﻿ 龙卷风维持特性的探索<sup>*</sup>
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DI Haoyu, XU Jinglei, GAO Ge
School of Energy and Power Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100083, China
Received: 2017-06-07; Accepted: 2017-10-13; Published online: 2017-12-04 17:16
Foundation item: National Defense Science and Technology Key Laboratory Foundation of China (9140C410505150C41192)
Corresponding author. XU Jinglei, E-mail: xujl@buaa.edu.cn
Abstract: A numerical model of the tornado was established by using computational fluid dynamics (CFD) method. Based on the speed type of the tornado in the plane, which was fitted to be the function relation, the initial velocity field and the related boundary condition were set in the 3D CFD program. Different initial temperature fields were carried out on a series of numerical simulations of tornado maintenance and development. The Ranque-Hilsch effect of the whirlpool and the convergence heat transfer principle were used to analyze the changes of the internal flow field variables of the two different temperature types in the tornado. It reveals the possibility of how the tornado was produced and continued, that is, the hot and cold air flow mixing and heat transfer which generated a temperature field may be the direct cause for producing and continuing a tornado. And a method to make tornado weak or even disappear was proposed, that is, destroying the temperature field.
Key words: computational fluid dynamics (CFD)     tornado     numerical simulation     convergence heat transfer principle     temperature field

1 数值模拟设置 1.1 数值模拟几何模型

 图 1 龙卷风数值模拟的网格划分 Fig. 1 Mesh generation for numerical simulation of tornado
1.2 控制方程及计算方法

1.3 初始速度场及边界条件的设置

 图 2 初始速度场的速度分布 Fig. 2 Velocity distribution of initial velocity field

1.4 不同初始温度场的设置

1) 算例1初始温度场为均一的温度场，即场域中初始温度均一样，为288 K。

2) 算例2的初始温度场采用类似于算例1相对稳定后的形式。

2 模拟结果与分析

2.1 算例1

 图 3 不同计算步数下的速度变化曲线(算例1) Fig. 3 Velocity variation curves under different calculation steps (Case 1)

 图 4 不同计算步数下的温度变化曲线(算例1) Fig. 4 Temperature variation curves under different calculation steps (Case 1)

 图 5 不同计算步数下的压力变化曲线(算例1) Fig. 5 Pressure variation curves under different calculation steps (Case 1)
 图 6 不同计算步数下的密度变化曲线(算例1) Fig. 6 Density variation curves under different calculation steps (Case 1)

2.2 算例2

 图 7 不同计算步数下的速度变化曲线(算例2) Fig. 7 Velocity variation curves under different calculation steps (Case 2)
 图 8 速度变化曲线对比 Fig. 8 Comparison of velocity variation curve

 (1)
 图 9 不同计算步数下的温度变化曲线(算例2) Fig. 9 Temperature variation curves under different calculation steps (Case 2)

 (2)

 图 10 不同计算步数下的压力变化曲线(算例2) Fig. 10 Pressure variation curves under different calculation steps (Case 2)
 图 11 不同计算步数下的密度变化曲线(算例2) Fig. 11 Density variation curves under different calculation steps (Case 2)
3 结论

1) 均一温度场的旋涡在旋转过程中会发生Ranque-Hilsch效应，产生一个不均一的温度场，通过这个温度场产生过程中气流内能所转化的动能来维持旋转，与此同时引起压力场和密度场的变化，最终这些变量互相匹配成一个新的旋涡变量场。由于新旋涡变量场是自适应生成的，所以其具有的变量场形式可代表所有稳定旋涡的变量场。

2) 特征如算例2的不均一的温度场更加贴近于实际龙卷风的温度场，其通过将气流汇聚到核心区域的加大旋转气流质量的同时加强气流旋转速度，来强化龙卷风旋涡并加剧其破坏力，其是由汇流换热原理所引起的。

3) 通过算例1的引申和算例2的验证，得到龙卷风的生成和强化主要依托于其温度场的变化，温度场梯度的大小在一定程度上决定了该龙卷风的破坏能力。因此，为使龙卷风的强度迅速降低甚至消亡，破坏龙卷风的温度场也许是一种行之有效的方法。

#### 文章信息

DI Haoyu, XU Jinglei, GAO Ge