A new method for simulating multiple wind turbine wakes under yawed conditions

Counter-rotating vortices generated in wake steering not only deform the turbine wake, but also can make the wake trajectory of a non-yawed downwind turbine deviate from its rotor centerline, referred to as "secondary wake steering" phenomenon. Recent studies have also shown that the vortex interactions become clearer when the wind farm includes multiple turbines. However, in the common analytical models for active yaw control, the effects of these vortices are not considered. Evidently, this omission can lead to a decrease in model prediction accuracy. To compensate for it, a new analytical wind farm model is proposed. It adopts a physical-based momentum conserving wake superposition method to deal with the interaction of multiple wakes, in which, not only combining the streamwise velocity deficit of each individual yawed wind turbine, but also the transverse velocity from different wakes. Additionally, an "added yaw angle" is defined for a downwind turbine operating in upstream yawed turbine wakes, to reflect the change in local wind direction it perceives. For validation purposes, the LES wind field obtained from the SOWFA tool is used as a reference, and the newly proposed model is found to agree well with LES results and outperforms the representative conventional analytical model in almost all test cases. The new model can successfully reproduce the "secondary wake steering" phenomenon in the overlapped wake, and provides significant improvements in predicting power production of wind turbines.