RANS and DDES simulations of a horizontal-axis wind turbine under stalled flow condition using OpenFOAM

Abstract

This paper presents a numerical study of a horizontal axis wind turbine under stalled flow condition with the tip speed ratio λ=4.17. Both RANS and DDES simulations are performed using OpenFOAM in order to predict the aerodynamic characteristics of the wind turbine rotor. In addition, numerical results are compared with experimental data where a good agreement is achieved. The complex and unsteady root flow characteristics are comprehensively investigated. Numerical result shows that in terms of aerodynamic blade loading, DDES performs much better than RANS in aerodynamic prediction, where the error has been reduced from 20% to 5%. The Strouhal numbers are in the range 0.16≤St≤0.20 for blade sections r/R=0.25, 0.60 and 0.82, indicating two-dimensional bluff body vortex shedding occurs in stall or deep stall conditions. A very low Strouhal number is observed at r/R=0.92 with a value of 0.018. The low value of St corresponds the flow at r/R=0.92 section is in the near post-stall regime, with three-dimensional surface flow typologies, with periodic switching between stalled and unstalled conditions.