• 대한기계학회논문집
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• 제16권10호
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• pp.1915-1927
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• 1992

본 연구에서는 3차원 압축성 내부유동해석 코드를 개발하여 터어빈 정익이나 동익 내부의 차원 익렬 유동을 수치적으로 해석하고자 한다. 여기에서 사용된 코드 는 Obyashi의 LU-ADI기법을 이용한 기존의 2차원 익렬 유동해석 코드를 3차원 유동장 으로 학장한 것이고, 난류유동해석에는, Baldwin-Lomax의 박층 대수모델을 3차원으로 확장한 알고리즘을 적용하였다.Kiock등이 실험한 선형 터어빈 익렬 내부의 천음속 유동장에 적용하여 양끝 벽면에 의한 3차원 유동장 특성을 분석하고, 3차원 익렬 유동 코드의 적합성을 검토하였다.

• 한국항공우주학회지
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• 제34권12호
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• pp.18-24
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• 2006

슬롯과 다공판을 이용한 충격파와 난류 경계층 간섭유동의 피동제어에 관한 연구가 수행되었다. 슬롯의 다양한 형상 변화가 간섭유동에 미치는 영향이 관찰되었으며, 이를 위하여 간섭유동 후방에서 피토/벽압력 분포 및 쉴리렌, 유맥선, 오일막 간섭 줄무늬 형상과 같은 유동가시화 결과 등이 얻어졌다. 유동방향의 슬롯의 경우 간섭유동 후방에서 제어되지 않은 경우와 비교하여 보다 높은 피토압력이 국소적으로 관찰되었으나, 폭방향 슬롯제어는 전체적으로 제어되지 않은 경우에 비하여 피토압력 크기에서 큰 장점을 보이지 않았다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.260-263
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• 2005

The effects of internal manifold designs the reactant feed-stream in Polymer Electrolyte Fuel Cells (PEFCs) is studied to figure out mass flow-distribution patterns over an entire fuel cell stack domain. Reactants flows are modeled either laminar or turbulent depending on regions and the open channels in the bipolar plates are simulated by porous media where permeability should be pre-determined for computational analysis. In this work, numerical models for reactant feed-stream in the PEFC manifolds are classified into two major flow patterns: Z-shape and U-shape. Several types of manifold geometries are analyzed to find the optimal manifold configurations. The effect of heat generation in PEFC on the flow distribution is also investigated applying a simplified heat transfer model in the stack level (i.e. multi-cell electrochemical power-generation unit). This modeling technique is well suited for many large scale problems and this scheme can be used not only to account for the manifold flow pattern but also to obtain information on the optimal design and operation of a PEMC system.

• 동력기계공학회지
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• 제20권1호
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• pp.69-74
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• 2016

The local heat transfer and pressure drops of developed turbulent flows in the convergent channels with square cross-sectional areas along the streamwise distance have been investigated experimentally. Four different parallel angled ribs (a = $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$) are placed to the one sided wall only, respectively. The ribbed walls are manufactured with a fixed rib height (e)=10 mm and the ratio of rib spacing (p) to height (e) = 10. The measurement was run within the range of Reynolds numbers from 22,000 to 79,000. The result shows that the increases in the Nusselt numbers for the flow attack angles can be seen in the order of $30^{\circ}$, $45^{\circ}$, $60^{\circ}$ and $90^{\circ}$.

• 한국강구조학회 논문집
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• 제10권4호통권37호
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• pp.801-811
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• 1998

본 논문은 풍동실험을 통하여 ${\pi}$형단면을 가지는 강합성사장교의 공기역학적 특성과 제진방법에 대한 연구이다. 제진장치로는 Fairing, Extension, Post, Flap 등이 사용되었고, 가장 효과적인 개선단면을 선정하여 영각, 감쇠비와 난류실험을 수행하여 내풍안정성을 평가하였다. 실험결과 선정된 개선단면에서 공기역학적 내풍안정성이 향상되었고 공기역학적특성이 규명되었다. 따라서 본 연구에서 수행된 ${\pi}$형단면은 내풍설계의 기초 자료로 활용될 수 있을 것이다.

• 한국유체기계학회 논문집
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• 제3권1호
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• pp.19-27
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• 2000

A numerical study is presented for analysis of three-dimensional incompressible turbulent flows in a multi-blade centrifugal fan. Reynolds-averaged Navier-Stokes equations with a standard $k-{\espilon}$ turbulence model are discretized with finite volume approximations. The computational area is divided into three blocks; inlet core, impeller and scroll parts, which are linked by a multi-block method. The flow inside of the fan is regarded as steady flow, and the mathematical models for the impeller forces were established from a cascade theory and measured data. Empirical coefficients are obtained comparing between computational and experimental results for the case without scroll, and are employed to simulate the flow through the impeller with scroll. In comparisons with experimental data, the validity of the mathematical models for the impeller forces was examined. The characteristics of the flow in the scroll were also discussed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.49-55
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• 2004

This paper addresses a numerical simulation of the flow and heat transfer in a simplified model of helically coiled tube steam generator using a general purpose computational fluid dynamic analysis computer code. The steam generator model is comprised of a cylindrical shell and helically coiled tubes. A cold feed water entered the tubes is heated up, evaporates. and finally become a superheated steam with a large amount of heat transferred continuously from the hot compressed water at higher pressure flowing counter-currently through the shell side. For the calculation of tube side two-phase flow field formed by boiling, inhomogeneous two-fluid model is used. Both the internal and external turbulent flows are simulated using the standard k-e model. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. The numerical calculations are peformed for helically coiled tubes of steam generator at an integral type pressurized water reactor under normal operation. The effects of tube-side inlet flow velocity are discussed in details. The results of present numerical simulation are considered to be physically plausible based on the data and knowledge from previous experimental and numerical studies where available.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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• pp.42-48
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• 1998

Numerical study is presented for the analysis of three-dimensional incompressible turbulent flows in multiblade centrifugal fan. Reynolds-averaged Navier-Stokes equations with standard k - $\epsilon$ turbulence model are transformed to non-orthogonal curvilinear coordinates, and are discretized with finite volume approximations. Linear Upwind Differencing Scheme(LUDS) is used to approximate the convection terms in the governing equations. SIMPLEC algorithm is used as a velocity-pressure correction procedure. The computational area is divided into three blocks; core, impeller and scroll, which are linked by multi-block method. The flow inside of the fan is regarded as steady flow, and mathematical formula established from the cascade theory and empirical coefficient are employed to simulate tile flow through the impeller. From comparisons between the computational results and the experimental data, the validity of the mathematical formula for the blade forces was examined and good results were obtained qualitatively. Hence, we can get the flow characteristics of multi-blade centrifugal fan and it will be a corner stone of the development of the multiblade centrifugal fan.

• Nuclear Engineering and Technology
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• 제31권3호
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• pp.267-275
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• 1999

This paper deals with the industrial problem of thermal striping damage on the French prototype fast breeder reactor, Phenix and it was studied in coordination with the research program of IAEA. The thermomechanical and fracture mechanics evaluation procedure of thermal striping damage on the tee-junction of the secondary piping using Green's function method and standard FEM is presented. The thermohydraulic(T/H) loading condition used in the present analysis is the random type thermal loads computed by T/H analysis on the turbulent mixing of the two flows with different temperatures. The thermomechanical fatigue damage was evaluated according to ASME code section 111 subsection NH. The results of the fatigue analysis showed that fatigue failure would occur at the welded joint within 90,000 hours of operation. The assessment for the fracture behavior of the welded joint showed that the crack would be initiated at an early stage in the operation. It took 42,698.9 hours for the crack to propagate up to 5 mm along the thickness direction. After then, however, the instability analysis, using tearing modulus, showed that the crack would be arrested, which was in agreement with the actual observation of the crack. An efficient analysis procedure using Green's function approach for the crack propagation problem under random type load was proposed in this study. The analysis results showed good agreement with those of the practical observations.

• 동력기계공학회지
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• 제10권3호
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• pp.17-22
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• 2006

Surface modifications like rib-roughening and displaced insert devices like the twisted tape are commonly used in applications such as compact heat exchangers and cooling systems. In this paper, regionally averaged heat transfer distributions in square channels with twisted tape inserts and with twisted tape inserts plus interrupted ribs are respectively investigated. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. Each wall of the square channel is composed of isolated aluminum sections. Regionally averaged Nusselt number and channel averaged Nusselt number in turbulent air flows are presented for Reynold numbers from 8,900 to 29,000. We have obtained the following conclusions from the experimental study: 1) The local Nusselt number in the two-sided heated case is higher than that in the four-sided heated condition. 2) In the 4 heating wall channel with twisted tape inserts, Nusselt number based on bottom wall temperature is enhanced by 1.2 - 1.6 times if adding the axial interrupted ribs on the bottom wall only. 3) The twisted tape with interrupted ribs under the two-sided heating condition produces the highest heat transfer coefficient.