Air Entrainment in Pipe-Filling Bores and Pressurization Interfaces

Abstract

Certain closed conduits may undergo processes of rapid filling, in which the flow regime transits from open channel into pressurized flows. Air bubbles may be entrained through such pressurization interfaces, and this entrainment can have effects on the flow dynamics. Whereas air entrainment in static hydraulic jumps has been studied in closed conduits, such entrainment has not been investigated in moving pipe-filling bores. Experimental tests involving the creation of air-entraining pipe-filling bores were conducted, and key characteristics of the process were recorded. Theoretical propositions based on conservation laws are compared with results of experimental data to develop an expression to estimate air entrainment in the moving bores. The nondimensional dragged air flow rate in the two-phase flow generated by the jump is quantified based on a relatively small number of nondimensional parameters: supercritical Froude number, and the ratio between the bore velocity and the supercritical velocity, being grouped by the closed conduit slope. Agreement between the proposed expression and experimental data in terms of r2, the coeffcient of multiple determination in multiple regression, is good, and may indicate an alternative way to compute entrained air pocket volume during rapid filling processes.