Recent Improvement of a Semi-Empirical Aeroacoustic Prediction Code for Wind Turbines

Abstract

Two improvements were made to a semi-empirical aeroacoustic prediction code for wind turbines. The first improvement involved modifying the turbulent inflow noise model. The original model, developed by Amiet was combined with a model created by Guidati and compared to two-dimensional airfoil noise measurements. The improved model accurately predicted the absolute and relative sound pressure level changes caused by angles of attack, Mach number, and airfoil shape. The second improvement to the code, was the replacement of the current semi-empirical boundary layer thickness prediction with a boundary layer prediction routine, XFOIL. Using direct boundary layer thickness calculations improved the prediction of turbulent boundary layer trailing edge noise for most airfoils over a frequency range of 1-4 kHz and angles of attack smaller than 5°. The boundary layer calculation method did not improve the estimation of laminar vortex shedding noise because of sensitivity of this noise source to boundary layer transition, which is not accurately modeled in the noise prediction code.