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= f t2
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%
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.