About the Impact of Wind Turbine Blade Tip Vortices on Helicopter Rotor Trim and Rotor Blade Motion

With increasing numbers of large wind turbines on-shore and off-shore, interactions of their wake with helicopters become a subject worth investigating. In this paper the wake is modeled as a tip vortex helix with a vortex strength estimated from the wind turbine thrust. Helicopter rotors of different size and hub layout are subjected to the wake and the collective and cyclic control inputs required to keep the trim are compared to the maximum available control range of the rotorcraft. In addition the blade flapping response due to the vortex influence without pilot action is computed and compared to maximum allowed flapping angles. It is found that typical on-shore wind turbines could be a hazard for ultralight helicopters, but not for larger helicopters. Large off-shore wind turbines, however, could even be a danger for small helicopters that may be used for maintenance. In addition the results are compared to fixed-wing wake vortex interaction with a helicopter as given in the literature