Bubble convection and bubbly flow turbulent time and length scales in two-dimensional plunging jets

Abstract

Air entrainment and air-water mixing by a flow impingement are enhanced by the turbulent shear layer and associated instabilities in the receiving waterbody. This paper presents an experimental study aiming at a quantitative description of bubble-turbulence interplay in two-dimensional supported plunging water jets. In addition to the basic air-water flow properties, the turbulence intensity in the highly-aerated plunging pool was estimated based on void fraction and total pressure fluctuation measurements, while the turbulent time and length scales were recorded systematically. The coupling of bubble convection and formation of macroscopic turbulent structures was characterised in terms of bubble clustering behaviours and turbulent length and time scales of the bubbly flow eddy structures. The effects of jet impact velocity were investigated for a fixed jet length. These advanced data analyses were applied to plunging jet two-phase flow for the first time. The results would provide new benchmark data for numerical modelling of intense air-water flow at a higher level than the basic two-phase flow dynamic properties. A discussion was developed at the end on the turbulent length scales and the Schmidt number in the bubbly flow regions of horizontal hydraulic jump and vertical supported plunging jet.