KHz rate 3D white light particle tracking with a tunable acoustic gradient (TAG) lens

This work develops a 70 kHz tunable acoustic gradient (TAG) lens and high-speed camera configuration for three-dimensional diagnostics of multiphase particle flows. The experimental scene is back-illuminated with a pulsed LED, driven by custom hardware, to capture images with variable phase delays with respect to the sinusoidal TAG lens focal sweep. Proposed calibration methodology and data processing techniques automate the 3D localization and tracking of particles recorded by this configuration. Capabilities are quantitatively assessed by investigating the conically expanding particle field produced by a vibrating nozzle, and good agreement between the statistics of the velocity components demonstrates comparable accuracy in the in-plane and optical depth directions. Finally, capabilities are demonstrated for a challenging and practical measurement of hypergolic reaction of nitrogen tetroxide (NTO) and monomethylhydrazine (MMH). TAG recordings are shown to provide finer depth resolution and reduced susceptibility to imaging noise compared to the common digital inline holography (DIH) diagnostic. The developed capabilities are expected to have widespread utility to future study of transient and 3D multiphase flows.