• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.1
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• pp.83-92
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• 1999

In this paper, the wind tunnel test was carried to investigate the behavior of buffer layer in turbulent boundary layer with variation of surface temperature and roughness. The results were as follows; 1. The velocity in turbulent boundary layer was increased when the roughness height within viscous sublayer thickness was increased. 2. When the surface temperature was increased, the density of air was decreased and the velocity in turbulent boundary layer was increased. Thus, the thickness of turbulent boundary layer was decreased. 3. When the roughness height and surface temperature was increased simultaneously, the thickness of turbulent boundary layer was decreased. 4. The decrement of the thickness of turbulent boundary layer was more effected by the increment of the roughness height rather than the increment of surface temperature. 5. In this study, it was found that the condition of the highest velocity n turbulent boundary layer was the temperature 333K and roughness #100.

• Journal of the Korean Society of Visualization
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• v.4 no.2
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• pp.44-50
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• 2006

A visualization study on the boundary layer and near-wake of an NACA 0012 airfoil was con-ducted in order to investigate the influence of boundary layer behavior on the near-wake at low Reynolds numbers. The present study is investigated at static angles of attack ${\alpha}=0^{\circ},\;3^{\circ},\;6^{\circ}$ and $Re=2.3{\times}10^4,\;3.3{\times}10^4,\;4.8{\times}10^4$ by using a smoke-wire technique. The results of this study show that the laminar boundary layer on the airfoil surface is attached to the surface at ${\alpha}=0^{\circ}$, and that laminar separation of boundary layer on the airfoil surface occurs at ${\alpha}=3^{\circ}$. Furthermore, reattachment of the boundary layer occurs in the case of ${\alpha}=6^{\circ}$. In the current study, the location of the laminar separation point moves upstream as the Reynolds number and the angle of attack increase.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.10
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• pp.16-23
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• 2006

A study on the boundary layer behavior of an NACA 0012 airfoil at low Reynolds numbers was investigated in order to gain knowledge of a boundary layer that might be employed in a turbine blade and MAVs. A hot-wire anemometer was used to measure the boundary layer of an NACA 0012 airfoil at static angles of attack ${\alpha}$=$0^{\circ}$, $3^{\circ}$, and $6^{\circ}$, and Reynolds Numbers Re=$2.3{\times}10^4$, $3.3{\times}10^4$, and $4.8{\times}10^4$. The results of this study show that the laminar boundary layer on the airfoil surface is attached to the surface at ${\alpha}$=$0^{\circ}$, and the laminar separation of the boundary layer on the airfoil surface occurs at ${\alpha}$=$3^{\circ}$. Furthermore, the reattachment of the boundary layer in the present study occurs for the cases of Re=$3.3{\times}10^4$ and Re=$4.8{\times}10^4$at ${\alpha}$=$6^{\circ}$.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.14 no.4
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• pp.24-30
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• 2006

An experimental study was carried out in order to investigate the influence of boundary layer behavior on the near-wake at low Reynolds numbers. An X-type hot-film probe(55R51) was used to measure the near-wake of an NACA 0012 airfoil at static angles of attack ${\alpha}=0^{\circ}$, $3^{\circ}$, and $6^{\circ}$, and the Reynolds numbers Re=2.3${\times}10^4$, 3.3${\times}10^4$, and 4.8${\times}10^4$. The results of the study show that the characteristics of the boundary layer on the airfoil surface have a close relationship with the mean velocity and turbulence intensity profiles of a near-wake. Therefore, the development of the boundary layer, the position of the separation point, and the existence and non-existence of reattachment on the airfoil surface were represented by the differences in mean velocity and turbulence intensity profiles of the near-wake.

• Journal of Pharmaceutical Investigation
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• v.31 no.1
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• pp.13-18
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• 2001

This study was to investigate the relationship between the gel layer thickness and swelling boundary via strength measurements using texture analysis. The novel texture analysis approach was used to examine the dynamics of swelling behavior in a ternary polymeric matrix tablet. The method permitted the characterization of the changes occurring at the peripheral as well as within interior boundary of the swelling during water ingress. The increase in gel strength for pectin, HPMC, and a ternary mixture with gelatin was found to depend on polymer concentration. Therefore, this method is further applicable to characterize the swelling behavior and provide opportunity to differentiate the gel-layer from that of swelling boundary.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.10
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• pp.1210-1218
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• 2004

Experimental study was performed to investigate the flow behavior in boundary layer on the blade suction surface of a multi-stage axial flow compressor, which was focused on the third stage of the 4-stage Low Speed Research Compressor. Flow measurements in the boundary layer were obtained using a boundary layer hot wire probe, which was traversed normal to the blade suction surface at small increments by the probe traverse specially designed. Detailed boundary layer flow measurements covering most of the stator suction surface were taken and are described using time mean and ensemble averaged velocity profiles. Amplitude of the velocity fluctuation and turbulence intensity in the boundary layer flow are also discussed. At midspan, narrow but strong wake zone due to passing wake disturbances is generated in the boundary layer near the blade leading edge for the rotor blade passing period. Corner separation is observed at the tip region near the trailing edge, which causes to increase steeply the boundary layer thickness.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.426-432
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• 2004

Large-Eddy Simulation (LES) is applied for the simulation of compressible flat plate boundary with Reynolds number up to 5 X 10$^{5}$ . Numerical examples include shock/boundary layer interaction and boundary layer transition, aiming future application to the analysis of transonic fan/compressor cascades. The present LES code uses hybrid com-pact/WENO scheme for the spatial discretization and compact diagonalized implicit scheme for the time integration. The present code successfully predicted the bypass transition of subsonic boundary layer. As for supersonic turbulent boundary layer, mean and fluctuation velocity of the attached boundary, as well as the evolution of the friction coefficient and the displacement thickness both upstream and downstream of the separation region are all in good agreement with experiment. The separation point also agreed with the experiment. In the simulation of the shock/laminar boundary layer interaction, the dependence of the transition upon the shock strength is reproduced qualitatively, but the extent of the separation region is overpredicted. These numerical examples show that LES can predict the behavior of boundary layer including transition and shock interaction, which are hardly managed by the conventional Reynolds-averaged Navier-Stokes approach, although there needs to be more effort before achieving quantitative agreement.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.56-65
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• 2013

Two compression ramp problems and an impinging shock problem are computed to investigate influence of turbulence models and eddy viscosity on the shock-wave / boundary layer interaction. A Navier-Stokes boundary layer generation code was applied to the generation of inflow boundary conditions. Computational results are validated well with the experimental data and effects of turbulence models are investigated. It is shown that the behavior of turbulence (eddy) viscosity directly affects both the extent of the separation and shock-wave positions over the separation.

• Journal of applied mathematics & informatics
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• v.36 no.3_4
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• pp.331-348
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• 2018

In this paper, an initial value method for solving a class of singularly perturbed delay differential equations with layer behavior is proposed. In this approach, first the given problem is modified in to an equivalent singularly perturbed problem by approximating the term containing the delay using Taylor series expansion. Then from the modified problem, two explicit Initial Value Problems which are independent of the perturbation parameter, ${\varepsilon}$, are produced: the reduced problem and boundary layer correction problem. Finally, these problems are solved analytically and combined to give an approximate asymptotic solution to the original problem. To demonstrate the efficiency and applicability of the proposed method three linear and one nonlinear test problems are considered. The effect of the delay on the layer behavior of the solution is also examined. It is observed that for very small ${\varepsilon}$ the present method approximates the exact solution very well.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.3
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• pp.261-267
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• 2002

The integral boundary layer equation for the air side and the diffusion equation for the frost layer are numerically analyzed in order to predict the behavior of frost layer growth. The thickness and density of the frost layer obtained from the present study agree well with those of previous numerical results and experimental data with a maximum error of 13%. The characteristics of heat and mass transfer within the frost layer and the frost layer growth along the flow direction are investigated by performing numerical analysis. The effects of operating conditions on the frost layer growth are also examined.