• Proceedings of the KSME Conference
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• 2001.06e
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• pp.506-511
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• 2001

This paper presents how redevelopment of the boundary layer in a backward-facing step flow is affected by boundary conditions imposed on velocity at the inlet, top and exit of the flow. A two-dimensional, laminar, incompressible flow over a backward-facing step with an open top boundary has been computed by using numerical methods of second-order time and spatial accuracy and a fractional-step method that guarantees a divergence-free velocity field at all time. The inlet velocity profile above the step is of Blasius type. Along the top boundary, shear-tree and Dirichlet conditions on the streamwise velocity were considered and at the exit fully-developed and convective boundary conditions were examined. (The vertical velocity at all boundaries were assumed to be zero explicitly or implicitly.) From the computed flow fields, the reattachment on the bottom side of shear layer separated from the tip of the step and succeeding redevelopment of the boundary layer were investigated.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.3
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• pp.217-232
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• 1992

A Numerical study on two-dimensional laminar natural convection with and without surface radiation in fully or partially open square cavity was performed. The cavity has one vertical heated wall facing a vertical opening and two horizontal insulated walls. The pressure boundary condition was applied to the opening instead of the velocity boundary condition. The results of this study showed that the increase of partition length decreased the convective and the radiative Nusselt numbers. It was also found that the increase of wall emissivity decreased the convective Nusselt numbers but increased the radiative Nusselt numbers.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.698-703
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• 2000

In a computational fluid dynamics, the imposition of open boundary condition has an important part of the accuracy but it is not easy to find the optimal boundary rendition. This difficult is introduced by making artificial boundary in unbounded domairs. Such open boundary requires us to ensure the continuity of all primitive variables because the nature is in continuum. Here we introduce a revised well-conditioned open boundary condition particularly in FEM and apply it to various problems-entrainment, body force, short domains.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.61-62
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• 2003

In this paper, the new higher order wall boundary conditions are proposed for solving the incompressible flows. The square driven cavity flows are simulated by using the variable order method of lines with the present wall boundary conditions. The variable order method of lines is constructed by the spatial discretization, i.e., the variable order proper convective scheme for convective terms and the modified differential quadrature method for diffusive terms, and time integration. The 2nd, 4th, and 6th order solutions are presented and these results show this higher order boundary conditions are very promising for the incompressible flow simulations.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1358-1363
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• 2004

The objective of this work is to propose calibration facility in which a thin film type heat flux sensor can be calibrated under convective flow condition by using a small wind tunnel with the constant temperature plate condition. A small wind tunnel has been built to produce a boundary layer shear flow above a constant temperature copper plate. 12-independent copper blocks, thin film heaters, insulators and temperature controllers were used to keep the temperature of flat plate constant at a specified temperature. Three commercial thin film-type heat flux sensors were tested. Convective calibrations of these gages were performed over the available heat flux range of $1.4{\sim}2.5kW/m^2$. The uncertainty in the heat flux measurements in the convective-type heat flux calibration facility was ${\pm}2.07%$. Non-dimensional sensitivity is proposed to compare the sensitivity calibrated by manufacturer and that of experiment conducted in this study.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.76-78
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• 1999

This paper presents Galerkin- and Upwind-finite element analyses solution in the travelling magnetic filed problem. The travelling magnetic field problem is subject to convective- diffusion equation. Therefore, the solution derived from Galerkin-FEM with linear interpolation function may oscillate between the adjacent nodes. A simple model with Derichlet, Noumann and periodic boundary condition respectively, have been analyzed to investigate stabilities of solutions. It is concluded that the solution of Galerkin-FEM may oscillate according to boundary condition and element type, but that of Upwind-FEM is stable regardless boundary condition.

• Journal of Computational Design and Engineering
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• v.3 no.4
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• pp.330-336
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• 2016

The present work is concerned with heat and mass transfer of an electrically conducting second grade MHD fluid past a semi-infinite stretching sheet with convective surface heat flux. The analysis accounts for thermophoresis and thermal radiation. A similarity transformations is used to reduce the governing equations into a dimensionless form. The local similarity equations are derived and solved using Nachtsheim-Swigert shooting iteration technique together with Runge-Kutta sixth order integration scheme. Results for various flow characteristics are presented through graphs and tables delineating the effect of various parameters characterizing the flow. Our analysis explores that the rate of heat transfer enhances with increasing the values of the surface convection parameter. Also the fluid velocity and temperature in the boundary layer region rise significantly for increasing the values of thermal radiation parameter.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.315-320
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• 2009

A computational investigation is conducted on free convection from a thin plate having a surface heat source. The thermal configuration simulates the recently-proposed transparent film heater made of a single-walled carbon nanotube film on a glass substrate. The Navier-Stokes computations are carried out to study laminar free convection from the heater. Parallel numerical experiments are performed by using a simplified design analysis model which solve the conduction equation with the boundary conditions utilizing several existing correlations for convective heat transfer coefficient. Comparison leads to the most suitable boundary condition for the thermal model to evaluate the performance evaluation of a transparent thin-film heater.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.915-918
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• 2005

Acoustic holography uses Kirchhoff·Helmholtz integral equation and Green's function which satisfies Dirichlet boundary condition Applications of acoustic holography have been taken to the sound field neglecting the effect of flow. The uniform flow, however, changes sound field and the governing equation, Green's function and so on. Thus the conventional method of acoustic holography should be changed. In this research, one possibility to apply acoustic holography to the sound field with uniform flow is introduced through checking for the plane wave in a duct. Change of Green's function due to uniform flow and one method to derive modified form of Kirchhoff·Heimholtz integral is suggested for 1-dimensional sound field. Derivation results show that using Green's function satisfying Dirichlet boundary condition, we can predict sound pressure in a duct using boundary value.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1635-1643
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• 2000

The present work investigates a heat transfer phenomenon at the interface between a porous medium and an impermeable wall. In an effort to appropriately describe the heat transfer phenomenon at the interface, the heat transfer at the interface between the microchannel heat sink, which is an ideally organized porous medium, and the finite-thickness substrate is examined. From the examination, it is clarified that the he heat flux distribution at the interface is not uniform for the impermeable wall with finite thickness. On the other hand, the first approach, based on the energy balance for the representative elementary volume in the porous medium, is physically reason able. When the first approach is applied to the thermal boundary condition, and additional boundary condition based on the local thermal equilibrium assumption at the interface is used. This additional boundary condition is applicable except for the very th in impermeable wall. Hence, for practical situations, the first approach in combination with the local thermal equilibrium assumption at the interface is suggested as an appropriate thermal boundary condition. In order to confirm our suggestion, convective flows both in a microchannel heat sink and in a sintered porous channel subject to a constant heat flux condition are analyzed. The analytically obtained thermal resistance of the microchannel heat sink and the numerically obtained overall Nusselt number for the sintered porous channel are shown to be in close agreement with available experimental results when our suggestion for the thermal boundary conditions is applied.