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Large-eddy simulation and parameterization of buoyant plume dynamics in stratified flow

Published online by Cambridge University Press:  07 April 2016

Di Yang*
Affiliation:
Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA
Bicheng Chen
Affiliation:
Department of Meteorology, Pennsylvania State University, University Park, PA 16802, USA
Scott A. Socolofsky
Affiliation:
Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843, USA
Marcelo Chamecki
Affiliation:
Department of Meteorology, Pennsylvania State University, University Park, PA 16802, USA
Charles Meneveau
Affiliation:
Department of Mechanical Engineering and Center for Environmental and Applied Fluid Mechanics, Johns Hopkins University, Baltimore, MD 21218, USA
*
Email address for correspondence: diyang@uh.edu

Abstract

Characteristics of laboratory-scale bubble-driven buoyant plumes in a stably stratified quiescent fluid are studied using large-eddy simulation (LES). As a bubble plume entrains stratified ambient water, its net buoyancy decreases due to the increasing density difference between the entrained and ambient fluids. A large fraction of the entrained fluid eventually detrains and falls along an annular outer plume from a height of maximum rise (peel height) to a neutral buoyancy level (trap height), during which less buoyant scalars (e.g. small droplets) are trapped and dispersed horizontally, forming quasi-horizontal intrusion layers. The inner/outer double-plume structure and the peel/intrusion process are found to be more distinct for cases with small bubble rise velocity, while weak and unstable when the slip velocity is large. LES results are averaged to generate distributions of mean velocity and turbulent fluxes. These distributions provide data for assessing the performance of previously developed closures used in one-dimensional integral plume models. In particular, the various LES cases considered in this study yield consistent behaviour for the entrainment coefficients for various plume cases. Furthermore, a new continuous peeling model is derived based on the insights obtained from LES results. Comparing to previous peeling models, the new model behaves in a more self-consistent manner, and it is expected to provide more reliable performance when applied in integral plume models.

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Type
Papers
Copyright
© 2016 Cambridge University Press 

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