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 = 5.03×10-4) was chosen to emulate the surface contamination of the windturbine 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.
The size of wind turbine blade has been continuously increased. Large-scale wind turbine blades induce loud noise,
vibration; and maintenance difficulty is also increased. It causes the eventual increases of the cost of energy. The
vibration of wind turbine blade is caused by several reasons such as a blade rotation, tower shadow, wind shear, and flow
separation of a wind turbine blade. This wind speed variation changes in local angle of attack of the blades and create the
vibration. The variation of local angle of attack influences the lift coefficient and causes the large change of the lift. In
this study, we focus on the lift coefficient control using a flow control device to reduce the vibration. DU35-A15 airfoil
was employed as baseline model. A plasma actuator was installed to generate the upwind jet in order to control the lift
coefficient. Wind tunnel experiment was performed to demonstrate of the performance of the plasma actuator. The
results show the plasma actuator can induce the flow separation compared with the baseline model. In addition, the
actuator can delay the flow separation depending on the input AC frequency with the same actuator configuration.