兰州大学机构库 >土木工程与力学学院
大气表面层中大尺度湍流结构的三维形态特征及表征
Alternative TitleFeatures and Characterizations of Large-Scale Three-Dimensional Structures in the Atmospheric Surface Layer
刘洪佑
Thesis Advisor郑晓静
2017-04-14
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword高雷诺数壁湍流 大气表面层 大尺度结构 三维形态 空间尺度 结构倾角 层结稳定性
Abstract

由于高雷诺数实验设备和测量仪器的限制,目前对大尺度结构的认识还是非常有限的,其标度问题仍然有待解决。因此,为了获得高雷诺数的实验数据,本论文利用兰州大学在中国西部地区的青土湖沙漠建立的三维观测列阵(简称:“QLOA”)对大气表面层(ASL)进行了三维风速、温度和粉尘浓度的空间多点同步观测。从2013-2015年获得的大量实验数据中,通过严格的数据筛选和预处理,并将基本统计量与规范平板湍流边界层的理论和实验结果进行对比后,获得了可用于高雷诺数[Reτ~ O(106)]壁湍流分析的高质量数据。基于这些数据首先重构了大尺度结构的三维形态,对其空间尺度及结构倾角的变化规律进行了定量分析;然后建立了大尺度结构三维形态表征模型;最后,分析了热稳定性对大尺度结构形态特征的影响。

本论文得到的创新性结果主要有:1) 发现流向风速在垂向的速度梯度对大尺度结构的拉伸作用决定着其倾斜角度的大小,提出了一个无量纲参数表征结构倾角的变化,并给出了相应的标度关系;2) 在跨越3个量级的雷诺数范围内[Reτ ~ O (103) - O (106)]分析给出了大尺度结构的空间尺度随雷诺数及高度变化的一般规律:当流动尺度有明显的分离时(Reτ > 2000)空间尺度没有雷诺数依赖性,即可由外尺度标度;空间尺度随高度显著增加,但其增长速率逐渐减小,流向尺度在对数区顶部接近峰值,而展向和垂向尺度在整个边界层均持续增加,分别给出了相应的标度关系;3) 建立了大尺度湍流结构的三维形态表征模型,并通过与不同雷诺数条件下实验结果的对比,证实了该模型具有较高的预测精度;4) 不同热层结条件下大尺度结构三维形态的对比发现,在不稳定层结条件下,热力因素产生的浮力对大尺度结构有向上的抬升作用,增强了湍流输运和动量传输,使倾角和空间尺度增加;而稳定层结时热力因素对大尺度结构有向下的压制作用,使倾角和空间尺度减小;定量的分析表明,其空间尺度和倾斜角度随层结稳定性的变化均满足相似的对数线性规律。

Other Abstract

The understanding of the large-scale structures is still limited because of lacking high Reynolds numbers turbulent facilities and high resolution instruments. Therefore, in order to obtain high Reynolds numbers experimental data, we performed synchronous multi-point measurements for the three components of wind velocity, temperature and dust concentration in the atmospheric surface layer (ASL), which is located at the Qingtu Lake Observation Array (QLOA) site in western China. After applying the pre-processing and data selection criteria, high quality data which can be used in the study of high Reynolds [Reτ ~ O (106)] wall-bounded turbulent flows were acquired. Based on the selected high Reynolds numbers experimental data, the large-scale three-dimensional structures were investigated quantitatively, including constructing a volumetric view, scaling the feature quantity, and characterizing the three-dimensional shape of these structures. Furthermore, the thermal stability effects are also analyzed.

Some new results are obtained from the quantitative investigation. Firstly, we find that the inclination angle is dominated by the vertical velocity gradient (i.e., vertical wind shear). A non-dimensional is proposed to characterize the variation of the structure inclination angle. Secondly, the findings reveal the Reynolds number scaling of the spatial length and the general law of the scale growth over three orders of magnitude change in Reynolds number [Reτ ~ O (103) - O (106)]. The outer-scaled spatial length scales are found to have Reynolds number invariance when the scale separation is adequate (Reτ > 2000). The growth of the spatial length scales with the wall-normal distance shows a good collapse on outer-scaled axes for all the available data. The streamwise length scale exhibits a gradually slowing increase across the log region, while the spanwise and the wall-normal length scales display a piecewise linear increase throughout the boundary layer. Then, a characterization model of large-scale three-dimensional structures is proposed based on the quantitative analysis of the topological equivalent transformation of the two-dimensional (2D) ‘slice’. The calculated results agree well with the experimental results for both the current ASL and the laboratory boundary layer.

Finally, it is found that the large-scale structures change drastically under different stability conditions in the surface layer. In the unstable surface layer, the positive buoyancy has a ‘lifting’ effect that altering the orientation of the large-scale structures, enhancing the turbulent transport and momentum transfer, thus resulting in the relatively large spatial length and inclination angle. In the stable surface layer, the turbulent motions are suppressed by the negative buoyancy, the cold and denser air near the surface restricts the turbulent transport and momentum transfer, and resulting in the relatively short spatial length and small inclination angle. Furthermore, the spatial length and inclination angle varying systematically with the Monin-Obukhov stability parameter, increasing with the decrease of stability and follows a log-linear increase in the unstable regime. The present work contributes to a better understanding of the large-scale three-dimensional structures.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226621
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
刘洪佑. 大气表面层中大尺度湍流结构的三维形态特征及表征[D]. 兰州. 兰州大学,2017.
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