네트워크 모델을 이용한 가스터빈 연소기의 연소불안정 해석
Combustion instability analysis in a gas turbine combustor using the network modeling method
- 주제(키워드) Lean Premixed Combustor , Combustion Instability , Network Model , Thermoacoustic , FTF(Flame Transfer Function)
- 발행기관 강릉원주대학교
- 지도교수 김대식
- 발행년도 2017
- 학위수여년월 2017. 8
- 학위명 석사
- 학과 및 전공 일반대학원 정밀기계공학과
- 세부전공 연소불안정해석
- 실제URI http://www.dcollection.net/handler/kangnung/000000009838
- 본문언어 한국어
- 저작권 강릉원주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
In the areas of modern aero-engines and industrial gas turbines, it is required to maintain the high performances in the combustor and at the same time, to cut down on the low fuel consumption and reduce even the emissions of pollutant. The design for the combustion system, required to achieve these requirements, is to operate the combustion by premixing at low equivalence ratio, and the combustion system like this is called as the lean premixed combustion system. This system could satisfy the proper conditions for NOx emissions, the main problem to solve. However, this lean premixed combustor system has the problem of the combustion instability, resulting in the problems of the economic losses as well as the system stability, and many industries and research institutions have developed the ways to solve them. The mechanism of this combustion instability phenomenon is defined by the feedback relationship between acoustic pressure fluctuations and heat release fluctuations inside the combustor, which is showing that the acoustic characteristics in the combustion system may be the key parameters in determining the combustion instability phenomenon in the gas turbine combustor. The network model developed in this study is a method to interpret the combustion instability, which has the advantages of being easier and simpler than other modeling methods in the structure of formulas. This network model was modeled based on the physical conservation equations, along with the acoustic theory, and once getting the final solution, the information could be gained on the unstable frequency and initial growth rate causing the combustion instability. In addition, this model can represent the mode-shapes for each instability acoustic modes, the coordinate axis was constituted by using a cylindrical polar coordinate system, and the speed in the radial direction was assumed to be zero. Here, the network elements which constitute the network system are the inlet boundary conditions, length variations, area changes, combustion, and outlet boundary conditions. The numerical and analytical results were analyzed by comparing with the results measured in the experiment, according to each different shape. Firstly, the result from the can-type combustor (Case A) could be divided into two kinds; first of all, the FTF(Flame Transfer Function) was modeled by primarily using CFD, at this time, when executing a prediction on the phase difference changes of FTF by using a combustion model in which the heat transfer conditions were optimized, it could be successfully predicted. However, in the prediction on the gain value differences of FTF, it could be identified that it has some errors, compared to an experimental data. Subsequently, when conducting the acoustic analysis where the observed FTF was applied in the experiment, it was successful in the stable frequency and the growth rate prediction; yet, at this time, the tendency to overestimate in the unstable growth rate prediction could be confirmed. This overestimating tendency could be solved by applying the combustion model considering the realistic flame. In the second result, as a result of the annular combustor (Case B), before conducting the interpretation by applying FTF, the interpretation was carried out by only considering the cold-flow state and hot-flow state, and when considering the cold-flow state, the reliable results could be acquired in predicting the frequency and growth rate. However, in the result considering the hot-flow state, the good results in mode shapes were gained, but there were some errors in the prediction of frequency, and the consideration for the correct distribution of temperature fields was proposed as a method to resolve it. As the final result, in the result of annular combustor (Case C), it could be found that when implementing the acoustic analysis in the combustion state, it was successful, comparing with the experiment in predicting the mode shapes and the corresponding frequency. As a result, the network model developed in this study suggests the sufficient possibility for the combustion instability analysis in the can-type and annular-type combustor.
more목차
Abstract - ⅰ
List of tables - ⅲ
List of figures - ⅳ
Nomenclature - ⅶ
1. 서론 - 1
1.1. 연구 배경 - 1
1.2. 연소불안정 - 4
1.2.1. 피드백 시스템 - 4
1.2.2. 예측 기법 - 5
1.3. 가스터빈 연소기의 종류 - 7
1.4. 음향모드의 종류 - 7
1.5. 연구 동향 - 9
1.6. 연구 목적 - 11
2. 연구 방법 - 12
2.1. 지배 방정식 - 12
2.2. 네트워크 모델링 - 17
2.2.1. 음향 섭동의 분해 - 17
2.2.2. 단순 2단 덕트에서의 네트워크 모델 - 19
2.2.3. 다중 경로를 포함한 덕트에서의 면적변화 - 23
2.3. 연소 모델: 화염전달함수 - 25
3. 해석 대상 연소기 및 해석 조건 - 26
3.1. 캔형 연소기 - 26
3.1.1. 실험 연소기 및 해석 형상 - 26
3.1.2. 해석 조건 및 방법 - 28
3.2. 환형 연소기 - 29
3.2.1. 실험 연소기 및 해석 형상 - 29
3.2.2. 해석 조건 및 방법 - 31
4. 연구 결과 및 고찰 - 34
4.1. 캔형 연소기 - 34
4.1.1. 화염전달함수의 CFD 해석 - 34
4.1.2. 실험값과 네트워크 모델의 예측값 비교 - 38
4.2. 환형 연소기 - 43
4.2.1. 연소전과 연소후의 물성치만을 고려한 음향해석 결과- 43
4.2.2. 화염전달함수를 적용한 음향해석 결과 - 47
5. 결론 - 54
참고문헌 - 56
