• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.126-131
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• 2004

The interaction between the hypersonic free stream and the side jet flow at high altitudes is investigated by direct simulation Monte Carlo(DSMC) method. Since there is a great difference in density between the free stream and the side jet flow, the weighting factor technique which could control the number of simulation particles, is applied to calculate these two flows simultaneously. Chemical reactions are not considered in the calculation. For validation, the corner flow passing between a pair of plates that are perpendicularly attached is solved. The side jet flow is then injected into this comer flow and solution is found for the merged flow. Results are compared with the experiments. For a more realistic rocket model, the flow past a blunted cone cylinder shape is solved. The leeward or windward jet injection is merged with this flow. The effect on the rocket surface is observed at various flow angles. The lambda effect and the wake structure are found like low attitudes. High interaction between the free stream and the side jet flow is observed when the side jet is injected in the windward direction.

• 대한기계학회논문집B
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• 제41권10호
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• pp.649-657
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• 2017

고압의 파이프 파단 시 파이프 내에 있던 유체가 고속으로 대기로 분출될 때 압축성유동을 동반하는 초음속제트가 발생한다. 이러한 초음속제트는 일반적으로 복잡한 비정상거동을 보여줄 수 있다. 본 연구는 이러한 고압파이프에서 분출되는 초음속제트에 의해 생성되는 압축성유동을 고찰하기 위하여 전산유체역학 해석이 수행되었다. 분출기체의 종류 및 파이프직경 변화에 따른 비정상유동 특성을 해석하기 위해 SST $k-{\omega}$ 난류모델이 채택되었다. 전산해석 시 기본 경계조건은 파이프직경 10 cm, 제트 압력비 5, 기체온도 300 K로 가정하였다. 그 해석결과로 초음속제트로 인해 생성되는 충격파의 거동이 관찰되었고, 간접적인 영향으로 폭풍파도 발생됨을 알 수 있었다. 기체의 분자량이 가장 작은 $H_2$의 압력파 특성은 안전영역까지의 거리가 가장 짧았으며, 분자량이 비슷한 $N_2$, 공기 및 $O_2$는 큰 차이가 없었다. 또한 파이프직경이 커져 제트에 의한 영향범위도 더욱 증대됨을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제55권10호
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• pp.3754-3767
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• 2023

Turbulent jet discharges in subcooled water pools are essential for safety systems in nuclear power plants, specifically in the pressure suppression pool of boiling water reactors and In-containment Refueling Water Storage Tank of advanced pressurized water reactors. The gas and liquid flow in these systems is investigated using multiphase flow analysis. This field has been extensively examined using a combination of experiments, theoretical models, and Computational Fluid Dynamics (CFD) simulations. ANSYS CFX offers two approaches to model multiphase flow behavior. The non-homogeneous Eulerian-Eulerian Model has been used in this work; it computes global information and is more convenient to study interpenetrated fluids. This study utilized the Large Eddy Simulation Model as the turbulence model, as it is better suited for non-stationary and buoyant flows. The CFD results of this study were validated with experimental data and theoretical results previously obtained. The figures of merit dimensionless penetration length and the dimensionless buoyancy length show good agreement with the experimental measurements. Correlations for these variables were obtained as a function of dimensionless numbers to give generality using only initial boundary conditions. CFD numerical model developed in this research has the capability to simulate the behavior of non-condensable gases discharged in water.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.207-207
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• 2016

plasma group velocities of neon with oxygen admixture (ug) are obtained by intensified charge coupled device (ICCD) camera images at fixed gate width time of 5 ns. The propagation velocities outside interelectrode region are in the order of 104 m/s.The plasma ambipolar diffusion velocities are calculated to be in the order of 102 m/s. Plasma jet is generated by all fixed sinusoidal power supply, total gas flow and repetition frequency at 3 kV, 800 sccm and 40 kHz, respectively. The amount of oxygen admixture is varied from 0 to 2.75 %. By employing one dimensional convective wave packet model, the electron temperatures in non-thermal atmospheric-pressure plasma jet are estimated to be in a range from 1.65 to 1.95 eV.

• 한국산업융합학회 논문집
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• 제5권4호
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• pp.313-320
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• 2002

A 2-dimensional $k-{\varepsilon}$ numerical model was developed to explore the effects of vehicle movement, jet fan and wind speed for the ventilation of road tunnels. To consider the temperature distribution in the tunnel, the energy equation was solved with a source term of the energy exhausted from vehicles. Although the tunnel ventilation can be made by the piston effect of vehicle movement, an additional ventilation is necessary when a head wind is existing. Jet fans may assist the air flow in the tunnel. However, more efficient ventilation system should be necessary, because the exhaust gas from vehicles flow along the road surface and it cannot be diffused in the longitudinal tunnel.

• 한국추진공학회지
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• 제6권2호
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• pp.37-44
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• 2002

액체로켓엔진에 사용되는 2-유체 동축형 분사기의 분무 연소 특성을 수치적으로 해석하였다. 가스 역학적 상호작용에 의한 미립화 및 그에 따른 물리 현상들에 대해 유동에 대한 보존방정식과 이론식들을 적용, 수치화하여 액체 제트의 상태, 제트의 속도, 제트의 붕괴길이, 액적의 크기등을 예측 하였으며, 액체제트 분사공 크기에 따른 미립화의 변화를 고찰하였다. 모델 검증을 위하여 액체 제트의 접촉길이와 액적의 크기를 기존의 실험결과와 비교하였으며, 그 결과 정성적으로 일치함을 나타내었다. 액체 제트의 접촉길이는 분사공의 직경이 증가할수록 짧아지고 액적의 크기도 분사공의 직경이 증가할수록 작아진다. 액체 제트는 박리율 증가에 따른 분무화에 의하여 단면적이 감소되며, 그에 따른 질량유속의 보존과 가스로부터의 운동량 화산에 따라 미립화가 활발해지는 영역으로부터 그 속도가 급속히 증가된다.

• 한국가스학회지
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• 제26권1호
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• pp.20-26
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• 2022

대기 중으로 가스가 누출될 때, 누출구에서 비교적 가까운 위치에 누출 축을 따라 형성되는 인화성 증기운의 농도 및 속도에 관해 실험, 이론 및 수치해석을 이용한 결과를 비교하였다. 제트기류 확산(Jet dispersion) 과정에 대해 실험을 통해 농도를 측정하였고, 이론적 접근법으로써 자기유사성(Self-similarity) 이론을 적용하여 속도를 계산하였다. 그리고 두 가지 CFD 도구 - 서브그리드모델을 사용하는 FLACS와 범용 CFD 도구인 CFX-를 이용해 속도와 농도를 계산하여 각 결과와 비교하였다. 자기유사성 이론과 CFD의 가장 큰 차이점은 부력항에 의한 차이이며, 이는 누출원으로부터 거리가 멀어져 누출 모멘텀이 감소할 수록 영향력이 증가한다. 결과는 누출원 반경에 대한 무차원 거리와 최대 속도에 대한 무차원 속도를 이용하여 비교한다.

• 대한기계학회논문집
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• 제13권4호
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• pp.611-617
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• 1989

본 연구에서는 제트 분사 시스템을 제작하여 절단 성능에 관게하는 여러 변수중 고압수의 압력, 연마제의 크기 및 공급량, 그리고 공작물의 이송속도의 영향을 실험적으로 연구하였다.

• Journal of Mechanical Science and Technology
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• 제17권5호
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• pp.726-739
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• 2003

A multi-dimensioanl model is being increasingly used to predict the thermo-flow field in the gas turbine combustor. This article addresses an integrated survey of modeling of the liquid spray formation and fuel distribution in gas turbine with high-shear nozzle/swirler assembly. The processes of concern include breakup of a liquid jet injected through a hole type orifice into air stream, spray-wall interaction and spray-film interaction, breakup of liquid sheet into ligaments and droplet,5, and secondary droplet breakup. Atomization of liquid through hole nozzle is described using a liquid blobs model and hybrid model of Kelvin-Helmholtz wave and Rayleigh-Taylor wave. The high-speed viscous liquid sheet atomization on the pre-filmer is modeled by a linear stability analysis. Spray-wall interaction model and liquid film model over the wall surface are also considered.

• 대한기계학회논문집A
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• 제24권9호
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• pp.2159-2166
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• 2000

Recently, high performance machining center requires special type of sealing mechanism that prevent a leakage of oil jet or oil mist lubrication system. Sealing of oil-air mixture plays important r oles to have an enhanced lubrication for performance machining center. Current work emphasizes on investigations of the air jet effect on the protective collar type labyrinth seal. To improve sealing capabilities of conventional labyrinth seals, air jet is injected against the leakage flow. In this study, an adapted model is introduced to improve sealing capability of conventional non-contact type seals. It has a combined geometry of a protective collar type and an air jet type. Both of a numerical analysis by CFD (Computational Fluid Dynamics) and experimental measurements are carried out to verify sealing improvement. The sealing effects of the leakage clearance and the air jet magnitude aic studied in various parameters. Gas or liquid has been used as a working fluid for most of nori-contact types seals including the labyrinth seal. However, it is more reasonable to regard two-phase flows because oil mist or oil jet are used for high performance spindle's lubrication. In this study, working fluid is regarded as two phases that are mixed flow of oil and air phase. Both of turbulence and compressible flow model are also introduced in a CFD analysis to represent an isentropic process. Estimation of non-leaking property is determined by amount of pressure drop in the leakage path. Results of pressure drop in the experiment match reasonably to those of the simulation by introducing a flow coefficient. Effect of the sealing improvement is explained as decreasing of leakage clearance by air jetting. Thus, sealing effect is improved by amount of air jetting even though clearance becomes larger