Adrian Kummerländer

Bio: Adrian Kummerländer is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Lattice Boltzmann methods & Computer science. The author has an hindex of 1, co-authored 1 publications receiving 31 citations.

OpenLB—Open source lattice Boltzmann code

Abstract: We present the OpenLB package, a C++ library providing a flexible framework for lattice Boltzmann simulations. The code is publicly available and published under GNU GPLv2, which allows for adaption and implementation of additional models. The extensibility benefits from a modular code structure achieved e.g. by utilizing template meta-programming. The package covers various methodical approaches and is applicable to a wide range of transport problems (e.g. fluid, particulate and thermal flows). The built-in processing of the STL file format furthermore allows for the simple setup of simulations in complex geometries. The utilization of MPI as well as OpenMP parallelism enables the user to perform those simulations on large-scale computing clusters. It requires a minimal amount of dependencies and includes several benchmark cases and examples. The package presented here aims at providing an open access platform for both, applicants and developers, from academia as well as industry, which facilitates the extension of previous implementations and results to novel fields of application for lattice Boltzmann methods. OpenLB was tested and validated over several code reviews and publications. This paper summarizes the findings and gives a brief introduction to the underlying concepts as well as the design of the parallel data structure.

Implicit propagation of directly addressed grids in lattice Boltzmann methods

Abstract: Lattice Boltzmann methods (LBM) are well suited to highly parallel computational fluid dynamics simulations due to their separability into a perfectly parallel collision step and a propagation step that only communicates within a local neighborhood. The implementation of the propagation step provides constraints for the maximum possible bandwidth‐limited performance, memory layout and usage of vector instructions. This article revisits and extends the work on implicit propagation on directly addressed grids started by A‐A and its shift‐swap‐streaming (SSS) formulation by reconsidering them as transformations of the underlying space filling curve. In this work, a new periodic shift (PS) pattern is proposed that imposes minimal restrictions on the implementation of collision operators and utilizes virtual memory mapping to provide consistent performance across a range of targets. Various implementation approaches as well as time dependency and performance anisotropy are discussed. Benchmark results for SSS and PS on SIMD CPUs including Intel Xeon Phi as well as Nvidia GPUs are provided. Finally, the application of PS as the propagation pattern of the open source LBM framework OpenLB is summarized.

Simulation of Temperature Driven Microflows Using a Lattice Boltzmann Method in Slip and Moderate Transition Regimes

Abstract: Micro-electromechanical systems (MEMS) are very small devices that usually contain gas under low pressure. The motion of the fluid inside such structures is affected by rarefaction effects, which are not visible in macroscale flows. To accurately predict the behavior of the fluid in such microstructures, the Lattice Boltzmann Method needs to be modified to account for these new effects. This can be done by introducing relative fluid-wall velocity in the form of slip boundary conditions. Furthermore, temperature effects like temperature jump and thermal creep can be included using wall boundary conditions. In this paper, different models for the slip are explored and evaluated over the Knudsen number. Then, a thermal flow is simulated and benchmarked by Direct Simulation Monte-Carlo (DSMC). The results show that these extensions offer a good approximation in the slip and moderate transition regimes (Knudsen number (Kn) < 1).

Lattice-Boltzmann LES modelling of a full-scale, biogas-mixed anaerobic digester

Abstract: Abstract An Euler–Lagrange multicomponent, non-Newtonian Lattice-Boltzmann method is applied for the first time to model a full-scale gas-mixed anaerobic digester for wastewater treatment. Rheology is modelled through a power-law model and, for the first time in gas-mixed anaerobic digestion modelling, turbulence is modelled through a Smagorinsky Large Eddy Simulation model. The hydrodynamics of the digester is studied by analysing flow and viscosity patterns, and assessing the degree of mixing through the Uniformity Index method. Results show independence from the grid size and the number of Lagrangian substeps employed for the Lagrangian sub-grid simulation model. Flow patterns are shown to depend mildly on the choice of bubble size, but not the asymptotic degree of mixing. Numerical runs of the model are compared to previous results in the literature, from a second-ordered Finite-Volume Method approach, and demonstrate an improvement, compared to literature data, of 1000-fold computational efficiency, massive parallelizability and much finer attainable spatial resolution. Whilst previous research concluded that the application of LES to full-scale anaerobic digestion mixing is unfeasible because of high computational expense, the increase in computational efficiency demonstrated here, now makes LES a feasible option to industries and consultancies.

Low-Mach hybrid lattice Boltzmann-finite difference solver for combustion in complex flows

Abstract: A hybrid solver for low-Mach combustion simulations has been proposed and validated through different test-cases in a previous publication [Hosseini et al., “Hybrid lattice Boltzmann-finite difference model for low Mach number combustion simulation,” Combust. Flame 209, 394–404 (2019)]. However, all the considered configurations were laminar, far from realistic applications. To check the performance of this approach for more complex physical processes, the developed solver is used here to model a variety of transitional and turbulent reacting flows. It is first used to compute an established benchmark, the Taylor–Green vortex, for (a) an iso-thermal single-component fluid, (b) a thermal non-reacting mixture, and (c) a thermal reacting mixture (hydrogen/air flame). Detailed comparisons of the results against a high-order in-house direct numerical simulation solver show that the proposed hybrid lattice Boltzmann solver correctly captures the dynamics of the flow at relatively low numerical cost. This same solver is then used to model the interaction of a methane/air flame with a vortex pair, revealing different interaction regimes of interest for turbulent combustion models. It is further employed to model the interaction of an expanding circular flame kernel with a pair of vortices and correctly captures the characteristic regimes. To showcase its ability to deal with turbulent flows, it is finally applied to a homogeneous isotropic turbulent configuration.

Evaluation of a Near-Wall-Modeled Large Eddy Lattice Boltzmann Method for the Analysis of Complex Flows Relevant to IC Engines

Abstract: In this paper, we compare the capabilities of two open source near-wall-modeled large eddy simulation (NWM-LES) approaches regarding prediction accuracy, computational costs and ease of use to predict complex turbulent flows relevant to internal combustion (IC) engines. The applied open source tools are the commonly used OpenFOAM, based on the finite volume method (FVM), and OpenLB, an implementation of the lattice Boltzmann method (LBM). The near-wall region is modeled by the Musker equation coupled to a van Driest damped Smagorinsky-Lilly sub-grid scale model to decrease the required mesh resolution. The results of both frameworks are compared to a stationary engine flow bench experiment by means of particle image velocimetry (PIV). The validation covers a detailed error analysis using time-averaged and root mean square (RMS) velocity fields. Grid studies are performed to examine the performance of the two solvers. In addition, the differences in the processes of grid generation are highlighted. The performance results show that the OpenLB approach is on average 32 times faster than the OpenFOAM implementation for the tested configurations. This indicates the potential of LBM for the simulation of IC engine-relevant complex turbulent flows using NWM-LES with computationally economic costs.