Geometry effects on thermal striping in nuclear reactors: POD analysis of large-eddy simulations and experiments

Oana Marin, Elia Merzari, Aleks Obabko, Andres Alvarez, Stephen Lomperski, Paul Fischer

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Thermal striping is of particular significance in nuclear reactor applications, primarily in sodium cooled fast reactors. The mixing chamber of the upper plenum of a nuclear reactor can be subjected to thermal striping unless designed such that the coolant is sufficiently mixed prior to reaching the top wall of the upper plenum. In order to conduct a systematic analysis of this phenomenon a simplified experimental set-up was designed and built at Argonne National Laboratory. In a parallel effort a similar simulation was conducted using the spectral-element code Nek5000. The set-up consists of two turbulent jets entering a rectangular tank via two hexagonal inlets, the interesting phenomena being the mixing within the tank. Two different inlet geometries were studied previously, both experimentally and via high-fidelity large-eddy simulations reporting various turbulent statistical quantities. To further assess the flow behavior we hereby perform a Proper Orthogonal Decomposition (POD) to identify the most dominant energetic modes and quantify their impact on the top wall of the upper plenum. The POD analysis of the experimental data in both inlet geometrical configurations is compared with LES and presented to highlight the impact of geometry on the velocity and thermal fields. We find a qualitative coherence between both simulation and experiment, characterized by a strong backflow in the weakly stable geometry, as indicated by the first mode, and the presence of three stagnation points in the strongly stable geometry setup. Also we identify a pairing of modes 1 and 3 with higher frequency than the second mode. This pairing is opposite in the two flow configurations leading to a faster decay of one of the jets in one case and a stable flow in the other.

Original languageEnglish (US)
Title of host publicationSymposia
Subtitle of host publicationFluid Measurement and Instrumentation; Fluid Dynamics of Wind Energy; Renewable and Sustainable Energy Conversion; Energy and Process Engineering; Microfluidics and Nanofluidics; Development and Applications in Computational Fluid Dynamics; DNS/LES and Hybrid RANS/LES Methods
PublisherAmerican Society of Mechanical Engineers (ASME)
ISBN (Electronic)9780791858059
StatePublished - 2017
EventASME 2017 Fluids Engineering Division Summer Meeting, FEDSM 2017 - Waikoloa, United States
Duration: Jul 30 2017Aug 3 2017

Publication series

NameAmerican Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM
ISSN (Print)0888-8116


OtherASME 2017 Fluids Engineering Division Summer Meeting, FEDSM 2017
Country/TerritoryUnited States

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering


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