Abstract: In order to study the flow in the completely symmetric structure of the converging-diverging tube such as Venturi, the incompressible unsteady flow numerical models are established respectively for two dimensional channels and three dimensional tubes, and the numerical simulation method is adopted in the study. This paper confirms the flow bifurcation phenomenon, and mainly discusses the asymmetric flow in the symmetric structure. The simulation results show that, when Reynolds number reaches a critical value, the flow field in the symmetric Venturi tube will appear the asymmetric phenomenon, and produce irregular recirculation zones in the extended corner. In addition, the study indicates that the flow characteristics in the symmetric converging-diverging tube are affected by Reynolds number and geometry shape of tube, and the variation rules which flow asymmetric characteristics change with Reynolds number and geometry shape are obtained.

Key words: Venturi tube, symmetric structure, asymmetry, turbulent flow, numerical simulation, CFD, instability

摘要： 针对文丘里管这类具有完全对称结构的缩扩管道，分别对二维通道和三维管内流动建立了不可压缩非稳态数学模型，采用数值模拟的方法，研究了流动分岔现象，重点探讨了在这种对称结构下出现的非对称流动。数值模拟结果表明，当Reynolds数超过某临界值，对称结构的文丘里管内流场都出现了非对称现象，在扩展角部产生不规则的回流区。其流动主要受Reynolds数和管道几何形状的影响，并具体说明了流动不对称特性随这两者的变化规律。

关键词: 文丘里管, 对称结构, 非对称, 湍流, 数值模拟, 计算流体力学, 不稳定性