Events Calendar

AME Department Seminar

Speaker: Joanna M. Austin, Assistant Professor, Department of Aerospace Engineering, College of Engineering, University of Illinois at Urbana-Champaign, IL

Talk Title: The Role of Thermochemistry in Hypersonic Shear Flows

Abstract: In high enthalpy hypersonic flight, thermochemical relaxation times are typically comparable to flow residence times, leading to nonlinear coupling between chemical reactions, vibrational excitation, and fluid mechanics. The chemical species and internal energy of the gas depart significantly from equilibrium. Experimental data in hypervelocity flows are scarce, partly because creating high enthalpy conditions in ground test facilities is extremely challenging and flight tests are expensive.

A new expansion tube facility capable of test gas Mach numbers from 3.0 to 7.4 has been built at Illinois and carefully characterized with experimental measurements and numerical simulations. Two canonical shear flows are being examined in the high enthalpy free stream: triple-point generated free shear layers and boundary layers flows. Initial experiments identified an opposing wedge configuration used to generate a Mach reflection with associated triple-point shear layers. The experimental configuration is chosen to give well-characterized inflow and boundary conditions. In addition, a Mach reflection results in a shear layer that separates a gas stream that has passed through a normal shock from a gas stream that has passed through two oblique shocks, leading to dramatically different temperatures and degree of dissociation across the shear layer. Key diagnostic tools include spectroscopic measurements confirming the presence of dissociated NO behind the Mach reflection, flow visualizations, and temperature measurements benchmarked against calculations using detailed and reduced chemical kinetic mechanisms.

The experimental work is complemented by spatial linear stability analysis. This study is the first linear stability analysis of a hypersonic shear layer to include detailed modeling of molecular effects. An existing molecular-molecular energy transfer rate model is extended to higher collisional energies. Non-equilibrium model results are compared with calculations assuming equilibrium and frozen flow over a range of (frozen) convective Mach numbers from 0.341 to 1.707. Non-equilibrium effects appear in the creation of nitrous oxide due to dissociation. Dissociation and vibration transfer effects on the perturbation evolution remain closely correlated at all convective Mach numbers.

Biography: Joanna Austin is an Assistant Professor in the Aerospace Engineering Department at the University of Illinois at Urbana-Champaign. She received B.E. (Mechanical and Space Engineering) and B.Sc. (Mathematics) degrees from the University of Queensland, Australia in 1996 and 1997, and M.S. and Ph.D. degrees from GALCIT at the California Institute of Technology in 1998 and 2003. She directs the Compressible Fluid Mechanics Laboratory at Illinois, where her research interests include hypervelocity flows, bubble collapse under dynamic loading, detonation, compressible geological flows, and experimental fluid mechanics. Honors and awards include the Richard Bruce Chapman award for distinguished research in hydrodynamics in the Engineering and Applied Sciences Division at Caltech, 2003, the Young Investigator Award from the Air Force Office of Scientific Research, 2007, and the National Science Foundation CAREER award in 2010.

Host: Prof. V. Eliasson

More Info: http://ame-www.usc.edu/seminars/1-26-11-austin.shtml

Location: Seaver Science Library (SSL) - 150

Audiences: Everyone Is Invited

Contact: April Mundy

Event Link: http://ame-www.usc.edu/seminars/1-26-11-austin.shtml