Two-phase air-water measurements in fully-rough free-surface flows

Fully-rough turbulent free-surface flows are encountered in a variety of natural and man-made applications. When strong turbulence interacts with the water surface, the intense air–water mixing yields a complicated two-phase gas–liquid flow structure due to the cumulative contribution of entrained bubbles and droplets. This study presents an in-depth investigation of fully-rough turbulent free-surface flows, through some experimental measurements in high-velocity free-surface flows over macro-roughness. The measurements focused on skimming flow conditions. Downstream of the inception region of self-aeration, some strong air entrapment and intense turbulence was recorded. The void fraction profiles compared well with a theoretical model, and the relationship between void fraction and bubble count rate exhibited a quasi-parabolic profile. The interfacial velocity distributions followed a power law, while high turbulence levels were recorded across the air–water column. A large proportion of clustered particles was observed in both the lower bubbly flow region and upper spray region, with a strong correlation between the percentage of clustered particles and void/liquid fraction.