Computational Investigation of Multi-Rotor Interactional Aerodynamics with Hub Lateral and Longitudinal Canting

This study investigates the interactional aerodynamics for laterally and longitudinally canted two-rotor systems with a front rotor and an aft rotor aligned with the flow. The 5.5-ft-diameter, three-bladed fixed-pitched rotors are simulated using computational fluid dynamics at a targeted 5  lb/ft² disk loading and 30 kt edgewise freestream. Simulations are performed using the commercial Navier—Stokes solver AcuSolve with a detached eddy simulation model. In addition to an uncanted case, two laterally canted cases (10° advancing sides up and 10° advancing sides down) as well as two longitudinally canted cases (10° inward and 10° outward) are simulated. Aft rotor performance is compared to isolated rotors operating at the same revolutions per minute, speed, and shaft tilt angle in order to quantify the effect of rotor–rotor aerodynamic interaction. For all configurations, the aft rotors experience a lift deficit at the front of the rotor disk, which also results in a nose-down pitching moment relative to an isolated rotor. The lift deficit for the uncanted rotor was around 15%. Lateral canting only slightly increases the lift deficit (to 16–18%) but also produces 28–38% change in roll moments. Change in aft rotor nose-up pitching moments for the uncanted and laterally canted rotors were in the 55–64% range. Longitudinal canting produces larger changes in the magnitude of the lift deficit and pitching moment, but has minimal effect on roll moments. In particular, canting inward results in a lift deficit as high as 21% and a 94% change in pitching moment. Canting outward, on the other hand, reduces the aft rotor lift deficit to 11% and the pitching moment change to 19%. The paper explains the changes in the flowfield and the underlying physics for the different cases in detail.