Experimental investigation of the turbulent boundary-layer footprint on the wake of a wing section

This experimental study examines the downstream wake development influenced by attached turbulent boundary layers under adverse and favorable pressure gradients (APG, FPG) on the suction and pressure sides of a National Advisory Committee for Aeronautics 4412 airfoil. Experiments were performed at a chord-based Reynolds number of Rec=400 000 and angles of attack of 5° and 8°. Surface pressure scans and hot-wire anemometry were used to characterize boundary layer and wake profiles, extending three chord lengths downstream of the trailing edge. The key contributions are: (i) demonstrating a strong memory effect whereby upstream boundary-layer characteristics persist into the very-near- and near-wake; (ii) establishing a unified inner/outer velocity scaling framework that enables direct comparison of boundary-layer and wake profiles; and (iii) identifying distinct suction- vs pressure-side routes to self-similarity driven by the sign of the pressure gradient. Inner scaling of wake velocity profiles using friction velocity and viscous length scale proves valid only within the very-near-wake. In contrast, outer-scaled velocity-defect profiles using the Zagarola–Smits velocity reveal self-similarity on the suction side from the trailing edge across the entire wake region, whereas pressure-side profiles retain significant upstream influence initially, with self-similarity emerging from the near-wake onward. Turbulence analysis via streamwise velocity variance and premultiplied power spectral densities further shows distinct development patterns on the suction and pressure sides of the wake. The APG on the suction side promotes early development of wake-type structures and self-similarity, while the FPG on the pressure side preserves boundary-layer features deeper into the wake. These findings demonstrate how upstream pressure gradients modulate the transition from boundary-layer-dominated to wake-dominated behavior, providing new physical insight into wake development and supporting improved aerodynamic modeling and wake prediction for aeronautical and wind energy applications.