Measured transition from laminar to turbulent flow and subsequent growth of turbulent wakes

Turbulent Wake and Shock Shape of Hypervelocity Spheres

“…This tends to support the suggestion that the transition values quoted in Ref. 12 are in fact the points at which the turbulent inner wake emerged from the inviscid outer wake. This type of transition seems to be significant since it apparently may be this point of breakthrough which provides a backscattered radar return.…”

“…22a and b show turbulence orders of magnitude sooner than do the data of Ref. 12 encourages the belief that the lower l%e®Xtr represents transition of the inner viscous wake. Accordingly, all the available sphere wake data in the Mach number range of 5 to 20 are plotted in Fig.…”

“…-diam sphere has been derived from a doppler analysis of the radar return (Ref. 12) and is plotted in Fig. 23.…”

Far wake behavior of hypersonic spheres.

“…[1][2][3] indicates that turbulence onset, or transition, occurs within 10 body diam behind the body at Reynolds numbers (Re m , &) greater than 10 5 , where Re^, D = U^D/vî s determined by ambient kinematic viscosity v mj flight speed U m , and body diameter D. In another report, however, turbulence was first detected some 50 to 100 diam behind the body at these Reynolds numbers. 4 This long distance to transition appears inconsistent, even with previous reports by the same authors, 2 and it has been suggested that the phenomenon was not transition but, rather, fully developed turbulence, earlier turbulence having been masked by inadequate instrument sensitivity. 1 ' 4 The studies reported here were undertaken, in part, to attempt to resolve these discrepancies and uncertainties by performing schlieren studies of the wake development behind models in free flight in the ballistic range, and in part to aid in understanding the radar backscatter and radiation studies of the wake already under way in the ballistic range.…”

“…In fact, the inviscid wake is so well defined at re-entry speeds that it has been erroneously identified by others as a viscous wake. 4 At lower speeds the inviscid gradients lessen, and no inviscid wake can be defined; and at subsonic speeds, with the disappearance of the bow shock, no inviscid, shock-heated wake can exist. Thus the concept of an inviscid wake appears to apply only to near-re-entry conditions.…”