This paper compares two methods for predicting transonic rotor noise for helicopters in hover and forward ight. Both methods rely on a computational uid dynamics (CFD) solution as input to predict the acoustic near and far elds. For this work, the same full-potential rotor code has been used to compute the CFD solution for both acoustic methods. The rst method employs the acoustic analogy as embodied in the Ffowcs Williams{Hawkings (FW{H ) equation, including the quadrupole term. The second method uses a rotating Kirchho formulation. Computed results from both methods are compared with one other and with experimental data for both hover and advancing rotor cases. The results are quite good for all cases tested. The sensitivity of both methods to CFD grid resolution and to the choice of the integration surface/volume is investigated. The computational requirements of both methods are comparable; in both cases these requirements are much less than the requirements for the CFD solution.
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