Turbulent Ramp Flow Control Using Unsteady Blowing Upstream of the Separation Point
The control of a two-dimensional turbulent flow separation from a 25°—backward-facing-ramp is experimentally studied using an unsteady upstream blowing through a spanwise slit with a view to reducing the recirculation length. The Reynolds number examined is 9.38 × 104, based on the ramp height h. Three control parameters are examined, i.e. the blowing amplitude, frequency and duty cycle. Extensive measurements of the flow are carried out using PIV, pressure and hotwire techniques. The results are compared with those of the natural flow and under unsteady blowing. The time-averaged recirculation bubble is found to contract in length by 40% under the optimum control parameters, which correspond to a very small fraction of input energy. It is further found that the optimization control frequency is close to the shedding frequency of the uncontrolled shear layer captured at 1 h downstream of the separation point.
KeywordsFlow control Backward-facing ramp Unsteady blowing actuation
The financial support given from Shenzhen Government through grant JCYJ20150625142543469 is gratefully acknowledged.