Progress in Shock Wave/Boundary Layer Interactions

Abstract

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 some cases be 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. Of interest are not only reduction in separation and surface loads, but also the 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 which are woven into the discussion, as are limitations in current capability and understanding.

Unsteady Behavior of a Pressure-Induced Turbulent Separation Bubble

“…These vortices might have an effect on the unsteady character of the flow. In fact, the appearance of such vortices was thought to be a possible explanation for the low-frequency unsteadiness observed in impinging-shock experiments [27], though recent observations of the same unsteady mode in an axisymmetric configuration tend to mitigate this hypothesis [28]. Second, the physical mechanism driving the lowfrequency breathing motion, its frequency scaling with the velocity and the bubble size, and its possible relationship with the flapping mode of fixed-separation flows should be investigated.…”

“…This unsteadiness has been observed on several flow configurations (2D ramps, 2D impinging shocks, 3D blunt fins) [29], in many supersonic wind tunnels [27], in a quiet wind tunnel [49], and even in flight [28]. The unsteadiness is characterized by a large-scale, low-frequency oscillation of the separation shock and its associated separation bubble.…”

“…STBLIs that are sufficiently strong to produce a separation bubble are known to be affected by a large-scale, low-frequency unsteadiness [27][28][29]. This unsteadiness has been observed on several flow configurations (2D ramps, 2D impinging shocks, 3D blunt fins) [29], in many supersonic wind tunnels [27], in a quiet wind tunnel [49], and even in flight [28].…”

“…A comprehensive review of past results would be out of the scope of the present paper and the reader is referred to the recent reviews of Dussauge et al [27], Gaitonde [28], and Clemens and Narayanaswamy [29]. The typical configurations in this field of study are shock waveturbulent boundary-layer interactions (STBLIs) generated by a compression ramp or an oblique shock impinging on a flat test surface.…”

Investigation of turbulent shock boundary interaction unsteadiness and its effects on aero-optics in a Mach 2 ramp flow

“…SBLIs themselves have a vast literature and the reader is referred to the papers cited and reviews by: Delery, 14 Andreopoulos, 15 Dolling, 1 the book by Smits & Dussuage 2 and the recent review of experimental and computational results by Gaitonde. 16 Recent reviews focusing on the the issue of shock unsteadiness are given by Poggie,et. al.…”