Novel vortex generator for mitigation of shock-induced flow separation
A novel vortex generator, termed as "slotted vortex generator," is proposed in this study. Computations are conducted for supersonic flow at a freestream Mach number of 2.5 past single vortex generators of three different heights. For each device height h, three values of the slot radius r = 0.3h, 0.4h, and 0.6h are used. Comparisons made with a standard wedge-type vortex generator using streamwise-velocity profiles, near-surface streamwise-velocity contours, pitot pressure deficit contours, etc., indicate that the new device has less device drag and produces fuller near-surface streamwise velocities downstream of the device. It is observed that the primary counter-rotating vortex pair formed due to the vortex generator lifts off at a slower rate when a slotted vortex generator is used. Computations of an impinging oblique-shock/boundary-layer interaction at Mach 2.5 for a flow turning angle of 7 deg, with flow control using (separately) an array of slotted and standard vortex generators, indicate that the slotted vortex generators with r/h =0.6 are most effective in reducing the region with reversed flow when placed closer to the shock/boundary-layer interaction region.
Evaluation of some wedge-shaped vortex generators using swirl center tracking
The primary vortex pair generated due to a vortex generator, used in the control of boundary-layer separation, is considered to energize the near-wall flow downstream of the device. Depending on the orientation of the device with respect to the flow, a pair of primarily streamwise co-rotating or counter-rotating vortex pair is formed. In this paper, the evolution of the primary vortex pair is tracked for different types of wedge shaped vortex generators. The present study makes an attempt to compare the vortex evolution using a swirl center tracking technique. Near surface contours of axial velocity, and contours of heliciity, will be compared to evaluate the effects of vortex strength, and rates of lift-off of the primary vortex pair formed due to the different devices. The computations performed in this work involve supersonic flows past single vortex generators at Mach 2.5 and uses an immersed-boundary method to render the control devices. The flow solver used, REACTMB, is suitable for high-speed turbulent flows, and has been extensively validated in earlier works. The turbulence model used is Menter’s k-ω/k-ε SST version.
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).
Evaluation of ramp-type micro vortex generators using swirl center tracking
The evolution of the primary vortex pair downstream of micro vortex generators placed in a supersonic stream is compared using a swirl center tracking technique, for standard, slotted, and split-ramp-type vortex generators. Evolution of vortex strength, determined using circulation, and distribution of vortices, determined using contours of helicity, are also compared. Results show that secondary vortices emerge stronger, and liftoff heights drop, with the introduction of slot (slotted micro vortex generator) or gaps (split-ramp micro vortex generator). Near-surface contours of axial velocity and integral properties of the boundary layer are then compared to evaluate the effects of the evolution of the vortical structures on the flowfield. Results shows that the split-ramp device results in the most energetic near-surface flow but the worst outgoing boundary-layer integral properties, whereas the slotted-ramp devices with taper fare well on both counts. The computations performed in this work involve supersonic flow past single micro vortex generators at Mach 2.5 and use an immersed-boundary method to render the control devices. The flow solver is suitable for high-speed turbulent flows and has been extensively validated in earlier works. The turbulence model used is Menter's k − ω∕k − ε shear-stress transport version.