Turbulent flow-field comparisons of RANS and les for a twisted pin lattice geometry at low Reynolds number

Adam R. Kraus, Elia Merzari, Paul F. Fischer

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

1 Scopus citations

Abstract

The accurate evaluation of fuel and cladding peak temperatures is of prime importance for nuclear reactor design and safety. The Global Threat Reduction Initiative reactor conversion program often encounters exotic flow geometries in its mission to aid in converting reactors from high-enriched to low-enriched fuel. These geometries can pose modeling challenges. Analysis presented here concerns a reactor with twisted fuel pins that are in direct contact with each other in a large, hexagonal-pitch lattice. The Reynolds number for a unit cell is only 7500. Such flow conditions can present difficulties for standard approaches based on Reynolds-Averaged Navier- Stokes (RANS). Moreover there are no available experimental data and a small expected margin to the limiting cladding surface temperature. Given some of the geometric uncertainties, reducing the turbulence model uncertainty is thus important for meaningful calculations. A computational fluid dynamics model of a full-length unit cell was built using the commercial code STAR-CCM+. Multiple RANS models were employed, which gave disparate results. To provide higher-fidelity data for comparison, given the lack of experimental data, a periodic single-helical-pitch simulation with a Large Eddy Simulation (LES) approach was performed using Nek5000, a massivelyparallel spectral-element code. This was compared with singlepitch RANS simulations from STAR-CCM+. Stream-wise velocity profile shape was generally well-represented by RANS. Cross-velocities and peak turbulent kinetic energy (TKE) were underestimated for most of the turbulence models with respect to LES, while mean flow TKE was universally underestimated. The overall results suggest that the Realizable k-ε Two-Layer model, which was the best at reproducing the LES TKE distribution, would likely be the most appropriate turbulence model choice for this flow. Future work includes full conjugate heat transfer simulations of 1/6 sectors of fuel assemblies featuring this type of pin lattice.

Original languageEnglish (US)
Title of host publicationSymposia
Subtitle of host publicationAdvances in Fluids Engineering Education; Turbomachinery Flow Predictions and Optimization; Applications in CFD; Bio-Inspired Fluid Mechanics; Droplet-Surface Interactions; CFD Verification and Validation; Development and Applications of Immersed Boundary Methods; DNS, LES, and Hybrid RANS/LES Methods
PublisherAmerican Society of Mechanical Engineers (ASME)
ISBN (Electronic)9780791846216
DOIs
StatePublished - Jan 1 2014
EventASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting, FEDSM 2014, Collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels - Chicago, United States
Duration: Aug 3 2014Aug 7 2014

Publication series

NameAmerican Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM
Volume1A
ISSN (Print)0888-8116

Other

OtherASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting, FEDSM 2014, Collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels
CountryUnited States
CityChicago
Period8/3/148/7/14

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering

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    Kraus, A. R., Merzari, E., & Fischer, P. F. (2014). Turbulent flow-field comparisons of RANS and les for a twisted pin lattice geometry at low Reynolds number. In Symposia: Advances in Fluids Engineering Education; Turbomachinery Flow Predictions and Optimization; Applications in CFD; Bio-Inspired Fluid Mechanics; Droplet-Surface Interactions; CFD Verification and Validation; Development and Applications of Immersed Boundary Methods; DNS, LES, and Hybrid RANS/LES Methods (American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM; Vol. 1A). American Society of Mechanical Engineers (ASME). https://doi.org/10.1115/FEDSM2014-22166