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1 – 10 of 969This study aims to present a numerical analysis of the behavior of the electric field and flow field characteristics under electrohydrodynamics (EHD) force. The influence of the…
Abstract
Purpose
This study aims to present a numerical analysis of the behavior of the electric field and flow field characteristics under electrohydrodynamics (EHD) force. The influence of the jet airflow under the EHD force is investigated when it impacts the inclined flat plate.
Design/methodology/approach
The high electrical voltage and angle of an inclined flat plate are tested in a range of 0–30 kV and 0–90°, respectively. In this condition, the air is set in a porous medium and the inlet jet airflow is varied from 0–2 m/s.
Findings
The results of this study show that the electric field line patterns increase with increasing the electrical voltage and it affects the electric force increasing. The angle of inclined flat plate and the boundary of the computational model are influenced by the electric field line patterns and electrical voltage surface. The electric field pattern is the difference in the fluid flow pattern. The fluid flow is more expanded and more concentrated with increasing the angle of an inclined flat plate, the electrical voltage and the inlet jet airflow. The velocity field ratio is increased with increasing the electrical voltage but it is decreased with increasing the angle of the inclined flat plate and the inlet jet airflow.
Originality/value
The maximum Reynolds number, the maximum velocity field and the maximum cell Reynolds number are increased with increasing the electrical voltage, the inlet jet airflow and the angle of the inclined flat plate. In addition, the cell Reynolds number characteristics are more concentrated and more expanded with increasing the electrical voltage. The pattern of numerical results from the cell Reynolds number characteristics is similar to the pattern of the fluid flow characteristics. Finally, a similar trend of the maximum velocity field has appeared for experimental and numerical results so both techniques are in good agreement.
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Ahad Ramezanpour, Iraj Mirzaee, David Firth and Hassan Shirvani
This paper seeks to conduct a numerical study to investigate heat transfer in turbulent, unconfined, submerged, and inclined impinging jet discharged from a slot nozzle, utilising…
Abstract
Purpose
This paper seeks to conduct a numerical study to investigate heat transfer in turbulent, unconfined, submerged, and inclined impinging jet discharged from a slot nozzle, utilising finite volume code FLUENT.
Design/methodology/approach
Two re‐normalisation group k‐ε and the basic Reynolds stress models by using enhanced wall treatment for near wall turbulent modelling were applied and the local Nusselt numbers were compared with experiments. The enhanced wall treatment solves the fully turbulent region and viscous sublayer by considering a single blended function of both layers.
Findings
In inclined impinging jet by movement of stagnation point to the uphill side of the impinging plate, the location of the maximum Nusselt number moves to the uphill side of the plate. However, this movement increases by increasing of H/D and by decreasing of Reynolds number and inclination angle. For a flat plate impinging jet, the results were found to be less than 8 per cent different and for inclined impinging jet, more sensitive to H/D, 5‐20 per cent different in comparison with experiments. In addition, the flow streamlines were consistent with location of the heat transfer peak on the impinging surface.
Research limitations/implications
Reynolds numbers in range of 4,000‐16,000, the ratio of nozzle height to hydraulic diameter of the nozzle (H/D) in range of 4‐10, and inclination angle of air jet and plate in range of 40‐90° were considered.
Originality/value
A unique achievement of this study in comparison with experimental data was locating the exact peak of the local Nusselt number on impinging plate by change of Reynolds number, H/D, and inclination angle.
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M.A. Hossain, M.K. Chowdhury and Rama Subba Reddy Gorla
An analysis is performed to study the skin‐friction, the couple‐stress and heat transfer characteristics of a laminar free‐convection boundary layer flow of a micropolar fluid…
Abstract
An analysis is performed to study the skin‐friction, the couple‐stress and heat transfer characteristics of a laminar free‐convection boundary layer flow of a micropolar fluid past an isothermal plate inclined at a small angle to the horizontal. When the inclination is positive, series solutions, one valid near the leading edge and the other at a large distance from it, are obtained. Introducing a strained coordinate transformation, the local nonsimilar boundary layer equations are also derived for the flow from the leading edge to downstream, solutions of which are obtained by using an implicit finite difference method. When the inclination is negative, the boundary layer separates. The effects of the material parameters on the skin‐friction, the local couple‐stress, the local Nusselt number and the point of separation for a negatively inclined plate have been investigated.
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Minakshi Poonia and R. Bhargava
The purpose of this paper is to deal with the study of free convection magnetohydrodynamic (MHD) boundary layer flow of an incompressible viscoelastic fluid along an inclined…
Abstract
Purpose
The purpose of this paper is to deal with the study of free convection magnetohydrodynamic (MHD) boundary layer flow of an incompressible viscoelastic fluid along an inclined moving plate and heat transfer characteristics with prescribed quadratic power-law surface temperature.
Design/methodology/approach
The governing partial differential equations are transformed into non-dimensional, non-linear coupled ordinary differential equations which are solved numerically by robust Galerkin finite element method.
Findings
Numerical results for the dimensionless velocity and temperature profiles are displayed graphically for various physical parameters such as viscoelasticity, Prandtl number, angle of inclination parameter, magnetic and buoyancy parameter. The local Nusselt number is found to be the decreasing function of magnetic field parameter whereas it increases with increasing values of Prandtl number, viscoelastic parameter and buoyancy parameter.
Practical implications
The present problem finds significant applications in MHD power generators, cooling of nuclear reactors, thin film solar energy collector devices.
Originality/value
The objective of this work is to analyze the heat transfer of convective MHD viscoelastic fluid along a moving inclined plate with quadratic power law surface temperature. An extensively validated, highly efficient, variation finite element code is used to study this problem. The results are validated and demonstrated graphically.
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A. Zeeshan, R. Ellahi, F. Mabood and F. Hussain
The purpose of this study is to examine the simultaneous effects of Hafnium particles and partially submerged metallic particles for the flow of bi-phase coupled stress fluid over…
Abstract
Purpose
The purpose of this study is to examine the simultaneous effects of Hafnium particles and partially submerged metallic particles for the flow of bi-phase coupled stress fluid over an inclined flat plane.
Design/methodology/approach
An unflinching free stream flow that stretches far from the surface of the plane with the possibility of containing some partially submerged metallic particles is considered. Innovative model has been proposed and designed using Runge–Kutta–Fehlberg method.
Findings
The findings show that the drag force resists the couple stress fluid, whereas the Newtonian flow is supported by increasing the velocity. For both types of flows, movement of the particle is retarded gradually against the drag force coefficient.
Originality/value
To the best of the authors’ knowledge, this model is reported for the first time.
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Lelanie Smith, Oliver Oxtoby, A. Malan and Josua Meyer
– The purpose of this paper is to introduce a unique technique to couple the two-integral boundary layer solutions to a generic inviscid solver in an iterative fashion.
Abstract
Purpose
The purpose of this paper is to introduce a unique technique to couple the two-integral boundary layer solutions to a generic inviscid solver in an iterative fashion.
Design/methodology/approach
The boundary layer solution is obtained using the two-integral method to solve displacement thickness point by point with a local Newton method, at a fraction of the cost of a conventional mesh-based, full viscous solution. The boundary layer solution is coupled with an existing inviscid solver. Coupling occurs by moving the wall to a streamline at the computed boundary layer thickness and treating it as a slip boundary, then solving the flow again and iterating. The Goldstein singularity present when solving boundary layer equations is overcome by solving an auxiliary velocity equation along with the displacement thickness.
Findings
The proposed method obtained favourable results when compared with the analytical solutions for flat and inclined plates. Further, it was applied to modelling the flow around a NACA0012 airfoil and yielded results similar to those of the widely used XFOIL code.
Originality/value
A unique method is proposed for coupling of the boundary layer solution to the inviscid flow. Rather than the traditional transpiration boundary condition, mesh movement is employed to simulate the boundary layer thickness in a more physically meaningful way. Further, a new auxiliary velocity equation is presented to circumvent the Goldstein singularity.
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Ming‐Han Lin and Chin‐Tai Chen
The purpose of this paper is to study the effects of ion‐slip current and Hall current on the formation of longitudinal vortices in natural convection flow over a heated…
Abstract
Purpose
The purpose of this paper is to study the effects of ion‐slip current and Hall current on the formation of longitudinal vortices in natural convection flow over a heated horizontal plate.
Design/methodology/approach
The criterion on the position marking on the onset of longitudinal vortices is defined in the present paper. The results show that the onset position characterized by the Grashof number depends on the Prandtl number, the Reynolds number, the wave number, the Hall parameter, the ion‐slip parameter, and the Hartmann number.
Findings
The flow becomes more stable as the magnetic field increases. However, the destabilizing effect is found on the flow when the Hall and ion‐slip currents are presented.
Research limitations/implications
The standard method of linear stability model is applied, with terms higher than first order in disturbance quantities being neglected.
Practical implications
The problem of MHD natural convection flow with Hall and ion‐slip currents has many important engineering applications, e.g. power generators, Hall accelerators and flows in channels and ducts.
Originality/value
This study is to check the validity of the assumptions that the conditions of Hall and ion‐slip currents can be ignored.
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Abdelkader Frendi and Michael R. Brown
The purpose of this paper is to carry out an extensive numerical study in order to understand the flow structures and the resulting noise generated by a supersonic impinging jet…
Abstract
Purpose
The purpose of this paper is to carry out an extensive numerical study in order to understand the flow structures and the resulting noise generated by a supersonic impinging jet on a flat plate. One of the parameters varied in this study is the distance between the jet exit plane and the flat plate.
Design/methodology/approach
Because of the unsteady nature of the problem a time-dependent computation is carried out using the detached eddy simulation turbulence model. The OVERFLOW 2 CFD code was used with a highly resolved grid and small time steps.
Findings
The authors found that as the separation distance increases, the dominant frequencies in the noise spectrum decrease. In addition, the relative strength of the various frequencies to each other changes with changing distance, indicating the changing modes of the jet. The CFD results indicate a strong interaction between the acoustic waves emanating from the impingement plate and the jet plume. This feedback mechanism is responsible for destabilizing the jet shear layer leading to the jet changing modes. The computed near field spectra, convection velocities of the jet vortical structures and mean jet centerline velocity profile are in good agreement with experimental measurements. The results also show very high sound pressure levels all over the impingement plate but especially near the impingement point. These levels, if sustained, are detrimental to both human operators as well as the surrounding structures.
Research limitations/implications
Given the large-scale nature of the computations carried out, it is very costly to run the computations long enough to collect a good, statistically steady time sample to achieve a low frequency bandwidth resolution. Such a long time sample could actually improve the results in terms of frequency resolution and obtained an even better agreement with experiments. Off course there is always the issue of grid resolution as well, but given the good agreement with experiments that the authors obtained, the authors are confident in their results.
Practical implications
The practical implications of the results the authors obtained are significant in that, the authors now know that hybrid RANS-large eddy simulation methods can be used for this complex, unsteady engineering problems. In addition, the results also show the high noise level both on the impingement surface and in the surroundings of the jet. This could have a negative impact on the structural integrity of the flat surface.
Social implications
Noisy environments are never desirable anywhere especially in places where human operations take place. Therefore, given the high noise levels obtained in the simulations and confirmed by experiments, any human presence around the jet will be harmful to hearing and precautions need to be taken.
Originality/value
This is a physics-based study; i.e. understanding the physical phenomena involved in supersonic jet impingement. Of particular interest is the interaction of the jet shear layer with the acoustic waves emanating from the impingement area. This feedback loop is found to be responsible for intensifying the instability of the jet shear layer.
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WHERE computer programmes are not available for the solution of kinetic heating problems, the estimation of equilibrium and transient surface temperatures on bodies in supersonic…
Abstract
WHERE computer programmes are not available for the solution of kinetic heating problems, the estimation of equilibrium and transient surface temperatures on bodies in supersonic flow becomes tedious, especially where the transient conditions are to be analysed. A current method of performing these calculations for a turbulent boundary layer is here synthesised into nomogram form.
Esmail M.A. Mokheimer, S. Sami and B.S. Yilbas
This paper's aim is to examine flow and heat transfer through vertical channels between parallel plates, which is of prime importance in the design of cooling systems for…
Abstract
Purpose
This paper's aim is to examine flow and heat transfer through vertical channels between parallel plates, which is of prime importance in the design of cooling systems for electronic equipment such as that of finned cold plates in general, plate‐and‐frame heat exchangers, etc.
Design/methodology/approach
Numerical and analytical solutions are presented to investigate the heat transfer enhancement and the pressure drop reduction due to buoyancy effects (for buoyancy‐aided flow) for the developing laminar mixed convection in vertical channel between parallel plates in the vicinity of the critical values of the buoyancy parameter (Gr/Re)crt that are obtained analytically. The numerical solutions are presented for a wide range of the buoyancy parameters Gr/Re that cover both of buoyancy‐opposed and buoyancy‐aided flow situations under each of the isothermal boundary conditions under investigation.
Findings
Buoyancy parameters greater than the critical values result in building‐up the pressure downstream of the entrance such that the vertical channel might act as a thermal diffuser with possible incipient flow reversal. Locations at which the pressure gradient vanishes and the locations at which the pressure‐buildup starts have been numerically obtained and presented for all the investigated cases.
Research limitations/implications
The study is limited to the laminar flow situation.
Practical implications
The results clearly show that for buoyancy‐aided flow, the increase of the buoyancy parameter enhances the heat transfer and reduces the pressure drop across the vertical channel. These findings are very useful for cooling channel or chimney designs.
Originality/value
The study is original and presents new findings, since none of the previous studies reported the conditions for which pressure buildup might take place due to mixed convection in vertical channels between parallel plates.
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