ISPIV 2023 Ronald J. Adrian Award Lecture: "Four Decades of Chasing Particles"

Abstract

We recount 40 years of our involvement in developing particle based imaging techniques for flow velocimetry with focus on particle image velocimetry and aperture-encoded imaging. Based on experiences gained with photograph-based particle streak velocimetry by M. Gharib at JPL, the approach was implemented fully digitally by C. Willert in late 1980s at UC San Diego. Subsequent work quickly led to the introduction of digital particle image velocimetry (DPIV) initially allowing PIV measurements of water flows at a (video) frame rate of 30 Hz but rapidly improving with the advancement of digital imaging technology. Three-dimensional imaging of particles using a single camera was also demonstrated using an triplet aperture placed in the camera's lens, a technique that we initially termed "defocusing particle tracking velocimetry." We provide an overview of recent applications using these and derived measurement techniques to illustrate their wide-spread utilization throughout present day experimental fluid dynamics and related fields. Given the steady advancements in both imaging technology and computational capabilities along with emerging technologies (e.g. machine learning, event-based imaging) we predict a continuous further evolution of particle-image based measurement techniques.