The flow past a flatback airfoil with flow control devices: benchmarking numerical simulations against wind tunnel data

As wind turbines grow larger, the use of flatback airfoils has become standard practice for the root region of the blades. Flatback profiles provide higher lift and reduced sensitivity to soiling at significantly higher drag values. A number of flow control devices have been proposed to improve the performance of flatback profiles. In the present study, the flow past a flatback airfoil at a chord Reynolds number of 1.5×106 with and without trailing edge flow control devices is considered. Two different numerical approaches are applied, unsteady Reynolds-Averaged Navier Stokes (RANS) simulations and detached eddy simulations (DES). The computational predictions are compared against wind tunnel measurements to assess the suitability of each method. The effect of each flow control device on the flow is examined based on the DES results on the finer mesh. Results agree well with the experimental findings and show that a newly proposed flap device outperforms traditional solutions for flatback airfoils. In terms of numerical modelling, the more expensive DES approach is more suitable if the wake frequencies are of interest, but the simplest 2D RANS simulations can provide acceptable load predictions.

The flow past a flatback airfoil with flow control devices: Benchmarking numerical simulations against wind tunnel data

As wind turbines grow larger, the use of flatback airfoils has become standard practice for the root region of the blades. Flatback profiles provide higher lift and reduced sensitivity to soiling at significantly higher drag values. A number of flow control devices has been proposed to improve the performance of flatback profiles. In the present study, the flow past a flatback airfoil at a chord Reynolds number of 1.5 × 106 with and without trailing edge flow control devices is considered. Two different numerical approaches are applied, Unsteady Reynolds Averaged Navier Stokes (RANS) simulations and Detached Eddy Simulations (DES). The computational predictions are compared to wind tunnel measurements to assess the suitability of each method. The effect of each flow control device on the flow is examined based on the DES results on the finer mesh. Results agree well with the experimental findings and show that a newly proposed flap device outperforms traditional solutions for flatback airfoils. In terms of numerical modelling, the more expensive DES approach is more suitable if the wake frequencies are of interest, but the simplest 2D RANS simulations can provide acceptable load predictions.

Investigation of Flatback Airfoil Effect in the Wind Turbine Blade

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.