Level of Turbulence Intensity Associated with Bluff-Body Separation for Large Values of the Reynolds Number

The paper concerns a rational and physically feasible description of gross separation from the surface of a plane and more-or-less bluff obstacle in an incompressible and otherwise perfectly uniform stream for arbitrarily large values of the globally formed Reynolds number. The analysis is initialized by a remarkable conclusion drawn from recent theoretical results that is corroborated by experimental findings but apparently contrasts common reasoning: the attached boundary layer extending from the front stagnation point to the position of separation at the body surface never attains a fully developed turbulent state, even in the limit of infinite Reynolds number. As a consequence, the boundary layer exhibits a certain level of turbulence intensity that is determined by the separation process governed by locally strong viscous/inviscid flow interaction. This mechanism is expected to be associated with rapid transition of the separating shear layer towards an almost fully developed turbulent state. Here a rigorous asymptotic analysis, essentially carried out without resorting to a specific turbulent closure and supported by a numerical investigation, of the topology of the boundary layer flow close to separation is presented.