Experimental study on hydrodynamic performance of a cavitating centrifugal pump during transient operation

An experimental study has been carried out in order to analyze the cavitation of a centrifugal pump and its effect on transient hydrodynamic performance during transient operation. The transient characteristics of the centrifugal pump were tested under various suction pressure and starting conditions. In transient operation of continuous starting and stopping process, instantaneous rotational speed, head, flow rate and suction pressure of the pump were measured. The effect of cavitation on transient performance of the centrifugal pump during transient operation was analyzed, and then the effects of starting acceleration rate and suction pressure of pump on cavitation were presented. Results showed that the cavitation would be delayed during rapid starting period. However, in the condition of low suction pressure and high rotational speed, pump cavitation is inescapable even if the starting period is less than a second. After the serious transient cavitation occurred, the transient performance of centrifugal pump would decline obviously, and the instantaneous head of pump would fluctuate.     

螺旋离心泵叶轮离心段叶片对泵性能影响的数值模拟

以150×100 LN-32型螺旋离心泵为研究对象,选用标准k-ε模型,采用CFD软件Fluent计算了原形机和去掉了离心段叶片的模型机的三维内部流场。通过对两种叶轮泵内部流动速度、压力分布与捕捉到的回流等重要现象的研究,分析了离心段的作用。针对以上分析结果,提出了在设计螺旋离心泵的一些改进建议。     

Effect of stacking conditions on performance of a centrifugal pump

Journal of Mechanical Science and Technology - In this study, the effect of stacking condition of centrifugal pump impeller was investigated by Computational fluid dynamics (CFD). The performance...     

离心泵叶轮叶片的加工方法研究

此篇论文主要写了叶轮直纹叶片在DMU-70eV的五轴数控铣中的加工方法.首先介绍了叶片的造型方法,通过木模截线图和轴面投影图获取型值点进行三维造型;然后根据叶片成型原理来进行刀路规划,让工作台旋转至合适角度,使刀具能够沿轴面截线方向走刀;接着详述了刀距和刀具加工起始点坐标的计算方法,通过B样条曲线插值方法来求新的型值点坐标;最后编写刀路,并进行加工模拟仿真.     

Effects of the number of inducer blades on the anti-cavitation characteristics and external performance of a centrifugal pump

Installing an inducer upstream of the main impeller is an effective approach for improving the anti-cavitation performance of a highspeed centrifugal pump. For a high-speed centrifugal pump with an inducer, the number of inducer blades can affect its internal flow and external performance. We studied the manner in which the number of inducer blades can affect the anti-cavitation characteristics and external performance of a centrifugal pump. We first use the Rayleigh-Plesset equation and the mixture model to simulate the vaporliquid flow in a centrifugal pump with an inducer, and then predict its external performance. Finally, we tested the external performance of a centrifugal pump with 2-, 3-and 4-bladed inducers, respectively. The results show that the simulations of external performance in a centrifugal pump are in accordance with our experiments. Based on this, we obtained vapor volume fraction distributions for the inducer, the impeller, and in the corresponding whole flow parts. We discovered that the vapor volume fraction of a centrifugal pump with a 3-bladed inducer is less than that of a centrifugal pump with 2-or 4-bladed inducers, which means that a centrifugal pump with a 3-bladed inducer has a better external and anti-cavitation performance.

     

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.     

The cavitation behavior with short length blades in centrifugal pump

A CFD code with 2-D cascade model was developed to predict the cavitation behavior around the impeller blades of impeller in a centrifugal pump. The governing equations are the two-phase Reynolds Averaged Navier-Stokes equations in a homogeneous form in which both liquid and vapor phases are treated as incompressible fluid. To close the model, a standard k-ɛ turbulence model is introduced. And the mass transfer rates between liquid and vapor phases are implemented as well. The validations are carried out by comparing with reference data in impeller of a centrifugal pump impeller. The cavitation characteristics of current centrifugal pumps is tested at an ondesign point (V=8 m/s) and two off-design points (V=20 m/s and V=30 m/s), respectively. The criteria of cavitation and flow instability around blades are presented. The results show that the current centrifugal pump can safely operate without cavitation at on-design point. Also, the simulation shows cavitation develops inhomogeneously among the blades at off-design points. Moreover, the effects of additional blades in the impeller are studied as well. From the numerical results, it is expected that a half-length blade is the optimum configuration as additional blades in cavitation point of view.     

Microhaemodynamics within the blade tip clearance of a centrifugal turbodynamic blood pump

A persistent challenge facing the quantitative design of turbodynamic blood pumps is the great disparity of spatial scales between the primary and auxiliary flow paths. Fluid passages within journals and adjacent to the blade tips are often on the scale of several blood cells, confounding the application of macroscopic continuum models. Yet, precisely in these regions there exists the highest shear stress, which is most likely to cause cellular trauma. This disparity has motivated these microscopic studies to visualize the kinematics of the blood cells within the small clearances of a miniature turbodynamic blood pump. A transparent model of a miniature centrifugal pump having an adjustable tip clearance (50-200 microm) was prepared for direct optical visualization of the region between the impeller blade tip and the stationary housing. Synchronized images of the blood cells were obtained by a microscopic visualization system, consisting of an inverted microscope fitted with long-working-distance objective lens (40x), mercury lamp, and high-resolution charge-coupled device camera electronically triggered by the rotation of the impeller. Experiments with 7 microm fluorescent particles revealed the influence of the gap dimension on the trajectory across the blade thickness. The lateral component of velocity (perpendicular to the blade) was dramatically enhanced in the 50 microm gap compared with the 200 microm gap, thereby reducing the exposure time. Studies with diluted bovine blood (Ht = 0.5 per cent) showed that the concentration of cells traversing the gap is also reduced dramatically (30 per cent) as the blade tip clearance is reduced from 200 microm to 50 microm. These results motivate further investigation into the microfluidic phenomena responsible for cellular trauma within turbodynamic blood pumps.     

Investigation on the influence of number of blades on flow-induced noise optimization design of a centrifugal pump

Journal of Mechanical Science and Technology - Aiming at the quiet centrifugal pump design, the effect of number of blades on the flow-induced noise is explored. The results show that the sound...     

Effect of number of blades and distribution of cracks on vibration localization in a cracked pre-twisted blade system

A number of several blades can be grouped at their tips to increase their stiffness. This work examines how the effect of number of grouped blades and distribution of cracks affect the mode localization of a mistuned blade system. The pre-twisted blade and the effect of twist angle on localization are also considered in this article. Dynamic characteristics of blades in a blade system are focused to study. Periodically coupled pre-twisted beams were used to approximate shrouded blades. The Euler–Bernoulli beam model was employed to characterize the tapered pre-twisted blade. The mode localization equations associated with the local blade crack defects in the rotating grouped blade system were formulated using Hamilton's principle. The Galerkin method was used to discretize the localization equations of the mistuned system. The numerical results herein reveal that the number of grouped blades and the distribution of multi-disorders in a rotating blade system may markedly affect the localization phenomenon.     

离心泵性能预测新方法

介绍了离心泵性能预测支持软件的新方法,不仅能更真实和准确地绘制和预测出泵的性能曲线,也为离心泵设计的性能预测提供了思路。     

Influence of blade thickness on transient flow characteristics of centrifugal slurry pump with semi-open impeller

As the critical component, the impellers of the slurry pumps usually have blades of a large thickness. The increasing excretion coefficient of the blades affects the flow in the impeller resulting in a relatively higher hydraulic loss, which is rarely reported. In order to investigate the influence of blade thickness on the transient flow characteristics of a centrifugal slurry pump with a semi-open impeller, transient numerical simulations were carried out on six impellers, of which the meridional blade thickness from the leading edge to trailing edge varied from 5-10 mm, 5-15 mm, 5-20 mm, 10-10 mm, 10-15 mm, and 10-20 mm, respectively. Then, two of the six impellers, namely cases 4 and 6, were manufactured and experimentally tested for hydraulic performance to verify the simulation results. Results of these tests agreed reasonably well with those of the numerical simulation. The results demonstrate that when blade thickness increases, pressure fluctuations at the outlet of the impeller become severe. Moreover, the standard deviation of the relative velocity in the middle portion of the suction sides of the blades decreases and that at the outlet of the impeller increases. Thus, the amplitude of the impeller head pulsation for each case increases. Meanwhile, the distribution of the time-averaged relative flow angle becomes less uniform and decreases at the outlet of the impeller. Hence, as the impeller blade thickness increases, the pump head drops rapidly and the maximum efficiency point is offset to a lower flow rate condition. As the thickness of blade trailing edge increases by 10 mm, the head of the pump drops by approximately 5 m, which is approximately 10 % of the original pump head. Futhermore, it is for the first time that the time-averaged relative flow angle is being considered for the analysis of transient flow in centrifugal pump. The presented work could be a useful guideline in engineering practice when designing a centrifugal slurry pump with thick impeller blades.

     

离心泵的性能预测进展

对近几年逐步发展起来的离心泵的性能预测方法及计算模型进行了详细评述，对各种预测方法进行了比较并讨论了其间的相互关系，同时对性能预测的发展方向作了展望，为预测方法的进一步研究提供了清晰的思路。     

Optimization on the impeller of a low-specific-speed centrifugal pump for hydraulic performance improvement

In order to widen the high-efficiency operating range of a low-specific-speed centrifugal pump, an optimization process for considering efficiencies under 1.0Q_d and 1.4Q_d is proposed. Three parameters, namely, the blade outlet width b_2, blade outlet angle β_2, and blade wrap angle φ, are selected as design variables. Impellers are generated using the optimal Latin hypercube sampling method. The pump efficiencies are calculated using the software CFX 14.5 at two operating points selected as objectives. Surrogate models are also constructed to analyze the relationship between the objectives and the design variables. Finally, the particle swarm optimization algorithm is applied to calculate the surrogate model to determine the best combination of the impeller parameters. The results show that the performance curve predicted by numerical simulation has a good agreement with the experimental results. Compared with the efficiencies of the original impeller, the hydraulic efficiencies of the optimized impeller are increased by 4.18% and 0.62% under 1.0Q_d and 1.4Q_d, respectively. The comparison of inner flow between the original pump and optimized one illustrates the improvement of performance. The optimization process can provide a useful reference on performance improvement of other pumps, even on reduction of pressure fluctuations.     

离心泵蜗壳喉部面积对泵性能的影响

介绍厂通过调整离心泵蜗壳喉部面积的大小，使泵在大流量点获得一条陡降的流量扬程特性曲线，使泵的运行更加节能和安全可靠。     

Multi-point optimization on meridional shape of a centrifugal pump impeller for performance improvement

A wide operating band is important for a pump to safely perform at maximum efficiency while saving energy. To widen the operating range, a multi-point optimization process based on numerical simulations in order to improve impeller performance of a centrifugal pump used in nuclear plant applications is proposed by this research. The Reynolds average Navier Stokes equations are utilized to perform the calculations. The meridional shape of the impeller was optimized based on the following four parameters; shroud arc radius, hub arc radius, shroud angle, and hub angle as the design variables. Efficiencies calculated under 0.6Q _d, 1.0Q _d and 1.62Q _d were selected as the three optimized objectives. The Design of experiment method was applied to generate various impellers while 35 impellers were generated by the Latin hypercube sampling method. A Response surface function based on a second order function was applied to construct a mathematical relationship between the objectives and design variables. A multi-objective genetic algorithm was utilized to solve the response surface function to obtain the best optimized objectives as well as the best combination of design parameters. The results indicated that the pump performance predicted by numerical simulation was in agreement with the experimental performance. The optimized efficiencies based on the three operating conditions were increased by 3.9 %, 6.1 % and 2.6 %, respectively. In addition, the velocity distribution, pressure distribution, streamline and turbulence kinetic energy distribution of the optimized and reference impeller were compared and analyzed to illustrate the performance improvement.     

基于UG平台的离心泵叶片的三维几何建模及优化

研究基于UG软件的强大建模功能和曲面编辑功能,采用NURBS方法建立离心泵叶片的空间样条曲线,并应用类流线的方法对叶片进行优化,使叶片在保持原有形状的基础上更为光滑,对叶片进行几何造型.本研究为离心泵的CFD分析和性能预测提供了准确的几何物理模型.     

两种不同叶片的离心叶轮的数值模拟

基于N-S方程和雷诺平均法的RNG k-ε湍流模型,采用压强连接的隐式修正SIMPLIEC算法,对两个有相同设计工况但叶片类型不同的单级双吸离心泵进行了数值模拟,荻碍了叶轮内流场的速度、压力分布,捕捉到了一些重要的流动现象.并对数值计算结果进行了深入的分析研究,揭示了两种不同叶片叶轮内的流动规律,为认识两种叶片的不同的流动特征提供了参考信息.     

分流叶片对微型离心式风泵性能影响的数值研究

为了研究分流叶片对微型离心式风泵性能的影响,对现有叶轮模型进行了流体力学数值研究。采用Realized k－ε湍流模型和SIMPLE算法,研究分流叶片的周向位置、长度、倾角以及长短叶片数等参数对离心式风泵性能的影响。在额定转速为5500 r／min且风量风压曲线的实验结果和计算结果吻合较好的情况下,对其进行了优化。仿真结果表明,对于现有叶轮模型,当分流叶片处于长叶片间周向位置4时、分流叶片进口直径Ds为叶轮外径Do的0．75倍、分流叶片内部斜边与离心式风泵轴线夹角为12．5°时,离心式风泵的性能较为优异。此外,计算结果还表明,在现有模型中,对分流叶片几何参数进行优化,长短叶片数目均为11时,该离心式风泵的性能有较明显的改善。