Numerical Investigation of the Influence of Impeller-Diffuser Gap (A- and B-Gaps) on Unsteady Flow in a Centrifugal Pump at Part Flows

2019 ◽  
Author(s):  
Taiki Takamine ◽  
Satoshi Watanabe
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Internal Flow ◽  
Leading Edge ◽  
High Energy ◽  
Rotating Stall ◽  
Rotor System ◽  
The Other ◽  
High Energy Density

Abstract Because of the high energy density of multi-stage centrifugal pump, it is really important to ensure the reliability of the pumps thus the stability of rotor system in the wide flow rate range. Rotating stall is a well-known unsteady flow phenomenon in which one or several stall cell structures propagate circumferentially in impeller and/or diffuser. Rotating stall alters the peripheral pressure distribution of rotors, and therefore it is often regarded as one of the primary trigger of unstable fluid force acting on the rotor system. One possible factor which could affect the rotating stall is a geometrical relationship between the rotor and the stator. In the present study, unsteady RANS simulations of internal flow in a centrifugal pump are carried out. The pump is the partial model of the final stage of the three-stage centrifugal pump used in our previous study. In order to investigate the effect of the gap between impeller trailing edge and diffuser leading edge on the unsteady flow of the pump, three cases of impeller-diffuser gap is simulated; one is the smaller gap case with original impeller. The other cases are two larger gap cases with only cutting the impeller blades and with cutting the both impeller blades and impeller shroud walls. For all gap cases, the computations are conducted for the nominal flow rate and the low flor rate with 10% of the nominal flow rate. As a result, the rotating stall is observed only in the larger gap case with the cut shroud walls, indicating that the key phenomenon for the stable formation of the stall cell is not only the weakened rotor-stator interaction, but also the other phenomenon attributed to the enlarged gap between the impeller shroud walls and the diffuser walls. In the shroud cut case, a part of the main flow blocked by the stalled region and the secondary flow on the diffuser walls tend to flow into the side gaps more easily than other cases. They might be the important phenomenon associated with the diffuser rotating stall in the enlarged wall gap condition.

scholarly journals Unsteady Flow Characteristics of Rotating Stall and Surging in a Backward Centrifugal Fan at Low Flow-Rate Conditions

Processes ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 872 ◽  
Author(s):  
Biao Zhou ◽  
Ximing He ◽  
Hui Yang ◽  
Zuchao Zhu ◽  
Yikun Wei ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Rotating Stall ◽  
Low Flow ◽  
Small Scale ◽  
Centrifugal Fan ◽  
Unsteady Characteristics ◽  
Low Flow Rate

The steady and unsteady flow characteristics of internal flow in a backward centrifugal fan of double inlet at low flow-rate condition are investigated by computational fluid dynamics in this paper. The investigation aims to reveal insights into generation mechanisms and our physical understanding of the rotating stall and surge. The numerical results mainly demonstrate that, with decreasing flow rate, a large number of vortex flows almost increasingly occupy the internal flow of the impeller. The reverse flow and separation vortices increasingly appear near the outlet of volute, and the internal flow of the impeller is completely blocked by the separated vortex flow at low flow-rate conditions. Results indicate that, due to a synchronization of the impeller rotation and separation vortex, these separated vortices act intensely on the pressure surface of the blade with time evolution, and the interaction between the separated vortices and surface of blade increasingly yields small-scale eddies. It is further found that the amplitude of pressure and velocity fluctuations gradually increase with the decrease of flow rate in a certain range. The unsteady characteristics acting on the volute tongue gradually increase in a range of Qd to 0.3 Qd (Qd is the design volume flow rate) with the decrease of flow rate, and the unsteady characteristics acting on the volute tongue are weakened at the working condition of 0.15 Qd. These insights clearly explain the unsteady nature of the rotating stall and surge phenomenon in the double inlet backward centrifugal fan.

Flow Instability in Off Design Condition of Vaned and Vaneless Diffuser Centrifugal Pump

2015 ◽  
Author(s):  
Hideto Hiramatsu ◽  
Akiha Shibata ◽  
Shutaro Komaki ◽  
Kazuyoshi Miyagawa ◽  
Takeshi Sano
Keyword(s):  
Centrifugal Pump ◽  
Pressure Loss ◽  
Total Pressure ◽  
Internal Flow ◽  
Leading Edge ◽  
Propagation Speed ◽  
Rotating Stall ◽  
Total Pressure Loss ◽  
Speed Ratio ◽  
Vaneless Diffuser

In this study, the performance and the internal flow of one stage model centrifugal pump with both vaned and vaneless diffuser were investigated. To measure the internal flow of the diffuser and the impeller easily, air was used in this pump test. As a result of measuring pressure fluctuation, the rotating stall was observed in the vaned and vaneless diffuser. We clarified the generating mechanism and characteristics of the rotating stall in the diffuser and the difference between the unsteady flow fields in both diffusers. In case of the vaned diffuser, the number of rotating stall cells were 4 in the diffuser and the cell propagation speed ratio was about 5 percent of the impeller rotating speed. On the other hand, in case of the vaneless diffuser, the cell number was 2, and the propagation speed ratio was about 10 percent of that. These phenomena in both diffuser pumps were simulated by unsteady 2D and 3D CFD computations. By using these computations, the vortex at the trailing edge of the diffuser vanes blocked the flow and induced separate flow at the leading edge resulted in the rotating stall. This research indicated that these vortices induced the total pressure loss increasing. Also, the rotating stall was found not only in the diffuser but also in the impeller by the flow simulation of the vaneless diffuser. And it was confirmed that the vortices at the impeller trailing edge and leading edge in the stall cells cause the total pressure loss.

scholarly journals Investigation of unsteady flow in a centrifugal pump at low flow rate

2016 ◽  
Vol 8 (12) ◽  
pp. 168781401668215 ◽  
Author(s):  
Yi Li ◽  
Xiaojun Li ◽  
Zuchao Zhu ◽  
Fengqin Li
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Internal Flow ◽  
Low Flow ◽  
Experimental Result ◽  
Vortical Structures ◽  
Visualization Experiment ◽  
Rate Ratios ◽  
Low Flow Rate

Due to the characteristics of unsteady flow in the centrifugal pump at low flow rate is not revealed well, a simulation of the internal flow at different flow rates is carried out with renormalization group k–ε turbulence model and multiple reference frame. For analyzing the influence of flow rate, ratios of flow rate ( Q/ Qd) are set to 0.1, 0.3, 0.6, and 1.0 at this study. The hydraulic performance of the centrifugal pump obtained by numerical calculation has matched well with the corresponding experimental result. From the characteristics of the internal flow captured by the numerical simulation, it can be seen that backflow occurs in the inlet of impeller at low flow rate, which prevents fluid discharging into impeller passages and leads to vortical structures in suction region. With further decrease in flow rate, the strength of backflow has been intensified, and the number of vortex has significantly increased. A visualization experiment of the backflow evolution in suction pipe is carried out to validate the unsteady simulated results. Results show that the prerotation is an important factor for the deterioration of centrifugal pump performance.

Suppression of Diffuser Rotating Stall in a Centrifugal Pump by Use of Slit Vane

2021 ◽  
Author(s):  
Shunya Takao ◽  
Shinichi Konno ◽  
Shinichiro Ejiri ◽  
Masahiro Miyabe
Keyword(s):  
Flow Rate ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Time History ◽  
Internal Flow ◽  
Rotating Stall ◽  
The Other ◽  
Wave Form ◽  
Other Hand

Abstract The objective of this research is to suppress pressure fluctuation by machining slits to the diffuser vanes and clarify its effect on the diffuser rotating stall from the hydrodynamics point of view. In order to investigate pressure fluctuations due to the diffuser rotating stall, both experiment and CFD (Computational Fluid Dynamics) calculations were conducted. In the experiment, two kinds of pump (one is original and another is with slit vanes) characteristics and time history of static pressure were measured. Then, data processing of wave form were conducted by FFT (Fast Fourier Transform) analysis. The static pressure transducers were mounted at casing-side of diffuser inlet in two passages. On the other hand, the CFD calculations were carried out to investigate the behavior of the diffuser rotating stall and the effect of slit vanes using a commercial CFD software, ANSYS CFX. A positive slope of head-flow characteristics is confirmed around at ϕ = 0.036 in the case of original pump. On the other hand, it has been shifted to lower flow rate, ϕ = 0.020 in the case of slit vanes. The periodic pressure fluctuations were observed for both cases at those flow rate, respectively. Then, it was confirmed that the diffuser rotating stall occurs and the number of cell is one from the co-relation between pressure wave form of two flow passages. The unsteady RANS (Reynolds-averaged Navier-Stokes) calculations were conducted for two kinds of pump. Then the internal flow within the diffuser were compared and the differences were clarified.

Internal unsteady flow characteristics of centrifugal pump based on entropy generation rate and vibration energy

2018 ◽  
Vol 233 (3) ◽  
pp. 456-473 ◽  
Author(s):  
Xiao-Qi Jia ◽  
Zu-Chao Zhu ◽  
Xiao-Li Yu ◽  
Yu-Liang Zhang
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Flow Condition ◽  
Pressure Pulsation ◽  
Internal Flow ◽  
Exciting Force ◽  
Entropy Generation Rate ◽  
Vibration Energy ◽  
Flow Loss

The transient fluid exciting force induced by unsteady flow in the centrifugal pump is the only exciting force that cannot be effectively eliminated. In order to explore the vibration problem caused by unsteady flow in the centrifugal pump, the steady and unsteady numerical calculations of the internal flow in a centrifugal pump with low specific speed were carried out under different flow rate conditions. With volute circumferential pressure pulsation test, the accuracy of numerical calculations was verified. At the same time, the vibration acceleration sensors were arranged in different positions of the pump body to complete the vibration characteristics experiment under different working conditions. Based on the numerical results, the amount and location of the internal flow loss of the centrifugal pump were predicted by the entropy generation rate method. According to the results of the vibration test, the vibration energy distribution of the centrifugal pump under different working conditions was obtained. In combination with the entropy generation rate and vibration energy distribution, the change rules of flow loss and the vibration energy with the flow condition of the pump were analyzed. By using the frequency-domain analysis method, the pressure pulsation, the unsteady radial fluid exciting force fluctuation and the vibration acceleration were compared and analyzed to study the change rules of the pressure pulsation, the unsteady fluid exciting force and the vibration characteristics with the flow rate. The results show that the internal flow loss is mainly concentrated in the impeller runner near the volute tongue under low flow condition and the internal flow loss under large flow rate condition is mainly concentrated in the volute channel near the pump outlet. The vibration induced by the unsteady flow in the centrifugal pump is mainly low-frequency vibration, which is very sensitive to the change of the flow rate. The vibration energy in the middle- and high-frequency ranges is almost not affected by the working condition. The internal flow loss and the low-frequency vibration energy change with the flow condition, showing similar change rules.

Comparison of Stratification in a Water Tank and a PCM-Water Tank

2007 ◽  
Author(s):  
A. Castell ◽  
C. Sole´ ◽  
M. Medrano ◽  
M. Nogue´s ◽  
L. F. Cabeza
Keyword(s):  
Phase Change ◽  
Phase Change Material ◽  
Temperature Change ◽  
High Energy ◽  
Hot Water ◽  
The Other ◽  
High Energy Density ◽  
Water Tank ◽  
Charging And Discharging Processes ◽  
Change Material

Most of the storage systems available on the market use water as storage medium. Enhancing the storage performance is necessary to increase the performance of most systems. The stratification phenomenon is employed to improve the efficiency of storage tanks. Heat at an intermediate temperature, not high enough to heat up the top layer, can still be used to heat the lower, colder layers. There are a lot of parameters to study the stratification in a water tank such as the Mix Number and the Richardson Number among others. The idea studied here was to use these stratification parameters to compare two tanks with the same dimensions during charging and discharging processes. One of them is a traditional water tank and the other is a PCM-water (a water tank with a Phase Change Material). A PCM is good because it has high energy density if there is a small temperature change, since then the latent heat is much larger than the sensible heat. On the other hand, the temperature change in the top layer of a hot water store with stratification is usually small as it is held as close as possible at or above the temperature for usage. In the system studied the Phase Change Material is placed at the top of the tank, therefore the advantages of the stratification still remain. The aim of this work is to demonstrate that the use of PCM in the upper part of a water tank holds or improves the benefit of the stratification phenomenon.

Effects of the Clocking on the Internal Flow in a 1.5 Stage Axial Turbine

2006 ◽  
Author(s):  
Jongil Park ◽  
Minsuk Choi ◽  
Jehyun Baek
Keyword(s):  
Unsteady Flow ◽  
Relative Efficiency ◽  
Message Passing Interface ◽  
Flow Simulation ◽  
Internal Flow ◽  
Leading Edge ◽  
Maximum Efficiency ◽  
Axial Turbine ◽  
Flow Solver ◽  
Local Efficiency

A three-dimensional unsteady flow simulation is conducted to investigate clocking effects of a row of stators on the performance and internal flow in a 1.5 stage axial turbine. Although the original turbine has 22 blades of the first stator, 28 blades of the rotor and 28 blades of the second stator, the first stator is reduced by a factor of 22/28 to fit the blade ratio 1:1:1. The unsteady flow solver is implemented using the second order time marching and sliding mesh scheme between blade rows. And then, this flow solver is parallelized using MPI (Message Passing Interface) libraries to overcome the limitation of memories and to save the calculation time. Six relative positions of two rows of stators are investigated by positioning the second stator being clocked in a step of 1/6 pitch. The relative efficiency benefit of about 1% is obtained depending on clocking positions. At mid-span, the first stator wake is mixed up with the rotor wake before arriving at the leading edge of the second stator. The time-averaged local efficiency along the span at the maximum efficiency shows more uniform distribution than that at the minimum efficiency. Moreover, the variation of local efficiency at the mid-span does not coincide with that of overall efficiency. Therefore, it is found in this case that the only wake trajectory of the first stator is not a proper means of predicting the best and worst efficiency positions. This is why the relative efficiency benefit depending on the clocking position is obtained near the hub and casing in this study. So, it is necessary to find a general cause of the clocking effect which is applicable to every test case. The difference between maximum and minimum instantaneous efficiencies during one period is found to be smaller at the maximum efficiency than at the minimum efficiency.

Numerical study on instantaneous radial force of a centrifugal pump for different working conditions

2019 ◽  
Vol 37 (2) ◽  
pp. 458-480
Author(s):  
Xiaoqi Jia ◽  
Sheng Yuan ◽  
Zuchao Zhu ◽  
Baoling Cui
Keyword(s):  
Numerical Simulation ◽  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Working Conditions ◽  
Flow Rate ◽  
Pressure Pulsation ◽  
Radial Force ◽  
Leakage Rate ◽  
Content Type ◽  
Three Components

Purpose Instantaneous radial force induced from unsteady flow will intensify vibration noise of the centrifugal pump, especially under off-design working conditions, which will affect safety reliability of pump operation in severe cases. This paper aims to conduct unsteady numerical computation on one centrifugal pump; thus, unsteady fluid radial force upon the impeller and volute is obtained, so as to study the evolution law of instantaneous radial force, the internal relationship between radial force and pressure pulsation, the relationship among each composition of radial force that the impeller received and the influence of leakage rate of front and back chamber on radial force. Design/methodology/approach The unsteady numerical simulation with SST k-ω turbulence model was carried out for a low specific-speed centrifugal pump using computational fluid dynamics codes FLUENT. The performance tests and pressure tests were conducted by a closed loop system. The performance curves and the pressure distribution from numerical simulation agree with that of the experiment conducted. The unsteady pressure distributions and the instantaneous radial forces induced from unsteady flow were analyzed under different flow rates. Contribution degrees of three components of the radial force on the impeller and the relation between the radial force and leakage rate were analyzed. Findings Radial force on the volute and pressure pulsation on the volute wall have the same distribution tendency, but in contrast to the distribution trend of the radial force on the impeller. In the component of radial force that the impeller received, radial force on the blade accounts for the main position. With the decrease of flow rate, ratio of the radial force on front and back casings will be increased; under large flow rate, vortex and flow blockage at volute section will enhance the pressure and radial force fluctuation greatly, and the pulsation degree may be much more intense than that of a smaller flow rate. Originality/value This paper revealed the relation of the radial force and the pressure pulsation. Meanwhile, contribution degrees of three components of the radial force on the impeller under different working conditions as well as the relation between the radial force and leakage rate of front and rear chambers were analyzed.

Fluid-Dynamic Pulsations and Radial Forces in a Centrifugal Pump With Different Impeller Diameters

2005 ◽  
Author(s):  
Eduardo Blanco ◽  
Rau´l Barrio ◽  
Jorge Parrondo ◽  
Jose´ Gonza´lez ◽  
Joaqui´n Ferna´ndez
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Fluid Dynamic ◽  
Front Wall ◽  
Numerical Predictions ◽  
Radial Forces ◽  
Flow Through ◽  
Radial Gap

A study is presented on the numerical computation of the unsteady flow through a single suction and single volute centrifugal pump equipped with three impellers of different outlet diameter. Computations were performed by means of the Fluent code, solving the 3D URANS equations. The study was focused on the effect of varying the impeller-volute radial gap on the flow perturbations associated to the fluid-dynamic blade-tongue interaction. In order to contrast the numerical predictions, an experimental series of tests was conducted for the pump with the bigger impeller, to obtain pressure fluctuation data along the volute front wall. Finally, the results from the numerical simulations were used to compute the radial forces at the blade passing frequency, as a function of flow-rate and blade-tongue radial gap.

304 3-D Simulation of internal flow in Screw-Type Centrifugal Pump at Low Flow Rate

2000 ◽  
Vol 005.2 (0) ◽  
pp. 75-76
Author(s):  
Yasushi TATEBAYASHI ◽  
Kazuhiro TANAKA ◽  
Masamichi IINO
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Internal Flow ◽  
Low Flow ◽  
Low Flow Rate
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