This presentation will discuss results from an experimental investigation of the compressible dynamic stall characteristics of an SSC-A09 airfoil in an unsteady freestream. While traditional dynamic stall investigations study only the pitch oscillation characteristics in a steady freestream, this work incorporates the effects of an unsteady freestream (time-varying velocity). 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 Ohio State University 6′′ × 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 effects of the phase relationship between the angle of attack and Mach oscillation waveforms were studied, in order to study the impact of the Mach oscillations on dynamic stall. Furthermore, the features of dynamic stall between a steady compressible and an unsteady compressible freestream were compared, in order to explore the feasibility of simulating unsteady freestream dynamic stall physics using data acquired with a steady freestream.
Dr. James Gregory
Professor in the Department of Mechanical and Aerospace Engineering, and Director of the Aerospace Research Center at The Ohio State University. He received his doctorate and master's degrees in Aeronautics and Astronautics from Purdue University in 2005 and 2002, respectively. He received his Bachelor of Aerospace Engineering from Georgia Tech in 1999, graduating with the highest honors. Dr. Gregory’s research interests lie in the field of unsteady aerodynamics – with specific interests in understanding and controlling compressible dynamic stall of rotorcraft blades; unsteady, compressible airfoil aerodynamics; and study of low-Re, unsteady rotor wakes subjected to wind gusts. He is also active in Unmanned Aircraft Systems (drone) research, including flight testing of vehicle performance, systems integration studies, and robust flight of UAS in all weather conditions (wind and icing). Dr. Gregory is an instrument-rated private pilot, with over 280 hours in single-engine aircraft, and is one of the first holders of a remote pilot certificate.