Validations of Rotor Load Analysis Using Flexible Multibody Dynamics with Multiple Wake Panels for Low-Speed Flights

Abstract

Rotor load predictions of the UH-60A helicopter in low-speed flights are validated using nonlinear flexible multibody dynamic analyses with multiple wake panels. A nonlinear flexible multibody dynamic analysis code, DYMORE II, is used for predicting the blade section airloads and structural loads of the UH-60A rotor in low-speed forward and descending flights at the advance ratio of 0.15. The freewake model with multiple wake panels is integrated implicitly into DYMORE II to represent effectively the BVI (blade–vortex interaction) phenomenon of the rotor in low-speed flights. For both low-speed forward and descending flights, the multiple wake panel and single wake panel models both validate the blade section normal forces (or lift forces) moderately or well with the flight test data; however, they predict the blade section pitching moments moderately or poorly. For blade structural loads, two analyses using the multiple wake panel and single wake panel models validate the oscillatory flap bending moments moderately for both flight conditions; however, they correlate the oscillatory lead–lag bending moments poorly with the measured data. In addition, the multiple wake panel and single wake panel models both validate the oscillatory torsion moment well for the low-speed descending flight; but they predict it moderately or poorly for the low-speed forward flight. Through the present study, the analyses using multiple wake panels show better predictions of the rotor loads in low-speed flights as compared to the results with a single wake panel, along with efficient and reasonable computation resource and time.