Delayed detached eddy simulation of the wind turbine airfoil S809 for angles of attack up to 90 degrees

Delayed detached eddy simulation (DDES) based on Spalart-Allmaras one-equation turbulence model is conducted to investigate the flows over the three-dimensional (3D) S809 airfoil at a wide range of angles of attack (AOA) from 0° to 90°. In addition to 3D DDES, for comparison purpose, simulations of 2D steady Reynolds-Averaged Navier-Stokes (2D RANS), 2D unsteady Reynolds-Averaged Navier-Stokes (2D URANS) and 3D URANS are also performed. The results obtained from 3D DDES have an excellent agreement with the experiment at all the studied AOAs. The 2D URANS and 3D URANS have a similar performance, both overpredicting the lift and drag coefficients at all the separated AOAs. The 2D RANS overpredicts the lift and drag coefficients when AOA is between the stall AOA and about 30°, and underpredicts beyond 30°. In the attached flow regime at low AOAs, all the simulations can give consistent results in agreement with experiment. Visualization of flows shows that 3D DDES can reproduce the realistic 3D flow structures that are incorrectly revealed in the 3D URANS simulations. It is demonstrated that the DDES mode outperforms the RANS/URANS mode in the overall predictions of wind turbine airfoil flows at AOAs from 0° to 90°.