Preconditions and limitations of the postulate of scalar-dissipation-conductivity independence in a variable conductivity medium.
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Classical turbulent mixing paradigm--ingrained in scaling laws and closure models--is revisited in a variable-conductivity inhomogeneous medium. We perform direct numerical simulations to study the evolution of a passive scalar (temperature) field in a fluid with large conductivity gradients and investigate the behavior of scalar dissipation, conditional scalar dissipation, and velocity-to-scalar time scale ratio. Subject to the conditions of the investigation, it is found that these mixing characteristics become reasonably insensitive to conductivity after about one-third eddy turnover time. While the results support the classical paradigm, important preconditions and limitations are clearly identified.