水力装置空化空蚀数值计算与试验研究

发布时间：2018-02-09 09:48

本文关键词： 文丘里管孔板离心泵空化发生器试验测试　出处：《江苏大学》2015年博士论文　论文类型：学位论文

【摘要】：本文在国家自然科学基金项目(51239005,51309120)、国家留学基金委公派联合培养博士生项目、欧洲太空总署(European Space Agency,ES A)项目"Cavitation in Thermosensible Fluids"和江苏省高校博士研究生创新基金(CXLX12_0640)的资助下开展工作。随着科技的进步以及工业制造精度的提高,水力机械得到了迅猛的发展,然而伴随着其大型化高速化而产生的空化问题则更加凸显。空化的存在不仅会降低水泵等水力机械的运行效率,还会产生振动和噪声,甚至会对水力机械固体表面造成破坏,严重影响系统的安全稳定运行。另一方面,空化由于具有复杂的物理化学相变流动特征与特殊的非定常动力特性,已成为污水处理、水下兵器减阻和管道清理等领域的一种高效低能耗新兴技术手段。本文首先对文丘里管和孔板两种结构简单的水力装置进行空化空蚀研究,采用理论分析、数值计算和实验测量相结合的方法研究空化空蚀形成机理与相互关系。随后以此为基础,对应用更为广泛、结构更为复杂的旋转类水力机械——离心泵进行空化空蚀的研究,改进离心泵空化数值计算模型,揭示离心泵内空化的非定常特性,建立离心泵空蚀预测方法。最后对一种水力空化发生器进行系统研究,为空化应用的研究提供一定的参考。本文的主要工作和创新性成果有：1.针对水力装置与机械空化数值模拟过程中需人为不断调整边界条件的问题,基于批处理(Batch)和ANSYS-CFX建立了一种空化数值模拟自动运行方法,实现了CFD计算软件的自动调用和边界条件的自动修改,使计算能够直接执行下一步。该方法保证了数值模拟过程的无缝衔接,缩短了计算周期。2.通过对文丘里管空化空蚀的研究,建立了一套试验研究—数值计算—图像后处理相结合的空化空蚀研究方法,具体研究了空泡各发展阶段与空蚀的内在联系。基于RNG k-ε模型提出了一种考虑空化可压缩性及湍流粘度修正的CDM湍流模型,有效地解决了常用湍流模型对湍流粘度过预测的问题：采用两台高速相机同时对文丘里管空泡结构演变与空蚀过程进行记录,实现了空化与空蚀的同步测量；采用蚀点计算法对空化空蚀数据进行分析,并辅以可压缩数值模拟方法,研究了空泡不同发展阶段时的空蚀破坏力。研究结果表明：空泡团的脱落与溃灭过程均会释放高能量的冲击波,并对固壁表面造成破坏,且后者为主要原因；蚀点的数量与面积的增长规律并非线性,而是呈阶梯状递增,空蚀大多在空泡溃灭或脱落时发生。3.基于孔板射流的空化空蚀试验研究,建立了一种基于空泡图像的空蚀预测方法。采用MATLAB软件对空化试验数据,即高速相机采集的连续空泡图像进行标准方差与平均值处理,预测出了潜在的空蚀区域以及相应的破坏程度,并反映出空泡的分布情况。空蚀试验结果证明了该方法的有效性与准确性,孔板射流空化的空蚀区域位于脱落空泡的溃灭点位置呈环状形态,其半径与采用空泡图像空蚀预测方法的半径相同。试验研究还揭示了流场速度与空蚀的关系,在空化数相同的前提下,流场流速越高,空蚀的程度越严重。4.以本文建立的CDM湍流模型为基础,考虑离心泵的旋转效应与大曲率结构特征,建立了一种适用于离心泵空化数值模拟的RCD湍流模型,并与试验结果进行了对比,结果表明：相比标准κ-ε模型与SST k-ω模型,RCD模型有效地抑制了传统湍流模型对湍流粘度的过预测,并准确地捕捉到更为细致的泵内湍流涡团与速度分布,使得数值计算能够准确地模拟出离心泵内空化流非定常脱落与溃灭的现象。当空化数不变时,在一个旋转周期内每一流道的空泡会依次经历发展、局部脱落、缩小再发展的周期性非定常过程。5.研究了ZGB空化模型中空泡半径、汽化与凝结经验系数对离心泵空化扬程下降曲线预测精度的影响,结果表明：空泡半径与汽化经验系数同时影响空泡的长度及含气量大小,凝结系数主要影响空泡的长度；高空泡含气量区域主要影响叶片吸力面进口前缘低压区的范围,低压区的长度与高空泡含气量的长度相当,而高空泡含气量区域的大小对离心泵扬程的影响较小,影响扬程预测精度的主要因素为空泡长度。6.考虑离心泵的旋转运动特性和流体湍动能与空泡结构演变的内在联系,基于ZGB空化模型发展了一种适用于离心泵空化数值模拟的RZGB空化模型,建立了离心泵转速和几何结构与空泡半径的函数关系。对RZGB模型对不同比转速离心泵的预测精度进行了评估,结果表明：对于低、中比转速泵,RZGB模型的汽化凝结项经验系数分别为5000和0.001时预测精度更高；对于高比转速泵采用汽化凝结项经验系数为50和0.01计算更为准确。与可视化空化试验结果对比表明,RZGB模型能够更准确地捕捉到离心泵进口空泡的三维特殊结构以及空穴尾端的不稳定现象。7.以本文建立的空泡图像空蚀预测方法为基础,建立了适用于旋转水力机械的空蚀预测方法,并通过空蚀试验证明了该方法的准确性与可靠性。该方法对连续的高速摄影图像或数值计算图像进行一系列的图形变换,保证各叶轮流道固定不变,再以图像标准方差与平均值处理方法进行分析,从而获得了离心泵叶片表面的空蚀区域与空泡分布。结果表明空蚀位置与空泡区域基本相当,但主体偏向空穴尾端,即离心泵中附着空泡尾端的高湍流不稳定现象同样会对固壁表面造成破坏。8.基于RCD湍流模型与RZGB空化模型,并结合试验对一种转子一定子型水力空化发生器的性能进行了系统的研究。研究结果表明,空化发生器内主要有三种空化类型,即转子与定子相对运动形成的楔形槽空化、转子高速旋转形成的转子叶片前缘空化和尾端低压区空化。在相同转速下空化发生器内的压力脉动随着流量的增加而增大；在相同流量下空化发生器内的压力脉动随着转速的增加而增大；增大转子与定子的间距将小幅度地降低腔内的压力幅值；空化发生器内的主要空蚀区域为转子叶片尾端,定子叶片前缘空泡附着部分及其尾端；空蚀主要在转子与定子完全交错时发生,此时形成的空化强度高且贴近固壁表面,这表明空泡在水力机械近壁面处的溃灭是导致空蚀发生的必要条件。
[Abstract]:Based on the National Natural Science Fund Project (5123900551309120), joint training doctoral project CSC public school, the European Space Agency (European Space Agency, ES A Cavitation in Thermosensible Fluids) project ", and the Jiangsu Province universities graduate student innovation fund (CXLX12_0640) to carry out the work of funding. With the progress of Science and technology and to improve the manufacturing precision of the hydraulic machinery industry, has been developing rapidly, however, the cavitation problems with its large high-speed and is more prominent. The efficiency of cavitation would not only lower the pumps and other hydraulic machinery, will produce vibration and noise, and even cause damage to the solid surface of hydraulic machinery, serious influence safe and stable operation of the system. On the other hand, because of its physical and chemical characteristics of cavitation flow transition complex and special unsteady dynamic characteristics, has become the For sewage treatment, underwater weapon drag and pipeline cleaning and other fields with high efficiency and low energy consumption in emerging technology. This paper studies on the hydraulic cavitation device two which has the advantages of simple structure of the Venturi tube and hole plate, by theoretical analysis, numerical calculation and experimental measurement of the combination of mechanism and the relationship between the formation of the method study on cavitation. Then on the basis of more extensive application, the structure is more complex on the rotating hydraulic machinery - centrifugal pump cavitation, cavitation of centrifugal pump to improve numerical calculation model, the unsteady characteristics revealed in the centrifugal pump cavitation, a centrifugal pump cavitation prediction method. Finally a systematic study of the hydrodynamic cavitation generator, to provide a reference for the research of cavitation application. The main work and innovative results are as follows: 1. for the hydraulic machinery cavitation device and numerical simulation. People constantly adjust the boundary conditions of the problem should be based on the batch process (Batch) and ANSYS-CFX is built to simulate the automatic operation method of cavitation numerical, automatically modify automatically call and boundary conditions of the CFD calculation software, the calculation can be directly executed next. This method guarantees the seamless process of numerical simulation.2., shorten the calculation period through the study of the Venturi tube cavitation, a combination of cavitation on the image processing method after a test of numerical calculation, relationship specific study of the cavitation and cavitation in different development stage. The RNG k- model based on a compressible turbulence model CDM the modified and turbulent viscosity considering cavitation is proposed to effectively solve the problem of the prediction of turbulence models of turbulent viscosity by two high-speed camera and cavity structure of Venturi tube The evolution was recorded and the cavitation process, realize the synchronous measurement of cavitation; cavitation corrosion was used to analyze the data of calculation method, supplemented by compressible numerical simulation method of cavitation bubble in different stages of development of the destructive force. The results show that shock wave cavitation shedding and group collapse of will release high energy, and caused damage to the wall surface, and the latter is the main reason; the number and area of the corrosion spot growth law and nonlinear, but the ladder was increasing, mostly in the cavitation bubble collapse or fall off occurs when the.3. experimental study on cavitation jet orifice based on established a prediction method of cavitation bubble image based on cavitation. The test data using MATLAB software, the continuous acquisition of the bubble image high speed camera standard deviation and average value, predict the cavitation region of potential And the corresponding damage degree, and reflect the distribution of cavitation. Cavitation test results prove the validity and accuracy of this method, the collapse point of cavitation cavitation jet orifice area is located in the form of a ring cavity shedding, the same radius and the cavitation cavitation image prediction method study radius. It reveals the relationship between flow velocity and cavitation, cavitation number in the premise of the same flow rate, the higher the CDM turbulence model of cavitation more serious degree of.4. basing on the view of the rotating effect of centrifugal pump with large curvature structural features, establish a suitable numerical cavitation of centrifugal pump simulation of the RCD turbulence model, and compared with the test results showed that: compared to the standard k-e model and SST k- turbulence model, RCD model can effectively suppress the traditional turbulence model to predict turbulent viscosity, and accurately. To capture more detailed pump turbulent eddies and the velocity distribution, the numerical calculation can accurately simulate the centrifugal pump cavitation flow unsteady shedding and collapse phenomenon. When the cavitation number is constant, in a revolving cycle cavity of each flow passage will in turn experience Development Bureau of the Ministry, fall off, narrow the unsteady process of.5. on the ZGB cavitation model of hollow bubble radius periodic RE development, vaporization and condensation experience coefficient decline, precision curve prediction of centrifugal pump cavitation bubble radius and the results show that the lift coefficient and cavitation effect experience of vaporization length and gas bubble size, length of condensation coefficient has great effect on high altitude; global gas range mainly affects the area of the suction side of the blade inlet front low pressure area, and the length of the high altitude area of the global air content length, while a high global content area size of centrifugal pump Less impact head, considering the inner relation between the centrifugal pump rotating motion and fluid turbulent kinetic energy and cavity structure of the cavity length of.6. main factors affecting the accuracy of the predicted head, ZGB cavitation model based on the development of a suitable for the numerical simulation of the RZGB centrifugal pump cavitation cavitation model, establishes the function relation of centrifugal pump speed and geometry the structure and bubble radius. The RZGB model for different prediction accuracy over speed centrifugal pump were evaluated, the results show that: for the low specific speed pump, empirical coefficient were 5000 and 0.001 when setting higher prediction accuracy of RZGB model for vaporization; high specific speed pump uses the experience of vaporization condensation coefficient is 50 0.01 and the calculation is more accurate. Compared with the visualization of cavitation test results, RZGB model can more accurately capture the special three-dimensional structure of imported centrifugal pump cavitation and air hole Bubble image cavitation instabilities in the.7. at the end of this prediction method based on prediction method of cavitation was established for hydraulic machinery, and proves the accuracy and reliability of this method through the test. The method of image graphic transformation of a series of continuous high speed photography or numerical calculation, ensure the impeller is fixed, then the standard deviation and image processing method of the average value were analyzed to obtain the centrifugal pump blade surface cavitation region and void distribution. The results show that the cavitation and cavitation region location is quite basic, but the main bias hole end, high turbulence is the tail end of the attached cavitation in centrifugal pump the unstable phenomenon also will damage the.8. model and RZGB RCD model based on turbulence cavitation on the solid wall surface, combined with the test of a rotor stator generator of cavitation It was systematically studied. The results show that the cavitation generator has three main types: wedge groove cavitation cavitation, the rotor and the stator relative motion of formation of the rotor blade leading edge and end area of low pressure cavitation cavitation high-speed rotating rotor formation. The pressure fluctuation at the same speed of cavitation in the generator increases with the increase of flow rate at the same flow; pressure fluctuation of cavitation in the generator increases with increasing engine speed; increasing the distance between the rotor and the stator will be a small decrease in amplitude of pressure chamber; the main cavitation region within the cavitation generator for the rotor blade end, stator blade leading edge and the end part of the bubble attached; cavitation occurs mainly in the rotor and the stator completely staggered, the cavitation intensity high and close to the wall surface, which indicates that the cavitation in hydraulic machinery near the wall is the cause of cavitation bubble collapse The necessary conditions for the occurrence.

【学位授予单位】：江苏大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TH311;TK72

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