Assessment of the RANS Turbulence Models for a Turbulent Flow and Heat Transfer in a Rod Bundle

2005 ◽  
Vol 150 (3) ◽  
pp. 231-250 ◽  
Author(s):  
Wang-Kee In ◽  
Tae-Hyun Chun
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Turbulence Models ◽  
Rod Bundle ◽  
Flow And Heat Transfer ◽  
Rans Turbulence Models

Computations of Turbulent Flow and Heat Transfer in Staggered Tube Banks

1996 ◽  
Author(s):  
M. C. Sharatchandra ◽  
David L. Rhode
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Finite Volume ◽  
Cross Flow ◽  
Turbulence Models ◽  
Curvilinear Coordinates ◽  
Flow And Heat Transfer ◽  
Finite Volume Approach ◽  
Tube Banks ◽  
Limiting Case

Abstract Turbulent Flow in closely spaced staggered tube bundles is numerically investigated using a finite-volume approach in general curvilinear coordinates. Attention if focused on the hydrodynamic and thermal effects of the longitudinal displacement of alternate tube rows. The computations used both standard and 2-layer k–ϵ turbulence models in conjunction with a streamwise periodic finite volume formulation. The computations are in excellent agreement with experimental data for the limiting case of flow and heat transfer in undisplaced tube banks. Furthermore, the results indicate increases in both pressure drop and heat transfer with an increase in displacement. The results of this study may serve as an aid in the design of shell and tube cross flow heat exchangers.

Design of a Closely-Spaced Rod Bundle for a Reference Direct Numerical Simulation

2018 ◽  
Author(s):  
Afaque Shams ◽  
Tomasz Kwiatkowski
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Fuel Assembly ◽  
Turbulence Models ◽  
Heat Transfer Analysis ◽  
Passive Scalars ◽  
Rod Bundle ◽  
Rans Turbulence Models

Detailed knowledge of a coolant flow in a fuel assembly of a reactor core has always been a major factor in the design of new nuclear systems. In this regard, traditionally adopted subchannel analysis codes cannot take into account local phenomena, which are quite essential. On the other hand, Computational Fluid Dynamic (CFD) is being recognized as a valuable research tool for thermal-hydraulics phenomenon in the fuel assembly geometries. Because of the high Reynolds number and geometric complexities, the practical CFD calculations are mostly limited to pragmatic Reynolds Averaged Navier-Stokes (RANS) type modelling approaches. A good prediction of the flow and heat transport inside the fuel rod bundle is a challenge for such RANS turbulence models and these models need to be validated. Although the measurement techniques are constantly getting improved, however, the CFD-grade experiments of flow mixing and heat transfer in the subchannel scale are often impossible or quite costly to be performed. In addition, lack of experimental databases makes it impossible to validate and/or calibrate the available RANS turbulence models for certain flow situations. In that context, Direct Numerical Simulation (DNS) can serve as a reference for model development and validation. The aim of this work is to design a numerical experiment in order to generate a high quality DNS database for a tight lattice bare rod bundle, which will serve as a reference for the validation purpose. The considered geometric design is based on the well-known Hooper experiment, which contains a bare rod bundle with pitch-to-diameter ratio of P/D = 1.107. Performing a DNS computation corresponding to the Hooper experiment requires a huge computational power. Hence, a wide range of unsteady RANS (URANS) study has been performed to scale-down the Reynolds number such that it is feasible for a DNS computation and at the same time it still preserves the main flow characteristics. In addition to the flow field, a parametric study for three different passive scalars is performed to take into account the heat transfer analysis. These passive scalars correspond to the Prandtl numbers of air, water and liquid metal fluids. The heat transfer of these three fluids has been studied in combination with two different boundary conditions at the walls, i.e. a constant temperature and a constant heat flux. Finally, the obtained URANS results are used to compute the Kolmogorov and Batchelor length scales in order to estimate the overall meshing requirements for the targeted DNS.

scholarly journals Three-dimensional numerical investigation of turbulent flow and heat transfer inside a horizontal semi-circular cross-sectioned duct

2014 ◽  
Vol 18 (4) ◽  
pp. 1145-1158 ◽  
Author(s):  
Kamil Arslan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Forced Flow ◽  
Flow And Heat Transfer ◽  
Darcy Friction Factor

In this study, steady-state turbulent forced flow and heat transfer in a horizontal smooth semi-circular cross-sectioned duct was numerically investigated. The study was carried out in the turbulent flow condition where Reynolds numbers range from 1?104 to 5.5?104. Flow is hydrodynamically and thermally developing (simultaneously developing flow) under uniform surface heat flux with uniform peripheral wall heat flux (H2) boundary condition on the duct?s wall. A commercial CFD program, Ansys Fluent 12.1, with different turbulent models was used to carry out the numerical study. Different suitable turbulence models for fully turbulent flow (k-? Standard, k-? Realizable, k-? RNG, k-? Standard and k-? SST) were used in this study. The results have shown that as the Reynolds number increases Nusselt number increases but Darcy friction factor decreases. Based on the present numerical solutions, new engineering correlations were presented for the average Nusselt number and average Darcy friction factor. The numerical results for different turbulence models were compared with each other and similar experimental investigations carried out in the literature. It is obtained that, k-? Standard, k-? Realizable and k-? RNG turbulence models are the most suitable turbulence models for this investigation. Isovel contours of velocity magnitude and temperature distribution for different Reynolds numbers, turbulence models and axial stations in the duct were presented graphically. Also, local heat transfer coefficient and local Darcy friction factor as function of dimensionless position along the duct were obtained in this investigation.

Numerical Investigation of Flow and Heat Transfer Characteristics in Wire-Wrap Tight Lattice 19-Rod Bundle

2013 ◽  
Author(s):  
Minggang Li ◽  
Jun Wang ◽  
Changhua Nie ◽  
Xiao Yan ◽  
Yanping Huang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Heat Transfer Characteristics ◽  
Transfer Velocity ◽  
Transfer Characteristics ◽  
Rod Bundle ◽  
Flow And Heat Transfer ◽  
Tight Lattice

Flow and heat transfer characteristics in wire-wrap tight lattice rod bundle have been investigated through CFD code ANSYS CFX 13.0. The bundle consists of 19 fuel rods with triangular tight lattice configuration. The rod ratio of rod pitch to rod diameter is 1.167. Four wires with a diameter of 0.5 mm are helically wrapped on the surface of each fuel rod. The ratio of wire-wrap helical pitch to the rod diameter is varied from 27.5 to 52.5. Through simulating wire-wrap 3-rod bundle with tetrahedron and hexahedron grid systems, the grid system which applies to simulating the wire-wrap tight lattice rod bundle has been obtained. The predicted results of eddy viscosity based turbulence models (k–ε, SST) and Reynolds stress turbulence models (BSL, SSG) are compared with each other and several experimental correlations for friction factor and Nusselt number. The predicted results of all the turbulence models are almost the same in some respects, but the friction factor predicted by the eddy viscosity models is higher than that predicted by the RSM. The effect of wire-wrap on pressure drop, friction factor, secondary flow, heat transfer, velocity distribution and temperature distribution in different subchannels (interior, edge and corner) has been analyzed by comparing with those of the bare rod bundle. The effect of wire-wrap pitch on the flow and heat transfer characteristics has also been studied.

scholarly journals CFD SIMULATION OF VERTICAL SEVEN-ROD BUNDLE COOLED WITH SUPERCRITICAL FREON-12

2014 ◽  
Vol 3 (01) ◽  
pp. 17-28 ◽  
Author(s):  
X. Huang ◽  
K. Podila ◽  
Y.F. Rao
Keyword(s):  
Heat Transfer ◽  
Cfd Simulation ◽  
Turbulence Models ◽  
Flow Conditions ◽  
Transfer Coefficients ◽  
Cfd Simulations ◽  
Ansys Fluent ◽  
Heat Transfer Coefficients ◽  
Rod Bundle ◽  
Flow And Heat Transfer

In this paper, a seven-rod bare bundle was simulated using ANSYS Fluent 6.3.26 to accurately predict the fluid flow and heat transfer behaviour under supercritical flow conditions. Seven turbulence models were compared to identify the appropriate model to predict the experiments performed at the Institute of Physics and Power Engineering on a vertically oriented seven-rod bare bundle cooled with supercritical Freon-12. It was found that predictions of wall temperatures and heat transfer coefficients are sensitive to the choice of turbulence model as well as to the near-wall treatment. Overall, the CFD simulations were able to predict the measured sheath temperature profiles along the length of the bundle within reasonable accuracy.

Heat Transfer and Hydraulic Resistance in Turbulent Flow in Vertical Round Tubes At Supercritical Pressures. Part II. Results From Numerical Simulation with Differential Turbulent Viscosity Models

2020 ◽  
Author(s):  
Georgii Glebovich Yankov ◽  
Vladimir Kurganov ◽  
Yury Zeigarnik ◽  
Irina Maslakova
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Model Verification ◽  
Wall Functions ◽  
Flow And Heat Transfer ◽  
Numerical Studies ◽  
Viscosity Models ◽  
Mesh Independence

Abstract The review of numerical studies on the turbulent flow and heat transfer of supercritical pressure (SCP) coolants in heated vertical round tubes, which were conducted using different differential turbulent viscosity models, is presented. It is shown that most often the turbulent viscosity models only qualitatively predict the deteriorated heat transfer effects, which appear due do buoyancy forces and thermal acceleration effects at strongly variable physical properties of a coolant. At the same time, the regimes of normal heat transfer are successfully reproduced by "standard" k- and RNG models with wall functions, as well as by two-layer models. The conclusion is made that none of the presently known turbulent viscosity models can be confidently recommended for predicting any flow regimes and heat transfer of SCP coolants. Strongly variable properties of SCP coolant stipulate more strict demands for validating mesh independence of the obtained results and for an accuracy of approximation of the tabulated values of the coolant properties. It was ascertained that using more and more numerous calculation codes and the results from their application requires certain caution and circumspection. In some works, the parameters of the regimes used for turbulent viscosity model verification and those of the experiments attracted for such verification did not correspond each other. It is pointed out that the crying discrepancy in the predictions of different authors conducted using the same CFD codes and turbulence models and possible reasons for such a discrepancy are not analyzed.

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