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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Numerical performance estimates for a generic hypersonic forebody

The computation of a hypersonic flow past the forebody of a hypersonic vehicle is analyzed for two sets of flow conditions: the first represents flow conditions of an experimental test of the model in the Calspan 96-inch shock tunnel, and the second set is chosen to represent actual flight conditions. Solutions are derived for sharp- and blunt-nose versions of the geometry in order to understand the effects of the entropy layer on the forebody pressure and heat transfer rates. Some sensitivity of predicted heating rates to grid refinement is observed, but it is found to be small compared to the effects of bluntness. Real-gas effects are studied for the blunt-nose version at flight-like conditions, and these effects are found to have a significant effect on inlet-face performance measures such as mass capture and kinetic energy efficiency.

Lawrence, Scott L.↗
NASA NTRS1992

Advanced ballistic range technology

Experimental interferograms, schlieren, and shadow-graphs are routinely used for validating ideal- and real-gas computational fluid dynamics (CFD) codes. Interferograms are used for quantitative comparisons of integrated density. Schlieren and shadowgraphs are used for comparing the locations of flow field features; the types of flowfield features recorded in these images include shocks, shear layers, and expansion fans. By constructing images from flow field simulations, one-to-one comparisons of computation and experiment are possible. During the period from 1 May 1991 to 31 Jan. 1992, the emphasis of this research was on developing techniques for constructing these images from flow field simulations.

Yates, Leslie A.↗
NASA NTRS1992

Inlet technology

At hypersonic flight Mach numbers, particularly above Mo = 10, the inlet compression process is no longer adiabatic, real gas chemistry takes on extra importance, and the combined effects of entropy layer and viscous effects lead to highly nonuniform flow profile characteristics at the combustor entrance. Under such conditions, traditional inlet efficiency parameters can be unnecessarily cumbersome and/or lacking in the ability to appropriately characterize the inlet flow and to provide insight into propulsion system performance. Recent experience suggests that the use of inlet entropy increases inlet efficiency in hypersonic applications.

Kutschenreuter, Paul↗
NASA NTRS1991

Three-dimensional calculations of supersonic reacting flows using an LU scheme

A 3-D numerical program that incorporates comprehensive real gas property models was developed to simulate supersonic reacting flows. The code employs an implicit, finite volume, Lower-Upper (LU), time-marching method to solve the complete Navier-Stokes and species equations in a fully-coupled and efficient manner. A chemistry model with 9 species and 18 reaction steps is adopted in the program to represent the chemical reactions of H2 and air. To demonstrate the capability of the program, flow fields of underexpanded hydrogen jets transversely injected into the supersonic airstream inside the combustors of scramjets are calculated. Results clearly depict the flow characteristics, including the shock structure, the separated flow regions around the injector, and the distribution of the combustion products.

Yu, Sheng-Tao↗
NASA NTRS1992

CFD goes to school

The part that universities should play in the future development of CFD, which must be evaluated in light of CFD's pacing elements and challenges, is discussed. Attention is given to CFD pacing items that must be in place before routine aerodynamic simulation can be performed including grid generation and geometry surface definition, solution adaptive meshing, more efficient time-accurate simulation, modeling of real-gas effects, multiple relative body motion, and prediction of transition and turbulence modeling. As universities have contributed to research in CFD from its inception, this research should continue to enhance and motivate teaching, improve CFD as a discipline, and stimulate faculty and students.

Steger, Joseph L.↗
NASA NTRS1990

Hypersonic flow simulations using DSMC (direct simulation Monte Carlo)

A review of the DSMC method of Bird is presented. The DSMC method provides the capability of simulating real gas flows in the rarefied flow regime. Recent developments and applications of the method for hypersonic flows are reported for both ground-based tests and during entry. Results obtained using both axisymmetric and 3D codes are included.

Moss, James N.↗
NASA NTRS1992

Effective treatments of the singular line boundary problem for three dimensional grids

The axis singularity problem for 3D blunt body flows is examined. Two techniques of eliminating the axis-singularity difficulty are presented for utilization with finite-difference codes: (1) the 3D Navier-Stokes equations are reformulated utilizing a redefined Jacobian that is nonzero at the singular line, and (2) the 3D Navier-Stokes equations are solved using the Roe flux-difference splitting technique with a finite-volume based method for evaluation of the grid Jacobian and the metrics, and appropriate boundary conditions. Real-gas and viscous computations are also presented, demonstrating the generality of the two methods.

Palmer, Grant↗
NASA NTRS1992

A non-linearly stable implicit finite element algorithm for hypersonic aerodynamics

A generalized curvilinear coordinate Taylor weak statement implicit finite element algorithm is developed for the two-dimensional and axisymmetric compressible Navier-Stokes equations for ideal and reacting gases. For accurate hypersonic simulation, air is modeled as a mixture of five perfect gases, i.e., molecular and atomic oxygen and nitrogen as well as nitric oxide. The associated pressure is then determined via Newton solution of the classical chemical equilibrium equation system. The directional semidiscretization is achieved using an optimal metric data Galerkin finite element weak statement, on a developed 'companion conservation law system', permitting classical test and trial space definitions. Utilizing an implicit Runge-Kutta scheme, the terminal algorithm is then nonlinearly stable, and second-order accurate in space and time on arbitrary curvilinear coordinates. Subsequently, a matrix tensor product factorization procedure permits an efficient numerical linear algebra handling for large Courant numbers. For ideal- and real-gas hypersonic flows, the algorithm generates essentially nonoscillatory numerical solutions in the presence of strong detached shocks and boundary layer-inviscid flow interactions.

Iannelli, G. S.↗
NASA NTRS1992

An improved PNS scheme for predicting complex three-dimensional hypersonic flows

Upwinding is incorporated into a numerical technique for predicting hypersonic viscous flows over lifting configurations at moderate angles of attack. A general real-gas flux-vector-splitting technique based on Van Leer's (1982) approach is employed to model upwinding, and three techniques are examined for flux-vector differencing. The three methods are evaluated by applying them to an axisymmetric configuration with a 10-deg afterbody flare. The results indicate that an oscillation-free shock front can be described by using first-order full upwinding across the embedded shock and central-differencing for the other zones. This combined approach is found to be highly convergent for the near-wall region, and its performance is examined for predicting a Mach 15 flow over a finned missile. Attention is given to the effects of gas chemistry which can significantly affect the flows over the missile configurations.

Bhutta, Bilal A.↗
NASA NTRS1992

Parabolized reduced Navier-Stokes computational techniques

A review is presented of methods in which composite or reduced Navier-Stokes (RNS) equations are treated with a pressure-gradient-based flux-vector splitting. The methods are similar to large Re asymptotic formulations, and streamwise diffusion terms are ignored in favor of an explicit deferred corrector based on higher-order diffusion terms. The methods can be used for 2D and 3D supersonic flows in which the effects of real gas are incorporated. Several examples of the procedure are given, and subsonic and supersonic flows are handled well with relaxation procedures that incorporate multigrid acceleration. Effective solutions are described for problems ranging from incompressible flows and supersonic flows to sharp shocks and reverse-flow capturing.

Rubin, Stanley G.↗
NASA NTRS1992

A three-dimensional upwind PNS code for chemically reacting scramjet flowfields

A new upwind, parabolized Navier-Stokes (PNS) code has been developed to compute the three-dimensional (3D) chemically reacting flow in scramjet (supersonic combustion ramjet) engines. The code is a modification of the 3D upwind PNS (UPS) airflow code which has been extended in the present study to permit internal flow calculations with hydrogen-air chemistry. With these additions, the new code has the capability of computing aerodynamic and propulsive flowfields simultaneously. The algorithm solves the PNS equations using a finite-volume, upwind TVD method based on Roe's approximate Riemann solver that has been modified to account for 'real gas' effects. The fluid medium is assumed to be a chemically reacting mixture of thermally perfect (but calorically imperfect) gases in thermal equilibrium. The new code has been applied to two test cases. These include the Burrows-Kurkov supersonic combustion experiment and a generic 3D scramjet flowfield. The computed results compare favorably with the available experimental data.

Wadawadigi, Ganesh↗
NASA NTRS1991

Enhancements and applications of DSMC for hypersonic rarefied flows

A review of the direct simulation Monte Carlo (DSMC) method of Bird is presented. The DSMC method provides the capability of simulating real gas flows in the rarefied flow regime. Recent developments and applications of the method for hypersonic flows are reported for both ground-based tests and during entry. The flows considered were three-dimensional, and both an existing general code and a new code under development were used.

Moss, James N.↗
NASA NTRS1992

A time-accurate algorithm for chemical non-equilibrium viscous flows at all speeds

A time-accurate, coupled solution procedure is described for the chemical nonequilibrium Navier-Stokes equations over a wide range of Mach numbers. This method employs the strong conservation form of the governing equations, but uses primitive variables as unknowns. Real gas properties and equilibrium chemistry are considered. Numerical tests include steady convergent-divergent nozzle flows with air dissociation/recombination chemistry, dump combustor flows with n-pentane-air chemistry, nonreacting flow in a model double annular combustor, and nonreacting unsteady driven cavity flows. Numerical results for both the steady and unsteady flows demonstrate the efficiency and robustness of the present algorithm for Mach numbers ranging from the incompressible limit to supersonic speeds.

Shuen, J.-S.↗
NASA NTRS1992

Images constructed from computed flowfields

A method for constructing interferograms, schlieren, and shadowgraphs from ideal- and real-gas, two- and three-dimensional computed flowfileds is described. The computational grids can be structured or unstructured, and multiple grids are an option. The constructed images are compared to experimental images for several types of flow, including a ramp, a blunt-body, a nozzle, and a reacting flow. The constructed images simulate the features observed in the experimental images. They are sensitive to errors in the flowfield solutions and can be used to identify solution errors. In addition, techniques for obtaining phase shifts from experimental finite-fringe interferograms and for removing experimentally induced phase-shift errors are discussed. Both the constructed images and calculated phase shifts can be used for validation of computational fluid dynamics (CFD) codes.

Yates, Leslie A.↗
NASA NTRS1987

The validation of numerical computations

Information is given in viewgraph form on the validation of computational fluid dynamics codes. Topics covered include the types of validation required, aerodynamic heating to a slender 5 degree cone, heat transfer on cones with isentropic compression surfaces, the validation of turbulence data, modeling of thermodynamic and transport properties, real gas code validation, the Flight Dynamics Laboratory validation efforts, and reacting gas experimental data in low density flow.

Buck, Melvin L.↗
NASA NTRS1992

Visualization of hydrogen injection in a scramjet engine by simultaneous PLIF imaging and laser holographic imaging

Flowfield characterization has been accomplished for several fuel injector configurations using simultaneous planar laser induced fluorescence (PLIF) and laser holographic imaging (LHI). The experiments were carried out in the GASL-NASA HYPULSE real gas expansion tube facility, a pulsed facility with steady test times of about 350 microsec. The tests were done at simulated Mach numbers 13.5 and 17. The focus of this paper is on the measurement technologies used and their application in a research facility. The HYPULSE facility, the models used for the experiments, and the setup for the LHI and PLIF measurements are described. Measurement challenges and solutions are discussed. Results are presented for experiments with several fuel injector configurations and several equivalence ratios.

Anderson, Robert C.↗
NASA NTRS1992

Parabolized Navier-Stokes methods for hypersonic flows

The development and numerical solution of the Parabolized Navier-Stokes (PNS) equations is discussed. Special emphasis is placed on numerical integration algorithms for PNS solvers, most notably recent applications of upwind schemes. Application of this technology to high speed, high Reynolds number flows was the focus, and modeling techniques for real gas effects and turbulence were discussed. Experiences in validating the UPS upwind PNS flow solver for relatively simple body shapes are presented. The test cases range in complexity from two dimensional perfect gas cases to three dimensional finite rate chemistry cases.

Lawrence, S. L.↗
NASA NTRS1992

Issues and approach to develop validated analysis tools for hypersonic flows: One perspective

Critical issues concerning the modeling of low-density hypervelocity flows where thermochemical nonequilibrium effects are pronounced are discussed. Emphasis is on the development of validated analysis tools. A description of the activity in the Ames Research Center's Aerothermodynamics Branch is also given. Inherent in the process is a strong synergism between ground test and real-gas computational fluid dynamics (CFD). Approaches to develop and/or enhance phenomenological models and incorporate them into computational flow-field simulation codes are discussed. These models have been partially validated with experimental data for flows where the gas temperature is raised (compressive flows). Expanding flows, where temperatures drop, however, exhibit somewhat different behavior. Experimental data for these expanding flow conditions are sparse; reliance must be made on intuition and guidance from computational chemistry to model transport processes under these conditions. Ground-based experimental studies used to provide necessary data for model development and validation are described. Included are the performance characteristics of high-enthalpy flow facilities, such as shock tubes and ballistic ranges.

Deiwert, George S.↗