Three dimensional disturbances in two dimensional reattaching flows

Two possible causes of the pronounced periodic spanwise disturbances that have been observed in nominally two-dimensional or axi-symmetric reattaching laminar and turbulent separated flows are studied theoretically. Approximate analytical compressible small disturbance flow models for both a local vortex instability mechanism and the effect of a row of incoming streamwise vortices are set up, solved and compared with available experimental data on surface disturbance pattern, pressure and heat transfer. The results on all counts confirm the predictions of the vortex instability model.