Skip to main content
Thermodynamics and Fluids

Thermodynamics and fluids

Turbulent mixing in buoyant, stratified and shock-induced flows

We conduct experimental, computational and analytic investigations into complex buoyant, stratified and shock-induced flows. Applications include building ventilation, riverine mixing and inertial confinement fusion.

Our research

We use numerical simulation, experiment and analysis to investigate the fundamental behaviour of mixing and entrainment in buoyancy and shock-driven and stratified flows. Such flows occur, for example, in the mixing of saline inflows and in the diurnal heating and cooling processes in rivers; in building heating ventilation and cooling; in the discharge of high-salinity effluent from desalination plants; mixing and transport in lakes and reservoirs; and inertial confinement fusion. This research leads to the development of predictive tools, both numerical and analytical, that are used in the design of associated devices and in the management of rivers and other water bodies.

Our experts: Associate Professor Michael Kirkpatrick, Dr Nicholas Williamson, Professor Steve Armfield

Thermal stratification is common in Australia’s rivers due to our drought-prone climate and high human demands. It inhibits mixing, creating stagnant conditions, characterised by low oxygen levels and increased concentrations of contaminants. It leads to algal blooms, fish kills and systemic damage to ecosystems. Our aim is to develop predictive models to maximise physical processes such as night-time cooling, wind, turbulence and currents on riverine thermal stratification. Our goal is to enable a more accurate determination of the flow rates required to maintain the health of our river systems.

We use a combination of high resolution numerical simulations – direct numerical simulation (DNS) and large eddy simulation (LES) – scaling analysis and stability analysis. Maintaining the health of our river systems involves balancing the needs of agriculture, domestic and commercial users, fisheries, power generators, industry, tourism, recreational users and the environment. We aim to provide the scientific foundations for a new generation of river management tools to allow authorities to better optimise water allocations and river flows to maximise both economic and environmental benefits.

Our experts: Dr Nicholas Williamson, Professor Steve Armfield, Associate Professor Michael Kirkpatrick

Volcanic eruptions, building air ventilation, smoke stack releases and brine discharge from desalination plants are all examples of fluid flows where differences in density between the fluid release and its surrounding environment can control the flow behavior. These flows can be classified as turbulent fountains, buoyant jets or plumes depending on the specific release conditions. We need the ability to accurately predict entrainment of ambient fluid into the fountain/jet/plume. Our research scrutinises the turbulent structure of fountains and plumes using numerical simulation and laboratory experiments. We work to understand and quantify this entrainment and develop new more sophisticated modeling tools to support the next generation of engineers.

Our experts: Professor Steve Armfield, Dr Nicholas Williamson, Associate Professor Michael Kirkpatrick, Professor John Patterson, Associate Professor Chengwang Lei

Natural convection flows occur in a wide range of industrial and environmental settings. These range  from the cooling of computer components to heat transfer in the earth’s mantle. It acts to enhance the transfer of heat from regions of high to low temperatures. The rate of heat transfer is determined by the state of the flow, whether laminar, transition or fully turbulent.

Understanding such flows is critical in the design of heat exchangers, building heating ventilation and cooling systems. It is also crucial in the prediction of many large-scale environmental features such as the occurrence of convective overturns and near-shore transport in lakes and reservoirs. Our research relies on large-scale direct numerical simulation of the governing Navier-Stokes equations, the use of semi-analytic stability techniques, scaling and laboratory experiments. These provide a deeper understanding of the transitional behaviour of the thermal boundary layer and aid the development of predictive tools and strategies for controlling transition and limiting or enhancing heat transfer. 

Our experts: Associate Professor Ben Thornber

Society faces a critical need for a long-term energy source. Inertial confinement fusion (ICF) provides a potential pathway towards utilisation of fusion power as an energy source. In ICF, powerful lasers are employed to rapidly compress a small sphere of deuterium/tritium to the required temperature and pressure to produce fusion. Such small spheres could be imploded multiple times per second, with each pulse providing a small release of energy. With even a modest conversion rate, a system could provide enough energy to sustain mankind for many centuries. However, fluid instabilities develop and these can prevent fusion being achieved.

Our research aims to understand how the instabilities develop and transition to turbulence. Accordingly, we aim to inform the future design of the fuel capsules, utilising very high-resolution computations undertaken on several thousand computational cores. We explore the fundamentals of compressible turbulent mixing, simplified modelling of mixing problems and new numerical approaches to compute unsteady turbulent mixing problems. This work is in collaboration with multiple institutions worldwide and employs the top supercomputing facilities in Australia to deliver an unprecedented insight into the turbulent physics.