Particle Size Distributions in Turbulent Air-Water Flows

Turbulent multiphase gas-liquid flows occur in a large variety of natural environments and play an important role in many industrial processes. A common characteristic of these flows is the presence of a dispersed phase, for example air bubbles or water droplets, that are embedded in a continuous phase. In highly-aerated flows, bubbles and droplets influence the energy dissipation and make a substantial contribution in terms of air-water mass transfer. The chord-sizes and the size distribution of dispersed liquid particles are traditionally measured with phase-detection intrusive probes. Despite the long-standing use of this measurement technique, the interpretation of measurement results in turbulent flows is still challenging. The present study investigated the effects of turbulent motion on measured chord-lengths by means of stochastic modelling. A virtual dual-tip phase-detection probe was placed within a pattern of synthetic particles, impacting the tips of the probe. A newly developed adaptive window cross-correlation (AWCC) technique was shown to outperform conventional approaches, demonstrating that instantaneous velocities must be considered when calculating chord length distributions to avoid erroneous results. The approach was further applied to real two-phase flow signals recorded in a laboratory stepped spillway, providing an unbiased assessment of chord-length distributions in turbulent air-water flows.