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Article
Publication date: 15 May 2009

Mehrdad Raisee and Arman Rokhzadi

The purpose of this paper is to investigate turbulent fluid flow and heat transfer through passages with an array of either detached or alternative attached‐detached ribs…

Abstract

Purpose

The purpose of this paper is to investigate turbulent fluid flow and heat transfer through passages with an array of either detached or alternative attached‐detached ribs of square cross‐section.

Design/methodology/approach

The finite‐volume method in a partially staggered grid system has been applied. For the modeling of turbulence, the zonal as well as the linear and non‐linear low‐Reynolds number k  −  ε models have been employed.

Findings

The numerical results show that the presence of the ribs produces a very complex flow in the channel. The mean flow predictions for the channel with detached ribs show that the low‐Re k  −  ε models are able to reproduce most of the experimentally observed flow features away from the ribbed wall, but return lower stream‐wise velocities close to the wall. Additionally, all low‐Re k  −  ε models underpredict the stream‐wise turbulence intensity whilst producing correct cross‐stream turbulence intensity levels close to the measured data. All three turbulence models fail to completely reproduce the distribution of Nusselt number. Among three turbulence models examined in this work, the zonal k  −  ε model produces the best heat transfer predictions.

Originality/value

The work contributes in understanding of the flow and thermal development in passages with detached ribs. The present set of 2D and steady heat and fluid flow comparisons establishes a base‐level for more realistic three‐dimensional and unsteady computations. The results of this study may be of interest to engineers attempting to re‐design the internal cooling system of gas turbine blades and to researchers interested in the turbulent flow‐modification aspects of heat transfer enhancement of forced convection in ribbed passages.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 3/4
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 5 March 2018

Zhitao Yan, Yongli Zhong, William E. Lin, Eric Savory and Yi You

This paper examines various turbulence models for numerical simulation of a steady, two-dimensional (2-D) plane wall jet without co-flow using the commercial CFD software…

Abstract

Purpose

This paper examines various turbulence models for numerical simulation of a steady, two-dimensional (2-D) plane wall jet without co-flow using the commercial CFD software (ANSYS FLUENT 14.5). The purpose of this paper is to decide the most suitable and most economical method for steady, 2-D plane wall jet simulation.

Design/methodology/approach

Seven Reynolds-averaged Navier–Stokes (RANS) turbulence models were evaluated with respect to typical jet scaling parameters such as the jet half-height and the decay of maximum jet velocity, as well as coefficients from the law of the wall and for skin friction. Then, a plane wall jet generating from a rectangular slot of 1:6 aspect ratio located adjacent to the wall was investigated in a three-dimensional (3-D) model using large eddy simulation (LES) and the Stress-omega Reynolds stress model (SWRSM), with the results compared to experimental measurements.

Findings

The comparisons of these simulated flow characteristics indicated that the SWRSM was the best of the seven RANS models for simulating the turbulent wall jet. When scaled with outer variables, LES and SWRSM gave generally indistinguishable mean velocity profiles. However, SWRSM performed better for near-wall mean velocity profiles when scaled with inner variables. In general, the results show that LES performed reasonably well when predicting the Reynolds stresses.

Originality/value

The main contribution of this article is in determining the capabilities of different RANS turbulence closures and LES for the prediction of the 2-D steady wall jet flow to identify the best modelling approach.

Details

Engineering Computations, vol. 35 no. 1
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 1 January 1995

C.D. Pérez‐Segarra, A. Oliva, M. Costa and F. Escanes

In this paper a numerical simulation, based on finite differencetechniques, has been developed in order to analyse turbulent natural andmixed convection of air in internal…

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Abstract

In this paper a numerical simulation, based on finite difference techniques, has been developed in order to analyse turbulent natural and mixed convection of air in internal flows. The study has been restricted to two‐dimensional cavities with the possibility of inlet and outlet ports, and with internal heat sources. Turbulence is modelled by means of two‐equation k‐ε turbulence models, both in the simplest form using wall functions and in the more general form of low‐Reynolds‐number k‐ε models. The couple time average governing equations (continuity, momentum, energy, and turbulence quantities) are solved in a segregated manner using the SIMPLEX method. An implicit control volume formulation of the differential equations has been employed. Some illustrative numerical results are presented to study the influence of geometry and boundary conditions in cavities. A comparison of different k‐ε turbulence models has also been presented.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 5 no. 1
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 15 May 2009

Junye Wang and Geoffrey H. Priestman

The purpose of this paper is to simulate the behaviour of the symmetrical turn‐up vortex amplifier (STuVA) to obtain insight into its maximum through‐flow operation within…

Abstract

Purpose

The purpose of this paper is to simulate the behaviour of the symmetrical turn‐up vortex amplifier (STuVA) to obtain insight into its maximum through‐flow operation within the eight‐port STuVA, and understand the relation between its design parameters and flow characteristics. Furthermore, it is to test the performance of different turbulent models and near‐wall models using the same grid, the same numerical methods and the same computational fluid dynamics code under multiple impingement conditions.

Design/methodology/approach

Three turbulence models, the standard k‐ε, the renormalization group (RNG) k‐ε model and the Reynolds stress model (RSM), and three near‐wall models have been used to simulate the confined incompressible turbulent flow in an eight‐port STuVA using unstructured meshes. The STuVA is a special symmetrical design of turn‐up vortex amplifier, and the simulation focused on its extreme operation in the maximum flow state with no swirling. The predictions were compared with basic pressure‐drop flow rate measurements made using air at ambient conditions. The effect of different combinations of turbulence and near‐wall models was evaluated.

Findings

The RSM gave predictions slightly closer to the experimental data than the other models, although the RNG k‐ε model predicted nearly as accurately as the RSM. They both improved errors by about 3 per cent compared to the standard k‐ε model but took a long time for convergence. The modelling of complex flows depends not only on the turbulence model but also on the near‐wall treatments and computational economy. In this study a good combination was the RSM, the two layer wall model and the higher order discretization scheme, which improved accuracy by more than 10 per cent compared to the standard k‐ε model, the standard wall function and first order upwind.

Research limitation/implications

The results of this paper are valid for the global pressure drop flow rate. It should be desirable to compare some local information with the experiment.

Originality/value

This paper provides insight into the maximum through‐flow operation within the eight‐port STuVA to understand the relation between its design parameters and flow characteristics and study the performance of turbulence and near wall models.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 3/4
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 27 March 2008

Hector Iacovides and Mehrdad Raisee

This paper aims to compute flow and heat transfer through a straight, orthogonally rotating duct, with ribs along the leading and trailing walls, in a staggered…

Abstract

Purpose

This paper aims to compute flow and heat transfer through a straight, orthogonally rotating duct, with ribs along the leading and trailing walls, in a staggered arrangement and at an angle of 45° to the main flow direction.

Design/methodology/approach

Flow computations have been produced using a 3D non‐orthogonal flow solver, with two two‐layer models of turbulence (an effective‐viscosity model and a second‐moment closure), in which across the near‐wall regions the dissipation rate of turbulence is obtained from the wall distance. Flow comparisons have been carried out for a Reynolds number of 100,000 and for rotation numbers of 0 (stationary) and 0.1. Temperature comparisons have been obtained for a Reynolds number of 36,000, a Prandtl number of 5.9 (water) and rotation numbers of 0 and 0.2 and also at a Prandtl number of 0.7 (air) and a rotation number of 0.

Findings

It was found that both two‐layer models returned similar flow and thermal predictions which are also in close agreement with the flow and thermal measurements. The flow and thermal developments are found to be dominated by the rib‐induced secondary motion, which leads to strong span‐wise variations in the mean flow and the local Nusselt number and to a uniform distribution of turbulence intensities across the duct. Rotation causes the development of stronger secondary motion along the pressure side of the duct and also the transfer of the faster fluid to this side. The thermal predictions, especially those of the second‐moment closure, reproduce the levels and most of the local features of the measured Nusselt number, but over the second half of the rib interval over‐predict the local Nusselt number.

Originality/value

The work contributes to the understanding of the flow and thermal development in cooling passages of gas turbine blades, and to the validation of turbulence models that can be used for their prediction, at both effective viscosity and second‐moment closure levels.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 18 no. 2
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 March 1998

D. Xu, B.C. Khoo and M.A. Leschziner

The flow inside an axisymmetric diffuser with a curved surface centre body is numerically simulated using different turbulence models, namely a high‐Reynolds number k‐ε in…

Abstract

The flow inside an axisymmetric diffuser with a curved surface centre body is numerically simulated using different turbulence models, namely a high‐Reynolds number k‐ε in conjunction with wall function turbulence model, a high‐Reynolds number k‐ε with one‐equation turbulence model, a low‐Reynolds number k‐ε turbulence model, a RNG turbulence model and an anisotropic turbulence model. For the separation and reattachment positions, the comparisons made between the various numerical predictions and experimental measurements show that the high‐Reynolds number k‐ε with one‐equation turbulence model is superior to other models in the present study.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 8 no. 2
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 16 September 2021

Sílvio Aparecido Verdério Júnior, Vicente Luiz Scalon and Santiago del Rio Oliveira

The purpose of this study is to analyze the influence of the main physical–numerical parameters in the computational evaluation of natural convection heat transfer rates…

Abstract

Purpose

The purpose of this study is to analyze the influence of the main physical–numerical parameters in the computational evaluation of natural convection heat transfer rates in isothermal flat square plates in the laminar regime. Moreover by experimentally validate the results of the numerical models and define the best parameter settings for the problem situation studied.

Design/methodology/approach

The present work is an extension of the study by Verderio Junior et al. (2021), differing in the modeling, results analysis and conclusions for the laminar flow regime with Rade=1×105. The analysis of the influence and precision of the physical–numerical parameters: boundary conditions, degree of mesh refinement, refinement layers and κω SST and κε turbulence models, occurred from the results from 48 numerical models, which were simulated using the OpenFOAM® software. Comparing the experimental mean Nusselt number with the numerical values obtained in the simulations and the analysis of the relative errors were used in the evaluation of the advantages, restrictions and selection of the most adequate parameters to the studied problem situation.

Findings

The numerical results of the simulations were validated, with excellent precision, from the experimental reference by Kitamura et al. (2015). The application of the κω SST and κε turbulence models and the boundary conditions (with and without wall functions) were also physically validated. The use of the κω SST and κε turbulence models, in terms of cost-benefit and precision, proved to be inefficient in the problem situation studied. Simulations without turbulence models proved to be the best option for the physical model for the studies developed. The use of refinement layers, especially in applications with wall functions and turbulence models, proved unfeasible.

Practical implications

Use of the physical–numerical parameters studied and validated, and application of the modeling and analysis methodology developed in projects and optimizations of natural convection thermal systems in a laminar flow regime. Just like, reduce costs and the dependence on the construction of experimental apparatus to obtain experimental results and in the numerical-experimental validation process.

Social implications

Exclusive use of free and open-source computational tools as an alternative to feasible research in the computational fluid dynamics area in conditions of budget constraints and lack of higher value-added infrastructure, with applicability in the academic and industrial areas.

Originality/value

The results and discussions presented are original and new for the applied study of laminar natural convection in isothermal flat plate, with analysis and validation of the main physical and numerical influence parameters.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 9 January 2009

Mohamed Omri and Nicolas Galanis

The purpose of this paper is to evaluate the capacity of two equation turbulence models to reproduce mean and fluctuating quantities in the case of both natural convection…

Abstract

Purpose

The purpose of this paper is to evaluate the capacity of two equation turbulence models to reproduce mean and fluctuating quantities in the case of both natural convection and isothermal flows.

Design/methodology/approach

Numerical predictions of mean velocity profiles, air and wall temperatures as well as turbulent kinetic energy by three different two equation models (standard kε, renormalisation group kε and shear‐stress transport‐kω) are compared with corresponding experimental values.

Findings

The prediction of mean velocities and temperatures is in all cases satisfactory. On the other hand, the prediction of turbulent quantities is less precise.

Originality/value

The three models under consideration in this paper can be used for engineering applications such as HVAC calculations.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 1
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 July 2005

K.J. Hsieh and F.S. Lien

Performance of various kε models on turbulent forced convection in a channel with periodic ribs is assessed.

Abstract

Purpose

Performance of various kε models on turbulent forced convection in a channel with periodic ribs is assessed.

Design/methodology/approach

The influence of the Yap correction and the non‐linear stress‐strain relation on the predictions of mean‐flow, turbulence quantities and local heat transfer rate is examined. The effect of thermal boundary conditions on the heat transfer predictions is investigated by employing both the prescribed heat flux approach and the conjugate heat transfer approach.

Findings

It was found that the inclusion of the Yap correction in the ε‐equation significantly improves the predictions of mean velocity and wall heat transfer for both high‐Reynolds number and low‐Reynolds number kε models in the present ribbed channel flow with massive flow separation. The employment of the non‐linear stress‐strain relation only marginally improves the predictions of turbulence quantities: the turbulence anisotropy is reproduced although the level of turbulence intensity is still too low. In general, the conjugate heat transfer approach predicts better average Nusselt number than the prescribed heat flux approach. However, both approaches under‐predict the experimental value by about 28‐33 percent when the low‐Reynolds number kε model of Lien and Leschziner (1999) with the Yap term is adopted.

Originality/value

Thorough numerical treatments of the thermal boundary conditions at the solid‐liquid interface, and detailed periodic condition in the periodic regime, were given in the paper to benefit researchers interested in solving similar problems.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 15 no. 5
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 March 2001

H. Iacovides and M. Raisee

Low‐Re turbulence models are used in the computation of convective heat transfer in two‐dimensional ribbed passages. The cases computed include ribbed annular channels…

Abstract

Low‐Re turbulence models are used in the computation of convective heat transfer in two‐dimensional ribbed passages. The cases computed include ribbed annular channels, pipes and plane channels. The models investigated cover both zonal models, that obtain the near‐wall dissipation rate from the wall distance, and full low‐Re models. Effective viscosity modes and simple (basic) second‐moment closures are used. Zonal models display predictive weaknesses in the rib‐induced separation region, but return reasonable heat transfer levels. For the low‐Re models an alternative length‐scale‐correction term to the one proposed by Yap is developed, which is independent of the wall distance. This wall‐independent correction term is found to improve heat transfer predictions, especially for the low‐Re k‐ε model. The low‐Re models produce a more realistic heat transfer variation in the separation region and reasonable Nusselt number levels. The differential second‐moment closure (DSM) models improve heat transfer predictions after re‐attachment and over the rib surface. The effect of Reynolds number on the Nusselt number is not, however, fully reproduced by the models tested.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 11 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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