• Journal of Mechanical Science and Technology
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• 제17권11호
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• pp.1793-1800
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• 2003

The present study addresses an experimental investigation of the near field flow structures of supersonic, dual, coaxial, free, jet, which is discharged from the coaxial annular nozzle. The secondary stream is made from the annular nozzle of a design Mach number of 1.0 and the primary inner stream from a convergent-divergent nozzle. The objective of the present study is to investigate the interactions between the secondary stream and inner supersonic jets. The resulting flow fields are quantified by pitot impact and static pressure measurements and are visualized by using a shadowgraph optical method. The pressure ratios of the primary jet are varied to obtain over-expanded flows and moderately under-expanded flows at the exit of the coaxial nozzle. The pressure ratio of the secondary annular stream is varied between 1.0 and 4.0. The results show that the secondary annular stream significantly changes the Mach disc diameter and location, and the impact pressure distributions. The effects of the secondary annular stream on the primary supersonic jet flow are strongly dependent on whether the primary jet is under-expanded or over-expanded at the exit of the coaxial nozzle.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2862-2867
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• 2007

The steady non-reacted compressible flow field in a symmetric micro-thruster, which is used for the accurate attitude control of a satellite, is analyzed varying the nozzle pressure ratio (NPR) to investigate the plume characteristics. The nozzle throat diameter is 0.06 inch and the area ratio is 56. The recirculation region is found just behind the normal shock at the several NPRs due to the locally adverse pressure gradient along the nozzle centerline when the environmental pressure is atmospheric. This phenomenon, the cause of flow loss, is similar to the flow behind a blunt body. As NPR increases the location of Mach disk, characteristics of the normal shock, moves downstream and its strength increases. The Mach number distribution appears in a wave-type patter after the normal shock because oblique shocks are reflected on the shock boundaries especially when NPRs are very high.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2000년도 제14회 학술강연논문집
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• pp.20-20
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• 2000

초음속 과소팽창 제트는 베럴충격파(Barrel shock), 팽창파(Expansion fan), 반사충격파(Reflected shocks), 마하디스크(Mach disc), 그리고 제트경계면(Exhaust-gas Jet boundary)로 이루어지는 여러 충격파 셀(Shock ceil)의 유동 형태를 나타난다. 이러한 초음속 과소팽창 제트가 수직 평판에 충돌하면 초음속 자유 제트와는 다른 변형된 유동장이 형성된다.

• 한국추진공학회지
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• 제4권3호
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• pp.11-18
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• 2000

초음속 노즐 뒤에서 형성되는 과소팽창 제트(Underexpanded jet)가 분사될 때 베럴 충격파(Barrel shock), 팽창과(Expansion fan), 마하 디스크(Mach disc), 제트 경계면(Exhaust-gas jet boundary), 그리고 반사 충격파(Reflected shocks)와 같은 구조의 풍격파 셀(Shock cell)이 연속적으로 나타난다. 이러한 충격파 셀은 난류 소산에 의해 희미해지며 거리가 멀어지면 사라진다. 과소팽창 제트가 수직 평판에 충돌하게 되면 챔버 압력 및 출구 마하수 등 여러 인자들에 따라 달라지는 복잡한 유동장을 형성하게 된다. 본 논문에서는 평판에 충돌하는 과소팽창 제트가 형성하는 유동장을 압축성 Navier-Stokes 방정식에 유한체적법을 적용하여 수치적으로 구한 해존 실험 데이터와 비교 검증하였다. 실험 데이터와 계산 결과의 압력구배 및 유동가시화 사진 비교 견과 노즐과 평판이 가까운 경우에 충돌제트유동을 잘 예측할 수 있었으며, 과소팽창비가 작을 때 과소팽창비에 따른 충돌제트 유동분포의 영향은 자게 나타남을 알 수 있었다.

• 대한기계학회논문집B
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• 제33권2호
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• pp.93-100
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• 2009

Characteristics of micro-sonic/supersonic axi-symmetric jet impinging on a flat plate with a pre-drilled hole were both experimentally and numerically studied, to observe the role of assist-gas jet to eject melted materials from the cut zone in the laser machining. For various Mach numbers of the nozzle and the total pressures of the assist gas, detailed impinging jet flow structures over the plate and the variations of mass flux through the pre-drilled hole were observed. It was found that the present experimental and numerical results show a good agreement, which proves the accountability of the present work. From the present study, it was also observed that the mass flow rate through the hole was closely related with the total pressure loss caused by the Mach disc on the work piece, and that supersonic nozzle could perform more efficient roles as blowing the assist-gas jet in the laser machining, as compared to sonic nozzles.

• 한국추진공학회지
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• 제18권5호
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• pp.54-61
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• 2014

본 연구에서는 비정렬격자계를 사용하는 2차원 축대칭 DSMC 법을 사용하여 로켓 노즐에서 사출되는 플룸을 해석하였다. 오리피스의 출구 전압에 대한 배압의 비율이 높은 경우와 낮은 경우의 플룸에 대하여 해석을 실시하여 저고도와 고고도를 대표하는 두 가지 조건에서 플룸 유동의 차이를 관찰하였다. 저고도 플룸은 Mach disc 등 복잡한 유동 구조를 보인 반면 고고도 플룸은 단순 팽창만을 보였으며, 유동이 상류 방향으로 심하게 꺾였다. 또한 고도 20 km의 대기 조건에서 소형 로켓 노즐에서 사출되는 플룸에 대한 해석을 수행하여 연속체 해석 결과와 비교하였으며 과소팽창되는 로켓 플룸의 유동구조가 잘 나타났다. 또한, 플룸 내부에 국지적인 천이 유동이 발생할 수 있음을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.494-498
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• 2001

When supersonic jet impinges on wall from the nozzle, complex flow pattern appears such as Mach disc, expansion fan, and jet boundary. The numerical computation of this supersonic jet is important on flame deflecctor design for launch space especially. In this paper, we analyzed supersonic jet structure impinging on deflector wall using three dimensional steady and unsteady compressible equation and showed temperature and pressure distribution on the wall surface. As a result, some dominant factors of jet flows are discussed for conceptual design of flame deflector.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.453-460
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• 2000

A test rig is developed for performance test of 1 stage axial-type turbine which is designed by meanline analysis, streamline curvature method, and blade design method using configuration parameters. The purpose of this study is to find the best configuration parameters for designing a high efficiency axial-type turbine blade. To measure the efficiency of turbine stage, a dynamo-meter is installed. Two different stators which are manufactured as an integrated type are developed, and a rotor blade and 5 sets disc are developed for setting different stagger angle. The tip and hub diameters of the test turbine are 300 and 206.4mm, respectively. The rotating speed is 1800RPM, and the extracted power is 2.5kW. Flow coefficient is 1.68 and the reaction factor at meanline is 0.373. The number of stator and rotor of test turbine are 31 and 41, respectively. The Mach number of stator exit flow near hub is 0.164.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.285-288
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• 2007

레이저가공에서 나타나는 가공부위의 용융된 물질을 밀어내는 가스의 역할을 모사하기 위하여, 구멍이 있는 평판 상부에 충돌하는 마이크로 초음속 제트유동의 경계층 효과가 수치해석적으로 연구되었다. 충돌유동과 충격파의 구조 및 구멍통과 질량유량이 관찰되어 경계층 영향이 고려되지 않은 과거 연구와 비교되었다. 노즐내부 유동의 경계층 효과로 인하여 가공부위 상부에서 보다 강한 마하디스크가 생성되고, 아울러 구멍통과 질량유량도 줄어드는 것이 관찰되었다.

• 천문학회보
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• 제44권1호
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• pp.69.3-69.3
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• 2019

The CHIMPS2 survey is to extend the JCMT HARP $^{13}CO/C^{18}O$ J=3-2 Inner Milky-Way Plane Survey (CHIMPS) and the ${12}^CO$ J=3-2 survey (COHRS) into the inner Galactic Plane, the Central Molecular Zone (CMZ), and a section of the Outer Plane. When combined with the complementary $^{12}CO/^{13}CO/C^{18}O$ J=1-0 survey at the Nobeyama 45m (FUGIN) at matching 15" resolution and sensitivity, and other current CO surveys, the results will provide a complete set of transition data with which to calculate accurate column densities, gas temperatures and turbulent Mach numbers. These will be used to: analyze molecular cloud properties across a range of Galactic environments; map the star-formation efficiency (SFE) and dense-gas mass fraction (DGMF) in molecular gas as a function of position in the Galaxy and its relation to the nature of the turbulence within molecular clouds; determine Galactic structure as traced by molecular gas and star formation; constrain cloud-formation models; study the relationship of filaments to star formation; test current models of the gas kinematics and stability in the Galactic center region and the flow of gas from the disc. It will also provide an invaluable legacy data set for JCMT that will not be superseded for several decades. In this poster, we will present the current status of the CHIMPS2.