Adverse pressure gradient effects on the turbulent boundary layer around a NACA 4412 wing profile

Abstract: The effects of non-equilibrium adverse pressure gradients (APGs) on the turbulent boundary layer (TBL) developing around a NACA 4412 wing profile are studied both experimentally and numerically. The experimental campaign was conducted in the Minimum Turbulence Level (MTL) wind tunnel at KTH. In order to characterize experimentally the TBL, pressure scans and hot-wire anemometry (HWA) measurements are conducted, including two-point HWA correlation measurements in the wall-normal and spanwise directions. Moreover, oil-film interferometry is used as a direct measurement of the skin friction, avoiding the estimation of the friction velocity (critical for scaling of the data) from composite profiles. A thorough analysis of the current data and of existing APG databases show that such estimation may be inadequate for strong adverse pressure gradients (such as the ones occurring around a wing). Lastly, the experimental data acquired is thoroughly cross-validated against the high-fidelity (quasi-DNS), numerical simulations conducted with the spectral-element method Nek5000.