Instability in Hypersonic Flow about Blunt Bodies

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Abstract
Studies of the flow field associated with hypersonic helium flow over blunt bodies with surface cavities have shown a very violent instability to be connected with these cavities. The mechanism of this instability appears to involve the formation within the cavity of vortices which are subsequently ejected. Cavity shapes more conducive to vortex formation are associated with the least stable flow. Experiments using the hydraulic analogy for compressible gas flow have clarified the nature of these unstable flows. It is suggested that the violent action of such vortices may explain some of the deeper pits observed in many meteorites. The continuous ejection of vortices during atmospheric passage would ablate material from the cavities, whence the depth of any cavities initially present on a meteoric body would increase during passage through the earth's atmosphere.

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