bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of random vortex method to simulate turbulent flows of non-Newtonian fluids
Authors: Zaboli Mehrdad , Shahmardan Mohammad Mohsen , Norouzi Mahmood
Published: October 2024

This paper presents an unsteady numerical method for investigating the flow of generalized Newtonian fluids at high Reynolds numbers. The study develops the random vortex method (RVM) to solve turbulent flows of non-Newtonian fluids, based on a Lagrangian perspective of the vorticity equation. The shear-dependent viscosity in non-Newtonian fluids leads to the emergence of an inhomogeneous term in the vorticity equation. The convection term in the vorticity equation is addressed by considering the movement and interaction of vortices and by calculating the induction velocity of these vortices. The diffusion term in the vorticity equation, which is inhomogeneous, is solved using the Green's function. To develop this method, benchmark problems involving the flow of non-Newtonian fluids in a channel and over a backward-facing step are examined, with Reynolds numbers of 50 000 and 37 500, respectively. Finally, the study investigates vortex dynamics, streamlines, and velocity vectors, along with additional characteristics such as the length of the fully developed flow region in the channel and the recirculation zone over the backward-facing step in turbulent flow of non-Newtonian fluids. The results were compared with and validated against experimental data, analytical solutions, and other numerical methods.
High-sensitivity solution sensor based on a phoxonic crystal nanobeam with lateral fins
Authors: Sun Xiao-Wei , Luo Chao , Liu Yao-Hui , Gao Xing-Lin , Tan Mao-Ting , Song Ting
Published: October 2024

This work presents a high-sensitivity solution sensor based on a phoxonic crystal nanobeam with lateral fins. The fins improve the stability of the suspended nanobeam and its detection performance is unaffected. Acoustic–optic dual-mode cross-detection improves the detection accuracy over the single-mode method. The acoustic and optical energies are concentrated in the defect and slot regions due to the combination of the gradient cavity and slot, which enhances the acoustic–optic interaction with the object to be measured, improving the detection sensitivity. Using the mode bandgaps of photonic and phononic crystals, the sensing characteristics are investigated using the finite element method. The impact of various concentrations on the transmission spectra of optical electromagnetic waves and acoustic elastic waves is investigated. The maximum sensitivity is 2149.5 kHz/ms−1, with Q of over 105 in the acoustic mode and 457.1 nm/RIU in the optical mode. The proposed nanobeam cavity with lateral fins can be used to realize miniaturized multi-mode acoustic–optic sensors. It also provides mechanical support, thermal transport, and channels for lateral carrier injection for the suspended nanobeam.
Study on the influence of casing bionic chamber on the performance of a compressor cascade
Authors: Xu Wenfeng , Lu Wenxin , Sun Dan , Ren Guozhe , Zou Shilong
Published: October 2024

This paper introduces a casing bionic chamber structure into the transonic compressor, inspired by the airflow control mechanisms observed in dragonfly wings. Numerical simulations are employed to examine how variations in the height and placement of the casing bionic chamber affect compressor performance and flow field structure. The results indicate that the trapped vortex generated by the casing bionic chamber increases the airflow resistance near the casing, reduces the clearance leakage flow, and suppresses the influence of the leakage vortex along the pitchwise direction. The optimal placement for the casing bionic chamber is near the starting position of the leakage vortex. The inhibition of the clearance leakage is enhanced and then weakened with the increased chamber height. When the chamber is located near the leading edge to the trailing edge, with a height equal to 0.6% of the blade height, the leakage flow rate is reduced by 1.82%.
Hydrodynamic vortex flow in magnetic fluid: Under continuous rotation of a rare earth magnet
Authors: Shah Shailee P. , Desai Rucha P. , Joshi Pankaj S.
Published: October 2024

Vortex is the most natural phenomenon observed in the universe. It has various industrial and household applications. Interestingly, researchers are now utilizing the knowledge of hydrodynamic vortex flow to develop laboratory-based mimicking models of black hole—analogue black holes. Although it covers various aspects of black holes, the gravitomagnetic effects in the analogue models are yet to be explored. The magnetically modulated vortex created in the magnetizable system can open up a diverse research path in the field of analogue black holes. This motivated us to explore magnetically driven hydrodynamic vortex flow in the magnetizable system. Albeit, researchers have explored the formation of micro-vortices in the magnetic fluid by applying the rotating magnetic field. However, the hydrodynamic vortex formation in the magnetic fluid is yet to be explored. In view of this, the present work focuses on the experimental development of hydrodynamic vortex flow in magnetizable systems by applying continuous rotation of the rare earth magnet.
A novel deep learning approach for flow field prediction around airfoils leveraging computational space representation
Authors: Caraccio Paride , Marseglia Guido , Lauria Agostino , De Giorgi Maria Grazia
Published: October 2024

The optimization workflow for airfoil shapes, crucial for maximizing the lift/drag ratio, involves numerous computational fluid dynamics (CFD) simulations. Convolutional neural networks (CNNs) expedite this process by creating fast reduced order models. However, using uniformly spaced grids for CNN training is inadequate for complex scenarios, like those with wall-bounded turbulence, due to their inability to represent spatial variability effectively. A novel method addresses this limitation by preliminarily transforming flow fields into a new computational space, enabling concise representation of crucial information. The developed neural network architectures, comprising fully connected and transposed convolution layers, accurately infer transformed field maps for incompressible flow around a NACA0012 airfoil based on Reynolds (Re) number and angle of attack. In particular, the performance of a traditional transposed convolutional neural network (TCNN) architecture is compared with that of a conditional generative adversarial network (cGAN) with a TCNN generator. The most important aspect of the proposed spatial transformation lies in the ability to transfer the learned weights onto new geometries, allowing for training with fewer CFD data than would be required for training from scratch. By applying transfer learning to cGAN models trained with 15 cases for the prediction of velocity fields around the NACA4412 airfoil, the average error is up to 70% lower than training without weight transfer. This approach streamlines the optimization process by facilitating rapid model training and precise inference of flow fields, overcoming challenges posed by complex aerodynamic scenarios.
Neural network-based finite volume method and direct simulation Monte Carlo solutions of non-equilibrium shock flow guided by nonlinear coupled constitutive relations
Authors: Garg Gagan , Mankodi Tapan K. , Esmaeilifar Esmaeil , Myong Rho Shin
Published: October 2024

For understanding many real-world problems involving rarefied hypersonic, micro-, and nanoscale gas flows, the primary method may be the direct simulation Monte Carlo (DSMC). However, its computational cost is prohibitive in comparison with the Navier–Stokes–Fourier (NSF) solvers, eclipsing the advantages it provides, especially for situations where flow is in the near continuum regime or three-dimensional applications. This study presents an alternate computational method that bypasses this issue by taking advantage of data-driven modeling and nonlinear coupled constitutive relations. Instead of using numerical solutions of higher-order constitutive relations in conventional partial differential equation-based methods, we build compact constitutive relations in advance by applying deep neural network algorithms to available DSMC solution data and later combine them with the conventional finite volume method for the physical laws of conservation. The computational accuracy and cost of the methodology thus developed were tested on the shock wave inner structure problem, where high thermal non-equilibrium occurs due to rapid compression, for a range of Mach numbers from 2 to 10. The simulation results obtained with the computing time comparable to that of the NSF solver showed almost perfect agreement between the neural network-based combined finite volume method and DSMC and original DSMC solutions. We also present a topology of DSMC constitutive relations that allows us to study how the DSMC topology deviates from the NSF topology. Finally, several challenging issues that must be overcome to become a robust method for solving practical problems were discussed.
Heterojunction semiconductor nanocatalysts as cancer theranostics
Authors: Sabu Arjun , Kandel Manoj , Sarma Ritwick Ranjan , Ramesan Lakshminarayan , Roy Ekta , Sharmila Ramalingam , Chiu Hsin-Cheng
Published: October 2024

Cancer nanotechnology is a promising area of cross-disciplinary research aiming to develop facile, effective, and noninvasive strategies to improve cancer diagnosis and treatment. Catalytic therapy based on exogenous stimulus-responsive semiconductor nanomaterials has shown its potential to address the challenges under the most global medical needs. Semiconductor nanocatalytic therapy is usually triggered by the catalytic action of hot electrons and holes during local redox reactions within the tumor, which represent the response of nontoxic semiconductor nanocatalysts to pertinent internal or external stimuli. However, careful architecture design of semiconductor nanocatalysts has been the major focus since the catalytic efficiency is often limited by facile hot electron/hole recombination. Addressing these challenges is vital for the progress of cancer catalytic therapy. In recent years, diverse strategies have been developed, with heterojunctions emerging as a prominent and extensively explored method. The efficiency of charge separation under exogenous stimulation can be heightened by manipulating the semiconducting performance of materials through heterojunction structures, thereby enhancing catalytic capabilities. This review summarizes the recent applications of exogenous stimulus-responsive semiconducting nanoheterojunctions for cancer theranostics. The first part of the review outlines the construction of different heterojunction types. The next section summarizes recent designs, properties, and catalytic mechanisms of various semiconductor heterojunctions in tumor therapy. The review concludes by discussing the challenges and providing insights into their prospects within this dynamic and continuously evolving field of research.
X-ray visualized unstable displacements of water by gas in sandstone slabs for subsurface gas storage
Authors: Beteta A. , Wang G. , Sorbie K. S. , Mackay E. J.
Published: October 2024

A series of experiments have been performed studying the displacement of water by gas in consolidated porous media at an adverse viscosity ratio of μw/μg = 100, from the perspective of subsurface gas storage. The gas/water relative permeability functions (RPs) produced in the laboratory to model these processes generally use short cores from which the RPs are derived using conventional analysis and assumptions. In this work, we present results that challenge some of these assumptions and bring into question some of the currently used RP functions to design storage scenarios gas/water systems. Using a novel visualization technique, large two-dimensional sandstone slabs are imaged via x-rays during the gas → water unstable drainage processes. Three experiments were carried out evaluating the impact of rate and vertical flow direction. In the bottom-to-top experiments, we observed the rate dependence on the evolution of viscous fingers from an initially stable bank resulting from the effect of capillary dispersion stabilizing the early finger growth. In the case of top-to-bottom displacement, we observe that the combined capillary and gravity forces are not sufficient to fully stabilize the system, although a visible “stable” bank is formed prior to the emergence of the gas fingering instability. Finally, these results are compared to a water → oil drainage carried out under the same conditions and viscosity ratio. The results are then discussed in the context of subsurface gas storage, and recommendations are made for future experiments designed to derive appropriate gas/water RP functions and for upscaling the results from the laboratory to the field.
The influence of micro-blowing/suction on flow and heat transfer characteristics in a rectangular channel
Authors: Niu Jintao , Wang Jiansheng , Liu Xueling , Gong Jiarui , Dong Liwei
Published: October 2024

This study numerically investigates the impact of micro-blowing/suction parameters on the flow and heat transfer characteristics. Different models and parameters are evaluated by energy saving rate and comprehensive performance coefficients. The numerical results indicate that micro-blowing reduces the wall friction drag, while micro-suction increases the wall friction, and the magnitude of drag reduction (or drag increase) increases with the augment of the micro-blowing/suction coefficient. The maximum drag reduction rates of the three models are 2.60%, 3.59%, and 3.83%, respectively. When micro-blowing and micro-suction are arranged at the bottom and top of the channel, respectively, or both arranged at the bottom of the channel, the Nusselt number increases by at least 69.75% and 89.45%, respectively. The arrangement of micro-blowing and micro-suction both arranged at the bottom of the channel is optimal for heat transfer and drag reduction. In addition, with the present three arrangements, energy saving in the channel flow can be achieved.
Thermal characterization of vertical interface by scanning photothermal radiometry
Authors: Mateos-Canseco Alejandro , Kusiak Andrzej , Battaglia Jean-Luc , Museau Matthieu , Villeneuve François
Published: October 2024

In this work, scanning photothermal radiometry is used for imaging and to characterize a submicron crack. From the thermal images, the evolution of the crack is mapped in the space with micrometer resolution. A vertical contact interface at the steel–steel junction is used to represent a micro-crack with a thickness less than 0.5 μm. The thermal quadrupole approach is used to model the heat transfer within the semi-infinite vertical crack. Then, using the phase mapping and that calculated from the model, the estimation of both the equivalent thermal boundary resistance of the interface and the average interface thickness was done.
Computational fluid–structure interaction in biology and soft robots: A review
Authors: Pramanik R. , Verstappen R. W. C. P. , Onck P. R.
Published: October 2024

The omnipresence of fluid–structure interaction (FSI) in biological systems is indisputable—from the vibration of leaves to the locomotion of fish, to the flying of birds, and to the cardiovascular biomechanics; FSI is indeed ubiquitous. Even in stimuli-responsive soft robots that typically operate inside a fluid medium, these physical interactions are prevalent. Therefore, it becomes mandatory to have a thorough understanding of their fully coupled physics involving strong two-way interaction between the solid and fluid domains. Although state-of-the-art computational frameworks and robust numerical techniques have been developed to study their complex physical mechanisms and associated nonlinearities involving multiple spatiotemporal scales, we believe that a timely review of the current development, emerging techniques, and future challenges in computational FSI would further stimulate research along this direction. Therefore, we explore the broad landscape of the myriad research avenues that herald FSI emphasizing their manifold occurrences in biology and advanced soft robotic technologies, while underlining the plethora of numerical techniques adopted to study these fundamental phenomena.
Dynamics of inertial particles on the ocean surface with unrestricted reserve buoyancy
Authors: Beron-Vera F. J.
Published: October 2024

The purpose of this note is to present an enhancement to a Maxey–Riley theory proposed in recent years for the dynamics of inertial particles on the ocean surface [Beron-Vera et al., “Building a Maxey–Riley framework for surface ocean inertial particle dynamics,” Phys. Fluids 31, 096602 (2019)]. This updated model removes constraints on the reserve buoyancy, defined as the fraction of the particle volume above the ocean surface. The refinement results in an equation that correctly describes both the neutrally buoyant and fully buoyant particle scenarios.
Analysis of the wave energy dissipation in the interaction between waves and horizontal plate breakwaters through the smoothed particle hydrodynamics
Authors: Chen Yong-kun , Meringolo Domenico D. , Liu Yong , Li Fu-heng
Published: October 2024

This paper presents a numerical comparison of the wave energy dissipation behaviors of a Horizontal Plate Breakwater (HPB), a Perforated HPB (PHPB), a Downward Twin HPB (DTHPB), and an Upward Twin HPB (UTHPB) through the Large Eddy Simulation (LES) model introduced in the Smoothed Particle Hydrodynamics (SPH) by Di Mascio et al. [Phys. Fluids 29, 035102 (2017)], known as δ-LES-SPH model. The majority of existing studies in this context concentrate on the analysis of structures' hydrodynamic coefficients, while an in-depth analysis of the wave dissipation process involved in the wave-structure interaction is lacking. The analyses presented in this paper address this research gap by considering the interactions between waves and the HPB, PHPB, DTHPB, and UTHPB through the calculation and comparison of the time evolutions of the dissipated wave energy of the water body in the vicinity of these structures. The numerical results demonstrate that for the HPB, the wave energy is dissipated in a violent manner in the water body above and behind the structure. In contrast, for the PHPB, the outflow from the slots on the structure collides with the water body in the vicinity of the slots, resulting in the dissipation of wave energy due to the presence of large velocity gradients. The similarity in the wave energy dissipation behavior of the HPB and DTHPB is evident, and the hydrodynamic coefficients including reflection, transmission, and wave energy dissipation coefficients of these two structures show insignificant differences. The UTHPB, on the other hand, exhibits a different wave energy dissipation behavior. One of the horizontal plate structures placed at the still water level results in a shallow water effect and wave breaking that occurs above the UTHPB to a lesser extent than that observed above the HPB.
Experimental, theoretical, and numerical investigation on sloshing behavior in annular sectored containers
Authors: Xie Fei , Liu Yu , Zhu Yuxuan , Feng Zhimao , Lu Daogang , Zhang Feifan , Zhou Yixian
Published: October 2024

Annular sectored containers are widely used in nuclear engineering, aerospace, marine, and civil engineering. It is crucial for the safety assessment of such containers to accurately describe their sloshing behavior under external disturbances and seismic conditions. Many studies have been conducted on the sloshing behavior in regular-shaped containers (rectangular, circular, and annular cross sections); however, the studies on the sloshing in annular sectored containers are relatively limited. Specifically, there is a lack of studies on sloshing damping and nonlinear behaviors under large-amplitude resonance conditions and earthquakes. This paper examines the effects of excitations and geometry (curvatures and sizes) on the dynamic sloshing characteristics and transient response of annular sectored containers through shaking table experiments. Experimental results show significant nonlinear sloshing, including breaking waves, at sharp inner corners of annular sectored containers under large harmonic and seismic excitations. It also shows that curvature has a small effect on the frequency and sloshing damping; however, it significantly influences wave heights and hydrodynamic pressures on the outer curved surface. Based on potential flow theory, we derived a wave height formula with damping for the annular sectored container under arbitrary ground motion excitation. Through experiments, we also determined a correction factor for wave height under large-amplitude excitation. The results were compared with experimental data, volume-of-fluid (VOF) results, and the corrected wave height formula for rectangular containers. The comparison shows that under large-amplitude excitation, both the VOF method and potential flow theory show significant errors compared to experimental results, while the corrected formula for the annular sectored container agrees well with the experimental results.
Spectral adjoint-based assimilation of sparse data in unsteady simulations of turbulent flows
Authors: Plogmann Justin , Brenner Oliver , Jenny Patrick
Published: October 2024

The unsteady Reynolds-averaged Navier–Stokes (URANS) equations provide a computationally efficient tool to simulate unsteady turbulent flows for a wide range of applications. To account for the errors introduced by the turbulence closure model, recent works have adopted data assimilation (DA) to enhance their predictive capabilities. Recognizing the challenges posed by the computational cost of four-dimensional variational DA for unsteady flows, we propose a three-dimensional DA framework that incorporates a time-discrete Fourier transform of the URANS equations, facilitating the use of the stationary discrete adjoint method in Fourier space. Central to our methodology is the introduction of a corrective, divergence-free, and unsteady forcing term, derived from a Fourier series expansion, into the URANS equations. This term aims at mitigating discrepancies in the modeled divergence of Reynolds stresses, allowing for the tuning of stationary parameters across different Fourier modes. While designed to accommodate multiple modes in general, the basic capabilities of our framework are demonstrated for a setup that is truncated after the first Fourier mode. The effectiveness of our approach is demonstrated through its application to turbulent flow around a two-dimensional circular cylinder at a Reynolds number of 3900. Our results highlight the method's ability to reconstruct mean flow accurately and improve the vortex shedding frequency (Strouhal number) through the assimilation of zeroth mode data. Additionally, the assimilation of first mode data further enhances the simulation's capability to capture low-frequency dynamics of the flow, and finally, it runs efficiently by leveraging a coarse mesh.
A piecewise-hierarchical particle count method suitable for the implementation of the unified gas-kinetic wave–particle method on graphics processing unit devices
Authors: Yu Hang , Xie Wenjia , Ren Weijie , Tian Zhengyu
Published: October 2024

The particle counting part in the unified gas-kinetic wave–particle method on graphics processing unit (GPU) devices is computationally intensive. This paper introduces a piecewise-hierarchical (P-H) particle counting strategy tailored for the Single Instruction Multiple Threads architecture, which leverages GPU memory hierarchy to reduce access conflicts. The strategy was evaluated based on throughput, roofline performance, and computation time metrics. Compared to the global counting strategy, the P-H approach achieved a 3.37× speedup for the particle counting kernel, and the overall program experienced a performance boost of more than 30%.
Large scale analysis of three-dimensional turbulent von Kármán swirling flows
Authors: Bousquet R. , Chaffard O. , Creff M. , Lucor D. , Nore C.
Published: October 2024

In this paper, we are interested by the large-scale structures and dynamics of turbulent von Kármán (vK) swirling flows. In particular, we investigate the symmetry properties of these structures for a wide range of turbulent flow regimes. Results from scheme-consistency preserving large eddy simulations model, performed at different Reynolds numbers (Re), are carefully analyzed with different handy modal decompositions to understand the dynamical ingredients affecting the flow symmetries. Applying proper orthogonal decomposition (POD) on three-dimensional three-components simulated velocity fields, we numerically corroborate for the first time previous experimental studies which showed that the flow can be characterized by a metastable state at Re>104, associated with an axisymmetric one-cell structure that breaks the Rπ− symmetry (rotation of π with respect to any radial axis passing through the center of the container), inducing long term intermittent fluctuations in the angular momentum. Then, applying POD on a two-dimensional three-component Fourier representation of the velocity fields, we show in detail how the different azimuthal Fourier modes contribute to the statistically stationary mean state and to the large fluctuations, relying on energy decomposition, symmetry, and spatial analysis of the flow.
Finite-difference-informed graph network for solving steady-state incompressible flows on block-structured grids
Authors: Zou Yiye , Li Tianyu , Lu Lin , Wang Jingyu , Zou Shufan , Zhang Laiping , Deng Xiaogang
Published: October 2024

Advances in deep learning have enabled physics-informed neural networks to solve partial differential equations. Numerical differentiation using the finite-difference (FD) method is efficient in physics-constrained designs, even in parameterized settings. In traditional computational fluid dynamics (CFD), body-fitted block-structured grids are often employed for complex flow cases when obtaining FD solutions. However, convolution operators in convolutional neural networks for FD are typically limited to single-block grids. To address this issue, graphs and graph networks are used to learn flow representations across multi-block-structured grids. A graph convolution-based FD method (GC-FDM) is proposed to train graph networks in a label-free physics-constrained manner, enabling differentiable FD operations on unstructured graph outputs. To demonstrate model performance from single- to multi-block-structured grids, the parameterized steady incompressible Navier–Stokes equations are solved for a lid-driven cavity flow and the flows around single and double circular cylinder configurations. When compared to a CFD solver under various boundary conditions, the proposed method achieves a relative error in velocity field predictions in the order of 10−3. Furthermore, the proposed method reduces training costs by approximately 20% compared to a physics-informed neural network. To further verify the effectiveness of GC-FDM in multi-block processing, a 30P30N airfoil geometry is considered, and the predicted results are reasonably compared with those given by CFD. Finally, the applicability of GC-FDM to a three-dimensional (3D) case is tested using a 3D cavity geometry.
Designing lotus-like superhydrophobic self-cleaning surface using carbon nanotubes
Authors: Rahal Shubham , Choudhury Moutushi Dutta , Das Sarit K. , Samanta Devranjan , Agnihotri Prabhat K.
Published: October 2024

Artificial superhydrophobic and self-cleaning surfaces are desirable in many engineering applications. Lotus leaves have long been the benchmark for the design and fabrication of artificial non-wetting surfaces. Here, we report the design and fabrication of superhydrophobic surfaces that mimic the behavior of lotus leaves. Akin to the microstructure of lotus leaves, an intrinsically hierarchical microstructure is created using carbon nanotubes (CNTs). The conventional CNT growth protocol is modified to induce multiscale features with lower diameter CNTs on the top of thicker CNTs. Together they form a dandelion seed head type structure with thicker CNTs such as “beak” and thinner CNTs such as “pappus.” The wetting and self-cleaning behavior of the CNT coated surface is compared with the lotus leaves. The wetting behavior of never-wet commercial spray and Cu and Ni foils are also recorded for comparison. The contact angle, contact angle hysteresis, and sliding angle of water drops on CNT coated surface are comparable with the lotus leaves. The wobbling motion of water drops on the CNT coated surface is similar to that on the lotus leaves and spray coated surface with varying contact line length with time. It also induces the self-cleaning characteristics of CNT coated surfaces similar to lotus leaves. Finally, the present study demonstrates a feasible strategy to design and fabricate lotus leaves like artificial superhydrophobic surfaces with hierarchical CNT structures.
Effect of return channel on performance and pressure fluctuation of pump turbine
Authors: Wang Wenjie , Qiu Gai , Pei Ji , Pavesi Giorgio , Tai Geyuan , Yuan Shouqi
Published: October 2024

To stabilize the operation of pumped storage power station, an orthogonal experimental design was proposed to optimize the return channel with the splitter blades of the pump turbine. The calculation results of various return channel models under multiple operating conditions indicated that inlet distance a1 and blade number z considerably affect the efficiency and flow pattern in the flow passage. The optimal scheme improved efficiency by nearly 3% at 0.6Qd. The Savitzky–Golay filtering method and Fast Fourier Transform were used to analyze the unsteady characteristics of the pump turbine in pump model. The amplitude of pressure pulsations at the blade passing frequency in the vaneless space and the interference zone between the guide vane and return channel reduced considerably, and the pressure pulsation amplitude in the vaneless zone decreased by 50%, 48%, and 20% for 0.6Qd, 1.0Qd, and 1.1Qd operating conditions. A Continuous Wavelet Transform was used to analyze frequency signals during the shutdown transition process. The optimization of the splitter blades improved the flow pattern in their corresponding flow passages and suppressed high-amplitude pressure pulsations in the unit for the stable operation of the pumped storage power station.
Effects of texture arrangement and texture shape on the static characteristics of a four-lobe bearing
Authors: Yu Tao , Zhang Zheng , Shen Wenhao , Liu Quanzhong
Published: October 2024

This study investigates the effects of texture on the static characteristics of a four-lobe bearing in turbulence flow state. Three texture arrangements and four texture shapes are considered. By solving the coupled oil film thickness equation and Reynolds equation, we obtain the thickness and pressure distributions of the bearing oil film and further obtain the bearing load carrying capacity (LCC) and film friction coefficient (FFC). Results indicate that the LCC increases with higher eccentricity, preload, length-to-diameter ratio, and rotating speed, while the FFC decreases. The textured bearings show decreases and stabilization in LCC with increasing texture radius. There exist optimal texture depth and texture circumferential spacing that maximize the LCC and minimize the FFC, while the texture's axial spacing has minimal impact. Case III arrangement and triangle-shaped texture notably improve static characteristics, with case III boosting the LCC by 68.70% and reducing the FFC by 39.45% and the triangle-shaped texture increasing the LCC by 165.23% and reducing the FFC by 60.17%. This study also elucidates the mechanisms of texture effects and serves as a valuable reference for the design and analysis of four-lobe bearings.
Vortex-induced vibration of a circular cylinder in the supercritical regime
Authors: Sahu Tulsi Ram , Chopra Gaurav , Mittal Sanjay
Published: October 2024

Vortex-induced vibration (VIV) of a low mass ratio circular cylinder (m*=10), that is free to vibrate in crossflow and in-line directions, at supercritical Reynolds number (3×105) has been studied using large-eddy simulation for a range of reduced speed (2≤U*≤11). In the supercritical regime, the boundary layer transitions to a turbulent state via the formation of a laminar separation bubble (LSB). The regime is associated with weakened vortex shedding, resulting in subdued VIV response. Lock-in is observed for U*≥3. The cylinder vibration frequency is identical in the crossflow and in-line directions, leading to an elliptical trajectory. The rms of the force coefficients is similar to that for a stationary cylinder in the desynchronization regime while it decreases with increase in U* during lock-in. The spatiotemporal dynamics of LSB is explored. The LSB is sedentary in the desynchronization regime, while it undergoes significant circumferential movement, in each cycle of cylinder oscillation, in the lock-in regime. The mode of vortex shedding, determined from the arrangement of vortices in the span-averaged instantaneous flow as well as the phase difference between the lift and cylinder response, is C(2S) in the desynchronization regime. It is 2P0 in the lock- in regime.
Experimental study and modal analysis of methane explosion-induced deposited coal dust participation
Authors: Wang Haiyan , Zhang Yanwei , Tian Siyu , Hu Yang , Xu Jingde
Published: October 2024

This study investigates the evolution of wave systems during methane explosions involving deposited coal dust in enclosed pipelines. The flame front velocity distribution was measured using schlieren image velocimetry. Proper orthogonal decomposition and dynamic mode decomposition techniques were applied to identify the primary flow structures and fluctuation frequencies in the flow field during the dust-lifting process. The experimental results indicate that while deposited coal dust does not significantly affect the shock wave, it notably increases flame velocity, with a maximum acceleration of up to 180 m/s, and extends flame propagation distance. The primary cause of flame enhancement is the interaction with reflected shock waves. The pressure gradient created by these reflected waves generates Archimedean forces on the particles, driving the coal dust toward the flame. This early contact between the coal dust and the flame intensifies the methane explosion. Modal analysis further reveals that the shear layer is the most critical flow structure during dust-lifting, with vortex shedding being the main driver of flow field oscillations.
Evaluation of the permeability anisotropy of three-dimensional fractured rock masses based on a pair of orthogonal measuring windows
Authors: Wang Xiaohong , Wang Jingyong , Cheng Yongjin , Chu Weijiang , Liu Ning , Shi Mengnan , Zeng Jun
Published: October 2024

The seepage capacity of fractured rock masses is a critical parameter in various engineering and geoscience projects. Due to the complex geometric distribution of fracture network, the permeability of rock masses typically exhibits an anisotropic behavior, necessitating detailed and comprehensive investigation of fracture characteristics to accurately determine permeability anisotropy in three-dimensional (3D) space. In this study, we developed an improved method for determining permeability anisotropy that significantly reduces the need for extensive input of geometric information. We employ the anisotropic ellipsoid, which is a mathematical representation of permeability tensor, to evaluate permeability anisotropy. Through in-depth mathematical derivation, we present a procedure for constructing the anisotropic ellipsoid using geometric trace information from a pair of orthogonal planes, which aligns well with the practical application scenario of underground tunnel excavation. Numerical experiments were conducted to validate our developed method. The mean prediction error rates were 5.2%, 16.8%, and 13.6% across three sets of experiments, experiments, demonstrating the validity of our approach.
Application and structural optimization design of magnetic fluid sealing in valve plate pairs of plunger pumps
Authors: Yang Chao , Li Zhenggui , Cheng Chuanshi , Shen Changrong , Qing Jie , Wan Ye , He Xinyue
Published: October 2024

The flow distribution pair of the piston pump, the largest contact area among the three friction pairs in a plunger pump, significantly influences the pump's overall performance. Magnetic fluid sealing, a novel sealing method, offers advantages such as zero leakage, long lifespan, high reliability, and no pollution, making it widely applicable across various fields. This approach provides a new solution for the end-face sealing valve plate pairs in plunger pumps. To address the leakage issue of the flow distribution pair, we designed a magnetic fluid radial sealing structure for the end face of the flow distribution pair and optimized the key parameters of the sealing structure by numerical simulation. Based on the optimization results, we developed a corresponding magnetic fluid sealing device and tested its pressure resistance performance under both static and dynamic conditions. The experimental results indicate that the sealing performance is superior when sealing gases compared to liquids, especially under dynamic conditions. This is attributed to the instability of the sealing interface caused by centrifugal force, leading to seal failure. Under static conditions, the sealing performance primarily depends on the saturation magnetization of the magnetic fluid and is independent of other physical properties. In dynamic conditions, the pressure resistance decreases with increasing speed. While the viscosity of the magnetic fluid impacts the sealing performance, the saturation magnetization remains the critical factor determining the critical sealing capacity. These findings provide valuable insights for the design of end-face radial magnetic fluid sealing devices.
Two-fluid model with physics-based inertial coupling for boiling flows
Authors: López-de-Bertodano M. , López-de-Bertodano A. , Clausse A.
Published: October 2024

The two-fluid model (TFM) has become the basis of numerical codes for engineering analysis of two-phase flows in most of the energy systems where boiling is present. However, the completeness of the model is still disputed because, in its usual form, the momentum conservation equations are elliptic, which, among other things, causes the solutions of short wavelength perturbations to have infinite growth rate. Recently, it has been shown that well-posed instances of the TFM can be derived using the variational principles. This paper presents a complete formulation of the TFM for boiling flows that renders the equations hyperbolic by incorporating physics-based inertial coupling between phases. The equations are cast into two canonical motion modes, namely, the center-of-mass flow and the relative motion between the fluids, which have different temporal and spatial scales, and so are easier to analyze independently. The influence of the inertial coupling parameters is analyzed in a case study of boiling channel oscillations.
Lattice Boltzmann modeling of individual and collective cell dynamics in the presence of fluid flows
Authors: Wu Yihao , Qin Chujin , Xing Hui , Sun Dongke
Published: October 2024

Dynamics of individual and collective cells with fluid flow is an important and attractive topic in both the areas of fluid science and biomedical engineering. The kinetic theory-based lattice Boltzmann model is presented to describe the multicellular dynamics coupled with fluid flows. In the model, the Bhatnagar–Gross–Krook (BGK) Boltzmann equation is extended to describe both cellular and fluid dynamics. Through the Chapman–Enskog analysis, the BGK–Boltzmann equation for cells can be recovered to the phase field equation, capturing the intricate processes of cell motion and deformation. Simultaneously, the BGK–Boltzmann equation governing fluid dynamics can be recovered to the Navier–Stokes equations, enabling accurate representation of fluid flow characteristics. Both BGK–Boltzmann equations are directly discretized into the lattice Boltzmann scheme, providing an efficient and robust computational approach. After model validation and verification, the dynamical behavior of an individual cell and multicellular spheroids in shear flows were sequentially investigated. Apart from the observation of elongation and rotation of multicellular spheroids, quantitative analyses were conducted across several key factors. The results show that the physical properties of cells and flow significantly impact the rheology of multicellular spheroids, and this effect is related to intercellular interactions. Furthermore, the morphogenesis of multicellular aggregate under the influence of inflow was investigated, revealing the remarkable cellular deformation along with the formation of a cavity. This study demonstrates the potentiality of the proposed kinetic theory based method in simulating microscopic biofluidic systems, providing a novel numerical tool to explore the intricate interactions between cells and their hydrodynamical environments.
On the adaption of biological transport networks affected by complex domains
Authors: Li Yibao , Lv Zhixian , Xia Qing
Published: October 2024

This paper aims to simulate and analyze scenarios involving obstacles and parasitic organisms during the growth of biological structures. We introduce an innovative model of biological transport networks in complex domains. By manipulating sources and sinks, we simulate two distinct types of domains. One obstructs nutrient transport without absorbing energy. The other one obstructs transport and absorbs energy. Our model adheres to the continuous functional energy dissipation law. Employing a Crank–Nicolson type method ensures second-order time accuracy. The phase field-based discrete system is decoupled, linear, and unconditionally stable, facilitating straightforward implementation of the algorithm. Our scheme maintains stability in addressing the stiffness of the hybrid system. Our research demonstrates that effective mathematical modeling and numerical methods can accurately simulate and analyze the growth of biological transport networks in complex domains.
Unraveling the impact of annealing and magnetic field on MnFePSi microwires
Authors: Salaheldeen Mohamed , Zhukova Valentina , Zhukov Arcady
Published: October 2024

The impact of high-temperature annealing on the magnetic and microstructural properties of MnFePSi glass-coated microwires is studied. A comparative analysis is conducted to elucidate the influence of annealing conditions (temperature and time) on physical characteristics MnFePSi glass-coated microwires compared to the as-prepared sample. The results reveal a significant influence of the annealing process on MnFePSi-based glass-coated microwires. A notable observation is the increased coercivity (Hc) for the sample annealed at 973 K for 1 h, rising from 761 Oe (as-prepared) to 1200 Oe. However, increasing the annealing time to 2 h leads to a sharp reduction in the coercivity value to 253 Oe. Thermomagnetic curves [field-cooling (FC) and field-heating (FH)] of the annealed samples, measured at both low and high magnetic fields, exhibit perfect matching. This indicates that the relevant contribution of the internal stresses induced by glass coating in the magnetic behavior in both FC and FH protocols. We demonstrate the possibility for tailoring and modification of relevant magnetic phenomena such as metamagnetic phase transition, magnetic behavior, and the control of magnetic response (hardness/softness). These tailored properties pave the way for the exploitation of MnFePSi glass-coated microwire in a wide range of glass-coated microwire applications.
Theoretical development in the realm of pentagonal 2D-materials
Authors: Shah Nayyar Abbas , Janjua Raheel Ahmed , Jin Yi , Evans Julian , Shen Jian Qi , He Sailing
Published: October 2024

Beyond hexagons, a distinctive family of pentagonal two-dimensional materials (2DMs) has emerged, featuring asymmetric geometry, exotic characteristics, and promising applications. Pentagonal tessellation of 2DMs generally leads to semiconducting bandgaps and directional electrical and optical properties. The theoretical prediction of penta-graphene and the experimental realization of materials, such as PdSe2, PdPSe, PdPS, and NiN2, have revealed a new horizon for penta-materials, showcasing high air stability and inherent auxeticity. Due to the rarity of pentagonal topology in nature, it is crucial to employ computational models and simulations to establish the stable configurations of these materials and understand their behavior in pentagonal arrangements. Consequently, the multitude of theoretically predicted penta-materials far surpasses the number of experimentally synthesized ones, numbering in the hundreds. A comprehensive catalog encapsulates recent progress, properties, and future perspectives, unlocking their full potential and paving the way for experimental realization. This review presents an extensive compilation of predicted penta-materials to date, elucidating their properties and potential applications.
Interaction between flow topology and interface curvature of heat transfer interfaces during the evaporation process of liquid fuel droplets in a temporally evolving high-temperature gas jet
Authors: Huang Dongqi , Fang Zixuan , Han Wang , Yang Lijun
Published: October 2024

Spray evaporation is a classical fluid dynamic problem. Although many previous studies have been done, there are still blind spots in the knowledge of the turbulent spray evaporation mechanism. This work aims to reveal the evaporation mechanism of fuel droplets in high-temperature gas jet. First, a high-resolution direct numerical simulation method is used to solve the evaporation process of n-heptane droplets in a high-temperature air jet. Second, the interactions between different flow topology structures in the flow field and the curvature of the heat transfer interface is analyzed to elucidate the mechanism of the influence of flow topology on the evaporation process of n-heptane droplets in a high-temperature air jet. It can be observed that the unstable focus compressing (UFC) topology structure exerts the most significant influence on conditional strain rate of the flow field. Additionally, the curvature of the temperature iso-surfaces is negatively correlated with the conditional strain rate. It can also be found that the increasing of conditional strain rate in turn promotes the generation of sheet and concave structures, thus causes the heat transfer interfaces smoother and temperature scalar dissipation rate higher. Hence, increasing UFC topology structures may help improve evaporation efficiency.