Application of a roughness-length representation to parameterize energy loss in 3-D numerical simulations of large rivers
Application of a roughness-length representation to parameterize energy loss in 3-D numerical simulations of large rivers
复制标题
应用粗糙度-长度表示来参数化大型河流 3-D 数值模拟中的能量损失
DOI：
10.1029/2011wr011284
复制
发表时间：
2012
影响因子：
5.4
通讯作者：
Sandbach S
中科院分区：
文献类型：
--
作者：
Sandbach S
遥感技术的最新进展使人们能够对大河的形态动力学和水动力学进行调查。然而，测量这些非常大的河流的地形和流量是耗时的，因此往往限制了空间分辨率和可监测的河段长度尺度。大型河流的计算流体动力学（CFD）研究也存在类似的限制，需要最大化网格或网格单元尺寸，并意味着减少模型网格单元数量级或更少的底形粗糙度元素的表示，即使它们在可用的地形数据中表示。这些“子网格”元素必须参数化，本文应用并考虑粗糙度长度处理的影响，包括由于“未测量”地形的床面粗糙度的影响。发现CFD预测对粗糙度-长度规范敏感。模型优化的基础上声学多普勒流速剖面仪测量和各种粗糙度长度的水面坡度的估计。这被证明是困难的，因为用于评估最佳模型性能的指标由于粗糙度-长度处理中没有很好参数化的大型底形的影响而出现分歧。然而，一般的空间流模式是有效的预测模型。粗糙度长度的变化被证明有一个主要的影响后，在通道尺度的流量路由。研究结果还表明，在所研究的河段中没有二次流循环单元，并表明更简单的二维模型在大型河流的水流调查中可能具有很大的实用性。
Recent technological advances in remote sensing have enabled investigation of the morphodynamics and hydrodynamics of large rivers. However, measuring topography and flow in these very large rivers is time consuming and thus often constrains the spatial resolution and reach‐length scales that can be monitored. Similar constraints exist for computational fluid dynamics (CFD) studies of large rivers, requiring maximization of mesh‐ or grid‐cell dimensions and implying a reduction in the representation of bedform‐roughness elements that are of the order of a model grid cell or less, even if they are represented in available topographic data. These “subgrid” elements must be parameterized, and this paper applies and considers the impact of roughness‐length treatments that include the effect of bed roughness due to “unmeasured” topography. CFD predictions were found to be sensitive to the roughness‐length specification. Model optimization was based on acoustic Doppler current profiler measurements and estimates of the water surface slope for a variety of roughness lengths. This proved difficult as the metrics used to assess optimal model performance diverged due to the effects of large bedforms that are not well parameterized in roughness‐length treatments. However, the general spatial flow patterns are effectively predicted by the model. Changes in roughness length were shown to have a major impact upon flow routing at the channel scale. The results also indicate an absence of secondary flow circulation cells in the reached studied, and suggest simpler two‐dimensional models may have great utility in the investigation of flow within large rivers.