A numerical study of passive scalar evolution in peripheral regions
A numerical study of passive scalar evolution in peripheral regions
复制标题
外围区域被动标量演化的数值研究
DOI：
10.1063/1.2736341
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发表时间：
2007
影响因子：
4.6
通讯作者：
P. Haynes
中科院分区：
文献类型：
--
作者：
H. Salman;P. Haynes
我们研究了滑移和无滑移壁边界对空间平滑且随机时间速度场中被动标量衰减率的影响。进行数值模拟以验证外围（近壁）区域对标量方差衰减的影响。使用两个具有简单速度场的运动流模型，我们表明，在滑移边界的情况下，被动标量的特征是初始快速搅拌，然后是标量方差的指数衰减。与此形成鲜明对比的是，无滑移边界情况的结果表明，在标量在主体内初始快速搅拌之后，存在一个中间时间状态，其中方差遵循幂律衰减。这种中间状态是由于标量被捕获在靠近无滑移壁的外围区域中而建立的。最后，标量方差的行为切换到以指数衰减率为特征的最终状态。这里提出的结果表明，最近关于外围区域无源标量演化的基于系综的理论正确地预测了单流实现中出现的标量演化的主要阶段。
We study the effect of slip and no-slip wall boundaries on the decay rate of a passive scalar in a spatially smooth and random in time velocity field. Numerical simulations are carried out to verify the effect of the peripheral (near-wall) regions on the decay of the scalar variance. Using two kinematic flow models with simple velocity fields, we show that, in the case of slip boundaries, the passive scalar is characterized by an initial rapid stirring followed by an exponential decay of the scalar variance. In stark contrast, results for the case with no-slip boundaries show that, following an initial rapid stirring of the scalar within the bulk, there is an intermediate-time regime where the variance follows a power-law decay. This intermediate regime is established as a result of the trapping of the scalar in the peripheral regions near the no-slip walls. Finally, the behavior of the scalar variance switches to a final regime that is characterized by an exponential decay rate. The results presented here indicate that the recent ensemble-based theories regarding the evolution of a passive scalar in the peripheral regions correctly predict the main stages of the scalar evolution that arise in a single flow realization.