Briefing: Experimental study on air-phase frequency in self-aerated flow

Abstract

The distribution and development of air frequency in self-aerated open channel flows were experimentally investigated. A series of experiments was conducted in a rectangular flume with various initial flow velocities (3·50–6·35 m/s) and the test area was in the self-aerated developing region. Analysis of the results shows that the position of maximum air frequency is generally in the relatively low air concentration region in the self-aerated developing region of an open channel flow, and the air concentration with the maximum air frequency becomes greater and gradually approaches 0·50 with the development of self-aeration downstream. Further analysis reveals that the positions of maximum air frequency remain around the centre of the self-aerated region and, with an increase in initial flow velocity, the air frequency distributions over the cross-section gradually tend to a simple normal distribution. The reason for the distribution and development of air frequency in the self-aerated developing region is mainly from the free surface into the limit of self-aeration; the distribution of an air–water flow structure is a developing process involving the coexistence of entrapped air and entrained air, and this air–water structure leads to the difference in air frequency distributions and development in the self-aerated developing region.