유체 공급 배관내 압력진동 억제에 미치는 오리피스의 음향학적 효과에 관한 수치적 연구

손채훈,김철희 한국항공우주학회 2006 한국항공우주학회 학술발표회 논문집 Vol.- No.-

복사 열손실로 인한 확산 화염의 맥동 불안정에 관한 연구

손채훈,김종수,Sohn, Chae Hoon,Kim, Jong Soo 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.9

Radiation-induced oscillatory instability in diffusion flames is numerically investigated with nonlinear dynamics considered. As the simplest flame model, a diffusion flame established in the stagnant mixing layer is employed with optically thin gas-phase radiation and unity Lewis numbers for all species. Attention is focused on the radiation-induced extinction regime, which occurs at large $Damk\ddot{o}hler$ number. Once the steady flame structure is obtained for a prescribed value of the initial $Damk\ddot{o}hler$ number, transient solution of the flame is calculated after a finite amount of the $Damk\ddot{o}hler$-number perturbation is imposed on the steady flame. Transient evolution of the flame exhibits three types of flame-evolution behaviors, namely decaying oscillatory solution, diverging solution to extinction and stable limit-cycle solution. A dynamic extinction boundary is identified for laminar flamelet library.

Computational studies of diffusion cool flame structures of n-heptane with/without ozone sensitization with a reduced chemistry

손채훈,손진우,Sang Hee Won,Yiguang Ju 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3

The diffusion cool flame structures of n-heptane are studied numerically with a comprehensively reduced chemistry. For this study, nheptane/oxygen diffusion flame is self-sustained in a counterflow flame configuration with ozone sensitization. N-heptane is diluted bynitrogen to lower flame temperature and a small amount of ozone is added to oxygen to enhance oxygen atom production. N-heptanediffusion flame shows both hot-flame and cool-flame behaviors in high and low temperature regimes, respectively. Its S-shaped curvehas two upper branches of hot and cool flame branches. The upper branch of cool flame is observed at low strain rates with the order ofmagnitude from O(1) to O(102) s-1 and its zone is much narrower than that of hot flame. N-heptane cool flame survives irrespective ofozone addition, but ozone extends the viable or stable flame zone to higher strain rate. Cool-flame temperatures are below 800 K andradical-induced ignition comes into play. N-heptane is highly diluted by nitrogen and extinction strain rate is more sensitive to mole fractionof n-heptane rather than mole fraction of ozone. Heat release rates of elementary reaction steps and concentrations of major radicalsare far lower in cool flames than in hot flames. Main characteristics of cool flame structures at low strain rates and low temperatures areprovided although the present low-temperature kinetics is not complete.

Pressure dependence of mass burning rates in diluent premixed flames of H₂/O₂at high pressures

손채훈 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.3

Pressure dependence of mass burning of diluted hydrogen premixed flames is studied numerically over a full range of pressure. Massburning rate is selected to be a parameter for burning capability of flames. First, positive linear dependence of mass burning rate has beenconfirmed at low pressures and negative pressure dependence has appeared in the medium range of pressure, which complies with theresults reported in previous experimental works. And then, when the pressure range is extended more, positive pressure dependence isrecovered or shows up again at high pressures. The flame structures of temperature and species profiles in each pressure regime are demonstrated. They show that the latter two dependences of negative and positive can be explained by enhanced recombination reactionsproducing HO₂at high pressures and chain re-branching to OH production via H₂O₂, respectively. There are three distinct dependencesof mass burning or global chemistry in hydrogen flames. Two onset pressures, at which pressure dependence changes, depend on equivalenceratio, degree of dilution, diluent species, and unburned-gas temperature. Accordingly, the onset pressure can be used as a parametercharacterizing burning of premixed flames.

희석된 메탄/산소 대향류 확산화염에서 확산-열 불안정으로 인한 화염의 비선형 동적 거동에 관한 수치해석

손채훈 대한기계학회 2004 大韓機械學會論文集B Vol.28 No.6

수소/공기 예혼합기의 정상 및 이상 연소에 관한 수치해석 ( A Numerical Study of Normal and Abnormal Combustion in Hydrogen/Air Premixture )

손채훈,정석호 대한기계학회 1994 대한기계학회 춘추학술대회 Vol.- No.-

로켓 연소실에서 배플형 분사기의 설치 간극에 의한음향 감쇠 효과에 관한 수치적 연구

손채훈,이중연 한국추진공학회 2007 한국추진공학회지 Vol.11 No.3

Acoustic damping induced by gap width between baffled injectors is investigated numerically, which are installed to suppress pressure oscillations in a model rocket combustor. The previous work reported that the baffled injectors show larger acoustic damping with the gap width between injectors. It is simulated numerically and its mechanism is examined. Damping factors are calculated as a function of gap width and it is found that the optimum gap is 0.1 mm or so. For understanding of the improved damping induced by the gap, dissipation rate of turbulent kinetic energy and vorticity are calculated as a function of the gap. Both parameters have their maximum values at the specific gap and especially, the dissipation rate has the same profile as that of damping factor. It verifies that the improved damping made by the gap is attributed to the increased acoustic-energy dissipation. 로켓 엔진의 음향 불안정을 제어하기 위해 모형 연소실에 배플형 분사기가 장착된 경우의 음향 감쇠 특성을 수치해석적으로 조사하였다. 기존에 보고된 배플형 분사기의 효용성을 확인하였고 분사기간 간극이 존재할 때 음향 감쇠 효과가 증대되는 메커니즘을 규명하였다. 여러 가지 크기의 간극에 따라 음향학적 감쇠능력을 조사하였고, 본 연소실에서는 0.1 mm 정도의 간극에서 최적의 감쇠능력을 가짐을 알 수 있었다. 음향 감쇠 효과가 증대되는 메커니즘을 규명하기 위해, 분사기 사이의 간극에 따른 에너지 소산율과 와도를 계산하였고, 소산율 변화 추이와 감쇠인자 변화 추이가 유사함을 알았다. 이를 통해, 간극에 의한 에너지 소산의 증대로 음향 감쇠 효과가 증가함을 알았다.

액체 로켓엔진에서 선형 연소 안정한계에 미치는 유한화학반응 효과

손채훈,박이선,허환일 朝鮮大學校 機械技術硏究所 2005 機械技術硏究 Vol.8 No.1

로켓엔진에서 선형 연소 안정한계에 미치는 유한화학반응의 열적 효과를 조사하였다. 안정한계를 평가하기위해 3차원 연소실에서 유한화학반응을 채택한 반응 유동장 계산으로부터 구한 유통변수들을 사용하였다. 주요 유통변수들의 값은 유한화학반응 모델의 채택으로 인해 상당히 달라졌으며 결과적으로 안정한계도 수정되었다. 유한화학반응은 열적 관점에서 안정성 향상에 기여함을 알았다. In this study, thermal effect of finite-rate chemistry on stability are investigated. To evaluate stability limits, various flow variables from reactive flow fields are required. The flow variables are obtained from CFD analyses with finite-rate chemistry adopted in three dimensional chamber. When finite reaction is adopted, the establishment of reactive flow field is delayed. Accordingly. major flow variables are modified and the calculated stability limits are affected moderately by finite-rate chemistry. It is found that finite-rate chemistry contributes to stability enhancement in thermal point of view.

고압하에서 수소-산소 확산화염의 소염 특성에 관한 수치 해석

손채훈,김종수,정석호,이수룡,Son, Chae-Hun,Kim, Jong-Su,Jeong, Seok-Ho,Lee, Su-Ryong 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.9

Extinction characteristics of pure hydrogen-oxygen diffusion flames, at high pressures in the neighborhood of the critical pressure of oxygen, is numerically studied by employing counterflow diffusion flame as a model flame let in turbulent flames in rocket engines. The numerical results show that extinction strain rate increases almost linearly with pressure up to 100 atm, which can be explained by comparison of the chain-branching-reaction rate with the recombination-reaction rate. Since contributions of the chain-branching reactions, two-body reactions, are found to be much greater than those of the recombination reactions, three-body reactions, extinction is controlled by two-body reactions, thereby resulting in the linearity of extinction strain rate to pressure. Therefore, it is found that the chemical kinetic behaviors don't change up to 100 atm. Consideration of the pressure fall-off reactions shows a slight increase in extinction strain rate, but does not modify its linearity to pressure. The reduced kinetic mechanisms, which were verified at low pressures, are found to be still valid at high pressures and show good qualitative agreement in prediction of extinction strain rates. Effect of real gas is negligible on chemical kinetic behaviors of the flames.

액체추진제 공급 배관내 압력진동 감쇠에 미치는 Block의 위치 효과

손채훈,김철희 朝鮮大學校 機械技術硏究所 2005 機械技術硏究 Vol.8 No.2

연료탱크 등에 연결되어 있는 배관 내에서는 유체의 이동에 따른 압력진동이 배관의 공진 주파수와 일치 되었을 때 공진현상이 발생하여 배관의 구조적 결함이나 기계적 손실을 유발 할 수 있다. 본 연구에서는 이러한 배관 내의 압력진동을 감쇠할 수 있는 방법으로 배관 내부에 block을 설치하여 그 위치에 따른 효과를 수치해석적으로 조사하였다. 배관의 앞 단면에서 가진한 압력이 기본 공진주파수에 영향을 끼침을 확인하였고, block의 설치 위치가 압력진동 억제에 미치는 효과를 알아 보았다. 그 결과 압력진동 값이 0이 되는 지점에서 block에 의한 감쇠효과가 가장 컸으며, 압력진동 값이 최대 또는 최소가 되는 지점에서는 감쇠효과가 서로 유사하였으며, 작은 억제효과가 관찰되었다. When pressure wave caused by fluid flow oscillates in phase with resonant modes in feeding line, which is connected with propellants tank, pressure oscillation is amplified, leading to structural vibration or fracture. In this study, block is installed inside feeding line for suppression of pressure oscillation and the effect of installation position is investigated numerically. In case that the block is installed at pressure node, maximum suppression effect is observed. However, the block installed at pressure antinode has negligible effect on acoustic damping.