Coupled CFD-Simulation of a Helicopter in Free-Flight Trim

This paper presents a feasibility study for trimming the computational fluid dynamics model of a complete helicopter to free flight conditions by coupling it to a comprehensive rotor code. Rotor controls and fuselage pitch and yaw attitude are set as free trim variables to realize load equilibrium for a steady cruise flight condition. Through weak fluid-structure coupling aeroelastic effects at the main rotor are accounted for, while fuselage loads are transferred in form of temporal mean values. Aerodynamic simulation of the Eurocopter EC145 helicopter fuselage is characterized by separated and partially irregular flow, and interference between rotor and fuselage renders flight mechanics rich in non-linearity. Special attention therefore is given to the convergence rate, precision and stability of the expanded trim scheme. The work is motivated by an expected gain in the prediction capability for helicopter performance and interactional loads from exploiting high-fidelity aerodynamic modeling simultaneously for flight attitude prediction.