Single-Shot Pressure-Sensitive Paint Measurements of Static and Dynamic Stall on a Wind Turbine Airfoil

Results of a first application of pressure-sensitive paint (PSP) to a low Reynolds number wind turbine airfoil in static and dynamic stall are reported. Recognizing the need for global surface measurement techniques to resolve the unsteady three-dimensional loading on a moving wind turbine blade, fast-responding PSP was applied to the suction side of a Delft DU97-W-300 airfoil (maximum thickness-to-chord ratio of 30%) at a chord Reynolds number of 225,000 in the University of Wyoming open-return wind tunnel. Static and dynamic stall behaviors are compared using instantaneous and phase-averaged global pressure maps. In particular, a three-dimensional pressure topology resembling a stall cell pattern is prominently observed in static shallow stall. The dynamic stall case was characterized by a sinusoidal pitching motion with mean angle of 15.7°, amplitude of 11.2°, and reduced frequency of 0.106 based on semichord. PSP images were acquired at selected phase positions, capturing the breakdown of nominally two-dimensional flow near lift stall, development of post-stall suction near the trailing edge, and a highly three-dimensional reattachment. By using a laser-based excitation system, the PSP signal was sufficiently strong to capture the dominant surface dynamics under these historically challenging test conditions.