【作者】 林松；

【导师】 敬成君；

【作者基本信息】 西南交通大学 ， 供热、供燃气、通风及空调工程， 2006， 硕士

【摘要】 本研究以晶体生产系统为基础设计了简化的物理数学模型。模型是关于固定几何尺寸的方腔里的热对流。该热对流是由浮力或(与)表面张力的驱动作用而产生的。其中,浮力由Grashof准则数Gr确定,表面张力由Marangoni准则数Ma确定。通过大量的数值模拟发现,不同的准则数Gr与Ma组合有不同的流动状况。小Gr与Ma时获得定态解,大Gr与Ma时会得到振荡解。 首先,调节准则数Gr或(与)Ma以改变表面张力或(与)浮力的大小,考察流场各参量的特征,寻求流态由定态向振荡转化的过渡区,为后继研究提供数据样本;然后,利用正交分解法解剖复杂振荡流场的流体结构,抽出简单的基本流动模式及其模式在完整流场中的权重;接着,通过流场各参量定态时的定态值、振荡时的平均值及扰动值基本模式的对比,判断不同条件下的表面张力与浮力各自对热对流的贡献程度;最后,提出抑制热对流不稳定性的一种新方法。 本研究利用正交分解法对振荡流场进行分解,以获取的扰动场基本模式分析流动不稳定性。同时,提出研究热对流不稳定性的一种新方法,即通过各种流场信息的对比分析来判断不同条件下表面张力与浮力对热对流的贡献,并预测了热对流不稳定性的一种新的控制方法,即表面张力可以抑制由浮力引起的热对流不稳定性。 在理论方面,利用正交分解法来分析流动不稳定性,有可能开创研究流动稳定性的新方法,丰富了计算流体力学分析流动稳定性方面的内容;在实践应用方面,为强烈需求热对流稳定性的单晶生产工艺预测了新控制方法,为热环境设计提供了新思路,使高品质大直径单晶的生长成为可能。 本研究意图是在于研究新方法的可行性试验,以便在后继的增加维数、驱动力数,并由定性分析到定量分析的深入研究中,获得各驱动力不同条件下贡献的百分比。更多还原

【Abstract】 A simplified physical and mathematical model based on the Czochlarski crystal growth system was designed in this study. The model dealt with the thermal convection in a cavity of length to height being 2 to 1. The thermal convection was driven by two forces: buoyancy, described by Grashof number Gr, and surface tension, described by Marangoni number Ma. A lot of numerical simulations shew that various flow regimes occurred under various sets of Gr and Ma. When both Gr and Ma are small, stationary solutions are common. With the increase of Gr and Ma, oscillatory solution occurred. The main interest of the studies was focused on the contribution of Gr and/or Ma to the formation of flow field. Proper orthogonal decomposition (POD) was applied to investigate the role played by Gr and Ma. POD is a powerful method of analyzing the flow structure, with which basic flow modes of any complex flow could be extracted. By the comparison of the basic flow modes and other characteristics such as average values and vortices of flow fields caused by Gr and/or Ma, it was suggested that POD could found its important application in analyzing the mechanism of thermal convection. The details are as follows.The many characteristics of flow were investigated. In order to find the transition region between the stationary state and oscillatory state, researcher adjusted the surface tension and buoyancy by changing the value of Gr and Ma. By comparing the values and the distributions of variables at stationary states and the change with time and the average value of variables at oscillatory state, researcher reached conclusion about the contribution of the surface tension and buoyancy to the flow under different conditions. The mechanism of thermal convection was made clearer, with which a new way to suppress thermal convection was suggested.It is the first time that using POD to decompose oscillatory flow and get useful information about the fluctuation, such as the basic flow modes and the percent of every basic flow mode to thermal convection. This Study put forward a new method of investigation the instability of thermal convection by comparingthe major information of the flow field. The contribution of the surface tension and the buoyancy to the instability of thermal convection was revealed. A new way to control the instability of thermal convection was suggested. A proper surface tension could suppress the instability of thermal convection caused by buoyancy.This study proposed and tested a new way to analyze oscillatory flow. It will enrich the method of thermal convection instability analysis. Researcher put forward a suggestion of how to control the instability of thermal convection for crystal growth, where stable flows are strictly required. The crystal of high quality and large diameter may be grown.In order to increase dimensions and the number of driven forces in continuing studies, the purpose of this study is to try out the feasibility of this new method. Researcher hopes reaching not only qualitatively but also quantitatively the conclusion of the percent of different driven force under different conditions at last.更多还原