Analysis of scale-dependent kinetic and potential energy in sheared, stably stratified turbulence
Analysis of scale-dependent kinetic and potential energy in sheared, stably stratified turbulence
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DOI：
10.1017/jfm.2022.554
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发表时间：
2021-10
影响因子：
3.7
通讯作者：
Xiaolong Zhang;R. Dhariwal;G. Portwood;S. M. de Bruyn Kops;A. Bragg
中科院分区：
文献类型：
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作者：
Xiaolong Zhang;R. Dhariwal;G. Portwood;S. M. de Bruyn Kops;A. Bragg
本文用滤波方法分析了剪切稳定层结湍流中不同尺度的湍流动能和湍流位能收支。考虑了流动中的竞争效应，沿着控制尺度间能量通量的物理机制，并利用预算分析了浮力雷诺数Re_B=O（100）$时的直接数值模拟数据。在大尺度下，平均TKE超过TPE一个数量级，随着$\ell$的减小，差异减小。在更大的尺度上，从未观察到浮力是正的，浮力总是将TKE转换为TPE。随着$\ell$的减小，局部对流区域的概率增加，尽管它在奥兹米多夫尺度下仍然很小。尺度之间的TKE和TPE通量都是尺度下的平均值，它们的瞬时值正相关，但不强烈，这是由于不同的物理机制，这些通量。此外，这些通量所产生的子网格领域的贡献被证明是显着的，除了过滤规模的贡献与应变自放大，涡拉伸和密度梯度放大的过程。概率密度函数（PDF）的$Q，R$不变量的过滤速度梯度被认为是和显示，作为$\ell$增加，剪切下降的PDF形状变得不那么明显，PDF变得更加对称约$R=0$。
Abstract Budgets of turbulent kinetic energy (TKE) and turbulent potential energy (TPE) at different scales $\ell$ in sheared, stably stratified turbulence are analysed using a filtering approach. Competing effects in the flow are considered, along with the physical mechanisms governing the energy fluxes between scales, and the budgets are used to analyse data from direct numerical simulation at buoyancy Reynolds number $Re_b=O(100)$. The mean TKE exceeds the TPE by an order of magnitude at the large scales, with the difference reducing as $\ell$ is decreased. At larger scales, buoyancy is never observed to be positive, with buoyancy always converting TKE to TPE. As $\ell$ is decreased, the probability of locally convecting regions increases, though it remains small at scales down to the Ozmidov scale. The TKE and TPE fluxes between scales are both downscale on average, and their instantaneous values are correlated positively, but not strongly so, and this occurs due to the different physical mechanisms that govern these fluxes. Moreover, the contributions to these fluxes arising from the sub-grid fields are shown to be significant, in addition to the filtered scale contributions associated with the processes of strain self-amplification, vortex stretching and density gradient amplification. Probability density functions (PDFs) of the $Q,R$ invariants of the filtered velocity gradient are considered and show that as $\ell$ increases, the sheared-drop shape of the PDF becomes less pronounced and the PDF becomes more symmetric about $R=0$.