Improved RANS methodology to account for flow separation on rough blades

The RANS inaccuracy in predicting flow separation becomes relevant in thick-modern blades, especially once they get dirt or eroded. The literature has tackled the problem by modifying the coefficient a 1 in the k − ω − SST turbulence model without considering its dependency on the adverse pressure gradient condition. This study aims to assess the mentioned dependency by estimating a 1 per blade side and angle of attack. Pressure-coefficient measurements for 18 %, 25 %, and 30 % thick airfoils in clean-inflow conditions at a Reynolds number based on chord of 3 × 10 6 are considered in the estimation. Hence, a unique variation of a 1 is obtained per each airfoil, justifying the need to adapt a 1 locally within the OpenFOAM code. This modification considerably improves the flow separation prediction with respect to the standard a 1 value and the f b method. As a result, the C L error is reduced by 8 %, whereas a certain C D error remains for all the RANS solutions. Finally, an aeroelastic model of a 4.5 MW wind turbine reveals that the non-corrected RANS solution causes an overshoot of power and loads near rated power, whereas the corrected RANS replicates the shape of the power and loads curves. Consequently, the suggested methodology can be used to search for the required a 1 relation to local flow conditions.