THE NATURE OF INSTABILITIES IN BUBBLY FLOWS/ A COMPARISON BETWEEN EULERIAN-EULERIAN AND EULERIAN-LAGRANGIAN APPROACHES

Paper in proceedings, 2017

Bubble columns are used in many industrial processes, ranging from nuclear to chemical reactors, waste water and waste gas treatments. Their prediction is fundamental for a better efficiency and design of industrial plants and our current knowledge in modelling this kind of flows is still poor. One of the issues that are still not sufficiently understood is the appearance of a non-uniform volume fraction field in the form of meso-scale structures. We apply an Eulerian-Eulerian two-fluid model approach to investigate the existence of unstable modes that generate meso-scale structures. The ability of this numerical framework in detecting the correct dynamics of the unstable modes is still debated. For this reasons, the results of the Eulerian-Eulerian model are compared with an additional modelling framework like the Eulerian-Lagrangian approach. The primary aim of this comparison is to verify that the observations made using the two-fluid model are not numerical artefacts but real representations of the physical phenomenologies described by the equations. Both approaches show the formation of characteristic elongated meso-scale structures in the steady regime. Moreover, a good agreement appears in the force balance between the two methodologies supporting a physical nature of the heterogeneities detected with the Eulerian/Eulerian model.