Probability distribution, conditional dissipation, and transport of passive temperature fluctuations in grid‐generated turbulence

The evolution of the scalar probability density function (pdf), the conditional scalar dissipation rate, and other statistics including transport properties are studied for passive temperature fluctuations in decaying grid‐generated turbulence. The effect of filtering and differentiating the time series is also investigated. For a nonzero mean temperature gradient it is shown that the pdf of the temperature fluctuations has pronounced exponential tails for turbulence Reynolds number (Rel) greater than 70 but below this value the pdf is close to Gaussian. The scalar dissipation rate, conditioned on the fluctuations, shows that there is a high expectation of dissipation in the presence of the large, rare fluctuations that produce the exponential tails. Significant positive correlation between the mean square scalar fluctuations and the instantaneous scalar dissipation rate is found when exponential tails occur. The case of temperature fluctuations in the absence of a mean gradient is also studied. Here, the...

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