叶顶间隙对低比转数小流量泵性能的影响

为建立叶顶间隙对低比转速小流量泵性能的影响关系,采用数值计算的方法,以叶顶间隙宽s和叶轮出口宽b的比值(s/b)表征间隙大小,对不同间隙下泵的性能展开对比分析。分析发现,随着间隙的增加,泵的扬程和效率均逐渐降低,最大和最小间隙下的扬程和效率差分别达15.4%,5.5%。当间隙较小即s/b<0.2时,扬程曲线在小流量工况会出现不稳定的“驼峰”现象,在s/b>0.3后,设计工况附近效率的降幅显著增大。从流动特性来看,随着叶顶间隙的增大,间隙泄漏流对叶轮内主流区影响加剧,会诱导严重的二次流和旋涡的产生,同时间隙内不稳定流动也会产生能量损失,造成扬程和效率下降。为低比转数小流量泵的设计与优化提供借鉴意义。     

高比转数轴流泵水力模型设计与紊流数值分析

为满足低扬程泵站工程建设的需要,采用简单径向平衡流动模型和二维叶栅面元法叶片造型方法设计高比转数轴流泵水力模型。并用RNG k-ε紊流模型对水力模型进行数值分析,分析过程考虑了叶轮叶顶间隙的影响。模型试验表明,设计点相当准确。数值分析在设计点附近精度较好,能满足工程应用的要求,但在非设计工况误差较大。计算还表明,叶轮在正扬程时就出现了负的轴向力,从而解释了立式泵在低扬程运行时的抬机现象。     

立式轴流泵水力不稳定工况流场数值预测

为了研究轴流泵位于水力不稳定工况的流动特性,基于N-S方程以及RNGκ-ε湍流模型,对轴流泵进行三维湍流数值计算。预测得到设计工况下的扬程与模型参数接近,说明所采用的数值计算方法可以较为准确地预测轴流泵内部流动特性。计算结果表明:在0.35Q_d至0.5Q_d流量区间内,轴流泵的流量-扬程曲线呈现正曲率特性,此区间内流量工况即为其水力不稳定工况;伴随着流量由设计工况Q_d依次减小至0.5Q_d和0.35Q_d的过程中,轴流泵内部流态逐渐恶化。在0.35Q_d工况点,叶轮进口前水流存在强烈的预旋,进口存在漩涡导致流体不能有效进入叶轮室,同时叶轮室内流体脱流现象严重,严重堵塞流道,致使叶轮无法有效对流体做功。     

一种改进升力法的研究

针对我国轴流泵效率普遍偏低的情况,著者试图提出一种改进的轴流泵升力设计法。考虑到轴流泵叶轮外缘、轮毂处的边界层及间隙流的影响,在传统的升力法模型中引入修正系数A（R,6）,对传统的升力法公式加以改进,得到了改进升力法模型。本文同时应用传统升力法和改进升力法对一轴流泵进行了叶轮叶片的设计,并利用NUMECA软件进行流动模拟,分别得到叶轮叶片表面及轮毂、轮缘处的速度一压力分布以及各工况的效率计算结果,证明了改进升力法较传统升力法优越,改进效果明显,有效地提高了轴流泵的效率,改善了泵内部流动的速一压分布。为轴流泵的设计提供了一种崭新的模式。     

基于iSIGHT平台的轴流泵叶片水力性能优化研究

将数值优化技术与CFD流场计算相结合,由数学过程代替设计人员的经验,控制叶片设计修改方向,构建轴流泵叶片自动优化设计平台。以多学科优化软件iSIGHT为基础,以现有优秀的轴流泵叶片模型为研究对象,建立了参数化建模、网格划分、流场计算和数值优化相结合的轴流泵叶片自动优化设计平台。以叶轮效率最高为目标函数,以扬程和汽蚀余量为约束条件,用该平台对设计工况下的初始叶片进行自动优化设计。对比分析优化前后叶片的水力性能,优化后叶片的水力性能有所提高,表明本文采用的自动优化设计方法是有效和可行的。     

半开式叶轮与导流器间隙对自吸泵性能的影响

为分析射流式自吸离心泵的半开式叶轮与导流器前盖之间的间隙大小对其性能的影响,采用数值模拟的方法得到了4种不同间隙下射流式自吸离心泵水力性能、径向力变化规律、自吸过程泵内部气液两相分布及流动情况,结果表明:间隙大小对射流式自吸离心泵水力性能影响明显,随着间隙增大,泵扬程和效率呈明显下降趋势,额定工况点间隙为0.5时的扬程和效率相对于间隙2mm时的扬程和效率分别下降14.43%、7.07%;叶轮与导流器上径向力也随间隙增大而减小;叶轮含气率、导流器两个不对称出口及泵体出口的气相质量流率随间隙增大而降低.兼顾考虑水力性能、自吸性能及加工装配工艺,最终确定叶轮与导流器前盖的间隙为0.5mm.样机试验结果表明:在额定工况点扬程34.21m,效率55.29%,当自吸高度为5m时,自吸时间45s,达到设计要求。     

中低比转速离心泵叶轮多目标优化设计

中低比转速离心泵效率普遍不高，主要因素是泵的损失过大，在减小泵的损失时，容易使汽蚀余量增大，扬程曲线产生驼峰，为提高泵效率，减少汽蚀余量，消除扬程曲线驼峰，本文论述了以中低比转速泵的能量损失最小，汽蚀余量最小及消除扬程曲线驼峰为多目标函数，以叶轮主要参数为设计变量的泵叶轮优化设计方法，通过优化，获得了满足一定扬程和流量的最优参数组合。     

诱导轮和离心泵叶轮内部空化流动数值分析

为了提高诱导轮离心泵的空化性能和运行稳定性,阐明诱导轮和离心泵叶轮几何参数对空化性能的影响规律,基于空泡可压缩性影响修正的RNG k-ε模型和改进的空化模型,对诱导轮和离心泵叶轮内部流场进行空化数值计算。数值结果表明:在小流量工况和额定工况下,空化性能曲线基本一致;在大流量工况下,空化特性曲线波动相对比较严重,空化性能较差。额定流量下泵蜗壳水力损失最小,小流量工况下蜗壳水力损失最大。临界汽蚀余量时,蜗壳水力损失突升。无空化条件下,随着前口环间隙值的增大,诱导轮扬程、效率和前口环间隙泄漏量增大,泵和叶轮的扬程、效率值降低,泵的空化特性曲线的稳定性变差,使诱导轮叶片出口液流角发生偏转,导致诱导轮和离心泵叶轮内部产生周期性的交变空化流。     

末级密封间隙对自平衡多级离心泵性能的影响

为了阐明不同末级密封间隙值变化对自平衡多级离心泵性能及其流动特性的影响,以某型号的自平衡多级离心泵为研究对象,基于泵的几何参数,建立4组不同末级密封间隙值的匹配方案,通过CFD软件对不同方案进行全流场数值模拟,并与试验结果进行对比分析。研究结果表明:随着末级密封间隙值的增加,不同工况下整泵的扬程和效率逐渐减小,泵高效点向小流量点偏移;同时在设计工况下,低压区从首级泵腔向次级泵腔移动,次级泵腔的压力梯度明显,而首级泵腔的压力梯度减弱,导致泵的首级轴向力不断增大,次级轴向力先减小后增大,总轴向力大小增加,方向指向首级叶轮进口。     

核主泵高温工况下叶轮结构力学分析

为了验证主泵叶轮在设计工况下的完整性,通过三维软件Pro/E对主泵叶轮进行三维造型,应用计算流体力学软件ANSYS—CFX和Workbench对主泵叶轮进行耦合计算,分析了在轴向力载荷、转矩载荷、离心力载荷、混合载荷以及125%1临ti界同步转速与1.252倍转矩M。载荷工况下叶轮的最大应力强度分布。分析了叶轮应力、应变的分布规律,揭示出转子部件由于变形过大以及强度不足而引发失效事故。计算结果表明,在反应堆一回路额定工况下,在轴向力+离心力载荷工况下,叶轮产生最大应力变形,叶轮叶片最大变形发生在叶片出口尖部,变形量约0.58 nll/l;最大应力位于叶轮体及叶轮外径之间的过渡区,叶片出口区域最大应力值为112.4 MPa。     

串列式双级轴流泵性能的数值模拟

为了揭示串列泵的内部流动机理及其能量特性,采用两个具有试验结果的轴流式叶轮和一新设计的导叶串联组成了一串列式轴流泵模型。应用Pro-E对该串列泵进行三维实体造型,用数值模拟的方法计算泵内的流场。数值计算采用NUMECA商业软件。在不同的工况条件下获得前后叶轮内部的速度矢量分布。基于流场计算结果,预测包括扬程、效率和轴功率在内的串列泵性能。将数值计算的结果与原叶轮的试验结果进行对比并与首级叶轮比较,串列轴流泵次级叶轮压力面和吸力面的速度具有较大的差值。与一般的轴流泵比较,串列式轴流泵具有比较宽的高效区,最优工况点向大流量区域偏移,其轴功率不再像普通轴流泵那样随流量的增加而减小。为了分析前后叶轮的相互作用,预测不同的后叶轮叶片偏转角条件下的串列泵性能,结果表明后叶轮的叶片偏转角对串列泵性能有重大的影响。     

对旋轴流叶轮不同转速比的设计及CFD分析

在相同的设计流量和设计扬程条件下，设计了3种不同转速比的对旋轴流叶轮，得到了叶片不同的特征参数。结果表明：对旋式轴流泵前置叶轮与后置叶轮的转速比采用稍小于l的设计是较为合理的，并且可以获得较宽的运行高效区。以此叶片设计结果为数值模拟的对象，对前后叶轮采用7种不同的转速比进行数值模拟，得到各自全流道下紊流流场的压力、速度等值线及分布云图，预测一定转速比下的叶轮外特性性状，为实际运行和选型应用提供了依据。     

Design optimization of mixed-flow pump impellers with various shaft diameters at the same specific speed

In this study, the hydraulic performance of a mixed-flow pump depending on the impeller hub ratio was analyzed using Computational- fluid-dynamics (CFD). The impeller inlet shape varies according to the hub ratio even at the same specific speed. It is important to ensure an optimum impeller design according to the hub ratio in order for the impeller shape to provide the desired performance at constant specific speed. The design variables of inlet part for meridional plane and vane plane development were defined for optimum impeller design. The objective functions were defined as the total head and total efficiency of the mixed-flow pump impellers. The optimum impeller design was carried out by controlling the design variables of impeller inlet parts by using the Response-surface-method (RSM). The tendency of impeller design variables depending on the hub ratio was identified by analyzing the optimum impeller design. Further, the impeller shape was designed on the basis of the tendency of the design variables depending on the hub ratio. Finally, the performance of an impeller with the designed shape was verified by numerical analysis.     

低比转数高效率蜗壳泵的开发

为了开发出一种高效率低比转数 (ns<70 )的蜗壳泵 ,总结了比转数ns=60时的两种试验结果 ,进行了叶轮设计和蜗壳设计的优化 ,并进行了新的试验 ,以揭示叶轮与蜗舌之间的流动干扰。结果表明 ,低比转数蜗壳泵不宜采用常规设计 ,进而提出了一种新的设计方法。     

Effects of meridional flow passage shape on hydraulic performance of mixed-flow pump impellers

During the process of designing the mixed-flow pump impeller, the meridional flow passage shape directly affects the obtained meridional flow field, which then has an influence on the three-dimensional impeller shape. However, the meridional flow passage shape is too complicated to be described by a simple formula for now. Therefore, reasonable parameter selection for the meridional flow passage is essential to the investigation. In order to explore the effects of the meridional flow passage shape on the impeller design and the hydraulic performance of the mixed-flow pump, the hub and shroud radius ratio (HSRR) of impeller and the outlet diffusion angle (ODA) of outlet zone are selected as the meridional flow passage parameters. 25 mixed-flow pump impellers, with specific speed of 496 under the design condition, are designed with various parameter combinations. Among these impellers, one with HSRR of 1.94 and ODA of 90° is selected to carry out the model test and the obtained experimental results are used to verify accuracies of the head and the hydraulic efficiency predicted by numerical simulation. Based on SIMPLE algorithm and standard k-ε two-equation turbulence model, the three-dimensional steady incompressible Reynolds averaged Navier-Stokes equations are solved and the effects of different parameters on hydraulic performance of mixed-flow pump impellers are analyzed. The analysis results demonstrate that there are optimal values of HSRR and ODA available, so the hydraulic performance and the internal flow of mixed-flow pumps can be improved by selecting appropriate values for the meridional flow passage parameters. The research on these two parameters, HSRR and ODA, has further illustrated influences of the meridional flow passage shape on the hydraulic performance of the mixed-flow pump, and is beneficial to improving the design of the mixed-flow pump impeller.     

EXPERIMENTAL STUDY ON HIGH-SPEED CENTRIFUGAL PUMPS WITH DIFFERENT IMPELLERS

The experimental study is carried out on high-speed centrifugal pumps with three different impellers. The experimental results and analysis show that high-speed centrifugal pumps with a closed complex impeller can achieve thehighest efficiency and the lowest head coefficient followed by those with half-open impeller and open-impeller, and canobtain much easily stable head-capacity characrastic curve, while those with a half-open complex impeller can't. Thecharacteristic curve with a open impeller is almost constant horizontal line before dropping sharply. The results also showthat the axial clearance between pump casing and impeller can influence greatly on the performance of centrifugal pumps.     

Effects of Blade Number on Characteristics of Centrifugal Pumps

The blade number of impeller is an important design parameter of pumps,which affects the characteristics of pump heavily.At present,the investigation focuses mostly on the performance characteristics of axis flow pumps,the influence of blade number on inner flow filed and characteristics of centrifugal pump has not been understood completely.Therefore,the methods of numerical simulation and experimental verification are used to investigate the effects of blade number on flow field and characteristics of a centrifugal pump.The model pump has a design specific speed of 92.7 and an impeller with 5 blades.The blade number is varied to 4,6,7 with the casing and other geometric parameters keep constant.The inner flow fields and characteristics of the centrifugal pumps with different blade number are simulated and predicted in non-cavitation and cavitation conditions by using commercial code FLUENT.The impellers with different blade number are made by using rapid prototyping,and their characteristics are tested in an open loop.The comparison between prediction values and experimental results indicates that the prediction results are satisfied.The maximum discrepancy of prediction results for head,efficiency and required net positive suction head are 4.83%,3.9% and 0.36 m,respectively.The flow analysis displays that blade number change has an important effect on the area of low pressure region behind the blade inlet and jet-wake structure in impellers.With the increase of blade number,the head of the model pumps increases too,the variable regulation of efficiency and cavitation characteristics are complicated,but there are optimum values of blade number for each one.The research results are helpful for hydraulic design of centrifugal pump.     

Influence of blade wrap angle on centrifugal pump performance by numerical and experimental study

The existing research on improving the hydraulic performance of centrifugal pumps mainly focuses on the design method and the parameter optimization. The traditional design method for centrifugal impellers relies more on experience of engineers that typically only satisfies the continuity equation of the fluid. In this study, on the basis of the direct and inverse iteration design method which simultaneously solves the continuity and motion equations of the fluid and shapes the blade geometry by controlling the wrap angle, three centrifugal pump impellers are designed by altering blade wrap angles while keeping other parameters constant. The three-dimensional flow fields in three centrifugal pumps are numerically simulated, and the simulation results illustrate that the blade with larger wrap angle has more powerful control ability on the flow pattern in impeller. The three pumps have nearly the same pressure distributions at the small flow rate, but the pressure gradient increase in the pump with the largest wrap angle is smoother than the other two pumps at the design and large flow rates. The pump head and efficiency are also influenced by the blade wrap angle. The highest head and efficiency are also observed for the largest angle. An experiment rig is designed and built to test the performance of the pump with the largest wrap angle. The test results show that the wide space of its efficiency area and the stability of its operation ensure the excellent performance of the design method and verify the numerical analysis. The analysis on influence of the blade wrap angle for centrifugal pump performance in this paper can be beneficial to the optimization design of the centrifugal pump.     

不同形式高速离心叶轮内部流动的数值模拟

为分析叶轮结构对于叶轮内部流动的影响,对8叶片的闭式和半开式两种形式低比转速高速离心复合叶轮进行研究.采用S-A湍流模型和雷诺时均N-S方程,对叶轮内部的流动进行三维紊流数值计算和分析,并对离心泵进行试验研究.数值计算结果表明,两种形式叶轮内部都存在回流,其中半开式叶轮内部的回流区域较少,液流在间隙里的相对流动大致为圆周方向;叶轮内部的静压力都是由叶片进口到出口逐渐升高,等静压曲线几乎是沿圆周方向,半开式叶轮叶片顶部的静压力低于相应位置根部的静压力,闭式叶轮出口的压力系数高于半开式叶轮.试验结果表明,半开式叶轮离心泵的效率较高,说明叶轮内部的回流是影响离心泵性能的重要因素.     

Hydraulic Optimization of a Double-channel Pump’s Impeller Based on Multi-objective Genetic Algorithm

Computational fluid dynamics (CFD) can give a lot of potentially very useful information for hydraulic optimization design of pumps, however, it cannot directly state what kind of modification should b...