No abstract

A parametric study has been conducted into the effects of device height (h = 6 − 10 mm), Mach number (M ∞ = 1.5−2.5) and Reynolds number (Re ∞ = 28−63×10 6 m −1 ) on the effectiveness of micro-ramp vortex generators as flow control devices. The control authority of the micro-ramp comes from the two counter-rotating vortices it introduces into the boundary layer. The vortices transport high-momentum fluid towards the wall, thus creating a fuller velocity profile which is less prone to separation. This momentum transport, however, comes at the price of a low-momentum wake that is formed downstream of the ramp. The induced flow field has been studied by means of particle image velocimetry, oil-flow and Schlieren visualizations. Most of the geometric flow features were found to scale linearly with micro-ramp height h: the wake height, wake strength, vortex core height and the momentum flux added to the near-wall region of the flow all increase linearly with h. The control effectiveness of the micro-ramp is reduced for higher Mach numbers, as less momentum is added to the near-wall region of the flow and a stronger wake is recorded. Only a weak Reynolds number effect is observed in the results, with the micro-ramp becoming slightly more effective at higher Reynolds numbers.