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

Abstract

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 (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 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.