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The Distribution Function of the Fluctuations of a Passive Scalar in Homogeneous Isotropic Turbulence

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  • 1 Istael Institute for Biological Research, Ness-Ziona, Israel
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Abstract

The knowledge of the distribution function of concentration fluctuations in a turbulent medium is very important and relevant to problems, like hazard estimation, smoke obscuration, and combustion problems.

In the present work, we implement a 3-D Lagrangian model in homogeneous isotropic turbulence and calculate the first four moments of concentration fluctuations from a single source as functions of space and time. We also study the interference of four simultaneous line sources.

The moments of the single source are compared with the moments of an exponential distribution function and with the moments of the clipped normal distribution function.

Calculated results from the multiple line source are compared with the experiments performed by Warhaft. We compared the total variance of the four line sources and the cross correlations between all six possible pairs. We found fair agreement between the model and measurements, in spite of the fact that experiments were conducted in a decaying turbulence.

Abstract

The knowledge of the distribution function of concentration fluctuations in a turbulent medium is very important and relevant to problems, like hazard estimation, smoke obscuration, and combustion problems.

In the present work, we implement a 3-D Lagrangian model in homogeneous isotropic turbulence and calculate the first four moments of concentration fluctuations from a single source as functions of space and time. We also study the interference of four simultaneous line sources.

The moments of the single source are compared with the moments of an exponential distribution function and with the moments of the clipped normal distribution function.

Calculated results from the multiple line source are compared with the experiments performed by Warhaft. We compared the total variance of the four line sources and the cross correlations between all six possible pairs. We found fair agreement between the model and measurements, in spite of the fact that experiments were conducted in a decaying turbulence.

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