• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.240-243
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• 2003

Combustion instability phenomena have been observed in various different combustion systems. For each specific combustion system, pressure fluctuations measured during high frequency combustion instability presented many different characteristics. High frequency instability occurring in a lean premixed gas turbine combustor mar be dominantly affected by a nonlinear relation between pressure oscillations and heat release rate fluctuations, and gas dynamics plays a crucial role in determining an amplitude of a limit cycle for a liquid rocket thrust chamber. Combustion instability phenomena manifest their inherent nonlinear characteristics. One is a limit cycle and the other bifurcation described by nonlinear time series analysis.

• International Journal of Aerospace System Engineering
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• 제2권2호
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• pp.58-61
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• 2015

Combustion instability in solid rocket motors is a long-term open problem since the first rockets were used. Based on the numerous previous studies, it is known that the limit cycle amplitude is one of the key characteristics of the nonlinear combustion instability in solid rocket motors. Flandro's extended energy balance corollary, aims to predict the limit cycle amplitude of complex, nonlinear pressure oscillations for rockets or air-breathing engines, and leads to a precise assessment of nonlinear combustion instability in solid rocket motors. However, based on the comparison with experimental data, it is revealed that the Flandro's method cannot accurately describe such a complex oscillatory pressure. Thus in this work we make modifications of the nonlinear term in the nonlinear wave equations which represents the interaction of different modes. Through this modified method, a numerical simulation of the cylindrical solid rocket has been carried out, and the simulated result consists well with the experimental data. It means that the added coefficient makes the nonlinear wave growth equations describe the experimental data better.

• Journal of Mechanical Science and Technology
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• 제18권7호
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• pp.1246-1257
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• 2004

The objective of this paper is to characterize dynamic pressure traces measured at self-excited combustion instabilities occurring in two combustion systems of different hardware. One system is a model lean premixed gas turbine combustor and the other a fullscale bipropellant liquid rocket thrust chamber. It is commonly observed in both systems that low frequency waves at around 300㎐ are first excited at the onset of combustion instabilities and after a short duration, the instability mode becomes coupled to the resonant acoustic modes of the combustion chamber, the first longitudinal mode for the lean premixed combustor and the first tangential mode for the rocket thrust chamber. Low frequency waves seem to get excited at first since flame shows the higher heat release response on the lower frequency perturbations with the smaller phase differences between heat release and pressure fluctuations. Nonlinear time series analysis of pressure traces reveals that even stable combustion might have chaotic behavior with the positive maximum Lyapunov exponent. Also, pressure fluctuations under combustion instabilities reach a limit cycle or quasi-periodic oscillations at the very similar run conditions, which manifest that a self-excited high frequency instability has strong nonlinear characteristics.

• 한국연소학회지
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• 제8권1호
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• pp.46-56
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• 2003

The present paper is concerned with the development of the computational biology in the past half century and its relationship with combustion. The modem computational biology is considered to be initiated by the work of Alan Turing on the morphogenesis in 1952. This paper first touches the life and scientific achievement of Alan Turing and his theory on the morphogenesis based on the reactive-diffusive instability, called the Turing instability. The theory of Turing instability was later extended to the nonlinear realm of the reactive-diffusive systems, which is discussed in the framework of the excitable media by using the Oregonator model. Then, combustion analogies of the Turing instability and excitable media are discussed for the cellular instability, pattern forming combustion phenomena and flame edge. Finally, the recent efforts on numerical simulations of biological systems, employing the detailed bio-chemical knietic mechanism is discussed along with the possibility of applying the numerical combustion techniques to the computational cell biology.

• 한국추진공학회지
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• 제16권6호
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• pp.41-47
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• 2012

연소 불안정 현상을 완전하게 이해하기 위해서는 천이 과정과 한계 진폭과 같은 비선형 거동에 대한 예측이 매우 중요하다. 가스터빈 희박 예혼합 연소기에서 이러한 비선형 거동은 화염의 비선형 동특성에 크게 의존하게 된다. 본 연구에서는 기존에 선형 해석으로부터 비선형 열음향 해석으로 확장하기 위해서 화염 묘사 함수를 통한 시스템 안정성 해석 기법이 소개되었다. 이를 위하여, 주파수 뿐만 아니라 속도 진폭에 따른 열발생율의 변동 특성이 실험 결과로부터 모델링되었다. 현재 해석 조건에서 비선형 모델링 결과, 주어진 연소기 길이에서 속도 진폭이 불안정 주파수에 미치는 영향은 미비하였으나, 성장률에는 크게 영향을 미치는 것으로 나타났다. 향후 다양한 조건에서 비선형 모델의 검증과 한계 진폭의 예측 결과에 대한 실험 결과와의 비교가 요구된다.

• 대한기계학회논문집B
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• 제30권7호
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• pp.671-681
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• 2006

This study focuses on the development of numerical procedure to analyze the nonlinear combustion instabilities in liquid rocket engine. Nonlinear behaviors of acoustic instabilities are characterized by the existence of limit cycle in linearly unstable engines and nonlinear or triggering instability in linearly stable engines. To discretize convective fluxes with high accuracy and robustness, approximated Riemann solver based on characteristics and Euler-characteristic boundary conditions are employed. The present procedure predicts well the transition processes from initial harmonic pressure disturbance to N-like steep-fronted shock wave in a resonant pipe. Longitudinal pressure oscillations within the SSME(Space Shuttle Main Engine) engine have been analyzed using the pressure-sensitive time lag model to account for unsteady combustion response. It is observed that the pressure oscillations reach a limit cycle which is independent of the characteristics of the initial disturbances and depends only on combustion parameters and operating conditions.

• 한국추진공학회지
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• 제20권1호
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• pp.20-27
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• 2016

연소 불안정 현상은 연료의 응답 함수, 연소율, 국부 연료 표면의 유동 속도에 영향을 미치기 때문에 고체로켓 모터 설계 시 성능이나 구조적 안정성을 다루는 측면에서 매우 중요한 부분이다. 연소 불안정 현상은 음향 모드가 연소/유동과정에서 발생하는 진동수와 결합(coupled)되었을 때 발생한다. 본 연구에서는 비선형 파동방정식으로부터 음향 비선형 불안정 모델을 유도하여 실린더형 고체로켓 모터의 연소 불안정 현상을 분석하였다. 또한 고체로켓 모터 연소실 압력, 연소 속도가 연소 불안정에 미치는 영향을 조사하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.115-116
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• 2015

In the present approach, the flame-acoustics interaction is represented by FDF (Flame Describing Function) which is a important source term in the Helmholtz' equation. In this study, the combustion instability is analyzed by the forced mode strategy with the measured FDF. Numerical results indicate that the present approach reasonably well predicts the essential features of the combustion instability characteristics in the lean premixed combustor under the gas-turbine like environment.

• 한국추진공학회지
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• 제2권1호
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• pp.41-49
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• 1998

램제트 혹은 오그멘터에서 발생하는 길이방향 비선형 연소불안정성 해석을 위하여 모달해석법을 사용하여 수학적 모델을 만들었다. 이 모델은 2-모드 공식에 국한되며, 지배 방정식을 분석적으로 또한 수치적으로 풀었다. 이 2-모드 비선형 모델은 비선형 속도 민감 연소 반응의 특징인 부트스트래핑 효과를 예측할 수 있다. 또한, 파라미터 연구를 수행하였다.

• 한국연소학회지
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• 제17권3호
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• pp.9-16
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• 2012

Nonlinear dynamics of pulsating instability in radiating counterflow diffusion flames is numerically investigated by imposing Damk$\ddot{o}$hler number perturbation. Stable limit-cycle solutions occur in small ranges of Damk$\ddot{o}$hler numbers past bifurcation point of instability. Period doubling cascade and chaotic behaviors appear just before dynamic extinction occurs. Nonlinear dynamics is also studied when large disturbances are imposed to flames. For weak steady flames, the dynamic extinction range shrinks as the magnitudes of disturbances are increased. However, strong steady flames can overcome relatively large disturbances, thereby the dynamic extinction range extending. Stable limit-cycle behaviors reappears prior to dynamic extinction when the steady flames are strong enough.