New visualization method for vortex structure in turbulence by lambda2 and vortex filaments

In this paper, a new visualization method for vortex structure is presented. Several widely used techniques for local vortex visualization in turbulent flows are reviewed and compared. Among these techniques, lambda2 and Q   method are the most prominent and they are considered to be the best methods in visualizing vortical structures. However, as we illustrate, there are some defects in those iso-surface based methods. They may cause fake vortex breakdown since they can only capture the strong rotation centers and may not reveal the true vortex structure, i.e., the λ2λ2 iso-surface may only represent rotation cores but not necessarily vortex tubes. To better illustrate the real vortical structures and distinguish the vortex, which has a rotation core but vorticity lines can penetrate, from the vortex tubes, which vorticity lines cannot penetrate, we present a new visualization method via a hybrid of lambda2 and vortex filaments. As shown in our examples, the new method enables us to find the accurate vortex structure and well capture the physics.