Exploration and Control of Transverse Jet Shear Layer Instabilities

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

PROPOSAL NO.: CTS-0457413 PRINCIPAL INVESTIGATOR: A. KARAGOZIAN INSTITUTION: UNIVERSITY OF CALIFORNIA-LOS ANGELES EXPLORATION AND CONTROL OF TRANSVERSE JET SHEAR LAYER INSTABILITIES The intellectual merits of this study involve an examination of the fundamental evolution of near field shear layer instabilities and the development of approaches in the control of such instabilities for the jet in crossflow, or transverse jet. This flow is related to many practical applications such as cooling in turbomachinery and jet engine combustors within which effective control could lead to significant improvements in efficiency and reductions in pollutant emissions. As the crossflow velocity increases and the jet transitions from the "free jet" to the "transverse jet", remarkable alterations in the spectral character of the instability have been observed under a prior NSF grant. The nature of this change in the stability characteristics suggests that at critical values of blowing ratio, there is a transition in the transverse jet from being convectively unstable to absolutely unstable or self-excited. Such stability characteristics may explain the transverse jet's ability to mix with surrounding gases in a superior manner to that of the free jet. These differences in the stability characteristics of the jet in crossflow suggest a strategic approach for future control studies in optimizing transverse jet penetration, mixing, and spread. This program will characterize the nature of these instabilities more completely, for a wide range of jet and crossflow conditions, through experiments, theory, and numerical simulations. The role of helical modes in the jet stability will also be explored and exploited in this control methodology. Feedback and feed-forward control will feature prominently in the temporal waveform shaping that is critical to this jet control approach, and will involve extensive testing and analysis. The proposed program has significant broader impacts, including involvement of undergraduate researchers. Outreach presentations and demonstrations will continue to be provided for local high school and, in the future, middle school students, with special focus on Girl Scout troops and students at public schools. Opportunities for local high school students to gain laboratory experiences in the summer will be provided. Cutbacks in funding by the state of California to the public schools' MESA (Mathematics Engineering Science Achievement) programs has made it even more important for universities such as UCLA to extend outreach programs to public middle schools and high schools as a means of encouraging the development of future engineers and scientists. The proposed project will afford an appropriate mechanism for this outreach to take place.