Investigation of the Interaction Tones Produced by Contra-Rotating Unmanned Aerial Vehicle Rotor Systems

Abstract

This paper investigates the interaction tones produced by the periodic unsteady loading on the blades of two different contra-rotating unmanned aerial vehicle (UAV) rotor systems using computational, analytical, and experimental methods. Computational fluid dynamics (CFD) simulations are used to predict the unsteady loading on the rotor blades and to visualize the flow through the rotors. Semi-analytical models are also presented for predicting the portion of this unsteady loading due to the interaction of each blade with the bound potential field of the adjacent rotor. A comparison of the unsteady loading predicted using the CFD simulations and the semi-analytical models shows that, for the cases considered, the semi-analytical models accurately predict the unsteady loading on the top rotor and that the bound potential field interaction source is a significant contributor to the total unsteady loading on the bottom rotor. A frequency-domain acoustic analogy method is also presented, which is used to calculate the interaction tones produced by the unsteady loading on the rotor blades at various observer locations. Predictions of the sound pressure levels of the prominent interaction tones at different observer locations are presented and compared with experimental measurements showing generally good agreement. The effect of rotor spacing on the amplitude of the interaction tones is also explored, and it is shown that the methods predict a decrease in sound pressure level produced by increasing the rotor spacing and that these predictions are in reasonable agreement with experimental measurements.