-edge model was flown with the flight test fixture, a low-aspect ratio fin mounted beneath an F-104G aircraft. Test points were obtained over a unit Reynolds number range of 1.5 to 2.5 million/ft and a Mach number range of 0.5 to 0.8. Results for a smooth surface showed that laminar flow extended to approximately 12 in. behind the leading edge at Mach number 0.7 over a unit Reynolds number range of 1.5 to 2.0 million/ft. The maximum size of the gap-and-step configuration over which laminar flow was maintained consisted of two 0.06-in. gaps with a 0.02-in. step at a unit Reynolds number of 1.5 million/ft.

Zuniga, Fanny A.; Drake, Aaron; Kennelly, Robert A., Jr.; Koga, Dennis J.; Westphal, Russell V.

1994-01-01

443

Numerical solution of the Navier-Stokes equations for high Reynolds number incompressible turbulent flow. M.S. Thesis  

NASA Technical Reports Server (NTRS)

The full Navier-Stokes equations for incompressible turbulent flow must be solved to accurately represent all flow phenomena which occur in a high Reynolds number incompressible flow. A two layer algebraic eddy viscosity turbulence model is used to represent the Reynolds stress in the primitive variable formulation. The development of the boundary-fitted coordinate systems makes the numerical solution of these equations feasible for arbitrarily shaped bodies. The nondimensional time averaged Navier-Stokes equations, including the turbulence mode, are represented by finite difference approximations in the transformed plane. The resulting coupled system of nonlinear algebraic equations is solved using a point successive over relaxation iteration. The test case considered was a NACA 64A010 airfoil section at an angle of attack of two degrees and a Reynolds number of 2,000,000.

Thompson, D. S.

1980-01-01

444

Micropatterned biofilm formations by laminar flow-templating.  

PubMed

We present a microfluidic device capable of patterning linear biofilm formations using a flow templating approach. We describe the design considerations and fabrication methodology of a two level flow-templating micro-bioreactor (FT-?BR), which generates a biofilm growth stream surrounded on 3 sides by a growth inhibiting confinement stream. Through a combination of experiments and simulations we comprehensively evaluate and exploit control parameters to manipulate the biofilm growth template stream dimensions. The FT-?BR is then used to grow biofilm patterns with controllable dimensions. A proof-of-principle study using the device demonstrates its utility in conducting biofilm growth rate measurements under different shear stress environments. This opens the way for quantitative studies into the effects of the local shear environment on biofilm properties and for the synthesis of a new generation of functional biomaterials with controllable properties. PMID:24722812

Aznaveh, Nahid Babaei; Safdar, Muhammad; Wolfaardt, Gideon; Greener, Jesse

2014-08-01

445

Pore-scale simulation of laminar flow through porous media  

NASA Astrophysics Data System (ADS)

The experimental investigation of flow through porous media is inherently difficult due to the lack of optical access. The recent developments in the fields of X-ray micro-tomography (micro-CT hereafter), digital sample reconstruction by image-processing techniques and fluid-dynamics simulation, together with the increasing power of super-computers, allow to carry out pore-scale simulations through digitally-reconstructed porous samples. The scientific relevance of pore-scale simulations lies in the possibility of upscaling the pore-level data, yielding volume-averaged quantities useful for practical purposes. One of the best-known examples of upscaling is the calculation of absolute and relative permeability of reservoir rocks. This contribution presents a complete work-flow for setting up pore-scale simulations, starting from the micro-CT of a (in general small) porous sample. Relevant applications are discussed in order to reveal the potential of the proposed methodology.

Piller, M.; Casagrande, D.; Schena, G.; Santini, M.

2014-04-01

446

Characterization of chemiluminescence from singlet oxygen under laminar flow conditions in a micro-channel and its quenching with beverages  

Microsoft Academic Search

Singlet oxygen was generated by reaction of sodium hypochlorite and hydrogen peroxide in a micro-channel. The two reagent solutions were delivered into the micro-channel by a syringe pump, providing a laminar flow liquid–liquid interface. The chemiluminescence from the singlet oxygen was emitted in the collapse of the interface due to molecular diffusion under laminar flow conditions. The chemiluminescence intensity was

Kazuhiko Tsukagoshi; Kazuaki Fukumoto; Riichiro Nakajima; Kenichi Yamashita; Hideaki Maeda

2007-01-01

447

Laminar flow effects in the coil planet centrifuge  

NASA Technical Reports Server (NTRS)

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

Herrmann, F. T.

1984-01-01

448

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 relat