On void fraction and flow fragmentation in two-phase gas-liquid free-surface flows

In free-surface flows, the interactions between high-velocity liquid and atmosphere may lead to strong gas-liquid mixing and complex multiphase flow interactions. In this study, the void fraction power spectrum density (PSD) is used to provide an alternative view of the air-water flow composition. The high frequency range of the PSD curve reflects contributions of small chord times, while the low frequency range contains contributions of both small and large chord times. Likewise, the interactions between the smallest bubbles contribute approximately uniformly to the entire frequency range of the spectrum, while any interaction involving large bubbles/drops will be modulated by 1/f2. It is shown that the void fraction spectra are a powerful tool in providing an alternative view of the air-water flow composition.