ON THE IMPACT OF TURBULENT INFLOW ON THE NOISE GENERATED BY A PROPELLER OPERATING AT LOW REYNOLDS NUMBER

Ingested turbulence affects propeller noise at frequencies higher than the 2nd blade passing frequency. The extension of Amiet’s model to rotating blades represents a useful tool for predicting this phenomenon. However, it relies on assumptions that are not fully valid in reality, e.g., it neglects the distortion of turbulence. This paper investigates how the propeller-induced flow field alters incoming turbulence paving the way, in future studies, to extend Amiet’s model with these features. Lattice Boltzmann Very Large Eddy Simulations of a reference propeller, for which experimental data exist, operating at low-Reynolds number and subject to turbulent inflow are performed. The spatial and temporal evolution of isotropic grid-generated turbulence approaching the propeller plane is characterized. It is found that the propeller leading edge interacts with anisotropic turbulence. This is due to the rotational flow induced by the propeller, stream tube contraction, and leading-edge distortion. In addition, the impact of the inflow turbulence on the laminar separation bubble on the propeller suction side, whose dynamic affects the acoustics at high frequencies, is analyzed. Finally, the aerodynamics flow features are linked to the far-field acoustic spectra, obtained through the Ffowcs-Williams and Hawkings analogy applied to the propeller surface.