scholarly journals Evolution Characteristics of Suction-Side-Perpendicular Cavitating Vortex in Axial Flow Pump under Low Flow Condition

2021 ◽  
Vol 9 (10) ◽  
pp. 1058
Author(s):  
Lin Wang ◽  
Fangping Tang ◽  
Ye Chen ◽  
Haiyu Liu
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
High Speed ◽  
Axial Flow ◽  
Suction Side ◽  
Low Flow ◽  
Stage Of Development ◽  
Evolution Characteristics ◽  
Axial Flow Pump ◽  
Flow Pump

In order to study the evolution characteristics of suction-side-perpendicular cavitating vortex in an axial-flow pump under low flow conditions, model tests, high-speed imaging, and an SST-CC turbulence model were used to simulate the external characteristics and cavitation morphology of the pump. The evolution law of suction-side-perpendicular cavitating vortex (SSPCV) was revealed by turbulent kinetic energy, liutex vortex identification, and vorticity transport equation. The results show that the evolution of suction-side-perpendicular cavitating vortex at low cavitation number can be divided into three stages: generation, development, and breaking stage. In the generation stage, the turbulent kinetic energy, velocity gradient and vortex kinetic energy continue to increase, reaching the maximum at the early stage of development. Afterwards, due to the viscosity of the water, the vortex slowly dissipates and enters the stage of development. Finally, it is affected by the next blade and enters the breaking stage, which accelerates the dissipation of the vortex. The vortex stretching term and vortex expansion term are the main contributors to the vorticity. During the development of the vortex, the vorticity is mainly caused by the deformation of the fluid micelle. The breaking stage mainly affects the stretching term, and the Coriolis force term cannot be ignored in the rotating coordinates.

Experimental and Numerical Investigation on Pressure Fluctuation of the Impeller in an Axial Flow Pump

2019 ◽  
Author(s):  
Xi Shen ◽  
Desheng Zhang ◽  
Bin Xu ◽  
Yongxin Jin ◽  
Xiongfa Gao
Keyword(s):  
Pressure Fluctuation ◽  
High Speed ◽  
Axial Flow ◽  
Suction Side ◽  
High Speed Photography ◽  
Detached Eddy Simulation ◽  
Transient Pressure ◽  
Unstable Flow ◽  
Axial Flow Pump ◽  
Flow Pump

Abstract The Detached Eddy Simulation (DES) has been used to simulate the pressure fluctuation of the impeller in an axial flow pump. The results were combined with experiments including high-speed photography and transient pressure measurements to investigate the unstable flow induced by tip leakage vortex (TLV). Numerical results show that maximum predictive error values of head is 2.9%, compared with experimental results. The pressure fluctuation at different monitoring points present a certain regularity, with 3 peaks and 3 troughs in a period, corresponding to the number of blades. The amplitude of pressure fluctuation at P1 (impeller inlet) is the highest among those monitoring points, where the amplitude decreases with the flow rates. The dominant frequency of pressure fluctuation at impeller under cavitation condition is the blade passing frequency (BPF). Besides, there are also N* = 6, 9, 12 and other more harmonic frequencies. The cavitation flow was analyzed with the pressure fluctuation of the blade tip. For the existence of the pressure difference between pressure side and suction side, the pressure at monitoring points change alternately. The amplitude of the fluctuation near tip is affected seriously by the cavitation bubbles, as the cavitation could is a low pressure region with unstable fluctuation.

Numerical simulation on hydraulic performance and tip leakage vortex of a slanted axial-flow pump with different blade angles

2021 ◽  
pp. 095440622110329
Author(s):  
Zhaodan Fei ◽  
Hui Xu ◽  
Rui Zhang ◽  
Yuan Zheng ◽  
Tong Mu ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Strain Tensor ◽  
Axial Flow ◽  
Hydraulic Performance ◽  
Tip Leakage Flow ◽  
Blade Angle ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump

The blade angle has a great effect on hydraulic performance and internal flow field for axial-flow pumps. This research investigated the effect of the blade angle on hydraulic performance and tip leakage vortex (TLV) of a slanted axial-flow pump. The hydraulic performance and the TLV are compared with different setting angles. The dimensionless turbulence kinetic energy (TKE) is used to investigate the TLV. A novel variable fv is utilized to analyze the relation among the TLV, strain tensor and vorticity tensor. The proper orthogonal decomposition (POD) method is used to analyze TLV structure. The results show that with the increase of the blade angle, the pump head is getting larger, the flow rate of the best efficiency moves to be larger, and both the primary TLV (P-TLV) and the secondary TLV (S-TLV) are getting stronger. The P-TLV often exists in the outer edge of TKE distribution and S-TLVs often exist in the largest value area of TKE. This phenomenon is more evident with blade angle increasing. Through POD method, it shows that the first six modes contain more than 90% of TKE. The reason why the TKE value near the region of S-TLV is high is that the tip leakage flow is a kind of jet-like flow with high kinetic energy. The main structure of the P-TLV is shown in modes 4−6, resulting in a reflux zone but not with the highest TKE.

An Investigation of the Vortex in a Submersible Axial Flow Pump Impeller

2015 ◽  
Vol 741 ◽  
pp. 481-485
Author(s):  
Hong Ming Zhang ◽  
Li Xiang Zhang
Keyword(s):  
Pressure Pulsation ◽  
Axial Flow ◽  
Suction Side ◽  
Transfer Model ◽  
Mass Transfer Model ◽  
Governing Equations ◽  
Pump Impeller ◽  
Axial Flow Pump ◽  
Volume Method ◽  
Flow Pump

The paper presents numerical simulation of the vortex in a submersible axial flow pump impeller using OpenFoam code. A mixture assumption and a finite rate mass transfer model were introduced to analyze vortex. The finite volume method is used to solve the governing equations of the mixture model and the pressure-velocity coupling is handled via a Pressure Implicit with Splitting of Operators (PISO) procedure. Simulation results have shown that the cavitation may occur on the lower portion of impeller suction side. And the blade channel vortex will be formed in the impeller. It can induce the pressure pulsation in the impeller and can result in reduced efficiency of the submersible axial flow pump.

Experimental Investigation of Tip Cavitating Vortices in Axial-Flow Pump

2017 ◽  
Author(s):  
Desheng Zhang
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Axial Flow ◽  
Operating Conditions ◽  
High Speed Imaging ◽  
Cavitation Performance ◽  
Stable Operating ◽  
Wide Range ◽  
Axial Flow Pump ◽  
Flow Pump

The primary goal of this work focuses on the cavitating vortices in the tip region of an axial-flow pump with 3 and 4 blades mainly based on the high-speed imaging experiments, with special attention on the trajectory and dynamics of a large-scale cavitation structure. The hydraulic and cavitation performance between two impellers were compared, and it can be found that the model with 4 blades has a relative wide range of stable operating conditions as well as the better anti-cavitation ability. By the analysis of the cavitation curves, it confirms that the highly unsteady tip cavitation cloud near the blade trailing edge should be responsible for the severe degradation of the performance. According to the detailed study on the cavitation evolution in the two impellers, it is observed that the trajectory of tip cavitating vortices for different flow rates seems very similar determined by the operating conditions. However, the dynamics varies significantly, which is associated with the blade loading and flow passage width.

scholarly journals Analysis of the Formation Mechanism and Evolution of the Perpendicular Cavitation Vortex of Tip Leakage Flow in an Axial-Flow Pump for Off-Design Conditions

2021 ◽  
Vol 9 (10) ◽  
pp. 1045
Author(s):  
Hu Zhang ◽  
Jianbo Zang ◽  
Weidong Shi ◽  
Desheng Zhang
Keyword(s):  
Formation Mechanism ◽  
High Speed ◽  
Axial Flow ◽  
Axial Direction ◽  
High Speed Photography ◽  
Tip Leakage Flow ◽  
Origin And Evolution ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump

To understand the formation mechanism and evolution process of the perpendicular cavitation vortex (PCV) of an axial flow pump for off-design conditions, turbulent cavitating flows were numerically investigated using the rotation curvature-corrected shear stress transport (SST-CC) turbulence model and the Zwart–Gerber–Belamri cavitation model. In this work, the origin and evolution of a PCV were analyzed through a high-speed photography experiment and numerical simulation. The results showed that the PCV came from a secondary tip leakage vortex (S-TLV) and was aggregated by the action of the re-entrant jet, combined with the cavitation bubbles driven by the radial flow to form the cavitation vortex (CV). With the joint action of leakage jet lifting and TLV entrainment, the PCV was reoriented and gradually became perpendicular to the chord direction. Then, the PCV and TLV collided, mixed, and entrained, which formed a strong pressure pulsation. The PCV was gradually divided into upper and lower parts. One part was combined with the residual part of the TLV and flowed to the next blade, and the other part flowed out of the impeller area along the axial direction. At the same time, the generation, evolution, and dissipation of the PCV formed high pulsation amplitudes and frequencies in the middle and rear above the blade suction.

Experimental Investigation of the Transient Patterns and Pressure Evolution of Tip Leakage Vortex and Induced-Vortices Cavitation in an Axial Flow Pump

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Shen Xi ◽  
Zhang Desheng ◽  
Xu Bin ◽  
Jin Yongxin ◽  
Shi Weidong ◽  
...  
Keyword(s):  
High Speed ◽  
Axial Flow ◽  
Operating Conditions ◽  
High Speed Photography ◽  
Transient Pressure ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump

Abstract Cavitating flow is extremely complex in axial and mixed flow pumps, resulting in several adverse effects on pump performance. In this paper, the tip leakage vortex (TLV) cavitation patterns in an axial flow pump model were studied based on high-speed photography and transient pressure measurements. The TLV cavitation morphology and transient development of the induced suction-side-perpendicular cavitating vortices (SSPCVs) were investigated at multi-operating conditions. The time-domain of the transient pressure was employed to clarify the relationship between the tip cavitation and the pressure field. The results showed that cavitation inception occurred earlier with an unstable TLV cavitation shape at part-load conditions. Cavitation was more intense with a decrease of the cavitation number, presenting a larger area of triangular cavitation with the shedding of SSPCV. The inception of SSPCV was attributed to the tail of the shedding cavitation cloud originally attached to the suction surface (SS) of the blade, moving in the direction of the adjacent blade perpendicular to the SS, resulting in a flow blockage. With a further decrease in pressure, the SSPCVs grew in size and strength, accompanied by a rapid degradation in performance of the pump. The cavitation images and the corresponding circumferential pressure distributions showed that the lowest pressure point coincided with the SS corner. After this position, the pressure fluctuated as the cavitation intensity changed. The transient characteristics of SSPCV are a basis for revealing the instability mechanism of its evolution in the axial flow pump.

Experiments of Tip Leakage Vortex Cavitation Cloud and Suction-Side-Perpendicular Cavitating Vortices in an Axial Flow Pump

2018 ◽  
Author(s):  
Xi Shen ◽  
Desheng Zhang
Keyword(s):  
Pressure Pulsation ◽  
Axial Flow ◽  
Suction Side ◽  
High Speed Photography ◽  
Suction Surface ◽  
Rate Condition ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump

The tip leakage vortex (TLV) cavitation mechanism of axial flow pump was investigated with the results of high speed photography and pressure pulsation measurement. The tip leakage vortex cavitation morphology and the transient characteristics of the TLV-induced suction-side-perpendicular cavitating vortices (SSPCV) were analyzed under different flow rates and different cavitation numbers which were combined with the time domain spectrum of pressure fluctuation to elucidate the relationship between the tip cavitation and pressure pulsation. The results showed that cavitation inception occurs earlier with more unstable tip leakage vortex cavitation shape under part-load flow rate condition, and the cavitation is more intense with the decrease of the cavitation number. The inception of SSPCV is attributed to the tail of the shedding cavitation cloud originally attached on the suction side (SS) surface of blade, moving toward the adjacent blade perpendicular to the suction surface, resulting in a flow blockage. With further decrease of pressure, the SSPCVs grow in size and strength, accompanied with a rapid degradation in performance of the pump. The cavitation images and the corresponding circumferential pressure distribution with the same phase showed that the lowest pressure coincides with the suction surface (SS) corner, The pressure was found to decrease along with the occurrence of the cavitation structure.

Influence of Vane Number on the Performance of Axial-Flow Pump Under Low-Flow-Rate Conditions

2013 ◽  
Author(s):  
Can Kang ◽  
Qifeng Huang ◽  
Yunxiao Li
Keyword(s):  
Energy Dissipation ◽  
Flow Rate ◽  
Low Frequency ◽  
Axial Flow ◽  
Low Flow ◽  
Fast Fourier Transformation ◽  
Rotor Stator Interaction ◽  
Dimensional Parameters ◽  
Axial Flow Pump ◽  
Flow Pump

In order to further probe the relations between hydraulic features and instantaneous vibration of impeller pump, an axial flow pump designed with different combination schemes of rotor and stator is numerically investigated. Vane numbers of 5, 7 and 9 are separately adopted to match the same impeller with 4 blades. Attentions are paid on the pump’s performance under low flow rates. Saddle-shaped performance curves are proved during the three pumps’ operation with the variation of flow rate. With pre-defined non-dimensional parameters, distributions of axial velocity near the impeller and vane are described. Pressure waves and wake in the region between impeller and vane influence significantly the turbulent flow patterns and energy dissipation. Typical frequencies achieved through fast Fourier transformation of fluctuating pressures also indicate that the emergence of low-frequency components and energy dissipation in the rotor-stator interaction (RSI) region arouse more non-deterministic factors of hydraulic excitation.

Improving the Performance of an Axial Flow Pump: An Overview

2021 ◽  
Vol 107 ◽  
pp. 15-25
Author(s):  
M. Prince Moifatswane ◽  
Nkosinathi Madushele ◽  
Noor A. Ahmed
Keyword(s):  
Design Optimization ◽  
Axial Flow ◽  
Optimization Methods ◽  
Hydraulic Performance ◽  
Low Flow ◽  
Flow Conditions ◽  
Pump Performance ◽  
Operational Conditions ◽  
Axial Flow Pump ◽  
Flow Pump

Thus far, axial flow pumps remain a significant hydrodynamic unit. These pumps have common applications for various systems that require a high flow rate and a lower head. They tend to be less efficient and consume excessive power when operating at low flow conditions. Most of the studies focus on improving the hydraulic performance of these pumps based on the best efficiency point (BEP) flow conditions. This approach is mostly based on the assumption that the pump will always operate at BEP. However, this is not always the case, because the operational condition of the pump may require an adjustment to meet certain system demands. Hence, it is necessary to emphasize the need to improve the hydraulic performance of these pumps for multiple flow conditions. This means that in addition to BEP, the lowest, and the highest operational conditions need to be considered when improving the pump performance. Also, it is important to review the phenomenon of cavitation in every design optimization investigation, given its significance to pump performance and some misrepresentation which are sometimes associated with its assessment. Therefore. the main contribution of this article is to briefly discuss the successful and unsuccessful design optimization methods of an axial flow pump. Furthermore, it highlights the significance of improving the pump performance at multiple flow conditions and also to incorporate the analysis of using CFD methods to analyze the results of cavitation performance in every pump performance improvement investigation.

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