Influence of free-stream turbulence on the boundary layer stability of a wind turbine airfoil and near wake

Abstract Free-stream turbulence (FST) alters the boundary layer of wind turbine blades, changing hydrodynamic stability and near wake. Large-eddy simulations (LES) a blade section with laminar separation bubble for several intensities ( TI ) Reynolds number 10 5 are performed. The effects boundary-layer streaks generated by FST on Tollmien-Schlichting (TS) Kelvin-Helmholtz (KH) instabilities analyzed model based parabolized equations (PSE). Two competing flow identified. spanwise-averaged mean-flow distortion stabilizes primary TS/KH modes increasing . However, this contribution seems dominant only ≥ 8.6%. For lower , spanwise-oscillating caused destabilizes flow, growth rates secondary modal increase streak amplitude. destabilization occurs mainly at spanwise locations negative since inflection point shifts away from wall, enhancing inviscid instabilities. Inflection points in direction formed also contribute to destabilization. structures PSE LES agree. Finally, trailing-edge near-wake coherent more energetic 8.6% due partial stabilization instabilities, delaying turbulent breakdown.