热力非均匀下垫面对流边界层流场结构特征研究

利用对流水槽成功模拟热力非均匀下垫面对流边界层的发生发展。仿照数值模拟中常用的马赛克方法在对流水槽的底部铺了一些导热率缓慢的材料(橡胶薄板),使下垫面的加热存在差异,进而产生非均匀加热。利用温度廓线和准直光系统共同决定边界层顶部的位置和对流速度尺度。采用PTV测量技术获得高精度的二维流场,看到流场具有复杂的空间结构和尺度特征。相对于均匀下垫面来说,底部的非均匀加热使得混合层湍流的组织性得到加强,具有稳定的环流结构。非均匀下垫面对流边界层的方差随高度的变化曲线与均匀下垫面的特征明显不同。为了分析非均匀下垫面对流边界层的环流特征和水平输送对湍流变化的贡献,计算了湍流动能的湍流输送。计算结果表明,加热开始不久,由于不同下垫面的的温差较大,水平输送也较大;而当一段时间后,温差变小,水平输送也变小了。由此可以看出非均匀下垫面对流边界层的水平输送依赖于下垫面的非均匀强度。

Abstract

The simulation of convective boundary layer(CBL) over thermally inhomogeneous surface is made using water tank for study on flow properties. By imitating the mosaic method in the numerical simulation, the low thermal conductivity materials are placed on the bottom of the water tank so that heating from the bottom is inhomogeneous. The CBL height and velocity scales are obtained by temperature profiles and collimated-laser system. PTV technique is used for retrieval of two dimensional flow fields. The flow fields have complex structures and scales. Compared with the homogeneous surface, the surface inhomogeneous heating makes the mixed layer strengthen turbulence organization and has stable local circulations. The variations of statistics of velocities with height are different from the homogeneous situation. In order to analyze the contribution of thermal inhomogeneity to the horizontal advection, the turbulent advections for turbulent kinetic energy are calculated. Results show that at the beginning and developing period the horizontal advection is large due to the large heating difference and the horizontal advection becomes weak at the end of development of CBL due to the little heating difference. Based on these results, it can be concluded that the horizontal advection depends on the thermally inhomogeneous intensity.

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袁仁民, 罗涛, 吴徐平, 卢超, 孙鉴泞, 刘辉志. 热力非均匀下垫面对流边界层流场结构特征研究[J]. 大气与环境光学学报, 2009, 4(6): 421. YUAN Ren-min, LUO Tao, WU Xu-ping, LU Chao, SUN Jian-ning, LIU Hui-zhi. Study on Flow Properties of Convective Boundary Layer over Thermally Inhomogeneous Surface[J]. Journal of Atmospheric and Environmental Optics, 2009, 4(6): 421.

热力非均匀下垫面对流边界层流场结构特征研究

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