화염전달함수와 Helmholtz solver를 이용한 모델 연소기의 연소불안정 연구

김성구(Seong-Ku Kim),최환석(Hwan-Seok Choi),김대식(Daesik Kim),차동진(Dong Jin Cha) 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.5

본 연구에서는 최근에 개발된 Helmholtz solver를 이용하여 예혼합 가스터빈 모델 연소기에서 종방향 음향 모드로 발생하는 자발 연소불안정을 해석하였다. 음향섭동에 대한 화염의 응답특성은 속도감응 시간지연모델을 적용하였으며, 모델 파라미터들은 실험으로부터 계측된 화염전달함수를 통해 결정하였다. 연소실 길이를 변경시켰을 때, 연소시험 결과와 유사한 구간에서 2차 종 방향 모드의 자발 불안정이 예측되었으며, 입구의 음향 특성은 연소불안정의 발생 여부뿐만 아니라 공진 주파수와 모드 형태에도 큰 영향을 미치는 것으로 나타났다. This study investigated numerically longitudinal combustion instability of a lean premixed model gas-turbine combustor using a recently developed Helmholtz solver. The response of heat release rate to acoustic perturbation was modeled based on the velocity-sensitive time-lag theory, whose parameters were determined by experimentally measured FTF (Flame Transfer Function). The present model predicted spontaneous instabilities in second longitudinal mode for certain range of combustion chamber length, which is in line with the experiment. The numerical result clearly reveals that the acoustic boundary condition at the inlet affects greatly the resonant frequency and mode shape of the combustion instability as well as its growth rate.

연소응용 기술 : Helmholtz solver를 이용한 연소불안정 예측 기법 소개

임재영 ( Jaeyoung Lim ),김대식 ( Deasik Kim ),김성구 ( Seong-ku Kim ),차동진 ( Dong Jin Cha ) 한국액체미립화학회 2015 한국액체미립화학회 학술강연회 논문집 Vol.2015 No.-

Lean premixed combustion system has been used to meet strengthened NOx emission regulations. However, it can be easily affected by combustion instability. This paper introduces a FEM(Finite Element Method)-based Helmholtz solver developed to predict numerically longitudinal combustion instability. The results such as complex valued eigenfrequency and acoustic pressure field can predict resonant frequency, growth rate and modal shape for acoustic modes.

음향 경계 조건이 가스터빈 연소기에서의 연소불안정에 미치는 영향

임재영(Jaeyoung Lim),김대식(Deasik Kim),김성구(Seong-Ku Kim),차동진(Dong Jin Cha) 한국추진공학회 2015 한국추진공학회 학술대회논문집 Vol.2015 No.5

본 연구는 유한요소해석 기반의 Helmholtz solver인 ASCI3D를 사용하여 예혼합 가스터빈 연소기에서 연소불안정 현상과 관련된 주요 결과들을 예측하였다. 해석 결과 실험 결과와 비교할 때 일반적인 불안정 특성 예측에는 성공하였으나, 불안정 구간이 나타나는 영역을 다소 과대 예측하는 경향이 발견되었다. 이를 개선하기 위한 노력으로 반사계수가 불안정 특성에 미치는 영향이 분석되었다. 결과로부터 반사계수는 불안정 특성에 큰 영향을 미치고, 정확한 예측 결과를 얻기 위해서는 정확한 음향 경계조건의 정의가 필수적인 것으로 나타났다. This study predicts the basic characteristics of combustion instabilities in a gas turbine lean premixed combustor using ASCI3D code which is a FEM(Finite Element Method)-based Helmholtz solver. The prediction results show the good agreement with the measured data in modeling the overall combustion instability features, however, the code is found to overpredict the unstable conditions. As one of the efforts to improve the model accuracy, the effects of acoustic boundary conditions on the instability growth rate are analyzed. As a result, it is shown that the acoustic reflection coefficient has a great impact on the instability and the prediction accuracy can be enhanced by defining the precise acoustic conditions.

고주파 연소불안정 예측을 위한 해석기술 개발 사례

김성구(Seong-Ku Kim),조미옥(Miok Joh),한상훈(Sanghoon Han),최환석(Hwan-Seok Choi) 한국추진공학회 2017 한국추진공학회 학술대회논문집 Vol.2017 No.5

고주파 연소불안정은 비정상 화염의 열방출율 섭동과 연소실 내부에서 공진되는 음향파의 상호 결합으로 발생하는 열음향 문제로, 다양한 해석적 접근방법이 존재한다. 본 논문에서는 주파수 영역에서 선형음향 가정과 시간지연 이론을 이용한 3차원 FEM Helmholtz solver의 개발 사례를 소개하였으며, 가변길이 희박 예혼합 연소기의 자발 연소불안정 예측과 수동제어기구(배플, 음향공진기)의 설계분석 결과를 제시하였다. 또한 시간 영역에서 시간지연 이론을 이용한 압축성 유동 해석코드를 통해, 고진폭 압력섭동에 의해 야기되는 비선형 음향 특성과 한계사이클 현상을 분석하였다. High-frequency combustion instability results from a feedback coupling between the unsteady heat release rate and the acoustic waves formed resonantly in the combustion chamber. It can be modeled as thermoacoustic problems with various degrees of the assumptions and simplifications. This paper presents numerical analysis of self-excited combustion instabilities in a variable-length lean-premixed combustor and designs of passive control devices such as baffle and acoustic resonators in a framework of 3-D FEM Helmholtz solver. Nonlinear behaviors such as steep-fronted shock waves and a finite amplitude limit cycle are also investigated with a compressible flow simulation technique.

국부 화염전달함수 모델링과 Helmholtz solver를 이용한 연소불안정 해석

임재영(Jaeyoung Lim),표영민(Youngmin Pyo),김성구(Sung-Ku Kim),차동진(Dong Jin Cha),김대식(Daesik Kim) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5

대부분의 열음향 모델은 얇은 화염면을 가정하고 해석하기 때문에 이러한 과도한 화염장의 단순화로부터 정의된 모델의 예측값은 실험 결과와 비교할 때, 무시할 수 없는 오차가 존재하였다. 따라서 본 논문에서는 화염의 공간적인 분포를 고려하기 위한 하나의 방법인 국부화염전달함수를 소개하고 이를 적용하여 열음향 해석 문제에서 열분포가 불안정 예측 결과에 미치는 영향을 비교, 평가하였다. 전역 화염전달함수를 이용한 모델보다 국부 화염전달함수를 적용한 모델이 성장률 예측에 있어서 오차가 줄어드는 것으로 나타났다. Most thermoacoustic(TA) models assume that the rate of heat release occurs at infinitely thin flames. This over-simplification of the reaction zone in the model is found to affect the prediction accuracy. The current paper introduces a local flame transfer function(FTF) as one of the methods considering heat release distribution. From the TA modeling results, the prediction accuracy when using the local FTF can be improved in comparison with the models using the global FTF.

음향 경계 조건이 가스터빈 연소기에서의 연소불안정에 미치는 영향

임재영(Jaeyoung Lim),김대식(Deasik Kim),김성구(Seong-Ku Kim),차동진(Dong Jin Cha) 한국추진공학회 2015 한국추진공학회지 Vol.19 No.4

This study predicts the basic characteristics of combustion instabilities in a gas turbine lean premixed combustor using ASCI3D code which is a FEM(Finite Element Method)-based Helmholtz solver. The prediction results show the good agreement with the measured data in modeling the overall combustion instability features, however, the code is found to overpredict the unstable conditions. As one of the efforts to improve the model accuracy, the effects of acoustic boundary conditions on the instability growth rate are analyzed. As a result, it is shown that the acoustic reflection coefficient has a great impact on the instability and the prediction accuracy can be enhanced by defining the precise acoustic conditions.

Finite element analysis of self-excited instabilities in a lean premixed gas turbine combustor

Kim, Seong-Ku,Kim, Daesik,Cha, Dong Jin Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.120 No.-

<P><B>Abstract</B></P> <P>The present study numerically simulates self-excited instabilities of hydrogen-blended natural gas flames in a lean premixed gas turbine combustor with variable chamber length. In order to effectively predict the thermoacoustic instability within the detailed geometry of the combustor, the Helmholtz equation is discretized with a Galerkin finite element method on a three-dimensional hybrid unstructured mesh. The unsteady heat release rate is modeled with an experimentally measured flame transfer function. The nonlinearity associated with the flame response term is handled with an iterative method, and the large-scale eigenvalue problem is solved by means of the shift-invert method of the ARPACK (ARnoldi PACKage) software. The present Helmholtz solver reproduces the experimentally observed instabilities in terms of the mode frequency and the chamber length range of self-excited pressure oscillations which are significantly affected by the hydrogen enrichment of natural gas fuel. The effects of the acoustic boundary condition and the flame response model on the predictive accuracy are also discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This study has successfully developed an in-house Helmholtz solver by adopting the FEM on a mixed element mesh and the shift-invert method for solving the eigen-value problem. </LI> <LI> It has been applied to simulate self-excited instabilities in a lean premixed, swirl stabilized, model gas turbine combustor with well-established measurements. </LI> <LI> The current work has quantitatively investigated the effects of flame response model and the acoustic condition at the inflow boundary on the mode shape and acoustic loss. </LI> <LI> These discussions point to further research directions for improving predictive accuracy. </LI> </UL> </P>

헬름홀츠 솔버 기반의 3차원 열음향해석을 통한 발전용 단일 캔 연소기에서의 공진 모드 분석

정준우,김대식 한국분무공학회 2024 한국액체미립화학회지 Vol.29 No.1

This study conducted a 3D thermo-acoustic analysis based on the helmholtz solver to analyze the major resonance modes causing combustion instability in a single-can combustor. The experimental investigations were carried out on a test rig designed by the Korea Institute of Machinery & Materials (KIMM) under various conditions of hydrogen co-firing and fuel staging. Through these experiments, two primary unstable frequencies were identified. To determine the resonance modes of these frequencies, a 3D thermo-acoustic analysis was conducted using temperature information from the test rig. The results confirmed that the unstable frequencies observed in the experiments were all longitudinal modes. Additionally, the mode shapes identified in the analysis facilitated a simplification of the exit geometry for the low-order network model, confirming that this did not significantly affect the fundamental resonance modes.

가스터빈에서의 연소불안정 - 모델링 접근법

김대식 ( Daesik Kim ) 한국액체미립화학회 2018 한국액체미립화학회 학술강연회 논문집 Vol.2018 No.-

Various combustion modeling approaches have been developed and verified in a combustion system such as rockets, gas turbines, and so on. This study introduces basic theory and recent research activities on 1D network model where a system is divided into a series of acoustic element and mass/momentum/energy conservations are applied in the component. Each component is connected to the neighboring ones with proper jump conditions. In addition, Helmholtz solver based on 3D FEM approach is applied to study the thermoacoustic behaviors in a gas turbine combustor and compared with the 1D modeling results.

환형 연소기 시스템에서 비연소 3D 음향장 해석

임재영,김대식 한국추진공학회 2017 한국추진공학회지 Vol.21 No.6

The current study has developed an in-house 3D FEM code in order to model thermoacoustic problems in an annular system and compared the acoustic field calculation results with measured ones from a benchmark combustor. From the comparison of calculation results with the measured data, the current acoustic code could successfully capture the various acoustic mode found in the annular system. In addition, it was found that the transverse waves in the combustor were strongly affected by the nozzle acoustic impedances, as well, the pressure distributions were closely related with the combustor acoustic pressure field. 연구에서는 환형 시스템에서 열음향 문제를 모델링하기 위하여 자체 3D 유한요소해석을 모델 개발을 통하여 음향장을 해석하였고, 다양한 음향 모드를 벤치마크 연소기의 실험 결과와 비교/검증하였다. 비교 결과, 본 해석에서 사용된 음향장 해석 코드는 환형 시스템에서 실험으로 계측된 다양한 음향 모드들을 예측하는데 성공하였다. 또한 연소실의 횡방향 모드는 노즐의 음향 경계 조건의 영향을 크게 받게 되고, 노즐에서의 압력 분포 역시 연소실의 압력장과 밀접한 관련이 있는 것으로 나타났다.