Lattice Boltzmann Method Solver Research Articles

Direct aeroacoutic simulation of a ducted axial fan with acoustic liners using a volume penalization lattice Boltzmann solver on heterogeneous massively parallel platforms

Aeroacoustic noise of an axial fan is directly solved to understand its mechanism, using our in-house Lattice Boltzmann Method (LBM) solver. To make the LBM solver industrially successful, we must reduce calculation time while maintaining its accuracy. We adopt Volume Penalization method for moving boundaries to achieve independent parallelism, and to utilize GPU (Graphical Processing Units) for parallel computation. In this study, we present a comparison between numerical and experimental results of an axial fan in a lined duct. The acoustic liner is designed to reduce 2nd BPF noise, and the noise reduction of 9.8dB is observed in the experiment. With our LBM code, the noise reduction was reproduced within an accuracy of 2.5dB, and profound insights are provided through the detailed investigation of the numerical results.

Computation of three-dimensional incompressible flows using high-order weighted essentially non-oscillatory finite-difference lattice Boltzmann method

In the present work, an accurate and robust solution methodology based on the high-order weighted essentially non-oscillatory (WENO) finite-difference lattice Boltzmann method (LBM) in the three-dimensional generalized curvilinear coordinates is presented and applied for simulating the three-dimensional incompressible flows over complicated configurations with curved boundaries. Here, the incompressible form of the lattice Boltzmann equation in three dimensions is considered and the discretization of the spatial derivative terms is performed with the fifth-order WENO finite-difference method and the temporal derivative term is discretized with the fourth-order Runge–Kutta scheme to ensure the accuracy and stability of the solution method for both the steady and unsteady problems. The three-dimensional lattice Boltzmann equation applied here is based on a nineteen discrete velocity model for transforming the microscopic properties to the macroscopic ones. To assess the accuracy and robustness of the present three-dimensional high-order finite-difference LBM solver, different incompressible flow benchmarks and practical test cases are studied that are the cavity flow, the Beltrami flow, the flow in the curved ducts of rectangular cross sections, and the flow over a sphere for different flow conditions. The decay of the homogeneous isotropic turbulence is also computed to examine the suitability of the present solution method to be applied as the direct numerical simulation of turbulent flows. It is demonstrated that the solution methodology presented based on the high-order WENO finite-difference LBM in the three-dimensional generalized curvilinear coordinate can be used for accurately and effectively computing the three-dimensional practical incompressible flow problems.

Large eddy simulation of fire-induced flows using Lattice-Boltzmann methods

Large-eddy simulations (LES) of the near-field region of large-scale fire plumes are performed for the first time with a pressure-based Lattice Boltzmann method (LBM) with low-Mach number approximation. Two scenarios are considered: the large-scale non-reactive helium plume and the 1 m methane pool fire, both investigated experimentally at Sandia. In the second scenario, a simplified modeling of the combustion and radiation processes is introduced involving a one-step irreversible reaction eddy-dissipation concept-based combustion model and a radiant fraction model, respectively. In both scenarios, a quantitative agreement is observed with the experimental data and model predictions are consistent with previously-published numerical studies. Our simulations demonstrate the computational efficiency of the proposed LBM solver to tackle fire-induced flows, suggesting that LBMs are a good alternative candidate for the modeling of fire-related problems.

HPC performance study of different collision models using the Lattice Boltzmann solver Musubi

Over the past decades, the lattice Boltzmann method (LBM) has become increasingly popular thanks to its capabilities in the domain of Large-Eddy Simulations (LES). Different collision schemes have been proposed to extend the scope of application to higher Reynolds number flows. This study compares the accuracy and the performance of some of these schemes on a D3Q27 lattice, including the original Multiple Relaxation Times (MRT) model, the Hybrid Recursive Regularized Bhatnagar–Gross–Krook (HRR) operator, as well as the Projected Recursive Regularized Bhatnagar–Gross–Krook (PRR) operator and the parametrized Cumulant collision scheme. For this purpose, the above-mentioned schemes are implemented in the HPC LBM solver Musubi and tested on a well-documented test-case describing the flow past a circular cylinder at a Reynolds number of 3900. Three different subgrid scale (SGS) models are used to account for the unresolved turbulence, i.e. the Smagorinsky model, the Wall-Adapting Local Eddy-viscosity (WALE) model, and the Vreman model. The Cumulant scheme uses an Implicit LES (ILES) subgrid scale model and shows the best agreement with the experimental data followed by MRT with WALE, and HRR with Vreman. The examined collision models are able to capture the second peak at f=3fvs of the power spectra density of the y velocity component first discovered in experiments.With respect to performance, the collision models are compared in terms of MLUPs/node and parallel efficiency for a strong scaling analysis. Again the Cumulant scheme outperforms the other collision models even when they are run on the reduced D3Q19 stencil. All the collision schemes show a strong scaling parallel efficiency above 60% on up to 16384 cores in our implementation.

A DNS investigation by LBM: Acoustic characteristics of a flow around rod-hydrofoil configuration at different angles of attack

The interaction noise caused by the periodic impingement of the forward blade wake on the backward blade widely exists in underwater rotating machinery. The rod-hydrofoil configuration is a model problem for interaction noise. Based on our in-house code of lattice Boltzmann method (LBM) solver accelerated by graphics processing unit (GPU), a direct numerical simulation (DNS) of rod-hydrofoil configuration with angles of attack (AoA) from 0° to 30° is carried out in the present work to study acoustic characteristics of the rod-hydrofoil configuration. The results show that GPU-accelerated LBM solver can achieve a DNS of hydrodynamics and acoustics in a short time and obtain the characteristics of the global noise field of rod-hydrofoil configuration accurately and efficiently. With the increase of AoA, the compound vortex structure of the rod-hydrofoil configuration changes greatly, and the hydrodynamic and acoustics characteristics also fluctuate greatly. When AoA <15°, the pure tonal noise caused by Karmen vortex street plays a dominant role. When AoA >15°, the effect of wake noise caused by the shedding of compound vortex structure in the wake region of hydrofoil becomes strong.

Assessment of polymer feedback coupling approaches in simulation of viscoelastic fluids using the lattice Boltzmann method

The lattice Boltzmann method (LBM) has emerged as a popular approach to simulate complex non-Newtonian fluid mechanics problems, such as those involving viscoelastic fluids. In these cases, the LBM solver often requires modelling additional non-linear and non-ideal hydrodynamic contributions to the flow resulting from the addition of polymer molecules. These additional contributions, commonly referred to as the polymer feedback, are either incorporated directly in the Boltzmann stress (pressure method) or alternatively in the momentum field as a forcing contribution (forcing method). The choice of coupling approach has in previous works been strongly speculated to impact the numerical accuracy and stability of LBM solvers for viscoelastic fluids, however no formal comparison has been conducted. In this work, we compare the two popular polymer feedback coupling approaches, as well as the various schemes commonly used in the forcing method, namely, the explicit forcing (EF) scheme (He et al., 1998), the Guo et al. scheme (Guo et al., 2002), and the exact-difference-method (EDM) (Kupershtokh et al., 2009). First, through a theoretical comparison in recovering the macroscopic equations, we show that both the EF and Guo et al. forcing schemes retain the exact hydrodynamic representation up to second-order, whereas the EDM scheme includes additional lattice error terms. Similarly, the pressure method retains additional unphysical terms, which are known to violate Galilean invariance. Through numerical tests, involving the steady and time-dependent Poiseuille flow cases, as well as the four-roll mill problem under both steady and transient regimes, it is shown that the forcing method has enhanced numerical accuracy and stability at varying elastic effects. Alternatively, owing to the violation of Galilean invariance, the pressure method proved to be unstable even for moderate elastic effects. The obtained results are useful in determining the optimal polymer feedback coupling approach when simulating viscoelastic fluids using LBM, as well as further testing the generality of previous LBM findings on non-ideal coupling approaches for viscoelastic fluids.

(Digital Presentation) Numerical Characterization of Physical Properties of Microstructures in Lithium-Ion Batteries

In this paper, we present calculations of some of the key physical properties of microstructures of electrodes and separators present in lithium-ion batteries with porous electrode architectures. We analyze three-dimensional models of public domain real commercial porous anodes, cathodes and polyethylene (PE) separator, in order to characterize some of their microstructural properties. First, a pore space analysis of the binarized microstructure reveals the location and distribution of pores of various sizes, the overall porosity distribution and connectivity. Next, diffusion simulations using a random-walk method are performed to compute and accurately validate in-plane and through-plane effective transport coefficients and tortuosities, for different electrodes and calendaring levels. Single phase fluid flow simulations are performed using a commercial Lattice Boltzmann Method (LBM) solver to accurately validate the permeability of the microstructures. Next, multi-phase fluid flow simulations are done using this LBM solver to simulate the electrolyte in-filling process for various solvents. We predict that in-filling process may result in residual gas bubbles, which effect is shown in subsequent diffusion simulations to reduce the effective transport. The calculated McMillan numbers after in-filling show good agreement with experimental results. Next, we simulate the mechanical deformation of these microstructures under compressive strain using a finite element analysis (FEA) solver. This work illustrates how the use of multi-physics simulation tools can help to design these microstructures to satisfy the mechanical and electrochemical properties required of them. Figure 1

Characterization of condensation on nanostructured surfaces and associated thermal hydraulics using a thermal lattice Boltzmann method

The dynamics of the condensation process on nanostructured surfaces can be modulated substantially by tuning the surface architecture. Present study uses the mesoscopic framework of lattice Boltzmann method (LBM) to explore the role of surface morphology and cold spot temperature in determining the visual state of the condensate droplet, mode of nucleation, and associated rates of energy and mass interactions. A multiple relaxation time-(MRT)-based LBM solver, coupled with pseudopotential model, has been developed to simulate a rectangular domain of saturated vapor, housing a cold spot on the bottom rough surface. Superhydrophobicity has been achieved for certain combinations of surface parameters, with the intercolumn spacing being the most influential one. Gradual increase in the spacing modifies the nucleation mode from top through side to bottom, while the droplet changes from Cassie to Wenzel state. The Cassie drop in top nucleation mode exhibits the largest contact angle and least rate of surface heat transfer. Both types of Wenzel drops display large rate of condensation and two peaks in heat transfer, along with very short nucleation time in comparison with Cassie drops. Couple of phase diagrams have been developed combining all four scenarios of condensation predicted by the present model. One important novelty of the present study is the consideration of nonisothermal condition within LB structure. Enhancement in the degree of subcooling at the cold spot encourages greater condensation and Cassie-to-Wenzel transition.

Simulation of free-surface flows using the Lattice Boltzmann method with the AMR technique

High resolution grids are generally preferred near the free surface to capture desired phenomena. In the present paper, an adaptive mesh refinement (AMR) framework based on the hash table data structure is introduced to the lattice Boltzmann method (LBM). The AMR refinement criterion is based on the movement of the free surface captured through interface nodes. The performance of the AMR-based LBM solver is analyzed through several benchmark cases. Results show that the proposed numerical framework can properly track the free surface with a spatial convergence rate between the first and second order. In addition, the AMR framework is of benefit to efficiently simulating free-surface flows since it requires much less nodes to achieve high resolution near the interface.

Improved wall model treatment for aerodynamic flows in LBM

The article deals with an improved treatment of wall models for the simulation of turbulent flows in the framework of Immersed Wall Boundaries on Cartesian grids. The emphasis is put on the implementation in a Lattice-Boltzmann Method solver without loss of generality, since the proposed approach can be used in Navier–Stokes-based solvers in a straightforward way. The proposed improved wall model implementation relies on the combination of several key elements, namely i) the removal of grid points too close to the solid surface and ii) an original computation of wall normal velocity gradient and iii) the interpolation scheme. The new method is successfully assessed considering URANS simulations focusing on steady solutions of the Zero Pressure Gradient turbulent flat plate boundary layer and the turbulent flow around a NACA0012 airfoil at several angles of attack.

A high-performance three-dimensional lattice Boltzmann solver for water waves with free surface capturing

The lattice Boltzmann method (LBM) is a numerical method with high parallel computational efficiency. However, currently few 3D numerical wave model based on LBM can be widely applied to water wave simulations in coastal engineering due to several problems related to numerical instability and numerical accuracy. To develop a high-performance 3D LBM solver for water wave simulations with free surface capture, a new 3D collision operator with sufficient numerical stability for wave simulation is first proposed. Then, wave generation and active wave absorption methods for the volume of fluid coupled with LBM are implemented in the solver to ensure accurate wave motion. The performances of this solver and other popular numerical wave solvers are analyzed and compared. The parameters of the numerical model are tested and determined to simulate wave transformation around structures. Through the comparison with three benchmark physical experiments, the accuracy of the presented solver proves that the present model is a promising tool for wave propagation and transformation simulation in practice. Benchmark tests and comparisons with the IHFoam and SPHysics solvers prove that the 3D LBM solver developed in this paper has a very good computational efficiency and parallel scalability. Overall, the work in this paper provides a new high-performance 3D solver for water wave simulations with free surface capturing for coastal and ocean engineering applications.

Upscaling LBM-TPM simulation approach of Darcy and non-Darcy fluid flow in deformable, heterogeneous porous media

This paper presents a numerical approach for the simulation of fluid flow through porous media by proposing a theoretical and numerical meso-to-macro multiscale framework, which combines the advantages of the lattice Boltzmann method (LBM) with the continuum Theory of Porous Media (TPM) to efficiently and accurately model fluid transport in heterogeneous porous media. In particular, LBM presents an alternative to experiments by studying the flow from a mesoscopic perspective, which in turn, allows the derivation of the material parameters needed for simulating the flow in the macroscopic TPM model. In this work, a meso-macro hierarchic upscaling scheme is applied to investigate the deformation-dependent intrinsic permeability properties and the Darcy/non-Darcy fluid flow regime. Concerning the mesoscale, the intrinsic permeability of the porous domain is computed by means of the LBM model at the first stage. Subsequently, deformation of the medium takes place in furtherance of determining the relation of the aforementioned deformation dependency. Thereupon, these findings are input into the TPM model in order to compute the primary unknown variables, where special focus is laid on the stability challenges in the compaction and near compaction states. With respect to the criteria of non-Darcy fluid flow, the conditions of its onset, i.e. the induced pressure gradient and mean fluid flow velocity, are computed as well using the LBM solver and conveyed afterwards to the macroscopic TPM model. Herein, the non-Darcy intrinsic permeability has been investigated in the TPM approach based on the Forchheimer equation. Simulations done on a synthetic porous micro-structure show that the combined framework proved to stand well between the two approaches.

Comparative analysis on pore‐scale permeability prediction on micro‐CT images of rock using numerical and empirical approaches

AbstractVarieties of pore‐scale numerical and empirical approaches have been proposed to predict the rock permeability when the pore structure is known, for example, microscopic computerized tomography (micro‐CT) technology. A comparative study on these approaches is conducted in this paper. A reference dataset of nine micro‐CT images of porous rocks is generated and processed including artificial sandpacks, tight sandstone, and carbonate. Multiple numerical and empirical approaches are used to compute the absolute permeability of micro‐CT images including the image voxel‐based solver (VBS), pore network model (PNM), Lattice Boltzmann method (LBM), Kozeny‐Carman (K‐C) equation, and Thomeer relation. Computational accuracy and efficiency of different numerical approaches are investigated. The results indicate that good agreements among numerical solvers are achieved for the sample with a homogeneous structure, while the disagreement increases with an increase in heterogeneity and complexity of pore structure. The LBM and VBS solver both have a relative higher computation accuracy, whereas the PNM solver is less accurate due to simplification on the topological structure. The computation efficiency of the different solver is generally computation resources dependent, and the PNM solver is the fastest, followed by VBS and LBM solver. As expected, empirical relation can over‐estimate permeability by a magnification of 50 or more, particularly for those strong heterogeneous structures reported in this study. Nevertheless, empirical relation is still applicable for artificial rocks.

Actuator-Line Model in a Lattice Boltzmann Framework for Wind Turbine Simulations

This paper presents the development of a solver based on a Lattice Boltzmann Method (LBM) to perform reliable wind turbine simulations: LaBoheMe. LBM offers an interesting framework with low dissipation and high performance computing compared to usual Computational Fluid Dynamics (CFD) solvers based on Navier-Stokes equations. In order to take wind turbines into account in the LBM solver, LaBoheMe is enhanced by the addition of local force terms representing the influence of the wind turbines on the flow. These forces are computed using an Actuator-Line Model (ALM). The present solver is a 2D LBM/ALM solver allowing the simulation of “slices” of a Vertical Axis Wind Turbine (VAWT).The Lattice Boltzmann and the Actuator Line methods are described and the coupling adopted in this work is detailed. Validation cases for pure LBM (Backward Facing Step, BFS) and coupled LBM/ALM are performed. The LBM/ALM coupling is validated against experimental data and compared with a vortex method and a large eddy simulation of the wake. Both blade forces and wake velocities are considered.

Shape-constrained level set segmentation for hybrid CPU–GPU computers

Due to its intrinsic advantages such as the ability to handle complex shapes, the level set method (LSM) has been widely applied to image segmentation. Nevertheless, the LSM is computationally expensive. In order to improve the performance of the traditional LSM both in terms of efficiency and effectiveness, we propose a novel algorithm based on the lattice Boltzmann method (LBM). Using local region statistics and prior shape, we design an effective and local speed function for the LSM, from which we deduce a shape prior based body force for LBM solver. An NVIDIA graphics processing units (GPU) is used to accelerate the method. Our introduced algorithm has several advantages. First, it is accurate even if there are some geometric transformations (rotation angle, scaling factor and translation vector) between the object to be segmented and the prior shape. Second, it is local and therefore suitable for massively parallel architectures. Third, the use of local region information allows it to deal with intensity inhomogeneities. Fourth, including shape prior allows the method to handle occlusion and noise. Fourth, the model is fast. Finally the algorithm can be used without shape prior by means of minor modification. Intensive experiments demonstrate, objectively and subjectively, the performance of the introduced framework.

An Optimizing Code Generator for a Class of Lattice-Boltzmann Computations

The Lattice-Boltzmann method (LBM), a promising new particle-based simulation technique for complex and multiscale fluid flows, has seen tremendous adoption in recent years in computational fluid dynamics. Even with a state-of-the-art LBM solver such as Palabos, a user has to still manually write the program using library-supplied primitives. We propose an automated code generator for a class of LBM computations with the objective to achieve high performance on modern architectures. Few studies have looked at time tiling for LBM codes. We exploit a key similarity between stencils and LBM to enable polyhedral optimizations and in turn time tiling for LBM. We also characterize the performance of LBM with the Roofline performance model. Experimental results for standard LBM simulations like Lid Driven Cavity, Flow Past Cylinder, and Poiseuille Flow show that our scheme consistently outperforms Palabos—on average by up to 3× while running on 16 cores of an Intel Xeon (Sandybridge). We also obtain an improvement of 2.47× on the SPEC LBM benchmark.

High Performance Computation of a Jet in Crossflow by Lattice Boltzmann Based Parallel Direct Numerical Simulation

Direct numerical simulation (DNS) of a round jet in crossflow based on lattice Boltzmann method (LBM) is carried out on multi-GPU cluster. Data parallel SIMT (single instruction multiple thread) characteristic of GPU matches the parallelism of LBM well, which leads to the high efficiency of GPU on the LBM solver. With present GPU settings (6 Nvidia Tesla K20M), the present DNS simulation can be completed in several hours. A grid system of 1.5 × 108is adopted and largest jet Reynolds number reaches 3000. The jet-to-free-stream velocity ratio is set as 3.3. The jet is orthogonal to the mainstream flow direction. The validated code shows good agreement with experiments. Vortical structures of CRVP, shear-layer vortices and horseshoe vortices, are presented and analyzed based on velocity fields and vorticity distributions. Turbulent statistical quantities of Reynolds stress are also displayed. Coherent structures are revealed in a very fine resolution based on the second invariant of the velocity gradients.

A Comparative Study of Submicron Phonon Transport Using the Boltzmann Transport Equation and the Lattice Boltzmann Method

The subcontinuum energy transport mechanism in solids can be explained by the Lattice Boltzmann Method (LBM), a discrete representation of the Boltzmann Transport Equation (BTE). The present study focuses on a detailed comparison of the LBM and BTE. Results reveal that at continuum scale, the LBM follows the BTE almost precisely. However, as the device dimensions are reduced, approaching the ballistic limit, the LBM deviates from the BTE results in terms of thermal property estimation. The inherent nonisotropic lattice configuration has a dominant contribution to the performance of the LBM. A threshold length scale is also proposed for successful implementation of the LBM solver.

Towards aeraulic simulations at urban scale using the lattice Boltzmann method

The lattice Boltzmann method (LBM) is an innovative approach in computational fluid dynamics (CFD). Due to the underlying lattice structure, the LBM is inherently parallel and therefore well suited for high performance computing. Its application to outdoor aeraulic studies is promising, e.g. applied on complex urban configurations, as an alternative approach to the commonplace Reynolds-averaged Navier–Stokes and large eddy simulation methods based on the Navier–Stokes equations. Emerging many-core devices, such as graphic processing units (GPUs), nowadays make possible to run very large scale simulations on rather inexpensive hardware. In this paper, we present simulation results obtained using our multi-GPU LBM solver. For validation purpose, we study the flow around a wall-mounted cube and show agreement with previously published experimental results. Furthermore, we discuss larger scale flow simulations involving nine cubes which demonstrate the practicability of CFD simulations in building external aeraulics.

High-performance implementations and large-scale validation of the link-wise artificial compressibility method

The link-wise artificial compressibility method (LW-ACM) is a recent formulation of the artificial compressibility method for solving the incompressible Navier–Stokes equations. Two implementations of the LW-ACM in three dimensions on CUDA enabled GPUs are described. The first one is a modified version of a state-of-the-art CUDA implementation of the lattice Boltzmann method (LBM), showing that an existing GPU LBM solver might easily be adapted to LW-ACM. The second one follows a novel approach, which leads to a performance increase of up to 1.8× compared to the LBM implementation considered here, while reducing the memory requirements by a factor of 5.25. Large-scale simulations of the lid-driven cubic cavity at Reynolds number Re=2000 were performed for both LW-ACM and LBM. Comparison of the simulation results against spectral elements reference data shows that LW-ACM performs almost as well as multiple-relaxation-time LBM in terms of accuracy.