  The characteristics of complex turbulent boundary layers under adverse
pressure gradients are assessed through well-resolved large-eddy simulations
(LES) with the spectral-element code Nek5000. Two wing sections are analysed: a
NACA0012 at 0 degree angle of attack which presents a mild adverse-pressure
gradient (APG) along the chord and a NACA4412 at 5 degree angle of attack with
a strong adverse pressure gradient on the suction side, both profiles at Rec =
400,000. The turbulent statistics show that the mild-APG turbulent boundary
layer (TBL) of the NACA0012 presents a slight deviation of the velocity
fluctuations in the outer region while the strong-APG TBL of the NACA4412 shows
significantly larger fluctuations throughout the wall-normal direction with
respect to the zero-pressure-gradient (ZPG) TBL. These differences are more
substantial in the outer region of the boundary layer. Spectral analyses show
that the APG has a significant impact on the largest scales in the boundary
layer. Our results indicate that the APG increases the turbulent kinetic energy
(TKE) of the TBL, more prominently in the outer layer, and suggest a different
mechanism than the one related to high Re in ZPGs.
