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Turbulence Research, scalar the relatively fluid velocity field in terms of the physical quantities, passive scalar idealized object of the mechanism of transport processes in the scalar in turbulent scalar transport process, the scalar itself does not The flow field counterproductive impact. Passive scalar field is a hot topic in the current turbulence research the one hand, it will help to deepen the understanding of turbulence problems, on the other hand, improved engineering applications such as turbulent combustion model for understanding the spread of pollutants mechanism the practical problems of great significance. Scalar transport equation is a linear equation, the early researchers generally believe, the scalar nature should be more simple, the statistical results of the scalar field just reflects the nature of the turbulent velocity field from a different side. In the last ten years, however, a large number of experimental measurements, numerical simulations and theoretical analysis results show that the scalar field has its own unique properties, even nature does not depend on the velocity field. This has prompted people to re-understanding, amend or propose a new theory to replace traditional classical theory. In this paper, direct numerical simulation method, mean scalar gradient homogeneous isotropic stable turbulence statistics of Euler and Lagrange statistics analysis, to study the characteristics of the small-scale structure of passive scalar and how by turbulent flow field factors. Turbulent velocity field with a \The Reλ calculated 25 and 48, the Prandtl number from 0.3 to 4.0, the average scalar gradient of 1.0. Statistics show that: Euler statistics scalar dissipation rate of the spatial structure of the high strength of the sheet-like structure of the intermittent distribution; scalar dissipation of these high strength is formed mainly due to the compression action results strain tensor, and the vortex relatively weak on the direct impact of the scalar dissipation rate, however, it can destroy the scalar gradient between the strain tensor coupling to suppress the generation of high-intensity scalar dissipation; Lagrangian statistics analysis show that the scalar fields intermittent more strongly than the velocity field, the formation of the fine laminar structure strong scalar dissipation time scale is about 10 times Kolmogorov time scale, in the process of fine laminar structure formed strong scalar dissipation strain intensity scalar gradient synchronization increases, the vorticity decreases first, then increases, and the maximum 5 times the Kolmogorov time scale.
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