低比转速复合叶轮离心泵非定常流场的数值模拟

发布时间：2018-01-16 14:22

本文关键词：低比转速复合叶轮离心泵非定常流场的数值模拟　出处：《浙江理工大学》2012年硕士论文　论文类型：学位论文

【摘要】：离心叶轮是低比转速离心泵的主要过流部件之一，其作用是将原动机的机械能直接传给流体，以提高液体的静压能和动压能，因此叶轮的结构对离心泵内部流场及性能有着至关重要的作用。对此，本文基于三维N-S方程和RNG k-ε湍流模型对具有4叶片普通叶轮、8叶片和12叶片复合叶轮的三台低比转速离心泵进行了非定常数值模拟，并进行了外特性性能试验测试。主要研究内容如下：采用PRO/E三维造型软件对4叶片、8叶片和12叶片叶轮低比转速离心泵进行三维整机全流场造型，并用CFD软件FLUENT对其内部流动进行了数值模拟，分析了不同时刻3台离心泵内部的速度场和压力场；此外，在蜗壳具有代表性的四个断面的壁面附近以及蜗舌部位设置了监测点，对蜗壳壁面附近的压力脉动进行了分析；最后，对三台低比转速离心泵的外特性性能进行了数值预测和试验测试，并将数值结果和试验结果进行了对比。经过分析，得出了以下结论： (1)针对数值模拟得到的3个叶轮内部不同时刻的速度场进行了分析，发现由于普通叶轮中没有布置分流叶片，相邻长叶片间流道比较宽阔，流体的流动不可能完全被叶片所夹持，使得长叶片压力面较厚边界层内的液体不能顺利排出，因此在4叶片普通叶轮的流道中存在大面积的低速回流区，这种现象在8叶片复合叶轮中有所改善，而在12叶片叶轮中改善最为明显。在12叶片叶轮中液流基本沿叶片的曲率流动，可见分流叶片在一定程度上可以改善叶轮内部的速度分布； (2)对数值模拟得到的3个叶轮内部不同时刻的压力场进行了分析，发现12叶片叶轮内部的静压分布较为均匀，静压曲线基本上沿圆周方向分布，且静压系数明显大于4叶片叶轮相同半径上叶片的静压系数。此外，蜗壳腔体以及出口的静压系数也较大，说明分流叶片不仅可以改善泵内部的压力分布，同时也可以提高相同位置的压力值； (3)对数值模拟得到蜗壳壁面附近的压力脉动进行了分析，表明复合叶轮可以改善蜗壳内部的压力脉动，值得注意的是，复合叶轮产生的压力脉动的频率成分相比普通叶轮复杂，在复合叶轮中，除了基频及其倍频外，，长叶片产生的频率在低频区上也会占主导地位； (4)针对3台低比转速离心泵进行了外特性性能试验研究，试验结果表明，12叶片叶轮离心泵扬程较高，但随着叶片数的增大，轴功率会变大，在一定程度上会影响泵的效率。
[Abstract]:Centrifugal impeller is one of the main overflowing parts of low specific speed centrifugal pump. Its function is to transfer the mechanical energy of the prime mover directly to the fluid in order to improve the hydrostatic and dynamic pressure energy of the liquid. Therefore, the structure of impeller plays an important role in the flow field and performance of centrifugal pump. Based on the three-dimensional N-S equation and RNG k- 蔚 turbulence model, the impeller with four blades is studied in this paper. Three low specific speed centrifugal pumps with 8 vane and 12 vane composite impellers have been simulated by unsteady numerical simulation, and the external performance tests have been carried out. The main contents of the research are as follows: The whole flow field of the centrifugal pump with low specific speed of 4 vane 8 blade and 12 blade impeller was molded by PRO/E software. The internal flow is simulated with CFD software FLUENT, and the velocity field and pressure field of three centrifugal pumps at different times are analyzed. In addition, monitoring points were set up near the wall of the four sections of the volute and the part of the cochlea tongue, and the pressure pulsation near the wall of the volute was analyzed. Finally, the external performance of three low specific speed centrifugal pumps is predicted and tested numerically, and the numerical results are compared with the experimental results. After analysis, the following conclusions are obtained: 1) the velocity field of the three impellers at different times obtained by numerical simulation is analyzed. It is found that because there are no shunt blades arranged in the common impeller, the flow channels between adjacent long blades are relatively wide. The fluid flow can not be completely trapped by the blade, which makes the liquid in the thicker boundary layer of the long blade pressure surface can not be discharged smoothly. Therefore, there is a large area of low speed return zone in the passage of the 4 vane common impeller. This phenomenon has been improved in the compound impeller with 8 blades, but most obviously in the impeller with 12 blades. In the impeller with 12 blades, the liquid flow flows basically along the curvature of the blade. It can be seen that the shunt blade can improve the velocity distribution in the impeller to some extent. 2) the pressure field of three impellers at different times obtained by numerical simulation is analyzed. It is found that the static pressure distribution in 12 blade impellers is more uniform, and the hydrostatic pressure curve basically distributes along the circumferential direction. In addition, the static pressure coefficient of the volute cavity and outlet is larger, which indicates that the shunt blade can not only improve the pressure distribution inside the pump. At the same time, the pressure value of the same position can also be increased. 3) the pressure pulsation near the wall of the volute is analyzed by numerical simulation, which shows that the compound impeller can improve the pressure fluctuation inside the volute. The frequency component of pressure pulsation produced by composite impeller is more complex than that of common impeller. In compound impeller, the frequency produced by long blade also dominates in the low frequency region besides the fundamental frequency and frequency doubling. The external performance of three centrifugal pumps with low specific speed is studied. The experimental results show that the head of the centrifugal pump is higher, but with the increase of the number of blades, the shaft power will become larger. To some extent, it will affect the efficiency of the pump.
【学位授予单位】：浙江理工大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TH311

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