Effect of yaw on aerodynamic performance of co-planar multi-rotor wind turbines

Abstract

The multi-rotors wind turbine (MRWT) is a promising alternative to the large-scale single-rotor wind turbine for reductions of cost. Noteworthy, yawing in MRWT is a key engineering issue for its significant effect on the output power and structural aerodynamics. In this study, the aerodynamics and near wake dynamics of a co-planar multi-rotor wind turbine with different yaw modes (self-yaw and whole yaw) are investigated through the ALM-LES method. Comparatively, the effects of the blade tip vortex interactions between adjacent rotors on both the torque and thrust of the rotor and the mixing and recovery of the wake are taken into account as well. The numerical results show that the wake vortices of the two rotors attract and approach each other under self-yaw conditions. In the whole yaw conditions, the blade tip vortex in the region between rotors appears to neutralize each other due to the opposite direction of self-rotation of the wake vortex. Moreover, the wake enhancement effect increases the inlet velocity on the blades and has almost no effect on the lift-to-drag ratio. Nevertheless, the direct influence of the blade tip vortex increases the lift-to-drag ratio and decreases the inlet velocity at the location of 0.8∼1R on the front rotor blades in the self-yaw condition; it also decreases both the lift-to-drag ratio and the inlet velocity on the rear rotor blades. Furthermore, under the whole yaw condition, such a direct influence decreases the lift-to-drag ratio on the blades of the two rotors at the location of 0.8∼1R, and increases the average inlet velocity. Conclusively, among the investigated two yaw conditions, a 15°yaw angle shows a more considerable effect on the aerodynamics MRWT than the interaction of blade tip vortex.