湍流混合层中大尺度结构对湍流普朗特数的影响

K. Takamure, Y. Sakai, Yasumasa Ito, K. Iwano
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摘要

摘要本文对空间发展中的剪切混合层进行了直接数值模拟。本研究的目的是阐明大尺度结构对湍流普朗特数PrT的影响。主要结论是,在大尺度结构的优势区域,PrT值较小(PrT ~ 0.5)。对雷诺应力方程和标量通量方程的预算分析表明,动量传递和标量传递的差异是由与压力有关的项(即压力-应变相关项、压力-标量梯度相关项和压力扩散项)引起的。现象上,在大尺度涡旋共存的场中,动量在压力的影响下倾向于向反梯度方向输运,而标量则向梯度方向输运。因此,可以认为是动量输运和标量输运之间驱动力的差异导致了PrT的减小。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Influence of large-scale structure on the turbulent Prandtl number in a turbulent mixing layer
Influence of large-scale structure on the turbulent Prandtl number in a turbulent mixing layer Kotaro TAKAMURE, Yasuhiko SAKAI, Yasumasa ITO, Koji IWANO ABSTRACT We have run a Direct Numerical Simulation of a spatially developing shear mixing layer. The aim of this study is to clarify the influence of the large-scale structure on the turbulent Prandtl number PrT. As a main conclusion, PrT takes a small value (PrT ~ 0.5) in the dominant region of the large-scale structure. The budget analyses for the Reynolds stress equation and the scalar flux equation revealed that the differences between the momentum and scalar transfer are caused by terms related to pressure (i.e., pressure-strain correlation term, pressure-scalar gradient correlation term, and pressure diffusion terms). Phenomenally, the momentum in the field where a large-scale vortex coexists tends to be transported toward the countergradient direction under the influence of pressure, but the scalar is transported toward the gradient direction. As a result, it is thought that the difference in the driving force between the momentum and scalar transport causes the decrease of the PrT.
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