A Fast Kirchhoff Integration Technique for Rotor Noise Directivity Predictions

The main features of the fully non-compact Kirchhoff integration method KIM are recalled together with the CFD method (code WAVES) used for providing the aerodynamic input data. The computational efficiency of the Kirchhoff integration technique is shown through an application t o the prediction of the acoustic field radiated by the F30 model rotor in a non-lifting HSI noise case. The method is then used to address, for the first time, the effect of thrust on HSI noise directivity o f helicopter rotors in forward flight. The study is carried out on the ONERA 7A model rotor. The aerodynamic calculations are validated by comparisons of predicted blade pressure distributions with experimental data. Aeroacoustic results confirm, at least for these rectangular blades and in the delocalized cases studied, that the thrust coefficient has a negligible effect on the radiated HSI noise.