Broadband noise emission by a low-Mach low-Reynolds number propeller ingesting a boundary layer

The broadband noise radiated by a low-speed two-bladed propeller immersed in a planar turbulent boundary layer (BL) is predicted by using an analytical approach developed in the past in response to a similar aero-acoustic problem. The experimental results come from two independent facilities having analogous characteristics. Excess broadband noise is assumed to be generated by the BL turbulence hitting the propeller blades. The aero-acoustic model is based on the acoustic analogy. It accounts for the fact that vortices can be chopped several times by the blades as they pass through the propeller. The "cigar" shape of the turbulence near the wall surface is considered in the turbulence model. If possible, the input parameters are retrieved from the hot-wire measurements carried out in the boundary layer, otherwise they are modelled. The propeller performance is calculated using BEMT. The effect of the flat plate on aerodynamics and acoustics is ignored. The results obtained with this heuristic approach are satisfactory in the orthogonal plane but the levels are underestimated by more than 10 dB in the downstream region of the horizontal plane. This suggests that a major effect is not captured by the current models. Measurements and predictions agree upon the fact that blade-to-blade correlations are not prominent for this configuration.