Helicopter rotor noise prediction using ONERA and DLR Euler/Kirchhoff methods

Euler/Kirchhoff methods have been developed at ONERA and DLR to predict the High Speed Impulsive (HSI) noise generated by helicopter rotors in hover o r in forward flight. The main purpose of this common work is to validate an d to compare aeroacoustic computations on delocalized test cases. Code to c ode comparisons show rather close aerodynamic and acoustic predictions, Aco ustic results are identical when using the same aerodynamic inputs. In hove r, both aerodynamic and acoustic results obtained by each partner are in go od agreement with experiment. In forward night, a first set of computations relative to a non-rectangular blade rotor model is performed using three d ifferent sized grids. Correlation of blade pressure coefficients improve ex periment when the grid is refined. However, the capture of the shock waves beyond the blade is not accurate enough to get reasonable noise predictions with respect to the Kirchhoff surface location, whatever the grid refineme nt may be. In order to improve the aeroacoustic computations in the far-fie ld, an "adapted" grid has been generated. Acoustic predictions are clearly improved, showing the requirement for a grid adaptation to perform accurate HSI noise predictions on advanced blade geometries.