Turbulent Fluxes and their Relation to Surface Heterogeneity and Transient Mesoscale Motions

湍流通量及其与表面异质性和瞬态中尺度运动的关系

• 批准号: 9310576
• 负责人: Larry Mahrt
• 金额: $ 31.64万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1993
• 资助国家: 美国
• 起止时间: 1993-11-01 至 1998-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9310576&HistoricalAwards=false
• 关键词: Turbulent; Fluxes; their; Relation; Surface

9310576 Mahrt The objective of this work is to analyze several new and existing data sets toward the goal of improving our understanding of the response of boundary-layer flow to heterogeneous surfaces ranging from multiple, well defined, discontinuities to more complex surface heterogeneity. The new data include aircraft, tower and limited remote sensing observations and allow examination of classes of heterogeneity in detail not previously considered. One of the goals is to examine the main influences on the area averaged surface fluxes. These influences include: 1) enhancement of the momentum flux associated with pressure drag induced by scatter trees, forest edges and other obstacles, 2) non-equilibrium effects in transition zones downstream from changes of surface conditions, 3) extra Reynolds terms associated with spatial variability and the nonlinear relationship between fluxes and gradients and 4) direct transport by mesoscale motions. To approach this problem, the flow observed by repeated aircraft runs over the same track is formally decomposed into turbulence, transient mesoscale motions and stationary mesoscale motions (primarily associated with surface heterogeneity). The modulation of the turbulence flux by the two mesoscale components will be considered in detail. From a more practical point of view, the above influences on the area averaged flux will be implicitly incorporated into calculation of effective roughness lengths and exchange coefficients corresponding to the area averaged fluxes. These calculations will be preceded by an analysis of flux sampling errors which will include some research on the techniques for estimating flux errors. Proposed theoretical work will be limited to interpretation of the mesoscale circulations over heterogeneous terrain in terms of several existing linear and nonlinear predictions. ***

9310576 MAHRT这项工作的目的是分析几个新的和现有的数据集，以提高我们对边界层流对异质表面的响应的理解，从多个，定义良好的不连续性到更复杂的表面异质性。 新数据包括飞机，塔楼和有限的遥感观察结果，并允许检查以前未考虑的异质性类别。 目标之一是检查对平均表面通量区域的主要影响。 这些影响包括：1）增强与散点树，森林边缘和其他障碍物引起的压力阻力相关的动量通量，2）表面条件变化的下游过渡区域中的非平衡效应，3）3）额外的雷诺与空间变异性相关的额外雷诺术语，与渐变和梯度之间的非线性关系和4）直接运输和4）直接通过Messcale Motions进行运输。 为了解决这个问题，通过重复飞机在同一轨道上观察到的流量正式分解为湍流，瞬态中尺度运动和固定的中尺度运动（主要与表面异质性有关）。 将详细考虑通过两个中尺度组件对湍流通量的调节。 从更实际的角度来看，上述对平均通量区域的影响将被隐式地纳入有效的粗糙度长度和与该面积平均通量相对应的有效粗糙度长度和交换系数。 这些计算将在通量采样误差的分析之前进行分析，这将包括一些对估计通量误差的技术的研究。 提出的理论工作将仅限于在几种现有的线性和非线性预测方面对中尺度循环的解释。 ***