Wing Lift Enhancement from Aft Rotor Induced Suction

This study examines the aerodynamic interactions of rotor-wing units in which lifting rotors are mounted below and
behind a wing. The rotor-wing units are simulated using CFD, and their performance is compared to isolated rotors
and wings in order to understand the interference effects. Simulations are performed using the commercial Navier
Stokes solver, AcuSolve^®, with a delayed detached eddy simulation (DDES) model. Rotor-wing units with three wing
incidence angles (7°, 10° and 13°) as well as three rotor disk loadings (6, 9 and 12 lb/ft²) are considered. By simulating
the flow and comparing the pressure distribution around an isolated wing to one with the rotor installed, the rotor is
seen to introduce a low pressure region that extends over the wing’s top surface. The additional rotor-induced suction
on the top surface of the wing augments wing lift by up to 134%, and provides some stall mitigation at 13° incidence
angle. Suction near the leading edge of rotor-installed wings also counters the nominal wing drag, introducing a net
propulsive force on the wing at all incidence angles considered. On the rotor, downwash induced by the wing’s bound
circulation introduces a rotor thrust deficit up to 10% nominal thrust and torque penalty up to 4% nominal torque.
Despite the rotor performance penalties, interactions between the rotor and wing lead to equivalent lift to drag ratio
improvements ranging from 47% - 52% over a range of wing angles. As disk loading is increased, the rotor-induced
suction strengthens, extending the 66% wing lift increment at 6lb/ft² up to 115% at 12 lb/ft². These results suggest
that the interactional aerodynamics associated with mounting a rotor below and behind a wing can introduce enhanced
system performance over a range of wing angles and rotor loadings.