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Boundary-Layer Processes Hindering Contemporary Numerical Weather Prediction Models
Boundary-Layer Meteorology ( IF 4.3 ) Pub Date : 2022-09-05 , DOI: 10.1007/s10546-022-00742-5
Marc Calaf, Nikki Vercauteren, Gabriel G. Katul, Marco G. Giometto, Travis J. Morrison, Fabien Margairaz, Vyacheslav Boyko, Eric R. Pardyjak

Time integration of the unsteady Reynolds-averaged Navier–Stokes (URANS) equations is the principal approach used in numerical weather prediction. This approach represents a balanced compromise between accuracy and computational cost. The URANS equations require the flow to be decomposed into an ensemble mean and excursions that are presumed to be entirely related to turbulence, thereby enabling conventional closure schemes to be used to describe their statistics. Implicit in such a decomposition is the assumption of a spectral gap between the unsteadiness in the mean flow and the scales of turbulence. Modelling challenges arise when some of the unresolved fluctuations are related to non-turbulent, structured motions that can also blur the spectral gap and render conventional closure schemes ineffective. This work seeks to clarify modelling issues that occur when unresolved fluctuations include submesoscale motions and persistent secondary circulations related to surface heterogeneities. Because submeso motions and persistent secondary circulations are not random, new theoretical tactics are discussed to represent their effects on URANS transport. By reviewing the interpretation of fluctuating terms in the URANS equations, we suggest the use of large-eddy simulations, direct numerical simulations and field measurements to guide the development of closure schemes that explicitly include fluxes due to submeso motions and persistent secondary circulations.



中文翻译:

阻碍当代数值天气预报模型的边界层过程

非定常雷诺平均 Navier-Stokes (URANS) 方程的时间积分是数值天气预报中使用的主要方法。这种方法代表了准确性和计算成本之间的平衡折衷。URANS 方程要求将流动分解为集合平均值和偏移,这些偏移被假定为与湍流完全相关,从而能够使用传统的闭合方案来描述它们的统计数据。这种分解中隐含的假设是平均流的不稳定性和湍流尺度之间的谱间隙。当一些未解决的波动与非湍流结构化运动相关时,建模挑战就出现了,这些运动也会模糊光谱间隙并使传统的闭合方案无效。这项工作旨在澄清当未解决的波动包括亚尺度运动和与表面异质性相关的持续次级环流时发生的建模问题。由于亚中运动和持续的次级环流不是随机的,因此讨论了新的理论策略来表示它们对 URANS 传输的影响。通过回顾对 URANS 方程中波动项的解释,我们建议使用大涡模拟、直接数值模拟和现场测量来指导闭合方案的开发,其中明确包括由于亚中运动和持续次级环流引起的通量。由于亚中运动和持续的次级环流不是随机的,因此讨论了新的理论策略来表示它们对 URANS 传输的影响。通过回顾对 URANS 方程中波动项的解释,我们建议使用大涡模拟、直接数值模拟和现场测量来指导闭合方案的开发,其中明确包括由于亚中运动和持续次级环流引起的通量。由于亚中运动和持续的次级环流不是随机的,因此讨论了新的理论策略来表示它们对 URANS 传输的影响。通过回顾对 URANS 方程中波动项的解释,我们建议使用大涡模拟、直接数值模拟和现场测量来指导闭合方案的开发,其中明确包括由于亚中运动和持续次级环流引起的通量。

更新日期:2022-09-06
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