Behaviors of Bubble-Entrained Plumes in Air-Injection Artificial Upwelling

Abstract

This paper studies bubble-entrained plume (BEP) behaviors in a crossflow and proposes a theoretical approach for predicting BEP trajectories and the separation points from the bubble swarm. When rising in a crossflow, the BEP is separated from the bubble swarm and becomes a negatively buoyant fountain. By treating the BEP trajectory as two distinct parts based on the separation point from the bubble swarm, a new BEP trajectory can be expressed as a piecewise equation. Laboratory experiments conducted in different conditions study the effects of air flow rate and crossflow velocity on the BEP behaviors. Experimental results show that the larger the crossflow velocity is, the narrower the width and the smaller the spreading rate of air-bubble plume becomes. The theoretical approach developed in this study is also used to calculate the minimum air injection volume flow rate for artificial upwelling, which has a direct application for estimating the upwelling of nutrient-rich water into the euphotic layer as a way to enhance primary production in nutrient-depleted surface waters.