Intrusive measurements of air-water flow properties in highly turbulent supported plunging jets and effects of inflow jet conditions

A plunging jet is an efficient device to entrain gas into liquid flow. In many practical occasions, the gas entrainment needs to be carefully controlled, and the interaction between the shear flow turbulence and entrained bubbles has to be better understood. This paper presents a physical study of vertical supported two-dimensional plunging jets using a relatively large-size facility. The air-water flow and turbulence properties were measured with an intrusive phase-detection probe and a total pressure sensor simultaneously. The inflow pre-aeration and turbulence level of the falling jet were carefully characterised, and the effects of jet impact velocity and jet length on air entrainment in plunging pool were investigated. The experimental results were systematically compared to relevant studies. A discussion was developed on the quantification of turbulence intensity in highly-aerated flow based on total pressure measurement. The flow turbulence properties were derived respectively from the interfacial phase-detection signals and total pressure signals. The results highlighted difference in terms of the turbulence intensities between interfacial motions and water-phase turbulence. The present work showed that the jet impact velocity, jet length, inflow disturbance and pre-entrainment of air had considerable effects on air entrainment capacity and subsurface air-water flow properties in plunging jets hence should be carefully characterised in relevant studies.