© 1977 by Oxford University Press
SEPARATION OF JETS OR THERMAL BOUNDARY LAYERS FROM A WALL
( Mathematics Department, Imperial College London )
Consideration is given to the nature of the separation and subsequent reversed flow occurring when a jet-like boundary layer on a wall encounters a concave corner of finite angle 
or collides with an opposing jet. Separation is caused by a nonlinear upstream response, within the jet, wherein the motion acquires a double-deck structure of streamwise extent O(L*Re–1/2), L* and Re>>1 being a characteristic length scale and Reynolds number respectively. The upstream pressure rise at the wall is sustained by the inviscid displacement of most of the jet because the displacement generates an adverse pressure gradient across the jet. Throughout most of the flow the induced pressure is proportional to the curvature of the jet displacement, the external motion exerting little influence. Numerical solutions of the key problem of the upstream interaction lead to an apparently self-consistent description of the reversed flow far downstream in the double-deck. This description in turn leads to a tentative account of the complete departure and reattachment of the jet, and the separation point is predicted to occur at a distance O(L*Re–1/14) from the corner (or line of symmetry in the jet collision problem). The results apply to some well-known jet situations in rotating fluids, oscillatory motions and free convection boundary layers.