射流式离心泵气液两相流动特性研究

发布时间：2018-08-01 18:45

【摘要】：射流式离心泵作为节水灌溉的主要设备之一,提高其自吸性能对于节水灌溉的发展起到至关重要的作用。本文采用CFX软件所提供的双欧拉多相流模型对射流式离心泵进行气液两相流模拟。并对数值模拟结果进行对比分析,得到射流式离心泵内部气液两相流的流动规律,为后续优化自吸性能提供借鉴。本文选择浙江某企业的JET750射流式离心泵作为主要研究对象。其主要研究内容和创新成果如下:1)采用流场分析软件CFX对JET750射流式离心泵进行液相模拟,分析发现,喷嘴出口的循环流量随着运行工况增大,逐渐减小,对应的喷嘴出口处的涡量值以及喉管处的静压、射流器内部的湍流强度逐渐降低。射流器出口流体的速度趋向于均匀流,扩散段的流动分离逐渐减小,流体过流能力增强。2)为了研究射流式离心泵内部气液两相流动规律,对泵进口分别设置不同气相浓度同一运行工况以及同种进口气相浓度不同运行工况下的气液两相模拟。当对进口不同含气率模拟结果进行分析,发现随着进口气相含气率的增加,喷嘴循环流量逐渐降低,叶轮流道内的含气率以及射流器内部各截面上的气相含气率也逐渐增加,气相平均速度逐渐减小。当对同种进口含气率不同运行工况模拟结果分析发现,随着运行工况的增加,喷嘴出口的循环流量逐渐增加的,叶轮内部的气相过流能力加强,扬程下滑相对小流量工况要小。3)将射流式离心泵中射流器部分提取出来,单独进行气液相两相流数值模拟。以射流器喷嘴直径0P、喉管直径1P、喉管长度2P、喉嘴距3P四个参数为试验因素,出口气相的流速为目标函数,设置正交试验样本,根据模拟结果通过Isight软件对射流器的四个因素以及目标函数进行拟合得到近似模型。R-squared可到0.88,拟合优度满足求解要求,并得到各因素对射流器气相过流能力的影响程度,从大到小分别为P_o、P_o~2、P_1~2、P_1、P_1~*P_3、P_0~* P_1、P_1~*P_2 、P_2~2、P_3 、P_3~2。然而修改喷嘴直径以及喉管直径将改变面积比,面积比的变化对于外特性影响很大。在试验部分对候嘴距以及喉管长度这两个因素进行修改,通过自吸性能以及外特性性能试验,发现适当的增加喉管长度有利于改善自吸性能,自吸高度由原来的7.45米提高到9.1米,自吸时间也由原来的145s缩短到90s,而外特性基本保持不变,若继续增加喉管长度,射流器内流损失急剧增大,外特性开始下滑。通过模拟发现,适当的加长喉管长度不仅使过流能力上有所提升,喉管处的压力有所降低,卷吸能力有所提升,这对于气相过流能力都是有利的。本次对于自吸性能的优化已经应用到公司产品当中。
[Abstract]:As one of the main equipment of water-saving irrigation, jet centrifugal pump plays an important role in the development of water-saving irrigation. In this paper, the two-Euler multiphase flow model provided by CFX software is used to simulate the gas-liquid two-phase flow in the ejection centrifugal pump. By comparing and analyzing the numerical simulation results, the flow law of gas-liquid two-phase flow in the jet centrifugal pump is obtained, which provides a reference for the subsequent optimization of self-priming performance. In this paper, the JET750 jet centrifugal pump of a Zhejiang enterprise is chosen as the main research object. The main research contents and innovative results are as follows: (1) the liquid phase simulation of JET750 jet centrifugal pump is carried out by using the flow field analysis software CFX. It is found that the circulating flow rate at the nozzle outlet decreases gradually with the increase of the operating condition. The vorticity at the nozzle outlet and the static pressure at the throat reduce the turbulent intensity of the jet. In order to study the gas-liquid two-phase flow in the jet centrifugal pump, the velocity of the fluid at the outlet of the jet tends to be uniform, the flow separation of the diffusion section decreases gradually, and the flow capacity of the fluid overflows increases by .2) in order to study the gas-liquid two-phase flow in the jet centrifugal pump, The gas-liquid two-phase simulation was carried out at the pump inlet under the same operating condition with different gas concentration and different operating conditions with the same inlet gas concentration. When the simulation results of different inlet gas holdup are analyzed, it is found that with the increase of inlet gas holdup, the flow rate of nozzle cycle decreases gradually, and the gas holdup in impeller channel and in each section of the jet is gradually increased. The gas phase average velocity decreases gradually. When the simulation results of the same inlet gas content and different operating conditions are analyzed, it is found that with the increase of the operating conditions, the circulating flow rate of the nozzle outlet increases gradually, and the gas phase overflow capacity inside the impeller is strengthened. Compared with the low flow rate, the head slide is smaller than that of the small flow rate (3. 3) the jet part of the jet centrifugal pump is extracted and the gas-liquid two-phase flow numerical simulation is carried out separately. Taking the four parameters of jet nozzle diameter 0 P, throat pipe diameter 1 P, throat length 2 P, throat distance 3 P as test factors, and the velocity of gas phase at outlet as objective function, the orthogonal test samples were set up. According to the simulation results, the four factors and the objective function of the jet were fitted by Isight software to get the approximate model. R-squared can reach 0.88. The goodness of fit meets the requirements of the solution, and the degree of influence of each factor on the gas phase overflow capacity of the jet is obtained. From the big to the small, to the next, to the second, to the flesh, to the flesh; to the flesh, to the number of people; However, the area ratio will be changed by modifying the nozzle diameter and the throat diameter, and the change of the area ratio will have a great influence on the external characteristics. In the test part, two factors, the distance between the nozzle and the length of the pipe, are modified. Through the self-priming performance and the external characteristic test, it is found that the proper increase of the length of the pipe is beneficial to the improvement of the self-priming performance. The self-priming height is increased from 7.45 m to 9.1 m, and the self-priming time is shortened from 145s to 90s, but the external characteristic remains unchanged. If the length of the throat is increased, the loss of the inner flow of the jet will increase sharply, and the external characteristic will begin to decline. It is found by simulation that the proper length of the long pipe not only increases the overcurrent capacity, but also reduces the pressure and the entrainment capacity of the pipe, which is beneficial to the gas phase overcurrent capacity. This self-priming performance optimization has been applied to the company's products.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH311

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