Separation control applied to the turbulent flow around a NACA4412 wing section

We carried out high-resolution large-eddy simulations (LESs) to investigate the effects of several separation-control approaches on a NACA4412 wing section with spanwise width of $L_z = 0.6$ at an angle of attack of $AoA=11^{\circ}$ at a Reynolds number of $Re_c = 200,000$ based on chord length $c$ and free-stream velocity $U_{\infty}$. Two control strategies were considered: (1) steady uniform blowing and/or suction on the suction and/or pressure sides, and (2) periodic control on the suction side. A wide range of control configurations were evaluated in terms of aerodynamic efficiency (i.e., lift-to-drag ratio) and separation delay. Uniform blowing and/or suction effectively delayed flow separation, leading to a lift increase of up to $11\%$, but yielded only marginal improvements in aerodynamic efficiency. In contrast, periodic control neither enhanced separation delay nor improved efficiency. A detailed analysis of the interaction between uniform blowing and/or suction and turbulent boundary layers (TBLs) over the wing was performed, including assessments of (1) integral boundary-layer quantities, (2) turbulence statistics, and (3) power-spectral densities. Significant modifications in Reynolds stresses and spectral characteristics were observed. To the authors' best knowledge, this is the first numerical study utilizing high-resolution LESs to provide comprehensive assessments on separation control.