Measurement of instantaneous fully 3D scalar dissipation rate in a turbulent swirling flow.

This paper describes the measurement methodology for quantifying the instantaneous full 3D scalar dissipation rate (SDR or χ ) in order to characterize the rate of mixing. Measurements are performed in a near field of a jet-in-swirling-coflow configuration. All three components of χ are measured using a dual-plane acetone planar laser-induced fluorescence technique. To minimize noise, a Wiener filtering approach is used. The out-of-plane SDR component ( χ 3 ) is validated by assuming isotropy between axial and azimuthal components of SDR. An optimum laser-sheet separation distance ( Δ s ) is identified by comparing the SDR components on the basis of instantaneous, mean, and probability density function data. The in-plane resolution needs to match the Batchelor scale ( λ B ) for the central difference scheme-based SDR deduction. However, the out-of-plane resolution, Δ s , requirement is different owing to the use of two-point difference based SDR and systematic biases. The optimum Δ s is found to be 2.5 λ B . Finally, measurement guidelines are provided to assess the accuracy of 3D SDR measurements. [ABSTRACT FROM AUTHOR]