Multi Scale Color Coding of Fluid Flow Mixing Indicators along Integration Lines

This paper presents a multi scale color coding technique which enhances the visualization of scalar fields along integration lines in vector fields. In particular, this multi scale technique enables one to see detailed variations in selected small ranges of the scalar field while at the same time allowing one to observe the entire range of values of the scalar field. This type of visualization, observing small variations as well as the entire range of values, is usually not possible with uniform color coding. This multi scale approach, which is linear within each division of the scale (piecewise linear), is a general visualization technique that can be applied to many different scalar fields of interest. As an example, in this paper we apply it to the visualization of fluid flow mixing indicators along pathlines in computational fluid dynamics (CFD) simulations. Pathlines are the trajectories of fluid particles over time in the CFD simulations, and applying multi scale color coding on the pathlines brings out quantities of interest in the flow such as curvature, torsion and specific measure of length generation, which are indicators of the degree of mixing in the fluid system. In contrast to uniform color coding, this multi scale scheme can display small variations in the mixing indicators and still show the entire range of values of these indicators. In this paper, the mixing indicators are computed and displayed only along line structures (pathlines) in the flow field rather than at all points in the flow