Numerical Simulation of Aerodynamic Interference between Multiple Rotors in Horizontal Cruise Flight

Multiple rotor configurations are adopted in most electric vertical take-off and landing (eVTOL) aircraft concepts for urban air mobility. As a concept of high-speed eVTOL, this paper investigates a “Lift and Cruise” type configuration composed of multiple rotors and a thrust propeller to achieve a high-speed and compact rotorcraft design. This rotorcraft is designed for cruising flight with the fuselage and rotors in a horizontal attitude. The impact of aerodynamic interference between the rotors on the aerodynamic performance is investigated using high-fidelity CFD simulations. In the present study, the computational model consists only of the isolated quadrotors without the fuselage and the thrust propeller, and the influence of the vertical position of the rear rotors on the aerodynamics and flow field is explored. Two flight speeds, medium/high advance ratios of 0.297 and 0.594, are simulated. Different interactional effects depending on the rotor advance ratio are observed. At the high advance ratio condition, the aerodynamic performances of the rear rotors are slightly changed and obtain the highest effective lift-to-drag ratio despite at the same vertical position of the front rotor. The numerical results suggest that high advance ratio rotors can potentially reduce the interference effect between rotors.