Hypersonic wakes and trails

The distribution of observables in hypersonic wakes and trails is the result of a complex interaction of body shape, chemical kinetics, and the onset of laminar-turbulent transition This paper discusses progress and problems in these three areas with emphasis on scaling laws In the near the growth of the turbulent core and the cooling rate depend strongly on body shape The growth of the turbulent far wake is described by the universal relation YTf/(Ci)A)^^^'[x/(CDA)^]^ regardless of body shape or Reynolds number An analysis of data on laminar-turbulent transition in the wake of blunt bodies obtained in a wind tunnel and in a ballistic range shows that these data are correlated by taking a constant value of (Rex /)t = 5 6 X 10<i ± 15% over a Mach number range from 3 6 to 14 4. (Here x is distance from the body to the location of transition ) The minimum critical Reynolds number for a blunt body is about 5 X 10 at Mm — 20, based on freestream conditions and body diameter This value corresponds to an altitude of 220,000 ft for a body 6 ft in diameter For a sharp-nosed slender body, transition in the wake should appear at about the same altitude A tentative explanation of transition in hypersonic wakes is presented based on recent work on the instability of laminar compressible wakes Scaling parameters for oxygenelectron attachment and electron-ion recombination are derived, and theoretical calculations are compared with some recent experimental results For full-scale re-en try vehicles, oxygen-electron attachment in the wake is important below an altitude of about 150,000 ft This paper concludes with a brief discussion of some of the main problems for future research in this challenging field