Impeller Passage Research Articles

Numerical analysis of performance and internal flow characteristics of a gas-liquid multiphase rotodynamic pump

Abstract Inlet Gas Void Fraction (IGVF) and rotating speed are key parameters influencing the flow characteristics of gas-liquid multiphase pumps. To explore the influence of these two factors on the flow characteristics of gas-liquid multiphase rotodynamic pumps, CFD simulations were carried out based on the Euler two-fluid model to analyze the flow characteristics in an axial-flow pump at three different rotating speeds (1450 r/min, 2200 r/min, 2950 r/min) with different IGVFs. The numerical results indicate that the pump efficiency and head are first increased and then decreased with the increase of IGVF. When the IGVF is 5%, the head and efficiency reach their maximum values. This is attributed to the minimum vorticity and turbulence kinetic energy in the impeller passage at IGVF= 5%, and the small vortex range at the hub of the guide vane, thus resulting in the stable two-phase flow state in the impeller and guide vane. At the same IGVF, with the increase of the rotating speed, the head and efficiency of the multiphase pump increase accordingly. This is closely related to the smallest vortex range formed by gas-liquid flow separation at n=2950 r/min, indicating a better flow state.

Numerical and experimental examination of performance curve instabilities of a centrifugal fan

Abstract This paper investigates the performance curve instability of centrifugal fans used in industrial applications such as sintering or pelletizing plants. The study focuses on experimental and numerical analyses of the fan’s performance curve during operation. Model measurements of an optimized fan reveal instabilities in the characteristic curve around 73 % and 42 % of the volume flow at best efficiency point (Q/Qref) resulting in a sudden drop in pressure coefficient and the onset of low-frequency noise emission. Numerical investigations using ANSYS CFX predict the flow pattern accurately. Excellent agreement is observed between measured and calculated data for flow conditions, with deviations below 1 % in pressure coefficient. Notably, the calculated instability range occurs earlier at lower flow rates, leading to a 6 % shift in the data. The flow exhibits a detachment zone on the blade suction side and a complete blockage of a single impeller passage, corresponding to the pressure drop in the performance curve. Further investigations reveal that rotor-stator interaction causes the abrupt impeller rotating stall phenomena, significantly impacting pressure generation at lower flow rates. A FFT analysis confirms the presence of rotating stall, with its dominant frequency observed and multiple harmonics. The comparison of separation frequency with existing literature supports the assumption that rotating stall is the cause of the instability.

Unsteady Flow Behaviors and Vortex Dynamic Characteristics of a Marine Centrifugal Pump under the Swing Motion

Due to the effects of swing motion, the performances and internal flow characteristics of marine centrifugal pump undergo some unsteady variations in the marine environment. The hydraulic test system with six degree of freedom parallel motion platform is established to study the pump performance characteristics at the different heel angles of steady roll position and pitch position. The pump head gradually decreases as heel angle increases. The pump head has decreased by 7% to reach the minimum at the 15° heel angle of roll position. At the same heel angle, the head at the roll position is lower than that at the pitch position under the rated flow condition. The fluid in the impeller passage is subjected to the additional inertial force of roll motion or pitch motion under unsteady swing motion, inducing some flow bias phenomena in the velocity field. The unsteady development of flow velocity induces the intense vortex motion, and the shedding and dissipation of interblade vortices are affected. The periodic flow-induced pulsation characteristics obviously appear in the impeller passage. The pulsation periodicity and pressure amplitude are influenced due to the swing motion. The pitch motion induces the greater hydraulic excitation and fluid-induced vibration amplitude. In addition to the pressure pulsation at the low frequencies, the pulsation amplitude at 20 times the shaft frequency is evident under pitch motion.

Effect of impeller rotational phase on the FDA blood pump velocity fields.

The Food and Drug Administration (FDA) blood pump is an open-source benchmark cardiovascular device introduced for validating computational and experimental performance analysis tools. The time-resolved velocity field for the whole impeller has not been established, as is undertaken in this particle image velocimetry (PIV) study. The level of instantaneous velocity fluctuations is important, to assess the flow-induced rotor vibrations which may contribute to the total blood damage. To document these factors, time-resolved two-dimensional PIV experiments were performed that were precisely phase-locked with the impeller rotation angle. The velocity fields in the impeller and in the volute conformed with the previous single blade passage experiments of literature. Depending on the impeller orientation, present experiments showed that volute outlet nozzle flow can fluctuate up to 34% during impeller rotation, with a maximum standard experimental uncertainty of 2.2%. Likewise, the flow fields in each impeller passage also altered in average 33.5%. Considerably different vortex patterns were observed for different blade passages, with the largest vortical structures reaching an average core radii of 7 mm. The constant volute area employed in the FDA pump design contributes to the observed velocity imbalance, as illustrated in our velocity measurements. By introducing the impeller orientation parameter for the nozzle flow, this study considers the possible uncertainties influencing pump flow. Expanding the available literature data, analysis of inter-blade relative velocity fields is provided here for the first-time to the best of our knowledge. Consequently, our research fills a critical knowledge gap in the understanding of the flow dynamics of an important benchmark cardiovascular device. This study prompts the need for improved hydrodynamic designs and optimized devices to be used as benchmark test devices, to build more confidence and safety in future ventricular assist device performance assessment studies.

Coherent structures decomposition of internal flow in the double-suction centrifugal pump impeller

Abstract In order to understand the unsteady flow phenomenon of the centrifugal pump, the dynamic mode decomposition method (DMD) is introduced to extract the three-dimensional coherent structure of the rotating flow field in the impeller passage under three different working conditions of the double-suction centrifugal pump. The time series collection of flow field is constructed by CFD numerical simulation, and the approximate matrix characteristic parameters and different modal data are solved. The analysis results show that the position, form and spatial-temporal evolution of the coherent structure can be accurately captured by DMD method corresponding to a single frequency in the double suction pump. For the temporal evolution, the coherent structure corresponding to low frequency is the most stable and dominate the unsteady flow. For the spatial evolution, the coherent structure corresponding to even-fold rotational frequency mostly occurs near the pressure side of the blade at the outlet of the impeller, and the coherent structure corresponding to odd-fold rotational frequency is mostly located in the flow field inside the impeller or near the blade surface.

Influence of blade wrap angle on internal flow and wear performance of solid-liquid two-phase centrifugal pump with semi-open impeller

Blade wrap angle is one of the main parameters of centrifugal pump, which has an important influence on the internal flow characteristic and pump performance. In this work, five impeller models with different blade wrap angles (85°, 95°, 105°, 115°, and 125°) are established on the condition of other impeller parameters remain unchanged, whose external characteristic, internal flow, and wear were analyzed by numerical simulation method. The results show that the influence of blade wrap angle on efficiency is more significant than head, has a certain effect on the internal flow field of the centrifugal pumps and effects the wear position of pressure surface. With the increasing of blade wrap angle, the pump efficiency increases companied by the pump head decreases slightly, the area of higher speed at the outlet of the impeller tends to decrease, the higher speed wake area at the end of the blade pressure surface breaks and shrinks, the vortex in the impeller passage is fewer and smaller, the turbulent kinetic energy and morphology of vortex inside the pump decreases gradually, and the wear rate of the flow passage components shows a pattern of first decreasing and then increasing.

Insights into turbulent flow structure and energy dissipation in centrifugal pumps: A study utilizing time-resolved particle image velocimetry and proper orthogonal decomposition

The purpose of the study is to investigate the flow structure and energy dissipation mechanism within centrifugal pump impellers. The velocity fields at the mid-sections of the flow passages of 4- and 5-blade impellers were measured under various flow rates using the Time-resolved Particle Image Velocimetry (TR-PIV) technique; the proper orthogonal decomposition (POD) analysis was performed to extract flow structures with different scales; the dissipation rate was estimated using the large-eddy PIV method; the correlation between turbulent kinetic energy (TKE) and dissipation rate was measured using the cross-correlation analysis. The findings are as follows: impeller with more uniform and stable flow, the scale and energy contribution of large-scale structures in lower order modes are smaller, leading to higher impeller efficiency; large-scale structures identified in the low-order modes correspond to locations of high TKE and dissipation areas; the high velocity gradients within the impeller passage and the interactions between large-scale flow structures encourage the breakup of large-scale turbulent structures into dissipative-scale structures; the correlation between TKE and dissipation rate reflects the extent to which large-scale flow structures within the impeller passage break up into dissipative scales.

Analysis of unsteady flow and pressure pulsation of multistage centrifugal pump based on actual size

In this paper, the unsteady flow and pressure pulsation in 11-stage centrifugal pump were analyzed based on large eddy simulation. The performances from the numerical simulation agreed with the ones from the experiment. The numerical results show that large pressure gradient area appears on trailing edge of blade pressure surface, and large vorticity intensity area appears on blade suction surface and trailing edge. The vortexes in the impeller passage decrease obviously with the increase of flow rate from 0.4 Q to 1.2 Q. As the stage increase, there is a local high pressure area at the tongue and it affects the fluid backflow. The main frequency of the pulsation at the impeller inlet is the blade passing frequency ( fBPF), and the main frequency at the impeller outlet and the interface is 2 fBPF. Due to interstage interference, the main frequency of the second impeller includes blade passing frequency of the first stage impeller (5 fn) and its own blade passing frequency (7 fn). With the increase of the stages, the rule of pulsation gradually tends to be consistent.

Investigation on the unstable flow characteristic and its alleviation methods by modifying the impeller blade tailing edge in a centrifugal pump

In the field of the pumped storage plants, the unstable flow is universally caused by the rotating stall in the hydro-energy machinery, which further deteriorates the performance curves. To explore the alleviation method of the unstable flow, flow characteristic in a centrifugal pump with different impeller blade geometries is numerically investigated using a modified SST k-ω partially averaged Navier-Stokes model in this study. Numerical validation on the characteristic curves is carried out, which appears in accord with the experimental data of the test pump. Four types of available modification methods are attempted based on theoretical analysis, i.e., trimming the section side of the blade at trailing edge (TE) (named model A), decreasing the blade angle at TE (named model B), trimming the blade TE in spanwise direction with 45 degree (named model C) and adopting large lean angle blades (named model D). Results on the characteristic curves are first compared. In the test pump and model B, one positive slope region is observed under the same operation condition, while it is brought forward in the model A. On the contrary, the positive slope region is completely alleviated in model C and model D. Further exploration on the flow pattern in the impeller is conducted to give a comprehensive explanation. Due to the sudden increment of the energy loss, the flow pattern tends to be deteriorated, which further has impact on the characteristic curves. At last, unstable flow analysis in the impeller of the model D is carried out with emphasis on the evolution of the rotating stall. By using large lean angle blades, the rotating stall in the blade-to-blade passage of impeller is alleviated significantly with lower pressure fluctuation intensity.

Experimental Investigation on the Aerodynamic Instability Process of a High-Speed Axial-Centrifugal Compressor

Abstract Aerodynamic instability plays an important role in compressor design and may cause performance degradation and fatigue damage. In this paper, an experimental study on the evolution of aerodynamic instability is carried out on a compressor that combines the performance benefits of an axial stage and centrifugal stage. The spatiotemporal characteristics of unsteady wall pressure were obtained using fast-responding pressure transducers over a range of operating conditions. The results show that the axial stage works on the positive slope of the performance characteristic curve from choke to stall at low-speed operating conditions, and mainly features rotating instability. Rotating stall is also observed in the impeller (IMP) and diffuser passages. At medium-speed operating conditions, the centrifugal stage suffers a high-frequency mild surge, alternating with rotating stall. With the increase in back pressure, the mild surge diminishes, and rotating stall persists. This behavior is similar to a two-regime-surge, which has been reported for centrifugal compressors. At high-speed operating conditions, the compressor directly reaches surge without other instabilities. Further analysis of the spatial pattern of the rotating stall revealed the existence of a high-pressure region near the volute tongue, resulting in obvious pressure distortion along the circumferential direction at the volute inlet. This induced the amplitude difference of stall cells in corresponding diffuser passages. The disturbance caused by stall cells propagates upstream through the blade passage, and the largest pressure disturbance induced by the stall cell propagation appears in a circumferential position 45 deg downstream of the volute tongue at the impeller inlet and the axial stage inlet.

Influence of blade tip cutting on the flow loss characteristics of side channel pump

A comprehensive analysis of flow loss mechanisms in a side channel pump is put forth in this research. First, the correlation between the cutting angle and loss characteristics in each flow passage of the side channel pump is investigated. Second, the exact regions of the internal loss distributions in the flow passages of the pump are analyzed. Finally, the relationship between the dissipation effect and enstrophy is ascertained among the cutting angles. Generally, the flow loss steadily rises with the increase in cutting angle from 10° to 20° in the impeller. However, at 30°, the losses experience a substantial decrease and then increase thereafter. Meanwhile, the loss gradient in the side channel rises linearly with the increase in cutting angle from 10° to 40°. Cutting angles of 20°, 30°, and 40° revealed the minimum value of energy loss at the outer radius of the impeller compared to the original model. In the side channel passage, all cutting angles revealed a fairly lower magnitude of flow losses than in the original model. Noticeably, the dissipation effect and enstrophy share common resemblances, with a concentration of high enstrophy regions observed in plane 1. The impeller passage portrayed a higher dominancy of the enstrophy region, which nevertheless weakens to a minimum in the side channel for all the cutting angles. The findings of this study provide valuable insights into optimizing the design and performance of side channel pumps.

Low-frequency fluctuation propagation of rotating stall in the centrifugal compressor and pipe system

The characteristic signal judgment of rotating stall in a centrifugal compressor is necessary to avoid the compressor becoming instability in operation. This study investigates rotating stall in a centrifugal compressor and pipe system using experimental and numerical simulation methods. In the experiment, a low-frequency (approximately 10% of the impeller's rotational frequency) pressure fluctuation is observed in the inlet and outlet pipes as the pressure ratio curve declined at small flow rate. The frequency spectrum results of different measuring locations suggest that the low-frequency disturbance is in the flow direction within the pipe system during rotating stall. To further analyze this pressure fluctuation, a transient numerical simulation of the centrifugal compressor with plenum model is conducted. Rotating stall can be captured by the numerical model, and the low-frequency pressure fluctuation is also observed in the transient simulation, aligning with the experimental results. The periodic evolution of the tip leakage vortex influences the flow in the impeller passage, causing a fluctuation in the flow direction that propagates upstream and downstream as revealed by flow field analysis. The low-frequency pressure fluctuation in the inlet and outlet pipe system is a characteristic signal, which can be a new stall judgment of rotating stall in the operation of centrifugal compressor.

Investigation of Energy Loss Mechanism and Vortical Structures Characteristics of Marine Sediment Pump Based on the Response Surface Optimization Method

Marine sediment pumps are extensively applied in marine engineering fields with complex media and harsh flow conditions. Therefore, this study conducts a multi-factor optimization design for a marine sediment pump. The response surface optimization method is utilized to improve the efficiency by optimizing the number of impeller blades, the blade inlet angle, the blade outlet angle, and the blade wrap angle. Next, a response surface regression model is created, and the influence of geometric parameters on the efficiency is determined. Meanwhile, the energy loss mechanism and vortical structure characteristics after optimization are analyzed by applying entropy production and the method for identifying Omega vortices. The findings suggest a 6.33% efficiency enhancement in the optimized model under the design conditions. The impeller’s internal flow field is enhanced, and the entropy generation rate is significantly diminished. The fluid flow adhered more closely to the blade profile, and the velocity and pressure distribution exhibit better uniformity. The presence of large-scale vortices and occurrences of flow separation within the impeller passage experience a notable decrease, and the overall fluid pressure fluctuation amplitude decreased, resulting in a more stable flow. Therefore, the discoveries from the research offer references for the design and selection of marine sediment pumps.

Spatial-Temporal evolution characteristics of pre-Stage-stall in a centrifugal compressor with a vaneless diffuser and a volute

The continuous throttling process is of great interest for compressor designers. Previous experimental studies mainly consider the temporal evolution characteristics of the pre-stage stall at the impeller inlet or outlet regions. In this study, we explore the spatial-temporal evolution characteristics of pre-stage-stall using a pressure array consisting of 15 high-response sensors. The dynamic evolution characteristics of the pressure signal on the time and frequency domains and the underlying unsteady flow structure evolution during the transition process were analyzed. We find that the evolution characteristics of pressure irregularity varied with the streamwise positions. The evolution process from the pre-stage stall point to the stage stall point can be divided into three stages based on the disturbance scale and pressure fluctuations, namely (I) the coexistence of the impeller RI, the mild impeller stall, and the mild diffuser stall, (II) the interaction of stall cell and RI disturbance, (III) a single large stall cell. In stage I, the streamwise influential regions of the stall cells are mainly confined in the impeller passage. In stage II, the stall cell expands upstream and gradually interacts with the RI disturbance. The wavelength of RI-related disturbance increases while the related pressure fluctuation decreases. In stage III, several stall cells merge into one large cell.

The Influence of Blade Tip Clearance on the Flow Field Characteristics of the Gas–Liquid Multiphase Pump

Gas–liquid multiphase pumps are critical transportation devices in the petroleum and chemical engineering industries, and improving their conveyance efficiency is crucial. This study investigates the influence of blade tip clearance variations on the flow characteristics within a multiphase pump. Numerical simulations were conducted using Eulerian two-phase and SST k-ω turbulence models with four distinct tip clearance sizes (0 mm, 0.3 mm, 0.6 mm, and 0.9 mm). The performance curve, tip leakage flow (TLF), and internal gas distribution were subjected to analysis. The results indicate that the TLF is linearly related to the clearance size and traverses multiple flow passages, resulting in energy losses and a reduced pump head coefficient. Larger tip clearances (0.6 mm and 0.9 mm) exhibited a more uniform flow pattern, contrasting the irregularities seen with a 0.3 mm clearance. Compared to no tip clearance (0 mm), gas holdup within the impeller passages decreased by 18.39%, 39.62%, and 58.53% for clearances of 0.3 mm, 0.6 mm, and 0.9 mm, respectively, leading to decreased overall system efficiency. This study highlights the connection between tip clearance size and flow dynamics in multiphase pumps, offering insights for optimal tip clearance selection during multiphase pump design.

Systematic investigation of centrifugal slurry pump under different operating condition by DDPM method

The process characteristics of centrifugal slurry pump can be significantly affected by the operation strategy. However, their systematic quantifications and understandings are still lacking. This work studied the effects by applying the DDPM method, with confirmed validity. Via this model, the effects of distinct variables, including slurry flowrate (Q), impeller speed (N), particle size (ds) are quantified. Moreover, the interplays between solid concentration (Cs) to variables listed above are discussed, respectively. The results reveal that the flowrate plays significant influence on volute erosion distribution in circumference. The impeller speed increment greatly enforced the volute erosion severity, other than the distribution pattern. Fine particles intensify erosion in side-liner clearance and impeller passage, while greater particles are erosive in volute. This study offers a systematic operation evaluation with centrifugal slurry pump in fixed size, which herein provides guidance for pump selection and process trouble shooting in practice.

Redesign of a turbocharger compressor based on multi-component full-passage optimization

Self-recirculation casing treatment (SRCT) is often used to improve the flow stability of turbocharger compressors. However, it usually introduces penalties of the peak efficiency or the choke margin of compressors though assisted by auto-optimizations. For this, a multi-component optimization of SRCT and diffuser for a turbocharger compressor is implemented based on the full-passage computational model with a volute. As a result, the aerodynamic performances of the compressor are improved over the whole speed line. Specifically, the efficiency and pressure ratio at the design condition are increased by 1.23% and 1.31% respectively, those at the near-stall condition are improved by 1.84% and 3.13% respectively. The choke flow rate is improved by 1.44%, and the stable flow range is expanded by 2.7 percentage points. The flow mechanisms are as follows. Firstly, the bleed slot width is increased, then the recirculation flow rates in different impeller passages are improved and the low-energy fluids in corresponding passages are removed. The blockages and the circumferential asymmetry in impeller passages are reduced, hence, the flow stability is improved. Secondly, the flow area of diffuser passages is enlarged due to the reduced solidity of vaned diffuser, and then the swallowing capacity of the compressor is improved. Also, the mismatching effect introduced by the SRCT is compensated by the reduced solidity of vaned diffuser. Finally, the injection slot angle and height are decreased, then the distortions and mixing losses in impeller inlet are reduced. Also, the aerodynamic losses in impeller inducer are reduced by removing more stagnation fluids near inducer shroud due to the increased bleed slot width.

Studying the impact of impeller geometrical parameters on the high-efficiency working range of pump as turbine (PAT) installed in the water distribution network

The development plan for micro hydropower is expanding with an increasing focus on renewable energy sources. There is increasing attention to using PATs to recover extra hydraulic energy in the water distribution network (WDN) pipelines. In this paper, the performance curves of PAT installed instead of pressure-reducing valves in WDN were investigated. The quality and reliability of numerical simulations were validated compared to the experimental results. Investigating hourly flow rate variations in WDN shows that the PAT working conditions change frequently and operate for a long time under off-design conditions. Since there are no tools to control and guide the fluid to the impeller, there is no proper conformance between the inlet flow and the blade profile, and in this condition loss increases and efficiency decreases. In order to improve the PAT performance in the working range, the effect of modifying parameters of blade thickness, blade number, and blade inlet width is numerically investigated. Optimal geometric parameters for designing a special impeller were determined by considering the flow rate changes of the PRS over 4 working months. Analyzing the PAT performance with a special impeller indicates that losses caused by the flow separation at the leading and trailing edges of the blade as well as the formation of vortices are significantly reduced. Moreover, the fluid's tendency to follow the blade profile is improved due to the flow field form in impeller passages, and the PAT's high-efficiency working range is extended. The greatest increase in efficiency occurs in the overload flow rate (1.2QBEP) and is improved by 6.48%. In this case study, the power generation capacity of the soft pressure regulating system (SPRS) will increase by 5.1% using the special impeller.

Düşey Milli Eksenel Bir Pompada Zamana Bağlı Akışın Deneysel Olarak İncelenmesi

Due to the changes in the system characteristics, pumps may have to be operated far away from the design point, such as in part-load or over-load operating points. Operating the pumps far away from the design point may cause fluctuations in the flow. As a result of the fluctuations mechanical problems in the pump structure may occur. In order to overcome the problem, the operating characteristics of the pump must be determined at part load operating conditions as well as design point operating condition. In this study, flow inside a vertical shaft axial flow pump is investigated experimentally. The experimental setup is designed and constructed for the laboratory tests. The pump which is designed and manufactured is tested in the test setup. The performance of the pump is determined by measuring the flow rate, inlet and outlet pressures, rotational speed and power input of the pump. The part load and over load operating regions are determined. Pressure variations are measured at various performance points with the piezoelectric pressure transducer placed in between impeller and diffuser blade passage. Simultaneously, comparisons are made with the vibration spectrums obtained in the pump.

Research on energy loss characteristics during transient process of reactor coolant pump shaft stuck accident

After the stuck shaft accident (SSA), the unstable flow in the reactor coolant pump (RCP) will cause huge energy loss. In order to accurately elucidate the mechanism of energy loss in the pump, this paper realizes the total resistance matching and operating condition regulation of the system piping based on the isoflow cross-section method. A full three-dimensional simplified model of HPR1000 reactor coolant system (RCS) of three loops is established. And the transient flow inside the system is reproduced by numerical simulation method. The weak compressibility theory and entropy production theory are introduced to quantitatively analyze the energy loss characteristics of RCP Ⅰ in the accident loop under six typical operating conditions. The results show that: after the SSA, the flow rate and head of RCP I change abruptly in a short time, and then the change slows down gradually. The reverse flow in the accident loop starts to occur around 1 s, and the system reaches dynamic equilibrium again at 3 s. Comparing different operating conditions, the energy loss in the impeller and guide vane flow path is the most drastic. Due to the migration and development of the vortex, the energy losses of two components reach the maximum at TN0 and 0.5TQi, respectively, there is a peak misalignment phenomenon. When the liquid flow is positive, the energy losses are mainly concentrated in the working surface side in the impeller and guide vane passages, and the interference region of the two components. When the liquid flow is reversed, the energy losses are mainly concentrated the middle of the impeller passage and the interference region of the two components. During transient process of the SSA, the impact, vortex, flow separation, wall friction and other unstable flow is the internal cause of energy losses in the pump.