论文总字数：30106字

摘 要

离心泵在化工、水利、食品、制药等轻重工业领域有着广泛的应用。离心泵通常被认为是输送液体的设备，但在实际的生产实践中，离心泵常会混入气体，当离心泵输送气液两相流动介质时，其内部的流动状态会发生变化，使泵的各项性能下降，而且还常常伴有振动和噪声，严重时甚至可能会损害泵的结构，引发安全事故。因此，为了提高离心泵的效率和安全性，研究离心泵内部气液两相流动的演化规律是很有必要的。本文采用欧拉多相流模型和k-ε湍流模型对离心泵内部的气液两相流动进行了研究分析，研究的主要内容及结论如下：

（1）总结了国内外学者对气液两相流的基础理论研究、试验研究以及数值模拟研究的基本现状，并概括了他们的不足之处，指出了本文研究的方向。

（2）在单相定常模拟中，分析了离心泵内部压力和速度的变化，发现在叶轮通道中，越靠近流道出口的流体其压力越大。蜗壳中的流体压力很大但速度却很低。也分析了离心泵叶轮内的湍动能分布，发现靠近蜗舌的地方湍动能比其他地方大很多。另外还发现流量越小，湍动能就越大。

（3）通过进行纯水单相非定常模拟，对离心泵内部压力随时间的变化规律进行了分析。发现吸水室压力为负值，且有较大波动；蜗壳内各监测点的压力变化规律在一个旋转周期内都有6个波峰和波谷，这是由于有6个叶片造成的，且若监测点距离叶轮通道出口越近，其流动其压力波动的幅度也就越大。

（4）通过进行气液两相非定常模拟，分析了泵内流动从单相向气液两相发展的过渡过程的开始时刻与结束时刻，发现出口压力的变化先于气相体积分率的变化，这是由于气体未到达出口时便会对出口压力产生影响。通入气体后出口监测点的压力先是有所下降，然后保持不变。气体进入吸水室后聚集在吸水室的上壁面，且气相的速度要比液相快。在叶轮流道中气团首先从叶片的吸力侧被吸入，然后逐渐向叶片压力侧移动，最终向出口处移动。通入气体后的一段时间内，蜗壳各监测点处的气相体积分率均为0。在蜗壳内，距离叶轮出口越近，气相与液相的速度波动幅度越大；距离叶轮出口越远，气相与液相的速度波动幅度越小。

关键词：CFD；气液两相流；离心泵；输气过渡过程；数值模拟

Abstract

Centrifugal pump is widely used in light and heavy industries such as chemical industry, hydraulic engineering, food industry and pharmacy engineering. Centrifugal pump was usually considered as a fluid conveying equipment, but in the actual engineering practice, sometimes it will be mixed with gas in the centrifugal pump. When centrifugal pump conveyed the gas-liquid two phase flow medium, the state of its internal flow state will be changed. The performance of pump will also be changed. When the two-phase medium was conveyed, pumps also often accompanied by vibration and noise. When the vibration was serious, the structure of pump may be damaged seriously and this can even cause safety accidents. Therefore, in order to improve the efficiency and safety of centrifugal pumps, it is necessary to study the evolution of the gas-liquid two-phase flow in the centrifugal pump. In this dissertation, Euler multiphase flow model and k-ε turbulence model was used to study and analyze the gas-liquid two-phase flow inside the centrifugal pump. The main contents and conclusions of the study are as follows:

(1) The current situation of basic theoretical research, experimental research and numerical simulation research on the gas-liquid two-phase flow were summarized in this dissertation, and the research direction of this dissertation was pointed out.

(2) In the single-phase steady simulation, the changes of the internal pressure and speed of the centrifugal pump are analyzed It was found that in the impeller channel, the closer to the outlet of the flow channel, the greater the pressure was. The fluid in the volute is high in pressure but low in velocity. The distribution of turbulent kinetic energy in the impeller of centrifugal pump was also analyzed, and it was found that the turbulent kinetic energy near the tongue of cochlea was much larger than that in other places. It was also found that the smaller the flow, the greater the turbulent kinetic energy.

(3) Through the single-phase unsteady simulation, the variation law of the internal pressure of centrifugal pump with time was analyzed. It was found that the pressure in the suction chamber was negative and fluctuated greatly. The pressure variation rule of each monitoring point in the volute has 6 peaks and in a rotation cycle, which is caused by the presence of 6 blades. If the monitoring point is closer to the outlet of the impeller passage, the amplitude of pressure fluctuation of the flow will be larger.

(4) Through the unsteady simulation of gas-liquid two-phase, the starting and ending moments of the transition process from single-phase to gas-liquid two-phase flow in the pump were analyzed. It was found that the change of outlet pressure prior to the change of the volume fraction of the gas phase, because the gas would have an impact on the outlet pressure before reaching the outlet. The pressure at the outlet monitoring point first decreases and then remains the same. After gas enters the suction chamber, it concentrates on the upper wall of the suction chamber, and the velocity of the gas phase is faster than that of the liquid phase. In the impeller passage, the air mass is first inhaled from the suction side of the blade, then gradually moves to the pressure side of the blade, and finally moves to the outlet. The gas phase volume fraction at each monitoring point of the volute is 0. In the volute, the closer it is to the outlet of the impeller, the greater the velocity fluctuation between the gas phase and the liquid phase will be. The farther it is from the outlet of the impeller, the smaller the velocity fluctuation between the gas phase and the liquid phase will be.

目 录

摘要 I

Abstract II

目 录 IV

第一章 绪论 1

1.1 研究背景和意义 1

1.2 国内外研究现状与发展趋势 1

1.2.1 气液两相流的理论研究 1

1.2.2 气液两相流的试验研究 2

1.2.3 气液两相流的数值模拟 3

1.2.4 发展趋势 5

1.3 本课题研究的内容及拟采用的研究手段 5

1.3.1 研究内容 5

1.3.2 拟采用的研究手段 6

第二章 气液两相流的数值计算方法 7

2.1 几何模型 7

2.1.1 三维建模软件介绍 7

2.1.2 离心泵几何模型的建立 7

2.2 网格划分 8

2.2.1 网格的种类 8

2.2.2 几何模型的网格划分 8

2.3 多相流模型 9

2.3.1 多相流研究方法的比较 9

2.3.2 欧拉方法 9

2.4 湍流模型的选择 11

2.4.1 湍流模型的比较 11

2.4.2 标准k-ε模型 11

2.5 边界条件及计算设置 12

2.6 监测点的设置 13

2.7 本章小结 14

第三章 单相工况下数值计算结果与分析 15

3.1 定常的模拟及结果分析 15

3.1.1 离心泵的外特性曲线 15

3.1.2 不同流量下泵内压力和速度的分布 15

3.1.3 不同流量下叶轮的压力云图分析 18

3.1.4 不同流量工况下的湍动能分布 18

3.2 非定常的模拟及结果分析 19

3.2.1 非定常模拟方案 19

3.2.2 吸水管压力变化的结果分析 19

请支付后下载全文，论文总字数：30106字