A Computational Investigation of Canted Side-by-side Rotors In Ground Effect

This study investigates the interactional aerodynamics of canted side-by-side rotors hovering in ground effect. The 5.5 ft diameter 3-bladed fixed-pitched rotors are simulated using CFD at a targeted 5 lb/ft2 disk loading. Simulations are performed using the commercial Navier Stokes solver AcuSolve® with a delayed detached eddy simulation (DDES) model. Side-by-side rotors are simulated at a height above the ground equal to one rotor radius (z/R = 1.0) and with 2.5R hub-hub spacing. In addition to an uncanted case, side-by-side rotors are simulated in ground effect (IGE) with 10° differential lateral cant, 10° inwards cant, and 10° outwards cant. Between the uncanted side-by-side rotors IGE, a highly turbulent mixing region is identified where the wakes of each rotor collide and fountain up. As blades traverse the highly turbulent flow, strong vibratory loading is induced and a thrust loss is observed over the outboard blade sections. The associated unsteady vertical loading for uncanted, laterally canted, and canted outwards rotors is similar, ranging from 10% - 16% peak-to-peak whereas canted inwards rotors show increased vibratory loading at 22% peak-to-peak. Integrated thrust for uncanted rotors IGE is 4.3% more than if out of ground effect (OGE), though when laterally canted or canted outwards, thrust generation is reduced to within 1% of isolated OGE rotors. Canted inwards rotors produce even less thrust, generating 15.2% less thrust than isolated OGE rotors. Overall, canting side-by-side rotors IGE incurs thrust production and vibration penalties. If canting is required for improved control authority, laterally canted rotors generate the most thrust while canted outwards rotors generate the least vibratory loading.