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We have presented a novel lattice Boltzmann approach for the non‐uniform rectangular mesh based on the radial basis function approximation (RBF‐LBM). The non‐uniform rectangular mesh is a good option for local grid refinement, especially for the wall boundaries and flow areas with intensive change of flow quantities. Which allows, the total number of grid cells to be reduced and so the computational cost, therefore improving the computational efficiency. But the grid structure of the non‐uniform rectangular mesh is no longer applicable to the classic lattice Boltzmann method (CLBM), which is based on the famous BGK collision‐streaming evolution. This is why the present study is inspired by the idea of the interpolation‐supplemented LBM (ISLBM) methodology. The ISLBM algorithm is improved in the present manuscript and developed into a novel LBM approach through the radial basis function approximation instead of the Lagrangian interpolation scheme. The new approach is validated for both steady states and unsteady periodic solutions. The comparison between the radial basis function approximation and the Lagrangian interpolation is discussed. It is found that the novel approach has a good performance on computational accuracy and efficiency. Proving that the non‐uniform rectangular mesh allows grid refinement while obtaining precise flow predictions. [ABSTRACT FROM AUTHOR]

A 2-D Lattice Boltzmann Method, designed to ensure stability at high Reynolds numbers, is combined with an Actuator Line Model to compute the loads on a two-bladed vertical axis wind turbine. Tests on the kernel size at a high mesh resolution reveal that a size equal to half of the full chord length yields the most accurate results. The aerodynamic load solution is validated against a fully resolved Scale-Adaptive Simulation (SAS) output, demonstrating high correlation, and enabling an assessment of near wake and downstream effects. The model's adaptability to various rotor operating conditions is confirmed through tests at high and low tip-speed ratios. Additionally, a Biot–Savart-based Vortex Model (VM) is employed for further comparison, showing good agreement with the Lattice Boltzmann output. The results indicate that the Highly Stable Lattice Boltzmann Method integrated with the Actuator Line Model enhances the accuracy of flow field resolution and effectively captures complex aerodynamic phenomena, making it a valuable tool for simulating vertical axis wind turbines. [ABSTRACT FROM AUTHOR]

The permeability, heat conductivity, and reaction rate will be varied with the change of natural gas hydrate saturation when thermal fluid is injected into the natural gas hydrate reservoirs. In order to characterize the variation of the physical field parameters with hydrate saturation, DDF-LBM was applied to simulate the hydrate dissociation process by thermal fluid injection under pore-scale modelling. Based on the forced conjugate heat transfer case, the relaxation frequency of the thermal lattice in the pores is corrected. Based on the P-T phase equilibrium relationship of hydrates and considering the heat absorbed by the hydrate reaction, the solid–liquid state of the hydrate lattice is judged in real time, and the dynamic simulation of the heat flow solidification multi-physics field is realized. The simulation results show that the dissociation rate of the hydrates by thermal fluid injection was higher than that by heating the hydrate surface alone and was positively correlated with the hydrate saturation. On the basis of the above results, this paper provided exponential fitting equations between different hydrate saturations and average permeability, effective thermal conductivity, and inherent reaction rate. The fitting results show that saturation has a negative correlation with relative permeability and effective thermal conductivity, and a positive correlation with the inherent reaction rate. The above results can provide a reference basis for accurately describing the heat and mass transfer of natural gas hydrate under the macroscale. [ABSTRACT FROM AUTHOR]

A new optimization strategy based on system performance optimization life cycle (SPOLC) is introduced for high-performance lattice Boltzmann simulations of three-dimensional decaying isotropic turbulence. This strategy improves the performance of turbulent flow simulations in periodic boxes at different resolutions using the lattice Boltzmann method (LBM). The strategy improves the performance by modifying the lattice Boltzmann model, mathematical representation, computational algorithm, software implementation, and computing hardware utilization. The modifications include: (1) Establishing the slice concept as a logical grouping layer added to the LBM, applying an aggregation–disaggregation mechanism, enabling two-dimensional (2D) operation on the three-dimensional (3D) model, (2) improving lattice data access pattern by using an alternative one-dimensional (1D) array for numerical representation instead of the 3D cubic representation, (3) major reduction in memory access iterations by switching from function-wise iteration method to lattice-wise iteration method by applying code fusion to the streaming, velocity and collision model functions and iterations, (4) applying process parallelization and data vectorization, (5) achieving a much more efficient utilization of modern compute units by increasing the adaption of stream processing model. Furthermore, a correctness validation process has been applied by conducting lattice-wise value comparisons between the proposed solution output and the original implementation output. Simulations of decaying isotropic turbulence at resolutions ranging from 323 to 5123 using the LBM are carried out for these purposes. Calculations are performed on two systems with distinct specifications, to validate the effectiveness and portability of the SPOLC strategy. The calculation times are significantly reduced after applying the SPOLC strategy on S1 with the lattice Boltzmann relaxation time τ=0.503 by over 69% compared to S2’s original time, increasing to 95.47% at higher resolutions. Different features of the flow fields are depicted and their characteristics are discussed. Thin tubes are visualized, and the energy spectra are studied. All fields are initialized by a forced turbulent field simulated in a previous study using the LBM. [ABSTRACT FROM AUTHOR]

The present study investigates forced convection heat transfer of rarefied flow within a microchannel containing obstacles using the thermal lattice Boltzmann method using a double distribution function model and BGK approximation. Slip velocity and temperature jump conditions were employed across microchannel walls. The microchannel temperature and velocity input are constant. The microchannel configuration has three obstacles imposed along the lower microchannel wall. The study simulates rarefied fluid flow and heat transmission of forced convection inside the microchannel, considering separation between obstacles as the primary study objective. The findings represent the distribution of temperature and velocity. In addition, temperature jump and slip velocity in the function of Knudsen numbers were also represented. The findings highlight the substantial influence of barriers on temperature and velocity. As the distance between obstacles drops, the temperature diminishes. Additionally, a rise in separation distances significantly aids in the dropping of velocity. The results reveal a significant reduction in slip velocity as Knudsen numbers increase across the microchannel length. The outcomes of the present investigation could assist and be used as a cooling solution for various technologies, such as microelectronics and nanoelectromechanical systems. Additionally, the suggested configuration might be utilized to improve microfluidic device design.

AbstractThe architecture of porous skeletons and large crack defects in thermal barrier coatings significantly influence the thermal protective performance of the coatings. In this study, the quartet structure generation set method was applied to fabricate coatings with wedge-shaped pore structures. A temperature field prediction model was developed through the lattice Boltzmann method. The results indicate that lengthening crack length and reducing the crack inclination angle or depth elevate the peak temperature gradient and surface temperature. Specifically, the temperature gradient near a 933-μm-long crack was 1.3 times greater than that near a 248-μm-long crack, with the surface temperature reaching 1221°C. Similarly, the temperature gradient near a 50-μm-deep crack was twice that near a 200-μm-deep crack, and the surface temperature reached 1191°C. Conversely, the temperature gradient near a crack with a 30° inclination angle was 0.6 times that of a 10° crack, accompanied by a decrease in the coating surface temperature. [ABSTRACT FROM AUTHOR]

This study investigates the dynamics of granular flows in geotechnical centrifuge models, focusing on the effects of centrifugal and Coriolis accelerations. While conventional laboratory-scale investigations often rely on Froude scaling, geotechnical centrifuge modelling offers a unique advantage in incorporating stress-dependent processes that fundamentally shape flow rheology and dynamics. Using the Discrete Element Method (DEM) and the Lattice-Boltzmann Method (LBM), we simulate the collapse of a just-saturated granular column within a rotating reference frame. The model’s accuracy is validated against expected trends and physical experiments, demonstrating its strong performance in replicating idealised collapse behaviour. Acceleration effects on both macro- and grain-scale dynamics are examined through phase front and coordination number analysis, providing insight on how centrifugal and Coriolis accelerations influence flow structure and mobility. This work enhances our understanding of granular flow dynamics in geotechnical centrifuge models by introducing an interstitial pore fluid and considering multiple factors that influence flow behaviour over a wide parameter space. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhengzhou University: Engineering Science is the property of Editorial Office of Journal of Zhengzhou University: Engineering Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The simulation of the laminar mixed convection heat transfer inside a 2-D inclined channel was investigated here by employing the lattice Boltzmann method (LBM). The channel was equipped with conductive fins. The effects of inclination angle (φ), geometrical parameters (e and A), and a wide range of the Richardson numbers (Ri = 0.1-10) at fixed Reynolds number (Re = 100) on the heat transfer and flow structure were studied. The numerical model was validated by the published benchmark problems. Results were analyzed in terms of isotherms, streamlines, average Nusselt number, and average temperature. It found that the Nu increases with a decrease in the number, height, and width of fins. Results showed that when the channel equipped with 16 fins the reduction in Nu value reaches 62% compared to the empty channel. In addition, at Ri = 1 and N = 8, the Nusselt number decreased by about 52-77% for different fin widths compared to the channel without fins. However, the Richardson number and inclination angle enhanced the heat transfer rate in terms of the average Nusselt number. It revealed that a higher heat transfer rate belongs to the Ri = 10 and φ = 60°. The finding of this work showed the capability of LBM in simulating the mixed convection heat transfer in an inclined channel equipped with fins. A numerical analysis of the results produced a comprehensive set of results that could be utilized to reduce heat transfer. This paper can provide a novel framework for the design of air solar collectors and heat exchange systems. [ABSTRACT FROM AUTHOR]

The water-gas relative permeability is an important parameter to characterize multiphase flow in sediments. To study the water-gas relative permeability of hydrate-bearing porous media, multiphase flow simulations were carried out at the pore scale using the lattice Boltzmann method. The effects of hydrate saturation and hydrate-growth habits on the water-gas relative permeability, which is scaled by the relative permeability considering the hydrate only, were evaluated in a two-dimensional porous medium. Results show that the increase of hydrate saturation causes the decrease of water-gas effective permeability as expected. However, the effect of hydrate saturation on the water-gas relative permeability is different from that of hydrate saturation on the water-gas effective permeability. The water-gas relative permeability increases with the increase of hydrate saturation in the pore-filling case. The water-gas relative permeability decreases with the increase of hydrate saturation in the grain-coating case. The wettability of solid phase has a different effect on the relative permeability of wetting phase and nonwetting phase. The Jamin effect (phase blocking) was observed and may exist in the production of gas from natural gas hydrate reservoirs. This seriously affects the multiphase flow characteristics. The changes of microscale fluid distribution effect the changes of water-gas relative permeability. The relationship between the water-gas relative permeability and the characterization parameters of microscale fluid distribution was analyzed.

The present research investigates heat transfer and the flow characteristics of periodically corrugated wavy channels numerically under pulsatile flow conditions. The numerical method used here is Lattice Boltzmann Method (LBM), and the validation of the study is done by Ansys-Fluent which is finite volume based commercial Computational Fluid Dynamics (CFD) code. For modeling walls, bounce-back method, namely, staircase method and three different curved boundary treatments, which are extrapolation, Filippova-Hänel (FH) and Mei-Luo-Shy (MLS), are used. For modeling constant temperature at walls, staircase method and the same curved wall treatments are used. Corrugated channels have a sharp wavy peak, and its inclination angle is 30°. Two different minimum channel heights are considered, which are 5 and 10 mm in corrugated channels. Flow regime is assumed as laminar (50 < Re < 300) and Prandtl number is kept as 0.7. Four kinds of different sinusoidal pulsatile flows are used with a combination of two different dimensionless frequencies and dimensionless amplitudes. For varying Reynolds number range, Nusselt number and friction factor are calculated. Narrow channel creates higher Nusselt number and friction factor than wide channel. At low Reynolds number, Nusselt number does not changed with pulsatile flow conditions, however at high Reynolds number cases of lower dimensionless frequency and higher dimensionless amplitude produce higher Nusselt numbers. Lower dimensionless frequency cases produce higher Nusselt number than higher dimensionless frequency cases. Pulsatile flow conditions have no effect on friction factor and for narrow and wide channel. Nusselt number prediction of FVM is close to STR and EXT for all cases of narrow channels, and close to the FH, MLS and EXT for all cases wide channel. Correlation equations for Nusselt number and friction factor are constructed by deep neural network (DNN) algorithm. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present state of research in computational fluid dynamics (CFD) is marked by an ongoing process of refining numerical methods and algorithms with the goal of achieving accurate modeling and analysis of fluid flow and heat transfer phenomena. Remarkable progress has been achieved in the domains of turbulence modeling, parallel computing, and mesh generation, resulting in heightened simulation precision when it comes to capturing complex flow behaviors. Nevertheless, CFD faces a significant challenge due to the time and expertise needed for a meticulous simulation setup and intricate numerical techniques. To surmount this challenge, we introduce paint2sim—an innovative mobile application designed to enable on-the-fly 2D fluid simulations using a device's camera. Seamlessly integrated with OpenLB, a high-performance Lattice Boltzmann-based library, paint2sim offers accurate simulations. The application leverages the capabilities of the Lattice Boltzmann Method (LBM) to model fluid behaviors accurately. Through a symbiotic interaction with the open-source OpenCV library, paint2sim can scan and extract hand-drawn simulation domains, affording the capability for instant simulation and visualization. Notably, paint2sim can also be regarded as a digital twin, facilitating just-in-time representation and analysis of 2D fluid systems. The implications of this technology extend significantly to both fluid dynamics education and industrial applications, effectively lowering barriers and rendering fluid simulations more accessible. Encouragingly, the outcomes of simulations conducted with paint2sim showcase promising qualitative and quantitative results. Overall, paint2sim offers a groundbreaking approach to mobile 2D fluid simulations, providing users with just-in-time visualization and accurate results, while simultaneously serving as a digital twin for fluid systems. [ABSTRACT FROM AUTHOR]

In a gear transmission system in a closed space, the heat transfer between gears and fluids presents highly nonlinear characteristics due to the complex physical processes involved in heat exchange and fluid motion, and constructing and solving the thermodynamic model of the gearbox becomes a task that involves considerable difficulty. This paper takes a conical–cylindrical two-stage gearbox as the research object, proposes a fluid–solid coupled dynamics model based on the lattice Boltzmann (LBM) combined with the large eddy simulation (LES) method, and the adopted lattice model is the D3Q27 velocity model, which is used to numerically simulate the distribution of the flow field inside the gearbox and undertake in-depth research on the fluid motion law of the complex gear transmission system in the enclosed space. The model is solved to reveal the laws determining the gear speed and the effects of the lubricant's dynamic viscosity and thermal conductivity coefficient on the gear heat dissipation efficiency. By adopting the lattice Boltzmann method, we can simulate the fluid flow and heat transfer inside the gearbox more efficiently, which provides a new way to closely understand the thermodynamic behavior of closed complex gear transmission systems. The application of this method is expected to provide strong support for thermal performance optimization and the design of gear transmission systems. [ABSTRACT FROM AUTHOR]

This research paper presents an investigation into the behavior of rarefied flow and heat transfer in a rectangular microchannel utilizing a Cu-water nanofluid. The study employs the thermal lattice Boltzmann method (LBM) with a lattice featuring a double distribution function and a BGK collision model. The simulations are performed using Python software, incorporating slip velocity and temperature jump effects. The primary objective is to analyze the influence of various thermophysical parameters of the coolant fluid on the microchannel, specifically focusing on the characteristics of the Cu-water nanofluid. The study considers laminar flow conditions with nanofluid volume fractions of 2%, 4% and 6%. The findings reveal that both rarefaction effect and Reynolds numbers, as well as the nanoparticle volume fraction, significantly impact the system. Moreover, the investigation evaluates key parameters such as the Nusselt number, skin friction coefficient, temperature jump slip velocity and velocity and temperature profiles. Notably, the nanoparticle volume fraction exhibits minimal influence on the velocity distribution or temperature field, whereas the Nusselt number increases with higher nanoparticle volume fractions. Additionally, the rarefaction effect leads to a reduction in velocity and temperature. At a nanoparticle volume fraction of 2%, increasing the Reynolds number results in elevated velocities and lower temperatures. The skin friction coefficient displays a decreasing trend along the microchannel with increasing Reynolds numbers. Furthermore, an increase in Knudsen numbers corresponds to a decrease in the skin friction coefficient. Finally, an increase in the nanoparticle volume fraction is associated with a decrease in the skin friction coefficient. [ABSTRACT FROM AUTHOR]

The objective of this investigation is to assess the effect of obstacles on numerical heat transfer and fluid flow momentum in a rectangular microchannel (MC). Two distinct configurations were studied: one without obstacles and the other with alternating obstacles placed on the upper and lower walls. The research utilized the thermal lattice Boltzmann method (LBM), which solves the energy and momentum equations of fluids with the BGK approximation, implemented in a Python coding environment. Temperature jump and slip velocity conditions were utilized in the simulation for the MC and extended to all obstacle boundaries. The study aims to analyze the rarefaction effect, with Knudsen numbers (Kn) of 0.012, 0.02, and 0.05. The outcomes indicate that rarefaction has a significant impact on the velocity and temperature distribution. The presence of nine obstacles led to slower fluid movement inside the microchannel MC, resulting in faster cooling at the outlet. In MCs with obstacles, the rarefaction effect plays a crucial role in decreasing the Nusselt number (Nu) and skin friction coefficient (Cf). Furthermore, the study demonstrated that the obstacles played a crucial role in boosting fluid flow and heat transfer in the MC. The findings suggest that the examined configurations could have potential applications as cooling technologies in micro-electro-mechanical systems and microdevice applications. [ABSTRACT FROM AUTHOR]

A 2-D Lattice Boltzmann Method, designed to ensure stability at high Reynolds numbers, is combined with an Actuator Line Model to compute the loads on a two-bladed vertical axis wind turbine. Tests on the kernel size at a high mesh resolution reveal that a size equal to half of the full chord length yields the most accurate results. The aerodynamic load solution is validated against a fully resolved Scale-Adaptive Simulation (SAS) output, demonstrating high correlation, and enabling an assessment of near wake and downstream effects. The model’s adaptability to various rotor operating conditions is confirmed through tests at high and low tip-speed ratios. Additionally, a Biot–Savart-based Vortex Model (VM) is employed for further comparison, showing good agreement with the Lattice Boltzmann output. The results indicate that the Highly Stable Lattice Boltzmann Method integrated with the Actuator Line Model enhances the accuracy of flow field resolution and effectively captures complex aerodynamic phenomena, making it a valuable tool for simulating vertical axis wind turbines.

Natural circulation loops are thermohydraulic circuits used to transport heat from a source to a sink in the absence of a pump, using the forces induced by the thermal expansion of a working fluid to circulate it. Natural circulation loops have a wide range of engineering applications such as in nuclear power plants, solar systems, and geothermic and electronic cooling. The Lattice Boltzmann Method was applied to the simulation of this thermohydraulic system. This numerical method has several interesting features for engineering applications, such as parallelization capabilities or direct temporal convergence. A 2D model of a single-phase natural circulation mini-loop with a small inner diameter was implemented and tested under different operation conditions following a double distribution function approach (coupling a lattice for the fluid and a secondary lattice for the thermal field). An analytical relationship between the Reynolds number and the modified Grashof number was used to validate the numerical model. Two regimes were found for the circulation, a laminar regime for low Reynolds numbers and a non-laminar regime characterized by a traveling vortex near the heater and cooler’s walls. Both regimes did not present flux inversion and are considered stable. The recirculation of the fluid can explain some of the heat transfer characteristics in each regime. Changing the Prandtl number to a higher value affects the transient response, increasing the temperature and velocity oscillations before reaching the steady state.

In this research, we conduct a computational investigation into the mixed convection flow of copper/water nanofluids (NFs) within a rectangular cavity, utilizing the Lattice Boltzmann Method (LBM). The cavity is uniquely configured with five high-temperature obstructions (HOBs), and we vary their dimensions and positions to evaluate Nusselt numbers (Nu) across a range of Richardson numbers (Ri). The three walls of the cavity, excluding the moveable top wall, are thermally insulated, while the latter is maintained at a lower temperature. A constant magnetic field (MCF) exerts influence within the cavity, with Ri spanning from 0.01 to 100, HOBs ranging from 0.1 to 0.5, and HOBs at the bottom wall spanning from 0.25 to 0.4. This numerical investigation is executed using a customized in-house code, focusing on examining heat transfer (HTR) dynamics within the cavity. Our findings reveal that augmenting the height of the HOBs and positioning them closer to the cold wall significantly enhances the average Nusselt number (Nuav). Conversely, an increase in Ri leads to a reduction in Nuav on the cold wall. Specifically, the most notable enhancement, with a 66.7 % increase in Nuav, occurs at Ri = 0.01 when HOBs are elevated from 0.1 to 0.5. On the other hand, an increment in Ri from 0.01 to 100 results in a 79.4 % reduction in Nuav. Furthermore, elevating the HOBs from 0.25 to 0.4 produces a substantial 44.3 % increase in Nuav.

The Yangtze River basin (YRB) has experienced frequent extreme drought events in recent years. Many studies have explored the impact of anomalous tropical sea surface temperatures on seasonal meteorological droughts over the YRB, yet two critical issues remain: (1) the regimes of the El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) causing YRB droughts; (2) the timing and spatial pattern of YRB droughts caused by ENSO and IOD. To address these knowledge gaps, we employed a comprehensive investigation. First, the Severity–Area–Density (SAD) method is applied to identify seasonal drought events over the YRB during 1971–2022. Second, we utilize composite analysis to specify the effects of ENSO and IOD. Our findings indicate that YRB droughts are significantly increased in the August of combined Eastern Pacific (EP) El Niño and positive IOD developing years, October of Central Pacific (CP) El Niño developing years, January of EP La Niña years, and April of CP El Niño decaying years. Third, we conduct numerical simulations and conclude that ENSO and IOD events contribute to the YRB droughts by modulating large‐scale circulation patterns, triggering the formation of cyclones and anticyclones over the Western North Pacific (WNP) and the Tibetan Plateau, and affecting the westerlies and other water vapour transport processes. These results on the physical mechanisms causing seasonal drought in the YRB can guide drought monitoring and prediction in the region. [ABSTRACT FROM AUTHOR]

The investigation of magnetohydrodynamic (MHD) blood flow within configurations that are pertinent to the human anatomy holds significant importance in the realm of scientific inquiry because of its practical implications within the medical field. This article presents an exhaustive appraisal of the diverse applications of magnetohydrodynamics and their computational modeling in biological contexts. These applications are classified into two categories: simple flow and pulsatile flow. An alternative approach of traditional CFD methods called Lattice Boltzmann Method (LBM), a mesoscopic method based on kinetic theory, is introduced to solve complex problems, such as hemodynamics. The results show that the flow velocity reduces considerably by increasing the magnetic field intensity, and the flow separation area is minimized by the increase of magnetic field strength. The LBM with BGK collision model has shown good results in terms of precision. Finally, this literature review has revealed a number of potential avenues for further research. Suggestions for future works are proposed accordingly. [ABSTRACT FROM AUTHOR]

In this paper, the parameters of a prototype runner of an axial flow pump are optimized by using the immersion boundary–lattice Boltzmann numerical method based on a large-eddy simulation (LES-IB-LBM). A fish-friendly axial flow pump with a leading-edge thickness of 11.4 mm and blade cutting angle of 18° is proposed. Through experiments, the living conditions of many kinds of fish in extremely positive and negative pressure environments are explored, and the probability of damage caused by pump to fish is analyzed by taking −40 kPa as the low-pressure damage threshold. The flow passage of the fish-friendly axial flow pump effectively guides the fish to low-risk areas, reducing the risk of friction, shear, and impact damage to the fish. The total impact mortality ratio of runners before and after the axial flow pump optimization is close to 7:1. [ABSTRACT FROM AUTHOR]

• A simplified lattice boltzmann model is developed for simulating two-phase electro-hydrodynamics (EHD) flow. • The model reflects a direct update of macroscopic variables within lattice boltzmann framework. • The mode performs well in studying large-conductivity-ratio two-phase EHD flow problems. • We delineate regions in the (C r ,P r)-plane in which the role of electric force components on electric force is marked. This paper proposes a numerical scheme within the lattice Boltzmann framework for effective simulations of two-phase electro-hydrodynamic (EHD) flows, in which the simplified multiphase lattice Boltzmann method serves as the flow solver and a leaky dielectric model is utilized to recover electric potential equation. The resultant formulations present direct evolution of macroscopic variables, due to which the present method outperforms the conventional lattice Boltzmann method in terms of memory cost and boundary treatment. Numerical validations are first carried out under the same parametric conditions as the benchmarking experimental studies with the conductivity ratio ranging from 0.03 to 1000, demonstrating that the present method is a practical and accurate tool to study large-conductivity-ratio two-phase EHD flows in scientific applications. Through the comparison with previous theoretical and numerical studies, the performance of the present method is further evaluated by varying physical parameters such as electric capillary number, electric field strength, interfacial tension, and electrical properties of liquids. The good agreements with the reference data confirm the accuracy and robustness of the proposed method. Additional studies of the dynamics of a deformed droplet in uniform electric field are carried out using the validated method. Specifically, we conduct a close numerical examination on the effect of the electrical conductivity ratio and permittivity ratio on the electric forces, and highlight the role of the dielectric electrophoretic force and the Coulomb force on the electric forces the deformation of a leaky dielectric droplet in the electrical conductivity ratio and the permittivity ratio phase diagram. [ABSTRACT FROM AUTHOR]

This study numerically investigates the two-dimensional natural convection in a square enclosure with an isothermal diamond elliptic array at Rayleigh numbers of 104 ≤ Ra ≤ 107. Three cases are considered, i.e., case 1 where two pairs of circular heating bodies are used inside the cavity, one is placed on the vertical centerline (VC) of the cavity and the other on the horizontal centerline (HC), case 2 where one pair of horizontal elliptic heating bodies is placed on the VC of the cavity and the other on the HC and case 3 where the horizontal elliptic heating bodies are replaced by vertical elliptic heating bodies. Numerical simulation was carried out based on the mesoscopic approach (LBM). The effects of the horizontally and vertically heated arrays were investigated. We demonstrate that, only when the Rayleigh number increases to Ra = 107, the numerical solutions reach an unsteady state for all cases. The transition of the flow regime from the unsteady state to the steady state depends on the variation in the ratio of the elliptical cylinder. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Blood is a shear-thinning non-Newtonian fluid in which the viscosity reduces with the shear rate. When simulating arterial flow, it is well established that the non-Newtonian nature is important in the smallest vessels; however, there is no consistent view as to whether it is required in larger arteries, such as the carotid. Here, we investigate the importance of incorporating a non-Newtonian model when applying a plaque deposition model which is based on near-wall local haemodynamic markers: the time-averaged near wall velocity and the ratio of the oscillatory shear index to the wall shear stress. In both cases the plaque deposition was similar between the Newtonian and non-Newtonian simulations, with the observed differences being no more significant than the differences between the selected markers. More significant differences were observed in the haemodynamic properties in the stenosed region, the most significant being that lower levels of near-wall reverse flow were observed for a non-Newtonian fluid. [ABSTRACT FROM AUTHOR]

Coal and gas outburst mainly occurs in tectonically deformed coal (TDC). TDC has low strength and is difficult to core; thus, it is often replaced by briquette coal (BC) for research. However, whether the fracture and permeability in BC are consistent with TDC remains to be verified. This study used X-ray computer tomography to characterize the fracture of TDC and BC and further explored the difference of permeability between them through the triaxial permeability experiment and lattice Boltzmann method (LBM) simulation. The results showed that TDC has strong heterogeneity and developed mostly complex fracture systems with large apertures. The fractures are primarily flat with disorderly directions, slightly poor connectivity, but strong connection strength. However, BC is formed by the accumulation of particles and exhibits micro-fractures with good homogeneity, which are mostly tube and slit with good connectivity but weak connective strength. During the stress loading process, the permeability of TDC showed a three-stage (i.e., sharp → rapid → steady) declining trend, while the BC had a two-stage (i.e., sharp → rapid) decline. The fracture compressibility of TDC decreased first and then increased with the increase in stress, exhibiting mostly plastic deformation, while the fracture compressibility of BC is far less than that of TDC, exhibiting mostly elastic deformation. Moreover, the average permeability damage and irreversible permeability damage rates of TDC were 0.0133 mD (1 mD = 1 millidarcy = 9.869233−16 m2) and 52.56%, respectively, which were higher than those of BC. Therefore, a new digital rock physics method based on X-ray CT and LBM technology is proposed to study the fracture and permeability. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of mixed convective heat transfer in a two-dimensional enclosure with sinusoidal heat applied on the vertical walls by the Lattice Boltzmann Approach. Governing equations are resolved by the Single-Relaxation-Time Bhatnagar-Gross-Krook model. A two-dimensional, nine-directional lattice arrangement is chosen to attain better numerical stability with good accuracy. The results are presented for four different fluids having Prandtl numbers equal to 0.015, 0.7, 1.38, and 7.0 respectively for mercury, gaseous ammonia, noble gases, and water. This analysis is performed for selected Reynolds numbers (100 ≤ Re ≤ 2000) and Richardson numbers (0.0 ≤ Ri ≤ 10.0). The above parameters are optimized using the Design of the Experiment to achieve maximum heat transfer rate. Taguchi method is used to conduct the required numbers of numerical studies and the dominant parameters are quantitatively found using Analysis of Variance (ANOVA). The present numerical results are compared with the existing literature and found good agreements. Results show that the right-side wall has always a higher heat transfer rate than the left-side wall. The factor levels combination for maximum heat transfer rate is found as Pr = 7.0, Re = 2000, and Ri = 10.

This study delves into the occurrence of double-diffusive natural convection while being affected by a magnetic field within a cold square enclosure, containing a heated and concentrated semi-circular body made permeable. The fusion of both flat and curved boundaries, combined with the permeable attributes, stands as the central impetus driving this inquiry. The main aim is to scrutinize the impact of buoyancy force, permeability, magnetic field strength, and angle on the double-diffusive convection taking place inside and around the permeable structure. To achieve this, a comprehensive parametric investigation is undertaken, emphasizing the importance of Darcy number (Da), buoyancy ratio (BR), Hartmann number (Ha), and magnetic field angle (γM) in relation to the flow, heat, and concentration transfer. We utilize the Lattice Boltzmann method, incorporating the Darcy-Brinkmann-Forchheimer equation as a source term, to precisely address the complex flow within the porous medium. The results will provide insights into the importance of a semi-circular body with porous characteristics in the context of thermo-solutal convection influenced by magnetic effects. These findings hold practical significance in various applications, including electronic cooling, pollutant removal, and food processing industries. The inquiry discloses that elevating the buoyancy force, permeability, and the angle of the magnetic field leads to advantageous heat and concentration characteristics. Furthermore, positioning the magnetic force in opposition to gravity reduces the restraining impact of the magnetic force on the mean Nusselt number (NuM) and the mean Sherwood number (ShM). Remarkably, instances of unsteady behaviour are predominantly noted when the BR takes on a negative value, and these phenomena’s intensity and frequency are heightened by the Da and the γM. Remarkably, there are a few irregular spikes detected in the NuM and ShM, which can be attributed to the emergence of a strong singular vortex in the upper part of the enclosure.

Natural circulation loops are thermohydraulic circuits used to transport heat from a source to a sink in the absence of a pump, using the forces induced by the thermal expansion of a working fluid to circulate it. Natural circulation loops have a wide range of engineering applications such as in nuclear power plants, solar systems, and geothermic and electronic cooling. The Lattice Boltzmann Method was applied to the simulation of this thermohydraulic system. This numerical method has several interesting features for engineering applications, such as parallelization capabilities or direct temporal convergence. A 2D model of a single-phase natural circulation mini-loop with a small inner diameter was implemented and tested under different operation conditions following a double distribution function approach (coupling a lattice for the fluid and a secondary lattice for the thermal field). An analytical relationship between the Reynolds number and the modified Grashof number was used to validate the numerical model. Two regimes were found for the circulation, a laminar regime for low Reynolds numbers and a non-laminar regime characterized by a traveling vortex near the heater and cooler's walls. Both regimes did not present flux inversion and are considered stable. The recirculation of the fluid can explain some of the heat transfer characteristics in each regime. Changing the Prandtl number to a higher value affects the transient response, increasing the temperature and velocity oscillations before reaching the steady state. [ABSTRACT FROM AUTHOR]

Numerical simulation is performed for a cylinder-bound two-component liquid flow. Simulation model is based on the method of lattice Boltzmann equations. The collision integral in this model is defined from the MRT approximation. The interaction between liquid components is described by the diffusion interface model with the pseudopotential approximation. The main deficiency of this known approach is the disbalance of discrete forces of two-component interaction; this would generate a pseudo-current in the transition zone. The presented numerical study offers a qualitative view for the pseudopotential function providing a smallest value for intercomponent interaction coefficient. This means the low pseudo-currents and the smallest size for the diffusive transition. The example simulation is presented for a problem of rotation of two components in a cylinder. The simulation gives also the Reynolds number range and the cylinder aspect ratio that ensure the start of flow recirculation at the cylinder axis. It was demonstrated that simulation results comply with experimental data with a high accuracy. [ABSTRACT FROM AUTHOR]

Hydrophilicity is one of the most vital characteristics of titanium (Ti) implants. Surface structure design is a powerful and efficient strategy for improving the intrinsic hydrophilic ability of Ti implants. Existing research has focused on experimental exploration, and hence, a reliable numerical model is needed for surface structure design and corresponding hydrophilicity prediction. To address this challenge, we proposed a numerical model to analyze the droplet dynamics on Ti surfaces with specific microstructures designed through the lattice Boltzmann method (LBM). In this work, a Shan-Chen (SC) model was applied in the simulations. We simulated droplets spreading on smooth and micropillar surfaces with various wettability and provided a comprehensive discussion of the edge locations, contact line, droplet height, contact area, surface free energy, and forces to reveal more details and mechanisms. To better tune and control the surface hydrophilicity, we investigated the effects of micropillar geometric sizes (pillar width a, height h, and pitch b) on hydrophilicity via single factor analysis and the response surface method (RSM). The results show that the hydrophilicity initially increases and then decreases with an increasing a, increases with an increasing h, and decreases with an increasing d. In addition, the interaction effects of a-d and h-d are significant. The optimization validation of the RSM also demonstrates the accuracy of our lattice Boltzmann (LB) model with an error of 0.687%. Here, we defined a dimensionless parameter ξ to integrate the geometric parameters and denote the surface roughness. The hydrophilicity of Ti surfaces improves with an increasing surface roughness. In addition, the effect of the microstructure geometry shape was investigated under the same value of surface roughness. Surfaces with micropillars show the best hydrophilicity. Moreover, this study is expected to provide an accurate and reliable LB model for predicting and enhancing the intrinsic hydrophilicity of Ti surfaces via specific microstructure and roughness designs.

Whenever the drilling wellbore is at the state of gas–liquid two-phase flow, gas slips and migrates along the drilling fluid. Due to the decreased wellbore temperature and pressure during gas migration, gas volume will gradually increase. When the temperature and pressure reach the critical value of gas–liquid phase, phase change occurs. The volume of natural gas expands suddenly, and a large amount of gas is generated. It easily leads to a well blowout, which is a great challenge to well control. Therefore, analyzing the gas–liquid phase changes in drilling wellbore has important practical significance for realizing well control safety. In this paper, Lattice Boltzmann Method (LBM) is applied to simulate phase transition of wellbore gas–liquid​ two-phase system. Research results show that gas–liquid distribution after phase transition is closely related to the system original density. Compared to the critical density of gas–liquid phase change, when the system original density is lower, continuous gas forms in wellbore. While the system original density is higher, gas phase breaks out into small bubbles and migrates along the wellbore. Phase distribution directly determines gas–liquid two-phase flow pattern in wellbore, which is crucial to wellbore pressure accurate prediction. Some valuable attempts are conducted to investigate gas–liquid two-phase flow in wellbore by using LBM in this research.

This research focuses on the flow and heat transfer characteristics past three hot obstacles in a sudden expansion and contraction channel. To enhance the heat transfer, the MWCNT-Fe3O4 Water hybrid nanofluid is used. The effect of Reynolds number (40, 70 and 100), nanoparticle volume fraction of MWCNT-Fe3O4/water hybrid nanofluid (0.00, 0.001, and 0.003) and different arrangements of discrete heat sources (47 arrangements) on the flow pattern, temperature distribution and heat transfer characteristics have been investigated. The lattice Boltzmann method (LBM) is applied for the simulations. It is found that the heat transport performance of each heated obstacle is not only related to its position and the arrangements of the other two heat sources are important. Compared with the other arrangements, when three obstacles are located on the first row, all three hot sources can obtain relatively better heat transfer performances, and the corresponding Nuave is 5.1451 which is 1.72 times the minimum value of Nuave (Case 4). The obstacle located behind another obstacle would obtain low Nuavg. Besides, to achieve the highest heat transfer performance of one heat obstacle in a column, the position OBS#4 in Case 14 needs to be placed. [ABSTRACT FROM AUTHOR]

Droplet evaporation has great scientific significance in industrial and agricultural production as well as natural meteorological processes. Among many factors that affect evaporation, wettability and wall temperature are among the most important. The Lattice Boltzmann Method (LBM) was used to explore the effects of evaporative wall wettability and wall temperature on the Constant Contact Angle (CCA) model. We constructed a dual-distribution gas–liquid phase transition model and found that the higher the wall temperature, the more rapid the evaporation; however, nucleate boiling was more likely to occur at high temperatures, making the CCA (and thus evaporation) unstable. Compared to hydrophobic surfaces, hydrophilic surfaces have larger droplet spreading area, and generally higher evaporation rate; as the contact diameter decreased, droplet diffusion occurred and evaporation to dryness was observed. Droplets on hydrophobic surfaces tended to form nucleus of boiling, thus generating bubble and gas films. After the droplets shrunk and stabilized, the contact diameter reduced and evaporation slowed. Droplet evaporation can be regulated to improve energy efficiency depending on different applications. [ABSTRACT FROM AUTHOR]

Accurately describing the flow state of mine gas is the basis for the prevention and control of mine dust and toxic gases, computational fluid dynamics (CFD) method is often used to solve mine flow field, but CFD method is usually an iterative process with high calculation cost, time-consuming and high memory requirements. In order to realize the fast solution of mine flow field, a prediction model of mine flow field based on convolutional neural network (CNN) is proposed. The geometry flow field simulated by lattice Boltzmann method (LBM) is used as the training data. CNN is used to extract the basic characteristics of the flow field in the training data, establish the mapping relationship between the geometric boundary and the flow field, and quickly predict the mine flow field. The simulation experiment and the particle image velocimetry (PIV) test experiment of the air window flow field were carried out respectively. In LBM simulation experiment, the average values of mean square error (MSE), mean absolute error (MAE), R2, explained variance score (EVC), Pearson correlation coefficient (PCC) and cosine similarity between CNN predicted values and LBM simulated values of 10 groups of test samples are 0.2633, 0.2449, 0.9595, 0.9697, 0.9827, 0.9933, respectively. It shows that the accuracy of CNN flow field prediction model is similar to that of LBM simulation, and the computational speed of CNN model is increased by three orders of magnitude compared with LBM simulation. In PIV test experiment, the predicted values of CNN model are basically consistent with the PIV experiment results, no matter the velocity distribution of a section or the flow trend of the overall flow field. The LBM simulation experiment and PIV test experiment strongly prove the reliability and generalization ability of CNN model for predicting mine flow field. [ABSTRACT FROM AUTHOR]