Date of Award

2017

Document Type

Open Access Dissertation

Department

Civil and Environmental Engineering

First Advisor

Jasim Imran

Abstract

Density currents represent a broad classification of flows driven by the force of gravity acting on a fluid with variable density. With examples of density currents including turbidity currents, sand storms, salt wedges in tidal rivers, and oil spills, a great deal of attention has been previously given to understanding the underlying mechanisms of such flows and implications of those flows on fluid, species, and sediment transport. Although documented confluences occur naturally in terrestrial and submarine settings,little attention has been given to understanding the confluence of two density currents.

This study furthers the state of knowledge on density current confluences by systematically studying the unsteady flow phenomena and providing a methodology for describing the flows based on the bulk properties in the pre- and post-confluence density currents. Numerical simulations were conducted with experimental validation in which the effect of the initial density difference, channel depth, and junction angle were studied. The simulations revealed that the junction played a critical role in the combined current’s bulk properties.

In the junction zone, the density currents accelerated and became thicker. After the combined front continues downstream, an elevated plume of dense fluid remained in the junction zone for some time. It was concluded for the range of densities tested,that initial density difference has little effect on the bulk properties when nondimensionalized.

The role of the junction angle was isolated, and it is concluded that higher junction angles result in higher peak velocity in the junction zone and a larger plume.This notwithstanding, the effect of the junction is short-lived and the bulk properties of the combined current have little dependence on junction angle further downstream.

The initial conditions (initial density, channel depth, and junction angle) are combined via a Reynolds number giving an indication of the downstream oriented inertia entering the junction zone from both upstream branches of the channel network.Trends in bulk properties as functions of this Reynolds number are presented, but at high values of Reynolds number, many bulk properties approach a constant value independent of Reynolds number.

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