Analysing rotorcraft vortex encounter methods with a lattice-boltzmann method based gpu framework

This paper investigates the modeling approach for the simulation of a rotorcraft encountering a vortex or a wake trailing from a solid structure. The flow field surrounding the rotorcraft, including the inflow into the main rotor, was computed using a computationally efficient Lattice-Boltzmann method (LBM). The fluid solver was enhanced for GPU computing and an interface was included to exchange inflow and thrust between the flow and flight dynamics simulations. The interaction with the vortex and the wake was modeled by a superposition method and by a fully-coupled model. The superposition added the vortex/wake induced velocities on the inflow and the fully-coupled method computes a two-way coupling between the flow field aerodynamics and the rotorcraft flight dynamics. Representative vortices for wind turbines and a wing tip vortex of a B757 were used. The wake was computed by placing a generic platform structure in a free flow. The helicopter response for both modeling approaches was compared. The results showed that the superposition model predicts a stronger rotorcraft response than the fully-coupled model for the vortex encounters. Two flight speeds, 10 m/s and 50 m/s, were investigated, and it was found that the differences decreased with increasing forward flight speed. For the wake encounter with the trailed air wake from a solid structure the full coupling predicted a more severe response than the superposition method. It was concluded that for the vortex encounters the superposition can serve as the estimation of a worst-case scenario for rotorcraft flight in wind farms.