Experimental Evaluation of the Aerodynamic Rotor/Propeller Interactions on High Speed Helicopters, Efforts and Velocity Fields Measurements

This paper focuses on the experimental evaluation of the rotor/propeller interactions for hybrid compound configurations. Experiments are conducted in the ONERA L2 large size-low speed wind tunnel with a 1/7.7 Dauphin 365N model and a four-bladed small-scale propeller. Measurements are realized using two six-component balances, accelerometers, and blade pitch, flap and lead-lag angle sensors. PIV measurements are performed to visualize the velocity fields around the helicopter. Different flight conditions (wind speeds and propeller rotational speeds) have been tested. The comparison of the results obtained with an isolated main rotor and an isolated propeller with the complete assembly highlighted the influence of their interactions on their performances. In hover, the propeller is completely immersed in the rotor wake, and the thrust is therefore maximal. At low speed, the propeller is partially immersed and the flow on the propeller disk is highly asymmetrical. No direct interactions are measured at high speed, where the interactions increase the performances of the propeller due to the increased angle of attack of the flow on the propeller disk.