Defocusing digital particle image velocimetry: a 3-component 3-dimensionalDPIV 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 veloc imetry instrument records high resolution images of the bubble field and is capable of providing bubble size and bubble location within a cubic foot v olume. The velocity field is calculated from the volumetric cross-correlati on of consecutive three-dimensional sets of bubble locations. The bubble si ze information is estimated from the bubble scattered peak intensity. Both quantities correlate following a power law, as predicted by the Mie scatter ing theory. The technique is applied to the study of the dynamics of sub-mi llimeter air bubbles in a three-dimensional vortical flow generated by a pr opeller. Velocity, bubble size distribution and void fraction are briefly d iscussed.