A novel vortex generator for mitigation of shock-induced separation

A new geometry of a sub-boundary-layer vortex generator, which is termed as a slotted-ramp vortex generator, is proposed here. The geometry of the vortex generator is that of a ramp (triangular wedge) which has a semi-circular groove at its base. The centerplane of the groove or slot, which is basically like a tunnel that runs across the length of the ramp, is located at the spanwise plane of symmetry of the ramp. Preliminary computations of supersonic flow at a free-stream Mach number of 2.5 are conducted over vortex generators 2 mm, 3 mm, and 4 mm high. For each device height h, the flow is simulated for three values of the slot radius-0.2h 0.3h, and 0.4h. The incoming flow profile is based on the experiments conducted by Dr. Babinsky at Cambridge on control of shock/boundary-layer interaction with micro vortex generators at a free-stream Mach number of 2.5. An immersed-boundary technique suitable for high-speed turbulent flows is used for rendering the vortex generators. Comparisons are presented between the different slotted-ramp vortex generators with a standard ramp based vortex generator of the same device height using streamwise velocity profiles at different locations downstream of the device. Velocity plots show that the new device results in higher streamwise velocity along the centerline in the near wake region for the larger sized vortex generators and the effect improves when a higher slot radius is used. Comparisons are also presented with the standard ramp type vortex generator using span-averaged total pressure profiles and momentum-deflcit con-tours at different streamwise locations, and near surface axial velocity contours. Finally, results from computations of an impinging oblique-shock/boundary-layer interaction for a flow turning angle of 7 degrees at Mach 2.5 with and without flow control are presented. To achieve flow control two different cases are considered-one using an array of 3 x 3 mm high slotted-ramp vortex generators and the other using a similar array of the ramp type vortex generator. All the computations done as part of this study solves the Reynolds-averaged Navier-Stokes equations with Menter's k - ω/k – ε turbulence model (baseline or SST formulation).