Visualizing the Evolution and Interaction of Vortices and Shear Layers in Time-Dependent 3D Flow

In this paper, we present a visualization and tracking system for coherent structures. For this purpose, we propose to consider shear stress-the stretching and shear of particles inside a flow-in vortex dynamics. Based on a discussion and comparison of recent methods for computing shear stress, we introduce visualization techniques in order to provide a representation of shear layers according to their physical interpretation. This paper contributes a combination of theory in fluid mechanics and the corresponding visualization: 1) shear layer criteria are assessed according to how well they can be combined with common vortex identification criteria; 2) sheets of maximal shear are introduced as an appropriate visual representation of shear layers; 3) a visualization method is described for simultaneous tracking of vortices and shear layers as well as their interaction; and 4) the relevance of shear layers in vortex dynamics is demonstrated by means of several examples. We have implemented these new techniques in an interactive visualization system for time-dependent 3D flow. The system is used by fluid mechanics experts in their research of shear-vortex interaction.