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. γ flight path angle, deg θ aircraft pitch attitude, deg μ advance ratio σ rotor solidity φ aircraft roll angle, deg ψ aircraft yaw angle, deg rotor rotational frequency, rpm
CFD/CSD MethodologyThis section describes the CFD and CSD modeling including a brief description of the codes and the fluid/structure coupling interface. The RCAS comprehensive rotorcraft analysis code is used for the structural calculations, whereas the OVERFLOW-2 code is used for the flow calculations. These two codes are coupled using file i/o in both loosely coupled manner for steady-state calculations and tightly coupled manner for time-accurate calculations.
RCAS UH-60A modelingThe RCAS is a comprehensive multidisciplinary, computer software system for predicting rotorcraft aerodynamics, performance, stability and control, aeroelastic stability, loads, and vibration for a wide range of complex rotorcraft configurations operating in hover, forward flight, and in maneuvering conditions. RCAS was developed by the Aeroflightdynamics Directorate, U.S. Army Aviation and Missile Research, Development, and Engineering Center (RDECOM), to provide 032007-2
