Active control of separated flows on generic configurations at high reynolds numbers

A series of active flow control experiments conducted in a cryogenic pressurized wind tunnel on a generic separated configuration are described. The model simulates the upper surface of a 20% thick airfoil at zero angle of attack. A moderate favorable pressure gradient up to 55% of the chord is followed by a severe adverse pressure gradient that relaxes towards the trailing edge. The flow is turbulent throughout since the tunnel boundary layer flows over the model. The characteristics of the upstream boundary layer are controlled and monitored. Without control, the flow separates at the slope discontinuity and a large turbulent separation bubble is formed. Periodic excitation is applied to gradually eliminate the separation bubble. Two alternative blowing slot locations as well as the effect of sweep and steady suction or blowing were tested. The flow conditions were chord Reynolds numbers in the range of 2 to 40 million and Mach numbers in the range of 0.2 to 0.7. Besides streamwise and spanwise static pressure taps, the model is instrumented with 12 dynamic pressure transducers. This allows the quantification of dynamic effects due to the excitation. The model is also equipped with a boundary layer probe (instrumented with a dynamic pressure transducer) that can be traversed at several alternative locations. This paper is focused on the unswept incompressible flow conditions. Detailed effects due to variations in the excitation frequency, amplitude, and the steady mass flux are described and compared to steady suction or blowing. The data set will significantly enhance the understanding of active separation control at high Reynolds numbers, and is an excellent validation case for unsteady CFD tool development.