Impeller Passage Research Articles

Effect of Rotation Speed and Flow Rate on Slip Factor in a Centrifugal Pump

This work analyzes the causes of the slip phenomenon in the impeller on the basis of the internal flow mechanism. Detailed optical measurements of the flow inside the rotation passages of a five-bladed centrifugal pump impeller are obtained through particle image velocimetry (PIV). On the basis of experimental data, the deviation coefficient of slip velocity is proposed and then revised according to the slip factor calculation formula of Stechkin. Results show that, at the same rotation speed, the slip factor increases with the flow rate and reaches the maximum value at 1.0 QBEP flow rate. At different rotation speeds, the slip factor increases with the rotation speed and shows a relatively large variation range. Moreover, a revised slip factor formula is proposed. The modified model is suitable for the correction of slip factor at part-load flow rates and serves as a guide for the hydraulic performance design and prediction of centrifugal pumps.

Experiment and simulation about the effect of wear-ring abrasion on the performance of a marine centrifugal pump

The wear-ring abrasion can cause performance degradation of the marine centrifugal pump. In order to study the effect of front and back wear-ring clearance on a pump, test and numerical simulation were used to investigate the performance change of a pump. The test results show that the head and efficiency of pump decrease by 3.56% and 9.62% respectively at 1.0 Qd due to the wear-ring abrasion. Under 1.0 Qd, with the increase of the front wear-ring the vibration velocity at pump foot increases from 0.4 mm/s to 1.0 mm/s. The axis passing frequency (APF) at the measuring points increases significantly and there appears new characteristic frequency of 3APF and 4APF. The numerical simulation results show that the front wear-ring abrasion affects the flow at the inlet of the front chamber of the pump and impeller passage. And the back wear-ring abrasion has obvious effect on the flow in the back chamber of the pump and impeller passage, while the multi-malfunction of the front wear-ring abrasion and back wear-ring abrasion has the most obvious effect on the flow velocity and flow stability inside pump. The pressure pulsation at Blade Passing Frequency (BPF) of the three schemes all decrease with the increase of the clearance.

Research the Influence of Hydraulic Model on Vibration of Pump

In this paper, the cooling water pump of centrifugal equipment is taken as the research object in ship system. The pump set is normally open. And, it is also one of the main vibration sources of ship. On the premise of meeting the requirement of hydraulic performance parameters, several different hydraulic model prototypes of this pump set are manufactured. On the same test bench, the vibration tests of this pump show that the measured values are quite different. Fluid software is used to analyse these hydraulic models under the same boundary conditions. It is found that there are obvious differences in hydraulic fluctuations and fluid vortices among impeller passage, vortex chamber, inlet and outlet passages. In order to verify the inference, vibration test and analysis are carried out on the whole pump set and the foots of installation. The corresponding relationship was found out between the fluid fluctuation of hydraulic components and the vibration characteristics. Based on the corresponding relationship, the current hydraulic model of pump is optimized and improved. The parameters of hydraulic model which can affect the vibration sensitivity of pump are optimized. Finally, the experimental results prove that this method can reduce the vibration effectively.

Description of Unsteady Flow Characteristics in a Side Channel Pump With a Convex Blade

Abstract To investigate the unsteady flow characteristics in side channel pumps, the vortex structures and their evolutions in the impeller and side channel flow passages have been comprehensively studied. Systematically, three impeller schemes were designed with different ratios of convex blade height h to impeller blade length l (h/l = 0.2, 0.5, and 0.8) for detailed analysis. The findings indicated that the convex blade broadens the high-efficiency range and improves the efficiency at the best efficiency point (BEP) for scheme h/l = 0.2. Impeller scheme h/l = 0.2 records the highest vortex concentration region, scheme h/l = 0.5 displays as scattered spots, while scheme h/l = 0.8 exhibits significant flow pattern changes in the impeller. The vortex distribution area and vortex intensity in the lengthways between the impeller and side channel of h/I = 0.2 are almost analogous, but the other two impeller schemes have obvious separation and very chaotic. Although the shrinkages of axial vortexes in the impeller did not reflect on hydraulic performance, impeller schemes h/l = 0.5 and 0.8 provided an outstanding performance in reducing the pressure fluctuations. The objective of this study is to provide a theoretical basis for optimal design and analysis of strong vortex flows in side channel pumps.

PIV test of the flow field of a centrifugal pump with four types of impeller blades

Abstract Flow fields for various impellers were measured using water and a two-phase liquid–solid mixture with a particle image velocimetry system in a centrifugal rotating frame in controlled conditions. After measuring absolute velocity vectors in impeller passages, the vectors were decomposed based on the triangle speed principle and the distribution of relative velocity vectors within the impeller was obtained. Then, the distribution of particles and their influence on the performance of different impellers were analyzed. The following conclusions were made from the comparison of relative velocity vector field: first, the wear on the outlet of blades can be mitigated effectively by reducing the outlet angle of impeller blades; second, the pump with a double-arc-shaped profile had a more uniform and stable flow field distribution and higher performance than that with a single-arc profile; and finally, the “jet–wake” structure can be improved significantly by using impellers with long and short blades, resulting in a remarkable reduction in energy loss and improvement in pump efficiency. We also found that solid particles were mainly distributed at the outlet of the impeller and volute wall, while the concentration distribution of large particles tended to match the pressure surface. This research can provide some theoretical guidance for the design and optimization of two-phase flow centrifugal pumps.

Numerical Simulation and Experiment of the Effects of Blade Angle Deviation on the Hydraulic Characteristics and Pressure Pulsation of an Axial-Flow Pump

Inadequate blade angle adjustment or manufacturing errors will cause inconsistencies in the blade angle of an axial-flow pump. In this study, the hydrodynamic characteristics of an axial-flow pump with inconsistent blade angle are investigated by analyzing hydraulic performance and pressure pulsation. The analysis is conducted by performing a numerical simulation combined with a model test. Results show that, relative to the case without blade angle deviation, the case with blade angle deviation exhibits changes in the periodicity of the flow field in the impeller. Such changes result in uneven pressure changes in the impeller passage. The pressure pulsation induced by the blade angle deviation is mainly low-frequency pulsation; that is, it is twice the rotation frequency. The amplitude of the main frequency pulsation is 1.5–3 times that of the blade without angle deviation. This low frequency that dominates the whole pump device easily causes the vibration and weakens the safety and stability of the pump. The blade angle deviation exerts great influence on the unsteady characteristics. Hence, blade angle deviation seriously affects the safe and stable operation of axial-flow pumps and pump stations.

Numerical Simulation of Fine Particle Solid‐Liquid Two‐Phase Flow in a Centrifugal Pump

To study the effect of fine particle size and volume concentration on the performance of solid‐liquid two‐phase centrifugal pump, the mixture multiphase flow model, RNG k-ε turbulence model, and SIMPLEC algorithm were used to simulate the two‐phase flow of the centrifugal pump. The effects of particle size and volume concentration on internal pressure distribution, solid volume distribution, and external characteristics were analyzed. The results show that under the design discharge conditions, with the increase of particle size and volume concentration, the internal pressure of the flow field will decrease, and the volume fraction of solid phase in the impeller passage will also decrease as a whole. The solid particles gradually migrate from the suction surface to the pressure surface, and the particles in the volute channel are mainly concentrated in the flow channel near the outlet side of the volute. With the increase of particle size and volume concentration, the negative pressure value at the inlet of centrifugal pump increases, the total pressure difference at the inlet and outlet decreases, and the head and efficiency decrease accordingly.

Numerical Study on Energy Conversion Characteristics of Molten Salt Pump for Concentrating Solar Power Based on Energy Transport Theory

Molten salt pump (MSP) used to circulate the molten salt in concentrating solar power (CSP) system. The operation of MSP needs to understand the energy conversion characteristics in the flow field. In this study, the energy conversion characteristics of MSP were investigated based on energy transport theory. A significant portion of power is consumed in the propulsion of pressure between the inlet throat to the outlet throat of the impeller passage. The increase in the energy of medium by the Lamb vector divergence mainly occurs on the rear of the impeller passage. Whereas the enstrophy dissipation area is primarily located in the suction surface area at the impeller outlet. In addition, the pressure propulsion power is critical for energy transfer in the impeller, while the contribution of Lamb vector divergence and enstrophy dissipation is limited. It was observed that the distribution of energy transport dynamic parameters have a high degree of coincidence irrespective of the medium density, which indicates that the density of the medium does not have a significant impact on the law of energy conversion. Therefore, when the geometrical characteristics of the impeller are determined, the energy conversion characteristics of different medium do not change significantly.

The influence of a pipe impeller external shape on the pump parameters

Multi-piped impellers (name proposed by the authors) represent an innovative approach to the design of rotodynamic pumps operating at the specific speed of nq<10. In such a construction the energy increase is caused by the flow of liquid through the internal impeller passages as well as by an external flow around the passages, and sensible designing of such a construction is extremely difficult. The study investigates the flow phenomena and impact of the external shape of a multi–pipe impeller on the efficiency of the process of energy transfer into liquid. The main research method involves computational fluid dynamics (CFD) simulations.

Study on Improving Cavitation Performance of Centrifugal Pump by Perforation at the Front Cover Plate

To improve the cavitation performance of a centrifugal pump, the high-pressure liquid in the front pump cavity is introduced into the cavitation area on the back of the blade by perforated holes at the front cover of the impeller. Based on the RNG k-ε turbulence model and Zwart-Gerber-be1amri cavitation model, the numerical calculation and analysis of the cavitation flow field in the model before and after perforation under different cavitation numbers is carried out by FLUENT. The results show that: The perforation at the front cover plate can effectively improve the pressure value of the cavitation area on the back of the blade. To some extent, the change of pressure gradient restrains the development of cavitation. The perforation at the front cover plate can effectively reduce the integral value of the cavitation bubble in the passage, improve the flow passage conditions in the impeller passage, and reduce the blockage degree of the cavitation to the passage. At the same time, the fluctuation range of the cavitation volume in the impeller is small in a rotation cycle after the perforation. It can be seen that the way of perforation at the front cover plate can effectively improve the cavitation performance of the centrifugal pump.

Effect of particle size distribution on performance and particle kinetics in a centrifugal slurry pump handling multi-size particulate slurry

A significant variation in particle size distribution (PSD) is generally encountered in slurry transportation. The goal of this work is to establish the effect of variation in PSD on the centrifugal slurry pump (CSP) performance and particle kinetics. Computational fluid dynamics (CFD) modeling of a CSP with multi-size particulate slurry has been performed with a sliding mesh approach using the granular Eulerian-Eulerian model. The numerical model is validated with the experimental data of the pump performance for multi-size particulate fly ash slurry. The maximum deviations in the predicted head and efficiency compared to the measured values are of the order of ±2% and ±3.5%, respectively. Simulations with a single representative particle size for multi-size particulate slurry using median and weighted mean diameter approach are also carried out to understand the difference in performance prediction with equi-size and multi-size slurry. The predicted trend of pump performance variation with PSD is linear and non-linear with equi-size and multi-size slurries, respectively. The median and weighted mean approaches showed error in capturing the effect of variation in PSD on pump performance. The variation in PSD significantly affects the flow of particles inside the impeller and casing flow passages due to particle kinetics. Reduction in the intensity of granular pressure, maximum granular viscosity, and the head loss due to friction in impeller and casing flow passages are found with the increase in the fine size particles.

Counter-Propagating Rotating Stall of Vaned Diffuser in a Centrifugal Compressor Near Design Condition

Abstract Unstable flow in the vaned diffuser of a centrifugal compressor stage near design condition is investigated by numerical simulation. The simulation is performed with the unsteady Navier–Stokes equations and three different turbulence models. Comparisons of the characteristic curves of the stage have been carried out between simulation and experiment, and good agreement is obtained. The fluctuation signals near the interface between the impeller and the diffuser are also quantitatively analyzed from macro and micro scales under a series of mass flow conditions. The simulation results show that an abnormal counter-propagating rotating stall in the vaned diffuser is detected near design condition. The rotating stall displays that four stall cells near the shroud side of the vaned diffuser propagate slowly at a rate of approximately 0.675% of the impeller rotating frequency along the opposite direction of the impeller rotation. The propagation speed increases as the mass flow decreases. The generation and propagation mechanisms of this phenomenon are elucidated, respectively. It is found that flow separation near the diffuser shroud side is produced due to the spanwise variation of flow angles near the impeller exit, which leads to the generation of stall cells in the diffuser. The circumferential propagation of the rotating stall cells is propelled by the accumulation and release of the fluid energy from impeller passages. Further studies show that this phenomenon can be restrained by modifying the installation angle of diffuser vanes.

Numerical study of operating performance of a centrifugal pump as turbine at overload with special emphasis on unsteady blade load

Three-dimensional (3D) unsteady Reynolds-averaged Navier–Stokes (URANS) simulations are conducted to investigate the blade load and internal flow field for a low specific centrifugal pump operating as a turbine (PAT). Validation and grid independence of the simulation method are performed and ensured. A thorough inspection to flow variables in terms of pressure and radial velocity as well as circumferential velocity at strong rotor–stator interaction region is performed. Unsteady performance characteristics in terms of head and shaft power as well as transient blade loads are evaluated to assess the unsteady PAT performance. Significant decreasing of the blade load is revealed when impeller passage passes the volute tongue and associated with the strong vortex close to passage suction side caused by the sharp angle of suction side trailing edge with a discernible flow incidence angle. High negative radial velocity in the region close to suction side is originated from the vortex inducing velocity at the blade suction side and a high pressure gradient in the trailing edge region. The decrease of blade load is caused by periodical development and restriction of the vortex with an impeller passage passing tongue and a subsequent pressure variation on suction side that leads to temporally decreased blade loading. High positive radial velocity in pressure side region is originated from the blocking effect from the strong vortex at suction side, leading to the generation of a relatively weaker vortex fluctuating with impeller rotation at pressure side. That is the source of pressure variation on pressure side, contributing to the blade loading variation. These results provide a detailed insight into the complex overload flow field that might be utilized for an improved PAT design.

Analytical Methods and Verification of Impeller Outlet Velocity Slip of Solid–Liquid Disc Pump with Multi-Type Blades

The intensive exploration to improve the accuracy of the calculation model of velocity slip and theoretical head has always been a major issue in pump research. Discontinuous blade of disc pump is different from the continuous blade of traditional pump. Disc pump realizes energy transfer by the effect of boundary layer. In order to fill in the theoretical blank of current research on the velocity slip and theoretical head of blade disc pump, the velocity slip is calculated by the systematic analysis under solid–liquid flow. In this study, the current misconception of velocity slip was corrected. Based on the different normal velocity components between particle and liquid on the blade surface, a new method is proposed to further verify the difference of solid–liquid flow velocity in impeller passage. Through the proposed method of calculating average circumferential velocity, the calculation model of the velocity slip coefficient and theoretical head of disc pump with linear and curved blade are given and verified. The accuracy of calculation model is increased by 39.4%. This model has good application value in theoretical head calculation, which lays a foundation for further research on energy conversion, energy efficiency prediction and reverse optimization design of disc pump with different blade shapes.

Investigation of flow pattern and hydraulic performance of a centrifugal pump impeller through the PIV method

The objective of this study is to analyse the quantitative relationship between the local Euler head distribution and the internal flow in a centrifugal impeller and provide guidance for the design specifications of inverse design methods. The local Euler head at the inlet is mainly affected by the clockwise vortex on the blade suction side. At the outlet, it is affected by the relative motion of clockwise and counterclockwise vortexes. The effect of the two types of vortexes on the local Euler head makes the pump head almost constant under deep part-load conditions, proving that the impeller has an effective diameter. The mean local Euler head distribution along the impeller passage is closely interrelated with the flow pattern. The position in which the mean local Euler head increases fastest coincides with the radial position of the clockwise vortex centre. The position of its maximum value is consistent with the radial position of the end of the clockwise vortex. The position of its maximum value moves towards the inlet as the flow rate decreases, confirming the impeller has an extreme impeller diameter. The inflection points of the mean local Euler head ratio curve correspond to the appearance of vortex structures. • The distribution rules of local Euler head are investigated by PIV experiments. • The local Euler head distribution is related to the internal flow patterns. • The local Euler head distribution determines the hydraulic performance of pump. • The mean local Euler head ratio curve can reflect the position of vortex.

Dynamic Characterization of Vortex Structures and Their Evolution Mechanisms in a Side Channel Pump

Abstract To obtain a better insight into the unsteady flow behavior in side channel pumps by a robust vortex identification method, this study presents the efficacy of the new Ω-criterion in characterizing the evolution of vortex structures in the turbulent flows under different time steps. The flow behavior and the underlying vorticity dynamics were revealed as well. Compared to Q-criterion, the new Ω-criterion identified all vortex structures irrespective of the intensity at a universal threshold of 0.52. Three different types of vortex structures (longitudinal, axial, and radial) were identified to be responsible for the turbulent flows in the side channel pumps. The beneficial longitudinal vortex promotes the momentum exchange flow between the impeller and side channel which leads to the high hydraulic head of side channel pumps. On the other hand, the unfavorable axial and radial vortex structures restricted in the impeller passage mitigate the exchange process accounting for the low efficiency of the pumps. From this study, it can be established that the evolution of the axial vortex structures is responsible for the largest vortex distribution in the impeller compared to the total vortex evolved. The impeller outer radius contributes about 60% of the unfavorable axial structures evolved. Using the new Ω-criterion, many reported anomalous findings have been explained.

Effect of Blade Profile on the Performance of a Centrifugal Fan with Different Velocity Distribution Functions

The velocity distribution method is a way to design the blade profile according to the average relative velocity in the impeller passage. Present research is aimed to investigate the effect of blade profile on the performance of a centrifugal fan with different velocity distribution functions through numerical simulations. The results show that compared with common arc blade, the centrifugal fan with new blade profile designed by velocity distribution method gets a higher efficiency, the relative velocity distribution along impeller passages of the new model is more uniform, and the boundary layer separation is delayed than that in the original model.

Clocking effect in a centrifugal pump with a vaned diffuser

The performance and service life of centrifugal pumps can be influenced by the clocking effect. In this study, 3D numerical calculations based on the k-omega shear stress transport model are conducted to investigate the clocking effect in a centrifugal pump. Time-averaged behavior and transient behavior are analyzed. Results show that the optimum diffuser installation angle in the centrifugal pump is [Formula: see text] due to the minimum total pressure loss and radial force acting on the impeller. Total pressure loss, particularly in the volute, is considerably influenced by the clocking effect. The difference in total pressure loss in the volute at different clocking positions is 2.75 m under the design flow rate. The large total pressure loss in the volute is primarily caused by the large total pressure gradient within the vicinity of the volute tongue. The radial force acting on the impeller is also considerably affected by the clocking effect. When the diffuser installation angle is [Formula: see text], flow rate fluctuations in the volute and impeller passage are minimal, and flow rate distribution in the diffuser passage is more uniform than those in other diffuser installation angles. Moreover, static pressure fluctuations in the impeller midsection and the diffuser inlet section are at the minimum value. These phenomena explain the minimum radial force acting on the impeller. The findings of this study can provide a useful reference for the design of centrifugal pumps.

Evaluation of different turbulence models on simulation of gas-liquid transient flow in a liquid-ring vacuum pump

To analyze the prediction ability and applicability of different turbulence models to the complicated gas-liquid flow in the liquid-ring vacuum pump, three different turbulence models, namely RNG k-ε, SST k-ω and LES were respectively used to simulate the gas-liquid flow, and the numerical results were compared with the experimental results. The study shows that the trend of pump hydraulic performance with the flow rate and the shape of gas-liquid interface in pump calculated by the three turbulence models have a good agreement with the experimental results. The three models are difficult to capture the small-scale bubbles in liquid-ring, but LES model can capture larger scale bubbles near the gas-liquid interface. The prediction ability of RNG k-ε and SST k-ω models to the complex vortex structures is limited for the influence of Reynolds-averaged treatment, but the LES model can predict the complex channel vortices in impeller passage and the wake vortices of different scales at the impeller outlet. The computation cost of LES model is about three times of the other two models. The RNG k-ε and SST k-ω models have better applicability than LES model if we mainly focus on the distribution of phase and pressure fields in pump.

Effect of Diversion Cavity Geometry on the Performance of Gas-Liquid Two-Phase Mixed Transport Pump

For the purpose of improving the transport capability of the mixed transport pump, a new self-made three-stage deep-sea multiphase pump was taken as the research object. Based on the Euler-Euler heterogeneous flow model, liquid (water) and gas (air) are used as the mixed media to study the external characteristics and internal flow identities of the mixed pump under different gas volume fraction (GVF) conditions. According to the simulation results, a local optimal design scheme of the diversion cavity in the dynamic and static connection section is proposed. The numerical results before and after the optimization are compared and analyzed to explore the effect of the diversion cavity optimization on the performance, blade load and internal flow identities of the pump. The results show that the head and efficiency are obviously improved when the inner wall of the diversion cavity is reduced by 4 mm along the radial direction. After optimization, under the condition of 10% gas content, the head and efficiency is increased by 3.73% and 2.91% respectively. Meanwhile, the hydraulic losses of the diversion cavity and diffuser are reduced by 9.11% and 4.32% respectively. The gas distribution in the impeller is improved obviously and the phenomenon of a large amount of gas phase accumulation is eliminated in the channel. In addition, the abnormal pressure load on the blade surface is eliminated and the turbulent flow energy intensity is reduced. The average turbulent kinetic energy ( T K ) at i = 0.51 of the first stage impeller passage is reduced by 35%. Finally, the reliability of the numerical method is verified by the experimental results. To sum up, the performance and internal flow identities of the optimized mixed transport pump are improved, which verifies the availability and applicability of the optimization results. This provides a reference for the research and design of a multiphase mixed transport pump in the future.