Development of a variable-incidence-angle vortex generator for surface contaminated wind-turbine blades

Abstract

Wind-turbine blades always undergo several surface contaminations such as erosion or roughness variation during operation. Since these cause an early flow separation on the wind-turbine blades, the performance of the wind-turbine also decrease. The level of the surface roughness of blades continuously varies due to the seasonal environmental changes and the contamination accumulation; flow condition on the wind-turbine blades also continuously changes. The flow control devices, therefore, should be able to properly respond to the changes in flow condition. In this study, we evaluated a new type of the vortex generator called a variable-incidence-angle vortex generator (VIVG), which can adjust an incidence angle thereby appropriately responding to the changes in the flow condition. In order to confirm the flow control performance of the developed VIVG, we also designed an experimental airfoil model; the airfoil cross section is DU97-W-300, which was used in NREL 5MW wind-turbine blades. The sandpaper with a grit level of P80 (non-dimensional surface roughness level k/c = 5.03x10(-4)) was chosen to emulate the surface contamination of the wind-turbine blade. We investigated the effect of the incidence angles of the VIVG for surface contaminations through the wind-tunnel test. The VIVG could provide the most appropriate incidence angle with respect to the level of the surface contamination and the angles of attack of the model. These clearly show that the developed VIVG in this study can provide effective ways to overcome surface contaminations in operation.