Küllmer, Knut

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Küllmer, Knut

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    PublicationAccess status: Open Access ,
    Pseudopotentialbasierte Lattice-Boltzmann-Verfahren für Mehrphasenströmungen
    (2019)
    Küllmer, Knut
    Pseudopotential (PP)-based lattice Boltzmann methods are widely used to simulate multiphase flows. As they ground on a phenomenological approach, their usage involves a high modelling effort and, additionally, they suffer from so-called spurious velocities that compromise numerical stability and accuracy. Therefore, this work advances PP-models by three novel aspects. First, the PP-model is shown to develop spurious droplets when contact angles are modelled with common approaches in combination with enhanced forcing schemes. These droplets are eliminated by a novel approach that relies on additional boundary conditions for all interaction forces. This not only prevents the spurious droplets from emerging but also increases the stability in wallbound flows. Second, a novel procedure to reduce spurious velocities is introduced. Therefore, the discretization of the interaction forces is extended and the additional free coefficients are optimized numerically using static droplet simulations. The resulting scheme is shown to greatly reduce spurious velocities and is successfully validated in stationary and transient testcases. Third and final, the diffusion characteristics in multicomponent systems are investigated in detail, revealing a critical dependency between the macroscopic diffusion coefficients and the forcing scheme. This analysis forms the basis for the comparison and development of new potential functions (in multicomponent systems) and reduces the modeling effort.
    Source Type:Doctoral Thesis
    Series:Schriftenreihe des Lehrstuhls für Strömungs- und Thermodynamik
    Volume number:5
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    PublicationAccess status: Open Access ,
    The influence of forcing schemes on the diffusion properties in pseudopotential-based Lattice Boltzmann models for multicomponent flows
    (2017)
    Küllmer, Knut
    ;
    Krämer, Andreas
    ;
    Joppich, Wolfgang
    ;
    Reith, Dirk
    ;
    Foysi, Holger
    The talk presents the influence of the choice of forcing schemes in pseudopotential-based LBM methods for multi-phase flows (e.g. Shan & Doolen (1995) or He & Doolen (1998)) on the diffusion coefficient, obtained via Chapman-Enskog analysis. The critical value of G is obtained und known relations used in the literature are subsequently derived based on this theory (e.g. Huan et al. (2007)). The often observed shift at tau=1 for the critical value of G can be directly derived. Simulation show excellent agreement between the diffusion coefficient and Fick’s law for various values of G.
    Source Type:Other
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