Application of Computational Fluid Dynamics/Computational Structural Dynamics Coupling for Analysis of Rotorcraft Airloads and Blade Loads in Maneuvering Flight

This paper presents coupled calculations of both the airloads and structural loads for the UH-60A main rotor during the UTTAS pull-up maneuver performed under the NASA/Army UH-60A Airloads Program. These calculations were performed using OVERFLOW-2, a computational fluid dynamics (CFD) solver, coupled to the Rotorcraft Comprehensive Analysis System (RCAS), a rotorcraft comprehensive analysis. For time-varying maneuvers, the two codes were tightly coupled and exchanged airloads and structural deflections at every time step. The coupled solution methodology gives improved airload prediction because of the ability to model three-dimensional transonic effects on the advancing blade, stall events on the retreating blade, as well as the aeroelastic deformations. Correlation with data for both the airloads and structural loads is reasonably good. Control load predictions also show good correlation with data, which is a substantial improvement over conventional analyses. A quasisteady loosely coupled approximate solution was also examined and was found to give good airload and structural load predictions, for this relatively slow maneuver.