The objective of this work is to investigate mixing, turbulent flow and combustion of liquid propellants at high pressures including supercritical pressures. Conventional analysis of combustion processes is based mostly on low pressure, subcritical mechanisms. Ongoing Air Force propulsion and other combustion applications increasingly emphasize high pressures. Atomization and spray combustion mechanisms are fundamentally different in these regimes. At pressures exceeding the critical point of the propellant (731 psi for liquid oxygen), the sharp distinction between gas and liquid phases can entirely disappear, and classical liquid spray features such as droplets, ligament formation, and other interface effects become gradually less pronounced. Such flows will likely exhibit properties, which at some times are like those of turbulent jets and at other times are more like those of sprays. Even subcritical high pressures pose substantial challenges for combustion diagnostic techniques, most of which were developed for low-pressure applications. To be overcome are obstacles such as dense sprays, beam steering, molecular quenching, and spectral line broadening. Three principal areas of current interest include: (a) Experimental work in both nonreacting as well as reacting jets of non-premixed fuels at elevated pressures, (b) The development of data analysis methods to appropriately interpret optical as well as high speed pressure probe data using recent techniques in modal analysis and machine learning, and (c) A synthesis of experimental data and CFD using methods such as data assimilation applied to practical propulsive flows.  Numerous research opportunities are available to work with an established team of scientists and engineers to improve technology in these areas.

References:

"High-pressure flows for propulsion applications," edited by J. Bellan, AIAA Prog. Aero. Astro., V. 260, 2020

Garita, F., Yu, H., Juniper, M.P., "Assimilation of experimental data to create a quantitatively accurate reduced-order thermoacoustic model," J. Eng. Gas Turbines and Power, V. 143, 021008, 2021 

Taira, K., Hemati, M.S., Brunton, S.L., Sun, Y., Duraisamy, K., Bagheri, S., Dawson, S.T.M., Yeh, C.-A., "Modal analysis of fluid flows: Applications and outlook," AIAA J., V. 58, no. 3, 2020

Approved for Public Release; Distribution is Unlimited. AFRL-2021-3117

key words

Turbulent flows; Combustion; Liquid propellants; Supercritical fluids; Nonlinear dynamics;

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral and Senior applicants