Axial Flow Pump Research Articles

Influence of impeller energy dissipation characteristics of multi-blade axial flow pump impeller by the cascade density

Abstract This paper investigates the influence of cascade density on energy dissipation in the impeller of a multi-blade axial-flow pump. Three-dimensional transient numerical simulations were conducted using the SST k-ω turbulence model for impeller schemes with different cascade density, corresponding to different blade chord length and pitch. Entropy production theory was applied to locate the regions with high energy loss in the impeller. The relationships between local entropy generation, energy loss, and unsteady flow were analyzed for different cascade density. The results indicate that impeller entropy output of the multi-blade axial-flow pump is highly consistent with the head loss during testing. Turbulence dissipation accounts for more than 50% of the total energy loss, followed by wall friction, while direct dissipation is the smallest contributor. The relative loss of the impeller can be minimized by decreasing the number of blades or increasing the blade chord length. By comparing energy dissipation in blade rotation with different chord length and pitch, it is found that turbulent dissipation ability can be controlled more effectively by changing chord length, while the ability of direct dissipation can be controlled more effectively by changing the pitch.

Investigation of Non-Uniform Inflow Effects on Impeller Forces in Axial-Flow Pumps Operating as Turbines

Due to the existence of an inlet elbow, transmission shaft, and other structural components, the inflow of axial-flow pumps as turbines (PATs) becomes non-uniform, resulting in the complexity of internal flow and adverse effects such as structural vibration. In this paper, numerical methods were employed to explore the non-uniform inflow effects on impeller forces and internal flow field characteristics within an axial-flow PAT. The study results indicated that non-uniform inflow caused uneven pressure distribution inside the impeller, which leads to an imbalance in radial forces and offsetting the center of radial forces. With an increasing flow rate, the asymmetry of radial forces as well as the amplitude of their fluctuations increased. Non-uniform inflow was found to induce unstable flow structures inside the impeller, leading to low-frequency, high-amplitude pressure fluctuations near the hub. Using the enstrophy transport equation, it was shown that the relative vortex generation term played a major part in the spatiotemporal evolution of vortices, with minimal viscous effects.

AORTIC REGURGITATION INDEX IDENTIFIES SIGNIFICANT AORTIC REGURGITATION DURING IMPELLA SUPPORT FOR CARDIOGENIC SHOCK

Abstract Background Aortic regurgitation (AR) significantly hampers the unloading effect and the antegrade flow enhancement expected from the micro–axial flow pump Impella (Abiomed, Danvers). To date, no dedicated hemodynamic index is available to inform on the severity of AR during Impella support. Methods We included 100 patients receiving Impella support for CS with invasive hemodynamic assessment with pulmonary artery catheter (PAC). PAC measures were obtained 48 hours after Impella support initiation. AR grading was performed by either trans–thoracic or trans–esophageal echocardiography in the following strata: 0–none; 1–mild; 2–moderate; 3–moderate–severe; 4–severe. Study cohort was dichotomized according to AR severity≥2+. Several relevant hemodynamic indexes were validated against echocardiographic AR assessment to identify those mostly associated with significant AR (AR severity≥2+), including: AR index [ARI, calculated as (diastolic arterial pressure – pulmonary artery wedge pressure)/systolic arterial pressure, abbreviated in (DAP–PAWP)/SAP], diastolic pulse pressure (DPP, calculated as DAP–PAWP), MAP–adjuster ARI [ARIMAP calculated as (diastolic arterial pressure – pulmonary artery wedge pressure)/mean arterial pressure, abbreviated in (DAP–PAWP)/MAP)]. Results Significant AR (≥2+) was found in 31% patients. Patients with AR≥2+ had higher values of pulmonary artery wedge pressure (PAWP) after 48 hours from support initiation [15 (12, 21) vs 12 (10, 16) mmHg; p<0.021]. Several invasive hemodynamic indexes differentiated AR≥2+ vs AR<2 patients, including: ARI [0.42 (0.36, 0.51) vs 0.50 (0.44, 0.61); p<0.001], DPP [47 (37, 58) vs 57 (48.00, 68) mmHg; p=0.003] and ARIMAP [0.62 (0.54, 0.70) vs 0.70 (0.64, 0.75); p=0.005] (Figure 1). ARI demonstrated the strongest association and the greatest accuracy in identifying AR≥2+ (area under the curve 0.73; 95%CI: 0.61–0.85; p=0.002). The threshold of ARI 0.39 had excellent specificity (88.0%) and moderate sensitivity (62.9%), Figure 2. Conclusions The easy–to–use ARI metric [(DAP–PAWP)/SAP] accurately identifies patients with significant AR during Impella support, at the optimal cutoff of ARI 0.39. This index may be complementary to echocardiography in the assessment of AR during Impella support.

Hemocompatibility Evaluation of a Novel Ambulatory Pulmonary Assist System Using a Lightweight Axial-Flow Pump.

The Pulmonary Assist System (PAS) is currently under development as a wearable respiratory assist system. In this study, the hemocompatibility of the PAS's axial-flow mechanical pump (AFP) was compared to other contemporary mechanical pumps in an acute ovine model. The PAS was attached to a normal sheep in a venovenous configuration using one of three pumps: 1) AFP, 2) ReliantHeart HeartAssist 5 (control), or 3) Abbott Pedimag (control) (n = 5 each). Each sheep was supported on the PAS for 12 hours with two L/minute of blood flow and four L/minute of sweep gas. Hemolysis, coagulation, inflammation, and platelet activation and loss were compared among the groups. In this study, the plasma-free hemoglobin (pfHb) was less than 10 mg/dl in all groups. The pfHb was significantly lower in the AFP group compared to other groups. There was no significant clot formation in the pumps and oxygenators in all groups. Furthermore, no significant differences in coagulation (oxygenator resistance, fibrinopeptide A), inflammation (white blood cell counts, IL-8), and platelet activation and loss (p-selectin, platelet counts) were observed among the groups (all, p > 0.05). This study demonstrates equivalent hemocompatibility of the PAS's AFP to other contemporary mechanical pumps with a reduced level of hemolysis on startup.

Transient dynamic stress behavior analysis of the axial flow pump as turbine at part loads

To explore the structural dynamic characteristics of the impeller and shaft system of the axial flow pump as turbine, the variation law of impeller transient equivalent stress, deformation, and the impeller and shaft system mode are analyzed by the transient fluid-structure interaction method. Findings indicate that the equivalent stress is centralized at the blade root around the hub and tends to decrease as it moves towards the shroud. The maximum equivalent stress at 1.0Qbep and 1.1Qbep is 1.26 times and 2.0 times higher than that at 0.8Qbep. Blade deformation is significantly influenced by flow rate. The maximum deformation of the blade at 1.0Qbep and 1.1Qbep is 1.6 times and 3.6 times higher than that at 0.8Qbep. The impeller and shaft system with prestress in dry mode has an average natural frequency of the first 10 orders that is 16.7 Hz higher than without prestress. However, with the fluid adding mass and flow damping, the average natural frequency of the first 10 orders of the impeller and shaft system in wet mode is reduced by 278.08 Hz compared with dry mode. In fact, the impeller and shaft system of the axial flow pump as turbine is not prone to vibration.

Unsteady behaviour and plane blade angle configurations' effects on pressure fluctuations and internal flow analysis in axial flow pumps

Pumps play a crucial role in various applications, and this study employs the CFD method to simulate the internal flow of an axial pump. Utilizing a three-dimensional model with real clearances, our investigation focuses on the pump's internal flow and pressure pulsation under diverse operating conditions. Specifically, we operated an axial pump at varying blade angles (30°, 45°, 60°, and 75°) to determine transient flow fields, aiming to identify both qualitative and quantitative characteristics. In line with current research practices, we present a comparison between numerical calculations and experimental results, revealing reasonable agreement. The simulation results highlight the influence of flow rate and plane blade angle on key parameters such as static pressure, dynamic pressure, total pressure, velocity magnitude fluctuations, and shear stress. Notably, pressure increases near or at the blade tip, and hydraulic flow becomes more evident under different blade angles and conditions. The highest pressure and velocity are observed on the blade with a 45-degree plane angle. These findings provide valuable insights for enhancing the hydraulic performance of axial pumps. To ascertain the model's accuracy and reliability, our research establishes a side-by-side comparison between numerical predictions and experimental data, demonstrating a satisfactory level of agreement. The CFD simulations yield critical insights into the pump's performance, emphasizing the profound sensitivity of parameters to variations in flow rate and blade angle, crucial for understanding and optimizing the pump's behavior.

Effect of the impeller blade outlet setting angle on the performance of the helical axial-flow multiphase pump

Effect of the impeller blade outlet setting angle on the performance of the helical axial-flow multiphase pump

A novel self-supervised representation learning framework based on time-frequency alignment and interaction for mechanical fault diagnosis

Recently, supervised learning methods for intelligent mechanical fault diagnosis have achieved considerable advancements, while they heavily rely on labeled information and neglect massive unlabeled signals. Consequently, some self-supervised research has emerged and employs contrastive learning to mine general knowledge from unlabeled samples. However, these methods emphasize independent feature extraction and lack deep feature interaction, which limits better representation learning. Furthermore, it also restricts the performance improvement of fault diagnosis. To fill this gap, a novel self-supervised representation learning framework based on time-frequency alignment and interaction (TFAI) is proposed to improve the diagnosis reliability under limited labeled data. Comprising a dual encoder and a cross-modal encoder based on Transformers, the proposed TFAI model takes paired time-frequency data as input for self-supervised pretraining. Two self-supervised learning strategies, namely time-frequency alignment and time-frequency interaction, are proposed to enable the model to gain valuable knowledge from unlabeled data. The former leverages a time-frequency contrastive loss to drive the dual encoder to extract profound features from unlabeled data. The latter involves utilizing a time-frequency matching loss to guide the cross-modal encoder to perform deep feature fusion in an unsupervised manner. The well pretrained TFAI model can learn informative representations and can be fine-tuned for specific downstream fault diagnosis tasks to improve the diagnosis accuracy. By conducting three experimental cases on an axial flow pump system and a public gearbox platform system, the effectiveness, generalizability, and domain adaptability of the proposed method are validated.

Immediate inflammatory response to mechanical circulatory support in a porcine model of severe cardiogenic shock

BackgroundIn selected cases of cardiogenic shock, veno-arterial extracorporeal membrane oxygenation (V-A ECMO) is combined with trans valvular micro axial flow pumps (ECMELLA). Observational studies indicate that ECMELLA may reduce mortality but exposing the patient to two advanced mechanical support devices may affect the early inflammatory response. We aimed to explore inflammatory biomarkers in a porcine cardiogenic shock model managed with V-A ECMO or ECMELLA.MethodsFourteen landrace pigs had acute myocardial infarction-induced cardiogenic shock with minimal arterial pulsatility by microsphere embolization and were afterwards managed 1:1 with either V-A ECMO or ECMELLA for 4 h. Serial blood samples were drawn hourly and analyzed for serum concentrations of interleukin 6 (IL-6), IL-8, tumor necrosis factor alpha, and serum amyloid A (SAA).ResultsAn increase in IL-6, IL-8, and SAA levels was observed during the experiment for both groups. At 2–4 h of support, IL-6 levels were higher in ECMELLA compared to V-A ECMO animals (difference: 1416 pg/ml, 1278 pg/ml, and 1030 pg/ml). SAA levels were higher in ECMELLA animals after 3 and 4 h of support (difference: 401 ng/ml and 524 ng/ml) and a significant treatment-by-time effect of ECMELLA on SAA was identified (p = 0.04). No statistical significant between-group differences were observed in carotid artery blood flow, urine output, and lactate levels.ConclusionsLeft ventricular unloading with Impella during V-A ECMO resulted in a more extensive inflammatory reaction despite similar end-organ perfusion.

(574) - Acute Hemodynamic and Echocardiographic Consequences of Surgically-Implanted Axial Flow Pumps in Patients with Cardiogenic Shock

(574) - Acute Hemodynamic and Echocardiographic Consequences of Surgically-Implanted Axial Flow Pumps in Patients with Cardiogenic Shock

Improving the hydraulic performance of a high-speed submersible axial flow pump based on CFD technology

The hydraulic performance of a high-speed submersible axial flow pump is investigated to reduce its energy consumption. A more efficient and stable optimization method that combines parametric design, computational fluid dynamics, and a computer algorithm is proposed. The main aim is to broaden the high-efficiency operating zone, so the average efficiency under multiple conditions is optimized while considering rotor–stator matching. The design-of-experiments method and a radial-basis-function neural network are combined to form the optimization platform, and automatic optimization of the pump design is realized through repeated execution of design and simulation. The flow loss mechanism inside the pump is studied in depth via the entropy generation rate, and regression analysis shows that the pump efficiency is influenced mainly by the blade angles. After optimization, the target efficiency is increased by 8.34%, and the flow field distribution shows that the channel vortex and hydraulic loss are controlled effectively. Finally, the results are validated by experiment. The proposed optimization approach has advantages in saving manpower and obtaining globally optimal solutions.

Dynamic Analysis of Tip Leakage Phenomena in Axial Flow Pumps Using a Square-Cavity Jet Model

In the field of pump impeller studies, tip leakage flow (TLF) and the resultant tip leakage vortex (TLV) significantly influence hydraulic efficiency, cavitation, and noise generation. This paper builds a novel square-cavity jet model combined with Large Eddy Simulation (LES) technology to obtain precise the dynamic properties of the TLV, significantly simplifying the computational resources required for numerical simulations. The novel square-cavity jet model simplifies a single blade channel to a square-cavity, and then adds a longitudinal slit on the top wall of the square-cavity. The analysis of both instantaneous and time-averaged flow fields indicates that the interaction between the main flow and the jet is the primary source of TLV generation. This study successfully captures the formation process of the TLV and accurately reveals its turbulent coherent structures. The evolution of the TLV is divided into three main parts: the first part is the jet slot, predominantly characterized by negative vorticity flow. The second part is the TLV formation, which is mainly composed of significant negative streamwise vortices. The third part is the development of the TLV, where positive and negative vorticities begin to interact, resulting in a more complex overall structure. The entire evolution of the TLV phenomenon starts with a concentrated negative vortex, which, after breakdown, develops at a certain angle to the slot and continuously advances towards the sidewall, ultimately resulting in the formation of a large-scale intermingled group of small-scale positive and negative vortices. This research not only provides a new physical model for investigating the tip leakage phenomenon in axial flow pumps but also offers a powerful tool and methodology for future studies in similar complex flow domains.

Optimizing the design of axial flow pump blades based on fluid characteristics

Non-physiological blood flow conditions in axial blood pumps lead to some complications, including hemolysis, platelet activation, thrombosis, and embolism. The high speed of the axial blood pump destroys large amounts of erythrocytes, thereby causing hemolysis and thrombosis. Thus, this study aims to reduce the vortices and reflux in the flow field by optimizing the axial blood pump. The axial blood pump and arterial flow field were modeled by the finite element method. The blood was assumed to be incompressible, turbulent, and Newtonian. The SST k–ω turbulence model was used. The frozen rotor method was also used to calculate the snapshot of motion. Many vortices and reflux exist in the flow field of the blood pump without optimization. The improved flow field had almost no vortex and reflux, thereby reducing the exposure time of blood. The optimized blood pump had little influence on the pressure field and shear stress field. The optimized blood pump mainly reduced the vortex, reflux, and the risk of thrombosis in the flow field. The flow field characteristics of an axial blood pump were studied, and the results showed the risk of thrombosis and hemolysis in the blood pump. In accordance with the relationship between the blade shape and the flow field, the blade of the blood pump was optimized, reducing the vortex and reflux of the flow field, as well as the risk of thrombosis.

Impeller optimization using a machine learning-based algorithm with dynamic sampling method and flow analysis for an axial flow pump

Design optimization for widely used axial flow pumps presents a formidable challenge due to the significant impact of numerous parameters associated with impeller geometry on hydraulic performance. The expansive design space raises concerns about the cost and time implications of the optimization process. This paper introduces a machine learning-based algorithm with a dynamic sampling approach to enhance the hydraulic performance of axial flow pumps. The focus is on an axial flow pump designed for China’s South-to-North Water Diversion Project. Optimization involves selecting 15 design variables governing impeller geometry, considering meridional shape and mean blade profiles. The optimization process predicts hydraulic performance using CFD methods, with a primary objective of maximizing efficiency at the axial flow pump’s design point while maintaining pump head around the design value. The results indicate that the proposed machine learning-based algorithm exhibits commendable convergence, delivering a notable improvement in performance. For instance, the optimized axial flow pump displays 2% efficiency increase compared to the initial design. Further analysis employing concepts like entropy generation rate and boundary vorticity flux reveals that the optimized pump has more uniform flow near the pressure side of the impeller blade. Additionally, design optimization effectively suppresses flow separation at the blade trailing edge near the impeller hub. This study offers valuable insights and a practical tool for the design optimization of axial flow pumps.

Comparative study on stator corner separation vortex characteristics in axial-flow pump and tubular pump: To understand the effects of guide-vane cone diffusion on horn-like vortices

The guide-vane cone diffusion is a typical structural difference between an axial-flow pump and a tubular pump, which is shown as low diffusivity and high diffusivity respectively, but it is still unclear how this structural difference affects the vortex characteristics in stator corner separation flows. In this paper, a comparative study of stator corner separation flows in an axial-flow pump and a tubular pump was conducted, and the effects of guide-vane cone diffusion on vortical structures were clarified. Firstly, for the apparent vortical features, compared with the guide-vane of axial-flow pump with low diffusivity, the horn-like vortex in the guide-vane of tubular pump with high diffusivity has the features of smaller scale, weaker swirling strength, shorter evolution cycle and lower pressure fluctuations. Secondly, for the vortex dynamics mechanism, the guide-vane cone diffusion of tubular pump can cause additional pressure energy recovery, which leads to higher adverse pressure gradients, so it is easier to induce additional shroud backflow near the suction surface. In this coupled flow field of main flow, namely hub corner separation flow and shroud backflow, the streamwise periodic oscillation of the pressure function gradient ωS ·▽(▽p/ρ) is found, and it induces the unique vortex-street-like distributions of the deformational vorticity ωS and the rigid vorticity ωR . This physical effect causes a mutual competition between the horn-like vortex near the hub corner and the opposite backflow vortex near the shroud side. It is this competition effect originating from the guide-vane cone diffusion that greatly suppresses the development of the horn-like vortex in a tubular pump.

Experimental study on multi-condition of axial flow pump in the whole flow field based on piv test

To study the internal flow characteristics of the axial flow pump in the whole flow field under different flow conditions, particle image velocimetry technology was used to measure the steady and unsteady flow fields of the axial flow pump, analyzed the velocity field distribution at the impeller inlet, impeller inner, guide vane inner, and guide vane outlet of the pump under different flow conditions (Q/Q des=0.8, 1, 1.1). Through the test and data analysis: under the three flow conditions, the velocity distribution trend of the impeller inlet of the axial flow pump is consistent and basically along the axis direction; there is a large velocity gradient in the flow field inside the impeller, and there is a significant acceleration near the hub trend, and there is a high-speed concentrated area; the velocity distribution trend in the guide vane is basically the same, and the fluid velocity changes more uniformly at the rated flow rate, and the flow tends to be more stable; a local high-speed area appears at the outer edge of the guide vane outlet, but in the second half The flow velocity in the pipeline is relatively uniform. The test results can provide a reference for the internal flow characteristics and performance optimization design of the axial flow pump.

Cavitation performance analysis and optimal design of the portable electric-driven axial flow pump

Based on the ISIGHT optimization platform, the impeller parameterization modeling and simulation process of the portable axial flow pump is carried out through CFturbo, ICEM and CFX software, and the impeller is optimized with the help of multi-island genetic algorithm to target the two optimization objectives of efficiency and head. The optimization results show that the hydraulic efficiency increased by 6.3% under design conditions. At the same time, compared with the original solution, the optimized cavitation performance is significantly improved. Additionally, overall entropy production is significantly reduced. Field test results show that the head deviation is 1.42% and the efficiency deviation is 4.52% under design conditions, proving that the optimization results are reliable.

Numerical and field experimental study on the start-up process of a prototype axial-flow pump system considering the motion characteristics of cutoff facilities

Clarifying the evolutionary mechanism of the start-up process of a large axial-flow pump that includes cutoff facilities is of great significance for ensuring the safe and stable operation of such a system. However, the three-dimensional dynamic characteristics of the start-up process of a prototype axial-flow pump system (PAPS), considering cutoff facilities, are still unknown. In this paper, a method combining motor starting characteristic experiment, computational fluid dynamics, and field test of prototype pump system is proposed to study the starting process of PAPS. The results indicate that flow interruption facilities will significantly affect the start-up process of the pump system. High-speed forward fluid particles collide with reverse fluid particles in the guide vane channel during the acceleration of the pump owing to the influence of the cutoff facilities. A large number of wall vortex structures block the guide vane channel. This leads to a brief plateau period during the increase in instantaneous head. As the start-up process progresses, a clear horseshoe-shaped vortex structure is formed at the trailing edge of the guide vane, which subsequently falls back. The accelerated shedding of horseshoe-shaped vortical structures at the trailing edge of the guide vane induces high-frequency pulsating components, leading to a high-energy region of the pressure fluctuation signal at the outlet of the guide vane, which gradually expands toward higher frequencies. During this transition process, the flow field near the cutoff facility also exhibited significant unstable flow behavior. After the interaction between the outflow at the flap gate and the outflow at the gate, entrainment occurs, forming a region of circulating motion, and a large number of vortices with a jet-like structure are formed at the exit of the flap gate.

Research on cavitation characteristics of water-jet pumps with different blade tip clearances based on entropy production theory

Water-jet pumps are widely used in ship and other power fields. An axial-flow water-jet pump is studied with different size of tip clearance, and the cavitation characteristics are studied based on the theory of entropy production. Modified SST with curvature correction and modified Zwart cavitation model based on vortex identification are adopted, and the numerical calculation method is verified by reference experiments of a model pump. Under normal operating conditions, the results show that when the size of the tip clearance varies from 1.6‰ to 7.9‰ of the impeller diameter, efficiency takes a linear decrease accordingly, and the total entropy production increases linearly. At the same time, the main energy dissipation mode changes from wall dissipation to turbulent dissipation. Under severe cavitation conditions the total entropy production adds 30%. The water-jet pump shows that the entropy production in the impeller section is the highest, which accounts for 40%-50% and is closely related to the vortex and cavitation flow field in the tip clearance of the impeller. The tip leakage vortex region causes cavitation, but significant energy dissipation occurs at the outer edge of leakage vortex and on the nearby wall area, while the attached cavitation on the blade surface is the main source of turbulent dissipation.

Research on blade tip clearance cavitation and turbulent kinetic energy characteristics of axial flow pump based on the partially-averaged Navier-Stokes model

Research on blade tip clearance cavitation and turbulent kinetic energy characteristics of axial flow pump based on the partially-averaged Navier-Stokes model