arXiv subjects

Otto Mierka

Publications and source records attributed to Otto Mierka.

3 recordsLinked to original sources

arXiv2025

Feasibility study for physics-informed direct numerical simulation describing particle suspension in high-loaded compartments of air-segmented flow

The Archimedes Tube Crystallizer (ATC) employs air-segmented flow in coiled tubes to achieve narrow residence time distributions for continuous crystallization. Taylor and Dean vortices drive particle suspension in this system. However, one-way coupled models fail to capture the fluid-particle feedback that becomes critical at higher loadings. We present a particle-resolved Direct Numerical Simulation (DNS) framework based on a Finite Element-Fictitious Boundary Method with hard-contact modeling of particle interactions. Simulations of L-alanine suspensions across varying particle sizes, solid contents, and rotational speeds are validated against experimental side-view imaging. Three quantitative metrics-axial distribution, radial index, and vertical asymmetry-are introduced to classify suspension regimes. The DNS results reproduce the experimentally observed flow map zones (green, yellow, red/yellow, red) and resolve subtle transitions such as rear loading and loss of vertical symmetry. This feasibility study demonstrates that DNS can reliably predict dense suspension behavior and provides a mechanistic foundation for crystallizer design.

physics.flu-dyn↗

arXiv2025

A Chimera domain decomposition method with weak Dirichlet-Robin coupling for finite element simulation of particulate flows

We introduce a new multimesh finite element method for direct numerical simulation of incompressible particulate flows. The proposed approach falls into the category of overlapping domain decomposition / Chimera / overset grid meshes. In addition to calculating the velocity and pressure of the fictitious fluid on a fixed background mesh, we solve the incompressible Navier-Stokes equations on body-fitted submeshes that are attached to moving particles. The submesh velocity and pressure are used to calculate the hydrodynamic forces and torques acting on the particles. The coupling with the background velocity and pressure is enforced via (i) Robin-type boundary conditions for an Arbitrary-Lagrangian-Eulerian (ALE) formulation of the submesh problems and (ii) a Dirichlet-type distributed interior penalty term in the weak form of the background mesh problem. The implementation of the weak Dirichlet-Robin coupling is discussed in the context of discrete projection methods and finite element discretizations. Detailed numerical studies are performed for standard test problems involving fixed and moving immersed objects. A comparison of Chimera results with those produced by fictitious boundary methods illustrates significant gains in the accuracy of drag and lift approximations.

math.NA↗

arXiv2025

Effective viscosity closures for dense suspensions in CSP systems via lubrication-enhanced DNS and numerical viscometry

Dense particle suspensions are promising candidates for next-generation Concentrated Solar Power (CSP) receivers, enabling operating temperatures above 800 degrees C. However, accurate modeling of the rheological behavior of granular flows is essential for reliable computational fluid dynamics (CFD) simulations. In this study, we develop and assess numerical methodologies for simulating dense suspensions pertinent to CSP applications. Our computational framework is based on Direct Numerical Simulation (DNS), augmented by lubrication force models to resolve detailed particle-particle and particle-wall interactions at volume fractions exceeding 50\%. We conducted a systematic series of simulations across a range of volume fractions to establish a robust reference dataset. Validation was performed via a numerical viscometer configuration, permitting direct comparison with theoretical predictions and established benchmark results. Subsequently, the viscometer arrangement was generalized to a periodic cubic domain, serving as a representative volume element for CSP systems. Within this framework, effective viscosities were quantified independently through wall force measurements and energy dissipation analysis. The close agreement between these two approaches substantiates the reliability of the results. Based on these findings, effective viscosity tables were constructed and fitted using polynomial and piecewise-smooth approximations. These high-accuracy closure relations are suitable for incorporation into large-scale, non-Newtonian CFD models for CSP plant design and analysis.

physics.flu-dyn↗