• Title/Summary/Keyword: Acoustic Instability

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Numerical Prediction of Performance and Acoustic Instability in KSR-III Liquid Rocket Engine (KSR-III 액체 로켓엔진의 성능예측과 음향 불안정성 해석)

  • 문윤완;손채훈;김영목
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2001.04a
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    • pp.17-20
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    • 2001
  • Combustion characteristics of KSR-III liquid rocket engine are investigated numerically in the standpoints of engine performance and acoustic instability. In the present calculation, engine performance for design and off-design conditions is estimated effectively with reasonable error. Numerical results of acoustic instability show that engine operation for the design condition has sufficient stability margin, but for a certain off-design condition, acoustic instability can be triggered by artificial pressure perturbation. The present results are in a good agreement with the available experimental results and can be adopted for the prediction of engine performance and stability, depending on the specific operating condition.

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Experimental Study of Transition to Secondary Acoustic Instability at Downward-Propagating Premixed Flame in a Tube (튜브 내 하향 전파하는 예혼합 화염의 이차 열음향 불안정성 천이에 관한 실험적 연구)

  • Park, Juwon;Kim, Daehae;Park, Dae Geun;Yoon, Sung Hwan
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.26 no.7
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    • pp.915-921
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    • 2020
  • Thermoacoustic instability caused by air conditioning in a combustion chamber has emerged as a problem that must be solved to establish a stable combustion system. Thermoacoustic instability is largely divided into primary and secondary acoustic instability. In this study, an experimental study of the effects of heat losses was conducted to investigate the mechanism of secondary acoustic instability. To generate the secondary acoustic instability, a quarter-wavelength resonator with one open end and one closed end was used, and the inside of the resonator was filled with premixed gases. Subsequently, secondary acoustic instability with downward-propagating flames could be realized via thermal expansion on the burnt side. To control heat losses qualitatively, an additional co-axial tube was installed in the resonator with air or nitrogen supply. Therefore, additional diffusion flames can be formed at the top of the resonator depending on the injection of the oxidizer into the co-axial tube when rich premixed flames are used. Consequently, secondary acoustic instability could not be achieved by increasing heat losses to the ambient when the additional diffusion flame was not formed, and the opposite result was obtained with the additional diffusion flame.

Nonlinear Acoustic-Pressure Responses of Oxygen Droplet Flames Burning in Gaseous Hydrogen

  • Chung, Suk-Ho;Kim, Hong-Jip;Sohn, Chae-Hoon;Kim, Jong-Soo
    • Journal of Mechanical Science and Technology
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    • v.15 no.4
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    • pp.510-521
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    • 2001
  • A nonlinear acoustic instability of subcritical liquid-oxygen droplet flames burning in gaseous hydrogen environment are investigated numerically. Emphases are focused on the effects of finite-rate kinetics by employing a detailed hydrogen-oxygen chemistry and of the phase change of liquid oxygen. Results show that if nonlinear harmonic pressure oscillations are imposed, larger flame responses occur during the period that the pressure passes its temporal minimum, at which point flames are closer to extinction condition. Consequently, the flame response function, normalized during one cycle of pressure oscillation, increases nonlinearly with the amplitude of pressure perturbation. This nonlinear response behavior can be explained as a possible mechanism to produce the threshold phenomena for acoustic instability, often observed during rocket-engine tests.

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Numerical Analysis of Acoustic Characteristics in Gas Turbine Combustor with Spatial Non-homogeneity

  • Sohn, Chae-Hoon;Cho, Han-Chang
    • Journal of Mechanical Science and Technology
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    • v.18 no.8
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    • pp.1461-1469
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    • 2004
  • Acoustic characteristics in an industrial gas-turbine combustor are numerically investigated by a linear acoustic analysis. Spatially non-homogeneous temperature field in the combustor is considered in the numerical calculation and the characteristics are analyzed in view of acoustic instability. Acoustic analyses are conducted in the combustors without and with acoustic resonator, which is one of the acoustic-damping devices or combustion stabilization devices. It has been reported that severe pressure fluctuation frequently occurs in the adopted combustor, and the measured signal of pressure oscillation is compared with the acoustic-pressure response from the numerical calculation. The numerical results are in good agreement with the measurement data. In this regard. the phenomenon of pressure fluctuation in the combustor could be caused by acoustic instability. From the numerical results for the combustor with present acoustic resonators installed, the acoustic effects of the resonators are analyzed in the viewpoints of both the frequency tuning and the damping capacity. It is found that the resonators with present specifications are not optimized and thus, the improved specification or design is required.

A Numerical Analysis of Acoustic Characteristics in Gas Turbine Combustor with Spatial Non-homogeneity (불균질한 온도장을 고려한 가스터빈 연소기의 음향장 해석)

  • Sohn, Chae-Hoon;Cho, Han-Chang
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1292-1297
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    • 2004
  • Acoustic characteristics in an industrial gas-turbine combustor are numerically investigated by adopting linear acoustic analysis. Spatially non-homogeneous temperature field in the combustor is considered in the numerical calculation and the characteristics are analyzed in view of acoustic instability. Acoustic analysis are conducted in the combustors without and with acoustic resonator, which is one of combustion stabilization devices. It has been reported that severe pressure fluctuation frequently occurs in the adopted combustor, and the measured signal of pressure oscillation is compared with the acoustic-pressure response from the numerical calculation. The numerical results are in a good agreement with the measurement data. In this regard, the phenomenon of pressure fluctuation in the combustor could be caused by acoustic instability. The acoustic effects of the resonators are analyzed in the viewpoints of both the frequency tuning and the damping capacity.

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A CFD Study on Thermo-Acoustic Instability of Methane/Air Flames in Gas Turbine Combustor

  • Sohn, Chae-Hoon;Cho, Han-Chang
    • Journal of Mechanical Science and Technology
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    • v.19 no.9
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    • pp.1811-1820
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    • 2005
  • Thermo-acoustic instability of methane/ air flames in an industrial gas-turbine combustor is numerically investigated adopting CFD analysis. The combustor has 37 EV burners through which methane and air are mixed and then injected into the chamber. First, steady fuel! air mixing and flow characteristics established by the burner are investigated by numerical analysis with single burner. And then, based on information on the flow data, the burners are modeled numerically via equivalent swirlers, which facilitates the numerical analysis with the whole combustion system including the chamber and numerous burners. Finally, reactive flow fields within the chamber are investigated numerically by unsteady analysis and thereby, spontaneous instability is simulated. Based on the numerical results, scaling analysis is conducted to find out the instability mechanism in the combustor and the passive control method to suppress the instability is proposed and verified numerically.

Theoretical Study on Acoustic Instability in Liquid Rocket Engine (액체 로켓 엔진의 음향 불안정 예측에 관한 이론적 연구)

  • Sohn, Chae-Hoon
    • 한국연소학회:학술대회논문집
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    • 2000.12a
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    • pp.92-100
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    • 2000
  • One method to analyse acoustic modes is proposed to predict the characteristics of acoustic instability in liquid rocket engine. It is based on the similarity between transverse acoustic modes and adopts two-dimensional axisymmetric geometry. Using this method, the first tangential mode in the prototype combustor can be analysed through the analysis of the first radial mode in the model combustor with doubled chamber diameter. Sample numerical calculation is demonstrated applying this method to sample rocket engine and thereby acoustic instabilities of the engine are investigated. The present results show a good agreement with the previous findings. The numerical analysis based on the proposed method is cost-effective and serves as the first approximation to the true solution.

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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.

A Study on Damping Characteristic under the Thermo-acoustic Condition using the Rijke Tube (Rijke Tube를 이용한 열환경에서의 음향공 감쇠 특성연구)

  • Kim, Geun-Cheol;Jeon, Jun-Soo;Kim, Joong-Il;Ko, Young-Sung;Kim, Hong-Jip
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2011.04a
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    • pp.47-50
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    • 2011
  • A Rijke tube which has an electric heater and a flow controller was designed and thermo-acoustic instability was induced by the Rijke tube. The thermo-acoustic instability was damped by a resonator and the damping characteristics were investigated and compared to room temperature acoustic test. Results show that decay time of the thermo-acoustic condition was increased by about 40% compared to that of room temperature acoustic test.

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Numerical Analysis of Acoustic Behavior in Gas Turbine Combustor with Acoustic Resonator (음향공명기가 장착된 가스터빈 연소실의 음향장 해석)

  • Park, I-Sun;Sohn, Chae-Hoon
    • Proceedings of the KSME Conference
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    • 2004.11a
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    • pp.1110-1115
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    • 2004
  • Acoustic behavior in gas turbine combustor with acoustic resonator is investigated numerically by adopting linear acoustic analysis. Helmholtz-type resonator is employed as acoustic resonator to suppress acoustic instability passively. The tuning frequency of acoustic resonator is adjusted by varying its length. Through harmonic analysis, acoustic-pressure responses of chamber to acoustic excitation are obtained and the resonant acoustic modes are identified. Acoustic damping effect of acoustic resonator is quantified by damping factor. As the tuning frequency of acoustic resonator approaches the target frequency of the resonant mode to be suppressed, mode split from the original resonant mode to lower and upper modes appears and thereby complex patterns of acoustic responses show up. Considering mode split and damping effect as a function of tuning frequency, it is desirable to make acoustic resonator tuned to broad-band frequencies near the maximum frequency of those of the possible upper modes.

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