Computational flight path analysis of a helicopter in an offshore wind farm using a lattice-boltzmann method

This paper presents the modeling approach and results of an investigation regarding the severity of rotorcraft operation in an off-shore wind farm. The computational model consists of a highly efficient Lattice-Boltzmann method based fluid solver two-way coupled to the rotorcraft flight mechanics. The existing framework was extended by coupling a pre-computed external flow field to the rotorcraft induced flow computation to account for non-uniform flow outside the computational domain. The resulting framework allows the coupling of a time variant or a time invariant external flow field depending on the investigated scenario. Two different mission scenarios are investigated, that are adopted from operational servicing scenarios in off-shore wind farms. The first scenario investigates flight in the wake of an active wind turbine with varying distances to the wind turbine and varying altitudes for over 100 trajectories. This is done for a wind speed of 11.3 m/s (maximum bound vorticity of the wind turbine blades) and 25 m/s, which is close to the currently allowed maximum operational wind speeds. The second scenario investigates the approach to an inactive wind turbine followed by a 20 seconds hover above the nacelle. This scenario is investigated for wind speeds of 11.3 and 25 m/s as well. In both scenarios the helicopter is modeled as an EC135 type and stability is ensured by a flight controller. The results show that all control inputs are well within limits and no severe positional or angular changes occur during approach or hover. However, simplifications in the modeling approach and non-existent experimental validation data for these or similar operations need to be taken into account before more definite conclusions are drawn for real-world operations within a wind farm.