轴流泵必需汽蚀余量的优化方法

本文提出一种优化轴流泵必需汽蚀余量（NPSHr）的方法。首先，利用现有的叶栅实验数据确定一个使必需汽蚀余量出现最小值的叶轮直径。然后，调整叶轮出口流体速度矩使必需汽蚀余量出现最小值，进行第二次优化。叶轮出口流体速度矩由速度矩分布函数表示。速度矩分布函数是由两个参数确定的二次多项式。在第二次优化过程中，利用径向平衡方程和激盘理论确定叶片进出口角和叶片形状；采用二维涡元法计算叶片表面流体速度、压力分布和汽蚀余量；建立必需汽蚀余量与确定速度矩分布的两个参数的响应面。结果表明，在第一次优化基础上，第二次优化使必需汽蚀余量下降了37．5％，有较明显的效果。     

5-29风机三元设计及实验结果分析

本文介绍5—29风机的三元设计理论和实验结果。理论设计部分包括叶片型面图,叶片几何角和周向角变化规律,叶道内速度和压力分布规律,实验部分包括叶轮出口速度和压力分布,风机的特性曲线等。实验结果同原叶轮风机的测试结果进行了比较。     

轴流泵叶轮出口速度矩采用不同的二次多项式分布规律时的特性研究

研究了轴流泵叶片设计中叶轮出口液体速度矩采用不同的二次多项式形式分布规律时，叶轮出口绝对速度圆周分速度、轴面速度、理论扬程、扩压系数、水力效率、汽蚀余量、叶片安放角等参数沿叶片高度分布的情况。采用了4种分布形式。研究表明，叶轮出口速度矩采用不同形式的二次多项式分布时。叶轮出口绝对速度圆周分速度、理论扬程、轴面速度和叶片安放角沿叶片高度分布均有较大变化。但汽蚀余量、扩压系数和水力效率沿叶片高度分布变化较小。分布3、4是比较好的分布形式。当必需汽蚀余量有要求时，分布3可以减小必需汽蚀余量5％左右；否则，分布4是比较好的。对于分布3，叶片安放角沿叶片高度分布可能出现拐点。通过增大k1，降低k2和增大k3可以避免出现拐点。对于分布3，k2位置的改变对叶片安放角影响甚微。     

离心泵叶轮内部流场模拟及其结构改进设计

叶轮是离心泵的关键部件,对泵的水力性能影响很大。利用Pro/E软件建立了离心泵叶轮的三维几何模型,并结合CFD仿真技术和Fluent软件完成了离心泵叶轮内部的流场数值模拟,得到了叶轮内部流场的速度和压力分布规律,流场分析结果为离心泵叶轮的结构设计提供了理论依据。最后,在流场模拟的基础上研究了叶轮叶片的出口宽度和工作面型线对离心泵性能的影响,给出了离心泵叶轮结构改进的建议:叶片出口宽度宜选为8mm,并采用先急后缓的叶片工作面型线较合适,改进后的叶轮水力效率提高了约3%。     

梯形断面蜗壳式离心泵作透平叶轮的设计与试验

为提高非圆形断面蜗壳式离心泵作透平的效率,以一比转速为193的梯形断面螺旋形蜗壳式离心泵为原型,设计了适应此类泵作透平运行的透平专用叶轮。根据原型泵梯形断面蜗壳几何参数,依据面积相等的原则,推导梯形断面几何参数与当量圆断面半径的换算关系式;依据等速度矩定律确定叶轮进口速度矩,推导出叶片进口安放角与设计流量的关系表达式;对于叶片进口较宽的情况,在轴面投影图中划分三条流线,分别计算三条流线与叶片出口边交点处的出口安放角;基于ANSYS BladeGen与NX软件建立新叶轮的三维模型,制作试验叶轮,开展外特性试验,并进行数值模拟分析。结果表明:新叶轮将透平最高效率由71.9%提高到了77.3%,较原型叶轮透平最高效率提高了7.5%,且新叶轮在75~130 m~3/h的流量区间均能高于72%的效率运行,效率曲线较平坦,高效区运行范围宽。数值计算结果分析表明新叶轮进口能较好地适应螺旋形蜗壳的出流;从叶片进口到叶片出口,液体压能得以较均匀地转换,叶轮内的水力损失较原型泵叶轮内部显著减小。透平试验高效点与给定的设计流量一致,验证了该文提出的透平叶轮设计理论和方法是合理可行的。     

抛雪离心风机叶轮内部流场分析及结构优化

为优化抛雪离心风机性能和内部流场结构,对型号为P4-35-01No.03的抛雪离心风机叶轮内部流场结构进行数值模拟计算。首先,在建模软件Creo中建立三维实体模型,将其导入ANSYS软件中,形成流体域,再用Fluent软件进行流体分析。通过改变主要结构参数,观察不同结构参数下离心风机叶轮区的流场特征。叶轮入口直径增大,则离心风机出口处雪流量减小,出口处雪颗粒速度大幅增加;减小叶片起始直径,离心风机出口处雪流量会急剧减小,并且阻碍出口处雪颗粒速度上升;减小叶片出口角,则会改善叶轮区域速度矢量分布不均匀现象;当叶片出口角为20°时,叶轮所有流道内速度分布沿圆周方向完全一致。随着研究的深入,发现了初步设计中的缺陷,研究结果为今后实际抛雪离心风机叶轮的设计生产提供了参考依据。     

几何参数对离心叶轮强度和气动性能影响的研究

使用有限元计算软件和内部流场计算软件对所设计的几个具有不同几何尺寸的离心压气机叶轮的强度和气动性能进行了计算。结果表明反弯叶片可降低叶轮出口处叶片根部附近的应力,但会造成叶片根部前缘区域应力集中,且反弯叶轮的气动性能和原型叶轮差别不大。前倾叶片能在很大程度上降低叶轮出口处叶片根部应力,前倾角越大出口叶根处应力减小越多;随前倾角增大,叶轮气动性能恶化程度加剧;叶轮的背盘形状对叶轮的应力影响较大,尤其是出口处的背盘厚度对出口处叶片根部区域的应力起主因作用。研究得出叶片几何及背盘形状因素对叶轮应力分布的影响规律,另外还得到了叶片几何形状对气动性能的影响规律,这些工作为叶轮的多学科优化设计提供良好的基础。     

风机叶型杂交命题的有限元解法

本文以任意旋成面叶栅C类杂交命题矩函数型的变分原理为基础,提供了一种能同时考虑气动、强度和制造工艺等多种性能要求的新的风机叶片设计方法。对于给定的叶片厚度分布和吸力面上的设计压力或速度分布,应用本文方法可求得满足设计要求的叶片几何形状和叶栅流场。     

轴流叶轮叶片设计与计算流体动力学气动特性分析

为了解决低功率轴流叶轮叶片设计研究不足的问题,以叶片结构参数为基础,通过分析计算,提出了一种基于叶型参数的叶片设计方法。该方法依据速度三角形原理,针对叶片几何进口角、几何出口角及叶片弦长等相关要素进行优化与调试,实现轴流叶轮叶片的外形设计,并运用计算流体动力学(Computational Fluid Dynamics,CFD)进行气动模拟验证。验证结果表明,该叶片功率曲线服从翼型及叶片气动特性规律,输出功率为4.46 W,满足低功率风力机设计要求。     

叶片数对螺旋离心泵内部流场影响研究

利用工程上普遍采用的k-ε两方程模型和SIMPLE算法,对单叶片和双叶片螺旋离心泵的内部流场进行了数值模拟.得出了叶轮与蜗壳内的速度分布和压力分布等流场信息,比较了单叶片和双叶片螺旋离心泵的特性曲线,单叶片和双叶片螺旋离心泵内部流场的区别与联系,分析了叶片数对螺旋离心泵内部流动规律的影响.     

固液两相离心泵内部非定常流动特性研究

为研究固液两相流离心泵内部的非定常流动特性,基于滑移网格方法,采用RNGκ-ε湍流模型以及ASMM代数滑移混合物模型,对一台高比转速固液两相离心泵内部流场进行非定常流动的数值模拟,通过分析清水工况数值计算结果、外特性性能实验结果以及固液两相流非定常数值计算结果,获得了非定常条件下固液两相输送离心泵的瞬时外特性曲线和内部流动及磨损规律。研究结果表明:在一个转动周期内,离心泵的扬程、效率和轴功率均呈现正弦波动特征;动静干涉效应使得叶轮出口处的速度和静压分布均呈现周期性波动;模型泵叶轮前后盖板的磨损情况比蜗壳壁面的磨损严重。上述计算结果可为实现高比转速固液两相流离心泵的优化水力设计和减轻磨损提供一定的理论参考。     

Application of gamma-ray computed tomography for the analysis of gas holdup distributions in centrifugal pumps

In this work, gas–liquid distributions in an industrial centrifugal pump operated at various steady state conditions have been quantitatively determined. Therefore, high-resolution gamma-ray computed tomography (HireCT) has been applied, operated in time-averaging rotation-synchronized CT scanning mode. Detailed studies have been performed on a hydraulic test facility providing authentic operating conditions for industrial centrifugal pumps. The gas phase distribution in the centrifugal pump has been studied for swirling gas–liquid two-phase flow as an inlet flow regime and at defined inlet gas volumetric flow rates between 0% and 5%. In this way, the influence of the inlet flow boundary conditions on the performance of the centrifugal pump as well as the gas holdup distribution within the impeller region could be successfully determined.     

Effects of contraction-type impeller on non-overloaded performance for low-specific-speed sewage pump

With the expansion of the engineering application of solid-liquid two-phase flow, the overload characteristics of low-specific-speed sewage pumps become an important obstacle to the development of the products. In this paper, the traditional diffusion-type impeller is utilized to carry out hydraulic design of a low-specific-speed sewage pump. And on this basis, the thickness of the blades is increased for getting an impeller with contractive-type flow channel. It was found out that through external characteristics, the efficiency of contraction-type impeller is slightly lower than that of diffusion-type impeller, but it shows obvious non-overload performance. PIV experiment is arranged to find the inherent. The results show that although internal flow field distribution of contraction-type impeller is better than that of diffusion-type impeller, the severe uneven distribution of absolute velocity of the impeller outlet along the circumference is one of main reasons of inefficiency. In addition, another five impellers with different contraction ratio are designed to research relationship between contraction ratio and character of non-overload. The characteristics are predicted by CFD, and after comparing the results, it is found out that, the smaller the contraction ratio is, the closer the condition of power extreme is to the design condition, which has important implications for the engineer.     

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.     

Numerical simulation and analysis of solid-liquid two-phase flow in centrifugal pump

The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far.There exist two main problems in the operation of the two-phase flow pumps,i.e.,low overall efficiency and severe abrasion.In this study,the three-dimensional,steady,incompressible,and turbulent solid-liquid two-phase flows in a low-specific-speed centrifugal pump are numerically simulated and analyzed by using a computational fluid dynamics(CFD) code based on the mixture model of the two-phase flow and the RNG k-two-equation turbulence model,in which the influences of rotation and curvature are fully taken into account.The coupling between impeller and volute is implemented by means of the frozen rotor method.The simulation results predicted indicate that the solid phase properties in two-phase flow,especially the concentration,the particle diameter and the density,have strong effects on the hydraulic performance of the pump.Both the pump head and the efficiency are reduced with increasing particle diameter or concentration.However,the effect of particle density on the performance is relatively minor.An obvious jet-wake flow structure is presented near the volute tongue and becomes more remarkable with increasing solid phase concentration.The suction side of the blade is subject to much more severe abrasion than the pressure side.The obtained results preliminarily reveal the characteristics of solid-liquid two-phase flow in the centrifugal pump,and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.     

Numerical investigation of two-phase flow characteristics in multiphase pump with split vane impellers

Multiphase pump is a cost-effective option for subsea oil and gas field development. The ability to handle different inlet gas volume fractions (GVFs) especially high inlet GVF is critical to the development of pump performance. In this study, the two-phase flow characteristics in normal impeller and split vane impeller at different inlet GVFs were investigated by steady numerical simulations. The gas distribution on blade-to-blade plane and meridional flow channel at different inlet GVFs were analyzed and compared. Gas accumulation area and movement characteristics of the gas-liquid flow in impeller flow passage were also pointed out by unsteady simulations. Experimental results of the pump differential pressure were compared with the numerical simulation results, to validate the accuracy of numerical simulation method. The flow characteristics in pump with modified impeller and its performance at different inlet GVFs were both compared with that of the normal impeller. The steady simulation results of normal impeller in different inlet GVFs show that gas concentrating area in the flow passage increases as inlet GVF grows. The unsteady simulation results indicate that gas pocket firstly occurs on the pressure side of impeller, then moves to the suction side in the middle area of blade and finally transfers to outlet of impeller and disappears. The errors between numerical simulation results and experiment data are below 10 %, which validated the feasibility of the numerical simulation method. Simulation results on the split vane impeller demonstrate that the gas accumulation area in flow passage of the modified impeller is dramatically decreased compared to that of the normal impeller. The performance of the modified impeller is generally better than the normal impeller especially in high inlet GVF conditions.

     

Cavitation optimization for a centrifugal pump impeller by using orthogonal design of experiment

Cavitation is one of the most important performance of centrifugal pumps. However, the current optimization works of centrifugal pump are mostly focusing on hydraulic efficiency only, which may result in poor cavitation performance. Therefore, it is necessary to find an appropriate solution to improve cavitation performance with acceptable efficiency. In this paper, to improve the cavitation performance of a centrifugal pump with a vaned diffuser, the influence of impeller geometric parameters on the cavitation of the pump is investigated using the orthogonal design of experiment(DOE) based on computational fluid dynamics. The impeller inlet diameter D_1, inlet incidence angle Δβ, and blade wrap angle φ are selected as the main impeller geometric parameters and the orthogonal experiment of L_9(3*3) is performed. Three-dimensional steady simulations for cavitation are conducted by using constant gas mass fraction model with second-order upwind, and the predicated cavitation performance is validated by laboratory experiment. The optimization results are obtained by the range analysis method to improve cavitation performance without obvious decreasing the efficiency of the centrifugal pump. The internal flow of the pump is analyzed in order to identify the flow behavior that can affect cavitation performance. The results show that D_1 has the greatest influence on the pump cavitation and the final optimized impeller provides better flow distribution at blade leading edge. The final optimized impeller accomplishes better cavitation and hydraulic performance and the NPSHR decreases by 0.63 m compared with the original one. The presented work supplies a feasible route in engineering practice to optimize a centrifugal pump impeller for better cavitation performance.     

基于轴流泵间隙流动的新水力设计方法

轴流泵叶轮轮毂与轮缘处间隙流动及边界层对轴流泵性能的影响很大,应用Numeca及Flu-ent等软件对轴流泵叶轮轮缘间隙中的流动进行数值模拟,根据流动模拟结果对叶轮叶片型线及轮毂、轮缘处的叶型设计进行修正,使其速度-压力分布比较理想,并提出了基于间隙流动的轴流泵水力设计方法,这种新的水力设计方法有利于改进轮缘和轮毂处边界层以及轮缘间隙中的流动,达到提高轴流泵效率的目的。     

离心式固液两相流泵的叶轮设计

阐述离心式固液两相流泵的叶轮设计的方法，分析了基于不同两相流理论的叶轮参数的选择方法，指出叶轮型线设计是固液两相流泵设计的重要环节，并阐述了基于边界层理论的叶片型线设计方法。     

Time resolving gamma-tomography for periodically changing gas fraction fields and its application to an axial pump

In the paper a novel non-intrusive tomographic method is presented to visualise the gas fraction distribution inside the rotating impeller of an axial pump delivering a two-phase flow. The device has been developed for an axial pump (inducer), which has an impeller with three helical blades rotating at 1500 rpm. Model fluid is air–water mixture created by a gas distributor upstream the pump inlet nozzle. The developed gamma-tomography set-up consists of a Cs-137 source and an arc of 64 scintillation detectors. Each of the detectors is connected to a number of counters grouped into banks. Each bank is active only during a 100 μs long interval of the rotation period, which corresponds to a well-defined angular interval of the impeller rotation. A trigger pulse, generated at the beginning of each revolution, forces the control unit to restart the counting process from the first bank. In this way, the device is able to measure ensemble averaged projections of the gamma absorption density distribution, which are resolved according to the rotating angle of the impeller. An image reconstruction by filtered back-projection provides density distributions inside the impeller. Void fraction distributions are visualised by means of differential tomography, i.e. by subtracting sets of projections obtained for two-phase operation and for plain liquid.