Numerical modelling of an air-helium buoyant jet in a two vented enclosure
Résumé
We present a DNS study of an air-helium buoyant jet rising in a two vented cavity. The
geometrical configuration mimics the helium release in an experimental set-up [1] built at
CEA Saclay in the framework of security assessment of hydrogen-based systems with an
indoor usage. The dimension of the enclosure was chosen to ensure a laminar-turbulent
transition occurring at about the middle height of the cavity.
This study aims at determining the relevant computational domain and boundary con-
ditions necessary to accurately model the jet development in a vented cavity where the
mass flow rates crossing the vents are not prescribed. We observe that applying constant
pressure outlet boundary conditions directly at the vent interfaces underestimates the
volumetric flow rate of air entering the enclosure and thus overestimates the helium mass
inside the cavity. On the contrary, adding a surrounding volume into the computational
domain better predicts the air flow-rate across the vents and leads to a better agreement
with the experimental Particle Image Velocimetry measurements along the vents but also
inside the cavity.
Once the numerical model being set, helium distribution inside the cavity is compared to
the Linden theory [2]. Then the dominant terms of the Turbulent Kinetic Energy equation
expressed in the Reynolds averaged formulation are investigated and in particular the
buoyancy production term.
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