Validation of a RANS CFD Model for a S833 Wind Turbine Airfoil with a Trailing Edge Flap Using Oil Visualization and Pressure Taps

The aerodynamics of a small wind turbine blade was captured using a γ - Reθ k - ω SST transitional turbulence model tuned with production limiter coefficients at a Reynolds number of 1.70×10^5. The CFD simulations were validated against wind tunnel experiments that included airfoil pressure tap measurements and surface oil flow visualization (SOFV) to capture the flow field. The uniqueness of this blade included a trailing edge flap that was 20% of the chord controlled using a servomotor. The test matrix included angle of attack (AOA) between 1° and 7° with flap angles of 10° in the upward and downward position. Two locations were always observed on the airfoil: a leading edge region of high shear, a midsection of flow separation. Within the flow separation section, two distinct regions existed: a complete detachment of flow from the airfoil surface creating a stagnation region which was followed by a reverse flow region. A third location of flow reattachment near the trailing edge was observed for all cases excluding a downward angled trailing edge flap. The utilization of the flap resulted in changes to the size of the separation zone and the movement of the separation zone along the chord. The numerical skin friction coefficient, oil residue profiles from the SOFV and pressure tap measurements all showed onset of separation locations on the chord within 10%. The CFD model also predicted the coefficient of pressure across the chord of the airfoil within 10% in comparison to the experimental measurements.