Axial Leakage Research Articles

Thermodynamic Study on the Vortex Teeth of Electric Scroll Compressors Based on Gradient Tooth Height

Through the analysis of the adhesion between the tooth head and axial clearance leakage attributed to vortex tooth shape deformation, an innovative tooth shape design concept has been introduced entitled “progressive change tooth high vortex tooth”. This unique design includes a gradual change in tooth height and an elevated vortex tooth profile, using temperature-sensitive materials to enhance the resolution of temperature loading on the vortex disc. By refining the process of resolving the temperature loading on the vortex disc, the mean temperature function of the fluid domain along the wall of the vortex tooth is calculated, and a steady-state temperature distribution model for the solid domain of the vortex tooth is formulated. Subsequently, a finite element model for the high eddy current disc is constructed using Abaqus 2021 finite element software, which facilitates the calculation of stress–strain distribution within the high eddy current disc under both gas pressure and temperature field loads. The results show that, especially under conditions of low speed and low exhaust pressure, the temperature load mainly influences the maximum deformation and stress distribution of the vortex tooth. Specifically, under the influence of heat-solid coupling, the maximum deformation of the progressive change tooth high vortex tooth occurs in close proximity to the central compression cavity, reaching up to 13 microns. These results provide a crucial theoretical basis for the structural design and performance optimization of the compressor.

Design of Torque Density Improved Spoke-Type IPMSM for Electric Brake Booster Take Into Account Axial Leakage Flux

Design of Torque Density Improved Spoke-Type IPMSM for Electric Brake Booster Take Into Account Axial Leakage Flux

Study on Performance Improvement through Reducing Axial Force of Ferrite Double-Layer Spoke-Type Permanent Magnet Synchronous Motor with Core Skew

Recently, due to the price fluctuation and supply instability of rare earth mineral resources, there has been a lot of development of electric motors using non-rare-earth permanent magnets. As a result, motors using Dy-free permanent magnets and ferrite permanent magnets are being researched, and, in particular, ferrite permanent magnets often utilize spoke-type structures, which are magnetic flux concentrators, to compensate for their low coercivity and residual flux density. However, in general, spoke-type PMSMs do not use much reluctance torque, so double-layer spoke-type PMSMs have been studied for their more efficient design. Unlike general spoke-type PMSMs, double-layer spoke-type PMSMs can utilize high reluctance torque by increasing the difference between d-axis and q-axis reluctance. However, as the difference in magnetic resistance increases, vibration and noise are generated, which adversely affects the mechanical part and shortens the life of the motor. Although this problem seemed to be solved by applying core skew in the previous study, it was confirmed that the axial force caused by the axial leakage flux occurred in the maximum torque per ampere (MTPA) control section and the torque ripple was increased. Therefore, in this paper, a model that can apply symmetrical core skew and reduce axial force is proposed. First, the causes of the axial force generated in previous studies were analyzed. Based on the analysis of these causes, a new symmetrical core skew structure was proposed, and its justification was verified through FEA.

The spatiotemporal distribution characteristics analysis and suppression of the axial tip clearance leakage flow for the liquid-ring vacuum pump

The clearance leakage flow of liquid-ring pump has complex spatiotemporal distribution characteristics, and it has severe negative impact on its performance. In order to suppress the axial blade tip leakage flow of liquid-ring pump, the spatiotemporal distribution characteristics of leakage flow was analyzed in detail by numerical simulation method. The composite tip of winglet and squealer was introduced to the liquid-ring pump, and its suppression mechanism was analyzed. The RNG k-ε turbulence model and VOF multiphase flow model were selected to simulate transient flow in liquid-ring pump. The results show that the leakage flow in the suction zone gradually decreases from hub to rim, and the leakage flow intensity gradually increases along the rotation direction of the impeller. The gas leakage velocity of compression zone is the highest, and the leakage flow intensity gradually increases along the rotation direction of the impeller. In the exhaust zone, the reverse leakage flow forms near the hub, which flows from the clearance suction side to the pressure side, and the leakage flow intensity gradually decreases from the hub to the rim. Near the rim, the leakage flow direction changes, flowing from pressure side to suction side. In the transition zone, as the impeller flow passage approaching suction zone gradually, the pressure decreases continuously. The pressure on the clearance suction side is greater than that of the pressure side, and the reverse leakage flow forms near the hub. The composite tip blade of winglet and squealer not only lengthens the clearance channel but also blocks the clearance by the pressure side squealer corner vortex and the squealer vortex, thus the leakage flow was effectively suppressed. To some extend the composite tip can suppress the leakage flow, the vacuum values are improved by 3.5%, 3.9%, and 5.3% under different conditions respectively.

Effect of suction temperature on the internal flow characteristics of hydrogen circulation pump

This paper explores the effects of suction temperature (ST) on the internal flow and pressure pulsation characteristics of a roots hydrogen circulation pump (HCP). The study analyzes the suction and discharge chamber pressure pulsation, as well as the inlet and outlet flow pulsation, at different STs. The research finds that an increase in ST leads to a decrease in the amplitude and fluctuation intensity of the pressure pulsation in both suction and discharge chambers. Moreover, the average flow rate of the HCP decreases with increasing ST, while the frequency and waveform remain unchanged. The maximum and minimum values of the inlet flow pulsation decrease, while the maximum value of the outlet flow pulsation decreases, and the minimum value increases, indicating a reduction in fluctuation intensity. The turbulent energy within the discharge and transport chambers also changes with increasing ST. The inter-lobe leakage flow (ILF) is slightly affected by ST, while the radial leakage flow (RLF) and axial leakage flow (ALF) exhibit slight increases. Overall, these findings reveal the importance of considering ST as a critical design parameter for optimizing the performance and stability of the HCP.

The impact of mainstream ingress on the leakage flow and loss in partial shrouded turbines

The vital source of the leakage loss in shrouded LP turbines is the interaction between the leakage flow and mainstream at the exit cavity and downstream of the rotor tip. This paper numerically investigates the effect of the shroud design on the leakage loss. The results show that the mainstream ingress in the exit cavity is the key flow feature affecting the intensity and the resultant loss of the interaction between the two flows, which is highly intenser in partial shrouded turbines than full shrouded turbines and causes three aspects of impact: Firstly, the abundant amount of ingested mainstream raises the pressure in the exit cavity, reducing the axial leakage flow rate through the sealing structure. However, there is circumferential leakage flow at the rotor trailing edge due to the lack of the blockage of the shroud platform. In addition, the ingested mainstream also develops into backflow and a streamwise vortex in the exit cavity, intensifying the mixing of the leakage flow and mainstream. Thirdly, the pressure raise in the cavity promotes the convergence of the cavity outflow at the suction side of the rotor blade, thus expanding the impact region of the leakage flow and increasing the mixing loss downstream. The above impacts result in an efficiency decrease of up to 0.90% in the partial shrouded turbine compared to the full shrouded turbine. Based on the loss mechanisms of mainstream ingress, this paper presents an optimized shroud design, which can effectively reduce the loss in the rotor tip by suppressing the mainstream ingress phenomenon. In this way, the optimized shroud design has improved considerably the aerodynamic efficiency by about 0.50%.

Basic Design Parameters Influencing on Axial Stiffness of the Spiral Wound Gasket.

The article presents the influence of important design parameters of a spiral gasket on axial stiffness and leakage level. These parameters were the angle of inclination of the central part of the spiral section, the length of the vertical part of the spiral section, and the degree of densification of the material filling the metal coils. The scope of work was divided into two stages. In the first, experimental tests were conducted to determine the stiffness and tightness of a standard spiral gasket at two extreme levels of densification of the filler material, and the elastic-plastic properties of expanded graphite, which is the filler material of the metal spirals, were determined. In the second stage, multivariate numerical calculations were carried out to determine the axial stiffness of the gasket and to evaluate the distribution of contact pressure on the sealing surface. A novel aspect of the work is the proposal of a mathematical model to estimate the averaged value of the modulus of elasticity of the filler material as a function of the degree of densification and the execution of an experimental plan that significantly allowed the adoption of a limited number of analysed model variants used in the numerical calculations.

A flow control method for the leakage reduction of annular gas seals using the helical gas curtain generator

Advanced sealing technology is crucial for turbine efficiency. To reduce seal leakage, the flow control method based on gas injection is an attractive solution. The traditional flow control methods primarily focus on blocking the axial leakage flow, neglecting the helical flow effect of the leakage flow at the design stage. In this paper, a novel flow control method is proposed for the leakage reduction of annular gas seals using the helical gas curtain generator (HGCG). The helical flow effect of the leakage flow is first considered for further sealing enhancement. The design conception of the HGCG involves connecting seal cavities and teeth tips using the specially designed pad with helical injection slots. Driven by the intrinsic pressure difference between the connected areas, helical gas curtains are passively generated, producing multi-row fluidic barriers against the helical leakage flow at each teeth tip. Numerical investigation of a labyrinth seal with HGCGs shows that the proposed method effectively enforces flow resistance at teeth tips, resulting in an extra dissipation effect. The performance of the HGCG is enhanced as the helical flow effect increases. The maximum leakage reduction ratio reaches 59.2%, over eight times higher than that of the traditional air curtain technology (ACT). In addition, the HGCG increases the effective damping coefficient by 45% compared to the ACT. The proposed HGCG presents significant superiority in sealing improvement and rotordynamic stability enhancement.

Research on distribution of winding leakage magnetic field of three-phase dry type transformer under short-circuit condition

Leakage flux magnitude and pattern greatly affect transformer short-circuit resistance. In this paper, finite element calculations and experimental measurements is used to calculate the leakage magnetic field of a transformer. This paper analyzed the radial and axial leakage flux distribution of each winding under different operating conditions to obtain a comprehensive view of the magnetic flux leakage distribution in all directions. This analysis can provide valuable insights for optimizing the anti-short-circuit ability of transformers.

Electromagnetic Vibration Characteristics of Inter-Turn Short Circuits in High Frequency Transformer

As a common fault of transformer winding, inter-turn short circuits cause severe consequences, such as excessive current and serious deformation of winding. Aiming to solve the problem of inter-turn short circuit at the end-winding and middle-winding of high frequency transformers (HFT), this paper considers the electromagnetic vibration characteristics of inter-turn short circuits (interleaved winding and continuous winding) at different positions, and the HFT is established by the multi-physical field coupling principle. Coupling equations for the inter-turn short circuit, as well as electromagnetic force and sound pressure level, are established to characterize the vibration noise mechanism of inter-turn short circuits. Furthermore, the HFT equivalent model is simulated in 3D finite element method (FEM) to emulate the real transformer operation and investigate the impact of interleaved winding and continuous winding under inter-turn short circuit faults. The short-circuit current and axial flux leakage, as well as the harmonic response of vibration acceleration and sound pressure level distribution, are obtained when inter-turn short circuits occur at different positions. Finally, the results show that the electromagnetic effect of the inter-turn short circuit in end-winding is worse than it is in middle-winding. Advantages in resisting impulse current make interleaved winding superior to continuous winding in terms of vibration and noise.

Effect of pressure ratio on transient flow in hydrogen circulating pump

The pressure ratio has an important influence on the performance and internal flow characteristics of the positive displacement pump. In this paper, the influence of the four pressure ratios 1.1/1.2/1.3/1.4 on the internal flow characteristics of the hydrogen circulating pump is studied, the internal relationship between the change of pressure ratio and the flow pattern in the pump are clarified, and the leakage flow pattern and its coupling mechanism in each gap are revealed. The results show that the gap leakage flow induced by pressure difference is an important reason for flow disorder in the pump, however, the generation and growth of gap leakage flow will be affected not only by the pressure difference, but also by the shear drive. The scale and influence of axial gap leakage are far greater than the other two types of gap leakage. The existence of gap leakage flow makes the rate of flow and pressure presents a large amplitude high-frequency pulsation characteristic. The research results of this paper provide a reference for the efficient and stable operation of hydrogen circulating pump in fuel cell system.

Analysis of 3D Transient Flow in a High-Speed Scroll Refrigeration Compressor

In mobile devices such as aircraft and electric vehicles, due to limited space, there are strict requirements on the volume and weight of the compressor mounted on the vehicle. Therefore, high-speed scroll compressors have attracted more and more attention because of their small size and light weight. In this paper, the numerical calculations and analysis of the three-dimensional (3D) transient flows in a high-speed scroll refrigeration compressor were established and validated. Circumferential gas intake was used in the simulation. According to the actual compressor size, the mesh generation accurately considers clearances. The radial and the axial clearances were both set as 0.01 mm. A dynamic and high-quality hexahedral structured mesh was generated for the working chamber, and the problem of insufficient grid density in radial clearance was solved. When the rotational speed was set as 3000 rpm, 6000 rpm, and 9000 rpm alternatively, the difference in the volume efficiency of the simulation and the experiment results was below 6.3%. The results show that the higher rotational speed contributed to the greater pressure fluctuation in the compression chamber and the discharge process, and the over-compression phenomenon was more obvious. The maximum leakage velocity was 160 m/s, and the tangential leakage velocity was higher than the radial leakage velocity. Meanwhile, radial leakage velocity will increase significantly in high-speed operation mode. With the increasing rotational speed, the position of the maximum axial and tangential leakage velocity was closer to the start of the scroll. Therefore, the seal of the scroll starting part is very important in the design of a high-speed scroll compressor.

An Experimental Facility with the High-Speed Moving Endwall for Axial Compressor Leakage Flow Research

The moving endwall has a great influence on the development and stability of axial compressor leakage flow. This paper presents a novel experimental facility with a high-speed moving endwall for studying axial compressor leakage flow. The uniqueness of the design concept is that using a large disk simulates the high-speed moving endwall. When R/Cx = 16, theoretical analysis shows that the maximum linear velocity difference is about 2.5% while the maximum axial velocity difference of the mid-three passages is less than 5%. Single-passage simulations show that the disk radius of R/Cx = 16 can achieve an acceptable accuracy in terms of static pressure, total pressure, and density flow. Seven-passage simulations confirm that the mid-three passages have small errors from the axial velocity difference. Subsequently, preliminary experimental results obtained from the experimental facility are presented. The results reveal that the moving endwall significantly changes the distributions of the total pressure loss and static pressure coefficient. The relative difference in the averaged total pressure loss between the experiment and CFD is 11.33% and 7.69% for the static and moving endwall, respectively. It is expected that the experimental facility will make more useful contributions to the understanding of axial compressor leakage flow in the future.

Improvement of the 3D MOC/DD neutron transport method with thin axial meshes

Significant accuracy loss has been observed in the MOC/DD method using thin axial meshes. A theoretical analysis indicates that the accuracy loss results from the deviation in the transverse leakage. For this reason, the MOC/DD with the correction (MOC/DDC) method is proposed. To obtain the reasonable axial leakage, three variants of the MOC/DDC method are discussed in theory. The results show that the MOC/DD with one correction step and zero-value parameters (MOC/DDC100) method is effective. Then, the MOC/DDC100 method is verified against a 2D C5G7 UO2 assembly benchmark problem, the C5G7-3D extension benchmark problems, and mini pebble-bed benchmark problems. Although more computing time is needed in the MOC/DDC100 method, it can be further improved by delaying the switching time from the MOC/DD method to the MOC/DDC100 method. The numerical results indicate that the MOC/DDC100 method can effectively improve the accuracy as well as maintain high computational efficiency and numerical stability.

Influence of curvature radius on the axial crack signal of the magnetic flux leakage detection for tapered roller bearing rings

Tapered roller bearings are widely used in heavy machinery, railway transportation, aviation, and other fields. Their quality and reliability are related to the operational safety of mechanical equipment. In the axial crack magnetic flux leakage (MFL) detection of the bearing ring, the MFL signals obtained by the sensor from different curvature radius of the surface are inconsistent, affecting the detection accuracy of cracks and subsequent quantitative analysis. In order to address the above problems, the finite element simulation is performed to analyze the influence of the surface curvature radius of the bearing ring on the magnetic field distribution inside the workpiece and the MFL signal in the circumferential magnetization. Through the parallel magnetic circuit, the difference in curvature radius is identified as the basic reason for non-uniform magnetization. On this basis, the compensation method based on the normalization of surface magnetization is proposed. Furthermore, the effectiveness of the compensation method is verified by experiments. The relative change in the amplitude of the crack MFL signal is reduced from 30% to 5%.

Analysis and Modeling of Axial Leakage for Spoke-Type Hybrid Permanent Magnet Machines

In this study, we propose a novel analysis method for a spoke-type permanent magnet (PM) synchronous motor (PMSM) using two types of PMs that consider axial leakage flux using a magnetic equivalent circuit (MEC). Spoke-type ferrite PMSM have the advantage of concentrating magnetic flux; however owing to the shape in which the PMs are arranged along the radial direction, some magnetic flux leaks in the axial direction, which causes inconsistency between the 2D and 3D finite element analysis (FEA) results. Because 3D FEA requires considerable analysis time, using it in the initial design stage of the motor is inefficient. Therefore, we present a new analytical method combined with MEC to overcome the existing inefficient approach. To obtain analysis results equivalent to 3D FEA, the new residual magnetic flux density considering axial flux leakage was applied to 2D FEA PMs using MEC and 2D FEA. The validity of the proposed method was verified through 3D FEA and experiments conducted on the test models using two magnet types.

Electromagnetic Field Analysis of Distributed Winding Permanent Magnet Synchronous Motor Considering Axial Leakage Flux using Two-Dimensional Finite-Element Analysis

This paper proposes a method for the electromagnetic field analysis of permanent magnet synchronous motors (PMSMs) considering the axial leakage flux. To the axial leakage flux while employing two-dimensional (2D) finite-element analysis (FEA), the permeance of the axial leakage path is added into a slot region by increasing the permeability of elements in that region. The increased permeability is calculated based on the permeance relationship of the main magnetic and axial leakage paths, which are calculated using the equivalent magnetic circuit method. The effect of the proposed method is verified by comparing it with the 3-dimensional FEA results. The proposed coupling method uses finite element analysis and is developed from the lumped method proposed in our previous research. The developed method enables the analysis of distributed winding machines, which is not possible with the existing method.

A Study on Reduction of Cogging Torque and Magnet Usage through Intersect Magnet Consequent Pole Structure

Owing to the shortage of rare-earth magnetic materials, various methods are being examined to reduce the use of magnets. One of these is a consequent pole. The consequent pole model can reduce the use of magnets by 50% using only one pole of the magnet and replacing the other pole with iron. However, the consequent pole has the disadvantage of generating back EMF asymmetry and a high cogging torque. In this study, an intersect magnet consequent pole structure is proposed to overcome the disadvantages of the existing consequent pole. Two methods have been proposed to improve axial leakage magnetic flux caused by the intersect magnet consequent pole structure. Finally, we propose a method to reduce the cogging torque and minimize the use of magnets with the same performance standard. For motor design, two-dimensional and three-dimensional finite element analysis was used, and comparative analysis was performed via simulations for several models. The existing model and the final model were compared and verified.

Deep Transfer Learning-Based Sizing Method of Permanent Magnet Synchronous Motors Considering Axial Leakage Flux

The sizing process is necessary to analyze the electromagnetic characteristics according to the major shape parameters during the early design stage of permanent magnet synchronous motors (PMSMs). However, predicting the performance of PMSMs with 2-D finite element analysis (FEA) has errors due to axial leakage flux. Therefore, the axial leakage flux should be considered in the sizing process. The most accurate way to consider the axial leakage flux is to perform 3-D FEA, but it has a disadvantage of high computational cost. In this view, we propose a deep transfer learning-based surrogate modeling method to reduce the computational cost for calculating 3-D FEA-based motor parameters. The transfer learning is conducted using a large amount of 2-D FEA-based and small amount of 3-D FEA-based motor parameters. Using the proposed process, it is possible to accurately predict the motor characteristics according to size-related variables that satisfy the required specifications with small amount of 3-D FEA-based motor parameters. The proposed method was verified through 3-D FEA and experiments for pancake-type PMSMs, which is highly affected by axial leakage flux.

Modelling of a novel progressive cavity pump with a special internal compression process used in oil wells

As a submersible pump, the progressive cavity pump is used to pump fluids from oil wells, and plays a crucial role in determining the oil production. In order to improve the fluid pressurization process and increase the outlet pressure of the progressive cavity pump, a novel all-metal progressive cavity pump (AMPCP) with gradually reducing closed working cavities and variable clearances between its rotor and stator was proposed in this study, so the working processes contain a special internal fluid compression process during operation for petroleum lift. A pair of new rotor and stator with variable clearances were designed, and a novel AMPCP was proposed. Furthermore, the changing law of clearances between the rotor and stator along the axial position of the rotor was studied and controlled, and equations of both their cross-sectional profiles of the rotor as well as stator and the flow area of the AMPCP were derived. The working process including the special internal fluid compression process of the proposed AMPCP and the fluid flows were analyzed by numerical simulations, and the distributions of its internal pressure fields and velocity fields were obtained. Study results show that the proposed AMPCP has a higher outlet pressure and a smaller axial leakage speed than the conventional progressive cavity pump with constant clearances for the same values of other parameters, and the internal compression process of the AMPCP will contribute to increasing the discharge pressure. The research content has important reference value for improving the comprehensive performance and increasing its scope of applications for the oil artificial lift.