Lattice Boltzmann Method Simulation Research Articles

Numerical study of transition hydraulic jumps in different types of stilling basins using lattice Boltzmann methods

Transition hydraulic jumps, also known as low-Froude number jumps, have been less studied compared to high Froude number jumps, despite their significance in high-discharge and low-head dams. A three-dimensional (3D) Lattice Boltzmann method simulation was conducted to investigate submerged transition hydraulic jumps in both normal and expanded stilling basins, focusing on turbulent flow characteristics such as velocity fields, vorticity features, pressure fluctuations, and coherent structures. In expanded basins, two symmetric separated rollers were observed, with the rollers detaching from the submerged jump as the width of basin increased. The length of submerged roller in normal basins is observed as Lr/Ht = 6.19, while it is decreased to Lr/Ht = 4 in expanded basins because of the occurrence of roller lateral diffusion toward sidewalls. The transition of vortex structures from y- to z-vortical was analyzed, and three-dimensional shear layers are captured using the iso-surface of vorticity magnitude ω = 6.5. To further describe the internal structure of turbulence within the transition hydraulic jump, the coherent flow structures are qualitatively examined using the Ω criterion that is the third generation of vortex identification technique. Pressure fluctuations in low-Froude number stilling basins, described using root mean square (RMS), are first presented. High patches of RMS are found in the flow fields and at the bottom of basins, and it is qualitatively noted that shear effects make great contributions to the pressure fluctuations. Distribution of bottom pressure fluctuation RMS in different types of basin was also analyzed. The peak RMS value occurs at the ogee region of the weir, specifically at x/L = −0.2, and it is mainly affected by the width of expansion. Bottom pressure fluctuation RMS decreases in the following order: Normal, 5 m gradual expansion, 10 m gradual expansion, 5 m sudden expansion, and 10 m sudden expansion, due to the lateral diffusion of rollers toward sidewalls. This research introduces an innovative numerical simulation approach to studying pressure fluctuations, offering valuable insights for hydraulic engineering applications.

Direct hydroacoustics analyses of pipe orifice using lattice Boltzmann method

Acoustic waves in water pipes pose a structural threat but also offer a valuable tool for non-invasive inspection. Complex pipe geometries such as bends and surface liners create complex fluid boundaries, triggering interactions between fluid flow and acoustics. The lattice Boltzmann method (LBM) excels at capturing these interactions near complex boundaries, in contrast to the finite volume method, which can result in errors. However, the application of LBM in water pipes has been limited by stability problems. This study proposes a two-step (DM-TS) collision operator based on a direct method (LBM-HA) for stable LBM simulations in water pipes. LBM-HA enables direct hydroacoustic predictions for both acoustic and dynamic flow fields in a pipe orifice. A novel acoustic-dynamic complex boundary condition was formulated from the linearized Euler's equation to account for the physical effects of the bounded domain of the LBM-HA analysis. To distinguish between dynamic and acoustic components, wavenumber and frequency decomposition techniques were applied to the pressure data obtained within the pipe. In addition, mode decomposition of the acoustic pressure was conducted to identify the dominant acoustic modes. By comparing the LBM-HA results with experimental data, we highlighted the method's potential for direct hydroacoustic analysis considering the acoustic characteristics of the water pipe.

Novel lattice Boltzmann method for simulation of strongly shear thinning viscoelastic fluids

AbstractThe simulation of viscoelastic liquids using the Lattice–Boltzmann method (LBM) in full three dimensions remains a formidable numerical challenge. In particular the simulation of strongly shear‐thinning fluids, where the ratio between the high‐shear and low‐shear viscosities is large, is often prevented by stability problems. Here we present a novel approach to overcome this issue. The central idea is to artificially increase the solvent viscosity which allows the method to benefit from the very good stability properties of the LBM. To compensate for this additional viscous stress, the polymer stress is reduced by the same amount. We apply this novel method to simulate two realistic cell carrier fluids, methyl cellulose and alginate solutions, of which the latter exhibits a viscosity ratio exceeding 10,000.

A GPU-Based Lattice Boltzmann Method for Predicting Near- and Far-Field Jet Noise

Jet flow and noise are simulated using the lattice Boltzmann method (LBM). The D3Q19 lattice model calculates the flow field with a high-order distribution function to overcome LBM limitations in solving high Mach number flows. Multiple relaxation times (MRT) and large eddy simulation (LES) are used in this study. Compressible LBM was applied to the simulation jet flow to demonstrate the ability of the fifth-order equilibrium distribution function to simulate compressible flows efficiently. The results from the LBM simulation were then employed in Kirchhoff's surface integral approach to predict far-field jet noise. In this research, we used the compute unified device architecture (CUDA) to implement the LBM in a graphics processing unit (GPU), thus creating a hybrid code, LBM-MRT-LES. The obtained results agreed with the experimental and numerical results in the literature.

Modeling aeroacoustic interaction of rotating propeller with porous treatments using LBM (Lattice Boltzmann method) simulations

Porous treatments are more and more employed in presence of flow as passive noise control means to mitigate the generated noise. They are generally designed according to their acoustic dissipation properties under no-flow conditions. Nevertheless, in-flow porous treatments can alter the aerodynamic properties, modify the main acoustic source itself or even generate secondary acoustic sources. While most of the modelling methods (analytical, FEM, ...) are able to model the acoustic dissipation, they do not allow to model the interaction with the main source or the possible generation of spurious acoustic sources. The Lattice Boltzmann Method (LBM) is a computational fluid dynamics method able to run Direct Numerical Simulations (DNS) as well as Large Eddy Simulations (LES). The LES method resolves the macroscopic scale of turbulence and uses a sub-grid model for the small scales of turbulence. The low numerical dissipation of the LBM enables to compute both fluid flow and acoustics quantities in a single run. In this work, the LBM implemented in ProLB software is used to model the airborne noise generated by an electric propeller installed on an aircraft wing and the effects of sound absorbing treatments. Various treatments are investigated numerically and compared to experimental data when available.

Effects of Varying Oil/Water Saturations on Miscible and Immiscible CO2 Flooding in Heterogeneous Porous Media: A Lattice Boltzmann Method Simulation Study

Effects of Varying Oil/Water Saturations on Miscible and Immiscible CO₂ Flooding in Heterogeneous Porous Media: A Lattice Boltzmann Method Simulation Study

Dielectrophoresis effect on anti-icing characteristics of superhydrophobic surface

In present study, icing experiment using semiconductor refrigeration method and 3D LBM (Lattice Boltzmann method) simulation by employing improved Shan-Chen model coupling the electric field model are conducted to confirm dielectrophoresis effect on freezing characterisitic of a sessile droplet at superhydrophobic surface. Tests are performed with the same droplet diameter of d = 2.6 mm, cold wall temperature of TW = -5 °C and ambient condition (TA = 20 °C, RH = 48%). The sessile droplet freezing process is recorded at different contact angles and electric field intensities. The improved Shan-Chen model with large density ratio (ρl/ρv = 36.55), electric field model and new wettability model are applied to simulate droplet deformation. The present results show that the droplet icing time has a positive relationship with contact angle and electric field intensity, the droplet icing time is extended up to about 40 times by the couple effect of superhydrophobic coating and the electric field. The size of droplet-solid interface and electric-induced convection are the key factors of anti-icing performance.

Double Droplets Impact an Inclined Superhydrophobic Surface.

The rebound dynamics of double droplets impacting an inclined superhydrophobic surface decorated with macro-ridges are investigated via lattice Boltzmann method (LBM) simulations. Four rebound regions are identified, that is, the no-coalescence-rebound (NCR), the partial-coalescence-rebound of the middle part bounces first (PCR-M), and the side part bounces first (PCR-S), as well as the complete-coalescence-rebound (CCR). The occurrence of the rebound regions strongly depends on the droplet arrangement, the center-to-center distance of the droplets, and the Weber number. Furthermore, the contact time is closely related to the rebound regions. The PCR-M region can significantly reduce the contact time because the energy dissipation in this region may decrease which can promote the rebound dynamic. Intriguingly, the contact time is also affected by the droplet arrangement; i.e., droplets arranged parallel to the ridge dramatically shorten the contact time since this arrangement increases the asymmetry of the liquid film. Therefore, for multidrop impact, the contact time can be effectively manipulated by changing the rebound region and the droplet arrangement. This work focuses on elucidating the wetting behaviors, rebound regions, and contact time of the multiple-droplet impacting an inclined superhydrophobic surface decorated with macro-ridges.

CFD simulation of a multi-rotor system using diffuser augmented wind turbines by lattice Boltzmann method

A diffuser-augmented wind turbine (DAWT) achieves greater power generation efficiency by increasing wind speed through the diffuser. Nevertheless, scaling up this technology is difficult because of the considerable amount of wind drag on the diffusers. To overcome this difficulty, a multi-rotor system with two or more wind turbines on the same structure is one approach to increasing wind turbine power output. This research proposes a computational fluid dynamics (CFD) method to evaluate the hydrodynamic performance of a large-scale multi-rotor system of DAWTs. Compared to conventional wind turbines, CFD simulations of DAWTs necessitate higher computational costs because of the need of high-resolution meshes for the diffuser. Furthermore, the computational cost of a multi-rotor system increases with the number of rotors. To address the issue of high computational cost, we use the Lattice Boltzmann Method (LBM), which is well suited to large-scale CFD simulations. A wind turbine is modeled as an actuator line model and a diffuser as a wall boundary. An adaptive mesh refinement approach generates higher resolution meshes near the rotor and diffuser. LBM simulations were conducted for a single DAWT and a multi-rotor system with five DAWTs. The LBM results of the wake velocity and pressure distributions were in agreement with those obtained from wind tunnel experiments and general CFD methods in earlier studies. To investigate the diffuser gap effects, we simulated five DAWTs with diffuser gaps of 5%–25% of the diffuser diameter. The power gain of each DAWT was assessed. Great performance improvements were found with diffuser gaps of 20% and 25% of the diffuser diameter. On average, the five DAWTs achieved a power gain of more than 10%. These findings confirmed the accurate evaluation capability of the proposed CFD method for hydrodynamic characteristics of multi-rotor systems using DAWTs.

Morphological characteristics and cleaning effects of collapsing cavitation bubble in fractal cracks

When a cavitation bubble collapses in a crack, due to the lack of symmetry, spatial uniformity, and obvious correlations during the collapse process, it is difficult to effectively explore the interaction mechanism between the bubble and crack walls. In this paper, a combination of numerical simulation and experimental approaches are used to explore the collapse process of a cavitation bubble in a fractal crack. The numerical model is based on the pseudopotential multi-relaxation-time lattice Boltzmann method (LBM). The experiment platform including an underwater pulsed discharge device combined with a high-speed camera system. Moreover, the morphological analysis method based on Minkowski functionals is used to quantitatively depict the morphological features in this paper. The validity of the numerical model is qualitatively verified by the experimental platform, whereas the influence of the complexity and geometric features of the crack wall on the cavitation bubble collapse process is quantitatively studied by LBM simulation and Minkowski functionals. The research findings indicate that the complexity and geometric features of the crack wall markedly influence the collapse time and behavior of the cavitation bubble. Specifically, the collapse time of the cavitation bubble increases with the increasing complexity of the crack wall. Moreover, the maximum jet direction of cavitation bubble toward the wall is closest to the cavitation bubble. Furthermore, as the fractal dimension increases, the intensity of the pressure wave and jet acting upon the crack wall increase while the radiation range decreases. Cavitation cleaning can be applied to arbitrary complex solid surfaces in various environments.

Pore-scale insights into relative permeability in strongly and weakly wet natural fractures: A Lattice Boltzmann Method 2D simulation study

The simplified view of two-phase flow, such as oil and gas, in a fracture is often assumed to occur in a stratified behavior. However, recent studies and production practices have revealed that two-phase flow in fractures exhibits diverse flow patterns. This paper investigates the control of the fracture aperture, fluids viscosity, and wettability on two-phase flow in a 2D cross section of a 3D Berea fracture. Lattice Boltzmann Method (LBM) simulations are used to model the impact of these properties on relative permeability curves. Notably, in strongly wet fractures, two distinct permeability regimes emerge. High aperture values exhibit behavior resembling parallel planes, while low aperture values lead to a linear decrease in permeability due to fluid interactions between fracture surfaces. Conversely, anomalous behavior of the relative permeability curves is identified in weakly wet fractures within specific aperture ranges. This behavior is associated with the occurrence of specific flow patterns within the fracture. Results also emphasize that changes in viscosity ratio do not affect the presence or the saturation range of the anomalous behavior but do influence its intensity for each fluid. Comparisons with Poiseuille profile equations reveal the limited impact of the fracture roughness. These findings enhance our understanding of the interactions between aperture, viscosity, and wettability and how they control the shape of the relative permeability curves. These curves are pivotal parameters for the continuum scale modeling (reservoir models) in oil and gas application, for instance.

An inverse analysis of fluid flow through granular media using differentiable lattice Boltzmann method

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.

Turbulent flow boiling simulation based on pseudopotential lattice boltzmann method with developed wall boundary treatments and unit conversion

The lattice Boltzmann method (LBM) is widely studied for complex flow simulations, including liquid–vapor phase change phenomena. Although previous studies extended the LBM simulation capability from single-phase to two-phase boiling simulations, most of them are restricted to no-flow (pool boiling) or low-flow-rate (laminar flow) boiling conditions owing to the stability problem in collision at low viscosity, representing high Reynolds numbers. However, a high Reynolds number flow is essential for investigating the effects of turbulence on bubble dynamics. Recently, the central moment-based collision method is used to enable high Reynolds numbers for bulk flow; however, extending the method for multiphase-flow simulation with high Reynolds numbers is limited owing to the boundary treatment near the wall. In this study, we augment the previous boundary treatment in LBM simulation with a forcing term, which increases the stability of the simulation even under two-phase conditions. With the improved boundary treatment, the flow boiling phenomena at high Reynolds numbers (up to Re = 107,000) are successfully reproduced. Moreover, in this study, unit conversion is reconsidered with the relationship between conversion factors because the poor outcomes of bubble dynamics are attributed to misinterpreted unit conversion. The new unit conversion method satisfies the necessary conditions for mapping the physical bubble behavior to lattice frame, reproducing bubble dynamics effectively following the Reynolds number, with reasonable spatial and temporal resolution. Consequently, the flow boiling simulation can accurately predict the bubble departure diameter from the real experimental results and the heat transfer trend as a function of the Reynolds number.

LBM Simulation of Free Convection Heat Transfer of Cu/Water Nanofluid in Inclined Cavity with Non-Uniform Heating Temperature Distribution

In the present study, natural convection of Cu/water nanofluid in an inclined square cavity has been investigated numerically using lattice Boltzmann method (LBM). The left wall of the cavity is maintained at a constant hot temperature, while the right wall is subjected to non-uniform temperature distribution. The upper and lower walls are insulated. The fluid flow and heat transfer characteristics are investigated over a wide range of parameters, including Rayleigh numbers (Ra = 103, 104 and 105), solid volume fractions (Φ = 0%, 2%, 4% and 6%), amplitude ratio (A = 0, 0.5 and 1) and phase deviations of sinusoidal temperature distribution (Φ = 0, π/4, π/2, 3π/4 and π). The results are presented graphically in the form of streamlines, isotherms and Nusselt numbers for the different combinations of the considered parameters. The heat transfer rate inside the nanofluid increases as the Rayleigh number and the volume fraction of nanoparticles increase. Further, an increase in the amplitude ratio results in a decrease in the heat transfer rate, with a reduction of up to 8.67% at A = 1. On the other hand, changes in the phase deviation of the sinusoidal temperature distribution lead to an increase in the heat transfer rate, with a surge of up to 32.04% observed at Φ = π.

Effect of the tip speed ratio on the wake characteristics of wind turbines using LBM‐LES

AbstractIn this paper, the wake characteristics of Zell 2000 wind turbine under different tip velocity ratios are studied by using the lattice Boltzmann method and large eddy simulation. The adaptive mesh refinement method is performed to capture the fine flow structure and wake characteristics development. In this paper, we mainly focus on the effect of the tip speed ratio on the flow structure and unsteady characteristics of wind turbine wake. The three‐dimensional flow vorticity structures, the section vorticity diagram, the pressure fluctuation of wake and the lift coefficient of wind turbine wake are utilized to explore the effect of the tip speed ratio on the unsteady physics mechanism of wind turbine wake. With the increase of the tip speed ratio, the distance between two adjacent vortex rings along the axial direction gradually decreases, as the position of the broken vortex circles gradually approaches the center of the blade, separated vortexes are rapidly generated, and the coherent structure appears closer to the wind turbine. A relationship is established between the tip speed ratios and the positions of the broken vortex circles. It is further found that the dominant frequency amplitude gradually increases with the increase of tip speed ratio and the pressure amplitude spectra of vortex increases with the decrease of the distance between the wake and the center of the blade axis. The above series of studies can provide significant physical insight into deep understanding the influence of the tip speed ratio on the wake characteristics of wind turbines.

Morphological analysis for thermodynamics of cavitation collapse near fractal solid wall

A fractal geometric boundary with natural wall features is introduced into a hybrid lattice-Boltzmann-method (LBM) multiphase model. The physical model of cavitation bubble collapse near the irregular geometric wall is established to study the thermodynamic characteristics of the bubble collapse. Due to the lack of periodicity, symmetry, spatial uniformity and obvious correlation in the LBM simulation of the bubble collapse near the fractal wall, the morphological analysis based on Minkowski functional is introduced into the thermodynamic investigation of cavitation bubble so as to analyze and obtain the effective information. The results show that the Minkowski functional method can employed to study the temperature information in complex physical fields hierarchically and quantitatively. The high/low temperature region of the cavitation flow is explored, and thermal effect between irregular and fractal geometric wall and cavitation bubble can be revealed. It illustrates that LBM and morphological analysis complement each other, and morphological analysis can also be used as an optional and potential tool in research field of complex multiphase flows.

Anisotropic temperatures in multi-layered 2D materials

For multi-layered 2D materials, although its c-axis has a much lower thermal conductivity than the a-axis, its phonon mean free path has been confirmed to be very long, e.g., in the order of 100s nm at room temperature for multi-layered graphene. An anisotropic specific heat concept has been proposed in the past to explain this very long mean free path. This work carries out detailed atomistic modeling to quantify the anisotropic specific heat concept and reports the discovery of anisotropic temperatures in multi-layered 2D materials under ultrafast surface heating. Extremely fast c-phonon energy transport is discovered, and the non-Fourier effect is observed for both a-phonons and c-phonons. The energy coupling factor between these two modes of phonons is determined to be in the order of 1016 W K−1 m−3, with the specific number depending on the structure location. The anisotropic temperature concept is also quantitatively confirmed based on the lattice Boltzmann method simulation. The anisotropic temperature concept does not violate the physics that temperature is a scalar; rather, it is developed to distinguish the temperatures of phonons that travel in different directions. This concept is universally applicable to other 2D materials to describe the heat conduction in the in-plane and out-of-plane directions that feature different interatomic bonds.

Boosting Bulk Oxygen Transport with Accessible Electrode Nanostructure in Low Pt Loading PEMFCs.

Despite the high potential for reducing carbon emissions and contributing to the future of energy utilization, polymer electrolyte membrane fuel cells (PEMFCs) face challenges such as high costs and sluggish oxygen transport in cathode catalyst layers (CCLs). In this study, the impact of pore size distribution on bulk oxygen transport behavior is exploredby introducing nano calcium carbonate of varying particle sizes for pore-forming. Physicochemical characterizationsfor are employed to examine the electrode structure, while in situ electrochemical measurements are used to scrutinize bulk oxygen transport resistance, effective oxygen diffusivity ( ) and fuel cell performance. Additionally, the CCLs are constructed with aid of Lattice Boltzmann method (LBM) simulations and for CCLs with different pore size distribution are calculated. The findings reveal that initially increases and then decreases as the most probable pore size increases. A "sphere-pipe" model is proposed to describe practical bulk oxygen transport in CCLs, highlighting the significant role of not only the pore size of secondary pores but also the number of primary pores in bulk oxygen transport.

Lattice Boltzmann Method Simulation of Nanofluid Natural Convection Heat Transfer in a Square Cavity with Constant Heat Flux at Walls

In this study, for the first time, a nanofluid's natural convection heat transfer in a two-dimensional square cavity has been numerically investigated by use of the lattice Boltzmann method with the constant heat flux boundary condition. The horizontal walls of the cavity are insulated, and the vertical walls are kept at a constant heat flux. The diameters of the nanoparticles inside the cavity are the same and have a homogeneous distribution, and there is no chemical reaction between the particles. The flow is also assumed to be the steady state and two-dimensional. Constant temperature, streamlines, velocity, and average Nusselt have been investigated for different nanoparticle volume fractions and Rayleigh numbers. The results showed that the lattice Boltzmann method efficiently analyzes the natural heat transfer of nanofluids; moreover, by use of nanofluid in the cavity increases the heat transfer rate. With the increase in the nanoparticle volume fraction, the average Nusselt number on the right wall of the cavity increased. For a volume fraction of 20% with Grashof number 105, the average Nusselt number increased by almost 50% compared to the base fluid at the same Grashof number. It has been observed that as the volume fraction of nanoparticles in the fluid increases, the fluid’s viscosity also increases; consequently, the velocity of the fluid is found to decrease.

Interactional aerodynamics and acoustics of a rotor with an airframe in hover

The demand for the development of urban air mobility (UAM) powered by electric systems has been steadily rising across private and public sectors. Most UAM flights incorporate a distributed electric propulsion system to enhance aircraft safety and reliability, which entails an increase in the number of rotors or propellers. Consequently, aerodynamics and aeroacoustics are significantly influenced by strong interactions between the rotor and the airframe. In this study, we conducted a computational investigation to examine the impact of rotor–airframe interaction on aerodynamic and aeroacoustic characteristics. This examination considered variations in airframe shape and the distance between the rotor and airframe. The aerodynamic analysis was executed using the lattice-Boltzmann method simulation, in which acoustic predictions were made using the Ffowcs Williams–Hawkings(FW–H) acoustic analogy with a permeable surface. The airframe consists of two geometries: a cylinder and a cone. Tip vortex breakdown and the transition into the turbulent wake state were captured in both airframes, and a fountain flow was affected by the downwash circulation generated under certain proximity of airframe cases. The acoustic prediction results showed that high-intensity noise radiated over the broad surface of the airframe in the conical airframe case. Significant thrust force fluctuations and an increase in noise level were observed at the smallest rotor tip clearance, S/R=−0.1, compared to the isolated rotor. Furthermore, the noise contribution of the rotor and airframe was compared, revealing that the airframe noise level was even higher than the rotor noise at S/R=−0.1.