Experimental assessment of presumed filtered density function models

V. Stetsyuk, N. Soulopoulos, Y. Hardalupas, A. M. K. P. Taylor

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Abstract

Measured filtered density functions (FDFs) as well as assumed beta distribution model of mixture fraction and “subgrid” scale (SGS) scalar variance z′′2⎯⎯⎯⎯⎯⎯⎯z′′2¯, used typically in large eddy simulations, were studied by analysing experimental data, obtained from two-dimensional planar, laser induced fluorescence measurements in isothermal swirling turbulent flows at a constant Reynolds number of 29 000 for different swirl numbers (0.3, 0.58, and 1.07). Two-dimensional spatial filtering, by using a box filter, was performed in order to obtain the filtered variables, namely, resolved mean and “subgrid” scale scalar variance. These were used as inputs for assumed beta distribution of mixture fraction and top-hat FDF shape estimates. The presumed beta distribution model, top-hat FDF, and the measured filtered density functions were used to integrate a laminar flamelet solution in order to calculate the corresponding resolved temperature. The experimentally measured FDFs varied with the flow swirl number and both axial and radial positions in the flow. The FDFs were unimodal at flow regions with low SGS scalar variance, z′′2⎯⎯⎯⎯⎯⎯⎯<z′′2¯< 0.01, and bimodal at regions with high SGS variance, z′′2⎯⎯⎯⎯⎯⎯⎯>z′′2¯> 0.02. Bimodal FDF could be observed for a filter size of approximately 1.5-2 times the Batchelor scale. Unimodal FDF could be observed for a filter size as large as four times the Batchelor scale under well-mixed conditions. In addition, two common computational models (a gradient assumption and a scale similarity model) for the SGS scalar variance were used with the aim to evaluate their validity through comparison with the experimental data. It was found that the gradient assumption model performed generally better than the scale similarity one.
Original languageEnglish
Article number065107
Number of pages19
JournalPhysics of Fluids
Volume27
Issue number6
Early online date10 Jun 2015
DOIs
Publication statusPublished - Jun 2015
Externally publishedYes

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    Stetsyuk, V., Soulopoulos, N., Hardalupas, Y., & Taylor, A. M. K. P. (2015). Experimental assessment of presumed filtered density function models. Physics of Fluids, 27(6), [065107]. https://doi.org/10.1063/1.4922169