Euler–Euler large eddy simulations for dispersed turbulent bubbly flows T. Ma a,⇑ , T. Ziegenhein a , D. Lucas a , E. Krepper a , J. Fröhlich b a Helmholtz-Zentrum Dresden-Rossendorf, Institute of Fluid Dynamics, Dresden, Germany b Technische Universität Dresden, Institut für Strömungsmechanik, Dresden, Germany article info Article history: Received 24 February 2015 Received in revised form 8 May 2015 Accepted 17 June 2015 Available online 20 July 2015 Keywords: Bubble column Two-fluid model Large eddy simulation Energy spectra abstract In this paper we present detailed Euler–Euler Large Eddy Simulations (LES) of dispersed bubbly flow in a rectangular bubble column. The motivation of this study is to investigate the potential of this approach for the prediction of bubbly flows, in terms of mean quantities. The physical models describing the momentum exchange between the phases including drag, lift and wall force were chosen according to previous experiences of the authors. Experimental data, Euler–Lagrange LES and unsteady Euler–Euler Reynolds-Averaged Navier–Stokes results are used for comparison. It is found that the present model combination provides good agreement with experimental data for the mean flow and liquid velocity fluctuations. The energy spectrum obtained from the resolved velocity of the Euler–Euler LES is presented as well. Ó 2015 Elsevier Inc. All rights reserved. 1. Introduction Many flow regimes in nuclear engineering and chemical engi- neering are gas–liquid flows with a continuous liquid phase and a dispersed gaseous phase. Computational Fluid Dynamics (CFD) simulations become more and more important for the design of the related processes, for process optimization as well as for safety considerations. Because of the large scales that need to be consid- ered for such purposes, the two-fluid or multi-fluid approach is often the most suitable framework. During the last years, clear pro- gress was achieved for modelling dispersed bubbly flows. At Helmholtz-Zentrum Dresden-Rossendorf, in cooperation with ANSYS, the inhomogeneous Multiple Size Group (iMUSIG) model was developed (Krepper et al., 2008). It is based on bubble size classes for the mass balance as well as for the momentum balance. This model has been later on extended by adding a continuous gas phase for a generalized two-phase flow (GENTOP) (Hänsch et al., 2012). The aim of the GENTOP concept is to treat both unresolved and resolved multiphase structures. The present study concen- trates on the turbulence modelling of the unresolved structures. Turbulence in the liquid phase is an important issue in bubbly flows as it has a strong influence on the local distribution of the dispersed phase and on the bubble size by bubble fragmentation and coalescence. Compared to the liquid phase the influence of the turbulence in the gas phase is generally negligible because of the low density of the gas and the small dimensions of bubbles. A bubble column provides a good experimental system for the study of turbulent phenomena in bubbly flows. In bubble columns a wide range of length and time scales exists on which turbulent mixing takes place. The largest turbulence scales are comparable in size to the characteristic length of the mean flow and depend on reactor geometry and boundary conditions. The smaller scales depend on the bubble dynamics and hence are proportional to the bubble diameter. In bubbly flows, the small scales are respon- sible for the dissipation of the turbulent kinetic energy as in single-phase flow, but the bubbles can also generate back-scatter, i.e. energy transfer from smaller to larger scales (Dhotre et al., 2013). The combination of both effects can yield an overall enhancement or attenuation of the turbulence intensity. In the present paper the effect of turbulence modelling is investigated. In the CFD simulations of bubble columns, Reynolds-Averaged Navier–Stokes (RANS) models are used for modelling turbulence in the traditional way, using isotropic closures without resolution of turbulent scales. Large Eddy Simulation (LES) offers the possibility to resolve the large-scale anisotropic turbulent motion and to model the small scales with a Subgrid-Scale (SGS) model. Large eddy simulations for such kind of flows have been per- formed by different authors employing the Euler–Euler approach. Zhang et al. (2006) used LES with the Smagorinsky model to simulate a square cross-sectional bubble column, with the gas inlet placed in the centre of the bottom. They compared the results obtained with different values of the Smagorinsky constant C s and found that too high values lead to an unphysically high effec- tive viscosity which in turn damps the bubble plume dynamics. http://dx.doi.org/10.1016/j.ijheatfluidflow.2015.06.009 0142-727X/Ó 2015 Elsevier Inc. All rights reserved. ⇑ Corresponding author. E-mail address: tian.ma@hzdr.de (T. Ma). International Journal of Heat and Fluid Flow 56 (2015) 51–59 Contents lists available at ScienceDirect International Journal of Heat and Fluid Flow journal homepage: www.elsevier.com/locate/ijhff