Compressible Dynamic Stall of an SSC-A09 Airfoil Subjected to Coupled Pitch and Freestream Mach Oscillations

This work presents results from an experimental investigation of the compressible dynamic stall characteristics of an SSC-A09 airfoil. It is a study of not only the effects of airfoil pitch oscillations, but also coupled free stream Mach/pitch oscillations. The objective of this study is to evaluate the impact of local sinusoidal velocity that is encountered in the blade frame of reference on rotorcraft in forward flight. This investigation was undertaken in the OSU 6" x 22" unsteady transonic wind tunnel. The pitch and/or flow can be oscillated at a rate up to 21 Hz (reduced frequency up to 0.05), with a Mach number of 0.40 ± 0.05 and a mean Reynolds number from 2 to 3.5 million. Steady data was also taken without freestream oscillations but with pitch oscillations, at Mach numbers ranging from 0.2 to 0.6. The results presented in this paper investigate the effects of the phase relationship between the angle of attack and Mach oscillation waveforms, in order to study the impact of the Mach oscillations on dynamic stall. Periods of flow acceleration were found to have a stabilizing effect on the dynamic stall event.