Title:

Measurement of non-equilibrium in high-speed hydrogen jet flames using spontaneous Raman scattering

Speaker:

Prof. Philip Varghese

Affiliation:

University of Texas at Austin

When:

Thursday, November 17, 2022 at 11:00:00 AM   Add to Calendar

Where:

MRDC Building, Room 4211

Host:

Ellen Mazumdar
ellen.mazumdar@gatech.edu
6172334392

Abstract

Mixing-induced vibrational non-equilibrium was studied in the turbulent shear layer between a high-speed jet and a surrounding hot-air co-flow. The vibrational and rotational temperatures of N2 and O2 were determined by fitting measured spontaneous Raman scattering spectra to a model that allows for different vibrational and rotational temperatures. The mixing of the jet fluid with the co-flow gases occurs over microsecond time scales, which is sufficiently fast to induce vibrational non-equilibrium in the mixture of hot and cold gases. The effect of fluctuating temperatures on the time-averaged Raman measurement was quantified using single-shot Rayleigh thermometry. The Raman scattering results were found to be insensitive to fluctuations except where the flame is present intermittently. Vibrational non-equilibrium was detected in nitrogen but not in oxygen. This difference between species temperatures violates the two-temperature assumption often used in the modeling of high-temperature non-equilibrium flow. A multiple-pass cell was constructed to obtain single-shot Raman scattering measurements in the turbulent shear layer using a pulsed stretched laser. These measurements agreed with the previous time-average results and allowed us to make measurements near the fluctuating base of a lifted flame -- a region where time-averaged measurements do not give meaningful results.

Biography

Prof. Varghese holds the Ernest H. Cockrell Centennial Chair in Engineering and is the Director of the Center for Aeromechanics Research at UT Austin. His research focuses on understanding the basic molecular processes occurring in high speed and high temperature, and non-equilibrium flows. This is an inter-disciplinary field, requiring a synthesis of physics and chemistry with the more traditional engineering disciplines of fluid mechanics, heat transfer, and thermodynamics. He applies his work to the study of hypersonic and rarefied flows, plasmas, and combustion. He was a Fulbright Senior Scholar in France in 1993. He received the Lockheed Martin Aeronautics Company Award for Excellence in Engineering Teaching in Spring 2003, and was elected to the Academy of Distinguished Teachers at the University of Texas in 2005. In February 2012 he was selected Professor of the Year by the Senate of College Councils and was awarded The University of Texas System Regents’ Outstanding Teaching Award in August 2016.

Notes

Refreshments will be served.