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Article
Publication date: 1 February 2000

A.N. Pavlov, S.S. Sazhin, R.P. Fedorenko and M.R. Heikal

Detailed results of numerical calculations of transient, 2D incompressible flow around and in the wake of a square prism at Re = 100, 200 and 500 are presented. An…

Abstract

Detailed results of numerical calculations of transient, 2D incompressible flow around and in the wake of a square prism at Re = 100, 200 and 500 are presented. An implicit finite‐difference operator‐splitting method, a version of the known SIMPLEC‐like method on a staggered grid, is described. Appropriate theoretical results are presented. The method has second‐order accuracy in space, conserving mass, momentum and kinetic energy. A new modification of the multigrid method is employed to solve the elliptic pressure problem. Calculations are performed on a sequence of spatial grids with up to 401 × 321 grid points, at sequentially halved time steps to ensure grid‐independent results. Three types of flow are shown to exist at Re = 500: a steady‐state unstable flow and two which are transient, fully periodic and asymmetric about the centre line but mirror symmetric to each other. Discrete frequency spectra of drag and lift coefficients are presented.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 10 no. 1
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 February 1997

Shuichi Torii and Wen‐Jei Yang

A numerical study is performed to investigate turbulent Couette flow and heat transfer characteristics in concentric annuli with a slightly heated inner cylinder moving in…

Abstract

A numerical study is performed to investigate turbulent Couette flow and heat transfer characteristics in concentric annuli with a slightly heated inner cylinder moving in the flow direction. A two‐equation k‐ε turbulence model is employed to determine the turbulent viscosity and the turbulent kinetic energy. The turbulent heat flux is expressed by Boussinesq approximation in which the eddy diffusivity for heat is given as functions of the temperature variance t2‐ and the dissipation rate of temperature fluctuations εt, together with k and ε. The governing boundary‐layer equations are discretized by means of control volume finite‐difference technique and numerically solved using a marching procedure. It is disclosed from the study that the streamwise movement of the inner core causes substantial reductions in the turbulent kinetic energy and the temperature variance, particularly near the inner wall region, resulting in the deterioration of the Nusselt number, and that an attenuation in heat transfer performance is induced by the velocity ratio of the moving inner cylinder to the fluid flow.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 7 no. 1
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 April 1994

S. Torii and W. ‐J. Yang

A theoretical study is performed to investigate turbulent flow and heattransfer characteristics in a concentric annulus with a heated inner cylindermoving in the direction…

Abstract

A theoretical study is performed to investigate turbulent flow and heat transfer characteristics in a concentric annulus with a heated inner cylinder moving in the direction of flow (Couette flow). The two‐equation k‐ε model is employed to determine turbulent viscosity and kinetic energy. The Reynolds stress and turbulent heat flux are expressed by Boussinesq’s approximation. The governing boundary‐layer equations are discretized by means of a control volume finite‐difference technique and numerically solved using a marching procedure. Results are obtained for the time‐averaged streamwise velocity profile, turbulent kinetic energy profile, friction factor, and Nusselt number. These results agree well with experimental data in the existing literature. It is concluded from the study that the streamwise movement of the inner wall induces an attenuation in the turbulent kinetic energy, resulting in a reduction in the heat transfer performance and an increase in the velocity ratio of the moving inner cylinder to the fluid flow causes a substantial decrease in both the friction factor and the Nusselt number as well as a drastic reduction in the turbulent kinetic energy in the inner wall region.

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

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Article
Publication date: 1 January 2004

G. Comini, G. Croce and C. Nonino

Most compact heat exchangers and heat dissipating components rely on convection enhancement mechanisms that reduce the continuous growth of boundary layers. Usually…

Abstract

Most compact heat exchangers and heat dissipating components rely on convection enhancement mechanisms that reduce the continuous growth of boundary layers. Usually surface irregularities, in the form of interruptions and/or vortex generators, are introduced in the flow passages. The resulting geometric configurations are periodic in space and, after a short distance from the entrance, induce velocity and thermal fields that repeat themselves from module to module. The numerical models presented here consider the space‐periodicity and allow flows that are stationary at sub‐critical values of the Reynolds number, but become time‐periodic, or quasi periodic, above the critical value of the Reynolds number. Space discretizations are achieved by an equal order finite element procedure based on a projection algorithm. Two‐dimensional schematizations are employed to analyze the effects of surface interruptions and transverse vortex generators, while three‐dimensional schematizations are employed for longitudinal vortex generators.

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International Journal of Numerical Methods for Heat & Fluid Flow, vol. 14 no. 1
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 7 March 2016

Ranganayakulu Chennu

The purpose of this paper is to carry out numerical modeling of single-blow transient analysis using FLUENT porous media model for estimation of heat transfer and pressure…

Abstract

Purpose

The purpose of this paper is to carry out numerical modeling of single-blow transient analysis using FLUENT porous media model for estimation of heat transfer and pressure drop characteristics of offset and wavy fins.

Design/methodology/approach

A computational fluid dynamics program FLUENT has been used to predict the design data in terms of j and f factors for plate-fin heat exchanger wavy and offset strip fins, which are widely used in aerospace applications.

Findings

The suitable design data in terms of Colburn j and Fanning friction f factors is generated and presented correlations for wavy fins covering the laminar, transition and turbulent flow regimes.

Originality/value

The correlations for the friction factor f and Colburn factor j have been found to be good by comparing with other references. The correlations can be used by the heat exchanger designers and can reduce the number of tests and modification of the prototype to a minimum for similar applications and types of fins.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 2
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 28 October 2014

Z.X. Yuan and L. Chen

The purpose of this paper is to study the thermal and flow characteristics of a single annually finned-tube condenser. The velocity and the temperature field inside the…

Abstract

Purpose

The purpose of this paper is to study the thermal and flow characteristics of a single annually finned-tube condenser. The velocity and the temperature field inside the fin channel are revealed. Changes of the heat transfer and the flow resistance for typical fin configurations are analyzed. The optimal combinations of the fin dimension in terms of the enhancement of heat transfer are suggested.

Design/methodology/approach

The problem has been numerically investigated with the FLUENT software. K-ɛ model is applied in the solution of the turbulent cases. The local and the average feature of the thermal performance and the friction factor are determined. Furthermore, the effect of the fin spacing, the fin height, and the fin thickness on the heat transfer and the flow resistance are verified.

Findings

The numerical results reveal that the fin spacing is the most influential factor of all fin dimensions not only to the heat transfer but also to the flow resistance. Both the heat transfer and the flow resistance are compared with those related data available in the public literature. On the other hand, the fin height and the fin thickness affect the heat transfer of the condenser in a much less significant way in comparison to that of the fin spacing.

Originality/value

This paper provides some meaningful information of the fin-dimensional effect on the heat transfer and the flow resistance for a single finned tube condenser. For such kind of heat exchanger, the heat transfer coefficient, the friction factor, and the heat transfer amount per unit length tube are all important to describe the performance feature.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 8
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 4 January 2016

Sajjad Miran and Chang Hyun Sohn

– The purpose of this paper is to focus on the variation of wake structures and aerodynamic forces with changes in the cylinder corner radius and orientation.

Abstract

Purpose

The purpose of this paper is to focus on the variation of wake structures and aerodynamic forces with changes in the cylinder corner radius and orientation.

Design/methodology/approach

Numerical simulations were performed for flow past a square cylinder with different corner radii placed at an angle to the incoming flow. In the present study, the rounded corner ratio R/D=0 (square cylinder), 0.1, 0.2, 0.3, and 0.4 (where R is the corner radius and D is the characteristic dimension of the body) and the angle of incidence α in the range of 0°-45° were considered.

Findings

The numerical model was validated by comparing the present results with results in the available literature, and they were found to be in good agreement. The critical incidence angle for the rounded corner cylinder – corresponding to the minimum mean drag coefficient (C D ), the minimum root mean square value of the lift coefficient C L,RMS), and the maximum Strouhal number – shifted to a lower incidence angle compared with the sharp corner square cylinder. The minimum drag and lift coefficient at R/D=0 were observed for the critical incidence angle αcri=12°, whereas for R/D=0.1-0.4, the minimum drag and lift coefficient were found to be within the range of 5°-10° for α.

Originality/value

The presented results shows the importance of the incidence angle and rounded corners of the square cylinder for reduction of aerodynamic forces. The two parameters support the shear layer flow reattachment on the lateral surface of the cylinder, have a strong correlation with the reduction of the wake width, and hence reduced the values of C D and C L .

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 1
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 5 May 2015

Sajjad Miran and Chang Hyun Sohn

– The purpose of this paper is to numerically investigate the influence of corner radius on flow past a square cylinder at a Reynolds number 500.

Abstract

Purpose

The purpose of this paper is to numerically investigate the influence of corner radius on flow past a square cylinder at a Reynolds number 500.

Design/methodology/approach

Six models were studied, for R/D=0 (square cylinder), 0.1, 0.2, 0.3, 0.4, and 0.5 (circular cylinder), where R is the corner radius and D is the characteristic dimension of the body. The transient two-dimensional (2D) laminar and large eddy simulations (LES) models were employed using finite volume code. The Strouhal number, mean drag coefficient (CD), and root mean square (RMS) value of lift coefficient (CL,RMS), for different R/D values, were computed and compared with experimental and other numerical results.

Findings

The computational results showed good agreement with previously published results for a Reynolds number, Re=500. It was found that the corner effect on a square cylinder greatly influences the flow characteristics around the cylinder. Results indicate that, as the corner radius ratio, R/D, increases, the Strouhal number increases rapidly for R/D=0-0.2, and then gradually rises between R/D=0.2 and 0.5. The minimum values of the mean drag coefficient and the RMS value of lift coefficient were found around R/D=0.2, which is verified by the time averaged streamwise velocity deficit profile.

Originality/value

On the basis of the numerical results, it is concluded that rounded corners on a square cylinder are useful in reducing the drag and lift forces generated behind a cylinder. Finally, it is suggested that with a rounded corner ratio of around R/D=0.2, the drag and oscillation of the cylinder can be greatly reduced, as compared to circular and square cylinders.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 25 no. 4
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 November 2001

Arash Saidi and Bengt Sundén

Numerical analysis of the instantaneous flow and heat transfer has been carried out for offset strip fin geometries in self‐sustained oscillatory flow. The analysis is…

Abstract

Numerical analysis of the instantaneous flow and heat transfer has been carried out for offset strip fin geometries in self‐sustained oscillatory flow. The analysis is based on the two‐dimensional solution of the governing equations of the fluid flow and heat transfer with the aid of appropriate computational fluid dynamics methods. Unsteady calculations have been carried out. The obtained time‐dependent results are compared with previous numerical and experimental results in terms of mean values, as well as oscillation characteristics. The mechanisms of heat transfer enhancement are discussed and it has been shown that the fluctuating temperature and velocity second moments exhibit non‐zero values over the fins. The creation processes of the temperature and velocity fluctuations have been studied and the dissimilarity between these has been proved.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 11 no. 7
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 December 2005

Jun‐Jie Zhou and Wen‐Quan Tao

To provide some heat transfer and friction factor results for fin‐and‐tube heat transfer surfaces which may be used in air conditioning industry.

Abstract

Purpose

To provide some heat transfer and friction factor results for fin‐and‐tube heat transfer surfaces which may be used in air conditioning industry.

Design/methodology/approach

Numerical simulation approach was adopted to compare the plain plate fin and three types of radial slotted fin surfaces.

Findings

It is found that at the same frontal velocity (1.0‐3 m/s) the plain plate fin has the lowest heat transfer rate with the smallest pressure drop. The full slotted fin surface has the highest heat transfer rate with the largest pressure drop penalty. The partially slotted fin (where the strips are mainly located in the rear part of the fin) and the back slotted fin are some what in between. Under the identical pumping power constraint, the partially slotted fin surface behaves the best.

Research limitations/implications

The results are only valid the two‐row fin surface.

Practical implications

The results are very useful for the design of two‐row tube fin surfaces with high efficiency.

Originality/value

This paper provides original information of slotted fin surface with radial strips from the field synergy principle.

Details

Engineering Computations, vol. 22 no. 8
Type: Research Article
ISSN: 0264-4401

Keywords

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