• 한국추진공학회지
• /
• 제17권1호
• /
• pp.18-25
• /
• 2013

초음속 축소-확대 노즐 유동을 정확하게 해석하기 위하여, 실험치와 해석값 사이의 비교를 통해 난류모델 성능평가를 수행한다. Boussinesq 가정을 적용한 RANS 방정식으로 2차원 노즐 유동을 해석하되, Spalart-Allmaras, RNG k-${\varepsilon}$, 그리고 k-${\omega}$ SST 난류모델을 평가에 사용한다. 각 모델들로 계산된 노즐 벽면의 압력구배 및 충격파 구조는 실험 데이터와 유사한 결과를 보였는데, 그 중에서도 SST 난류모델이 실험값에 가장 근접한 해석결과를 나타내었다.

• 대한기계학회논문집B
• /
• 제26권7호
• /
• pp.951-958
• /
• 2002

Rapid expansion of a moist air or a stream through a supersonic nozzle often leads to non-equilibrium condensation shock wave, causing a considerable energy loss in flow field. Depending on amount of latent heat released due to non-equilibrium condensation, the flow is highly unstable or a periodical oscillation accompanying the condensation shock wave in the nozzle. The unsteadiness of the condensation shock wave is always associated with several kinds of instabilities as well as noise and vibration of flow devices. In the current study, a passive control technique using a porous wall with a plenum cavity underneath is applied for the purpose of alleviation of the condensation shock oscillations in a transonic nozzle. A droplet growth equation is coupled with two-dimensional Navier-Stokes equation system. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. An experiment using an indraft wind tunnel is made to validate the present computational results. The results show that the oscillations of the condensation shock wave are completely suppressed by the current passive control method.

• 한국추진공학회지
• /
• 제6권2호
• /
• pp.1-7
• /
• 2002

추진기관은 노즐을 통해 추력을 발생하며 축소-확대 형상의 초음속 노즐에서는 노즐의 설계 팽창비가 내부 유동의 전압력과 배압의 압력비보다 매우 클 때 충격파의 발생과 함께 경계층 박리를 유발한다. 노즐 내부에서의 충격파 발생과 유동의 박리는 주어진 유동의 압력비에 가장 적합한 노즐형상을 구현하는 것으로 실제의 구조적 노즐의 형상보다 짧은 노즐에서 나타나는 유동과 같은 현상을 보인다. 수치 해석적 방법으로 고정된 형상의 2차원 노즐 내부의 충격파와 경계층 박리 현상에 관한 연구를 수행하였고 Hunter가 행한 실험적 연구와 비교하였다. 수치해석은 TVD 기법을 이용한 압축성 유체 해석 코드와 SST 2방정식 난류 모델을 이용하여 수행되었다. 낮은 압력비에서의 충격파와 경계층과의 상호작용에 의한 $\lambda$형태의 충격파 시스템을 잘 보여주고 있고 추력 값의 비교를 통해 고정된 형상의 노즐을 이용하여 필요한 운용범위를 충족할 수 있음을 알 수 있었다.

• 대한기계학회논문집
• /
• 제14권2호
• /
• pp.463-469
• /
• 1990

A rapid expansion of moist air of condensible gas through a supersonic nozzle gives rise to condensation of nonequilibrium and equilibrium processes. Because most of the effects of condensation on the flow are caused by process of nonequilibrium condensation, it is very important to know the onset. condition of nonequilibrium condensation. In the present study, the relation between the initial relative stagnation humidity and the onset Mach number, for the case of the similarity law suggested by Zierep and Lin. Furthermore, the present theoretical result number is compared with the experimental, numerical and other results.

• 대한기계학회논문집B
• /
• 제29권12호
• /
• pp.1329-1334
• /
• 2005

Synthesis of silver nanoparticles by the supersonic nozzle expansion method with corona discharge ions was investigated. Corona discharge ions functioned as seeds for heterogeneous nucleation in the silver nanoparticles formation process and provided silver nanoparticles with electronic repulsive force that prevents aggregation of the particles. For ion ejecting, we used sonic-jet corona discharger. Upon application of the corona discharge ions, the mean diameter of the produced particles was decreased from 12.54 to 6.22nm and the standard deviation was decreased from 5.02 to 3.34nm. In addition, the agglomeration of silver nanoparticles was reduced.

• Journal of Mechanical Science and Technology
• /
• 제15권8호
• /
• pp.1174-1180
• /
• 2001

Various experimental data, including mixing areas, cross correlation factors, surface flow patterns on nozzle walls, and far field noise spectra, was used to draw a noise control mechanism in a supersonic jet. In the underexpanded case, mixing of the jet air with ambient air was significantly enhanced as presented before, and mixing noise was also dramatically reduced. Screech tones, in the overexpanded case, were effectively suppressed by trailing edge modifications, although mixing enhancement was not noticeable. From mixing and noise performance of nozzles with modified trailing edges, enhancing mixing through streamwise vortices seems an effective way to reduce mixing noise in the underexpanded flow regime. However, screech tones in the overespanded flow regime is well controlled or suppressed by making shock cells and/or spanwise large scale structures irregular and/or less organized by a proper selection of trailing edges. The noise field in the overexpanded flow regime was greatly affected by the symmetricity of the nozzle exit geometry. In the underexpanded flow regime, the effects of the symmetricity of the nozzle exit on mixing were negligible.

• 한국기계가공학회지
• /
• 제9권5호
• /
• pp.14-19
• /
• 2010

A computational study was carried out to analyze the characteristics of supersonic (Mach 2.0) coaxial/off-axis jet's impingements on a slanted kerf surface in laser machining. The effects of various parameters such as gas pressure, distance between nozzle exit and kerf edge surface, and application of off-axis nozzles on the impingement phenomena of the assist-gas on kerf surface were observed. The present study showed that simply increasing the assist-gas pressure for coaxial supersonic nozzle was not effective to alleviate the strength of flow separation on kerf surface. It also presented the optimized operating condition of the coaxial nozzle to have the highest skin friction values over kerf surface.

• 한국항공우주학회지
• /
• 제32권8호
• /
• pp.129-137
• /
• 2004

본 연구에서 시험부 크기 $30mm{\times}35.6mm$, Run Time 20초인 소형-저가의 초음속 풍동을 개발하였다. 개발원 교육용 초음속 풍동은 단속적 불어내기식형이며 , 노즐 블록 교체형으로 설계되었다. 본 연구를 통하여 초음속 풍동에 사용되는 대형-고가의 기계장비를 기존 소형의 상용 제품으로 대체하여 제작 단가를 낮추었다. 그리고 초음속 풍동의 핵심 기술인 노즐 설계를 비롯한 전체적인 초음속 풍동 설계 기술을 확보하였다. 풍동 시험부에서의 초음속 유동장 형성 및 유동 안정성에 대한 성능검증 실험을 수행하였다.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
• /
• pp.13-19
• /
• 2003

램제트 및 스크램 제트 엔진의 개발을 위한 초음속 지상 추진 시험설비는 고고도, 고속 비행 조건을 모사하기 위해 고도 및 마하수에 따른 공기의 전압력과 전온도, 연소실 유입공기의 산소 농도 및 비열비 등의 조건을 구현할 수 있어야 한다. 그리고 비행체에서 발생하는 경사충격파의 영향을 모사할 수 있어야 한다. 본 연구에서 설계한 지상 추진 시험 설비는 초음속 자유 제트 불어내기(Supersonic free-jet blowdown)방식으로, 고압공기 공급원(최대 가압 압력 32MPa), 가열기(Vitiation 타입), 초음속 디퓨저, 이젝터 및 시험부(노즐 출구=200mm$\times$200mm)등으로 구성되어 있다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1738-1743
• /
• 2004

Turbo-pump system, an essential component of liquid rockets and induced weapons, adopts a partial admission axial turbine which drives pump. And the turbine of a turbo-pump system is usually operated at supersonic condition due to its high loading chracteristics. Therefore, reseaches about flow and performance characteristics of a partial admission supersonic turbine must be preceeded to progress the aerospace and defense industries as well as the development of turbo-pump systems. In this study, flow characterisitics within blades of the partial admission supersonic turbine are numerically investigated by using Fine Turbo, a commercial CFD Code. Before performing the numercial analyses, to verify accuracy of the numerical result computed by Fine Turbo, I performed the comparison between the numerical results with J.J.Cho' experimental results. It is found that the numerical results show good agreement with the experimental results. Computations about the partial admission supersonic turbine have been performed to investigate flow characteristics including shock patterns. It is also found that the flow and performance of partial admission supersonic turbine are largely depend on shocks ocurred in the nozzle and at the leading edge of blades, expansion or compression at exit of nozzle and separations occurred in passage.