arXiv subjects

Michael Breuer

Publications and source records attributed to Michael Breuer.

3 recordsLinked to original sources

arXiv2025

Investigation of cohesive particle deagglomeration in homogeneous isotropic turbulence using particle-resolved DNS

In this study, agglomerate breakage in homogeneous isotropic turbulence is investigated using particle-resolved direct numerical simulations. Single agglomerates composed of 500 monodisperse spherical particles are considered, and their interaction with the turbulent flow is resolved through an immersed boundary method coupled with a soft-sphere discrete element model. A range of Reynolds numbers and cohesion levels is examined to assess their influence on the breakup behavior. Detailed insights into the underlying breakage mechanisms are provided through the analysis of local flow structures and fluid stresses. Strain-dominated regions are identified as the primary contributors to the onset and propagation of particle erosion. The benefits of the particle-resolved simulation framework in capturing these physical processes in detail are demonstrated. The predicted fragment size distributions and breakup modes are analyzed leading to the outcome that erosion-driven breakage is the dominating mechanism. The time evolution of the fragment number and the main agglomerate structure is quantified. The breakage rate is evaluated and its dependence on the modified adhesion number is established, showing a power-law decay that agrees with general trends reported in the literature. In addition, the analysis of the fragment ejection direction reveals a strong alignment with the local deformation plane spanned by the most extensional and compressive strain-rate eigenvectors, indicating that breakage results from the interplay between flow stretching and compression. The results contribute to the development of physics-informed breakup kernels for use in efficient but less-detailed simulation approaches such as point-particle Euler--Lagrange predictions with agglomerates represented by effective spheres or Euler--Euler simulations.

physics.flu-dyn↗

arXiv2025

An improved numerical simulation methodology for nanoparticle injection through aerodynamic lens systems

Aerosol injectors applied in single-particle diffractive imaging experiments demonstrated their potential in efficiently delivering nanoparticles with high density. Continuous optimization of injector design is crucial for achieving high-density particle streams, minimizing background gas, enhancing X-ray interactions, and generating high-quality diffraction patterns. We present an updated simulation framework designed for the fast and effective exploration of the experimental parameter space to enhance the optimization process. The framework includes both the simulation of the carrier gas and the particle trajectories within injectors and their expansion into the experimental vacuum chamber. A hybrid molecular-continuum-simulation method (DSMC/CFD) is utilized to accurately capture the multi-scale nature of the flow. The simulation setup, initial benchmark results of the coupled approach, and the validation of the entire methodology against experimental data are presented.

physics.flu-dyn↗

arXiv2024

Accuracy and Performance Evaluation of Low Density Internal and External Flow Predictions using CFD and DSMC

The Direct Simulation Monte Carlo (DSMC) method was widely used to simulate low density gas flows with large Knudsen numbers. However, DSMC encounters limitations in the regime of lower Knudsen numbers (Kn<0.1). In such cases, approaches from classical computational fluid dynamics (CFD) relying on the continuum assumption are preferred, offering accurate solutions at acceptable computational costs. In experiments aimed at imaging aerosolized nanoparticles in vacuo a wide range of Knudsen numbers occur, which motivated the present study on the analysis of the advantages and drawbacks of DSMC and CFD simulations of rarefied flows in terms of accuracy and computational effort. Furthermore, the potential of hybrid methods is evaluated. For this purpose, DSMC and CFD simulations of the flow inside a convergent-divergent nozzle (internal expanding flow) and the flow around a conical body (external shock generating flow) were carried out. CFD simulations utilize the software OpenFOAM and the DSMC solution is obtained using the software SPARTA. The results of these simulation techniques are evaluated by comparing them with experimental data (1), evaluating the time-to-solution (2) and the energy consumption (3), and assessing the feasibility of hybrid CFD-DSMC approaches (4). Keywords: DSMC; SPARTA; Continuum assumption; Transition regime; Rarefied flow; high-performance computing

physics.flu-dyn↗