Particle Image Velocimetry Near the Leading Edge of a Sikorsky SSC-A09 Wing During Dynamic Stall

Abstract

Dynamic stall has proven to be a complex problem in helicopter aerodynamics because it limits the helicopter flight regime. Dynamic stall is characterized by drastic increases in lift and a delay of stall due to rapid pitching motions of aerodynamic surfaces. Prediction and control of dynamic stall requires an understanding of the leading edge flow structure.

An investigation was conducted of dynamic stall near the leading edge of a large-scale Sikorsky SSC-A09 airfoil, dynamically pitching about its quarter chord, under realistic helicopter flight conditions (M_infinity = 0.1, k = 0.1, Re_c = 1.0 x 10^6). A testing model with a chord of 0.46 m and a span of 2.13 m was designed and constructed for experimentation in the Dynamic Stall Facility at Texas A&M University. Particle image velocimetry data were recorded for the first 15% of the airfoil chord. Mean velocities, Reynolds stresses, and vorticity were computed. Analyses revealed that during the upstroke, stall onset is delayed in the leading edge region and the first indications of separation are observed at 18 degree angle of attack. The edge of the boundary layer has been characterized for alpha = 18 degrees. The roles of the Reynolds stresses and vorticity are examined.