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Fluids 2018, 3(3), 53;

Quality Measures of Mixing in Turbulent Flow and Effects of Molecular Diffusivity

School of Chemical, Biological and Materials Engineering, The University of Oklahoma, Norman, OK 73019, USA
Author to whom correspondence should be addressed.
Received: 27 June 2018 / Revised: 23 July 2018 / Accepted: 27 July 2018 / Published: 30 July 2018
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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Results from numerical simulations of the mixing of two puffs of scalars released in a turbulent flow channel are used to introduce a measure of mixing quality, and to investigate the effectiveness of turbulent mixing as a function of the location of the puff release and the molecular diffusivity of the puffs. The puffs are released from instantaneous line sources in the flow field with Schmidt numbers that range from 0.7 to 2400. The line sources are located at different distances from the channel wall, starting from the wall itself, the viscous wall layer, the logarithmic layer, and the channel center. The mixing effectiveness is quantified by following the trajectories of individual particles with a Lagrangian approach and carefully counting the number of particles from both puffs that arrive at different locations in the flow field as a function of time. A new measure, the mixing quality index Ø, is defined as the product of the normalized fraction of particles from the two puffs at a flow location. The mixing quality index can take values from 0, corresponding to no mixing, to 0.25, corresponding to full mixing. The mixing quality in the flow is found to depend on the Schmidt number of the puffs when the two puffs are released in the viscous wall region, while the Schmidt number is not important for the mixing of puffs released outside the logarithmic region. View Full-Text
Keywords: turbulent transport; turbulent mixing; Lagrangian modeling; turbulence simulations turbulent transport; turbulent mixing; Lagrangian modeling; turbulence simulations

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Nguyen, Q.; Papavassiliou, D.V. Quality Measures of Mixing in Turbulent Flow and Effects of Molecular Diffusivity. Fluids 2018, 3, 53.

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