大气表面层中大尺度湍流结构的三维形态特征及表征

发布时间：2018-03-19 08:42

本文选题：高雷诺数壁湍流　切入点：大气表面层　出处：《兰州大学》2017年博士论文　论文类型：学位论文

【摘要】：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[Re_t~(46)(10~6)]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[Re_t~(46)(10~3)-(46)(10~6)]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(Re_t2000)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。
[Abstract]:Due to the limitation of high Reynolds number experimental equipment and measuring instruments, the understanding of large scale structure is still very limited, and the scaling problem remains to be solved. Therefore, in order to obtain the experimental data of high Reynolds number, In this paper, the three-dimensional observation array ("QLOA") established by Lanzhou University in the Qingtuhu Desert in western China is used to carry out the three-dimensional wind speed of the atmospheric surface layer (ASL). From a large number of experimental data obtained from 2013-2015, through strict data screening and pretreatment, the basic statistics are compared with the theoretical and experimental results of the turbulent boundary layer of the plate. The high quality data which can be used in the analysis of high Reynolds number wall turbulence are obtained. Based on these data, the three-dimensional shape of large scale structure is reconstructed, and the variation of spatial scale and structure inclination is quantitatively analyzed. Then, the three-dimensional morphological representation model of large-scale structure is established. The effect of thermal stability on the morphological characteristics of large scale structures is analyzed. The main innovative results obtained in this paper are: 1) it is found that the tensile action of velocity gradient of flow velocity in vertical direction determines the angle of inclination of large scale structure. A dimensionless parameter is proposed to characterize the variation of the structure inclination. The corresponding scaling relation is given. In the range of Reynolds number across three orders of magnitude, the general law of spatial scale variation with Reynolds number and height of large scale structure is given: when the flow scale is separated obviously, Ret2000). The spatial scale has no Reynolds number dependence. The spatial scale increases significantly with the height, but the growth rate decreases gradually, the flow scale approaches the peak value at the top of the logarithmic region, while the span and vertical scales increase continuously in the whole boundary layer. In this paper, the corresponding scale relation is given. (3) the three-dimensional morphological representation model of large scale turbulent structures is established, and the results are compared with the experimental results under different Reynolds numbers. It is proved that the model has a high prediction accuracy. (4) the comparison of three-dimensional morphology of large scale structures under different thermal stratification conditions shows that under unstable stratification conditions, the buoyancy produced by thermodynamic factors has upward uplifting effect on large scale structures. The turbulent transport and momentum transport are enhanced, the inclination angle and spatial scale are increased, while the thermal factors have a downward suppression effect on the large scale structure during the stable stratification, and the inclination angle and the spatial scale are decreased, and the quantitative analysis shows that, The variation of spatial scale and inclination angle with the stability of stratification satisfies the similar logarithmic linear law.
【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O357.5

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