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Title: Steady and unsteady calculations on thermal striping phenomena in triple-parallel jet

Abstract

The phenomenon of thermal striping is encountered in liquid metal cooled fast reactors (LMFR), in which temperature fluctuation due to convective mixing between hot and cold fluids can lead to a possibility of crack initiation and propagation in the structure due to high cycle thermal fatigue. Using sodium experiments of parallel triple jets configuration performed by Japan Atomic Energy Agency (JAEA) as benchmark, numerical simulations were carried out to evaluate the temperature fluctuation characteristics in fluid and the transfer characteristics of temperature fluctuation from fluid to structure, which is important to assess the potential thermal fatigue damage. In this study, both steady (RANS) and unsteady (URANS, LES) methods were applied to predict the temperature fluctuations of thermal striping. The parametric studies on the effects of mesh density and boundary conditions on the accuracy of the overall solutions were also conducted. The velocity, temperature and temperature fluctuation intensity distribution were compared with the experimental data. As expected, steady calculation has limited success in predicting the thermal–hydraulic characteristics of the thermal striping, highlighting the limitations of the RANS approach in unsteady heat transfer simulations. The unsteady results exhibited reasonably good agreement with experimental results for temperature fluctuation intensity, as well as themore » average temperature and velocity components at the measurement locations.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1417294
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nuclear Engineering and Design; Journal Volume: 312; Journal Issue: C
Country of Publication:
United States
Language:
English

Citation Formats

Yu, Y. Q., Merzari, E., Thomas, J. W., Obabko, A., and Aithal, S. M. Steady and unsteady calculations on thermal striping phenomena in triple-parallel jet. United States: N. p., 2017. Web. doi:10.1016/j.nucengdes.2016.06.015.
Yu, Y. Q., Merzari, E., Thomas, J. W., Obabko, A., & Aithal, S. M. Steady and unsteady calculations on thermal striping phenomena in triple-parallel jet. United States. doi:10.1016/j.nucengdes.2016.06.015.
Yu, Y. Q., Merzari, E., Thomas, J. W., Obabko, A., and Aithal, S. M. Wed . "Steady and unsteady calculations on thermal striping phenomena in triple-parallel jet". United States. doi:10.1016/j.nucengdes.2016.06.015.
@article{osti_1417294,
title = {Steady and unsteady calculations on thermal striping phenomena in triple-parallel jet},
author = {Yu, Y. Q. and Merzari, E. and Thomas, J. W. and Obabko, A. and Aithal, S. M.},
abstractNote = {The phenomenon of thermal striping is encountered in liquid metal cooled fast reactors (LMFR), in which temperature fluctuation due to convective mixing between hot and cold fluids can lead to a possibility of crack initiation and propagation in the structure due to high cycle thermal fatigue. Using sodium experiments of parallel triple jets configuration performed by Japan Atomic Energy Agency (JAEA) as benchmark, numerical simulations were carried out to evaluate the temperature fluctuation characteristics in fluid and the transfer characteristics of temperature fluctuation from fluid to structure, which is important to assess the potential thermal fatigue damage. In this study, both steady (RANS) and unsteady (URANS, LES) methods were applied to predict the temperature fluctuations of thermal striping. The parametric studies on the effects of mesh density and boundary conditions on the accuracy of the overall solutions were also conducted. The velocity, temperature and temperature fluctuation intensity distribution were compared with the experimental data. As expected, steady calculation has limited success in predicting the thermal–hydraulic characteristics of the thermal striping, highlighting the limitations of the RANS approach in unsteady heat transfer simulations. The unsteady results exhibited reasonably good agreement with experimental results for temperature fluctuation intensity, as well as the average temperature and velocity components at the measurement locations.},
doi = {10.1016/j.nucengdes.2016.06.015},
journal = {Nuclear Engineering and Design},
number = C,
volume = 312,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
  • Thermal striping phenomena characterized by stationary random temperature fluctuations are observed in the region immediately above the core exit of liquid-metal-cooled fast reactors (LMFRs) due to the interactions of cold sodium flowing out of a control rod (C/R) assembly and hot sodium flowing out of adjacent fuel assemblies (F/As). Two thermohydraulics computer programs AQUA and DINUS-3, which are represented by both time- and volume-averaged transport analysis and direct numerical simulation of turbulence, respectively, were developed and validated for the evaluation of thermal striping phenomena. These codes were incorporated with higher order difference schemes to approximate the convection terms in conservationmore » equations and adaptive time-step size control systems based on the fuzzy theory to eliminate numerical instabilities. From validation analyses with fundamental experiments in water and sodium, it was concluded that (a) thermal striping conditions such as spatial distributions of the intensity and the frequency of the fluid temperature fluctuations can be estimated efficiently by a combined approach incorporating the AQUA code and the DINUS-3 code, and (b) the thermal striping phenomena for the in-vessel components of actual liquid-metal-cooled fast reactors can be evaluated by the numerical method without conventional approaches such as large scale model experiments using sodium.« less
  • We present velocity and temperature field measurements for a 0.9 x 0.9 x 1.7 m glass tank in which two air jets at Re=10000 mix and impinge upon the lid at ambient temperature and pressure. Flow patterns are characterized across a 350 x 200 mm plane located 3 mm below the lid for two inlet geometries: 1) “extended”, in which inlet channels protrude above the tank base, and 2) “flush”, a flat base without protrusions. This minor geometry variation produced distinct changes in the lid flow field, appearing as three stagnant regions for the extended case and only one formore » flush. The dichotomy is attributed to system stability characteristics: jets are stable in the extended case and unstable for flush. In a separate set of nonisothermal tests, the impingement temperature field was measured for inlet temperature mismatches of 4 oC and jets near Re=10000. A 50 m-long fiber optic distributed temperature sensor positioned 2 mm below the lid measured at 1350 locations. Like the velocity fields, the temperature fields differ for the two inlet geometries: good thermal mixing for the flush case and subdued mixing for the extended case. Simulations with the spectral element code Nek5000 replicated the observed stability dichotomy, duplicating the number of stagnant regions observed in the experiment and matching their locations within ±10 mm. Simulation data suggests that flush case instability is due to interactions between jets and wall flows at the bottom of the tank. The clear flow dichotomy exhibited by this two-jet setup presents an unambiguous case to test the ability of CFD tools to predict subtle flow field changes driven by minor modifications in geometry in the context of thermal striping.« less
  • We present velocity and temperature field measurements for a 0.9 × 0.9 × 1.7 m glass tank in which two air jets mix and impinge upon the lid at ambient temperature and pressure. At jet Re ≈ 10,000, flow patterns below the lid were characterized for two inlet geometries: (1) “extended”, in which inlet channels protrude above the tank base, and (2) “flush”, a flat base without protrusions. This minor geometry variation produced distinct changes in the lid velocity field, appearing as three stagnant regions for the extended case and only one for flush. The dichotomy is attributed to systemmore » stability characteristics: jets are stable in the extended case and unstable for flush. In a separate set of nonisothermal tests, the impingement temperature field was measured for inlet temperature mismatches of 4 °C with jets again near Re = 10,000. A 50 m-long fiber optic distributed temperature sensor beneath the lid measured at 1350 locations. Like the velocity fields, the temperature fields differ for the two inlet geometries: good thermal mixing for the flush case and subdued mixing for the extended case. Simulations with the spectral element code Nek5000 replicated the observed stability dichotomy, duplicating the number of stagnant regions observed in the experiment and matching their locations within ±10 mm. Simulation data suggests that flush case instability is due to interactions between jets and wall flows at the bottom of the tank. The clear flow dichotomy exhibited by this two-jet setup presents an unambiguous case to test the ability of CFD tools to predict subtle flow field changes driven by minor modifications in geometry in the context of thermal striping« less