A Systematic CFD-Based Examination of Rotor-Rotor Separation Effects on Interactional Aerodynamics for Large eVTOL Aircraft

This study systematically investigates the aerodynamic interactions of a two-rotor system with a front rotor and an aft rotor aligned with the direction of flow. The rotors are 5.5 ft diameter fixed-pitch rotors operating at around 12 lb/ ft2 disk loading, representative of large eVTOL aircraft. Fluid flow is simulated using the commercial Navier-Stokes solver, AcuSolve, with a Detached Eddy Simulation (DES) model. Simulations were performed at 40 kts edgewise flight for 9 cases corresponding to three values of longitudinal hub-hub separation (2.5R, 3R, 3.5R) and three values of vertical offset (0, 0.25R, 0.5R). Aft rotor performance was compared to an isolated rotor operating in the same conditions in order to quantify the effects of rotor-rotor interaction. For the cases where the aft rotor is closest to the front rotor (2.5R longitudinal offset, zero vertical offset), the aft rotor produced 8.4% less thrust, and required 13.4 percent higher torque than a rotor in isolation. When vertical rotor separation was increased, interactional aerodynamic effects decreased. For a 2.5R longitudinal offset, increasing the vertical offset to 0.5R decreased the lift deficit to 4.6% and the torque penalty to 6.8%. Increasing the longitudinal offset to 3.5R (while keeping the vertical offset at zero) also reduced interactional aerodynamic effects, but reductions in lift deficit and torque penalty were smaller than those observed with 0.5R vertical offset.