Browsing by Author "Kijanski, Nadine"

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Open Access
Benchmark simulations of dense suspensions flow using computational fluid dynamics
(2022) Haustein, Martin A.; Eslami Pirharati, Mahmoud; Fataei, Shirin; Ivanov, Dimitri; Jara Heredia, Daniel; Kijanski, Nadine; Lowke, Dirk; Mechtcherine, Viktor; Rostan, Daniel; Schäfer, Thorsten; Schilde, Carsten; Steeb, Holger; Schwarze, Rüdiger
The modeling of fresh concrete flow is still very challenging. Nevertheless, it is of highest relevance to simulate these industrially important materials with sufficient accuracy. Often, fresh concrete is assumed to show a Bingham-behavior. In numerical simulations, regularization must be used to prevent singularities. Two different regularization models, namely the 1) Bi-viscous, and 2) Bingham-Papanastasiou are investigated. Those models can be applied to complex flows with common simulation methods, such as the Finite Volume Method (FVM), Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH). Within the scope of this investigation, two common software packages from the field of FVM, namely Ansys Fluent and OpenFOAM, COMSOL Multiphysics (COMSOL) from FEM side, and HOOMD-blue.sph from the field of SPH are used to model a reference experiment and to evaluate the modeling quality. According to the results, a good agreement of data with respect to the velocity profiles for all software packages is achieved, but on the other side there are remarkable difficulties in the viscosity calculation especially in the shear- to plug-flow transition zone. Also, a minor influence of the regularization model on the velocity profile is observed.
Open Access
Direct numerical simulation and analysis of solid body motion in dilute suspensions using Smoothed Particle Hydrodynamics
(Stuttgart : Institute of Applied Mechanics, 2024) Kijanski, Nadine; Steeb, Holger (Prof. Dr.-Ing.)
Suspensions and their applications are found in many engineering, environmental or medical fields. While the effective rheological behavior is well understood in the framework of non-Newtonian fluid mechanics, contributions in the field of pore-scale fully resolved numerical simulations with non-spherical particles are rare. The motion of single particles immersed in the fluid is still on-going research and depends on hydromechanical forces as well as on solid-solid interactions. Using Smoothed Particle Hydrodynamics, a modeling approach for Direct Numerical Simulations of a single-phase fluid containing non-spherically formed solid aggregates is presented. The motion of single particles in dilute suspensions are observed to analyze effects like shear-wall migration or rolling, as seen in experiments. To be able to simulate the behavior of for example fresh concrete or mud flow as realistic as possible, the simulations taking into account a Newtonian as well as a non-Newtonian material model for the carrier fluid.
Open Access
An SPH approach for non-spherical particles immersed in Newtonian fluids
(2020) Kijanski, Nadine; Krach, David; Steeb, Holger
Solid particles immersed in a fluid can be found in many engineering, environmental or medical fields. Applications are suspensions, sedimentation processes or procedural processes in the production of medication, food or construction materials. While homogenized behavior of these applications is well understood, contributions in the field of pore-scale fully resolved numerical simulations with non-spherical particles are rare. Using Smoothed Particle Hydrodynamics (SPH) as a simulation framework, we therefore present a modeling approach for Direct Numerical Simulations (DNS) of single-phase fluid containing non-spherically formed solid aggregates. Notable and discussed model specifications are the surface-coupled fluid-solid interaction forces as well as the contact forces between solid aggregates. The focus of this contribution is the numerical modeling approach and its implementation in SPH. Since SPH presents a fully resolved approach, the construction of arbitrary shaped particles is conveniently realizable. After validating our model for single non-spherical particles, we therefore investigate the motion of solid bodies in a Newtonian fluid and their interaction with the surrounding fluid and with other solid bodies by analyzing velocity fields of shear flow with respect to hydromechanical and contact forces. Results show a dependency of the motion and interaction of solid particles on their form and orientation. While spherical particles move to the centerline region, ellipsoidal particles move and rotate due to vortex formation in the fluid flow in between.