Experimental investigation of turbulent flow characteristics in cross-flow planes of a 5×5 rod bundle with a spacer grid

Camila F. Matozinhos; Gabriel C.Q. Tomaz; Thien Nguyen; Yassin Hassan

doi:10.1016/j.ijheatfluidflow.2020.108757

Experimental investigation of turbulent flow characteristics in cross-flow planes of a 5×5 rod bundle with a spacer grid

Camila F. Matozinhos, Gabriel C.Q. Tomaz, Thien Nguyen, Yassin Hassan

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21 Scopus citations

Abstract

This study summarizes experimental investigations of the flow field characteristics in the cross-flow planes of a 5×5 rod bundle with spacer grid and split-type mixing vanes. Under the isothermal and atmospheric conditions, the velocity fields in the cross-flow planes are obtained by applying the matched-index-of-refraction and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of Re₁=14,000 and Re₂=28,000. The cross-flow planes axially start from the tips of the mixing vanes of the spacer grid and end at 11.73D_h (D_h is the hydraulic diameter of the rod bundle). From the acquired TR-PIV velocity fields, flow statistics such as the in-plane mean velocity and vorticity, turbulent kinetic energy and Reynolds stress are computed and presented for four cross-flow planes of interest axially located at 0,2D_h,5D_h, and 11D_h. Two counter rotating vortices are observed near the spacer grid. After a change in elevation to z/D_h=5, the vortices merge into a single vortex centered in the middle of the subchannel. In addition, the turbulence flow characteristics at the elevations of interest are discussed through calculations of integral length scales and spectral analysis. No dominant frequency is observed, and the turbulence characteristics are strongly influenced by the proximity to the spacer grid. The mass transfer between the subchannels and the associated turbulent mixing flow rate is calculated for all elevations; hence, this study is a step toward improving the correlations currently used in subchannel codes. Results for secondary flow intensities, lateral velocity profiles and velocity contours are compared with large-eddy simulation results from the literature for Re₁=14,000, and a reasonable agreement is observed.

Original language	English
Article number	108757
Journal	International Journal of Heat and Fluid Flow
Volume	87
DOIs	https://doi.org/10.1016/j.ijheatfluidflow.2020.108757
State	Published - Feb 2021
Externally published	Yes

Funding

The authors acknowledge CAPES for doctoral research scholarship funding of Gabriel C.Q. Tomaz (project ID: 88881.129678/2016-01) at the Department of Nuclear Engineering of Texas A&M University. The experimental study is partially funded by the U.S. Department of Energy, Idaho National Laboratory. Simulation results obtained from Dr. Giacomo Busco are appreciated.

Funders	Funder number
Department of Nuclear Engineering of Texas A&M University
Gabriel C.Q. Tomaz	88881.129678/2016-01
U.S. Department of Energy
Idaho National Laboratory
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Keywords

5×5 rod bundle
Matched-refractive-index
PIV uncertainty calculation
Particle image velocimetry
Subchannel analysis
Two-point cross correlations

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10.1016/j.ijheatfluidflow.2020.108757

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@article{48117b38d5684c15ac445c45393140af,

title = "Experimental investigation of turbulent flow characteristics in cross-flow planes of a 5×5 rod bundle with a spacer grid",

abstract = "This study summarizes experimental investigations of the flow field characteristics in the cross-flow planes of a 5×5 rod bundle with spacer grid and split-type mixing vanes. Under the isothermal and atmospheric conditions, the velocity fields in the cross-flow planes are obtained by applying the matched-index-of-refraction and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of Re1=14,000 and Re2=28,000. The cross-flow planes axially start from the tips of the mixing vanes of the spacer grid and end at 11.73Dh (Dh is the hydraulic diameter of the rod bundle). From the acquired TR-PIV velocity fields, flow statistics such as the in-plane mean velocity and vorticity, turbulent kinetic energy and Reynolds stress are computed and presented for four cross-flow planes of interest axially located at 0,2Dh,5Dh, and 11Dh. Two counter rotating vortices are observed near the spacer grid. After a change in elevation to z/Dh=5, the vortices merge into a single vortex centered in the middle of the subchannel. In addition, the turbulence flow characteristics at the elevations of interest are discussed through calculations of integral length scales and spectral analysis. No dominant frequency is observed, and the turbulence characteristics are strongly influenced by the proximity to the spacer grid. The mass transfer between the subchannels and the associated turbulent mixing flow rate is calculated for all elevations; hence, this study is a step toward improving the correlations currently used in subchannel codes. Results for secondary flow intensities, lateral velocity profiles and velocity contours are compared with large-eddy simulation results from the literature for Re1=14,000, and a reasonable agreement is observed.",

keywords = "5×5 rod bundle, Matched-refractive-index, PIV uncertainty calculation, Particle image velocimetry, Subchannel analysis, Two-point cross correlations",

author = "Matozinhos, {Camila F.} and Tomaz, {Gabriel C.Q.} and Thien Nguyen and Yassin Hassan",

note = "Publisher Copyright: {\textcopyright} 2020 Elsevier Inc.",

year = "2021",

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doi = "10.1016/j.ijheatfluidflow.2020.108757",

language = "English",

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AU - Matozinhos, Camila F.

AU - Tomaz, Gabriel C.Q.

AU - Nguyen, Thien

AU - Hassan, Yassin

PY - 2021/2

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N2 - This study summarizes experimental investigations of the flow field characteristics in the cross-flow planes of a 5×5 rod bundle with spacer grid and split-type mixing vanes. Under the isothermal and atmospheric conditions, the velocity fields in the cross-flow planes are obtained by applying the matched-index-of-refraction and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of Re1=14,000 and Re2=28,000. The cross-flow planes axially start from the tips of the mixing vanes of the spacer grid and end at 11.73Dh (Dh is the hydraulic diameter of the rod bundle). From the acquired TR-PIV velocity fields, flow statistics such as the in-plane mean velocity and vorticity, turbulent kinetic energy and Reynolds stress are computed and presented for four cross-flow planes of interest axially located at 0,2Dh,5Dh, and 11Dh. Two counter rotating vortices are observed near the spacer grid. After a change in elevation to z/Dh=5, the vortices merge into a single vortex centered in the middle of the subchannel. In addition, the turbulence flow characteristics at the elevations of interest are discussed through calculations of integral length scales and spectral analysis. No dominant frequency is observed, and the turbulence characteristics are strongly influenced by the proximity to the spacer grid. The mass transfer between the subchannels and the associated turbulent mixing flow rate is calculated for all elevations; hence, this study is a step toward improving the correlations currently used in subchannel codes. Results for secondary flow intensities, lateral velocity profiles and velocity contours are compared with large-eddy simulation results from the literature for Re1=14,000, and a reasonable agreement is observed.

AB - This study summarizes experimental investigations of the flow field characteristics in the cross-flow planes of a 5×5 rod bundle with spacer grid and split-type mixing vanes. Under the isothermal and atmospheric conditions, the velocity fields in the cross-flow planes are obtained by applying the matched-index-of-refraction and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of Re1=14,000 and Re2=28,000. The cross-flow planes axially start from the tips of the mixing vanes of the spacer grid and end at 11.73Dh (Dh is the hydraulic diameter of the rod bundle). From the acquired TR-PIV velocity fields, flow statistics such as the in-plane mean velocity and vorticity, turbulent kinetic energy and Reynolds stress are computed and presented for four cross-flow planes of interest axially located at 0,2Dh,5Dh, and 11Dh. Two counter rotating vortices are observed near the spacer grid. After a change in elevation to z/Dh=5, the vortices merge into a single vortex centered in the middle of the subchannel. In addition, the turbulence flow characteristics at the elevations of interest are discussed through calculations of integral length scales and spectral analysis. No dominant frequency is observed, and the turbulence characteristics are strongly influenced by the proximity to the spacer grid. The mass transfer between the subchannels and the associated turbulent mixing flow rate is calculated for all elevations; hence, this study is a step toward improving the correlations currently used in subchannel codes. Results for secondary flow intensities, lateral velocity profiles and velocity contours are compared with large-eddy simulation results from the literature for Re1=14,000, and a reasonable agreement is observed.

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KW - Matched-refractive-index

KW - PIV uncertainty calculation

KW - Particle image velocimetry

KW - Subchannel analysis

KW - Two-point cross correlations

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SN - 0142-727X

VL - 87

JO - International Journal of Heat and Fluid Flow

JF - International Journal of Heat and Fluid Flow

M1 - 108757

ER -

Experimental investigation of turbulent flow characteristics in cross-flow planes of a 5×5 rod bundle with a spacer grid

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