基于现有的文氏咀流量供给管道, 提取出轴对称2维计算模型, 计算了不同背压下文氏咀及下游管道的流场特性。计算结果显示, 随着背压的升高, 激波在管道内经历了3种状态, 在直管道内为斜激波, 到转接段时为拟正激波, 进入文氏咀后则为正激波。在进行文氏咀流量计的设计时, 应尽量将正激波控制在文氏咀喉道或向下游延伸的一小段距离内, 此时是文氏咀的最佳工作状态。另外, 采用壁面开孔法在文氏咀下游选取测压点时, 为了准确测量截面上的静压, 应将测压点选取在距离直管道入口数倍管径处, 一般不低于8倍管径。

Based on the existing Venturi nozzle fluid supply system, an axisymmetric two-dimension computation model was presented. Flow field characteristics of Venturi nozzle under different back pressures were calculated using computational fluid dynamic methods. The numerical simulations demonstrate that, shock waves in the pipeline go through three states owing to back pressure’s increasing: oblique shock wave in straight circular pipeline, pseudo-normal shock wave in endocone adapter connector, and normal shock wave in Venturi nozzle. During the design of Venturi nozzle flowmeter, normal shock waves must be restricted beside the throat of Venturi nozzle or within a short distance downstream from the throat, which offers the advantages of low total pressure loss and stable flow field. Wall-drilling method is usually selected to measure the static pressure downstream of Venturi nozzle. In order to ensure the accuracy of measurement, the optimal distance between the static pressure orifice and the straight circular pipeline entrance plane should be several times, generally no less than eight times, the nominal diameter of straight circular pipeline.