Performance of the NREL S826 airfoil at low to moderate Reynolds numbers—A reference experiment for CFD models

Abstract

Abstract Lift, drag and surface pressure measurements are performed on a wing section of the NREL S826 wind turbine airfoil at eight Reynolds numbers ranging from 0 . 5 × 1 0 5 to 6 . 0 × 1 0 5 . Alongside with the measurements two types of Reynolds averaged Navier–Stokes (RANS) simulations are performed, one of which includes a laminar to turbulent transition model. The lift and drag characteristics are observed to be dominated by low Reynolds number effects for R e 0 . 7 × 1 0 5 , related to the presence of laminar separation bubbles (LSBs) on the suction side of the profile. For R e ≥ 0 . 7 × 1 0 5 the airfoil’s performance is rather independent of the Re-number for the present free stream turbulence intensities, while significantly higher peak lift is measured than in earlier experiments on the same airfoil. At high angles of attack, strong three-dimensional spanwise surface flow distribution reminiscent of a single stall cell is observed. The RANS simulations in a two-dimensional domain including the Langtry–Menter γ − R e θ transition model accurately predict lift and drag coefficients as long as the flow is fairly attached. Further, the γ − R e θ model simulations are observed to predict the location and average size of the LSBs in this region.