Two-phase flow measurements of an unsteady breaking bore

A key feature of breaking bores, jumps, and spilling breakers is the roller region, characterised by intense shear and recirculation, associated with air bubble entrainment and splashing. Detailed unsteady air-water flow measurements were conducted in a breaking bore propagating in a large-size channel, using an array of dual-tip phase-detection probes and an ultra-high-speed video camera. The results showed a steep roller front, with a very-dynamic air-water bubbly region, albeit with a relatively limited air-water roller region. In this study, a major challenge was the inconsistency in light intensity linked to the travelling nature of the bore. A simple flow visualisation technique was applied to retrieve the two-dimensional side-looking profile of the roller edge and average void fraction. The results were validated independently with a phase-detection probe. While the probe data lacked spatial variability, the study reinforces the needs of high-quality validation data set, including in unsteady transient flows.