The flatback airfoil effect in the inboard region of large wind turbine blade has been investigated by numerical analysis. Complicated flow phenomena in the wind turbine blade were captured by Reynolds-averaged Navier-Stokes flow simulation (RANS) with SST (Shear Stress Transport) turbulence model.
The inboard region of the blade without the flatback airfoils is dominated by the separated vortex. The separated vortex starts to be formed near the blade mid-chord. The separated vortex core is generated by the large pressure difference in the blade inboard trailing edge region. The separated vortex grows nearly in the outboard direction, which is so-called secondary flow on the blade surface. The flatback airfoils are designed, and applied to the wind turbine inboard region. The scale of the separated vortex can be decreased, and the blade performance enhanced up to nearly 6% in the flatback airfoil region. However, the blade with large wake thickness due to the flatback airfoil has a negative impact on the aerodynamic noise.
Regardless of the flatback airfoils, the tip vortex core of the outboard region is formed on the suction surface leading edge, and strongly rolled-up by the pressure surface boundary layers due to the large pressure difference between the suction surface and the pressure surface in the blade tip region. This remarkably strong tip vortex develops downstream, and rakes up the blade trailing edge boundary layer with low energy.