arXiv subjects

Julius Weinmiller

Publications and source records attributed to Julius Weinmiller.

6 recordsLinked to original sources

arXiv2026

Lattice Boltzmann Methods with Anisotropic Equilibrium Distributions

Lattice Boltzmann methods are usually derived under the assumption of isotropy. In this work, we present a derivation of a Lattice Boltzmann method for anisotropic fluid flow. Starting from an anisotropic equilibrium distribution, we show a full derivation of the resulting lattice Boltzmann method. We ensure that our method correctly reproduces macroscopic behavior via Chapman-Enskog analysis for a single-relaxation time collision operator. As a result, we are able to show that a properly discretized anisotropic Maxwell-Boltzmann equilibrium does macroscopically in fact lead to an anisotropic variation of the Navier-Stokes equations. All desired properties of lattice Boltzmann methods, such as locality of the collision operator, isotropic discrete position and velocity space, or mass and momentum conservation are retained. While it is explicitly shown in the context of fluid flow, the presented scheme is straight-forward to adopt to advection-diffusion problems.

physics.flu-dyn↗

arXiv2024

Homogenized Lattice Boltzmann Model for Simulating Multi-Phase Flows in Heterogeneous Porous Media

A new homogenization approach for the simulation of multi-phase flows in heterogeneous porous media is presented. It is based on the lattice Boltzmann method and combines the grayscale with the multi-component Shan-Chen method. Thus, it mimics fluid-fluid and solid-fluid interactions also within pores that are smaller than the numerical discretization. The model is successfully tested for a broad variety of single- and two-phase flow problems. Additionally, its application to multi-scale and multi-phase flow problems in porous media is demonstrated using the electrolyte filling process of realistic 3D lithium-ion battery electrode microstructures as an example. The new method shows advantages over comparable methods from literature. The interfacial tension and wetting conditions are independent and not affected by the homogenization. Moreover, all physical properties studied here are continuous even across interfaces of porous media. The method is consistent with the original multi-component Shan-Chen method. It is accurate, efficient, easy to implement, and can be applied to many research fields, especially where multi-phase fluid flow occurs in heterogeneous and multi-scale porous media.

physics.flu-dyn↗

arXiv2024

Decomposing the collision operator in the lattice Boltzmann method

In transport theory, physical phenomena are well described using the Boltzmann equation, which is efficiently simulated and discretized with the lattice Boltzmann method. The collision step defines the microscopic molecules behavior, and thus the simulated physical phenomena. For complex phenomena, the collision step becomes complex as well. In this paper, we propose a framework to systematically decompose the collision step into individual collision rules. Each collision rule is easier to understand, thus a faster understanding of the whole is achieved. By inverting the process, i.e. composing multiple collision rules together, one can create novel collision steps, which can better describe the underlying complex phenomena. This framework's applications are manyfold, from both a theoretical and an application standpoint. Shown here is the decomposition of Robin boundary condition into Dirichlet and Neumann boundary conditions, extending it to a partial Robin boundary condition, and semi-permeable reactive membranes.

physics.flu-dyn↗

arXiv2023

High-Performance Computing in Battery Development: From Pore Scale to Continuum

An application for high-performance computing (HPC) is shown that is relevant in the field of battery development. Simulations of electrolyte wetting and flow are conducted using pore network models (PNM) and the lattice Boltzmann method (LBM), while electrochemical simulations are conducted using the tool BEST. All aforementioned software packages show an appropriate scaling behavior. A workflow for optimizing battery performance by improving the filling of battery components is presented. A special focus is given to the unwanted side effect of gas entrapment encountered during filling. It is also known to adversely affect the electrochemical performance of batteries and can be partially prevented by appropriate microstructure design such as electrode perforation.

cs.CE↗

arXiv2023

General Local Reactive Boundary Condition for Dissolution and Precipitation Using the Lattice Boltzmann Method

A general and local reactive boundary condition (RBC) for studying first-order equilibrium reactions using the lattice Boltzmann method (LBM) is presented. Its main characteristics are accurate reproduction of wall diffusion, invariance to the wall and grid orientation, and absence of nonphysical artefacts. The scheme is successfully tested for different benchmark cases considering diffusion, advection, and reactions of fluids at solid-liquid interfaces. Unlike other comparable RBCs from the literature, the novel scheme is valid for a large range of Péclet and Damköhler numbers, and shows realistic pattern formation during precipitation. In addition, quantitative results are in good accordance with analytical solutions and values from literature. Combining the new RBC with the rest fraction method, Péclet-Reynolds ratios of up to 1000 can be achieved. Overall, the novel RBC accurately models first-order reactions, is applicable for complex geometries, and allows efficiently simulating dissolution and precipitation phenomena in fluids at the pore scale.

physics.comp-ph↗

arXiv2022

Understanding Electrolyte Filling of Lithium-Ion Battery Electrodes on the Pore Scale Using the Lattice Boltzmann Method

Electrolyte filling is a time-critical step during battery manufacturing that also affects the battery performance. The underlying physical phenomena during filling mainly occur on the pore scale and are hard to study experimentally. In this paper, a computational approach, i.e.\ the lattice Boltzmann method, is used to study the filling process and corresponding pore-scale phenomena in 3D lithium-ion battery cathodes. The electrolyte flow through the nanoporous binder is simulated using a homogenization approach. Besides the process time, the influence of structural and physico-chemical properties is investigated. Those are the particle size, the binder distribution, and the volume fraction and wetting behavior of active material and binder. Optimized filling conditions are discussed by capillary pressure-saturation relationships. It is shown how the aforementioned influencing factors affect the electrolyte saturation. Moreover, the amount of the entrapped residual gas phase and the corresponding size distribution of the gas agglomerates are analyzed in detail. Both factors are shown to have a strong impact on mechanisms that can adversely affect the battery performance. The results obtained here indicate how the filling process, the final electrolyte saturation, and potentially also the battery performance can be optimized by adapting process parameters and the electrode and electrolyte design.

physics.comp-ph↗