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首页> 外文期刊>International Journal of Heat and Mass Transfer >Comparison of backwards and forwards scalar relative dispersion in turbulent shear flow
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Comparison of backwards and forwards scalar relative dispersion in turbulent shear flow

机译：湍流剪切流中前后标量相对色散的比较

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摘要

Turbulent mixing is characteristically identifiable with backwards relative dispersion, where pairs of particles get transported to the mixing location. However, relative dispersion models are insensitive to this fact and predominantly apply forwards relative dispersion concepts. The goal of the current study is to highlight and interpret differences, if any, between the forwards and backwards relative dispersion. Direct numerical simulation is used to obtain the flow field in an infinitely long channel. A Lagrangian technique is used in conjunction with the direct numerical simulation to track scalar markers released into this flow field. Two different types of flow, Poiseuille channel flow, where the walls of the channel are stationary, and plane Couette flow, where the walls of the channel move in opposite directions relative to each other, are simulated. Forwards relative dispersion is found to be faster in the viscous sub-layer, the transition region and the logarithmic regions of the Poiseuille channel flow, while the back wards relative dispersion is faster in the center of the channel. Faster forwards relative dispersion is seen in the center of the Couette flow channel and the logarithmic region, while higher rate of backwards relative dispersion is observed in the viscous sub-layer and the transition region. The underlying reason for differences in relative dispersion is related to the turbulence velocity structure and the velocity fluc tuation probability density function that the particle pairs experience while traveling towards or away from a point. It is also found that the Prandtl number affects rates of forwards and backwards relative dispersion in a systematic manner.
机译：湍流混合的特征是向后相对分散，其中成对的颗粒被输送到混合位置。但是，相对分散模型对此事实不敏感，主要应用向前的相对分散概念。当前研究的目的是突出和解释向前和向后相对分散之间的差异（如果有）。直接数值模拟用于获得无限长通道中的流场。拉格朗日技术与直接数值模拟结合使用，可以跟踪释放到该流场中的标量标记。模拟了两种不同类型的流动，即Poiseuille通道流动（其中通道壁是固定的）和平面Couette流动（其中通道的壁相对于彼此以相反的方向移动）。发现向前的相对分散在粘性子层，泊瓦伊耶河道水流的过渡区和对数区更快，而向后的相对分散在河道中心更快。在库埃特流道和对数区域的中心观察到更快的向前相对分散，而在粘性子层和过渡区域观察到更高的向后相对分散速率。相对色散差异的根本原因与湍流速度结构和粒子对在朝向或远离某个点传播时所经历的速度波动概率密度函数有关。还发现普朗特数以系统的方式影响前向和后向相对分散的速率。

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