Coupled Flight Dynamics and Computational Fluid Dynamics Simulations of Rotorcraft/Terrain Interactions

Abstract

The objective of this study is the investigation of rotorcraft/terrain interactions using Navier–Stokes computational fluid dynamics 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 computational fluid dynamics solution. Simultaneously, the computational fluid dynamics calculates induced velocities that are fed back to the simulation and affect the aeroloads in the flight dynamics. The computational fluid dynamics solver models the inflow, ground effect, and interactional aerodynamics in the flight dynamics simulation. 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 and sloped ground, and near a wall. A transition into forward-flight maneuver was performed, where a recirculation flow and ground vortex is shown. To verify the computational fluid dynamics predictions, predicted outwash flows were compared with recently published measurement data and showed reasonable correlation. Simulations of ground effect are shown to correlate well with recent experimental measurements of the power reduction of a rotor at constant thrust near a ground plane.