A 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, 3 bladed fixed pitched rotors are simulated using CFD
at a targeted 5lb/ ft² disk loading and 30 kts. Simulations are performed using the commercial Navier Stokes solver
AcuSolve with a detached eddy simulation (DES) model. In addition to an uncanted case, two laterally canted cases
(10deg advancing sides up and 10deg advancing sides down) as well as two longitudinally canted cases (10deg inward and
10deg outward) are simulated. Aft rotor performance is compared to isolated rotors operating at the same RPM, 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 16-17%) but also produces 28-38% change in roll moments. Change in 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 flow field and the underlying physics for the different cases in detail.