Turbulent mixing in stably stratified flow: a laboratory and field based study


In stably stratified shear flows, turbulent mixing is suppressed by the background stratification. This project will examine this dynamic using laboratory experiments and field measurements in strongly thermally stratified Australian rivers.


Dr Nicholas Williamson, Professor Steven Armfield

Research Location

Aerospace, Mechanical and Mechatronic Engineering

Program Type



Stable stratified shear flows occur in numerous environmental settings such as in rivers, estuaries and in the atmospheric boundary layer. These conditions are also common in industrial flows such as within heat exchangers and building and ventilation flows. There is a strong motivation to understand the behaviour of these flows. One critical aspect addressed in this study is how turbulent mixing is damped by stable stratification. In river environments, turbulent mixing is a critical process which transports heat, oxygen and nutrients. When turbulence is damped there can be adverse consequences for aquatic life. A particular motivation of this study is how this damped state of mixing encourages algal blooms in Australian river systems. This project will investigate the fundamental fluid mechanics of mixing in these scenarios using both field measurements supported by a large multidisciplinary team and also with controlled laboratory experiments.

Additional Information

This project is based in the School of Aerospace, Mechanical and Mechatronic Engineering and is supported by the ARC Discovery Project Grant: `Thermal stratification, overturning and mixing in riverine environments’. We have industry partners: Murray Darling Basin Authority, Water NSW and Hunter Water corporation and further collaboration with freshwater ecologists outside our school of engineering. The outcomes of this work are both fundamental and applied. The field measurements of stably stratified flow will be unique and provide insights into turbulent mixing at large Reynolds numbers that is relevant to a wide range of environmental and industrial flows. The work is also focused on laying the foundations of a hydraulic model to predict the onset of algal blooms, which is the primary interest of the industrial partners.  In this project you will work is other research students, research fellows and academic staff in our very capable fluid mechanics laboratory and be part of a large fluid mechanics community at USYD. On a day to day basis you will be designing and performing laboratory experiments to study stratified flow using particle image velocimetry and laser induced fluorescence (PIV/LIF). You will also play a large part in designing and deploying lab scale instrumentation in field investigations such as on the Murray River. In particular, you will be working with Acoustic Doppler Current Profilers to measure properties of turbulence in the field and calibrated these with laboratory experiments.Eligibility: International students will be asked to apply for `University of Sydney International Scholarship’. Domestic students with Australian permanent residency or New Zealand Citizenship will be asked to apply for `Australian Government Research Training Program (RTP) scholarships’. Further competitive Faculty of Engineering funding may be available if these scholarship applications are unsuccessful.

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fluid mechanics, turbulence, mixing, stratified flow, diapycnal mixing, turbulence modelling, environmental fluid mechanics, experimental fluid dynamics, field study, algal blooms

Opportunity ID

The opportunity ID for this research opportunity is: 2329

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