bluuebunny/crossref_metadata_2025 huggingface dataset:
Comprehensive performance study of boiling battery temperature management system with trapezoidal fins microchannel cooling plate
Authors: Tang Zhiguo , Lu Kuan , Li Yan , Cheng Jianping
Published: December 2024

A flow-boiling battery temperature management system (BTMS) is considered a valid way to achieve heat dissipation of high-energy-density batteries at high charging and discharging rates due to its strong heat-transfer performance. A microchannel cooling plate with trapezoidal fins (TFMP) to introduce secondary flow between adjacent main channels is proposed in this study, as part of a flow-boiling BTMS to cool rectangular lithium-ion batteries. The results show that, as the inlet Reynolds of the coolant number inside the cooling plate increases from 25 to 825, the heat transfer mode of the coolant becomes from boiling heat transfer to single-phase convective heat transfer. Meanwhile, in the boiling heat-transfer mode, compared with traditional straight channels, as the long edge length of the trapezoidal fins, the width of the secondary channel, and the bottom angle of the fins increase, the temperature characteristics of the batteries, and the heat transfer performance and overall performance of the cooling plate are improved, while the flow resistance and entropy production of the cooling plate are also smaller. At a 3C discharge rate, when the Reynolds number is 450, the coolant is boiling heat-transfer mode, mainly, and the BTMS has the highest comprehensive performance. At this time, compared to traditional straight channel cooling plate, the heat transfer performance and the performance evaluation criterion of the TFMP are enhanced by 1.89 and 1.31 times, respectively, while the irreversible loss is only 64% of it, and the maximum temperature of the batteries (Tmax) in the BTMS is 34.03 °C, their maximum temperature difference (ΔTmax) is 2.51 °C, which is 2.55 and 1.37 °C lower than the BTMS with traditional straight channel cooling plate, respectively.
Broadening mechanisms of donor-bound exciton photoluminescence in Ga-doped ZnO nanowires
Authors: Watkins S. P. , Riahi S. , Lister D. , Lohn C. , Stirling K. , Mohammadbeigi F. , Darbandi A. , Senthil Kumar E.
Published: December 2024

Donor spins in ZnO NWs have promise for quantum information (QI) applications due to high crystalline quality, narrow excitonic luminescence linewidths, and a direct bandgap of this material. It is important to understand the processes that can lead to inhomogeneous broadening of the excitonic transitions for realization of QI devices. We investigate the effect of Ga dopant concentration on the low temperature photoluminescence (PL) of Ga-doped ZnO nanowires. Spectrometer-resolution-limited donor-bound exciton (D0X) PL lines are observed at low concentrations with linewidths of around 0.1 meV. A clear increase in the Ga D0X line is observed as trace amounts of Ga are added. Above a certain concentration threshold, we observe a strong increase in the lateral growth coupled with a significant tail on the low energy side of the D0X emission, which scales linearly with dopant precursor concentration. We have analyzed this behavior using different models, including a model based on a bound exciton wavefunction overlap with neigbhouring donors and a Stark effect model due to random charged impurities. We rule out both of these models based on PL excitation spectroscopy measurements and show that a simple exponential model of the Urbach form gives the best fit and points to disorder in the more heavily doped shells.
Sparsified time-dependent Fourier neural operators for fusion simulations
Authors: Rahman Mustafa Mutiur , Bai Zhe , King Jacob Robert , Sovinec Carl R. , Wei Xishuo , Williams Samuel , Liu Yang
Published: December 2024

This paper presents a sparsified Fourier neural operator for coupled time-dependent partial differential equations (ST-FNO) as an efficient machine learning surrogate for fluid and particle-based fusion codes such as NIMROD (Non-Ideal Magnetohydrodynamics with Rotation - Open Discussion) and GTC (Gyrokinetic Toroidal Code). ST-FNO leverages the structures in the governing equations and utilizes neural operators to represent Green's function-like numerical operators in the corresponding numerical solvers. Once trained, ST-FNO can rapidly and accurately predict dynamics in fusion devices compared with first-principle numerical algorithms. In general, ST-FNO represents an efficient and accurate machine learning surrogate for numerical simulators for multi-variable nonlinear time-dependent partial differential equations, with the proposed architectures and loss functions. The efficacy of ST-FNO has been demonstrated using quiescent H-mode simulation data from NIMROD and kink-mode simulation data from GTC. The ST-FNO H-mode results show orders of magnitude reduction in memory and central processing unit usage in comparison with the numerical solvers in NIMROD when computing fields over a selected poloidal plane. The ST-FNO kink-mode results achieve a factor of 2 reduction in the number of parameters compared to baseline FNO models without accuracy loss.
Metamaterials for high-performance smart sensors
Authors: Guan Renquan , Xu Hao , Lou Zheng , Zhao Zhao , Wang Lili
Published: December 2024

In recent years, metamaterials have shown great potential in various fields such as optics, acoustics, and electromagnetics. Sensors based on metamaterials have been gradually applied in daily production, life, and military. Metamaterials are artificial materials with unique properties that ordinary materials do not possess. Through clever microstructure design, they can achieve different properties and have demonstrated significant potential in areas like holographic projection, absorbing materials, and super-resolution microscopy. Sensors are devices that convert external environmental changes into recognizable signals, playing a crucial role in various fields such as healthcare, industry, and military. Therefore, the development of sensors with high sensitivity, low detection limit, wide detection range, and easy integration is of great significance. Sensors based on metamaterials can not only achieve these improvements but also offer advantages like anti-interference and stealth sensing, which traditional sensors lack. These enhancements and new features are significant for the sensor field's development. This article summarizes the benefits of metamaterial sensors in terms of increased sensitivity, expanded detection range, and ease of system integration. It also systematically discusses their applications in various fields such as biomedical and gas sensing. The focus is on the potential applications and development trends of metamaterial-based sensors in the future of human life, providing systematic guidance for the field's advancement.
Numerical simulation study of hydrogen/air flame propagation and detonation characteristics in an annular cross section of gas turbine combustion chamber
Authors: Zhao Minghao , Qiu Hua , Liang Yong , Xiong Cha , He Xinlu , Chen Huangwei
Published: December 2024

The trends and future directions of hydrogen safety research cannot be separated from the thermodynamic behavior of combustion and explosion, hydrogen spontaneous combustion, flame propagation behavior, thermodynamic mechanisms, and other related topics. In this paper, through the method of numerical simulation, considering the hydrogen flame propagation and detonation characteristics in the annular section of the combustion chamber commonly used in gas turbines, the form of detonation and detonation impact in the channel are evaluated. By discussing the deflagration to detonation transition of hydrogen/air premixed gas and premixed gas under different working conditions, it is found that the flame in the annular channel propagates close to the inner wall and forms a strong expansion and turbulence between the outer wall and the outer wall of the flame. The flame surface and the airflow shear accelerate the detonation of hydrogen. The area close to the wall on the outer side of the flame surface and the tip of the flame surface are prone to set off detonation. The high-pressure area after the detonation mainly acts on the symmetrical end face of the outer wall surface and ignition area. There is a critical working temperature to make the impact strength strongest when the detonation occurs. Reducing the equivalence ratio of the filling gas can significantly reduce the reaction speed and weaken the impact strength of the wall. When the equivalence ratio is less than a certain value, the filling gas is completely consumed in the form of deflagration.
On the singularity of Lie-transform perturbation approach to the guiding-center problem
Authors: Lin W. H. , Garcia J. , Li J. Q.
Published: December 2024

We present a novel scheme of carrying out the Lie-transform perturbation for the guiding-center motion, with an aim at addressing directly the problem of singularity, which exists intrinsically in the determining equation for the generating vector, and which gives rise to the formidable gauge functions in the pure oscillating part of the Lie transformation. While such gauge functions must be approximately solved from some partial differential equations in most applications of Lie-transform perturbation, it can be naturally produced through explicit integral over the gyro-angle in the present scheme, which is characterized by a staggered determination of the generating vectors and leaves no unaccountable error of high order in all the succeeding transformation. Based on such scheme, a formalism of guiding-center transformation has been derived in a unified manner retaining the effects of the strong E×B shearing as well as those of electromagnetic fluctuations.
An evaluation of two-way coupled Euler–Lagrange methodology through direct comparison with particle-resolved simulations
Authors: Kim Jungyun , Apte Sourabh V. , Balachandar S.
Published: December 2024

The two-way coupled Euler–Lagrange (EL) methodology is an efficient computational tool for investigating multiphase flows, enabling simulations with tens of millions of particles without Reynolds number limitations. This method resolves the fluid motion on scales larger than a filter length scale, which typically exceeds the particle size and the inter-particle spacing. However, EL simulations require closure models to account for unresolved scales. This work compares particle-resolved (PR) and EL simulations to assess the accuracy of EL solutions. We examine how well EL simulations capture the statistical distribution of particle and fluid quantities in multiphase flows by comparing them with PR solutions. The focus is on modeling the force on particles and understanding the influence of the filter scale on EL simulation accuracy. The results show that, due to variations in feedback forces at individual particle locations, the forces computed in the EL method do not consistently correlate with those obtained from the PR simulations.
Correlation between spin-dependent recombination centers and long-lived polarons generated in organic photovoltaic devices revealed by successive ESR and EDMR measurements
Authors: Suzuki T. , Marumoto K.
Published: December 2024

Using a successive detection technique with electron spin resonance (ESR) and electrically detected magnetic resonance (EDMR), this study clarifies the quantitative correlation between photoinduced spin amounts and spin-dependent recombination (SDR) currents in organic photovoltaic devices (OPVs). Using this unique method of sequentially switching between ESR and EDMR measurements under light irradiation, we find that the intensities of light-induced ESR and EDMR spectra increase along with the light irradiation power. Although positive correlation exists between the number of photo-generated radicals and the SDR currents, the relation is not proportional, which demonstrates that most of the photo-generated radicals are residual accumulated charges. Additionally, phases of the EDMR spectra under light irradiation were found to be changed because of a delay of modulated EDMR signals. The phase variation is probably caused by recombination centers: positive polarons that have arrived at the interface between an aluminum electrode and an active layer by charge drifting after charge separation. Because positive polarons are expected to transport positive charges to the opposite-side electrode of the aluminum as a negative charge collector, this leakage current can be a factor of disturbing an optimal charge collection. This combined technique of ESR and EDMR is useful to explore the different roles of polarons in the photovoltaic conversion processes, thereby providing important information for improving the fill factors and open-circuit voltages of the OPVs, which generate long-lived polarons.
A windowed mean trajectory approximation for condensed phase dynamics
Authors: Polley Kritanjan
Published: December 2024

We propose a trajectory-based quasi-classical method for approximating dynamics in condensed phase systems. Building upon the previously developed optimized mean trajectory approximation that has been used to compute linear and nonlinear spectra, we borrow some ideas from filtering trajectory methods to obtain a novel semiclassical method for the dynamical propagation of density matrices. This new approximation is tested rigorously against standard multistate electronic models, spin-boson models, and models of the Fenna–Matthews–Olson complex. For dissipative systems, the current method is significantly better or as good as many other semiclassical methods available, especially at low temperatures and for off-diagonal density matrix elements, whereas for scattering models, the current method bears similar limitations as mean-field propagation schemes. All results are tested against the numerically exact hierarchical equations of motion method. The new method shows excellent agreement across various parameter regimes with numerically exact results, highlighting the robustness and accuracy of our approach.
Dual effects of pressure difference for long-wave stratified flow in horizontal microchannels
Authors: Zhao Qishan , Li Shicheng , Ma Xuehu
Published: December 2024

In this work, the linear stability analysis combining with energy balance theory is performed to clarify the suppressing and boosting long-wave instabilities driven by pressure difference in horizontal microchannels as well as its corresponding physical meanings. It is found that, for a specific fluid combination, there exists a certain relative liquid film thickness (hN,c) at which the disturbance work done by interfacial shear stress over unit wavelength (denoted by ISS) is exactly equal to the total viscous dissipation rate over unit wavelength within both phase bulk flows (denoted by DIStot). When the liquid film thickness (hN) exceeds hN,c, ISS is smaller than DIStot, indicating that the initial disturbance energy cannot be replenished from the primary flow until its completely disappear due to the viscosity dissipation. Conversely, ISS is larger than DIStot, indicating that the initial disturbance can acquire energy from the primary flow and grow up. The strength of suppressing and boosting effect can be influenced by liquid film thickness, flow rate, and channel height. However, the demarcation of the dual effects remains unchanged. An analytical expression of hN,c with respect to the viscosity ratio is established by means of long-wave approximation method, which matches well with the numerical results. The energy balance mechanisms revealed in the present study provide a new insight into the wave mode in the confined space and help the design of microfluidic systems.
Advancing graph neural network architecture for fluid flow and heat transfer surrogate modeling: Variable boundary conditions and geometry
Authors: Travnikov Vladislav , Plokhikh Ivan , Mullyadzhanov Rustam
Published: December 2024

Graph neural networks (GNNs) represent a promising instrument for surrogate modeling, capable of handling unstructured computational meshes naturally. We address a typical issue of the accuracy degradation for larger computational domains due to the limited receptive field of GNN models and long-range global interactions between nodes of the mesh. We propose a modification of the GNN architecture allowing to improve the accuracy by a factor of 3 without significant increase in computational costs. The validation tests of the model concentrate on the two-dimensional stationary fluid flow around a bluff body in a channel and corresponding heat transfer. The problem formulation includes bluff bodies of randomly generated shapes and various boundary conditions. The model shows a robust performance for the out-of-domain data, i.e., the flow over an airfoil for different angles of attack.
Radiation-photon converter based on GaN single crystal coupled with multi-quantum-well luminescence structure
Authors: Wang Fangbao , Zhang Silong , Wang Jing , He Shiyi , Lu Xing , Wang Jianfeng , Zhong Silei , Zeng Deke , Zhou Leidang , Chen Liang , OuYang Xiaoping
Published: December 2024

Converting radiation into optical signals is a fundamental method for nuclear radiation detection. However, traditional scintillators encounter a trade-off between efficiency and response speed. This research proposes a radiation-photon converter constructed from multi-quantum-well (MQW) structures integrated into radiation-sensitive materials, providing a unique solution to this challenge. The prototype was fabricated using a homogeneous epitaxial layer of GaN on a semi-insulating substrate. The radiation-photon conversion process was facilitated by directing charge carriers generated from radiation energy deposited in the semi-insulating substrate to the MQW layer via an external electric field. The converter exhibited a sensitive and rapid response to x-ray irradiation, enabling modulation of the excited photon wavelength through the MQW layers. Luminescence spectrum tests demonstrated that the net luminescence intensity increased with rising device voltage. Imaging experiments revealed that the grayscale values of device photographs, under the combined influence of electric fields and x rays, correlated with the trend in net current variation. These findings confirmed the effective conversion of radiation into optical signals through the modulation mechanism of the electric field, highlighting significant implications for the development of advanced radiation detection methodologies.
Design of a novel high-speed tensile method for testing the high strain rate tensile behavior of aluminum alloys
Authors: Chen Li , Shi Hao , Li Weihao , Shi Huantong , Li Xingwen , Hao Shiyu , Li Chengcheng , An Ran
Published: December 2024

The high-strain rate mechanical behavior of aluminum alloys is crucial for the stability of electromagnetic launch systems. However, current high-strain rate testing methods are not suitable for large-scale screening of materials needed in electromagnetic launch systems due to their low precision and high cost. In this paper, a novel method for high-strain rate tensile testing of aluminum alloys based on magnetic pulse driving was proposed. The method can generate a fast-rising edge and adjustable stress pulses to enable uniaxial tensile deformation, reaching a target strain rate quickly and keeping it constant. Based on the theory of stress wave transmission, a single-point method for measuring stress–strain relationship of the specimen combining digital image correlation (DIC) technology is proposed. Finite element simulations using the explicit finite element software LS-DYNA demonstrate a good agreement between the strains and strain rate with experimental values. Tensile tests were conducted on AA7075 in the strain rate range of 1000–3000 s−1, the stress–strain relationship obtained from DIC agrees well with the results of traditional Hopkinson bar experiments.
1500 V recessed-free GaN-based HEMTs with ultrathin barrier epitaxial structure
Authors: Sun Nan , Wang Ronghua , Huang Huolin , Lei Yun , Dai Jianxun , Han Rong , Zuo Qingyuan , Tao Pengcheng , Liu Yanhong , Song Shukuan , Ren Yongshuo , Cheng Wanxi , Liang Huinan
Published: December 2024

This Letter demonstrates a 1500-V enhancement-mode (E-mode) GaN-based high electron mobility transistors (HEMTs) based on the recessed-free structure. The E-mode GaN-based HEMTs fabricated based on the ultrathin barrier epitaxial structure have a small gate interface traps density (Dit) of ∼1012 cm−2 eV−1, which can be attributed to the avoidance of AlGaN etching in the gate region. Meanwhile, a small threshold voltage (Vth) hysteresis of 19 mV and a small subthreshold swing of 101 mV/dec are achieved in the fabricated devices with a Vth around 1.91 V. A small Vth shift of 0.05 V was achieved under positive gate voltage stress, indicating that the devices have good Vth stability. Meanwhile, a high yield of more than 90% has been achieved on 6-in. wafer, which provides a good scheme for the commercialization of E-mode HEMTs.
Thermal mean-field theories
Authors: Gu Pinhao , Hirata So
Published: December 2024

Several closely related ab initio thermal mean-field theories for fermions, both well-established and new ones, are compared with one another at the formalism level and numerically. The theories considered are Fermi–Dirac theory; thermal Hartree–Fock (HF) theory; two modifications of the thermal single-determinant approximation of Kaplan and Argyres, Ann. Phys. 92, 1–24 (1975); and the first-order finite-temperature many-body perturbation theory based on a zero-temperature or thermal HF reference. Thermal full-configuration-interaction theory is used as the benchmark.
Thermal quasiparticle theory
Authors: Hirata So
Published: December 2024

The widely used thermal Hartree–Fock (HF) theory is generalized to include the effect of electron correlation while maintaining its quasi-independent-particle framework. An electron-correlated internal energy (or grand potential) is postulated in consultation with the second-order finite-temperature many-body perturbation theory (MBPT), which then dictates the corresponding thermal orbital (quasiparticle) energies in such a way that all fundamental thermodynamic relations are obeyed. The associated density matrix is of a one-electron type, whose diagonal elements take the form of the Fermi–Dirac distribution functions, when the grand potential is minimized. The formulas for the entropy and chemical potential are unchanged from those of Fermi–Dirac or thermal HF theory. The theory thus stipulates a finite-temperature extension of the second-order Dyson self-energy of one-particle many-body Green’s function theory and can be viewed as a second-order, diagonal, frequency-independent, thermal inverse Dyson equation. At low temperatures, the theory approaches finite-temperature MBPT of the same order, but it may outperform the latter at intermediate temperatures by including additional electron-correlation effects through orbital energies. A physical meaning of these thermal orbital energies is proposed (encompassing that of thermal HF orbital energies, which has been elusive) as a finite-temperature version of Janak’s theorem.
Enhanced wind energy harvesting through omnidirectional airflow metamaterial concentrators
Authors: Zhou Mengjing , Ding Fan , Yuan Xujin , Yuan Honglin , Zhao Xiaojian
Published: December 2024

Wind energy generation is constrained by low density and intermittency. To address these challenges, this study proposes an omnidirectional airflow metamaterial concentrator lens that utilizes a novel complex gradient structure inspired by metamaterial principles. The study's framework includes the design, simulation, and performance evaluation of the concentration lens under varying wind conditions. The lens amplifies the local flow energy density by up to 360% compared to the impinging influx. Numerical simulation analysis elucidates the underlying operational mechanism, demonstrating a significant reduction in the startup wind speed and increased energy capture efficiency. Results indicate that concentrator lens can enhance wind energy exploitation by improving the efficiency of energy capture and providing a viable solution to mitigate the limitations of current wind energy technologies.
Considering the changes in unsaturated soil saturation after pipeline leakage: A modified Terzaghi model
Authors: Yu Hao , Liu Yanshun , Zhang Xiao , Lan Xiongdong , Yin Zhanchao , An Qiyi
Published: December 2024

Pipeline leakage leads to the saturation and weakening of the surrounding soil, increasing the pressure exerted by the overlying soil on underground engineering structures and posing a serious threat. Therefore, it is necessary to thoroughly understand the influence of pipeline leakage on the overlying soil pressure. Based on the saturation distribution within different diffusion ranges, an analysis model for pressure in loose soil under the influence of pipeline leakage was presented. Considering the variation in the matric suction of the unsaturated soil, the soil pressure can be modeled based on the incomplete arch effect. The influence of the relevant parameters on the overlying soil pressure was analyzed, and the accuracy and rationality of the modified model were verified using a trapdoor test. These findings indicate that the modified model can accurately estimate the soil pressure caused by a pipeline leakage. The overlying soil pressure is directly proportional to the diffusion distance, tunnel width, and slip surface inclination angle and inversely proportional to the relative deformation. The rate of change was mainly influenced by the parameters affecting the soil arching effect. The modified model presented in this study can be used to directly calculate the overlying soil pressure affected by pipeline leakage. This calculation is based on the known physical and mechanical parameters of unsaturated soil, pipeline leakage range, and relative deformation of the tunnel, thus providing a theoretical basis for the design of structures under urban pipelines.
Effect of annealing on flexoelectricity in hafnium oxide (HfO2)
Authors: Moreno-Garcia Daniel , Villanueva Luis Guillermo
Published: December 2024

Flexoelectricity is universal in all dielectrics, effective at high temperatures, and a promising transduction technique for nanoelectromechanical systems (NEMS). However, as flexoelectricity is still in its early stages, many aspects require further investigation. Understanding how flexoelectricity depends on material parameters like crystallographic phase and how temperature might affect it is important for selecting and optimizing the right material for technological applications. This work studies the influence of high-temperature annealing (and the consequent crystallization) in the flexoelectricity of hafnium oxide (HfO2), a material with significant technological relevance. We measure the flexoelectric coefficient for amorphous (not annealed) and annealed (slightly crystalline) phases of HfO2, with samples annealed in nitrogen or oxygen atmospheres. Our results indicate that the amorphous phase of HfO2 exhibits the highest flexoelectric coefficient (105 ± 10 pC/m), while annealed samples show a significant decrease, with the lowest value in nitrogen-annealed samples (26 ± 4 pC/m). Samples annealed in an oxygen atmosphere improve flexoelectric properties (54 ± 6 pC/m) compared to those annealed in nitrogen. Using cross-sectional imaging, x-ray diffraction, resonance frequency characterization, and relative permittivity measurements, we find that annealing promotes crystallization into the tetragonal phase and increases internal stress within the HfO2 layer, while most other parameters remain constant. We attribute the differences in flexoelectricity from the annealed samples to the quantity of oxygen vacancies in hafnium oxide. These oxygen vacancies in hafnium oxide seem to negatively affect the flexoelectric coefficient. This finding can be applied to optimize materials to enhance their flexoelectric properties.
Large eddy simulations and experimental studies of the influence of equivalence ratio on the combustion characteristics of turbulent NH3–CH4 premixed flames
Authors: Wang Ping , Zhang Zeyu , Cheng Kang , Qian Weijia , Shuai Ruiyang , Dai Kailun , Ferrante Antonio , Qi Haotian
Published: December 2024

As one of the most promising zero-carbon fuels, ammonia has attracted widespread attention. However, ammonia combustion faces problems such as high nitrogen oxide emissions. This work aims to investigate the combustion characteristics of fuel gas mixture of 60% NH3 and 40% CH4 by volume, under five different equivalence ratios, i.e., 0.7, 0.85, 1.0, 1.15, and 1.3, respectively. Both large eddy simulation (LES) and experimental test are conducted. The results reveal that flame temperature and nitric oxide (NO) emissions exhibit an initial increase, followed by a decrease with rising equivalence ratios. Notably, the highest temperature is observed at ϕ = 1.0, while peak NO emission is found at ϕ = 0.85. As the equivalence ratio changes, the variation of turbulent flow fields and mass recirculation rates is not significant. On the contrary, NO and OH radicals exhibit distinct shifts in relation to the equivalence ratio. The NO emissions predicted by LES agree well with the experimental results. A chemical reaction network (CRN) analysis is also conducted, which effectively predicts NO variation trends and clarifies NO generation pathways and key mechanisms. The CRN analysis highlights variations in the sensitivities of crucial constituents, such as NH3, OH, and NO, to variations in the equivalence ratio.
Aerodynamic interaction mechanisms in typical wingtip-mounted tractor propeller configurations
Authors: Gao Zeming , Yue Haifeng , Shao Xueming , Zhang Sheng , Zeng Lifang , Pan Dingyi
Published: December 2024

The wingtip-mounted tractor propeller configuration has been extensively studied due to its great potential for improving wing aerodynamic performance. In the present work, the aerodynamic interaction mechanisms in typical wingtip-mounted tractor propeller configurations are analyzed in depth using the reformulated vortex particle method. The results show that the elliptical lift distribution over the entire wing is altered by the installation of the tip-mounted propeller. The lift coefficient increases with inboard-up rotation and decreases with outboard-up rotation. Three key aerodynamic interaction mechanisms, swirl recovery, slipstream distortion, and slipstream impingement, are investigated. The swirl recovery mechanism generated by the inboard-up rotating propeller positively contributes to the performance of downstream wing. For the outboard-up rotation, the propeller-induced downwash results in reduced lift and increased induced drag. The interaction between the propeller-induced spanwise velocity and the wingtip-induced crossflow results in slipstream distortion. At α = 0°, for either inboard-up or outboard-up rotation, the slipstream on the retreating side is moved toward the propeller axis and away from the propeller axis on the advancing side. With the change of the rotation direction and angle of attack, the slipstream geometry exhibits different features. The slipstream impingement induced by the propeller generates time-varying loads on the downstream wing at the blade passing frequency. The propeller-induced tip vortices start to bend close to the leading edge and their vorticity increases, and then the vortex tube begins to deform. A higher angle of attack results in larger fluctuations in the downstream wing's drag coefficient.
Analysis of electroosmotic flow in a symmetric wavy channel containing anisotropic porous material with varying zeta potential
Authors: Ghiya Neelima , Tiwari Ashish
Published: December 2024

The present study examines an asymptotic analysis of electroosmotic flow phenomena bounded by the symmetrical wavy channel containing an anisotropic porous material under the variable pressure gradient and zeta potential. The incorporation of anisotropic porous material introduces additional complexities to the flow behavior. Electric potential is regulated by the non-linear Poisson–Boltzmann equation, which is linearized by the Debye–Hückel linearization process, and flow velocity inside the porous channel is governed by the Brinkman equation. The aspect ratio of the channel is considered to be significantly small, i.e., (δ2≪1). Obtaining analytical solutions to these non-linear coupled equations is a formidable challenge. To address this challenge, the equations are tackled by employing an asymptotic series expansion with respect to a small parameter, specifically the ratio of the channel thickness, where δ2≪1. The graphical analysis based on the derived expressions for flow quantities—such as fluid velocity, flow rate, flow resistance, wall shear stress, and pressure gradient along the wall—demonstrates the considerable impact of various governing parameters. These parameters, including the Debye–Hückel parameter, anisotropic ratio, slip length, and fluctuation amplitude, play a crucial role in influencing the behavior of these flow characteristics, highlighting their importance in determining the system's overall flow dynamics. The results demonstrate that an increment in the anisotropic ratio corresponds to an enhancement in fluid velocity and augmented flow rate. This relationship stems from the observed phenomenon wherein an enhancement in the anisotropic ratio leads to an augmentation in the permeability along the x-direction, thereby leading to an elevation in velocity and subsequently enhancing the flow rate. The study also examines the impact of flow reversal at the crests of the wavy channel resulting from the anisotropic ratio. The findings from our study have confirmed the axial fluid velocity in a purely pressure-driven flow system, where electroosmotic effects are not present. These results enhance our understanding of how anisotropic permeability affects fluid flow in microfluidic systems, especially when electrokinetic forces are at play.
Examination of forces acting on two circular cylinders in tandem arrangement
Authors: Shen Linwei , He Fang
Published: December 2024

Flow-induced vibrations of a two-dimensional circular cylinder in the wake of another stationary equal-sized cylinder under a Reynolds number of 150 are numerically simulated by a well-developed in-house code. The center-to-center distance between two cylinders is 4 diameters, and the downstream cylinder with a mass ratio of 50 is free to oscillate in the transverse direction only. The instantaneous frequencies of lift forces acting on both cylinders are obtained by the combined singular spectrum analysis and Hilbert transform method. The time-varying frequencies are consistent with those obtained by the wavelet transform of the original lift forces and also show very good agreement with the vortex shedding frequencies from both cylinders. The time-varying frequency and envelope of lift forces acting on the downstream cylinder are the result of nonlinear fluid–structure interactions, which is ascribed to the presence of multi-frequency components in the frequency spectrum obtained by harmonic analysis. Vibration of the downstream cylinder is the result of vortex shedding from both cylinders. The vortex shedding frequency from the downstream cylinder is greatly influenced by the wake from the upstream cylinder. On the other hand, the movement of the downstream cylinder slightly affects the vortex shedding frequency from the upstream cylinder. Consequently, the cylinder movement is locked upon the natural frequency when the vortex shedding frequency is close to the value of 0.155 in stationary situation, which results in a small synchronized region of the reduced velocity ranging from 6.2 to 6.4.
Enhancing generalization in endwall film cooling prediction: Incorporating the superposition principle into transformer-based neural operators
Authors: Wang Qineng , Song Liming , Liu Tianyuan , Guo Zhendong
Published: December 2024

In this study, a physics-enhanced neural operator framework is proposed to enhance the generalization prediction ability of the cooling layout of a turbine end wall with variable number of film holes. Specifically, inspired by the film cooling superposition principle, the superposition-based deep neural operator (SDNO) network is proposed, which divides the turbine end wall's temperature field prediction into two stages. In the first stage, the cooling layout of a turbine end wall is divided into several sub-parts, and a transformer-based neural operator network, namely Calculate Net, is designed to predict the temperature field of each sub-part. Then, in the second stage, another neural operator network, i.e., Superposition Net, is designed to combine all the temperature fields of each sub-part and obtain the final superposed field of full cooling layout. Additionally, instead of directly taking the film cooling layout as binary pixel data, a signed distance function which is sensitive to the variable locations of cooling holes is designed to preprocess the input layout information. Furthermore, the proposed end wall film cooling prediction model is trained with samples varying the number of film holes from 1 to 5 at different locations. Then, the trained prediction shows excellent generalization prediction ability, which can accurately predict the film effectiveness of the cooling layout with 10–20 film cooling holes that are unseen in the training samples. In the meantime, the proposed SDNO network also shows remarkable better prediction accuracy. With the above, the effectiveness of the SDNO has been well demonstrated.
Hybrid Runge–Kutta and lattice Boltzmann methods: Three-dimensional study of magnetohydrodynamics effect on heat exchange of electronic devices
Authors: Channouf Salaheddine , Benhamou Jaouad , Lahmer El Bachir , Derfoufi Soufiane , Horma Othmane , Jami Mohammed , Mezrhab Ahmed
Published: December 2024

This study explores the impact of the magnetic field on heat transfer and entropy generation in a simulated electronic device using magnetohydrodynamic principles through a three-dimensional hybrid Runge–Kutta and lattice Boltzmann method. By varying Rayleigh number (Ra) from 103 to 106 and Hartmann number (Ha) between 0 and 100, the research evaluated the influence of these parameters on the average Nusselt number (⟨Nu⟩), heat exchange ratio (R), and entropy generation within a confined cavity. The results demonstrated that higher Ra values, particularly for Ra ≥105, significantly enhance convective heat transfer, as reflected by an increase in ⟨Nu⟩. However, introducing a magnetic field (Ha = 50, 100) diminishes this effect by damping fluid motion, resulting in a reduction of ⟨Nu⟩. The heat exchange ratio increases with Ra, reaching a peak value of 0.93 for Ha = 100 and Ra = 105, indicating improved heat dissipation under the magnetic influence. In terms of entropy generation, at low Ra (Ra = 103), thermal conduction is the predominant heat transfer mechanism, with entropy primarily generated due to thermal effects. As Ra increases to 106, the system shifted toward a convection-dominated regime, where entropy generated by viscous effects becomes more significant. Under stronger magnetic fields, particularly at Ha = 100, magnetic entropy generation emerges as a dominant factor, further increasing energy dissipation. These results suggested that magnetic fields can be strategically applied to optimize thermal management in electronic devices by controlling both heat transfer and entropy generation. The effectiveness of this approach, however, is highly dependent on the specific flow conditions and the strength of the applied magnetic field.
Direct numerical simulation of boundary layer transition induced by roughness element in a low Reynolds number compressor blade
Authors: Ling Weihao , Gao Song , Wang Zhiheng , Zeng Min , Huang Wenlin , Xi Guang
Published: December 2024

The surface roughness of blades in low Reynolds number compressors significantly impacts the transition of the boundary layer and the profile loss. This paper employs direct numerical simulation (DNS) to investigate the boundary layer flow within a low Reynolds number compressor cascade, where an isolated roughness element is situated on the suction surface. A cylinder and a ramp are crafted and simulated by the embedded boundary method (EBM). The research centers on assessing the influence of varied roughness element shapes on the downstream velocity field, laminar separation bubble (LSB), and transition. DNS findings indicate that the cylinder's downstream shear and disturbances are relatively weaker, prompting separation-induced transition within its boundary layer, while the ramp's intense disturbances lead to bypass transition. The lift-up mechanism and the self-induced amplification of streamwise gradient of spanwise velocity are intrinsic to the flow instability during the bypass transition. Both cases can diminish total pressure loss, with the ramp yielding a relatively higher loss due to the contribution of a large-scale turbulent boundary layer to the total pressure loss. In terms of profile loss, the terms of mean kinetic energy dissipation and production associated with the suction-surface-normal gradient of mean streamwise velocity are predominant.
Efficiency-enhanced TM-mode gyrotron with down-taper interaction structure
Authors: Yang Tien-Fu , Nelson Anariba Jean Edward , Yao Hsin-Yu , Chang Chia-Chuan , Chang Tsun-Hsu
Published: December 2024

Recent advancements have shown that transverse magnetic (TM)-mode gyrotrons are feasible under specific conditions, yet their capabilities remain insufficiently explored. This article systematically investigates a W-band TM11-mode gyrotron within the down-tapered structure(s) to uncover its limitations and underlying physics. 2D interaction-efficiency maps are scanned as functions of the tube's geometrical parameters or beam parameters under magnetic-field tuning. An oversized tube integrated with short two-stage down tapers enhances the output efficiency of the fundamental axial mode and effectively alleviates the axial-mode competition. The peak electron-beam efficiency of the TM11 mode exceeds 50% with an idealized cold beam. The 3D particle-in-cell simulations are utilized to validate the real-time scheme including multiple transverse modes. Incorporating realistic beam spread, the first-harmonic TM11 mode effectively suppresses the second-harmonic and third-harmonic transverse electric modes with a maximum steady output of 130 kW, corresponding to an interaction efficiency of 37%. Complex dynamics regarding the mode-competing and mode-forming processes are revealed and discussed. This study not only facilitates the exploration of TM-mode gyrotrons but also provides insights into the harmonic gyrotron using the axis-encircling electron beam, where TM modes have more chances to be excited and dominate oscillations.
First-principles investigation of oxygen repulsion behavior on the Ir–Hf alloy surface
Authors: Liu Zhongyu , Hu Zhenfeng , Liu Quan , Fang Zhen , Wang Haoxu , Mo Jinyong , Bu Wengang , Liang Xiubing
Published: December 2024

Enhancing the oxidation resistance of hot-end components under extreme conditions is a key focus in aerospace equipment research. We used first-principles simulations to investigate a series of IrxHf100−x (at. %) coatings. By employing density functional theory and the local density approximation method, we studied the surface oxygen repulsion energy and estimated the optimal composition ratio of IrxHf100−x for the strongest oxidation resistance. The results indicate that as the Hf content increases, the oxygen repulsion energy first rises and then falls, reaching a maximum value of 3.04 eV at x = 10 at. %, with active oxygen adsorption occurring when X exceeds 45 at.%. To understand the mechanism of the oxygen repulsion process, we analyzed the electronic characteristics between Ir, Hf, and O. O preferentially hybridizes its atomic orbitals with Ir, and the improvement in oxidation resistance of the Ir–Hf coating is attributed to the reduction in Ir atomic spacing due to Hf doping, which reduces O–Ir orbital hybridization.
Comparing methods for reducing artificial pressure fluctuations using large eddy simulation in high-rise building wind load assessment
Authors: Chen Lingwei , Li Chao , Wang Jinghan , He Xin , Wang Xiangjie , Hu Gang , Wang Xiaolu
Published: December 2024

Reducing artificial pressure fluctuations (RAPF) is one of the key challenges in simulating atmospheric boundary layer turbulence. This study, based on the synthetic turbulence method, compares the performance of three RAPF methods: inlet mass correction (IMC), divergence-free correction (DFC), and local pressure correction (LPC). First, large eddy simulations of an empty domain show that the IMC and DFC methods effectively suppress unrealistic pressure fluctuations throughout the flow field. As the turbulence develops downstream, the pressure fluctuations decay rapidly and become almost insignificant. Conversely, the LPC method only reduces local nonphysical pressure fluctuations by adjusting the pressure reference location, but as the distance from the reference point increases, the pressure fluctuations gradually increase. Moreover, the IMC and DFC methods adjust the initial turbulent field to meet inlet mass balance or divergence-free conditions, which results in changes to the initial turbulence characteristics. However, the LPC method avoids modifying the initial turbulence, allowing it to better maintain the original turbulence properties. Finally, the simulations for wind loads on the high-rise building indicate that the application of the IMC, DFC, and LPC methods results in reasonable mean, standard deviation and peak values of pressures on the building surfaces, as well as accurate calculations of the integrated base forces and moments.
Evolution characteristics of shock waves in the muzzle flow field of an underwater gun in series launch
Authors: Bai Wenbin , Yu Yonggang , Zhang Xinwei
Published: December 2024

The muzzle flow field of underwater guns involves the interaction and reflection of shock waves within the propellant gas jet. When underwater guns are fired in series, the evolution of the shock wave structure in the muzzle flow field becomes more complex due to the superposition effect of the propellant gas jets. This study establishes a transient two-dimensional axisymmetric muzzle flow field computational model to simulate the dynamics of the muzzle flow field as it evolves during series launch of an underwater gun. The results show that the initial propellant gas jet expands further due to the impelling effect of the subsequent projectile. In the strong coupling series launch mode, the axial size of the bottle-shaped shock structure of the initial propellant gas jet exhibits a dynamic change of “growth decay.” However, in conventional coupling and weak coupling series launch conditions, the axial expansion of the bottle-shaped shock structure shows a single “growth” process. For the subsequent launch, in all three launch modes, the subsequent propellant gas jet will form two oblique shock waves under the compression of the gas–liquid interface and undergo several “shock reconstruction” processes at the axis, ultimately forming a stable bottle-shaped shock wave structure.