Noise Prediction of Multi-rotor Unmanned Aerial Vehicle Considering Wake Interaction Effect

Wake interaction phenomenon severely occurs in the unmanned aerial vehicles (UAVs) with multi-rotor configuration. In the present work, the computational study of a small-scale quadcopter UAV was carried out to investigate the wake interaction effects in terms of the aerodynamic performance, wake structure, and acoustic characteristics. Numerical simulation of DJI Phantom 2 model in hover flight has been carried out using nonlinear vortex lattice method (NVLM) with vortex particle method (VPM) and acoustic analogy based on Farassat-1A formula. Calculations for quadcopter configuration with various separation distances between neighboring rotors were compared with the isolated rotor to study the complex wake flow of the multi-rotor system. It is found that the average thrust coefficient decreases and the thrust coefficient begins to fluctuate dramatically, as an interval between the rotors gets smaller. In addition, wake geometry appears to radially shift toward the neighboring rotors, thus leading to strong wake-to-wake interaction. The sound pressure level of the quadcopter is much higher than that of the isolated rotor, and tonal noise associated with the rotor blade passing frequency (BPF) can be captured.