Computation of hypersonic flow past blunt body for nonequilibrium weakly ionized air

Abstract

A computational study has been performed on hypersonic flow past blunt bodies at zero incidence for flows that are in chemical and thermal nonequlibrium and are weakly ionized. The Mach number range considered was from 16 to 35 with altitudes up to 71 km and with nose radii of 0.OOGG m, 0.0762 m, and 0.1524 m. The high tcmperature air was assumed to decompose into the following species: N z , N, 0 2 , 0, NO, NO+, and e . The Navier-Stokes equations with the necessary modifications were solved using the Roe flux-difference split scheme. The presence of an additional eigenvalue due to the electron translational temperature was implemented in the f l ~ ~ splitting procedure and was studied with reference to the physics of the flow. The inclusion of the additional eigenvalue resulted in a 13 percent higher predicted electron pressure on the body surface for the RAM-C I1 flight test case at Alt. = 61 km. Also, due to the additional eigenvalue, the electron temperature across the shock was better captured with fewer points along a shorter distance. For the smallest n a e radius considered, the numerical code gave excellent agreement between predicted stagnation point heat transfer and experiment. The comparison of the predicted and experimental electron densities along the stagnation streamline and on the body surface is reasonable. The multi-temperatures of the ions and electrons are compared to the temperature, obtained from the Saha equation for equilibrium. The temperature deviation due to the thermal nonequlibrium was confirmed by the comparison for the larger radii bodies. Nomenclature speed of sound mass fraction of species concentration, pi f p specific heat at constant volume Diffusion coefficient electron energy per unit mass vibrational energy per unit mass for species i vibrational energy per unit mass, based on translational temperature electric field specific internal energy, J C, dT + h; electron charge, internal energ)., r i+ (u2+v2) /2 energy contained in the excited electronic states enthalpy, Planck's constant heat of formation Boltzmann's constant Knudsen number electron mass Mach number number density static pressure electron pressure electron-vibration energy transfer rate translation-vibration ei;.:i::. riilnsfer rate translation-electron energy transfer rate heat flux vector Reynolds number based on nose radius gas constant nose radius Stanton number, St = n'.i/p,u,(h, -hWan) translational-rotational temperature of heavy particles rate controlling temperature for forward reaction Tb rate controlling temperature for backward reaction T, temperature obtained fiom Saha Equation for equilibrium u, v velocity components in axial and radial direcli velocity vector aii diffusion velocity vector *Aerospace Engineer, CFD Research Branch, Aeromechanics Div., Senior Member AIAA tion This paper is declared a work of the U.S. Government and is not subject to copyright protectionin the United States