Predicting performance of radial flow type impeller of centrifugal pump using CFD

The main objective of this work is to use the computational fluid dynamics (CFD) technique in analyzing and predicting the performance of a radial flow-type impeller of centrifugal pump. The impeller analyzed is at the following design condition: flow rate of 528 m³/hr; speed of 1450 rpm; and head of 20 m or specific speed (N_s) of 3033 1/min in US-Units. The first stage involves the mesh generation and refinement on domain of the designed impeller. The second stage deals with the identification of initial and boundary conditions of the mesh-equipped module. In the final stage, various results are calculated and analyzed for factors affecting impeller performance. The results indicate that the total head rise of the impeller at the design point is approximately 19.8 m. The loss coefficient of the impeller is 0.015 when 0.6 < Q/Q_design < 1.2. Maximum hydraulic efficiency of impeller is 0.98 at Q/Q_design = 0.7. Based on the comparison of the theoretical head coefficient and static pressure rise coefficient between simulation results and experimental data, from previous work reported in the literature [Guelich, Kreiselpumpen, Springer, Berlin, 2004], it is possible to use this method to simulate the performance of a radial-flow type impeller of a centrifugal pump. This paper was recommended for publication in revised form by Associate Editor Seungbae Lee Somchai Wongwises is currently a Professor of Mechanical Engineering at King Mongkut’s University of Technology Thonburi, Bangmod, Thailand. He received his Doktor Ingenieur (Dr.Ing.) in Mechanical Engineering from the University of Hannover, Germany, in 1994. His research interests include two-phase flow, heat transfer enhancement, and thermal system design. Professor Wongwises is the head of the Fluid Mechanics, Thermal Engineering and Two-Phase Flow Research Laboratory (FUTURE). Suthep Kaewnai obtained a B. S. degree in Mechanical Engineering, 1980 from the King Monkut’s University of Technology Thonburi and M. S. degree in Mechanical Engineering, 1983 from Chulalongkorn University. He is currently an assistant professor at King Mongkut’s University of Technology Thonburi. Suthep’s research interests are in the area of pumps and small hydroturbine. Manuspong Chamaoot received a B. S. degree, 1972 and M.S. degree in Mechanical Engineering, 1979 from the King Monkut’s University of Technology Thonburi. He is currently an assistant professor at King Monkut’s University of Technology Thonburi. His research interests are in the field of mechanical vibration for rotating equipment and computational fluid dynamics.     

离心泵通用轴面流道中线的数学模型研究

国内许多泵厂和研究单位推出多种优秀的离心泵水力模型,为泵的设计提供了宝贵的经验,而一般方法均需给定轴面流线,通常是用试凑法不断地修改给定数据,给设计带来一定的盲目性。笔者结合优秀水力模型,利用数理统计的方法给出统一的流道中线数学模型,经验证,方法是可行的,并可运用于前、后盖板流线的数学模型的建立。     

浅析整体齿轮式离心压缩机设计

离心压缩机属于技术门槛高,且需整合多学科关键技术的透平机械。本文主要描述了整体齿轮式离心压缩机的设计理念、流程及关键气动参数的取值分析,并利用商用软件结合工程实例阐述单级整体齿轮式离心压缩机主要气动部件的设计流程、参数输出及实物机的验证。     

Gas-liquid flow patterns visualization in a self-priming centrifugal pump

The self-priming pumps are ubiquitous in gas-liquid mixtures lift and transportation areas. The fast self-priming time is a vital evaluation index for a self-priming pump. However, the bubble movement path and the bubble size distribution characteristics during the self-priming process are still an open issue. This paper aims to obtain the gas-liquid flow patterns inside a centrifugal pump during the self-priming process and evaluate the effect of the rotational speed and the position of the back-flow hole on the self-priming time through experiments. A centrifugal pump with a double-blade was designed as a visualization prototype. The high-speed photography technology was used to capture the bubble motion and size in the pump during the self-priming process. The bubble image processing method was used to identify the bubble size distribution in the diffuser during the self-priming process. The bubble number and size distribution images were presented to understand the influence of the rotational speed and the position of the back-flow hole. The higher rotational speed accelerates the gas-liquid mixing rate and shortens the self-priming time. However, there is a limited value of the self-priming time as the speed goes up to a certain high level. Moreover, the position of the back-flow hole slightly affects the self-priming time.     

离心泵内流场的数值模拟

运用Cfdesign流体分析软件,对离心泵内三维不可压缩斋流流动进行了数值模拟.分析了离心泵吸入室、蜗室内流体不同截面处的压力及速度特性;并得到了泵的流量及扬程值,其结果与实验值达到了很好的吻合.通过对泵内流体数值结果分析,可以揭示其内部的流场特性,从而为今后泵的性能预测、设计提供依据,缩短开发周期及其成本.     

高速离心叶轮内部三维粘性流场的数值模拟

采用一种快速求解三维黏性流场的计算方法求解某离心压气机内部复杂的流场，该方法利用Denton J．D．教授的粘性体积力法模拟粘性对叶轮机械内部流动的影响，采用时间推进法和有限体积差分格式对叶轮机械内部的流动进行求解。为加速收敛，使用了多重网格法，当地时间步长和局部残差光顺技术。对某离心压气机内部流动进行了详细的数值模拟，得出了压气机转子性能、叶顶周向平均静压以及准正交面上子午速度分布图，计算结果与试验结果吻合良好。采用该方法详细分析了不同工况下离心压气机内部流场。     

叶轮结构对离心风机流动特性及性能影响的研究现状

通过回顾近年来国内外对叶轮性能的研究现状,结合叶轮结构形式及参数对离心风机不同方面的影响,得出离心风机叶轮内的损失主要是叶道内沿程摩擦损失,叶片上边界层分离,叶轮径向出口速度分布不均匀引起的尾迹流,轴向涡流,叶道进口冲击损失等。并指出今后的研究应以试验研究与采用CFD相结合的方法,在风机设计时考虑上述影响因素,从而降低叶轮内损失,提高离心风机性能。     

Estimating uncertainty of measurements for cavitation detection in a centrifugal pump

Measurement of noise and vibration signal in audible frequency range to detect cavitation in centrifugal pumps is rather unknown technique. There were already some studies performed on this technique and they showed quite good results. Due to many factors that influence the quality of the measurement, an uncertainty analysis should be performed. This paper deals with estimation of a measurement uncertainty for different kinds of measurement ways to detect the cavitation in a centrifugal pump with noise and vibration signal in audible frequency range from 20 Hz to 20 kHz. Especially the measurement uncertainties for cavitation detection in broad frequency range and at a discrete frequency were analyzed. Results showed that this technique is reliable despite many possible influences on uncertainty.     

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%。     

离心泵叶轮抗汽蚀优化设计

针对循环水系统离心泵的汽蚀问题对叶轮进行优化,通过选择适当的叶轮折引直径,改变叶轮入口角度来改善泵的吸入性能及改变叶轮的制造工艺和选择抗汽蚀性能好的双相不锈钢,较好解决了循环水泵叶轮汽蚀问题并设计制造焊接式叶轮.     

离心泵叶轮内水流相对速度的实验研究

该研究应用PIV系统(粒子成像测速仪)这种先进的流场测试技术在不干扰流场的情况下,进行高精度的测量,即利用撒在流体中的粒子对光的散射作用,用光学的方法记录下粒子在不同时刻的位置,从而得到粒子的位移,基于粒子对流场的跟随性,测出水流在离心泵叶片流道内的绝对速度分布,并利用软件进行数据处理,得到离心叶轮内部从吸力边到压力边相对速度的分布,为离心泵的设计提供了更为可靠的理论依据。     

A five-axis rough machining approach for a centrifugal impeller

A clear trend shows that most products or mechanical components, especially those regarding aerospace applications, are designed to fit the requirements of free form surface features. When a 3-axis computer numerical controlled (CNC) machining centre is used to produce a typical centrifugal impeller, great difficulties, i.e., collisions between the cutting tool and impeller, need to be overcome. In this case, sophisticated five-axis machines have to be utilised. Presently, most commercial computer-aided manufacturing (CAM) systems for five-axis control are lacking generality, and functions for the rough tool-path generation are far less than required. The rough machining is recognised as the most important procedure influencing the machining efficiency and is critical for the success of the following finishing process. However, great difficulties are expected to arise in performing five-axis rough machining. The main objective of the present study is to overcome this problem by combining related machining technology. As a result, CL data based on the geometry model of blade and hub of the impeller are generated. Finally, the CL data is confirmed through software simulation. The results of verification prove the machining methodology and procedure to be successful.     

Development of a performance prediction method for centrifugal compressor channel diffusers

A hybrid performance prediction method is proposed in the present study. A channel diffuser is divided into four subregions: vaneless space, semi-vaneless space, channel, and channel exit region. One-dimensional compressible core flow and boundary layer calculation of each region with an incidence loss model and empirical correlation of residuary pressure recovery coefficient of a channel predict the performance of diffusers. Three channel diffusers are designed and tested for validating the developed prediction method. The pressure distributions from an impeller exit to the channel diffuser exit are measured and discussed for various operating conditions from choke to nearly surge conditions. The strong non-uniform pressure distribution which is caused by impeller-diffuser interaction is obtained over the vaneless and semi-vaneless spaces. The predicted performance shows good agreement with the measured performance of diffusers at a design condition as well as at off-design conditions.     

泵内部流场的三维数值仿真

采用Fluent软件对泵内部流场进行了三维数值仿真,从仿真结果与设计结果对比可以看出,通过泵内部流场的三维数值仿真可以对泵的主要性能参数做出较为准确的预测,为泵的改进设计和优化提供了理论依据.     

Evaluation of subgrid-scale models in large-eddy simulations of turbulent flow in a centrifugal pump impeller

The current research of large eddy simulation (LES) of turbulent flow in pumps mainly concentrates in applying conventional subgrid-scale (SGS) model to simulate turbulent flow, which aims at obtaining the flow field in pump. The selection of SGS model is usually not considered seriously, so the accuracy and efficiency of the simulation cannot be ensured. Three SGS models including Smagorinsky-Lilly model, dynamic Smagorinsky model and dynamic mixed model are comparably studied by using the commercial CFD code Fluent combined with its user define function. The simulations are performed for the turbulent flow in a centrifugal pump impeller. The simulation results indicate that the mean flows predicted by the three SGS models agree well with the experimental data obtained from the test that detailed measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller performed using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The comparable results show that dynamic mixed model gives the most accurate results for mean flow in the centrifugal pump impeller. The SGS stress of dynamic mixed model is decompose into the scale similar part and the eddy viscous part. The scale similar part of SGS stress plays a significant role in high curvature regions, such as the leading edge and training edge of pump blade. It is also found that the dynamic mixed model is more adaptive to compute turbulence in the pump impeller. The research results presented is useful to improve the computational accuracy and efficiency of LES for centrifugal pumps, and provide important reference for carrying out simulation in similar fluid machineries.     

Failure analysis of melt urea pump impeller

Abstract

A melt urea pump is out of work after only 6 days in service. The failure of the melt urea pump impeller is analysed using different methods including chemical composition analysis, metallographic observation, SEM and energy dispersive spectroscopy analyses, etc. The results show that the material of the impeller is not the reported AISI 321 stainless steel but AISI 316 stainless steel. There are many honeycombed holes on its impeller, which is the typical feature of cavitation damage. Therefore, the main failure reason of the impeller is the cavitation erosion, and the electrochemical corrosion of the medium also accelerated the failure of the impeller. The failure of the impeller is not related with the as casted defects of the material because no obvious as casted defects are found in the material.     

Particle image velocimetry in a centrifugal pump: Details of the fluid flow at different operation conditions

Centrifugal pumps are present in the daily life of human beings. They are essential to several industrial processes that transport single- and multi-phase flows with the presence of water, gases, and emulsions, for example. When pumping low-viscous liquids, the flow behavior in impellers and diffusers may affect the centrifugal pump performance. For these flows, complex structures promote instabilities and inefficiencies that may represent a waste of energetic and financial resources. In this context, this paper aims at characterizing single-phase water flows in one complete stage of a centrifugal pump to improve our understanding of the relationship between flow behavior and pump performance. For that, a transparent pump prototype was designed, manufactured and installed in a test facility, and experiments using particle image velocimetry (PIV) were conducted at different conditions. The acquired images were then processed to obtain instantaneous flow fields, from which the flow characteristics were determined. Our results indicate that the flow morphology depends on the rotational speed of the impeller and water flow rate: (i) the flow is uniform when the pump works at the best efficiency point (BEP), with streamlines aligned with the blades, and low vorticity and turbulence in the impeller; (ii) the velocity field becomes complex as the pump begins to operate at off-design conditions, away from BEP. In this case, velocity fluctuations and energy losses due to turbulence increase to higher numbers. Those results bring new insights into the problem, helping validate numerical simulations, propose mathematical models, and improve the design of new impellers.     

离心压缩机叶轮的形状优化设计

提出一种新的优化方法离心叶轮的形状优化问题，即在遗传算法中加入自适应算子调节个体变异概率，来保证搜索的全局性和种群的多样性。并在寻优过程中加入生物生长来加快其寻优速度。最后，采用遗传算法和改进的遗传算法－生物生长法两种方法，对叶轮进行优化设计。计算结果表明改进的遗传算法－生物生长法，在较少的优化时间得到最优解。     

Numerical evaluation of flow and performance of turbo pump inducers

Steady state flow calculations are executed for turbo-pump inducers of modern design to validate the performance of Tascflow code. Hydrodynamic performance of inducers is evaluated and structure of the passage flow and leading edge recirculation are also investigated. Calculated results show good coincidence with experimental data of static pressure performance and velocity profiles over the leading edge. Upstream recirculation, tip leakage and vortex flow at the blade tip and near leading edge are main sources of pressure loss. Amount of pressure loss from the upstream to the leading edge corresponds to that of whole pressure loss through the blade passage. The viscous loss is considerably large due to the strong secondary flow. There appears more stronger leading edge recirculation for the backswept inducer. and this increases the pressure loss. However, blade loading near the leading edge is considerably reduced and cavitation inception delayed.     

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.