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Hall thrusters are electric propulsion devices widely used on spacecraft. The stability of Hall thrusters is often disturbed by low-frequency oscillations (LFOs) around 5–100 kHz, known as the 'breathing mode', typically observed through fluctuations in channel discharge current and plasma parameters. Experimental studies on Hall thrusters with a wide range of sizes show that LFOs exhibit distinct characteristics depending on the channel structures. The size of the channel can modify the particle-wall interactions, electric potential distribution, and electron temperature, thereby influencing the performance of LFOs. Furthermore, the long-term operation of thrusters can cause significant wall erosion, altering the geometry of the discharge channel, which further impacts LFOs. In this work, a one-dimensional fluid model is established to explore the influences of structure sizes and wall erosion of the channel on the LFO characteristics. Both the thruster channel and the plume region are included in the model, and a modified and more precise approach to calculating the electron energy loss at the wall is proposed, which takes into account the influences of secondary electron emission and the channel cross-sectional area. The simulation results indicate that choosing a narrower or longer channel structure has a significantly suppressing effect on LFOs. An erosion model is established according to the cited experimental data to construct the eroded channel structure and to investigate the effect of channel erosion on the breathing mode, which shows that wall erosion can exacerbate LFOs and impact the performance of the thruster. [ABSTRACT FROM AUTHOR]

One of the main factors that limit the lifetime of the Hall effect Thrusters (HETs) is the erosion of the acceleration channel caused by the flux of energetic ions. The magnetic field that is curved and convex towards the anode has been widely used in HETs because of its role in reducing the divergence angle of the ion beam and the channel wall erosion. However, the mechanism of the influence of the magnetic field line curvature on the wall erosion is not clear. Therefore, in this paper, a 2D3V numerical model based on the immersed-finite-element and particle-in-cell (IFE-PIC) method is established to simulate the radial-azimuthal plane near the exit of the Hall thruster. The effect of the tilt angle of the magnetic field line on the wall sputtering erosion rate is analyzed. The results show that compared to the case with the electric field E perpendicular to the magnetic field B, the energy of the ions hitting the channel wall is smaller and the wall erosion is weaker when the magnetic field lines are convex to the anode. As the tilt angle of the magnetic field lines increases from 0° to 60°, the erosion rate is reduced by 90%. Conversely, when the magnetic field lines are convex to the exit plane of the channel, the wall erosion is much more serious compared to the case with the orthogonal electric field E and the magnetic field B. As the tilt angle of the magnetic field line changes from 0° to 60°, the erosion rate is enhanced by 171%. The results in this paper are instructive for the design and optimization of the magnetic field of the HETs. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Erosion characteristics to particle-fluid interaction force is elaborated. • Particles accumulate at the trailing side of blade in rotation of impeller. • Increment in particle size distribution (PSD) intensifies the total pump erosion. • Compartment-wise erosion is greatly influenced by the equivalent particle size. [ABSTRACT FROM AUTHOR]

The compact structure restrains the application of magnetic shielding in low-power Hall thrusters (LpHTs), leading to an asymmetric magnetic field or partial magnetic shielding of the channel wall. This study employs a trim coil to implement an asymmetric magnetic configuration in a 100Â W laboratory Hall thruster. The locations of the maximum curvature of magnetic lines are deflected toward the inner and outer channel wall corresponding to the inward and outward deflected magnetic field configurations. Effects of the magnetic field deflection on the position of the ionization zone, efficiency of the thruster, discharge oscillations, and wall erosion are studied. Optical imaging and electrostatic probes are employed to monitor and scan the plasma beam. Experimental results show that the outward deflection induces a change in the magnetic mirror effect and alters the location of the ionization zone. The radial movement of the ionization zone away from the inner channel wall decreases the near-wall conductivity, reducing the electron current by 13.5% and promoting the current efficiency. Discharge oscillations are suppressed, and the propellant utilization efficiency is improved by 8.2%. Erosion of the channel wall shows an improvement of 40%. Generally, an outward deflected magnetic configuration can significantly improve the performance of LpHTs. [ABSTRACT FROM AUTHOR]

Hall thrusters function as power plants on spacecraft, and its development is crucial for the aerospace industry. The wall erosion of the on-orbit Hall thruster cannot be measured by the control center through ground measurement, but can obtain the discharge current low-frequency oscillation data. Therefore, this study proposes an inversion method to obtain the wall erosion information based on low-frequency oscillation signals and neural networks. Firstly, we use an improved one-dimensional quasi-neutral dynamic fluid mathematical model to build a low-frequency oscillation simulation platform which obtains the corresponding data by varying the cross-sectional area. Secondly, a nonlinear neural network model is established based on the obtained low-frequency oscillation data to invert the wall erosion information. The training function, transfer function, number of hidden layer nodes, and other parameters affecting the results are analyzed and the best model parameters are obtained. The Elman neural network is established and compared with the BP neural network and RBF neural network. The training results of the Elman neural network algorithm present small and stable errors, and the results of multiple predictions remain consistent. The root means square error, average absolute error, and average absolute percentage are 0.0084, 0.0637, and 0.045%, respectively.

The inlet and sideline configuration modifications are widely investigated to alter regional particle fluid flow conditions, considering pressure, turbulence and erosion, therefore to improve energy saving and compartment longevity of centrifugal slurry pump. This paper aims to analyse pump hydraulic and erosion characteristics with proposed pump sideline and inlet configuration retrofit by the DDPM method. Specifically, the inlet guide vane number () and angle (), and sidelining vane (SDV) curvature are investigated in quantitative manner. Accordingly, by adjusting inlet vane configuration and placement, a trade-off between wall erosion and hydraulic performance is observed. The sidelining vane (SDV) design is suggested to avoid resultant counter-current flow formulation, therefore, to mitigate turbulence induced erosion in impeller and volute. However, the SDV modification effect on pump hydraulic head and efficiency is found marginal. In general, this study offers realistic guideline for performance improvement and device upgrading of centrifugal slurry pumps. [Display omitted] • Designated pump configuration effectiveness is justified with particle fluid flow dynamic and erosion condition. • The inlet guide vane number (N v) and angle (β) are analysed in quantitative manner. • The sidelining vane (SDV) modification presents trade-off on performance improvement and erosion mitigation. • The proposed inlet and sideline flow condition impacts volute erosion characteristics greatly. [ABSTRACT FROM AUTHOR]

One of the main factors that limit the lifetime of the Hall effect Thrusters (HETs) is the erosion of the acceleration channel caused by the flux of energetic ions. The magnetic field that is curved and convex towards the anode has been widely used in HETs because of its role in reducing the divergence angle of the ion beam and the channel wall erosion. However, the mechanism of the influence of the magnetic field line curvature on the wall erosion is not clear. Therefore, in this paper, a 2D3V numerical model based on the immersed-finite-element and particle-in-cell (IFE-PIC) method is established to simulate the radial-azimuthal plane near the exit of the Hall thruster. The effect of the tilt angle of the magnetic field line on the wall sputtering erosion rate is analyzed. The results show that compared to the case with the electric field E perpendicular to the magnetic field B, the energy of the ions hitting the channel wall is smaller and the wall erosion is weaker when the magnetic field lines are convex to the anode. As the tilt angle of the magnetic field lines increases from 0° to 60°, the erosion rate is reduced by 90%. Conversely, when the magnetic field lines are convex to the exit plane of the channel, the wall erosion is much more serious compared to the case with the orthogonal electric field E and the magnetic field B. As the tilt angle of the magnetic field line changes from 0° to 60°, the erosion rate is enhanced by 171%. The results in this paper are instructive for the design and optimization of the magnetic field of the HETs.

A 3D gas–slag–metal model for a 120t converter with nozzle‐twisted lance is established, and the gas jet characteristics, slag–metal interface fluctuations, wall erosion, and changes in the molten pool flow field of the nozzle‐twisted lance of the blowing process are studied. The results reveal that, with the increase in the swirl angle, the length of the jet high‐velocity section, maximum velocity, and dynamic pressure decrease, radial distance increases, and wall shear stress first decreases and then increases. With an increase in the blowing time, the fluctuating intensity of the slag surface and the molten steel surface changes significantly, fluctuating slag surface stabilizes after 1.7 s (fluctuating intensity is 1.08–1.12), and fluctuating steel surface stabilizes after 1.3 s (fluctuating intensity is 1.23–1.33). The turbulent kinetic energy of the gas–slag–metal three‐phase interaction area increases and the wall shear stress gradually increases. [ABSTRACT FROM AUTHOR]

Pneumatic conveying of coal particles widely used for environmental friendliness and automation. In this study, orthogonal experiments were carried out in 90° elbows of large coal particles (7–15 mm) to study the effect of the elbow shape, particle size, airflow velocity, and gas supply pressure on elbow erosion. Elbows with double-layer wall structures were designed to present the erosion characteristics, particle breakage ratio, and pressure drop. Results indicate that the angle between the erosion center and the tangential direction of the elbow inlet is approximately 25°–30°. The elbow shape and airflow velocity have significant effects on all three evaluation indices, whereas the particle size and gas supply pressure have significant effects on the pressure drop. The optimal parameters of each factor were confirmed: the blind elbow with a plug, particle size of 9–11 mm, airflow velocity of 20 m/s, and gas supply pressure of 0.4 MPa. [Display omitted] • The angle between erosion centre and elbow inlet was achieved. • The erosion characteristics of four elbows were studied. • Wall erosion, particle breakage and pressure drop were studied by orthogonal design. • The optimal parameters of elbow pneumatic conveying were summarized. [ABSTRACT FROM AUTHOR]

In this work, a novel bottom blowing approach based on inclined injection bubbles to enhance the multiphase flow mixing is proposed. An Eulerian-Eulerian model, validated via published experimental data, is established to numerically reproduce the stirring process of a bottom blowing converter. The effects of injection angle on the multiphase flow characteristics and wall erosion are then systematically investigated. Firstly, the influence of bottom blowing flow rate (10 m/s, 14 m/s, 20 m/s) on the mixing efficiency is discussed. Then, the effects of injection angle (0°, 5°, 10°, 15°, 20°) on the flow characteristics, mixing efficiency and wall erosion are studied in detail based on the bottom blowing flow rate of 14 m/s. The results show that increasing the bottom blowing flow rate is beneficial to shorten the mixing time. With the increase of the injection angle, the mixing time first decreases and then increases. As a result, the optimal angle for the most efficient mixing is determined as 5° when the flow rate is 14 m/s. When the injection angle is 5°, the air velocity on the axis and the negative tangent line is maximum. But the velocity is minimal on the positive tangent line. The injected air forms bubble plume that promotes the circulation of water. The most serious erosion area of the converter wall is located at the junction of molten steel surface and converter wall, followed by vicinity of the tuyere. However, with the increase of the injection angle, the average wall shear stress fluctuates only slightly. The obtained results are helpful to better understand the mechanism of bubble flow field in gas-liquid two-phase and also to improve the smelting efficiency in iron and steel metallurgy. [Display omitted] • A new technology of inclined bottom blowing for optimizing converter steelmaking is proposed. • Optimal injection angle for the inclined bottom blowing process is obtained. • Influence mechanism of injection angle and flow rate on mixing and erosion is revealed. [ABSTRACT FROM AUTHOR]

Cyclones are widely applied in industry, but unscheduled shutdowns due to wall erosion is an urgent problem. To reduce the wall erosion in cyclone separators especially caused by the top ash ring phenomenon, the cyclone with extra inlets is optimized and analyzed by response surface methodology (RSM) and computational fluid dynamics (CFD) in this study. The obtained results indicate a 14.5% reduction in pressure drop and a 10% increase in total separation efficiency for the optimal cyclone. The Lapple cyclone suffers from additional erosion under the roof due to the top ash ring, while the optimal cyclone can avoid this unfavorable phenomenon. Meanwhile, the erosion of the optimal cyclone is also significantly reduced around the cone bottom. [Display omitted] • A cyclone separator with extra inlets is proposed and optimized. • Comparison analysis of the Lapple and optimal cyclone. • The optimal cyclone has a higher separation efficiency and a lower pressure drop. • Top ash ring is observed in the Lapple, which is avoided in the optimal cyclone. • The optimal cyclone reduces the wall erosion caused by particle-wall collision. [ABSTRACT FROM AUTHOR]

Wall erosion is a critical problem encountered in operation and maintenance of centrifugal slurry pumps. This paper presents a numerical study of the particle-fluid flow and wall erosion of industrial pumps. This is done by the dense discrete phase model. The model is validated by comparing the simulated results with the experimental measurements of pump hydraulic performance and jet erosion. Then, the effects of feed solid concentration are quantified under fixed motor power. The numerical results show that with increasing solid concentration, the pump efficiency increases first to a maximum and then decreases. The volute casing suffers the most erosion, which is generally not much sensitive to solid concentration. This is not the case for pre swirl vane and frame plate, whose erosion rate increases rapidly at relatively high solid concentrations. The results suggest that the model can be used as a cost-effective tool for pump design and control. [Display omitted] • The dense discrete phase model is applied to study centrifugal slurry pumps. • It focuses on the effects of solid concentration on flow and wall erosion. • Volute casing suffers most erosion but is much insensitive to solid concentration. • The erosion of pre swirl vane and frame plate is sensitive to solid concentration. [ABSTRACT FROM AUTHOR]

The two major problems with Hall thrusters are the sputtering erosion of the discharge channel wall and the low-frequency oscillation. A new design for a Hall thruster with an innovative buffer chamber, in which part of the propellant is ionized, shows effective ability to restrain the low-frequency oscillation. However, how the preionization affects the erosion of the channel wall has not been well studied. In this paper, a 2-D axisymmetric fully kinetic particle-in-cell and Monte Carlo collision model is developed to investigate the effect of preionization on erosion of the channel wall of a Hall thruster. The geometry of this simulation model corresponds to the typical SPT-70 thruster, and the computational domain includes the whole discharge chamber of the thruster and the near-field plume region. Some scaling laws are introduced to accelerate this simulation. A preionization model and an erosion model are imported into the simulation to investigate the effect of different preionization ratios on the erosion of the channel wall. The results indicate that the effect of preionization on the change in the electric field is not obvious, in that it does not change the energy of the sputter ions significantly. When the preionization ratio increases, the ion incidence angle decreases slightly, but the number of sputter ions increases markedly. Overall, the erosion of the channel wall increases with the increasing preionization ratio. It needs further consideration for the application of the buffer chamber that preionizes the discharge plasma. [ABSTRACT FROM PUBLISHER]

Hall thrusters function as power plants on spacecraft, and its development is crucial for the aerospace industry. The wall erosion of the on-orbit Hall thruster cannot be measured by the control center through ground measurement, but can obtain the discharge current low-frequency oscillation data. Therefore, this study proposes an inversion method to obtain the wall erosion information based on low-frequency oscillation signals and neural networks. Firstly, we use an improved one-dimensional quasi-neutral dynamic fluid mathematical model to build a low-frequency oscillation simulation platform which obtains the corresponding data by varying the cross-sectional area. Secondly, a nonlinear neural network model is established based on the obtained low-frequency oscillation data to invert the wall erosion information. The training function, transfer function, number of hidden layer nodes, and other parameters affecting the results are analyzed and the best model parameters are obtained. The Elman neural network is established and compared with the BP neural network and RBF neural network. The training results of the Elman neural network algorithm present small and stable errors, and the results of multiple predictions remain consistent. The root means square error, average absolute error, and average absolute percentage are 0.0084, 0.0637, and 0.045%, respectively., Competing Interests: The authors declare no conflict of interest., (© 2022 The Author(s).)

Abstract: Hall thrusters are promising space propulsion options for spacecraft. Current major interest in Hall thrusters is their life time evaluation for long time operation. Sputtering erosion of the insulation wall determines the life time of the thrusters. In this study, we present two-dimensional Hybrid-PIC modeling of Hall thrusters, which predicts the wall erosion effect. The principle challenges of our modeling is (1) solving both the plasma generation and acceleration in the channel and the exhaust plume in the near field of the exit and (2) predicting the channel erosion by ion sputtering with deforming the calculation grid. As a result, it was shown that the modeling simulated successive operations and wall erosions by ion sputtering during 2000h operation of a Hall thruster. [Copyright &y& Elsevier]

A curved, convex towards the channel bottom magnetic field is an important feature of an advanced Hall thruster that allows confining the plasma flow in the channel center, reducing the divergence angle of the ejected ion beam, and improving the discharge performance. In this article, the discharge behaviour of a Hall thruster in magnetic fields with different degrees of curvature is simulated with a particle‐in‐cell numerical method, and the effect of curved magnetic field on the ion bombardment and wall erosion and the associated mechanisms are studied and analysed. The results show that, as the curvature of the magnetic field increases, the propellant ionization becomes more confined at the channel center, the potential drop inside the channel decreases, and the acceleration region shifts outside the channel, which lead to the attenuation of the ion energy bombarding the wall and the deviation of the bombardment angle from the optimal sputtering angle. Conversely, the ion flux bombarding the wall near the channel exit increases. Nevertheless, the bombardment energy and angle are the dominant factors for the wall erosion, and the wall erosion rate clearly decreases with the increasing curvature of the magnetic field. These findings are closely related to the behaviour of electron conduction under a curved magnetic field; the relevant mechanisms are clarified in this article. [ABSTRACT FROM AUTHOR]