bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency doubler utilizing hetero gate dielectric tunnel field-effect transistor
Authors: Min Ju Hong , Shin Dongho , Kim Hyunwoo , Kim Jang Hyun
Published: March 2024

With the rapid advancements in wireless communication and high-density integrated circuits, the demand for high-frequency sources has become paramount for transmitting vast amounts of information. Modern communication systems often utilize low-frequency sources at the transmitting end, converting them into high-frequency carriers through Intermediate Frequency (IF) for transmission to the receiving end. However, challenges arise in stabilizing high-frequency Voltage Controlled Oscillators (VCOs), leading to the necessity of Frequency Multipliers (FMs) in high-frequency circuits. While existing FMs face issues like harmonic distortion due to internal nonlinear devices, this paper proposes a single-device Frequency Doubler (FD) operation using Hetero-Gate Tunnel Field Effect Transistor (HG-TFET) with ambipolar characteristics. HG-TFET integrates high-κ (HK) materials and an HG structure in the gate dielectric, achieving independent control of tunneling distances and synchronous operation of source-to-channel and channel-to-drain tunneling currents (I
SC and I
CD) to facilitate FD operation. The paper presents the HG-TFET structure, process flow, and simulation models, followed by an exploration of its operating mechanism and characteristics. The FD circuit configuration, operational principles, and conditions for normal operation are detailed, emphasizing the importance of aligning I
SC and I
CD. The impact of adjusting HK lengths on I
SC and I
CD is analyzed, demonstrating the ability to independently control these currents through HG-TFET. Simulation results for FD operation under varying HK lengths (1–10 nm) validate the proposed approach. Additionally, the paper investigates the influence of dielectric constant (10–32) and gate dielectric thickness (2–5 nm) on FD performance, highlighting the potential for further optimization. In conclusion, this study establishes a foundation for normal FD operation through the symmetrical control of ambipolar and on currents using HG-TFET. The proposed structure and techniques open avenues for improving the efficiency and reliability of frequency-doubling applications in high-frequency circuits.
Investigation of spacer-engineered stacked nanosheet tunnel FET with varying design attributes
Authors: Jain Garima , Sawhney Ravinder Singh , Kumar Ravinder
Published: March 2024

The stacked nanosheet field-effect transistors (SNS-FETs) are potential contenders for sub-7 nm technology. Device miniaturization leads to a larger off-state current and a higher subthreshold slope in SNS-FETs. Unlike SNS-FETs, the stacked nanosheet tunnelling field effect transistors (SNS-TFETs) function as switches in integrated circuits, featuring high performance and low power consumption. The endeavour aims to investigate how each design parameter optimises the switching characteristics of the SNS-TFET device. This paper examines various design attributes, such as different dielectric spacer materials, nanosheet width (NW), nanosheet thickness (NT), source doping, drain doping, etc. The Cogenda Visual TCAD serves as a tool for conducting device simulations. According to the simulation study, the use of a high-k hafnium dioxide (HfO2) spacer produces a higher switching ratio (

7.28
×

10

11

) and a lower subthreshold swing (20.303 mV/decade). Using either low-k or no spacers reduces the overall gate capacitance and unit frequency gain compared to high-k spacers. Upscaling the nanosheet width (10 to 50 nm) enhances the switching ratio by

1.11
×

10

1

and transconductance by 61.92%. Downscaling the nanosheet thickness (6 to 4 nm) at the optimized nanosheet width (50 nm) improves the switching ratio by 1.88. Increasing the gate length from 8 to 16 nm reduces the leakage current by

2.34
×

10

−
2

A and improves the switching ratio by

2.90
×

10

1

.

An increase in the source doping level from

1
×

10

20

to

5
×

10

20

cm−3 results in a

1.07
×

10

2

decrease in the switching ratio and a 2.48-fold increase in the subthreshold swing. Furthermore, the findings indicate that drain doping is crucial in determining ambipolar current. In SNS-TFET, ambipolar current reduces significantly when drain doping is

1
×

10

17

cm−3. Thus, the proposed work addresses the limitations of scaling and optimised design parameter characteristics for low-power nanoscale circuits.
Theoretical study on optoelectronic properties of layered In2O3 and Ga2O3
Authors: Lionel Chrislene , Das Shubham , Banik Diparnab , Koley S
Published: March 2024

Composite oxides have been indeed proved to be valuable materials in optoelectronic applications. The combination of indium oxide and gallium oxide and other materials can lead to enhanced optical and electronic properties, making them suitable for a variety of optoelectronic devices. Meticulous analysis of the various optical properties helped to draw conclusions about the heterostructure of Indium and Gallium oxide and its use as a suitable semiconducting material in the medium bandgap range. The density of states and the band structure have been obtained from the density functional theory calculations. Real frequency phonon density of states supports dynamical stability of the crystal structure. A favorable energy band gap is achieved in the visible region of the spectrum, indicating that this mixed oxide is well suited for optoelectronic devices such as LEDs and solar cells.
Magnetic soliton and breather interactions for the higher-order Heisenberg ferromagnetic equation via the iterative N-fold Darboux transformation
Authors: Liu Xue-Ke , Wen Xiao-Yong , Zhang Ting
Published: March 2024

This paper focuses on a higher-order Heisenberg ferromagnetic equation, which may describe the motion of the magnetic vector of isotropic ferromagnetism. The iterative N-fold Darboux transformation is first constructed to generate the dark and anti-dark magnetic solitons on the non-zero constant backgrounds, bright and dark breathers on the trigonometric function and non-zero constant backgrounds as well as breathers on the trigonometric function and vanishing backgrounds. We discover that the soliton structures of three different components can generate rotation with different constant seed solutions. Meanwhile, the trajectory curve and the direction of the magnetic vector are also discussed from the perspective of magnetism, we find that for constant seed solutions, the motion of the magnetic vector is limited to the hemisphere, while for trigonometric seed solutions, the motion of the magnetic vector can be distributed throughout the whole sphere. These novel phenomena may be helpful to understand the dynamics of the magnetic vector in the magnetic materials.
Complex pattern evolution of a two-dimensional space diffusion model of malware spread
Authors: Cheng Haokuan , Xiao Min , Lu Yunxiang , Bao Haibo , Rutkowski Leszek , Cao Jinde
Published: March 2024

In order to investigate the propagation mechanism of malware in cyber-physical systems (CPSs), the cross-diffusion in two-dimensional space is attempted to be introduced into a class of susceptible-infected (SI) malware propagation model depicted by partial differential equations (PDEs). Most of the traditional reaction-diffusion models of malware propagation only take into account the self-diffusion in one-dimensional space, but take less consideration of the cross-diffusion in two-dimensional space. This paper investigates the spatial diffusion behaviour of malware nodes spreading through physical devices. The formations of Turing patterns after homogeneous stationary instability triggered by Turing bifurcation are investigated by linear stability analysis and multiscale analysis methods. The conditions under the occurence of Hopf bifurcation and Turing bifurcation in the malware model are obtained. The amplitude equations are derived in the vicinity of the bifurcation point to explore the conditions for the formation of Turing patterns in two-dimensional space. And the corresponding patterns are obtained by varying the control parameters. It is shown that malicious virus nodes spread in different forms including hexagons, stripes and a mixture of the two. This paper will extend a new direction for the study of system security theory.
Testing multi-field inflation with LiteBIRD
Authors: Jinno Ryusuke , Kohri Kazunori , Moroi Takeo , Takahashi Tomo , Hazumi Masashi
Published: March 2024

We investigate expected constraints on the primordial tensor power spectrum from the future cosmic microwave background polarization experiment LiteBIRD as a test of multi-field inflation, where we specifically consider spectator models as representative examples. We argue that the measurements of the tensor-to-scalar ratio and the tensor spectral index, in combination with the constraints on the scalar spectral index from the Planck observation, are useful in testing multi-field inflation models. We also discuss implications for multi-field inflationary model building.
Non-Gaussianity in rapid-turn multi-field inflation
Authors: Iarygina Oksana , Marsh M.C. David , Salinas Gustavo
Published: March 2024

We show that theories of inflation with multiple, rapidly turning fields can generate large amounts of non-Gaussianity. We consider a general theory with two fields, an arbitrary field-space metric, and a potential that supports sustained, rapidly turning field trajectories. Our analysis accounts for non-zero field cross-correlation and does not fix the power spectra of curvature and isocurvature perturbations to be equal at horizon crossing. Using the δN formalism, we derive a novel, analytical formula for bispectrum generated from multi-field mixing on super-horizon scales.
Rapid-turn inflation can produce a bispectrum with several
potentially large contributions that are not necessarily of the local shape.
We exemplify the applicability of our
formula with a fully explicit model and show that the new contributions indeed can generate a large amplitude of local non-Gaussianity, f
NL
loc ∼ 𝒪(1). These results will be important when interpreting the outcomes of future observations.
Quantum coherence and entanglement under the influence of decoherence
Authors: Sun Wen-Yang , Ding A-Min , He Juan , Shi Jiadong , Wang Le , Xu Hui-Fang , Wang Dong , Ye Liu
Published: March 2024

In this work, we delve into the dynamic traits of the relative entropy of quantum coherence (REQC) as the quantum system interacts with the different noisy channels, drawing comparisons with entanglement (concurrence). The research results demonstrate the broader prevalence and stronger robustness of the REQC as opposed to concurrence. It’s worth noting that the bit flip channel cannot uphold a constant nonzero frozen the REQC, besides, the concurrence follows a pattern of temporary reduction to zero, followed by recovery after a certain time span. More importantly, the REQC maintains its presence consistently until reaching a critical threshold, whereas concurrence experiences completely attenuation to zero under the influence of phase damping and amplitude damping channels.
Defect production in tungsten under sub-threshold energy irradiation: role of hydrogen and surface effects
Authors: Huang Hao-Xuan , Li Yu-Hao , Li Jin-Liang , Ma Fang-Fei , Ren Qing-Yuan , Liu Li-Min , Zhou Hong-Bo , Lu Guang-Hong
Published: March 2024

Despite the low solubility of hydrogen isotopes (HIs) in tungsten (W), their concentration can reach up to ∼10 at.% after low-energy plasma irradiation. This is generally attributed to the vacancies that may accommodate excessive HIs. However, the kinetic energy of incident HIs transferred to W is far below the energy threshold to create a Frenkel pair, the underlying mechanism of defect production is still unclear. Here, we investigate the influence of H on the defect production in W using the molecular dynamic (MD) simulations. It is found that the threshold displacement energy (TDE) in bulk W slight decreases with the increasing of H concentration. This is due to the formation of H-vacancy complexes, which prevents the vacancy-interstitial recombination. More importantly, the H effects are significantly magnified in the surface region. On the one hand, the maximum kinetic energy transferred from 400 eV H to W can reach up to ∼21 eV due to the double-hit process, which is two times higher than that predicted by elastic collision model. On the other hand, the momentum transferred to W is completely random, including both the recoil direction upward and downward from the surface. Accordingly, the lowest TDE in W surface is only 15–21 eV at sub-surface layers with the depth of 6.7–11.1 Å, which is lower than the maximum kinetic energy transferred to W. Therefore, the low-energy HIs irradiation can create the defects in W surface directly. Our findings provide deep insight into defect production in W at sub-threshold energy and have wider implications for materials performance under low-energy ions irradiation.
Structural optimization of S-CO2 Brayton cycle compressor impeller based on evolutionary algorithm
Authors: Xie Liangtao , Yang Jianguo , Hu Nao , Fan Yu , Sun Sicong
Published: March 2024

As the critical components for marine low-speed diesel engine flue gas waste heat recovery (WHR) supercritical carbon dioxide (S-CO2) Brayton cycle system, the structure of the compressor impeller is optimized by the evolutionary algorithm (EA) based on the co-simulation of the CAESES, ANSYS CFX and Opti Slang. The law of impeller pressure ratio, efficiency and power consumption in S-CO2 Brayton cycle (SCBC) as a function of rotational speed, inlet temperature, pressure and impeller structural parameters are revealed, and the method of improving SCBC efficiency for marine low-speed diesel engine flue gas waste heat recovery is studied. The optimized impeller structure is greatly enhanced in aerodynamic performance and safety, and the isentropic efficiency is increased by 2.54%, the pressure ratio is increased by 35.64%, and the temperature rise is increased by only 4.6%. A 100kW S-CO2 compression cycle test bench was set up to verify the simulation-optimized impeller results. The final results show that the optimized impeller structure, aerodynamic performance and safety are greatly improved. It provides theoretical support for selecting and optimising compressor impellers for marine low-speed diesel engine flue gas waste heat recovery S-CO2 Brayton cycle.
Investigation on unsteady characteristics of flow separation in a supercritical carbon dioxide centrifugal compressor
Authors: Yang Zimu , Jiang Hongsheng , Zhuge Weilin , Qian Yuping , Zhang Yangjun
Published: March 2024

As one of the core components of supercritical carbon dioxide (S-CO2) closed Brayton cycle, the efficiency of S-CO2 centrifugal compressor plays a crucial role. Affected by the special thermophysical properties of S-CO2 fluid, the flow mechanism of S-CO2 centrifugal compressor is different from the centrifugal compressor of conventional fluid, such as air. Previous studies have found that the flow separation within the flow domain of this kind of compressor is easily to occur downstream the pressure surface. Many steady computational fluid dynamics (CFD) studies have been conducted on the S-CO2 centrifugal compressors, but few studies focused on the unsteady evolution of this flow separation. In this paper, the unsteady CFD simulation is carried out in the flow passage of a S-CO2 centrifugal compressor. The solution domain of CFD simulation includes compressor blades, diffuser and volute. The performance and the unsteady flow behavior of S-CO2 centrifugal compressor is obtained. Under low flow rate conditions, the flow separation on the pressure surface of the blade of S-CO2 centrifugal compressor is more likely to occur, causing the decrease of compressor performance. This flow separation has strong unsteady characteristics, which deteriorates several times during a rotation cycle, meanwhile the vortex shedding happens. At the time steps of vortex shedding, the pressure near the trailing edge of the impeller fluctuates greatly, indicating that this unsteady flow separation brings a large flow loss to the S-CO2 centrifugal compressor.
Numerical investigation on the flow resistance characteristics of balance block in the rotary compressor
Authors: Zeng Wang , Pan Xi , Xie Junlong
Published: March 2024

With the increasing demand for energy saving, the air conditioner with variable frequency becomes the mainstream of the market, which leads to a high requirement for the dynamic balance characteristics of the rotary compressor at variable speed conditions. The balance block is the key part in the eccentric shaft system to balance the rotational inertia force brought by the eccentric wheel, and its flow resistance during rotating process has a large impact on the power consumption. In this paper, CFD simulations will be carried out to study the flow characteristics of several different compressor balance blocks and the results can provide reference for the optimization design of the balance block in the rotary compressor.
A numerical study of clogging analysis in submersible drainage pump
Authors: Rakibuzzaman Md , Suh Sang-Ho , Song Kwang Chul , Song Kyung Hee , Zhou Ling
Published: March 2024

Erosion of material surface due to collisions with solid particles has become a challenge to several engineering fields. Therefore, it is necessary to effectively design radial flow pumps that mitigate the sediment particles’ clogging effect from the system performance. This study aims to analyse and identify the clogging development of a newly designed submersible pump using computational fluid dynamics (CFD) techniques. The particle trajectory was accounted Tabakoff–Grant erosion model for predicting the clogging impact. The experimental pump performance results obtained by this study were used to validate the numerical results of the submersible pump. Pump results revealed a good agreement between the two marks, especially the head of the pump was obtained at a flow rate of 0.165 m3/min. When considering the motor power factor of 0.78, the pump efficiency was found to be 46%, and the test result was well-matched. Also, for combined cavitation-erosion, the performance characteristics of erosion rate density increase linearly. At a flow rate of 0.16 m3/min, the erosion rate density of the original model was more significant than the revised model. Furthermore, compared to the original model significantly reduced the adverse clogging effects on the impeller blades of the revised model.
The effect of the impeller eccentricity on the hydrodynamic characteristics of a centrifugal pump
Authors: Fancheng Wanli , Ni Hengtai , Liu Jing
Published: March 2024

To explore the effect of impeller eccentricity caused by shaft parallel misalignment on the hydrodynamic characteristics of a centrifugal pump, a numerical simulation model based on computational fluid dynamics (CFD) is established. The SST k-ω turbulence model is used to describe the flow field in centrifugal pump. The eccentric motion of the impeller is described by the sliding mesh method (SMM). The results indicates that the nonuniformity and instability of flow field will be aggravated with the increment of impeller eccentricity, which then reduce the pump head and efficiency to a certain extent. The radial force exerted on the impeller is directly proportional to the eccentricity of the impeller. In addition, the impeller eccentricity has a significant impact on the peak rotation frequency of shaft frequency. This study can provide a numerical reference for eccentricity fault diagnosis and vibration control of centrifugal pump impellers to carry out optimal design and vibration reduction.
Numerical investigation on vortex dynamics characteristics of a large vertical centrifugal pump operating in the hump region under cavitation conditions
Authors: Yang Gang , Shen Xi , Zhang Desheng , Luo Wenhua , Meng Jia
Published: March 2024

The large vertical centrifugal pump (LVCP) is widely used in major hydraulic engineering such as cross-region water transfer. This paper focuses on the hydraulic stability of LVCP under extremely operating conditions. The transient numerical simulations of cavitation in LVCP in the hump region are conducted based on delayed detached eddy simulation coupled with a homogeneous cavitation model. The main research is the effect of cavitation on the flow pattern and the vortex dynamics of the LVCP under stall conditions. The results of the numerical investigations show that the variation of the pump performance parameters is consistent with the experimental data under cavitation conditions. Under deep stall conditions, the H drop due to cavitation in the pump can happen earlier. Under the critical cavitation of the stall condition, backflow vortex cavitation, sheet cavitation and separation vortex cavitation can be observed at the impeller inlet. The vortex structures generated at the cavitation tail can result in worse flow patterns in the impeller. The vortex dynamics analysis shows that severe cavitation in the impeller deteriorates the inlet conditions of the vaned diffuser and induces sheet cavitation at the LE of vanes. The cavitations in the vaned diffuser accelerate the production and development of stall vortices and result in increased flow instability. The research in this paper can be helpful to improve the operation stability of LVCP.
Analysis of internal flow characteristics of a multistage pump during start-up
Authors: Xia Yinling , Mao Jieyun , Li Guidong , Zhao Danhua , Zhang Jinfeng , Wang Peng
Published: March 2024

In order to study the transient characteristics during the startup process of a multi-stage pump, the Flowmaster software was used to obtain the rotating speed and flow characteristic curves of the pump under different valve openings, and analyze its internal flow and structural characteristics based on numerical simulation. The study results indicate that the time required for the flow to reach a steady state lags significantly behind the time required for the rotational speed to reach a stable state during the initial stage of pump start-up. By comparing the pressure distributions of a multistage pump under quasi-steady state and transient conditions, it can be seen that the internal flow field evolution of the pump under transient condition during the startup process lagged behind that under quasi-steady state condition, which makes using quasi-steady state laws were not suitable for describing the changes in transient flow field. The deformation law of the first-stage impeller under stable and start-up conditions was similar. The impact of increased flow rate on deformation was relatively weak and the difference in deformation values under different flow rates was relatively small under transient condition.
High-temperature molten salt circulating cold salt pump shaft system prestress response analysis research
Authors: Gao Xiongfa , Zhao Yang , Zhu Zhiyu , Zhang Desheng , Wang Daohong
Published: March 2024

To investigate the response characteristics of the rotor system in a high-temperature molten salt pump, a specific model of a cold salt pump was selected as the research object. The natural frequencies and mode shapes, critical speeds, and harmonic response analysis based on modal analysis of the rotor system with and without prestress were computed. The results indicate that with prestress, the natural frequencies of the rotor are higher compared to the rotor without prestress, and there is no clear pattern among the various vibration modes. The calculated critical speed for the second mode is much higher than the rotor’s operating speed. This suggests that the rotor system will not experience resonance at its operating speed, meeting design requirements and ensuring stable operation. When the rotor of the cold salt pump is subjected to unbalanced forces, vibrations occur in the x, y, and z directions. The region with the largest vibration amplitude is located at the fifth-stage impeller. At a frequency of 52 Hz, the corresponding harmonic response displacement reaches its maximum value, and this frequency remains unchanged with variations in the magnitude and position of the unbalanced force. Therefore, it is advisable to avoid operating the rotor system at the critical speeds corresponding to the first and second modes. Furthermore, the operating speed of the rotor system is much lower than the critical speeds corresponding to the first and second modes, so axial unbalanced forces generally do not affect the normal operation of the rotor system.
A computational fluid dynamic method for dense-phase carbon dioxide centrifugal pump
Authors: Han Kejia , Li Zhen , Ju Yaping , Du Zhenming , Liu Zhipeng , Wang Zhenwei , Zhang Chuhua
Published: March 2024

As an advanced approach for large-scale low-carbon utilization of fossil energy, the carbon capture, utilization and storage technology is a promising means to achieve the carbon-neutrality target by 2060. Among the most widely used approaches for carbon storage is the enhanced oil recovery technique, for which the centrifugal pump is used to inject high-pressure dense-phase carbon dioxide (CO2) into the stratum. This work focuses on real fluid effects and inter-stage matching deviation from the incompressibility assumption for a dense-phase CO2 centrifugal pump, of which the inlet condition is close to the fluid critical point. With a thermophysical-state table for CO2 based on the thermophysical-property database of the National Institute of Standards and Technology embedded into a computational fluid dynamics solver, a numerical simulation method for compressible dense-phase CO2 pumps is established. The developed method is validated in the 50kW main compressor for a supercritical CO2 cycle and then applied to the simulation of a multistage dense-phase CO2 pump designed for carbon storage. The stage with the most remarkable fluid compressibility is determined, which provides a priori basis for the follow-up design optimization of the pump. This work is of promising application prospect for design of advanced dense-phase fluid machinery.
Comparative analysis of internal flow characteristics and particle trajectories of centrifugal pumps with different impeller structures under solid-liquid two-phase flow conditions
Authors: Chen Zhengsu , Heng Yaguang , Jiang Qifeng , Liu Tielin , Luo Xipeng
Published: March 2024

The disc pump is a non-conventional centrifugal pump that utilizes centrifugal force and boundary layer effects to transport fluids. This pump is widely used in industries such as petrochemicals. However, due to the presence of particles in the solid-liquid two-phase flow, it causes wear and performance degradation of the pump’s flow components. However, due to the presence of particles in the solid-liquid two-phase flow, it can cause wear and performance degradation of the pump components. To study the internal flow characteristics of solid-liquid flow and the particle trajectory in a bladed disc pump, numerical simulation method was adopted to perform steady-state numerical simulation of spherical particles with different diameters (0.1 mm, 0.25 mm, 0.4 mm) in the bladed disc pump. The results indicate that compared to conventional centrifugal pumps, the performance of the bladed disc pump is lower. The variation in particle diameter has a minor influence on the intensity of the internal flow field in the bladed disc pump. The particle trajectories inside the impeller of the bladed disc pump are more chaotic, with larger diameter particles exhibiting a wider range of trajectory variations, while smaller diameter particles maintain relatively stable motion trajectories.
Cavitation performance analysis and optimal design of the portable electric-driven axial flow pump
Authors: Tian Ding , Lu Rong , Zhu Han , Liu Jinfeng , Zhang Yong , Wei Guangjuan , Li Gangyuan , Si Qiaorui
Published: March 2024

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.
Pressure pulsation test of Wanjiazhai Francis turbine at different loads
Authors: Li Jinjun , Liu Qiang , Wang Weigang , Song Xijie , Wang Zhengwei , Zhu Di , Tao Ran
Published: March 2024

In this paper, the pressure pulsation of Wanjiazhai Francis turbine at six monitoring points under different loads is monitored. Fast Fourier Transform(FFT) was used to perform time-frequency conversion, and the data was analyzed from both time-domain and frequency-domain perspectives. From a time perspective, the pressure pulsation at the upstream bladeless area is the most sensitive to changes in power. From a frequency perspective, the frequency components of pressure pulsation are more complex when P=40kW, while the frequency domain diagrams of pressure pulsation at each monitoring point are similar when P=80kW and P=120kW.
Application of DMD method to eccentric self-excited vibration of tubular turbine runner
Authors: Wu Yanzhao , Hu Zilong , Zhu Di , Tao Ran , Xiao Ruofu
Published: March 2024

Tubular turbines are widely used in the development and utilization of low-head marine energy. The cantilever type runner inevitably leads to gap between the chamber and blade tip, and non-standard installation can easily lead to eccentric runner, affecting the safe and stable operation of turbine. The overall process of self-excited vibration is an obvious nonlinear process, so the applicability of traditional methods needs to be discussed. In recent years, reduced-order modelling methods based on linear dynamic systems have gradually been introduced into the analysis of hydraulic machinery, and have achieved certain results. Therefore, this study combines computational fluid dynamics (CFD) and dynamic mode decomposition (DMD) methods to conduct low-dimensional mode decomposition and comparative analysis of self-excited vibration caused by different runner eccentricities of tubular turbine. The research shows that as the runner eccentricity continues to increase, the modal frequency distribution of self-excited vibration becomes complex. The DMD method disassembles the low-level representations of self-excited vibration signals, greatly enriching the understanding of eccentric self-excited vibration of the runner, and providing assurance for the safe and stable operation of tubular turbines.
On improved active disturbance rejection controller design for a pumped storage hydro unit
Authors: Ding L H , Pei J
Published: March 2024

The pumped storage hydro unit (PSHU) shows bad dynamic performance because of the frequent switching of working conditions and the S-shaped characteristics of pump turbine. This paper proposes an improved fixed-time active disturbance rejection controller to improve the control performances and counteract the influences of uncertainties including modeling error and friction. A disturbance observer is designed to estimate the total uncertainty by using the information of the states and outputs, compensating the adverse effects of the total uncertainty actively by feed-forward principle as a result. The outstanding benefit of the disturbance observer lies in that it can be designed separately from the original controller and can enhance the performances of the PSHU without changing the original controller. Simulation results show that comparing with the conventional active disturbance rejection controller, the improved active disturbance rejection controller has better adaptability and higher robustness towards the system load disturbance, and the dynamic performance of the system is improved.
Numerical investigation of hydrodynamic damping of a pitching hydrofoil at different flow regimes
Authors: Bahrami Mohammad Amin , Raisee Mehrdad , Cervantes Michel J , Nourbakhsh Ahmad
Published: March 2024

Due to the development of intermittent renewable energy resources, hydropower plants are mostly operated under off-design conditions. This may lead to natural frequency excitation shortening the turbine life-span. To accurately estimate the fatigue life, it is necessary to evaluate the hydrodynamic damping parameters. In the present study, different flow regimes and their relationship with hydrodynamic damping are analyzed numerically using the γ - Reθt
transition SST ĸ - ω turbulence model. The test case is a NACA0009 hydrofoil pitching around its center of mass. A good agreement between the present and previous numerical results is obtained. Consistent with the literature, hydrodynamic damping coefficient demonstrate consistently two different regions. The phase shift between the displacement and moment increases with the rise of the pitching frequency. After reaching a peak value at a reduced frequency of around κ = 5, the phase shift starts to decrease, and eventually approaches zero again. The damping behavior demonstrates an opposite trend. First, it reduces in spite of the phase shift increase, and after the inflection point, where the flow field changes from the drag mode to the thrust mode, it rises due to the torque development. The maximum of the damping occurs at the low frequencies.
Active control of thermoacoustic oscillation based on the x-nlms algorithm
Authors: Zeng Qingwen , Hu Chunyan , Miao Keqiang , Sun Jiaxian
Published: March 2024

Thermoacoustic oscillations, caused by the coupling of unsteady heat release and pressure fluctuation, can result in severe damage to the combustion chamber of gas turbines. This paper presents a novel approach to active control of thermoacoustic oscillations, which is based on a Filtered-X normalized least mean square algorithm (X-NLMS). The controller employs the pressure magnitude at a predetermined axial position preceding the flame as the control variable, which is acquired through microphones installed around the combustor periphery. Control is accomplished by modifying the output frequency and phase of a loudspeaker. The performance of the control system is evaluated through simulations on a Rijke tube, with the classical PID method used as a comparison. The experimental results showcase the efficacy of the X-NLMS algorithm in actively controlling thermoacoustic oscillations. By adaptively estimating and attenuating pressure fluctuations, the algorithm effectively suppresses the undesired acoustic disturbances associated with thermoacoustic instabilities. Comparative analysis reveals that the X-NLMS algorithm outperforms PID control in terms of oscillation suppression and system stability. Its ability to adapt to time-varying dynamics and its low computational complexity make it a promising candidate for real-time thermoacoustic control applications.
Study of the effect of rotating channel rib structure on fuel flow and heat transfer characteristics
Authors: Dong Mengqiang , Huang Hongyan
Published: March 2024

Hypersonic vehicles can be affected by incoming hot air. In order to ensure that the power generation turbine blades can operate properly, the fuel in the engine is used to cool the turbine blades. In this paper, the heat transfer characteristics of fuel in smooth and 45° ribbed channels under rotating conditions are investigated. Their results show that, unlike the smooth channel, the heat transfer coefficient of the 45° ribbed channel decreases as Ro increases under the combined influence of the rib structure and the physical properties of the fuel. The rib structure disrupts the high-velocity fluid near the trailing surface of the centrifugal section, which promotes doping between the fuels and weakens the effect of the Coriolis force. The Nu increase in ribbed channels ranged from 11.4% to 55.1% compared to smooth channels.
A review of research on turbines for supercritical carbon dioxide power systems
Authors: Hu Zhuo , Jiang Hongsheng , Zhuge Weilin , Qian Yuping , Zhang Yangjun
Published: March 2024

Supercritical carbon dioxide (S-CO2) Brayton cycle has been known as a potential power cycle technology because of its high efficiency, compact structure and suitability for different heat sources. As one of the key components in the cycle, the turbine has an important impact on the cycle efficiency. Compared with traditional steam and gas turbines, S-CO2 turbines have high working pressure and small size. The internal flow characteristics are significantly different. In this paper, the research progress of S-CO2 turbines in recent years is reviewed. The design and performance evaluation methods for S-CO2 turbines of different types and power levels are summarized, and research on loss correlations and optimization algorithms are introduced. The features of flow field in S-CO2 turbines are discussed. Current studies mainly evaluate the flow field and flow losses through Computational Fluid Dynamics (CFD), and some studies further analyze the influencing mechanism of turbine geometric parameters on flow characteristics. The applications of multi-physical field analysis on S-CO2 turbines are also reviewed. The construction and operation of S-CO2 test loops, and relevant turbine experimental study findings are introduced. Future research directions of S-CO2 turbines are proposed.
Flow field prediction of S-shaped shock vectoring nozzle with rear deck based on deep learning
Authors: Miao Mingcong , Shi Jingwei , Liang Shuang , Wang Zhanxue , Zhou Li
Published: March 2024

The S-shaped shock wave vectoring nozzle with afterdeck can significantly improve the overall performance of the exhaust system, taking into account Thrust vectoring, infrared stealth and afterbody fusion. One of the technical difficulties in its design process lies in the complex flow field characteristics under different operating conditions. Currently, the mainstream method is to obtain nozzle flow field characteristics through CFD numerical simulation, but the CFD method is time-consuming and costly. Therefore, based on the depth learning principle, a depth Convolutional neural network based on U-NET framework is established to quickly predict the flow field of S-shaped shock wave vectoring nozzle with afterdeck. Using CFD data for training, the results show that the depth learning model has high prediction accuracy and can clearly predict the flow field characteristics inside the nozzle, especially the secondary flow and the complex wave structure near the afterdeck. The correction Coefficient of determination of the prediction model is greater than 0.97. And the time consumption is about 0.0689% of that of a conventional solver. It has good application prospects in quickly evaluating the flow field of S-shaped nozzles.
Experimental study on the internal temperature rise of a high-speed canned motor pump for liquid rocket engines
Authors: Wang Jiangning , Cai Guobiao , Yu Nanjia , Zhou Chuang , Gu Xiaoming , Cao Li
Published: March 2024

High-speed electric pumps are now gradually applied in liquid rocket engines. Compared with the pumps with dynamic seals, the canned motor pumps are more reliable, and thus suitable for delivering risky propellants. However, the partial flow diverted to the air-gap for cooling and lubrication faces the risk of overheating caused by its friction against the rotor. This paper performed an experiment on this issue with a high-speed canned motor pump for a notional rocket engine. Impellers with and without balance holes, as well as different configurations of jet holes, were adopted and their effects were analysed. Results showed that the internal temperature rise decreased by up to 78% when the balance holes were removed, and decreased by up to 40% when the jet hole configuration was modified. Both factors influenced the internal temperature rise by varying the flow rate of the cooling recirculation. The study suggested that the high-speed canned motor pump should be designed with an appropriate flow rate of the cooling recirculation, so as to control the temperature rise of the propellant and ensure safe operation of the rocket engine.
Effect of surface roughness on lubrication performance of water-lubricated bearing for energy recovery turbocharger
Authors: Ning Yanqiang , Zhang Desheng , Li Yan , Ye Xiaoyan , Ding Jingfei
Published: March 2024

In this study, the lubrication performance of the water-lubricated bearing of the energy recovery turbocharger was studied considering the surface roughness. By simulating the rough surface of the bearing with the Weierstrass-Mandelbrot function and combining the water film thickness equation, Reynolds average equation, Greenwood-Tripp contact model and motion equation, the theoretical model of water-lubricated bearing is established and its solution is developed. The variational rules for the hydrodynamic pressure and force, asperity contact pressure and force, and other performance parameters of the water lubricated bearings during start-up and stable operation were obtained by solving this model, and the effect of different surface roughness on the start-up performance and steady operation lubrication performance is studied. The results show that the hydrodynamic force increases rapidly and the asperity contact force sharp decreases during the early start-up stage, and the smaller the surface roughness, the faster the hydrodynamic increase and asperity contact force decrease. The thickness distribution and pressure distribution of water film with different surface roughness have slight differences in stable operation. Therefore, the surface roughness has an important effect on the lubrication performance of the water lubricated bearing in the start-up stage, but has little effect on the stable operation.
Control of separated flow at low Reynolds number around NACA0012 airfoil by boundary layer suction
Authors: Wang A , Lai H
Published: March 2024

The separated flow at low Reynolds number around the NACA0012 airfoil is numerically studied by large-eddy simulation. Strategies of boundary layer suction to control flow separation are investigated. A method of using two-zone suctions, near the leading edge and near the trailing edge, are calculated. Based on verification with direct numerical simulation (DNS) and experimental data, the results of the lift and the drag, the vortices, and the strength of near-field pressure fluctuations, are checked. The results show that the two-zone suctions can supress flow transition and separation, thereby increase the lift and reduce the drag. The shedding of vortices is weakened, and the near-field pressure fluctuations are attenuated. For comparison with the two-zone suctions, the strategies of suction near the leading edge only and suction near the trailing edge only are also studied. It is found that suction near the leading edge only may suppress transition and delay separation when the suction zone is large enough, but the flow property deteriorates due to shedding vortices in the wake. The suction near the trailing edge only may improve the flow performance by reducing the size of the vortices in the rear section of the airfoil and in the wake region, but it has little effect on the separation bubble and transition.
Compressed air energy storage system: Effect of variable relative stator installation angle on nozzle governing turbine performance
Authors: Guan Yin , Li Wen , Zhu Yangli , Wang Xing , Zhang Yifeng , Chen Haisheng
Published: March 2024

The air storage pressure of compressed air energy storage system gradually decreases during the process of energy release, and a reasonable air distribution method for the turbine is required to make the turbine work efficiently in this process. In this paper, based on the single nozzle governing method, the effect of the variation of the full circumferential relative stator installation angle on the system performance improvement under the rated output work condition is investigated. It is shown that the specific work of the variable relative stator installation angle can be improved by up to 6.3 % relative to the design stator installation angle and up to 15.7 % relative to the throttle governing method under the base pressure of 10.0 MPa. With the same absence of throttling losses, the specific work of 3-nozzle inlets method is higher than that of 4-nozzle inlets method, and the turbine internal losses are reduced by 10.6 %. This study provides a theoretical basis for the design, optimization and operation control of nozzle governing turbines.
Optimized design of smart toilet spray bar flow channel based on CFD
Authors: Zhou Qiwei , Zhu Chenbing , Chen Jianchong , Yang Xuelong
Published: March 2024

Currently, there are significant issues with the intelligent toilets available on the market, such as a large swing of the spray bar when spraying water column and eccentricity. This paper presents four optimization schemes for the intelligent toilet spray bar channel by analysing and redesigning a specific model. Computational Fluid Dynamics (CFD) technology was employed to analyse the water flow conditions inside the spray bar of the intelligent toilet. The calculation results indicate that for the same water inlet flow rate, the optimal structure in optimization scheme 1 is the block with a length (L) of 1.5 mm. In optimization scheme 2, the optimal structure is the block located at position (3). In optimization scheme 3, the optimal structure is a 15° rotation, which exhibits the least swirls and pressure loss while maintaining the prototype structure. When the prototype structure is modified, the optimal structure in optimization scheme 4 is the excision bend pipe. This structure exhibits the lowest swirl number and pressure loss among all the optimization schemes. The determined structure offers valuable insights for enhancing the flow characteristics of the improved product.
Numerical erosion prediction of aluminum induced by cavitating jet using an Eulerian–Lagrangian method
Authors: Wang Zhengdong , Li Linmin , Li Xiaojun , Zhu Zuchao
Published: March 2024

Cavitation-induced erosion in pump machinery is a significant issue that leads to material loss and increased operating costs. This study develops a numerical method based on an energy balance approach to address the risk of cavitation erosion. Compared with other published methods, three improvements are made. Firstly, it assumes that the local instantaneous pressure is the driving force behind cavity collapse, rather than the far-away ambient pressure field. Secondly, it counts erosion only at the moment that the released shock wave is strong enough to cause surface damage. Thirdly, an Eulerian–Lagrangian method is introduced to simulate multiscale cavitation, in which the volume of fluid (VOF) method and a discrete bubble model (DBM) are combined to reproduce resolvable water-vapor interfaces and unresolvable discrete bubbles, respectively. The developed numerical modeling framework is validated by predicting the erosion of pure aluminum surface caused by a cavitating jet, and it is shown that the simulated erosion region fits well against the experimental results. Additionally, appropriate model coefficients of the erosion prediction method are introduced to achieve quantitative prediction of material mass loss, and the detailed erosion behavior is discussed.