Cinematic two-phase PIV for bubbly flows

The objective of this research was to develop a cinematic two-phase particle image velocimetry (PIV) system and evaluate its performance using a test flow of bubble dispersion in a two-stream, turbulent, planar free shear layer. It was desired to track detailed characteristics of individual bubbles through a temporally and spatially varying turbulent flowfield. The water shear layer under investigation has a velocity ratio of 0.23 and a Reynolds number of 26,200 based on velocity thickness and velocity difference. Air bubbles were injected directly into the shear layer through a single slender tube. The cinematic PIV was accomplished with an argon-ion laser, a rotating polygonal mirror and a 35 mm movie camera. The experimental data obtained with cinematic PIV yields a combined spatial and temporal evolution of the two-dimensional liquid velocity and spanwise vorticity fields. From the triple-pulsed bubble images in a sequence of PIV pictures, the bubble size and bubble trajectory can be accurately determined. From these two simultaneous data sets, the liquid velocity, acceleration, vorticity, and stress gradient at the instantaneous bubble location, and the bubble's velocity, acceleration and buoyancy force were obtained. Application of a bubble dynamics equation is then possible to allow further investigation of interphase momentum transport for modeling of multi-phase flows, which is the subject of future work.