• Journal of computational fluids engineering
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• v.11 no.4 s.35
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• pp.62-66
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• 2006

High-speed flight vehicle have various cavities. The supersonic cavity flow is complicated due to vortices, flow separation, reattachment, shock waves and expansion waves. The general cavity flow phenomena includes the formation and dissipation of vortices, which induce oscillation and noise. The oscillation and noise greatly affect flow control, chemical reaction, and heat transfer processes. The supersonic cavity flow with high Reynolds number is characterized by the pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions. The resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the unsteady, compressible three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with the ${\kappa}-{\omega}$ turbulence model. The cavity model used for numerical calculation had a depth(D) of 15mm cavity aspect ratio (L/D) of 3, width to spanwise ratio(W/D) of 1.0 to 5.0. Based on the PSD(Power Spectral Density) and CSD(Cross Spectral Density) analysis of the pressure variation, the dominant frequency was analyzed and compared with the results of Rossiter's Eq.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.530-533
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• 2010

This paper presents numerical analysis and design optimization of various turbine blade cooling techniques with three-dimensional Reynolds-averaged Navier-Stokes(RANS) analysis. The fluid flow and heat transfer have been performed using ANSYS-CFX 11.0. A fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness with the radial basis neural network method. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. The impingement jet cooling has been performed to investigate heat transfer characteristic with geometry variables. Distance between jet nozzle exit and impingement plate, inclination of nozzle and aspect ratio of nozzle hole are considered as geometry variables. The area averaged Nusselt number is evaluated each geometry variables. A rotating rectangular channel with staggered array pin-fins has been investigated to increase heat transfer performance ad to decrease friction loss using KRG modeling. Two non-dimensional variables, the ratio of the eight diameter of the pin-fins and ratio of the spacing between the pin-fins to diameter of the pin-fins selected as design variables. A rotating rectangular channel with staggered dimples on opposite walls are formulated numerically to enhance heat transfer performance. The ratio of the dimple depth and dimple diameter are selected as geometry variables.

• Journal of Power System Engineering
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• v.4 no.2
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• pp.11-16
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• 2000

Simultaneous quantitative measurements are made of the velocity fields for two-dimensional natural convection in a rectangular enclosure using PIV(Particle Image Velocimetry). The experiments are performed at a Prandtl number of 6.62, an aspect ratio of 1.0, Rayleigh numbers from $1.294{\times}10^6\;to\;3.8841{\times}10^6$, and angles of inclination of $0^{\circ},\;30^{\circ}\;and\;60^{\circ}$ inside a $30mm{\times}30mm{\times}8mm$ cavity made of an acrylic glass 10mm, with two isothermal copper walls kept at a prescribed temperature. The experimental results agreed very well with the numerical results. It was found that the flow consisted of a large double convection cell at angle of inclination of $60^{\circ}$.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.293-296
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• 2003

We report on the fabrication and field emission of carbon nanotube field emitters for mass spectrometer. Due to its high aspect ratio and mechanical strength, we use vertically aligned multi-wall carbon nanotubes prepared by thermal chemical vapour deposition as cathodes, Electrons emitted from a CNT are to ionize some sample molecules. We have successfully attained patterned carbon nanotubes grown on two-dimensional 0.7 mm by 0.7 mm Ni square blocks on Si. The emission characteristics show that the field emission initiates at 200 V.

• KIEAE Journal
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• v.8 no.3
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• pp.101-106
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• 2008

The use of daylighting has been increased recently due to energy and visual comfort. The aims of interior daylighting are to adequately illuminate visual tasks, to create an attractive visual environment, and to save electrical energy. Lightpipe can improve the distribution of light to interior spaces. This study aims to evaluate the comparative daylighting performance of lightpipe under different sky conditions with mock-up model, sized $6m{\times}6m{\times}4m$ ($w{\times}d{\times}h$). For the purpose, perpendicular lightpipe system was designed as 650 diameter, with an aspect ratio of 2. Totally 49 measuring points of and two of outdoor illuminance on the horizontal plane were monitored from 09:00 to 18:30 on April 29 and May 15 2008. Agilent data logger and photometric sensor were used. Light factor were used to analyse daylight performance under different sky condition. Under overcast sky condition and clear sky condition, the lightpipe system is suitable for KS recommendation level of illuminance.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.205-208
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• 2008

The wind load on building surface is numerically investigated. The geometry of target building is a square cross section and aspect ratio (height (H) to width (d)) is 6. On building surface, the pressure was measured, compared to obtained value from numerical simulation. The numerical simulations were done using URANS with three different turbulence models such as v2-f model, k-${\omega}$model, and k-${\varepsilon}$ model, respectively. The v2-f model showed the best agreement with experimental data in simulating mean pressure coefficients on front, rear and side surface. But unsteady characteristics of pressure history measured on surface is shown a discrepancy between experiment and numerical simulation.

• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.29-32
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• 2012

변장비의 변화가 사각실린더에 작용하는 유체력에 미치는 영향을 알기 위해 EDISON_열유체를 사용하여 수치해석을 하였다. 낮은 레이놀즈수 영역($100{\leq}Re{\leq}200$)에서 사각실린더의 변장비(W/H)를 0.5, 0.75, 1, 2로 변화시키며 해석을 수행하였고, 레이놀즈수와 변장비에 따른 스트로할수(St), 항력계수($C_D$), 양력계수($C_L$)를 비교하였다. 본 논문에서는 레이놀즈수와 실린더의 변장비가 스트로할수, 항력계수, 양력계수에 미치는 영향을 알아보는 데 중점을 두었다. 해석결과 레이놀즈수가 증가하고 변장비가 감소할수록 스트로할수, 항력계수, 양력계수가 증가하는 것을 확인하였다. 본 논문을 통해서 레이놀즈수와 사각실린더의 변장비가 사각실린더에 작용하는 유체력에 영향을 미친다는 것을 알 수 있었다.

• Journal of Power System Engineering
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• v.11 no.4
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• pp.56-64
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• 2007

A numerical simulation is carried out mixed convection in horizontal channel with a heat source from below of rectangular cavity. Finite volume method was employed for the discretization and PISO algorithm was used for calculating pressure term. The parameters governing the problem are the Reynolds number ($10^{-2}{\leq}Re{\leq}50$), the Rayleigh number ($10^3{\leq}Ra{\leq}2.06{\times}10^5$), the Prandtl number ($0.72{\leq}Pr{\leq}909$), the aspect ratio ($0.5{\leq}AR=W/H{\leq}2$) and the angle of inclination ($0^{\circ}{\theta}60^{\circ}$). Mean Nusselt number distributions were obtained and effect of Reynolds number, Rayleigh number and Prandtl number on mixed convection in the horizontal channel with rectangular cavity were investigated.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.483-488
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• 2005

The complex three-dimensional miniature components are needed for a wide range of applications from the aerospace to the biomedical industries. To manufacture these products, micro machining that can make a high aspect ratio part and has good accuracy is widely researched. In this paper, cutting characteristics were analyzed in micro machining using cutting force coefficients, which are the specific cutting force for normal and frictional direction of rake surface. From measured cutting force in micro end milling, cutting condition independent cutting force coefficients were determined and used for analysing the characteristics of micro cutting. Using the cutting force coefficient, 써써써.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.113-116
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• 2006

Some nano hair systems in the nature are found to show excellent adhesive characteristic, which is called dry adhesive, and synthetic nano hairs to mimic these adhesiveness are believed to have many applications. To develop a practical synthetic dry adhesive system, we mold nano hairs on plastic substrates using thermoplstic materials including COC, PP, PC and PMMA. and estimate the moldability and the adhesive characteristic. As a template for molding nano hairs, AAO membrane is first adopted, which is 60um thick and 13mm in diameter. This membrane has about a billion of through-holes of which diameter is around 200nm. This AAO membrane and the pellet of materials are stacked in the mold and pressed to mold after heating up to be melted. The AAO membrane is removed using KOH to obtain the molded nano hairs. As a result, the diameter of the molded hairs is around 200nm and the length is $2um{\sim}60um$ depending on the molding conditions and materials. The molded nano hair substrates is estimated to show much better adhesive characteristic than a substrate without nano hairs.