On the structure of Vorticity and Turbulence Fields in a separated flow around a finite wing; analysis using Direct Numerical Simulation

TL;DR

This study uses Direct Numerical Simulation to analyze vorticity and turbulence structures around a finite wing, revealing complex flow separation, vortex formation, and energy production mechanisms in three-dimensional, non-equilibrium flow fields.

Contribution

It provides detailed insights into vortex dynamics and turbulence production around a finite wing, highlighting the influence of flow separation and vortex interactions near the wingtip.

Findings

Flow separation near the leading edge influences vortex formation.

Three vortices develop close to the leading edge with distinct mechanisms.

Turbulent kinetic energy production is linked to vortex stretching and tilting.

Abstract

We investigate the spatial distributions and production mechanisms of vorticity and turbulent kinetic energy around a finite NACA 0018 wing with square wingtip profile at $Re_c=10^4$ and $10^{\circ}$ angle of attack with the aid of Direct Numerical Simulation (DNS). 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 main wing tip vortex. The early formation mechanisms of three vortices close to the leading edge are elucidated and discussed. More specifically, we analyse 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 leading edge plays an important role on 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, non-equilibrium flows and can lead to better actuation methods to manipulate these flows.