Structure of vorticity and turbulence fields in a separated flow around a finite wing: Analysis using direct numerical simulation

We investigate the spatial evolution of vorticity dynamics and production mechanisms of turbulent kinetic energy around a finite NACA 0018 wing with a square wingtip profile at Rec = 104 and a 10 degrees angle of attack with the aid of direct numerical simulation. The analysis focuses on the highly inhomogeneous region around the tip and the near wake; this region is highly convoluted, strongly three-dimensional, and far from being self-similar. The flow separates close to the leading edge creating a large, open recirculation zone around the central part of the wing. In the proximity of the tip, the flow remains attached but another smaller recirculation zone forms closer to the trailing edge; this zone strongly affects the development of the main wing tip vortex. The early formation mechanisms of three vortices close to the leading edge are elucidated and discussed. More specifically, we analyze the role of vortex stretching/compression and tilting, and how it affects the strength of each vortex as it approaches the trailing edge. We find that the three-dimensional flow separation at the sharp tip close to the trailing edge plays an important role in the subsequent vortical flow development on the suction side. The production of turbulent kinetic energy and Reynolds stresses is also investigated and discussed in conjunction with the identified vortex patterns. The detailed analysis of the mechanisms that sustain vorticity and turbulent kinetic energy improves our understanding of these highly three-dimensional, nonequilibrium flows, and it can lead to better actuation methods to manipulate these flows.