Numerical simulation of flows with interfaces in Trio_U
 Direct numerical simulation of wall boiling

Wall boiling is a physical problem that is important from an industrial point of view and difficult from a scientific point of view. The techniques dedicated to the direct numerical simulation of two-phase flows are getting mature enough to study this phenomenon at the scale of one or a few bubbles.

Thanks to the Front-Tracking method developed in the Trio_U code, we can study complex phenomena such as that illustrated of the figure.

These numerical simulations have two mains objectives. First, we aim at understanding the basic physical mechanisms of nucleate boiling. Second, we aim at deducing information that are useful for averaged models, that are the only models that can be used for industrial applications.

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 Simulation of the interaction of a deformable bubble with a homogeneous isotropic turbulence

Turbulent two-phase flows abound in nature and engineering applications. The complex interactions between interfaces and turbulence strongly impact the flow properties. Consequently, there is both a scientific and industrial interest to study this two-way coupling phenomenon.

The objective is to use direct numerical simulation (DNS) to better understand this two-way coupling and to develop simulation tools adapted to industrial applications.  In this perspective, we seek to develop a concept for two-phase flows that would be equivalent to the single-phase Large Eddy Simulation (LES).

In this concept, the interface geometry is fully resolved but part of the interactions between interface and turbulence is accounted for through dedicated subgrid models. The development of these models lies in particular on the analysis of a priori tests that allow to sort out the terms of the equations that require to be modeled. The most relevant of these DNS is the interaction of a strongly deformable bubble and a homogeneous isotropic turbulence (cf. image).  The analysis of these results shows that it is necessary to use a modeling based on the Leonard and Germano decomposition, which provides subgrid models that integrate the two-way coupling phenomenon.  An analysis based on the matched asymptotic expansion method allowed to determine the jump conditions that must be imposed at a under-resolved interface. The first results are very promising.

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 Simulation of a bubble column

The new super-computer Titane (managed by GENCI and the CCRT) allowed us to perform this exceptionnaly detailed simulation of a dispersed intermittent bubbly flow. The simulation has been performed by Sylvain Magdeleine during his PdD and uses a lagrangian front tracking method together with subgrid scale models developped by Adrien Toutant (see his PdD thesis).

See the movie (mpeg4)
See the movie (mpeg1)
Publications (A.Toutant or S.Magdeleine)
CCRT (CEA Computing Center)
GENCI (Grand Equipement National de Calcul Intensif)

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