Defocusing Digital Particle Image Velocimetry: A 3-Component 3-Dimensional DPIV Measurement Technique. Application to Bubbly Flows

This paper describes a three-dimensional imaging system for the purpose of mapping two-phase bubbly flows. The defocusing digital particle image ve-locimetry instrument records high resolution images of the bubble field and is capable of providing bubble size and bubble location within a cubic foot volume. The velocity ield is calculated from the volumetric cross-correlation of consecutive three-dimensional sets of bubble locations. The bubble size information is estimated from the bubble scattered peak intensity. Both quantities correlate following a power law, as predicted by the Mie scattering theory. The technique is applied to the study of the dynamics of sub-millimeter air bubbles in a three-dimensional vortical flow generated by a propeller. Velocity, bubble size distribution and void fraction are briely discussed.