Numerical and Experimental Analysis of Flow Phenomena in a Centrifugal Pump Operating Under Low Flow Rates

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Yanxia Fu ◽  
Jianping Yuan ◽  
Shouqi Yuan ◽  
Giovanni Pace ◽  
Luca d'Agostino ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
High Speed ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Internal Flow ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Low Flow ◽  
Flow Rates ◽  
Wide Range

The characteristics of flow instabilities as well as the cavitation phenomenon in a centrifugal pump operating at low flow rates were studied by experimental and numerical means, respectively. Specially, a three-dimensional (3D) numerical model of cavitation was applied to simulate the internal flow through the pump and suitably long portions of the inlet and outlet ducts. As expected, cavitation proved to occur over a wide range of low flow rates, producing a characteristic creeping shape of the head-drop curve and developing in the form of nonaxisymmetric cavities. As expected, the occurrence of these cavities, attached to the blade suction sides, was found to depend on the pump's flow coefficient and cavitation number. The experiments focused on the flow visualization of the internal flow patterns by means of high-speed digital movies and in the analysis of the inlet pressure pulsations near the impeller eye by means of fast response pressure transducers. The experimental results showed that the unsteady behavior of the internal flow in the centrifugal pump operating at low flow rates has the characteristics of a peculiar low-frequency oscillation. Meanwhile, under certain conditions, the low-frequency pressure fluctuations were closely correlated to the flow instabilities induced by the occurrence of cavitation phenomena at low flow rates. Finally, the hydraulic performances of the centrifugal pump predicted by numerical simulations were in good agreement with the corresponding experimental data.

Experimental Investigation of Pressure Fluctuations on Inner Wall of a Centrifugal Pump

2019 ◽  
Vol 36 (4) ◽  
pp. 401-410 ◽  
Author(s):  
Xiao-Qi Jia ◽  
Bao-Ling Cui ◽  
Zu-Chao Zhu ◽  
Yu-Liang Zhang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
High Flow ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Pressure Distributions ◽  
Blade Passing Frequency

Abstract Affected by rotor–stator interaction and unstable inner flow, asymmetric pressure distributions and pressure fluctuations cannot be avoided in centrifugal pumps. To study the pressure distributions on volute and front casing walls, dynamic pressure tests are carried out on a centrifugal pump. Frequency spectrum analysis of pressure fluctuation is presented based on Fast Fourier transform and steady pressure distribution is obtained based on time-average method. The results show that amplitudes of pressure fluctuation and blade-passing frequency are sensitive to the flow rate. At low flow rates, high-pressure region and large pressure gradients near the volute tongue are observed, and the main factors contributing to the pressure fluctuation are fluctuations in blade-passing frequency and high-frequency fluctuations. By contrast, at high flow rates, fluctuations of rotating-frequency and low frequencies are the main contributors to pressure fluctuation. Moreover, at low flow rates, pressure near volute tongue increases rapidly at first and thereafter increases slowly, whereas at high flow rates, pressure decreases sharply. Asymmetries are observed in the pressure distributions on both volute and front casing walls. With increasing of flow rate, both asymmetries in the pressure distributions and magnitude of the pressure decrease.

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.

Suppression of Self-Excited Flow Instability in a Radial Diffuser Using Rough Surfaces

2006 ◽  
Author(s):  
Saad A. Ahemd ◽  
Hayder Salem
Keyword(s):  
Flow Rate ◽  
Smooth Surface ◽  
Flow Instability ◽  
Rough Surfaces ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Low Flow ◽  
Flow Rates ◽  
Flow Limit ◽  
Stable Operating

Flow instabilities in a compression system at low flow rates set the flow limit of the stable operating range. Experiments to investigate the feasibility of controlling the stall in the radial diffuser of a low speed centrifugal compressor were carried out. The technique was very simple and involved using rough surfaces (i.e., sand papers) attached to the diffuser shroud. The results showed that the flow instability in the diffuser (stall) was delayed to a lower flow coefficient (the mass flow rate could be reduced to 70% of its value with the smooth surface) when the rough surfaces were positioned on the diffuser shroud.

scholarly journals Investigation of the Noise Induced by Unstable Flow in a Centrifugal Pump

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 589
Author(s):  
Jiaxing Lu ◽  
Xiaobing Liu ◽  
Yongzhong Zeng ◽  
Baoshan Zhu ◽  
Bo Hu ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Frequency Band ◽  
Acoustic Pressure ◽  
Low Frequency ◽  
Internal Flow ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Instabilities ◽  
Unstable Flow ◽  
Pump Inlet

In order to investigate the mechanism and the characteristics of the noise induced by unstable flow in a centrifugal pump, the internal flow characteristics in the pump were numerically researched, and the acoustic pressure fluctuations at the pump inlet and outlet were experimentally investigated. Obvious corresponding relationships between the flow instabilities, the cavitation and the noise were established. It was found that the rotating stall, the backflow, the hump, the occurrence of unstable flow and the cavitation in such a centrifugal pump were effectively detected through the noise, which could help to provide fundamental information on flow instabilities and guarantee safe and steady operating conditions for the system. The recirculation and prewhirl regions in the pump upstream pipe, which were caused by the backflow and the rotation of the impeller, presented the circumferential movement with a spiral shape, causing apparent broadband fluctuations at low frequency band of the acoustic pressure. The backflow and rotating stall could also result in broadband fluctuations of the pump outlet noise, which was distributed from 100 Hz to 150 Hz. Meanwhile, the broadband fluctuations of the pump outlet acoustic pressure distributed in the low frequency range, which was produced by the occurrence of cavitation, moved to the lower frequency band as the flow rate increased. The enhanced broadband fluctuations of the pump inlet and outlet noise distributed from 1 kHz to 6 kHz were caused by the coupling between the cavitation-induced noise and the system-produced noise. The broadband fluctuations of the pump inlet noise distributed between 6 kHz and 9 kHz were regarded as the typical frequency band of cavitation in the centrifugal pump.

Unsteady Flow Simulation Through a Centrifugal Pump

2005 ◽  
Author(s):  
Yulin Wu ◽  
Naixiang Chen ◽  
Zhaohui Xu ◽  
Shuhong Liu
Keyword(s):  
Centrifugal Pump ◽  
Guide Vane ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Flow Simulation ◽  
Boundary Layer Separation ◽  
Flow Instabilities ◽  
Structural Vibration ◽  
Flow Through ◽  
Vane Diffuser

Flow in a typical centrifugal pump is known to be unsteady due to flow instabilities and mutual interactions between the rotating part and the stationary parts. Flow instabilities are mostly viscous phenomena such as boundary layer separation and vortex shedding that produces relatively low frequency and small amplitude pressure fluctuations. Mutual interaction between the impeller blades and the guide vane diffuser produces relatively high frequency and large amplitude pressure fluctuations. This phenomenon is more closely related to compressibility than viscosity. It is important because it may cause structural vibration and noise. In this paper, the steady and unsteady turbulent flow through the whole flow passage of an entire centrifugal pump, has been computed to predict the pressure fluctuation of flow in the pump.

scholarly journals Vibration Characteristics Induced by Cavitation in a Centrifugal Pump with Slope Volute

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Ning Zhang ◽  
Minguan Yang ◽  
Bo Gao ◽  
Zhong Li
Keyword(s):  
Centrifugal Pump ◽  
High Frequency ◽  
Low Frequency ◽  
Local Maximum ◽  
Rotating Stall ◽  
Low Flow ◽  
Vibration Level ◽  
Flow Rates ◽  
Frequency Bands ◽  
Cavitation Process

Cavitation is one of the instability sources in centrifugal pump, which would cause some unexpected results. The goal of this paper was to analyze the influence of cavitation process on different frequency bands in a centrifugal pump with slope volute. And special attention was paid to low frequency signals, which were often filtered in the reported researches. Results show that at noncavitation condition, vibration level is closely related to flow structure interior pump. At partial flow rates, especially low flow rates, vibration level increases rapidly with the onset of rotating stall. At cavitation condition, it is proved that cavitation process has a significant impact on low frequency signals. With cavitation number decreasing, vibration level first rises to a local maximum, then it drops to a local minimum, and finally it rises again. At different flow rates, vibration trends in variable frequency bands differ obviously. Critical point inferred from vibration level is much larger than that from 3% head drop, which indicates that cavitation occurs much earlier than that reflected in head curve. Also, it is noted that high frequency signals almost increase simultaneously with cavitation occurring, which can be used to detect cavitation in centrifugal pump.

scholarly journals Research on Visualization of Inducer Cavitation of High-Speed Centrifugal Pump in Low Flow Conditions

2021 ◽  
Vol 9 (11) ◽  
pp. 1240
Author(s):  
Zhenfa Xu ◽  
Fanyu Kong ◽  
Hongli Zhang ◽  
Kun Zhang ◽  
Jiaqiong Wang ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
High Speed ◽  
Low Flow ◽  
Rapid Decline ◽  
High Speed Photography ◽  
Flow Conditions ◽  
Inlet Pipe ◽  
Flow Rates ◽  
Cavitation Performance

Inducer is often used to improve the cavitation performance of pump. In order to study the cavitation characteristics of inducer under low flow condition of high-speed pump, high-speed photography technology was employed in this paper to carry out visual experiments on the inducer of a high-speed centrifugal pump. In low flow rates, Cavitation distribution and evolution among the inducer were captured. The experimental results revealed that a band-shaped backflow vortex in the inlet pipe would occur when the flow rate was less than 0.3 Qd. Moreover, the backflow vortex in the inlet pipe rotated with the inducer and the rotational speed of backflow vortex was approximately half of the inducer. The visualization test of 0.27 Qd was carried out: when the NPSH was greater than 6.72 m, the bubbles in the inlet pipe were asymmetrical; When the NPSH dropped to 5.41 m, the cavitation was becoming less asymmetrical; When NPSH dropped to 3.81 m, cavitation evolved to the deteriorating stage, plenty of bubbles entered into the main impeller, resulting in a rapid decline of pump performance. Furthermore, the cavitation performance was worse at an extreme flow rate, and the NPSH value of 0.27 Qd was 7.5% greater than that under design condition.

Observations of Oscillating Cavitation of an Inducer

1997 ◽  
Vol 119 (4) ◽  
pp. 775-781 ◽  
Author(s):  
Yoshinobu Tsujimoto ◽  
Yoshiki Yoshida ◽  
Yasukazu Maekawa ◽  
Satoshi Watanabe ◽  
Tomoyuki Hashimoto
Keyword(s):  
High Speed ◽  
Pressure Fluctuations ◽  
Linear Analysis ◽  
Cavitation Number ◽  
Flow Coefficient ◽  
The Other ◽  
General View ◽  
Pressure Measurements ◽  
High Speed Video ◽  
Wide Range

Oscillating cavitation of an inducer was observed through unsteady inlet pressure measurements and by use of high speed video picture, covering a wide range of flow coefficient and cavitation number. One of the purposes of the study is to identify a mode of rotating cavitation predicted by a linear analysis, and the other is to obtain a general view of oscillating cavitation. The number of rotating cavitation cells and their propagation velocity were carefully determined from the phase difference of pressure fluctuations at various circumferential locations. Various kinds of oscillating cavitation were observed: rotating cavitation rotating faster/slower than impeller rotation, cavitation in backflow vortices, and surge mode oscillations. Effects of inlet and outlet (effective) pipelength were also studied.

scholarly journals Pressure Fluctuation Characteristics of High-Speed Centrifugal Pump with Enlarged Flow Design

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2261
Author(s):  
Jianyi Zhang ◽  
Hao Yang ◽  
Haibing Liu ◽  
Liang Xu ◽  
Yuwei Lv
Keyword(s):  
Centrifugal Pump ◽  
High Speed ◽  
Guide Vane ◽  
Pressure Fluctuations ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Impeller Outlet ◽  
Low Specific Speed ◽  
Blade Frequency ◽  
Large Flow

The pressure fluctuations of high-speed centrifugal pumps are the hotspot in pump research. Pressure fluctuations is differ for different structural designs and flow structures. High-speed centrifugal pumps are usually designed to increase efficiency with an enlarged flow design at a low specific speed, which changes the structure of the pump. In order to analyze the pressure fluctuations of a high-speed centrifugal pump with an enlarged flow design, the pressure was measured, and the flow field of the pump was simulated with different flow rates. Through analysis, we found that pressure fluctuations varied periodically and was consistent with the blade frequency. The pressure fluctuations at the guide vane and the interference region were also closely related to the vortices at the impeller outlet, which changed differently at different flow rates. The results showed that the high-speed centrifugal pump with an enlarged design had better performance at a large flow rate. The results in this paper can provide reference for the design of a pump that should be designed with the enlarged flow method.

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