Multi-pathline flow visualization using raw PIV images

Flow visualization qualitatively and quantitatively highlights the salient features of fluid flow. One of the oldest and simplest methods for visualizing a flow field is pathline visualization. With the advent of quantitative flow measurement, such as particle tracking velocimetry (PTV) and particle image velocimetry (PIV), the old art of multi-pathline visualization has taken a backseat. However, the raw particle images generated as a precursor to PIV can be superimposed to create multi-pathline visualization without additional experiments. Moreover, the high-temporally resolved sequence of particle images provides flexibility during the superimposition post-processing. This allows one to observe the same flow from different perspectives, which can offer more insight, enhance aesthetics, and make quantitative analysis more robust.

Here, we demonstrate several methods for post-processing raw particle images to generate multi-pathline visualizations. We will show the processing that 1) controls exposure time (pathline integration length), 2) encodes temporal information, and 3) changes frame of reference. These methods will be demonstrated on various flows, 1) vortex ring formation, 2) leading edge vortex roll-up, and 3) turbulent boundary layers.