Sonic Line and Stand–Off Distance on Re–entry Capsule Shapes
In hypersonic flow over a sphere, the shock wave stand–off distance is related to the density ratio by
where Δ is the stand–off distance, r is the sphere radius, ρ ∞ is the free–stream density and \(\overline\rho\) is the average density along the stagnation streamline, see e. g., Hornung . For a sharp cone of a given angle, the stand–off distance increases linearly with \(\rho_\infty/\overline\rho\) from a critical onset point and is scaled by the base radius R of the cone, see e. g., Leyva . For a spherically blunted cone, one may therefore expect a transition to occur between sphere behavior and sharp cone behavior. This would be undesirable for stability and heat–flux reasons. A possibly more benign shape is an oblate ellipsoid, as suggested by Brown . We study features of such flows on the basis of perfect–gas computations. Since the density ratio is very sensitive to reaction rate in flows with vibrational and chemical relaxation, these phenomena are very important in entry of vehicles into atmospheres such as that of Mars. The computations are therefore extended to include the effects of reacting CO2 flows.
KeywordsDensity Ratio Standoff Distance Sonic Line Oblate Ellipsoid Sharp Cone
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