• 대한기계학회논문집
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• 제18권3호
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• pp.645-652
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• 1994

The leading edge of a turbine blade was simulated as a circular cylindrical surface. The effect of free-stream turbulence on the mass transfer upstream of the injectionhole has been investigated experimentally. The effects of injection location, blowing ratio on the Sherwood number distribution were examined as well. The mass transfer coefficients were measured by a naphthalene sublimation technique. The free-stream Reynolds number based on the cylinder diameter is 53,000. Other conditions investigated are: free-stream turbulence intensities of 3.9% and 8.0%, injection locations of $40^{\circ}$, $50^{\circ}$, and $60^{\circ}$ from the front stagnation point of the cylinder, and blowing ratios of 0.5 and 1.0. The role of the horseshoe vortex formed upstream edge of the injected jet is dicussed in detail. When the blowing ratio is unity, and the coolant jet is injected at $40^{\circ}$, the mass transfer upstream of the jet is not affected by the coolant jet at all. On the other hand, when the injection hole is located beyond $50^{\circ}$, the mass transfer upstream edge of the injection hole suddenly increases due to the formation of the horseshoe vortex, but it dereases as the free-stream turbulence intensity increases because the strength of the horseshoe vortex structure becomes weakened. The role of the horseshoe vortex is clearly evidenced by placing a rigid rod at the injection hole instead of issuing the jet. In the case of the rigid rod, the spanwise Sherwood number upstream of the injection hole is much larger due to the intense influence of the horseshoe vortex.

• Wind and Structures
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• 제30권6호
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• pp.547-558
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• 2020

With the development of economy and construction technology, more and more bridges are built in complex mountainous areas. Accurate assessment of wind parameters is important in bridge construction at complex terrain. In order to investigate the wind characteristics in the high-altitude difference area, a complex mountain terrain model with the scale of 1:2000 was built. By using the method of wind tunnel tests, the study of wind characteristics including mean wind characteristics and turbulence characteristics was carried out. The results show: The wind direction is affected significant by the topography, the dominant wind direction is usually parallel to the river. Due to the sheltering effect of the mountain near the bridge, the wind speed and wind attack angle along the bridge are both uneven which is different from that at flat terrain. In addition, different from flat terrain, the wind attack angle is mostly negative. The wind profiles obey exponential law and logarithmic law. And the fitting coefficient is consistent with the code which means that it is feasible to use the method of wind tunnel test to simulate complex terrain. As for turbulence characteristics, the turbulence intensity is also related to the topography. Increases sheltering effect of mountain increases the degree of breaking up the large-scale vortices, thereby increasing the turbulence intensity. Also, the value of turbulence intensity ratio is different from the recommended values in the code. The conclusions of this study can provide basis for further wind resistance design of the bridge.

• 대한기계학회논문집B
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• 제25권10호
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• pp.1417-1426
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• 2001

Turbulent flow characteristics in the near wake of a square cylinder have been studied experimentally by using a Digital PIV method. Experiments are performed at the Reynolds numbers of 1600 and 3900 based on the free-stream velocity and the square height. The ensemble averaged turbulence statistics are acquired from 2030 realizations of instantaneous fluctuating velocity field after the conventional Reynolds decomposition. The differences in turbulent intensity and Reynolds shear stress profiles fur both oases indicate that the effect of Reynolds number seems to be descernible mainly due to the occurrence of transition in the separated shear layer. Because of the periodic nature of vortex shedding process, transverse velocity fluctuations contribute dominantly , to turbulent kinetic energy distribution. A comparison with previous LDV data obtained at much higher Reynolds number shows a fairly good agreement each other. It turns out that the effect of Reynolds number diminishes as increasing Reynolds number, which is a well-known feature of a sharp-edged bluff body wake. The streamwise variation of turbulence intensities are compared with those from a circular cylinder along the centerline at the same Reynolds number. The overall magnitudes and the decay rates of turbulence intensities are quite similar, but some differences are noticeble especially in the transverse intensity variation.

• 한국해안해양공학회지
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• 제8권1호
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• pp.28-36
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• 1996

조류와 취송류의 비선형 상호작용에 대한 연직확산계수의 영향을 점모형을 이용하여 살펴보았다. q$^2$-q$^2$1 난류모형을 난류운동에너지의 생성과 감쇄가 균형을 이룬다는 가정 하에 단순화한 0-방정식 난류모형을 도입하고 마찰수심의 영향을 적절히 반영하도록 수정하여 연직확산계수를 산정하였다. 0-방정식 난류모형의 유도과정과 전향력 항이 포함됨으로써 공진이 발생될 수 있음을 제시하였다. 왕복성 수면경사력과 바람응력이 복합된 경우, 고려된 바람응력에 의한 조류 진폭의 변화는 무시할만한 크기였으나, 왕복성 수면경사력만에 의해서는 발생되지 않았던 2배조의 조류 성분이 파생되었다. 취송류의 연직구조는 조류에 의한 배경난류가 지배적인지의 여부에 따라 상당한 차이를 보였다. 따라서 황해와 같이 강한 조류가 존재하는 해역의 취송순환을 파악함에 있어 조류에 의한 배경난류를 무시할 경우는 실제와는 상당히 다른 결과가 나타날 수 있다.

• Wind and Structures
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• 제20권4호
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• pp.527-548
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• 2015

Aeroelastic wind tunnel experiments were conducted for conventional and tapered super-tall building models to investigate the effect of taper on fundamental aeroelastic behaviors in various incident flows. Three incident flows were simulated: a turbulent boundary-layer flow representing urban area; a low-turbulent flow; and a grid-generated flow. Results were summarized focusing on the effect of taper and the effect of incident flows. The suppression of responses by introducing taper was profound in the low-turbulence flow and boundary-layer flow, but in the grid-generated flow, the response becomes larger than that of the square model when the wind is applied normal to the surface. The effects of taper and incident flows were clearly shown on the normalized responses, power spectra, stability diagrams and probability functions.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.269-272
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• 2006

Numerical analysis of wind turbine scale effect was performed by using computational fluid dynamics. For the numerical analysis of wind turbine. Three dimensional Navier-Stokes solver with various turbulence models was tested and realizable k-e turbulence model was selected for the simulation of wind turbines. To validate the present method, performance of NREL (National Renewable Energy Laboratory) Phase VI wind turbine model was analyzed and compared with experiment and blind test data. Using the present method, numerical simulations for various size of wind tunnel model were carried out and characteristics were observed in detail. The power loss due to the interference between wind turbine and nacelle was also computed for relatively larger nacelle installation in wind tunnel test. The present results showed good correlations with experimental data and reasonable trends of scale effect of wind turbine.

• Journal of Advanced Marine Engineering and Technology
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• 제36권6호
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• pp.814-822
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• 2012

선박용 SCR 시스템에서 유동 및 혼합특성을 개선하기 위해 상하유도 및 스월 형상의 혼합기가 고려되었다. 본 연구의 목적은 혼합기 구조에 따른 난류강도 및 균일지수(Uniformity Index)를 상세히 분석하여 SCR 성능을 개선하는 것이다. 그 결과, 촉매부 전단에서의 농도균일도는 혼합기를 사용하였을 경우 약 5% 개선됨을 알 수 있었다. 상하유도형 혼합기의 사용에 따라 주위에서 높은 RMS 수치 및 상대난류강도를 보이지만, 하류로 진행하면서 두 값은 감소하는 경향을 보였다. 스월형 혼합기의 경우 유동의 진행에 대해 RMS 수치와 상대난류강도의 감소가 비교적 적고 상대난류강도의 경우 상대적으로 균일한 분포를 보였다. 두 혼합기에서 발생하는 유동특성에 의해 혼합효과 및 혼합거리가 달랐음을 알 수 있었다.

• Wind and Structures
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• 제13권6호
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• pp.557-580
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• 2010

A new inflow turbulence generation method and a combined dynamic SGS model recently developed by the authors were applied to evaluate the wind effects on 508 m high Taipei 101 Tower. Unlike the majority of the past studies on large eddy simulation (LES) of wind effects on tall buildings, the present numerical simulations were conducted for the full-scale tall building with Reynolds number greater than $10^8$. The inflow turbulent flow field was generated based on the new method called discretizing and synthesizing of random flow generation technique (DSRFG) with a prominent feature that the generated wind velocity fluctuations satisfy any target spectrum and target profiles of turbulence intensity and turbulence integral length scale. The new dynamic SGS model takes both advantages of one-equation SGS model and a dynamic production term without test-filtering operation, which is particular suitable to relative coarse grid situations and high Reynolds number flows. The results of comparative investigations with and without generation of inflow turbulence show that: (1) proper simulation of an inflow turbulent field is essential in accurate evaluation of dynamic wind loads on a tall building and the prescribed inflow turbulence characteristics can be adequately imposed on the inflow boundary by the DSRFG method; (2) the DSRFG can generate a large number of random vortex-like patterns in oncoming flow, leading to good agreements of both mean and dynamic forces with wind tunnel test results; (3) The dynamic mechanism of the adopted SGS model behaves adequately in the present LES and its integration with the DSRFG technique can provide satisfactory predictions of the wind effects on the super-tall building.

• 한국항행학회논문지
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• 제25권6호
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• pp.498-509
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• 2021

선행 항공기의 날개 끝단에서 발생하는 후류 요란으로 인해 후행 항공기는 정상적인 운항에 영향을 받을 수 있다. 현재는 항공기 최대이륙중량에 따라 4개의 카테고리로 분류하여, 기준 거리별 항공기 수평 분리를 적용하고 있다. FAA 및 EURO-CONTROL을 중심으로 항공기 후류 요란의 크기와 영향이 기존의 거리 분리치보다 더 작다는 것이 연구되었고, 이것을 바탕으로 분리 기준을 7개의 카테고리로 세분화한 규정(RECAT)이 제시되었다. 본 연구에서는 ICAO Doc. 10122의 초안을 이용하여 국내 공항의 RECAT 도입 필요 여부를 확인하고, 활주로 절대 수용량 계산 방법의 하나인 Harris 모델을 이용하여 인천국제공항의 절대 수용량을 산출하였다. 분석 결과 RECAT 도입에 따라 활주로 절대 수용량의 증가가 가능할 것으로 확인되었으며, 계산된 결과 및 계산에 활용한 방법은 국내 공항의 RECAT 도입 검토에 기본 자료로 활용될 수 있을 것이다.

• 대한기계학회논문집
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• 제18권11호
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• pp.3039-3045
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• 1994

The k-$\varepsilon$ turbulence models by Launder et al.(1977, LPS) and Leschziner and Rodi(1981, LR) are modified to account for the secondary straining effect with having a generality in the present paper. The modified models are obtained by replacing the gradient Richardson number used to account for the secondary straining effect in the original models by a new parameter with a tensor-invariant correction form. These two modified models are used to predict the turbulent flow over a backward-facing step. In contrast to both standard and modified LR models, the modified LPS model is found to predict the reattachment point fairy well, as well as mean velocity, wall static pressure, turbulent kinetic energy and Reynolds shear stress in the recirculating region.