Fluid Mechanics of Compressible Dynamic Stall Control Using Dynamically Deforming Airfoils

This report summarizes the key results from the two components of the study: (1) development of the knowledge and understanding of the fundamental fluid mechanics of the interactions of the unsteady flow occurring under the influence of the time scales of airfoil reduced frequency and dynamic leading edge adaptation at different flow conditions; (2) understanding of the role of the surface flow in compressible dynamic stall onset. For the former, a systematic investigation of the dynamic stall flow (or lack thereof) was carried out using a dynamically deforming leading edge airfoil, which allowed us to establish the fact there are some airfoil leading edge geometries that are indeed dynamic stall free. This offers the hope that rotor blade geometries can be adapted to avoid the destructive dynamic stall effects, while retaining its benefits. In the latter, 148 surface shear stress sensors were installed on an NACA 0012 airfoil and the flow behavior studied for various flow conditions, which showed the various stall onset mechanisms discovered earlier and also that the surface behavior becomes singular prior to stall onset.U.S. Army Research Office ARO-36477-EG.10U.S. Army Research Office ARO-36477-EG.1