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수소/공기 대향류 확산화염의 비선형 음향파 응답특성에 관한 연구
김홍집,정석호,손채훈,Kim, Hong-Jip,Chung, Suk-Ho,Sohn, Chae-Hoon 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.8
Steady-state structure and acoustic-pressure responses of $H_2$/Air counterflow diffusion flames are studied numerically with a detailed chemistry in view of acoustic instability. The Rayleigh criterion is adopted to judge acoustic amplification or attenuation from flame responses. Steady-state flame structures are first investigated and flame responses to various acoustic-pressure oscillations are numerically calculated in near-equilibrium and near-extinction regimes. The acoustic responses of $H_2$/Air flame show that the responses in near-extinction regime always contribute to acoustic amplification regardless of acoustic-oscillation frequency Flames near extinction condition are sensitive to pressure perturbation and thereby peculiar nonlinear responses occur, which could be a possible mechanism in generating the threshold phenomena observed in combustion chamber of propulsion systems.
김홍집,손채훈,정석호,Kim, Hong Jip,Sohn, Chae Hoon,Chung, Suk Ho 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.1
Reignition as special cases of acoustic pressure responses of flame are numerically studied by employing methanol droplet flame as a laminar flamelet. Quasi-steady flame responses occur in the range of small amplitude, low frequency oscillation. Reignition phenomena can occur when, by increasing the frequency of large amplitude acoustic pressure, the magnitude of characteristic acoustic time is the same order of that of characteristic reaction time of flames. And more increasing of amplitude of acoustic pressure induces the direct extinction of flame. Flame can sustain its own intensity even under the steady extinction temperature in case of high frequency acoustic oscillation, and this tendency is remarkable with increasing frequency. Reignition regime with respect to amplitude and frequency of acoustic pressure doesn't exist in low frequency($10^2$ Hz, in this study), but broadens with frequency of acoustic pressure.
김홍집(Hong Jip Kim),최환석(Hwan-Seok Choi) 한국추진공학회 2010 한국추진공학회 학술대회논문집 Vol.2010 No.5
연료링의 위치 및 열차폐 코팅의 종류에 따른 연소기의 재생냉각 특성을 검토하였다. 연료링을 노즐의 중간 부분에 위치시키고 냉각채널을 분기시켜서 설계하는 방법이 열적으로 타당함을 확인하였다. 또한 복합재를 이용한 노즐확장부가 적용 가능한 기술적 상황이라면, 팽창비가 높고 열유속이 낮은 노즐 후류 부분은 이를 이용하는 것이 매우 적절하다고 판단된다. 적용 가능한 열차폐 코팅 중에서 30톤급 연소기 및 가스발생기 개발과정에서 사용했던 Y2O3 stabilized ZrO2과 내산화성이 우수한 Ni/Cr을 고려하였다. 내산화성이 우수한 Ni/Cr에 비해 세라믹 코팅(Y2O3 stabilized ZrO2)이 열차폐 효과가 우수한 것으로 파악되었다. Thermal analyses have been performed to study the effect of location of fuel ring and thermal barrier coatings in regenerative cooling channels in a full-scale combustor. For the effective cooling, the fuel ring has better be installed near axial location of the low expansion ratio and low heat flux, and branching of cooling channels is preferable. Also, the radiative cooled nozzle extension is thought to be reasonable for the cooling of combustion walls. Among the possible coatings, Y2O3 stabilized ZrO2 coating and Ni/Cr coating have been adopted. Compared with Ni/Cr coating which has high oxidation resistance, Y2O3 stabilized ZrO2 coating, one of ceramic coatings is found to be much effective to sustain the thermal survivability of combustion walls.
로켓연소실에서 음향공의 음향학적 감쇠에 대한 정량적 고찰
김홍집(Hong-Jip Kim),김성구(Seong-Ku Kim),최환석(Hwan-Seok Choi) 한국항공우주연구원 2006 항공우주기술 Vol.5 No.2
로켓엔진에서의 고주파 연소불안정을 제어하기 위하여 널리 사용되는 음향공에 대하여, 3차원 선형 음향해석을 수행하여 음향공의 감쇠 능력을 정량화하고자 하였다. 선형음향해석에 의한 공진주파수는 상온에서 고전적 이론에 의한 공진주파수와 약 6%, 압력 배에 의한 결과와는 약 10%의 차이를 보임을 확인하였다. 음향공의 개수에 따른 acoustic impedance 특성을 살펴보았고, 본 연구의 결과가 기존의 결과와 정량적으로 유사함을 확인하였다. 기하학적으로 동일한 음향공이 여러 개 설치된 연소실에서는 음향장의 특성과는 상관없이 각각의 음향공이 동일한 acoustic impedance 특성을 보임을 확인하였다. 이로써 acoustic impedance를 도입하여 음향공의 최적 동조를 위한 설계 절차를 확립하였다. A linear acoustic analysis has been performed to elucidate damping characteristics of acoustic cavities in a liquid rocket combustor. Results have shown that resonant frequencies of acoustic cavity obtained by classical theoretic approach and by the present linear analysis are somewhat different with each other. This difference is attributed to the limitation of the simplified classical theory. To quantify the damping characteristics, acoustic impedance has been introduced and resultant absorption coefficient and conductance have been evaluated. Satisfactory agreement has been achieved with previous experiment. Finally the design procedure for an optimal tuning of acoustic cavity has been established.