Effects of Micro-Ramps on a Shock Wave/Turbulent Boundary Layer Interaction

Abstract

Stereoscopic particle image velocimetry is used to investigate the effects of micro-ramp sub-boundary layer vortex generators, on an incident shock wave/boundary layer interaction at Mach 1.84. Single-and double-row arrangements of micro-ramps are considered. The micro-ramps have a height of 20% of the unperturbed boundary layer thickness and the measurement planes are located 0.1 and 0.6 boundary layer thicknesses from the wall. The micro-ramps generate packets of individual vortex pairs downstream of their vertices, which produce counter-rotating longitudinal streamwise vortex pairs in a time-averaged view. These structures induce a pronounced spanwise variation of the flow properties, namely the mixing across the boundary layer interface. The probability of reversed-flow occurrence is decreased by 20 and 30% for the single-and double-row configurations, respectively. Both configurations of micro-ramps stabilize the shock motion by reducing the length of its motion by about 20% in the lower measurement plane. The results are summarized by a conceptual model describing the boundary layer's and interaction's flow pattern under the effect of the micro-ramps.

Decay of the supersonic turbulent wakes from micro-ramps

“…Sun et al [16] measured the three-dimensional structure of K-H vortices using tomographic PIV (Tomo-PIV). The experiments returned more an arch-like vortex rather than full ring or hairpin, which stands in some contrast to the work of Li & Liu [14] and Blinde et al [13], respectively. More in particular, the discrepancy with the vortex ring model has not been reconciled so far and motivates the present study.…”

“…From the unsteady behavior of the wake, the clearest feature emerging from both experiments and simulations is the vortex shedding from the quasi-circular free shear layer emanating from the ramp trailing edge. Blinde et al [13] inferred this from the wall-normal counter-rotating vortex pairs from the stereoscopic particle image velocimetry (Stereo-PIV) analysis in planes parallel to the wall. The numerical study of Li & Liu [14] showed that those vortices were rolled up from the growth of Kelvin-Helmholtz (K-H) shear layer instability and finally developed into ring-shaped vortices.…”

Supersonic flow control

“…The main motivation behind applying any flow control effort is to reduce the detrimental effects of flow separation or compressible mixing with the intention of improving the overall performance. The first and foremost step in this direction lies in altering the characteristics of the incoming boundary layer by adding energy to its mean velocity profile [10]. By doing so, the resulting relatively more energetic boundary layer becomes more resistant to conditions imposed by the adverse pressure gradient, which helps to reduce the overall extent of the separation and the associated flow unsteadiness.…”

“…However, active flow control devices, as already mentioned before, can be complex, expensive and also difficult to implement and maintain [25]. Various groups in USA [29][30][31][32][33], Europe [10,28,34,35], UK [26,27], India [36,37] and China [38] are looking at different methods of shock-induced control in various areas of research applications.…”

“…5a). A more recent approach for achieving effective flow control is through the use of "micro" mechanical control devices (with h < δ) that introduce mixing in the boundary layer, are fail-safe and most importantly, are mechanically simpler and rugged [10,26,27]. The boundary layer mixing is achieved by the generation of streamwise vortices (coor counter-rotating) in the wake of these control devices, near the wall (see Fig.…”