• Title/Summary/Keyword: Acoustic Instability

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Acoustic Analysis of KSR-III Combustion Chamber with Various 5-Blade Baffles under Non-Reacting Condition (5-블레이드 배플이 설치된 로켓엔진 연소실에서의 상온음향 해석)

  • Kim, Hong-Jip;Kim, Seong-Ku;Sohn, Chae-Hoon
    • 한국연소학회:학술대회논문집
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    • 2003.05a
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    • pp.167-171
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    • 2003
  • Acoustic characteristics of baffled combustion chamber to elucidate suppressing effect of baffle on combustion instability are numerically investigated by linear acoustic analysis. A hub-blade baffle of 5 blades is selected as a candidate one and five variants of baffles with various configuration are designed. Resonant-frequency shift and damping factor are analyzed quantitatively as damping parameters. When the hub is located radially at the pressure node, the decrease of resonant frequency and increase of damping factor in 1R mode are dominant. But sub-1T mode is formed within hub, therefore, there would be a possibility of initiating 1T mode in unbaffled region, which would occur another problem. For smaller hub size, four kinds of axial baffle length is selected. As the axial baffle length increases, resonant frequency shift and increase of damping factor of transverse acoustic modes is obtained. Especially, two close acoustic modes such as 1L and 1T could be overlapped for a certain axial length, resulting in extreme increase of damping factor. The present study based on linear acoustic analysis is expected to be a useful confirming tool to predict acoustic field and design a passive control devices such as baffle and acoustic cavity.

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An Experimental Study of Instability Mode Analysis in a Model Gas Turbine Combustor (모형 가스터빈 연소기에서의 연소 불안정 모드 분석에 관한 실험적 연구)

  • Lee, Jang-Su;Kim, Min-Ki;Park, Sung-Soon;Lee, Jong-Guen;Yoon, Young-Bin
    • Journal of the Korean Society of Combustion
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    • v.15 no.1
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    • pp.12-21
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    • 2010
  • The main objective of this study was investigation of combustion instability characteristics in a lean partially premixed gas turbine dump combustor. Dynamic pressure transducers were located on combustor and inlet section to observe combustion pressure oscillation and difference at each measurement places. Also flame shape and $CH^*$ chemiluminescence were measured using a high speed ICCD camera. The combustor length was varied in order to have different acoustic characteristics from 800 to 1090 mm. The first section of this paper shows the stability map in model gas turbine combustor. And the effects of combustor length, mixture velocity in the mixing section and equivalence ratio were studied by the pressure perturbation and heat release oscillation. Also, the instability frequency and mode analysis were studied in last two sections. We observed two dominant instability frequencies in this study. Lower frequencies were obtained at lower equivalence ratio region and it was associated with a fundamental longitudinal mode of combustor length. Higher frequencies were observed in higher equivalence ratio conditions. It was related to secondary longitudinal mode of combustor and mixing section. In this instability characteristics, pressure oscillation of mixing section part was larger than pressure oscillation of combustor. As a result, combustion instability was strongly affected by acoustic characteristics of combustor and mixing section geometry.

The effect of ion to electron mass ratio on Ion beam driven instability and ion holes by PIC simulation

  • Hong, Jin-Hy;Lee, En-Sang;Min, Kyoung-Wook;Parks, George.K.
    • The Bulletin of The Korean Astronomical Society
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    • v.37 no.1
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    • pp.92.2-92.2
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    • 2012
  • Previous simulations posed a problem that they used reduced ion to electron mass ratios to save computation time. It was assumed that ion and electron dynamics are sufficiently separated, but it was not clearly verified. In this study, we examine the effect of ion to electron mass ratios on the generation of ion holes by ion beam driven instability. Ion holes are generated via electron holes in an applied electric field with the given initial condition. First, the ion acoustic instability is excited and nonlinearly develops. After the ion acoustic instability nonlinearly develops, the ion two-stream instability is excited and develops into ion holes. This implies that the previously suggested ion beam driven instability is strongly affected by the coupling between ions and electrons and the ion to electron mass ratio is important on the development of the instability. The energy transition and detail variation is different as reduced mass ratio under the same observation value based on FAST satellite. Although, the parameters are rescaled by conserving the kinetic energy to obtain the proper results, the nonlinear evolution is not perfectly identical.

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A Case Study on Combustion Instability of a Model Lean Premixed Gas Turbine Combustor with Open Source Code OSCILOS (온라인 개방코드 OSCILOS를 이용한 모델 희박 예혼합 가스터빈 연소기의 연소불안정 해석 사례)

  • Cha, Dong Jin;Song, Jin Kwan;Lee, Jong Geun
    • Journal of the Korean Society of Combustion
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    • v.20 no.4
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    • pp.10-18
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    • 2015
  • Combustion instability is a major issue in design and maintenance of gas turbine combustors for efficient operation with low emissions. With the thermoacoustic view point the instability is induced by the interaction of the unsteady heat release of the combustion process and the change in the acoustic pressure in the combustion chamber. In an effort to study the combustion dynamics of gas turbine combustors, Morgans et al (2014) have developed OSCILOS (open source combustion instability low order simulator) code and it is currently available online. In this study the code has been utilized to predict the combustion instability of a reported case for lean premixed gas turbine combustion, and then its prediction results have been compared with the corresponding experimental data. It turned out that both the predicted and the experimental combustion instability results agree well. Further the effects of some typical inlet acoustic boundary conditions on the prediction have been investigated briefly. It is believed that the validity and effectiveness of the open source code is reconfirmed through this benchmark test.

Experimental Study on the Characteristics of Pressure Fluctuation in the Combustion Chamber with Branch Tube (분기관을 가진 연소 챔버 내 압력변동 특성에 관한 실험적 연구)

  • Park, Jang-Hee;Lee, Dae-Keun;Shin, Hyun-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.7
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    • pp.552-558
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    • 2009
  • An experimental study using the combustor with branch tube was conducted in order to model the industry combustor with FGR (flue gas recirculation) system and to study a thermo-acoustic instability generated by a branch tube. The branch tube is a structure used to modify a system geometry and then to change its pressure field, and the thermo-acoustic instability, usually occurs in a confined geometry, can result in serious problems on industrial combustors. Thus understanding of the instability created by modifying geometry of combustor is necessary to design and operate combustor with FGR system. Pressure fluctuation in the combustion chamber was observed according to diameter and length of branch and it was compared with the solution of 1-D wave equation. It was found that branch tube affects the pressure field in the combustion chamber, and the pressure fluctuation in the combustion chamber was reduced to almost zero when phase difference between an incipient wave in the combustion chamber and a reflected wave in the branch tube is $\pi$ at the branch point. Also, the reduction of pressure fluctuation is irrespective of the installed height of branch tube if it is below $h^*=0.9$ in the close-open tube and open-open tube.

Research on Damping Characteristics of a Helmholtz Resonator using a Rijke Tube (Rijke tube를 이용한 열유동 환경하에서의 음향공 감쇠 특성 연구)

  • Kim, Geun-Cheol;Jeon, Jun-Su;Kim, Jai-Ho;Ko, Young-Sung;Kim, Hong-Jip;Kim, Young-Moon
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2011.11a
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    • pp.873-876
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    • 2011
  • In this research, a Helmholtz resonator was applied to the thermo-acoustic environment that has thermal gradient using Rijke tube. The thermo-acoustic instability was invoked by a Rijke tube which use a DC power supplier and a Blower. A target instability frequency was appeared by the Rijke tube. A preliminary experiment on damping characteristics of the resonator in the thermo-acoustic environment was performed and compared with the room temperature experiment data.

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Hybridal Analysis of High-Frequency Combustion Instability with Pressure-Coupled Combustion Response Model (압력섭동과 연관된 연소응답모델에 기초한 고주파 연소불안정의 이론-수치적 고찰)

  • 윤웅섭;이길용
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2003.05a
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    • pp.253-257
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    • 2003
  • Theoretical-numerical analysis of wave instability is conducted with parametric response function model. Fluctuating instantaneous mass evaporation rate functionally coupled with pressure perturbations with phase lag is assumed to examine the validity of the method. With sufficiently large amplitude and less phase lag to perturbation, combustion response is resonant to pressure waves, unstable waves are amplified, and the system is driven to instability. Magnitude of response is a crucial instability parameter in the determination of a stability margins and makes a critical change of balancing conditions between the amplifying and damping acoustic energies. In the phase regime the unstable waves are amplified, whereas, the acoustic waves are attenuated in the out-of-phase regime. In the intermediate regime, no distinct tendency of unstable waves was determined.

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Numerical Prediction of Thermoacoustic Instability in Rijke Tube Using Non-linear Model for Heat Source (비선형 열원모델을 이용한 Rijke tube 내열음향 불안정 곡선의 수치예측기법)

  • Song, Woo-Seog;Lee, Seung-Bae
    • Proceedings of the KSME Conference
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    • 2008.11b
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    • pp.2524-2529
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    • 2008
  • The thermal system like a combustion chamber is believed to experience a significant instability problem with vibration in case that the thermal energy or the acoustic energy are transformed into a different form through a relevant path. This study deals with a numerically- predicted, Thermoacoustic instability in a Rijke tube by using a non-linear model for a heat source. The heating part where the energy transformation occurs actively is modeled after simulating two-dimensional cylinder case with constant surface temperature, and a nonlinear model that accounts for the transfer function of magnitude- and phase-characteristics is properly implemented so as to be dependent on the pulsation strength in the tube. The heat source model is observed to result in equivalent Thermoacoustic instabilities in the Rijke tube except low flow-rate cases in which the natural convection is dominant.

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Analysis of Combustion Instabilities in a 2-stage Duct System using Transfer Functions (전달함수를 이용한 2단 덕트 시스템에서의 연소불안정 해석)

  • Kim, Seonyeong;Kim, Daesik
    • Journal of ILASS-Korea
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    • v.26 no.4
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    • pp.182-188
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    • 2021
  • In this paper, using a transfer function-based analytical model, major factors influencing the acoustics and combustion instability in a two-stage duct system composed of a nozzle and a combustor were derived and their quantitative effects were evaluated. From the acoustic analysis, it was confirmed that the change in reflection coefficient and mean flow could have a great influence on the instability growth rate, and the area ratio and speed of sound ratio between the nozzle and the combustor are also key parameters to determine combustion instability as well as flame transfer functions.

Acoustic Tests on Atmospheric Condition in a Liquid Rocket Engine Chamber (액체로켓엔진 연소실에서의 상온 음향 시험)

  • Ko, Young-Sung;Lee, Kwang-jin;Kim, Hong-Jip
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.1
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    • pp.16-23
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    • 2004
  • Acoustic characteristics of unbaffled and baffled combustion chamber are experimentally investigated under atmospheric condition to preliminarily determine baffle for mitigation of combustion instability. To investigate the effect of the baffle which has several configurations such as radial baffles and hub/blade baffle, resonant-frequency shift and damping factors of the chamber were analyzed and compared quantitatively with those of the unbaffled combustion chamber. From a view of acoustic characteristics, radial baffles with several configurations have not much difference in resonant-frequency shift and damping factor ratio with each other. On the other hand, hub and blade baffle is very effective to suppress the first tangential mode which was found to be the most harmful acoustic mode in KSR(Korean Sounding Rocket)-III engine. But more study on design parameters such as hub size and axial length should be done for complete optimization of hub and blade baffle. The present study based on linear acoustic analysis is expected to be a useful confirming tool to predict acoustic field and design a passive control devices such as baffle and acoustic cavity.