The computation of turbulent natural convection flows - Turbulence ...

stable test case, the computed three-dimensional structures are weaker. In con-
trast to the experimental evidence, the time-dependent three-dimensional k-ε-
AWF simulations returned a mainly stable and largely two-dimensional flow
field. With the introduction of the RSM model, on the other hand, the time-
dependent RANS are able to reproduce the three-dimensional flow features,
though not to the same degree as the experimental data. The Nu variation pre-
dicted by the RSM is in reasonable agreement with the measurements in terms
of the Nu levels and variations, while the EVM returned the correct levels for
the Nusselt number, but not the correct variation.
The horizontal annular penetration case involves a horizontal annular pas-
sage, closed at one end, with the inner core maintained at a lower temperature.
The inner core cools the fluid around it, which makes it heavier. The heavier
fluid drops out of the penetration, from the open end, and new warm fluid
enters to take its place. In the lower Ra case, the time-dependent simulation
showed that downward flow which separates from the cold tube was not uni-
form all along the tube and over most of the penetration there were strong
oscillations. In the higher Ra case, the contours of the instantaneous vertical
velocity, in common with those at the lower Rayleigh number, showed flow
oscillations within the penetration, but with smaller amplitude.
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