• International Journal of Aeronautical and Space Sciences
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• 제6권1호
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• pp.1-7
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• 2005

The inlet boundary condition of computations about the supersonic turbine flow is commonly applied as far-field inlet boundary condition with specified velocity. However, the inflow condition of supersonic turbine is sometimes affected by the shocks or expansion waves propagated from leading edges of blade. These shocks and expansion waves alter the inlet boundary condition. In this case, the inlet boundary condition can not be specified Therefore, in this paper, numerical analyses for three different inlet conditions - fa-field inlet boundary condition, inlet boundary condition with a linear nozzle and inlet boundary condition with a converging-diverging nozzle - have been performed and compared with experimental results to solve the problem. It is found that the inlet condition with a linear nozzle or a converging-diverging nozzle can prevent changing of inlet boundary condition, and thus predict more accurately the supersonic flow within turbine cascade than a far-field inlet boundary condition does.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.165-170
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• 2001

The main purpose of this study is to generate a fine copper oxide powder of high purity, with a compact structure and a uniform particle size by a spray pyrolysis process. The raw material is a waste copper chloride solution formed in the manufacturing process of Print Circuit Board (PCB). This study also examines the influences of various factors on the properties of the generated powder. These factors include the reaction temperature, the inflow speed of the raw material solution, the inflow speed of the air, the size of the nozzle tip, and the concentration of the raw material solution. It is discovered that, as the reaction temperature increases from 80$0^{\circ}C$ to 100$0^{\circ}C$ , the particle size of the generated powder increases accordingly, and that the structure of the powder becomes much more compact. When the reaction temperature is 100$0^{\circ}C$, the particle size of the generated powder increases as the concentration of copper in the raw material solution increases to 40g/l, decreases as the concentration increases up to 120g/l, and increases again as the concentration reaches 200g/1. In the case of a lower concentration of the raw material solution, the generated powder appears largely in the form of CuO. As the concentration increases, however, the powder appears largely in the form of CuCl. When the concentration of copper in the raw material solution is 120g/1, the particle size of the generated powder increases as the inflow speed of the raw material solution increases. When the concentration of copper in the raw material solution is 120g/1, there is no evident change in the particle size of the generated powder as the size of the nozzle tip and the air pressure increases. When the concentration is 40g/1, however, the particle size keeps increasing until the air pressure increases to 0.5kg/$\textrm{cm}^2$, but decreases remarkably as the air pressure exceeds 0.5kg/$\textrm{cm}^2$.

• 한국항공우주학회지
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• 제43권8호
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• pp.712-721
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• 2015

펄스데토네이션엔진은 넓은 작동 범위와 높은 열효율로 인하여 잠재력 있는 미래 추진기관 시스템으로 연구되어왔다. 이러한 잠재력을 개선하기 위하여 지난 10여 년간 다양한 요소 기술들에 대한 연구가 진행되었다. 고주파수의 환경에서 PDE를 안정적으로 작동시키기 위하여, inflow-driven 밸브, 회전 밸브 등을 포함하는 새로운 밸브 시스템과 무밸브 시스템이 개발되었다. 작은 점화 에너지로 빠르게 데토네이션을 발생시키기 위하여 플라즈마 점화 방법과 경사 장애물 기술과 같은 DDT 가속 방법이 연구되었다. 또한 PDE 추진 성능 극대화를 위하여 유체노즐 등의 노즐 시스템도 진행 중인 연구 주제의 하나이다. 본 논문에서는 지난 수년간 개발된 PDE의 최신 부체계 핵심 기술에 대하여 소개하고자 한다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.148-155
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• 2011

In this study, numerical analysis was performed for 150kW arc heater and inflow around specimen was studied. Pressure, voltage, etc. were similar to experimental data, however efficiency was over estimated. In order to correct efficiency, swirl effect and modified radiative heat flux using configuration factor were considered. It was shown that Swirl had little effect on efficiency although radiative heat flux played an important role on decreasing the efficiency of arc heater. In addition, non-equilibrium analysis that plasma flows moves from an arc heater's nozzle to a specimen were performed.

• Journal of Ship and Ocean Technology
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• 제12권1호
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• pp.1-15
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• 2008

An edgetone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, 2-dimensional edgetone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle is presented using lattice Boltmznan model with 21 bits, which is introduced a flexible specific heat ratio y to simulate diatomic gases like air. The blown jet is given a parabolic inflow profile for the velocity, and the edges consist of wedges with angle 20 degree (for symmetric wedge) and 23 degree (for inclined wedge), respectively. At a stand-off distance w, the edge is inserted along the centerline of the jet, and a sinuous instability wave with real frequency is assumed to be created in the vicinity of the nozzle exit and to propagate towards the downward. Present results presented have shown in capturing small pressure fluctuating resulting from periodic oscillation of the jet around the edge. The pressure fluctuations propagate with the speed of sound. Their interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. It is found that, as the numerical example, satisfactory simulation results on the edgetone can be obtained for the complex flow-edge interaction mechanism, demonstrating the capability of the lattice Boltzmann model with flexible specific heat ratio to predict flow-induced noises in the ventilating systems of ship.

• Journal of Advanced Marine Engineering and Technology
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• 제36권8호
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• pp.1030-1035
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• 2012

본 연구에서는 OTEC에 적용가능한 구심터빈을 대상으로 암모니아를 적용하여 8kW급 구심터빈의 설계 및 CFD 해석을 수행하였다. 구심터빈은 스크롤 케이싱, 18개의 베인노즐, 13개의 로터 블레이드로 구성된다. 질량유량과 입구온도는 0.5kg/s와 $25^{\circ}C$이며, 가변회전수 12,000~36,000 rpm 범위내에서 9가지 조건에 대해 해석을 수행하였다. 회전수 변화에 따른 해석결과, 설계회전수 24,000 rpm에서 최대효율점을 보였으며, 이때 최고효율은 88.66 %, 출력은 8.52kW이다. 향후, 팽창비가 1.4~1.5 정도의 범위를 갖도록 최적설계 과정을 통한 연구가 필요하다. 본 연구를 통해 분석된 해석결과는 다양한 작동유체 조건에서 목표출력에 해당하는 구심터빈의 최적 설계파라미터 구성을 위한 설계자료로 유용하게 활용될 것으로 기대한다.

• 한국화재소방학회논문지
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• 제30권4호
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• pp.39-45
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• 2016

화재발생시 가장 큰 인명피해를 유발시키는 연기의 안전한 구역으로 유입을 차단하기 위해 방화문 등 출입구 상부에 설치되는 에어커튼 노즐의 최적 설계를 수행하였다. 연기의 유입을 차단을 목적으로 개구부 상부에 설치되는 에어커튼 노즐의 슬릿에서 유동이 편심되지 않고 외부로 균일하게 배출되어야 한다. 유입 풍량, 내부 슬릿 형상, 외부 슬릿 두께 등을 변수로 고려하여 다양한 조건별로 수치해석을 수행하여 최종 형상을 선정하였다. 최종 형상을 시제품으로 제작하여 수치해석 결과와 비교 검증한바 모든 슬릿의 평균 속도에 대한 시험과 수치해석 결과의 상대오차는 1% 미만으로 매우 일치하는 경향을 보였다.

• 한국추진공학회지
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• 제8권1호
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• pp.44-53
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• 2004

본 논문에서는 슬릿형 분사노즐의 출구 종횡비에 따라 3차원 화학반응 유동장을 수치적 계산을 통하여 그 특성을 조사하고 연소／혼합 촉진 방법을 고찰하였다. 내부유입유동과 슬릿측면 와동들 둘 다 혼합관점에서 고려되어야 한다는 것을 보여 주었다. 연소효율은 종횡비1.0을 기준으로 작은 경우가 낮고 압력손실 역시 종횡비가 작은 경우가 적다. 모든 결과들은 유동방향으로 긴 슬릿이 연소와 압력손실에 대해 바람직함을 나타내고 있다.

• 태양에너지
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• 제9권2호
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• pp.42-50
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• 1989

The Buoyant Jets were analysed experimentally changing flow rate (0.0291/s, 0.0371/s, 0.0451/s), ratio of nozzle tip area to throat area (aspect ratio ${\beta}$=0.4, 1.0, 1.9), and also the temperature difference (${\Delta}T=Ti-T{\infty}$) between the temperature of the inflow water into the storage tank ($1m{\times}1m{\times}3m$) and the mean temperature of the water in the storage tank were changed as $25^{\circ}C,\;35^{\circ}C$ and $45^{\circ}C$. The more aspect ratio decreased, the more the trajectories of Buoyant Jets center-line were decreased and not the more the trajectories of Buoyant Jets centerline were influenced by the increment of the difference of the temperature. The more aspect ratio decreased, the more the half widths and dilution ratio of Buoyant Jets were increased and not the more the half widths and dilution ratio of Buoyant Jets were influenced by the increment of the difference of the temperature. Fr number is the factor that can predict the flow pattern over the whole flow field. And yet for the consideration the near field of Buoyant Jets flow pattern is dominated by magnitude of momentum and buoyancy force.

• 한국분무공학회지
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• 제24권4호
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• pp.171-177
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• 2019

This paper describes numerical study of combustion characteristics in CNG(compressed natural gas) DI(direct injection) engine using gaseous sphere injection model. Simulations were conducted using KIVA-3V Release 2 code. Gaseous sphere injection model, which is modified model of liquid fuel injection, was used to simulate the CNG direct injection. Until now, a very fine mesh smaller than the injector nozzle has been required to resolve the gas-jet inflow boundary. However, the gaseous sphere injection model simulates gaseous fuel injection using a coarse mesh. This model injects gaseous spheres as in liquid fuel injection and the gaseous spheres evaporate together without the latent heat of evaporation. Therefore, it does not require a very fine mesh and reduce calculation time. Combustion simulation were performed under various injection timings and injection pressures.