Aerodynamic and Aeroacoustic Investigation for the Operation Arrangement of Contra-rotating Rotors

Contra-rotating rotors have the advantage of improving the load capacity of multi-rotor Unmanned Aerial Vehicle (UAV) under the space limit, and thus it gains interest from industry and can be observed in a lot of applications. By alleviating the interference effect, the performance of the contra-rotating rotors can be augmented further. This research investigates the rotation speed combination of the upper and lower rotor to find the optimal operation conditions. The aerodynamic and acoustic results are measured by two force balances and microphones respectively in an anechoic chamber, respectively. The results indicate that the better performance occurs when the rotational speed of the lower rotor is higher than that of the upper rotor, because the aerodynamic loss of the lower rotor will significantly arise with the increase of the upper rotor RPM. The noise emission does not follow the same trend as the aerodynamic performance, which shows two local minimum values when decreasing the lower rotor RPM and increasing the upper rotor RPM.