연소불안정 해석을 위한 1D 열음향 모델 개발
- 발행기관 강릉원주대학교 일반대학원
- 발행년도 2016
- 학위수여년월 2017. 2
- 학위명 석사
- 학과 및 전공 도움말 일반대학원 정밀기계공학과
- 실제URI http://www.dcollection.net/handler/kangnung/000000009331
- 본문언어 한국어
초록/요약 도움말
The lean premixed combustion method which satisfies low pollution emissions and is highly efficient has a problem in that combustion instability easily occurs; this is not only an economical problem but also a problem in terms of stability, so many industries and laboratories have developed a prediction technique for this phenomenon. In order to control combustion instability in lean premixed gas turbine combustors, linear system dynamics such as instability frequency, conditions that cause combustion instability, and nonlinear system dynamics limit amplitude should be predicted. Among the various prediction methods, there is a 1D network model that can predict the thermoacoustic characteristics of a combustor without changing the mesh information about its shape and various other conditions. In this study, existing thermoacoustic code based on the 1D network model was changed to present the acoustic characteristics of the combustor as an acoustic transfer function(ATF). The properties of the combustion field were assigned in the form of an model through the flame transfer function(FTF) obtained experimentally or by CFD analysis, and then the characteristics of combustion instability were predicted in benchmark combustors. First, the flame was assumed to be thin and located at the dump plane of a two-duct combustor, which is the simples structure. From this, the instability frequency and unstable region were predicted and compared with the experimental results, which were quite corresponsive with qualitative trends but overestimated quantitatively. I presumed that the causes of the errors were due to linear fitting of the phase of FTF and the oversimplification of the flame shape compared to actual one, so I tried to reduce the errors in the prediction. To achieve this, methods were added to te code: a nonlinear fitting of FTF, changing the location of the thin flame, and considering of heat release distribution, which reduced the errors with the experimental values by about 10%. It was shown that accurate flame dynamics are important in predicting characteristics of combustion instability. Second, the FTF was extended to a function of frequencies and velocity perturbations amplitude to become the flame describing function for predicting the limit cycle amplitude of a combustor. The predicted results showed an error rate of approximately 25%, thought to have arisen from the definition of the 1D network model. In order to expand the thermoacoustic model, the three-duct system was selected as a benchmark combustor and the acoustics from the premixing chamber were investigated. From analyzing the pole of the ATF, the resonance frequencies that best reflect the acoustics of the system were predicted, so it was assumed that resonance frequencies are affected by the length of each element (premixing chamber, nozzle, and combustion chamber) and the area ratio between the premixing chamber and the nozzle. Based on these assumptions, the resonance frequencies in the premixing chamber and nozzle() and in the combustion chamber() were predicted. was affected by both the premixing chamber length and the combustion chamber length while was only affected by the combustion chamber length. From these results, it was concluded that the premixing chamber has a decisive effect on the acoustic mode of the whole system. Subsequently, was greatly affected when the area ratio between the premixing chamber and the nozzle was small, but this influence decreased as the area ratio increased. On the other hand, had little effect on the ara ratio. Through this, it was confirmed that the area ratio is an important factor affecting the acoustic mode of the system.
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목 차
Abstract ··································································································· ⅰ
List of Tables ·························································································· ⅳ
List of figures ·························································································· ⅴ
Nomenclature ··························································································· ⅶ
1. 서 론 ····································································································· 1
1.1 연구 배경 ························································································· 1
1.2 연소불안정 ······················································································· 3
1.3 연소불안정 예측 기법 소개 ································································· 5
1.4 연구 동향 ························································································· 9
1.5 연구 목적 ······················································································· 11
2. 연구 방법 ····························································································· 12
2.1 지배방정식 ····················································································· 12
2.2 음향전달함수 ·················································································· 16
2.2.1 2단 연소 시스템 ······································································· 16
2.2.2 3단 연소 시스템 ······································································· 20
2.3 화염전달함수 ·················································································· 23
3. 해석 대상 연소기 및 해석 조건 ······························································· 26
3.1 2단 연소 시스템 ·············································································· 26
3.1.1 해석 대상 연소기 및 실험 조건 ·················································· 26
3.1.2 해석 방법 및 해석 조건 ···························································· 28
3.2 3단 연소 시스템 ·············································································· 30
3.2.1 해석 대상 연소기 및 실험 조건 ·················································· 30
3.2.2 해석 방법 및 해석 조건 ···························································· 32
4. 연구 결과 및 고찰 ················································································· 35
4.1 2단 연소 시스템 ·············································································· 35
4.1.1 선형 연소불안정 특성 예측 결과 ················································ 35
1) 단순화 된 화염 형상에 대한 결과 ··············································· 37
2) 화염전달함수의 비선형 위상에 대한 결과 ···································· 39
3) 수정된 화염 위치에 대한 결과 ··················································· 42
4) 열발생 분포의 영향을 고려한 결과 ············································· 45
4.1.2 비선형 연소불안정 특성 예측 결과 ············································· 48
4.2 3단 연소 시스템 ·············································································· 51
4.2.1 예혼합실과 연소실의 길이 변화에 대한 음향장 해석 결과 ·············· 51
4.2.2 예혼합실과 노즐의 면적비 변화에 대한 음향장 해석 결과 ·············· 53
5. 결 론 ··································································································· 55
Reference ································································································ 57
감사의 글 ································································································· 62
