NASA Astrophysics Data System (ADS)
Svá?ek, Petr
2014-12-01
In this paper the numerical approximation of turbulent and laminar incompressible turbulent flow is considered. The main attention is paid to approximation of flow in fluid-structure interaction problems. The mathematical model is either based on incompressible Navier-Stokes equations or on Reynolds averaged Navier-Stokes (RANS) equations enclosed by a turbulence model. The problem is discretized in space by the stabilized finite element method. The application and finite element approximation of turbulence and transition models is. The numerical results are shown.
NASA Technical Reports Server (NTRS)
Thiede, P.
1978-01-01
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.
Laminarization effects on the dynamics of a disk levitated by incompressible fluid flow
Warinner, D.K.; Pearson, J.T.
1984-01-01
This paper develops a nonlinear ordinary differential equation of motion for a disk parallel to a flat plat and levitated by incompressible turbulent fluid flow supplied from a central orifice. The transient flow-velocity and pressure-field for the turbulent flow are found by integrating the time-averaged Navier-Stokes equation with power-law velocity and shear stress correlations. The results for the turbulent film are coupled with the authors' recently published study of inertia effects on the dynamics of a disk levitated by incompressible laminar flow to determine the results for a laminarizing flow. The transient pressure field is then integrated to use in Newton's second law to determine the O.D.E. for the height of the disk (or its fluid film thickness) as a function of time when the disk is perturbed from its equilibrium state by a forcing function. The theoretical magnitudes, frequencies, and damping coefficients of oscillation are shown to be within 8% of those measured. The cases of highest inertia are predicted within 13%. Fortunately, the numerical solution differs only slightly from the linearized solution; the latter provides relatively accurate closed-form expressions for the frequencies and damping coefficients in terms of the geometry, load (or weight of disk), mass flow rate, and the fluid properties.
NASA Technical Reports Server (NTRS)
Sohn, Jeong L.
1988-01-01
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.
NASA Astrophysics Data System (ADS)
Cochran, Robert James
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.
Laminar Flow Aircraft Certification
NASA Technical Reports Server (NTRS)
Williams, Louis J. (compiler)
1986-01-01
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.
NASA Astrophysics Data System (ADS)
Tyliszczak, Artur
2014-11-01
The paper presents a novel, efficient and accurate algorithm for laminar and turbulent flow simulations. The spatial discretisation is performed with help of the compact difference schemes (up to 10th order) for collocated and half-staggered grid arrangements. The time integration is performed by a predictor-corrector approach combined with the projection method for pressure-velocity coupling. At this stage a low order discretisation is introduced which considerably decreases the computational costs. It is demonstrated that such approach does not deteriorate the solution accuracy significantly. Following Boersma B.J. [13] the interpolation formulas developed for staggered uniform meshes are used also in the computations with a non-uniform strongly varying nodes distribution. In the proposed formulation of the projection method such interpolation is performed twice. It is shown that it acts implicitly as a high-order low pass filter and therefore the resulting algorithm is very robust. Its accuracy is first demonstrated based on simple 2D and 3D problems: an inviscid vortex advection, a decay of Taylor-Green vortices, a modified lid-driven cavity flow and a dipole-wall interaction. In periodic flow problems (the first two cases) the solution accuracy exhibits the 10th order behaviour, in the latter cases the 3rd and the 4th order is obtained. Robustness of the proposed method in the computations of turbulent flows is demonstrated for two classical cases: a periodic channel with Re?=395 and Re?=590 and a round jet with Re=21 000. The solutions are obtained without any turbulence model and also without any explicit techniques aiming to stabilise the solution. The results are in a very good agreement with literature DNS and LES data, both the mean and r.m.s. values are predicted correctly.
NASA Technical Reports Server (NTRS)
Joslin, Ronald D.
1998-01-01
Aircraft laminar flow control (LFC) from the 1930's through the 1990's is reviewed and the current status of the technology is assessed. Examples are provided to demonstrate the benefits of LFC for subsonic and supersonic aircraft. Early studies related to the laminar boundary-layer flow physics, manufacturing tolerances for laminar flow, and insect-contamination avoidance are discussed. LFC concept studies in wind-tunnel and flight experiments are the major focus of the paper. LFC design tools are briefly outlined for completeness.
Supersonic laminar flow control research
NASA Technical Reports Server (NTRS)
Lo, Ching F.
1994-01-01
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.
Compressible laminar flow in a channel
NASA Astrophysics Data System (ADS)
Venerus, D. C.; Bugajsky, D. J.
2010-04-01
Laminar flow of a compressible Newtonian fluid in a channel is analyzed. An analytic solution to the vorticity-stream function form of the hydrodynamics equations is found for weakly compressible flow using a regular perturbation method. In contrast with previous studies, the present analysis does not invoke the lubrication approximation and, consequently, predicts both a nonzero transverse velocity and a nonzero transverse pressure gradient. Predicted velocity and pressure fields from the perturbation solution are compared with previously published analytical and numerical solutions. Expressions for pressure drop are also given for compressible laminar flow in a channel that display significant deviations from the incompressible case. In addition, experimental data from the literature for the flow of gases in microchannels are analyzed and compared with predictions from the analytical solution. We find that a commonly used method for analyzing microchannel flow experiments obscures a rather simple dependence of pressure drop on the same dimensionless parameter used in the perturbation solution.
Flight experiences with laminar flow
NASA Technical Reports Server (NTRS)
Holmes, Bruce J.
1986-01-01
A review of natural laminar flow (NLF) flight experiences over the period from the 1930's to the present has been given to provide information on the achievability and maintainability of NLF in typical airplane operating environments. Significant effects of loss of laminar flow on airplane performance have been observed for several airplanes, indicating the importance of providing information on these changes to laminar flow airplane operators. Significant changes in airplane stability and control and maximum lift were observed in flight experiments with the loss of laminar flow. However, these effects can be avoided by proper selection of airfoils. Conservative laminar flow airfoil designs should be employed which do not experience significant loss of lift (caused by flow separation) upon the loss of laminar flow. Mechanisms have been observed for the effects of insect accumulation, flight through clouds and precipitation, and propeller slipstreams on laminar flow behavior. Fixed transition testing, in addition to free transition testing, is recommended as a new standard procedure for airplanes with surfaces designed to support laminar flow.
Triangular spectral elements for incompressible fluid flow
NASA Technical Reports Server (NTRS)
Mavriplis, C.; Vanrosendale, John
1993-01-01
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.
Unified approach for incompressible flows
NASA Technical Reports Server (NTRS)
Chang, Tyne-Hsien
1993-01-01
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.
Laminar flow in a recess of a hydrostatic bearing
NASA Technical Reports Server (NTRS)
San Andres, Luis A.; Velthuis, Johannes F. M.
1992-01-01
The flow in a recess of a hydrostatic journal bearing is studied in detail. The Navier-Stokes equations for the laminar flow of an incompressible liquid are solved numerically in a two-dimensional plane of a typical bearing recess. Pressure- and shear-induced flows, as well as a combination of these two flow conditions, are analyzed. Recess friction, pressure-ram effects at discontinuities in the flow region, and film entrance pressure loss effects are calculated. Entrance pressure loss coefficients over a forward-facing step are presented as functions of the mean flow Reynolds number for pure-pressure and shear-induced laminar flows.
Overview of Laminar Flow Control
NASA Technical Reports Server (NTRS)
Joslin, Ronald D.
1998-01-01
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.
Computation of viscous incompressible flows
NASA Technical Reports Server (NTRS)
Kwak, Dochan
1989-01-01
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.
Improved Algorithm Computes Incompressible Flow
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.
1993-01-01
Algorithm numerically integrates Navier-Stokes equations of time-dependent or steady flow of incompressible, viscous fluid. Simulates realistic three-dimensional flows bounded by stationary or moving surface(s) of complicated shape(s). Only two arbitrary parameters specified by user. Algorithm described in "Numerical Simulation Of Flow Through An Artificial Heart" (ARC-12478). Algorithm tested by application to number of steady and unsteady flows, including flow in artificial heart discussed in noted prior article.
Tomographic reconstruction of incompressible flow.
Nemirovsky, Jonathan; Lifshitz, Asaf; Be'ery, Ilan
2011-05-01
In many experiments facilitating tomography the reconstruction problem is under-determined, meaning there are many possible solutions consistent with the measurements. If the sampling rate is fast relative to the typical evolution time, the known physical dynamics of the system can be used as additional reconstruction constraints. Here we demonstrate that incorporating the requirement of incompressible flow can improve significantly the fidelity of the reconstructed sequence. The incompressibility of the reconstruction is assured by requiring the conservation of the density moments. It is demonstrated that the "incompressible" reconstruction can be significantly more accurate than the reconstruction using standard methods. A consequence of the density moments' conservation is the conservation of the density histogram throughout the reconstructed sequence. PMID:21639546
Hybrid laminar flow control study
NASA Technical Reports Server (NTRS)
1982-01-01
Hybrid laminar flow control (HLFC) in which leading edge suction is used in conjunction with wing pressure distribution tailoring to postpone boundary layer transition and reduce friction drag was examined. Airfoil design characteristics required for laminar flow control (LFC) were determined. The aerodynamic design of the HLFC wing for a 178 passenger commercial turbofan transport was developed, and a drag was estimated. Systems changes required to install HLFC were defined, and weights and fuel economy were estimated. The potential for 9% fuel reduction for a 3926-km (2120-nmi) mission is identified.
Laminar flow control for transport aircraft applications
NASA Technical Reports Server (NTRS)
Wagner, R. D.
1986-01-01
The incorporation of laminar flow control into transport aircraft is discussed. Design concepts for the wing surface panel of laminar flow control transport aircraft are described. The development of small amounts of laminar flow on small commercial transports with natural or hybrid flow control is examined. Techniques for eliminating the insect contamination problem in the leading-edge region are proposed.
High performance parallel algorithms for incompressible flows
Sambavaram, Sreekanth Reddy
2002-01-01
The generalized Stokes problem, which arises frequently in the simulation of Navier-Stokes equations for incompressible fluid flow, gives rise to symmetric linear system of equations. These systems are indefinite because of the incompressibility...
Laminar-flow flight experiments
NASA Technical Reports Server (NTRS)
Wagner, Richard D.; Maddalon, Dal V.; Bartlett, D. W.; Collier, F. S., Jr.; Braslow, A. L.
1989-01-01
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.
Operational considerations for laminar flow aircraft
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.; Wagner, Richard D.
1986-01-01
Considerable progress has been made in the development of laminar flow technology for commercial transports during the NASA Aircraft Energy Efficiency (ACEE) laminar flow program. Practical, operational laminar flow control (LFC) systems have been designed, fabricated, and are undergoing flight testing. New materials, fabrication methods, analysis techniques, and design concepts were developed and show much promise. The laminar flow control systems now being flight tested on the NASA Jetstar aircraft are complemented by natural laminar flow flight tests to be accomplished with the F-14 variable-sweep transition flight experiment. An overview of some operational aspects of this exciting program is given.
Gas flow measurement using laminar flow elements
Weigand, J. [Meriam Instrument, Cleveland, OH (United States)
1994-12-31
An instrument that measures gas volumetric flow rate using a capillary tube laminar-flow principle is described. Irs construction, operation, accuracy, and rangeability are presented. Discussion includes integrating the differential-pressure-producing flowmeter with appropriate temperature find pressure devices to produce a digital flowmeter system capable of measuring volumetric and mass flow rates. Typical applications are described.
Laminar and Turbulent Flow in Water
ERIC Educational Resources Information Center
Riveros, H. G.; Riveros-Rosas, D.
2010-01-01
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…
Upwind-Differencing Computations Of Incompressible Flows
NASA Technical Reports Server (NTRS)
Rogers, Stuart; Kwak, Dochan
1995-01-01
Report discusses application of upwind-differencing numerical-integration scheme in conjunction with method of pseudocompressibility to computations of flows of incompressible fluids, with emphasis on steady-state flows. Three test cases presented: driven flow in square cavity, flow over backward-facing step, and flow around circular cylinder.
Accurate solution algorithms for incompressible multiphase flows
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
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.
Turbulent crossed fluxes in incompressible flows
Sancho
2000-02-01
We show in the framework of the stochastic calculus the existence of turbulent crossed fluxes in incompressible flows. Physically, these fluxes are related to the dependence of the phenomenological coefficients on the temperature and concentration variables. PMID:11046507
Orifice contraction coefficient for inviscid incompressible flow
NASA Astrophysics Data System (ADS)
Grose, R. D.
1985-03-01
The theory for steady flow of an incompressible fluid through an orifice has been semi-empirically established for only certain flow conditions. In this paper, the development of a more rigorous theory for the prediction of the orifice flow contraction effect is presented. This theory is based on the conservation of momentum and mass principles applied to global control volumes for continuum flow. The control volumes are chosen to have a particular geometric construction which is based on certain characteristics of the Navier-Stokes equations for incompressible and, in the limit, inviscid flow. The treatment is restricted to steady incompressible, single phase, single component, inviscid Newtonian flow, but the principles that are developed hold for more general conditions. The resultant equations predict the orifice contraction coefficient as a function of the upstream geometry ratio for both axisymmetric and two-dimensional flow fields. The predicted contraction coefficient values agree with experimental orifice discharge coefficient data without the need for empirical adjustment.
Laminar Motion of the Incompressible Fluids in Self-Acting Thrust Bearings with Spiral Grooves
Velescu, Cornel; Popa, Nicolae Calin
2014-01-01
We analyze the laminar motion of incompressible fluids in self-acting thrust bearings with spiral grooves with inner or external pumping. The purpose of the study is to find some mathematical relations useful to approach the theoretical functionality of these bearings having magnetic controllable fluids as incompressible fluids, in the presence of a controllable magnetic field. This theoretical study approaches the permanent motion regime. To validate the theoretical results, we compare them to some experimental results presented in previous papers. The laminar motion of incompressible fluids in bearings is described by the fundamental equations of fluid dynamics. We developed and particularized these equations by taking into consideration the geometrical and functional characteristics of these hydrodynamic bearings. Through the integration of the differential equation, we determined the pressure and speed distributions in bearings with length in the “pumping” direction. These pressure and speed distributions offer important information, both quantitative (concerning the bearing performances) and qualitative (evidence of the viscous-inertial effects, the fluid compressibility, etc.), for the laminar and permanent motion regime. PMID:24526896
Magnetohydrodynamic equilibria with incompressible flows: Symmetry approach
NASA Astrophysics Data System (ADS)
Cicogna, G.; Pegoraro, F.
2015-02-01
We identify and discuss a family of azimuthally symmetric, incompressible, magnetohydrodynamic plasma equilibria with poloidal and toroidal flows in terms of solutions of the Generalized Grad Shafranov (GGS) equation. These solutions are derived by exploiting the incompressibility assumption, in order to rewrite the GGS equation in terms of a different dependent variable, and the continuous Lie symmetry properties of the resulting equation and, in particular, a special type of "weak" symmetries.
Incompressible viscous flows on adaptive, multi-block grids
NASA Technical Reports Server (NTRS)
Kim, Young-Mog; Gatlin, Boyd
1993-01-01
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.
Efficient solutions of two-dimensional incompressible steady viscous flows
NASA Technical Reports Server (NTRS)
Morrison, J. H.; Napolitano, M.
1986-01-01
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.
Research in natural laminar flow and laminar-flow control, part 3
Hefner, J.N.; Sabo, F.E.
1987-12-01
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.
Research in natural laminar flow and laminar-flow control, part 3
J. N. Hefner; F. E. Sabo
1987-01-01
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
NASA Technical Reports Server (NTRS)
Brooks, Cuyler W., Jr.; Harris, Charles D.; Harvey, William D.
1991-01-01
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.
NASA Technical Reports Server (NTRS)
Dwoyer, D. L.
1980-01-01
A method for solving the Navier-Stokes equations based on splitting the velocity vector into its rotational and irrotational parts was sucessfully applied to internal flow computations. The applicability of the method to external flows is examined by studying several model problems. The model problems are those of laminar and turbulent incompressible flow past a semi-infinite flat plate and laminar incompressible flow past a finite flat plate. For these problems, the procedure accurately reproduces the known solutions and is computationally very efficient even at high Reynolds numbers. Computational aspects of the method are discussed along with the possibility of using the procedure to retrofit a viscous capability into existing potential flow codes.
Equilibria with incompressible flows from symmetry analysis
NASA Astrophysics Data System (ADS)
Kuiroukidis, Ap; Throumoulopoulos, G. N.
2015-08-01
We identify and study new nonlinear axisymmetric equilibria with incompressible flow of arbitrary direction satisfying a generalized Grad Shafranov equation by extending the symmetry analysis presented by Cicogna and Pegoraro [Phys. Plasmas 22, 022520 (2015)]. In particular, we construct a typical tokamak D-shaped equilibrium with peaked toroidal current density, monotonically varying safety factor, and sheared electric field.
Computing Incompressible Flows With Free Surfaces
NASA Technical Reports Server (NTRS)
Kothe, D.
1994-01-01
RIPPLE computer program models transient, two-dimensional flows of incompressible fluids with surface tension on free surfaces of general shape. Surface tension modeled as volume force derived from continuum-surface-force model, giving RIPPLE both robustness and accuracy in modeling surface-tension effects at free surface. Also models wall adhesion effects. Written in FORTRAN 77.
Optical flow for incompressible turbulence motion estimation
NASA Astrophysics Data System (ADS)
Chen, Xu; Zillé, Pascal; Shao, Liang; Corpetti, Thomas
2015-01-01
We propose in this paper a new formulation of optical flow dedicated to 2D incompressible turbulent flows. It consists in minimizing an objective function constituted by an observation term and a regularization one. The observation term is based on the transport equation of the passive scalar field. For non-fully resolved scalar images, we propose to use the mixed model in large eddy simulation to determine the interaction between large scales and unresolved ones. The regularization term is based on the continuity equation of 2D incompressible flows. Compared to prototypical method, this regularizer preserves more vortex structures by eliminating constraints over the vorticity field. The evaluation of the proposed formulation is done over synthetic and experimental images, and the improvements in term of estimation are discussed.
Progress in natural laminar flow research
B. J. Holmes
1984-01-01
For decades, since the earliest attempts to obtain natural laminar flow (NLF) on airplanes, three classical objections to its practicality have been held in the aeronautical community. These objectives concerned first, the capability to manufacture practical airframe surfaces smooth enough for NLF; second, the apparent inherent instability and sensitivity of NLF; and third, the accumulation of contamination such as insect
Flight research on natural laminar flow
B. J. Holmes; C. C. Croom; E. C. Hastings Jr.; C. J. Obara; C. P. Vandam
1986-01-01
Five decades of flight experiences with natural laminar flow (NLF) have provided a basis of understanding how this technology can be used for reduction of viscous drag on modern practical aircraft. The effects of cruise unit Reynolds number on NLF achievability and maintainability; compressibility effects on Tollmein-Schlichting growth; flight experiment on the Cessna Citation III business jet; flight instrumentation on
Incompressible flow over delta wings
Nathman, James Kirwin
1976-01-01
advances in stall and buffet bound- aries, and increased performance for VTOL and STOL craft. Texas AEM University is under contract to ONR to investigate theoretically and experimentally the flow over delta wings. This thesis is a report...
High-End Computing for Incompressible Flows
NASA Technical Reports Server (NTRS)
Kwak, Dochan; Kiris, Cetin
2001-01-01
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.
Laminar Flow in the Ocean Ekman Layer
NASA Astrophysics Data System (ADS)
Woods, J. T. H.
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
Feasibility study of laminar flow bodies in fully turbulent flow
Sarkar, T.; Sayer, P.G.; Fraser, S.M. [Univ. of Strathclyde, Glasgow (United Kingdom)
1994-12-31
One of the most important design requirements of long range autonomous underwater vehicles (AUVs) is to minimize propulsive power. An important and relatively easy way of achieving this is by careful selection of hull shape. Two main schools of thought in this respect are: if laminar flow can be maintained for a long length of the body, the effective drag can be reduced; it is not possible to maintain laminar flow for a significant length of the body and hull design should be based on turbulent flow conditions. In this paper, a feasibility study of laminar flow designs is undertaken under the assumption that flow will be turbulent over the entire length. For comparison two laminar flow designs X-35 and F-57 are selected and results are compared with those of two typical torpedo shaped bodies, namely AFTERBODY1 and AFTERBODY2 of DTNSRDC. It has been shown that laminar flow bodies have 10--15% higher drag when flow is turbulent over the entire length. Hence there is some hydrodynamic risk involved in adopting such laminar bodies without further consideration.
Flow Solver for Incompressible Rectangular Domains
NASA Technical Reports Server (NTRS)
Kalb, Virginia L.
2008-01-01
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.
Smoothed Two-Dimensional Edges for Laminar Flow
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Liu, C. H.; Martin, G. L.; Domack, C. S.; Obara, C. J.; Hassan, A.; Gunzburger, M. D.; Nicolaides, R. A.
1986-01-01
New concept allows passive method for installing flaps, slats, iceprotection equipment, and other leading-edge devices on natural-laminar-flow (NLF) wings without causing loss of laminar flow. Two-dimensional roughness elements in laminar boundary layers strategically shaped to increase critical (allowable) height of roughness. Facilitates installation of leading-edge devices by practical manufacturing methods.
Numerical simulation of laminar flow in a curved duct
Lopez, A.R.; Oberkampf, W.L.
1995-01-01
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.
Insect contamination protection for laminar flow surfaces
NASA Technical Reports Server (NTRS)
Croom, Cynthia C.; Holmes, Bruce J.
1986-01-01
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.
Progress In Incompressible Pump Flow Calculations
NASA Technical Reports Server (NTRS)
Kiris, Cetin; Kwak, Dochan; Kutler, Paul (Technical Monitor)
1994-01-01
Steady and unsteady flows for propulsion systems are efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. Current computations use one equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard kappa - epsilon model equations. The resulting computer code is applied to the flow analysis inside an advanced rocket pump impeller in steadily rotating reference frames. Numerical results are compared with experimental measurements. The effects of exit and shroud cavities with the leak-age flow are investigated. Time-accurate incompressible Navier-Stokes formulation with the overlapped grid scheme capability was evaluated by using MIT flapping foil experiment. The grid dependency, turbulence model effects, and the effect of order of differencing were investigated. Numerical results were compared against experimental data. The resulting procedure were applied to unsteady flapping foil calculations. Two upstream NACA 0025 foils perform high frequency synchronized motion and generate unsteady flow conditions to the downstream larger stationary foil. Comparison between unsteady experimental data and numerical results from two different moving boundary procedures will be presented.
Skin-Friction Measurements in Incompressible Flow
NASA Technical Reports Server (NTRS)
Smith, Donald W.; Walker, John H.
1959-01-01
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.
Adjoint operator approach to shape design for internal incompressible flows
NASA Technical Reports Server (NTRS)
Cabuk, H.; Sung, C.-H.; Modi, V.
1991-01-01
The problem of determining the profile of a channel or duct that provides the maximum static pressure rise is solved. Incompressible, laminar flow governed by the steady state Navier-Stokes equations is assumed. Recent advances in computational resources and algorithms have made it possible to solve the direct problem of determining such a flow through a body of known geometry. It is possible to obtain a set of adjoint equations, the solution to which permits the calculation of the direction and relative magnitude of change in the diffuser profile that leads to a higher pressure rise. The solution to the adjoint problem can be shown to represent an artificially constructed flow. This interpretation provides a means to construct numerical solutions to the adjoint equations that do not compromise the fully viscous nature of the problem. The algorithmic and computational aspects of solving the adjoint equations are addressed. The form of these set of equations is similar but not identical to the Navier-Stokes equations. In particular some issues related to boundary conditions and stability are discussed.
Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames
NASA Technical Reports Server (NTRS)
Dai, Z.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.
2002-01-01
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.
Supercomputing Aspects for Simulating Incompressible Flow
NASA Technical Reports Server (NTRS)
Kwak, Dochan; Kris, Cetin C.
2000-01-01
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.
Boundary Layer Theory. Part 1; Laminar Flows
NASA Technical Reports Server (NTRS)
Schlichting, H.
1949-01-01
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.
Geometries for roughness shapes in laminar flow
NASA Technical Reports Server (NTRS)
Holmes, Bruce J. (inventor); Martin, Glenn L. (inventor); Domack, Christopher S. (inventor); Obara, Clifford J. (inventor); Hassan, Ahmed A. (inventor)
1986-01-01
A passive interface mechanism between upper and lower skin structures, and a leading edge structure of a laminar flow airfoil is described. The interface mechanism takes many shapes. All are designed to be different than the sharp orthogonal arrangement prevalent in the prior art. The shapes of the interface structures are generally of two types: steps away from the centerline of the airfoil with a sloping surface directed toward the trailing edge and, the other design has a gap before the sloping surface. By properly shaping the step, the critical step height is increased by more than 50% over the orthogonal edged step.
Incompressible flow in stepped labyrinth seals
NASA Technical Reports Server (NTRS)
Morrison, G. L.; Chi, D.
1985-01-01
A steped labyrinth seal was experimentally investigated to determine the effects of pressure ratio, shaft speed, number of teeth, and tooth/step location upon the leakage through the seal for incompressible flow. The dependence of the flow coefficient upon the number of throttles and pressure ratio are similar to those for straight-through labyrinth seals. It can be noted that the axial location of the throttle with respect to the step had a special effect upon the flow coefficient. That is, the dependency of the flow coefficient upon rotation rate and the number of throttles changes with axial location. It was found that the minimum flow coefficient was obtained when the seal teeth were centered on the step surface. Axial pressure distribution measurements show that when the teeth are centered on the step, the pressure drop from cavity to cavity is almost uniform. It is speculated that the obtaining of this uniform pressure gradient is the cause for the enhanced performance of the stepped labyrinth seal when operated in that configuration.
Unsaturated incompressible flows in adsorbing porous media V. Solonnikov
Fasano, Antonio
of situations (chemically reacting media, deformable media, capillarity effects, mass exchange, flowsUnsaturated incompressible flows in adsorbing porous media A. Fasano V. Solonnikov Abstract We of mixtures, media with complex structure, pollution, remediation, ground freezing, composite material
Laminar flow control flight experiment design
NASA Astrophysics Data System (ADS)
Tucker, Aaron Alexander
Demonstration of spanwise-periodic discrete roughness element laminar flow control (DRE LFC) technology at operationally relevant flight regimes requires extremely stable flow conditions in flight. A balance must be struck between the capabilities of the host aircraft and the scientific apparatus. A safe, effective, and efficient flight experiment is described to meet the test objectives, a flight test technique is designed to gather research-quality data, flight characteristics are analyzed for data compatibility, and an experiment is designed for data collection and analysis. The objective is to demonstrate DRE effects in a flight environment relevant to transport-category aircraft: [0.67 -- 0.75] Mach number and [17.0M -- 27.5M] Reynolds number. Within this envelope, flight conditions are determined which meet evaluation criteria for minimum lift coefficient and crossflow transition location. The angle of attack data band is determined, and the natural laminar flow characteristics are evaluated. Finally, DRE LFC technology is demonstrated in the angle of attack data band at the specified flight conditions. Within the angle of attack data band, a test angle of attack must be maintained with a tolerance of +/- 0.1° for 15 seconds. A flight test technique is developed that precisely controls angle of attack. Lateral-directional stability characteristics of the host aircraft are exploited to manipulate the position of flight controls near the wing glove. Directional control inputs are applied in conjunction with lateral control inputs to achieve the desired flow conditions. The data are statistically analyzed in a split-plot factorial that produces a system response model in six variables: angle of attack, Mach number, Reynolds number, DRE height, DRE spacing, and the surface roughness of the leading edge. Predictions on aircraft performance are modeled to enable planning tools for efficient flight research while still producing statistically rigorous flight data. The Gulfstream IIB aircraft is determined to be suitable for a laminar flow control wing glove experiment using a low-bank-angle-turn flight test technique to enable precise, repeatable data collection at stabilized flight conditions. Analytical angle of attack models and an experimental design were generated to ensure efficient and effective flight research.
Base pressure in laminar supersonic flow.
NASA Technical Reports Server (NTRS)
Messiter, A. F.; Hough, G. R.; Feo, A.
1973-01-01
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.
Direct numerical simulation of incompressible axisymmetric flows
NASA Technical Reports Server (NTRS)
Loulou, Patrick
1994-01-01
In the present work, we propose to conduct direct numerical simulations (DNS) of incompressible turbulent axisymmetric jets and wakes. The objectives of the study are to understand the fundamental behavior of axisymmetric jets and wakes, which are perhaps the most technologically relevant free shear flows (e.g. combuster injectors, propulsion jet). Among the data to be generated are various statistical quantities of importance in turbulence modeling, like the mean velocity, turbulent stresses, and all the terms in the Reynolds-stress balance equations. In addition, we will be interested in the evolution of large-scale structures that are common in free shear flow. The axisymmetric jet or wake is also a good problem in which to try the newly developed b-spline numerical method. Using b-splines as interpolating functions in the non-periodic direction offers many advantages. B-splines have local support, which leads to sparse matrices that can be efficiently stored and solved. Also, they offer spectral-like accuracy that are C(exp O-1) continuous, where O is the order of the spline used; this means that derivatives of the velocity such as the vorticity are smoothly and accurately represented. For purposes of validation against existing results, the present code will also be able to simulate internal flows (ones that require a no-slip boundary condition). Implementation of no-slip boundary condition is trivial in the context of the b-splines.
AN IMMERSED BOUNDARY METHOD FOR COMPLEX INCOMPRESSIBLE FLOWS
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...
Laminar flow control SPF/08 feasibility demonstration
NASA Astrophysics Data System (ADS)
Ecklund, R. C.; Williams, N. R.
1981-10-01
The feasibility of applying superplastic forming/diffusion bonding (SPF/DB) technology to laminar flow control (LFC) system concepts was demonstrated. Procedures were developed to produce smooth, flat titanium panels, using thin -0.016 inch sheets, meeting LFC surface smoothness requirements. Two large panels 28 x 28 inches were fabricated as final demonstration articles. The first was flat on the top and bottom sides demonstrating the capability of the tooling and the forming and diffusion bonding procedures to produce flat, defect free surfaces. The second panel was configurated for LFC porous panel treatment by forming channels with dimpled projections on the top side. The projections were machined away leaving holes extending into the panel. A perforated titanium sheet was adhesively bonded over this surface to complete the LFC demonstration panel. The final surface was considered flat enough to meet LFC requirements for a jet transport aircraft in cruising flight.
Laminar flow control perforated wing panel development
NASA Technical Reports Server (NTRS)
Fischler, J. E.
1986-01-01
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.
Progress in natural laminar flow research
NASA Technical Reports Server (NTRS)
Holmes, B. J.
1984-01-01
For decades, since the earliest attempts to obtain natural laminar flow (NLF) on airplanes, three classical objections to its practicality have been held in the aeronautical community. These objectives concerned first, the capability to manufacture practical airframe surfaces smooth enough for NLF; second, the apparent inherent instability and sensitivity of NLF; and third, the accumulation of contamination such as insect debris in flight. This paper explains recent progress in our understanding of the achieveability and maintainability of NLF on modern airframe surfaces. This discussion explains why previous attempts to use NLF failed and what has changed regarding the three classical objections to NLF practicality. Future NASA research plans are described concerning exploring the limits of NLF usefulness, production tolerances, operational considerations, transition behavior and measurement methods, and NLF design applications.
Inductively coupled plasma torch with laminar flow cooling
Rayson, Gary D. (Las Cruces, NM); Shen, Yang (Las Cruces, NM)
1991-04-30
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.
Implicit runge-kutta methods to simulate unsteady incompressible flows
Ijaz, Muhammad
2009-05-15
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 ...
NASA F-16XL supersonic laminar flow control program overview
NASA Technical Reports Server (NTRS)
Fischer, Michael C.
1992-01-01
The viewgraphs and discussion of the NASA supersonic laminar flow control program are provided. Successful application of laminar flow control to a High Speed Civil Transport (HSCT) offers significant benefits in reductions of take-off gross weight, mission fuel burn, cruise drag, structural temperatures, engine size, emissions, and sonic boom. The ultimate economic success of the proposed HSCT may depend on the successful adaption of laminar flow control, which offers the single most significant potential improvements in lift drag ratio (L/D) of all the aerodynamic technologies under consideration. The F-16XL Supersonic Laminar Flow Control (SLFC) Experiment was conceived based on the encouraging results of in-house and NASA supported industry studies to determine if laminar flow control is feasible for the HSCT. The primary objective is to achieve extensive laminar flow (50-60 percent chord) on a highly swept supersonic wing. Data obtained from the flight test will be used to validate existing Euler and Navier Stokes aerodynamic codes and transition prediction boundary layer stability codes. These validated codes and developed design methodology will be delivered to industry for their use in designing supersonic laminar flow control wings. Results from this experiment will establish preliminary suction system design criteria enabling industry to better size the suction system and develop improved estimates of system weight, fuel volume loss due to wing ducting, turbocompressor power requirements, etc. so that benefits and penalties can be more accurately assessed.
Acoustic waves superimposed on incompressible flows
NASA Technical Reports Server (NTRS)
Hodge, Steve
1990-01-01
The use of incompressible approximations in deriving solutions to the Lighthill wave equation was investigated for problems where an analytical solution could be found. A particular model problem involves the determination of the sound field of a spherical oscillating bubble in an ideal fluid. It is found that use of incompressible boundary conditions leads to good approximations in the important region of high acoustic wave number.
Natural laminar flow airfoil analysis and trade studies
NASA Technical Reports Server (NTRS)
1979-01-01
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.
General Equation Set Solver for Compressible and Incompressible Turbomachinery Flows
NASA Technical Reports Server (NTRS)
Sondak, Douglas L.; Dorney, Daniel J.
2002-01-01
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.
Current Laminar Flow Control Experiments at NASA Dryden
NASA Technical Reports Server (NTRS)
Bowers, Al
2010-01-01
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.
Laminar Flow Control Leading Edge Systems in Simulated Airline Service
NASA Technical Reports Server (NTRS)
Wagner, R. D.; Maddalon, D. V.; Fisher, D. F.
1988-01-01
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.
Assessment of the National Transonic Facility for Laminar Flow Testing
NASA Technical Reports Server (NTRS)
Crouch, Jeffrey D.; Sutanto, Mary I.; Witkowski, David P.; Watkins, A. Neal; Rivers, Melissa B.; Campbell, Richard L.
2010-01-01
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.
Numerical simulation of incompressible viscous flow in deforming domains.
Colella, P; Trebotich, D P
1999-05-11
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. PMID:10318891
Laminar flow heat exchangers. Viscosity induced non-uniform flow
NASA Astrophysics Data System (ADS)
Putnam, G. R.
1984-06-01
Laminar flow heat exchangers which cool oil in non-interconnected parallel passages can experience non-uniform flows and 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. Also included is the prediction of the effect of radial viscosity variation on the constant property magnitudes of friction and heat transfer coefficient.
Selected experiments in laminar flow: An annotated bibliography
NASA Technical Reports Server (NTRS)
Drake, Aaron; Kennelly, Robert A., Jr.
1992-01-01
Since the 1930s, there have been attempts to reduce drag on airplanes by delaying laminar to turbulent boundary layer transition. Experiments conducted during the 1940's, while successful in delaying transition, were discouraging because of the careful surface preparation necessary to meet roughness and waviness requirements. The resulting lull in research lasted nearly 30 years. By the late 1970s, airframe construction techniques had advanced sufficiently that the high surface quality required for natural laminar flow (NLF) and laminar flow control (LFC) appeared possible on production aircraft. As a result, NLF and LFC research became widespread. This report is an overview of that research. The experiments summarized herein were selected for their applicability to small transonic aircraft. Both flight and wind tunnel tests are included. The description of each experiment is followed by corresponding references. Part One summarizes NLF experiments; Part Two deals with LFC and hybrid laminar flow control (HLFC) experiments.
Laminar and intermittent flow in a tilted heat pipe.
Rusaouen, E; Riedinger, X; Tisserand, J-C; Seychelles, F; Salort, J; Castaing, B; Chillà, F
2014-01-01
Heat transfer measurements performed by Riedinger et al. (Phys. Fluids, 25, 015117 (2013)) showed that in an inclined channel, heated from below and cooled from above with adiabatic walls, the flow is laminar or intermittent (local bursts can occur in the laminar flow) when the inclination angle is sufficiently high and the applied power sufficiently low. In this case, gravity plays a crucial role in the characteristics of the flow. In this paper, we present velocity measurements, and their derived tensors, obtained with Particle Image Velocimetry inside the channel. We, also, propose a model derived from a jet interpretation of the flow. Comparison between experiment and model shows a fair agreement. PMID:24464137
Finite volume and finite element methods applied to 3D laminar and turbulent channel flows
NASA Astrophysics Data System (ADS)
Louda, Petr; Svá?ek, Petr; Kozel, Karel; P?íhoda, Jaromír
2014-12-01
The work deals with numerical simulations of incompressible flow in channels with rectangular cross section. The rectangular cross section itself leads to development of various secondary flow patterns, where accuracy of simulation is influenced by numerical viscosity of the scheme and by turbulence modeling. In this work some developments of stabilized finite element method are presented. Its results are compared with those of an implicit finite volume method also described, in laminar and turbulent flows. It is shown that numerical viscosity can cause errors of same magnitude as different turbulence models. The finite volume method is also applied to 3D turbulent flow around backward facing step and good agreement with 3D experimental results is obtained.
NASA Astrophysics Data System (ADS)
Ikeno, Tsutomu; Kajishima, Takeo
2007-10-01
An immersed boundary method to achieve the consistency with a desired wall velocity was developed. Existing schemes of immersed boundary methods for incompressible flow violate the wall condition in the discrete equation system during time-advancement. This problem arises from the inconsistency of the pressure with the velocity interpolated to represent the solid wall, which does not coincide with the computational grid. The numerical discrepancy does not become evident in the laminar flow simulation but in the turbulent flow simulation. To eliminate this inconsistency, a modified pressure equation based on the interpolated pressure gradient was derived for the spatial second-order discrete equation system. The conservation of the wall condition, mass, momentum and energy in the present method was theoretically demonstrated. To verify the theory, large eddy simulations for a plane channel, circular pipe and nuclear rod bundle were successfully performed. Both these theoretical and numerical validations improve the reliability and the applicability of the immersed boundary method.
A Numerical Method for Incompressible Flow with Heat Transfer
NASA Technical Reports Server (NTRS)
Sa, Jong-Youb; Kwak, Dochan
1997-01-01
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.
A monolithic mass tracking formulation for bubbles in incompressible flow
Aanjaneya, Mridul Patkar, Saket Fedkiw, Ronald
2013-08-15
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.
Lockheed laminar-flow control systems development and applications
NASA Technical Reports Server (NTRS)
Lange, Roy H.
1987-01-01
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.
Laminar flow control, 1976 - 1982: A selected annotated bibliography
NASA Technical Reports Server (NTRS)
Tuttle, M. H.; Maddalon, D. V.
1982-01-01
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.
Laminar flow integration: Flight tests status and plans
NASA Technical Reports Server (NTRS)
Wagner, R. D.; Fisher, D. F.; Fischer, M. C.; Bartlett, D. W.; Meyer, R. R., Jr.
1986-01-01
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.
Computational Analysis of the G-III Laminar Flow Glove
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.; Liao, Wei; Lee-Rausch, Elizabeth M.; Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan
2011-01-01
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.
Brief history of laminar flow clean room systems
Whitfield, W J
1981-01-01
This paper reviews the development and evolution of laminar flow clean rooms and hoods and describes the underlying principles and rationales associated with development of this type of clean room system and Federal Standard No. 209. By the mid 1970's, over a thousand hospitals in the US had installed laminar flow equipment in operating rooms. During the past several years a great deal of attention has been focused on conserving energy in clean rooms. Some gains in energy conservation have been achieved by improved design, off hours shutdown, and closer evaluation of requirements for clean rooms. By the early 1970's, the laminar flow principle had been carried from the Laboratory and applied to production hardware to create a mature industry producing and marketing a variety of laminar flow equipment in less than 10 years time. This achievement was made possible by literally dozens of persons in industry, government, military, and private individuals who developed hardware, added numerous innovations, and had the foresight to apply the technology to many fields other than industrial clean rooms. Now, with laminar flow devices available, class 100 levels are readily achievable and maintained, and at the same time require fewer operating restrictions than previously possible.
Lecture Series "Boundary Layer Theory". Part I - Laminar Flows. Part 1; Laminar Flows
NASA Technical Reports Server (NTRS)
Schlichting, H.
1949-01-01
In the lecture series starting today author want to give a survey of a field of aerodynamics which has for a number of years been attracting an ever growing interest. The subject is the theory of flows with friction, and, within that field, particularly the theory of friction layers, or boundary layers. A great many considerations of aerodynamics are based on the ideal fluid, that is the frictionless incompressibility and fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid, (potential theory) has been made possible. Actual liquids and gases satisfy the condition of incomressibility rather well if the velocities are not extremely high or, more accurately, if they are small in comparison with sonic velocity. For air, for instance, the change in volume due to compressibility amounts to about 1 percent for a velocity of 60 meters per second. The hypothesis of absence of friction is not satisfied by any actual fluid; however, it is true that most technically important fluids, for instance air and water, have a very small friction coefficient and therefore behave in many cases almost like the ideal frictionless fluid. Many flow phenomena, in particular most cases of lift, can be treated satisfactorily, - that is, the calculations are in good agreement with the test results, -under the assumption of frictionless fluid. However, the calculations with frictionless flow show a very serious deficiency; namely, the fact, known as d'Alembert's paradox, that in frictionless flow each body has zero drag whereas in actual flow each body experiences a drag of greater or smaller magnitude. For a long time the theory has been unable to bridge this gap between the theory of frictionless flow and the experimental findings about actual flow. The cause of this fundamental discrepancy is the viscosity which is neglected in the theory of ideal fluid; however, in spite of its extraordinary smallness it is decisive for the course of the flow phenomena.
Turning waves and breakdown for incompressible flows
Castro, Angel; Córdoba, Diego; Fefferman, Charles L.; Gancedo, Francisco; López-Fernández, María
2011-01-01
We consider the evolution of an interface generated between two immiscible, incompressible, and irrotational fluids. Specifically we study the Muskat and water wave problems. We show that starting with a family of initial data given by (?,f0(?)), the interface reaches a regime in finite time in which is no longer a graph. Therefore there exists a time t? where the solution of the free boundary problem parameterized as (?,f(?,t)) blows up: ???f?L?(t?) = ?. In particular, for the Muskat problem, this result allows us to reach an unstable regime, for which the Rayleigh–Taylor condition changes sign and the solution breaks down.
Lattice Boltzmann model for incompressible flows through porous media.
Guo, Zhaoli; Zhao, T S
2002-09-01
In this paper a lattice Boltzmann model is proposed for isothermal incompressible flow in porous media. The key point is to include the porosity into the equilibrium distribution, and add a force term to the evolution equation to account for the linear and nonlinear drag forces of the medium (the Darcy's term and the Forcheimer's term). Through the Chapman-Enskog procedure, the generalized Navier-Stokes equations for incompressible flow in porous media are derived from the present lattice Boltzmann model. The generalized two-dimensional Poiseuille flow, Couette flow, and lid-driven cavity flow are simulated using the present model. It is found the numerical results agree well with the analytical and/or the finite-difference solutions. PMID:12366250
An update on projection methods for transient incompressible viscous flow
Gresho, P.M.; Chan, S.T.
1995-07-01
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.
Numerical studies of incompressible viscous flow in a driven cavity
NASA Technical Reports Server (NTRS)
1975-01-01
A series of project papers is presented in computational fluid dynamics. The work was performed during the 1973-74 academic year at Old Dominion University. Each paper briefly examines a numerical method(s) that can be applied to the Navier-Stokes equations governing incompressible flow in a driven cavity. Solutions obtained with a cubic spline procedure are also included.
Blow up criterion for incompressible nematic liquid crystal flows
Guochun Wu
2012-10-27
In this paper, we consider the short time classical solution to a simplified hydrodynamic flow modeling incompressible, nematic liquid crystal materials in dimension three. We establish a criterion for possible breakdown of such solutions at a finite time. More precisely, if $(u,d)$ is smooth up to time $T$ provided that $\\int_0^T|\
Incompressible Flow Iterative Solution Software (IFISS) Installation & Software Guide 1
Silvester, David J.
as published by the Free Software Foundation; either version 2.1 of the License, or any later versionIncompressible Flow Iterative Solution Software (IFISS) Installation & Software Guide 1 David J conditions . . . . . . . . . . . . . . . . 17 0 #12;IFISS 3.3 Software Guide 1 1.1 Background This document
NASA Technical Reports Server (NTRS)
Chen, Y. S.
1986-01-01
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.
Roughness and waviness requirements for laminar flow surfaces
NASA Technical Reports Server (NTRS)
Obara, Clifford J.; Holmes, Bruce J.
1986-01-01
Many modern metal and composite airframe manufacturing techniques can provide surface smoothness which is compatible with natural laminar flow (NLF) requirements. An important consideration is manufacturing roughness of the surface in the form of steps and gaps perpendicular to the freestream. The principal challenge to the design and manufacture of laminar flow surfaces today appears to be in the installation of leading-edge panels on wing, nacelle, and empennage surfaces. A similar challenge is in the installation of access panels, doors, windows, fuselage noses, and engine nacelles. Past work on roughness and waviness manufacturing tolerances and comparisons with more recent experiments are reviewed.
THE BERNOULLI EQUATION AND COMPRESSIBLE FLOW THEORIES
The incompressible Bernoulli equation is an analytical relationship between pressure, kinetic energy, and potential energy. As perhaps the simplest and most useful statement for describing laminar flow, it buttresses numerous incompressible flow models that have been developed ...
Computational Optimization of a Natural Laminar Flow Experimental Wing Glove
NASA Technical Reports Server (NTRS)
Hartshom, Fletcher
2012-01-01
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.
Method and apparatus for detecting laminar flow separation and reattachment
NASA Technical Reports Server (NTRS)
Stack, John P. (inventor); Mangalam, Sivaramakrishnan M. (inventor)
1989-01-01
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.
CFD Investigations of a Transonic Swept-Wing Laminar Flow Control Flight Experiment
Neale, Tyler P.
2011-08-08
Laminar flow control has been studied for several decades in an effort to achieve higher efficiencies for aircraft. Successful implementation of laminar flow control technology on transport aircraft could significantly ...
Conservative properties of finite difference schemes for incompressible flow
NASA Technical Reports Server (NTRS)
Morinishi, Youhei
1995-01-01
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.
Application of laminar flow control to supersonic transport configurations
NASA Technical Reports Server (NTRS)
Parikh, P. G.; Nagel, A. L.
1990-01-01
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.
Electrostatic quadrupole focused particle accelerating assembly with laminar flow beam
Maschke, Alfred W. (East Moriches, NY)
1985-01-01
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.
Design optimization of natural laminar flow bodies in compressible flow
NASA Technical Reports Server (NTRS)
Dodbele, Simha S.
1992-01-01
An optimization method has been developed to design axisymmetric body shapes such as fuselages, nacelles, and external fuel tanks with increased transition Reynolds numbers in subsonic compressible flow. The new design method involves a constraint minimization procedure coupled with analysis of the inviscid and viscous flow regions and linear stability analysis of the compressible boundary-layer. In order to reduce the computer time, Granville's transition criterion is used to predict boundary-layer transition and to calculate the gradients of the objective function, and linear stability theory coupled with the e(exp n)-method is used to calculate the objective function at the end of each design iteration. Use of a method to design an axisymmetric body with extensive natural laminar flow is illustrated through the design of a tiptank of a business jet. For the original tiptank, boundary layer transition is predicted to occur at a transition Reynolds number of 6.04 x 10(exp 6). For the designed body shape, a transition Reynolds number of 7.22 x 10(exp 6) is predicted using compressible linear stability theory coupled with the e(exp n)-method.
Incompressible viscous flow simulations of the NFAC wind tunnel
NASA Technical Reports Server (NTRS)
Champney, Joelle Milene
1986-01-01
The capabilities of an existing 3-D incompressible Navier-Stokes flow solver, INS3D, are extended and improved to solve turbulent flows through the incorporation of zero- and two-equation turbulence models. The two-equation model equations are solved in their high Reynolds number form and utilize wall functions in the treatment of solid wall boundary conditions. The implicit approximate factorization scheme is modified to improve the stability of the two-equation solver. Applications to the 3-D viscous flow inside the 80 by 120 feet open return wind tunnel of the National Full Scale Aerodynamics Complex (NFAC) are discussed and described.
RIPPLE: A new model for incompressible flows with free surfaces
Kothe, D.B.; Mjolsness, R.C.
1991-01-01
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.
Numerical Modeling for Multiphase Incompressible Flow with Phase Change
Xiao-Yong Luo; Ming-Jiu Ni; Alice Ying; M. A. Abdou
2005-01-01
A general formula for the second-order projection method combined with the level set method is developed to simulate unsteady, incompressible multifluid flow with phase change. A subcell conception is introduced in a modified mass transfer model to accurately calculate the mass transfer across the interface. The third-order essentially nonoscillatory (ENO) scheme and second-order semi-implicit Crank-Nicholson scheme is employed to update
Mathematical aspects of finite element methods for incompressible viscous flows
NASA Technical Reports Server (NTRS)
Gunzburger, M. D.
1986-01-01
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.
Numerical Methods for the Solution of Incompressible and Compressible Fluid Flows
Jeffrey Peter van Doormaal
1985-01-01
Traditionally the methods used to solve viscous fluid flow problems have been separated into the methods developed for incompressible fluid flows and those developed for compressible fluid flows. Relatively few methods have been developed for both incompressible and compressible fluid flows and most methods which are applicable to both types of flows have been developed from methods originally advanced for
Incompressible Turbulent Wing-Body Junction Flow
NASA Technical Reports Server (NTRS)
Krishnamurthy, R.; Cagle, Corey D.; Chandra, S.
1998-01-01
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
Thermal coherent sets and heat transfer in chaotic laminar flows
NASA Astrophysics Data System (ADS)
Naik, Shibabrat; Grover, Piyush
2013-11-01
The relation between the chaotic nature of the advection flow field and heat transfer in laminar flow heat exchangers is known to be subtle. We use the Perron-Frobenius transfer operator approach to analyze thermal transport in a coiled tube with 3D laminar flow and Dirichlet thermal boundary condition. The usual advection-only transfer operator is combined with a finite-difference diffusion operator via an operator-splitting technique. We compute various coherent sets of this approximate advection-diffusion operator. These coherent sets correspond to the important ``thermal structures'' which govern the heat transfer in this problem. This analysis gives an insight into the effect of chaotic advection field on the heat transfer performance of such devices. We study the dependence of heat transfer enhancement factor on Peclet number.This transfer operator based analysis could lead to systematic geometric optimization of micrometer sized heat exchangers.
Dumb-bell model for polymer transport in laminar flows
NASA Astrophysics Data System (ADS)
DeLucia, M.; Mazzino, A.; Vulpiani, A.
2002-10-01
Polymer transport is investigated, in the limit of the so-called dumb-bell model, for two paradigmatic laminar flows having open and closed streamlines, respectively. For both types of flows we find transport depletion owing to the action of the polymers elastic degree of freedom. For flows with closed streamlines the leading mechanism for the observed transport reduction is the (dynamical) formation of barriers. For flows with open streamlines the reduction of transport is induced by the renormalization of the bare diffusion coefficient. Results have been obtained by means of Lagrangian simulations.
Optimized profiles for incompressible flow metering nozzles
NASA Astrophysics Data System (ADS)
Lakshminarayanan, R.; Haji-Sheikh, A.; Lou, D. Y. S.; Spindler, M.
1988-04-01
The Euler-Lagrange equation was used to minimize shear stress in designing a flow-metering nozzle. The flow field in the nozzle was computed by solving the momentum equation in integral form. The profile of the nozzle was obtained by minimizing the shear losses in the converging section of the nozzle. Following computation of the profile, a metering nozzle was designed, constructed, and subsequently tested to evaluate the validity of the analysis. The nozzle was designed for a pipe diameter of 15.24 cm (6 in.) and a throat diameter of 9.266 cm (3.648 in.). The test results indicated a marked increase in the value of the discharge coefficient when it is compared with that for the ASME standard nozzle. The computed pressure distribution is in good agreement with the experimental data.
McHugh
1995-01-01
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
Viscous Incompressible Flow Computations for 3-D Steady and Unsteady Flows
NASA Technical Reports Server (NTRS)
Kwak, Dochan
2001-01-01
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.
Incompressible lattice Boltzmann model for axisymmetric flows through porous media
NASA Astrophysics Data System (ADS)
Rong, Fumei; Shi, Baochang
2015-09-01
In this paper, an axisymmetric LBE model for incompressible flows through porous media is proposed. In this model, the influence of density change caused by large pressure difference can be overcome by replacing density distribution function with pressure distribution function. A more simple processing format for external force is introduced so as to make the involved method in this paper more perfect. The coupling between flow velocity and pressure also can be significantly reduced when calculating the macroscopic quantities. Good agreement between the analytical solution and numerical results is also obtained based on this model and it also can provide guidance for other problem with such complicated force forms.
Gyrotactic trapping in laminar and turbulent Kolmogorov flow
Francesco Santamaria; Filippo De Lillo; Massimo Cencini; Guido Boffetta
2014-10-07
Phytoplankton patchiness, namely the heterogeneous distribution of microalgae over multiple spatial scales, dramatically impacts marine ecology. A spectacular example of such heterogeneity occurs in thin phytoplankton layers (TPLs), where large numbers of photosynthetic microorganisms are found within a small depth interval. Some species of motile phytoplankton can form TPLs by gyrotactic trapping due to the interplay of their particular swimming style (directed motion biased against gravity) and the transport by a flow with shear along the direction of gravity. Here we consider gyrotactic swimmers in numerical simulations of the Kolmogorov shear flow, both in laminar and turbulent regimes. In the laminar case, we show that the swimmer motion is integrable and the formation of TPLs can be fully characterized by means of dynamical systems tools. We then study the effects of rotational Brownian motion or turbulent fluctuations (appearing when the Reynolds number is large enough) on TPLs. In both cases we show that TPLs become transient, and we characterize their persistence.
Development of laminar flow control wing surface porous structure
NASA Technical Reports Server (NTRS)
Klotzsche, M.; Pearce, W.; Anderson, C.; Thelander, J.; Boronow, W.; Gallimore, F.; Brown, W.; Matsuo, T.; Christensen, J.; Primavera, G.
1984-01-01
It was concluded that the chordwise air collection method, which actually combines chordwise and spanwise air collection, is the best of the designs conceived up to this time for full chord laminar flow control (LFC). Its shallower ducting improved structural efficiency of the main wing box resulting in a reduction in wing weight, and it provided continuous support of the chordwise panel joints, better matching of suction and clearing airflow requirements, and simplified duct to suction source minifolding. Laminar flow control on both the upper and lower surfaces was previously reduced to LFC suction on the upper surface only, back to 85 percent chord. The study concludes that, in addition to reduced wing area and other practical advantages, this system would be lighter because of the increase in effective structural wing thickness.
Coherent synchrotron radiation for laminar flows
NASA Astrophysics Data System (ADS)
Schmekel, Bjoern S.; Lovelace, Richard V. E.
2006-11-01
We investigate the effect of shear in the flow of charged particle equilibria that are unstable to the coherent synchrotron radiation (CSR) instability. Shear may act to quench this instability because it acts to limit the size of the region with a fixed phase relation between emitters. The results are important for the understanding of astrophysical sources of coherent radiation where shear in the flow is likely.
Aerodynamic Design for Swept-wing Laminar Flow
Belisle, Michael Joseph
2013-11-08
Improvement (AFRL/NGC) AFRL Air Force Research Laboratory ATTAS Advanced Technologies Testing Aircraft System (German Aerospace Center) BL Wing buttock line, measured in inches from aircraft centerline CAD Computer-aided design CC Complex conjugate CFD... PSE Parabolized stability equations xi RMS Root-mean-square SARGE Subsonic Aircraft Roughness Glove Experiment SCRAT Subsonic Research Aircraft Testbed SWIFT Swept-Wing In-Flight Testing (AFRL/TAMU) SWLFC Swept-wing laminar flow control TAMU Texas A...
Ground vibration test of the laminar flow control JStar airplane
NASA Technical Reports Server (NTRS)
Kehoe, M. W.; Cazier, F. W., Jr.; Ellison, J. F.
1985-01-01
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.
Mixing and reaction fronts in laminar flows.
Leconte, M; Martin, J; Rakotomalala, N; Salin, D; Yortsos, Y C
2004-04-22
Autocatalytic reaction fronts between unreacted and reacted mixtures in the absence of fluid flow propagate as solitary waves. In the presence of imposed flow, the interplay between diffusion and advection enhances the mixing, leading to Taylor hydrodynamic dispersion. We present asymptotic theories in the two limits of small and large Thiele modulus (slow and fast reaction kinetics, respectively) that incorporate flow, diffusion, and reaction. For the first case, we show that the problem can be handled to leading order by the introduction of the Taylor dispersion replacing the molecular diffusion coefficient by its Taylor counterpart. In the second case, the leading-order behavior satisfies the eikonal equation. Numerical simulations using a lattice gas model show good agreement with the theory. The Taylor model is relevant to microfluidics applications, whereas the eikonal model applies at larger length scales. PMID:15267641
Mixing and reaction fronts in laminar flows
NASA Astrophysics Data System (ADS)
Leconte, M.; Martin, J.; Rakotomalala, N.; Salin, D.; Yortsos, Y. C.
2004-04-01
Autocatalytic reaction fronts between unreacted and reacted mixtures in the absence of fluid flow propagate as solitary waves. In the presence of imposed flow, the interplay between diffusion and advection enhances the mixing, leading to Taylor hydrodynamic dispersion. We present asymptotic theories in the two limits of small and large Thiele modulus (slow and fast reaction kinetics, respectively) that incorporate flow, diffusion, and reaction. For the first case, we show that the problem can be handled to leading order by the introduction of the Taylor dispersion replacing the molecular diffusion coefficient by its Taylor counterpart. In the second case, the leading-order behavior satisfies the eikonal equation. Numerical simulations using a lattice gas model show good agreement with the theory. The Taylor model is relevant to microfluidics applications, whereas the eikonal model applies at larger length scales.
Laminar Flow Control Flight Experiment Design
Tucker, Aaron 1975-
2012-11-29
with lateral control inputs to achieve the desired flow conditions. The data are statistically analyzed in a split-plot factorial that produces a system response model in six variables: angle of attack, Mach number, Reynolds number, DRE height, DRE spacing...
Laminar-turbulent separatrix in a boundary layer flow
NASA Astrophysics Data System (ADS)
Biau, Damien
2012-03-01
The transitional boundary layer flow over a flat plate is investigated. The boundary layer flow is known to develop unstable Tollmien-Schlichting waves above a critical value of the Reynolds number. However, it is also known that this transition can be observed for sub-critical Reynolds numbers. In that case, the basin of attraction of the laminar state coexists with the sustained turbulence. In this article, the trajectory on the separatrix between these two states is simulated. The state on the separatrix is independent from the initial condition and is dynamically connected to both the laminar flow and the turbulence. Such an edge state provides information regarding the basic features of the transitional flow. The solution takes the form of a low speed streak, flanked by two quasi-streamwise sinuous vortices. The shape of the streaks is close to that simulated with the linear optimal perturbation method. This solution is compared to existing results concerning streak breakdown. The simulations are realized in a temporal framework for a local boundary layer, with periodic boundary conditions in the streamwise direction. A dedicated model, based on a scale separation, is presented. The mean flow is a solution of the Prandtl boundary layer equations while the superposed small-scale fluctuations are a solution of the periodic Navier-Stokes equations. The model is validated with turbulent flow simulations and satisfactorily reproduces the physical characteristics of a boundary layer flow, especially in the outer region, where external fluid is entrained toward the boundary layer.
Finite element formulation of general boundary conditions for incompressible flows
NASA Astrophysics Data System (ADS)
Becker, Roland; Capatina, Daniela; Luce, Robert; Trujillo, David
2015-10-01
We study the finite element formulation of general boundary conditions for incompressible flow problems. Distinguishing between the contributions from the inviscid and viscid parts of the equations, we use Nitsche's method to develop a discrete weighted weak formulation valid for all values of the viscosity parameter, including the limit case of the Euler equations. In order to control the discrete kinetic energy, additional consistent terms are introduced. We treat the limit case as a (degenerate) system of hyperbolic equations, using a balanced spectral decomposition of the flux Jacobian matrix, in analogy with compressible flows. Then, following the theory of Friedrich's systems, the natural characteristic boundary condition is generalized to the considered physical boundary conditions. Several numerical experiments, including standard benchmarks for viscous flows as well as inviscid flows are presented.
Visualization tools for vorticity transport analysis in incompressible flow.
Sadlo, Filip; Peikert, Ronald; Sick, Mirjam
2006-01-01
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
Pseudo-compressibility methods for the incompressible flow equations
NASA Technical Reports Server (NTRS)
Turkel, Eli; Arnone, A.
1993-01-01
Preconditioning methods to accelerate convergence to a steady state for the incompressible fluid dynamics equations are considered. The analysis relies on the inviscid equations. The preconditioning consists of a matrix multiplying the time derivatives. Thus the steady state of the preconditioned system is the same as the steady state of the original system. The method is compared to other types of pseudo-compressibility. For finite difference methods preconditioning can change and improve the steady state solutions. An application to viscous flow around a cascade with a non-periodic mesh is presented.
New discretization and solution techniques for incompressible viscous flow problems
NASA Technical Reports Server (NTRS)
Gunzburger, M. D.; Nicolaides, R. A.; Liu, C. H.
1983-01-01
This paper considers several topics arising in the finite element solution of the incompressible Navier-Stokes equations. Specifically, the question of choosing finite element velocity/pressure spaces is addressed, particularly from the viewpoint of achieving stable discretizations leading to convergent pressure approximations. Following this, the role of artificial viscosity in viscous flow calculations is studied, emphasizing recent work by several researchers for the anisotropic case. The last section treats the problem of solving the nonlinear systems of equations which arise from the discretization. Time marching methods and classical iterative techniques, as well as some recent modifications are mentioned.
Finite element solvers for incompressible fluid flows and heat transfer
NASA Technical Reports Server (NTRS)
Sohn, Jeong L.; Kim, Yongmo; Chung, T. J.
1989-01-01
Two different finite-element solvers for incompressible viscous flow, i.e., the mixed interpolation method and the SIMPLE-type iterative method, are compared and tested with some benchmark problems. The advantages of the SIMPLE-type iterative method are the decoupling of the governing equations and the use of equal-order interpolation functions for both velocity and pressure. Even though there is a significant difference between the two methods in terms of the pressure field, similar solutions are obtained for the velocity field.
A boundary element method for steady incompressible thermoviscous flow
NASA Technical Reports Server (NTRS)
Dargush, G. F.; Banerjee, P. K.
1991-01-01
A boundary element formulation is presented for moderate Reynolds number, steady, incompressible, thermoviscous flows. The governing integral equations are written exclusively in terms of velocities and temperatures, thus eliminating the need for the computation of any gradients. Furthermore, with the introduction of reference velocities and temperatures, volume modeling can often be confined to only a small portion of the problem domain, typically near obstacles or walls. The numerical implementation includes higher order elements, adaptive integration and multiregion capability. Both the integral formulation and implementation are discussed in detail. Several examples illustrate the high level of accuracy that is obtainable with the current method.
Preconditioning and the limit to the incompressible flow equations
NASA Technical Reports Server (NTRS)
Turkel, E.; Fiterman, A.; Vanleer, B.
1993-01-01
The use of preconditioning methods to accelerate the convergence to a steady state for both the incompressible and compressible fluid dynamic equations are considered. The relation between them for both the continuous problem and the finite difference approximation is also considered. The analysis relies on the inviscid equations. The preconditioning consists of a matrix multiplying the time derivatives. Hence, the steady state of the preconditioned system is the same as the steady state of the original system. For finite difference methods the preconditioning can change and improve the steady state solutions. An application to flow around an airfoil is presented.
Natural laminar flow experiments on modern airplane surfaces
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Obara, C. J.; Yip, L. P.
1984-01-01
Flight and wind-tunnel natural laminar flow experiments have been conducted on various lifting and nonlifting surfaces of several airplanes at unit Reynolds numbers between 0.63 x 10 to the 6th power/ft and 3.08 x 10 to the 6th power/ft, at Mach numbers from 0.1 to 0.7, and at lifting surface leading-edge sweep angles from 0 deg to 63 deg. The airplanes tested were selected to provide relatively stiff skin conditions, free from significant roughness and waviness, on smooth modern production-type airframes. The observed transition locations typically occurred downstream of the measured or calculated pressure peak locations for the test conditions involved. No discernible effects on transition due to surface waviness were observed on any of the surfaces tested. None of the measured heights of surface waviness exceeded the empirically predicted allowable surface waviness. Experimental results consistent with spanwise contamination criteria were observed. Large changes in flight-measured performance and stability and control resulted from loss of laminar flow by forced transition. Rain effects on the laminar boundary layer caused stick-fixed nose-down pitch-trim changes in two of the airplanes tested. No effect on transition was observed for flight through low-altitude liquid-phase clouds. These observations indicate the importance of fixed-transition tests as a standard flight testing procedure for modern smooth airframes.
An Hybrid Finite Volume-Finite Element Method for Variable Density Incompressible Flows
Frey, Pascal
An Hybrid Finite Volume-Finite Element Method for Variable Density Incompressible Flows Caterina density flows, Finite Element method, Finite Volume method, Rayleigh-Taylor instability. AMS Subject to the numerical simulation of variable density incompressible flows, modeled by the Navier-Stokes system. We
Polymer Effects on Heat Transport in Laminar Boundary Layer Flow
Roberto Benzi; Emily S. C. Ching; Vivien W. S. Chu
2011-04-27
We consider a laminar Blasius boundary-layer flow above a slightly heated horizontal plate and study the effect of polymer additives on the heat transport. We show that the action of the polymers can be understood as a space-dependent effective viscosity that first increases from the zero-shear value then decreases exponentially back to the zero-shear value as one moves away from the boundary. We find that with such an effective viscosity, both the horizontal and vertical velocities near the plate are decreased thus leading to an increase in the friction drag and a decrease in the heat transport in the flow.
Interpolation between DarcyWeisbach and Darcy for laminar and turbulent flows
Walter, M.Todd
Weisbach; Porous media; Open channels; Turbulent flow; Laminar flow 1. Introduction Grassed waterways in the following. This famous formula was obtained by Darcy [5] from his careful measurement of turbulent flowsInterpolation between DarcyWeisbach and Darcy for laminar and turbulent flows W.L. Hogarth a, *, J
A conservative sharp interface method for incompressible multiphase flows
NASA Astrophysics Data System (ADS)
Luo, J.; Hu, X. Y.; Adams, N. A.
2015-03-01
In this work, we develop a conservative sharp interface method based on [25] for incompressible flows with viscous and surface tension effects. Employing a weakly compressible framework, the method is simple, mass conserving and capable of handling flows with large density and viscosity ratios and high surface tension. Since the viscosity jump at the material interface is directly imposed by an interface-flux term, momentum conservation is ensured when capillary effects are absent. Furthermore, a subcell-resolution method for volume-fraction evaluation is developed to achieve accurate interface reconstruction. A number of two and three dimensional numerical examples, are considered to demonstrate that the present method is able to simulate a wide range of flow problems with good robustness and high accuracy.
NASA Technical Reports Server (NTRS)
Fischer, Michael C.; Vemuru, Chandra S.
1991-01-01
The NASA Supersonic Laminar Flow Control (SLFC) program encompasses the development of refined CFD methods and boundary layer stability codes for the highly 3D supersonic flow conditions encountered by the F-16XL technology demonstration aircraft and the prospective High Speed Civil Transport (HSCT). While the F-16XL-1 aircraft continues to gather SLFC data, work is under way on the F-16XL-2 aircraft: which will furnish attach-line design criteria, code-calibration data, and an improved understanding of the flowfield over a wing that will add confidence to the design of HSCTs' boundary layer-controlling air-suction panels.
A Model for Steady Laminar Flow through a Deformable Gel-Coated Channel.
Yang, Canghu; Grattoni, Carlos A.; Muggeridge, Ann H.; Zimmerman, Robert W.
2000-06-01
A model for the steady laminar flow of an incompressible fluid through a deformable gel-coated channel with slowly varying tapered shape is presented. Previous work has shown that the flow rate through such a channel is less than that which would be expected from the Hagen-Poiseuille equation (1973, J. Lahav, N. Eliezer, and A. Silberberg, Biorheology 10, 595; 1979, P. Krindel and A. Silberberg, J. Colloid Interface Sci. 71, 39). Krindel and Silberberg also observed the onset of turbulent flow at lower rates than would normally be expected; they attributed these phenomena to a turbulent boundary layer near the channel walls. Our analysis shows that the rate reduction is in fact due to kinetic energy effects related to the converging flowlines. A model to describe this rate reduction is presented and is shown to agree well with experimental results, successfully predicting the observed flow rate reduction over Reynolds numbers ranging from 1 to 1000. Copyright 2000 Academic Press. PMID:11401353
Numerical simulation of laminar hypersonic flows about an ellipsoid
NASA Astrophysics Data System (ADS)
Riedelbauch, S.; Mueller, B.
The laminar hypersonic flow about a double ellipsoid, which idealizes the nose and cockpit of a spacecraft, were numerically simulated. The calculation method solves the three dimensional thin layer Navier-Stokes equations in a conservative formulation on a surface oriented calculation grid using an implicit/explicit finite difference technique. The conservative formulation allows the correct calculation of embedded compression shocks, while the head wave was treated with a shock-fitting procedure. The calculated flow fields about the ellipsoid show shock-shock and shock-boundary layer interactions in connection with separated flow. Wall flow lines and heat transfer agree qualitatively very well with film-of-oil and thermographic pictures.
NASA Technical Reports Server (NTRS)
Vijgen, Paul M. H. W.; Holmes, Bruce J.
1987-01-01
Fuelled by a need to reduce viscous drag of airframes, significant advances have been made in the last decade to design lifting surface geometries with considerable amounts of laminar flow. In contrast to the present understanding of practical limits for natural laminar flow over lifting surfaces, limited experimental results are available examining applicability of natural laminar flow over axisymmetric and nonaxisymmetric fuselage shapes at relevantly high length Reynolds numbers. The drag benefits attainable by realizing laminar flow over nonlifting aircraft components such as fuselages and nacelles are shown. A flight experiment to investigate transition location and transition mode over the forward fuselage of a light twin engine propeller driven airplane is examined.
NASA Technical Reports Server (NTRS)
Albers, J. A.; Gregg, J. L.
1974-01-01
Finite-difference computer program calculates viscous compressible boundary layer flow over either planar or axisymmetric surfaces. Flow may be initially laminar and progress through transitional zone to fully turbulent flow, or it may remain laminar, depending on imposed boundary conditions, laws of viscosity, and numerical solution of momentum and energy equations.
Aircraft energy efficiency laminar flow control wing design study
NASA Technical Reports Server (NTRS)
Bonner, T. F., Jr.; Pride, J. D., Jr.; Fernald, W. W.
1977-01-01
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.
A sharp interface method for incompressible two-phase flows
NASA Astrophysics Data System (ADS)
Sussman, M.; Smith, K. M.; Hussaini, M. Y.; Ohta, M.; Zhi-Wei, R.
2007-02-01
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. Sussman, A second order coupled levelset and volume of fluid method for computing growth and collapse of vapor bubbles, Journal of Computational Physics 187 (2003) 110-136] in which the previous method treated the gas pressure as spatially constant and the present method treats the gas as a second incompressible fluid. The new method yields solutions in the zero gas density limit which are comparable in accuracy to the method in which the gas pressure was treated as spatially constant. This improvement in accuracy allows one to compute accurate solutions on relatively coarse grids, thereby providing a speed-up over continuum or "ghost-fluid" methods.
A viscous instability in axially symmetric laminar shear flows
NASA Astrophysics Data System (ADS)
Shakura, Nikolay; Postnov, Konstantin
2015-08-01
A viscous instability in shearing laminar axisymmetric hydrodynamic flows around a gravitating center is described. In the linearized hydrodynamic equations written in the Boussinesq approximation with microscopic molecular transport coefficients, the instability arises when the viscous dissipation is taken into account in the energy equation. Using the local WKB approximation, we derive a third-order algebraic dispersion equation with two modes representing the modified Rayleigh modes R+ and R-, and the third X-mode. We show that in thin accretion flows the viscosity destabilizes one of the Rayleigh modes in a wide range of wavenumbers, while the X-mode always remains stable. In Keplerian flows, the instability increment is found to be a few Keplerian rotational periods at wavelengths with $kr\\sim 10-50$. This instability may cause turbulence in astrophysical accretion discs even in the absence of magnetic field.
A viscous instability in axially symmetric laminar shear flows
NASA Astrophysics Data System (ADS)
Shakura, N.; Postnov, K.
2015-04-01
A viscous instability in shearing laminar axisymmetric hydrodynamic flows around a gravitating centre is described. In the linearized hydrodynamic equations written in the Boussinesq approximation with microscopic molecular transport coefficients, the instability arises when the viscous dissipation is taken into account in the energy equation. Using the local WKB approximation, we derive a third-order algebraic dispersion equation with two modes representing the modified Rayleigh modes R+ and R-, and the third X-mode. We show that in thin accretion flows the viscosity destabilizes one of the Rayleigh modes in a wide range of wavenumbers, while the X-mode always remains stable. In Keplerian flows, the instability increment is found to be a few Keplerian rotational periods at wavelengths with kr ˜ 10-50. This instability may cause turbulence in astrophysical accretion discs even in the absence of magnetic field.
A viscous instability in axially symmetric laminar shear flows
Shakura, Nikolai
2015-01-01
A viscous instability in shearing laminar axisymmetric hydrodynamic flows around a gravitating center is described. In the linearized hydrodynamic equations written in the Boussinesq approximation with microscopic molecular transport coefficients, the instability arises when the viscous dissipation is taken into account in the energy equation. Using the local WKB approximation, we derive a third-order algebraic dispersion equation with two modes representing the modified Rayleigh modes R+ and R-, and the third X-mode. We show that in thin accretion flows the viscosity destabilizes one of the Rayleigh modes in a wide range of wavenumbers, while the X-mode always remains stable. In Keplerian flows, the instability increment is found to be a few Keplerian rotational periods at wavelengths with $kr\\sim 10-50$. This instability may cause turbulence in astrophysical accretion discs even in the absence of magnetic field.
Low temperature high current ion beams and laminar flows
NASA Astrophysics Data System (ADS)
Cavenago, Marco
2014-07-01
Self-consistent Vlasov-Poisson equilibria for the extraction of ions with low temperature Ti are discussed, with comparison to the laminar flow case Ti = 0, in two dimensional diodes. Curvilinear coordinates aligned with laminar beam flow lines are extended to the low ion temperature case, with a reduced current density jd, expressed with cathode integrals. This generalizes one-dimensional interpolation between rays along the cathode coordinate to multidimensional integrations, including also the momentum components, so that jd is free from the granularity defect and noise, typical of standard ray tracing approach. A robust numerical solution procedure is developed, which allows studying current saturated extraction and drift tube effects. A discussion of particle initial conditions determines the emission angles and shows that temperature effect at beam edge is partly balanced by the focus electrode inclination. Results for a typical diode are described, with detail about normalized emittance, here taken strictly proportional to the x - px phase space area, for a beam with non uniform velocities. Contribution to the Topical Issue "Theory and Applications of the Vlasov Equation", edited by Francesco Pegoraro, Francesco Califano, Giovanni Manfredi and Philip J. Morrison.
Simplified thermal lattice Boltzmann model for incompressible thermal flows.
Peng, Y; Shu, C; Chew, Y T
2003-08-01
Considering the fact that the compression work done by the pressure and the viscous heat dissipation can be neglected for the incompressible flow, and its relationship with the gradient term in the evolution equation for the temperature in the thermal energy distribution model, a simplified thermal energy distribution model is proposed. This thermal model does not have any gradient term and is much easier to be implemented. This model is validated by the numerical simulation of the natural convection in a square cavity at a wide range of Rayleigh numbers. Numerical experiments showed that the simplified thermal model can keep the same order of accuracy as the thermal energy distribution model, but it requires much less computational effort. PMID:14525142
Incompressible Navier-Stokes Calculations in Pump Flows
NASA Technical Reports Server (NTRS)
Kiris, Cetin; Chang, Leon; Kwak, Dochan
1993-01-01
Flow through pump components, such as the SSME-HPFTP Impeller and an advanced rocket pump impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. The equations are solved in steadily rotating reference frames and the centrifugal force and the Coriolis force are added to the equation of motion. Current computations use one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside an 11-inch SSME High Pressure Fuel Turbopump impeller, and an advanced rocket pump impeller. Numerical results of SSME-HPFTP impeller flow are compared with experimental measurements. In the advanced pump impeller, the effects of exit and shroud cavities are investigated. Flow analyses at design conditions will be presented.
A multilevel adaptive projection method for unsteady incompressible flow
NASA Technical Reports Server (NTRS)
Howell, Louis H.
1993-01-01
There are two main requirements for practical simulation of unsteady flow at high Reynolds number: the algorithm must accurately propagate discontinuous flow fields without excessive artificial viscosity, and it must have some adaptive capability to concentrate computational effort where it is most needed. We satisfy the first of these requirements with a second-order Godunov method similar to those used for high-speed flows with shocks, and the second with a grid-based refinement scheme which avoids some of the drawbacks associated with unstructured meshes. These two features of our algorithm place certain constraints on the projection method used to enforce incompressibility. Velocities are cell-based, leading to a Laplacian stencil for the projection which decouples adjacent grid points. We discuss features of the multigrid and multilevel iteration schemes required for solution of the resulting decoupled problem. Variable-density flows require use of a modified projection operator--we have found a multigrid method for this modified projection that successfully handles density jumps of thousands to one. Numerical results are shown for the 2D adaptive and 3D variable-density algorithms.
Computation of incompressible viscous flows through turbopump components
NASA Technical Reports Server (NTRS)
Kiris, Cetin; Chang, Leon
1993-01-01
Flow through pump components, such as an inducer and an impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudocompressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. the equations are solved in steadily rotating reference frames and the centrifugal force and the Coriolis force are added to the equation of motion. Current computations use a one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside a generic rocket engine pump inducer, a fuel pump impeller, and SSME high pressure fuel turbopump impeller. Numerical results of inducer flow are compared with experimental measurements. In the fuel pump impeller, the effect of downstream boundary conditions is investigated. Flow analyses at 80 percent, 100 percent, and 120 percent of design conditions are presented.
High-flaps for natural laminar flow airfoils
NASA Technical Reports Server (NTRS)
Morgan, Harry L.
1986-01-01
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.
Predicting Transition from Laminar to Turbulent Flow over a Surface
NASA Technical Reports Server (NTRS)
Rajnarayan, Dev (Inventor); Sturdza, Peter (Inventor)
2013-01-01
A prediction of whether a point on a computer-generated surface is adjacent to laminar or turbulent flow is made using a transition prediction technique. A plurality of boundary-layer properties at the point are obtained from a steady-state solution of a fluid flow in a region adjacent to the point. A plurality of instability modes are obtained, each defined by one or more mode parameters. A vector of regressor weights is obtained for the known instability growth rates in a training dataset. For each instability mode in the plurality of instability modes, a covariance vector is determined, which is the covariance of a predicted local growth rate with the known instability growth rates. Each covariance vector is used with the vector of regressor weights to determine a predicted local growth rate at the point. Based on the predicted local growth rates, an n-factor envelope at the point is determined.
Stability theory applications to laminar-flow control
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.
1987-01-01
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.
Erosion of a granular bed driven by laminar fluid flow
NASA Astrophysics Data System (ADS)
Lobkovsky, Alexander E.; Orpe, Ashish V.; Molloy, Ryan; Kudrolli, Arshad; Rothman, Daniel H.
Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed driven by a laminar fluid to give us new insights into the relationship between hydrodynamic stress and surface granular flow. A closed cell of rectangular cross-section is partially filled with glass beads and a constant fluid flux Q flows through the cell. The refractive indices of the fluid and the glass beads are matched and the cell is illuminated with a laser sheet, allowing us to image individual beads. The bed erodes to a rest height hr which depends on Q. The Shields threshold criterion assumes that the non-dimensional ratio > yields a collapse of the measured Einstein number q* to a power-law function of 0.25. The dynamics of the bed height relaxation are described well by the power-law relationship between the granular flux and the bed stress.
Global pressure relaxation for laminar two-dimensional internal flow
NASA Technical Reports Server (NTRS)
Rosenbaum, D.; Rubin, S. G.
1990-01-01
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.
Unsteady laminar flow and convective heat transfer in a sharp 180 bend
Chung, Yongmann M.
Unsteady laminar flow and convective heat transfer in a sharp 180° bend Yongmann M. Chung a , Paul Unsteady laminar flow and heat transfer in a sharp 180° bend is studied numerically to investigate a convective heat transfer regime of especial relevance to electronic systems. Due to the high geometrical
Kenis, Paul J. A.
2005-01-01
Electrochimica Acta 50 (2005) 53905398 Membraneless laminar flow-based micro fuel cells operating) in membraneless, laminar flow-based micro fuel cells (LF-FCs) eliminates several PEM-related issues such as fuel the anode is in acidic media while the cathode is in alkali, or vice versa. Operating a fuel cell under
Aerodynamic design of a natural laminar flow nacelle and the design validation by flight testing
H. Riedel; K.-H. Horstmann; A. Ronzheimer; M. Sitzmann
1998-01-01
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
Laminar Wall Jet Flow and Heat Transfer over a Shallow Cavity
Maheandera Prabu, P.; Padmanaban, K. P.
2015-01-01
This paper presents the detailed simulation of two-dimensional incompressible laminar wall jet flow over a shallow cavity. The flow characteristics of wall jet with respect to aspect ratio (AR), step length (Xu), and Reynolds number (Re) of the shallow cavity are expressed. For higher accuracy, third-order discretization is applied for momentum equation which is solved using QUICK scheme with SIMPLE algorithm for pressure-velocity coupling. Low Reynolds numbers 25, 50, 100, 200, 400, and 600 are assigned for simulation. Results are presented for streamline contour, velocity contour, and vorticity formation at wall and also velocity profiles are reported. The detailed study of vortex formation on shallow cavity region is presented for various AR, Xu, and Re conditions which led to key findings as Re increases and vortex formation moves from leading edge to trailing edge of the wall. Distance between vortices increases when the step length (Xu) increases. When Re increases, the maximum temperature contour distributions take place in shallow cavity region and highest convection heat transfer is obtained in heated walls. The finite volume code (FLUENT) is used for solving Navier-Stokes equations and GAMBIT for modeling and meshing.
Laminar flow control leading edge glove flight test article development
NASA Technical Reports Server (NTRS)
Pearce, W. E.; Mcnay, D. E.; Thelander, J. A.
1984-01-01
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.
An efficient pressure-correction method for incompressible multifluid flows
NASA Astrophysics Data System (ADS)
Dodd, M.; Ferrante, A.
2013-11-01
We present a new pressure-correction (PC) method for solving incompressible multifluid flows with large density ratios. The novelty of the method is that the variable coefficient Poisson equation that arises in solving the variable-density Navier-Stokes equations has been reduced to a constant coefficient equation, which can then be solved directly using a fast Poisson solver. The new method is coupled to our mass-conserving volume-of-fluid (VoF) method to capture the interface between the moving fluids. First, we verified the new PC/VoF solver using the capillary wave test-case up to density and viscosity ratios of 10,000. Then, we validated the new flow solver by simulating the motion of a falling water droplet in air by comparing the droplet terminal velocity with the experimental value (Beard, 1976) for 95 . 6 <= Re <= 473 , 0 . 06 <= We <= 0 . 61 , and 0 . 05 <= Bo <= 0 . 26 . We also verified the solver for a rising air bubble in water. The algorithm is shown to be second-order accurate, and stable for density and viscosity ratios up to 10,000. Also, we show that our fast Poisson solver is more than ten times faster than the Hypre multigrid solver up to a 10243 grid and 1024 cores. We present a new pressure-correction (PC) method for solving incompressible multifluid flows with large density ratios. The novelty of the method is that the variable coefficient Poisson equation that arises in solving the variable-density Navier-Stokes equations has been reduced to a constant coefficient equation, which can then be solved directly using a fast Poisson solver. The new method is coupled to our mass-conserving volume-of-fluid (VoF) method to capture the interface between the moving fluids. First, we verified the new PC/VoF solver using the capillary wave test-case up to density and viscosity ratios of 10,000. Then, we validated the new flow solver by simulating the motion of a falling water droplet in air by comparing the droplet terminal velocity with the experimental value (Beard, 1976) for 95 . 6 <= Re <= 473 , 0 . 06 <= We <= 0 . 61 , and 0 . 05 <= Bo <= 0 . 26 . We also verified the solver for a rising air bubble in water. The algorithm is shown to be second-order accurate, and stable for density and viscosity ratios up to 10,000. Also, we show that our fast Poisson solver is more than ten times faster than the Hypre multigrid solver up to a 10243 grid and 1024 cores. NSF CAREER #1054591.
NASA Astrophysics Data System (ADS)
Venezuela, A. L.; Pérez-Guerrero, J. S.; Fontes, S. R.
2009-03-01
The confined flows in tubes with permeable surfaces are associated to tangential filtration processes (microfiltration or ultrafiltration). The complexity of the phenomena do not allow for the development of exact analytical solutions, however, approximate solutions are of great interest for the calculation of the transmembrane outflow and estimate of the concentration polarization phenomenon. In the present work, the generalized integral transform technique (GITT) was employed in solving the laminar and permanent flow in permeable tubes of Newtonian and incompressible fluid. The mathematical formulation employed the parabolic differential equation of chemical species conservation (convective-diffusive equation). The velocity profiles for the entrance region flow, which are found in the connective terms of the equation, were assessed by solutions obtained from literature. The velocity at the permeable wall was considered uniform, with the concentration at the tube wall regarded as variable with an axial position. A computational methodology using global error control was applied to determine the concentration in the wall and concentration boundary layer thickness. The results obtained for the local transmembrane flux and the concentration boundary layer thickness were compared against others in literature.
Computations of Laminar Flow Control on Swept Wings as a Companion to Flight Test Research
Rhodes, Richard G.
2010-01-14
The high cost of energy has resulted in a renewed interest in the study of reducing skin-friction drag in aeronautical applications. Laminar Flow Control (LFC) refers to any technique which alters the basic-state flow-field ...
Postfragmentation density function for bacterial aggregates in laminar flow
NASA Astrophysics Data System (ADS)
Byrne, Erin; Bortz, David M.; Dzul, Steve; Solomon, Michael; Younger, John
2011-04-01
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.
Progress Toward Efficient Laminar Flow Analysis and Design
NASA Technical Reports Server (NTRS)
Campbell, Richard L.; Campbell, Matthew L.; Streit, Thomas
2011-01-01
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.
The effect of mako sharkskin on laminar flow separation
NASA Astrophysics Data System (ADS)
Bradshaw, Michael; Lang, Amy; Motta, Philip; Habegger, Maria; Hueter, Robert
2013-11-01
Many animals possess effective performance enhancing mechanisms, such as the denticles found on the skin of the shortfin mako shark (Isurus oxyrinchus). The shortfin mako, one of the fastest sharks on the planet, is covered by small, tooth-like scales that vary in flexibility over the body. Previous biological findings have shown that the scales increase in flexibility from the leading to trailing edge over the pectoral fin as well as on various sections of the body. It is believed that the scale bristling may provide a mechanism for flow separation control that leads to decreased drag and increased maneuverability. This study involved testing a left pectoral fin of a shortfin mako shark as well as a cylinder with a sharkskin specimen applied circumferentially in a water tunnel facility under static, laminar conditions. Digital Particle Image Velocimetry (DPIV) was used to characterize the flow over the surfaces. Various Reynolds numbers were tested for both configurations, as well as several AOAs for the pectoral fin. The flow over the fin and cylinder were compared to a painted fin and a smooth PVC cylinder, respectively. The study found that the shark scales do, in fact, help to control flow separation. However, in order for the scales to bristle and trap the reversing flow, a certain magnitude of reversed flow and shear is required. This phenomenon seems to be most effective at near stall conditions and at higher Reynolds numbers. Many animals possess effective performance enhancing mechanisms, such as the denticles found on the skin of the shortfin mako shark (Isurus oxyrinchus). The shortfin mako, one of the fastest sharks on the planet, is covered by small, tooth-like scales that vary in flexibility over the body. Previous biological findings have shown that the scales increase in flexibility from the leading to trailing edge over the pectoral fin as well as on various sections of the body. It is believed that the scale bristling may provide a mechanism for flow separation control that leads to decreased drag and increased maneuverability. This study involved testing a left pectoral fin of a shortfin mako shark as well as a cylinder with a sharkskin specimen applied circumferentially in a water tunnel facility under static, laminar conditions. Digital Particle Image Velocimetry (DPIV) was used to characterize the flow over the surfaces. Various Reynolds numbers were tested for both configurations, as well as several AOAs for the pectoral fin. The flow over the fin and cylinder were compared to a painted fin and a smooth PVC cylinder, respectively. The study found that the shark scales do, in fact, help to control flow separation. However, in order for the scales to bristle and trap the reversing flow, a certain magnitude of reversed flow and shear is required. This phenomenon seems to be most effective at near stall conditions and at higher Reynolds numbers. Support from REU grant 1062611 is greatfully acknowledged.
Analysis of Compressible and Incompressible Flows Through See-through Labyrinth Seals
Woo, Jeng Won
2011-08-08
of incompressible flow based on the simulations for various seal geometries and operating conditions, for a given Reynolds number, the carry-over coefficient strongly depended on radial clearance to tooth width ratio. Moreover, in general, the lower the Reynolds...
Incomplete mixing and reactions in laminar shear flow
NASA Astrophysics Data System (ADS)
Paster, A.; Aquino, T.; Bolster, D.
2015-07-01
Incomplete mixing of reactive solutes is well known to slow down reaction rates relative to what would be expected from assuming perfect mixing. In purely diffusive systems, for example, it is known that small initial fluctuations in reactant concentrations can lead to reactant segregation, which in the long run can reduce global reaction rates due to poor mixing. In contrast, nonuniform flows can enhance mixing between interacting solutes. Thus, a natural question arises: Can nonuniform flows sufficiently enhance mixing to restrain incomplete mixing effects and, if so, under what conditions? We address this question by considering a specific and simple case, namely, a laminar pure shear reactive flow. Two solution approaches are developed: a Lagrangian random walk method and a semianalytical solution. The results consistently highlight that if shear effects in the system are not sufficiently strong, incomplete mixing effects initially similar to purely diffusive systems will occur, slowing down the overall reaction rate. Then, at some later time, dependent on the strength of the shear, the system will return to behaving as if it were well mixed, but represented by a reduced effective reaction rate.
Measurements of laminar and turbulent flow in a curved duct with thin inlet boundary layers
NASA Technical Reports Server (NTRS)
Taylor, A. M. K. P.; Whitelaw, J. H.; Yianneskis, M.
1981-01-01
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.
The exact calculation of quadrupole sources for some incompressible flows
NASA Technical Reports Server (NTRS)
Brentner, Kenneth S.
1988-01-01
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.
NASA Technical Reports Server (NTRS)
Tetervin, Neal; Lin, Chia Chiao
1951-01-01
A general integral form of the boundary-layer equation, valid for either laminar or turbulent incompressible boundary-layer flow, is derived. By using the experimental finding that all velocity profiles of the turbulent boundary layer form essentially a single-parameter family, the general equation is changed to an equation for the space rate of change of the velocity-profile shape parameter. The lack of precise knowledge concerning the surface shear and the distribution of the shearing stress across turbulent boundary layers prevented the attainment of a reliable method for calculating the behavior of turbulent boundary layers.
The effect of obstructions and thermals in laminar-flow systems
Whyte, W.; Shaw, B. H.
1974-01-01
The influence of obstructions and thermals on the air flow in unidirectional or laminar flow systems was studied with special reference to operating rooms. It was shown that thermals induced in the operating rooms would have little influence in the normal laminar-flow system. The importance however of obstructions such as operating lamps and personnel was shown. ImagesPlate 2Plate 3Plate 3Plate 4Plate 4Plate 1 PMID:4526407
Aircraft energy efficiency laminar flow control glove flight conceptual design study
NASA Technical Reports Server (NTRS)
Wright, A. S.
1979-01-01
A laminar flow control glove applied to the wing of a short to medium range jet transport with aft mounted engines was designed. A slotted aluminum glove concept and a woven stainless steel mesh porous glove concept suction surfaces were studied. The laminar flow control glove and a dummy glove with a modified supercritical airfoil, ducting, modified wing leading and trailing edges, modified flaps, and an LFC trim tab were applied to the wing after slot spacing suction parameters, and compression power were determined. The results show that a laminar flow control glove can be applied to the wing of a jet transport with an appropriate suction system installed.
NASA Technical Reports Server (NTRS)
Carmichael, B. H.
1979-01-01
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.
Erosion of a granular bed driven by laminar fluid flow
A. E. Lobkovsky; A. V. Orpe; R. Molloy; A. Kudrolli; D. H. Rothman
2008-05-01
Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed driven by a laminar fluid to give us new insights into the relationship between hydrodynamic stress and surface granular flow. A closed cell of rectangular cross-section is partially filled with glass beads and a constant fluid flux $Q$ flows through the cell. The refractive indices of the fluid and the glass beads are matched and the cell is illuminated with a laser sheet, allowing us to image individual beads. The bed erodes to a rest height $h_r$ which depends on $Q$. The Shields threshold criterion assumes that the non-dimensional ratio $\\theta$ of the viscous stress on the bed to the hydrostatic pressure difference across a grain is sufficient to predict the granular flux. Furthermore, the Shields criterion states that the granular flux is non-zero only for $\\theta >\\theta_c$. We find that the Shields criterion describes the observed relationship $h_r \\propto Q^{1/2}$ when the bed height is offset by approximately half a grain diameter. Introducing this offset in the estimation of $\\theta$ yields a collapse of the measured Einstein number $q^*$ to a power-law function of $\\theta - \\theta_c$ with exponent $1.75 \\pm 0.25$. The dynamics of the bed height relaxation are well described by the power law relationship between the granular flux and the bed stress.
LAMINAR FLOW ELEMENT: ITS USE AS A FLOW STANDARD
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...
F-16XL Ship #2 SLFC - Laminar flow research flight over Lake Mead, Nevada
NASA Technical Reports Server (NTRS)
1996-01-01
NASA Dryden Flight Research Center's modified F-16XL conducts testing on laminar flow during an Oct. 1996 research mission over Lake Mead, Nevada. The research being conducted involves a delta-winged F-16XL modified with a 'glove' which is made of titanium. The glove contains more than 10 million holes and has a suction system attached to the lower surface which is comprised of tubes, valves and a compressor. During research flight the suction systems pulls a small part of the boundary layer of air through the glove's porous surface to create laminar (or smooth) air flow. Researchers believe that laminar flow conditions can reduce aerodynamic drag (friction) and contribute to reduced operating costs by improving fuel consumption and lowering aircraft weight. This Supersonic Laminar Flow Control (SLFC) experiment represents a collaborative effort between NASA and aerospace industry (specifically Boeing, Rockwell, and McDonnell Douglas), with Boeing assembling the panel and McDonnell Douglas designing the suction system.
F-16XL Ship #2 SLFC - Laminar flow research flight over Grand Canyon
NASA Technical Reports Server (NTRS)
1996-01-01
NASA Dryden Flight Research Center's modified F-16XL conducts testing on laminar flow during an Oct. 1996 research mission over the Grand Canyon. The research being conducted involves a delta-winged F-16XL modified with a 'glove' which is made of titanium. The glove contains more than 10 million holes and has a suction system attached to the lower surface which is comprised of tubes, valves and a compressor. During research flight the suction systems pulls a small part of the boundary layer of air through the glove's porous surface to create laminar (or smooth) air flow. Researchers believe that laminar flow conditions can reduce aerodynamic drag (friction) and contribute to reduced operating costs by improving fuel consumption and lowering aircraft weight. This Supersonic Laminar Flow Control (SLFC) experiment represents a collaborative effort between NASA and aerospace industry (specifically Boeing, Rockwell, and McDonnell Douglas), with Boeing assembling the panel and McDonnell Douglas designing the suction system.
A flight test of laminar flow control leading-edge systems
NASA Technical Reports Server (NTRS)
Fischer, M. C.; Wright, A. S., Jr.; Wagner, R. D.
1983-01-01
NASA's program for development of a laminar flow technology base for application to commercial transports has made significant progress since its inception in 1976. Current efforts are focused on development of practical reliable systems for the leading-edge region where the most difficult problems in applying laminar flow exist. Practical solutions to these problems will remove many concerns about the ultimate practicality of laminar flow. To address these issues, two contractors performed studies, conducted development tests, and designed and fabricated fully functional leading-edge test articles for installation on the NASA JetStar aircraft. Systems evaluation and performance testing will be conducted to thoroughly evaluate all system capabilities and characteristics. A simulated airline service flight test program will be performed to obtain the operational sensitivity, maintenance, and reliability data needed to establish that practical solutions exist for the difficult leading-edge area of a future commercial transport employing laminar flow control.
Study of Laminar Flow Forced Convection Heat Transfer Behavior of a Phase Change Material Fluid
Ravi, Gurunarayana
2010-01-14
The heat transfer behavior of phase change material fluid under laminar flow conditions in circular tubes and internally longitudinal finned tubes are presented in this study. Two types of boundary conditions, including ...
Laminar boundary layer in conditions of natural transition to turbulent flow
NASA Technical Reports Server (NTRS)
Polyakov, N. F.
1986-01-01
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.
Rheology of sediment transported by a laminar flow
M. Houssais; C. P. Ortiz; D. J. Durian; D. J. Jerolmack
2015-09-28
Understanding the dynamics of fluid-driven sediment transport remains challenging, as it is an intermediate region between a granular material and a fluid flow. Boyer \\textit{et al.}\\citep{Boyer2011} proposed a local rheology unifying dense dry-granular and viscous-suspension flows, but it has been validated only for neutrally-buoyant particles in a confined system. Here we generalize the Boyer \\textit{et al.}\\citep{Boyer2011} model to account for the weight of a particle by addition of a pressure $P_0$, and test the ability of this model to describe sediment transport in an idealized laboratory river. We subject a bed of settling plastic particles to a laminar-shear flow from above, and use Refractive-Index-Matching to track particles' motion and determine local rheology --- from the fluid-granular interface to deep in the granular bed. Data from all experiments collapse onto a single curve of friction $\\mu$ as a function of the viscous number $I_v$ over the range $10^{-5} \\leq I_v \\leq 1$, validating the local rheology model. For $I_v < 10^{-5}$, however, data do not collapse. Instead of undergoing a jamming transition with $\\mu \\rightarrow \\mu_s$ as expected, particles transition to a creeping regime where we observe a continuous decay of the friction coefficient $\\mu \\leq \\mu_s$ as $I_v$ decreases. The rheology of this creep regime cannot be described by the local model, and more work is needed to determine whether a non-local rheology model can be modified to account for our findings.
A perspective of laminar-flow control. [aircraft energy efficiency program
NASA Technical Reports Server (NTRS)
Braslow, A. L.; Muraca, R. J.
1978-01-01
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.
Laminar film flow phenomena-theory and application to the two-phase closed thermosyphon
R. I. Hirshburg
1980-01-01
The hydrodynamic and thermal characteristics of thin, laminar wavy-film flow are considered. A theoretical model is developed to predict the hydrodynamic features of asymptotic wavy-flow states. The mathematical closure question arising in asymptotic-state analysis satisfactorily resolved. The model accurately predicts published experimental data for mean film thickness, trough-to-crest dimension, wave clarity, and wavelength. The Nusselt theory for laminar film condensation
Development of laminar flow control wing surface composite structures
NASA Technical Reports Server (NTRS)
Lineberger, L. B.
1984-01-01
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.
Distributed acoustic receptivity in laminar flow control configurations
NASA Technical Reports Server (NTRS)
Choudhari, Meelan
1992-01-01
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.
Hydrodynamics and heat transfer for pulsating laminar flow in channels
NASA Astrophysics Data System (ADS)
Valueva, E. P.; Purdin, M. S.
2015-09-01
The problem about laminar pulsating flow and heat transfer with high pulsation amplitudes of average cross-section velocity in a round tube and in a flat channel is solved using the finite element method. The difference scheme's optimal parameters are determined. Data on the pulsation amplitude and phase are obtained for the hydraulic friction coefficient, tangential stress on the wall, liquid temperature, heat flux on the wall q w (at ?w = const), and wall temperature ?w (at q w = const) are obtained. Two characteristic modes, namely, quasi steady-state and high-frequency ones are separated based on the value of dimensionless pulsation frequency. During operation in the quasi steady-state mode, the values of all hydrodynamic and thermal quantities correspond to the values of time-average velocity at the given time instant. For operation in the high-frequency mode, it is shown that the dependences of the pulsating components of hydrodynamic and thermal quantities on the dimensionless pulsation frequency have the same pattern for rectilinear channels having different shapes of their cross section. It is found that certain nodal points exist on the distribution of thermal characteristics along the tube (liquid temperature, heat flux density on the wall at ?w = const, and wall temperature at q w = const) in which the values of these quantities remain unchanged. The distances between the nodal points decrease with increasing the pulsation frequency. The pulsations of thermal quantities decay over the tube length.
NASA Technical Reports Server (NTRS)
Srokowski, A. J.
1994-01-01
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.
An efficient algorithm for incompressible N-phase flows
Dong, S.
2014-11-01
We present an efficient algorithm within the phase field framework for simulating the motion of a mixture of N (N?2) immiscible incompressible fluids, with possibly very different physical properties such as densities, viscosities, and pairwise surface tensions. The algorithm employs a physical formulation for the N-phase system that honors the conservations of mass and momentum and the second law of thermodynamics. We present a method for uniquely determining the mixing energy density coefficients involved in the N-phase model based on the pairwise surface tensions among the N fluids. Our numerical algorithm has several attractive properties that make it computationally very efficient: (i) it has completely de-coupled the computations for different flow variables, and has also completely de-coupled the computations for the (N?1) phase field functions; (ii) the algorithm only requires the solution of linear algebraic systems after discretization, and no nonlinear algebraic solve is needed; (iii) for each flow variable the linear algebraic system involves only constant and time-independent coefficient matrices, which can be pre-computed during pre-processing, despite the variable density and variable viscosity of the N-phase mixture; (iv) within a time step the semi-discretized system involves only individual de-coupled Helmholtz-type (including Poisson) equations, despite the strongly-coupled phase–field system of fourth spatial order at the continuum level; (v) the algorithm is suitable for large density contrasts and large viscosity contrasts among the N fluids. Extensive numerical experiments have been presented for several problems involving multiple fluid phases, large density contrasts and large viscosity contrasts. In particular, we compare our simulations with the de Gennes theory, and demonstrate that our method produces physically accurate results for multiple fluid phases. We also demonstrate the significant and sometimes dramatic effects of the gravity, density ratios, pairwise surface tensions, and drop sizes on the N-phase configurations and dynamics. The numerical results show that the method developed herein is capable of dealing with N-phase systems with large density ratios, large viscosity ratios, and pairwise surface tensions, and that it can be a powerful tool for studying the interactions among multiple types of fluid interfaces.
Preconditioned solenoidal basis method for incompressible fluid flows
Wang, Xue
2006-04-12
) on Omega, (1.3) for any given u0, is usually prescribed and assumed to satisfy the incompressibility constraint, i.e., nabla? u0 = 0. The difficulties with the Navier-Stokes equations are the nonlinear terms u? nablau, and the incompressibility condition... defined parametrically using the element basis functions, xe(xi,eta) = 6summationdisplay i=1 ?ixei, ye(xi,eta) = 6summationdisplay i=1 ?iyei , (3.3) where (xei,yei ) are nodal coordinates defining Omegae. For the quadratic velocities, the basis functions...
McHugh, P.R.
1995-10-01
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.
Numerical methods for incompressible viscous flows with engineering applications
NASA Technical Reports Server (NTRS)
Rose, M. E.; Ash, R. L.
1988-01-01
A numerical scheme has been developed to solve the incompressible, 3-D Navier-Stokes equations using velocity-vorticity variables. This report summarizes the development of the numerical approximation schemes for the divergence and curl of the velocity vector fields and the development of compact schemes for handling boundary and initial boundary value problems.
The solution of the two-dimensional incompressible flow equations on unstructured triangular meshes
NASA Astrophysics Data System (ADS)
Williams, Morgan
1993-05-01
A numerical method for calculating two-dimensional turbulent incompressible flow on unstructured triangular meshes is developed. A primitive variable formulation is used. The Helmholtz pressure equation algorithm is used to enforce the velocity continuity relation for incompressible flow. A careful treatment of the pressure dissipation model is presented. A standard k-epsilon turbulence model with wall functions is used to provide closure for the governing equations. A backward-facing step turbulent flow is calculated using an unstructured triangular mesh, and the results are compared to experimental and computational data.
Hybrid laminar flow control tests in the Boeing Research Wind Tunnel
NASA Technical Reports Server (NTRS)
Parikh, P. G.; Lund, D. W.; George-Falvy, D.; Nagel, A. L.
1990-01-01
The hybrid laminar flow control (HLFC) concept has undergone wind tunnel testing at near full-scale Reynolds number on an infinite wing of 30-deg sweep on which boundary-layer suction was furnished over the first 20 percent of chord of the upper surface. Depending on the external pressure distribution, the HLFC extended the laminarity of the boundary layer as far back as 45 percent of chord; this corresponds to a transition Reynolds number of about 11 million. The maximum chordwise extent of laminar run was found to be insensitive to the suction level over a wide range.
Stokes flow in the presence of a planar interface covered with incompressible surfactant
Loewenberg, Michael
ARTICLES Stokes flow in the presence of a planar interface covered with incompressible surfactant The Lorentz solution for Stokes flow in the presence of a plane wall is generalized to a surfactant particle in the presence of the interface. The surfactant is insoluble and nondiffusing. The effects
A front-tracking method for viscous, incompressible, multi-fluid flows
Salih O. Unverdi; Gretar Tryggvason
1992-01-01
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
An Adaptive Level Set Approach For Incompressible Two-Phase Flows1 Mark Sussman
Frey, Pascal
An Adaptive Level Set Approach For Incompressible Two-Phase Flows1 Mark Sussman Department in Two Phase Flow Please send proofs to: Mark Sussman Department of Mathematics University of California, Davis Davis, CA 95616 Fax: 916-752-6635 Email: sussman@math.ucdavis.edu 2 #12;Abstract In Sussman
Incompressible SPH method for simulating Newtonian and non-Newtonian flows with a free surface
NASA Astrophysics Data System (ADS)
Shao, Songdong; Lo, Edmond Y. M.
An incompressible smoothed particle hydrodynamics (SPH) method is presented to simulate Newtonian and non-Newtonian flows with free surfaces. The basic equations solved are the incompressible mass conservation and Navier-Stokes equations. The method uses prediction-correction fractional steps with the temporal velocity field integrated forward in time without enforcing incompressibility in the prediction step. The resulting deviation of particle density is then implicitly projected onto a divergence-free space to satisfy incompressibility through a pressure Poisson equation derived from an approximate pressure projection. Various SPH formulations are employed in the discretization of the relevant gradient, divergence and Laplacian terms. Free surfaces are identified by the particles whose density is below a set point. Wall boundaries are represented by particles whose positions are fixed. The SPH formulation is also extended to non-Newtonian flows and demonstrated using the Cross rheological model. The incompressible SPH method is tested by typical 2-D dam-break problems in which both water and fluid mud are considered. The computations are in good agreement with available experimental data. The different flow features between Newtonian and non-Newtonian flows after the dam-break are discussed.
Front Speed Enhancement by Incompressible Flows in Three or Higher Dimensions
NASA Astrophysics Data System (ADS)
El Smaily, Mohammad; Kirsch, Stéphane
2014-07-01
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.
NASA Technical Reports Server (NTRS)
Goodyear, M. D.
1987-01-01
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.
Viscosity induced non-uniform flow in laminar flow heat exchangers
NASA Astrophysics Data System (ADS)
Putnam, G. R.; Rohsenow, W. M.
1985-05-01
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.
Multi-material incompressible flow simulation using the moment-of-fluid method
Garimella, R V [Los Alamos National Laboratory; Schofield, S P [Los Alamos National Laboratory; Lowrie, R B [Los Alamos National Laboratory; Swartz, B K [Los Alamos National Laboratory; Christon, M A [SIMULIA; Dyadechko, V [EXXON-MOBIL
2009-01-01
The Moment-of-Fluid interface reconstruction technique is implemented in a second order accurate, unstructured finite element variable density incompressible Navier-Stokes solver. For flows with multiple materials, MOF significantly outperforms existing first and second order interface reconstruction techniques. For two material flows, the performance of MOF is similar to other interface reconstruction techniques. For strongly driven bouyant flows, the errors in the flow solution dominate and all the interface reconstruction techniques perform similarly.
Method and apparatus for detecting laminar flow separation and reattachment
NASA Technical Reports Server (NTRS)
Stack, John P. (inventor); Mangalam, Sivaramakrishnan M. (inventor)
1990-01-01
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.
Local experimental heat transfer of single-phase pulsating laminar flow in a square mini-channel
Khandekar, Sameer
Local experimental heat transfer of single-phase pulsating laminar flow in a square mini in revised form 1 January 2015 Accepted 4 January 2015 Available online Keywords: Mini-channels Pulsating a single-phase laminar internal convective flow with a particular pulsating flow frequency alters
A History of Suction-Type Laminar Flow Control with Emphasis on Flight Research
NASA Technical Reports Server (NTRS)
Braslow, Albert L.
1999-01-01
Laminar-flow control is an area of aeronautical research that has a long history at NASA's Langley Research Center, Dryden Flight Research Center, their predecessor organizations, and elsewhere. In this monograph, the author, who spent much of his career at Langley working with this research, presents a history of that portion of laminar-flow technology known as active laminar-flow control, which employs suction of a small quantity of air through airplane surfaces. This important technique offers the potential for significant reduction in drag and, thereby, for large increases in range or reductions in fuel usage for aircraft. For transport aircraft, the reductions in fuel consumed as a result of laminar-flow control may equal 30 percent of present consumption. Given such potential, it is obvious that active laminar-flow control with suction is an important technology. In this study, the author covers the early history of the subject and brings the story all the way to the mid-1990s with an emphasis on flight research, much of which has occurred at Dryden. This is an important monograph that not only encapsulates a lot of history in a brief compass but also does so in language that is accessible to non-technical readers. NASA is publishing it in a format that will enable it to reach the wide audience the subject deserves.
Boundary-Layer Transition Results from the F-16XL-2 Supersonic Laminar Flow Control Experiment
NASA Technical Reports Server (NTRS)
Marshall, Laurie A.
1999-01-01
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.
Shen, Jie
DECOUPLED ENERGY STABLE SCHEMES FOR A PHASE-FIELD MODEL OF TWO-PHASE INCOMPRESSIBLE FLOWS approximations of two-phase incompressible flows with different densities and viscosities. We present a variational derivation for a thermodynami- cally consistent phase-field model that admits an energy law. Two
A comparison of two incompressible Navier-Stokes algorithms for unsteady internal flow
NASA Technical Reports Server (NTRS)
Wiltberger, N. Lyn; Rogers, Stuart E.; Kwak, Dochan
1993-01-01
A comparative study of two different incompressible Navier-Stokes algorithms for solving an unsteady, incompressible, internal flow problem is performed. The first algorithm uses an artificial compressibility method coupled with upwind differencing and a line relaxation scheme. The second algorithm uses a fractional step method with a staggered grid, finite volume approach. Unsteady, viscous, incompressible, internal flow through a channel with a constriction is computed using the first algorithm. A grid resolution study and parameter studies on the artificial compressibility coefficient and the maximum allowable residual of the continuity equation are performed. The periodicity of the solution is examined and several periodic data sets are generated using the first algorithm. These computational results are compared with previously published results computed using the second algorithm and experimental data.
Felderhof, B U
2015-01-01
A mechanical model of swimming and flying in an incompressible viscous fluid is studied on the basis of assumed equations of motion. The system is modeled as an assembly of rigid spheres subject to elastic direct interactions and to periodic actuating forces which sum to zero. Hydrodynamic interactions are taken into account in the virtual mass matrix and in the friction matrix of the assembly. An equation of motion is derived for the velocity of the geometric center of the assembly. The mean power is calculated as the sum of the mean rate of dissipation and a mean energy loss which is related to the rate of change of the virtual mass. The full range of viscosity is covered, so that the theory can be applied to the flying of birds, as well as to the swimming of fish or bacteria. As an example a system of three equal spheres moving along a common axis is studied.
Bubble transport in three-dimensional laminar gravity-driven flow mathematical formulation
Pilon, Laurent
Bubble transport in three-dimensional laminar gravity-driven flow mathematical formulation This paper presents a complete set of coupled equations that govern the bubble transport in three-dimensional gravity-driven flow. The model accounts for bubble growth or shrinkage due to pressure and temperature
Bubble transport in three-dimensional laminar gravity-driven flow numerical results
Pilon, Laurent
Bubble transport in three-dimensional laminar gravity-driven flow numerical results Laurent Pilon is the second part of a study on bubble transport, growth and shrinkage in three-dimensional gravity driven flow equation is solved for the bubble density function using the backward method of characteristics. The zeroth
Air-Breathing Laminar Flow-Based Direct Methanol Fuel Cell with Alkaline Electrolyte
Kenis, Paul J. A.
Air-Breathing Laminar Flow-Based Direct Methanol Fuel Cell with Alkaline Electrolyte Ranga S flow-based fuel cell LFFC operated in alkaline and acidic media. These direct methanol fuel cells are focused on the development and miniaturization of promising fuel cell technologies, including direct
Heat transfer in laminar tube flow of beef cattle manure slurries
Chen, Y.R.
1986-01-01
This report describes a concentric-tube heat exchanger and presents the preliminary results of the study of the heat transfer characteristics of the beef cattle manure slurries flowing in laminar region in the inner pipe of the concentric tube heat exchanger with hot water flowing concurrently in the annual space and serving as a heat source.
Determination of kinetic parameters in laminar flow reactors. I. Theoretical aspects
Determination of kinetic parameters in laminar flow reactors. I. Theoretical aspects T. Carraro1- mization of chemical flow reactors. The goal is the reliable determination of unknown kinetic parameters. The underlying mathematical model is the full set of the compressible Navier-Stokes equations accompanied
On projected NewtonKrylov solvers for instationary laminar reacting gas flows
Vuik, Kees
methods Laminar reacting flows Chemical vapor deposition a b s t r a c t Numerical aspects of computational modeling of chemical vapor deposition are discussed. Large sparse strongly nonlinear algebraic deposition (CVD) [8] and flows with combustion [19] requires the simultaneous solution of many strongly
Investigation of Flow Maldistribution in a Concentric-Tube, Counterflow, Laminar Heat Exchanger
E. B. RATTS
1998-01-01
An analysis is made to quantify the effect of flow maldistribution on the performance of a laminar, counterflow, high-effectiveness heat exchanger. An investigation of the ability of thermally connected fins in one passage (screen mesh) to correct the uneven heat transfer distribution from the maldistributed mass flow in the other passage is made. A heat transfer model is developed for
Low-Disturbance Flow Characteristics of the NASA-Ames Laminar Flow Supersonic Wind Tunnel
NASA Technical Reports Server (NTRS)
Wolf, Stephen W. D.; Laub, James A.; Davis, Sanford S. (Technical Monitor)
1994-01-01
A unique, low-disturbance (quiet) supersonic wind tunnel has been commissioned at the NASA-Ames Fluid Mechanics Laboratory (FML) to support Supersonic Laminar Flow Control (SLFC) research. Known as the Laminar Flow Supersonic Wind Tunnel (LFSWT), this tunnel is designed to operate at potential cruise Mach numbers and unit Reynolds numbers (Re) of the High Speed Civil Transport (HSCT). The need to better understand the receptivity of the transition phenomena on swept (HSCT) wings to attachment-line contamination and cross-flows has provided the impetus for building the LFSWT. Low-disturbance or "quiet" wind tunnels are known to be an essential part of any meaningful boundary layer transition research. In particular, the receptivity of supersonic boundary layers to wind tunnel disturbances can significantly alter the transition phenomena under investigation on a test model. Consequently, considerable effort has gone into the design of the LFSWT to provide quiet flow. The paper describes efforts to quantify the low-disturbance flows in the LFSWT operating at Mach 1.6, as a precursor to transition research on wing models. The research includes: (1) Flow measurements in both the test section and settling chamber of the LFSWT, using a full range of measurement techniques; (2) Study of the state of the test section boundary layer so far by using a single hot-wire mounted above the floor centerline, with and without boundary layer trips fitted at the test section entrance; (3) The effect of flow quality of unsteady supersonic diffuser flow, joint steps and gaps, and wall vibration.
NASA Technical Reports Server (NTRS)
Eckert, E R; Livingood, John N B
1953-01-01
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.
Summary of Transition Results From the F-16XL-2 Supersonic Laminar Flow Control Experiment
NASA Technical Reports Server (NTRS)
Marshall, Laurie A.
2000-01-01
A variable-porosity suction glove has been flown on the F-16XL-2 aircraft to demonstrate the feasibility of this technology for the proposed High-Speed Civil Transport. Boundary-layer transition data on the titanium glove primarily have been obtained at speeds of Mach 2.0 and altitudes of 15,240-16,764 m (50,000-55,000 ft). The objectives of this flight experiment have been to achieve 0.50-0.60 chord laminar flow on a highly swept wing at supersonic speeds and to provide data to validate codes and suction design. The most successful laminar flow results have not been obtained at the glove design point, a speed of Mach 1.9 at an altitude of 15,240 m (50,000 ft); but rather at a speed of Mach 2.0 and an altitude of 16,154 m (53,000 ft). Laminar flow has been obtained to more than 0.46 wing chord at a Reynolds number of 22.7 x 10(exp 6). A turbulence diverter has been used to initially obtain a laminar boundary layer at the attachment line. A lower-surface shock fence was required to block an inlet shock from the wing leading edge. This paper discusses research variables that directly impact the ability to obtain laminar flow and techniques to correct for these variables.
Parametric study on laminar flow for finite wings at supersonic speeds
NASA Technical Reports Server (NTRS)
Garcia, Joseph Avila
1994-01-01
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.
Program of Research in Laminar Flow Control in the JIAFS at NASA Langley Research Center
NASA Technical Reports Server (NTRS)
Pfenninger, W.
1981-01-01
At high Reynolds numbers, the performance of a low drag suction LFC airplane is essentially controlled by the induced drag and the turbulent friction drag of the nonlaminarized area. The question then arises as to how the airplane cruise lift to drag ratio (L/D) sub cruise) cruise increases with increasing extent of laminar flow 0 sub lam./0 sub total (0 = airplane wetted area). In particular, the question arises as to the airplane performance in the optimum case with all laminar flow over the airplane wetted area. Design approaches of all laminar flow LFC airplanes which optimize the airplane range . R = eta sub ov times (L/D) times H times lambda n(W sub 0/W sub E) are considered.
NASA Technical Reports Server (NTRS)
1999-01-01
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.
Flight investigation of natural laminar flow on the Bellanca Skyrocket II
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Obara, C. J.; Gregorek, G. M.; Hoffman, M. J.; Freuhler, R. J.
1983-01-01
Two major concerns have inhibited the use of natural laminar flow (NLF) for viscous drag reduction on production aircraft. These are the concerns of achieveability of NLF on practical airframe surfaces, and maintainability in operating environments. Previous research in this area left a mixture of positive and negative conclusions regarding these concerns. While early (pre-1950) airframe construction methods could not achieve NLF criteria for waviness, several modern construction methods (composites for example) can achieve the required smoothness. This paper presents flight experiment data on the achieveability and maintainability of NLF on a high-performance, single-propeller, composite airplane, the Bellanca Skyrocket II. The significant contribution of laminar flow to the performance of this airplane was measured. Observations of laminar flow in the propeller slipstream are discussed, as are the effects of insect contamination on the wing. These observations have resulted in a new appreciation of the operational feasibility for achieving and maintaining NLF on modern airframe surfaces.
An approach to the constrained design of natural laminar flow airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford Earl
1995-01-01
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.
Natural Laminar-Flow blades for vertical-axis wind turbines
Klimas, P.C.
1982-01-01
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)
NASA Technical Reports Server (NTRS)
Wornom, S. F.
1971-01-01
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.
Numerical simulation of the incompressible internal flow through a tilting disk valve
NASA Technical Reports Server (NTRS)
Chang, I-Dee; Rogers, Stuart E.; Kwak, Dochan; Kiris, Cetin
1990-01-01
A numerical simulation of the incompressible viscous flow through a prosthetic tilting disk heart valve is presented in order to demonstrate the current capability to model unsteady flows with moving boundaries. Both steady and unsteady flow calculations are performed by solving the incompressible Navier-Stokes equations in three-dimensional generalized curvilinear coordinates. In order to handle the moving boundary problems, the chimera grid embedding scheme which decomposes a complex computational domain into several simple subdomains is used. An algebraic turbulence model for internal flows is incorporated to reach the physiological values of Reynolds number. Good agreement is obtained between the numerical results and experimental measurements. It is found that the tilting disk valve causes large regions of separated flow, and regions of high shear.
a Level Set Approach for Computing Solutions to Incompressible Two-Phase Flow
Mark Sussman; Peter Smereka; Stanley Osher
1994-01-01
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.
Olshanskii, Maxim A.
with surface tension Kirill D. Nikitin Maxim A. Olshanskii Kirill M. Terekhov Yuri V. VassilevskiÂ§ Abstract to surface tension forces. The method splits one time step into a semi-Lagrangian treatment of the surface models a free surface flow of viscous incompressible fluid subject to surface tension forces. Further
NASA Astrophysics Data System (ADS)
Khater, A. H.; Callebaut, D. K.; Abdelhameed, T. N.; Hady, A.
In this paper, we apply the general theory of Arnold (1965, 1966) and Moffatt et al. (1997). We search sufficient conditions for the linear stability of steady three-dimensional incompressible gravitating flows in ideal magnetohydrodynamics (MHD). The results suggest that the solar and the stellar convection zones must be sensitive to the density stratification.
A sharp interface method for incompressible two-phase flows M. Sussman *,1
Frey, Pascal
A sharp interface method for incompressible two-phase flows M. Sussman *,1 , K.M. Smith, M is an extension of the sec- ond-order method presented by Sussman [M. Sussman, A second order coupled levelset.06.020 * Corresponding author. Tel.: +1 850 644 7194; fax: +1 850 644 4053. E-mail address: sussman@math.fsu.edu (M
NASA Technical Reports Server (NTRS)
Kiris, Cetin
1995-01-01
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.
Simulation of Homogeneous and Incompressible Cinlar Flows Mine Ca~glar
Caglar, Mine
Simulation of Homogeneous and Incompressible Cinlar Flows Mine Ca~glar Princeton University is the solution of the ordinary di erential equation d dt Xt = uXt;t X0 = x : 4 Our aim is to simulate a variety- teristics of ows in several regions of ocean.4 The positions of current following surface drifters, xed
A versatile sharp interface immersed boundary method for incompressible flows with complex; Immersed boundary method; Ghost-cell; Body non-conformal grid methods 1. Introduction Immersed boundary-interpolation errors. Immersed boundary methods can broadly be characterized under two categories [34]; first
On the Rayleigh-Taylor instability for incompressible, inviscid magnetohydrodynamic flows
On the Rayleigh-Taylor instability for incompressible, inviscid magnetohydrodynamic flows Ran Duana magneto- hydrodynamic (MHD) fluids with zero resistivity, evolving with a free interface in the presence-linear problem in some sense. Keywords: Rayleigh-Taylor instability, MHD, ill-posedness, Hadamard sense. 1
Start of fluidization of a bulk granular material in laminar flow
Rozhdestvenskii, O.I.; Bednyakov, G.E.; Zayats, E.I.; Kirillov, I.N.; Serebryakova, T.V.
1982-04-20
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.
NASA Technical Reports Server (NTRS)
Manuel, Gregory S.; Doty, Wayne A.
1990-01-01
A modified T210R general aviation aircraft incorporating natural laminar flow (NLF) technology has been subjected to flight tests in order to evaluate its stability and control characteristics. Attention is given to this aircraft's ability to meet certification requirements with significant NLF, as well as with the boundary-layer transition fixed near the leading edge. It is established that the large regions of NLF achieved yielded a significant cruise performance enhancement; loss of laminar flow did not result in significant changes in the stability and control characteristics of the aircraft. FAR Part 23 certification requirements were met.
Ford, Ian
The laminar flow tube reactor as a quantitative tool for nucleation studies: Experimental results, United Kingdom Received 24 March 2000; accepted 2 June 2000 A laminar flow tube reactor was designed boundary conditions on the reactor walls, accuracy of the calculations of the thermodynamic parameters
Manufacturing all-polymer laminar flow-based fuel cells A.S. Hollinger, P.J.A. Kenis*
Kenis, Paul J. A.
Manufacturing all-polymer laminar flow-based fuel cells A.S. Hollinger, P.J.A. Kenis* Department, Urbana, IL 61801, USA h i g h l i g h t s Manufactured a lightweight, all-polymer direct methanol April 2013 Keywords: Manufacturing Polymer Laminar flow Microfluidic Fuel cell Stack a b s t r a c
An approach to aerodynamic sound prediction based on incompressible-flow pressure
NASA Astrophysics Data System (ADS)
Martínez-Lera, P.; Schram, C.; Bériot, H.; Hallez, R.
2014-01-01
Curle's analogy provides a solution to Lighthill's equation to predict flow-generated sound in the presence of rigid boundaries. Nevertheless, Curle's solution requires the flow pressure, including its acoustic component, to be known in the source region. If the pressure corresponds to an incompressible-flow description instead and the surface is not acoustically compact, significant errors can arise in the acoustic prediction. In this work, it is argued that flow wall pressure can be used to define appropriate boundary conditions of an equivalent acoustic boundary value problem for an arbitrary geometry, and a formulation of a boundary condition based on incompressible-flow pressure is proposed. The theoretical analysis suggests that if the flow is incompressible, the error has the leading order of a dipole plus a quadrupole for Curle's analogy and of just a quadrupole for the proposed alternative approach, thus making the latter more accurate when dipole sources are dominant. A numerical test case is presented as a proof of concept, consisting of a trailing edge noise problem due to the flow past a slender body.
Incompressible viscous flow computations for the pump components and the artificial heart
NASA Technical Reports Server (NTRS)
Kiris, Cetin
1992-01-01
A finite-difference, three-dimensional incompressible Navier-Stokes formulation to calculate the flow through turbopump components is utilized. The solution method is based on the pseudocompressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. Both steady and unsteady flow calculations can be performed using the current algorithm. In this work, the equations are solved in steadily rotating reference frames by using the steady-state formulation in order to simulate the flow through a turbopump inducer. Eddy viscosity is computed by using an algebraic mixing-length turbulence model. Numerical results are compared with experimental measurements and a good agreement is found between the two. Included in the appendix is a paper on incompressible viscous flow through artificial heart devices with moving boundaries. Time-accurate calculations, such as impeller and diffusor interaction, will be reported in future work.
Feasibility and benefits of laminar flow control on supersonic cruise airplanes
NASA Technical Reports Server (NTRS)
Powell, A. G.; Agrawal, S.; Lacey, T. R.
1989-01-01
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.
Spraying Powder Materials by the High-Enthalpy Laminar Plasma Flow
Khutsishvili, M.; Kikvadze, L.
2008-03-19
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.
DRE-Enhanced Swept-Wing Natural Laminar Flow at High Reynolds Numbers
NASA Technical Reports Server (NTRS)
Malik, Mujeeb; Liao, Wei; Li, Fe; Choudhari, Meelan
2013-01-01
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.
Biomimetic structures for fluid drag reduction in laminar and turbulent flows.
Jung, Yong Chae; Bhushan, Bharat
2010-01-27
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. PMID:21386280
Biomimetic structures for fluid drag reduction in laminar and turbulent flows
NASA Astrophysics Data System (ADS)
Jung, Yong Chae; Bhushan, Bharat
2010-01-01
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.
On a modification of GLS stabilized FEM for solving incompressible viscous flows
NASA Astrophysics Data System (ADS)
Burda, P.; Novotný, J.; Ístek, J.
2006-07-01
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.
Chung, B.T.F.; Hsia, R.P.
1994-10-01
Hydrodynamically developed and thermally developing laminar incompressible forced-convective flow in ducts containing twisted-tape inserts is analyzed. The flow is subjected to either uniform temperature or uniform heat flux on the curved duct surface, and the straight duct surfaces are insulated. The heat input into the fluid is only from the curved duct surface and is uniform axially. The thermal properties are assumed constant; the axial conduction and viscous dissipation are negligibly small. Numerical calculations of the temperature field and Nusselt number march forward axially in the thermal entrance region. The solutions of the developing temperature field as well as the heat transfer coefficient are presented as functions of axial distance for different opening angles of sector. Comparisons are made between computed results and some analytical and numerical findings reported in the literature. In all cases, satisfactory comparisons are attained.
Croze, Ottavio A; Sardina, Gaetano; Ahmed, Mansoor; Bees, Martin A; Brandt, Luca
2013-04-01
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
NASA Technical Reports Server (NTRS)
Meyer, J. S.; Kosovich, J.
1973-01-01
An anesthetic gas flow pop-off valve canister is described that is airtight and permits the patient to breath freely. Once its release mechanism is activated, the exhaust gases are collected at a hose adapter and passed through activated coal for adsorption. A survey of laminar air flow clean rooms is presented and the installation of laminar cross flow air systems in operating rooms is recommended. Laminar flow ventilation experiments determine drying period evaporation rates for chicken intestines, sponges, and sections of pig stomach.
NASA Technical Reports Server (NTRS)
Albers, J. A.; Gregg, J. L.
1974-01-01
A finite-difference program is described for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain the factors of arbitrary Reynolds number, free-stream Mach number, free-stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile.
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,...
Technology Transfer Automated Retrieval System (TEKTRAN)
Little research has been conducted to investigate fate and transport of colloids in surface vegetation in overland flow under unfavorable chemical conditions. In this work, single collector attachment efficiency (a) of colloid capture by a simulated plant stem (i.e. cylindrical collector) in laminar...
Design of a Slotted, Natural-Laminar-Flow Airfoil for Business-Jet Applications
NASA Technical Reports Server (NTRS)
Somers, Dan M.
2012-01-01
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.
NASA Technical Reports Server (NTRS)
Irani, E.; Snyder, M. H.
1988-01-01
An averaging total pressure wake rake used by the Cessna Aircraft Company in flight tests of a modified 210 airplane with a laminar flow wing was calibrated in wind tunnel tests against a five-tube pressure probe. The model generating the wake was a full-scale model of the Cessna airplane wing. Indications of drag trends were the same for both instruments.
Testing of laminar flow, HEPA filter, clean installations at Mount Facility
Mielke
1981-01-01
The essentials needed to operate and maintain a good laminar flow, HEPA filter, clean room program are: testing and certification of the clean enclosures, operations correctly placed within the clean enclosures, and people awareness of clean enclosure procedures. The methods used for the testing and certification program of clean enclosures (clean benches and clean rooms) at Mound Facility are described.
Magnetic filtration of particles in laminar flow through a bed of spheres
C. Moyer; M. Natenapit; Sigurds Arajs
1984-01-01
We present a theory for the capture of magnetic particles by a bed of spheres in HGMS. The laminar approximation to fluid flow is used in conjunction with the free surface condition (Happel's model) to obtain the fluid velocity profile near a representative collector sphere in the assemblage. An effective medium treatment is used to model the magnetic field, thus
An analytical approach to fully developed heating of laminar flows in circular pipes
Piva, S.
1995-11-01
An analytical solution is proposed to predict the fully developed Nusselt number for laminar flow in circular pipes, as arising from exponential heating. The solution is obtained in terms of Confluent Hypergeometric Functions, characterized by fast convergence and easy implementation. Both positive and negative exponents are considered. The range of practical interest is discussed.
Performance of laminar-flow leading-edge test articles in cloud encounters
NASA Technical Reports Server (NTRS)
Davis, Richard E.; Maddalon, Dal V.; Wagner, Richard D.
1987-01-01
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.
Polymer Brushes Patterned with Micrometer-Scale Chemical Gradients Using Laminar Co-Flow
Braun, Paul
a diffusion-driven concentration gradient, and thus a gradient in reaction rate at the interface of the two miscible laminar flow streams becomes a diffusion-driven gradient in concentration. This well-defined concentration gradient has been used as is to generate a temporary dynamic physicochemical gradient, for example
EXPERIMENTS WITH HEAVY GAS JETS IN LAMINAR AND TURBULENT CROSS-FLOWS
A wind tunnel study was performed to determine the dispersion characteristics of gas jets with densities heavier than that of air. he experiments were done in a laminar cross-flow and then repeated in a turbulent boundary layer. ll major boundary-layer characteristics were measur...
Analysis of Thermal Dispersion in an Array of Parallel Plates with Fully-Developed Laminar Flow
Fleck, Norman A.
basic heat transfer problems are addressed, each for steady fully-developed laminar fluid flow: (a, m Greek letters ratio of solid to fluid molecular conductivity, s fk k = structure porosity, 2 2 H such as packed beds, cellular foams and lattice materials have complex geometries, making an accurate evaluation
Laminar and turbulent nozzle-jet flows and their acoustic near-field
NASA Astrophysics Data System (ADS)
Bühler, Stefan; Obrist, Dominik; Kleiser, Leonhard
2014-08-01
We investigate numerically the effects of nozzle-exit flow conditions on the jet-flow development and the near-field sound at a diameter-based Reynolds number of ReD = 18 100 and Mach number Ma = 0.9. Our computational setup features the inclusion of a cylindrical nozzle which allows to establish a physical nozzle-exit flow and therefore well-defined initial jet-flow conditions. Within the nozzle, the flow is modeled by a potential flow core and a laminar, transitional, or developing turbulent boundary layer. The goal is to document and to compare the effects of the different jet inflows on the jet flow development and the sound radiation. For laminar and transitional boundary layers, transition to turbulence in the jet shear layer is governed by the development of Kelvin-Helmholtz instabilities. With the turbulent nozzle boundary layer, the jet flow development is characterized by a rapid changeover to a turbulent free shear layer within about one nozzle diameter. Sound pressure levels are strongly enhanced for laminar and transitional exit conditions compared to the turbulent case. However, a frequency and frequency-wavenumber analysis of the near-field pressure indicates that the dominant sound radiation characteristics remain largely unaffected. By applying a recently developed scaling procedure, we obtain a close match of the scaled near-field sound spectra for all nozzle-exit turbulence levels and also a reasonable agreement with experimental far-field data.
Laminar and turbulent nozzle-jet flows and their acoustic near-field
Bühler, Stefan; Obrist, Dominik; Kleiser, Leonhard
2014-08-15
We investigate numerically the effects of nozzle-exit flow conditions on the jet-flow development and the near-field sound at a diameter-based Reynolds number of Re{sub D} = 18?100 and Mach number Ma = 0.9. Our computational setup features the inclusion of a cylindrical nozzle which allows to establish a physical nozzle-exit flow and therefore well-defined initial jet-flow conditions. Within the nozzle, the flow is modeled by a potential flow core and a laminar, transitional, or developing turbulent boundary layer. The goal is to document and to compare the effects of the different jet inflows on the jet flow development and the sound radiation. For laminar and transitional boundary layers, transition to turbulence in the jet shear layer is governed by the development of Kelvin-Helmholtz instabilities. With the turbulent nozzle boundary layer, the jet flow development is characterized by a rapid changeover to a turbulent free shear layer within about one nozzle diameter. Sound pressure levels are strongly enhanced for laminar and transitional exit conditions compared to the turbulent case. However, a frequency and frequency-wavenumber analysis of the near-field pressure indicates that the dominant sound radiation characteristics remain largely unaffected. By applying a recently developed scaling procedure, we obtain a close match of the scaled near-field sound spectra for all nozzle-exit turbulence levels and also a reasonable agreement with experimental far-field data.
NASA Technical Reports Server (NTRS)
Beatty, T. D.
1975-01-01
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.
PHYSICS REQUIRES A SIMPLE LOW MACH NUMBER FLOW TO BE COMPRESSIBLE
Radial, laminar, plane, low velocity flow represents the simplest, non-linear fluid dynamics problem. Ostensibly this apparently trivial flow could be solved using the incompressible Navier-Stokes equations, universally believed to be adequate for such problems. Most researchers ...
Numerical fluid mechanics - Incompressible flows with complex boundaries
NASA Astrophysics Data System (ADS)
Schoenung, Bernhard E.
An overview is presented of the state of the art in flow mechanical calculative methods which use geometrical coordinates. The topics addressed include: flow mechanical partial differential equations, behavioral equations, numerical methods for solving Navier-Stokes equations, discretization of the region to be calculated, ordering of variables, discretization of differential equations, coupled and uncoupled calculative methods, solution of algebraic systems of equations, 3D calculative methods for general curved coordinates, examples of 2D and 3D flow calculations.
Analysis and evaluation of an integrated laminar flow control propulsion system
NASA Technical Reports Server (NTRS)
Keith, Theo G., Jr.; Dewitt, Kenneth J.
1993-01-01
Reduction of drag has been a major goal of the aircraft industry as no other single quantity influences the operating costs of transport aircraft more than aerodynamic drag. It has been estimated that even modest reduction of frictional drag could reduce fuel costs by anywhere from 2 to 5 percent. Current research on boundary layer drag reduction deals with various approaches to reduce turbulent skin friction drag as a means of improving aircraft performance. One of the techniques belonging to this category is laminar flow control in which extensive regions of laminar flow are maintained over aircraft surfaces by delaying transition to turbulence through the ingestion of boundary layer air. While problems of laminar flow control have been studied in some detail, the prospect of improving the propulsion system of an aircraft by the use of ingested boundary layer air has received very little attention. An initial study for the purpose of reducing propulsion system requirements by utilizing the kinetic energy of boundary layer air was performed in the mid-1970's at LeRC. This study which was based on ingesting the boundary layer air at a single location, did not yield any significant overall propulsion benefits; therefore, the concept was not pursued further. However, since then it has been proposed that if the boundary layer air were ingested at various locations on the aircraft surface instead of just at one site, an improvement in the propulsion system might be realized. The present report provides a review of laminar flow control by suction and focuses on the problems of reducing skin friction drag by maintaining extensive regions of laminar flow over the aircraft surfaces. In addition, it includes an evaluation of an aircraft propulsion system that is augmented by ingested boundary layer air.
Formation of a laminar electron flow for 300 GHz high-power pulsed gyrotron
Yamaguchi, Yuusuke; Tatematsu, Yoshinori; Saito, Teruo; Ikeda, Ryosuke; Mudiganti, Jagadish C.; Ogawa, Isamu; Idehara, Toshitaka [Research Center for Development of Far-Infrared Region, University of Fukui, 3-9-1 Bunkyo, Fukui-shi 910-8507 (Japan)
2012-11-15
This paper describes the design of a triode magnetron injection gun for use in a 200 kW, 300 GHz gyrotron. As power and frequency increase, the performance of the gyrotron becomes quite sensitive to the quality of the electron beam. Formation of a laminar electron flow is essential for the realization of a high quality beam with a small velocity spread. In this study, a new method is developed for a quantitative evaluation of the laminarity and is applied to optimize the electrode design. The laminarity depends not only on conventional design parameters such as the cathode slant angle but also on the spatial distribution of the electric field along the beam trajectory. In the optimized design, the velocity pitch factors, {alpha}, larger than 1.2 are obtained at 65 kV, 10 A with spreads, {Delta}{alpha}, less than 5%.
NASA Astrophysics Data System (ADS)
Maynes, D.; Jeffs, K.; Woolford, B.; Webb, B. W.
2007-09-01
This paper reports results of an analytical and experimental investigation of the laminar flow in a parallel-plate microchannel with ultrahydrophobic top and bottom walls. The walls are fabricated with microribs and cavities that are oriented parallel to the flow direction. The channel walls are modeled in an idealized fashion, with the shape of the liquid-vapor meniscus approximated as flat. An analytical model of the vapor cavity flow is employed and coupled with a numerical model of the liquid flow by matching the local liquid and vapor phase velocity and shear stress at the interface. The numerical predictions show that the effective slip length and the reduction in the classical friction factor-Reynolds number product increase with increasing relative cavity width, increasing relative cavity depth, and decreasing relative microrib/cavity module length. Comparisons were also made between the zero shear interface model and the liquid-vapor cavity coupled model. The results illustrate that the zero shear interface model underpredicts the overall flow resistance. Further, the deviation between the two models was found to be significantly larger for increasing values of both the relative rib/cavity module width and the cavity fraction. The trends in the frictional pressure drop predictions are in good agreement with experimental measurements made at similar conditions, with greater deviation observed at increasing size of the cavity fraction. Based on the numerical predictions, an expression is proposed in which the friction factor-Reynolds number product may be estimated in terms of the important variables.
FORMATION OF ROLL WAVES IN LAMINAR SHEET FLOW
Julien, Pierre Y.
number critical Froude number gravitational acceleration uniform flow depth flow depth for flow sheet flow characteristics . 3 2.2 Critical Froude number and Vedernikov criteria . 4 2.3 Distance . . . . . . . . . . . . . . . . . . . . . . 14 3.3.1 Wavelength, period and celerity . . . . . . . . . . 14 3 . 3 . 2 Critical distance
Response of hot element flush wall gauges in oscillating laminar flow
NASA Technical Reports Server (NTRS)
Giddings, T. A.; Cook, W. J.
1986-01-01
The time dependent response characteristics of flush-mounted hot element gauges used as instruments to measure wall shear stress in unsteady periodic air flows were investigated. The study was initiated because anomalous results were obtained from the gauges in oscillating turbulent flows for the phase relation of the wall shear stress variation, indicating possible gauge response problems. Flat plate laminar oscillating turbulent flows characterized by a mean free stream velocity with a superposed sinusoidal variation were performed. Laminar rather than turbulent flows were studied, because a numerical solution for the phase angle between the free stream velocity and the wall shear stress variation that is known to be correct can be obtained. The focus is on comparing the phase angle indicated by the hot element gauges with corresponding numerical prediction for the phase angle, since agreement would indicate that the hot element gauges faithfully follow the true wall shear stress variation.
Correlation of Water Frost Porosity in Laminar Flow over Flat Surfaces
NASA Technical Reports Server (NTRS)
Kandula, Max
2011-01-01
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.
Higher-Order Compact Schemes for Numerical Simulation of Incompressible Flows
NASA Technical Reports Server (NTRS)
Wilson, Robert V.; Demuren, Ayodeji O.; Carpenter, Mark
1998-01-01
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.
Scaling laws for drag of a compliant body in an incompressible viscous flow
NASA Astrophysics Data System (ADS)
Zhu, Luoding
Motivated by an important discovery on the drag scaling law (the 4/3 power law) of a flexible fibre in a flowing soap film by Alben et al. (Nature vol. 420, 2002, p.479) at high Reynolds numbers (2000
Multigrid Computations of 3-D Incompressible Internal and External Viscous Rotating Flows
NASA Technical Reports Server (NTRS)
Sheng, Chunhua; Taylor, Lafayette K.; Chen, Jen-Ping; Jiang, Min-Yee; Whitfield, David L.
1996-01-01
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.
Eddy-resolving numerical scheme for simulation of turbulent incompressible flows
NASA Astrophysics Data System (ADS)
Kozelkov, A. S.; Kurulin, V. V.
2015-07-01
The properties of existing numerical schemes for discretizing convective fluxes are examined. An alternative scheme is proposed that is formulated on the basis of normalized variable diagrams. The dissipation properties of this scheme are analyzed by simulating turbulent incompressible flows with the use of eddy-resolving models. It is shown that the scheme does not lead to spurious oscillations and it is superior in dissipation properties to similar central-difference schemes. For the scheme proposed, an LES model is calibrated for both free and near-wall flows and the numerical solution of a plane channel flow problem is shown to converge by applying direct numerical simulation of turbulence.
On Varifold Solutions of Two-Phase Incompressible Viscous Flow with Surface Tension
NASA Astrophysics Data System (ADS)
Yeressian, Karen
2015-09-01
In this paper using diffuse approximations the existence of a varifold solution to the two-phase Newtonian incompressible viscous flow problem is derived. On the free surface between the two phases we consider surface tension force. Also we prove that for axisymmetric, possibly with swirl, initial velocities and cylindrically symmetric initial volumes occupied by each fluid there exists a global in time axisymmetric, with swirl, solution.
A p-version finite element method for steady incompressible fluid flow and convective heat transfer
NASA Technical Reports Server (NTRS)
Winterscheidt, Daniel L.
1993-01-01
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.
An adaptive levelset method for computing solutions to incompressible two-phase flows
Mark Sussman; Emad Fatemi; Peter Smereka; Stan Osher
1997-01-01
We present an adaptive level set method for computing 2d axisymmetric and fully 3d incompressible two-phase flow. Our methodology is specifically targeted at problems characterized by large density and viscosity jumps (e.g. air\\/water) and stiff, singular source terms, such as those due to surface tension. One such application is the modeling of ink-jet printers in which one wants to accurately
Influence of compatibility conditions in numerical simulation of inhomegeneous incompressible flows
F. Montigny-Rannou
1983-01-01
The compatibility conditions in numerical simulation of inhomogeneous incompressible flows are examined for a two-dimensional Stokes problem defined on a slab geometry. A pseudo-spectral space-time method is used by means of Chebyshev approximations in space and in time. It is shown that this method associated with a Poisson solver for the pressure, gives less accurate results than the same method
Influence of compatibility conditions in numerical simulation of inhomegeneous incompressible flows
NASA Astrophysics Data System (ADS)
Montigny-Rannou, F.
The compatibility conditions in numerical simulation of inhomogeneous incompressible flows are examined for a two-dimensional Stokes problem defined on a slab geometry. A pseudo-spectral space-time method is used by means of Chebyshev approximations in space and in time. It is shown that this method associated with a Poisson solver for the pressure, gives less accurate results than the same method applied on a staggered grid to the direct treatment of the continuity equation.
On Varifold Solutions of Two-Phase Incompressible Viscous Flow with Surface Tension
NASA Astrophysics Data System (ADS)
Yeressian, Karen
2015-06-01
In this paper using diffuse approximations the existence of a varifold solution to the two-phase Newtonian incompressible viscous flow problem is derived. On the free surface between the two phases we consider surface tension force. Also we prove that for axisymmetric, possibly with swirl, initial velocities and cylindrically symmetric initial volumes occupied by each fluid there exists a global in time axisymmetric, with swirl, solution.
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.; Braslow, Albert L.
1990-01-01
The effectiveness and practicality of candidate leading edge systems for suction laminar flow control transport airplanes were investigated in a flight test program utilizing a modified JetStar airplane. The leading edge region imposes the most severe conditions on systems required for any type of laminar flow control. Tests of the leading edge systems, therefore, provided definitive results as to the feasibility of active laminar flow control on airplanes. The test airplane was operated under commercial transport operating procedures from various commercial airports and at various seasons of the year.
NASA Astrophysics Data System (ADS)
Moreira, David; Bandaru, Prabhakar R.
2015-05-01
An analytical methodology to characterizing the effects of heat transport in internal laminar flows over ridged patterns, mimicking superhydrophobic surfaces, is indicated. The finite slip velocity on such surfaces and the thermal conductivity characteristics of the constituent material are both shown to modify the convective heat transport in the fluid. We use an effective medium approach to model the lowered thermal conductivity caused by the presence of air in the ridge interstices. The proposed analytical solutions for fully developed flow were verified through comparison with numerical simulations for a periodically ridged geometry in laminar flow. While the convective heat transport and the Nusselt Number (Nu) increase due to the modified fluid velocity profile on superhydrophobic surfaces, the decrease in the thermal conductivity of the substrate may play a larger role in determining the overall heat transfer in the channel.
Simulation of large incompressible flows by the finite element method
NASA Astrophysics Data System (ADS)
Bercovier, M.; Engelman, M.
Super computers together with low cost 32 bit machines with graphics render more actual the challenge of designing a general purpose Fluid Dynamic code. Such an approach was the key to the introduction of computational structural mechanics into the design cycle. There FEM codes have replaced experiments and are evaluation tools at every stage. Except for a very limited domain (low Reynolds numbers for instance) this "black box" concept cannot be aplied in fluid mechanics. Nevertheless the success of the modular approach of FIDAP, the addition of new models and the extension of its pre and post-processing capabilities bring a new bridge between the fluid mechanics engineer and the design floor shop. It is now the task of the scientific community to design acceptable models in domains like turbulent flows,multiphase flows slightly compressible flows and so on. At the same time faster and robust algorithms for highly non linear problems must be devised.
Numerical study of incompressible slightly viscous flow past blunt bodies and airfoils
Cheer, A.Y.L.
1981-05-01
A grid free numerical method is used to simulate incompressible flow at high Reynolds number. The numerical method simulates the flow inside the boundary layer by vortex sheets and the flow outside this layer by vortex blobs. The algorithm produces a smooth transition between the sheets and the blobs. The accuracy of this hybrid numerical method is tested in several numerical experiments. In the first experiment, the algorithm is used to simulate slightly viscous flow past a circular cylinder. In the second experiment, the algorithm is used to simulate flow past a Joukowski airfoil at various angles of attack. In the latter case, there is no evidence of blow-up of the flow at the trailing edge of the airfoil. In both experiments, the calculated flow and its functionals (such as lift and drag coefficients) are in good agreement with both theoretical results and wind tunnel experiments.
NUMERICAL MODELING FOR MULTIPHASE INCOMPRESSIBLE FLOW WITH PHASE CHANGE
Abdou, Mohamed
complex deformation of the interface and account for the effect of liquidvapor phase change. 1 environments, and operating circumstances of nuclear power plant design. These processes may have complexities interactions among many effects such as fluid flow, surface tension, and heat and mass transfer with phase
Hybrid algorithm for modeling of fluid-structure interaction in incompressible, viscous flows
NASA Astrophysics Data System (ADS)
Young, Yin Lu; Chae, Eun Jung; Akcabay, Deniz Tolga
2012-08-01
The objective of this paper is to present and to validate a new hybrid coupling (HC) algorithm for modeling of fluid-structure interaction (FSI) in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled (LC) and tightly coupled (TC) algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible structures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incompressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen's analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical instability issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.
Dynamical Slowdown of Polymers in Laminar and Random Flows
Antonio Celani; Alberto Puliafito; Dario Vincenzi
2006-09-22
The influence of an external flow on the relaxation dynamics of a single polymer is investigated theoretically and numerically. We show that a pronounced dynamical slowdown occurs in the vicinity of the coil-stretch transition, especially when the dependence on polymer conformation of the drag is accounted for. For the elongational flow, relaxation times are exceedingly larger than the Zimm relaxation time, resulting in the observation of conformation hysteresis. For random smooth flows hysteresis is not present. Yet, relaxation dynamics is significantly slowed down because of the large variety of accessible polymer configurations. The implications of these results for the modeling of dilute polymer solutions in turbulent flows are addressed.
NASA Astrophysics Data System (ADS)
German, Brian Joseph
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.
NASA Technical Reports Server (NTRS)
Chang, J. L. C.; Rosen, R.; Dao, S. C.; Kwak, D.
1985-01-01
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.
Challenges and Accomplishments of Viscous Incompressible Flow Computations in Aerospace and Beyond
NASA Technical Reports Server (NTRS)
Kwak, Dochan
1996-01-01
Recent progress in incompressible Navier-Stokes solution methods will be presented. Discussions are focused on the methods designed for complex geometry applications in three dimensions, and thus are limited to primitive variable formulation. Both steady- and unsteady-solution algorithms and their salient features are discussed. A summary of our recent progress in flow solver development is given followed by numerical studies of a few example problems of our current interest. Solvers discussed here are based on structured-grid approach using finite-difference or finite-volume frame work. This short course will be delivered in three one-our lectures. The material in the course are collected from the work performed by the Incompressible Navier-Stokes group at NASA Ames Research Center over the past several years, and can be found in our publications widely disseminated in the US and abroad. This short course is sponsored by AGARD Consultant and Exchange Program under Support Project P-110.
A multiple-scale turbulence model for incompressible flow
NASA Technical Reports Server (NTRS)
Duncan, B. S.; Liou, W. W.; Shih, T. H.
1993-01-01
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.
Actuator disk theory for incompressible highly rotating flows.
NASA Technical Reports Server (NTRS)
Oates, G. C.
1971-01-01
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.
Frequency-selection mechanism in incompressible open-cavity flows via reflected instability waves.
Tuerke, F; Sciamarella, D; Pastur, L R; Lusseyran, F; Artana, G
2015-01-01
We present an alternative perspective on nonharmonic mode coexistence, commonly found in the shear layer spectrum of open-cavity flows. Modes obtained by a local linear stability analysis of perturbations to a two-dimensional, incompressible, and inviscid sheared flow over a cavity of finite length and depth were conditioned by a so-called coincidence condition first proposed by Kulikowskii [J. Appl. Math. Mech. 30, 180 (1966)] which takes into account instability wave reflection within the cavity. The analysis yields a set of discrete, nonharmonic frequencies, which compare well with experimental results [Phys. Fluids 20, 114101 (2008); Exp. Fluids 50, 905 (2010)]. PMID:25679706
Two-dimensional MRT LB model for compressible and incompressible flows
NASA Astrophysics Data System (ADS)
Chen, Feng; Xu, Ai-Guo; Zhang, Guang-Cai; Wang, Yong-Long
2014-04-01
In the paper we extend the Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) model proposed in [ Europhys. Lett., 2010, 90: 54003] so that it is suitable also for incompressible flows. To decrease the artificial oscillations, the convection term is discretized by the flux limiter scheme with splitting technique. A new model is validated by some well-known benchmark tests, including Riemann problem and Couette flow, and satisfying agreements are obtained between the simulation results and analytical ones. In order to show the merit of LB model over traditional methods, the non-equilibrium characteristics of system are solved. The simulation results are consistent with the physical analysis.
Control of airborne nickel welding fumes by means of a vertical laminar air flow system
Helms, T.C.
1980-12-08
The purpose of this study was to evaluate the effeciveness of a clean room facility with laminar air flow in the control of nickel fumes released from metal inert gas (MIG) and shielded metal arc (SMA) welding operations performed on mild steel using nickel filler materials. From data observed in these experiments, it appears that the laminar flow clean room approach to controlling welding fumes can be successful in certain small table top welding operations. However, almost any interferences that obstruct the downward airflow can result in eddy currents and subsequent build-up of fumes by entrapment. Airflow patterns differ significantly when comparing table top operations to welding on large cylindrical and/or doughnut shaped items. (JGB)
Design aspects of long range supersonic LFC airplanes with highly swept wings. [laminar flow control
NASA Technical Reports Server (NTRS)
Pfenninger, W.; Vemuru, C. S.
1990-01-01
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.
NASA Technical Reports Server (NTRS)
1999-01-01
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.
A multiple-scale turbulence model for incompressible flow
NASA Technical Reports Server (NTRS)
Duncan, B. S.; Liou, W. W.; Shih, T. H.
1993-01-01
A multiple-scale eddy viscosity model is described in this paper. 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 has been 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.
Laminar film flow phenomena: Theory and application to the two phase closed thermosyphon
R. T. Hirshburg; L. W. Florschuetz
1980-01-01
A theoretical model is developed to predict the hydrodynamic features of asymptotic wavy flow states. The model accurately predicts published experimental data for mean film thickness, trough-to-crest dimension, wave celerity, and wavelength. The Nusselt theory for laminar film condensation is shown to significantly under-predict existing experimental data due to the presence of waves on the condensate film surface. A heat
Phase separation of parallel laminar flow for aqueous two phase systems in branched microchannel
Yangcheng LuYang; Yang Xia; Guangsheng Luo
2011-01-01
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
Anna Moisala; Albert G. Nasibulin; David P. Brown; Hua Jiang; Leonid Khriachtchev; Esko I. Kauppinen
2006-01-01
A gas-phase process of single-walled carbon nanotube (SWCNT) formation, based on thermal decomposition of iron pentacarbonyl or ferrocene in the presence of carbon monoxide (CO), was investigated in ambient pressure laminar flow reactors in the temperature range of 600–1300°C. Ferrocene was found to be a better catalyst precursor in the studied conditions since iron pentacarbonyl decomposes at lower temperatures resulting
Numerical study of laminar and turbulent flows past two-dimensional and axisymmetric bodies
NASA Astrophysics Data System (ADS)
Choi, Seok Ki
A numerical study of laminar and turbulent flows past two-dimensional bodies and axisymmetric bodies is presented. Numerical methods are developed to solve Navier-Stokes equations for two-dimensional and axisymmetric flows in the arbitrary geometries. The complex physical geometry is resolved by use of numerically generated, body-fitted coordinates. The governing equations are written in the transformed domain using the orthogonal velocity components as dependent variables for momentum equation. The governing equations are discretized using both the finite analytic method and the finite volume method. Both one velocity staggered grid method and two velocities staggered method are employed for grid arrangements. The velocity and pressure coupling techniques in these grid arrangements are presented. The solution procedure of the SIMPLER numerical algorithm is used with a parabolic marching technique and a global pressure calculation method. For turbulent flow calculations, both the k-epsilon turbulence model and the two-layer model are used. Calculations are performed for laminar and turbulent flows past a finite flat plate and turbulent flow past axisymmetric bodies with different solution domains, numerical methods and turbulence models. Calculations include the development of a wake function method for the prediction of turbulent wake of a flat plate, predictions of laminar and turbulent flows past a finite flat plate, predictions of turbulent flow past axisymmetric bodies by the wall function method and by the two-layer turbulence model and predictions of turbulent flow past finite axisymmetric bodies. Comparisons of predictions by finite analytic method with those by finite volume method are made for some calculations.
K. Takayama; W. S. Liu
1979-01-01
Analyses are made of the mutual interactions between shock structure and the sidewall laminar boundary-layer and their effects on the quasi-steady flat-plate laminar boundary layer in ionizing argon shock-tube flows. The mutual interactions are studied using effective quasi-one-dimensional equations derived from an area-averaged-flow concept in a finite-area shock tube. The effects of mass, momentum and energy non-uniformities and the wall
NASA Astrophysics Data System (ADS)
Natarajan, Ganesh; Sotiropoulos, Fotis
2009-11-01
We propose a generalisation of the CURVIB methodology (Ge & Sotiropoulos, JCP 2007) for the solution of the unsteady incompressible Navier--Stokes equations on arbitrary polygonal meshes in domains containing arbitrarily complex, moving immersed bodies. The new finite volume flow solver employs the hybrid staggered/non--staggered approach of Ge & Sotiropoulos (2007) in conjunction with generalised and robust discretisation procedures, so that it can be readily extended to handle adaptive meshes. The flow solver is combined with an isotropic adaptation strategy that effectively tracks flow features of interest and selectively enhances grid resolution. The resulting generic adaptive finite volume flow solver allows for computationally efficient, high resolution numerical simulations of a wide range of engineering and biological flows at Reynolds numbers much higher than what was possible with the original CURVIB methodology.
Borazjani, Iman; Ge, Liang; Le, Trung; Sotiropoulos, Fotis
2013-04-01
We develop an overset-curvilinear immersed boundary (overset-CURVIB) method in a general non-inertial frame of reference to simulate a wide range of challenging biological flow problems. The method incorporates overset-curvilinear grids to efficiently handle multi-connected geometries and increase the resolution locally near immersed boundaries. Complex bodies undergoing arbitrarily large deformations may be embedded within the overset-curvilinear background grid and treated as sharp interfaces using the curvilinear immersed boundary (CURVIB) method (Ge and Sotiropoulos, Journal of Computational Physics, 2007). The incompressible flow equations are formulated in a general non-inertial frame of reference to enhance the overall versatility and efficiency of the numerical approach. Efficient search algorithms to identify areas requiring blanking, donor cells, and interpolation coefficients for constructing the boundary conditions at grid interfaces of the overset grid are developed and implemented using efficient parallel computing communication strategies to transfer information among sub-domains. The governing equations are discretized using a second-order accurate finite-volume approach and integrated in time via an efficient fractional-step method. Various strategies for ensuring globally conservative interpolation at grid interfaces suitable for incompressible flow fractional step methods are implemented and evaluated. The method is verified and validated against experimental data, and its capabilities are demonstrated by simulating the flow past multiple aquatic swimmers and the systolic flow in an anatomic left ventricle with a mechanical heart valve implanted in the aortic position. PMID:23833331
Borazjani, Iman; Ge, Liang; Le, Trung; Sotiropoulos, Fotis
2013-01-01
We develop an overset-curvilinear immersed boundary (overset-CURVIB) method in a general non-inertial frame of reference to simulate a wide range of challenging biological flow problems. The method incorporates overset-curvilinear grids to efficiently handle multi-connected geometries and increase the resolution locally near immersed boundaries. Complex bodies undergoing arbitrarily large deformations may be embedded within the overset-curvilinear background grid and treated as sharp interfaces using the curvilinear immersed boundary (CURVIB) method (Ge and Sotiropoulos, Journal of Computational Physics, 2007). The incompressible flow equations are formulated in a general non-inertial frame of reference to enhance the overall versatility and efficiency of the numerical approach. Efficient search algorithms to identify areas requiring blanking, donor cells, and interpolation coefficients for constructing the boundary conditions at grid interfaces of the overset grid are developed and implemented using efficient parallel computing communication strategies to transfer information among sub-domains. The governing equations are discretized using a second-order accurate finite-volume approach and integrated in time via an efficient fractional-step method. Various strategies for ensuring globally conservative interpolation at grid interfaces suitable for incompressible flow fractional step methods are implemented and evaluated. The method is verified and validated against experimental data, and its capabilities are demonstrated by simulating the flow past multiple aquatic swimmers and the systolic flow in an anatomic left ventricle with a mechanical heart valve implanted in the aortic position. PMID:23833331
Computation of incompressible viscous flows through artificial heart devices with moving boundaries
NASA Technical Reports Server (NTRS)
Kiris, Cetin; Rogers, Stuart; Kwak, Dochan; Chang, I.-DEE
1991-01-01
The extension of computational fluid dynamics techniques to artificial heart flow simulations is illustrated. Unsteady incompressible Navier-Stokes equations written in 3-D generalized curvilinear coordinates are solved iteratively at each physical time step until the incompressibility condition is satisfied. The solution method is based on the pseudo compressibility approach and uses an implicit upwind differencing scheme together with the Gauss-Seidel line relaxation method. The efficiency and robustness of the time accurate formulation of the algorithm are tested by computing the flow through model geometries. A channel flow with a moving indentation is computed and validated with experimental measurements and other numerical solutions. In order to handle the geometric complexity and the moving boundary problems, a zonal method and an overlapping grid embedding scheme are used, respectively. Steady state solutions for the flow through a tilting disk heart valve was compared against experimental measurements. Good agreement was obtained. The flow computation during the valve opening and closing is carried out to illustrate the moving boundary capability.
Notes on Newton-Krylov based Incompressible Flow Projection Solver
Robert Nourgaliev; Mark Christon; J. Bakosi
2012-09-01
The purpose of the present document is to formulate Jacobian-free Newton-Krylov algorithm for approximate projection method used in Hydra-TH code. Hydra-TH is developed by Los Alamos National Laboratory (LANL) under the auspices of the Consortium for Advanced Simulation of Light-Water Reactors (CASL) for thermal-hydraulics applications ranging from grid-to-rod fretting (GTRF) to multiphase flow subcooled boiling. Currently, Hydra-TH is based on the semi-implicit projection method, which provides an excellent platform for simulation of transient single-phase thermalhydraulics problems. This algorithm however is not efficient when applied for very slow or steady-state problems, as well as for highly nonlinear multiphase problems relevant to nuclear reactor thermalhydraulics with boiling and condensation. These applications require fully-implicit tightly-coupling algorithms. The major technical contribution of the present report is the formulation of fully-implicit projection algorithm which will fulfill this purpose. This includes the definition of non-linear residuals used for GMRES-based linear iterations, as well as physics-based preconditioning techniques.
NASA Astrophysics Data System (ADS)
Kumarasamy, Sanjay
Computation of flow generated noise is increasingly possible due to the availability of increasingly detailed numerical solutions to the flow. The most general way to compute the noise radiation by a turbulent flow is to numerically solve the Navier-Stokes equation. The computation needs to be performed over a large spatial domain for long time intervals, simultaneously, with the ability to resolve small scales. This requirement overwhelms present day computing power. However, depending on the speed and nature of the flow, certain simplifications can be used to make the computations feasible. For low Mach number flows in which there is no significant back reaction from the acoustics on the flow, the noise calculations can be reduced to a two step procedure: (1) Computation of the underlying flow. (2) Acoustic computations. Since Mach number of the underlying flow is small, incompressibility is still a valid assumption for the flow simulation. The second step can be accomplished by Acoustic Analogy or Kirchhoff's method with the sources calculated from the solution available from the first step. The present work uses the two step procedure just outlined, with the numerical solution to the flow problem obtained by solving the incompressible, time dependent Reynolds Averaged Navier Stokes equation. Experiments were conducted at the Glenn L. Martin Wind Tunnel to ascertain the accuracy of the computational simulation. The acoustic solution is obtained by solving the two dimensional Lighthill's wave equation which is transformed to the Helmholtz equation for the generalized body fitted coordinate system and reduced to a finite number of algebraic equations using the Finite Analytic technique. The two step procedure is demonstrated for the case of a half cylinder in and out of ground effect by enforcing the Dirichlet boundary condition derived from the computational simulations. The computed far field noise radiation shows dipole patterns for both the lift and drag type for the free stream case with a considerable change in the directivity pattern when the ground is present.
NASA Technical Reports Server (NTRS)
Goodrich, John W.
1991-01-01
An algorithm is presented for unsteady two-dimensional incompressible Navier-Stokes calculations. This algorithm is based on the fourth order partial differential equation for incompressible fluid flow which uses the streamfunction as the only dependent variable. The algorithm is second order accurate in both time and space. It uses a multigrid solver at each time step. It is extremely efficient with respect to the use of both CPU time and physical memory. It is extremely robust with respect to Reynolds number.
Laminar channel flow over a (long)wavy surface
McCready, Mark J.
by Mark J. McCready Professor and Chair of Chemical Engineering University of Notre Dame Notre Dame, if you use it, this notice remain visible to other users. There is no charge for copying of studies have suggested that regime transitions from stratified to slug and/or annular flow occur when
Hysteretic transition from laminar to vortex shedding flow in soap films
Viktor K. Horváth; J. Rob Cressman; Walter I. Goldburg; Xiao-Lun Wu
2000-07-21
There are different ways for fluid flow to become turbulent, but usually many instabilities take place before that. Among these instabilities the transition from laminar flow to vortex shedding carries significant practical importance. Here we study a flow, where at high enough flow rates, vortices are generated by a fixed obstacle (cylinder), which penetrates a flowing, quasi-two dimensional soap film. We present experimental results that demonstrate that the transition from laminar flow to a periodic K\\'arm\\'an vortex street can be hysteretic, i.e. changing the mean flow rate $\\bar V$ vortices can survive at velocities lower than the velocity needed to generate them. This is an unexpected result since 3D experiments are well described by the Hopf equation, which is incompatible with hysteresis. Beyond that, our data cannot be satisfactorily fitted by the generic model of hysteresis, i.e. the 5th order Landau equation. It is found that a phenomenological model describes our experimental findings very well. Evidences are presented that wetting properties of the rod, mechanical instabilities (i.e. vibrations) of the setup, and the effect of the surrounding air are not the cause of the hysteresis. To reduce three dimensional effects, the rod was replaced by a disk having a thickness roughly eight times that of the film. The replacement of the rod by a disk increases the gap width and the shedding frequency. Behaviour of the system (for instance the unstable trajectory) in the hysteretic gap is investigated by means of transient measurements.
Mimicking Natural Laminar to Turbulent Flow Transition: A Systematic CFD Study Using PAB3D
NASA Technical Reports Server (NTRS)
Pao, S. Paul; Abdol-Hamid, Khaled S.
2005-01-01
For applied aerodynamic computations using a general purpose Navier-Stokes code, the common practice of treating laminar to turbulent flow transition over a non-slip surface is somewhat arbitrary by either treating the entire flow as turbulent or forcing the flow to undergo transition at given trip locations in the computational domain. In this study, the possibility of using the PAB3D code, standard k-epsilon turbulence model, and the Girimaji explicit algebraic stresses model to mimic natural laminar to turbulent flow transition was explored. The sensitivity of flow transition with respect to two limiters in the standard k-epsilon turbulence model was examined using a flat plate and a 6:1 aspect ratio prolate spheroid for our computations. For the flat plate, a systematic dependence of transition Reynolds number on background turbulence intensity was found. For the prolate spheroid, the transition patterns in the three-dimensional boundary layer at different flow conditions were sensitive to the free stream turbulence viscosity limit, the reference Reynolds number and the angle of attack, but not to background turbulence intensity below a certain threshold value. The computed results showed encouraging agreements with the experimental measurements at the corresponding geometry and flow conditions.
a General Formula for Calculating Forces on a 2-D Arbitrary Body in Incompressible Flow
NASA Astrophysics Data System (ADS)
Pan, L. S.; Chew, Y. T.
2002-01-01
In the present paper, a general integral equation is presented to calculate the forces exerted on a two-dimensional (2-D) body of arbitrary shape immersed in unsteady, incompressible flows. By finding the general solutions of a set of Laplace equations with particular boundary conditions, the equation can be simplified to produce a simplified formula for calculating the forces. The simplified formula consists of three parts, representing contributions from different physical phenomena: added mass force and/or inertial force in inviscid flow, the force caused by the deformation of fluid and viscosity and the force caused by the convection of fluid with nonzero circulation. It can be applied to any 2-D arbitrary body in viscous or inviscid, steady or unsteady incompressible flow. As the formula excludes either temporal derivatives of velocity or spatial derivatives of vorticity in the flow field, the numerical errors contained in the numerical solution of velocity and vorticity fields will not be magnified, and therefore the resulting force calculated is more accurate. Most importantly, the formula presents an alternative method for obtaining the added mass of a 2-D body of arbitrary shape accelerating in a fluid. For bodies of simple shape, such as a circle, ellipse and plate, the added masses predicted using the present method are in agreement with that obtained by conventional methods. For bodies of complex shape, the present method only requires the calculation of the first two coefficients of the conformal transformation and cross-sectional area.
Cauchy's almost forgotten Lagrangian formulation of the Euler equation for 3D incompressible flow
NASA Astrophysics Data System (ADS)
Frisch, Uriel; Villone, Barbara
2014-09-01
Two prized papers, one by Augustin Cauchy in 1815, presented to the French Academy and the other by Hermann Hankel in 1861, presented to Göttingen University, contain major discoveries on vorticity dynamics whose impact is now quickly increasing. Cauchy found a Lagrangian formulation of 3D ideal incompressible flow in terms of three invariants that generalize to three dimensions the now well-known law of conservation of vorticity along fluid particle trajectories for two-dimensional flow. This has very recently been used to prove analyticity in time of fluid particle trajectories for 3D incompressible Euler flow and can be extended to compressible flow, in particular to cosmological dark matter. Hankel showed that Cauchy's formulation gives a very simple Lagrangian derivation of the Helmholtz vorticity-flux invariants and, in the middle of the proof, derived an intermediate result which is the conservation of the circulation of the velocity around a closed contour moving with the fluid. This circulation theorem was to be rediscovered independently by William Thomson (Kelvin) in 1869. Cauchy's invariants were only occasionally cited in the 19th century - besides Hankel, foremost by George Stokes and Maurice Lévy - and even less so in the 20th until they were rediscovered via Emmy Noether's theorem in the late 1960, but reattributed to Cauchy only at the end of the 20th century by Russian scientists.
Micropatterned biofilm formations by laminar flow-templating.
Aznaveh, Nahid Babaei; Safdar, Muhammad; Wolfaardt, Gideon; Greener, Jesse
2014-08-01
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
Laminar flow effects in the coil planet centrifuge
NASA Technical Reports Server (NTRS)
Herrmann, F. T.
1984-01-01
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.
Erosion of a granular bed by laminar fluid flow
NASA Astrophysics Data System (ADS)
Orpe, Ashish; Lobovsky, Alex; Molloy, Ryan; Kudrolli, Arshad; Rothman, Daniel
2007-03-01
Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed as a function of fluid flow rate to give us new insight concerning the relationship between hydrodynamic stress and surficial granular flow. A closed channel of rectangular cross section is partially filled with glass beads and a fluid and a constant flux Q is circulated through the channel. The fluid has same refractive index as the glass beads and is illuminated with a laser sheet away from the sidewalls. The bed erodes quadratically in time to a height hc which depends on Q. The Shields criterion, which is proportional to the ratio of the viscous shear stress and gravitational normal stress, describes the observed hc?Q when a height offset of approximately half a grain diameter is introduced. The offset can be interpreted as arising due to differences between the flow near a porous boundary and a smooth wall. Introducing this offset in the estimation of the shear stress yields a grain flux qx in the bed load regime proportional to (?- ?c)^2, where ? is the non-dimensional shear stress, and ?c corresponds to the Shields criteria.
Effects of Pulsatility on the Laminar Mixing Surface in Converging Microchannel Flows
NASA Astrophysics Data System (ADS)
Prabhu, R. D.; Hitt, Darren L.
2001-11-01
Continuing developments in MEMS based fluidic systems require innovative approaches to the problem of microscale mixing. Owing to the low Reynolds number characteristic of these flows, non-traditional strategies have been proposed. In this work, we investigate the effects of flow pulsatility on the laminar mixing surface formed between two converging flows. The basic motivation is drawn from blood flow, with governing parameters adapted to a MEMS setting. Parametric studies involving flow-ratio, viscosity-ratio, frequency-ratio and the flow geometry will be reported. Our results have indicated complex interfacial distortions at high frequency pulsations ( 1kHz). The extent of mixing will also be quantified in terms of the interfacial distortion achieved by the pulsatile inlets.
A microfluidic chip for generating reactive plasma at gas–gas interface formed in laminar flow
NASA Astrophysics Data System (ADS)
Hashimoto, Masahiro; Tsukasaki, Katsuki; Kumagai, Shinya; Sasaki, Minoru
2015-01-01
A gas–gas interface is used for generating a localized reactive plasma flow at an atmospheric pressure. A microfluidic chip is fabricated as the reactor integrating a small plasma source located upstream. Within a Y-shaped microchannel, a discharging gas flows with a chemical gas. Owing to the small width of the microchannel, the gas flow is stabilized in a laminar flow. The resultant gas–gas interface is formed in the area where two gases flow facing each other activating the chemical gas through the energetic species in the discharging gas. A characteristic stream pattern is observed as the etching profile of a carbon film with a sub-µm sharp step change that can be explained by the spatial distribution of the reactive oxygen. This etching profile is different from that obtained when plasma discharging occurs near the channel exit being affected by the turbulent flow.
Implicit/Multigrid Algorithms for Incompressible Turbulent Flows on Unstructured Grids
NASA Technical Reports Server (NTRS)
Anderson, W. Kyle; Rausch, Russ D.; Bonhaus, Daryl L.
1997-01-01
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.
Changes in the adiabatic invariant and streamline chaos in confined incompressible Stokes flow.
Vainshtein, D. L.; Vasiliev, A. A.; Neishtadt, A. I.
1996-03-01
The steady incompressible flow in a unit sphere introduced by Bajer and Moffatt [J. Fluid Mech. 212, 337 (1990)] is discussed. The velocity field of this flow differs by a small perturbation from an integrable field whose streamlines are almost all closed. The unperturbed flow has two stationary saddle points (poles of the sphere) and a two-dimensional separatrix passing through them. The entire interior of the unit sphere becomes the domain of streamline chaos for an arbitrarily small perturbation. This phenomenon is explained by the nonconservation of a certain adiabatic invariant that undergoes a jump when a streamline crosses a small neighborhood of the separatrix of the unperturbed flow. An asymptotic formula is obtained for the jump in the adiabatic invariant. The accumulation of such jumps in the course of repeated crossings of the separatrix results in the complete breaking of adiabatic invariance and streamline chaos. (c) 1996 American Institute of Physics. PMID:12780237
Non-stationary helical flows for incompressible 3D Navier-Stokes equations
Ershkov, Sergey V
2015-01-01
In fluid mechanics, a lot of authors have been executing their researches to obtain the analytical solutions of Navier-Stokes equations, even for 3D case of compressible gas flow. But there is an essential deficiency of non-stationary solutions indeed. In our presentation, we explore the case of non-stationary helical flow (where vorticity is proportional to the flow velocity) of the Navier-Stokes equations for incompressible fluids. Such a non-stationary helical flow is proved to be decreasing exponentially in regard to the time-parameter, the extent of time-dependent exponential component is given by the coefficient of kinematic viscosity, multiplied by the square of the coefficient of proportionality between the vorticity and velocity field.
Development of Advanced High Lift Leading Edge Technology for Laminar Flow Wings
NASA Technical Reports Server (NTRS)
Bright, Michelle M.; Korntheuer, Andrea; Komadina, Steve; Lin, John C.
2013-01-01
This paper describes the Advanced High Lift Leading Edge (AHLLE) task performed by Northrop Grumman Systems Corporation, Aerospace Systems (NGAS) for the NASA Subsonic Fixed Wing project in an effort to develop enabling high-lift technology for laminar flow wings. Based on a known laminar cruise airfoil that incorporated an NGAS-developed integrated slot design, this effort involved using Computational Fluid Dynamics (CFD) analysis and quality function deployment (QFD) analysis on several leading edge concepts, and subsequently down-selected to two blown leading-edge concepts for testing. A 7-foot-span AHLLE airfoil model was designed and fabricated at NGAS and then tested at the NGAS 7 x 10 Low Speed Wind Tunnel in Hawthorne, CA. The model configurations tested included: baseline, deflected trailing edge, blown deflected trailing edge, blown leading edge, morphed leading edge, and blown/morphed leading edge. A successful demonstration of high lift leading edge technology was achieved, and the target goals for improved lift were exceeded by 30% with a maximum section lift coefficient (Cl) of 5.2. Maximum incremental section lift coefficients ( Cl) of 3.5 and 3.1 were achieved for a blown drooped (morphed) leading edge concept and a non-drooped leading edge blowing concept, respectively. The most effective AHLLE design yielded an estimated 94% lift improvement over the conventional high lift Krueger flap configurations while providing laminar flow capability on the cruise configuration.
a Segregated Solution Algorithm for Incompressible Flows in General Co-Ordinates
NASA Astrophysics Data System (ADS)
Sheu, Tony W. H.; Lee, Shi-Min
1996-03-01
To analyse an incompressible Navier-Stokes flow problem in a boundary- fitted curvilinear co-ordinate system is definitely not a trivial task. In the primitive variable formulation, choices between working variables and their storage points have to be made judiciously. The present work engages contravariant velocity components and scalar pressure which stagger each other in the mesh to prevent even-odd pressure oscillations from emerging. Now that smoothness of the pressure field is attainable, the remaining task is to ensure a discrete divergence-free velocity field for an incompressible flow simulation. Aside from the flux discretizations, the indispensable metric tensors, Jacobian and Christoffel symbols in the transformed equations should be approximated with care. The guiding idea is to get the property of geometric identity pertaining to these grid-sensitive discretizations. In addition, how to maintain the revertible one-to-one equivalence at the discrete level between primitive and contravariant velocities is another theme in the present staggered formulation. A semi-implicit segregated solution algorithm felicitous for a large-scale flow simulation was utilized to solve the entire set of basic equations iteratively. Also of note is that the present segregated solution algorithm has the virtue of requiring no user-specified relaxation parameters for speeding up the satisfaction of incompressibility in an optimal sense. Three benchmark problems, including an analytic problem, were investigated to justify the capability of the present formulation in handling problems with complex geometry. The test cases considered and the results obtained herein make a useful contribution in solving problems subsuming cells with arbitrary shapes in a boundary-fitted grid system.
Laminar flame and acoustic waves in two-dimensional flow
Zaytsev, M. L. Akkerman, V. B.
2011-03-15
The complete system of fluid dynamics equations describing the development of instability of a reaction front in a two-dimensional flow in reversed time are reduced to a closed system of equations of front dynamics by using Lagrangian variables and integrals of motion. The system can be used to analyze processes behind the front without solving the complete system of fluid dynamics and chemical kinetics equations. It is demonstrated how the gas density disturbances induced by the moving front can be described in the adiabatic approximation.
Pattern of reaction diffusion fronts in laminar flows.
Leconte, M; Martin, J; Rakotomalala, N; Salin, D
2003-03-28
Autocatalytic reaction between reacted and unreacted species may propagate as solitary waves, namely, at a constant front velocity and with a stationary concentration profile, resulting from a balance between molecular diffusion and chemical reaction. The effect of advective flow on the autocatalytic reaction between iodate and arsenous acid in cylindrical tubes and Hele-Shaw cells is analyzed experimentally and numerically using lattice Bhatnagar-Gross-Krook simulations. We do observe the existence of solitary waves with concentration profiles exhibiting a cusp and we delineate the eikonal and mixing regimes recently predicted. PMID:12688909
F-16XL Ship #2 during last flight showing titanium laminar flow glove on left wing
NASA Technical Reports Server (NTRS)
1996-01-01
Dryden research pilot Dana Purifoy bends NASA F-16 XL #848 away from the tanker on the 44th flight in the Supersonic Laminar Flow Control program recently. The flight test portion of the program ended with the 45th and last data collection flight from NASA's Dryden Flight Research Center, Edwards, California, on Nov. 26, 1996. The project demonstrated that laminar--or smooth--airflow could be achieved over a major portion of a wing at supersonic speeds. The flight tests at Dryden involved use of a suction system which drew boundary-layer air through millions of tiny laser-drilled holes in a titanium 'glove' that was fitted to the upper surface of the F-16XL's left wing.
F-16XL Ship #2 during last flight showing titanium laminar flow glove on left wing
NASA Technical Reports Server (NTRS)
1996-01-01
The perforated titanium overlay mounted on the upper surface of the left wing is clearly evident on this view of NASA 848, a highly modified F-16XL aircraft flown by NASA's Dryden Flight Research Center in the Supersonic Laminar Flow Control (SLFC) research program. The two-seat, single-engine craft, one of only two 'XL' F-16s built, recently concluded the SLFC project with its 45th data collection mission. The project demonstrated that laminar--or smooth--airflow could be achieved over a major portion of a wing at supersonic speeds by use of a suction system. The system drew a small part of the boundary-layer air through millions of tiny laser-drilled holes in the 'glove' fitted to the upper left wing.
NASA Technical Reports Server (NTRS)
1976-01-01
The feasibility of using porous composite materials (Kevlar, Doweave, and Leno Weave) as lightweight, efficient laminar flow control (LFC) surface materials is compared to the metallic 319L stainless Dynapore surfaces and electron beam drilled composite surfaces. Areas investigated include: (1) selection of the LFC-suitable surface materials, structural materials, and fabrication techniques for the LFC aircraft skins; (2) aerodynamic static air flow test results in terms of pressure drop through the LFC panel and the corresponding effective porosity; (3) structural design definition and analyses of the panels, and (4) contamination effects on static drop and effective porosity. Conclusions are presented and discussed.
Demonstration of a plasma mirror based on a laminar flow water film
Panasenko, Dmitriy; Shu, Anthony; Gonsalves, Anthony; Nakamura, Kei; Matlis, Nicholas; Toth, Csaba; Leemans, Wim
2011-07-22
A plasma mirror based on a laminar water film with low flow speed 0.5-2 cm/s has been developed and characterized, for use as an ultrahigh intensity optical reflector. The use of flowing water as atarget surface automatically results in each laser pulse seeing a new interaction surface and avoids the need for mechanical scanning of the target surface. In addition, the breakdown of water does notproduce contaminating debris that can be deleterious to vacuum chamber conditions and optics, such as is the case when using conventional solid targets. The mirror exhibits 70percent reflectivity, whilemaintaining high-quality of the reflected spot.
Magnetohydrodynamics of laminar flow in slowly varying tubes in an axial magnetic field
McMichael, J.M.; Deutsch, S.
1984-01-01
Laminar flow of a conducting fluid in round, straight tubes with axially varying radius, with a uniform magnetic field applied parallel to the tube axis, is treated theoretically as a regular perturbation problem at finite hydrodynamic Reynolds number, finite magnetic Reynolds number, and Hartmann numbers as large as O(..cap alpha../sup -1//sup ///sup 2/), where ..cap alpha.. is a small parameter characteristic of the slope of the tube wall. The first-order solution is examined numerically for local tube dilations and for local constrictions. Flow separation along both converging and diverging sections of the tube is discussed. Pressure, current density, and induced magnetic field distributions are also presented.
Law Jr., C.G.; Pierini, P.; Newman, J.
1980-07-01
Experimental data and theoretical calculations are presented for the mass-transfer rate to rotating disks and rotating rings when laminar, transition, and fully developed turbulent flow exist upon different portions of the surface. Good agreement of data and the model is obtained for rotating disks and relatively thick rotating rings. Results of the calculations for thin rings generally exceed the experimental data measured in transition and turbulent flow. A y{sup +{sup 3}} form for the eddy diffusivity is used to fit the data. No improvement is noticed with a form involving both y{sup +{sup 3}} and y{sup +{sup 3}}.
Quasicellular-Automata Simulation for Laminar and Turbulent Flows.
NASA Astrophysics Data System (ADS)
Wu, Hungming Jeremy
Cellular-automata (CA) simulation is one of the most popular techniques for studying fluid dynamics from the microscopic point of view. It applies a finite and small number of molecules (cells), with some simple collision rules, to the simulated model instead of the unacceptably large number of molecules (or cells) that actually comprises the fluid. By doing so it proves that the CA method is able to simulate complicated phenomena like turbulence. It is necessary to compromise between computational time and memory capacity of the computer. A new, modified CA model has been proposed, developed and verified for the situations occurred in real flows. Four dominant parameters: two viscosity indices, one velocity index, and one density index, are introduced in the algorithm to substitute and interpret the physical properties of a real fluid. These four indices are also termed the simulation indices in the text. The similarities between the simulation parameters and the real physical properties of a fluid are shown and interrelated by using statistical approaches. Turbulent flows are simulated then verified by using the Kolmogorov power spectrum law and the density correlation function. Some peculiar phenomena such as the collective behavior of the cells are discussed and verified by experiments, as are limitations and difficulties of the algorithm. Possible further studies are outlined.
Erosion of a granular channel bed by laminar fluid flow
NASA Astrophysics Data System (ADS)
Kudrolli, A.; Chopin, J.; Ameer, F. A.
2012-12-01
We discuss the onset of erosion in a channel and the subsequent particle transport using particle-fluid index matching and particle image velocimetry (PIV) techniques with laboratory experiments. The experiments focus on the low to moderate Reynolds numbers because of its relevance to flow through porous media and in channel heads where seepage fluid flow emerges on the surface leading to erosion. We discuss the effect of particle roughness on observed erosion rates with rough quartz particles and smooth glass beads. Studies so far at the grain level have been conducted exclusively with mono-disperse spherical beads which are different from natural shapes. Non-spherical grains are harder to dislodge and pack with different porosity compared with spherical grains. We will present analysis of the onset and the rate of erosion for the different kind of particle. We will present comparisons of the data with constitutive laws by Boyer, Guazzelli and Pouliquen (2011) who propose a rheology of dense suspensions which breaks the stress into a contact and hydrodynamic contributions.
A Multiblock Approach for Calculating Incompressible Fluid Flows on Unstructured Grids
NASA Technical Reports Server (NTRS)
Sheng, Chunhua; Whitfield, David L.; Anderson, W. Kyle
1997-01-01
A multiblock approach is presented for solving two-dimensional incompressible turbulent flows on unstructured grids. The artificial compressibility form of the governing equations is solved by a vertex-centered, finite-volume implicit scheme which uses a backward Euler time discretization. Point Gauss-Seidel relaxations are used to solve the linear system of equations at each time step. This work introduces a multiblock strategy to the solution procedure, which greatly improves the efficiency of the algorithm by significantly reducing the memory requirements while not increasing the CPU time. Results presented in this work shows that the current multiblock algorithm requires 70% less memory than the single block algorithm.
Time-marching solution of incompressible Navier-Stokes equations for internal flow
NASA Technical Reports Server (NTRS)
Soh, W. Y.
1987-01-01
Primitive variables with central differencing on a staggered grid are used in the present, factored ADI finite-difference scheme for artificial compressibility method solution of the incompressible Navier-Stokes equations, leading to a close coupling between velocity and pressure that both enhances stability and eliminates the need for artificial damping. Computational efficiency is enhanced through the use of a spatially variable, fixed Courant number-based time-step. The numerical results obtained for a driven cavity at Re of 10,000, with local cell Re as high as 100, exhibits no flow variable spatial oscillations on a 40 x 40 stretched grid solution.
Analytic solutions for three dimensional swirling strength in compressible and incompressible flows
NASA Astrophysics Data System (ADS)
Chen, Huai; Adrian, Ronald J.; Zhong, Qiang; Wang, Xingkui
2014-08-01
Eigenvalues of the 3D critical point equation (?u)? = ?? are normally computed numerically. In the letter, we present analytic solutions for 3D swirling strength in both compressible and incompressible flows. The solutions expose functional dependencies that cannot be seen in numerical solutions. To illustrate, we study the difference between using fluctuating and total velocity gradient tensors for vortex identification. Results show that mean shear influences vortex detection and that distortion can occur, depending on the strength of mean shear relative to the vorticity at the vortex center.
A level set approach for computing solutions to incompressible two-phase flow
Sussman, M.; Smereka, P.; Osher, S. (Univ. of California, Los Angeles, CA (United States))
1994-09-01
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. We use a second-order projection method which implements a second-order upwinded procedure for differencing the convection terms. A new treatment of the level set method allows us to include large density and viscosity ratios as well as surface tension. We consider the motion of air bubbles in water and falling water drops in air.
Wave Number Selection for Incompressible Parallel Jet Flows Periodic in Space
NASA Technical Reports Server (NTRS)
Miles, Jeffrey Hilton
1997-01-01
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.
Time-Accurate Computation of Viscous Incompressible Flow Around Deforming Bodies Using Overset Grids
NASA Astrophysics Data System (ADS)
Fast, Petri
2001-11-01
We solve the incompressible Navier-Stokes equations on moving overset grids. Near dynamically deforming boundaries we use thin, body-fitted grids and cover most of the computational domain with fixed Cartesian grids. Large scale deformation of the flow boundaries can be handled efficiently without global regridding. We'll discuss a velocity-pressure formulation of the Navier-Stokes equations for domains with elastic boundaries. Time permitting, we'll present ongoing work on modeling the recent experiments of Zhang, Childress, Libchaber and Shelley on a 1D flapping flag in a two dimensional wind. (Joint work with William D. Henshaw and Michael J. Shelley.)
Heat transport by laminar boundary layer flow with polymers
Roberto Benzi; Emily S. C. Ching.; Vivien W. S. Chu
2011-04-23
Motivated by recent experimental observations, we consider a steady-state Prandtl-Blasius boundary layer flow with polymers above a slightly heated horizontal plate and study how the heat transport might be affected by the polymers. We discuss how a set of equations can be derived for the problem and how these equations can be solved numerically by an iterative scheme. By carrying out such a scheme, we find that the effect of the polymers is equivalent to producing a space-dependent effective viscosity that first increases from the zero-shear value at the plate then decreases rapidly back to the zero-shear value far from the plate. We further show that such an effective viscosity leads to an enhancement in the drag, which in turn leads to a reduction in heat transport.
A Numerical Investigation of Controllably Flexible Hydrofoil in Laminar Flows
NASA Astrophysics Data System (ADS)
He, G. Y.; Zhang, X.; Zhang, S. G.; He, G. W.
Aquatic animals, such as fishes, whales, seals and penguins, are naturally born to be flexible and deformable, which promise their effective locomotion through water. They are able to produce hydrodynamic thrust by active control of their body configurations. That is, the aquatic animals could wiggle their flexible bodies at an appropriate frequency and amplitude suitable to the hydrodynamics surrounding them. However, the mechanism for the active controls has not been adequately understood yet and attracts current research. One obstacle which hinders such investigation is the difficulty in experimental measurements of the flows around the wiggling bodies, and thus numerical simulation is becoming an indispensable alternative. In the paper, an immersed boundary method is developed to simulate the NACA 65-10 hydrofoil. It is observed that a wiggling hydrofoil exhibits a higher thrust while a stationary hydrofoil offers little improvement.
Numerical simulation of laminar reacting flows with complex chemistry
Day, Marcus S.; Bell, John B.
1999-12-01
We present an adaptive algorithm for low Mach number reacting flows with complex chemistry. Our approach uses a form of the low Mach number equations that discretely conserves both mass and energy. The discretization methodology is based on a robust projection formulation that accommodates large density contrasts. The algorithm uses an operator-split treatment of stiff reaction terms and includes effects of differential diffusion. The basic computational approach is embedded in an adaptive projection framework that uses structured hierarchical grids with subcycling in time that preserves the discrete conservation properties of the underlying single-grid algorithm. We present numerical examples illustrating the performance of the method on both premixed and non-premixed flames.
NASA Astrophysics Data System (ADS)
Linnick, Mark N.; Fasel, Hermann F.
2005-03-01
Immersed boundary methods and immersed interface methods are becoming increasingly popular for the computation of unsteady flows around complex geometries using a Cartesian grid. While good results, both qualitative and quantitative, have been obtained, most of the methods rely on low-order corrections to account for the immersed boundary. The objective of the present work is to present, as an alternative, a high-order modified immersed interface method for the 2D, unsteady, incompressible Navier-Stokes equations in stream function-vorticity formulation. The method employs an explicit fourth-order Runge-Kutta time integration scheme, fourth-order compact finite-differences for computation of spatial derivatives, and a nine-point, fourth-order compact discretization of the Poisson equation for computation of the stream function. Corrections to the finite difference schemes are used to maintain high formal accuracy at the immersed boundary, as confirmed by analytical tests. To validate the method in its application to incompressible flows, several physically relevant test cases are computed, including uniform flow past a circular cylinder and Tollmien-Schlichting waves in a boundary layer.
Prediction of laminar and turbulent primary and secondary flows in strongly curved ducts
NASA Technical Reports Server (NTRS)
Kreskovsky, J. P.; Briley, W. R.; Mcdonald, H.
1981-01-01
The analysis is based on a primary secondary velocity decomposition in a given coordinate system, and leads to approximate governing equations which correct an a priori inviscid solution for viscous effects, secondary flows, total pressure distortion, heat transfer, and internal flow blockage and losses. Solution of the correction equations is accomplished as an initial value problem in space using an implicit forward marching technique. The overall solution procedure requires significantly less computational effort than Navier-Stokes algorithms. The solution procedure is effective even with the extreme local mesh resolution which is necessary to solve near wall sublayer regions in turbulent flow calculations. Computed solutions for both laminar and turbulent flow compared very favorably with available analytical and experimental results. The overall method appears very promising as an economical procedure for making detailed predictions of viscous primary and secondary flows in highly curved passages.
NASA Astrophysics Data System (ADS)
Urban, O.; Jehli?ka, J.; Pokorný, J.; Rouzaud, J. N.
2003-08-01
In order to estimate the role of laminar flow of viscous, aromatic matter of carbonaceous precursor on microtextural preorientation in pregraphitization stage, we performed experiments with coal tar pitch (CTP). The principal hypothesis of preorientation of basic structural units (BSUs) in the case of laminar flow (pressure impregnation of CTP into porous matrix) and secondary release of volatiles during carbonization were studied. Glass microplates, planar porous medium with average distance between single microplates 5 ?m were used as suitable porous matrix. Samples of CTP were carbonized up to 2500 °C. Optical microscopy reveals large flow domains in the sample of cokes carbonized between glass microplates. Raman microspectroscopy and high resolution transmission electron microscopy (HRTEM) show that at nanometric scale, the samples do not support the proposed hypotheses. With increasing temperature of pyrolysis, the graphitization of CTP impregnated into porous matrix proceeds to lower degree of structural ordering in comparison with single pyrolyzed CTP. This is explained by the release of volatile matter during carbonization in geometrically restricted spaces. More evident structural changes were discovered with the sample of single coke, where parts of fine grain mosaics, relicts of 'so called QI parts', reveal higher structural organization, in comparison with large and prolonged flow domains, similar to flow domains of cokes from microplates.
NASA Astrophysics Data System (ADS)
Lashgari, Iman; Picano, Francesco; Breugem, Wim-Paul; Brandt, Luca
2014-12-01
The aim of this Letter is to characterize the flow regimes of suspensions of finite-size rigid particles in a viscous fluid at finite inertia. We explore the system behavior as a function of the particle volume fraction and the Reynolds number (the ratio of flow and particle inertia to viscous forces). Unlike single-phase flows, where a clear distinction exists between the laminar and the turbulent states, three different regimes can be identified in the presence of a particulate phase, with smooth transitions between them. At low volume fractions, the flow becomes turbulent when increasing the Reynolds number, transitioning from the laminar regime dominated by viscous forces to the turbulent regime characterized by enhanced momentum transport by turbulent eddies. At larger volume fractions, we identify a new regime characterized by an even larger increase of the wall friction. The wall friction increases with the Reynolds number (inertial effects) while the turbulent transport is weakly affected, as in a state of intense inertial shear thickening. This state may prevent the transition to a fully turbulent regime at arbitrary high speed of the flow.
NASA Technical Reports Server (NTRS)
Weinan, E.; Shu, Chi-Wang
1992-01-01
High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth order central differences through Fast Fourier Transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large-scale features, such as the total circulation around the roll-up region, are adequately resolved.
NASA Technical Reports Server (NTRS)
Weinan, E.; Shu, Chi-Wang
1994-01-01
High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth-order central differences through fast Fourier transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large scale features, such as the total circulation around the roll-up region, are adequately resolved.
Planar Limits of Three-Dimensional Incompressible Flows with Helical Symmetry
NASA Astrophysics Data System (ADS)
Lopes Filho, Milton C.; Mazzucato, Anna L.; Niu, Dongjuan; Nussenzveig Lopes, Helena J.; Titi, Edriss S.
2014-12-01
Helical symmetry is invariance under a one-dimensional group of rigid motions generated by a simultaneous rotation around a fixed axis and translation along the same axis. The key parameter in helical symmetry is the step or pitch, the magnitude of the translation after rotating one full turn around the symmetry axis. In this article we study the limits of three-dimensional helical viscous and inviscid incompressible flows in an infinite circular pipe, with respectively no-slip and no-penetration boundary conditions, as the step approaches infinity. We show that, as the step becomes large, the three-dimensional helical flow approaches a planar flow, which is governed by the so-called two-and-half Navier-Stokes and Euler equations, respectively.
NASA Technical Reports Server (NTRS)
Morino, L.
1986-01-01
Using the decomposition for the infinite-space, the issue of the nonuniqueness of the Helmholtz decomposition for the problem of the three-dimensional unsteady incompressible flow around a body is considered. A representation for the velocity that is valid for both the fluid region and the region inside the boundary surface is employed, and the motion of the boundary is described as the limiting case of a sequence of impulsive accelerations. At each instant of velocity discontinuity, vorticity is shown to be generated by the boundary condition on the normal component of the velocity, for both inviscid and viscous flows. In viscous flows, the vorticity is shown to diffuse into the surroundings, and the no-slip conditions are automatically satisfied. A trailing edge condition must be satisfied for the solution to the Euler equations to be the limit of the solution of the Navier-Stokes equations.
Numerical studies of incompressible flow around delta and double-delta wings
NASA Technical Reports Server (NTRS)
Krause, E.; Liu, C. H.
1989-01-01
The subject has been jointly investigated at NASA Langley Research Center and the Aerodynamisches Institut of the RWTH Aachen over a substantial period. The aim of this investigation has been to develop numerical integration procedures for the Navier-Stokes equations - particularly for incompressible three-dimensional viscous flows about simple and double delta wings - and to study the low speed flow behavior, with its complex vortex structures on the leeward side of the wing. The low speed flight regime poses unusual problems because high incidence flight conditions may, for example, encounter symmetric and asymmetric vortex breakdown. Because of the many difficulties to be expected in solving the problem, it was divided into two - analysis of the flow without vortex breakdown and analysis of the breakdown of isolated vortices. The major results obtained so far on the two topics are briefly described.
Incompressible turbulent swirling flow computations using a boundary-fitted grid system
NASA Astrophysics Data System (ADS)
Halal, Afif S.; Lilley, David G.
1992-07-01
This study is concerned with the prediction of incompressible turbulent swirling flows in irregular-shaped geometries. The study focuses on the fundamental nonorthogonal grid coverage of an axisymmetric flow domain with irregular boundaries, and involves incorporating swirl and turbulence effects into a stream function-vorticity simulation. Turbulence is simulated by way of a two-equation k-epsilon turbulence model, together with wall functions for the treatment of near-wall flows. The finite difference equations are derived at points of a general boundry-fitted nonorthogonal grid using displaced, linear, and quadratic interpolation. The solution procedure is implemented in a new computer code which features generalized boundaries, rectangular and/or nonrectangular grids, swirl, turbulence, time-dependent calculations, and adaptive stability. Model evaluation is accomplished through a comparative study between predictions and available experimental data.
Scaling laws for drag of a compliant body in an incompressible viscous flow
NASA Astrophysics Data System (ADS)
Zhu, Luoding
2007-11-01
Motivated by an important discovery on the drag scaling law (the four-thirds power law) of a flexible fiber in a flowing soap film by Alben, Shelley and Zhang (Nature 420, 479 (2002)) at high Reynolds numbers (2,000 < Re < 40,000), we investigate drag scaling laws at moderate Re for a compliant fiber tethered at the midpoint submerged in an incompressible viscous flow using the Immersed Boundary (IB) method. Our work shows that the scalings of drag with respective to oncoming flow speed vary with Re and the range of a dimensionless parameter ? that measures the relative importance of fluid kinetic energy and body elastic potential energy. In particular, the exponents of the power laws gradually decrease from approximately two to approximately four-thirds as Re decreases from 10 to 800 for ? in a certain range.
Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames
NASA Technical Reports Server (NTRS)
Dai, Z.; Faeth, G. M.
1999-01-01
Nonpremixed (diffusion) flames are attractive for practical applications because they avoid the stability, autoignition, flashback, etc. problems of premixed flames. Unfortunately, soot formation in practical hydrocarbon-fueled diffusion flames reduces their attractiveness due to widely-recognized public health and combustor durability problems of soot emissions. For example, more deaths are attributed to the emission of soot (15,000-60,000 deaths annually in the U.S. alone) than any other combustion-generated pollutant. In addition, continuum radiation from soot-containing flames is the principle heat load to combustor components and is mainly responsible for engine durability problems of aircraft and gas turbine engines. As a result, there is considerable interest in controlling both soot concentrations within flames and soot emissions from flames. Thus, the objective of the present investigation is to study ways to control soot formation in diffusion flames by manipulating the mixing process between the fuel and oxidant streams. In order to prevent the intrusion of gravity from masking flow properties that reduce soot formation in practical flames (where effects of gravity are small), methods developed during past work will be exploited to minimize effects of buoyant motion.
Stability of the laminar boundary-layer flow behind a roughness element
NASA Astrophysics Data System (ADS)
Shin, Yong-su; Rist, Ulrich; Krämer, Ewald
2015-01-01
Roughness elements in laminar boundary layers generate both high shear layers and streaky structures. Because these phenomena interact, it is difficult to precisely ascertain the dominant instability mechanisms. With the goal of explicating such interactions, we study the stability of a laminar boundary layer subject to a single roughness element at a Reynolds number subcritical of bypass transition. Our work involves two parts: bi-global linear stability theory (LST) analysis and corroborating experimental measurements. Linear stability analysis of a flat-plate boundary layer perturbed by streamwise streaks reveals the presence of several unstable modes. Of the dominant two modes, one exhibits spanwise symmetry and the other is antisymmetric. These modes are termed `varicose' and `sinuous,' respectively. Corroborating experiments were conducted in the laminar water channel of the University of Stuttgart. By simultaneously traversing two hot-film probes, we are able to confirm the presence of both eigenmodes predicted by LST and to extract relevant data for each: eigenvalues, eigenfunctions, growth rates and phase distributions. The main part of the experiments has been performed under `natural' conditions, i.e., in the absence of external forcing. As the amplitude of the sinuous part of the results is much smaller than the varicose one and hence affected by measurement noise, a case with asymmetric external forcing is presented as well. Despite some deficiencies of the setup, it is possible to enhance the sinuous mode with respect to the unforced case and to confirm its existence as an eigenmode of the flow.
Mechanical and statistical study of the laminar hole formation in transitional plane Couette flow
NASA Astrophysics Data System (ADS)
Rolland, Joran
2015-03-01
This article is concerned with the numerical study and modelling of two aspects the formation of laminar holes in transitional turbulence of plane Couette flow (PCF). On the one hand, we consider quenches: sudden decreases of the Reynolds number R which force the formation of holes. The Reynolds number is decreased from featureless turbulence to the range of existence of the oblique laminar-turbulent bands [ R g; R t]. The successive stages of the quench are studied by means of visualisations and measurements of kinetic energy and turbulent fraction. The behaviour of the kinetic energy is explained using a kinetic energy budget: it shows that viscosity causes quasi modal decay until lift-up equals it and creates a new balance. Moreover, the budget confirms that the physical mechanisms at play are independent of the way the quench is performed. On the other hand we consider the natural formation of laminar holes in the bands, near R g. The direct numerical simulations (DNS) show that holes in the turbulent bands provide a mechanism for the fragmented bands regime and orientation fluctuations near R g. Moreover the analysis of the fluctuations of kinetic energy toward low values demonstrates that the disappearance of turbulence in the bands can be described within the framework of large deviations. A large deviation function is extracted from the probability density function of the kinetic energy.
Moderated, Water-Based, Condensational Particle Growth in a Laminar Flow
Hering, Susanne V.; Spielman, Steven R.; Lewis, Gregory S.
2014-01-01
Presented is a new approach for laminar-flow water condensation that produces saturations above 1.5 while maintaining temperatures of less than 30°C in the majority of the flow and providing an exiting dew point below 15°C. With the original laminar flow water condensation method, the particle activation and growth occurs in a region with warm, wetted walls throughout, which has the side-effect of heating the flow. The “moderated” approach presented here replaces this warm region with a two sections – a short, warm, wet-walled “initiator”, followed by a cool-walled “moderator”. The initiator provides the water vapor that creates the supersaturation, while the moderator provides the time for particle growth. The combined length of the initiator and moderator sections is the same as that of the original, warm-walled growth section. Model results show that this new approach reduces the added heat and water vapor while achieving the same peak supersaturation and similar droplet growth. Experimental measurements confirm the trends predicted by the modeling. PMID:24839342
Deng, Bin; Tian, Yu; Yu, Xu; Song, Jian; Guo, Feng; Xiao, Yuxiu; Zhang, Zhiling
2014-04-11
A novel microfluidic chip with simple design, easy fabrication and low cost, coupled with high-sensitive laser induced fluorescence detection, was developed to provide continuous single-cell analysis based on dynamic cell manipulation in flowing streams. Making use of laminar flows, which formed in microchannels, single cells were aligned and continuously introduced into the sample channel and then detection channel in the chip. In order to rapidly lyse the moving cells and completely transport cellular contents into the detection channel, the angle of the side-flow channels, the asymmetric design of the channels, and the number, shape and layout of micro-obstacles were optimized for effectively redistributing and mixing the laminar flows of single cells suspension, cell lysing reagent and detection buffer. The optimized microfluidic chip was an asymmetric structure of three microchannels, with three microcylinders at the proper positions in the intersections of channels. The microchip was evaluated by detection of anticancer drug doxorubicin (DOX) uptake and membrane surface P-glycoprotein (P-gp) expression in single leukemia K562 cells. An average throughput of 6-8 cells min(-1) was achieved. The detection results showed the cellular heterogeneity in DOX uptake and surface P-gp expression within K562 cells. Our researches demonstrated the feasibility and simplicity of the newly developed microfluidic chip for chemical single-cell analysis. PMID:24745743
Incompressible SPH Model for Simulating Violent Free-Surface Fluid Flows
NASA Astrophysics Data System (ADS)
Staroszczyk, Ryszard
2014-06-01
In this paper the problem of transient gravitational wave propagation in a viscous incompressible fluid is considered, with a focus on flows with fast-moving free surfaces. The governing equations of the problem are solved by the smoothed particle hydrodynamics method (SPH). In order to impose the incompressibility constraint on the fluid motion, the so-called projection method is applied in which the discrete SPH equations are integrated in time by using a fractional-step technique. Numerical performance of the proposed model has been assessed by comparing its results with experimental data and with results obtained by a standard (weakly compressible) version of the SPH approach. For this purpose, a plane dam-break flow problem is simulated, in order to investigate the formation and propagation of a wave generated by a sudden collapse of a water column initially contained in a rectangular tank, as well as the impact of such a wave on a rigid vertical wall. The results of simulations show the evolution of the free surface of water, the variation of velocity and pressure fields in the fluid, and the time history of pressures exerted by an impacting wave on a wall.
Identification of whistling ability of a single hole orifice from an incompressible flow simulation
Lacombe, Romain; Moussou, Pierre
2012-07-01
Pure tone noise from orifices in pipe result from vortex shedding with lock-in. Acoustic amplification at the orifice is coupled to resonant condition to create self-sustained oscillations. One key feature of this phenomenon is hence the ability of an orifice to amplify acoustic waves in a given range of frequencies. Here a numerical investigation of the linear response of an orifice is undertaken, with the support of experimental data for validation. The study deals with a sharp edge orifice. Its diameter equals to 0.015 m and its thickness to 0.005 m. The pipe diameter is 0.030 m. An air flow with a Mach number 0.026 and a Reynolds number 18000 in the main pipe is present. At such a low Mach number; the fluid behavior can reasonably be described as locally incompressible. The incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved with the help of a finite volume fluid mechanics software. The orifice is submitted to an average flow velocity, with superimposed small harmonic perturbations. The harmonic response of the orifice is the difference between the upstream and downstream pressures, and a straightforward calculation brings out the acoustic impedance of the orifice. Comparison with experiments shows that the main physical features of the whistling phenomenon are reasonably reproduced. (authors)
An adaptive level set approach for incompressible two-phase flows
Sussman, M. [Univ. of California, Davis, CA (United States). Dept. of Mathematics] [Univ. of California, Davis, CA (United States). Dept. of Mathematics; Almgren, A.S.; Bell, J.B.; Colella, P.; Howell, L.H.; Welcome, M.L. [Lawrence Berkeley National Lab., CA (United States). Center for Computational Sciences and Engineering] [Lawrence Berkeley National Lab., CA (United States). Center for Computational Sciences and Engineering
1999-01-01
The authors 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 level set function, which is smooth. In addition, the free surface can merge or break up with no special treatment. The authors maintain the level set function as the signed distance from the free surface in order to accurately 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 free surface with a minimum of addition expense. The authors present two-dimensional axisymmetric and fully three-dimensional results of air bubble and water drop computations.
Efficient simulation of incompressible viscous flow over multi-element airfoils
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan
1992-01-01
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.
Efficient simulation of incompressible viscous flow over multi-element airfoils
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan
1993-01-01
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.
NASA Technical Reports Server (NTRS)
Harris, Charles D.; Harvey, William D.; Brooks, Cuyler W., Jr.
1988-01-01
A large-chord, swept, supercritical, laminar-flow-control (LFC) airfoil was designed and constructed and is currently undergoing tests in the Langley 8 ft Transonic Pressure Tunnel. The experiment was directed toward evaluating the compatibility of LFC and supercritical airfoils, validating prediction techniques, and generating a data base for future transport airfoil design as part of NASA's ongoing research program to significantly reduce drag and increase aircraft efficiency. Unique features of the airfoil included a high design Mach number with shock free flow and boundary layer control by suction. Special requirements for the experiment included modifications to the wind tunnel to achieve the necessary flow quality and contouring of the test section walls to simulate free air flow about a swept model at transonic speeds. Design of the airfoil with a slotted suction surface, the suction system, and modifications to the tunnel to meet test requirements are discussed.
Evaluation of laminar flow control systems concepts for subsonic commercial transport aircraft
NASA Technical Reports Server (NTRS)
Pearce, W. E.
1983-01-01
An evaluation was made of laminar flow control (LFC) system concepts for subsonic commercial transport aircraft. Configuration design studies, performance analyses, fabrication development, structural testing, wind tunnel testing, and contamination-avoidance techniques were included. As a result of trade studies, a configuration with LFC on the upper wing surface only, utilizing an electron beam-perforated suction surface, and employing a retractable high-lift shield for contamination avoidance, was selected as the most practical LFC system. The LFC aircraft was then compared with an advanced turbulent aircraft designed for the same mission. This comparison indicated significant fuel savings and reduced direct operating cost benefits would result from using LFC.
Second Law Analysis of Laminar Flow In A Channel Filled With Saturated Porous Media
NASA Astrophysics Data System (ADS)
Makinde, O. D.; Osalusi, E.
2005-06-01
The entropy generation rate in a laminar flow through a channel filled with saturated porous media is investigated. The upper surface of the channel is adiabatic and the lower wall is assumed to have a constant heat flux. The Brinkman model is employed. Velocity and temperature profiles are obtained for large Darcy number (Da) and used to obtain the entropy generation number and the irreversibility ratio. Generally, our result shows that heat transfer irreversibility dominates over fluid friction irreversibility (i.e. 0 < ø < 1), and viscous dissipation has no effect on the entropy generation rate at the centerline of the channel.
Preliminary design characteristics of a subsonic business jet concept employing laminar flow control
NASA Technical Reports Server (NTRS)
Turriziani, R. V.; Lovell, W. A.; Price, J. E.; Quartero, C. B.; Washburn, G. F.
1978-01-01
Aircraft configurations were developed with laminar flow control (LFC) and without LFC. The LFC configuration had approximately eleven percent less parasite drag and a seven percent increase in the maximum lift-to drag ratio. Although these aerodynamic advantages were partially offset by the additional weight of the LFC system, the LFC aircraft burned from six to eight percent less fuel for comparable missions. For the trans-atlantic design mission with the gross weight fixed, the LFC configuration would carry a greater payload for ten percent fuel per passenger mile.
Natural laminar flow airfoil design considerations for winglets on low-speed airplanes
NASA Technical Reports Server (NTRS)
Vandam, C. P.
1984-01-01
Winglet airfoil section characteristics which significantly influence cruise performance and handling qualities of an airplane are discussed. A good winglet design requires an airfoil section with a low cruise drag coefficient, a high maximum lift coefficient, and a gradual and steady movement of the boundary layer transition location with angle of attack. The first design requirement provides a low crossover lift coefficient of airplane drag polars with winglets off and on. The other requirements prevent nonlinear changes in airplane lateral/directional stability and control characteristics. These requirements are considered in the design of a natural laminar flow airfoil section for winglet applications and chord Reynolds number of 1 to 4 million.
Simulated airline service experience with laminar-flow control leading-edge systems
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.; Fisher, David F.; Jennett, Lisa A.; Fischer, Michael C.
1987-01-01
The first JetStar leading edge flight test was made November 30, 1983. The JetStar was flown for more than 3 years. The titanium leading edge test articles today remain in virtually the same condition as they were in on that first flight. No degradation of laminar flow performance has occurred as a result of service. The JetStar simulated airline service flights have demonstrated that effective, practical leading edge systems are available for future commercial transports. Specific conclusions based on the results of the simulated airline service test program are summarized.
Flight evaluation of an insect contamination protection system for laminar flow wings
NASA Technical Reports Server (NTRS)
Croom, C. C.; Holmes, B. J.
1985-01-01
The maintenance of minimum wing leading edge contamination is critical to the preservation of drag-reducing laminar flow; previous methods for the prevention of leading edge contamination by insects have, however, been rendered impractical by their excessive weight, cost, or inconvenience. Attention is presently given to the results of a NASA flight experiment which evaluated the performance of a porous leading edge fluid-discharge ice protection system in the novel role of insect contamination removal; high insect contamination conditions were also noted in the experiment. Very small amounts of the fluid are found to be sufficient for insect contamination protection.
Unique laminar-flow stability limit based shallow-water theory
Chen, Cheng-lung
1993-01-01
Two approaches are generally taken in deriving the stability limit for the Froude member (Fs) for laminar sheet flow. The first approach used the Orr-Sommerfeld equation, while the second uses the cross-section-averaged equations of continuity and motion. Because both approaches are based on shallow-water theory, the values of Fs obtained from both approaches should be identical, yet in the literature they are not. This suggests that a defect exists in at least one of the two approaches. After examining the governing equations used in both approaches, one finds that the existing cross-section -averaged equation of motion is dependent on the frame of reference.
Multiple-relaxation-time lattice Boltzmann modeling of incompressible flows in porous media
Qing Liu; Ya-Ling He; Chao He
2014-09-20
In this paper, a two-dimensional eight-velocity (D2Q8) multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is proposed for incompressible porous flows at the representative elementary volume scale based on the Brinkman-Forchheimer-extended Darcy formulation. In the model, the porosity is included into the pressure-based equilibrium moments, and the linear and nonlinear drag forces of the porous media are incorporated into the model by adding a forcing term to the MRT-LB equation in the moment space. Through the Chapman-Enskog analysis, the generalized Navier-Stokes equations can be recovered exactly without artificial compressible errors. Numerical simulations of several typical two-dimensional porous flows are carried out to validate the present MRT-LB model. The numerical results of the present MRT-LB model are in good agreement with the analytical solutions and/or other numerical solutions reported in the literature.
Parallel solution of high-order numerical schemes for solving incompressible flows
NASA Technical Reports Server (NTRS)
Milner, Edward J.; Lin, Avi; Liou, May-Fun; Blech, Richard A.
1993-01-01
A new parallel numerical scheme for solving incompressible steady-state flows is presented. The algorithm uses a finite-difference approach to solving the Navier-Stokes equations. The algorithms are scalable and expandable. They may be used with only two processors or with as many processors as are available. The code is general and expandable. Any size grid may be used. Four processors of the NASA LeRC Hypercluster were used to solve for steady-state flow in a driven square cavity. The Hypercluster was configured in a distributed-memory, hypercube-like architecture. By using a 50-by-50 finite-difference solution grid, an efficiency of 74 percent (a speedup of 2.96) was obtained.
A new approach to wall modeling in LES of incompressible flow via function enrichment
Krank, Benjamin
2015-01-01
A novel approach to wall modeling for the incompressible Navier-Stokes equations including flows of moderate and large Reynolds numbers is presented. The basic idea is that a problem-tailored function space allows prediction of turbulent boundary layer gradients with very coarse meshes. The proposed function space consists of a standard polynomial function space plus an enrichment, which is constructed using Spalding's law-of-the-wall. The enrichment function is not enforced but "allowed" in a consistent way and the overall methodology is much more general and also enables other enrichment functions. The proposed method is closely related to detached-eddy simulation as near-wall turbulence is modeled statistically and large eddies are resolved in the bulk flow. Interpreted in terms of a three-scale separation within the variational multiscale method, the standard scale resolves large eddies and the enrichment scale represents boundary layer turbulence in an averaged sense. The potential of the scheme is shown...
Flutter control of incompressible flow turbomachine blade rows by splitter blades
NASA Technical Reports Server (NTRS)
Chiang, Hsiao-Wei D.; Fleeter, Sanford
1991-01-01
Splitter blades as a passive flutter control technique is investigated by developing a mathematical model to predict the stability of an aerodynamically loaded splittered-rotor operating in an incompressible flow field. The splitter blades, positioned circumferentially in the flow passage between two principal blades, introduce aerodynamic and/or combined aerodynamic-structural detuning into the rotor. The two-dimensional oscillating cascade unsteady aerodynamics, including steady loading effects, are determined by developing a complete first-order unsteady aerodynamic analysis together with an unsteady aerodynamic influence coefficient technique. The torsion mode flutter of both uniformly spaced tuned rotors and detuned rotors are predicted by incorporating the unsteady aerodyamic influence coefficients into a single-degree-of-freedom aeroelastic model. This model is then utilized to demonstrate that incorporating splitters into unstable rotor configurations results in stable splittered-rotor configurations.
NASA Astrophysics Data System (ADS)
Sabir, O.; Ya, T. M. Y. S. Tuan; Ahmad, Norhafizan; Nukman, Y.
2013-12-01
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.
Frequency-selection mechanism in incompressible open-cavity flows via reflected instability waves
NASA Astrophysics Data System (ADS)
Tuerke, F.; Sciamarella, D.; Pastur, L. R.; Lusseyran, F.; Artana, G.
2015-01-01
We present an alternative perspective on nonharmonic mode coexistence, commonly found in the shear layer spectrum of open-cavity flows. Modes obtained by a local linear stability analysis of perturbations to a two-dimensional, incompressible, and inviscid sheared flow over a cavity of finite length and depth were conditioned by a so-called coincidence condition first proposed by Kulikowskii [J. Appl. Math. Mech. 30, 180 (1966), 10.1016/0021-8928(66)90066-9] which takes into account instability wave reflection within the cavity. The analysis yields a set of discrete, nonharmonic frequencies, which compare well with experimental results [Phys. Fluids 20, 114101 (2008), 10.1063/1.3005435; Exp. Fluids 50, 905 (2010), 10.1007/s00348-010-0942-9].
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
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.
Three-dimensional measurement of the laminar flow field inside a static mixer
NASA Astrophysics Data System (ADS)
Speetjens, Michel; Jilisen, Rene; Bloemen, Paul
2011-11-01
Static mixers are widely used in industry for laminar mixing of viscous fluids as e.g. polymers and food stuffs. Moreover, given the similarities in flow regime, static mixers often serve as model for compact mixers for process intensification and even for micro-mixers. This practical relevance has motivated a host of studies on the mixing characteristics of static mixers and their small-scale counterparts. However, these studies are primarily theoretical and numerical. Experimental studies, in contrast, are relatively rare and typically restricted to local 2D flow characteristics or integral quantities (pressure drop, residence-time distributions). The current study concerns 3D measurements on the laminar flow field inside a static mixer using 3D Particle-Tracking Velocimetry (3D-PTV) Key challenges to the 3D-PTV image-processing procedure are the optical distortion and degradation of the particle imagery due to light refraction and reflection caused by the cylindrical boundary and the internal elements. Ways to tackle these challenges are discussed and first successful 3D measurements in an actual industrial static mixer are presented.
Response of hot element wall shear stress gages in laminar oscillating flows
NASA Technical Reports Server (NTRS)
Cook, W. J.; Murphy, J. D.; Giddings, T. A.
1986-01-01
An experimental investigation of the time-dependent response of hot element wall shear stress gages in unsteady periodic air flows is reported. The study has focused on wall shear stress in laminar oscillating flows produced on a flat plate by a free stream velocity composed of a mean component and a superposed sinusoidal variation. Two types of hot element gages, platinum film and flush wire, were tested for values of reduced frequency ranging from 0.14 to 2.36. Values of the phase angle of the wall shear stress variation relative to the free stream velocity, as indicated by the hot element gages, are compared with numerical prediction. The comparisons show that the gages indicate a wall shear stress variation that lags the true variation, and that the gages will also not indicate the correct wall shear stress variation in periodic turbulent flows.
Dispersion in cylindrical channels on the laminar flow at low Fourier numbers.
Kucza, Witold; D?browa, Juliusz; Nawara, Katarzyna
2015-06-30
A numerical solution of the uniform dispersion model in cylindrical channels at low Fourier numbers is presented. The presented setup allowed to eliminate experimental non-idealities interfering the laminar flow. Double-humped responses measured in a flow injection system with impedance detection agreed with those predicted by theory. Simulated concentration profiles as well as flow injection analysis (FIA) responses show the predictive and descriptive power of the numerical approach. A strong dependence of peak shapes on Fourier numbers, at its low values, makes the approach suitable for determination of diffusion coefficients. In the work, the uniform dispersion model coupled with the Levenberg-Marquardt method of optimization allowed to determine the salt diffusion coefficient for KCl, NaCl, KMnO4 and CuSO4 in water. The determined values (1.83, 1.53, 1.57 and 0.90)×10(-9)m(2)s(-1), respectively, agree well with the literature data. PMID:26041524
Convective Heat Transfer Augmentation by Flexible fins in Laminar Channel Pulsating flow
Joshi, Rakshitha U; Bhardwaj, Rajneesh
2015-01-01
Fluid-structure interaction (FSI) of thin flexible fins coupled with convective heat transfer has applications in energy harvesting and in understanding functioning of several biological systems. We numerically investigate FSI of the thin flexible fins involving large-scale flow-induced deformation as a potential heat transfer enhancement technique. An in-house, strongly-coupled fluid-structure interaction (FSI) solver is employed in which flow and structure solvers are based on sharp-interface immersed boundary and finite element method, respectively. We consider twin flexible fins in a heated channel with laminar pulsating cross flow. The vortex ring past the fin sweep higher sources of vorticity generated on the channel walls out into the downstream - promoting the mixing of the fluid. The moving fin assists in convective mixing, augmenting convection in bulk and at the walls; and thereby reducing thermal boundary layer thickness and improving heat transfer at the channel walls. The thermal augmentation is...
Attenuation of Sinusoidal Perturbations Superimposed on Laminar Flow of a Liquid in a Long Line
NASA Technical Reports Server (NTRS)
Holland, Carl M.; Blade, Robert J.; Dorsch, Robert G.
1965-01-01
The attenuation constant for sinusoidal pressure and flow perturbations superimposed on the laminar flow of a viscous liquid was measured in a system consisting of a long, straight, cylindrical hydraulic line. The upstream and downstream ends of the line were securely fastened t o the ground. A sinusoidal perturbation was imposed on the mean flow at the upstream end by means of a s m a l l oscillation of a throttle valve abmt a partly open mean position. The downstream end was terminated in a restricting orifice. Pressure perturbations were measured at three locations along the line for frequencies from 15 t o 100 cps. These pressure measurements were reduced by use of a pair of complex damped acoustic one-dimensional wave equations to obtain the attenuation constant along with the phase constant and the dimensionless downstream admittance. For the range of frequencies investigated, the experimental values of the attenuation constant are in good agreement with classical theory.
Direct calibration framework of triple-hole pressure probes for incompressible flow
NASA Astrophysics Data System (ADS)
Argüelles Díaz, K. M.; Fernández Oro, J. M.; Blanco Marigorta, E.
2008-07-01
This paper carries out a mathematical analysis of the limits and data reduction techniques of three-hole pressure (THP) probes operating in a 'non-nulling' mode for incompressible flow. As a result of this analysis, a direct procedure is advanced, based on the distinction of several zones within the angular range, where different relations can be applied to obtain the flow variables. This proposal provides a considerable increment of the operative angular range of THP probes: about ±70° instead of the typical ±35° for a cylindrical probe. This may extend the application of these probes in highly unsteady flows, or reduce the acquisition and data reduction effort minimizing the necessity of probe reorientation. The influence of the data reduction technique on the uncertainty transmission is also presented in the paper. From detailed considerations, it is demonstrated that the results uncertainty depends on the specific probe, but it is unaffected by the mathematical procedure employed to calculate the flow variables. Validation measurements with pneumatic probes have been made for Reynolds numbers from 4 × 103 to 3.5 × 104. In addition, a highly unsteady measurement in a low-speed axial flow fan is succinctly analysed. Taking into account both attainable angular range and uncertainty, it is determined that the optimal construction angle for the holes of a low frequency response THP probe lies between 30° and 60°, while for fast response probes, in order to avoid the separated flow region, the optimal construction angle is around 30°.
NASA Astrophysics Data System (ADS)
Wang, Y.; Shu, C.; Huang, H. B.; Teo, C. J.
2015-01-01
A multiphase lattice Boltzmann flux solver (MLBFS) is proposed in this paper for incompressible multiphase flows with low- and large-density-ratios. In the solver, the flow variables at cell centers are given from the solution of macroscopic governing differential equations (Navier-Stokes equations recovered by multiphase lattice Boltzmann (LB) model) by the finite volume method. At each cell interface, the viscous and inviscid fluxes are evaluated simultaneously by local reconstruction of solution for the standard lattice Boltzmann equation (LBE). The forcing terms in the governing equations are directly treated by the finite volume discretization. The phase interfaces are captured by solving the phase-field Cahn-Hilliard equation with a fifth order upwind scheme. Unlike the conventional multiphase LB models, which restrict their applications on uniform grids with fixed time step, the MLBFS has the capability and advantage to simulate multiphase flows on non-uniform grids. The proposed solver is validated by several benchmark problems, such as two-phase co-current flow, Taylor-Couette flow in an annulus, Rayleigh-Taylor instability, and droplet splashing on a thin film at density ratio of 1000 with Reynolds numbers ranging from 20 to 1000. Numerical results show the reliability of the proposed solver for multiphase flows with high density ratio and high Reynolds number.
Base pressure associated with incompressible flow past wedges at high Reynolds numbers
NASA Technical Reports Server (NTRS)
Warpinski, N. R.; Chow, W. L.
1979-01-01
A model is suggested to study the viscid-inviscid interaction associated with steady incompressible flow past wedges of arbitrary angles. It is shown from this analysis that the determination of the nearly constant pressure (base pressure) prevailing within the near wake is really the heart of the problem and this pressure can only be determined from these interactive considerations. The basic free streamline flow field is established through two discrete parameters which should adequately describe the inviscid flow around the body and the wake. The viscous flow processes such as boundary-layer buildup along the wedge surface, jet mixing, recompression, and reattachment which occurs along the region attached to the inviscid flow in the sense of the boundary-layer concept, serve to determine the aforementioned parameters needed for the establishment of the inviscid flow. It is found that the point of reattachment behaves as a saddle point singularity for the system of equations describing the viscous recompression process. Detailed results such as the base pressure, pressure distributions on the wedge surface, and the wake geometry as well as the influence of the characteristic Reynolds number are obtained. Discussion of these results and their comparison with the experimental data are reported.
New Finite Difference Methods Based on IIM for Inextensible Interfaces in Incompressible Flows.
Li, Zhilin; Lai, Ming-Chih
2011-01-01
In this paper, new finite difference methods based on the augmented immersed interface method (IIM) are proposed for simulating an inextensible moving interface in an incompressible two-dimensional flow. The mathematical models arise from studying the deformation of red blood cells in mathematical biology. The governing equations are incompressible Stokes or Navier-Stokes equations with an unknown surface tension, which should be determined in such a way that the surface divergence of the velocity is zero along the interface. Thus, the area enclosed by the interface and the total length of the interface should be conserved during the evolution process. Because of the nonlinear and coupling nature of the problem, direct discretization by applying the immersed boundary or immersed interface method yields complex nonlinear systems to be solved. In our new methods, we treat the unknown surface tension as an augmented variable so that the augmented IIM can be applied. Since finding the unknown surface tension is essentially an inverse problem that is sensitive to perturbations, our regularization strategy is to introduce a controlled tangential force along the interface, which leads to a least squares problem. For Stokes equations, the forward solver at one time level involves solving three Poisson equations with an interface. For Navier-Stokes equations, we propose a modified projection method that can enforce the pressure jump condition corresponding directly to the unknown surface tension. Several numerical experiments show good agreement with other results in the literature and reveal some interesting phenomena. PMID:23795308
Kaushik, D. K.; Keyes, D. E.; Smith, B. F.
1999-02-24
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.
Laminar flow in a microchannel with superhydrophobic walls exhibiting transverse ribs
NASA Astrophysics Data System (ADS)
Davies, J.; Maynes, D.; Webb, B. W.; Woolford, B.
2006-08-01
One approach recently proposed for reducing the frictional resistance to liquid flow in microchannels is the patterning of microribs and cavities on the channel walls. When treated with a hydrophobic coating, the liquid flowing in the microchannel wets only the surfaces of the ribs, and does not penetrate the cavities, provided the pressure is not too high. The net result is a reduction in the surface contact area between channel walls and the flowing liquid. For microribs and cavities that are aligned normal to the channel axis (principal flow direction), these micropatterns form a repeating, periodic structure. This paper presents results of a study exploring the momentum transport in a parallel-plate microchannel with such microengineered walls. The investigation explored the entire laminar flow Reynolds number range and characterized the influence of the vapor cavity depth on the overall flow field. The liquid-vapor interface (meniscus) in the cavity regions is treated as flat in the numerical analysis and two conditions are explored with regard to the cavity region: (1) The liquid flow at the liquid-vapor interface is treated as shear-free (vanishing viscosity in the vapor region), and (2) the liquid flow in the microchannel core and the vapor flow within the cavity are coupled by matching the velocity and shear stress at the interface. Regions of slip and no-slip behavior exist and the velocity field shows distinct variations from classical laminar flow in a parallel-plate channel. The local streamwise velocity profiles, interfacial velocity distributions, and maximum interfacial velocities are presented for a number of scenarios and provide a sound understanding of the local flow physics. The predictions and accompanying measurements reveal that significant reductions in the frictional pressure drop (enhancement in effective fluid slip at the channel walls) can be achieved relative to the classical smooth-channel Stokes flow. Reductions in the friction factor and enhancements in the fluid slip are greater as the cavity-to-rib length ratio is increased (increasing shear-free fraction) and as the channel hydraulic diameter is decreased. The results also show that the slip length and average friction factor-Reynolds number product exhibit a flow Reynolds dependence. Furthermore, the predictions reveal the global impact of the vapor cavity depth on the overall frictional resistance.
Data Analysis for the NASA/Boeing Hybrid Laminar Flow Control Crossflow Experiment
NASA Technical Reports Server (NTRS)
Eppink, Jenna L.; Wlezien, Richard
2011-01-01
The Hybrid-Laminar Flow Control (HLFC) Crossflow Experiment, completed in 1995. generated a large database of boundary layer stability and transition data that was only partially analyzed before data analysis was abruptly ended in the late 1990's. Renewed interest in laminar flow technologies prompted additional data analysis, to integrate all data, including some post-test roughness and porosity measurements. The objective is to gain new insights into the effects of suction on boundary layer stability. A number of challenges were encountered during the data analysis, and their solutions are discussed in detail. They include the effect of the probe vibration, the effect of the time-varying surface temperature on traveling crossflow instabilities, and the effect of the stationary crossflow modes on the approximation of wall location. Despite the low turbulence intensity of the wind tunnel (0.01 to 0.02%), traveling crosflow disturbances were present in the data, in some cases at amplitudes up to 1% of the freestream velocity. However, the data suggests that transition was dominated by stationary crossflow. Traveling crossflow results and stationary data in the presence of suction are compared with linear parabolized stability equations results as a way of testing the quality of the results.
Heat transfer properties of liquid-solid suspensions in laminar flow
Wright, A.W.
1983-01-01
Thermal properties of liquid-solid suspensions were evaluated relative to solid volumetric concentration and solid particle size or size distribution. The approach taken in this investigation was: a theoretical analysis and an experimental program involving liquid-solid suspensions. The theoretical analysis considered uniform wall heat flux to a suspension in laminar flow. Conditions modelled were: one in which no phase change occurs relative to the solids, and the second where a phase transition is present. The numerical solutions utilized explicit finite difference techniques. A unique feature of this research was the experimental technique. This method consisted of steady-state analysis on a dynamic system. The suspensions were in laminar flow in a vertical tube with a constant wall heat flux. The thermal property of particular importance was the effective thermal conductivity. Two fluid systems were tested, water and a suspension of water and hollow glass micropheres. Three size classifications were used ranging from 20 to 130 micron diameter spheres. The maximum concentration was 20% by volume.
Miami, University of
eyewall formation in tropical cyclones by using two-dimensional incompressible flow. Those studies as the tropical cyclone core or as purely asymmetric vorticity perturbations that are an order of magnitude weaker than the core. However, both observations and full-physics simulations of tropical cyclones indicate
A coupled volume-of-fluid and level set (VOSET) method for computing incompressible two-phase flows
Frey, Pascal
2009 Available online 10 November 2009 Keywords: VOF method LS method VOSET method Volume fractionA coupled volume-of-fluid and level set (VOSET) method for computing incompressible two-phase flows function Level set function a b s t r a c t A coupled volume-of-fluid and level set (VOSET) method, which
An efficient implicit direct forcing immersed boundary method for incompressible flows
NASA Astrophysics Data System (ADS)
Cai, S.-G.; Ouahsine, A.; Smaoui, H.; Favier, J.; Hoarau, Y.
2015-01-01
A novel efficient implicit direct forcing immersed boundary method for incompressible flows with complex boundaries is presented. In the previous work [1], the calculation is performed on the Cartesian grid regardless of the immersed object, with a fictitious force evaluated on the Lagrangian points to mimic the presence of the physical boundaries. However the explicit direct forcing method [1] fails to accurately impose the non-slip boundary condition on the immersed interface. In the present work, the calculation is based on the implicit treatment of the artificial force while in an effective way of system iteration. The accuracy is also improved by solving the Navier-Stokes equation with the rotational incremental pressure- correction projection method of Guermond and Shen [2]. Numerical simulations performed with the proposed method are in good agreement with those in the literature.
A narrow-band gradient-augmented level set method for multiphase incompressible flow
NASA Astrophysics Data System (ADS)
Lee, Curtis; Dolbow, John; Mucha, Peter J.
2014-09-01
A finite-difference based numerical method for the simulation of multiphase incompressible flows is presented. The proposed algorithm adapts the gradient-augmented level set method of Nave et al. [25] for use in multiphase fluid simulations by interpolating the fluid velocity and introducing a simple reinitialization procedure. The method is carried out only along a narrow band surrounding the interface, reducing computational effort while preserving the advantages of the gradient-augmented method. Numerical results show excellent agreement with an analytical solution and available experimental data. A new experimental benchmark is introduced, using data gathered in a wedge-driven wave tank. In addition to the optimally local advection scheme and sub-grid resolution afforded by the new method, numerical comparisons with the standard level set method reveal superior volume conservation.
A GPU cluster optimized multigrid scheme for computing unsteady incompressible fluid flow
Tegze, György
2013-01-01
A multigrid scheme has been proposed that allows efficient implementation on modern CPUs, many integrated core devices (MICs), and graphics processing units (GPUs). It is shown that wide single instruction multiple data (SIMD) processing engines are used efficiently when a deep, 2h grid hierarchy is replaced with a two level scheme using 16h-32h restriction. The restriction length can be fitted to the SIMD width to fully utilize the capabilities of modern CPUs and GPUs. This way, optimal memory transfer is also ensured, since no strided memory access is required. The number of the expensive restriction steps is greatly reduced, and these are executed on bigger chunks of data that allows optimal caching strategies. A higher order interpolated stencil was developed to improve convergence rate via minimizing spurious interference between the coarse and the fine scale solutions. The method is demonstrated on solving the pressure equation for 2D incompressible fluid flow: The benchmark setups cover shear driven la...
Effects of mistuning on bending-torsion flutter and response of a cascade in incompressible flow
NASA Technical Reports Server (NTRS)
Kaza, K. R. V.; Kielb, R. E.
1981-01-01
This paper presents an investigation of the effects of blade mistuning on the aeroelastic stability and response of a cascade in incompressible flow. 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.
Analysis of two-dimensional incompressible flows by a subsurface panel method
NASA Technical Reports Server (NTRS)
Moran, J.; Cole, K.; Wahl, D.
1980-01-01
A new approach to panel methods is explored for two-dimensional steady incompressible flows. The method uses linear distributions of sources and vortices on straight-line panels, but satisfies boundary conditions on the actual body surface, at nodes that are also end points of the panels. The result is continuity in body-surface velocity distribution, without recourse to numerical quadrature for the velocity influence coefficients. The method is unusually sensitive to the distribution of the nodes. For example, it almost always fails to give acceptable results when the nodes are distributed randomly. However, the continuity of the velocity distribution makes possible a unique node redistribution scheme, which may be iterated to give accurate results reliably.
Weyand, Birgit; Israelowitz, Meir; Kramer, James; Bodmer, Christian; Noehre, Mariel; Strauss, Sarah; Schmälzlin, Elmar; Gille, Christoph; von Schroeder, Herbert P.; Reimers, Kerstin; Vogt, Peter M.
2015-01-01
A three-dimensional computational fluid dynamics- (CFD-) model based on a differential pressure laminar flow bioreactor prototype was developed to further examine performance under changing culture conditions. Cell growth inside scaffolds was simulated by decreasing intrinsic permeability values and led to pressure build-up in the upper culture chamber. Pressure release by an integrated bypass system allowed continuation of culture. The specific shape of the bioreactor culture vessel supported a homogenous flow profile and mass flux at the scaffold level at various scaffold permeabilities. Experimental data showed an increase in oxygen concentration measured inside a collagen scaffold seeded with human mesenchymal stem cells when cultured in the perfusion bioreactor after 24?h compared to static culture in a Petri dish (dynamic: 11% O2 versus static: 3% O2). Computational fluid simulation can support design of bioreactor systems for tissue engineering application.
Transition from laminar to space charge dominated flow in a low energy electron beam in ELTRAP.
NASA Astrophysics Data System (ADS)
Pozzoli, R.; Bettega, G.; Cavaliere, F.; Illiberi, A.; Rome', M.; Cavenago, M.; Tsidulko, Yu.
2003-10-01
The dynamics of a low energy electron beam is studied in the Malmberg-Penning trap ELTRAP, where an electron plasma continuously flows from the emitting thermionic cathode to a collector (phosphor screen), held at a potential of few kV. The transition from a laminar to a space charge dominated flow is characterized by the formation of a reflection surface which prevents the central part of the beam from reaching the screen, and by the rapid development of seemingly 2D coherent structures in the resulting annular beam. The experimental investigation is performed by means of a CCD camera diagnostic, which allows to measure the density distribution of the electrons reaching the phosphor screen. It is shown that the transition corresponds to a bifurcation of the system. The observed processes are interpreted using fluid models and a recently developed 3D drift-Poisson PIC code.
Development of an explicit time marching procedure for laminar and turbulent flow
NASA Technical Reports Server (NTRS)
1986-01-01
A finite-volume based, time-marching method for turbulent and laminar flows is described. Extensions to the computational procedure to allow the handling of shock induced separation and large regions of strong backflow are emphasized. Two test cases are considered, the United Technologies Research Center (UTRC) separated and reattached turbulent boundary layer and the strong shock case in the McDonnell Douglas Research Lab (MDRL) transonic diffuser G. The extended method worked well on the UTRC flow with a boundary layer blockage of 58% and a maximum backflow velocity of 37% of the local maximum free-stream velocity. It also worked well on the MDRL diffuser with a shock Mach number of 1.353 and a maximum backflow velocity of -71.7 m/s. A Mach number dependent interpolation formula for effective pressure was developed for use in density-update time-marching methods.
Lubricant-impregnated surfaces for drag reduction in viscous laminar flow
NASA Astrophysics Data System (ADS)
Solomon, Brian; Khalil, Karim; Varanasi, Kripa; MIT Team
2013-11-01
For the first time, we explore the potential of lubricant impregnated surfaces (LIS) in reducing drag. LIS, inspired by the surface of the Nepenthes pitcher plant, have been introduced as a novel way of functionalizing a surface. LIS are characterized by extremely low contact angle hysteresis and have been show to effectively repel various liquids including water, oils, ketchup and blood. Motivated by the slippery nature of such surfaces, we explore the potential of LIS to reduce drag in internal flows. We observe a reduction in drag for LIS surfaces in a viscous laminar drag flow and model the impact of relevant system parameters (lubricant viscosity, working fluid viscosity, solid fraction, depth of texture, etc.).
Choudhari, Meelan; Chang, Chau-Lyan; Jiang, Li
2005-05-15
Laminar flow control (LFC) is one of the key enabling technologies for quiet and efficient supersonic aircraft. Recent work at Arizona State University (ASU) has led to a novel concept for passive LFC, which employs distributed leading edge roughness to limit the growth of naturally dominant crossflow instabilities in a swept-wing boundary layer. Predicated on nonlinear modification of the mean boundary-layer flow via controlled receptivity, the ASU concept requires a holistic prediction approach that accounts for all major stages within transition in an integrated manner. As a first step in developing an engineering methodology for the design and optimization of roughness-based supersonic LFC, this paper reports on canonical findings related to receptivity plus linear and nonlinear development of stationary crossflow instabilities on a Mach 2.4, 73 degrees swept airfoil with a chord Reynolds number of 16.3 million. PMID:16105770
NASA Astrophysics Data System (ADS)
Barakos, G.; Mitsoulis, E.; Assimacopoulos, D.
1994-04-01
Numerical simulations have been undertaken for the benchmark problem of natural convection flow in a square cavity. The control volume method is used to solve the conservation equations for laminar and turbulent flows for a series of Rayleigh numbers (Ra) reaching values up to 10(exp 10). The k-epsilon model has been used for turbulence modelling with and without logarithmic wall functions. Uniform and non-uniform (stretched) grids have been employed with increasing density to guarantee accurate solutions, especially near the walls for high Ra-values. ADI and SIP solvers are implemented to accelerate convergence. Excellent agreement is obtained with previous numerical solutions, while some discrepancies with others for high Ra-values may be due to a possibly different implementation of the wall functions. Comparisons with experimental data for heat transfer (Nusselt number) clearly demonstrates the limitations of the standard k-epsilon model with logarithmic wall functions, which gives significant overpredictions.
Fourth-generation endovascular stent-graft: the concept of laminar flow.
Bortone, Alessandro Santo; De Cillis, Emanuela; Raguso, Giovanni
2013-09-01
The stent graft is a noncompliant system inserted in a semi-compliant structure. This generates a mismatch. The media also shows a composite movement and is oriented 45° resulting in an arterial spiral movement that contributes to maintaining the clockwise orientation of laminar flow with an 80° deflection. Our multilayer stent is constituted by a single Nitinol thread, worked on 3 surfaces in order to realize a proper exoskeleton that reproduces the architecture of the tunica media, in particular its flexo-torsional forces, thus restoring the energy transmission and the match between the wall and the blood flow. A first in vivo implantation was performed by using an experimental pig model in our veterinary department. The pig underwent general anesthesia and the right femoral artery was surgically exposed in order to accommodate a 12F long introducer sheath. Under fluoroscopy three multilayer stents were consecutively implanted from the aortic isthmus to the iliac bifurcation in an overlap fashion. All the intercostal artery and visceral branches were covered by the overlapped stents. The final control angiography revealed an optimal sealing of the implanted stent with an evident flexotorsional oscillatory movement, which follows the conical architecture of the thoracic aorta and the complete patency of all the branches that arise from the aorta. After two months, the multilayer showed a normal endothelialization process with an optimal adhesion to the aortic wall both proximally and distally without provoking any inflammatory response or thickness wall alterations. The perfect and homogenous endothelialization preserved the patency of all the collateral branches arising from the treated aorta, in particular all the intercostal arteries, celiac trunk, and renal arteries. The disease of the aorta essentially concerns the tunica media as it causes disruption of the media components. This exoskeleton works like a neo-tunica media, is perfectly endothelialized, and seems to optimally transmit the flexotorsional forces, restoring the match between wall and flow that represents the primary condition for laminar flow and branch perfusion. PMID:24081853
Further analyses of laminar flow heat transfer in circular sector ducts
Lei, Q.M.; Trupp, A.C. )
1989-11-01
Heat transfer in circular sector ducts is often encountered in multipassage tubes. Certain flow characteristics of circular sector ducts for apex angles up to {pi} have been determined as documented by Shah and London (1978). Recently, Lei and Trupp (1989) have more completely analyzed the flow characteristics of fully developed laminar flow for apex angles up to 2{pi}, including the location of the maximum velocity. Heat transfer results of fully developed laminar flow in circular sector ducts are also available for certain boundary conditions. Trupp and Lau (1984) numerically determined the average Nusselt number (Nu{sub T}) for isothermal walls. Eckert et al. (1958) initially derived an analytical expression for the temperature profile for the case of H1. Sparrow and Haji-angles up to {pi}. However, the above work required numerical integration (or equivalent) to obtain a value for Nu{sub H1}. Regarding the H1{sub ad} boundary condition, Date (1974) numerically obtained a limiting value of Nu{sub H1}{sub ad} for the semicircular duct from the prediction of circular tubes containing a twisted tape (straight and nonconducting tape). Hong and Bergles (1976) also reported an asymptotic value of Nu{sub H1}{sub ad} for the semicircular duct from their entrance region solution. Otherwise it appears that there are no published analytical results of Nu{sub H1}{sub ad} for circular sector ducts. The purpose of this technical note is to communicate these results. In addition, a novel series expression for Nu{sub H1} is presented together with results for apex angles up to 2{pi}.
Mittal, R.; Dong, H.; Bozkurttas, M.; Najjar, F.M.; Vargas, A.; von Loebbecke, A.
2010-01-01
A sharp interface immersed boundary method for simulating incompressible viscous flow past three-dimensional immersed bodies is described. The method employs a multi-dimensional ghost-cell methodology to satisfy the boundary conditions on the immersed boundary and the method is designed to handle highly complex three-dimensional, stationary, moving and/or deforming bodies. The complex immersed surfaces are represented by grids consisting of unstructured triangular elements; while the flow is computed on non-uniform Cartesian grids. The paper describes the salient features of the methodology with special emphasis on the immersed boundary treatment for stationary and moving boundaries. Simulations of a number of canonical two- and three-dimensional flows are used to verify the accuracy and fidelity of the solver over a range of Reynolds numbers. Flow past suddenly accelerated bodies are used to validate the solver for moving boundary problems. Finally two cases inspired from biology with highly complex three-dimensional bodies are simulated in order to demonstrate the versatility of the method. PMID:20216919
A spectral-element discontinuous Galerkin lattice Boltzmann method for nearly incompressible flows
NASA Astrophysics Data System (ADS)
Min, Misun; Lee, Taehun
2011-01-01
We present a spectral-element discontinuous Galerkin lattice Boltzmann method for solving nearly incompressible flows. Decoupling the collision step from the streaming step offers numerical stability at high Reynolds numbers. In the streaming step, we employ high-order spectral-element discontinuous Galerkin discretizations using a tensor product basis of one-dimensional Lagrange interpolation polynomials based on Gauss-Lobatto-Legendre grids. Our scheme is cost-effective with a fully diagonal mass matrix, advancing time integration with the fourth-order Runge-Kutta method. We present a consistent treatment for imposing boundary conditions with a numerical flux in the discontinuous Galerkin approach. We show convergence studies for Couette flows and demonstrate two benchmark cases with lid-driven cavity flows for Re = 400-5000 and flows around an impulsively started cylinder for Re = 550-9500. Computational results are compared with those of other theoretical and computational work that used a multigrid method, a vortex method, and a spectral element model.
Wake effects on drift in two-dimensional inviscid incompressible flows
NASA Astrophysics Data System (ADS)
Melkoumian, Sergei; Protas, Bartosz
2014-12-01
This investigation analyzes the effect of vortex wakes on the Lagrangian displacement of particles induced by the passage of an obstacle in a two-dimensional incompressible and inviscid fluid. In addition to the trajectories of individual particles, we also study their drift and the corresponding total drift areas in the Föppl and Kirchhoff potential flow models. Our findings, which are obtained numerically and in some regimes are also supported by asymptotic analysis, are compared to the wakeless potential flow which serves as a reference. We show that in the presence of the Föppl vortex wake, some of the particles follow more complicated trajectories featuring a second loop. The appearance of an additional stagnation point in the Föppl flow is identified as a source of this effect. It is also demonstrated that, while the total drift area increases with the size of the wake for large vortex strengths, it is actually decreased for small circulation values. On the other hand, the Kirchhoff flow model is shown to have an unbounded total drift area. By providing a systematic account of the wake effects on the drift, the results of this study will allow for more accurate modeling of hydrodynamic stirring.
The Dynamics Of Finite Size Impurities In Time-dependent Three-dimensional Incompressible Flows.
NASA Astrophysics Data System (ADS)
Cartwright, J. H. E.; Piro, O.; Tuval, I.
The dynamics of finite size spherical impurities suspended in thee-dimensional fluid flows is discussed in general. Particular emphasis is then made on situations in which either neutrally and non-neutrally buoyant spheres are driven by 3D time-periodic incompressible flows that display Lagrangian chaos. The case of neutrally buoyant particles is first studied qualitatively by means of iterated maps. These maps are constructed by applying a procedure called "bailout embedding" to a 3D volume- preserving map that represents the base flow to obtain a composite map that cap- tures the main features of the particle dynamics. The accumulation of impurities in tubular vortical structures, detachment of particles from fluid trajectories near hyper- bolic invariant lines and the formation of nontrivial 3D structures in the distribution of particles are predicted in this way. The predictions are later verified for more real- istic continuous-time flows. Finally, some nontrivial features of the evolution of non- neutrally-buoyant particle distributions in three-dimensions are shown and discussed.
Kenis, Paul J. A.
Air-Breathing Laminar Flow-Based Microfluidic Fuel Cell Ranga S. Jayashree, Lajos Gancs, Eric R@uiuc.edu This communication reports the design, assembly, and perfor- mance of an air-breathing laminar flow this cathode limitation by the integration of a porous air-exposed gas diffusion electrode (GDE) as the cathode
NASA Astrophysics Data System (ADS)
Geshev, P. I.
2015-05-01
A stratified laminar flow of several fluids in a channels with an arbitrarily shaped cross section is considered. It is assumed that the hydrostatic problem of finding free boundaries between different fluids is solved and domains of motion of individual fluids are known. Under the assumption that the medium motion arises under the action of an applied pressure gradient and volume gravity forces (or forces of inertia), the property of reciprocity between the applied forces F j and the flows of different components Q i , which is manifested as symmetry of the matrix of the flow rate coefficients L ij ( Q i = L ij F j ), is proved in the general form. General symmetric solutions of the problem for a plane channel and a circular tube are presented. Formulas for the coefficient of increasing of the fluid flow rate owing to the presence of a near-wall layer of the gas are derived. It is shown that the flow rate of water in a partly filled channel may exceed the flow rate in a completely filled channel by more than an order of magnitude.
NASA Astrophysics Data System (ADS)
Kadian, Arun Kumar; Biswas, Pankaj
2015-08-01
Friction stir welding has been quite successful in joining aluminum alloy which has gained importance in almost all industrial sectors over the past two decades. It is a newer technique and therefore needs more attention in many sectors, flow of material being one among them. The material flow pattern actually helps in deciding the parameters required for particular tool geometry. The knowledge of material flow is very significant in removing defects from the weldment. In the work presented in this paper, the flow behavior of AA6061 under a threaded tool has been studied. The convective heat loss has been considered from all the surfaces, and a comparative study has been made with and without the use of temperature-dependent properties and their significance in the finite volume method model. The two types of models that have been implemented are turbulent and laminar models. Their thermal histories have been studied for all the cases. The material flow velocity has been analyzed to predict the flow of material. A swirl inside the weld material has been observed in all the simulations.
NASA Astrophysics Data System (ADS)
Nam, Jaewook; Carvalho, Marcio S.
2015-08-01
An efficient algorithm based on the matrix transformation method (Valério et al., 2007) is presented for solving the generalized eigenvalue problem (GEVP) derived from linear stability analysis of incompressible viscous flow. The proposed method uses the formulation based on primitive variables, i.e. velocity and pressure, instead of streamfunction used by typical Orr-Sommerfeld equation. A series of matrix operations removes non-physical eigenvalues at infinity and leads to a non-singular smaller size eigenvalue problem (EVP), which contains full eigenspectrum, than the original GEVP. Two different solution strategies for the transformed EVP are proposed, and their accuracies are discussed. The proposed procedure is used to solve the stability of two layer rectilinear flow. The computed eigenspectrum are compared to previously reported values.
NASA Astrophysics Data System (ADS)
Shen, Fang; Wu, Wangyi
2009-06-01
Basic function method is developed to treat the incompressible viscous flow. Artificial compressibility coefficient, the technique of flux splitting method and the combination of central and upwind schemes are applied to construct the basic function scheme of trigonometric function type for solving three-dimensional incompressible Navier-Stokes equations numerically. To prove the method, flows in finite-length-pipe are calculated, the velocity and pressure distribution of which solved by our method quite coincide with the exact solutions of Poiseuille flow except in the areas of entrance and exit. After the method is proved elementary, the hemodynamics in two- and three-dimensional aneurysms is researched numerically by using the basic function method of trigonometric function type and unstructured grids generation technique. The distributions of velocity, pressure and shear force in steady flow of aneurysms are calculated, and the influence of the shape of the aneurysms on the hemodynamics is studied.
N.-S. Liu
1976-01-01
Motivated by blood flow and diffusion problems in cardiovascular and bronchial systems, an integration technique is presented for solving the Navier-Stokes equations of an incompressible homogeneous fluid flow through vessels with time- and space-dependent cross-sections. The equations of motion are written for generalized, nonorthonormal coordinates, and the finite-difference equations are obtained by applying Gauss' divergence theorem to a finite volume
Gregory Larson; Deryl Snyder; David Vanden Abeele; Tanja Clees
2008-01-01
Single- and multi-level iterative methods for sparse linear systems are applied to unsteady flow simulations via implementation\\u000a into a direct numerical simulation solver for incompressible turbulent flows on unstructured meshes. The performance of these\\u000a solution methods, implemented in the well-established SAMG and ML packages, are quantified in terms of computational speed\\u000a and memory consumption, with a direct sparse LU solver
Convective heat transfer in foams under laminar flow in pipes and tube bundles
Attia, Joseph A.; McKinley, Ian M.; Moreno-Magana, David; Pilon, Laurent
2014-01-01
The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux. PMID:25552745
Net inflow method for incompressible viscous flow with moving free surface
NASA Astrophysics Data System (ADS)
Wang, S. P.; Wang, K. K.
1994-04-01
A new finite element procedure called the net inflow method has been developed to simulate time-dependent incompressible viscous flow including moving free surfaces and inertial effects. As a fixed mesh approach with triangular element, the net inflow method can be used to analyse the free surface flow in both regular and irregular domains. Most of the empty elements are excluded from the computational domain, which is adjusted successively to cover the entire region occupied by the liquid. The volume of liquid in a control volume is updated by integrating the net inflow of liquid during each iteration. No additional kinetic equation or material marker needs to be considered. The pressure on the free surface and in the liquid region can be solved explicitly with the continuity equation or implicitly by using the penalty function method. The radial planar free surface flow near a 2D point source and the dam-breaking problem on either a dry bed or a still liquid have been analysed and presented in this paper. The predictions agree very well with available analytical solutions, experimental measurements and/or other numerical results.
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Tuttle, M. H.
1979-01-01
A survey was conducted and a bibliography compiled on attainment of laminar flow in air through the use of favorable pressure gradient and suction. This report contains the survey, summaries of data for both ground and flight experiments, and abstracts of referenced reports. Much early information is also included which may be of some immediate use as background material for LFC applications.
Sara Rainieri; Fabio Bozzoli; Marco Mordacci; Giorgio Pagliarini
2012-01-01
Scraped Surface Heat Exchangers (SSHEs) provide a versatile solution in the process industry for treating highly viscous fluids that may also contain particulate matter. Although SSHEs are frequently used in industrial applications, literature on this topic, particularly on the laminar flow regime, is limited. Moreover, due to the specificity of each product, it is difficult to generalise the few data
An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...
An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...
NASA Technical Reports Server (NTRS)
Pfenninger, Werner; Vemuru, Chandra S.
1988-01-01
The achievement of 70 percent laminar flow using modest boundary layer suction on the wings, empennage, nacelles, and struts of long-range LFC transports, combined with larger wing spans and lower span loadings, could make possible an unrefuelled range halfway around the world up to near sonic cruise speeds with large payloads. It is shown that supercritical LFC airfoils with undercut front and rear lower surfaces, an upper surface static pressure coefficient distribution with an extensive low supersonic flat rooftop, a far upstream supersonic pressure minimum, and a steep subsonic rear pressure rise with suction or a slotted cruise flap could alleviate sweep-induced crossflow and attachment-line boundary-layer instability. Wing-mounted superfans can reduce fuel consumption and engine tone noise.
Investigation of radiative interaction in laminar flows using Monte Carlo simulation
NASA Technical Reports Server (NTRS)
Liu, Jiwen; Tiwari, S. N.
1993-01-01
The Monte Carlo method (MCM) is employed to study the radiative interactions in fully developed laminar flow between two parallel plates. Taking advantage of the characteristics of easy mathematical treatment of the MCM, a general numerical procedure is developed for nongray radiative interaction. The nongray model is based on the statistical narrow band model with an exponential-tailed inverse intensity distribution. To validate the Monte Carlo simulation for nongray radiation problems, the results of radiative dissipation from the MCM are compared with two available solutions for a given temperature profile between two plates. After this validation, the MCM is employed to solve the present physical problem and results for the bulk temperature are compared with available solutions. In general, good agreement is noted and reasons for some discrepancies in certain ranges of parameters are explained.
Evaluation of laminar flow control system concepts for subsonic commercial transport aircraft
NASA Technical Reports Server (NTRS)
1978-01-01
A two-year study conducted to establish a basis for industry decisions on the application of laminar flow control (LFC) to future commercial transports was presented. Areas of investigation included: (1) mission definition and baseline selection; (2) concepts evaluations; and (3) LFC transport configuration selection and component design. The development and evaluation of competing design concepts was conducted in the areas of aerodynamics, structures and materials, and systems. The results of supporting wind tunnel and laboratory testing on a full-scale LFC wing panel, suction surface opening concepts and structural samples were included. A final LFC transport was configured in incorporating the results of concept evaluation studies and potential performance improvements were assessed. Remaining problems together with recommendations for future research are discussed.
Evaluation of Laminar Flow Control System Concepts for Subsonic Commercial Transport Aircraft
NASA Technical Reports Server (NTRS)
Sturgeon, R. F.
1980-01-01
Alternatives in the design of laminar flow control (LFC) subsonic commerical transport aircraft for opeation in the 1980's period were studied. Analyses were conducted to select mission parameters and define optimum aircraft configurational parameters for the selected mission, defined by a passenger payload of 400 and a design range of 12, 038 km (6500 n mi). The baseline aircraft developed for this mission was used as a vehicle for the evaluation and development of alternative LFC system concepts. Alternatices in the areas of aerodynamics, structures and materials, LFC systems, leading-edge region cleaning, and integration of auxiliary systems were studied. Relative to a similarly-optimized advanced technology turbulent transport, the final LFC configuration is approximately equal in DOC but provides descreases of 8.2% in gross weight and 21.7% in fuel consumption.
NASA Astrophysics Data System (ADS)
Freebairn, G. S.; Boyce, R. R.; Mudford, N.
2009-01-01
The interaction between a circular sonic jet and a Mach 6.65 cross flow on a flat plate have been investigated experimentally in a free piston shock tunnel. Turbulent wedges of varying widths were created upstream of the interaction using distributed and isolated wall roughness elements and the effects on the jet interaction flowfield were assessed using a combination of surface pressure measurements and schlieren visualisation. In all cases it was found that laminar-like and turbulent-like separation occurred simultaneously in the flowfield. The effects on the associated near field pressure distributions were found to depend on both the spanwise location of the wedge and its size relative to the expanding jet.
Laminar flow of a gas in a tube with large temperature differences
NASA Astrophysics Data System (ADS)
Higuera, F. J.
2011-12-01
The laminar low Mach number flow of a gas in a tube is analyzed for very small and very large values of the inlet-to-wall temperature ratio. When this ratio tends to zero, pressure forces confine the cold gas to a thin core around the axis of the tube. This core is neatly bounded by an ablation front that consumes it at a finite distance from the tube inlet. When the temperature ratio tends to infinity, the temperature of the gas increases smoothly from the wall to the axis of the tube and the shear stress and heat flux are positive at the wall despite the fact that the viscosity and thermal conductivity of the gas scaled with their inlet values tend to zero at the wall.
A fixed-mesh method for incompressible flow structure systems with finite solid deformations
NASA Astrophysics Data System (ADS)
Zhao, Hong; Freund, Jonathan B.; Moser, Robert D.
2008-03-01
A fixed-mesh algorithm is proposed for simulating flow-structure interactions such as those occurring in biological systems, in which both the fluid and solid are incompressible and the solid deformations are large. Several of the well-known difficulties in simulating such flow-structure interactions are avoided by formulating a single set of equations of motion on a fixed Eulerian mesh. The solid's deformation is tracked to compute elastic stresses by an overlapping Lagrangian mesh. In this way, the flow-structure interaction is formulated as a distributed body force and singular surface force acting on an otherwise purely fluid system. These forces, which depend on the solid elastic stress distribution, are computed on the Lagrangian mesh by a standard finite-element method and then transferred to the fixed Eulerian mesh, where the joint momentum and continuity equations are solved by a finite-difference method. The constitutive model for the solid can be quite general. For the force transfer, standard immersed-boundary and immersed-interface methods can be used and are demonstrated. We have also developed and demonstrated a new projection method that unifies the transfer of the surface and body forces in a way that exactly conserves momentum; the interface is still effectively sharp for this approach. The spatial convergence of the method is observed to be between first- and second-order, as in most immersed-boundary methods for membrane flows. The algorithm is demonstrated by the simulations of an advected elastic disk, a flexible leaflet in an oscillating flow, and a model of a swimming jellyfish.
Experimental design studies and flow visualization of proportional laminar-flow fluidic amplifiers
NASA Technical Reports Server (NTRS)
Hellbaum, R. F.; Mcdermon, J. N.
1977-01-01
The effects of certain parameter variations on the performance characteristics of laminar, proportional, jet-deflection fluidic amplifiers were studied. The matching and staging of amplifiers to obtain high pressure gain was included, but dynamic effects were not. The parameter variations considered were aspect ratio, setback, control length, splitter distance, receiver-duct width, width of center-vent duct, and bias pressure. Usable pressure gains of 19 per stage were achieved, and 5 amplifier stages were integrated to yield an overall pressure gain of 2,000,000.
Berezovski, Maxim V; Mak, Tak W; Krylov, Sergey N
2007-01-01
Chemical cytometry studies the molecular composition of individual cells by means of capillary electrophoresis or capillary chromatography. In one of its realizations an intact cell is injected inside the capillary, the plasma membrane is disrupted to release the cellular contents into the separation buffer, and, finally, the molecules of interest are separated and detected. The solubilization of the plasma membrane with a surfactant is a simple and efficient way of achieving cell lysis inside the capillary. To facilitate cell lysis by a surfactant the cell has to be contacted with the surfactant inside the capillary. We recently introduced a generic method for mixing solutions inside the capillary termed transverse diffusion of laminar flow profiles (TDLFP). In this work, we propose that TDLFP can facilitate efficient cell lysis inside the capillary. Conceptually, a short plug of the surfactant is injected by pressure prior to cell injection. The cell is then injected by pressure within a plug of the physiological buffer. Due to the parabolic profiles of pressure-driven laminar flows the interface between the plug of the surfactant and that of the physiological buffer is predominantly longitudinal. Transverse diffusion mixes the surfactant with the physiological buffer, which leads to surfactant's contact with the cell and subsequent cell lysis. Here, we demonstrate that the proposed concept is valid. TDLFP-facilitated cell lysis by a short plug of the surfactant allows us to exclude the surfactant from the run buffer, and, hence, facilitates modes of separation, which are incompatible with the surfactant's presence in the run buffer. In addition to cell lysis, TDLFP will be used to mix the cellular components with labeling reactants, affinity probes, inhibitors, etc. We foresee that the generic nature and enabling capabilities of TDLFP will speed up the maturation of chemical cytometry into a practical bioanalytical tool. PMID:17066286
Fatigue response of perforated titanium for application in laminar flow control
NASA Technical Reports Server (NTRS)
Johnson, W. Steven; Miller, Jennifer L.; Newman, Jr., James
1996-01-01
The room temperature tensile and fatigue response of non-perforated and perforated titanium for laminar flow control application was investigated both experimentally and analytically. Results showed that multiple perforations did not affect the tensile response, but did reduce the fatigue life. A two dimensional finite element stress analysis was used to determine that the stress fields from adjacent perforations did not influence one another. The stress fields around the holes did not overlap one another, allowing the materials to be modeled as a plate with a center hole. Fatigue life was predicted using an equivalent MW flow size approach to relate the experimental results to microstructural features of the titanium. Predictions using flaw sizes ranging from 1 to 15 microns correlated within a factor of 2 with the experimental results by using a flow stress of 260 MPa. By using two different flow stresses in the crack closure model and correcting for plasticity, the experimental results were bounded by the predictions for high applied stresses. Further analysis of the complex geometry of the perforations and the local material chemistry is needed to further understand the fatigue behavior of the perforated titanium.
Information barriers for noisy Lagrangian tracers in filtering random incompressible flows
NASA Astrophysics Data System (ADS)
Chen, Nan; Majda, Andrew J.; Tong, Xin T.
2014-09-01
An important practical problem is the recovery of a turbulent velocity field from Lagrangian tracers that move with the fluid flow. Here, the filtering skill of L moving Lagrangian tracers in recovering random incompressible flow fields defined through a finite number of random Fourier modes is studied with full mathematical rigour. Despite the inherent nonlinearity in measuring noisy Lagrangian tracers, it is shown below that there are exact closed analytic formulas for the optimal filter for the velocity field involving Riccati equations with random coefficients for the covariance matrix. This mathematical structure allows a detailed asymptotic analysis of filter performance, both as time goes to infinity and as the number of noisy Lagrangian tracers, L, increases. In particular, the asymptotic gain of information from L-tracers grows only like ln L in a precise fashion; i.e., an exponential increase in the number of tracers is needed to reduce the uncertainty by a fixed amount; in other words, there is a practical information barrier. The proofs proceed through a rigourous mean field approximation of the random Ricatti equation. Also, as an intermediate step, geometric ergodicity with respect to the uniform measure on the period domain is proved for any fixed number L of noisy Lagrangian tracers. All of the above claims are confirmed by detailed numerical experiments presented here.
Incompressible Navier-Stokes Simulation Procedure for a Wingtip Vortex Flow Analysis
NASA Technical Reports Server (NTRS)
Dacles-Mariani, Jennifer; Kwak, Dochan; Zilliac, Greg
1995-01-01
The pacing items to reach the highly desirable goal of obtaining computationally accurate flow simulation of a wingtip vortex include; super-computer development, solver accuracy, grid generation and turbulence modeling. In these four areas, many advances have been made but the fact remains that most wing computations are, at best, five percent accurate (in drag coefficient, for example). This level of accuracy has been sufficient for many purposes such as airfoil design, rudimentary wing design, and some forms of optimization. However, this accuracy level will not allow commercial aircraft designers to extract the remaining few percent of efficiency theoretically possible for conventional aircraft configurations. Thus further research is needed, particularly in the areas of solver development and turbulence modeling, to advance the state of the art of viscous computational techniques as applied to problems in aerodynamics. During the course of this study, a substantial amount of measured and computed results have been acquired. In this paper, only a small selection of experimental and computational results will be presented. This paper will outline and discuss a simulation procedure for a wingtip vortex flow analysis using the method of artificial compressibility to solve the three-dimensional, incompressible, Navier-Stokes equations (INS3D-UP).
Clausen, Jonathan R
2013-01-01
An alternative artificial compressibility (AC) scheme is proposed to allow the explicit simulation of the incompressible Navier-Stokes (INS) equations. Traditional AC schemes rely on an artificial equation of state that gives the pressure as a function of the density, which is known to enforce isentropic behavior. This behavior is nonideal, especially in viscously dominated flows. An alternative, the entropically damped artificial compressibility (EDAC) method, is proposed that employs a thermodynamic constraint to damp the pressure oscillations inherent to AC methods. The EDAC method converges to the INS in the low-Mach limit, and is consistent in both the low- and high-Reynolds-number limits, unlike standard AC schemes. The proposed EDAC method is discretized using a simple finite-difference scheme and is compared with traditional AC schemes as well as the lattice-Boltzmann method for steady lid-driven cavity flow and a transient traveling-wave problem. The EDAC method is shown to be beneficial in damping pressure and velocity-divergence oscillations when performing transient simulations. The EDAC method follows a similar derivation to the kinetically reduced local Navier-Stokes (KRLNS) method [Borok et al., Phys. Rev. E 76, 066704 (2007)]; however, the EDAC method does not rely on the grand potential as the thermodynamic variable, but instead uses the more common pressure-velocity system. Additionally, a term neglected in the KRLNS is identified that is important for accurately approximating the INS equations. PMID:23410462
HyPAM: A hybrid continuum-particle model for incompressible free-surface flows
Zhang Qinghai [School of Civil and Environmental Engineering, Cornell University, Ithaca, NY 14853 (United States); Applied Numerical Algorithms Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)], E-mail: QHZhang@lbl.gov; Liu, Philip L.-F. [School of Civil and Environmental Engineering, Cornell University, Ithaca, NY 14853 (United States); Institute of Hydrological and Oceanic Sciences, National Central University, Jhongli, Taiwan (China)], E-mail: pll3@cornell.edu
2009-03-01
Three major issues associated with numerical simulations of complex free-surface flows, viz. interface tracking, fragmentation and large physical jumps, are addressed by a new hybrid continuum-particle model (HyPAM). The new model consists of three parts: (1) the Polygonal Area Mapping method [Q. Zhang, P.L.-F. Liu, A new interface tracking method: the polygonal area mapping method, J. Comput. Phys. 227(8) (2008) 4063-4088]; (2) a new algorithm that decomposes the interested (water) phase into a continuum zone, a buffer zone and a particle zone, based on material topology and graph theory; (3) a 'passive-response' assumption, in which the air phase is assumed to respond passively to the continuum part of the water phase. The incompressible inviscid Euler equations and the equations describing the free fall of rigid bodies are used as the governing equations for the continuum-buffer zone and the particle zone, respectively, and separately. A number of examples, including water droplet impact, solitary wave propagation, and dam-break problems, are simulated for the illustration and validation of HyPAM. It is shown that HyPAM is more accurate and versatile than a continuum-based Volume-of-Fluid model. One major contribution of this work is the single-phase decomposition algorithm, useful for many other hybrid formulations. Neglecting surface tension, viscosity and particle interactions, HyPAM is currently limited to mildly-fragmented free-surface flows with high Reynolds and Weber numbers.
NASA Astrophysics Data System (ADS)
Reeks, Michael; Meneguz, Elena
2012-11-01
We report recent measurements of the segregation of small inertial particles advected via Stokes drag in an isotropic homogeneous incompressible turbulent flow using a full Lagrangian method (FLM) to calculate the compressibility of an elemental volume of particles measured along a particle trajectory. The flow field was generated by a random Fourier mode kinematic simulation (KS) and by DNS. Numerical results show that the average compressibility decreases continuously with time if the value of the Stokes number is below a threshold value 1, indicating that the segregation continues indefinitely. We find that the probability distribution of the compression tends to a Gaussian distribution except in the wings due to the occurrence of singularities in the particle concentration which makes the process highly intermittent. The distribution of singularities over a fixed interval of time for a range of Stoke numbers is shown to be well approximated by a Poisson distribution. Finally, we show that the occurrence of singularities is related to the formation of caustics and the occurrence of random uncorrelated motion (RUM).
An incompressible two-dimensional multiphase particle-in-cell model for dense particle flows
Snider, D.M. [SAIC, Albuquerque, NM (United States); O`Rourke, P.J. [Los Alamos National Lab., NM (United States); Andrews, M.J. [Texas A and M Univ., College Station, TX (United States). Dept. of Mechanical Engineering
1997-06-01
A two-dimensional, incompressible, multiphase particle-in-cell (MP-PIC) method is presented for dense particle flows. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Difficulties associated with calculating interparticle interactions for dense particle flows with volume fractions above 5% have been eliminated by mapping particle properties to a Eulerian grid and then mapping back computed stress tensors to particle positions. This approach utilizes the best of Eulerian/Eulerian continuum models and Eulerian/Lagrangian discrete models. The solution scheme allows for distributions of types, sizes, and density of particles, with no numerical diffusion from the Lagrangian particle calculations. The computational method is implicit with respect to pressure, velocity, and volume fraction in the continuum solution thus avoiding courant limits on computational time advancement. MP-PIC simulations are compared with one-dimensional problems that have analytical solutions and with two-dimensional problems for which there are experimental data.
NASA Astrophysics Data System (ADS)
Clausen, Jonathan R.
2013-01-01
An alternative artificial compressibility (AC) scheme is proposed to allow the explicit simulation of the incompressible Navier-Stokes (INS) equations. Traditional AC schemes rely on an artificial equation of state that gives the pressure as a function of the density, which is known to enforce isentropic behavior. This behavior is nonideal, especially in viscously dominated flows. An alternative, the entropically damped artificial compressibility (EDAC) method, is proposed that employs a thermodynamic constraint to damp the pressure oscillations inherent to AC methods. The EDAC method converges to the INS in the low-Mach limit, and is consistent in both the low- and high-Reynolds-number limits, unlike standard AC schemes. The proposed EDAC method is discretized using a simple finite-difference scheme and is compared with traditional AC schemes as well as the lattice-Boltzmann method for steady lid-driven cavity flow and a transient traveling-wave problem. The EDAC method is shown to be beneficial in damping pressure and velocity-divergence oscillations when performing transient simulations. The EDAC method follows a similar derivation to the kinetically reduced local Navier-Stokes (KRLNS) method [Borok , Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.76.066704 76, 066704 (2007)]; however, the EDAC method does not rely on the grand potential as the thermodynamic variable, but instead uses the more common pressure-velocity system. Additionally, a term neglected in the KRLNS is identified that is important for accurately approximating the INS equations.
NASA Astrophysics Data System (ADS)
Escudier, M. P.; Oliveira, P. J.; Pinho, F. T.; Smith, S.
2002-06-01
Experimental data are reported for fully developed laminar flow of a shear-thinning liquid through both a concentric and an 80% eccentric annulus with and without centrebody rotation. The working fluid was an aqueous solution of 0.1% xanthan gum and 0.1% carboxymethylcellulose for which the flow curve is well represented by the Cross model. Comparisons are reported between numerical calculations and the flow data, as well as with other laminar annular-flow data for a variety of shear-thinning liquids previously reported in the literature. In general, the calculations are in good quantitative agreement with the experimental data, even in situations where viscoelastic effects, neglected in the calculations, would be expected to play a role.
R. T. Hirshburg; L. W. Florschuetz
1980-01-01
In Part I the hydrodynamic and thermal characteristics of thin, laminar wavy-film flow are considered. A theoretical model is developed to predict the hydrodynamic features of asymptotic wavy-flow states. The mathematical closure question arising in asymptotic-state analyses is satisfactorily resolved here for the first time. The model accurately predicts published experimental data for mean film thickness, trough-to-crest dimension, wave celerity,
WENO schemes on arbitrary unstructured meshes for laminar, transitional and turbulent flows
Tsoutsanis, Panagiotis Antoniadis, Antonios Foivos Drikakis, Dimitris
2014-01-01
This paper presents the development and implementation of weighted-essentially-non-oscillatory (WENO) schemes for viscous flows on arbitrary unstructured grids. WENO schemes up to fifth-order accurate have been implemented in conjunction with hybrid and non-hybrid unstructured grids. The schemes are investigated with reference to numerical and experimental results for the Taylor–Green vortex, as well as for laminar and turbulent flows around a sphere, and the turbulent shock-wave boundary layer interaction flow problem. The results show that the accuracy of the schemes depends on the arbitrariness of shape and orientation of the unstructured mesh elements, as well as the compactness of directional stencils. The WENO schemes provide a more accurate numerical framework compared to second-order and third-order total variation diminishing (TVD) methods, however, the fifth-order version of the schemes is computationally too expensive to make the schemes practically usable. On the other hand, the third-order variant offers an excellent numerical framework in terms of accuracy and computational cost compared to the fifth-order WENO and second-order TVD schemes. Parallelisation of the CFD code (henceforth labelled as UCNS3D), where the schemes have been implemented, shows that the present methods offer very good scalable performance.
Friction factor correlations for laminar, transition and turbulent flow in smooth pipes
NASA Astrophysics Data System (ADS)
Joseph, Daniel D.; Yang, Bobby H.
2010-07-01
In this paper we derive an accurate composite friction factor vs. Reynolds number correlation formula for laminar, transition and turbulent flow in smooth pipes. The correlation is given as a rational fraction of rational fractions of power laws which is systematically generated by smoothly connecting linear splines in log-log coordinates with a logistic dose curve algorithm. This kind of correlation seeks the most accurate representation of the data independent of any input from theories arising from the researchers’ ideas about the underlying fluid mechanics. As such, these correlations provide an objective metric against which observations and other theoretical correlations may be applied. Our correlation is as accurate, or more accurate, than other correlations in the range of Reynolds numbers in which the correlations overlap. However, our formula is not restricted to certain ranges of Reynolds numbers but instead applies uniformly to all smooth pipe flow data for which data is available. The properties of the classical logistic dose response curve are reviewed and extended to problems described by multiple branches of power laws. This extended method of fitting which leads to rational fractions of power laws is applied to data of Marusic and Perry (1995) [1] for the velocity profile in a boundary layer on a flat plate with an adverse pressure gradient, to data of Nikuradse (1932) [2] and McKeon et al. (2004) [3] on friction factors for flow in smooth pipes and to the data of Nikuradse [4] for effectively smooth pipes.
NASA Astrophysics Data System (ADS)
Guido, Joseph D.
1992-09-01
An experimental study of laminar flow heat transfer of an ethylene glycol/water mixture in an electrically heated horizontal tube using wire mesh (HEATEX) and twisted tape inserts was investigated. Twelve thermocouples, inserted in the tube wall at four longitudinal locations, enabled a mean inside experimental heat-transfer coefficient to be accurately measured. A constant wall heat flux boundary condition was placed on the wall by wrapping six 200 W flexible heater tapes tightly around the tube. The ethylene glycol/water mixture provided a coolant Reynolds number between 200-5000 and a Prandtl number between 30-140. Two smooth inside diameters and a roped tube profile were tested with and without the inserts. Heat-transfer correlations for tubes without inserts were developed and compared with theory for both thermally and hydrodynamically developing flow. Correlations were also developed for the two types of inserts. Nusselt numbers for fully developed flow were found to be a function of Reynolds and Prandtl numbers for the wire mesh insert and a function of tape twist ratio, Reynolds and Prandtl numbers for the twisted tape insert. Heat transfer enhancements of over 7 for the wire mesh insert and over 4 for the twisted tape insert at high Reynolds numbers were obtained over the empty tube.
NASA Astrophysics Data System (ADS)
Peres, N.; Afonso, A.; Alves, M. A.; Pinho, F. T.
2008-07-01
A finite-volume method is applied to the three-dimensional simulation of heat transfer of a viscoelastic fluid in laminar flow through a rectangular channel with an aspect ratio of 2 and constant heat flux at the channel walls. The objectives of the present work are twofold: (a) to compare the numerical results with the heat transfer experimental data of Hartnett and Kostic [l]; (b) to analyze the influence of the secondary flow on the heat transfer enhancement on account of the non-zero second normal-stress difference. The rheology of the viscoelastic fluid is represented by the Phan-Thien-Tanner constitutive equation with non-zero second normal-stress difference. The simulations show the strong effect of secondary flows on the correct prediction of experimental results. The predictions confirm the enhancement of local and mean Nusselt numbers, as found experimentally by Hartnett and Kostic [1], and show that free convection has a major influence in the experimental heat transfer results for Newtonian fluid, but less so as fluid elasticity is increased.
Green's function of the linearized Saint-Venant equations in laminar and turbulent flows
NASA Astrophysics Data System (ADS)
di Cristo, Cristiana; Iervolino, Michele; Vacca, Andrea
2012-02-01
In the present paper, an analytical expression of the Green's function of linearized Saint-Venant equations (LSVEs) for shallow water waves is provided and applied to analyse the propagation of a perturbation superposed to a uniform flow. Independently of the kinematic character of the base flow, i.e., subcritical or supercritical uniform flow, the effects of a non-uniform vertical velocity profile and a non-constant resistance coefficient are accounted for. The use of the Darcy-Weisbach friction law allows a unified treatment of both laminar and turbulent conditions. The influence on the wave evolution of the wall roughness and the fluid viscosity are finally discussed, showing that in turbulent regime the assumption of constant friction coefficient may lead to an underestimation of both amplification and damping factors on the wave fronts, especially at low Reynolds numbers. This conclusion has to be accounted for, particularly in describing hyper-concentrated suspensions or other kinds of Newtonian mixtures, for which the high values of the kinematic viscosity may lead to relatively low Reynolds numbers.
NASA Astrophysics Data System (ADS)
Fang, Pingping
1998-12-01
An extended numerical investigation of fully developed, forced convective laminar flows with heat transfer in eccentric annuli has been carried out. Both Newtonian and non-Newtonian (power-law or Ostwald-de Waele) fluids are studied, representing typical applications in petrochemical, bio-chemical, personal care products, polymer/plastic extrusion and food industries. For the heat transfer problem, with an insulated outer surface, two types of thermal boundary conditions have been considered: Constant wall temperature (T), and uniform axial heat flux with constant peripheral temperature (H1) on the inner surface of the annulus. The governing differential equations for momentum and energy conservation are solved by finite-difference methods. Velocity and temperature distributions in the flow cross section, the wall shear-stress distribution, and isothermal f Re, Nu i,T and Nu i,H1 values for different eccentric annuli (0/le?/*/le0.6,/ 0.2/le r/sp/*/le0.8) are presented. In Newtonian flows, the eccentricity is found to have a very strong influence on the flow and temperature fields. In an annulus with relatively large inner cylinder eccentricity, the flow tends to stagnate in the narrow section and has higher peak velocities in the wide section of the annulus. There is considerable flow maldistribution in the azimuthal direction, which in turn produces greater nonuniformity in the temperature field and a consequent degradation in the average heat transfer. Also, the H1 wall condition sustains higher heat transfer coefficients relative to the T boundary condition on the inner surface. For viscous, power-law type non-Newtonian flows, both shear thinning (n<1) and shear thickening (n>1) fluids are considered. Here, the non-linear shear behavior of the fluid is found to further aggravate the flow and temperature maldistribution, and once again the eccentricity is seen to exhibit a very strong influence on the friction and heat transfer behavior. Finally, the hydrodynamic characteristics of fully developed axial laminar flow of Newtonian fluids in eccentric annuli with a rotating inner cylinder are investigated. These are of significant importance to the design and operation of oil and gas drilling wells. Using finite-difference method to solve the governing flow equations in bipolar coordinates, computational results for a wide range of annulus geometry (0/le r/sp/*/le1,/ 0/le/varepsilon/sp/*/le0.8), and rotational Reynolds number (0/le Rer/le150) are presented, where the rotational speeds are restricted to the sub-critical Taylor number regime. The results delineate the effects of annuli r/sp/* and ?sp/*, and inner cylinder rotation speed on the flow structure and frictional losses.
NASA Astrophysics Data System (ADS)
Shyy, W.; Vu, T. C.
1986-12-01
A numerical study is conducted to analyse the two-dimensional incompressible Navier-Stokes flows through the rectilinear and radial cascade of turbine blades. The flows are turbulent and their characteristics are relevant to those of the hydraulic turbines. For the rectilinear cascade, calculations have been made for a NACA 80 series turbine blade with various angles of attack. The outflow turning angle, force coefficients and static pressure distribution have been compared between the prediction and measurement with satisfactory agreements being obtained. The implications of flow turning angles on the total pressure loss are also discussed. The effects of grid distribution on the numerical predictions are also observed.
Sylvain Laizet; Eric Lamballais
2009-01-01
In this paper, a finite difference code for Direct and Large Eddy Simulation (DNS\\/LES) of incompressible flows is presented. This code is an intermediate tool between fully spectral Navier–Stokes solvers (limited to academic geometry through Fourier or Chebyshev representation) and more versatile codes based on standard numerical schemes (typically only second-order accurate). The interest of high-order schemes is discussed in
Michal Beneš
2011-08-08
We study an initial-boundary-value problem for time-dependent flows of heat-conducting viscous incompressible fluids in channel-like domains on a time interval $(0,T)$. For the parabolic system with strong nonlinearities and including the artificial (the so called "do nothing") boundary conditions, we prove the local in time existence, global uniqueness and smoothness of the solution on a time interval $(0,T^*)$, where $0< T^* \\leq T$.
Reynolds number dependence of the drag coefficient for laminar flow through fine-scale screens
O'Hern, T.J.; Torczynski, J.R.
1991-01-01
The laminar flow downstream of fine-mesh screens is studied experimentally and numerically. Two different screen types are examined experimentally, both with open areas greater than 50% and wire dimensions less than 100 {mu}m. Such screens produce flow disturbances of much smaller scale than those examined in most previous studies of flow-conditioning screens and grid-generated turbulence. Instead of using standard woven-wire screens, high- uniformity screens are used which are fabricated by photoetching holes into 50.8 {mu}m thick Inconel sheets. The holes thus produced are square with rounded corners, arranged to form a square array, with a minimum wire thickness (located halfway between wire crossings) of D = 50.8 {mu}m. A flow facility has been constructed for experiments with these screens. Air at 85 kPa and 295 K is passed through each screen at upstream velocities of 1 to 12 m/s, yielding Reynolds numbers Re{sub D} = {rho}UD/{mu} in the range 2 {le} Re{sub D} {le} 35. Pressure drops across the screens are measured at these conditions using pressure transducers and manometers. From these data, the Reynolds number dependence of the drag coefficient c{sub D} is determined. Three-dimensional flow simulations are performed using the spectral-element code NEKTON. The geometry of the photoetched screens is simulated by a similar geometry with the same open area and minimum wire thickness. The drag coefficients are determined from the computed pressure differences across the screens and are in reasonable agreement with the experimental values, although the agreement degrades slightly with increasing Reynolds number. Such correlations are applicable for the present screens so long as the correct choices for screen open area fraction O and minimum wire thickness D are used in correlation. 12 refs., 11 figs.
Reynolds number dependence of the drag coefficient for laminar flow through fine-scale screens
NASA Astrophysics Data System (ADS)
Ohern, T. J.; Torczynski, J. R.
The laminar flow downstream of fine mesh screens is studied experimentally and numerically. Two different screen types are examined experimentally, both with open areas greater than 50 percent and wire dimensions less than 100 micro-m. Such screens produce flow disturbances of much smaller scale than those examined in most previous studies of flow conditioning screens and grid generated turbulence. Instead of using standard woven wire screens, high uniformity screens are used which are fabricated by photo-etching holes into 50.8 micro-m thick Inconel sheets. The holes thus produced are square with rounded corners, arranged to form a square array, with a minimum wire thickness (located halfway between wire crossings) of D = 50.8 micro-m. A flow facility has been constructed for experiments with these screens. Air at 85 kPa and 295 K is passed through each screen at upstream velocities of 1 to 12 m/s, yielding Reynolds numbers Re(sub D) = (rho)UD/mu in the range 2 less than or equal to Re(sub D) less than or equal to 35. Pressure drops across the screens are measured at these conditions using pressure transducers and manometers. From these data, the Reynolds number dependence of the drag coefficient c(sub D) is determined. Three dimensional flow simulations are performed using the spectral element code NEKTON. The geometry of the photo-etched screens is simulated by a similar geometry with the same open area and minimum wire thickness. The drag coefficients are determined from the computed pressure differences across the screens and are in reasonable agreement with the experimental values, although the agreement degrades slightly with increasing Reynolds number. Such correlations are applicable for the present screens so long as the correct choices for screen open area fraction O and minimum wire thickness D are used in correlation.
Laser Doppler flowmetry for measurement of laminar capillary blood flow in the horse
NASA Astrophysics Data System (ADS)
Adair, Henry S., III
1998-07-01
Current methods for in vivo evaluation of digital hemodynamics in the horse include angiography, scintigraphy, Doppler ultrasound, electromagnetic flow and isolated extracorporeal pump perfused digit preparations. These techniques are either non-quantifiable, do not allow for continuous measurement, require destruction of the horse orare invasive, inducing non- physiologic variables. In vitro techniques have also been reported for the evaluation of the effects of vasoactive agents on the digital vessels. The in vitro techniques are non-physiologic and have evaluated the vasculature proximal to the coronary band. Lastly, many of these techniques require general anesthesia or euthanasia of the animal. Laser Doppler flowmetry is a non-invasive, continuous measure of capillary blood flow. Laser Doppler flowmetry has been used to measure capillary blood flow in many tissues. The principle of this method is to measure the Doppler shift, that is, the frequency change that light undergoes when reflected by moving objects, such as red blood cells. Laser Doppler flowmetry records a continuous measurement of the red cell motion in the outer layer of the tissue under study, with little or no influence on physiologic blood flow. This output value constitutes the flux of red cells and is reported as capillary perfusion units. No direct information concerning oxygen, nutrient or waste metabolite exchange in the surrounding tissue is obtained. The relationship between the flowmeter output signal and the flux of red blood cells is linear. The principles of laser Doppler flowmetry will be discussed and the technique for laminar capillary blood flow measurements will be presented.
NASA Astrophysics Data System (ADS)
Liang, H.; Shi, B. C.; Guo, Z. L.; Chai, Z. H.
2014-05-01
In this paper, a phase-field-based multiple-relaxation-time lattice Boltzmann (LB) model is proposed for incompressible multiphase flow systems. In this model, one distribution function is used to solve the Chan-Hilliard equation and the other is adopted to solve the Navier-Stokes equations. Unlike previous phase-field-based LB models, a proper source term is incorporated in the interfacial evolution equation such that the Chan-Hilliard equation can be derived exactly and also a pressure distribution is designed to recover the correct hydrodynamic equations. Furthermore, the pressure and velocity fields can be calculated explicitly. A series of numerical tests, including Zalesak's disk rotation, a single vortex, a deformation field, and a static droplet, have been performed to test the accuracy and stability of the present model. The results show that, compared with the previous models, the present model is more stable and achieves an overall improvement in the accuracy of the capturing interface. In addition, compared to the single-relaxation-time LB model, the present model can effectively reduce the spurious velocity and fluctuation of the kinetic energy. Finally, as an application, the Rayleigh-Taylor instability at high Reynolds numbers is investigated.
A parallel second-order adaptive mesh algorithm for incompressible flow in porous media.
Pau, George S H; Almgren, Ann S; Bell, John B; Lijewski, Michael J
2009-11-28
In this paper, we present a second-order accurate adaptive algorithm for solving multi-phase, incompressible flow in porous media. We assume a multi-phase form of Darcy's law with relative permeabilities given as a function of the phase saturation. The remaining equations express conservation of mass for the fluid constituents. In this setting, the total velocity, defined to be the sum of the phase velocities, is divergence free. The basic integration method is based on a total-velocity splitting approach in which we solve a second-order elliptic pressure equation to obtain a total velocity. This total velocity is then used to recast component conservation equations as nonlinear hyperbolic equations. Our approach to adaptive refinement uses a nested hierarchy of logically rectangular grids with simultaneous refinement of the grids in both space and time. The integration algorithm on the grid hierarchy is a recursive procedure in which coarse grids are advanced in time, fine grids are advanced multiple steps to reach the same time as the coarse grids and the data at different levels are then synchronized. The single-grid algorithm is described briefly, but the emphasis here is on the time-stepping procedure for the adaptive hierarchy. Numerical examples are presented to demonstrate the algorithm's accuracy and convergence properties and to illustrate the behaviour of the method. PMID:19840985
Additional interfacial force in lattice Boltzmann models for incompressible multiphase flows.
Li, Q; Luo, K H; Gao, Y J; He, Y L
2012-02-01
The existing lattice Boltzmann models for incompressible multiphase flows are mostly constructed with two distribution functions: one is the order parameter distribution function, which is used to track the interface between different phases, and the other is the pressure distribution function for solving the velocity field. In this paper, it is shown that in these models the recovered momentum equation is inconsistent with the target one: an additional force is included in the recovered momentum equation. The additional force has the following features. First, it is proportional to the macroscopic velocity. Second, it is zero in every single-phase region but is nonzero in the interface. Therefore it can be interpreted as an interfacial force. To investigate the effects of the additional interfacial force, numerical simulations are carried out for the problem of Rayleigh-Taylor instability, droplet splashing on a thin liquid film, and the evolution of a falling droplet under gravity. Numerical results demonstrate that, with the increase of the velocity or the Reynolds number, the additional interfacial force will gradually have an important influence on the interface and affect the numerical accuracy. PMID:22463354
A Convective-like Energy-Stable Open Boundary Condition for Simulations of Incompressible Flows
Dong, Suchuan
2015-01-01
We present a new energy-stable open boundary condition, and an associated numerical algorithm, for simulating incompressible flows with outflow/open boundaries. This open boundary condition ensures the energy stability of the system, even when strong vortices or backflows occur at the outflow boundary. Under certain situations it can be reduced to a form that can be analogized to the usual convective boundary condition. One prominent feature of this boundary condition is that it provides a control over the velocity on the outflow/open boundary. This is not available with the other energy-stable open boundary conditions from previous works. Our numerical algorithm treats the proposed open boundary condition based on a rotational velocity-correction type strategy. It gives rise to a Robin-type condition for the discrete pressure and a Robin-type condition for the discrete velocity on the outflow/open boundary, respectively at the pressure and the velocity sub-steps. We present extensive numerical experiments on...
A Parallel Second-Order Adaptive Mesh Algorithm for Incompressible Flow in Porous Media
Pau, George Shu Heng; Almgren, Ann S.; Bell, John B.; Lijewski, Michael J.
2008-04-01
In this paper we present a second-order accurate adaptive algorithm for solving multiphase, incompressible flows in porous media. We assume a multiphase form of Darcy's law with relative permeabilities given as a function of the phase saturation. The remaining equations express conservation of mass for the fluid constituents. In this setting the total velocity, defined to be the sum of the phase velocities, is divergence-free. The basic integration method is based on a total-velocity splitting approach in which we solve a second-order elliptic pressure equation to obtain a total velocity. This total velocity is then used to recast component conservation equations as nonlinear hyperbolic equations. Our approach to adaptive refinement uses a nested hierarchy of logically rectangular grids with simultaneous refinement of the grids in both space and time. The integration algorithm on the grid hierarchy is a recursive procedure in which coarse grids are advanced in time, fine grids areadvanced multiple steps to reach the same time as the coarse grids and the data atdifferent levels are then synchronized. The single grid algorithm is described briefly,but the emphasis here is on the time-stepping procedure for the adaptive hierarchy. Numerical examples are presented to demonstrate the algorithm's accuracy and convergence properties and to illustrate the behavior of the method.
Analysis of the secondary instability of the incompressible flows over a swept wing
NASA Astrophysics Data System (ADS)
Xu, GuoLiang; Xiao, ZhiXiang; Fu, Song
2011-04-01
The crossflow instability of a three-dimensional (3-D) boundary layer is an important factor which affects the transition over a swept-wing. In this report, the primary instability of the incompressible flow over a swept wing is investigated by solving nonlinear parabolized stability equations (NPSE). The Floquet theory is applied to study the dependence of the secondary and high-frequency instabilities on curvature, Reynolds number and angle of swept (AOS). The computational results show that the curvature in the present case has no significant effect on the secondary instabilities. It is generally believed that the secondary instability growth rate increases with the magnitude of the nonlinear mode of crossflow vortex. But, at a certain state, when the Reynolds number is 3.2 million, we find that the secondary instability growth rate becomes smaller even when the magnitude of the nonlinear mode of the crossflow vortex is larger. The effect of the angle of swept at 35, 45 and 55 degrees, respectively, is also studied in the framework of the secondary linear stability theory. Larger angles of swept tend to decrease the spanwise spacing of the crossflow vortices, which correspondingly helps the stimulation of `z' mode.
Liang, H; Shi, B C; Guo, Z L; Chai, Z H
2014-05-01
In this paper, a phase-field-based multiple-relaxation-time lattice Boltzmann (LB) model is proposed for incompressible multiphase flow systems. In this model, one distribution function is used to solve the Chan-Hilliard equation and the other is adopted to solve the Navier-Stokes equations. Unlike previous phase-field-based LB models, a proper source term is incorporated in the interfacial evolution equation such that the Chan-Hilliard equation can be derived exactly and also a pressure distribution is designed to recover the correct hydrodynamic equations. Furthermore, the pressure and velocity fields can be calculated explicitly. A series of numerical tests, including Zalesak's disk rotation, a single vortex, a deformation field, and a static droplet, have been performed to test the accuracy and stability of the present model. The results show that, compared with the previous models, the present model is more stable and achieves an overall improvement in the accuracy of the capturing interface. In addition, compared to the single-relaxation-time LB model, the present model can effectively reduce the spurious velocity and fluctuation of the kinetic energy. Finally, as an application, the Rayleigh-Taylor instability at high Reynolds numbers is investigated. PMID:25353927
NASA Technical Reports Server (NTRS)
Kumar, A.; Graeves, R. A.
1980-01-01
A user's guide for a computer code 'COLTS' (Coupled Laminar and Turbulent Solutions) is provided which calculates the laminar and turbulent hypersonic flows with radiation and coupled ablation injection past a Jovian entry probe. Time-dependent viscous-shock-layer equations are used to describe the flow field. These equations are solved by an explicit, two-step, time-asymptotic finite-difference method. Eddy viscosity in the turbulent flow is approximated by a two-layer model. In all, 19 chemical species are used to describe the injection of carbon-phenolic ablator in the hydrogen-helium gas mixture. The equilibrium composition of the mixture is determined by a free-energy minimization technique. A detailed frequency dependence of the absorption coefficient for various species is considered to obtain the radiative flux. The code is written for a CDC-CYBER-203 computer and is capable of providing solutions for ablated probe shapes also.
NASA Astrophysics Data System (ADS)
Wu, J.; Shu, C.
2010-07-01
The recently proposed boundary condition-enforced immersed boundary-lattice Boltzmann method (IB-LBM) [14] is improved in this work to simulate three-dimensional incompressible viscous flows. In the conventional IB-LBM, the restoring force is pre-calculated, and the non-slip boundary condition is not enforced as compared to body-fitted solvers. As a result, there is a flow penetration to the solid boundary. This drawback was removed by the new version of IB-LBM [14], in which the restoring force is considered as unknown and is determined in such a way that the non-slip boundary condition is enforced. Since Eulerian points are also defined inside the solid boundary, the computational domain is usually regular and the Cartesian mesh is used. On the other hand, to well capture the boundary layer and in the meantime, to save the computational effort, we often use non-uniform mesh in IB-LBM applications. In our previous two-dimensional simulations [14], the Taylor series expansion and least squares-based lattice Boltzmann method (TLLBM) was used on the non-uniform Cartesian mesh to get the flow field. The final expression of TLLBM is an algebraic formulation with some weighting coefficients. These coefficients could be computed in advance and stored for the following computations. However, this way may become impractical for 3D cases as the memory requirement often exceeds the machine capacity. The other way is to calculate the coefficients at every time step. As a result, extra time is consumed significantly. To overcome this drawback, in this study, we propose a more efficient approach to solve lattice Boltzmann equation on the non-uniform Cartesian mesh. As compared to TLLBM, the proposed approach needs much less computational time and virtual storage. Its good accuracy and efficiency are well demonstrated by its application to simulate the 3D lid-driven cubic cavity flow. To valid the combination of proposed approach with the new version of IBM [14] for 3D flows with curved boundaries, the flows over a sphere and torus are simulated. The obtained numerical results compare very well with available data in the literature.
Structural development of laminar flow control aircraft chordwise wing joint designs
NASA Technical Reports Server (NTRS)
Fischler, J. E.; Jerstad, N. M.; Gallimore, F. H., Jr.; Pollard, T. J.
1989-01-01
For laminar flow to be achieved, any protuberances on the surface must be small enough to avoid transition to turbulent flow. However, the surface must have joints between the structural components to allow assembly or replacement of damaged parts, although large continuous surfaces can be utilized to minimize the number the number of joints. Aircraft structural joints usually have many countersunk bolts or rivets on the outer surface. To maintain no mismatch on outer surfaces, it is desirable to attach the components from the inner surface. It is also desirable for the panels to be interchangeable, without the need for shims at the joint, to avoid surface discontinuities that could cause turbulence. Fabricating components while pressing their outer surfaces against an accurate mold helps to ensure surface smoothness and continuity at joints. These items were considered in evaluating the advantages and disadvantages of the joint design concepts. After evaluating six design concepts, two of the leading candidates were fabricated and tested using many small test panels. One joint concept was also built and tested using large panels. The small and large test panel deflections for the leading candidate designs at load factors up to +1.5 g's were well within the step and waviness requirements for avoiding transition.The small panels were designed and tested for compression and tension at -65 F, at ambient conditions, and at 160 F. The small panel results for the three-rib and the sliding-joint concepts indicated that they were both acceptable. The three-rib concept, with tapered splice plates, was considered to be the most practical. A modified three-rib joint that combined the best attributes of previous candidates was designed, developed, and tested. This improved joint met all of the structural strength, surface smoothness, and waviness criteria for laminar flow control (LFC). The design eliminated all disadvantages of the initial three-rib concept except for unavoidable eccentricity, which was reduced and reacted satisfactorily by the rib supports. It should also result in a relatively simple low-cost installation, and makes it easy to replace any panels damaged in the field.
NASA Technical Reports Server (NTRS)
Brown, W Byron; Livingood, John N B
1952-01-01
Revised solutions of the laminar-boundary-layer equations for cases which involved cooling at the wall combined with large pressure gradients in the main stream produced specific-weight-flow profiles which locally exceeded free-stream values. Heat-transfer and friction coefficients, boundary-layer thicknesses, and velocity, temperature, and specific-weight-flow distributions resulting from the revised solutions are presented for Euler numbers of 0.5 and 1, stream-to-wall temperature ratios of 2 and 4, and cooling-air flow rates through porous walls designated by flow parameters of 0, -0.5, and -1.
NASA Technical Reports Server (NTRS)
Rozendaal, R. A.
1986-01-01
The linear boundary layer stability analyses and their correlation with data of 18 cases from a natural laminar flow (NLF) flight test program using a Cessna Citation 3 business jet are described. The transition point varied from 5% to 35% chord for these conditions, and both upper and lower wing surfaces were included. Altitude varied from 10,000 to 43,000 ft and Mach number from 0.3 to 0.8. Four cases were at nonzero sideslip. Although there was much scatter in the results, the analyses of boundary layer stability at the 18 conditions led to the conclusion that crossflow instability was the primary cause of transition. However, the sideslip cases did show some interaction of crossflow and Tollmien-Schlichting disturbances. The lower surface showed much lower Tollmien-Schlichting amplification at transition than the upper surface, but similar crossflow amplifications. No relationship between Mach number and disturbance amplification at transition could be found. The quality of these results is open to question from questionable wing surface quality, inadequate density of transition sensors on the wing upper surface, and an unresolved pressure shift in the wing pressure data. The results of this study show the need for careful preparation for transition experiments. Preparation should include flow analyses of the test surface, boundary layer disturbance amplification analyses, and assurance of adequate surface quality in the test area. The placement of necessary instruments and usefulness of the resulting data could largely be determined during the pretest phase.
M. Turkyilmazoglu
2009-01-01
Direct spatial resonance phenomenon occurring in the viscous incompressible boundary layer flow due to a rotating-disk is\\u000a investigated in this paper based on the linear stability theory. The possible effects of suction and injection are explored\\u000a on the direct spatial resonance instability mechanism detected earlier in the case of zero-suction. This instability leads\\u000a to an algebraic growth of disturbances while
NASA Technical Reports Server (NTRS)
Arena, A. V.; Mueller, T. J.
1979-01-01
The laminar separation, transition, and turbulent reattachment near the leading edge of a cylindrical nose-constant thickness airfoil model were investigated using a low turbulence, low speed smoke wind tunnel. The locations of separation, transition, and reattachment were obtained from smoke flow photographs and surface oil flow techniques for chord Reynolds numbers from about 150,000 to 470,000. These visual data combined with static pressure distributions and lift and drag measurements delineate the effects of angle of attack, flap deflection angle, and chord Reynolds number on the separation bubble characteristics. The data concerning the length of the laminar and turbulent portions of the bubble agree with the empirical prediction methods for short bubbles.
F-15B on ramp showing closeup of the Supersonic Natural Laminar Flow (SS-NLF) experiment attached ve
NASA Technical Reports Server (NTRS)
1999-01-01
A close up of the Supersonic Natural Laminar Flow (SS-NLF) experiment on the F-15B. The wing shape - designed by the Reno Aeronautical Corp. - had only minimal sweep and a short span. The low sweep angle gave this airfoil better take off and landing characteristics, as well as better subsonic cruise efficiency, than wings with a greater sweep angle. Engineers had reason to believe that improvements in aerodynamic efficiency from supersonic natural laminar flow might actually render a supersonic aircraft more economical to operate than slower, subsonic designs. To gather substantiate data, the SS-NLF experiment used an advanced, non-intrusive collection technique. Rather than instrumentation built into the wing, a high resolution infrared camera mounted on the F-15B fuselage recorded the data, a system with possible applications for future research aircraft.
A survey of grid-free methods for the simulation of 3-D incompressible flows in bounded domains
Gharakhani, A.
1997-09-01
The state-of-the-art in Lagrangian methods for the grid-free simulation of three-dimensional, incompressible, high Reynolds number, internal and/or external flows is surveyed. Specifically, vortex and velicity (or impulse) element methods are introduced. The relative merits of various available techniques and the outstanding challenges in simulating the processes of convection and diffusion, as well as in satisfying the wall boundary conditions are discussed individually. Issues regarding the stretch and solenoidality of vorticity are also discussed. A potentially successful algorithm for simulating the flow around a parachute is proposed as well.
Wu, Xiaohua; Moin, Parviz; Adrian, Ronald J; Baltzer, Jon R
2015-06-30
The precise dynamics of breakdown in pipe transition is a century-old unresolved problem in fluid mechanics. We demonstrate that the abruptness and mysteriousness attributed to the Osborne Reynolds pipe transition can be partially resolved with a spatially developing direct simulation that carries weakly but finitely perturbed laminar inflow through gradual rather than abrupt transition arriving at the fully developed turbulent state. Our results with this approach show during transition the energy norms of such inlet perturbations grow exponentially rather than algebraically with axial distance. When inlet disturbance is located in the core region, helical vortex filaments evolve into large-scale reverse hairpin vortices. The interaction of these reverse hairpins among themselves or with the near-wall flow when they descend to the surface from the core produces small-scale hairpin packets, which leads to breakdown. When inlet disturbance is near the wall, certain quasi-spanwise structure is stretched into a Lambda vortex, and develops into a large-scale hairpin vortex. Small-scale hairpin packets emerge near the tip region of the large-scale hairpin vortex, and subsequently grow into a turbulent spot, which is itself a local concentration of small-scale hairpin vortices. This vortex dynamics is broadly analogous to that in the boundary layer bypass transition and in the secondary instability and breakdown stage of natural transition, suggesting the possibility of a partial unification. Under parabolic base flow the friction factor overshoots Moody's correlation. Plug base flow requires stronger inlet disturbance for transition. Accuracy of the results is demonstrated by comparing with analytical solutions before breakdown, and with fully developed turbulence measurements after the completion of transition. PMID:26080447
A A Arrage; N Vasishtha; D Sundberg; G Bausch; H L Vincent; D C White
1995-01-01
A laminar flow biofilm-monitoring system was used to determine the efficacies of three antifouling (AF) coatings and five fouling-release (FR) coatings againstVibrio harveyi attachment. On-line measurements of tryptophan fluorescence and bioluminescence from each coating, normalized to an upstream stainless steel coupon, were used to determine the effects of AF and FR surfaces on biofilm formation. The AF coatings consisted of
NASA Technical Reports Server (NTRS)
Harris, Charles D.; Brooks, Cuyler W., Jr.; Clukey, Patricia G.; Stack, John P.
1992-01-01
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 of the perforated panels as designed are described. The experiment was conducted in the Langley 8-Foot Transonic Pressure Tunnel. Also included is an evaluation of the influence of the proximity of the tunnel liner to the upper surface of the airfoil pressure distribution.
Evaluation of laminar flow control system concepts for subsonic commercial transport aircraft
NASA Technical Reports Server (NTRS)
1980-01-01
A study was conducted to evaluate alternatives in the design of laminar flow control (LFC) subsonic commercial transport aircraft for operation in the 1980's period. Analyses were conducted to select mission parameters and define optimum aircraft configurational parameters for the selected mission, defined by a passenger payload of 400 and a design range of 12,038 km (6500 n mi). The baseline aircraft developed for this mission was used as a vehicle for the evaluation and development of alternative LFC system concepts. Alternatives were evaluated in the areas of aerodynamics structures, materials, LFC systems, leading-edge region cleaning and integration of auxiliary systems. Based on these evaluations, concept in each area were selected for further development and testing and ultimate incorporation in the final study aircraft. Relative to a similarly-optimized advanced technology turbulent transport, the final LFC configuration is approximately equal in direct operating cost but provides decreases of 8.2% in gross weight and 21.7% in fuel consumption.
Structural tests and development of a laminar flow control wing surface composite chordwise joint
NASA Technical Reports Server (NTRS)
Lineberger, L. B.
1984-01-01
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. The Lockheed-Georgia Company accomplished under NAS1-16235 Laminar-Flow-Control (LFC) 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 joint was demonstrated by fabricating and testing complex, concept selection specimens. The Lockheed-Georgia Company accomplishments, Development of LFC Wind Surface Composite Structures (WSCS), are documented. Tests were conducted on two CV2 panels to verify the static tension and fatigue strength of LFC wing surface chordwise joints.
Zizzari, A; Bianco, M; Miglietta, R; del Mercato, L L; Carraro, M; Sorarù, A; Bonchio, M; Gigli, G; Rinaldi, R; Viola, I; Arima, V
2014-11-21
Liquid flow in microchannels is completely laminar and uniaxial, with a very low Reynolds number regime and long mixing lengths. To increase fluid mixing and solubility of reactants, as well as to reduce reaction time, complex three-dimensional networks inducing chaotic advection have to be designed. Alternatively, turbulence in the liquid can be generated by active mixing methods (magnetic, acoustic waves, etc.) or adding small quantities of elastic materials to the working liquid. Here, polyelectrolyte multilayer capsules embodying a catalytic polyoxometalate complex have been suspended in an aqueous solution and used to create elastic turbulence and to propel fluids inside microchannels as an alternative to viscoelastic polymers. The overall effect is enhanced and controlled by feeding the polyoxometalate-modified capsules with hydrogen peroxide, H2O2, thus triggering an on-demand propulsion due to oxygen evolution resulting from H2O2 decomposition. The quantification of the process is done by analysing some structural parameters of motion such as speed, pressure, viscosity, and Reynolds and Weissenberg numbers, directly obtained from the capillary dynamics of the aqueous mixtures with different concentrations of H2O2. The increases in fluid speed as well as the capsule-induced turbulence effects are proportional to the H2O2 added and therefore dependent on the kinetics of H2O2 dismutation. PMID:25238401
A transonic interactive boundary-layer theory for laminar and turbulent flow over swept wings
NASA Technical Reports Server (NTRS)
Woodson, Shawn H.; Dejarnette, Fred R.
1988-01-01
A 3-D laminar and turbulent boundary-layer method is developed for compressible flow over swept wings. The governing equations and curvature terms are derived in detail for a nonorthogonal, curvilinear coordinate system. Reynolds shear-stress terms are modeled by the Cebeci-Smith eddy-viscosity formulation. The governing equations are descretized using the second-order accurate, predictor-corrector finite-difference technique of Matsuno, which has the advantage that the crossflow difference formulas are formed independent of the sign of the crossflow velocity component. The method is coupled with a full potential wing/body inviscid code (FLO-30) and the inviscid-viscous interaction is performed by updating the original wing surface with the viscous displacement surface calculated by the boundary-layer code. The number of these global iterations ranged from five to twelve depending on Mach number, sweep angle, and angle of attack. Several test cases are computed by this method and the results are compared with another inviscid-viscous interaction method (TAWFIVE) and with experimental data.
Hybrid laminar flow control experiments in the NASA - Ames, 11-foot tunnel
NASA Technical Reports Server (NTRS)
Saric, William S.
1995-01-01
It was proposed to design and conduct experiments in the NASA-Ames Research Center, 11-foot wind tunnel, that would assess the role of freestream turbulence and surface roughness on swept-wing transition to turbulence. The work was to be a cooperative effort that had direct application to hybrid laminar flow control (HLFC) airfoils. The first part of the proposed work, initiated in FY92 and continued into FY93, concentrated on the design of such an experiment whose results may be compared with results obtained in other wind-tunnel facilities. At the same time, concurrent work in the Arizona State University (ASU) Unsteady Wind Tunnel would be conducted on the effects of surface roughness. The second part of the work, which was to be initiated in FY94, would have consisted of experiments conducted in both the 11-foot tunnel at NASA-Ames and the ASU Unsteady Wind Tunnel. However, this work was not continued. This report summarizes the experimental design considerations and some preliminary experiments that made up the first part of the work.
Self similar growth of a 1D granular fan under laminar flow near threshold
NASA Astrophysics Data System (ADS)
Guerit, Laure; Métivier, François; Devauchelle, Olivier; Lajeunesse, Eric; Barrier, Laurie
2014-05-01
Alluvial fans are major sedimentary bodies that make the transition between the reliefs and the sedimentary basins. They are found at the outlet of some drainages catchments, where rivers are free to diverge and avulse, and to depose part of their sedimentary load. Understanding their dynamics of formation and evolution is a great problem of sediment transport. Rivers and fan profiles are usually described as diffusive systems but this is only true if the shear stress exerted on the bed is high compared to the critical shear stress. This might be the case for sand bed rivers, but not for gravel bed rivers, for which it is known that the shear stress is only slightly higher than the critical one. This is why we need to develop a new model to describe the evolution of alluvial fans built by gravel bed rivers. To do this analytically, we work in 1D, with a laminar flow and one grain-size in order to be able to describe both the fluid and the sediment transport. In addition, the conditions of the experiments insured that the boundary shear stress is near the critical value for motion inception of the granular material. Using Taylor expansion, we show that for asymptotically long times, the fan growth is self-similar and can be decomposed into a triangular ``threshold" shape plus a small quadratic deviation. We performed experiments with glass beads and glycerol to test and successfully validate this theory.
Length and time for development of laminar flow in tubes following a step increase of volume flux
NASA Astrophysics Data System (ADS)
Chaudhury, Rafeed A.; Herrmann, Marcus; Frakes, David H.; Adrian, Ronald J.
2015-01-01
Laminar flows starting up from rest in round tubes are relevant to numerous industrial and biomedical applications. The two most common types are flows driven by an abruptly imposed constant pressure gradient or by an abruptly imposed constant volume flux. Analytical solutions are available for transient, fully developed flows, wherein streamwise development over the entrance length is absent (Szymanski in J de Mathématiques Pures et Appliquées 11:67-107, 1932; Andersson and Tiseth in Chem Eng Commun 112(1):121-133, 1992, respectively). They represent the transient responses of flows in tubes that are very long compared with the entrance length, a condition that is seldom satisfied in biomedical tube networks. This study establishes the entrance (development) length and development time of starting laminar flow in a round tube of finite length driven by a piston pump that produces a step change from zero flow to a constant volume flux for Reynolds numbers between 500 and 3,000. The flows are examined experimentally, using stereographic particle image velocimetry and computationally using computational fluid dynamics, and are then compared with the known analytical solutions for fully developed flow conditions in infinitely long tubes. Results show that step function volume flux start-up flows reach steady state and fully developed flow five times more quickly than those driven by a step function pressure gradient, a 500 % change when compared with existing estimates. Based on these results, we present new, simple guidelines for achieving experimental flows that are fully developed in space and time in realistic (finite) tube geometries. To a first approximation, the time to achieve steady spatially developing flow is nearly equal to the time needed to achieve steady, fully developed flow. Conversely, the entrance length needed to achieve fully developed transient flow is approximately equal to the length needed to achieve fully developed steady flow. Beyond this level of description, the numerical results reveal interaction between the effects of space and time development and nonlinear Reynolds number effects.
On a Regularized Family of Models for Homogeneous Incompressible Two-Phase Flows
NASA Astrophysics Data System (ADS)
Gal, Ciprian G.; Medjo, T. Tachim
2014-12-01
We consider a general family of regularized models for incompressible two-phase flows based on the Allen-Cahn formulation in -dimensional compact Riemannian manifolds for . The system we consider consists of a regularized family of Navier-Stokes equations (including the Navier-Stokes--like model, the Leray- model, the modified Leray- model, the simplified Bardina model, the Navier-Stokes-Voight model, and the Navier-Stokes model) for the fluid velocity suitably coupled with a convective Allen-Cahn equation for the order (phase) parameter . We give a unified analysis of the entire three-parameter family of two-phase models using only abstract mapping properties of the principal dissipation and smoothing operators and then use assumptions about the specific form of the parameterizations, leading to specific models, only when necessary to obtain the sharpest results. We establish existence, stability, and regularity results and some results for singular perturbations, which as special cases include the inviscid limit of viscous models and the limit in models. Then we show the existence of a global attractor and exponential attractor for our general model and establish precise conditions under which each trajectory converges to a single equilibrium by means of a Lojasiewicz-Simon inequality. We also derive new results on the existence of global and exponential attractors for the regularized family of Navier-Stokes equations and magnetohydrodynamics models that improve and complement the results of Holst et al. (J Nonlinear Sci 20(5):523-567, 2010). Finally, our analysis is applied to certain regularized Ericksen-Leslie models for the hydrodynamics of liquid crystals in -dimensional compact Riemannian manifolds.
On a regularized family of models for homogeneous incompressible two-phase flows
Ciprian G. Gal; T. Tachim Medjo
2014-09-15
We consider a general family of regularized models for incompressible two-phase flows based on the Allen-Cahn formulation in n-dimensional compact Riemannian manifolds for n=2,3. The system we consider consists of a regularized family of Navier-Stokes equations (including the Navier-Stokes-{\\alpha}-like model, the Leray-{\\alpha} model, the Modified Leray-{\\alpha} model, the Simplified Bardina model, the Navier-Stokes-Voight model and the Navier-Stokes model) for the fluid velocity suitably coupled with a convective Allen-Cahn equation for the (phase) order parameter. We give a unified analysis of the entire three-parameter family of two-phase models using only abstract mapping properties of the principal dissipation and smoothing operators, and then use assumptions about the specific form of the parametrizations, leading to specific models, only when necessary to obtain the sharpest results. We establish existence, stability and regularity results, and some results for singular perturbations, which as special cases include the inviscid limit of viscous models and the {\\alpha}->0 limit in {\\alpha}-models. Then, we also show the existence of a global attractor and exponential attractor for our general model, and then establish precise conditions under which each trajectory converges to a single equilibrium by means of a LS inequality. We also derive new results on the existence of global and exponential attractors for the regularized family of Navier-Stokes equations and magnetohydrodynamics models which improve and complement the results of Holst et. al. [J. Nonlinear Science 20, 2010, 523-567]. Finally, our analysis is applied to certain regularized Ericksen-Leslie (RSEL) models for the hydrodynamics of liquid crystals in n-dimensional compact Riemannian manifolds.
NASA Technical Reports Server (NTRS)
Kolesar, C. E.
1987-01-01
Research activity on an airfoil designed for a large airplane capable of very long endurance times at a low Mach number of 0.22 is examined. Airplane mission objectives and design optimization resulted in requirements for a very high design lift coefficient and a large amount of laminar flow at high Reynolds number to increase the lift/drag ratio and reduce the loiter lift coefficient. Natural laminar flow was selected instead of distributed mechanical suction for the measurement technique. A design lift coefficient of 1.5 was identified as the highest which could be achieved with a large extent of laminar flow. A single element airfoil was designed using an inverse boundary layer solution and inverse airfoil design computer codes to create an airfoil section that would achieve performance goals. The design process and results, including airfoil shape, pressure distributions, and aerodynamic characteristics are presented. A two dimensional wind tunnel model was constructed and tested in a NASA Low Turbulence Pressure Tunnel which enabled testing at full scale design Reynolds number. A comparison is made between theoretical and measured results to establish accuracy and quality of the airfoil design technique.
Richard C. Martineau; Ray A. Berry; Aurélia Esteve; Kurt D. Hamman; Dana A. Knoll; Ryosuke Park; William Taitano
2009-01-01
This report illustrates a comparative study to analyze the physical differences between numerical simulations obtained with both the conservation and incompressible forms of the Navier-Stokes equations for natural convection flows in simple geometries. The purpose of this study is to quantify how the incompressible flow assumption (which is based upon constant density advection, divergence-free flow, and the Boussinesq gravitational body force approximation) differs from the conservation form (which only assumes that the fluid is a continuum) when solving flows driven by gravity acting upon density variations resulting from local temperature gradients. Driving this study is the common use of the incompressible flow assumption in fluid flow simulations for nuclear power applications in natural convection flows subjected to a high heat flux (large temperature differences). A series of simulations were conducted on two-dimensional, differentially-heated rectangular geometries and modeled with both hydrodynamic formulations. From these simulations, the selected characterization parameters of maximum Nusselt number, average Nusselt number, and normalized pressure reduction were calculated. Comparisons of these parameters were made with available benchmark solutions for air with the ideal gas assumption at both low and high heat fluxes. Additionally, we generated body force, velocity, and divergence of velocity distributions to provide a basis for further analysis. The simulations and analysis were then extended to include helium at the Very High Temperature gas-cooled Reactor (VHTR) normal operating conditions. Our results show that the consequences of incorporating the incompressible flow assumption in high heat flux situations may lead to unrepresentative results. The results question the use of the incompressible flow assumption for simulating fluid flow in an operating nuclear reactor, where large temperature variations are present. The results show that the use of the incompressible flow assumption with the Boussinesq gravitational body force approximation should be restricted to flows where the density change of a fluid particle along a pathline is negligible.
Elongational-flow-induced scission of DNA nanotubes in laminar flow Rizal F. Hariadi*
Winfree, Erik
.50.Jf, 62.25. g I. INTRODUCTION Elongational-flow-induced scission can break a long poly- mer of the scal- ing relations between key physical parameters 3,814 and measurement of the polymer bond strength between theory and scission experi- ments and showed the significance of turbulent flow in poly- mer
Yagi, Takanobu; Sato, Ayaka; Shinke, Manabu; Takahashi, Sara; Tobe, Yasutaka; Takao, Hiroyuki; Murayama, Yuichi; Umezu, Mitsuo
2013-01-01
This study experimentally investigated the instability of flow impingement in a cerebral aneurysm, which was speculated to promote the degradation of aneurysmal wall. A patient-specific, full-scale and elastic-wall replica of cerebral artery was fabricated from transparent silicone rubber. The geometry of the aneurysm corresponded to that found at 9 days before rupture. The flow in a replica was analysed by quantitative flow visualization (stereoscopic particle image velocimetry) in a three-dimensional, high-resolution and time-resolved manner. The mid-systolic and late-diastolic flows with a Reynolds number of 450 and 230 were compared. The temporal and spatial variations of near-wall velocity at flow impingement delineated its inherent instability at a low Reynolds number. Wall shear stress (WSS) at that site exhibited a combination of temporal fluctuation and spatial divergence. The frequency range of fluctuation was found to exceed significantly that of the heart rate. The high-frequency-fluctuating WSS appeared only during mid-systole and disappeared during late diastole. These results suggested that the flow impingement induced a transition from a laminar regime. This study demonstrated that the hydrodynamic instability of shear layer could not be neglected even at a low Reynolds number. No assumption was found to justify treating the aneurysmal haemodynamics as a fully viscous laminar flow. PMID:23427094
Yagi, Takanobu; Sato, Ayaka; Shinke, Manabu; Takahashi, Sara; Tobe, Yasutaka; Takao, Hiroyuki; Murayama, Yuichi; Umezu, Mitsuo
2013-05-01
This study experimentally investigated the instability of flow impingement in a cerebral aneurysm, which was speculated to promote the degradation of aneurysmal wall. A patient-specific, full-scale and elastic-wall replica of cerebral artery was fabricated from transparent silicone rubber. The geometry of the aneurysm corresponded to that found at 9 days before rupture. The flow in a replica was analysed by quantitative flow visualization (stereoscopic particle image velocimetry) in a three-dimensional, high-resolution and time-resolved manner. The mid-systolic and late-diastolic flows with a Reynolds number of 450 and 230 were compared. The temporal and spatial variations of near-wall velocity at flow impingement delineated its inherent instability at a low Reynolds number. Wall shear stress (WSS) at that site exhibited a combination of temporal fluctuation and spatial divergence. The frequency range of fluctuation was found to exceed significantly that of the heart rate. The high-frequency-fluctuating WSS appeared only during mid-systole and disappeared during late diastole. These results suggested that the flow impingement induced a transition from a laminar regime. This study demonstrated that the hydrodynamic instability of shear layer could not be neglected even at a low Reynolds number. No assumption was found to justify treating the aneurysmal haemodynamics as a fully viscous laminar flow. PMID:23427094
F-16XL Supersonic Laminar Flow Test Flight - Duration: 29 seconds.
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...
NASA Astrophysics Data System (ADS)
Laizet, Sylvain; Lamballais, Eric
2009-09-01
In this paper, a finite difference code for Direct and Large Eddy Simulation (DNS/LES) of incompressible flows is presented. This code is an intermediate tool between fully spectral Navier-Stokes solvers (limited to academic geometry through Fourier or Chebyshev representation) and more versatile codes based on standard numerical schemes (typically only second-order accurate). The interest of high-order schemes is discussed in terms of implementation easiness, computational efficiency and accuracy improvement considered through simplified benchmark problems and practical calculations. The equivalence rules between operations in physical and spectral spaces are efficiently used to solve the Poisson equation introduced by the projection method. It is shown that for the pressure treatment, an accurate Fourier representation can be used for more flexible boundary conditions than periodicity or free-slip. Using the concept of the modified wave number, the incompressibility can be enforced up to the machine accuracy. The benefit offered by this alternative method is found to be very satisfactory, even when a formal second-order error is introduced locally by boundary conditions that are neither periodic nor symmetric. The usefulness of high-order schemes combined with an immersed boundary method (IBM) is also demonstrated despite the second-order accuracy introduced by this wall modelling strategy. In particular, the interest of a partially staggered mesh is exhibited in this specific context. Three-dimensional calculations of transitional and turbulent channel flows emphasize the ability of present high-order schemes to reduce the computational cost for a given accuracy. The main conclusion of this paper is that finite difference schemes with quasi-spectral accuracy can be very efficient for DNS/LES of incompressible flows, while allowing flexibility for the boundary conditions and easiness in the code development. Therefore, this compromise fits particularly well for very high-resolution simulations of turbulent flows with relatively complex geometries without requiring heavy numerical developments.
The stability of a three-dimensional laminar boundary layer on a swept flat plate
NASA Technical Reports Server (NTRS)
Collier, F. S., Jr.; Mueller, B.; Bippes, H.
1990-01-01
The linear stability of the laminar boundary layer on a swept flat plate with an imposed favorable pressure gradient was studied utilizing a linear stability model which accounts for streamline curvature for three-dimensional incompressible flows. Calculations were performed for an effective leading-edge sweep angle of 42.5 degrees and freestream velocity of 19 m/s. Computed disturbance amplification rates for the spectrum of amplified frequencies and wavelengths for stationary crossflow vortices were compared with experimental results.
The stability of a three dimensional laminar boundary layer over a swept flat plate
NASA Technical Reports Server (NTRS)
Mueller, B.; Bippes, H.; Collier, F. S., Jr.
1990-01-01
The linear stability of the laminar boundary layer on a swept flat plate with an imposed favorable pressure gradient was studied utilizing a linear stability model which accounts for streamline curvature for three-dimensional incompressible flows. Calculations were performed for a leading-edge sweep angle of 45 degrees and freestream valocity of 19 m/s. Computed disturbance amplification rates and wavelengths for stationary crossflow vortices were compared with available experimental results.
Verification of the proteus two-dimensional Navier-Stokes code for flat plate and pipe flows
NASA Technical Reports Server (NTRS)
Conley, Julianne M.; Zeman, Patrick L.
1991-01-01
The Proteus Navier-Stokes Code is evaluated for 2-D/axisymmetric, viscous, incompressible, internal, and external flows. The particular cases to be discussed are laminar and turbulent flows over a flat plate, laminar and turbulent developing pipe flows, and turbulent pipe flow with swirl. Results are compared with exact solutions, empirical correlations, and experimental data. A detailed description of the code set-up, including boundary conditions, initial conditions, grid size, and grid packing is given for each case.