Investigation of Empirical Rotor Broadband Prediction using CFD Boundary Layer Parameters Extraction

Abstract

For small UAVs aeroacoustics predictions, an in-house acoustic code (ACUM) has been extended for broadband noise using empirical Brooks-Pope-Marcoloni (BPM) method. Then, the acoustic code is coupled with a comprehensive analysis tool (FLIGHTLAB) or Reynolds-Averaged Navier-Stokes (RANS) method to predict the noise from DJI 9443 CF rotor. The effect of two input parameters of BPM on the broadband noise was studied, which are effective angle of attack and boundary layer parameters. The empirical formula for the boundary layer parameters is replaced with predictions using two-dimensional RANS, which allows arbitrary airfoils other than NACA0012. The boundary layer parameters are predicted using three-dimensional RANS method to capture a three-dimensional flow effect which can be dominant on modern propeller designs operating at high rotational speeds. It was confirmed that the three-dimensional effect on boundary layer conflicted with BPM method because it was developed based on two-dimensional flow data base. Finally, higher frequency tonal noise was predicted from the unsteady three-dimensional RANS to be combined with BPM results. This results in improved noise spectra predictions at mid-range frequency.