Application of a multi-field concept to the dam-break case with an obstacle

This paper presents new results for a generalized approach developed for the simulation of two-phase flow problems with multi-scale interfacial structures. The inhomogeneous Multiple Size Group (MUSIG)-model (Krepper et al., 2008) is extended by a large-scale continuous gas phase whose filtered gas-liquid interface is captured within the Eulerian approach. In the framework of the coalescence- and breakup processes desribed by the MUSIG-model, mass transfers between the continuous gas phase and the bubble size groups have to be modelled additionally. The new concept enables transitions between dispersed and continuous gas morphologies, including the evanescence and appearance of a particular phase. Adequate interfacial transfer formulations, which are consistent with such an approach, are introduced for area density and drag. Following the free surface drag-formulation proposed by Höhne and Vallée (2010) shear stresses are considered within the free surface area.
The application of the concept to the dambreak-case demonstrates the breakup of continuous gas into a polydispersed phase consisting of different bubble sizes due to the collapse of a water column. Both resolved free surface structures as well as the entrainment of bubbles and their coalescence and breakup underneath the surface can be described. The computational results will be compared with experiments of Koshizuka et al. (1995). Simulations have been performed with the CFD-code CFX 14.0.
The paper will further investigate the possible improvement of such free surface simulations by including sub-grid information about small waves and instabilities at the free surface. Therefore a new treatment of turbulent kinetic energy at the free surface via source terms will be applied according to the proposal of Brocchini and Peregrine (2001). A comparison of the results will be used for a discussion of possible new mass transfer models between filtered free surface areas and dispersed bubble size groups as part of the future work.