Theoretical investigation of the turbulent inflow noise produced by a shrouded propeller

A theoretical model is presented for predicting the noise produced by the interaction of turbulence with a propeller operating inside an acoustically lined shroud in an axisymmetric mean-flow. The theory is developed in the frequency domain and incorporates rapid distortion theory to obtain the distorted turbulent field at the propeller face, accounting for the potential mean-flow effect of the propeller and the shroud. The unsteady loading on the rotating blades is calculated using isolated blade response functions. The noise radiated to the far-field is then evaluated using a tailored Green's function approach which accounts for the scattering effect of the shroud and is solved using a boundary integral approach. Results are presented for a propeller inside an acoustically rigid and lined shroud operating in flows with a range of different free-stream velocities. It is shown that lining the shroud can significantly reduce the turbulent inflow noise.