CFD 및 Helmholtz solver를 이용한 희박 예혼합 연소기의 연소불안정 연구
Study on combustion instability in a lean premixed combustor using CFD and Helmholtz solver
초록/요약
The lean premixed combustion method can achieve the high efficiency, while satisfying the enhanced exhaust gas regulations, but has a problem of the combustion instability because it operates at an equivalence ratio of the lean burnable limit. In order to understand and control the combustion instability phenomenon, numerous studies are currently underway. This study conducted the research for the combustion instability phenomenon by using CFD and Helmholtz solver. The research was divided into two types: the can-type combustor and the annular combustor. In order to control the combustion instability phenomenon, the unstable frequency, the generation condition, and the growth rate of the instability factors should be predicted. There are various methods for predicting unstable characteristics, but this study was conducted by using numerical analysis. In the can type combustor, the flame transfer function for the velocity perturbation and equivalent ratio perturbation on the combustor nozzle was obtained by utilizing Fluent, the CFD commercial code, and the instability characteristics were predicted by substituting the combustion characteristics data into the Helmholtz solver. In the initial stage of study, as a result of conducting the study by assuming the flame inside the combustion chamber to be a thin flame, the unstable frequency and the acoustic mode were predicted similarly, but the growth rate was overestimated. Subsequently, was substituted into the Helmholtz equation by considering the heat release area inside the combustion chamber. As a result, the growth rates similar to experimental data could be predicted. As the lean premixed combustion method is applied to the annular combustors, the necessity of research is increasing. In the annular combustor, since the aspect ratio of the combustion chamber is almost close to 1, the transverse acoustic mode, as well as the longitudinal acoustic mode, may occur in the combustion chamber. The transverse acoustic mode becomes to affect the mixing part of the nozzle, resulting in the unstable combustion phenomenon. Therefore, it is necessary to analyze the nozzle and the acoustic mode coupling inside the combustion chamber, to control the combustion instability phenomenon. In this study, we investigated the acoustic mode mechanism in the nozzle and combustion chamber by analyzing the acoustic mode inside the combustion chamber after changing the inlet boundary condition in the annular combustor nozzle. As a result, it could be confirmed that the acoustic mode inside the combustion chamber would be influenced depending on the nozzle inlet boundary conditions.
more목차
1. 서론
1.1 연구 배경
1.2 가스터빈 연소기 종류
1.3 연소불안정
1.4 연소불안정 모델링 연구동향
1.5 연구목적
2. 연구 방법
2.1 전산유체역학
2.1.1 전산유체역학의 소개
2.1.2 지배 방정식
2.1.3 연소모델
2.1.4 난류모델
2.1.5 화염전달함수
2.2 3차원 열음향 모델
2.2.1 Helmholtz equation
2.2.2 경계조건
2.2.3 연소응답모델
3. 해석 대상 연소기 및 해석 조건
3.1 캔형 연소기
3.1.1 모델 연소기 A
3.1.2 모델 연소기 B
3.2 환형 연소기
3.2.1 모델 연소기 C
3.2.2 모델 연소기 D
4. 연구결과 및 고찰
4.1 캔형 연소기
4.1.1 모델 연소기 A
4.1.2 모델 연소기 B
4.2 환형 연소기
4.2.1 모델 연소기 C
4.2.1 모델 연소기 D
5. 결론
참고문헌
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