Investigation of the Delay in Flow Separation on the Wind Turbine Blade by Combining the Slat and Longitudinal Slot Effects

This study is conducted on the effects of leading-edge slat and longitudinal slots in delaying the flow separation. The case study is a conventional wind turbine airfoil and four different types of slots have been investigated. The aerodynamic simulation is performed on the basis of a steady state air flow over the NREL S809 airfoil and the solution is obtained numerically using the structured grids. The results show that at Reynolds number of 1e+6 and an angle of attack equal to 16.22o, with the addition of leading-edge slat, the separation is delayed from x / c = 0.47 to x / c = 0.67 and the lift coefficient is increased by 64% (from 1.17 to 1.92). So, by adding several types of longitudinal slots, it is observed that a sinusoidal slot with 45o of phase lead, has the best performance.Through studying the values of the aperture, depth and location of the sinusoidal slot, the best values of these parameters were obtained as follows: 3% of the chord for the aperture value, 0.5% of the chord for the depth value and 0.85 for the x/c ratio. By completely removing the flow separation, at the mentioned Reynolds number with the same angle of attack, the lift coefficient has 117% increase, reaching the value of 2.54.