Hydrodynamic Instability Analysis of the Axial Flow Pump in an Ethylene Polymerization Loop Reactor

The hydrodynamic instability of the axial flow pump in a loop reactor has long been a troubling issue to be solved in the polyethylene industry due to the lack of a better mechanismic understanding.Generally,the instability of an axial flow pump can be reflected by the fluctuation of the pump head.In this study,the transient computational fluid dynamics(CFD)simulation is adopted to study the hydrodynamic instability of the axial flow pump used in an ethylene polymerization loop reactor.The results show that the pump head under single liquid phase nearly remains constant while the pump head under slurry phase fluctuates due to the variation of solid volume fraction distribution in the pump.Besides,under the combined effect of the maximum solid volume fraction difference in the pump and the turbulence intensity of the liquid phase,the fluctuation of the pump head under slurry phase increases when the solid volume fraction in the loop reactor increases from 0.10 to 0.29,and the fluctuation decreases,when the solid volume fraction increases from 0.29 to 0.35.Furthermore,there is a negative correlation between the pump head and the solid volume fraction in the pump;with the increase of solid volume fraction in the loop reactor,and the correlation coefficient increases as well.Moreover,a‘spiral particulate band’phenomenon is formed in the ascending leg caused by three mechanisms,viz.:the segregation of particles in all bends,the dispersion of particles by the secondary flow in the ascending leg,and the rotational movement of particles in the pump.

Research on blade tip clearance cavitation and turbulent kinetic energy characteristics of axial flow pump based on the partially-averaged Navier-Stokes model

To reveal the cavitation forms of tip leakage vortex(TLV)of the axial flow pump and the flow mechanism of the flow field,this research adopts the partially-averaged Navier-Stokes(PANS)model to simulate the cavitation values of an axial flow pump,followed by experimental validation.The experimental result shows that compared with the shear stress transport(SST)k-ωmodel,the PANS model significantly reduces the eddy viscosity of the flow field to make the vortex structure clearer and allow the turbulence scale to be more robustly analyzed.The cavitation area within the axial flow pump mainly comprises of TLV cavitation,clearance cavitation and tip leakage flows combined effect of triangular cloud cavitation formed.The formation and development of cavitation are accompanied by the formation and evolution of vortex,and variations in vortex structure also generate and promote the development of cavitation.In addition,an in-depth analysis of the relationship between the turbulent kinetic energy(TKE)transport equation and cavitation patterns was also conducted,finding that the regions with relatively high TKE are mainly distributed around gas/liquid boundaries with serious cavitation and evident gas-liquid change.This phenomenon is mainly attributed to the combined effect of the pressure action term,stress diffusion term and TKE production term.

Experimental study of flow field in interference area between impeller and guide vane of axial flow pump

Axial flow pump is a kind of typical pumps with rotor-stator interaction, thus the measurement of the flow field between impeller and guide vane would facilitate the study of the internal rotor-stator interaction mechanism. Through a structural modification of a traditional axial flow pump, the requirements of particle image velocimetry（PIV） measurement are met. Under the condition of opt.0.8Q, the axial vortex is identified between impeller hub and guide vane hub, which is developed into the main flow and to affect the movement when the relative positions of impeller and guide vane at different flow rates are the same. Besides, the development and the dissipation of the tip leakage and the passage vortex in impeller passages are mainly responsible for the difference of the flow field close to the outer rim. As the flow rate decreases, the distribution of the meridional velocities at the impeller outlet becomes more non-uniform and the radial velocity component keeps increasing. The PIV measurement results under the condition of opt.1.0Q indicate that the flow separation and the trailing vortex at the trailing edge of a blade are likely to result in a velocity sudden change in this area, which would dramatically destroy the continuity of the flow field. Moreover, the radial direction of the flow between impeller and guide vane on the measurement plane does not always point from hub to rim. For a certain position, the direction is just from rim to hub, as is affected by the location of the intersection line of the shooting section and the impeller blade on the impeller as well as the angle between the intersection line and the rotating shaft.

Performance Test and Flow Measurement of Contra-Rotating Axial Flow Pump

An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump. In the present paper, the advantage and disadvantage of using contra-rotating rotors are described in comparison with conventional type of rotor-stator, based on theoretical and experimental investigations. The advantages are as follows： （1） The pump is inherently designed as smaller sized and at lower rotational speed. （2） A stable head-characteristic curve for flow rate with negative slope appears. （3） As the rear rotor rotational speed is varied as independent control of front rotor, the wider range of high performance operation is obtained by rear rotor speed control in addition to front rotor speed control. The disadvantages are as follows： （1） The structure of double shaft system becomes complex. （2） The pump performance is inferior at over flow rate as the rear rotor loading is weakened. （3） The blade rows interaction from rear rotor to front rotor more strongly appears. Then the rear rotor design is a key to achieve higher pump performance. Some methods to overcome these disadvantages will be discussed in more details toward wider usage of contra-rotating axial flow pump in various industrial fields.

Numerical and Experimental Investigation of High-efficiency Axial-flow Pump

The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of the physical phenomena and laws involved in this complex flow field can＇t be fully determined. The flow characteristics of the high efficiency axial-flow pump have been simulated by RNG k-e turbulence model and SIMPLEC arithmetic based on FLUENT software. Numerical results indicate that the data from the prediction show agreement with the experimental results, static pressure on pressure side of blades increases slightly at circumferential direction with radius increasing, and keep almost constant at the same radial while increasing gradually from inlet to exit on the suction side along flow direction at design conditions. The static pressure, total pressure and velocity at inlet, impeller outlet and vane outlet were measured by a five-hole probe, and a contrastive experiment was done to investigate the influence of hub leakage. The experimental results show that inlet flow is almost axial and the prerotation is very small at various conditions. The meridional velocity and circulation distribution are almost identical at impeller outlet at design conditions due to steady flow and high efficiency. The residual circulation exits at downstream of the guide vane, and the circumferential velocity component increases linearly from hub to tip at small flow rate conditions. Hub leakage in adjustable blades results in the decrease of the meridional velocity and circulation at blade exit near hub. The results of numerical simulation and experiments supply important flow structure information for the high-efficiency axial-flow pump.

Flow Ripple of Axial Piston Pump with Computational Fluid Dynamic Simulation Using Compressible Hydraulic Oil

The flow ripple, which is the source of noise in an axial piston pump, is widely studied today with the computational fluid dynamic（CFD） technology development. In the traditional CFD modeling, the fluid compressibility, which strongly influences the accuracy of the flow ripple simulation results, is often neglected. So a compressible sub-model was added with user defined function（UDF） in the CFD model to predict the flow ripple. At the same time, a test rig of flow ripple was built to study the validity of simulation. The flow ripple of pump was tested with different working parameters, including the rotation speed and the working pressure. The comparisons with experimental results show that the validity of the CFD model with compressible hydraulic oil is acceptable in analyzing the flow tipple characteristics. In this paper, the improved CFD model increases the accuracy of flow ripple rate to about one-magnitude order. Therefore, the compressible model of hydraulic oil is necessary in the flow ripple investigation of CFD simulation. The compressibility of hydraulic oil has significant effect on flow ripple, and the compression ripple takes about 88% of the total flow ripple of pump. Leakage ripple has the lowest proportion of about 4%, and geometrical ripple leakage ripple takes the remnant 8%. Besides, the influence of working parameters was investigated through the CFD simulations and experimental measurements. Comparison results show that the amplitude of flow ripple grows with the increasing of rotation speed and working pressure, and the flow ripple rate is independent of the rotation speed. However, flow ripple rate of piston pump grows with the increasing of working pressure, because the leakage ripple will increase with the pressure growing. The investigation on flow ripple of an axial piston pump using compressible hydraulic oil provides a more validity simulation model for the CFD analyzing and is beneficial to further understanding of the flow ripple characteristics in an axial piston pump.

Impact of Typical Steady-state Conditions and Transient Conditions on Flow Ripple and Its Test Accuracy for Axial Piston Pump

The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated working conditions. However, the pump usually has to work in large-scale and time-variant working conditions. Therefore, the flow ripple characteristics of pump and analysis for its test accuracy with respect to variant steady-state conditions and transient conditions in a wide range of operating parameters are focused in this paper. First, a simulation model has been constructed, which takes the kinematics of oil film within friction pairs into account for higher accuracy. Afterwards, a test bed which adopts Secondary Source Method is built to verify the model. The simulation and tests results show that the angular position of the piston, corresponding to the position where the peak flow ripple is produced, varies with the different pressure. The pulsating amplitude and pulsation rate of flow ripple increase with the rise of pressure and the variation rate of pressure. For the pump working at a constant speed, the flow pulsation rate decreases dramatically with the increasing speed when the speed is less than 27.78% of the maximum speed, subsequently presents a small decrease tendency with the speed further increasing. With the rise of the variation rate of speed, the pulsating amplitude and pulsation rate of flow ripple increase. As the swash plate angle augments, the pulsating amplitude of flow ripple increases, nevertheless the flow pulsation rate decreases. In contrast with the effect of the variation of pressure, the test accuracy of flow ripple is more sensitive to the variation of speed. It makes the test accuracy above 96.20% available for the pulsating amplitude of pressure deviating within a range of ~6% from the mean pressure. However, with a variation of speed deviating within a range of ±2% from the mean speed, the attainable test accuracy of flow ripple is above 93.07%. The model constructed in this research proposes a method to determine the flow ripple characteristics of pump and its attainable test accuracy under the large-scale and time-variant working conditions. Meanwhile, a discussion about the variation of flow ripple and its obtainable test accuracy with the conditions of the pump working in wide operating ranges is given as well.

The 3D Modeling of Blades of Multiphase Flow Helico-Axial Pump's Rotor Based on Solidworks

The structure of multiphase flow helico-axial pump＇s rotor and how to model the rotor, especially the blades of the rotor, based on the Solidworks software. More important, the principle of the blade design is mainly introduced. Under the guide of the principle, the 3D coordinates of the blade data points can be got by matlab programming. In the paper, the design step and the modeling step are particularly described through a concrete example.

A New Magnetic Sealless Coupling Axial Flow Blood Pump

For rotating blood pump, the sealing problem is a very important one to solve. In this paper, it was introduced that we designed and made a small axial flow pump, applying the magnetic coupling method. The pump consisted of two pump housings, a brushless DC motor, an impeller with five wanes, a pair of magnetic discs, a spacer, an inlet and an outlet areas , bearings, a support frame, and etc. The pump is made of titanium and is 125 mm length, 147 ml volume, total 380g of weight. Performances of outputting, sealing, heat creating and damage to blood by the pump were investigated in vitro experiment. Results showed for external experiment that: (1)The pressure created by the pump was 90 mmHg, the flow rates were 1.2 L/min, 4 L/min, 5.9 L/min and 7.8 L/min correspondingly to 5000 rpm, 6000 rpm, 7000 rpm and 8000rpm rotation speeds. The hydrodynamic performance of the axial flow blood pump was enough to meet a patient need when the blood pump was used as a left ventricular assistant device. (2)The hemolysis test was studied by the normalized index of hemolysis(NIH). The NIH result of the axial flow pump was 0.08 g/100 L. (3)The outside temperature of the pump didnt change obviously in 120 hours of rotation, and the sealing function was very well.

Pre-Compression Volume on Flow Ripple Reduction of a Piston Pump

Axial piston pump with pre-compression volume（PCV） has lower flow ripple in large scale of operating condition than the traditional one. However, there is lack of precise simulation model of the axial piston pump with PCV, so the parameters of PCV are difticult to be determined. A finite element simulation model for piston pump with PCV is built by considering the piston movement, the fluid characteristic（including fluid compressibility and viscosity） and the leakage flow rate. Then a test of the pump flow ripple called the secondary source method is implemented to validate the simulation model. Thirdly, by comparing results among the simulation results, test results and results from other publications at the same operating condition, the simulation model is validated and used in optimizing the axial piston pump with PCV. According to the pump flow ripples obtained by the simulation model with different PCV parameters, the flow ripple is the smallest when the PCV angle is 13~, the PCV volume is 1.3 ~ I0-4 m3 at such operating condition that the pump suction pressure is 2 MPa, the pump delivery pressure 15 MPa, the pump speed 1 000 r/min, the swash plate angle 13~. At the same time, the flow ripple can be reduced when the pump suction pressure is 2 MPa, the pump delivery pressure is 5 MPa,15 MPa, 22 MPa, pump speed is 400 r/min, 1 000 r/rain, 1 500 r/rain, the swash plate angle is ll~, 13~, 15~ and 17~, respectively. The finite element simulation model proposed provides a method for optimizing the PCV structure and guiding for designing a quieter axial piston pump.

Numerical Investigation of an Idealized Total Cavopulmonary Connection Physiology Assisted by the Axial Blood Pump With and Without Diffuser

In order to improve the surgical treatment of the congenital heart disease patient with single ventricle defect,two axial flow blood pumps,one with diffuser and the other without diffuser,were designed and virtually implanted into an idealized total cavopulmonary connection(TCPC)model to form two types of Pump-TCPC physiological structure.Computational fluid dynamics(CFD)simulationswere performed to analyze the variations of the hemodynamic characteristics,such as flow field,wall shear stress(WSS),oscillatory shear index(OSI),relative residence time(RRT),between the two Pump-TCPC models.Numerical results indicate that the Pump-TCPC with diffuser has better flow field stability,less damage on endothelial cell of vessel wall,and lower risk of vascular injury and thrombosis formation than that without diffuser.

基于流固耦合的大型立式轴流泵机组运行稳定性分析

轴(贯)流泵机组在中国南水北调、“一带一路”等泵站群建设中运用广泛.为了研究大型轴流泵不同运行工况下流体激励力对机组振动的影响,采用CFX和Mechanical联合实现轴流泵叶片非定常应力的流固耦合计算模拟.流场计算基于RANS方法的N-S方程,结构计算采用弹性结构力学方程,使用任意拉格朗日-欧拉ALE法求解,得到了轴流泵转子变形、应力分布及模态特征.研究结果表明,叶频与压力波动频率一致,叶轮旋转是造成压力脉动的主要原因;叶片的最大变形出现在叶片轮缘处,叶片最大应力出现在叶片与轮毂连接处;在叶轮0.6~1.4倍额定转速内,难以找到转子各阶固有频率与叶频及其倍频均保持一定差值的合理转速,但在忽略次要共振可能性后,存在最优转速以达到固有频率和各阶主频的合理差值.

基于Pumplinx的斜盘式轴向柱塞泵缸体优化分析

柱塞泵是工程机械液压系统中十分重要的动力元件,依靠柱塞在缸体孔内做往复运动时产生的容积变化进行吸油和压油。斜盘式轴向柱塞泵的缸体一般呈柱形,其柱塞中心线平行于缸体的轴线。这种结构在同等流量输出下,缸体的体积会较大。该文以斜盘式轴向柱塞泵为例,对泵的局部结构进行改进。主要是对缸体进行了优化设计,从原先的直缸直腰式柱形缸变为斜缸斜腰式锥形缸体,以及将常用的滑靴包覆柱塞的结构形式改为柱塞包覆滑靴的结构形式等.在泵体相同体积大小的情况下,轴向柱塞泵的流量特性和自吸性能得到提高。运用泵专用软件pumplinx进行仿真对比缸体结构中斜缸斜腰角度,得出使柱塞泵整体性能最佳的组合。并通过建立斜盘式轴向柱塞泵的锥形缸体结构数学模型,根据缸体结构参数的调整与组合,得出满足工况使用要求,并达到缸体刚度与强度等条件的锥形缸体泵模型。研究结果对柱塞泵的结构设计有一定的参考价值。

Experimental study on inlet vortex in pump sump

In order to study the mechanism of the vortex generation at the bottom of the pump sump below the flare tube,twenty pressure pulsation monitoring points were arranged at the bottom of the pump sump below the flare tube,and the pressure fluctuation experiments were carried out under different flow conditions.The experimental results show that the frequency of pressure fluctuation at the bottom of the pump sump is twice of the rotational frequency of the impeller blade.The vortex below the flare tube is easy to generate under the large flow conditions and mainly concentrates at the right front position below the flare tube.The position of the vortex occurring is corresponding to the position of the low-pressure region below flare tube.

主动脉穿刺型轴流血泵折边结构叶轮的数值模拟及溶血分析

为解决血泵因叶顶间隙泄漏而造成溶血和血栓等问题,引入了一种折边不等间距叶轮,采用计算流体力学(computational fluid dynamics, CFD)进行内部流场的数值模拟,并与非折边不等间距叶轮及折边等间距叶轮进行对比分析,研究了它们的内流场动力学特性和血液相容性.结果表明:折边叶片结构血泵避免了叶顶间隙泄漏流的产生,同时折边不等间距叶轮减少了叶轮入口和出口处的回流和涡流,流道内整体切应力低于其他2种叶轮;3种叶轮的溶血指数HI均满足血泵的溶血设计指标,其中,折边不等间距叶轮血泵壁面切应力在0~150 Pa的占比达96.84%,曝光时间相对集中且满足人工血泵设计要求,溶血指数较非折边不等间距叶轮血泵下降了3.50%,较折边等间距叶轮血泵下降了12.50%,溶血性能最优.提出的折边不等间距叶轮血泵可有效降低红细胞破损概率,减少溶血和血栓的发生,可为轴流血泵的结构设计和优化提供一定参考.

泵站过流能力校核系统开发及应用

泵站长期运行阻力加大、出流能力减弱,影响城市排涝。基于Python编程语言和数字图像技术,开发了一套泵站过流能力校核评估系统,运用摄像机实时采集轴流泵电压表、电流表数据,同步采用超声波多普勒剖面仪、雷达水位计实时测量泵站出口流量和扬程。针对复杂流态、环境噪声干扰下流量数据偏差大的问题,建立了移动中值滤波法,并利用贝塞尔插值进行数据填充,有效提升了流量数据的准确性。实践应用于泵站出流能力校核,测得该泵站相同功率和相同扬程条件下出流能力均较理论值下降。

基于轴流泵改造的水泵水轮机转轮设计及优化

为探究基于轴流泵改造的轴流式水泵水轮机的水力性能,基于泵的流道,对轴流式水泵水轮机进行设计、数值计算。选取叶片进口安放角、出口安放角、叶片厚度、叶片数4个因素,应用L9(3^(4))正交表进行正交优化设计分析。结果表明,叶片数对轴流式水泵水轮机的性能影响最大,优化后的水泵工况效率提升了1.45%,水轮机工况效率提升了1.74%。优化得出的叶片水泵工况和水轮机工况的工作面背面的压力分布均匀,流态良好。泵工况下叶片做功效果良好,水轮机工况下的流道流线有明显改善,优化效果良好。设计的水泵水轮机在水泵工况下的工作流量为315~350 L/s,扬程范围为8.01~9.42 m;水轮机工况的工作流量为368~403 L/s,水头范围为6.80~10.72 m。研究结果可为泵站轴流泵改造抽水蓄能提供一定的理论支撑和性能参考。

障碍物对轴流泵空化内部流场的影响

空化会影响泵的正常工作和稳定运行,为了探索能够有效抑制轴流泵内发生空化的策略,提出了将矩形流向障碍物布置在轴流泵叶片背面的方法.以比转数700的轴流泵作为研究对象,采用全流道非定常数值模拟,分析障碍物对轴流泵外特性空化性能的影响.结果表明:在设计工况下布置障碍物的改进模型在空化各阶段均能有效减少空泡体积,尤其当空泡发展至障碍物位置时效果最好,空泡体积减少了72.5%;布置障碍物能够提高叶片背面出口压力,限制低压区向出口方向扩张,减小逆压梯度,阻挡轮毂侧发生偏流,梳理空化发展的流线,优化流场结构,抑制空化的发展,并将断裂扬程提升了10.19%.

基于响应面法的轴流泵结构参数匹配研究

为减小叶轮出口到导叶进口之间的水力损失,选取比转速为1296的轴流泵作为研究对象,通过响应面分析和数值模拟相结合的方法,研究叶轮、导叶不同结构参数的匹配关系对水力效率的影响。将叶轮出口角修正系数ξ、导叶进口冲角Δβ、轴向间距S作为优化设计变量,泵的效率作为响应值,建立了优化变量与水力效率之间的多元二次回归方程。研究结果表明,导叶进口冲角Δβ对轴流泵性能的影响最大,其次为轴向间距S,叶轮出口角修正系数ξ的影响最小。此外,导叶进口冲角Δβ与叶轮出口角修正系数ξ均与轴向间距S有明显交互作用。依据优化变量的取值范围,得到了最优参数组合为ξ=1.2,Δβ=-0.7°,S=8.5 mm。优化后的轴流泵在设计工况下扬程提高了0.61 m,效率提高了2.6%。研究结果为进一步提升轴流泵水力性能提供了参考。

立式轴流泵装置叶轮与导叶间非定常流场分析

为了分析立式轴流泵装置叶轮和导叶体的非定常流场特征,采用ANSYS CFX对立式轴流泵装置全流道进行三维非定常数值计算,预测泵装置的能量性能,并通过物理模型试验进行验证。结果表明,各流量工况时,叶轮进口圆周测线的轴向速度分布均呈类正弦分布,波峰、波谷数与叶轮的叶片数相一致。小流量工况时,叶轮进口面的速度分布受叶轮的影响明显,速度加权偏流角与导叶体出口的平均涡角均最大。随着流量的增大,肘形进水流道的能量损失逐渐增大;导叶体的能量损失随着流量的增大呈先减小后增大的趋势,在最优工况时导叶体的能量损失最小,在小流量工况时60°弯管和虹吸式出水流道的能量损失之和最大。研究结果有利于立式轴流泵装置的结构优化与能效提高。