Impeller Rotation Research Articles

Research on flow characteristics of discharge pipe during reverse operation of bidirectional axial flow pump

Bidirectional axial flow pumps are of growing importance in flood control and irrigation. Reverse operation is a common concern during the operation of bidirectional pumps. Therefore, this paper focuses on studying the flow state in the discharge pipe of a bidirectional pump operating in reverse at various flow rates, utilizing model testing and numerical simulation methods. Research shows that the spiral flow in the discharge pipe leads to the high head measurements. Moreover, reverse operation generates vortices in the discharge pipe, with greater vortex intensity and range occurring at lower flow rates, causing poor velocity distribution uniformity. The concentration of vortex kinetic energy and energy loss in the discharge pipe is primarily within a range of twice the impeller diameter. Furthermore, as the flow rate decreases, the pressure pulsation in the discharge pipe becomes unstable. At design and large flow rates, the pressure pulsations are mainly due to impeller rotation; however, running at a small flow rate results in low-frequency fluctuations in the discharge pipe, occurring at a cycle time 3.5 times the rotation frequency. This research holds both theoretical and practical significance for enhancing the operational stability and efficiency of bidirectional axial flow pumps.

Hydrogel impeller formation via vacuum degassing photopolymerization for micromixers

For effective mixing within microfluidic devices through the application of obstacle-based structures, a straightforward approach involves in-situ fabrication, such as the free-radical photopolymerization of hydrogel structures. However, oxygen inhibition presents a challenge for polydimethylsiloxane (PDMS)-based microfluidic chips. In this paper, we present a solution to the problem of hydrogel-structure formation hindered by oxygen inhibition at low light intensities and the photoinitiator concentration achieved using vacuum degassing. Furthermore, a kinetic model for photopolymerization under vacuum conditions was established and converted into an equation of light intensity and exposure time while keeping the other parameters constant. The exposure time range was successfully predicted by comparing the experimental data and analyzing scenarios. This method was used to fabricate an impeller for a passive micromixer. The impeller rotation was then analyzed. The results demonstrated that with an increased flow rate exceeding 6 mL/min, the mixing efficiency is significantly higher owing to the rotation of the impeller. The mixing efficiency was quantitatively assessed through experiments involving the mixing of three dyes, showing a three-fold increase compared to the chip without the impeller. Our research provides valuable insights into the fabrication of hydrogel structures in PDMS-based microfluidic chips under vacuum conditions.

Dynamics and stability analysis of unbalance responses in mid‐positioned electrically assisted turbocharger rotor

AbstractElectrically assisted turbochargers (EAT) improve intake efficiency by motor‐assisted compressor impeller rotation, enhancing the system's transient response. However, the addition of motor rotor components has increased the number of unbalanced positions in the shaft system, leading to problems such as excessive compressor end vibration and complex changes in oil film stability. To evaluate the effects of unbalance in the motor rotor, along with the parameters of floating ring bearings (FRB), on the dynamic response of EAT, a finite element model of an EAT rotor supported by nonlinear FRB is developed, and the vibration response of the compressor end bearing is obtained by numerical integration. The results indicate: (1) In contrast to the effect of compressor and turbine unbalance, proper motor rotor unbalance is more effective in suppressing oil whirl instability in the high‐speed operating range. However, a new inner oil film whirl “instability interval” is also induced in the low‐speed operating range, leading to an increase in the Y1 compressor‐end amplitude at low and medium speeds, and this “instability interval” increases with the amount of unbalance. (2) When an oil whirl occurs in the oil film, the maximum eccentricity of the bearing surges and is greater than 0.3, which can be used as an effective threshold for determining whether the oil film is unstable in engineering applications. (3) A suitable outer oil‐film clearance range should be , otherwise, a wide range of outer oil‐film whirl instability occurs. Controlling the amount of unbalance and oil‐film clearance to suppress the sub‐synchronous vibration of the EAT, provides a theoretical basis for the design of the dynamics of the nonlinear rotor bearing system and improves the stability of the turbocharger's operation.

Transient flow and noise characteristics of vortex-turbulence-noise interaction in centrifugal pump

Centrifugal pump operation noise is an avoidable common phenomenon in engineering practices, and its characteristics are closely influenced by the flow characteristics of the fluid. In this paper, a numerical simulation of centrifugal pump operation with different flow rates is carried out using the detached eddy simulation turbulence model and compared with the experimental results. Then the noise source and far-field radiated noise characteristics of the centrifugal pump are investigated using Lighthill’s analogy. The results show that the noise of centrifugal pump is closely related to the flow characteristics of impeller, especially the generation and development of vortex. The relationship between turbulent kinetic energy (TKE) and vortex is complex, involving the generation, development and shedding of vortex. The influence of flow rate variation on vortex structure in impeller is studied by vortex transport equation. It is found that the relative vortex stretching (RVS) term is the main driving force of vortex distribution. The distribution of the Coriolis force (CORF) term is mainly concentrated in the inlet and outlet areas of the flow channel, which is related to the rotational motion of the impeller and the dynamic characteristic of the fluid. The power spectral density inside the impeller is mainly concentrated in the low frequency region, indicating that the low frequency noise component is dominant in energy. The directivity curve of far-field noise pressure level is influenced by hydrodynamic effect, impeller rotation direction and pump design structure, and will have a certain deviation. The spectral curve analysis of velocity, vorticity, pressure and sound pressure level shows that these physical quantities have strong correlation on the spectrum, in which the low frequency component is large, and the high frequency component is complex and volatile.

Study on the inlet backflow characteristics and particle deposition of screw mixed-flow deep-sea mining pump under small flow conditions

Abstract When a screw mixed-flow deep-sea mining pump operates under small flow conditions, significant backflow occurs at the impeller inlet and in the inlet pipe, which seriously affects the pump performance. To investigate this backflow characteristic, this paper presents a numerical study of the internal flow field of the mining pump based on the CFD-DEM coupling method. The flow state at the impeller inlet, the velocity distribution law in the inlet pipe, and the particle motion state under the flow rate condition of 0.52Qd are obtained. The results show that, when the pump operates under small flow conditions, the leakage from the tip gap of the impeller head causes a screw high-speed backflow with the same rotation direction as the impeller on the wall of the inlet pipe. The backflow intensity attenuates as it propagates towards the pump inlet. The backflow mixes with the main flow in the middle of the pipe and reaches a balanced state, which causes the particles to deposit here. The deposition process can be divided into a formation stage and a stable stage. When the particles in the middle of the pipe reach the stable stage, their shape and position become stable. The velocity pulsation of the monitoring points near the wall is periodic, and its pulsation frequency is the same as the impeller rotation frequency.

Investigation of mechanisms on leading edge vortex generation and suppression in vaned diffuser of a centrifugal compressor

This study numerically investigates the mechanisms for generating and suppressing the leading edge vortex (LEV) in a vaned diffuser of a centrifugal compressor, aiming to enhance the compressor's stable operating range. Detailed analyses focus on the mechanisms of the rotating stall and the initiation process of the LEV. Notably, the end wall contouring method is applied to vaned diffuser to suppress the LEV and improve diffuser stability. The suppression mechanisms of the LEV are examined to deepen the understanding of stability enhancement mechanisms. Results demonstrate that, under stall conditions, the vaned diffuser experiences two-cell rotating stalls moving opposite to the impeller rotation direction, each rotating at approximately 12% of impeller rotation speed. The formation of diffuser stall is attributed to a longitudinal vortex developing from the LEV and causing the passage blockage. The increasing spanwise distortion of leading edge (LE) incidence angles and circumferential distortion of static pressures at the diffuser inlet promote the evolution of the longitudinal vortex from LEV. The end wall contouring of vaned diffuser effectively enhances the compressor's stable operating range by 15.10% and 8.90% toward lower flow rate conditions for machine Mach numbers 1.3 and 1.2, respectively. At near-stall points, the end wall contoured diffuser reduces spanwise distortion of LE incidence angles and circumferential distortion of static pressures at the diffuser inlet, mitigates the LE flow separation and corner separation, suppresses the generation and development of the LEV, delays the onset of rotating stall in vaned diffuser, and thereby improves the stable operating range of centrifugal compressor stage.

Internal flow stability analysis of vertical mixed-flow pump device based on EGT and FFT

With the purpose of researching the internal flow stability of the vertical mixed-flow pump device (VMFPD), the entire flow field was solved through the very large-eddy simulation (VLES) k- ω model and the internal flow characteristics of the pump device were quantitatively analyzed with the use of the energy gradient theory (EGT) along with the physical parameters of the flow field. The research elucidates the variety rule of the pressure along the VMFPD and the energy gradient function K as well as the time-frequency features of the pressure pulsation (PP) in the impeller and guide vane. The results demonstrate that the solid wall restriction of the guide vane and the impeller rotation cause a significant shift in the velocity and direction of the water flow. This causes a significant pressure difference between the water bodies, which makes it easier to create an unstable flow. The suction surface of the impeller blade possesses the great concentration of the area with energy gradient function K > 107, which is the critical area influencing the internal flow stability of the pump device.

CFD-DEM investigation of centrifugal slurry pump with polydisperse particle feeds

Polydisperse particle feed into centrifugal slurry complicates hydraulic performance and wall erosion but is poorly understood. This paper presents a numerical study of a centrifugal slurry pump, focusing on the effect of particle size distribution (PSD) using the combined computational fluid dynamics and discrete element method (CFD-DEM). It incorporates rigid impeller rotation and wall erosion. On this basis, the hydraulic and erosion model validity is verified by clear water performance and jet erosion test, respectively. Additionally, this CFD-DEM model is compared with the dense discrete phase model (DDPM), demonstrating more precise erosion prediction as its fully resolved particle-particle interactions. Generally, total pump erosion severity intensifies when the PSD is broadened. Compartment-wise, it indicates the necessity of tailoring flow structure to enlarge drag force, therefore, mitigate particle aggregation in the impeller. This in-house CFD-DEM model is promising for addressing particle-fluid flow problems in centrifugal pumps or coupling with data driven method.

Experimental investigation on aerodynamic noise of a small-scale multi-blade centrifugal fan

In this study, the aerodynamic noise of a small-scale centrifugal fan was experimentally investigated using acoustic testing techniques and time-resolved stereoscopic particle image velocimetry (SPIV). During the acoustic experiments, both far-field noise and near-field pressure fluctuations of the test fan were measured. The overall far-field noise towards the fan inlet side was found to be higher than that of the back side. The pressure fluctuations on the fan upper casing exceeded those on the side wall due to the uncontracted volute tongue, indicating pronounced flow-to-wall interactions. Moreover, based on a simultaneous measurement, the coherence between the near-field pressure fluctuations and far-field noise highlighted the significant contributions of impeller rotation to noise radiation. SPIV measurements uncovered the time-averaged and transient flow fields at the fan's inlet and outlet. The time-averaged results demonstrated the concentrated inlet flow and outlet flow separation, leading to high flow unsteadiness. Transient flow fields displayed an asymmetric jet-wake region characterized by both quasi-steady flow and rotational flow behaviours. The instantaneous flow results were analyzed using the dynamic mode decomposition (DMD) method, which clearly recognized the jet-wake patterns with frequencies corresponding to the rotational frequency. The observed consistency in frequency characteristics among noise, pressure fluctuations, and unsteady flow affirms that flow dynamics are crucial to the primary noise mechanisms.

The effect of impeller height and rotation speed on the Kambala reactor desulfurization process

To improve the utilization efficiency of desulfurizer in the Kambala reactor liquid iron desulfurization process and prolong the life of the impeller, the height of the impeller and its optimal matching rotation speed are optimized. Through numerical simulation, the mixing effect of different height impellers under different rotation speeds is studied, the movement and distribution modes of desulfurizer particles are analyzed, the pumping capacity and power are calculated, and the influence of impeller height and optimal matching rotation speed on the desulfurization effect has been clarified. The numerical simulation results show that the optimization of impeller height and optimal matching rotation speed can improve the mixing effect. The height of the impeller increases, and its optimal matching rotation speed decreases. Based on the results, in existing models, it is recommended to run at 60 r/min with an impeller height of 800 mm for optimal mixing performance.

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.

Dynamic characteristics of the tip leakage vortex in an oil–gas multiphase pump based on vorticity decomposition theory

AbstractThe paper combines experimental and numerical simulation methods to investigate the tip leakage vortex (TLV) in an oil–gas multiphase pump. The study aims to understand the evolution and dynamic characteristics of the TLV. The vorticity decomposition theory is used to analyze the spatial–temporal evolution, transient behavior, and rigid vorticity of the TLV. The findings reveal that the TLV is formed near the pressure surface when the tip clearance jet passes through the shear layer. In one impeller rotation period, transient fluctuations of the TLV are attributed to pressure differences and velocity changes across the tip clearance, and the TLV undergoes two split–dissipation–recurrence processes within one impeller rotation cycle. The presence of the gas phase enhances the scale and strength of the TLV while prolonging its existence in the flow channel. Analysis based on the rigid vorticity transport equation shows that the growth of the TLV and collapse are primarily governed by the rigid vortex generation term. The Coriolis force term contributes to stabilizing the TLV, while the rigid vorticity stretching term affects its shape. Furthermore, the gas phase significantly increases the value of the Rigid vorticity Curl of pseudo‐Lamb vector Term (RCT), which plays a crucial role in the prolonged existence of the TLV under gas–liquid two‐phase conditions. From an inlet gas void fraction of 0%–20%, the RCT value increases by 4.8 × 106/s2, the entropy production value increases by 75.55%, and the hydraulic efficiency decreases by 16.29%.

Energy dissipation and time–frequency analysis of characteristics induced by vortex breakdown in an axial flow pump

Vortex breakdown in a pump sump is a complex and negative factor for the pump. Different from my previous study that focused mainly on the development process of vortex and its damage to the pump, this paper is from a new perspective that studies the energy dissipation and time–frequency characteristics induced by vortex breakdown. The tested data of pressure and velocity in the process of vortex breakdown were obtained by the model. Considering the gas–liquid two-phase flow of the vortices, a new numerical simulation approach is conducted and verified. The results show that the development rules of vortex breakdown reveal that the breakdown is initiated near the blade. The residual disturbance in the flow field continues to propagate after vortex breakdown, inducing unstable flow inside the runner and causing additional energy dissipation. The time–frequency characteristics induced by vortex breakdown indicated that the runner rotation speed has a significant effect on the vortex breakdown. The frequency of vortex breakdown is relatively small under high-speed rotation. Through discussion, it can be concluded that in order to reduce the harm of vortex breakdown, it can take measures such as controlling the impeller rotation speed, stalling anti-vortex measures, and adjusting operating conditions.

Study on rotating stall characteristics of centrifugal pumps based on gamma transition model

The phenomenon of rotating stall in centrifugal pumps is closely associated with the evolution of the blade boundary layer. Aiming to accurately predict the characteristics of the boundary layer, this study investigates the phenomenon of rotating stall in centrifugal pump impellers using the gamma (γ) transition model. The accuracy of the numerical simulation was confirmed by comparing its conclusions with the results of the testing. In calculations considering transition characteristics, the distribution of low-pressure areas inside the impeller is relatively discontinuous, while the pressure distribution is more uniform. However, in calculations without considering transition, the low-pressure regions in neighboring flow channels exhibit a tendency to be interconnected, resulting in a more variable pressure distribution, and the pressure contour at the outlet is closer to parallel. The dynamic characteristics of the centrifugal pump impeller rotating stall were obtained through the dynamic mode decomposition method, including the frequency, structure, and dynamic evolution process of the stall vortex. Through modal reconstruction, it was discovered that the impeller's rotation causes the stall vortex to undergo periodic fluctuations. The stall vortex is not stationary but moves synchronously with the rotation of the blades. At different time points, the stall vortex exhibits periodic changes. At the blade suction entrance, the stall vortex initially appears. Subsequently, multiple vortex structures resulted in channel blockage. After a period of development, the excess vortex structures merge to generate a typical “8” shaped vortex structure and move toward the exit. Finally, the exit stall vortex disappears, and a new vortex structure is generated at the inlet of the blade suction surface.

Investigation of a rotating stall in a supercritical CO2 centrifugal compressor

Due to the nonlinear behavior of carbon dioxide properties at its critical point and the size effect of the supercritical carbon dioxide (S-CO2) centrifugal compressor, the stall causation mechanism differs between the S-CO2 centrifugal compressor and a conventional air compressor. The comprehension of the induced principle of the S-CO2 compressor rotating stall holds immense significance in enhancing stall margin and efficiency. This paper employs unsteady simulations to investigate the causes of the impeller rotating stall in the S-CO2 centrifugal compressor. The results show that the leading edge breakdown vortex (LEBV) formed by the tip leakage vortex (TLV) breakdown and the reverse flow in the passage are the reasons for blocking the passage and ultimately causing the rotating stall of the impeller. The migration motion of the LEBV not only induces the leading edge spillage phenomenon but also influences the intensity of the tip leakage flow (TLF) in adjacent passages, causing the propagation of the TLV breakdown phenomenon in the opposite direction to that of impeller rotation. The TLV undergoes intermittent breakdown in flow field, which is influenced by variations in TLF intensity. Additionally, there is a preceding process of breakdown-induced vortex formation and disappearance prior to TLV fragmentation.

Active mixing of two-component viscoelastic silicone ink at molecular level for spatiotemporally controlled 3D/4D printing of cellular silicones

3D printed silicones have demonstrated great potential in diverse areas such as soft robots, tissue engineering, flexible sensors and energy dissipation. However, most silicone inks face inevitable curing issue once it is prepared. During the materials extrusion based printing process, the curing-related viscosity change in silicone inks hamper the ink stability and printing controllability, leading to complex relationship among ink properties and printing parameters, as well as printing structures and material properties of final products. Herein, this work presents active mixing of two component silicone ink to realize stable printing, achieving exact and continuous match of ink properties and printing parameters. Using a specially formulated ink containing separate starting components with reactive groups, catalyst and thixotropic agents, this work studies the active mixing process thoroughly for the first time from molecular level to materials performances under various conditions regarding inlet flow rates, impeller rotation speed and component ratios. Besides, cellular silicones with controlled distribution of component ratios and tailored gradient structures are printed, leading to integrated manufacturing of compression performance and shape morphing property. This work will pave way for active mixing and printing of two-component silicones, and provide guidance for other reactive multi-material 3D printing systems.

Mass Transfer Behavior and Energy Utilization Efficiency of a Fixed Bed Suspended in a Stirred Tank Reactor

AbstractThe present study contributes to overcoming the serious drawback of the traditional stirred slurry catalytic reactor, namely, the costly and time‐consuming separation of the catalyst particles from the final product using a stationary fixed bed of Raschig rings placed above a rotating impeller. The rate of diffusion‐controlled reactions was measured in terms of the mass transfer coefficient under different conditions of impeller rotation speed, Raschig ring diameter, and bed height. The rate of mass transfer was determined by a technique which involves measuring the rate of diffusion‐controlled dissolution of copper in acidified dichromate. The data were correlated by a dimensionless correlation which can be used to scale up and design the reactor. The reactor performance was measured in terms of the mass transfer coefficient and the energy utilization efficiency. Possible applications of the reactor in conducting diffusion‐controlled reactions were highlighted.

Semicontinuous Blending of Pharmaceutical Ingredients and the Impact of Process Parameters on the Blending Performance of an Integrated Feeder Blender Operating Semicontinuously

The pharmaceutical industry is looking for new and innovative ways of manufacturing to improve product quality and reduce process complexity. In manufacturing oral solid dosage products, blending is a crucial step in ensuring the homogeneity of active pharmaceutical ingredients (APIs) in the final product. Currently, batch and continuous blending are the two commonly used modes for blending in the industry. However, these methods have limitations in terms of blending time, manual intervention, and flexibility in handling multiple ingredients. To address these limitations, this study aims to explore the feasibility and benefits of using a semicontinuous blending mode in the pharmaceutical industry. A case study is conducted using a binary blend of microcrystalline cellulose and acetaminophen to compare the performance of the semicontinuous mode of blending with the batch and continuous blending modes. The results show that the semicontinuous blending setup can produce blends with good blend uniformity and homogeneity and that the output can be used for both batch and continuous downstream operations. The effect of variation in the three most important process parameters, impeller rotation per minute, blending time, and fill level on the blend uniformity, is also investigated. The semicontinuous blending mode had a higher line rate of 12.5 kg/hour than a similarly sized batch blender at 3.6 kg/hour and less than that of a continuous blender. The benefits of the new blending mode include reduced blending time, minimal manual intervention, flexibility in blending multiple ingredients, easier scale-up, and a smaller footprint. Overall, this study highlights the relative advantages of using this new semicontinuous blending mode in pharmaceutical manufacturing and its potential as a good alternative to the existing blending modes. The semicontinuous mode is well placed between the batch blending and continuous blending mode, with many benefits over the former mode and performance comparable to the latter continuous mode.

Vibration Diagnostics for Predicting Pump Failures

This study investigates the predictive potential of specific vibration patterns in assessing the structural integrity of centrifugal pumps, vital for industrial fluid transport. Despite their importance, these pumps often encounter performance issues attributed to vibration-related damage such as cavitation and corrosion. Addressing this gap, we employ advanced vibration analysis techniques to identify distinct signatures indicative of cavitation and corrosion progression. Our research aims to provide an early detection tool for maintenance by understanding these patterns. Through our method, we reveal significant correlations between vibration patterns and pump condition, offering implications for extending pump lifespan and enhancing maintenance strategies in industries reliant on such machinery. Highlights: Centrifugal Pump Operation: Impeller rotation transfers fluid. Vibration Analysis Significance: Essential for predictive maintenance. Cavitation and Corrosion Effects: Trigger vibration, erode surfaces. Keywords: Centrifugal Pump, Corrosion, Vibration

Influence of rotor impeller structure on performance improvement of suspended axial flow blood pumps.

The hydrodynamic suspension structure design of the axial blood pump impeller can avoid the problems associated with using mechanical bearings. However, the particular impeller structure will impact the hydraulic performance and hemolysis of the blood pump. This article combines computational fluid dynamics (CFD) with the Lagrange particle tracking method, aiming to improve the blood pump's hydraulic and hemolysis performance. It analyzes the flow characteristics and hemolysis performance inside the pump. It optimizes the taper of the impeller hub, the number of blades, and the inclination angle of the circumferential groove at the top of the blade. Under certain rotational speed conditions, an increase in the taper of the impeller hub or the number of blades can increase the pumping pressure of a blood pump, but an increase in the number of blades will reduce the flow rate. The design of circumferential grooves at the top of the blade can increase the pumping pressure to a certain extent, with little impact on the hemolysis performance. The impeller structure is optimized based on the estimated hemolysis of each impeller model blood pump. It could be seen that when the pump blood pressure and flow rate were reached, the optimized impeller speed was reduced by 11.4%, and the estimated hemolysis value was reduced by 10.5%. In this paper, the rotor impeller structure of the blood pump was optimized to improve the hydraulic and hemolytic performance effectively, which can provide a reference for the related research of the axial flow blood pump using hydraulic suspension.