• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.431-436
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• 2013

본 연구에서는 정사각형으로 모델링 된 실린더 주위에 균일한 유동이 흐를 때, 나타나는 이차원 층류 유동을 분석하였다. EDISON_CFD를 이용하여 각도의 변화에 따른 사각 실린더의 박리점에 의한 주위 유동 현상을 해석하였다. 격자 분해능과 시간 간격에 따른 정확성을 분석하였다. 각도의 변화에 따른 정사각 실린더의 양력계수와 항력계수를 확인하였다. 또한 한 주기의 자료값을 평균한 유동에서 박리점의 위치 변화와 주 와흘림의 길이를 분석하였다.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.131-136
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• 2002

A computational analysis using Reynolds stress model in FLUENT is conducted to give a clear understanding of the effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan at design condition ($\phi$=0.25) and off-design condition ($\phi$=0.21 and 0.30). The roll-up of tip leakage flow starts near the minimum static wall pressure position, and the tip leakage vortex developes along the centerline of the pressure trough within the blade passages. Near tip region, a reverse flow induced by tip leakage vortex has a blockage effect on the through-flow. As a result, high momentum region is observed below the tip leakage vortex. As the blade loading increases, the reverse flow region is more inclined toward circumferential direction and the onset position of the rolling-up of tip leakage flow moves upstream. Because the casing boundary layer becomes thicker, and the mixing between the through-flow and the leakage jet with the different flow direction is enforced, the streamwise vorticity decays more fast with blade loading increasing. The computational results show that a distinct tip leakage vortex is observed downstream of the blade trailing edge at $\phi$=0.30, but it is not observed at $\phi$=0.21 and 0.25.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.12
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• pp.850-856
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• 2007

In a supercooled or capsule type ice storage system, aqueous solution (or water) may have trouble with non-uniform dissolution though the system contributes to the simplicity of system and ecological improvement. The non-uniform dissolution increases the instability of the system because it may cause an ice blockage in pipe or cooling part. In order to observe the supercooled state, a cooling experiment was performed with pressurization to an ethylene glycol(EG) 3 mass% solution in stationary state. Also, the effect of the pressurization from 101 to 505 kPa to the dissolution of supercooled aqueous solution was measured with the dissolution time of the supercooled aqueous solution at a fixed cooling rate of brine. At results, the dissolution of supercooled point decreased as the pressure of the aqueous solution in the vessel increased. Moreover, the dissolution point increased as the heat flux for cooling increased.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.140-150
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• 2004

In this study, the effect of relative position of the blade for the fixed vane has been investigated on blade surface heat transfer. The experiments were conducted in a low speed stationary annular cascade, and heat transfer of blade was examined for six positions within a pitch. Turbine test section has one stage composed of sixteen guide vanes and blades. The chord length of the tested blade is 150 mm and the mean tip clearance of the blade having flat tip is about $2.5\%$ of the blade chord. For the detailed mass transfer measurements on the blade surfaces, a naphthalene sublimation technique was used. The inlet flow Reynolds number is fixed to $1.5{\times}10^5$. Complex heat transfer characteristics are observed on the blade surface due to various flow characteristics, such as separation bubble, relaminarization, transition to turbulence and leakage vortices. The distributions of velocity and turbulence intensity change significantly with the relative position due to the blockage effect of the blade. This causes the variation of heat transfer patterns on the blade surface. The results show that the flow near the leading edge get highly disturbed and deflected toward the either side of the blade when the blade leading edge is positioned close to the trailing edge of the vane. Therefore, separation bubble disappears on the pressure side and overall heat transfer on the relaminarization region is increased. But, due to reduced tip gap flow at the upstream region, the effect of leakage flow on the upstream region of the blade surface is weakened. Thus, the heat transfer characteristics significantly change with the blade positions.

• Water for future
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• v.25 no.3
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• pp.65-77
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• 1992

The purpose of this study is to analyse existing hysteresis models and to propose a new type of model. The existing hysteresis models are classified by three types: interpolation model, scaling model and domain model, of which the domain model is based on the theoretical approach. Models which need one branch of hysteresis loop for calibration are developed based on the independent domain concept, however, they are not successful to accurately simulate the real data and Rubicon Sandy Loam and Dune Sand. There is a possibility that a new model is based on the dependent domain model considering the pore blockage effect against air entry for homogeneous porous media(modelIII-1, Mualem, 1984). Concludingly, a new type of hysteresis model is proposed by simplifying ModelIII-1 using a proper assumption.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.258-263
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• 2002

A numerical analysis using 2-D unsteady compressible program is conducted to explain characteristics of rotating stall such as rotating speed and number of stall cells in an one-stage axial compressor. Unlike an axial compressor which has only a rotor, in one-stage axial compressor a rotating stall is generated by rotor/stator interaction and tack pressure rising without any artificial disturbance and modeling. As a back pressure is raised, the separation of suction side at blades is increased uniformly, but because of the discrepancy of blockage effect by stator, the disturbances are generated to form a stall cell. Once the stall cell is formed, regularly the stall cell are rotating through rotor blades. When the speed of rotor is design speed the rotating speed of stall cell is $83.3\%$ of rotor rotating speed. When the speed of rotor is $80\%$ of design speed, the speed of rotating stall is $88.2\%$ of rotor speed. The number of generated stall cell are also varied for rotor speed and back pressure.

• The KSFM Journal of Fluid Machinery
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• v.19 no.6
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• pp.5-13
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• 2016

Three-dimensional unsteady numerical analysis has been performed to observe aerodynamic characteristics of a H-rotor. Generally, the structure of the H-rotor is simple but the aerodynamic characteristics are exceptionably complicated since the angle of attacks and incident velocities to a blade are considerably varied according to the azimuth angles and solidities. The blade in the upwind revolution between 0 to 180 degree obtains aerodynamic energy from the free stream but the blade in the downwind revolution between 180 to 360 degree does not. When the rotating speed increases, the blade in the downwind revolution accelerates the air around the blade like a fan and it consumes the energy and shows negative torque in the area. On the other hand, the direction of the free stream is bent because of the interaction between blade the free stream. Therefore, the operation point (highest power coefficient) appears at a lower tip-speed-ratio what it is expected.

• Journal of computational fluids engineering
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• v.19 no.4
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• pp.61-67
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• 2014

Since the most of the existing non-Newtonian models are not adequate to apply to the lattmce Boltzmann method, it is a challenging task from both the theoretical and the numerical points of view. In this research the hydro-kinetic model was modified and applied to the 3-D moving sphere in the circular channel flow and the characteristics of the shear thinning effect by the HK-model was evaluated and the condition of ${\Gamma}$ in the model was suggested for the stable simulation to generate non-trivial prediction in three dimension strong shear flows. On the wall boundaries of circular channel the curved wall surface treatment with constant velocity condition was applied and the bounceback condition was applied on the sphere wall to simulate the relative motion of the sphere. The condition is adequate at the less blockage than 0.7 but It may need to apply a multi-scale concept of grid refinement at the narrow flow region. to obtain the stable numerical results.

• Journal of Korean Society for Atmospheric Environment
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• v.14 no.3
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• pp.219-228
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• 1998

In the present investigation, a numerical model developed for the prediction of the wind flow over complex terrain is validated by comparing with the field experiments. For the solution of the Reynolds - Averaged Clavier- stokes equations which are the governing equations of the microscale atmospheric flow, the model is constructed based on the finite-volume formulation and the SIMPLEC pressure-correction algorithm for the hydrodynamic computation. The boundary- fitted coordinate system is employed for the detailed depiction of topography. The boundary conditions and the modified turbulence constants suitable for an atmospheric boundary- layer are applied together with the k- s turbulence model. The full- scale experiments of Cooper's Ridge, Kettles Hill and Askervein Hill are chosen as the validation cases . Comparisons of the mean flow field between the field measurements and the predicted results show good agreement. In the simulation of the wind flow over Askervein Hill , the numerical model predicts the three dimensional flow separation in the downslope of the hill including the blockage effect due to neighboring hills . Such a flow behavior has not been simulated by the theoretical predictions. Therefore, the present model may offer the most accurate prediction of flow behavior in the leeside of the hill among the existing theoretical and numerical predictions.

• Journal of Applied Biological Chemistry
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• v.56 no.2
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• pp.61-67
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• 2013

Due to their diversity and abundancy, marine resources have emerged as important biological resources to compensate the limited sources of terrestrial biological materials. Phaeodactylum tricornutum (PT) is one of classical model diatoms most widely studied for its ecology, physiology, biochemistry and molecular biology. In this study, four different PT extracts on lipopolysaccharide (LPS)-stimulated macrophages were compared for anti-inflammatory effect and investigated for the underlying mechanisms. The extracts of PT inhibited nitric oxide production from LPS stimulated RAW 264.7 cells in a dose dependent manner. These extracts also inhibited the expression of mRNA and production of proteins of pro-inflammatory cytokines such as interleukin (IL)-$1{\beta}$, IL-6 and tumor necrosis factor-${\alpha}$. These inhibitory effects were found to be caused by blockage of nuclear factor-${\kappa}B$ activation and phosphorylation of p38 mitogen-activated protein kinases, extracellular signal-regulated kinases 1 and 2 and c-Jun N-terminal kinase.