【作者】 李忠；

【导师】 杨敏官；

【作者基本信息】 江苏大学 ， 流体机械及工程， 2011， 博士

【摘要】 空化现象普遍存在于诸多领域内液体输送过程中,空化的发生会造成输送机械性能的下降,产生空蚀破坏,引起机组振动加剧,无法控制的空化会产生严重的甚至是灾难性的后果。对空化流动的研究属于多学科强交叉的范畴,揭示空化流动的机理从而实现对空化程度的有效控制是学术界和工程界急需解决的难题。目前对空化两相流动理论的研究仍处于探索之中,水力机械内部空化流动机理尚未被揭示。在国家自然科学基金项目(N0.50776040)的资助下,本文以自行设计的轴流式模型泵为研究对象,从理论分析、数值计算和实验研究三方面入手,对该型泵内空化演变过程、流动机理等问题进行了较为系统的研究,主要工作及取得的创新性成果如下：1、从分析水力机械内空化流动理论入手,详细阐述了影响空化发生和发展的因素以及水力机械内空化监测和定位的方法,提出采用(托马)空化系数判定轴流泵内空化程度、摄像法和振动法相结合的手段研究泵内空化流动细节的思路。2、结合轴流泵叶轮内液体运动规律的分析,阐述了变环量设计方法的实质,推导出了满足泵能量性能的环量分布系数表达式,并以此为基础设计了轴流式模型泵。通过泵性能试验,验证了设计方法的有效性。3、通过对不同湍流模型下计算结果的对比分析,确定了轴流泵内空化流动的合适计算模型。基于上述模型,对模型泵内的空化两相流场进行了全流道、三维定常计算,初步揭示了不同空化程度下泵内空化发生位置、空泡团形态的演变规律及对泵性能、空蚀破坏的影响,揭示了轴流泵叶顶间隙产生的空化流动的结构及特征。4、运用高速摄像技术和图像处理技术对不同空化程度下的非稳态空化流动细节进行捕捉、显示和测量分析,获得了空化初生、发展和恶化阶段空化流动的时空特性,从空泡团形态特征的角度提出了泵临界汽蚀的判定依据。研究中得到了空化初生空泡团的大致生命周期、旋涡空化的涡径尺寸分布规律以及空化发生区域随空化系数的演变过程等重要信息,基本掌握了轴流泵内空化流动的形态变化特性。5、提出了适合于模型泵的振动信号测量及分析方法,运用LMS多通道振动噪声测试与动力学分析系统对模型泵内水力因素诱发的振动进行了较为全面的测量,详细分析了能量工况、空化工况及不同调节方式下的振动特性,并从理论上分析了空化对振动的激励和阻尼的关系,基本掌握了模型泵振动随工况的变化规律。提出了利用振动法识别泵最优工况点、判断空化的不同发展阶段的方法。研究结果为有低振动传递要求的泵的安全运行提供了有益的参考。本文的研究成果、研究方法在一定程度上可以推广应用于其它类型水力机械内的空化流动的研究。更多还原

【Abstract】 The cavitation phenomenon exists widely in many domains with liquid transporting process. The occurrence of cavitation will decrease the performance of conveying machinery and cause cavitation erosion, lead to additional vibration. The uncontrollable cavitation will cause serious or even disastrous consequences. The study of cavitating flow belongs to categories of multidiscipline crossing. Revealing the mechanism of cavitation and then controlling the degree of cavitation effectively are the urgent need for academy and engineering. At present, researches on the cavitation two-phase flow theory are still on exploration road, especially in the internal field of hydraulic machinery. Under the support of National Natural Science Fund (No.50776040), the self-designed model axial-flow pump is adopted as the study object. Systematic study on cavitation evolution and cavitating flow mechanism in model pump has been done. The major works and achievements are as following.1. Based on the basic theories of cavitating flow in hydraulic machinery, detailed descriptions about influencing factors of cavitation and methods of cavitation monitoring and positioning were given. The idea of using Thomas-coefficient and combination research methods of vibration and photograph to study the cavitating flow in axial-flow pump was put forward.2. Combined with the analysis of flow mechanism in axial-flow pump, the nature of variable circulation design was discussed. The formula of distribution coefficient about outlet circulation meeting pump energy performance was derived. The axial-flow pump was designed with above method. The validity of design was verified by pump performance tests.3. According to comparative analysis of calculation results of four turbulence models, the adaptive simulation model of cavitating flow in axial-flow pump was determined. Based on conformed method, the three-dimensional steady turbulent cavitating flow in the pump was simulated. The preliminary study on location and evolution law of cavitation was carried out. The influence of cavitation on pump performance and erosion was alos given. The structure and features of cavitating flow through blade tip clearance was revealed.4. The details of unsteady cavitating flow under different cavitation coefficient were captured and measured by using high speed imaging and image processing technology. The time and space characteristics of cavitating flow in different stages were obtained. A judging basis for detecting pump’s cirtical cavitation point was proposed form perspective of cavitation shape. The lifecycle of incipient cavitation, distributation of vortex cavitation, occurrence region of cavitation were obtained. The variation characteristic of cavitating flow in the pump was basically grasped.5. The suitable measurement and analysis methods of vibration signal were proposed. The vibration induced by hydraulic factors was measured by using LMS sound&vibration measurement. The vibration characteristics of model pump under different situations were analysised and the relationship between vibration and pump running condition was approximately masted. The judging methods of best efficiency point and cavitation degrees of the pump were proposed. The research results provide an effective reference for safe operation of pump.Research achievements and methods form this paper can be extended and applied on study of cavitating flow in other types of hydraulic machinery.更多还原