One of the outstanding challenges in high speed flows is the Shockwave Boundary Layer Interaction (SBLI). The boundary layer separation is caused by impingement of oblique shock on the boundary layer. The adverse pressure gradient across the shock is the major factor in the separation mechanism. Shock induced separation causes the unsteadiness in the flow field and is a key field of research due to the rich flow physics exhibited. At high Mach numbers, intense localized heating of the surface is also observed due to SBLI phenomenon, which makes this subject even more important and interesting to study especially for high speed flow applications.
The focus of the current research is aimed at the control of SBLI and boundary layer separation in rarefied gas flows. In recent decades, researchers have utilized different types of active and passive control techniques to minimize the effect of SBLI. In the present research, sub-boundary layer vortex generator, also called as Micro-Ramp (MR), is used as the control technique. MR generates counter-rotating, stream-wise vortices that could potentially energize the low momentum fluid in the separated boundary layer thereby reducing the extent of separation.
Direct Simulation of Monte Carlo (DSMC) method, a kinetic particle based method proposed by G.A. Bird, has been used to perform simulations. The study was conducted at different Mach and Knudsen numbers for the same geometrical setup. Some of the significant observations noted from the investigation of shock wave boundary layer interaction are summarized as follows:
The wake flow downstream of the MR is dominated by primary vortices that act to entrain high momentum fluid from the outer regions of the boundary layer towards the surface. Consequently, the low momentum wake is transported away from the surface and has been observed to be deposited outside the boundary layer at some downstream distance from the MR.
MR was found to reduce separations in a high Mach oblique shock reflection, by breaking up a previously two-dimensional separation region into cells of separated flow. At the same time, the effect of the ramp size on the extent of separation and momentum deficit is also studied in the work.
References:
- Holden, H. A., Babinsky, H.: “Vortex Generators Near Shock/Boundary Layer Interactions”, American Institute of Aeronautics and Asronautics, Paper 2004-1242, (2004)
- McCormick D.C., (1993), "Shock/Boundary-Layer Interaction Control with Vortex Generators and Passive Cavity", AIAA Journal. Vol. 31, no. 1, pp. 91-96. January 1993.
- Lin J.C., (2002), "Review of Research on Low-Profile Vortex Generators to Control Boundary-Layer Separation", Progress in Aerospace Sciences, 2002.
- Bird, G.A., “Molecular Dynamics and Direct Simulation of Gas Flows”, Oxford Engineering Science Series, Clarendon Press, 1994.
