Prediction of Rotor Aeroacoustics in Forward Flight by a Lifting Surface Method

Calculation of flow around helicopter rotors in lifting forward flight requires a three-dimensional unsteady method. A boundary element method (Lifting Body Surface (LBS)) was successfully applied at DLR for the prediction of propeller aeroacoustics. Results from application to rotor aeroacoustic for non-lifting and lifting hover showed good agreement with Euler solutions and with experiment. Boundary element methods based on linear potential theory are efficient and easy to handle even for complex geometries. The aim of this work is to check the applicability of the LBS method to the rotor in lifting forward flight for design purposes. The LBS method is a supplement to lifting line methods used at DLR for the aerodynamic computation of rotors. It offers higher flexibility in planforms and profiles of rotor blades and it provides pressure distributions on blade surfaces, important for acoustic calculations. The unstaedy Euler methods also used at DLR are too expensive for design purposes at present time.