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 velocimetry 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 field 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 briefly discussed.