Flare Induced Shock Wave Boundary Layer Interaction and its Control using Micro Vortex Generators

Abstract

The present study focusses on Shock Wave- Boundary Layer Interactions (SWBLIs) caused by flared portions of a launch vehicle/missile body. In supersonic speeds, such flared sections effectively act as axisymmetric compression corners, which obstruct the incoming flow and turn it away from the vehicle centreline through a shock wave. This shock inevitably interacts with the boundary layer growing over the body, and if strong enough, results in the formation of a separation bubble around the compression corner. A series of numerical simulations were carried out initially to determine the influence of various geometrical and flow parameters on the scale and strength of the interaction. Flares with higher flow deflection angles caused more obstruction to the incoming supersonic flow and thus produced stronger shocks, which in turn lead to larger flow separations. Increasing the forebody length (L) ahead of the flare also made the incoming boundary layer thicker and more momentum deficit, causing larger interactions/separations. The diameter (d) of the forebody was also directly related to the separation length. Surface flow visualizations (both x numerical and experimental oil flow visualizations) showed mild three-dimensional perturbations in the separation region that appeared to be sensitive to the corner radius. It is suspected that these may be caused due to the presence of Goertler vortices (centrifugal instability). Among the flow parameters, the unit Reynolds number (Re) appeared to have very little influence on the interaction/separation length. However, an increase in the inflow Mach number caused a significant delay in the onset of separation. newline newlineThe primary objective of this study is to control the flow separation by placing Micro Vortex Generators (MVGs) ahead of the interaction region. These are sub-boundary layer protuberances that are capable of producing streamwise vortices, which can entrain high momentum fluid into the near-wall region of the boundary layer and mitigate flow separation. newline