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Steger, J. L.

Publications and source records attributed to Steger, J. L..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Computed Flow About The Integrated Space Shuttle, Revisited

Report discusses numerical simulations of flow of air about integrated space shuttle (complete space shuttle assembly including orbiter, solid rocket boosters, and external tank) in ascent. Updated version of report described in "Computed Flow About The Integrated Space Shuttle" (ARC-12685). Goal of studies to improve understanding of, and ability to predict how integrated space shuttle performs during both nominal and aborted ascent under various conditions.

Buning, P. G.↗
NASA NTRS1992

Dual-Potential Formulation Of Navier-Stokes Equations

Report discusses research on dual-potential formulation of Navier-Stokes equations. Purpose of study to extend capability of dual-potential method to computation of unsteady flows of viscous, compressible fluids.

Gegg, S. G.↗
NASA NTRS1991

Computed Flow About The Integrated Space Shuttle

Report discusses numerical simulations of flow of air about integrated Space Shuttle in ascent. Goal: to improve understanding of, and ability to predict, how integrated Space Shuttle will perform during both nominal and aborted ascent under various conditions. These and other numerical simulations intended both to supplement wind-tunnel data, corrupted to some extent by scaling and wall-interference effects, and to compensate for scarcity of valid flight data.

Buning, P. G.↗
NASA NTRS1991

Calculating Viscous/Inviscid Interactions

Report describes some experiences in numerical simulation of compressible, viscous flows by finite-difference approximations of Navier-Stokes equations. Focuses upon viscous/inviscid-interaction approach, in which flow mathematically modeled with interacting zones, within each of which different model of viscous or inviscid flow applies. Reduces task of computation by taking advantage of simpler models and coarser grids in some of zones.

Van Dalsem, W. R.↗
NASA NTRS1990

On computations of the integrated space shuttle flowfield using overset grids

Numerical simulations using the thin-layer Navier-Stokes equations and chimera (overset) grid approach were carried out for flows around the integrated space shuttle vehicle over a range of Mach numbers. Body-conforming grids were used for all the component grids. Testcases include a three-component overset grid - the external tank (ET), the solid rocket booster (SRB) and the orbiter (ORB), and a five-component overset grid - the ET, SRB, ORB, forward and aft attach hardware, configurations. The results were compared with the wind tunnel and flight data. In addition, a Poisson solution procedure (a special case of the vorticity-velocity formulation) using primitive variables was developed to solve three-dimensional, irrotational, inviscid flows for single as well as overset grids. The solutions were validated by comparisons with other analytical or numerical solution, and/or experimental results for various geometries. The Poisson solution was also used as an initial guess for the thin-layer Navier-Stokes solution procedure to improve the efficiency of the numerical flow simulations. It was found that this approach resulted in roughly a 30 percent CPU time savings as compared with the procedure solving the thin-layer Navier-Stokes equations from a uniform free stream flowfield.

Chiu, I-T.↗
NASA NTRS1989

A dual potential formulation of the Navier-Stokes equations

A dual potential formulation for numerically solving the Navier-Stokes equations is developed and presented. The velocity field is decomposed using a scalar and vector potential. Vorticity and dilatation are used as the dependent variables in the momentum equations. Test cases in two dimensions verify the capability to solve flows using approximations from potential flow to full Navier-Stokes simulations. A three-dimensional incompressible flow formulation is also described. An interesting feature of this approach to solving the Navier-Stokes equations is the decomposition of the velocity field into a rotational part (vector potential) and an irrotational part (scalar potential). The Helmholtz decomposition theorem allows this splitting of the velocity field. This approach has had only limited use since it increases the number of dependent variables in the solution. However, it has often been used for incompressible flows where the solution scheme is known to be fast and accurate. This research extends the usage of this method to fully compressible Navier-Stokes simulations by using the dilatation variable along with vorticity. A time-accurate, iterative algorithm is used for the uncoupled solution of the governing equations. Several levels of flow approximation are available within the framework of this method. Potential flow, Euler and full Navier-Stokes solutions are possible using the dual potential formulation. Solution efficiency can be enhanced in a straightforward way. For some flows, the vorticity and/or dilatation may be negligible in certain regions (e.g., far from a viscous boundary in an external flow). It is possible to drop the calculation of these variables then and optimize the solution speed. Also, efficient Poisson solvers are available for the potentials. The relative merits of non-primitive variables versus primitive variables for solution of the Navier-Stokes equations are also discussed.

Gegg, S. G.↗
NASA NTRS1988

A thin-layer solution of the flow about a prolate spheroid

Computational results are presented for the transitional or turbulent flow about a prolate spheroid, at alpha = 10 deg or 30 deg, correspondingly, using an implicit, approximately factored, partially flux-split algorithm, based on the thin-layer equations. The computed flow field is in good agreement with available experimental data.

Panaras, A. G.↗
NASA NTRS1988

Numerical investigation of a jet in ground effect with a crossflow

One of the flows inherent in V/STOL operations, the jet in ground effect with a crossflow, is studied using the Fortified Navier-Stokes (FNS) scheme. Through comparison of the simulation results and the experimental data, and through the variation of the flow parameters (in the simulation) a number of interesting characteristics of the flow have been observed. For example, it appears that the forward penetration of the ground vortex is a strong inverse function of the level of mixing in the ground vortex. An effort has also been made to isolate issues which require additional work in order to improve the numerical simulation of the jet in ground effect flow. The FNS approach simplifies the simulation of a single jet in ground effect, but will be even more effective in applications to more complex topologies.

Van Dalsem, W. R.↗
NASA NTRS1988

Numerical simulation of the integrated space shuttle vehicle in ascent

A simulation of the flow about the integrated space shuttle vehicle in ascent mode has been undertaken for various flight conditions using the Chimera composite grid discretization approach. Overset body-conforming grids were used to represent each geometric component, and an implicit approximately factored finite-difference procedure was used to solve the three-dimensional thin-layer Navier-Stokes equations. The computational results have been compared with both wind tunnel and flight test data. Although relatively good agreement is obtained with the experimental data, further refinement and evaluation of numerical error is under way.

Buning, P. G.↗
NASA NTRS1987

Some experiences with the viscous-inviscid interaction approach

Methods for simulating compressible viscous flow using the viscid-inviscid interaction approach are described. The formulations presented range from the more familiar full-potential/boundary-layer interaction schemes to a method for coupling Euler/Navier-Stokes and boundary-layer algorithms. An effort is made to describe the advantages and disadvantages of each formulation. Sample results are presented which illustrate the applicability of the methods.

Vandalsem, W. R.↗
NASA NTRS1987

A three-dimensional dual potential procedure with applications to wind tunnel inlets and interacting boundary layers

A dual potential decomposition of the velocity field into a scalar and a vector potential function is extended to three dimensions and used in the finite-difference simulation of steady three-dimensional inviscid rotational flows and viscous flow. The finite-difference procedure was used to simulate the flow through the 80 by 120 ft wind tunnel at NASA Ames Research Center. Rotational flow produced by the stagnation pressure drop across vanes and screens which are located at the entrance of the inlet is modeled using actuator disk theory. Results are presented for two different inlet vane and screen configurations. The numerical predictions are in good agreement with experimental data. The dual potential procedure was also applied to calculate the viscous flow along two and three dimensional troughs. Viscous effects are simulated by injecting vorticity which is computed from a boundary layer algorithm. For attached flow over a three dimensional trough, the present calculations are in good agreement with other numerical predictions. For separated flow, it is shown from a two dimensional analysis that the boundary layer approximation provides an accurate measure of the vorticity in regions close to the wall; whereas further away from the wall, caution has to be exercised in using the boundary-layer equations to supply vorticity to the dual potential formulation.

Rao, K. V.↗
NASA NTRS1986

Multiple Grids in Finite-Difference Flow Analysis

Multiple solutions superimposed to resolve flows about complex configurations. Use of multiple, overset grids in computational fluid dynamics extends application of finite-difference methods to more complex configurations. Rather than trying to generate single mesh about all components of configuration, multiple, individual meshes used, then overset on major grid. Major grid used to resolve flow field or wrapped around main component.

Dougherty, F. C.↗
NASA NTRS1986

Perturbation Method for Computational Fluid-Dynamical Equations

Perturbation technique yields accurate flow solutions using as few as one-fourth number of grid points required by finite-difference methods. Technique originally developed to solve Euler equations of two-dimensional, steady, inviscid transonic flow about airfoils, applicable to arbitrary equation sets and higher dimensions. New perturbations scheme used in design cycle where potential solutions generated routinely; Euler perturbation method used in second-cut analysis. Method also used to couple other equation sets.

Chow, L. J.↗
NASA NTRS1986

Numerical simulation of unsteady, viscous, high-angle-of-attack flows using a partially flux-split algorithm

Viscous separated flow surrounding a hemisphere-cylinder body at angles of attack ranging up to 19 deg in transonic flow has been computed using an implicit, approximately-factored, partially flux-split algorithm. The resulting flowfield structures, including the vortical flow on the leeward side of the body and the three-dimensional separation patterns, have been investigated. The computed results show good qualitative and quantitative agreement with experimental data. Furthermore, visualization of the flowfield patterns has yielded insight into the behavior of the three-dimensional separated flow.

Ying, S. X.↗
NASA NTRS1985

On applications of chimera grid schemes to store separation

A finite difference scheme which uses multiple overset meshes to simulate the aerodynamics of aircraft/store interaction and store separation is described. In this chimera, or multiple mesh, scheme, a complex configuration is mapped using a major grid about the main component of the configuration, and minor overset meshes are used to map each additional component such as a store. As a first step in modeling the aerodynamics of store separation, two dimensional inviscid flow calculations were carried out in which one of the minor meshes is allowed to move with respect to the major grid. Solutions of calibrated two dimensional problems indicate that allowing one mesh to move with respect to another does not adversely affect the time accuracy of an unsteady solution. Steady, inviscid three dimensional computations demonstrate the capability to simulate complex configurations, including closely packed multiple bodies.

Cougherty, F. C.↗
NASA NTRS1985

The efficient simulation of separated three-dimensional viscous flows using the boundary-layer equations

A simple and computationally efficient algorithm for solving the unsteady three-dimensional boundary-layer equations in the time-accurate or relaxation mode is presented. Results of the new algorithm are shown to be in quantitative agreement with detailed experimental data for flow over a swept infinite wing. The separated flow over a 6:1 ellipsoid at angle of attack, and the transonic flow over a finite-wing with shock-induced 'mushroom' separation are also computed and compared with available experimental data. It is concluded that complex, separated, three-dimensional viscous layers can be economically and routinely computed using a time-relaxation boundary-layer algorithm.

Van Dalsem, W. R.↗
NASA NTRS1985

Use of a hyperbolic grid generation scheme in simulating supersonic viscous flow about three-dimensional winged configuration

The present paper describes a numerical mesh generation technique to be used with an implicit finite difference method for simulating visous supersonic flow about low-aspect-ratio wing body configurations using a single grid strategy. The computational domain is segmented into multiple regions, with borders located in supersonic areas to avoid the otherwise costly interfacing procedure between adjacent segments. The numerical procedure is applied to calculate the turbulent flow around the shuttle orbiter and a canard projectile at supersonic free stream Mach number.

Rizk, Y. M.↗