• 한국농공학회지
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• 제34권E호
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• pp.30-44
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• 1992

A modification of the TEACH-like computer program based on the k-$\varepsilon$ turbulence transport was applied for predicting air mixing patterns and temperature distributions in a rectangular, slot-ventilated enclosure having obstructions ; a rectangular obstacle with heat flux, solid walls separates the passage and the pig pens, and purlins beneath the ceiling. Air flow patterns were calculated for the cases with and without the purlin, extending 300mm beneath the ceiling. Comparisons of prediction data of Randall & Battams(1976) showed air flow pattern predicted well for the case without the purlin. Heat was accumulated at the corner of the left side of the solid wall and the right-upper region of the simulated pigs. However the air distribution pattern was completely different from data for the case with the purlin. The deviation from the observation may be attributed to the difference of the geometric configuation. Exploring the cause of the deviation should be conducted in a further study. Temperature stratification was also observed due to incomplete mixing. The obstruction in the route of the inlet air jet at inlet should be avoided since most of kinetic energy dissipates at the abstacle duet to impingement.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.65-73
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• 2003

An experimental study on flame lift-off characteristics of propane jet flame highly diluted with nitrogen has been conducted introducing acoustic forcing with a tube resonant frequency. A flame stability curve is attained according to forcing strength and nozzle exit velocity for $N_2$ diluted flames. Flame lift-off behavior with forcing strength and nozzle exit velocity is globally categorized into three; a well premixed behavior caused by a collapsible mixing for large forcing strength, a coexistent behavior of well-premixed and edge flames interacting with well-organized inner fuel vortices for moderate forcing strengths, and edge flame behavior for small forcing strengths. Special focus is concentrated on the coexistent behavior of the flame base in lifted flame since this may give a hint to a possibility which the flame base behaves like a well-mixed premixed flame in highly turbulent lifted flames. It is also shown that the acoustic forcing to self-pulsating laminar lifted flame affects flame lift-off behavior considerably which is closely related to downstream flow velocity, mixture strength, effective fuel Lewis number, and flame stretch.

• 한국정밀공학회지
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• 제24권12호
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• pp.95-103
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• 2007

This paper presents a liquid cooling concept for heat rejection of high power electronic devices existing in notebook computers etc. The design, fabrication, and performance of the planar ECF pump and farced-liquid cooling system are summarized. The electro-conjugate fluid (ECF) is a kind of dielectric and functional fluids, which generates jet flows (ECF-jets) by applying static electric field through a pair of rod-like electrodes. The ECF-jet directly acts on the working fluid, so the proposed planar ECF pump needs no moving part, produces no vibration and noise. The planar ECF pump, consists of a pump housing and electrode substrate, achieves maximum flow rate and output pressure of $5.5\;cm^3/s$ and 7.2 kPa, respectively, at an applied voltage of 2.0 kV. The farced-liquid cooling system, constructed with the planar ECF pump, liquid-cooled heat sink and thermal test chip, removes input power up to 80 W keeping the chip surface temperature below $70\;^{\circ}C$. The experimental results demonstrate that the feasibility of forced-liquid cooling system using ECF is confirmed as an advanced cooling solution on the next-generation high power electronic devices.

• 한국추진공학회지
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• 제3권1호
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• pp.86-94
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• 1999

충격파가 초음속 수소-공기 제트화염의 화염 안정한계에 미치는 영향을 충격파의 강도와 위치를 변화시키면서 연구하였다. 이러한 목적으로 마하수 2.5의 초음속 연소기 벽면에 쐐기를 부착시켜 경사 충격파를 발생시켰다. 본 실험은 충격파가 초음속 화염에 미치는 영향을 연구한 최초의 실험연구이다. 쉬릴렌 가시화 사진과 벽면 정압, 화염 안정 한계를 측정하였으며 충격파가 없는 경우와 비교하였다. 보염 재순환 영역에 충격파를 적절히 간섭시킴으로써 화염 안정 한계가 대폭 개선되었다. 화염 안정한계가 대폭 향상된 이유는 충격파에 의해 발생한 역압력구배로 화염안정화에 중요한 아음속 재순환 영역의 크기가 증대된 때문으로 여겨진다.

• 한국유체기계학회 논문집
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• 제13권2호
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• pp.41-47
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• 2010

The effect of incidence angle on the three-dimensional flow and aerodynamic loss in the tip leakage flow region downstream of a turbine rotor cascade has been investigated for two tip gap-to-chord ratios of h/c=0.0% (no tip gap) and 2.0%. The incidence angle is changed to be $i=-10^{\circ}$, $0^{\circ}$, and $5^{\circ}$. The results show that for $i=5^{\circ}$, secondary flows including the passage vortex are intensified noticeably, and there is a strong interaction between the passage and tip leakage vortices. For $i=-10^{\circ}$, however, the passage vortex is weakened significantly, so that there exists only a strong leakage-jet-like secondary flows near the casing wall. For h/c=0.0% and 2.0%, aerodynamic loss tends to increase with increasing i from $-10^{\circ}$ to $5^{\circ}$. A small increment of i in its positive incidence range results in a remarkable aerodynamic loss increase, while increasing i in the negative incidence range leads to a small change in the aerodynamic loss generation.

• 대한기계학회논문집B
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• 제20권7호
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• pp.2267-2276
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• 1996

공정산업분야 및 분무연소분야에서 많이 사용되고 있는 2유체 분무기에서 출구 초음속유동의 가시화와 하류의 가스압력 측정 결과로부터 다음과 같은 결론을 얻었다. 1) 과소팽창 또는 과대팽창 초음속노즐 유동에서 출구 Mach수가 일정한 경우, 유동이 박리하지 않는다면 가스의 정체압력(유량)이 증가함에 따라 노즐출구에서 충돌정체점까지의 길이와 초음속 유동영역의 길이는 증가한다. 2) 스피팅 현상은 액체공급관 출구의 흡인압력은 분사가스압력이 증가함에 따라 단조증가하지만 분사가스압력이 0.5MPa이상이 되면 증감현상이 커지며 돌출형 노즐에서 유동박리시 급격히 증가한 다음 거의 일정하게 유지된다. 4) 액체공급관 하류축상의 압력변화는 출구의 음압에서 충돌정체점까지 상승한 다음 급강하하고 충격파 세포상의 구조에 따라 진동하면서 대기압에 도달한다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.135-140
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• 2006

충돌형(FOOF) 분사기의 불안정 영역을 결정하기 위해 질소분사 음향시험을 수행하였다. 파이프와 오리피스 형상을 가지는 분사기 내 산화제 부분에서 유동속도에 비례하고, 비정상적으로 jumping하는 특정 주파수를 가지는 whistling이 발생한다. 동일한 조건의 연소시험과 비교해 본 결과 whistling 현상은 연소현상에는 영향을 주지 않는다. 질소분사 음향시험과 연소시험에서 얻은 연소실 내 1T1L mode의 damping factor를 비교하여 불안정 영역을 구해보면, 비슷한 조건에서 불안정 영역을 가진다. 이것은 유동의 충돌, 혼합에 의한 유동불안정 현상이 연소시험에서 연소불안정을 발생시키는 주요한 인자임을 의미 한다.

• Advances in aircraft and spacecraft science
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• 제3권4호
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• pp.367-378
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• 2016

Thrust Vectoring is a dynamic feature that offers many benefits in terms of maneuverability and control effectiveness. Thrust vectoring capabilities make the satisfaction of take-off and landing requirements easier. Moreover, it can be a valuable control effector at low dynamic pressures, where traditional aerodynamic controls are less effective. A numerical investigation of Fluidic Thrust Vectoring (FTV) is completed to evaluate the use of fluidic injection to manipulate flow separation and cause thrust vectoring of the primary jet thrust. The methodology presented is general and can be used to study different techniques of fluidic thrust vectoring like shock-vector control, sonic-plane skewing and counterflow methods. For validation purposes the method will focus on the dual-throat nozzle concept. Internal nozzle performances and thrust vector angles were computed for several range of nozzle pressure ratios and fluidic injection flow rate. The numerical results obtained are compared with the analogues experimental data reported in the scientific literature. The model is integrated using a finite volume discretization of the compressible URANS equations coupled with a Spalart-Allmaras turbulence model. Second order accuracy in space and time is achieved using an ENO scheme.

• 한국해양공학회지
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• 제37권3호
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• pp.89-98
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• 2023

Analyzing the interactions of free surface waves caused by a submerged-body movement is important as a fundamental study of submerged-body motion. In this study, a two-dimensional mini-towing tank was used to tow an underwater body for analyzing the generation and propagation characteristics of free surface waves. The magnitude of the maximum wave height generated by the underwater body motion increased with the body velocity at shallow submerged depths but did not increase further when the generated wave steepness corresponded to a breaking wave condition. Long-period waves were generated in the forward direction as the body moved initially, and then short-period waves were measured when the body moved at a constant velocity. In numerical simulations based on potential flow, the fluid pressure changes caused by the submerged-body motion were implemented, and the maximum wave height was accurately predicted; however, the complex physical phenomena caused by fluid viscosity and wave breaking in the downstream direction were difficult to implement. This research provides a fundamental understanding of the changes in the free surface caused by a moving underwater body.

• 항공우주시스템공학회지
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• 제12권4호
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• pp.81-89
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• 2018

본 연구에서는 초음속 유동장 내 연료 분사시 연소기의 공간적인 제한 조건을 고려하여 복수의 분사기간 배치 간격을 변화시키고 그에 따른 유동 구조, 연료의 침투 거리 및 연료-공기의 혼합 특성을 비교 분석하였다. 이를 위하여 널리 알려진 단일 분사구를 이용한 실험 조건을 모사하여 적용된 수치 모델을 검토하였으며, 동일한 분사 조건을 갖는 복수의 분사기를 이용하여 비반응 유동 해석을 수행하였다. 해석 결과를 바탕으로 분사구 간 거리에 따라 전압력 손실, 침투 거리, 및 혼합 성능 등을 정량적으로 비교하였다. 해석 결과 분사구 간 배치 거리가 매우 짧은 경우 분사 연료가 서로 융합되면서 유동장이 2차원 특성을 나타내었고 전반적으로 낮은 혼합 효율 특성과 높은 전압력 손실을 발생하였다. 분사구 간 거리가 멀어짐에 따라 분사 가스간의 상호작용이 감소하면서 혼합 효율이 증가하고 전압력 손실이 낮아지는 것이 관찰되었다.