Using steady flow analysis for noise predictions

Three different methods based on steady Reynolds-averaged Navier-Stokes (RANS) solutions are used to calculate the noise emitted from airfoils. Their results are compared to the ones obtained from experiments, a semi-empirical airfoil self-noise prediction code called NAFNoise developed by NREL, and large eddy simulations (LES). The three methods considered are a noise metric developed by Hosder et al. which can only predict overall sound pressure levels (OASPL) but no frequency spectra and two different statistical models developed by Doolan et al. and Remmler et al. The method by Doolan et al. employs a Green's function solution for airfoil trailing-edge far-field noise whereas the method by Remmler et al. predicts the pressure spectrum on the airfoil surface which is then used to compute the far-field sound by means of a hybrid noise prediction. All noise predictions were made at low speed and moderate Reynolds number similar to the environment of a small unmanned aerial system and involved different NACA airfoils as well as the SD 7003 airfoil.