非均匀下垫面对流边界层热通量特征的物理模拟研究

利用对流水槽,通过在底面设置马赛克状隔热覆盖物,模拟热力非均匀下垫面对流边界层的发生发展.在对流边界层发展的同时,利用温度廓线测量仪器分别测量不同下垫面的温度廓线,获取不同时刻温度场的数据,由此计算了热通量廓线.结果表明,非均匀下垫面对流边界层的归一化热通量随高度表现出非线性特征,即具有上凸和下凹的特征.上凸和下凹特征随时间出现振荡,这明显不同于均匀下垫面的情形.从热通量等值线图上可以看出,总体平均的热通量廓线振荡较小,局地热通量廓线振荡较大,而且下垫面未覆盖区域的热通量廓线比覆盖区域振荡的频率更高、振幅更大.这表明,非均匀下垫面条件下的对流边界层和均匀下垫面条件下的对流边界层的湍流结构有很大的不同.热力非均匀下垫面湍流特征呈现出一些均匀下垫面所没有的物理特性.在均匀下垫面得到的边界层的参数化规律不能简单地用于热力非均匀下垫面的对流边界层发展过程.水槽模拟的结果可以为数值模拟和野外观测提供有益的参考.

Laboratory Study on Heat Flux in the Convective Boundary Layer on Thermal Heterogeneous Surface

Convective water-tank is used to model the development of the convective boundary layer on thermal heterogeneous surface. Mosaic-like cover is put on the bottom of the water-tank to achieve thermal heterogeneity. In the convective boundary layer development, temperature profiles were measured on different surface region and with which heat flux profiles are calculated. The results show that normalized heat flux profiles behave the non-linear characteristics, that is, the convex and concave features. Convex and concave features oscillate over time. This is obviously different from the case of homogeneous surface. From heat flux contour map, the oscillation of the overall average heat flux profiles is smaller than that of the uncovered and the covered surface regions. And the oscillation on the uncovered surface region has a higher frequency and greater amplitude. The results show that some turbulence structures of convective boundary layer on thermal heterogeneous surface are quite different from that on the homogeneous surface. The law of the parameters for homogeneous surface can not be applied alike for heterogeneous surface. The experimental results can provide useful reference for numerical simulation and field observations.