Distinct scale-dependent flow control mechanisms of passive vortex generators on the NREL Phase VI and IEA 15MW blades

While passive vortex generators are widely deployed on wind turbines, their interaction with three-dimensional rotational flows across disparate turbine scales remains insufficiently understood. This study addresses this gap by comparing the aerodynamic responses of the small-scale NREL Phase VI and the large-scale IEA 15 MW blades equipped with vortex generators. Fully-resolved Reynolds-Averaged Navier-Stokes simulations are performed, employing a compressible solver for the 15 MW case to rigorously account for high tip-speed Mach number effects. The results reveal fundamentally distinct, scale-dependent flow control mechanisms. For the rotation-dominated NREL Phase VI blade, vortex generators disrupt the beneficial centrifugal pumping in the transition region, causing a 3.96% power penalty at 11 m/s. Conversely, the inboard flow of the IEA 15 MW blade resembles quasi-two-dimensional bluff-body separation. In this separation-dominated regime, vortex generators effectively mitigate massive separation on thick airfoils, yielding a maximum power increase of 7.86% at 17 m/s. However, a critical failure limit is identified at extreme wind speeds, where submerged vortex generators degenerate into parasitic drag devices. These findings suggest that flow control strategies must be tailored to the specific aerodynamic dominance of the turbine scale, providing crucial physical insights for the aerodynamic design and optimization of next-generation gigantic turbines.