Numerical analysis of quad-rotor aerodynamic and aeroacoustic performance with automated trimming algorithm

The current work introduces a novel and affordable Computational Fluid Dynamics (CFD) methodology for the purpose of assessing the aerodynamic and aero-acoustic performance of multi-rotor systems under trimmed flight conditions. The approach couples a simple Proportional-Integral (P-I) based trim algorithm and steady state CFD solver to automate the process of determining the set of control variables that results in balanced flight conditions. The methodology’s low computational cost is primarily achieved by including the rotors’ effects on the flow field with actuator models. A partial validation of the rotor modeling approach in isolated hover conditions reveals slight discrepancies in the computed aerodynamic loads but good agreement with experimental results in terms of the prediction of tonal noise. The CFD procedure is subsequently applied to evaluate a quad-rotor Unmanned Aerial Vehicle’s (UAV) performance in varied flight scenarios. The obtained results demonstrate that this automated approach effectively predicts quad-rotor performance trends, aligning with previously published data. Key findings include the fact that a hybrid over-mounted fore rotor and under-mounted aft rotor configuration negatively affects forward flight performance, and that the airframe’s geometry and distribution around the Center of Gravity can have a significant impact on flight characteristics. Finally, comparisons between the automated trim procedure and manually imposed trim parameters in transient aero-acoustic simulations reveal a more accurate approximation of trim when using the automated method. The comparison additionally highlights the importance of simulating multi-rotor systems in physically representative flight conditions as notable differences in the UAV’s acoustic footprint are observed between cases.