Measurements obtained in boundary layers developing downstream of the
highly turbulent, separated flow generated at the leading edge of a bl
unt flat plate are presented. Two cases are considered: first, when th
ere is only very low (wind tunnel) turbulence present in the free-stre
am flow and, second, when roughly isotropic, homogeneous turbulence is
introduced. With conditions adjusted to ensure that the separated reg
ion was of the same length in both cases, the flow around reattachment
was significantly different and subsequent differences in the develop
ment rate of the two boundary layers are identified. The paper complem
ents, but is much more extensive than, the earlier presentation of som
e of the basic data (Castro & Epik 1996), confirming not only that the
development process is very slow, but also that it is nonmonotonic. T
urbulence stress levels fall below those typical of zero-pressure-grad
ient boundary layers and, in many ways, the boundary layer has feature
s similar to those found in standard boundary layers perturbed by free
-stream turbulence. It is argued that, at least as far as the turbulen
ce structure is concerned, the inner layer region develops no more qui
ckly than does the outer flow and it is the latter which essentially d
etermines the overall rate of development of the whole flow. Some nume
rical computations are used to assess the extent to which current turb
ulence models are adequate for such flows.