• The Journal of the Acoustical Society of Korea
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• v.15 no.5
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• pp.44-52
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• 1996

Acoustical characteristics of internal pipe structures and a loudspeaker of the thermoacoustic refrigerator are analyzed by using the transfer matrix method. The resonator system is dismantled into verious basic acoustic elements, and then linearized transfer matrices are serially combined with the dynamical system of linearized loudspeaker model, that the total system of thermoacoustic refrigerator can be analyzed in terms of frequency characteristics and acoustic field shape. Additionally, by using equations for energy flow through the capillary stack, the temperature distribution over the stack is numerically estimated. After expressing the acoustic work flow, thermoacoustic flow, and energy loss per unit length in a single capillary duct by using the transverse functional variations, overall energy flow rate and energy balance are obtained for the whole capillary stack. The final expression for energy flow through the stack is numerically evaluated by varying physical parameters obtained from the sound field analysis. After confirming good agreements between predicted and experimental results for the interior sound field of a refrigerator model, the thermoacoustic characteristics of Hofler's apparatus is analyzed by the proposed method and it is observed that the results agree well with Hofler's experimental results.

• The Journal of the Acoustical Society of Korea
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• v.14 no.6
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• pp.5-12
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• 1995

In this paper, acoustic analysis of thermoacoustic refrigerating system was given and the design procedure meeting the specifications was presented. The thermoacoustic refrigerator transforms the sound wave energy into the thermal energy via adiabatic process of inert gas. The system is composed of mainly three parts ; the acoustic motor utilizing loudspeaker the stack of plate for thermal transport and the resonator to form the standing wave. Based upon the acoustic analysis, resonator dimension and stack position and size were decided, and the entire refrigerating system was designed to the given specification. Also the mechanical Impedance of the designed resonator was obtained by simulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.443-449
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• 2014

Thermoacoustic (TA) models have been widely used to predict combustion instability characteristics in a gas turbine lean premixed combustor. However, these techniques have shown some limitations in improving the model accuracy related to an over-simplification of the combustion system and flame geometry. Efforts were made in the current study to improve the limitations of the TA models. One strategy was to modify the actual flame location in the model, and another was to consider the heat release distribution through the flames. The modified TA model results show better accuracy in predicting the growth rate of instabilities compared with the previous results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.2
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• pp.127-134
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• 2020

High supersonic aircraft are exposed to high temperature environments by aerodynamic heating during supersonic flight. Thermal protection system structures such as double-panel structures are used on the skin of the fuselage and wings to prevent the transfer of high heat into the interior of an aircraft. The thin-walled double-panel skin can be exposed to acoustic loads by supersonic aircraft's high power engine noise and jet flow noise, which can cause sonic fatigue damage. Therefore, it is necessary to examine the behavior of supersonic aircraft skin structure under thermal-acoustic load and to predict fatigue life. In this paper, we designed and fabricated thermal-acoustic test equipment to simulate thermal-acoustic load. Thermal-acoustic testing of the titanium specimen under thermal-acoustic load was performed. The analytical model was verified by comparing the thermal-acoustic test results with the finite element analysis results.

• The Journal of the Acoustical Society of Korea
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• v.16 no.1
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• pp.76-80
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• 1997

Acoustic resonance characteristics were analyzed and their effect on the refrigerating capability were experimentally verified on a fabricated Hofler-type thermoacoustic refrigerating system. Factors governing the overall resonance are the resonator composed of a cavity and two pipes, the loudspeaker driving the resonator, and rear side impedance characteristics of speaker housing. All these are coupled with electric constants of the speaker to exhibit electric resonance. Also the 'wall-effect' within the resonator causes attenuation to reduce the sharpness of the resonance. Analysis and experiments showed housing and the wall-effect of the resonator reduce the sharpness of resonance. Maintaining the accuracy of the resonance is, therefore, very important for efficient refrigeration.

• Journal of ILASS-Korea
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• v.27 no.1
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• pp.36-41
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• 2022

In this study, the combustion instability characteristics according to the change in the hydrogen ratio in the fuel in the single nozzle system of the hydrogen-natural gas mixed gas turbine for power generation was analyzed using a three-dimensional finite element analysis-based Helmholtz solver. This combustor shows the instability characteristics in which mode transition occurs from a mode having a low amplitude near 70 Hz to a mode having a high amplitude of 250 Hz or higher as the hydrogen fraction in the fuel increases. The current modeling results are found to reasonably predict the main characteristics of the change in measured instability frequency and growth rate with the change in fuel composition.

• 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.

• 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.

• 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.

• Journal of the Korean Society of Combustion
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• v.18 no.1
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• pp.1-6
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• 2013

Authors' previous works on thermoacoustic(TA) model development showed good results in predicting combustion instability characteristics in a gas turbine combustor. However, they also suggested there were some limitations in growth rate estimation, which might be related with over-simplification of flame structure. As a first trial for improving the model accuracy, the current paper introduces the modified TA model considering the actual flame location in the combustor. The combustor is divided into the unburned and the burned area before and after the flame location, and then acoustic equations are re-organized. The modified TA model results show a better accuracy in predicting the growth rate of instabilities comparing with the previous results. However, obtained results still overestimate the conditions where the combustor goes unstable. Further researches considering heat release distribution through flames are required.