| dc.description.abstract | The impact of freestream turbulence (FST) generated by an active turbulence grid (ATG) on the aerodynamic performance and behavior of a wingtip vortex in the near wake of a NACA-4412 airfoil was investigated using various experimental methods. The experiments were conducted in a large-scale closed-loop wind tunnel at four different FST conditions (Ti = 0.2%, Ti = 3%, Ti = 8%, and Ti = 13%), at a chord-based Reynolds number Re_c = 140 000 and for an angle of attack of 5°. Force balance measurements were performed to characterize the wing performance under each FST condition. Increasing FST was observed to slightly increase the maximum lift and delay the stall. Stereoscopic particle image velocimetry (SPIV) measurements were conducted at a distance of two wing chords downstream of the trailing edge. The results showed that FST enhanced the distribution of energy transport in all directions, resulting in an increased in vortex axis meandering. After conditionally averaging the fields based on the instantaneous vortex center, the increase in FST decreased the vortex strength and increased vortex diffusion. The maximum azimuthal velocity decreased with higher FST, while the core radius of the vortex shifted towards larger radii. FST also increased the meandering amplitude and the energy contained in the long-wavelength meandering motion, at the expense of the short-wavelength meandering motion. Furthermore, digital image correlation (DIC) analysis on on the displacement of the wingtip revealed a potential correlation between the wing deflection and the meandering motion. | |
