Loosely coupled multibody dynamics-CFD analysis for a rotor in descending flight

This paper conducts a loose-coupling analysis using the nonlinear flexible multibody dynamics, DYMORE, and the computational fluid dynamics (CFD), KFLOW, for a rotor correlation with the wind tunnel test data in descending flight. The present study investigates the three test cases of the HART II (second Higher-harmonic control Aeroacoustic Rotor Test): baseline (BL), minimum noise (MN), and minimum vibration (MV). The DYMORE/KFLOW coupled analysis uses two different models: an isolated rotor model and a rotor-fuselage model. The coupled analysis results are correlated with both the measured data and the stand-alone DYMORE analysis with the freewake model. Among the predicted sets of results, the coupled analysis using a rotor-fuselage model shows good agreement of the section normal forces and gives reasonable prediction of the trim control angles, against the measured data. As compared with the coupled analysis using an isolated rotor model, the rotor-fuselage model improves the phase of blade elastic torsion deformations in the BL case. In all three test cases, the coupled analyses show improved predictions on the flap bending moment than those by the stand-alone DYMORE analysis, while the inclusion of a fuselage model has only marginal effect on the blade structural loads predictions between the coupled analyses. It is observed that the inclusion of a fuselage model in the coupled analysis induces stronger upwash over the front disk region resulting in a close agreement with the measured data for the vortex positions, especially in the advancing side.