Very-large-scale motions in rough-bed open-channel flow
Very-large-scale motions in rough-bed open-channel flow
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DOI：
10.1017/jfm.2017.24
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发表时间：
2017-03-10
影响因子：
3.7
通讯作者：
Stewart, M. T.
中科院分区：
文献类型：
--
作者：
Cameron, S. M.;Nikora, V. I.;Stewart, M. T.
粗糙床明渠水流的长时间粒子图像测速表明，由于大尺度和超大尺度运动(分别为LSM和VLSM)的存在，流向速度的预乘谱呈双峰分布。边界层、管道和闭合航道中存在VLSM已经被承认了一段时间，但缺乏有力的证据支持它们在OCF中的存在。本文报告的数据填补了这一空白。OCF中LSM和VLSM的长度尺度表现出不同的尺度特性；LSM的流向长度随水流深度的变化而变化，而VLSM的流向长度并不单纯随水流深度的变化而变化，可能还取决于其他尺度，如通道宽度、粗糙度高度或粘性长度。LSM的横向范围随海拔的升高而增大，但VLSM的横向尺度主要固定在两个流动深度附近。LSM和VLSM的起源和性质仍有待解决，但它们在尺度上的差异表明，粗糙床OCFs中的VLSM独立形成，而不是作为LSM的空间排列。
Long-duration particle image velocimetry measurements in rough-bed open-channel flows (OCFs) reveal that the pre-multiplied spectra of the streamwise velocity have a bimodal distribution due to the presence of large-and very-large-scale motions (LSMs and VLSMs, respectively). The existence of VLSMs in boundary layers, pipes and closed channels has been acknowledged for some time, but strong supporting evidence for their presence in OCF has been lacking. The data reported in this paper fill this gap. Length scales of the LSMs and VLSMs in OCF exhibit different scaling properties; whereas the streamwise length of the LSM scales with the flow depth, the VLSM streamwise length does not scale purely with flow depth and may additionally depend on other scales such as the channel width, roughness height or viscous length. The transverse extent of the LSMs was found to increase with increasing elevation, but the VLSM transverse scale is anchored around two flow depths. The origin and nature of LSMs and VLSMs are still to be resolved, but differences in their scaling suggest that VLSMs in rough-bed OCFs form independently rather than as a spatial alignment of LSMs.