Progress in shock wave/boundary layer interactions

Recent advances in shock wave boundary layer interaction research are reviewed in four areas: (i) understanding low frequency unsteadiness, (ii) heat transfer prediction capability, (iii) phenomena in complex (multi-shock boundary layer) interactions and (iv) flow control techniques. Substantial success has been achieved in describing the phenomenology of low frequency unsteadiness, including correlations and coherent structures in the separation bubble, through complementary experimental and numerical studies on nominally 2-D interactions. These observations have been parlayed to propose underlying mechanisms based on oscillation, amplification and upstream boundary layer effects. For heat transfer prediction capability, systematic studies conducted under the auspices of AFOSR and RTO-AVT activities have shown that for axisymmetric laminar situations, heat transfer rates can be measured, and in many cases predicted, reasonably accurately even in the presence of high-temperature effects. Efforts have quantified uncertainty of Reynolds averaged turbulence models, and hybrid methods have been developed to at least partially address deficiencies. Progress in complex interactions encompass two of the major phenomena affected by SBLI in scramjet flowpaths: unstart and mode transition from ramjet (dual mode) to scramjet. Control studies have attempted to leverage the better understanding of the fundamental phenomena with passive and active techniques, the latter exploiting the superior properties of newer actuators. Objectives include reduction in size of the separation region, surface loads and modulation of spectral content. Finally, SBLI studies have benefited handsomely from successful ground and flight test campaigns associated with the HIFiRE-1 and HIFiRE-2 campaigns, results from which are woven into the discussion, as are limitations in current capability and understanding.