Vorticity Transport Analysis on Blunt Trailing-Edge Blades in Reverse Flow

High-advance-ratio rotorcraft face reverse flow effects on a substantial portion of the retreating blades. Similar to a leading-edge vortex, the reverse flow dynamic stall vortex was found to have a significant impact on unsteady blade loading and pitching moment evolution due to its strength and proximity to the blade surface. The present work aims to assess how reverse flow dynamic stall vortex formation and advection are affected by trailing-edge curvature and how the blade pitching moment can be reduced by altering the center of pressure. Experimental and numerical data at an advance ratio of 1.00 and high collective blade pitch angles revealed that vorticity transport within the reverse flow dynamic stall vortex is dominated by the shear flux at the aerodynamic leading edge. A blunt trailing edge reduced this shear flux and consequently the dynamic stall vortex growth significantly. Unlike in the case of a hovering rotor, the convection term was found to switch direction in the reverse flow region, which is likely related to vortex shedding in reverse flow. The selective use of blunt trailing-edged blade sections at inboard stations could mitigate severe pitching moments that lead to high pitch link loading.