Performance of the NREL 5826 airfoil at low to moderate Reynolds numbers-A reference experiment for CFD models

Lift, drag and surface pressure measurements are performed on a wing section of the NREL 5826 wind turbine airfoil at eight Reynolds numbers ranging from 0.5 x 10(5) to 6.0 x 10(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 Re < 0.7 x 10(5), related to the presence of laminar separation bubbles (LSBs) on the suction side of the profile. For Re >= 0.7 x 10(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 gamma-Re-theta transition model accurately predict lift and drag coefficients as long as the flow is fairly attached. Further, the gamma - Re-theta model simulations are observed to predict the location and average size of the LSBs in this region. (C) 2018 Elsevier Masson SAS. All rights reserved.