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NASA NTRS1989

Numerical models of two complex hypersonic flowfields

Numerical solutions of the compressible Navier-Stokes equations assuming a perfect gas and laminar flow are applied to two hypersonic experiments conducted at NASA Langley Research Center. The first is cooling by injection of a gas jet through the nose of an ogive-cone, and the second is the aerothermal environment in the gap formed by the wing and elevon section of a test model of the Space Shuttle. The simulations demonstrate that the model predicts accurate pressures and shock stand-off for the gas jet and accurate pressures for the wing-elevon cove. Experimental heating rates for the gas jet indicate turbulent mixing to be occurring, an effect not modeled in the numerical solution.

Macaraeg, M. G.↗

NASA NTRS1988

A decade of computer simulations for Space Shuttle aerodynamics

Ten years ago computer simulations of the flow field around the Space Shuttle Orbiter were limited to inviscid calculations for the windward side of the forebody and viscous calculations for selected 2-D problems. Advances in computer hardware and numerical methods during the past ten years made it possible to calculate viscous flow over the complete orbiter configuration at angle of attack. The equations solved are the Reynolds-averaged, Navier-Stokes equation, simplified by either the thin-layer or parabolized approximation. An algebraic eddy viscosity model is used for turbulent flow. The free stream is assumed to be a perfect gas for wind tunnel conditions and a real gas in thermodynamic equilibrium for flight conditions. Four examples of recent computer simulations are presented. Flow field results include oil flow patterns on the surface and Mach number contours, isobars, and cross-flow velocity vectors in the shock layer.

Inouye, Mamoru↗

NASA NTRS1989

A code calibration program in support of the Aeroassist Flight Experiment

The code calibration program for the Langley Aerothermodynamic Upwind Relaxation Algorithm to be used as support for the Aeroassist Flight Experiment (AFE) is discussed. Comparisons between experimental data and numerical simulations are made which focus on perfect-gas tests involving a scale model of the AFE. Aspects of the thermochemical nonequilibrium model are called into question by the results of ground tests performed in a ballistic range and in a shock tunnel.

Gnoffo, Peter A.↗

NASA NTRS1989

Algebraic turbulence models for the computation of two-dimensional high-speed flows using unstructured grids

The incorporation of algebraic turbulence models in a solver for the 2-D compressible Navier-Stokes equations using triangular grids is described. A practial way to use the Cebeci Smith model, and to modify it in separated regions is proposed. The ability of the model to predict high speed, perfect gas boundary layers is investigated from a numerical point of view.

Rostand, Philippe↗

NASA NTRS1989

Analysis of rotary engine combustion processes based on unsteady, three-dimensional computations

A new computer code was developed for predicting the turbulent, and chemically reacting flows with sprays occurring inside of a stratified charge rotary engine. The solution procedure is based on an Eulerian Lagrangian approach where the unsteady, 3-D Navier-Stokes equations for a perfect gas mixture with variable properties are solved in generalized, Eulerian coordinates on a moving grid by making use of an implicit finite volume, Steger-Warming flux vector splitting scheme, and the liquid phase equations are solved in Lagrangian coordinates. Both the details of the numerical algorithm and the finite difference predictions of the combustor flow field during the opening of exhaust and/or intake, and also during fuel vaporization and combustion, are presented.

Raju, M. S.↗

NASA NTRS1989

Euler and Navier-Stokes solutions for hypersonic flows

An upwind finite-element technique that uses cell-centered quantities and implicit and/or explicit time marching has been developed for computing hypersonic laminar viscous flows using adaptive unstructured grids in two and three dimensions. A perfect gas model as well as an equilibrium air model is implemented for solving high-speed flows. A first-order basic scheme and a higher-order flux-corrected transport (FCT) scheme have been implemented. This technique has been used to predict 'Type III and IV' shock interactions on a cylinder in two dimensions and a swept cylinder in three dimensions, with a view to determine the pressure and heating rate augmentation caused by an impinging shock on the leading edge of a cowl lip of an engine inlet. The predictions of wall pressure and heating rates compare very well with experimental data. The flow features are very distinctly captured with a sequence of adaptively-generated grids. Three-dimensional corner flow, typically encountered in engine inlets due to compression of the flow by ramps in the walls, is also modeled. This procedure is the first step in developing an integrated fluid, thermal, structural analysis capability for hypersonic flight vehicles like the National Aero-Space Plane.

Thareja, Rajiv R.↗

NASA NTRS1990

Analysis of rotary engine combustion processes based on unsteady, three-dimensional computations

A new computer code was developed for predicting the turbulent and chemically reacting flows with sprays occurring inside of a stratified charge rotary engine. The solution procedure is based on an Eulerian Lagrangian approach where the unsteady, three-dimensional Navier-Stokes equations for a perfect gas mixture with variable properties are solved in generalized, Eulerian coordinates on a moving grid by making use of an implicit finite volume, Steger-Warming flux vector splitting scheme, and the liquid phase equations are solved in Lagrangian coordinates. Both the details of the numerical algorithm and the finite difference predictions of the combustor flow field during the opening of exhaust and/or intake, and also during fuel vaporization and combustion, are presented.

Raju, M. S.↗

NASA NTRS1990

Application of the LAURA code for slender-vehicle aerothermodynamics

Application of a three-dimensional thin-layer Navier-Stokes code (LAURA) to compute the laminar, perfect gas aerothermodynamics of slender vehicles is demonstrated. Comparison of solutions with experimental data enabled an assessment of the code's aerodynamic heating prediction capabilities. The results show radial grid refinement to a wall cell Reynolds number of 2 to be accurate for predicting aerodynamic heating to a slender cone. Additional comparisons for an 80 deg slab-delta wing and a generic Aero-Space Plane vehicle show the method to be generally accurate using this radial cell spacing. Discrepancies between the predicted and measured heating in a region of crossflow separation on the Aero-Space Plane geometry are noted which indicates the need for further study. While additional applications and comparisons are required to fully test the LAURA program, the results of this study demonstrate the current level of confidence and the engineering utility of this particular code.

Thompson, Richard A.↗

NASA NTRS1990

Modification of the PARC Navier-Stokes Code to predict rocket engine nozzle performance

The PARC2D Navier-Stokes Code was modified to compute the performance parameters for rocket engine nozzles. The perfect gas code was applied to the SSME engine nozzle for inviscid, laminar and turbulent flow. Inviscid computations compare well with Rocketdyne computations. Performance degradation due to the boundary layers is very reasonable. Application of the code to nontraditional nozzle geometries and to low Reynolds nozzles is demonstrated. Modification of the code for equilibrium H2/O2 chemistry is described. Thermodynamic and equilibrium constants are determined from statistical mechanics and the transport properties from exact kinetic theory, using collison integrals determined from appropriate intermolecular potentials. The equilibrium code was used to compute the SSME flowfield. Modifications of the flowfield due to the change of composition are described.

Collins, Frank G.↗

NASA NTRS1989

Numerical simulation of flow through the Langley parametric scramjet engine

The numerical simulation of a three-dimensional turbulent, reacting flow through the entire Langley parametric scramjet engine has been obtained using a piecewise elliptic approach. The last section in the combustor has been analyzed using a parabolized Navier-Stokes code. The facility nozzle flow was analyzed as a first step. The outflow conditions from the nozzle were chosen as the inflow conditions of the scramjet inlet. The nozzle and the inlet simulation were accomplished by solving the three-dimensional Navier-Stokes equations with a perfect gas assumption. The inlet solution downstream of the scramjet throat was used to provide inflow conditions for the combustor region. The first two regions of the combustor were analyzed using the MacCormack's explicit scheme. However, the source terms in the species equations were solved implicitly. The finite rate chemistry was modeled using the two-step reaction model of Rogers and Chinitz. A complete reaction model was used in the PNS code to solve the last combustor region. The numerical solutions provide an insight of the flow details in a complete hydrogen-fueled scramjet engine module.

Srinivasan, Shivakumar↗

NASA NTRS1990

An upwind approach to unsteady flowfield simulation

A numerical method to determine unsteady solutions of the laminar, perfect gas Navier-Stokes equations has been developed. The structured finite-volume, approximately factored implicit scheme uses Newton subiterations to obtain the spatially and temporally second-order accurate time history of the interaction of blast-waves with stationary targets. The inviscid flux is evaluated using either of two upwind techniques, while the viscous terms are computed by central differencing. Comparisons of numerical, analytical, and experimental results are made in two and three dimensions. The results show accurate wave speed resolution and nonoscillatory discontinuity capturing.

Atwood, Christopher A.↗

NASA NTRS1989

Review of a code development and calibration program in support of the aeroassist flight experiment

The code development and calibration program for the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) is reviewed, with emphasis directed toward support of the Aeroassist Flight Experiment (AFE). The flight project is designed to obtain data which will be used in the validation of computational fluid dynamic approximation methods. Comparisons between experimental data and numerical simulation focus on perfect-gas tests over a scale model of the AFE and on flight and ground tests which challenge some aspect of the thermochemical nonequilibrium model. In the first case, the gas model is simple, but the grid-related problems of defining the real vehicle are present. In the second case, the vehicle geometries are simple, but thermochemical processes must be modeled correctly in order to compare with the experimental data. These comparisons are described as calibration runs because they test elements of the numerical simulation, but no single data set adequately simulates the full-scale AFE flight conditions. Comparisons between computation and experiment over a broad range of data sets show generally good agreement, though some aspects of the numerical model require further development.

Gnoffo, Peter A.↗

NASA NTRS1990

Stability theory for chemically reacting flows

Linear stability theory for chemically reacting (equilibrium and nonequilibrium) flows is applied to study the stability of hypersonic boundary layers under the equilibrium assumption. The results for Mach 15 flow indicate that the second mode instability shifts to lower frequencies, as compared to the perfect gas results. The peak second mode growth rate is also increased for the equilibrium gas model. However, the results for Goertler instability show very little real gas effect. The present theory has been applied to a sphere-cone flight transition experiment performed at freestream Mach of about 20.

Malik, Mujeeb R.↗

NASA NTRS1991

Viscous equilibrium computations using program LAURA

The Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) has been modified to compute viscous equilibrium flow. Periodic calls to the thermodynamic and transport property curve-fits enable solutions to be computed for small percentage increase in computer time when compared with perfect gas times. The code is used to compute the hypersonic flow over slender and blunt cones, and solutions are compared with other computational techniques and flight data.

Greene, Francis A.↗

NASA NTRS1991

Comparison of hypersonic experiments and PNS predictions. I - Aerothermodynamics. II - Aerodynamics

A 3D parabolized Navier-Stokes (PNS) technique is examined in terms of applications to equilibrium-air and perfect-gas hypersonic flows at different Mach numbers and angles of attack. The method renders sublayer approximation unnecessary, and treats axis-normal coupling effects first followed by a shock solution and a corrector step. Predictions of hypersonic flowfields over several blunt conical configurations are found to agree with established wind-tunnel and flight data, although those for the Dhawan-Narasimha (1958) transition model vary from the experimental data. The PNS technique is also applied to predictions of wall-pressure distributions and force and moment data, and the results agree with experimental values. The PNS method allows the calculation of a wide variety of configurations with only a slight increase over traditional computing times.

Bhutta, Bilal A.↗

NASA NTRS1991

Fluid dynamics of multiphase flow in volcanic environments on the Earth, Io, and other planets

Data was compiled on H2O, CO2, S, and SO2 and it was analyzed by various techniques to prepare phase diagrams relevant to conditions on the Earth, Io, Mars, and other planets. The use of Cray models for volcanic eruptions was examined. Attempts are being made to develop equations of state of the compounds listed above to be compatible with the Cray code so that they can be called as subroutines for the volcanic models. This is a major project, as the current code uses only the equation of state for a perfect gas, and requires that the atmosphere be the same composition as the volcanic gas. The analysis of the thermodynamic data is time consuming, and was complicated by changes from a VAX/VMS system to Macintosh's, Crays using CTSS, Crays using Unicos, and Sun workstations.

Kieffer, Susan Werner↗

NASA NTRS1990

A three-dimensional, compressible, laminar boundary-layer method for general fuselages. Volume 2: User's manual

This user's manual contains a complete description of the computer programs developed to calculate three-dimensional, compressible, laminar boundary layers for perfect gas flow on general fuselage shapes. These programs include the 3-D boundary layer program (3DBLC), the body-oriented coordinate program (BCC), and the streamline coordinate program (SCC). Subroutine description, input, output and sample case are discussed. The complete FORTRAN listings of the computer programs are given.

Wie, Yong-Sun↗

NASA NTRS1992

An Engineering Method for Interactive Inviscid-Boundary Layers in Three-Dimensional Hypersonic Flows

An engineering method has been developed that couples an approximate three dimensional inviscid technique with the axisymmetric analog and a set of approximate convective heating equations. The displacement effect on the boundary layer on the outer inviscid flow is calculated and included as a boundary condition in the inviscid technique. This accounts for the viscous interaction present at lower Reynolds numbers. The method is applied to blunted axisymmetric and three dimensional elliptic cones at angle of attack for the laminar hypersonic flow of a perfect gas. The method is applied to turbulent and equilibrium-air conditions. The present technique predicts surface heating rates, pressures, and shock shapes that compare favorably with experimental (ground-test and flight) data and numerical solutions of the Navier-Stokes and viscous shock-layer equations. In addition, the inclusion of viscous interaction significantly improves results obtained at lower Reynolds numbers. The new technique represents a major improvement over current engineering aerothermal methods with only a modest increase in computational effort.

Riley, Christopher J.↗