Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Mechanical and Materials Engineering

Collaborative Specialization

Scientific Computing

Supervisor

Ogden, Kelly A

Abstract

Topographic effects on internal hydraulic jumps in stratified flow over complex geometry are studied. The simulations are motivated by flow conditions present in a channel in Hood Canal, Washington with continuous density profiles and constant inlet velocities.

Results show that mixing in the domain is typically increased by topographic variation, where isolated expansions saw an increase in mixing, but the associated velocity decrease in expansions had contrasting effects on mixing. Likewise, a contraction with an increased velocity caused more mixing, seeing geometry change and velocity acting as compounding factors. 2D results including along channel topographic variation modelled after Hood Canal's topography and density profiles differed from observational results because channel width variation was excluded, but mixing was affected by the direction of the flow over the topography, and the density profile. Given these results, future work into more realistic 3D simulations is encouraged.

Summary for Lay Audience

A hydraulic jump is a phenomenon that can occur when a flow of relatively high speed is forced to abruptly transition to a low speed, typically due to a change in topography, or the meeting of high and low speed flows. This velocity transition is accompanied by a large amount of turbulence that is dissipative in nature, and often utilized by engineers in dams and spillways as a method of flow control. Hydraulic jumps also frequently occur in nature for and the turbulence associated with this phenomenon can modify water properties and affect aquaculture in various regions across the globe. Not only can this phenomenon occur at the surface of flows with a constant density, but they are also known to occur internally in flows that have density variation, like those seen in channels and straits, or in the open ocean. Of particular interest is the indication that a hydraulic jump is occurring in Hood Canal, a channel located in the Kitsap Peninsula, in Washington State, USA. Hood Canal periodically experiences a reduction in the amount of oxygen dissolved in the water, resulting in a large number of fish dying over a short period; the amount of mixing caused by a hydraulic jump in the channel may affect the severity of these events. Some observational data has shown that a hydraulic jump may be occurring in an area of the channel where the topography is complex, such as expanding then contracting walls, and a drastic and abrupt change in the channel depth. The effect that the complex boundaries have on the mixing and intensity of hydraulic jumps has not previously been thoroughly investigated, and is the focus of this work. Using computational fluid dynamics to simulate hydraulic jumps in 3 cases; a 3D domain with an expansion, a 3D domain with a contraction and a 2D domain with a complex bottom are investigated. The results show that as, the width of the channel expands or contracts, mixing increases, and that complex bottom topography is important to consider.

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