• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2001년도 Proceedings of 2001 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.108-122
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• 2001

In a continuing effect to study the mixmg enhancement by large-scale streamwise vortices in lobed mixing flows, an advanced PIV system named as dual-plane stereoscopic PIV system was used in the present study to conduct simultaneous vorticity (all three components) measurement of an air jet exhausted from a lobed nozzle. Unlike 'classical' 2-D PIV system or conventional 'single-plane' stereoscopic PIV system, the dual-plane stereoscopic PIV system used in the present study can obtain the flow velocity (all three components) fields at two spatially separated planes simultaneously. Therefore, it can provide the distributions of all the three components of vorticity vectors instantaneously and simultaneously. The evolution and interaction characteristics of the large-scale streamwise vortices and azimuthal Kelvin-Helmholtz vortices in the lobed jet mixing flow were revealed instantaneously and quantitatively from the measurement results of the dual-plane stereoscopic PIV system. The characteristics of the mixing process in the lobed jet mixing flow were analyzed based on the simultaneous measurement results of the steamwise vorticity and azimuthal Kelvin-Helmholtz vorticity distributions.

• 항공우주시스템공학회지
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• 제12권5호
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• pp.40-47
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• 2018

초음속 수축-확대 사각 노즐 내 강한 유동 박리를 동반한 초음속 유동에 적합한 난류 모델과 압축성 보정 모델을 평가하였다. 난류 모델로는 Yang과 Shih의 Low-Re $k-{\varepsilon}$ 모델, Menter의 $k-{\omega}$ SST모델, Wilcox의 $k-{\omega}$ 모델을 평가하였다. 압축성 효과를 보다 정확하게 예측하기 위하여 각각의 난류 모델에 Sarkar와 Wilcox의 압축성 보정 모델을 적용하였다. 각 난류 모델과 압축성 보정 모델의 결과는 실험 데이터와 비교하여 분석을 하였다. 난류 모델에 따라 충격파의 위치와 압력 회복률이 다르게 나타났으나 압축성 보정을 통해 더욱 개선된 결과를 얻었다.

• 한국추진공학회지
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• 제19권2호
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• pp.1-8
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• 2015

이중펄스 로켓 추진기관은 하나의 펄스분리장치에 의해 분리된 2개의 추진제 그레인을 가진 변형된 고체 추진기관이다. 이러한 추진기관의 주요 성능은 펄스분리장치 홀 면적대 노즐 목 면적비의 변화에 영향을 받는다. 본 연구에서는 펄스분리장치 홀 면적대 노즐 목 면적비 변화에 따른 내부유동특성을 고찰하기 위해 유동해석을 수행하였다. 유동해석에 사용된 기체로는 hot gas로 HTPB/AP계 복합추진제 연소가스와 cold gas로 질소가스롤 사용하였다. 이중펄스 로켓 추진기관의 내부유동해석 결과는 공압실험 결과와 비교 분석을 통해 검증하였다. 본 논문에서는 상용 CFD(Computational Fluid Dynamics) 코드인 ANSYS FLUENT V14.5를 이용하여 유동을 모사하였다.

• 대한기계학회논문집B
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• 제29권2호
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• pp.214-223
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• 2005

The characteristics of flow on two parallel plane jets was experimentally investigated. The two nozzles each with an aspect ratio of 20 were separated by 6 nozzle widths. Reynolds number based on nozzle width was set to 5,000 by nozzle exit velocity. The particle image velocimetry and pressure transducer were employed to measure turbulent velocity components and mean static pressure, respectively. In case of unventilated parallel plane jets, it was shown that a recirculation zone with sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plated. There was no recirculation zone in the ventilated parallel plane jets. It was found that the spanwise turbulent intensities of unventilated jets were higher than those of ventilated jets because of the interaction of jets, and the streamwise turbulent intensities of ventilated jets were higher than those of unventilated jets because of the effect of entrainment.

• Nuclear Engineering and Technology
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• 제44권7호
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• pp.727-734
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• 2012

A new advanced safety feature of DVI+ (Direct Vessel Injection Plus) for the APR+ (Advanced Power Reactor Plus), to mitigate the ECC (Emergency Core Cooling) bypass fraction and to prevent switching an ECC outlet to a break flow inlet during a DVI line break, is presented for an advanced DVI system. In the current DVI system, the ECC water injected into the downcomer is easily shifted to the broken cold leg by a high steam cross flow which comes from the intact cold legs during the late reflood phase of a LBLOCA (Large Break Loss Of Coolant Accident)For the new DVI+ system, an ECBD (Emergency Core Barrel Duct) is installed on the outside of a core barrel cylinder. The ECBD has a gap (From the core barrel wall to the ECBD inner wall to the radial direction) of 3/25~7/25 of the downcomer annulus gap. The DVI nozzle and the ECBD are only connected by the ECC water jet, which is called a hydrodynamic water bridge, during the ECC injection period. Otherwise these two components are disconnected from each other without any pipes inside the downcomer. The ECBD is an ECC downward isolation flow sub-channel which protects the ECC water from the high speed steam crossflow in the downcomer annulus during a LOCA event. The injected ECC water flows downward into the lower downcomer through the ECBD without a strong entrainment to a steam cross flow. The outer downcomer annulus of the ECBD is the major steam flow zone coming from the intact cold leg during a LBLOCA. During a DVI line break, the separated DVI nozzle and ECBD have the effect of preventing the level of the cooling water from being lowered in the downcomer due to an inlet-outlet reverse phenomenon at the lowest position of the outlet of the ECBD.

• 한국산업보건학회지
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• 제18권2호
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• pp.149-160
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• 2008

Bag-filter system has been widely used in industrial field to remove the particulate matters from the exhaust gas. The cylindrical type of bag-filter has been generally used. But it has many shortcomings. The reattachment of separated particles on the surface of bags could result in high pressure drop of bag-filter system and subsequent decrease of air flow rate since the cylindrical type bag-filter system should have the upward flow pattern. In addition, the supply of very high pressure pulse air jet to remove particulate matters on the surface of filter could result in a frequent rupture of bags. To overcome these shortcomings of the cylindrical type, the rectangular type was developed in the developed countries and imported to Korea. But, there was not many design data available to understand the mechanisms. Thus, the fundamental experiments were conducted in this study to get some ideas about the pulse jet cleaning of rectangular type bag filter system. The experimental factors are as follows; pulse distance, pulse duration, pulse interval, pulse pressure and pulse nozzle type. Experiments followed the factorial design method. With the shorter pulse distance, the distribution of pressure drops was relatively not uniform while the particulate removal efficiency was higher. With the longer duration of pulsing and the more number of pulse nozzle, the removal efficiency was higher and the pressure drop distribution was more uniform.

• 대한기계학회논문집B
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• 제27권1호
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• pp.1-8
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• 2003

The heat transfer and flow measurements on a cylindrical pedestal mounted on a flat surface with a turbulent impinging jet were made. The experiments were made for the jet Reynolds number of Re = 23,000, the dimensionless nozzle-to-surface distance of L/d = 2~10, the dimensionless pedestal height of H/D = 0~1.5. Measurements of the surface temperature and the Nusselt number distributions on the plate surface were made using liquid crystal and shroud-transient technique. Flow measurements involve smoke flow visualization and the wall pressure coefficient. The results show that the wall pressure coefficient sharply decreases along the upper surface of the pedestal. However, the pressure increases when the fluid escapes from the pedestal and then collides on the plate surface. The secondary maxima in the Nusselt numbers occur in the region of 1.0 $\leq$ r/d $\leq$ 1.9. Their values for the case of H/D = 0.5 are maximum 80% higher than those for other cases. The formation of the secondary maxima may be attributed to the reattachment of flow on the plate surface which was separated at the edge of the pedestal.

• 한국음향학회지
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• 제37권2호
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• pp.83-91
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• 2018

팁젯 로터의 소음원은 로터 블레이드 소음과 제트 소음으로 분리할 수 있다. 로터 블레이드 소음은 두께 소음, 하중 소음, 비선형 사중극 소음으로 구성되고 제트 소음은 노즐 모멘텀 소음과 제트 방사 소음으로 나뉜다. 로터 블레이드 소음을 해석하기 위해 유동 해석 정보를 전산유체역학(Computational Fluid Dynamics, CFD) 해석으로 얻은 뒤 투과면, 비투과면 FW-H(Ffowcs Williams-Hawkings) 음향 상사법을 동시에 적용하여 각 소음원을 구분하였다. 그리고 제트 소음은 노즐 출구 조건을 활용하여 투과면 FW-H 음향 상사법으로 노즐 모멘텀 소음을 구하고 기존 고정익 제트에 대한 경험식을 활용하여 제트 방사 소음을 얻었다. 검증 기체의 소음 측정값을 기준으로 해석 기법의 신뢰성을 검증하였고 스펙트럼 분석을 통해 팁젯 로터의 독특한 소음 특성을 확인하였다.

• 한국수정란이식학회지
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• 제27권1호
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• pp.37-43
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• 2012

This study evaluated a method of sorting X and Y chromosomes based on size using the forward angle light scatter related refractive index (FSC) of a flow cytometer. Hanwoo bulls sperm were separated to X and Y chromosomes by the parameters of FSC or Hoechst 33342 intensity. As a result, using monitor program linked flow cytometry during sorting processing, the purities were $97{\pm}0.57$ or $96{\pm}0.67%$ for the X-fraction and $96{\pm}0.33$ or $97{\pm}1.33%$ for the Y-fraction in the two sperm sorting methods. There were no differences in the X and Y ratios (X and Y %) between the sperm sorting methods based on FSC or DNA content. The proportions of female and male embryos used for in vitro fertilization and development were $66.03{\pm}3.31$ or $69.37{\pm}1.41%$, and $70.56{\pm}2.42$ or $56.11{\pm}3.09%$ when sperm were processed using the sex sorting method by FSC or Hoechst 33342. In conclusion, further study is needed to determine the optimum procedure and improve the nozzle to enhancing sorting accuracy or efficiency. Also, the findings of this study do not negate the possibility that the difference method of sperm sorting cannot use a UV laser beam.

• 한국추진공학회지
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• 제22권3호
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• pp.46-52
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• 2018

액체산소 및 탄화수소를 사용하는 연소기의 고주파 연소불안정을 해석하기 위해 단순모델로서 Crocco의 $n-{\tau}$ 시간지연 연소모델을 적용하고, 음향과 커플된 연소기 내 유동에 대해 선형해석을 수행하였다. 변수분리를 통해 편미분 포텐셜함수 식을 원통좌표계 미분방정식으로 만들고, 연소기의 접선방향 공진모드에 대한 고유 값을 계산하였다. 분사면 및 노즐입구를 경계조건으로 적용하여 미분식의 해를 구했다. 시스템의 안정성 판정을 위해 전달함수를 주파수 해석 하였으며, 관심 영역 주파수인 1T 모드 주변 주파수에서 시스템 게인 및 위상각으로 안정성 여유를 평가하였다. 또한 1T 모드 안정성 향상을 위해 배플 길이 및 형상에 대한 영향을 평가하였다.