URANS simulations of thermal stratification in a large enclosure for severe accident scenarios
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Copyright (2015) by American Nuclear Society All rights reserved. The introduction of a jet of fluid into a more or less stationary body fluid at a different temperature can lead to thermal stratification, and these processes are expected to be important in some severe nuclear accidents. Thermal stratification within the secondary containment could affect the ability of the containment to reject decay heat, for example. An ability to predict the behavior of the fluid under these circumstances is thus important. Such flows are complex, and computational fluid dynamics approaches are needed to resolve them, but they do present modeling challenges that go beyond those of more common 'forced' flows. In an effort to develop a computational methodology for CFD analyses of thermal stratification within large enclosures, the Twin Jet Water Facility (TJWF), discussed in previous works, was constructed to provide experimental data against which to assess the performance of various CFD modeling approaches. The TJWF allows for one or two heated jet(s) to enter vertically from below into a cooler pool of water, with either water recirculated, or with the water level allowed to rise. This work focuses on a single slender planar heated jet entering cooler water, and in which stratification is then seen to occur with a raising water level. In this study, CFD analyses using unsteady Reynolds averaged (URANS) turbulence models such as low- Re k-s and SST-k-m are conducted, and the experimental data from the TJWF for the same test cases are compared to the computational results. The modeling deficiencies and potential causes of errors arising from the use of each approach is discussed. The results and conclusions for this work provide guidance for URANS simulations of such circumstances. This work was performed using the CD-adapco's STAR- CCM+ v9.04 CFD code.
