Abstract:
Retreating Side Blowing (RSB) is a concept to blow air through the blade to suppress dynamic stall on the retreating side of the rotor, and enhance a vehicle's flight envelope at high speed and high loading forward flight conditions. Passive RSB utilizes a rotating blade as a centrifugal pump to drive flow from the inlet at the root to the outboard region. Current numerical studies examined the effectiveness of RSB in conjunction with validation against wind-tunnel measured data at high advance ratio conditions. The impact of varying freestream velocity on the performance of a blown pitching airfoil was also examined using two-dimensional airfoil calculations. The variation and timing of the freestream velocity significantly decreased the stall suppression benefit of a blown airfoil versus a fixed freestream. The validation of three-dimensional rotor simulations showed good correlation with measured data in predictions of integrated performance, section loading, and duct flow properties. Both measured data and numerical simulation showed no significant performance benefit from RSB in the tested flight conditions. Detailed examination indicated the RSB was able to reduce retreating side separation, but pumping torque, geometric modification due to slots, and increased retreating side horizontal force overwhelmed the retreating side torque benefit. Additional numerical explorative studies showed that powered-blowing could achieve significant performance improvement from pure aerodynamic perspective. However, the additional blowing power cancelled out most of benefit. An inlet valve model for simulation of scheduled blowing was also studied, but meaningful benefit was not observed. The retreating side blowing was able to reduce aerodynamic sources of retreating side vibration torsional load. However, the peak blade torsional load emerged on the advancing side at high advance ratio conditions.