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Measurements of the Statistical Distribution of the Scalar Dissipation Rate in Turbulent Axisymmetric Plumes

C. N. Markides
Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United Kingdom

E. Mastorakos
Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United Kingdom

ABSTRACT

High resolution Planar Laser-Induced Fluorescence (PLIF) measurements of mixing were performed in flows created by the continuous injection, with various velocity ratios, of a passive scalar from a finite sized round nozzle, into uniform turbulent co-flows confined within a cylindrical tube with a range of background Reynolds numbers (Re). The resulting data were processed for the accurate recovery of the spatial gradients of the normalized scalar concentration (ε), which resulted in measurements of the scalar dissipation rate (χ). The probability density functions (pdfs) of both χ and χ|ε were calculated and found to deviate slightly from a lognormal distribution. This deviation was more pronounced closer to the source and decayed downstream. The ratio of the standard deviation over the mean of χ and χ|ε increased with streamwise distance and reached values of 2.8 and 1.2 respectively.