Coupled Flight Dynamics and CFD Simulations of Rotorcraft/Terrain Interactions

摘要

The objective of this study is the investigation of rotorcraft/terrain interactions using Navier-Stokes CFD coupled with a helicopter flight dynamics model. In the coupled simulations, the flight dynamics model is free to move within a computational domain, where the main rotor forces are translated into source terms in the momentum equations of the CFD solution. Simultaneously, the CFD calculates induced velocities that are fed back to the simulation and affect the aero loads in the flight dynamics. The CFD solver models the inflow, ground effect, and interactional aerodynamics in the flight dynamics simulation. An actuator disk model was used to map rotor blade loads into the computational domain. In order to enhance stability and efficiency of the CFD solution, rotor source terms are applied onto vertically stacked planes with a 1D Gaussian distribution. Free flight simulations were performed with full rotorcraft flight dynamics regulated by a dynamic inversion controller. Simulation results are shown for a helicopter hovering in ground effect at different altitudes above the ground, over partial ground, sloped ground and near a wall. An acceleration maneuver was performed in low forward speed conditions where a ground vortex is expected. In order to verify CFD predictions, predicted outwash flows were compared with recently published measurement data and showed reasonable correlation. In ground effect simulations are shown to predict the power reduction when the helicopter flies in close proximity to the terrain.