Two-Phase Flow Measurements in Un-stationary Free-surface Flows: a New Signal Decomposition Technique

In free-surface flows, some flow instabilities may be observed, for example in pooled stepped spillways and hydraulic jumps. These instabilities may include some pulsations and oscillations. Most traditional two-phase flow analyses would yield some air-water turbulent flow results combining the contributions of the slow fluctuations and of the turbulent motion. Herein a new turbulence decomposition technique was introduced to quantify the relative contributions of slow and fast fluctuations. The method was developed for and applied to phase-detection probe signals collected in highly-aerated free-surface flows. The interfacial velocity and turbulence properties were calculated based upon some advanced correlation analyses of the dual-tip probe signals. The triple decomposition results were applied to some un-stationary pooled stepped spillway flows and they highlighted that the gross turbulent kinetic energy was mostly encompassed in the slow fluctuating signal component. Altogether this study showed the successful application of a new decomposition technique suitable to gas-liquid flows in industrial applications with high void fractions.