Visualizing vortex clusters in the wake of a high-speed train

Evolution Surfaces for Spatiotemporal Visualization of Vortex Features

“…The complete processing pipeline is given in Fig. 2, which expands on preliminary work with these surfaces [27]. A. Vortex Detection Despite the prominence and importance of vortices to flow dynamics, there is no universal definition for how to mathematically detect them [8,9,28,29].…”

Visualizing three-dimensional vortex shedding through evolution surface clusters

“…While this technique provides a static image for comparative tasks, chronovolumes suffer from occlusion at higher temporal resolutions or if multiple features share the same location making them ill-suited for ensemble visualization. A more simplified representation of vortex movement is a surface tracing the path of the vortex core, this allows multiple vortices to be presented simultaneously at a continuous temporal resolution (Ferrari et al 2020(Ferrari et al , 2017Theisel et al 2005). The low visual complexity of these surface-based representations is suitable for ensemble visualization, but these surfaces have not been previously applied to visualize quasi-periodic vortex shedding.…”

“…First, evolution surfaces must be extracted for the vortices over a given time interval with reduced visual clutter. This step has been detailed in prior work (Ferrari & Hu 2015;Ferrari et al 2020Ferrari et al , 2017 and is thus summarized here. Second, these surfaces must be grouped based on their geometry into a set of clusters.…”

“…While there are a variety of vortex core line detectors (Günther & Theisel 2018), we have used the maxima score based extraction due to its strong relationship to the λ2 domain for verification using isosurfaces. These extracted core lines are then tracked over time through partial shape matching via attribute correspondence (Ferrari et al 2020(Ferrari et al , 2017Reinders et al 2001). The extracted core lines are subdivided into a series of "segments" as illustrated in Fig.…”

“…In prior work we have presented "evolution surfaces," which represent the 4D spatiotemporal behavior of vortices as a surface tracing the motion of their core lines (Ferrari et al 2020(Ferrari et al , 2017. These surfaces produce compact representations of the entire lifetime of the vortex features including any evolution events (e.g., bifurcation, amalgamation (Samtaney et al 1994)) while retaining a low visual complexity.…”