Defocusing digitalparticle image velocimetry and the three-dimensional characterization oftwo-phase flows

Abstract

Defocusing digital particle image velocimetry (DDPIV) isthe natural extension of planar PIV techniques to the third spatialdimension. In this paper we give details of the defocusing opticalconcept by which scalar and vector information can be retrievedwithin large volumes. The optical model and computational proceduresare presented with the specific purpose of mapping the numberdensity, the size distribution, the associated local void fractionand the velocity of bubbles or particles in two-phase flows. Everyparticle or bubble is characterized in terms of size and of spatialcoordinates, used to compute a true three-component velocity field byspatial three-dimensional cross-correlation. The spatial resolutionand uncertainty limits are established through numerical simulations.The performance of the DDPIV technique is established in terms ofnumber density and void fraction. Finally, the velocity evaluationmethodology, using the spatial cross-correlation technique, isdescribed and discussed in terms of velocity accuracy.