Physics-Based Modeling of Maneuver Loads for Rotor and Hub Design

A hybrid Navier-Stokes free-wake computational-fluid-dynamics methodology, coupled with a multibody dynamics analysis code, has been applied to the UH-60A rotor to study the loads developed during a severe diving turn maneuver (flight counter 11680) characterized by a mean advance ratio of 0.388 and a mean load factor of 1.48. The helicopter undergoing flight counter 11680 experiences the most severe pitch-link loads and root torsional moments recorded in the NASA/Army UH-60A Airloads Program. The feasibility of a quasi-steady loosely coupled approach for predicting severe maneuver loads was explored for predicting critical aerodynamic and aeroelastic phenomena. The structural model is first validated through measured airloads, which helps in decoupling the physics of structural dynamics and aerodynamics. The blade aeromechanical loads, push-rod loads, and harmonic content of blade structural loads for a rotor revolution characterized by peak load factor (revolution 12) have been examined in detail. The prediction of advancing blade-stall phenomena unique to severe maneuvers and the extensive occurrence of stall are examined using contours plots of sectional airloads and through comparisons of surface pressure values.