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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.

Two‐dimensional finite difference calculations are carried out to study laminar flow in longitudinal and transverse convection rolls for three different geometries: a single rectangular cavity with high aspect ratio; a double cavity with a thin separation sheet; and a double cavity with a separation sheet and a honeycomb structure. The equations for the convection‐diffusion in the fluid and conduction in the solid region are solved simultaneously. Good agreement with experimental data is achieved for Rayleigh numbers not too high above the critical value for the onset of secondary convection rolls (Ra < 8500 for vertical and Ra < 2700 for horizontal cavities filled with air). Simulation fails for inclined cavities, where the flow structure is essentially three‐dimensional.

This paper deals with a numerical simulation of the thermal and fluid‐dynamic behaviour of double‐pipe condensers and evaporators. The governing equations of the fluid flow (continuity, momentum and energy) in both the tube (evaporating or condensing flow) and the annulus (single‐phase flow), together with the energy equation in the tube wall, are solved iteratively in a segregated manner using a one‐dimensional, transient formulation, based on an implicit step by step numerical scheme in the zones with fluid flow (tube and annulus), and an implicit central difference numerical scheme in the tube wall, solved by means of the Tri‐Diagonal Matrix Algorithm (TDMA). This formulation requires the use of empirical information for the evaluation of convective heat transfer, shear stress and void fraction. Two criteria to calculate the location of the points of transition between single‐phase and two‐phase flow are tested. An analysis of the different parameters used in the discretization is made. Some illustrative results corresponding to the solution of a condenser and an evaporator using two different working fluids (R–12 and R–134a) are presented.

The purpose of this paper is to present transient turbulent natural convection with surface thermal radiation in a square differentially heated enclosure using non-primitive variables like stream function and vorticity.

The governing equations formulated in dimensionless variables “stream function, vorticity and temperature,” within the Boussinesq approach taking into account the standard two equation k-ε turbulence model with physical boundary conditions have been solved using an iterative implicit finite-difference method.

It has been found that using of the presented algebraic transformation of the mesh allows to effectively conduct numerical analysis of turbulent natural convection with thermal surface radiation. It has been shown that the average convective Nusselt number increases with the Rayleigh number and decreases with the surface emissivity, while the average radiative Nusselt number is an increasing function of these key parameters. It has been shown that a presence of surface thermal radiation effect leads to an expansion of the eddy viscosity zones close to the walls.

It should be noted that for the first time in this paper we used stream function and vorticity variables with very effective algebraic transformation of the mesh in order to create a non-uniform mesh for an analysis of turbulent flow. Such method allows to reduce the computational time essentially in comparison with using of the primitive variables. The considered method has been successfully validated on the basis of the experimental and numerical data of other authors in case of turbulent natural convection without thermal radiation. The used numerical method would benefit scientists and engineers to become familiar with the analysis of turbulent convective heat and mass transfer, and the way to predict the properties of the turbulent flow in advanced nuclear systems, in industrial sectors including transportation, power generation, chemical sectors, ventilation, air-conditioning, etc.

The purpose of this study is to investigate the flow interaction between the cavities and its impact on heat transfer. The role of the openings is examined and three strategies are considered: one opening, two openings on single side and two openings on double sides.

A two-dimensional laminar natural convection heat transfer in multilayered open cavities was numerically investigated. The governing equations in primitive variables were discretized by the finite volume method and solved by SIMPLE algorithm.

The results show that for the cavities with one opening, the flow in the cavities is connected with each other. The exhaust hot fluid from the lower cavity was entrained into the upper cavities by thermal buoyancy and hence the heat transfer in the upper cavities was decreased because of thermal accumulation. Two openings on the single side could strengthen the flow interaction between the cavities and then enhance the heat transfer. However, the double-sided openings eliminated the flow interaction between the cavities and thus the fluid flow and heat transfer characteristics in all cavities are independent. It was concluded that the flow interaction between the multilayered open cavities has an importance effect on the heat transfer in the cavities.

The flow interaction between the multilayered open cavities was illustrated. The effect of flow interaction on the heat transfer in the cavities was investigated. The role of openings in the flow interaction and heat transfer in cavities was explored. The cavity below affects above cavity for the openings on single side. No interaction exists between the cavities with openings on double sides.

This paper aims to provide improvements to the newest version of the k‐ ω turbulence model of Wilcox for convective heat transfer prediction in turbulent axisymmetric jets impinging onto a flat plate.

Improvements to the heat transfer prediction in the impingement zone are obtained using the stagnation flow parameter of Goldberg and the vortex stretching parameter of Wilcox. The third invariant of the strain rate tensor in the form of Shih et al. and the blending function of Menter are applied in order make negligible the influence of the impingement modifications in the benchmark flows for turbulence models. Further, it is demonstrated that for two‐dimensional jets impinging onto a flat plate the stagnation region Nusselt number predicted by the original k‐ ω model is in good agreement with direct numerical simulation (DNS) and experimental data. Also for two‐dimensional jets, the proposed modification is deactivated.

The proposed modification has been applied to improve the convective heat transfer predictions in the stagnation flow regions of axisymmetric jets impinging onto a flat plate with nozzle‐plate distances H/D = 2, 6, 10 and Reynolds numbers Re = 23,000 and 70,000. Comparison of the predicted and experimental mean and fluctuating velocity profiles is performed. The heat transfer rates along a flat plate are compared to experimental data. Significant improvements are obtained with respect to the original k‐ ω model.

The proposed modification is simple and can be added to the k‐ ω model without causing stability problems in the computations.

The purpose of this paper is to solve Navier–Stokes equations including the effects of temperature and inner pipe rotation for fully developed turbulent flow in eccentric annuli by using finite difference scheme with fixing non-linear terms.

A mathematical model is proposed for fully developed turbulent flow including the effects of temperature and inner pipe rotation in eccentric annuli. Obtained equation is solved numerically via central difference approximation. In this process, the non-linear term is frozen. In so doing, the non-linear equation can be considered as a linear one.

The convergence analysis is studied before using the method to the proposed momentum equation. It reflects that the method approaches to the exact solution of the equation. The numerical solution of the mathematical model shows that pressure gradient can be predicted with a good accuracy when it is compared with experimental data collected from experiments conducted at Izmir Katip Celebi University Flow Loop.

The originality of this work is that Navier–Stokes equations including temperature and inner pipe rotation effects for fully developed turbulent flow in eccentric annuli are solved numerically by a finite difference method with frozen non-linear terms.

This paper seeks to describe a design approach which can be used to manufacture better‐performing reciprocating compressors. This design approach relates the drive kinematic characteristics to the thermodynamic performance of the compressor.

The presented approach is based on employing a stochastic optimisation algorithm to find the best piston trajectory within one cycle of operation and couple that with a gradient‐based technique to find the best dimensions of the mechanism which can realise this trajectory.

The mathematical models presented to implement the proposed design approach have been coded in a computer program which has been employed for simulation purposes. A case study given at the end of the paper asserts the usefulness of the proposed method and proves that a few percentage points increase in a defined set of performance indices has been gained from the optimisation exercise.

The presented models are only relevant to reciprocating compressors.

The promising results obtained in this paper will lead to the creation of better performing and more reliable compressor drives, designed to fulfil a set of desired performance criteria.

The paper offers originality in two different aspects. The mechanism design process has been undertaken in full consideration to the thermodynamic performance of the compressor; and the coupling of the stochastic and the gradient‐based optimisation methods to produce the desired outcome.

This paper aims to predict the effects of uniform injection or suction through a porous square cylinder on the flow field and on some aerodynamic parameters.

The finite volume method has been used for solving the ensemble averaged Navier–Stokes equations for incompressible flow in conjunction with the k‐ ε turbulence model equations including the Kato and Launder modification.

The parameters taken into account are injection or suction velocity, position of injection and suction surface, drag and lift coefficients and Strouhal number. The numerical results show that increasing suction velocity decreases the drag coefficient for all the suction configurations considered in the present study, except that of suction through rear surface. The vortex‐shedding motion gets weak by the suction application through top and bottom surfaces.

The problem is restricted with a 2‐D simple geometry such as square cylinder due to the limited computer capability. Further extensions of the present study could include the more complex configurations and some other aspects such as heat transfer between porous cylinder and main flow.

The injection or suction application through a porous bluff body can be used as an efficient drag and vortex control method in aerodynamics.

This paper describes an attempt to simulate numerically the flow around square cylinder with uniform injection and suction in a manner different from what is given in the literature.

Convective heat transfer features of a turbulent slot jet impingement are comprehensively studied using two different computational approaches, namely, URANS (unsteady Reynolds-averaged Navier–Stokes equations) and SAS (scale-adaptive simulation). Turbulent slot jet impingement heat transfer is used where a considerable heat transfer enhancement is required, and computationally, it is a quite challenging flow configuration.

Customized OpenFOAM 4.1, an open-access computational fluid dynamics (CFD) code, is used for SAS (SST-SAS k-ω) and URANS (standard k-ε and SST k-ω) computations. A low-Re version of the standard k-ε model is used, and other models are formulated for good wall-refined calculations. Three turbulence models are formulated in OpenFOAM 4.1 with second-order accurate discretization schemes.

It is observed that the profiles of the streamwise turbulence are under-predicted at all the streamwise locations by SST k-ω and SST SAS k-ω models, but follow similar trends as in the reported results. The standard k-ε model shows improvements in the predictions of the streamwise turbulence and mean streamwise velocity profiles in the zone of outer wall jet. Computed profiles of Nusselt number by SST k-ω and SST-SAS k-ω models are nearly identical and match well with the reported experimental results. However, the standard k-ε model does not provide a reasonable profile or quantification of the local Nusselt number.

Hybrid turbulence model is suitable for efficient CFD computations for the complex flow problems. This paper deals with a detailed comparison of the SAS model with URANS and LES for the first time in the literature. A thorough assessment of the computations is performed against the results reported using experimental and large eddy simulations techniques followed by a detailed discussion on flow physics. The present results are beneficial for scientists working with hybrid turbulence models and in industries working with high-efficiency cooling/heating system computations.