Low-Order Aerodynamic Model for Interference in Multirotor Systems

Abstract

The paper proposes an aerodynamic model capable of capturing interference effects in arbitrary multirotor systems. The current analysis is limited for nonoverlapping rotors. The model is based on a combined inflow theory approach, where self-induced and influence-induced velocities are obtained using different inflow models. The generalized dynamic wake model was used to obtain the self-induced velocity distribution, whereas the influence-induced velocity field was computed using Beddoes’s generalized wake model. The results of the combined inflow model were compared against free-vortex wake simulations of a twin-rotor system in edgewise flight. Furthermore, the study examined the effects of tip-to-tip separation distances and freestream orientation angles on overall system performance in terms of thrust and power ratios. The comparison indicated that the results of the proposed model agreed within around 5% with the free-vortex wake analysis over all operating conditions. The computational time of the combined inflow model was two to three orders of magnitude lower than the free-vortex wake approach, depending on the code architecture and domain discretization. The analysis shows that the proposed approach is adequate to model primary aerodynamic interference effects in multirotor systems operating at advance ratios greater than or equal to 0.15.