论文标题
在衰减各向同性湍流时，没有具有恒定平均梯度的被动标量的新缩放定律
No new scaling laws of passive scalar with a constant mean gradient in decaying isotropic turbulence
论文作者
论文摘要
在Sadeghi＆Oberlack [JFM 899，A10（2020）]的研究中，据称在不变平均梯度在衰减均匀的各向同性湍流中的影响下，针对被动标量动力学的情况得出了新的缩放定律。但是，这些扩展定律并不新鲜，并且已经在Bahri（2016）中得出和讨论。 Sadeghi＆Oberlack并未取得任何新颖的分析成就，因为他们的研究的标题误导了建议。实际上，与Sadeghi＆Oberlack通过过于复杂且不必要地执行的Lie-Group对称性分析获得的应用程序相比，Bahri通过简单的维度分析获得的已经建立的自相似标度定律已经在应用中更为笼统。声称它具有不作为临时方法的优点是不正确的。因为，Lie-Group方法不用使用先验集量表作为经典方法，而是必须使用一组先验的对称性，即从无限的和未锁定的集合中选择正确的相关对称性。例如，选择非物理缩放对称性，在分析过程中必须丢弃，因为它与模拟的数据不兼容。因此，湍流中的下群对称方法只是另一种常见的试验方法，而不是可以绕过封闭问题的第一原理方法。
In the study by Sadeghi & Oberlack [JFM 899, A10 (2020)] it is claimed that new scaling laws are derived for the case of passive scalar dynamics under the influence of a constant mean gradient in decaying homogeneous isotropic turbulence. However, these scaling laws are not new and have already been derived and discussed in Bahri (2016). No novel analytical achievements are made by Sadeghi & Oberlack, as the title of their study misleadingly wants to suggest. In fact, the already established self-similar scaling laws obtained by Bahri through simple dimensional analysis are already more general in the application than the ones obtained by Sadeghi & Oberlack through an overly complicated and therefore unnecessarily performed Lie-group symmetry analysis. The claim that it has the virtue of not being an ad-hoc method is not true. Because, instead of using an a priori set of scales as the classical method, the Lie-group method has to make use of an a priori set of symmetries, namely to select the correct relevant symmetries from an infinite and thus unclosed set. For example, a nonphysical scaling symmetry is selected which in the course of the analysis has to be discarded since it is not compatible with the data simulated. Hence, the Lie-group symmetry method in turbulence is just another common trial-and-error method and not a first-principle method that can bypass the closure problem.
