Semi-open Impeller Research Articles

Tip clearance influence on the performance of high-speed micro-pumps

The fast-paced development of the aerospace and shipping industry is promoting the development of lightweight and high-speed transfer pumps. High-speed micro-pumps with semi-open impellers are highly sensitive to tip clearance (TC), which crucially influences the head and efficiency. This study proposes a new design for a high-speed micro-semi-open impeller centrifugal pump with a 19 000 rpm rotational speed and 30 m hydraulic head. The performance of the proposed centrifugal pump under different inlet corrosion allowances and different impeller TC ratios (0.05, 0.08, 0.11, and 0.14) is investigated through numerical simulations and experiments. The interaction process between the leakage and main flows in the tip gap is recorded with a high-speed camera and is numerically calculated. The stability of the internal flow field is optimal under smaller TCs. This study provides the optimal TC and guidance for designing high-speed micro-pumps.

Flow instability in mixed-flow/axial-flow pump: A review of relationship between tip leakage flow distortion and rotating stall

Pumps represent a quintessential type of fluid machinery and play a pivotal role in global economic development, especially in the hydropower industry. However, as their application range and single unit capacity continue to increase, the occurrence of rotating stall phenomena caused by internal flow instability has become more frequent. This phenomenon is especially prominent in pumps with semi-open impellers, where the presence of tip leakage flow (TLF) instability accelerates the rotating stall phenomenon. Over the past few decades, extensive research has been conducted to investigate the characteristics of rotating stall in pumps. As a result, there is now a preliminary understanding of the phenomenon of rotating stall induced by tip leakage flow in pumps. However, a significant gap remains in fully comprehending the underlying mechanism of this phenomenon. This review comprehensively reviews the research progress made in understanding the relationship between pump tip leakage flow instability and rotating stall. It encompasses various aspects, including the formation mechanism of tip leakage flow, the structure of tip leakage vortex (TLV) under stall conditions, the correlation between dynamic characteristics of tip leakage flow and rotating stall, as well as methods for mitigating rotating stall through tip leakage suppression. Finally, some promising potential stall suppression method is discussed to provide some guidance for the fields of fluid machinery.

Emphasizing on the envelope spectra of hydraulic turbomachinery vibration response towards cavitation diagnosis

Cavitation attracts the interest of engineers who target the better understanding of its complex physics and the development of efficient detection tools. This research explores the effectiveness of vibration-based indicators in the prompt and effective diagnosis of cavitation initiating in the rotating flow fields of turbomachinery. The indicators are derived from the envelope spectra estimated with the use of Hilbert Transform, Spectral Kurtosis and Cyclic Spectral Correlation algorithms and data acquired from two semi-open impellers. By utilizing a transparent casing, the onset of cavitation can be observed, enabling the establishment of reliable criteria for evaluating the new indicators. Also, their applicability is assessed across a wide range of flow-rate and suction pressure conditions and in two different geometries. The results demonstrate the consistent ability of the indicators to exploit the high frequency carrier information related with the resonances excited from bubble implosions, to promptly and efficiently detect the phenomenon.

Optimization design of semi-open impeller based on thrombogenicity in a blood pump.

Blood clots are composed of aggregated fibrin and platelets, and thrombosis is the body's natural response to repairing injured blood vessels or stopping bleeding. However, when this process is activated abnormally, such as in a mechanical blood pump, it can lead to excessive thrombus formation. Therefore, how to avoid or reduce the probability of thrombus formation is an important indicator of the stable operation of a blood pump. In this paper, Lagrangian particle tracking trajectories are simulated to study platelet transport in a blood pump. The design of the thrombus blood pump was optimized using an orthogonal design method based on three factors: inlet angle, outlet angle, and blade number. The effect of blood pump pressure, rotational speed, impeller outlet angle, inlet angle, and number of blades on thrombus formation was analysed using Fluent software. The thrombogenic potential was derived by analyzing the trajectory and flow parameters of platelet particles in the blood pump, as well as the statistical parameters of residence time and stress accumulation thrombus in the platelet pump. When the impeller inlet angle is 30°, the outlet angle is 20°, and the number of blades is 6, the probability of thrombus formation is minimized in the orthogonal design method, aligning with the requirements for blood pump performance. These design parameters serve as a numerical guideline for optimizing the geometry of the semi-open impeller in blood pumps and provide a theoretical foundation for subsequent invitro experiments.

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.

Design of 10 L/s liquid hydrogen pump with integrated inducer and centrifugal impeller

With the global focus on energy and environmental issues, hydrogen energy development has become more and more important. The liquid hydrogen centrifugal pump is an important equipment for hydrogen transportation. In this paper, we designed an integrated impeller and the space guide vane used in 10L/s hydrogen pump. The integrated impeller which is closed structure combined of an inducer and an centrifugal impeller shows better performance than traditional Semi-open impeller. We optimized the structure of the pump and finally obtained the performance curves. This results provide a guidance for the manufacture of the liquid hydrogen pump, and also provide a reference for the design and manufacture of other liquid hydrogen pumps.

Leakage vortices and energy characteristics of semi-open sewage pump with various blade tip alterations

As one of the most commonly used fluid machineries, sewage pumps play a critical role in various sectors, including urban construction, industry, and environmental protection. Considering the clog-resistant performance, the impeller usually uses a semi-open structure, giving rise to a tip structure that introduces leakage flow. This exacerbates the instability of flow within the pump, thereby impacting the overall performance and operational stability of sewage pumps. In this study, four distinct blade tip structure schemes are developed through a combination of numerical calculations and experimental validation. The Liutex–Omega vortex identification method is employed to scrutinize the initiation and development mechanisms of the leakage vortex system. A comprehensive analysis is conducted to explore the influence of the tip structure on both the energy characteristics and the internal flow dynamics of semi-open sewage pumps. It is found that the complex mixing effect of the leakage flow with the main flow is the primary source of energy loss within the semi-open impeller. Additionally, the characteristic angle of the leakage flow exhibits a high correlation with the energy dissipation characteristics of the impeller. Meanwhile, the impeller with a rounded tip exhibits the poorest performance, with the most substantial reductions in head and efficiency amounting to 44.17% and 36.11%, respectively, compared to the original impeller. Conversely, the impeller featuring a T-shaped tip demonstrates a maximum increase in the head of up to 7.25% under conditions of a large clearance size. This study not only contributes to the theoretical understanding of the unsteady flow within the semi-open impeller but also offers valuable insights for the optimized design of semi-open impeller sewage pumps, holding both theoretical and practical significance.

Two-phase flow investigation of sewage pumps with different tip clearance via computational fluid dynamics and multi-factor ANOVA

Sewage pumps are widely utilized in various applications, including municipal wastewater treatment plants, industrial processes, and residential sewage systems. These pumps are specifically designed to handle the transportation of mixtures consisting of solid and liquid components, commonly observed as two-phase flow. In this study, semi-open sewage pumps with varying clearance sizes have been examined through adjustment of the geometrical model. Multi-factor analysis of variance is employed to investigate the combined influence of different two-phase flow conditions and tip clearance sizes on the performance of sewage pumps. The results show that the performance of the pump decreases significantly as the clearance size increases. Also, the sensitivity of pump efficiency to variations in tip clearance size is contingent upon the flow rate. Under part-load conditions, both particle concentration and clearance size exhibit a notable effect on efficiency. The two-phase flow will greatly enhance the intensity of the unsteady flow near the inlet and outlet of the semi-open impeller, which is the main reason for the performance degradation of the sewage pump. The findings of this research provide valuable insights for enhancing the hydraulic performance and operational stability of semi-open sewage pumps operating under two-phase flow conditions.

Numerical research on performance of new structure centrifugal compressor for supercritical CO2 power systems

The supercritical carbon dioxide (sCO2) power cycle system is a potential thermoelectric conversion system with the advantages of high efficiency and compactness, which can be used in the fields of solar thermal power, nuclear power, and other thermal power systems. The compressor is one of the important machines in sCO2 power systems. To improve the performance and reduce the condensation risk of sCO2 centrifugal compressors, a new structure sCO2 centrifugal compressor is proposed in this paper, which has a partial-cover impeller and self-circulation-channel casing (PISC). The internal flow of the compressor with the new structure is analyzed by the CFD method. The flow and condensation in sCO2 centrifugal compressors with the PISC structure and that with the semi-open impeller and traditional casing (SITC) are compared. The results show that the PISC sCO2 compressor has an inhibiting effect on the condensation at the compressor inlet location, reducing the condensation volume to approximately 82% of that of the original structure under design conditions. The total pressure ratio and isentropic efficiency of compressors are simulated, and the result shows that the minimum stable mass flow rate is reduced by about 13% by introducing the new PISC structure into the sCO2 centrifugal compressor, and the maximum isentropic efficiency is increased from 83.5% to 84.4% compared to that of the SITC compressor. A new design idea for the impeller and sCO2 compressor structure is provided in this paper. The research results can be applied to sCO2 compressors and improve the performance and stability of sCO2 power cycle systems.

Numerical Studies on Effects of Blade Number Variations on Performance of Sludge Pumps

The sedimentation of sludge in pangasius catfish ponds constitutes a notable challenge for the economic advancement of Vietnamese farmers. Sludge formation is the result of a composite process involving residual food, waste material, and algae, which undergo decomposition, thereby releasing hazardous gases such as hydrogen sulfide (H2S), ammonia (NH3), and nitrogen dioxide (NO2). These emissions subsequently diminish oxygen levels within the ponds, adversely affecting the growth of catfish. Removal of the accumulated sludge is deemed necessary every two months throughout the catfish cultivation cycle. A proficient sludge pump, designed to function effectively within the Vietnamese environmental context, becomes imperative to address this predicament. The primary objective of this research paper is to explore the influence of blade count on the performance metrics of a sludge pump. Given that pangasius ponds typically exhibit depths ranging from 2 to 4 meters, this study is predominantly centered on assessing pump performance within the specified head range of 2 to 4 meters. Employing the computational fluid dynamics (CFD) methodology, the research delves into the fluid dynamics of sludge pumps featuring impeller blades numbering 7, 8, 9, and 10. These pumps are modeled as semi-open impeller centrifugal pumps operating at a speed of 2200 revolutions per minute (rpm), with the k-e turbulence model and the time-averaged Navier-Stokes equation serving as the fundamental analytical framework.

State of the Art on Two-Phase Non-Miscible Liquid/Gas Flow Transport Analysis in Radial Centrifugal Pumps Part B: Review of Experimental Investigations

This paper aims to summarize the results of several experimental investigations regarding two-phase liquid–gas flows in radial centrifugal pumps. The main objective is to combine the corresponding experimental results and collect the obtained knowledge to provide a better understanding of this configuration. The simultaneous transport of the two phases, the phase segregation, and the regions of safe or critical pump performance were described for a wide variety of pump configurations. This review covers single- and two-phase pumping conditions, performance degradation, pump breakdown, performance hysteresis, different flow regimes, flow regime maps, flow instabilities, and surging. This manuscript also considers the influence of employing different pump configurations on pump performance and flow regimes. This includes comparisons between closed and semi-open impellers, standard and increased tip clearance gaps, and running the pump with and without an inducer. Many of the results discussed have been published in a series of research papers. They were all collected, summarized, and compared systematically in the present review.

Influence of the Spatial Position of the Semi-open Impeller on the Internal Flow Field in Centrifugal Fans

This paper takes as its background the study of centrifugal fans in powered air-purifying respirators. To improve the efficiency of the centrifugal fan and the uniformity of the internal flow field, a steady-state simulation based on the realizable k-ε turbulence model, using the “frozen rotor method”, was carried out to analyze the effect of the spatial position of the impeller in the centrifugal fan on the internal flow field by matching the impeller to the worm gear. The results show that varying the eccentric angle, eccentric distance, and longitudinal depth of the semi-open impeller in the volute affects the internal flow field of the centrifugal fan to varying degrees. The concentric arrangement was not found to be optimal, and when the impeller rotates slightly further away from the worm tongue, the flow field inside the centrifugal fan is more uniform and the phenomena such as “wake-jet” and boundary layer separation are significantly reduced. In addition, it was found that the pressure distribution at the inlet is approximately the same as the pressure distribution in the flow field.

Three-dimensional simulations of liquid/gas flow through radial centrifugal pumps and the effect of bubble coalescence and breakup on the formation of gas accumulations

Three-dimensional liquid/gas flow mixture simulations of a centrifugal pump are performed by a hybrid two-phase solver, which comprises a blending between a Volume-of-Fluid-like interface-sharpening scheme and a classical homogeneous mixture two-fluid model. The hybrid solver is combined with a population balance model and a turbulence-scale adaptive simulation approach. The experimentally measured head drop due to adherent gas pockets at elevated gas loadings is well reproduced. By a thorough validation with optical measurement data, it is shown that the transition from dispersed bubbles to coherent gas accumulations as well as the steady core of gas pockets and their unsteady wake could be captured without any parameter fitting of coalescence and breakup kernels. Regions of high coalescence activity correlate with locations of gas accumulations, stabilizing the gas pockets in the impeller region. Bubble breakup, in contrast, was primarily found in the wake of the accumulation zones where the tip leakage flow of the semi-open impeller re-enters the blade passage. The particular hybrid solver architecture, together with the resolution of turbulence scales and bubble populations, facilitates the reproduction of bubble coalescence and breakup effects on the formation of gas pockets in centrifugal pumps.

Development of Sewage Pumps with Numerical and Experimental Support

Especially in the field of sewage pumps, the design of radial impellers focuses not only on maximum efficiency but also on functionality in terms of susceptibility to clogging by fibrous media. In general, the efficiency of sewage impellers is significantly lower than that of clear water impellers. These sewage impellers are designed with a low number of blades to ensure that fibrous media can be pumped. This paper describes the methodology of an optimisation for a sewage impeller. The optimisation is carried out on a semi-open two-channel impeller as an example. Therefore, a new impeller is designed for a given volute casing. Based on a basic design for given boundary conditions, the impeller is verified by means of numerical simulation. The manufactured impeller is then tested on the test rig to verify the simulation. With regard to the optical investigations, the clogging behaviour of the impeller is specifically improved over three different modifications in order to finally present an impeller with good efficiency and a low clogging tendency.

Study of flow field and vibration characteristics of supersonic centrifugal impellers based on fluid-structure interaction

PurposeThere are three purposes in this paper: to verify the importance of bi-directional fluid-structure interaction algorithm for centrifugal impeller designs; to study the relationship between the flow inside the impeller and the vibration of the blade; study the influence of material properties on flow field and vibration of centrifugal blades.Design/methodology/approachFirst, a bi-directional fluid-structure coupling finite element numerical model of the supersonic semi-open centrifugal impeller is established based on the Workbench platform. Then, the calculation results of impeller polytropic efficiency and stage total pressure ratio are compared with the experimental results from the available literature. Finally, the flow field and vibrational characteristics of 17-4PH (PHB), aluminum alloy (AAL) and carbon fiber-reinforced plastic (CFP) blades are compared under different operating conditions.FindingsThe results show that the flow fields performance and blade vibration influence each other. The flow fields performance and vibration resistance of CFP blades are higher than those of 17-4PH (PHB) and aluminum alloy (AAL) blades. At the design speed, compared with the PHB blades and AAL blades, the CFP blades deformation is reduced by 34.5% and 9%, the stress is reduced by 69.6% and 20% and the impeller pressure ratio is increased by 0.8% and 0.14%, respectively.Originality/valueThe importance of fluid-structure interaction to the aerodynamic and structural design of centrifugal impeller is revealed, and the superiority over composite materials in the application of centrifugal impeller is verified.

Additive manufacturing of recycled plastics: a ‘techno-eco-efficiency’ assessment

Plastic materials have been widely used to replace metals in functional parts due to their lower cost and comparable technical properties. However, the increasing use of virgin plastic material in consumer and industrial applications has placed a significant burden on waste management due to the volume of waste created and the potential negative effects of its end-of-life processing. There is a need to adopt circular economy strategies such as plastic recycling within industrial applications in order to reduce this significant waste management pressure. The present study used recycled polylactic acid (PLA) material as a feedstock for the 3D printing of a centrifugal semi-open pump impeller. The technical performance of 3D printed recycled PLA material and virgin PLA material was compared in this study. The environmental impacts for technically feasible impellers were assessed through the environmental life cycle assessment, while costs were evaluated by life cycle costing. The results were incorporated into a techno-eco-efficiency framework to compare the technical properties, environmental impacts, and costs. The social impacts of additive manufacturing and recycled feedstock material were also explored. The technical assessment results indicated that tensile strength, fatigue strength, density, and hardness decreased with recycled material content compared to virgin material. Microscopy of the fracture surfaces revealed the presence of slightly higher porosity and defects in recycled specimens, which could result in slightly lower technical properties. However, the recycled material was accepted for further ecological analysis as it offered higher pumping performance when compared to the original component and could reduce the burden on virgin material-based production and waste material disposal. Importantly, the results showed that 3D printed recycled PLA impellers are more eco-efficient when compared to 3D printed virgin PLA impellers.

The impact of rotor configurations on hemodynamic features, hemocompatibility and dynamic balance of the centrifugal blood pump: A numerical study.

To investigate the effect of rotor design configuration on hemodynamic features, hemocompatibility and dynamic balance of blood pumps. Computational fluid dynamics was employed to investigate the effects of rotor type (closed impeller, semi-open impeller), clearance height and back vanes on blood pump performance. In particular, the Eulerian hemolysis model based on a power-law function and the Lagrangian thrombus model with integrated stress accumulation and residence time were applied to evaluate the hemocompatibility of the blood pump. This study shows that compared to the closed impeller, the semi-open impeller can improve hemolysis at a slight sacrifice in head pressure, but increase the risk of thrombogenic potential and disrupt rotor dynamic balance. For the semi-open impeller, the pressure head, hemolysis, and axial thrust of the blood pump decrease with increasing front clearance, and the risk of thrombosis increases first and then decreases with increasing front clearance. Variations in back clearance have little effect on pressure head, but larger on back clearance, worsens hemolysis, thrombogenic potential and rotor dynamic balance. The employment of back vanes has little effect on the pressure head. All back vanes configurations have an increased risk of hemolysis in the blood pump but are beneficial for the improvement of the rotor dynamic balance of the blood pump. Reasonable back vanes configuration (higher height, wider width, longer length and more number) decreases the flow separation, increases the velocity of blood in the back clearance, and reduces the risk of blood pooling and thrombosis. It was also found that hemolysis index (HI) was highly negatively correlated with pressure difference between the top and back clearances (r=-.87), and thrombogenic potential was positively correlated with pressure difference between the top and back clearances (r=.71). This study found that rotor type, clearance height, and back vanes significantly affect the hydraulic performance, hemocompatibility and rotor dynamic balance of centrifugal blood pumps through secondary flow. These parameters should be carefully selected when designing and optimizing centrifugal blood pumps for improving the blood pump clinical outcomes.

Lightweight design of the transonic centrifugal impeller based on fluid–structure coupling

The impeller is the core component of the centrifugal compressor. Aiming to solve problems related to a large mass, high-energy consumption, and large vibration of the existing centrifugal impeller, a semi-open supersonic centrifugal impeller provided by Krain et al. was redesigned in this paper. The redesign was based on Tsai–Wu failure theory and the two-way fluid–structure coupling method. First, the geometric and numerical models were established using the geometric data found in the literature. Then, the established geometric and numerical models were verified through experimental data. Finally, the impeller was optimized from three aspects: material lightweight, composite material layering, and tip clearance. The results have shown that following the optimization, the maximum impeller stress was reduced by 48.77% when compared to the traditional 17-4PH material impeller. The maximum vibration deformation was reduced by 60.4%, as well as the resonance probability. The pressure ratio was increased by 0.8%, and the pressure and velocity reverse gradient trend near the blade tip were significantly reduced, while the flow field was more stable. The research results presented in this paper hence provide a basis for the application of composite materials in centrifugal impellers.

Investigating the ‘techno-eco-efficiency’ performance of pump impellers: metal 3D printing vs. CNC machining

The economic, environmental, and social impacts caused by the extensive resource consumption and harmful emissions from the metal manufacturing industry should be lowered through innovative sustainable manufacturing strategies. This study aims to investigate the techno-eco-efficiency performance of metal 3D-printed parts in comparison with CNC-machined parts to determine the technical, economic, and environmental performance as a decision support tool for selecting the most techno-eco-efficient manufacturing method. In this study, a novel metal extrusion 3D printing technology has been used to create a centrifugal semi-open pump impeller in 316L stainless steel material. The technical feasibility of the impellers has been determined by evaluating the geometry, build material, mechanics, morphology, and functional performance of the impellers. The eco-efficiency performance of technically feasible impellers was evaluated through environmental life cycle assessment, life cycle costing, and portfolio analysis. This eco-efficiency analysis helped ascertain the cost-competitiveness and environmentally friendliness of the 3D-printed impellers by comparing it with the conventional impellers. The findings reveal that the AM impeller is eco-efficient mainly due to lower normalised environmental impacts (54.6%) compared to the SM impeller. The functional parts made by metal extrusion 3D printing are technically feasible, cost-effective, and environmentally friendly compared to the SM counterparts.

Experimental Study on Operational Stability of Centrifugal Pumps of Varying Impeller Types Based on External Characteristic, Pressure Pulsation and Vibration Characteristic Tests

This study performed external characteristics, dynamic pressure, and vibration tests on the closed impeller model, semi-open type impeller model, and open impeller model in order to study the influence of the impeller structure on the operational stability of the pump. According to the research findings, the external characteristics of the three impellers enjoyed favorable stability with flat curves under low flow rates. As the flow increases, the stability of the external characteristics weakens, and the poorest stability can be observed in the open impeller, while the enclosed impeller has the best stability under a large flow rate. In addition, intense pressure fluctuations arise near the casing tongue due to the dynamic and static interference between the blade and the casing tongue, causing a large amplitude of pressure pulsation near the casing tongue and the pump outlet. It can be seen that the stability of pressure pulsation of the closed impeller in the casing tongue area was the best, whereas the stability of pressure pulsation of the open impeller was the poorest. The minimum casing vibration can be found in the closed impeller, followed by the semi-open impeller, and the open impeller, with the maximum vibration. In addition, the optimum stability of rotor vibration can be observed in the closed impeller, semi-open impeller, and open impeller with similar stability of rotor vibration.