Application of a hybrid approach for far-field sound prediction from high-speed helicopter blades

The paper presents a method to predict the sound from helicopter rotor blades in high-speed forward flight conditions. Results of predictions are compared with experimenal data. The noise prediction method is based on an integral representation theorem which follows from the Lighthill acoustic analogy. The non-linear sources in the penetrable Ffowcs Williams–Hawkings formulation are supplied by the acoustically tailored near-field CFD computation. The near-field transonic flow is calculated in the reference frame moving with the helicopter blade. To compute the flow a shock-capturing finite-difference scheme with charactersitic flux-splitting is used. The use of numerically consistent approximation for non-inertial source terms and local non-reflecting boundary conditions makes the numerical solution particularly accurate.