Analysis of the flow produced by a low–Reynolds rotor optimized for low noise applications - Part II: Acoustics

Abstract

The demand in Micro–Air Vehicles (MAV) is increasing as well as their potential missions. Whether for discretion in military operations or noise pollution in civilian use, noise reduction of MAV is a goal to achieve. This contribution briefly describes a low–cost, numerical methodology to achieve noise reduction by optimization of MAV rotor blade geometry. It is suited for engineering purposes and dedicated to low–Reynolds number rotors. That methodology is applied to reduce noise from a MAV developped at ISAE–Supaero and a 8 dB(A) reduction on the acoustic power is found experimentally. Noise due to turbulence ingestion is found to be the dominant source of noise in MAV rotors. The innovative rotor blade geometry allowing this noise reduction is then analyzed in detail using high–fidelity numerical approaches such as Unsteady Reynolds Averaged Navier–Stokes (URANS) simulation and Large Eddy Simulation using Lattice Boltzmann Method (LES–LBM). That strategy gives insight on the flow features around the optimized rotor to allow higher noise reduction through passive control devices such as leading edge tubercles.