검색 상세

가스터빈 연소불안정 예측을 위한 수치 해석 기반 연소기 출구 음향 경계조건 도출 및 해석

Numerical Derivation and Analysis of Acoustic Boundary Conditions at the Combustor Exit for Gas-Turbine Combustion Instability Prediction

  • 정다빈 (국립강릉원주대학교 일반대학원)

초록/요약 도움말

In gas turbine combustors, acoustic waves induce perturbations in velocity and mixture fraction, and the resulting fluctuations in heat release interact again with the acoustic field to form a feedback loop, leading to combustion instability. In this process, the acoustic boundary condition at the combustor exit, i.e. at the turbine inlet, is a key factor governing the thermoacoustic behavior of the system; however, in practical power-generation gas turbines, the combined effects of turbine vanes, cross-talk sections, and the can-annular configuration make it difficult for simple open/closed boundary conditions or ideal choked-nozzle models to capture the realistic behavior. The aim of this study is to numerically derive frequency-dependent complex acoustic reflection coefficients for a full-scale gas turbine turbine inlet stage, taking into account the actual vane geometry and operating conditions, and to use them to analyze the thermoacoustic characteristics of a can-annular combustor. To this end, an unsteady RANS-based CFD simulation is first combined with a multi-microphone method for a two-dimensional vane model reported in the literature to compute the acoustic reflection coefficients, and the results are compared with existing data to validate the proposed methodology. The validated approach is then applied to a three-dimensional real gas turbine vane geometry, where vane stagger angle, combustor exit flow velocity, and turbine inlet temperature are selected as design parameters, and frequency-dependent complex reflection coefficients are obtained for each operating condition. These acoustic reflection coefficients are imposed as outlet boundary conditions in a three-dimensional FEM model based on the Helmholtz equation, enabling a quantitative analysis of the variations in resonant frequency and damping rate of axial modes, inter-can cross-talk modes, and coupled modes in a can-annular system. The results show that changes in the magnitude and phase of the reflection coefficients significantly alter the resonant frequencies and damping characteristics of mode clusters; in particular, increasing vane angle and combustor exit velocity increases the reflection magnitude and reduces the damping rate of certain modes. In contrast, variations in turbine inlet temperature have little influence on the reflection magnitude but shift the resonant frequency through changes in the speed of sound. These findings demonstrate that frequency-dependent acoustic boundary conditions reflecting the actual turbine inlet geometry and operating conditions must be accounted for in the thermoacoustic design and combustion instability prediction of gas turbine combustors, and that the CFD–multi-microphone–3D FEM coupled methodology proposed in this study can serve as a foundation for more realistic acoustic boundary modeling in future full-scale gas turbine combustor designs.

more

목차 도움말

1. 서론 1
1.1. 연소 불안정에서의 음향 경계조건 1
1.2. Lab-scale 음향 경계조건 3
1.3. 실제 연소실 출구 음향 경계조건 5
1.4. 실제 터빈 입구 음향 경계조건 도출의 제한점과 CFD 기반 접근 7
1.5. 연구 목적 9
2. 연구 방법 10
2.1. CFD 기반 음향 경계조건 도출 방법론 10
2.1.1. 해석 대상 시스템 10
2.1.2. 지배 방정식 11
2.1.3. 멀티 마이크로폰 기법 14
2.2. 수치 해석 방법론 검증 16
2.2.1. Simple duct (Cold condition) 16
2.2.2. Blade duct (Cold condition) 21
2.2.3. Blade duct (Real condition) 24
2.3. 실제 형상 대상 해석 방법 27
2.3.1. CFD 기반 음향 경계조건 도출을 위한 수치 해석 조건 27
2.3.2. Helmholtz 방정식 기반 열음향 해석 조건 (3D-FEM) 29
3. 해석 결과 32
3.1. CFD 기반 음향 경계조건 해석 결과 32
3.1.1. 격자 의존성 테스트 32
3.1.2. 베인 각도에 따른 음향 경계조건 (Without flow) 34
3.1.3. 터빈 입구 온도에 따른 음향 경계조건 (Without flow) 35
3.1.4. 베인 각도에 따른 음향 경계조건 (With flow) 36
3.1.5. 터빈 입구 온도에 따른 음향 경계조건 (With flow) 39
3.1.6. 연소기 출구 유속에 따른 음향 경계조건 40
3.2. 3D FEM 해석 결과 42
3.2.1. Can-annular 시스템에서의 음향 특성 42
3.2.2. 터빈 베인 각도에 따른 음향 해석 결과 44
3.2.3. 터빈 입구 온도에 따른 음향 해석 결과 45
4. 결론 47
참고문헌 49
APPENDIX 55

more
반출 Meta View 목록