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This paper aims to assess a conservative interface locating method based on levelset adapted to two fluid model for two phase flow. The objective of the work is twofold: first to check out the prediction of the model on bubble coalescence cases and then to introduce a first description of the multifield hybrid approach for twophase flow modelling. The interface locating method is part of a model dedicated to the simulation of large and distorted bubbles. At different liquid viscosities and densities, the model yields reasonable predictions of terminal velocities and shapes for rising bubble experiments. The overall method relies also on an existing building block, consisting of a set of averaged models dedicated to dispersed bubbles, which has already been validated and has given a reasonable agreement with experimental data in cases where the spherical shape assumption is still valid for the dispersed phase. As a consequence, we present the first step toward a new approach consisting of modelling the small bubbles as a dispersed field and simulating the large and distorted ones. The main outcome is the simulation of bubble coalescence where the distortion of the interface during the coalescence phenomena is followed. The capability to simulate correctly coalescence phenomena is an important point of the modelling of slug flows with interface locating methods.

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As a fi rst step towards a new approach for the simulation of two-phase fl ows, the objective of this work is to check out the prediction of a model dedicated to large and distorted bubbles on twobubble coalescence cases. The multifi eld hybrid approach for two-phase fl ow modelling consists in dealing separately with the small and spherical bubbles, treated with a dispersed approach, and with the large and distorted ones, whose interface is located. The overall method relies also on an existing building block, consisting in a set of averaged models dedicated to dispersed bubbles, which has already been validated and has given a reasonable agreement with experimental data in cases where the spherical shape assumption is still valid for the dispersed phase. This paper aims to assess a conservative interface locating method based on level set adapted to two-fl uid model for two-phase fl ows. The interface locating method is a part of a model dedicated to the simulation of large and distorted bubbles. At different liquid viscosities and densities, the model provides reasonable predictions of terminal velocities and shapes for rising bubble experiments. The main outcome is the simulation of bubble coalescence where the distortion of the interface during the coalescence phenomenon is followed. The ability to simulate coalescence phenomena correctly is an important issue in the modelling of slug fl ows with interface locating methods.