The small-scale structure of the fluctuating passive scalar field in a turbulent boundary layer

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ABSTRACTPROPOSAL NO.: CTS-0303406PROPOSAL TYPE: INVESTIGATOR INITIATEDPRINCIPAL INVESTIGATORS: DONALD R. WEBSTERINSTITUTION: GEORGIA TECH. THE SMALL-SCALE STRUCTURE OF FLUCTUATING PASSIVE SCALAR FIELD IN A TURBULENT BOUNDARY LAYERMixing and transport of passive scalars in turbulent flows are important processes occurring in many natural and engineered environments. Common examples include contaminant discharges in water bodies, chemical plumes in the atmosphere, and chemical mixing in reactors. Despite decades of research aimed at understanding the dynamics of turbulent transport, scalar fields continue to defy accurate theoretical predictions. The lack of a general theory to predict the statistical nature of turbulent transport ultimately requires experimental tests to predict and optimize mixing efficiency for many practical situations. This procedure is inefficient and costly, thus a universal theory for turbulent fluctuations of scalar quantities continues to be highly desirable. This study of a turbulent shear flow has the following objectives: (1) examine the dynamics of the scalar variance dissipation rate, and (2) study the behavior and usefulness of multi-point correlators as a tool to represent small-scale turbulence structure and its relation to the traditional structure functions. We additionally propose to examine the isotropic and anisotropic components of structure functions and their respective scaling behavior. Experiments will be performed for a chemical plume in a turbulent boundary layer of an open channel flow. The planar laser induced fluorescence (PLIF) technique will be used to record time series of the high Schmidt number concentration fields. The measurements resolve the Batchelor length scale of the scalar field. Variation among three Reynolds numbers and three mean scalar gradient cases will be examined. The proposed experimental results will impact both modeling strategies and our fundamental understanding of the coupling between small-scale and large-scale behavior in turbulent shear flows. One graduate student (Ph.D. level) and one undergraduate student will be trained in advanced experimental techniques and fundamental turbulence research. Georgia Tech is a national leader in graduate education of underrepresented groups, and every effort will be made to attract such a student to this project..