- Influence of a cost–efficient Langevin subgrid-scale model on the dispersed phase of large–eddy simulations of turbulent bubble–laden and particle–laden flows

# Influence of a cost–efficient Langevin subgrid-scale model on the dispersed phase of large–eddy simulations of turbulent bubble–laden and particle–laden flows

Publication date

2017

Document type

Research article

Author

Organisational unit

Scopus ID

ISSN

Series or journal

International Journal of Multiphase Flow

Periodical volume

89

First page

23

Last page

44

Peer-reviewed

✅

Part of the university bibliography

✅

Abstract

© 2016 Elsevier Ltd The paper is concerned with the development of a cost-efficient Langevin subgrid-scale model and the analysis of its influence on the dispersed phase of turbulent bubble–laden and particle–laden flows. For this purpose, the Langevin subgrid-scale model of [Pozorski, J., Apte, S. V., 2009. Filtered particle tracking in isotropic turbulence and stochastic modeling of subgrid-scale dispersion. Int. J. Multiphase Flow 35, 118–128.] is chosen as the starting point since it takes the temporal correlations of the subgrid-scale velocity fluctuations, the crossing-trajectory and the continuity effect into account. Based on the idea of [Minier, J.-P., Peirano, E., Chibbaro, S., 2004. PDF model based on Langevin equation for polydispersed two-phase flows applied to a bluff-body gas-solid flow. Phys. Fluids 16, 2419–2431.] [Minier, J.-P., Chibbaro, S., Pope, S. B., 2014. Guidelines for the formulation of Lagrangian stochastic models for particle simulations of single-phase and dispersed two-phase turbulent flows. Phys. Fluids 26, 113303.] to formulate the drift and diffusion terms in matrix form, the model is extended for an arbitrary direction of the particle motion. Considering turbulent downward channel flows of different setups covering a large range of parameters, the influence of the subgrid-scale model is analyzed. After a detailed validation of the bubble–laden flow the Langevin model and a simple trivial model are applied to investigate the effect of the subgrid-scales. It is found that the Langevin subgrid-scale model only marginally changes the velocity statistics or the volume fraction of the bubbles, which can be attributed to the small magnitude of the subgrid-scale velocities obtained by the Langevin model. The model is able to estimate the correct level of the turbulent kinetic energy of the subgrid-scales. Similar results are found for the second setup consisting of solid particles of Stokes number St+=1.67. In this case the influence of the Langevin subgrid-scale model on the velocity statistics of the particles is found to be more pronounced. Furthermore, it is observed that the model leads to a strongly increased volume fraction of the particles at the walls and thus to a significant increase of particle-wall collisions. To further investigate this behavior and to analyze the impact of the particle inertia, additional simulations containing smaller particles (St+=1 and 0.1) are carried out. The results show that the influence of the Langevin subgrid-scale model on the velocity fluctuations and the volume fraction increases with decreasing Stokes number. Thus, for these cases the extended but nevertheless still cost-efficient Langevin model is a reasonable approach.

Cite as

Enthalten in: International journal of multiphase flow. - Oxford : Pergamon Press, 1973 . - Bd. 89.2017, Seite 23-44

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