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

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_105 to 6:0_105. Alongside with the measurements two types of Reynolds averaged Navier-Stokes (RANS) simulations are performed, one of which in- cludes a laminar to turbulent transition model. The lift and drag characteristics are observed to be dominated by low Reynolds number e_ects for Re < 0:7_105, related to the presence of laminar separation bubbles (LSBs) on the suction side of the pro_le. For Re _ 0:7_105 the airfoil's performance is rather independent of the Re-number for the present free stream turbulence intensities, while sig- ni_cantly higher peak lift is measured than in earlier experiments on the same airfoil. At high angles of attack, strong three-dimensional spanwise surface ow distribution reminiscent of a single stall cell is observed. The RANS simulations in a two-dimensional domain including the Langtry-Menter ����� Re_ transition model accurately predict lift and drag coe_cients as long as the ow is fairly attached. Further, the ����� Re_ model simulations are observed to predict the location and average size of the LSBs in this region.