A Numerical Investigation of the Influence of the Blade-Vortex Interaction on the Dynamic Stall Onset in Simplified Rotor Environment

Two- and three-dimensional models representative of a helicopter rotor blade element during forward flight have been implemented. The rotor blade element is considered in pitching oscillation motion with a non-uniform translation to take into account the speed variation in forward flight. Two stalled flight conditions of the 7A rotor have been selected in wind tunnel test data. These flight conditions have been investigated in a previous study and the aerodynamic behavior of the rotor blades in realistic rotor environment is known, including stall mechanisms. The capability of simplified models to reproduce the aerodynamic behavior of the blade element has been validated for a first case. Then, the influence of the blade-vortex interaction on stall onset has been investigated since the previous work on full articulated-rotor configurations does not allow to conclude on the role of the blade-vortex interaction on stall onset. The simplified models allow to isolate the influence of a vortex passing close to the blade element on aerodynamic loads. This work shows that a dynamic stall event is triggered in both cases while a vortex is passing close to the blade element. This clearly highlights that blade-vortex interaction can trigger stall in realistic rotor environment.