Manfred Krafczyk

• Prof. Dr.-Ing. habil.
• Managing Director at Technische Universität Braunschweig

Matter, conceptually classified into fluids and solids, can be completely described by the microscopic physics of its constituent atoms or molecules. However, for most engineering applications, a macroscopic or continuum description has usually been sufficient due to the large disparity between the spatial and temporal scales relevant to these appl...

We provide the source code used for the numerical simulation of the transitional flow characteristics in gyroidal structures. The code is accompanied by a research context, outlining the significance and relevance of studying transitional flows in these structures. The code aims to explore the pressure drops between the inlet and outlet for specifi...

In this work, transitional flow characteristics in gyroidal structures are investigated. For specified flow rates corresponding to a range of Reynolds numbers from 400 to 7000, the pressure drop between inlet and outlet is determined. The experimentally obtained pressure drops are computed numerically with the cumulant lattice Boltzmann method whic...

Lattice-Boltzmann (LB) methods and kinetic schemes are clearly identified as promising alternatives to classical Navier-Stokes solvers, mainly due to (i) their suitability for high performance computing, (ii) their built in conservation properties for mass and momentum and (iii) their low dissipation properties in transporting acoustic waves. In pa...

Researchers develop software to process or generate data to test their scientific hypotheses. Especially researchers from STEM disciplines (Science, Technology, Engineering, and Mathematics) validate their models through self-developed software prototypes. However, they do not necessarily have a programming or software engineering background. Moreo...

In this paper, we present a framework for the modeling and simulation of a subset of physical/chemical processes occurring on different spatial and temporal scales in porous materials. In order to improve our understanding of such processes on multiple spatio-temporal scales, small-scale simulations of transport and reaction are of vital importance...

We present a comprehensive analysis of the cumulant lattice Boltzmann model with the three-dimensional Taylor–Green vortex benchmark at Reynolds number 1600. The cumulant model is investigated in several different variants, using regularization, fourth-order convergent diffusion and fourth-order convergent advection with and without limiters. In ad...

Porous trailing edges have been proposed as a means to reduce acoustic emissions from aircraft wings. However, the influence of the porous material on the aerodynamic performance of the wing has to be investigated. In this work we report DNS/LES simulations of turbulent flow over a DLR-F16 wing profile at a Reynolds number of \(10^6\) using a cumul...

Modeling of fluids with complex rheology in the lattice Boltzmann method (LBM) is typically realized through the introduction of an effective viscosity. For fluids with a yield stress behavior, such as so-called Bingham fluids, the effective viscosity has a singularity for low shear rates and may become negative. This is typically avoided by regula...

This review summarizes the rigorous mathematical theory behind the lattice Boltzmann equation (LBE). Relevant properties of the Boltzmann equation and a derivation of the LBE from the Boltzmann equation are presented. A summary of some important LBE models is provided. Focus is given to results from the numerical analysis of the LBE as a solver for...

The simulation of fire is a challenging task due to its occurrence on multiple space-time scales and the non-linear interaction of multiple physical processes. Current state-of-the-art software such as the Fire Dynamics Simulator (FDS) implements most of the required physics, yet a significant drawback of this implementation is its limited scalabil...

A hybrid Lattice Boltzmann(LB)-Finite Difference(FD) numerical scheme for the simulation of reacting flows at low Mach numbers is presented. The FD solver is used to model the energy and species fields while the LB model computes the flow field. The proposed LB solver is a modified version of the classical iso-thermal weakly compressible LB scheme...

This work explores the feasibility of real-time large-eddy simulations of flow over urban canopies at the neighborhood scale. The cumulant lattice Boltzmann method is employed using a single General Purpose Graphic Processing Unit (GPGPU). In order to demonstrate the validity and efficiency of this approach we simulate wind flow in a neighborhood o...

We present an efficient algorithm of a two-dimensional Gas Kinetic Scheme (GKS)suitable for General Purpose Graphics Processing Units (GPGPUs). The algorithm features conservative second order quadtree-type refinement for Cartesian meshes and nested time stepping. The implementation is validated for several incompressible and thermal compressible t...

Gas-kinetic schemes (GKS) have been developed as a kinetic Finite-Volume approach to computational fluid dynamics. The GKS a priori allows to obtain approximate solutions of the fully compressible Navier-Stokes equations. In our contribution we show simulation results of compressible natural convection at large temperature differences and low Mach...

In this paper a rotating grid technique for the cumulant lattice Boltzmann model is presented. The rotating object is embedded in a rotating mesh that communicates with an enclosing stationary mesh via compact quadratic interpolation. On the rotating mesh, Coriolis and centrifugal forces model the rotation with respect to the outer Eulerian frame o...

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Flow noise during takeoff and landing of commercial aircrafts can be substantially reduced by the use of porous surface layers in suitable sections of wing profiles. On the other hand (passive) porosity and roughness of surfaces tend to have an adverse effect on the boundary layer and thus on the lift of wings. This results in the need to be able t...

Acoustic properties of porous media are very important for numerous industrial applications, the typical goal being to maximize broadband absorption to decrease the sound pressure level of the engineering system under consideration. Up to now acoustic absorption for porous media with complex inner geometry is determined experimentally, as acoustic...

The turbulent boundary layer over a flat plate with porous inlay is investigated using three different approaches. Experiments and large eddy simulations (LES) computations based on the cumulant lattice Boltzmann approach help to assess the performance of a newly developed module that enables a RANS-solver to compute turbulent flow over pore space....

We present a new wall function implementation for the cumulant lattice Boltzmann method that sets a partial slip velocity on the wall by computing a skin frictional coefficient. Our approach uses local information and is particularly appropriate for implementations on general purpose graphics processing units. The validation of the model has been c...

http://dx.doi.org/10.1016/j.compfluid.2017.08.022

A two-phase flow Large Eddy Simulation (LES) model is developed within the framework of phase-field lattice Boltzmann methods (LBM). The proposed model is based on a standard Smagorinsky model for subgrid closure and uses the Multiple-Relaxation-Time (MRT) collision operator. Relevant test cases are considered to demonstrate the capability and accu...

A detailed numerical study of turbulent flow through a micro-orifice is presented in this work. The flow becomes turbulent due to the orifice at the considered Reynolds numbers (∼10 4). The obtained flow rates are in good agreement with the experimental measurements. The discharge coefficient and the pressure loss are presented for two input pressu...

The production of nano-particles from larger aggregates is an important industrial process, especially for life-science products. A micro-machined disperser is studied numerically by the cumulant lattice Boltzmann method. The aggregates are modeled as tracer particles with mass and drag coefficient. They record the history of the experienced stress...

Multiple numerical approaches have been developed to simulate porous media fluid flow and solute transport at the pore scale. These include 1) methods that explicitly model the three-dimensional geometry of pore spaces and 2) methods that conceptualize the pore space as a topologically consistent set of stylized pore bodies and pore throats. In pre...

Single-point measurements from towers in cities cannot properly quantify the impact of all terms in the turbulent kinetic energy (TKE) budget and are often not representative of horizontally-averaged quantities over the entire urban domain. A series of large-eddy simulations (LES) is here performed to quantify the relevance of non-measurable terms,...

A sliding mesh LBM approach for the simulation of the rotating objects

In many industrial and environmental problems we encounter turbulent flows over porous surfaces which also penetrate the porous medium to different extents. Although there is a wealth of literature on macroscopicmodels of such phenomena which do not take the pore scale explicitly into account, these approaches typically require some additional tran...

The dispersion process of ceramic agglomerates modeled as solid particles with mass and drag coefficient in a micro-machined disperser is simulated with the cumulant lattice Boltzmann method (LBM). A simplified particle model is used for tracking the pathlines by compact quadratic interpolation. The simulation of the disperser is validated with exp...

We studied the external aerodynamics of a car employing CFD numerical simulations with the cumulant LBM on GPUs. We performed the analysis for different grid resolutions and for single-and multi-GPU simulations. In order to evaluate the performance of our implementation, we also carried out numerical simulations with the FVM on a CPU cluster using...

We propose, analyze, and validate a lattice Boltzmann model with a cumulant collision operator. The new model is analytically and numerically shown to poses smaller errors than a moment based Multiple Relaxation Time lattice Boltzmann model. We demonstrate the usability of the cumulant lattice Boltzmann model by simulations of flow around a sphere...

To model flow-induced structural vibrations, an interface to couple fluid flow and poroelastic material in a finite element formulation has been developed. One parameter of this interface condition is the slip rate coefficient, resulting from the so-called Beavers-Joseph-Saffman condition. This condition states that the jump in tangential velocity...

A discrete adjoint sensitivity analysis for fluid flow topology optimization based on the lattice Boltzmann method (LBM) with multiple-relaxation-times (MRT) is developed. The lattice Boltzmann fluid solver is supplemented by a porosity model using a Darcy force. The continuous transition from fluid to solid facilitates a gradient based optimizatio...

In the present article, we extend and generalize our previous article [H. Safari, M. H. Rahimian, and M. Krafczyk, Phys. Rev. E 88, 013304 (2013)] to include the gradient of the vapor concentration at the liquid-vapor interface as the driving force for vaporization allowing the evaporation from the phase interface to work for arbitrary temperatures...

This study presents model extensions for a lattice Boltzmann (LB) approach to thermal axisymmetric flow including swirl or rotation. An incompressible axisymmetric lattice Boltzmann D2Q9 model was applied to solve the axial and radial velocities through inserting source terms into the two-dimensional lattice Boltzmann equation. The equations govern...

Der nachfolgende Beitrag setzt sich mit einigen Aspekten der Verantwortung von Ingenieuren auseinander, die primär (aber sicher nicht ausschließlich) für den Bereich der universitären Ingenieurausbildung relevant sind, offensichtlich keinen Anspruch auf Vollständigkeit erheben und durch die subjektive Sichtweise des Autors in seinem Tätigkeitsgebie...

In this article, a method based on the multiphase lattice Boltzmann framework is presented which is applicable to liquid-vapor phase-change phenomena. Both liquid and vapor phases are assumed to be incompressible. For phase changes occurring at the phase interface, the divergence-free condition of the velocity field is no longer satisfied due to th...

In diesem Beitrag werden Belüftungseffekte am Beispiel des EnergieForums Berlin untersucht. Um Erkenntnisse über den Einfluss fluktuierender Windfelder auf die Belüftung zu erzielen, wird die Windumströmung und Temperatur im und um das Atriumgebäude mit einer Large Eddy Simulation (LES)-Modell zeitaufgelöst und räumlich untersucht. Dazu wird das La...

In this paper, we present extensions, extensive validations and applications of our previously published hybrid volume-of-fluid-based (VOF) model for the simulation of free-surface flow problems. For the solution of the flow field, the lattice Boltzmann method is used, where the free surface is represented by a VOF approach. The advection equation...

This work investigated the validity and efficiency of the coupling of the Lattice Boltzmann Method with finite element schemes as well as rigid body approaches to model fluid-structure interaction (FSI). The results on two- and three-dimensional benchmark configurations are very promising and show that an explicit coupling scheme is able to produce...

Although much progress has been made in the last decades, grid generation is still an important topic in Computational Fluid Dynamics (CFD), especially when it comes to adap-tive meshes in massively parallel computations. Grid generation for three-dimensional flow simulations in arbitrarily complex boundaries is still very expensive in terms of har...

In this contribution a numerical study of a turbulent jet flow is presented. The simulation results of two different variants of the Lattice Boltzmann method (LBM) are compared. The first is the well-established D3Q19 MRT model extended by a Smagorinsky Large Eddy Simulation (LES) model. The second is the D3Q27 Factorized Cascaded Lattice Boltzmann...

Underwater landslides may be triggered by the reduction in soil strength caused by excess inter-granular pore pressures resulting from seismic loading. Our goal is to study micro-mechanical processes responsible for such excess pore pressure build up in soils, by way of microfluidics technologies and numeric al modeling. Thus, small-scale experimen...

The rotation of a neutrally buoyant spheroidal particle in a Couette flow is studied by a multi-relaxation-time (MRT) lattice Boltzmann method. We find several new periodic and steady rotation modes for a prolate spheroid for Reynolds numbers () exceeding 305. The simulations cover the regime up to . The rotational behaviour of the spheroid appears...

Surface erosion rills are dominant structures in young developing ecosystems, and as such they fundamentally affect water flows, for example by channeling surface runoff or by locally changing the infiltration capacity of the soil. To successfully model the systems hydrology it is indispensable to take the development of erosion rills into account....

We present an efficient implementation of the Lattice Boltzmann method (LBM) for the numerical simulation of the propagation of long ocean waves (e.g., tsunamis), based on the Nonlinear Shal-low Water (NSW) wave equation. The LBM solution of NSW equations is fully nonlinear and it is assumed that the surface el-evation is single-valued (hence, wave...

The relationship between rainfall and runoff in catchments is a nonlinear function largely controlled by hydrologically connected hillslope elements. In this study, we investigate material and geometrical hillslope properties determining connection of hillslope elements to form subsurface drainage pathways in an artificial catchment (Chicken Creek)...

The understanding of biological processes, e.g. related to cardio-vascular disease and treatment, can significantly be improved by numerical simulation. In this paper, we present an approach for a multiscale simulation environment, applied for the prediction of in-stent re-stenos is. Our focus is on the coupling of distributed, heterogeneous hardwa...

This paper describes the modeling and simulation approach for a water jet created from a propeller behind a ship which is an extension of a prestudy described in [6]. The three-dimensional propeller geometry is rotating on the Eulerian grid which is adapted accordingly in every time step. The river bed roughness was geometrically modeled by adaptin...

Numerous schemes have been proposed to incorporate a bulk forcing term into the lattice Boltzmann equation. In this paper we present a simple and straightforward comparative analysis of five popular schemes in which their differences and similarities are identified. From the analysis we classify the schemes into two groups; the behaviors of the sch...

Zhang and Chen proposed a lattice Boltzmann method for simulations of liquid-vapor thermal flows [Zhang and Chen, Phys. Rev. E 67, 066711 (2003)]. In their numerical test, the authors show simulation results with a temperature ratio of approximately 1.2 for a thermal two-phase flow with T<0.8T(c). However, we believe this to be erroneous and demons...

Evaporation is an important process in many natural and technical systems, such as the unsaturated zone of the subsurface or microchannel evaporators. For the understanding and prediction of the involved processes, numerical simulations of multiphase flow and transport processes are an important tool. In order to achieve an accurate, physically bas...

In this paper we present a new efficient approach for radiative heat transfer simulations for various applications in engineering, combining existing approaches from different fields of computer science and heat transfer. For these application fields we assume radiative exchange between gray, diffuse surfaces in a radiatively nonparticipating mediu...

In this paper, we present the implementation of a volume-of-fluid-(VOF)-based algorithm for the simulation of free-surface flow problems on general purpose graphical processing units (GPGPUs). For the solution of the flow field and the additional advection equation for the VOF fill level, the lattice Boltzmann method on the basis of an MRT collisio...

Two multi-thread based parallel implementations of the lattice Boltzmann method for non-uniform grids on different hardware platforms are compared in this paper: a multi-core CPU implementation and an implementation on General Purpose Graphics Processing Units (GPGPU). Both codes employ second order accurate compact interpolation at the interfaces,...

Under strong shock loading, the pressure distribution in porous material is very complicated. We simulate such a system using a mesoscopic particle method. Morphological analysis is used to characterize the high pressure regimes defined by P>=P"t"h, ...

In this work, the suitability of the lattice Boltzmann method is evaluated for the simulation of subcritical turbulent flows around a sphere. Special measures are taken to reduce the computational cost without sacrificing the accuracy of the method. A large eddy simulation turbulence model is employed to allow efficient simulation of resolved flow...

In-stent restenosis, the maladaptive response of a blood vessel to injury caused by the deployment of a stent, is a multiscale system involving a large number of biological and physical processes. We describe a Complex Automata model for in-stent restenosis, coupling bulk flow, drug diffusion, and smooth muscle cell models, all operating on differe...

Transitional flows are difficult to address by Reynolds Averaged Navier-Stokes (RANS) simulations as the spectrum is typically not fully developed. In this work the suitability of the lattice Boltzmann method is evaluated for the simulation of transitional flows. Special measures are taken to reduce the computational cost without sacrificing the ac...

In the recent years we investigated the validity and efficiency of coupling high order finite elements schemes for mechanics with the Lattice Boltzmann Method. The results on two dimensional and three dimensional benchmark configurations are very promising and show that an explicit coupling scheme is able to produce results which agree with referen...

This article provides a concise survey of the lattice Boltzmann equation: its mathematical theory and its capabilities for applications in computational fluid dynamics (CFD). The lattice Boltzmann method stems from the Boltzmann equation, and thus differentiates from any conventional method for CFD based on direct discretizations of the Navier–Stok...

Most computational fluid dynamics (CFD) simulations require massive computational power which is usually provided by traditional High Performance Computing (HPC) environments. Although interactivity of the simulation process is highly appreciated by scientists and engineers, due to limitations of typical HPC environments, present CFD simulations ar...

An explicit coupling model for the simulation of surface coupled fluid-structure interactions with large structural deflections is introduced. Specifically, the fluid modeled via the Lattice Boltzmann Method (LBM) is coupled to a high-order Finite Element discretization of the structure. The forces and velocities are discretely computed, exchanged...

In this work, we report on the development and initial validation of a new hybrid numerical model for strongly nonlinear free surface flows, including wave breaking and wave-structure interactions. Specifically, a two-dimensional numerical wave tank (NWT) based on Fully Non-linear Potential Flow (FNPF) theory, and a higher-order Boundary Ele-ment M...

A lattice Boltzmann approach to non-pure invasion of immiscible two-phase flow in porous media

Surface erosion rills are dominant structures in young developing ecosystems, and as such they fundamentally affect water flows by channeling surface runoff, by locally changing the infiltration capacity of the soil, or by preventing the establishing of a vegetation cover. Therefore, water balance and drainage pathways of such ecosystems cannot be...

The sustained drive for faster and smaller micro-electronic devices has led to a considerable increase in power density. The ability to effectively pump and enhance heat transfer in mini-/microchannels is of immense technological importance. Using oscillatory flow to enhance the convective heat transfer coefficients in micro-/minichannels is one of...

The lattice Boltzmann space/time discretisation, as usually derived from integration along characteristics, is shown to correspond to a Strang splitting between decoupled streaming and collision steps. Strang splitting offers a second-order accurate ...

Double-diffusive convection in vertical annuluses with opposing temperature and concentration gradients is of fundamental interest and practical importance. However, available literature especially for higher Rayleigh numbers beyond Ra⩽105 is sparse. In this study, we investigated double diffusion induced convection up to Ra=107 using a simple latt...

In this paper, we present a hybrid volume-of-fluid-based algorithm for the simulation of free-surface-flow problems. For the solution of the flow field, the lattice Boltzmann method is used. The additional advection equation for the volume-of-fluid (VOF) fill level is discretized with a classical finite volume method. For the interface reconstructi...

Over the last decade the Lattice Boltzmann Method (LBM) has matured as an efficient method for solving the Navier-Stokes equations. The p-version of the Finite Element Method (p-FEM) has proved to be highly efficient for a variety of problems in the field of structural mechanics. The focus of this contribution is to investigate the validity and eff...

COAST (Complex Automata Simulation Technique) is a European Union FP6 funded project which has developed a methodology for multi-science, multi-scale simulation of complex systems. The resulting framework (MUSCLE: Multiscale Simulation Coupling Library and Environment is now publically available. As an exemplar, MUSCLE has been applied to the model...

An model for the simulation of surface coupled fluid-structure interactions with large structural deflections is presented. Specifically, the fluid modeled via the Lattice Boltzmann Method (LBM) is coupled to a high-order Finite Element discretization of the structure. The forces and velocities are discretely computed, exchanged and applied at the...

High efficiency valve-less rectification micropumps are essential in developing effective microfluidic systems. Many parameters have been reported in the literature to have an effect on the efficiency of valve-less rectification micropumps. These parameters are related to the dynamics of fluid flow (such as Reynolds number), rectifying geometries,...

The advantages of valve-less rectification micro pumps include having no moving parts, low cost, reliable, having the ability to pump particles-laden fluids and live cells, being compatible with a wide range of micro channel materials and working fluids. Most valve-less rectification micro pumps are based on passive rectifying geometries such as a...

Developing multifunctional devices are essential to realize more efficient Microsystems. With miniaturization processes taking place in many different applications, the rooms for single function microfluidic devices are limited. In this study, we introduce a multifunctional micro fluidic device based on bifurcation geometry which is capable of perf...

In this study numerical predictions of entropy generation in turbulent natural convection due to internal heat generation in a square cavity are reported for the first time. Results of entropy generation analysis are obtained by solving the entropy generation equation. The values of velocity and temperature, which are the inputs of the entropy gene...

In the present work, dissipative particle dynamics (DPD) simulation of simple flows is studied based on coarse-graining parameter. Reference scales of DPD are expressed in terms of physical units and DPD parameters and equations are expressed in terms of Reynolds number and apparent Peclet number. DPD parameters for a given coarse-graining are calc...

We prove for generic steady solutions of the Lattice Boltzmann (LB) models that the variation of the numerical errors is set by specific combinations (called ''magic numbers'') of the relaxation rates associated with the symmetric and anti-symmetric ...

We propose a scheme to reconstruct the flow field up to second order in a cell com-posed of four lattices nodes in 2 dimensions. The information contained in the higher order moments of the distribution functions is used to construct an interpolation scheme of second order for the velocity field.

We prove for generic steady solutions of the Lattice Boltzmann (LB) models that the variation of the numerical errors is set by specific combinations (called ''magic numbers'') of the relaxation rates associated with the symmetric and anti-symmetric ...

The efficiency of the valve-less rectification micropump depends primarily on the microfluidic diodicity (the ratio of the backward pressure drop to the forward pressure drop). In this study, different rectifying structures, including the conventional structures (nozzle/diffuser and Tesla structures), were investigated at very low Reynolds numbers...

Over the last decade the Lattice Boltzmann method, which was derived from the kinetic gas theory, has matured as an efficient approach for solving Navier–Stokes equations. The p-FEM approach has proved to be highly efficient for a variety of problems in the field of structural mechanics. Our goal is to investigate the validity and efficiency of cou...

In this study, we investigate the phenomena of flow streaming in micro-/minichannel networks of symmetrical bifurcations using computer simulations with analytical validation. The phenomena of the flow streaming can be found in zero-mean velocity oscillat-ing flows in a wide range of channel geometries. Although there is no net mass flow (zero-mean...