Observations of turbulence and mean flow in the low-energy hypolimnetic boundary layer of a large lake: Deep water BBL flow and turbulence in a large lake
Observations of turbulence and mean flow in the low-energy hypolimnetic boundary layer of a large lake: Deep water BBL flow and turbulence in a large lake
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大型湖泊低能低湖边界层湍流和平均流量的观测：大型湖泊的深水 BBL 流动和湍流
DOI：
10.1002/lno.11007
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发表时间：
2018
影响因子：
4.5
通讯作者：
Troy, Cary D.
中科院分区：
文献类型：
--
作者：
Cannon, David J.;Troy, Cary D.
在分层和非分层期间，报告了密歇根湖深水层沃茨（55 m深）中的平均流和湍流结构的近床测量值，以确定预期壁律（LOW）行为的有效性和限制。近床流很弱（U 50 = 3.16 cm s− 1，平均值，最大值分别在50 cm高度），在所有季节都以亚惯性能量为主，尽管风强迫具有很强的季节性，但几乎没有季节性变化。无波条件下的速度结构在1 mab内显示出强烈的对数线性趋势，2152个速度剖面中超过98%在底部仪表内产生显著的对数线性拟合，严格的对数速度剖面平均仅延伸到66 cab（Cd 50= 0.0052;zo= 0.0015 m）。分层在动力学上对平均流和湍流不重要，但拟合的对数线性长度尺度表明，与严格对数速度结构的偏差可以用流动不稳定性来解释。在床的1米范围内测量的湍流量，包括耗散、湍流动能和湍流长度尺度，平均值低于预期，但个别估计值偏离了几个数量级。发现观察到的与低湍流结构的偏差与拟合平均速度剖面的对数线性长度尺度相关，并且与流动不稳定性的影响一致。
Near‐bed measurements are reported for both mean flow and turbulence structure in the deep hypolimnetic waters of Lake Michigan (55 m depth) during stratified and unstratified periods to determine validity and restrictions of the expected law‐of‐the‐wall (LOW) behavior. Near‐bed currents were weak (U50= 3, 16 cm s−1for mean, maximum currents respectively at 50 cm elevation), dominated by subinertial energy across all seasons, and showed little seasonal variation in spite of the strong seasonality to wind forcing. Velocity structure for wave‐free conditions showed strong log‐linear trends within 1 mab, with over 98% of the 2152 velocity profiles producing significant log‐linear fits within the bottom meter and a strictly logarithmic velocity profile extending to only 66 cmab on average (Cd 50= 0.0052;zo= 0.0015 m). Stratification was dynamically unimportant to mean flow and turbulence, but fitted log‐linear length scales suggest that deviations from strictly logarithmic velocity structure may be explained by flow unsteadiness. Turbulent quantities measured within 1 m of the bed including dissipation, turbulent kinetic energy, and turbulent length scales followed LOW expectations in the mean, but individual estimates deviated by several orders of magnitude. The observed deviations from LOW turbulent structure were found to be correlated with the log‐linear length scales fit to mean velocity profiles and were consistent with the effects of flow unsteadiness.