Aerodynamic and aeroacoustic design optimization of UAVs using a surrogate model

A multi-disciplinary design optimization framework is proposed to improve the noise emissions of a quadcopter in forward flight with only a small penalty in aerodynamic performance. The design parameters are the spanwise distribution of the sweep angle and chord length of the propeller blades. The intention is to minimize the aerodynamic interactions between the propellers, as well as with the airframe, as they are associated with the tonal noise emissions that are known to dominate the radiated acoustic field in such applications. The noise prediction is obtained following the principles of the aeroacoustic analogy, using in this work a URANS CFD solver for the calculation of the unsteady blade loading, and an in-house aeroacoustic solver for the resulting acoustic radiation. The results demonstrate that the aerodynamic and acoustic performance cannot be improved simultaneously if the noise level is estimated using an unweighted sound metric, but that significant noise reduction can be achieved with a minor degradation of the mean thrust when the A-weighted noise emissions are taken as objective function.