| Physical simulation has the characteristics of economic, practical, strong repeatability and easy control of experimental conditions. Physical simulation is one of the important means of atmospheric boundary layer research by controlling the parameters to study the phenomena of field observation and verify the results of numerical simulation. In this paper, water-tank is used to simulate the progress of convection layer development under the conditions of flat and inhomogeneous surface, analyzing the characteristics of temperature and flow structure on the mosaic and strip surface, respectively. And according to the similarity theory, a new kind of water-tank is designed to study the convective boundary layer with the horizontal shear. The main content is as follows:1. Physical simulation on horizontal temperature characteristics of the convective boundary layer.The characteristics of horizontal temperature of the convective boundary layer (CBL) were analyzed using water tank simulation. Based on the geometric similarity, kinematic similarity and dynamic similarity, the initial and boundary conditions can be set for simulation. The dimension of the water tank is1.5m×1.5m×0.6m. The degassed water was first filled with inversion stratification, then the bottom was heated and the convection was generated. The generation and evolution of the CBL were simulated. Temperature profiles and fluctuations at several heights were measured using fast response temperature sensors; optical turbulence was retrieved from the record using scintillation effect. Several parameters, such as the CBL depth, can be calculated. The AR power spectrum estimate was used to obtain the peak frequency of temperature fluctuations at those heights, which corresponds to the scale of quasi two-dimensional structure. The results show that scales of quasi two—dimensional structure at the low part of CBL increase with the height, reaching the maximum scale at about0.65z1, and then decrease with the height at the upper part of the CBI. The results show good agreement with the fields and the numerical simulation. At the upper part of CBL, the normalized scales decrease with stabilizations. Based on the results, a thermal pattern for the free CBL was proposed.2. Physical simulation on the convective boundary Layer over the thermal inhomogeneous surface.The Physical simulation experiment can be divided into two kinds of thermal heterogeneity surface in convective boundary layer:the strip surface and the mosaic surface.(1) The strip surface researches are mainly focused on the two strip thermal inhomogeneous surface using spectral analysis and dynamics method. By the results of the spectral analysis of the temperature and velocity fields, the following conclusions can be drawn:The Characteristics of the spectrum on the inhomogeneous surface is different with that on the homogeneous surface; the structure of the spectral peaks on the homogeneous surface is usually single; while on the stip inhomogeneous surface it is multitudinous. There are some large scale and some small scale of the spectral peak on the stip inhomogeneous surface. Analysis shows that:compared with the large scale the peak should be mainly by the stip inhomogeneous surface, the influence of smaller scale spectral peaks can be thought of as the result of the development of the mixed layer turbulence, due to the same as the scale of spectral peaks on the stip inhomogeneous surface. There is fluctuation of intensity relative to peak wavelength both the large and the small scales. This is actually a combined action of the Homogeneity and heterogeneity. On the two-striped inhomogeneous surface, a circulation will be lead similar to that of the land-sea breeze. The measurements show that the water-tank can get the typical structure of the sea breeze, even the minutiae of the sea breeze circulation. The scale method is applied to analyze the characteristics of the generating process of the land-sea breeze. The scale law of the land-sea breeze is different between the generating stages to the fully developing process stages according to the water-tank dataset. When the land-sea breeze is in the stage of full development, the scale law of the land-sea breeze is similar to that of field observation and numerical simulation results. However, in the stage of the generating process, the land-sea breeze complies with the additional length scale. Based on the water-tank dataset, we give generating conditions of the land-sea breeze. Water-tank experiment results show that the land-sea breeze is not formed immediately after the the land formed with upward heat flux and the temperature difference between land and sea in the morning. The analysis showed that the critical point can be interpreted as the sea breeze speed response to the accumulation of heat flux, that is to say when the land boundary layer has developed to a sufficient height,the land-sea breeze is able to occur. Water-tank experimental dataset are also used to the scaling analysis of the height and volume of the land-sea breeze. Although the results did not show the normalized depth of the land-sea breeze has stronger dependence relationship on∏1, and∏4than that on only∏1,, but the effectiveness of the volume flux scale indicates that the dependency between the land-sea breeze depth scale and stability. The Water-tank experiments also confirmed the balance of the land surface side heat convergence and air advection from the ocean to the land surface. The balance establishes and maintains between them in the period of the full development of the land-sea breeze.(2) From the viewpoint of thermodynamics, the heat flux oscillation characteristics over Mosaic inhomogeneous surface is analysised.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 uncovered and covered surface region. And the oscillation on uncovered surface region has a higher frequency and greater amplitude. The results show some turbulence structures of convective boundary layer on thermal heterogeneous surface are quite different from that on homogeneous surface. The law of the parameters for homogeneous surface cannot apply alike for heterogeneous surface. The laboratory experimental results of laboratory study can provide useful reference for numerical simulation and field observations.3. Physical simulation on the convective boundary layer with horizontal shear using the water-tank.Wind shear is the direct cause of mechanical turbulence. The Role and influence of mechanical turbulence in the atmospheric boundary layer has been great concern. Existing water-tank could do well in the simulation on the convective boundary layer. But the horizontal shear flow in CBL had not been implemented in our water-tank system before. The implement with heating and advection experiment in the water-tank has not been reported. The development process of the convective boundary layer with horizontal shear has been simulated using the convection water-tank while realizing horizontal flow. Fluctuating temperature are measured using the temperature sensor at eight different heights and two dimensional velocity fields are measured using particle tracking technology. The average temperature, temperature variance, turbulence intensity, average velocity and other parameters are calculated. The analysis results show that the temperature profile in close surface layer meet logarithmic relation, which is consistent with field observation. The hight of the boundary layer growing over time is deduced respectively using temperature variance and velocity field, and both results are consistent. The experimental results show that this water-tank can be well to simulate the development of the convective boundary layer with horizontal shear. And for the subsequent workes, it provides a good physical simulation platform. |
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