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BACKGROUND: As unmanned aerial spraying systems (UASS) usage grows rapidly worldwide, a critical research study was conducted to optimize the simulation of UASS applications, aiming to enhance pesticide delivery efficiency and reduce environmental impact. The study examined several key aspects for accurate simulation of UASS application with lattice Boltzmann method (LBM). Based on these discussions, the most suitable grid size and simulation parameters were selected to create a robust model for optimizing UASS performance in various pest management scenarios, potentially leading to more targeted and sustainable pest control practices. RESULTS: The effect of stability parameter, grid size around the rotor and near ground, and parameters at wake flow were carefully analyzed to improve the precision of pesticide drift predictions and deposition patterns. Optimal grid sizes were identified as 0.2 m generally, 0.025 m near rotors, and a 0.1 + 0.2 m scheme for ground proximity, with finer grids improving accuracy but increasing computation time. Wake resolution and threshold significantly influenced simulation results, while wake distance had minimal impact beyond a certain point. The LBM's accuracy was validated by comparing simulated downwash flow and droplet deposition with field test data. CONCLUSION: This study optimized UASS simulation parameters, balancing computational efficiency with accuracy. The validated model enhances our ability to design more effective UASS for pest management, potentially leading to more precise and targeted pesticide applications. These advancements contribute to the development of sustainable pest control strategies, aiming to reduce pesticide usage and environmental impact while maintaining crop protection efficacy. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

As the global concern over greenhouse gas emissions grows, CO2 storage in deep saline aquifers and depleted reservoirs has become crucial for climate change mitigation. This study evaluates the feasibility of Lithuanian deep saline aquifers, specifically, Syderiai and Vaskai, for effective CO2 storage. Unlike previous theoretical analyses, it provides experimental data on static and dynamic reservoir parameters that impact CO2 injection and retention. Using micro X-ray computed tomography (MXCT) and multi-resolution scanning at 8 µm and 22 µm, digital rock volumes (DRVs) from core samples were created to determine porosity and permeability. The method, validated against analogous samples, identified a representative element volume (REV) within sub-volumes, showing a homogeneous distribution of petrophysical properties in the Lithuanian samples. The results show that DRVs can accurately reflect pore-scale properties, achieving 90–95% agreement with lab measurements, and offer a rapid, efficient means for analyzing storage potentials. These insights confirm that Lithuanian aquifers are promising for CO2 sequestration, with recommendations for further long-term monitoring and applications of this technique across the region. [ABSTRACT FROM AUTHOR]

This paper applies a recently developed approach for modeling turbulence near wall regions within a lattice Boltzmann solver, in combination with a Hybrid RANS/LES turbulence model, to study turbulent separated flows at high Reynolds numbers. To simulate unsteady detached flows on a non-body-fitted Cartesian grid, wall models are employed to estimate the effects of unresolved near-wall turbulence on the overall flow. The article presents the extension of an equilibrium power law wall model to handle adverse pressure gradients and its application in simulating external aerodynamic flows. Hybrid RANS/LES simulations are conducted for two challenging test cases: a 3D NACA-4412 airfoil near stall and a complex Ahmed body configuration. Comparison with a reference simulation involving resolved boundary layers and experimental data demonstrates the strong performance of the wall model, when considering adverse pressure gradients, in simulating turbulent boundary layers under various conditions, ranging from fully attached to mild to high adverse pressure gradients. [ABSTRACT FROM AUTHOR]

This article reports the transient numerical solution of concave profile longitudinal fins under two cases of step-changing base boundary conditions involving heat flux and temperature, respectively. Although the analysis of concave fin has been carried out under step-changing base temperature, the transient solution of concave fin under step-changing base heat flux has seldom been reported in the literature. Additionally, earlier reported studies of a fin merely address the linear and power law temperature-dependent variation of thermal parameters. Herein, the thermal parameters of fin namely volumetric heat generation and thermal conductivity are treated to be a second-order polynomial function of temperature to address the nonlinear material properties. Furthermore, the convection coefficient is treated to be a power law function of temperature to mimic the different fluid regimes. The accumulated non-linearity arising in governing differential equations due to temperature-dependent thermal properties physically characterizes the realistic application of fins. The results of aforementioned governing equation with accumulated non-linearity are computed by employing Lattice Boltzmann method (LBM) accompanied by in-house MATLAB code. The reported results comprise time-temperature history at different fin locations until the attainment of an equilibrium state and instantaneous temperature variation at a specified time. In order to facilitate the designing of fins, a broad range of thermal parameters and their significance on temperature distribution is reported, it reveals that the exact curve fitting analysis pertinent to each material is inherently necessary for accurately predicting the temperature distributions in fins.

This paper considers the beta/alpha transformation of Ti–6Al–4V alloy using a lattice Boltzmann method (LBM) – cellular automata (CA) coupled method in terms of microstructural evolution during phase transformation. Particularly, the effects of the cooling rate on microstructures such as beta grain size, alpha colony size, and alpha lath thickness were examined as well as the overall morphologies. The LBM and CA were used to implement the diffusion of alloy components and phase transformation, respectively. Additionally, the thermodynamic and kinetic data for simulating the ternary alloy system were obtained from CALPHAD software to utilize the equilibrium phase diagram calculations. The initial states of the beta grain and its composition fields affect the processing of beta/alpha phase transformation and the final alpha + beta phase morphologies. Validation of the proposed method was conducted to compare the simulation results with experimental trends for microstructures of Ti–6Al–4V from the literature. The error in prediction of microstructural morphologies were 20% in the average alpha thickness with deviation of up to 5 μm.

Seismic wave propagation in fluid-solid coupled media is currently a popular topic. However, traditional wave equation-based simulation methods have to consider complex boundary conditions at the fluidsolid interface. To address this challenge, we propose a novel numerical scheme that integrates the lattice Boltzmann method (LBM) and lattice spring model (LSM). In this scheme, LBM simulates viscoacoustic wave propagation in the fluid area and LSM simulates elastic wave propagation in the solid area. We also introduce three different LBM-LSM coupling strategies, a standard bounce back scheme, a specular reflection scheme, and a hybrid scheme, to describe wave propagation across fluid-solid boundaries. To demonstrate the accuracy of these LBM-LSM coupling schemes, we simulate wave propagation in a two-layer model containing a fluid-solid interface. We place excitation sources in the fluid layer and the solid layer respectively, to observe the wave phenomena when seismic waves propagate to interface from different sides. The simulated results by LBM-LSM are compared with the reference wavefields obtained by the finite difference method (FDM) and the analytical solution (ANA). Our LBM-LSM coupling scheme was verified effective, as the relative errors between the LBM-LSM solutions and reference solutions were within an acceptable range, sometimes around 1.00%. The coupled LBM-LSM scheme is further used to model seismic wavefields across a more realistic rugged seabed, which reveals the potential applications of the coupled LBM-LSM scheme in marine seismic imaging techniques, such as reverse-time migration and full-waveform inversion. The method also has potential applications in simulating wave propagation in complex two- and multi-phase media. [ABSTRACT FROM AUTHOR]

Abstract This study investigates the influence of small control cylinders on the fluid dynamics around a square cylinder using the Lattice Boltzmann Method (LBM). Varying the gaps (L) between the main and control cylinders from 0 to 6, four distinct flow regimes are identified: the solo body regime (SBR), shear layer reattachment (SLR), suppressed fully developed flow (SFDF), and intermittent shedding (IS). The presence of control cylinders results in significant reductions in flow-induced forces, with drag coefficient (CD) and root mean square values of drag and lift coefficients (CD rms and CL rms ) decreasing by approximately 31%, 90%, and 81%, respectively. The SFDF flow regime exhibits the lowest fluid forces compared to other regimes. The effects of tiny control cylinders on the fluid flow characteristics of a square cylinder are examined using the Lattice Boltzmann Method (LBM) in this research work. The gaps (L) between the main and control cylinders are varied in the range from 0 to 6. The size of each control cylinder is equal to one-fifth of the primary cylinder. According to the findings, there are four distinct flow regimes as the gap spacing varies: solo body regime (SBR), shear layer reattachment (SLR), suppressed fully developed flow (SFDF), and intermittent shedding (IS) for gap spacing ranges 0 ≤ L ≤ 0.2, 0.3 ≤ L ≤ 0.9, 1 ≤ L ≤ 3, and 3.2 ≤ L ≤ 6, respectively. Additionally, it has been noted that the amplitude of variable lift force is reduced when the gap separation between the main and control cylinders is increased. When compared to solo cylinder values, it is found that the presence of small control cylinders in the flow field results in a considerable reduction of flow-induced forces. The SFDF flow regime was determined to have the lowest fluid forces compared to the other flow regimes studied. Our findings highlight the efficacy of small control cylinders in mitigating flow-induced forces and controlling flow characteristics. The LBM proves to be a valuable computational technique for such fluid flow problems.

Multifield coupling is frequently encountered and also an active area of research in geotechnical engineering. In this work, a particle-resolved direct numerical simulation (PR-DNS) technique is extended to simulate particle-fluid interaction problems involving heat transfer at the grain level. In this extended technique, an immersed moving boundary (IMB) scheme is used to couple the discrete element method (DEM) and lattice Boltzmann method (LBM), while a recently proposed Dirichlet-type thermal boundary condition is also adapted to account for heat transfer between fluid phase and solid particles. The resulting DEM-IBM-LBM model is robust to simulate moving curved boundaries with constant temperature in thermal flows. To facilitate the understanding and implementation of this coupled model for non-isothermal problems, a complete list is given for the conversion of relevant physical variables to lattice units. Then, benchmark tests, including a single-particle sedimentation and a two-particle drafting-kissing-tumbling (DKT) simulation with heat transfer, are carried out to validate the accuracy of our coupled technique. To further investigate the role of heat transfer in particle-laden flows, two multiple-particle problems with heat transfer are performed. Numerical examples demonstrate that the proposed coupling model is a promising high-resolution approach for simulating the heat-particle-fluid coupling at the grain level.

The high-resolution DEM-IMB-LBM model can accurately describe pore-scale fluid-solid interactions, but its potential for use in geotechnical engineering analysis has not been fully unleashed due to its prohibitive computational costs. To overcome this limitation, a message passing interface (MPI) parallel DEM-IMB-LBM framework is proposed aimed at enhancing computation efficiency. This framework utilises a static domain decomposition scheme, with the entire computation domain being decomposed into multiple subdomains according to predefined processors. A detailed parallel strategy is employed for both contact detection and hydrodynamic force calculation. In particular, a particle ID re-numbering scheme is proposed to handle particle transitions across sub-domain interfaces. Two benchmarks are conducted to validate the accuracy and overall performance of the proposed framework. Subsequently, the framework is applied to simulate scenarios involving multi-particle sedimentation and submarine landslides. The numerical examples effectively demonstrate the robustness and applicability of the MPI parallel DEM-IMB-LBM framework.

This study presents a method for the inverse analysis of fluid flow problems. The focus is put on accurately determining boundary conditions and characterizing the physical properties of granular media, such as permeability, and fluid components, like viscosity. The primary aim is to deduce either constant pressure head or pressure profiles, given the known velocity field at a steady-state flow through a conduit containing obstacles, including walls, spheres, and grains. The lattice Boltzmann method (LBM) combined with automatic differentiation (AD) (AD-LBM) is employed, with the help of the GPU-capable Taichi programming language. A lightweight tape is used to generate gradients for the entire LBM simulation, enabling end-to-end backpropagation. Our AD-LBM approach accurately estimates the boundary conditions for complex flow paths in porous media, leading to observed steady-state velocity fields and deriving macro-scale permeability and fluid viscosity. The method demonstrates significant advantages in terms of prediction accuracy and computational efficiency, making it a powerful tool for solving inverse fluid flow problems in various applications.

This study investigates the influence of small control cylinders on the fluid dynamics around a square cylinder using the Lattice Boltzmann Method (LBM). Varying the gaps (L) between the main and control cylinders from 0 to 6, four distinct flow regimes are identified: the solo body regime (SBR), shear layer reattachment (SLR), suppressed fully developed flow (SFDF), and intermittent shedding (IS). The presence of control cylinders results in significant reductions in flow-induced forces, with drag coefficient (CD) and root mean square values of drag and lift coefficients (CDrms and CLrms) decreasing by approximately 31%, 90%, and 81%, respectively. The SFDF flow regime exhibits the lowest fluid forces compared to other regimes. The effects of tiny control cylinders on the fluid flow characteristics of a square cylinder are examined using the Lattice Boltzmann Method (LBM) in this research work. The gaps (L) between the main and control cylinders are varied in the range from 0 to 6. The size of each control cylinder is equal to one-fifth of the primary cylinder. According to the findings, there are four distinct flow regimes as the gap spacing varies: solo body regime (SBR), shear layer reattachment (SLR), suppressed fully developed flow (SFDF), and intermittent shedding (IS) for gap spacing ranges 0 ≤ L ≤ 0.2, 0.3 ≤ L ≤ 0.9, 1 ≤ L ≤ 3, and 3.2 ≤ L ≤ 6, respectively. Additionally, it has been noted that the amplitude of variable lift force is reduced when the gap separation between the main and control cylinders is increased. When compared to solo cylinder values, it is found that the presence of small control cylinders in the flow field results in a considerable reduction of flow-induced forces. The SFDF flow regime was determined to have the lowest fluid forces compared to the other flow regimes studied. Our findings highlight the efficacy of small control cylinders in mitigating flow-induced forces and controlling flow characteristics. The LBM proves to be a valuable computational technique for such fluid flow problems. [ABSTRACT FROM AUTHOR]

A 2D numerical model has been created to simulate the gas flow in a porous hydrogen (H2) and air-fed solid oxide fuel cell (SOFC) and analyze the generation of entropy involved via the major key contributing factors. On this basis, flow, thermal, and mass transfers have been numerically handled with a validated lattice Boltzmann method (LBM), including flow channels that have an impact on the entropy generation assessment. Flow, thermal, and mass paths have been simulated throughout the SOFC. It turned out that the ohmic losses are largely predominant compared with those of the other factors (irreversibilities due to fluid friction, heat transfer, mass/chemical transfer, and activation). In addition, under equal current density, the partially obstructed anode channel exhibits lower entropy generation compared with the free (unobstructed) anode channel, thereby indicating higher heat and mass transfer performance. These findings indicate the modeling efficiency considered and the potential of the LBM approach to address the processes involved in a porous H2 SOFC. SOFCs directly convert chemical energy into electrical energy, with high efficiency, strong reliability, and low emissions. SOFCs have become attractive for automotive and aerospace industries due to their energy flexibility. The design of their channels directly affects heat and mass transfer capability and their output performance. For a better view of the thermal performance of any thermal system, aspects such as pressure drop and entropy generation must be considered in addition to heat transfer factors. Entropy generation analysis is one of the most used techniques to refine the SOFC design and investigate their performance. This can be achieved by modifying the anode channel. One option is to partially obstruct the channel with differently shaped obstacles. Further, the numerical simulations can provide a solid reference point for future CFD models and are relevant to thermal dynamics in these devices and chemical-to-electrical energy conversion industries. [ABSTRACT FROM AUTHOR]

Abstract In Proton Exchange Membrane Fuel Cells (PEMFCs), the presence of residual water within the Gas Diffusion Layer (GDL) poses challenges during cold starts and accelerates degradation. A computational model based on the Lattice Boltzmann Method (LBM) was developed to consider the capillary pressure inside the PEMFC and to analyze the exact geometries of the GDLs, which were obtained using the Computed Tomography scan. The novelty of this study is to suggest a methodology to compare the quantitative water removal performance of the GDLs without long-term experimental testing. Two different samples of GDLs were considered, pristine and aged. The results of quantitative measurements revealed the amount of water columns (breakthroughs) inside each sample. Considering the volume of 12,250,000 µm3 for each sample, the pristine and the aged samples are prone to have 774,200 µm3 (6.32%) and 1,239,700 µm3 (10.12%) as water columns in their porous domain. Micro-structural properties such as connectivity, mean diameter, effective diffusivity, etc. were also compared to observe the impacts of aging on the properties of the GDL.

The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs, where the flowback rate of shale fracturing fluid is lower than that of conventional reservoirs. At the early stage of flowback, there is no single-phase flow of the liquid phase in shale, but rather a gas-water two-phase flow, such that the single-phase flow model for tight oil and gas reservoirs is not applicable. In this study, pores and microfractures are extracted based on the experimental results of computed tomography (CT) scanning, and a spatial model of microfractures is established. Then, the influence of rough microfracture surfaces on the flow is corrected using the modified cubic law, which was modified by introducing the average deviation of the microfracture height as a roughness factor to consider the influence of microfracture surface roughness. The flow in the fracture network is simulated using the modified cubic law and the lattice Boltzmann method (LBM). The results obtained demonstrate that most of the fracturing fluid is retained in the shale microfractures, which explains the low fracturing fluid flowback rate in shale hydraulic fracturing.

As the global concern over greenhouse gas emissions grows, CO2 storage in deep saline aquifers and depleted reservoirs has become crucial for climate change mitigation. This study evaluates the feasibility of Lithuanian deep saline aquifers, specifically, Syderiai and Vaskai, for effective CO2 storage. Unlike previous theoretical analyses, it provides experimental data on static and dynamic reservoir parameters that impact CO2 injection and retention. Using micro X-ray computed tomography (MXCT) and multi-resolution scanning at 8 µm and 22 µm, digital rock volumes (DRVs) from core samples were created to determine porosity and permeability. The method, validated against analogous samples, identified a representative element volume (REV) within sub-volumes, showing a homogeneous distribution of petrophysical properties in the Lithuanian samples. The results show that DRVs can accurately reflect pore-scale properties, achieving 90–95% agreement with lab measurements, and offer a rapid, efficient means for analyzing storage potentials. These insights confirm that Lithuanian aquifers are promising for CO2 sequestration, with recommendations for further long-term monitoring and applications of this technique across the region.

In Proton Exchange Membrane Fuel Cells (PEMFCs), the presence of residual water within the Gas Diffusion Layer (GDL) poses challenges during cold starts and accelerates degradation. A computational model based on the Lattice Boltzmann Method (LBM) was developed to consider the capillary pressure inside the PEMFC and to analyze the exact geometries of the GDLs, which were obtained using the Computed Tomography scan. The novelty of this study is to suggest a methodology to compare the quantitative water removal performance of the GDLs without long-term experimental testing. Two different samples of GDLs were considered, pristine and aged. The results of quantitative measurements revealed the amount of water columns (breakthroughs) inside each sample. Considering the volume of 12,250,000 µm3 for each sample, the pristine and the aged samples are prone to have 774,200 µm3 (6.32%) and 1,239,700 µm3 (10.12%) as water columns in their porous domain. Micro-structural properties such as connectivity, mean diameter, effective diffusivity, etc. were also compared to observe the impacts of aging on the properties of the GDL. [ABSTRACT FROM AUTHOR]

Shale oil has become the focus of the exploration and development of unconventional oil and gas resources in the world, but its development faces many challenges. Aiming at the complex pore space, the unclear percolation mechanism, and the urgent need to explore research methods of shale oil, this paper systematically expounded the research status of microscopic percolation mechanism of shale oil in experimental methods and computational simulation, and discussed the existing problems and the development trend of future research from the perspective of pore-scale and core-scale. The results show that the combination of various experimental methods can well characterize the pore structure of shale, but the characterization of micro-scale and core-scale flow is still insufficient. The direct method represented by Lattice Boltzmann Method and the indirect method represented by pore network simulation are the main methods to study pore-scale flow mechanism, but the consideration of micro-scale effect needs to be improved. The study of core-scale flow mechanism is mainly to establish a percolation model considering boundary layer effect based on capillary bundle model and fractal theory. It is pointed out that the main future research direction is to fully consider the factors such as boundary adsorption/slip, density/viscosity heterogeneity, stress sensitivity, start-up pressure gradient of shale oil in micro-nano pores, realize multi-scale percolation mechanism coupling, and establish a mathematical model that can accurately characterize the multi-phase and multi-scale flow of shale oil.

The present paper investigates the flow field and heat transfer in a microchannel with incorporating surface hydrophobicity and considering its thickness. The microchannel is under partial magnetic field (MF), which is applied to the top thermal-insulated wall in Hartmann numbers 0 to 30. The results show that at Ha = 0, viscous dissipation (VD) and heat transfer decrease with increasing slip coefficient. Also, raising the Hartmann number (Ha) increases the friction coefficient. The Nusselt number (Nu) reaches its highest value at Ha = 20 for all cases, but then, as the Ha increases, the average Nu reduces.

Metal foam flow field shows great potential for next‐generation proton exchange membrane (PEM) fuel cell of high power density due to its well‐connected pore structure, high thermal and electrical conductivity. However, the complicated pore structure makes it a challenge for water management. To tackle this issue, a novel design of metal foam flow field with hierarchical pore structure was proposed. Based on lattice Boltzmann method (LBM), the structure‐performance relationship between hierarchical pore structure and water discharge capability of flow field was explored by using breakthrough time. Furthermore, an optimal hierarchical pore structure for metal foam flow field that shows superior water discharge capability was obtained. Compared with metal foam with uniform coarse pore structure, breakthrough time can be reduced roughly by 17.6% in the one with optimal hierarchical pore structures. This finding provides a theoretical foundation and technical guidance for developing metal foam flow field. [ABSTRACT FROM AUTHOR]

The study seeks to improve liquid-filled pipeline fluid-structure coupling project management in order to forecast vibration response and fatigue damage. To manage the complexity of fluid-structure interactions, our project management system employs Lattice Boltzmann theory and innovative optimization approaches. The study includes fluid characterization, Lattice Boltzmann Model optimization, fluid-structure interaction coupling, and vibration response analysis. Surrogate modeling, adaptive mesh refining, and parallel processing all contribute to increased simulation efficiency. The Lattice Boltzmann Method was chosen for its adaptability and computational efficiency in complex liquid-filled pipeline dynamics with varying flow conditions and external stressors. This work aimed to improve performance and simplify project administration. The emphasis is on early fluid-structure interaction, effective communication, and project performance monitoring throughout the lifecycle. We simulate liquid-filled pipeline dynamics in a variety of operating situations to forecast natural frequencies, stress distributions, and fatigue damage indicators. The Lattice Boltzmann Method and other advanced computational techniques improve project management fluid-structure coupling. This study describes the advantages of the Lattice Boltzmann Method over alternative approaches. Modeling liquid-filled pipeline dynamics under varying flow conditions and external forces necessitates adaptability and processing efficiency. Better results and more efficient project management. This option improves the liquid-filled pipe fluid-structure coupling project management. The study assists engineers and project managers in designing and operating cost-effective, structurally sound liquid-filled pipelines. This study also lays the groundwork for more powerful and diverse fluid-structure interaction analysis tools that are more practical. We improve pipeline fluid-structure coupling and provide researchers and practitioners with new problem-solving tools.

Abstract A numerical investigation of conjugate natural convection in a 2D square enclosure with multiple solid blocks, considering the impact of volumetric thermal radiation, was conducted using the lattice Boltzmann method (LBM). The effect of Planck number 0.01 ≤ P l ≤ 1 , wall surface emissivity 0 ≤ ε w ≤ 1 , extinction coefficient 0.1 ≤ β ≤ 5 , solid-to-fluid volume fraction 15 % ≤ χ ≤ 60 % , and the number of solid blocks 1 ≤ N ≤ 64 , on the fluid-structure and heat transfer within the enclosure were analyzed. The numerical model was validated using benchmark problems from the literature, showing good agreement. The results revealed that at P l = 0.01 and N = 16 , increasing wall surface emissivity significantly increased the Nusselt number, ranging from approximately 51-116% for different wall emissivity values, as compared to scenarios without surface radiation ( ε w ). On the other hand, reducing χ, Pl, and β improved the heat transfer rate. The results also demonstrated that subdividing the initial block reduced the heat transfer rate depending on the number of blocks and the value of the Planck number. For instance, when 64 solid blocks were present in the cavity and P l = 0.01 , the Nusselt number decreased by 59.36% compared to the case with a lower solid-to-fluid volume fraction (χ = 15%). The parametric analysis provided useful insights for engineering design in the modern construction industry, with possible applications in building block design and energy efficiency enhancements. [ABSTRACT FROM AUTHOR]

The present paper investigates the flow field and heat transfer in a microchannel with incorporating surface hydrophobicity and considering its thickness. The microchannel is under partial magnetic field (MF), which is applied to the top thermal-insulated wall in Hartmann numbers 0 to 30. The results show that at Ha = 0, viscous dissipation (VD) and heat transfer decrease with increasing slip coefficient. Also, raising the Hartmann number (Ha) increases the friction coefficient. The Nusselt number (Nu) reaches its highest value at Ha = 20 for all cases, but then, as the Ha increases, the average Nu reduces. [ABSTRACT FROM AUTHOR]

Suspensions of monodisperse spherical particles under shear flow were simulated using a solid-liquid two-phase model based on coupled lattice Boltzmann method (LBM) and discrete element method (DEM). Evaluating the shear stresses due to the viscous behavior of the bulk fluid, the hydrodynamic interaction between particles and fluid, and the physical contact between particles, the contribution of each factor to the suspension viscosity was investigated. The results showed that in the range of low to moderate particle volume fractions, the viscosity of suspensions is mainly determined by the action of the fluid, and that the contribution of particle contact increases with increasing particle volume fraction. In particular, the flow behavior of dense suspensions should be viewed not as a fluid motion but as the motion of a group of particles. From these results, in order to predict and control the rheological properties of particle suspensions, it is important to understand that the main factors increasing viscosity vary with the concentration range of interest. [ABSTRACT FROM AUTHOR]

Understanding and modeling flows over porous layers are of great industrial significance. To accurately solve the turbulent multi-scale flows on complex configurations, a rescaling algorithm designed for turbulent flows with the Chapman-Enskog analysis is proposed. The mesh layout and the detailed rescaling procedure are also introduced. Direct numerical simulations (DNSs) for a turbulent channel flow and a porous walled turbulent channel flow are performed with the three-dimensional nineteen-velocity (D3Q19) multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) to validate the accuracy, adaptability, and computational performance of the present rescaling algorithm. The results, which are consistent with the previous DNS studies based on the finite difference method and the LBM, demonstrate that the present method can maintain the continuity of the macro values across the grid interface and is able to adapt to complex geometries. The reasonable time consumption of the rescaling procedure shows that the present method can accurately calculate various turbulent flows with multi-scale and complex configurations while maintaining high computational efficiency. [ABSTRACT FROM AUTHOR]

Hydroacoustic analyses using direct methods are challenging in the field of computational physics. To date, hybrid methods are an alternative approach adopted for performing hydroacoustic analysis, although it demonstrates clear limitations in analyzing nonlinear turbulent noise. The lattice Boltzmann method (LBM) provides a solution to address the limitations of the hybrid method and is frequently applied in aeroacoustics. However, existing methods, such as the Bhatnagar–Gross–Krook (BGK) operator, suffer from instabilities that manifest in an oscillatory fashion in underwater conditions. Hydroacoustic situations are characterized by high Reynolds number (Re) to Mach number (Ma) ratios, and these conditions correspond to cases where stability problems occur. In this study, a direct-method-based two-step (DM-TS) LBM collision operator is introduced to solve the stability problem. The stability, accuracy, and consistency of the scheme are investigated and compared with the BGK-LBM. The DM-TS operator is developed to provide the same accuracy order as the BGK scheme while addressing the stability problem. Vortex shedding from a two-dimensional cylinder is simulated using the DM-TS operator to prove that the proposed method could be used to solve hydroacoustic problems. The results of the analysis indicate that dynamic and acoustic pressures can be obtained simultaneously using the DM–TS operator. [ABSTRACT FROM AUTHOR]

Numerical packings of spheres with uniform grain size distribution and maximum to minimum diameter ratio up to 15 are generated using the Discrete Element Method (DEM). Two numerical methods are used to compute their permeability by homogenization: the Lattice Boltzmann Method (LBM) and a Fast Fourier Transform (FFT) based method. The results given by both methods are shown to be consistent with semi-analytical and experimental results. For an identical discretization grid, the FFT method has the lowest memory and computational time requirements. The LBM is more accurate for coarse to moderately fine discretizations, while the FFT method converges linearly with the voxel size h with a relative discretization error below 1.5 times h / D 25 , where D 25 is the 25% passing by mass grain diameter. The issue of the variability of the permeability computed on finite sized samples is determined either directly by many realizations of similar random samples or indirectly by a faster filtering method on a single sample. Both methods yield similar results and indicate that a Representative Volume Element (RVE) size greater than 7 D 40 guarantees a variability of permeability below 5%. [ABSTRACT FROM AUTHOR]

This article investigates the effect of a synthetic jet (SJ) on the flow over a backward-facing step (BFS) in the weakly turbulent flow regime using the lattice Boltzmann method. The SJ operates with various momentum coefficients Cμ and forcing frequencies fjet*. As Cμ increases, the reattachment length decreases, whereas increasing fjet* causes the reattachment length at first decrease and then increase. A minimum reattachment length appears at Cμ = 0.3125, fjet* = 1.6, corresponding to a 40% reduction compared with the uncontrolled case. Two mechanisms for the mediated flow are found: (1) A suitable control frequency leads to a lock-on state that prompts vertical momentum transfer and laminarizes the flow near the separation point, (2) Regular vortices emerge after wall reattachment in controlled cases. Fast Fourier and wavelet transform of the velocity near the separation point reveal that the monitored frequency becomes locked-on when fjet* > 1.6, making the flow quasi-periodic and dramatically reducing the reattachment length. Turbulent kinetic energy spectra indicate that the monitored frequencies are dominated by the forcing frequency and that active control laminarizes the local flow. Proper orthogonal decomposition is used to extract coherent structures at multiple scales. In the dominant mode, reattaching wake vortices are regulated by active control. In the second mode, irregular wake vortices emerge after fjet* = 2, which attenuates the SJ forcing and increases the reattachment length. This study provides insights on typical flows past a BFS and will shed more light on the design of closed-loop control strategies for separation flows. [ABSTRACT FROM AUTHOR]

This study aims to investigate the aerodynamic analysis of a Darrieus-type vertical axis wind turbine (VAWT) using the Lattice Boltzmann Method (LBM). The objective is to assess the accuracy and performance of the meshless LBM approach in predicting torque coefficients, velocity, turbulence intensity, and vorticity distributions for VAWT aerodynamic analysis. Two turbulence modelling approaches, Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS), are employed to model the flow domain. The central problem revolves around comparing the performance of different turbulence models based on their agreement with experimental results for power and torque coefficients. The findings demonstrate the effectiveness of the WALE turbulence model in achieving the best agreement with experimental data. Overall, the study provides valuable insights into applying LBM in VAWT aerodynamic analysis and highlights the advantages of the meshless approach compared to traditional CFD methods. [ABSTRACT FROM AUTHOR]

As operating under quite high bearing speed with quite narrow clearance, the slip effect generally inevitable exists and closely relates to the performance of Gas Journal Bearing (GJB). However, singly the conventional macroscopic method may not be capable of fully exploring the influence of slip effect and seize tiny details such as slip velocity and flow vortex. In this article, both the Lattice Boltzmann Method (LBM) and the Reynolds equation method are applied to analyze the distributions of lubricant viscous dissipation heat, velocity, slip velocity, pressure, journal position and film thickness versus different operating parameters at multiscale. It shows that the slip effect weakens the squeezing function on lubricant film, reduces the viscous dissipation heat peaks, consumes the maximum pressure peaks, and decreases the bearing capacity, which is more obvious at larger Knudsen number. At higher bearing speed, the high viscous dissipation heat and pressure zone rapidly magnifies, in contrast, under larger bearing load, the high viscous dissipation heat zone concentrates. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method (LBM) has been increasingly used as a stand-alone CFD solver in various biomechanical applications. This study proposes a new fluid–structure interaction (FSI) co-modeling framework for the hemodynamic-structural analysis of compliant aortic valves. Toward that goal, two commercial software packages are integrated using the lattice Boltzmann (LBM) and finite element (FE) methods. The suitability of the LBM-FE hemodynamic FSI is examined in modeling healthy tricuspid and bicuspid aortic valves (TAV and BAV), respectively. In addition, a multi-scale structural approach that has been employed explicitly recognizes the heterogeneous leaflet tissues and differentiates between the collagen fiber network (CFN) embedded within the elastin matrix of the leaflets. The CFN multi-scale tissue model is inspired by monitoring the distribution of the collagen in 15 porcine leaflets. Different simulations have been examined, and structural stresses and resulting hemodynamics are analyzed. We found that LBM-FE FSI approach can produce good predictions for the flow and structural behaviors of TAV and BAV and correlates well with those reported in the literature. The multi-scale heterogeneous CFN tissue structural model enhances our understanding of the mechanical roles of the CFN and the elastin matrix behaviors. The importance of LBM-FE FSI also emerges in its ability to resolve local hemodynamic and structural behaviors. In particular, the diastolic fluctuating velocity phenomenon near the leaflets is explicitly predicted, providing vital information on the flow transient nature. The full closure of the contacting leaflets in BAV is also demonstrated. Accordingly, good structural kinematics and deformations are captured for the entire cardiac cycle. [ABSTRACT FROM AUTHOR]

Utilizing phase change materials (PCMs) is one of the most effective methods of storing thermal energy and is gaining popularity in renewable energy systems. In order to analyze PCM performance, various numerical methods have been deployed to study the transient behaviour during phase changes. PCMs' low thermal conductivity prevents their use as pure PCMs in industrial applications. There are various efficient methods of enhancing PCM thermal conductivity, which are addressed in this article. On the other hand, the lattice Boltzmann method (LBM) is very inclusive in the numerical simulation of complex fluid flows, thermal transport, and chemical interactions because of its ability to simply represent various complex physical phenomena, suitability for parallel programming, and easy coding and implementation. Many numerical studies have been conducted on PCMs using the LBM. This study aims to review these studies and categorize them in a way so that one may thoroughly understand the LBM's capabilities in the simulation of PCM-related investigations. First, PCM characteristics and applications are presented, then the LBM implementation in PCM problems is addressed. Afterward, the fabrication and types of PCMs are mentioned. Next, the improvement of thermal energy storage methods of PCMs is stated. Furthermore, governing equations are reviewed. Lastly, the opportunities and challenges of the LBM in PCMs are discussed. [ABSTRACT FROM AUTHOR]

In this paper we blend two lattice-Boltzmann (LB) numerical schemes with an a posteriori Multi-dimensional Optimal Order Detection (MOOD) paradigm to solve hyperbolic systems of conservation laws in 1D and 2D. The first LB scheme is robust to the presence of shock waves but lacks accuracy on smooth flows. The second one has a second-order of accuracy but develops non-physical oscillations when solving steep gradients. The MOOD paradigm produces a hybrid LB scheme via smooth and positivity detectors allowing to gather the best properties of the two LB methods within one scheme. Indeed, the resulting scheme presents second order of accuracy on smooth solutions, essentially non-oscillatory behaviour on irregular ones, and, an 'almost fail-safe' property concerning positivity issues. The numerical results on a set of sanity test cases and demanding ones are presented assessing the appropriate behaviour of the hybrid LBMOOD scheme in 1D and 2D. [ABSTRACT FROM AUTHOR]

In aerial spraying of plant protection UAVs, the continuous reduction of pesticides is an objective process. Under the condition of constant flight state (speed and altitude), the change of pesticide loading will inevitably lead to the shift of lift force and rotor speed generated by UAV rotor rotation, which will change the distribution of the rotor flow field and affect the effect of aerial spraying operation of plant protection UAV. Therefore, the rotor speed of UAV is taken as the research object in this paper, and the adaptive refinement physical model based on the Lattice Boltzmann Method (LBM) is used to numerically simulate the rotor flow field of the quadrotor plant-protection UAV at different speeds. A high-speed particle image velocimeter (PIV) was used to obtain and verify the motion state of the droplets emitted from the fan nozzle in the rotor flow field at different speeds. The results show that, with the increase of rotor speed, the maximum velocity and vorticity of the wind field under the rotor increase gradually, the top wind speed can reach 13m/s, and the maximum vorticity can reach 589.64s-1. Moreover, the maximum velocity flow value is mainly concentrated within 1m below the rotor, and the maximum vorticity value is primarily concentrated within 0.5m. However, with the increase of time, the ultimate value of velocity and vorticity decreases due to the appearance of turbulence, and the distribution of velocity and vorticity are symmetrically distributed along the centre line of the fuselage, within the range of (-1m, 1m) in the X direction. It is consistent with the motion state of droplets under the action of the rotor downwash flow field obtained by PIV. The study results are expected to reveal and understand the change law of the rotor flow field of plant protection UAVs with the dynamic change of pesticide loading to provide a theoretical basis for the development of precise spraying operation mode of plant protection UAVs and improve the operation effect. [ABSTRACT FROM AUTHOR]

Sharp phase interfaces and accurate temperature distributions are important criteria in the simulation of solid-liquid phase changes. The multi-relaxation-time lattice Boltzmann method (MRT-LBM) shows great numerical performance during simulation; however, the value method of the relaxation parameters needs to be specified. Therefore, in this study, a random forest (RF) model is used to discriminate the importance of different relaxation parameters to the convergence, and a support vector machine (SVM) is used to explore the decision boundary of the convergent samples in each dimensional model. The results show that the convergence of the samples is consistent with the sign of the decision number, and two types of the numerical deviations appear, i.e., the phase mushy zone and the non-physical heat transfer. The relaxation parameters chosen on the decision boundary can further suppress the numerical bias and improve numerical accuracy. [ABSTRACT FROM AUTHOR]

Micro-cracks commonly occur on the catalyst layers (CLs) during the manufacturing of catalyst coated membranes (CCMs). However, the crack shape parameters effect on CLs in-plane (IP) electronic conductivity λ s is not clear. In this work, the relationship between crack parameters and the λ s is obtained based on the two-dimensional (2D) multiple-relaxation time (MRT) lattice Boltzmann method (LBM). The LBM numerical model is validated by the normalized λ s experiment applied on three different home-made cracked CLs, and the parameter study focus on crack width, length, quantity and phase angle are carried out. The results show that the decrease of λ s has different sensitivity | k | to the parameters above. The crack width has little effect on λ s decrease, and the | k w | is 0.038. However, crack arm length and quantity show more significant impact, which | k l | and | k N | are 0.753 and 0.725, respectively. The CLs with different crack propagation directions show significant anisotropy on λ s , and a 53.53% decrease in λ s is observed between 0° and 90° crack phase angle change. To manufacture a high electronic conductivity CL, crack initiation and migration mitigation are highly encouraged. • Crack parameters are defined in the catalyst layer for the first time. • A homemade cracked domain reconstruction method is proposed. • In-plane conductivity is investigated using the 2D MRT lattice Boltzmann method. • Crack length and quantity show a more significant influence than crack width on in-plane conductivity. [ABSTRACT FROM AUTHOR]

In this work, we present an extension of the lattice Boltzmann method for solving radiative transfer equation (RTE) in emitting, absorbing, and non-scattering gaseous mixtures produced by combustion. A numerical procedure based on LBM is first developed for a single absorption coefficient avoiding spectral effect (gray gas model). Therefore, an infrared radiative global model is associated with the LBM to assess the radiative heat exchanges in molecular gaseous mixtures. A global model based on absorption distribution function (ADF) and a D2Q16 scheme are implemented to solve the 2D RTE. Results are presented in terms of temperature, radiative heat flux, and volumetric radiative power. Effects of radiative behavior and spectral structure of gaseous mixtures are put in evidence. The application of the LBM-ADF8 to gaseous mixture produced by combustion emphasizes the importance of taking into account its spectral structures. The error induced by the gray media approximation is put in evidence. [ABSTRACT FROM AUTHOR]

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ObjectivesNewly proposed in recent years, the liquid-infused surface (LIS) is a drag reduction surface which replaces the residual air conserved by the microgrooves of a traditional superhydrophobic surface with a lubricant, thereby vastly improving the stability of the drag reduction level. To fully understand the drag reduction stability of LIS, this paper focuses on the influence of lubricant solubility on drag reduction. MethodsBased on the lattice Boltzmann method (LBM), we simulated a conserving lubricant microstructure with microflow and studied the influence of the lubricant's dissolved density and shear velocity on slip length. ResultsThe liquid-infused surface results in a slip phenomenon, and there exists a linear relationship between slip length and cohesion force strength among its particles when the lubricant is completely dissolved or difficult to dissolve. ConclusionsWith greater cohesion force strength among its particles, a lubricant can result in more promising drag reduction when it is difficult to dissolve. The lubricant's shear velocity has little influence on slip length. The properties of the lubricant are similar to those of a traditional superhydrophobic surface.