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Large- and Small-Scale Structures and Their Interactions in an Axisymmetric Jet.


pdf icon Large- and Small-Scale Structures and Their Interactions in an Axisymmetric Jet. (21573 K)
Pitts, W. M.; Richards, C. D.; Levenson, M. S.

NISTIR 6393; 137 p. October 1999.

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900.
Website: http://www.ntis.gov
Order number: PB99-172363

Keywords:

axisymmetric jets; structures; cameras; Rayleigh light scattering; turbulent mixing; turbulent jets; scalar dissipation

Abstract:

A real-time line camera system has been used to record Rayleigh light scattering along a laser beam passing radially through a propane axisymmetric turbulent jet (Re = 3960) flowing into quiescent air. The measured intensities along with a wavelet analysis designed to minimiie digital noise provide quantitative measurements of propane mass fraction with sufficient temporal and spatial resolution to fully resolve the smallest scales over which turbulent concentration fluctuations occur. Direct differentiation of the data in the radial direction and use of Taylor's hypothesis to convert time derivatives to axial derivatives provide axial and radial components of scalar dissipation, x, as a function of time. An analysis described previously in the literature, which assumes the scalar dissipation is isotropic, has allowed the pdf for log(x) to be determined for the jet centerline. Space-time false-color images for mass fraction, the axial and radial components of log(x), and the angle of the mass fraction gradient in radial-axial plane are shown for various radial locations in the jet. The experimental measurements along with critical analysis of findings from previous investigations are used to address three topics of current interest in turbulent flow studies: 1) the presence and characteristics of organized large-scale turbulent structures in axisymmetric jets, 2) quantitative values of scalar dissipation and their variation with position and flow properties, and 3) whether or not there is coupling between small- and large-scale turbulent structures in shear flows and the implications for the breakdown of Kolmogorov's hypothesis. A listing of the major findings and conclusions for each of these topics is included in the last section.