Experimental investigation of a wet foam flow through a horizontal sudden expansion

In this study, the flow characteristics of an aqueous foam have been studied through a horizontal sudden expansion localized in the middle of a horizontal duct. With a square section 21 × 21 mm2 in the upstream and a rectangular section 21 × 42 mm2 in the downstream, this singularity has an aspect ratio of 0.5. Through this sudden expansion, the experimental study consists in determining, the static drainage, the regular pressure loss, the wet foam flow dynamics in the vicinity of the singularity using PIV, the thickness of the underlying liquid film, and finally local void fraction and bubble sizes. These later have been also determined using an optical probe. In the vicinity of the expansion, singular pressure rise is deduced by extrapolation using the linear static pressure measurement evolutions obtained in the upstream and downstream far from the singularity. However, the average and fluctuating velocities using PIV method near the singularity, were obtained from a series of 150 instantaneous snapshots for each chosen quality of the foam. At the immediate vicinity of the singularity, these local experimental results allowed to give the general tendency of the foam flow reorganization.