Application of CFD/CSD Coupling for Analysis of Rotorcraft Airloads and Blade Loads in Maneuvering Flight

This paper presents calculations of both the rotor airloads and structural loads in the UTTAS pull-up maneuver performed under the NASA/Army UH-60A Airloads Program. These calculations were performed using a computational fluid dynamics code, OVERFLOW-2, coupled to a rotorcraft comprehensive analysis, RCAS. For the time-varying maneuver calculations, the two codes were tightly coupled, and exchanged airloads and blade structural deflections at each time step. The coupled solution methodology gives substantial improvement in airloads prediction because of the ability to model three-dimensional transonic effects on the advancing blades, stall events on the retreating blade as well as the inter-dependent blade elastic deformations. Correlation with data for both the airloads and blade structural loads is very good. The use of quasi-steady, loosely coupled solutions to model parts of the maneuver is also examined. It is found that the airloads and structural loads predictions using this approach are almost as good as those with a time-accurate tightly coupled calculation.