On the Impact of Turbulent Inflow on the Noise Generated by a Propeller Operating at Low Reynolds Number
M. Ali (Politecnico di Torino)
A. Piccolo (TU Delft - Wind Energy)
R. Zamponi (Deutsches Zentrum für Luft- und Raumfahrt (DLR), TU Delft - Wind Energy)
D. Ragni (TU Delft - Wind Energy)
F. Avallone (TU Delft - Wind Energy)
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Abstract
Ingested turbulence affects propeller noise at frequencies above the 2nd Blade Passing Frequency. The extension of the Amiet model to rotating structures is a useful tool to predict this phenomenon. However, comparison with the experimental results reveal discrepancies between predicted and measured acoustic spectra. A likely explanation for this mismatch lies in turbulence distortion.This paper investigates the effects of the propeller-induced flow field on incoming turbulence to obtain a comprehensive description of the flow physics and enhance, in future studies, Amiet’s prediction model.Lattice Boltzmann Very Large Eddy Simulations of a reference propeller operating at low-Reynolds number and subjected to turbulent inflow are performed. The spatial and temporal evolution of isotropic grid-generated turbulence approaching the propeller plane is characterized . The analysis shows that the leading edge interacts with anisotropic turbulence. This is due to the rotational flow induced by the propeller, streamtube contraction, and leading edge distortion.In addition, the effect of turbulence on the laminar separation bubble, conventionally present in flow at low Reynolds number, whose dynamics affects the acoustics at high frequencies, is analyzed. Acoustic spectra, obtained through the Ffowcs-Williams and Hawkings analogy applied to the propeller surface, are then linked to the aerodynamic sources.
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