Assessment of Permeable Boundary Integral Formulations for Rotating Blades Noise Prediction

In this work the Ffowcs Williams and Hawkings Equation for permeable surfaces (FWHE-P) is used for the prediction of the noise generated by marine propellers and horizontal-axis wind turbines. Aim of the paper is to assess a boundary integral formulation yielding the acoustic pressure outside a permeable surface surrounding the rotating body and "all" possible nonlinear sources of sound. The acoustic effects of placement and extension of the surface are investigated, facing the issue of the outflow-disk that may be source of inaccuracies in the noise prediction. A cylindrical surface rigidly moving with the blades is choosen as integration domain of the P- FWHE whereas a zero-th Boundary Element Method (BEM) is used to solve the integral formu- lation. Steady RANS (Reynolds Averaged Navier Stokes) and DES (Detached Eddy Simulation) solvers are used to detect the sources of sound upon the porous surface, for the turbine and pro- peller, respectively. Numerical results compare the acoustic signals from the P-FWHE and those carried out directly by the RANS or DES simulations; drawbacks and goodness of the choices done about the porous surface are discussed.