My research interests include measurements of physical properties in chemically reacting and high-speed flows and plasmas.  Mostly I work in non-intrusive laser spectroscopic methods, but I also have an interest in instrumentation systems more generally.

The techniques I develop are deployed to improve understanding of high-speed and nonequilibrium thermodynamic processes in a range of applications, including

• Hypersonic flows and shock waves
• Plasmas
• Rarefied flows, including both low-density space applications and microscale flows and
• Combustion flows

The diagnostic techniques that I have developed include measurements of species concentrations, temperatures, densities and velocities.  They have included both fundamental laboratory-based studies of phenomena like diffusive mixing, and measurements on board high-speed aircraft.

Sean O'Byrne obtained undergraduate physics and education degrees from the University of New England, and Masters and PhD degrees in physics at the Australian National University.  His PhD research was on temperature and velocity distributions in hypersosic wake flows. From 2002 to 2004 he worked as a postdoctoral fellow at NASA Langley Research Center, studying supersonic combustion processes.   From 2004 to 2006 he was awarded a Vice Chancellor's fellowship at the University of New South Wales.  He joined the faculty of UNSW Canberra in 2006 and undertook research in laser-based diagnostics until 2023, when he joined ANU as Professor of Aerospace Engineering. He is a senior member of the Optica and the American Institute of Aeronautics and Aerospace professional societies, an editor for the Shock Waves and Frontiers in Physics journals and is on the International Advisory Committee for the International Symposium on Rarefied Gas Dynamics.  Dr O'Byrne has supervised 18 PhD students (10 as primary supervisor) and 1 ME Student. 

Current externally funded projects include:

• Development of a CO gasdynamic laser (DST group)
• Measurement of transition processes on conical bodies in hypersonic flows (USAFA)

Projects for Australian PhD students only (export controlled):

• Development of a gasdynamic lasser

This project involves modelling and experimental investigation of population inversion processes via vibrational pumping of CO molecules in a hypersonic expanding flow.  The state of the gas in the expansion is measured using absorption spectroscopy and compared to models of the vibrational nonequilibrium expansion process, to determine the most efficient ways of generating strong population inversions necessary for efficient laser action.

• Nitric oxide formation processes in free-piston shock tunnel air flows

In this project, infrared absorption spectroscopy is used to investigate the formation and nonequilibrium internal energy state of nitric oxide when air is heated to high temperature and suddenly expanded to hypersonic speed in a converging-diverging nozzle.  Measurements are made using supercontinuum absorption spectroscopy and are compared to state-resolved population models.

• Hypersonic transition sensor for flight testing

Focussed laser differential interferometry is a method that can be used to determine frequencies of evolving boundary layer structures in hypersonic flow at a point.  Using an acousto-optic deflector, it is possible to traverse the interrogation location across a boundary layer in real-time, providing a way of determining profiles of turbulence frequency across a boundary layer.  This project would involve developing and hardening a sensor designed for use in hypersonic flight testing (availability subject to funding).

Projects available for any students

• Development of a field-emission e-beam sensor for rarefied flows

Electron-beam fluorescence is a technique for measuring temperatures and species concentrations in rarefied flows like those experienced by low-earth-orbit satellites and hypersonic vehicles entering planetary atmospheres.  This project involves development of an electron-beam fluorescence system using field emitter arrays that can operate with low power and low temperatures - characteristics that are essential for deployment on satellites.  The system will be developed and tested initially in static gases and then in a hypersonic rarefied flow.

• Measurement of transport properties in dielectric barrier discharge plasmas

This project involves measurements of gas viscosity and diffusion processes in plasmas.  The plasma investigated in this project is generated by forming a dielectric barrier discharge in the low-pressure gas in a hollow-core photonic waveguide.  Comparisons will be made between the diffusion characteristics of low-temperature plasmas and neutral gases to determine what effect (if any) the electronic excitation  of the gas has on its transport properties.