Turbulence structure and heat transfer in a sudden expansion with a porous insert using linear and non-linear turbulence models

2019 ◽  
Vol 141 ◽  
pp. 1-13
Author(s):  
Marcelo J.S. de Lemos ◽  
Marcelo Assato
Keyword(s):  
Heat Transfer ◽  
Turbulence Models ◽  
Sudden Expansion ◽  
Turbulence Structure ◽  
Porous Insert ◽  
Non Linear

Flow and Heat Transfer Past a Sudden Contraction With a Porous Insert Using Linear and Non-Linear Turbulence Models

2004 ◽  
Author(s):  
Marcelo Assato ◽  
Marcelo J. S. de Lemos
Keyword(s):  
Heat Transfer ◽  
Turbulence Models ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Porous Insert ◽  
Macroscopic Models ◽  
Flow And Heat Transfer ◽  
Non Linear ◽  
Abrupt Contraction ◽  
Stream Lines

This work presents a numerical investigation for the turbulent flow and heat transfer in an abrupt contraction channel with a porous material placed in a flow passage. The channel has a contraction rate of 3:2. Results for the hybrid medium were obtained using linear and non-linear k-ε macroscopic models. It was used an inlet Reynolds number of Re = 132000 based on the height of the step. Parameters such as porosity, permeability and thickness of the porous insert were varied in order to analyze their effects on the flow pattern. The results of local heat transfer, friction coefficient and stream lines obtained by the two turbulence models were compared for the cases without and with porous insertion of thickness a/H=0.083, 0.166 and 0.250, where H is the step height. Insert porosity of varied between 0.85 and 0.95 with permeability in the range 10−6–10−2 m2.

Heat Transfer in a Suddenly Expanded Turbulent Flow Past a Porous Insert Using Linear and Non-Linear Eddy-Viscosity Models

2002 ◽  
Author(s):  
Marcelo J. S. de Lemos ◽  
Marcelo Assato
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Eddy Viscosity ◽  
Control Volume ◽  
Numerical Technique ◽  
Turbulence Models ◽  
Wall Functions ◽  
Porous Insert ◽  
Flow Past ◽  
Non Linear

This work presents numerical results for heat transfer in turbulent flow past a backward-facing-step channel with a porous insert using linear and non-linear eddy viscosity macroscopic models. The non-linear turbulence models are known to perform better than classical eddy-diffusivity models due to their ability to simulate important characteristics of the flow. Parameters such as porosity, permeability and thickness of the porous insert are varied in order to analyze their effects on the flow pattern, particularly on the damping of the recirculating bubble after the porous insertion. The numerical technique employed for discretizing the governing equations is the control-volume method. The SIMPLE algorithm is used to correct the pressure field. Wall functions for velocity and temperature are used in order to bypass fine computational close to the wall. Comparisons of results simulated with both linear and non-linear turbulence models are presented.

Assessment of Predictive Capability of Hybrid RANS/LES Turbulence Models for Thermofluid Applications

2021 ◽  
Author(s):  
Anup Zope ◽  
Avery Schemmel ◽  
Xiao Wang ◽  
Shanti Bhushan ◽  
Prashant Singh ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Flow Separation ◽  
Large Scale ◽  
Swirling Flow ◽  
Turbulence Models ◽  
Sudden Expansion ◽  
Oblique Shock Wave ◽  
Detached Eddy Simulation ◽  
Boundary Layer Interaction

Abstract In this study, we have assessed performance of URANS model, various hybrid RANS/LES turbulence models such as detached eddy simulation, Nichols-Nelson HRLES model, dynamic HRLES (DHRL) model, as well as LES for two classes of problems: (a) heat transfer due to subsonic swirling flow subjected to a sudden expansion leading to cylindrical chamber, and (b) flow separation due to oblique shock wave-turbulent boundary layer interaction (STBLI). The results are assessed using the heat transfer characteristics, separation and reattachment characteristics, and capability to predict flow unsteadiness. The study indicates that URANS can predict large scale flow features reasonably well. However, it fails to resolve turbulence. PANS improves TKE prediction, hence, improves heat transfer prediction. Among the hybrid RANS/LES models, DHRL coupled with ILES is capable of providing accurate prediction of flow separation/reattachment characteristics for boundary layer flows. For free-shear dominated flows, implicit LES performs better compared to the explicit LES models.

A Study on Flow and Heat Transfer in Strongly Curved U-Bend

2005 ◽  
Author(s):  
R. S. Amano ◽  
B. Song ◽  
M. S. Reza
Keyword(s):  
Heat Transfer ◽  
Difference Method ◽  
Turbulence Models ◽  
Secondary Flows ◽  
The Other ◽  
Interpolation Scheme ◽  
Flow And Heat Transfer ◽  
Flow Development ◽  
Non Linear ◽  
Volume Difference

The secondary flows inside a sharp U-bend are numerically studied by using several different turbulence models. The finite volume difference method incorporated with the higher-order bounded interpolation scheme has been employed in the present study. The present results reveal that non-linear low-Re k-ω model and the other models produce the quite different secondary flow patterns. It is shown that the present non-linear model produces satisfactory predictions of the flow development inside the sharp U-bend comparing with linear Launder-Sharma model.

scholarly journals RANS and LES Investigations of Vertical Flows in the Fuel Passages of Gas-Cooled Nuclear Reactors

2008 ◽  
Author(s):  
Amir Keshmiri ◽  
Mark A. Cotton ◽  
Yacine Addad ◽  
Stefano Rolfo ◽  
Flavien Billard
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Forced Convection ◽  
Turbulent Flows ◽  
Nuclear Reactors ◽  
Broad Class ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Turbulence Structure ◽  
Eddy Simulation

Coolant flows in the cores of current gas-cooled nuclear reactors consist of ascending vertical flows in a large number of parallel passages. Under post-trip conditions such heated turbulent flows may be significantly modified from the forced convection condition by the action of buoyancy, and the thermal-hydraulic regime is no longer one of pure forced convection. These modifications are primarily associated with changes to the turbulence structure, and indeed flow laminarization may occur. In the laminarization situation heat transfer rates may be as low as 40% of those in the corresponding forced convection case. The heat transfer performance of such ‘mixed’ convection flows is investigated here using a range of refined Reynolds-Averaged-Navier-Stokes (RANS) turbulence models. While all belong to the broad class of Eddy Viscosity Models (EVMs), the various RANS closures have different physical parameterizations and might therefore be expected to show different responses to externally-imposed conditions. Comparison is made against experimental and Direct Numerical Simulation (DNS) data. In addition, Large Eddy Simulation (LES) results have been generated as part of the study. Three different CFD codes have been employed in the work: ‘CONVERT’, ‘STAR-CD’, and ‘Code_Saturne’, which are respectively in-house, commercial, and industrial packages. It is found that the early EVM scheme of Launder and Sharma [1] is in the closest agreement with consistently-normalized DNS results for the ratio of mixed-to-forced convection Nusselt number (Nu/Nu0). However, in relation to DNS and experimental data for forced convection Nusselt number, other models perform better than the Launder-Sharma scheme. The present investigation has revealed discrepancies between direct-simulation, experimental, and the current LES studies.

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