On turbulent separation

Abstract

The present theoretical article, dedicated to the memory of James Lighthill and his research contributions, is directed towards the central features of turbulent separation. The focus is on the time-mean equations, where the ensemble-averaged motion for an incompressible fluid is modelled as planar and steady. Specific major recent developments are discussed which are closely concerned in one way or another with turbulent separation at increased Reynolds numbers. These developments include in particular the behaviour of relatively thick boundary layers, on the one hand, ad the intricate behaviour of breakaway separation on the other. The article brings the behaviours together in a discussion of large-scale structure and accompanying interactions. The work presented here applies to quite general turbulence models and for specific cases enables direct comparisons to be made with experiments. The work also leads to new suggestions involving a combination of low- and high-intensity turbulence for the fluid motion around a bluff body and in its wake.