An experimental investigation of organized structure and mixing in compressible turbulent free shear layers
Messersmith, Nathan Lee
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https://hdl.handle.net/2142/22703
Description
Title
An experimental investigation of organized structure and mixing in compressible turbulent free shear layers
Author(s)
Messersmith, Nathan Lee
Issue Date
1992
Doctoral Committee Chair(s)
Dutton, J. Craig
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Aerospace
Engineering, Mechanical
Language
eng
Abstract
The large scale structure and scalar transport characteristics of compressible turbulent mixing layers have been experimentally investigated at various levels of compressibility in order to study the fundamental effects of compressibility on the nature of the mixing layer. Nonintrusive optical diagnostic techniques were employed to image the large structures. Both Mie scattering from condensed ethanol droplets and laser-induced fluorescence from seeded nitric oxide were used. The LIF experiments were utilized to avoid potential particle dynamics effects associated with the Mie scattering experiments. Sizeable ensembles of digital images were collected for a variety of seeding styles, image planes and at three distinct flow conditions. Analysis of the samples provided mean and standard deviation profiles, two-dimensional spatial covariance fields and passive scalar probability density functions.
In the transverse image plane, the dimensionless structure size and eccentricity increased, while the angular orientation of the structures with respect to the streamwise flow direction decreased, as the relative Mach number increased. Oblique views revealed significant three-dimensionality, and the structures imaged in this view also increased in dimensionless size with compressibility. Very little difference in the total probabilities of finding mixed fluid within the shear layer was found for flows with relative Mach numbers of 0.63 and 1.49. A relative Mach number 0.98 flow, however, demonstrated substantially lower mixed fluid probabilities, concomitant with a very high peak standard deviation. Instability mode interactions may be the cause of the disturbed nature of the mixing layer at this condition. The results from the Mie scattering and laser-induced fluorescence experiments for similar shear layer conditions were very comparable.
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