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.

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.

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

contra-rotating 转子的一个应用程序对对开发更高特定的速度的一个要求被建议了轴的流动泵。在现在的纸，使用 contra-rotating 转子的优点和劣势与转子定子的常规类型比较被描述，基于理论、试验性的调查。优点如下：(1 ) 泵内在地作为更小被设计缩放并且以更低的旋转速度。(2 ) 为有否定斜坡的流动率的一条稳定的头特征曲线出现。(3 ) 作为后面的转子，旋转速度作为前面转子的独立控制被改变，高效操作的更宽的范围被后面的转子速度控制除了前面转子速度控制获得。劣势如下：(1 ) 两倍柄系统的结构变得复杂。(2 ) 泵表演是劣等的在在是的流动率上，装载的后面的转子被削弱。(3 ) 片更强烈从后面的转子划相互作用到前面转子出现。当时，后面的转子设计是一把钥匙完成更高的泵性能。克服这些劣势的一些方法将向 contra-rotating 的更宽的用法更详细地被讨论各种各样的工业地里的轴的流动泵。

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.

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.

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%.

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。

进出口流道对轴流泵性能影响的数值模拟分析

冷却剂流态是影响核主泵装置工作性能的重要因素,而进出水流道的结构影响着进出水流态。在保证叶轮和导叶结构不变的情况下,探究不同的进出口流道结构对泵水力性能的影响。本文基于SST k-ω湍流模型和SIMPLEC算法,使用三个常用的商业计算流体力学软件对采用不同入口弯管、蜗壳和出口直管的轴流泵进行网格无关性分析和全流域稳态数值计算。经计算,两个模型的外特性参数一致,流量特性曲线几乎重合,且轴流泵的进出水流态相似。不同商业流体力学计算软件得到的曲线和云图的趋势一致,各软件计算误差均在5%以内,证明本次研究中进出口结构改型对泵的水力性能没有产生明显的影响。

对置端曲面齿轮柱塞泵动态特性仿真研究

为了研究对置端曲面齿轮柱塞泵参数对泵动态特性的影响,根据端曲面齿轮柱塞泵工作原理,推导柱塞运动方程。利用Adams与AMESim软件建立对置端曲面齿轮柱塞泵联合仿真模型,通过联合仿真得到不同转速与偏心率下的柱塞泵出口流量与压力的相应曲线。结果表明:转速增大,泵出口流量与压力增大,脉动幅值与脉动频率增大;偏心率增加,泵出口流量与压力增大,脉动幅值增大,脉动频率不变。

自循环机匣提高轴流泵稳定性的参数化研究

为了探究有效扩大轴流泵稳定运行范围的方法,针对轴流泵进行自循环机匣处理的单通道定常数值模拟,分析周向覆盖比例、抽吸口位置和喉部高度对水泵扩稳性能的影响规律,并揭示自循环机匣对轴流泵扩稳的改善机理.结果表明,抽吸口位置保持不变,扩大周向覆盖比例和喉部高度都可以增大流量裕度,但设计点效率降低;喉部高度为1.8 mm的自循环机匣流量裕度随着抽吸口位置的后移先增加后降低,效率先降低后增加,说明在叶顶上方存在一个最佳位置.在研究的范围内,流量裕度最大达到5.93%,设计点的效率最低降低1.12%.通过自循环机匣处理,使叶顶泄漏流与主流在叶顶上方相互作用形成的堵塞区面积有所减小,从而可以扩大轴流泵流量范围和提升小流量工况效率.该研究可为轴流泵在自循环机匣的端壁处理方式下扩稳提供参考.

高速水下航行器低比转速轴流推进泵设计方法

对于水下航行器轴流泵喷水推进系统,现有升力法设计的高比转速轴流泵无法满足在浅水高速工况下正常工作的需求,为解决这一问题,提出一种针对低比转速轴流泵的设计方法。考虑所选NACA66_(a=0.8)翼型的叶栅特性,通过改变攻角和升力系数等参数的设计关系,建立适用于高航速工况的轴流泵模型,并运用SST k-ω湍流模型和多重参考系模型对设计泵的流场运动情况进行仿真。结果表明:设计工况下,设计泵的扬程和水力效率与设计值误差均控制在8%以内,同时测试了设计泵在不同水深下的抗空化性能,进一步探索设计泵工作的最小航深。

轴流泵式混合室内水力学特征的数值模拟

混合澄清槽是重要的萃取分离设备,采用计算流体力学(CFD)方法研究了一种新型轴流泵式混合澄清槽内流体流动与剪切力,确定了搅拌桨型对混合室内的平均剪切速率、剪切速率空间分布、剪切速率概率分布的影响,结果表明:与传统泵轮式混合室相比,轴流泵式混合室内锥形泵及双桨叶的搭配可以大幅提高混合室的抽吸力与剪切力,搭配六叶半闭式涡轮桨后抽吸力可提升87%,混合室平均剪切速率提升90%,同时轴流泵式混合室内剪切力的分布更加均匀。

轴流泵在叶轮和泵壳间隙不足情况下运行的碰磨振动特性研究

为提高水泵碰磨故障的诊断效率,以轴流泵在叶轮和泵壳间隙不足情况下运行的碰磨振动特性为研究对象,根据轴流泵发生碰磨时的受力情况,分析了其受到离心力、水体对叶轮的反作用力、碰撞摩擦力和各种激励外力的作用下产生的异常振动的振动特性,并用数值模拟和模型试验加以验证。得出了叶轮和泵壳间隙不足时,轴流泵的碰磨振动特性主要表现在频谱图中各整数倍频较为突出,奇数倍频和叶频的整数倍频相对其他频率更为突出,存在杂频和高频成分,当碰磨较为严重时,可以看到1/2倍频等分频成分等结论。研究成果在水泵振动特性研究和泵站故障诊断方面有一定的指导意义。