Thomas A. Edwards

Application of computational fluid dynamics to sonic boom near- and mid-field prediction

A technique combining a quasilinear extrapolation theory and a three-dimensional parabolized Navier-Stokes (PNS) code has been used to calculate the supersonic overpressure from three different geometries at near- and mid-fields. Wind-tunnel data is used for code validation. Comparison of the computed results with different grid refinements, and different extrapolation distances, are shown in this article. It is observed that a large number of grid points is needed to resolve the tail shock/expansion fan interaction. Therefore, an adaptive grid approach is employed to calculate the flowfield. The effects of a thin, attached boundary layer and the sting of the wind-tunnel model to the sonic boom have also been studied in this article. The agreement between the results and the wind-tunnel data confirms that this technique can be applied to the problem of sonic-boom prediction.

Application of CFD to sonic boom near and mid flow-field prediction

A three-dimensional parabolized Navier-Stokes (PNS) code has been used to calculate the supersonic overpressures from three different geometries at near- and mid-flow fields. Wind-tunnel data is used for code validation. Comparison of the computed results with different grid refinements is shown in this paper. It is observed that a large number of grid points is needed to resolve the tail shock/expansion fan interaction. Therefore, an adaptive grid approach is employed to calculate the flow field. The agreement between the numerical results and the wind-tunnel data confirms that computational fluid dynamics can be applied to the problem of sonic boom prediction.

Computation of hypersonic flows with finite catalytic walls

A computational study has been performed to explore the effects of finite catalytic walls on hypersonic flows. Boundary conditions for noncatalytic, fully catalytic, and finite catalytic walls have been incorporated into an upwind parabolized Navier-Stokes code. Nonequilibrium laminar airflows over sharp cones at 0 and 10 deg angle of attack were computed and the results are compared with previous results wherever possible. A study of finite catalytic cases was performed using varying recombination rates. Full ranges of catalycities were explored in the context of the surface energy balance as well as a constant wall temperature assumption. Detailed effects on specie concentrations, temperature, and heat transfer are presented.

Computational Fluid Dynamics Nose-to-Tail Capability: Hypersonic Unsteady Navier-Stokes Code Validation

Computational fluid dynamics (CFD) research for hypersonic flows presents new problems in code validation because of the added complexity of the physical models. This paper surveys code validation procedures applicable to hypersonic flow models that include real-gas effects. The current status of hypersonic CFD flow analysis is assessed with the compressible Navier-Stokes code as a case study. The methods of code validation discussed go beyond comparison with experimental data to include comparisons with other codes and formulations, component analyses, and estimation of numerical errors. Current results indicate that predicting hypersonic flows of perfect gases and equilibrium air are well in hand. Pressure, shock location, and integrated quantities are relatively easy to predict accurately, whereas surface quantities such as heat transfer are more sensitive to the solution procedure. Modeling transition to turbulence needs refinement, although preliminary results are promising.

Parabolized Navier--Stokes code for hypersonic flows in thermo-chemical equilibrium or nonequilibrium

Abstract A parabolized Navier–Stokes (PNS) code has been developed to efficiently compute three-dimensional flows in thermo-chemical equilibrium or nonequilibrium. The new code is an extension of NASA’s three-dimensional upwind PNS (UPS) code. The chemical, vibrational, and electronic nonequilibrium effects have been incorporated via a loosely-coupled approach. The new code has been used to compute air flows in thermo-chemical equilibrium and nonequilibrium through expanding hypersonic nozzles. The results are in good agreement with existing numerical and experimental results.

Effect of exhaust plume/afterbody interaction on installed scramjet performance

Newly emerging aerospace technology points to the feasibility of sustained hypersonic flight. Designing a propulsion system capable of generating the necessary thrust is now the major obstacle. First-generation vehicles will be driven by air-breathing scramjet (supersonic combustion ramjet) engines. Because of engine size limitations, the exhaust gas leaving the nozzle will be highly underexpanded. Consequently, a significant amount of thrust and lift can be extracted by allowing the exhaust gases to expand along the underbody of the vehicle. Predicting how these forces influence overall vehicle thrust, lift, and moment is essential to a successful design. This work represents an important first step toward that objective. The UWIN code, an upwind, implicit Navier-Stokes computer program, has been applied to hypersonic exhaust plume/afterbody flow fields. The capability to solve entire vehicle geometries at hypersonic speeds, including an interacting exhaust plume, has been demonstrated for the first time. Comparison of the numerical results with available experimental data shows good agreement in all cases investigated. For moderately underexpanded jets, afterbody forces were found to vary linearly with the nozzle exit pressure, and increasing the exit pressure produced additional nose-down pitching moment. Coupling a species continuity equation to the UWIN code enabled calculations indicating that exhaust gases with low isentropic exponents (gamma) contribute larger afterbody forces than high-gamma exhaust gases. Moderately underexpanded jets, which remain attached to unswept afterbodies, underwent streamwise separation on upswept afterbodies. Highly underexpanded jets produced altogether different flow patterns, however. The highly underexpanded jet creates a strong plume shock, and the interaction of this shock with the afterbody was found to produce complicated patterns of crossflow separation. Finally, the effect of thrust vectoring on vehicle balance has been shown to alter dramatically the vehicle pitching moment.

Toward a CFD nose-to-tail capability - Hypersonic unsteady Navier-Stokes code validation

Computational fluid dynamics (CFD) research for hypersonic flows presents new problems in code validation because of the added complexity of the physical models. This paper surveys code validation procedures applicable to hypersonic flow models that include real gas effects. The current status of hypersonic CFD flow analysis is assessed with the Compressible Navier-Stokes (CNS) code as a case study. The methods of code validation discussed to beyond comparison with experimental data to include comparisons with other codes and formulations, component analyses, and estimation of numerical errors. Current results indicate that predicting hypersonic flows of perfect gases and equilibrium air are well in hand. Pressure, shock location, and integrated quantities are relatively easy to predict accurately, while surface quantities such as heat transfer are more sensitive to the solution procedure. Modeling transition to turbulence needs refinement, though preliminary results are promising.