Flow Separation and Wake Behavior on Blunt Trailing-Edged Rotor Blades in Reverse Flow

Reverse flow on the retreating side of a rotor disk is an intrinsic aerodynamic limitation of high-speed, high advance ratio rotorcraft. Flow reversal can be a source of several unsteady flow phenomena such as vortex formation, which increases the pitch link loads what might ultimately lead to fatal crashes. The aim of the current work is to reduce pitch link loads by using blunt trailing-edged blades. Three different methods - experiments, numerical simulations, and low-order modeling - were compared to a simple low-order model for a quick blade design iteration process. A range of advance ratios and blade pitch angles were studied. A 29% pitching moment increase was measured in the reverse flow region with sharp trailing-edged blades compared to blunt blades. The blunt trailing-edged blade delayed flow separation and thus prevented the formation of a reverse flow dynamic stall vortex, reducing the pitching moment. The use of such blunt trailing-edged blades could save pitch links from failing and may ultimately prevent rotorcraft from fatal crashes.