• Title/Summary/Keyword: Thermoacoustic waves

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Linear Stability Analysis in a Gas Turbine Combustor Using Thermoacoustic Models (열음향 해석 모델을 통한 가스터빈 연소기에서의 선형 안정성 분석)

  • Kim, Daesik
    • Journal of the Korean Society of Combustion
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    • v.17 no.2
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    • pp.17-23
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    • 2012
  • In this study, thermoacoustic analysis model was developed in order to predict both eigenfrequencies and initial growth rate of combustion instabilities for lean premixed gas turbine combustors. As a first step, a model combustor and nozzle were selected and analytical linear equations for thermoacoustic waves were derived for a given combustion system. Then, methods showing how the equations can be used for analysis of the combustion instability were suggested. It was found that the prediction results showed a good agreement with the measurements. However, there were some limitation in growth rate predictions, which were related with over-simplification of flame structure, acoustic boundary conditions, and temperature distribution in the combustor.

A Comparative Study on the Characteristics of Thermoacoustic Waves by the Stack Channel Number (스택의 채널 수에 다른 열음향파의 특성 비교 연구)

  • Park, Sung-Seek;Cheon, Won-Gi;Kim, Nam-Jin
    • Journal of the Korean Solar Energy Society
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    • v.33 no.4
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    • pp.8-14
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    • 2013
  • The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level(SPL), onset time and the temperature gradient across the stack, with the Cell Per Square Inch(CPSI) of stack changed. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. As a result, when the supply electric power was 25W, maximum SPLs of 104.1 dB, 109.4 dB and 112.8 dB were detected for the stacks of 200, 300 and 400 CPSI and their respective stack positions of 70mm, 60mm and 50mm from the closed end.

Thermoacoustic Analysis Model for Combustion Instability Prediction - Part 1 : Linear Instability Analysis (연소 불안정 예측을 위한 열음향 해석 모델 - Part 1 : 선형 안정성 해석)

  • Kim, Daesik;Kim, Kyu Tae
    • Journal of the Korean Society of Propulsion Engineers
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    • v.16 no.6
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    • pp.32-40
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    • 2012
  • For predicting eigenfrequency and initial growth rate of combustion instabilities in lean premixed gas turbine combustor, linear thermoacoustic analysis model was developed in the current paper. A model combustor was selected for the model validation, which has well-defined inlet and outlet conditions and a relatively simple geometry, compared to the combustor in the previous works. Analytical linear equations for thermoacoustic waves were derived for a given combustion system. It was found that the prediction results showed a good agreement with the measurements, even though there was underestimation for instability frequencies. This underestimation was more obvious for a longer flame (i.e. wider temperature distribution) than for a shorter flame.

The Analysis of Acoustic Waves generated by a TA(ThermoAcoustic) Laser Pair (열음향(Thermoacoustic) 레이저의 음향파 특성 분석)

  • Oh, Seung-Jin;Chen, Kuan;Lee, Yoon-Joon;Shin, Sang-Woong;Lim, Sang-Hoon;Chun, Won-Gee
    • Journal of the Korean Solar Energy Society
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    • v.31 no.6
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    • pp.1-7
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    • 2011
  • Sound waves and acoustic energy generated by two identical TA (ThermoAcoustic) lasers were analyzed and studied. One end of the ceramic stack was heated by a thin NiCr wire wound around that end. The other end of the stack was cooled by natural convection of atmospheric air. The wavelength of the sound waves generated by a single TA laser was four times the tube length and the amplitude of the waves increased with the heating rate. SPL (SoundPressure Level) meters and microphones were employed to measure and study the sound waves at different distances from the glass tube opening and at the focusing point of the TA laser pair for different laser position arrangements. The sound waves of the two TA lasers at the focusing point were found to be almost 180 degrees out of phase when the openings of the two lasers were very close to each other and the angle between the laser axes was small. When the two TA lasers were placed far apart, the sound wave amplitudes and the phase difference between the two laser outputs varied periodically with time. The frequencies of the sound waves changed when the openings of the two TA lasers were in close vicinity and the angle between the laser axes exceeded a certain value. In this case, the glass tube opening was no longer a pressure anti-node and the wavelength of the fundamental mode was not equal to four times the tube length.

Introduction of Numerical Simulation Techniques for High-Frequency Combustion Instabilities (고주파 연소불안정 예측을 위한 해석기술 개발 사례)

  • Kim, Seong-Ku;Joh, Miok;Han, Sanghoon;Choi, Hwan-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.68-77
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    • 2017
  • 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.

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Active Control of Thermoacoustic Instability in Cylindrical Combustor with Low Speed Flow Field (저속 유동장이 있는 원통형 연소기에서의 열-음향학적 불안정에 대한 능동 제어 연구)

  • 조상연;이용석;이수갑;배충식
    • Journal of KSNVE
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    • v.8 no.5
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    • pp.914-921
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    • 1998
  • Combusion instability due to thermoacoustic feedback in a ducted combustor usually excites severe noise and vibration, which could lead to result in the failure of the system or environmental dispute. In the present study, an active noise control(ANC) method with an adaptive algotithm is hired to suppress instability which has very discrete behavior in the frequency domain. Especially a feedback system is composed to evade hot environment of the combustor, and as a preliminary, the performance and stability of the controller is chekced by simulating the real situation with harmonic waves. Application to the real combustor showed serious reductions in sound pressure level by 20∼30 dB. It was also shown that the selected control system was very stable and effective.

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A Comparative Study on the Characteristics of Thermoacoustic Laser for Applying Solar Energy (태양열 적용을 위한 열음향 레이저의 특성 비교 연구)

  • Park, Sung-Seek;An, Eoung-Jin;Oh, Seung-Jin;Chun, Won-Gee;Kim, Nam-Jin
    • Journal of the Korean Solar Energy Society
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    • v.32 no.2
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    • pp.105-112
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    • 2012
  • The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level (SPL), frequency, onset time and the temperature gradient across the stack. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. For a resonance tube of 100 mm, no acoustic waves were generated with a power input of 25W. By increasing its length to 200 mm, however, maximum SPLs of 96.4 dB, 106.3 dB and 112.8 dB were detected for the tubes of 10mm,20mm and 30mm in IDs and their respective stack positions of 70mm, 60mm and 50mm from the closed end.

A Comparative Study on the Characteristics of Thermoacoustic Laser for Using Solar Energy (태양에너지 이용을 위한 열음향 레이저의 특성 비교 연구)

  • Park, Sung-Seek;An, Eoung-Jin;Oh, Seung-Jin;Chun, Won-Gee;Kim, Nam-Jin
    • 한국태양에너지학회:학술대회논문집
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    • 2012.03a
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    • pp.516-521
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    • 2012
  • The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level (SPL), frequency, onset time and the temperature gradient across the stack. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. For a resonance tube of 100mm, no acoustic waves were generated with a power input of 25W. By increasing its length to 200mm, however, maximum SPLs of 96.4 dB, 106.3 dB and 112.8 dB were detected for the tubes of 10mm, 20mm and 30mm in IDs and their respective stack positions of 70mm, 60mm and 50mm from the closed end.

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Introduction to Thermoacoustic Models for Combustion Instability Prediction Using Flame Transfer Function (화염 전달 함수를 이용한 열음향 연소 불안정 해석 모델 소개)

  • Kim, Dae-Sik
    • Journal of the Korean Society of Propulsion Engineers
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    • v.15 no.6
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    • pp.98-106
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    • 2011
  • This paper reviews the state-of-the-art thermoacoustic(TA) modeling techniques and research trend to predict major parameters determining combustion instabilities in lean premixed gas turbine combustors. Linear TA modeling results give us an information on eigenfrequencies and initial growth rate of the instabilities. For the prediction, linear relation equation between acoustic waves and heat release oscillations should be derived in the determined system. Key information for this analysis is to determine the heat release fluctuations in the combustor, which is typically obtained by using n-${\tau}$ function from flame transfer function measurements and/or predictions. Great advancement in the linear TA modeling has been made over a couple of decades, and some successful prediction results have been reported in actual gas turbine combustors. However nonlinear TA model developments which are required to analyze nonlinear system behaviors such as limit cycle saturation and transition phenomena are still limited in a very simple system. In order to fully understand combustion instabilities in a complicated real system, nonlinear flame dynamics and acoustic wave interaction with nonlinear system boundary conditions should be explained from the nonlinear TA model developments.

3D Acoustic Field Analysis in an Annular Combustor System under a Cold Flow Condition (환형 연소기 시스템에서 비연소 3D 음향장 해석)

  • Lim, Jaeyoung;Kim, Daesik
    • Journal of the Korean Society of Propulsion Engineers
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    • v.21 no.6
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    • pp.49-56
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    • 2017
  • 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.