Wind Farm Performance Improvement by Using Wake Transport

Wake shielding on wind farms substantially reduces the efficiency of downstream wind turbines due to the interaction with the energy-depleted wakes from upwind turbines. This research considers a method to mitigate the wake shielding effect by tilting the turbine axes upward producing a download that causes streamwise vorticity so that the energy depleted wakes transport upward alleviating shielding, and pumping more energetic fluid into downstream turbines. The wake steering effect for tipped turbines is verified and the degree of effectiveness is assessed. The simulations utilize a specially developed free-wake method, appropriate for wind turbines, that utilizes constant circulation contours with a large degree of downwind vorticity diffusion. This approach has been implemented to capture the natural behavior of multi-filament multi-blade complex turbine wakes, with relatively short simulation time. Detailed turbine wake structure is studied to obtain insights into how to strengthen the steering effect. Besides a single rotor tilted turbine, two unconventional turbine configurations, each consisting of two overlapping counter-rotating rotors, have been studied to assess their potential to increase the upward transport of their wakes. The three turbine configurations are compared along with a discussion of potential advantages and challenges, and additional research goals going forward. Initial promising results from preliminary wind tunnel studies of the wake of a single tipped turbine are briefly described.