Interaction of Synthetic Jet Propulsion with Airfoil Aerodynamics at Low Reynolds Numbers

Abstract

The use of synthetic jets for propulsion of fixed-wing Micro Air Vehicles (MAVs) is investigated experimentally in the low Reynolds number range. Interaction of a synthetic jet located at the trailing-edge of the wing with wing aerodynamics is studied with flow visualization and velocity measurements at low Reynolds numbers. The effects of excitation frequency, momentum coefficient, angle of attack, and Reynolds number were studied in detail. The separated region in the wake becomes smaller as the momentum coefficient is increased gradually. Once the momentum coefficient reaches a critical value, there is zero net drag. There is also reattachment of the separated shear layer near the trailing-edge, with expected enhancement in lift. Above the critical value of the momentum coefficient, the jet produces net thrust. Even at relatively higher incidences, zero net drag can be obtained and the reattachment of the shear layer to the upper wing surface is possible. The reattachment of the separated shear layer becomes easier with increasing Reynolds number. The favorable effect of increasing Reynolds number is most apparent at low Reynolds numbers. There is a strong effect of pulsing frequency and the results suggest an optimum range of Strouhal number St = 2 to 5. Also, preliminary experiments for a generic airfoil with internal actuator were carried out. Although the drag of this design is somewhat larger, zero net drag can be achieved when the synthetic jet is activated.