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

摘要

A real-time line camera system has been used to record Rayleigh light scattering211u001ealong a laser beam passing radially through a propane axisymmetric turbulent jet 211u001e(Re = 3960) flowing into quiescent air. The measured intensities along with a 211u001ewavelet analysis designed to minimized digital noise provide quantitative 211u001emeasurements of propane mass fraction with sufficient temporal and spatial 211u001eresolution to fully resolve the smallest scales over which turbulent 211u001econcentration fluctuations occur. Direct differentiation of the data in the 211u001eradial direction and use of Taylor's hypothesis to convert time derivatives to 211u001eaxial derivatives provide axial and radial components of scalar dissipation chi, 211u001eas a function of time. Space-time false-color images for mass fraction, the axial 211u001eand radial components of log(X), and the angle of the mass fraction gradient in 211u001eradial-axial plane are shown for various radial locations in the jet. The 211u001eexperimental measurements along with critical analysis of findings from previous 211u001einvestigations are used to address three topics of current interest in turbulent 211u001eflows studies: (1) the presence and characteristics or organized large-scale 211u001eturbulent structures in axisymmetric jets, (2) quantitative values of scalar 211u001edissipation and their variation with position and flow properties, and (3)