蒙特利峡谷底边界层湍流特征分析

发布时间：2018-06-07 19:13

本文选题：蒙特利峡谷 + 底边界层　；参考：《中国海洋大学》2014年硕士论文

【摘要】：海洋中存在各种尺度的运动,通常能量的传递都是从大尺度到小尺度,最后以湍流运动的形式耗散。湍流是不同于层流且漫无规则的小尺度混乱运动,广泛存在于大气、海洋和工程技术等领域的流体运动中。湍流结构复杂多样,在时问和空问上具有问歇性、随机性、高涡度性、高非线性,在流体中产生强混合扩散效应。由于湍流的这些特殊性质,湍流很难直接观测,缺乏大范围、长时间的连续观测资料,湍流的结构、产生机制尚不清晰。基于海洋科学对湍流长期观测的需要,本文利用2011年4月24日到10月25日期间,蒙特利峡谷底边界层内ADV连续观测流速数据,分析峡谷底边界层内流速变化规律,估算湍流特征量,分析湍流特征。 ADV实测的每分钟平均流速数据分析表明,在蒙特利峡谷底边界层内存在很强的流动,平均流速可达0.398m/s。峡谷底部潮流属于逆时针旋转潮流系统,具有半日周期和全日周期的变化特征,其中半日周期占主导。日平均的流速数据谱分析和小波分析结果表明,峡谷底部潮流在5月和8月存在近似15天和5天的显著周期,6月、10月等时间段存在大约2-4天的显著周期。蒙特利峡谷底边界层内流速日平均和月平均数据显示,5月峡谷底部流速达到最大值,9月和10月流速变弱；水平方向流动多为西向和南向流动,垂直方向长期存在着上升流；观测期间4月到6月水平方向流动表现为南向流强于西向流,之后西向流速增大,超过南向流。蒙特利峡谷底边界层内,水流紊动特征表现为脉动速度分量一阶矩近似符合高斯标准正态分布,剪切应力相关的二阶协方差项分布表现为高锋态正偏特征,湍流动能相关的二阶方差项分布表现为高锋态负偏特征。在流速最小时刻,利用w’和u'w'的时间自相关函数曲线的第二个峰值近似模拟出的湍流猝发周期分别为5.5s和3s；在流速最大时刻,模拟出的湍流猝发周期分别为2.5s和2s；流速中间时刻,自相关函数曲线无明显的峰值。湍流特征研究发现,蒙特利峡谷底边界层内湍流存在明显的各向异性。脉动强度的水平分量与垂直分量相差一个数量级；湍流摩擦速度和拖曳系数日平均的变化范围是6.50×10-3-2.32×10m/s和6.30×10-3-4.36×10,月平均最小值发生在7月；湍流耗散率一个周日内变化可达2-3个数量级,观测期间变化范围是1.09×108-6.62×10-5W/kg。底边界层内湍流特征量存在显著的周期变化,在一个周日内都以半日周期占优；湍流脉动强度和耗散率存在全日周期和三分之一日周期,湍流耗散率还表现出四分之一日周期特征；摩擦速度和拖曳系数存在全日周期和四分之一日周期。脉动强度、摩擦速度和拖曳系数都表现出大约8天和4天的显著周期。利用估算的湍流耗散率ε、摩擦速度u*和湍流动能et对理论模型ε-u*和ε-et进行检验,结果表明其理论模型不完全适用于蒙特利峡谷底边界层,模型理论系数大约为实测资料所得的修正系数的10倍。
[Abstract]:The movement of various scales exists in the ocean. The transfer of energy is usually from the large scale to the small scale, and finally dissipated in the form of turbulent motion. Turbulence is a small scale chaos movement which is different from laminar flow and irregularity. It is widely found in the fluid movement in the fields of atmosphere, ocean and engineering. Turbulent structure is complex and varied. There is a strong mixed diffusion effect in the fluid. Because of these special properties of turbulence, turbulence is difficult to observe directly, lack of large range, long time continuous observation data, the structure of turbulence, and the mechanism of production is not clear. Based on the need of ocean science for the long-term observation of turbulence, In this paper, the flow velocity data in the bottom boundary layer of Monterey gorge is continuously observed from April 24, 2011 to October 25th. The flow velocity changes in the boundary layer at the bottom of the canyon are analyzed, the characteristics of the turbulence are estimated and the characteristics of the turbulence are analyzed.
The analysis of average velocity of velocity per minute measured by ADV shows that there is a strong flow in the bottom boundary layer of Monterey gorge, and the average flow rate can reach the bottom of 0.398m/s. Canyon, which belongs to the reverse clockwise rotation flow system, which has the characteristics of the semidiurnal and the whole daily cycle. The results of the wavelet analysis show that the flow of the bottom of the valley has a significant period of approximately 15 days and 5 days in May and August, and there is a significant period of about 2-4 days in June and October. The daily and monthly mean velocity of flow velocity in the bottom boundary layer of Monterey Gorge shows that the flow velocity at the bottom of the May Canyon reaches the maximum, and the velocity in September and October is weaker; water square is square. The flow in the direction of flow is mostly westward and southward, and there is an upward flow in the vertical direction for a long time. During the observation period from April to June, the flow in the horizontal direction is stronger than the westward flow, and then the westward flow velocity increases, exceeding the south flow.
In the bottom boundary layer of the Monterey gorge Valley, the turbulent flow characteristics show that the first order moment of the pulsating velocity component approximates the Gauss standard normal distribution. The two order covariance distribution related to the shear stress is characterized by the positive bias of the high front state, and the two order variance distribution related to the turbulent kinetic energy is characterized by the negative bias of the high front state. The second peaks of the time autocorrelation function curve of W 'and u'w' approximated the turbulent burst periods of 5.5s and 3S, respectively. At the maximum velocity, the simulated turbulent burst periods were 2.5s and 2s, respectively, and there was no obvious peak in the autocorrelation function curve at the middle time of flow velocity.
It is found that there is an obvious anisotropy in the turbulent flow in the bottom boundary layer of the Monterey gorge. The horizontal and vertical components of the pulsating intensity vary by one order of magnitude; the daily average variation range of the turbulent friction velocity and drag coefficient is 6.50 * 10-3-2.32 * 10m/s and 6.30 x 10-3-4.36 x 10, and the monthly mean minimum occurs in July; The flow dissipation rate can be changed to 2-3 orders of magnitude in one Sunday. The variation range of the observation period is a significant periodic variation in the turbulent characteristics in the bottom boundary layer of 1.09 x 108-6.62 x, which is dominant in a half day period in a Sunday. The turbulent fluctuation intensity and dissipation rate are all daily and 1/3 days, and the dissipation rate of turbulent flow is found. The 1/4 day periodic characteristics are also shown; the friction velocity and drag coefficient exist full day period and 1/4 day period. The pulsation strength, friction velocity and drag coefficient show a significant period of about 8 days and 4 days. The estimated turbulence dissipation rate, friction velocity u* and turbulent flow energy et are examined for the theoretical model epsilon -u* and epsilon -et The results show that the theoretical model is not entirely applicable to the bottom boundary layer of Monterey gorge, and the theoretical coefficient of the model is about 10 times that of the measured data.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P731.26

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