Analysis and Simulation of Mixing of Stratified Layers or Reservoirs by Air Bubble Plumes

Abstract

The goal of the research presented in this report is to analyze, understand, and simulate the flow field induced by a bubble plume in a lake or reservoir. This is useful and necessary for the design of lake or reservoir aeration and destratification projects. Three mathematical models were developed and laboratory experiments were performed. Experiments similar to the ones presented here are not available in the literature but were necessary to understand the governing physical processes and to verify the mathematical models. What makes these experiments unique, in comparison with other bubble plume measurements is the description of the entire flow field (not just the flow in vicinity of the bubble plume), the inclusion of stratified ambient water, and the evaluation of destrati:fication over time. The first. model developed is a modified version of a dynamic 1-D mathematical model originally formulated by Goossens[1979]. The improved model is based on the research described here and is linked to a general dynamic lake model MINLAKE. It is a tool useful for lake restoration projects, particularly for evaluation of different restoration techniques. The second model is also an integral model of a bubble plume. The flow field induced by an air bubble plume in stratified ambient water is presented in the general context of mixing mechanics of water jets and plumes. The third model is a 2-D numerical model that gives insight into the subregions of the flow field. The 2-D model solves the Reynolds' equations by using the buoyancy-extended version of the k-e model as a closure of the turbulent quantities. The effect of the bubbles in the fluid flow is modeled by imposing internal forces in the region where the air bubbles are present. A discussion of lake aeration as an oxygen transfer technique is beyond the scope of the research described herein.