Stiperski Ivana, Chamecki Marcelo, Calaf Marc
Department of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria.
Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, Los Angeles, USA.
Boundary Layer Meteorol. 2021;180(3):363-384. doi: 10.1007/s10546-021-00634-0. Epub 2021 Jun 15.
Classic Monin-Obukov similarity scaling states that in a stationary, horizontally homogeneous flow, in the absence of subsidence, turbulence is dictated by the balance between shear production and buoyancy production/destruction, whose ratio is characterized by a single universal scaling parameter. An evident breakdown in scaling is observed though, through large scatter in traditional scaling relations for the horizontal velocity variances under unstable stratification, or more generally in complex flow conditions. This breakdown suggests the existence of processes other than local shear and buoyancy that modulate near-surface turbulence. Recent studies on the role of anisotropy in similarity scaling have shown that anisotropy, even if calculated locally, may encode the information about these missing processes. We therefore examine the possible processes that govern the degree of anisotropy in convective conditions. We first use the reduced turbulence-kinetic-energy budget to show that anisotropy in convective conditions cannot be uniquely described by a balance of buoyancy and shear production and dissipation, but that other terms in the budget play an important role. Subsequently, we identify a ratio of local time scales that acts as a proxy for the anisotropic state of convective turbulence. This ratio can be used to formulate a new non-dimensional group. Results show that building on this approach the role of anisotropy in scaling relations over complex terrain can be placed into a more generalized framework.
经典的莫宁 - 奥布霍夫相似性标度理论指出，在稳定、水平均匀的流动中，若无下沉运动，湍流由剪切生成与浮力生成/破坏之间的平衡所决定，其比值由单一通用标度参数表征。然而，通过在不稳定分层条件下水平速度方差的传统标度关系中的大离散，或者更普遍地在复杂流动条件下，观察到了明显的标度失效。这种失效表明存在除局部剪切和浮力之外的其他调节近地表湍流的过程。最近关于各向异性在相似性标度中作用的研究表明，即使是局部计算的各向异性，也可能编码有关这些缺失过程的信息。因此，我们研究了在对流条件下控制各向异性程度的可能过程。我们首先使用简化的湍流动能收支来表明，对流条件下的各向异性不能仅通过浮力和剪切生成与耗散的平衡来唯一描述，而是收支中的其他项起着重要作用。随后，我们确定了一个局部时间尺度的比值，它可作为对流湍流各向异性状态的代理。这个比值可用于构建一个新的无量纲组。结果表明，基于这种方法，各向异性在复杂地形标度关系中的作用可以置于一个更广义的框架中。
