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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
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NASA NTRS1987

Finite element methods of analysis for high speed viscous flows

Over the past three years a finite element based procedure for the solution of high speed viscous compressible flows was developed. The approach followed was to compute steady state solutions via a false transient, using an explicit time stepping scheme, and to attempt to improve the solution quality by incorporating adaptive mesh procedures. The main thrust of the work was to continue on the extension of the approach to the solution of some realistic compressible viscous flows. When flows at high Reynolds number are investigated, is soon becomes apparent that explicit techniwues have to be supplemented if they are to deal effectively with the large variations in element size and aspect ratio which characterize the computational grids necessary for adequate resolutin of the primary flow features. For this reason, the Taylor-Galerkin solution algorithm was rewritten in an explicit/implicit form. Solutions were computed for the problems of a flow past a flat plate, M-3, Re-100; shock/boundary layer interaction, M-2, Re-296000; flow over a compression corner, M-11.68, Re246000; and unifrom flow past a circular cylinder, M-6.34, Re-39770. A summary of the results is included and demonstrates the numerical performance of the scheme.

Source record↗
NASA NTRS1988

Numerical analysis of three-dimensional viscous internal flows

A 3-D Navier-Stokes code has been developed for analysis of turbomachinery blade rows and other internal flows. The Navier-Stokes equations are written in a Cartesian coordinate system rotating about the x-axis, and then mapped to a general body-fitted coordinate system. Streamwise viscous terms are neglected using the thin-layer assumption, and turbulence effects are modeled using the Baldwin-Lomax turbulence model. The equations are discretized using finite differences on stacked C-type grids and are solved using a multistage Runge-Kutta algorithm with a spatially-varying time step and implicit residual smoothing. Calculations have been made of a horseshoe vortex formed in front of a flat plate with a round leading edge standing in a turbulent endwall boundary layer. Comparisons are made with experimental data taken by Eckerle and Langston for a circular cylinder under similar conditions. Computer and measured results are compared in terms of endwall flow visualization pictures and total pressure loss contours and vector plots on the symmetry plane. Calculated details of the primary vortex show excellent agreement with the experimental data. The calculations also show a small secondary vortex not seen experimentally.

Chima, Rodrick V.↗
NASA NTRS1988

Numerical simulation of unsteady incompressible viscous flows in generalized coordinate systems

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

Rosenfeld, Moshe↗
NASA NTRS1987

Ring vortex/cylinder sound production revisited

The acoustic radiation produced by the passage of a vortex ring near a circular cylinder is calculated utilizing the Coriolis acceleration of the vortex as the source term and the low frequency Green's function approach. Necessary integrals are evaluated exactly via complex integration techniques. The results exhibit good agreement (on a Pascal basis) with experimental data. Of particular interest is the rotation of the directivity pattern during this transient encounter and the extreme sensitivity of the results to the distance at which the vortex passes by the cylinder.

Hardin, Jay C.↗
NASA NTRS1987

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

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

Beeler, George B.↗
NASA NTRS1987

Computation of unsteady separation using Lagrangian procedures

The interaction between increased knowledge of unsteady separation processes and computational techniques is examined, emphasizing the use of Lagrangian coordinates. Examples include boundary layer solutions of two-dimensional unsteady flows, and separation from rotating and translating spheres. Advances in Lagrangian techniques for the Navier-Stokes equations are illusrated by means of high resolution random-walk computations of the impulsively started circular cylinder.

Van Dommelen, L. L.↗
NASA NTRS1987

Simulation of separated flow past a bluff body using Navier-Stokes equations

Two-dimensional flow past a bluff body is presently simulated on the basis of an analysis that employs the incompressible, unsteady Navier-Stokes equations in terms of vorticity and stream function. The fully implicit, time-marching, alternating-direction, implicit-block Gaussian elimination used is a direct method with second-order spatial accuracy; this allows it to avoid the introduction of any artificial viscosity. Attention is given to the simulation of flow past a circular cylinder with and without symmetry, requiring the use of either the half or the full cylinder, respectively.

Ghia, K. N.↗
NASA NTRS1988

An upwind differencing scheme for the time-accurate incompressible Navier-Stokes equations

The two-dimensional incompressible Navier-Stokes equations are solved in a time-accurate manner in using the method of pseudocompressibility. Using this method, subiterations in pseudotime are required to satisfy the continuity equation at each time step. An upwind differencing scheme based on flux-difference splitting is used to compute the convective terms. The upwind differencing is biased based on the sign of the local eigenvalue of the Jacobian matrix. Third-order or fifth-order spatial accuracy is maintained throughout the interior grid points. The equations are solved using an implicit line-relaxation scheme. This solution scheme is stable and is capable of running at large time steps in pseudotime, leading to fast convergence for each physical time step. A variety of computed results are presented to validate the present scheme. Results for the flow over an oscillating plate are compared with the exact analytic solution, good agreement is seen. Excellent comparison is obtained between the computed solution and the analytical results for inviscid channel flow with an oscillating back pressure. Flow solutions over a circular cylinder with vortex shedding are also presented. Finally, the flow past an airfoil at -90 deg angle-of-attack is also computed.

Rogers, Stuart E.↗
NASA NTRS1987

Turbulence modeling and surface heat transfer in a stagnation flow region

Analysis for the turbulent flow field and the effect of freestream turbulence on the surface heat transfer rate of a stagnation flow is presented. The emphasis is on modeling and its augmentation of surface heat transfer rate. The flow field considered is the region near the forward stagnation point of a circular cylinder in a uniform turbulent mean flow.

Wang, C. R.↗
NASA NTRS1988

Numerical analysis of three-dimensional viscous internal flows

A 3-D Navier-Stokes code has been developed for analysis of turbomachinery blade rows and other internal flows. The Navier-Stokes equations are written in a Cartesian coordinate system rotating about the x-axis, and then mapped to a general body-fitted coordinate system. Streamwise viscous terms are neglected using the thin-layer assumption, and turbulence effects are modeled using the Baldwin-Lomax turbulence model. The equations are discretized using finite differences on stacked C-type grids and are solved using a multistage Runge-Kutta algorithm with a spatially-varying time step and implicit residual smoothing. Calculations have been made of a horseshoe vortex formed in front of a flat plate with a round leading edge standing in a turbulent endwall boundary layer. Comparisons are made with experimental data taken by Eckerle and Langston for a circular cylinder under similar conditions. Computer and measured results are compared in terms of endwall flow visualization pictures and total pressure loss contours and vector plots on the symmetry plane. Calculated details of the primary vortex show excellent agreement with the experimental data. The calculations also show a small secondary vortex not seen experimentally.

Chima, Rodrick V.↗
NASA NTRS1989

Behavior in normal and reduced gravity of an enclosed liquid/gas system with nonuniform heating from above

The temperature and velocity fields have been investigated for a single-phase gas system and a two-layer gas-and-liquid system enclosed in a circular cylinder being heated suddenly and nonuniformly from above. The transient response of the gas, liquid, and container walls was modelled numerically in normal and reduced gravity (10 to the -5 g). Verification of the model was accomplished via flow visualization experiments in 10 cm high by 10 cm diameter plexiglass cylinders.

Ross, H. D.↗
NASA NTRS1988

Computational studies of an impulsively started viscous flow

Progress in validating incompressible Navier-Stokes codes is described using a predictor/corrector scheme. The flow field under study is the impulsive start of a circular cylinder and the unsteady evolution of the separation bubble. In the current code, a uniform asymptotic expansion is used as an initial condition in order to correctly capture the initial growth of the vortex sheet. Volocity fields at selected instants of time are decomposed into vectorial representations of Navier-Stokes equations which are then used to analyze dominant contributions in the boundary-layer region.

Davis, Sanford S.↗
NASA NTRS1989

Strengths of balloon films with flaws and repairs

The effects of manufacture flaws and repairs in high altitude scientific balloons was examined. A right circular cylinder was used to induce a biaxial tension-tension stress field in the polyethlene film used to manufacture these balloons. A preliminary investigation of the effect that cylinder geometry has on stress rate as a function of inflation rate was conducted. The ultimate goal was to rank, by order of degrading effects, the flaws and repairs commonly found in current high altitude balloons.

Portanova, M. A.↗
NASA NTRS1983

Aerodynamically-driven condensate layer thickness distributions on isothermal cylindrical surfaces

A simple yet rather general mathematical model is presented for predicting the distribution of condensate layer thickness when aerodynamic shear is the dominant mechanism of liquid flow along the surface. The Newtonian condensate film is treated using well-known thin-layer (lubrication theory) approximations, and condensate supply is taken to be the result of either convective diffusion or inertial impaction. Illustrative calculations for a circular cylinder in a crossflow at Re = 100,000 reveal the consequences of alternate condensate arrival mechanisms and the existence of thicker reverse-flow films behind the position of gas boundary-layer separation. The present formulation is readily generalized to include transient liquid layer flows on noncircular objects of variable surface temperature, as encountered in turbine-blade materials testing or operation.

Rosner, D. E.↗
NASA NTRS1988

An application of the WKBJ technique to the on-surface radiation condition

The on-surface radiation-condition method and the WKBJ method for approximating solutions to differential equations are used to derive an analytic formula for the surface currents on a two-dimensional perfectly conducting convex target. The currents are induced by an incident TE-polarized plane wave. The case of a circular cylinder is used to demonstrate the usefulness of the combined methods. It is shown that a two-term expansion yields good results for the surface currents and excellent results for the ensuing bistatic radar cross section.

Moore, Thomas G.↗
NASA NTRS1988

Element-by-element and implicit-explicit finite element formulations for computational fluid dynamics

Preconditioner algorithms to reduce the computational effort in FEM analyses of large-scale fluid-dynamics problems are presented. A general model problem is constructed on the basis of the convection-diffusion equation and the two-dimensional vorticity/stream-function formulation of the Navier-Stokes equations; this problem is then analyzed using element-by-element, implicit-explicit, and adaptive implicit-explicit approximation schemes. Numerical results for the two-dimensional advection and rigid-body rotation of a cosine hill, flow past a circular cylinder, and driven cavity flow are presented in extensive graphs and shown to be in good agreement with those obtained using implicit methods.

Tezduyar, T. E.↗
NASA NTRS1988

Heat transfer in gas turbine engines and three-dimensional flows; Proceedings of the Symposium, ASME Winter Annual Meeting, Chicago, IL, Nov. 27-Dec. 2, 1988

The present conference on heat transfer characteristics of gas turbines and three-dimensional flows discusses velocity-temperature fluctuation correlations at the flow stagnation flow of a circular cylinder in turbulent flow, heat transfer across turbulent boundary layers with pressure gradients, the effect of jet grid turbulence on boundary layer heat transfer, and heat transfer characteristics predictions for discrete-hole film cooling. Also discussed are local heat transfer in internally cooled turbine airfoil leading edges, secondary flows in vane cascades and curved ducts, three-dimensional numerical modeling in gas turbine coal combustor design, numerical and experimental results for tube-fin heat exchanger airflow and heating characteristics, and the computation of external hypersonic three-dimensional flow field and heat transfer characteristics.

Elovic, E.↗
NASA NTRS1989

Flow of rarefied gases over two-dimensional bodies

A kinetic-theory analysis is made of the flow of rarefied gases over two-dimensional bodies of arbitrary curvature. The Boltzmann equation simplified by a model collision integral is written in an arbitrary orthogonal curvilinear coordinate system, and solved by means of finite-difference approximation with the discrete ordinate method. A numerical code is developed which can be applied to any two-dimensional submerged body of arbitrary curvature for the flow regimes from free-molecular to slip at transonic Mach numbers. Predictions are made for the case of a right circular cylinder.

Jeng, Duen-Ren↗