Effect of the Section Area of Volute in Low Specific Speed Centrifugal Pumps on Hydraulic Performance

2009 ◽  
Author(s):  
Xiang Zhang ◽  
Yang Wang ◽  
Jianhui Fu ◽  
Cui Dai ◽  
Caihong Wang
Keyword(s):  
Flow Rate ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Blade Angle ◽  
Rate Condition ◽  
Section Area ◽  
Impeller Outlet ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Experimental Researches

The volute of low specific speed centrifugal pumps has a great impact on the performance of the pump in that the highest efficiency can only be achieved when the impeller is matched with a well-designed volute. At off-BEP conditions, the performance of pumps declines as a consequence of a mismatch between characteristics of the impeller and the volute. The section area is the most important factor of volute. Numerical simulations and experimental researches have been carried out on the routine-designed impeller and the non-overloading designed impeller (different impeller outlet blade angle between two types of impellers) in the hope of finding out the effect of the section area of volute on low specific speed centrifugal pumps. It has been found that the uneven flow rate on different volute sections caused by the backflow between volute and impeller is one of the reasons for the efficiency decline of pumps at off-BEP conditions, especially in the low flow rate condition. It has also been found that the routine-designed impeller is more easily affected by the section area of volute than non-overloading designed impeller.

Effects of short blades on performance and inner flow characteristics of a low-specific-speed centrifugal pump

2017 ◽  
Vol 231 (4) ◽  
pp. 290-302 ◽  
Author(s):  
Can Kang ◽  
Ning Mao ◽  
Chen Pan ◽  
Yang Zhu ◽  
Bing Li
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Low Flow ◽  
Back Surface ◽  
Flow Rates ◽  
Pump Operation ◽  
Low Specific Speed ◽  
Specific Speed

A low-specific-speed centrifugal pump equipped with long and short blades is studied. Emphasis is placed on the pump performance and inner flow characteristics at low flow rates. Each short blade is intentionally shifted towards the back surface of the neighboring long blade, and the outlet parts of the short blades are uniformly shortened. Unsteady numerical simulation is conducted to disclose inner flow patterns associated with the modified design. Thereby, a comparison is enabled between the two schemes featured by different short blades. Both practical operation data and numerical results support that the deviation and cutting of the short blades can eliminate the positive slope of pump head curve at low flow rates. Therefore, the modification of short blades improves the pump operation stability. Due to the shortening of the outlet parts of the short blades, velocity distributions between impeller outlet and radial diffuser inlet exhibit explicitly altered circumferential flow periodicity. Pressure fluctuations in the radial diffuser are complex in terms of diversified periodicity and amplitudes. Flow rate influences pressure fluctuations in the radial diffuser considerably. As flow rate decreases, the regularity of the orbit of hydraulic loads exerted upon the impeller collapses while hydraulic loads exerted upon the short blades remain circumferentially periodic.

Pressure Fluctuation of the Low Specific Speed Centrifugal Pump

2012 ◽  
Vol 152-154 ◽  
pp. 935-939 ◽  
Author(s):  
Qiang Fu ◽  
Shou Qi Yuan ◽  
Rong Sheng Zhu
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
High Frequency ◽  
Pressure Fluctuations ◽  
Radial Force ◽  
Design Flow ◽  
Rate Condition ◽  
Low Specific Speed ◽  
Specific Speed

In order to study the rules of pressure fluctuation and the radial force under different positions in a centrifugal pump with low specific speed, and to find the relationship between each other, the three-dimensional ,unsteady Reynolds-averaged Navier-stokes equations with shear stress transport turbulent models were solved. The pressure fluctuation was obtained. The results showed that the pressure fluctuations were visible. The pressure fluctuations in the volute were relatively low at the design flow rate condition. The blade passing frequency dominates the pressure fluctuations, high frequency contents were found on the outlet of impeller but no high frequency information occured in casing. The radial force on the impeller was unsteady especially at the small flow rate.

scholarly journals Comparison of energy parameters of a centrifugal pump with a multi-piped impeller in cooperation either with an annular channel and a spiral channel

2018 ◽  
Vol 8 (1) ◽  
pp. 513-522 ◽  
Author(s):  
Bartłomiej Chomiuk ◽  
Janusz Skrzypacz
Keyword(s):  
Centrifugal Pump ◽  
Annular Channel ◽  
Operating Parameters ◽  
Centrifugal Pumps ◽  
Impeller Outlet ◽  
Flow Geometry ◽  
Quantitative Verification ◽  
Flow Through ◽  
Low Specific Speed ◽  
Specific Speed

Abstract The article presents results of numerical analyzes, which raise a subject of influence of the cooperation the multi-piped impeller with a rationalized flow geometry of annular casing and volute casing for liquid flow through centrifugal pump and their operating parameters in the extremely low specific speed nq<10. The multi-piped impeller (patented by authors) is a major alternative to classic vane impellers. The stator type is responsible for the conversion of the kinetic energy of the liquid by the impeller outlet into potential energy, which determines the overall efficiency of the pump. Also, the article presents qualitative and quantitative verification of results obtained by computer modeling and an attempt to estimate their accuracy. The article focuses mainly on the comparison of the performance parameters of the pump with a multi-piped impeller in cooperation with two stator types with a rationalized flow geometry. Both outlet elements were tested in various configurations of constructional features. The complexity of the construction of the stator can significantly affect the manufacturing costs of pump unit. Knowledge concerning construction of hydraulic elements of centrifugal pumps working in the range of parameters corresponding specific speed (nq<10) is insufficient. As shown in the paper, the annular type casing model pump cooperating with a multi-piped impeller, designed in accordance with literature, reached far poorer operating parameters than the rational annular construction in a configuration with the same impeller.

scholarly journals Effects of Flow Rate and Viscosity on Slip Factor of Centrifugal Pump Handling Viscous Oils

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Wen-Guang Li
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Tangential Velocity ◽  
Low Flow ◽  
Liquid Viscosity ◽  
Blade Angle ◽  
Pump Impeller ◽  
Slip Factor ◽  
Hydraulic Design ◽  
Impeller Outlet

Slip factor is an important parameter in the hydraulic design of centrifugal pump impeller for handling viscous oils. How to extract the factor from CFD computational results and how flow rate and liquid viscosity to affect it remain unclear. In the present paper, the flip factor was estimated by means of two approaches: one is from the velocity triangles at the impeller outlet and the other is due to the impeller theoretical head of 3D turbulent viscous fluid. The velocity of water and viscous oils in the impeller and volute computed by CFD was validated with LDV measurements at the best efficiency point. The effect of exit blade angle on slip factor was clarified. It was shown that the two approaches result into two different slip factors. The factors are significantly dependent of flow rate; however, the liquid viscosity seems to take less effect on them. Volute is responsible for reduction in tangential velocity of liquid at the outlet of impeller at low flow rates. The slip factor of impeller with large exit blade angle is not sensitive to flow rate.

Very Low Specific Speed Centrifugal Pump—Hydraulic Design and Physical Limitations

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Grunde Olimstad ◽  
Morten Osvoll ◽  
Pål Henrik Enger Finstad
Keyword(s):  
Centrifugal Pump ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Hydraulic Design ◽  
New Findings ◽  
Gear Pumps ◽  
Disk Friction ◽  
Low Specific Speed ◽  
High Head ◽  
Specific Speed

For low-flow and high-head applications, pump types such as progressive cavity or gear pumps are often used. However, centrifugal pumps are much more robust and wear resistant, and are beneficial if they can handle the rated head and flows. By challenging the limitations of low specific speed (Nq), centrifugal pumps can be made to handle a combination of low flow and high head, which previously required other pump types. Conventional centrifugal pumps have specific speed down to 10, while in this paper a design with specific speed of 4.8 is presented. The paper describes several iterative steps in the design process of the low Nq pump. These iterations were done one physical pumps, which were successively tested in a test rig. Motivation for each step is explained theoretically and followed up by discussion of the measured results. Four different geometries of the pump were tested, all of them manufactured by rapid prototyping in nylon material. A substantial question is how low the specific speed of a centrifugal pump can be. Limitations of low Nq pumps are discussed and new findings are related to volute cavitation. In addition, limitations due to disk friction, volute losses, leakage flow, and pump stability are discussed and show to limit the design space for the pump designer.

Dynamic Stall Inception and Evolution Process Measured by High-Frequency PIV System in Low Specific Speed Impeller

2021 ◽  
Author(s):  
Xiaodong Liu ◽  
Yaojun Li ◽  
Zhuqing Liu ◽  
Wei Yang
Keyword(s):  
Flow Rate ◽  
Flow Separation ◽  
High Frequency ◽  
Suction Side ◽  
Dynamic Stall ◽  
Channel Inlet ◽  
Centrifugal Pumps ◽  
Stall Inception ◽  
Low Specific Speed ◽  
Specific Speed

Abstract Stall in centrifugal pumps is a complicated flow phenomenon, which is detrimental to the pumps' safety and stable operation. Using a high-frequency PIV system (f=10k Hz) and a bench-scale refractive index matching experimental setup, two measurement methods are introduced to observe the dynamic stall inception and evolution. In the first method, the flow rate was continuously reduced at an interval of 0.005Qd and the experiment was carried out under stable flow rate condition. It shows the flow adjacent to the blade suction side gradually evolved from the flow separation into a broken vortex. The stall vortex moved toward the impeller's inlet and continuously grew, and resulted in significant changes in the main flow direction at the channel inlet. The formation and development of the other vortex structures in channel were closely related to the stall vortex at the inlet. The second method is the dynamic flow rate measurement and the results show that the stall is not caused by the increase in the relative inflow angle. It was obtained that the velocity value in the stall channel near the suction side rapidly decreased; however in the non-stall channel, the velocity value increased at the channel inlet. By analyzing the velocity distribution in both flow channels before and after the stall, the mechanism of alternating stall is well explained. Meanwhile, it was obtained that the stall was more likely to originate from the flow separation near the blade suction side for low specific speed impeller

Analysis of the Pressure Pulsation and Vibration in a Low-Specific-Speed Centrifugal Pump

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Baoling Cui ◽  
Yingbin Zhang ◽  
Yakun Huang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Vortex Core ◽  
Pressure Pulsation ◽  
Radial Force ◽  
Design Flow ◽  
Low Flow ◽  
Pressure Pulsations ◽  
Low Specific Speed ◽  
Specific Speed

Abstract Unsteady pressure pulsation and fluid force induced by flow instabilities in the centrifugal pump is an important cause of vibration, which is detrimental to the safe operation of the pump. In this study, we numerically investigated the pressure pulsation and radial force in a low-specific-speed centrifugal pump by using the detached-eddy simulation method. We also performed a vibration displacement experiment on the shaft of the centrifugal pump. The vortex identification method was introduced to clarify the internal correlation between unsteady flow structures with pressure pulsations. The results showed that the pressure pulsations at the impeller outlet were closely associated with the periodic vortex shedding from the blade pressure surface. The rotor–stator interaction between a relatively big trailing vortex core and volute tongue generated larger pressure pulsation and radial force in the pump at a low flow rate. Under a large flow rate, the trailing vortex core was easily broken and dispersed, and this resulted in smaller pressure pulsation and radial force compared with that at a low flow rate. Under the design flow rate, the pressure pulsation intensity and the radial force in the impeller were smaller than that under the off-design flow rate. Compared with the spectra between the radial force on the impeller and radial displacement on the shaft, they both presented higher amplitude at the shaft frequency. The vibration of the pump shaft was closely related to the radial force on the impeller.

Multi Objective Shape Optimization of a Low Specific Speed Impeller for a Rocket Engine Turbopump

2010 ◽  
Author(s):  
Naoki Tani ◽  
Noriyuki Shimiya ◽  
Yoshiki Yoshida ◽  
Nobuhiro Yamanishi
Keyword(s):  
Secondary Flow ◽  
Flow Rate ◽  
High Efficiency ◽  
Rocket Engine ◽  
Blade Angle ◽  
Trailing Edge ◽  
Blade Loading ◽  
Multi Objective ◽  
Low Specific Speed ◽  
Specific Speed

A rocket engine should be small and low weight, a turbopump for a rocket engine must be smaller and have higher rotation speed than the conventional pumps. However, to achieve high thrust, pump discharge pressure must be high enough. As a result, a low specific speed impeller is often chosen for a rocket engine impeller. Generally speaking, efficiency of such a low specific speed impeller is lower since blade loading becomes high and large scale secondary flow will likely occur especially around the trailing edge. Therefore, to clarify the high efficiency shape, multi objective optimization of low specific speed impeller was carried out in the present study. The optimized result showed that there is a strong tradeoff between head and efficiency, and this tendency is not influenced by the flow rate. This means that performance dependency by a flow rate may be small by such a low specific speed impeller. Shape comparison between efficiency and head optimum results showed that not only outlet blade angle but also inlet blade angle are important for high efficiency impeller. By modifying these two blade angles, blade loading distribution is changed and blockage by secondary flow region is changed. As a result, for the high head impeller, large scales blockage occurs at the trailing edge, however, for the efficiency optimum result, blockage near the trailing edge becomes smaller.

Affinity laws for impellers trimmed in two partial emission pumps with very low specific speed

2020 ◽  
pp. 095440622093631
Author(s):  
Wen-Guang Li
Keyword(s):  
Flow Rate ◽  
Substantial Reduction ◽  
Flow Coefficient ◽  
Energy Utilization ◽  
Utilization Efficiency ◽  
Hydraulic Loss ◽  
Centrifugal Pumps ◽  
Recirculation Flow ◽  
Low Specific Speed ◽  
Specific Speed

Partial emission pumps or open impeller pumps or tangent pumps with very low specific speed at either fast or conventional speed have found extensive applications in aircraft, liquid rockets, cryogenic fluid systems, chemical and petroleum-chemical industries, energy and food processing systems, etc. Usually, impeller trimming of rotodynamic pumps serves as an effective tool to meet required hydraulic performance of a liquid transport system and also to improve the entire system energy utilization efficiency. However, the affinity laws for the impeller trimming in a partial emission pump have been unavailable so far. In the paper, such affinity laws in terms of constant and variable exponents were established for flow rate, head, efficiency, flow coefficient and head coefficient based on the existing experimental data of two partial emission pumps at best efficiency points. It was shown that the affinity laws differ from the counterparts for centrifugal pumps, especially the exponent of around 2 for flow rate and the exponent of approximately 1.5 for head in comparison with nearly 1.5 for flow rate and about 2 for head in centrifugal pumps. The underlying mechanism for this effect was disclosed in terms of the ratios of the hydraulic, volumetric and mechanical efficiencies after trimming to the efficiencies before trimming analytically. The hydraulic loss, leakage flow rate and recirculation flow rate in two pumps were estimated according to the elements of fluid mechanics. It was identified that the hydraulic loss in the volute is more dominant than in the impeller and responsible for the rise of hydraulic efficiency with the trimming in progress. Moreover, the significant increase of recirculation flow rate between the volute tongue and the impeller outlet contributes to the substantial reduction in flow rate after impeller trimming.

scholarly journals Effect of Short Blade Circumferential Position Arrangement on Gas-Liquid Two-Phase Flow Performance of Centrifugal Pump

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1317
Author(s):  
Biaobiao Wang ◽  
Haoyang Zhang ◽  
Fanjie Deng ◽  
Chenguang Wang ◽  
Qiaorui Si
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Two Phase Flow ◽  
Low Flow ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Suction Surface ◽  
Two Phase ◽  
Low Specific Speed ◽  
Specific Speed

In order to study the internal flow characteristics of centrifugal pumps with a split impeller under gas-liquid mixed transportation conditions, this paper conducted a steady calculation of the flow field in the centrifugal pump under the conditions of different inlet gas volume fractions based on the Eulerian-Eulerian heterogeneous flow model, using air and water as the working media and the Schiller Nauman model for the interphase resistance. This paper takes a low specific speed centrifugal pump as the research object, through the controlling variables, using the same pump body structure and pump body geometric parameters and setting three different arrangements of long and short blades (each plan uses the same long and short blades) to explore the influence of the short blade arrangement on the low specific speed centrifugal pump performance under a gas-liquid two-phase flow. The research results show that, under pure water conditions, the reasonable arrangement of the short blade circumferential position can eliminate the hump of the centrifugal pump under low-flow conditions, can make the flow velocity in the impeller more uniform, and can optimize the performance of the pump. Under the design conditions and the gas-liquid two-phase inflow conditions, when the circumferential position of the short blades is close to the suction surface of the long blades, some of the bubbles on the suction surface of the long blade can be broken under the work of the pressure surface of the short blade and flow out of the impeller with the liquid, which improves the flow state of the flow field in the impeller.

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