Abstract: In order to solve the problems of small mixing ratio and inaccurate mixing ratio of jet mixer, a two-stage injection jet mixer was designed. The method of computational fluid dynamics was used to numerically simulate the fluid flow characteristics of the two-stage injection jet mixer. According to venturi pipe design standards and combing with CFD to simulate and calculate the different nozzle diameters, best mixing diameters were obtained, which were 9 and 21 mm, respectively. Using a four-factor and four-level simulation design, the influence of different throat lengths, expansion tube short axis lengths and diffuser tube angle  on the uniformity of the mixer outlet surface were explored. The simulation results showed that when the length of the primary throat was 45 mm, the length of the secondary throat was 80 mm, the short axis length of the primary jet expansion tube was 26 mm, and the angle of the secondary jet diffusion tube was 7°, the coefficient of variation was the smallest and the best mixing uniformity. And then the influence of different mixing ratios on the mixing coefficient of variation of the mixer was simulated and analyzed, and it was concluded that the two-stage mixer  achieved the same mixing effect under different mixing ratios. According to the optimized simulation results, the test data of different flow rates and mixing ratios were selected to compare the mixers. The test results showed that the maximum error between the test value and the actual value of the same mixing ratio was 3.5%, and the mixing coefficient of variation was all below 0.041 2, which indicated that the mixer could achieve a better mixing effect when the mixer was from 300∶1 to 3 000∶1. The maximum error between the simulated value and the experimental value of the same mixing ratio was 12.1%, which proved that the two-stage injection jet mixer meets the design requirements.

Key words: CFD, two-stage injection jet mixer, numerical simulation, coefficient of variation

摘要： 为解决射流混合器混合比小且不精确的问题，设计了一种两级注入式射流混合器。采用计算流体力学方法对两级注入式射流混合器内部的药水流动特性进行数值模拟。根据文丘里管的设计标准，借助CFD模拟计算不同喷嘴直径，获得最佳混合的喷嘴直径分别为9和21 mm。利用四因素四水平仿真设计，探究了喉管长度、扩收管短轴长度和扩散管角度对混合器出口面均匀度的影响。模拟结果表明，在一级喉管长度45 mm、 二级喉管长度80 mm、一级射流扩收管短轴长度26 mm、二级射流扩散管角度7°时，变异系数最小，混合均匀度最佳。进一步仿真分析了不同混药比对混合器混合变异系数的影响，得出两级混合器可以在不同的混合比下达到相同混合效果。根据优化仿真结果，选取不同的流量与混药比对混合器进行对比试验，结果表明，同一混合比的试验值与实际值的最大误差为3.5%，且混合变异系数均在0.041 2以下，证明混合器在300∶1~3 000∶1时，均能达到较好的混合效果。同一混合比的模拟值与试验值的最大误差为12.1%，证明两级注入式射流混合器符合设计需求。

关键词: CFD, 两级注入式射流混合器, 数值模拟, 变异系数