• International Journal of Fluid Machinery and Systems
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• 제2권3호
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• pp.215-222
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• 2009

Jets issuing through small holes in a wall into a freestream has proven effective in the control of flow separation. This technique is known as the vortex generator jet (VGJs) method. If a precursor signal of separation is found, the separation control system using VGJs can be operated just before the onset of separation and the flow field with no separation is always attained. In this study, we measured the flow field and the wall static pressure in a two-dimensional diffuser to find a precursor signal of flow separation. The streamwise velocity measurements were carried out in the separated shear layer and spectral analysis was applied to the velocity fluctuations at some angles with respect to the diffuser. The pattern of peaks in the spectral analysis changes as the divergence angle increases over the angle of which the whole separation occurs. This change in the spectral pattern is related to the enhancement of the growth of shear layer vortices and appears just before the onset of separation. Therefore, the growth of shear layer vortices can be regarded as a precursor signal to flow separation.

• Journal of Advanced Marine Engineering and Technology
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• 제38권2호
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• pp.147-153
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• 2014

The centrifugal oil purifier is used in an engine for lubrication and to remove impurities. The momentum needed for the rotation of the cylindrical chamber is obtained by jet injections. An impure particle in the oil is separated by the centrifugal forces moving to the inner wall of the rotating cylindrical chamber body. The dust particles are eliminated when the particles are absorbed onto the surface of the inner wall of the chamber body. The flow characteristics and the physical behaviors of particles in this centrifugal oil purifier were investigated numerically and the filtration efficiencies was evaluated. For calculations, a commercial code is used and the SST (Shear Stress Transport) turbulence model has been adopted. The MFR (Multi Frames of Reference) method is introduced to consider the rotating effect of the flows. Under various variables, such as particle size, particle density and rotating speed, the filtration efficiencies are evaluated. It has been verified that the filtration efficiency is increased with the increments in the particle size, the particle density and the rotating speed of the cylindrical chamber.

• 한국수정란이식학회지
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• 제32권4호
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• pp.325-329
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• 2017

A 2-year-old female Maltese dog was admitted with a history of pyometra and resulting peritonitis and septicemia. Uterine specimen sampled by ovariohysterectomy was processed routinely for histopathological observation. Grossly, the uterine mucosa was covered with necrotic debris and on the cut surface, lesion extended into the uterine wall. Microscopically, severe necrosis was observed throughout thickened mucosa, submucosa, and wall of uterus. Tumorous lesions composed of anaplastic cells with bizarre nuclei or tubular structures of cuboidal to short columnar cells were infrequently observed around the necrotic lesions and muscular layer far from necrotic areas. Immunohistochemically, central necrotic area with ambiguous cell and tissue structures, peri-necrotic tumor lesions, and muscular layer were strongly positive for cytokeratin. Since huge necrosis of adenocarcinoma lesions in this case made it difficult to diagnose, immunohistochemical results enable to diagnose as a severe necrotizing adenocarcinoma. Thus, histopathological and immunohistochemical findings in this case may serve as an important knowledge to diagnose uterine adenocarcinoma with huge necrosis in the veterinary field.

• 한국가시화정보학회지
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• 제18권2호
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• pp.28-34
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• 2020

In this study, we numerically investigated the thermal stratification in solar seasonal thermal storage tanks. The vertical in/out flows were unsuitable for the thermal stratification in a large scale. The effect of an aspect ratio (AR) on the thermal stratification was investigated. When AR was less than 2, water adheres and flows along the upper wall due to buoyance and the surface effect. Thereafter, hot water flows down and a large scale vortex occurs in entire tank. For high AR, jet flows ejected from the inlet pipe impinges to the opposite wall and splits. The divided flows create two vortex flows in the upper and lower regions. These different flows strongly influence temperature and thermal stratification. The thermal stratification was evaluated in terms of the thermocline thickness and degree of stratification. Compared to ARs, the maximum degree of stratification was obtained with AR of 5 having the minimum thermocline thickness.

• 한국식품과학회지
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• 제28권6호
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• pp.1078-1083
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• 1996

쌀보리를 정맥기를 사용하여 도정한 정맥에 대해 제분기의 종류를 달리하여 제분한 결과 보리가루는 입도 분포에서 차이를 나타내 Jet mill로 제분한 보리가루의 입자 크기가 가장 작았으며 그 다음으로 Pin mill과 Cyclotec sample mill에 의한 입자 크기가 작았고 Ball mill과 Fitz mill에 의한 보리가루가 가장 큰 것으로 나타났다. 보리가루는 입자크기가 작을수록 색이 밝고 전분 손상도가 높은 경향을 나타냈다. 보리가루의 표면구조는 크고 작은 전분 입자, 주름진 세포벽 물질 등으로 관찰되었으며 가루 입자의 형태 및 크기가 제분기의 종류에 따라 다소 차이를 나타냈다. 보리가루는 손상된 전분의 양이 많을수록 높은 수분흡수지수 및 보수력을 나타냈으며 수분용해도지수 역시 증가하는 경향을 보여주었다. 보리가루의 호화 특성을 측정한 결과 보리가루의 점도는 입자가 크게 분쇄된 Fitz mill에 의한 보리가루에서 가장 낮았으며 Pin mill과 Cyclotec mill에서 높게 나타났다. 아주 미세하게 분쇄된 Jet mill은 호화가 빨리 진행된 반면 점도의 상승은 크지 않아 지나친 전분의 손상은 점도를 떨어뜨리는 것으로 판단되었다.

• 한국터널지하공간학회 논문집
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• 제23권6호
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• pp.535-547
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• 2021

국내에서는 수소경제 활성화 정책을 수립하고 수소사회 실현을 위해 수소 인프라 및 수소차 보급 확대를 계획 하고 있다. 이에 따라 수소차의 보급이 급속도로 이루어질 것으로 예상되며, 동시에 수소차의 사고에 대응하기 위한 대책의 확립이 요구되고 있다. 본 연구에서는 수소차에 의해서 발생되는 수소 제트화염이 터널 내부 벽체에 미치는 영향과 내부 복사열 특성 분석을 위해 실험적 연구를 수행하였다. 실험은 수소차에서 발생되는 조건과 동일하게 하기 위해 분사압력을 700 bar로 설정하고, 분사노즐 직경은 1.8 mm로 설정하였다. 또한, 일반 터널에 적용되고 있는 콘크리트 압축강도 40 MPa의 터널 내화 시험체를 제작하고 제트화염 분사노즐과 시험체간의 이격거리에 따른 영향을 검토하였다. 분사노즐과 터널 내화시험체의 이격거리를 변수로 하여 2 m와 4 m에 대해 결과를 분석하였다. 그 결과로부터 시험체 내부 최대 온도는 1,349.9℃ (이격거리 2 m)가 측정되었고, 제트화염 주위 복사열은 최대 39.16 kW/m²까지 나타났다.

• Wind and Structures
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• 제14권4호
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• pp.285-300
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• 2011

Researchers at the International Hurricane Research Center (IHRC), Florida International University (FIU), are working in stages on the construction of a large state-of-the-art Wall of Wind (WoW) facility to support research in the area of Wind Engineering. In this paper, the challenges of simulating hurricane winds for the WoW are presented and investigated based on a scale model study. Three wind profiles were simulated using airfoils, and/or adjustable planks mechanism with and without grids. Evaluations of flow characteristics were performed in order to enhance the WoW's flow simulation capabilities. Characteristics of the simulated wind fields are compared to the results obtained from a study using computational fluid dynamics (CFD) and also validated via pressure measurements on small-scale models of the Silsoe cube building. Optimal scale of the test model and its optimal distance from the WoW contraction exit are determined - which are two important aspects for testing using an open jet facility such as the WoW. The main objective of this study is to further the understanding of the WoW capabilities and the characteristics of its test section by means of intensive tests and validations at small scale in order to apply this knowledge to the design of the full-scale WoW and for future wind engineering testing.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1997년도 제15회 KOSCO SYMPOSIUM 논문집
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• pp.51-60
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• 1997

축대칭 곡면벽 제트 버너를 제작하여 화염의 안정화 특성을 실험적으로 연구하였다. 축대칭 곡면벽 제트 유동은 난류 강도의 증가와 더불어 버너 선단 부근에 재순환 영역을 형성하여 화염의 안정화를 촉진시킴으로서 기존의 튜브 버너에 비하여 화염의 안정화 특성이 향상되었다. 시간적으로 화염의 위치가 변동하는 난류 화염에서 화염의 안정화 특성과 밀접한 관계가 있는 OH 라디칼과 온도를 PLIF와 CARS를 각각 적용하여 측정하였다. 고유속으로 연소시키는 경우에 버너 선단에 형성된 재순환 영역에 OH 라디칼이 상당량 분포하고 있었으며 통계적으로 고온을 유지하였다. 이는 버너 선단에 형성되는 재순환 영역에 고온의 기연 가스가 점화원 역할을 하여 화학 반응이 활발하게 일어나고 있음을 의미한다. 이러한 결과로부터 고속의 출구유속에서 화염 안정화 특성은 재순환 영역에 의하여 영향을 받고 있음을 확인하였다.

• 한국전산유체공학회지
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• 제8권2호
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• pp.1-7
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• 2003

The V2F turbulence model, which has shown very good performance in several test cases at low speeds, has been applied to supersonic ramp flow with 20. corner angle at the free stream Mach number of 2.79. The flow is known to manifest strong shock wave/turbulent boundary layer interactions. As a comparative study, low-Reynolds k-ε models are also considered. While the V2F model predicts wall-pressure distribution well, it relatively predicts larger separation bubble and higher skin-friction after the reattachment than the experimental data. Although the ellpticity of f equation is the characteristics of incompressible flows, the converged solutions are acquired in the compressible flow with shock waves. The effect of the realizability constraints used in the model is also examined. In contrast to the result of impinging jet flows, the realizability bounds proposed by Durbin deterioate the overall solutions of the supersonic ramp flow.

• 대한기계학회논문집B
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• 제32권7호
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• pp.536-541
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• 2008

The Flow characteristics of a ship's propulsion mechanism of Weis-Fogh type, in which a airfoil(NACA0010) moves reciprocally in a channel, were investigated by the PIV. Velocity vectors and velocity profiles around the operating and stationary wings were observed at opening angles of ${\alpha}=15^{\circ}$ and $30^{\circ}$, velocity ratios of $V/U=0.5{\sim}1.5$ and Reynolds number of $Re=0.52{\times}104{\sim}1.0{\times}104$. As the results the fluid between wing and wall was inhaled in the opening stage and was jet in the closing stage. The wing in the translating stage accelerated the fluid in the channel. And the flow fields of this propulsion mechanism were unsteady and complex, but those were clarified by flow visualization using the PIV.