Entrainment Coefficient of a Turbulent Plume

An Experimental Investigation with PIV and LIF

Master thesis (2023)

Authors

D. Liu Mechanical Engineering

Contributors

K. Hooman Process and Energy (supervisor 1)
G.E. Elsinga Fluid Mechanics - Mechanical, Maritime and Materials Engineering (supervisor 1)
Faculty
Mechanical Engineering
Copyright: © 2023 Dongliang Liu
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Published Date

28-08-2023

Language

English

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Faculty

Mechanical Engineering

Abstract

Buoyancy-driven plumes are natural phenomena that occur in widespread applications, such as geological flows or pollutant dispersion from a chimney. One characteristic of plumes is the entrainment process, where the plume stream drags in ambient fluid and mixes with the ambient fluid, and classic plume theory has used an entrainment coefficient to describe the entrainment process. Literature research reveals that there is a general lack of experiment data on the entrainment process of an axisymmetric plume, and there is little consensus on the entrainment coefficient. The aims of the thesis are to address the problem of insufficient experimental evidence and to investigate the entrainment coefficient using two theories (classic entrainment theory and new energy-consistent theory).

The thesis’s method is experimental. Buoyancy-driven plumes with different initial conditions were created in a water tank, and the velocity field and buoyancy field were measured using particle image velocimetry (PIV) and laser induced fluorescence (LIF). In addition, a new combination of urea and sodium sulfate was proposed to perform the refractive index matching (RIM), which is a crucial step for accurate velocity and buoyancy measurements.

The thesis’s results highlighted that the entrainment coefficient is approximately 0.11, despite large variations when using the classic theory to determine the entrainment coefficient, which may help explain different values in previous literature. In addition, the existence of a refractive index field was observed to affect both the velocity and buoyancy measurements. Specifically, the refractive index field caused PIV and LIF to overestimate the velocity field and underestimate the buoyancy field, respectively.