• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.253-261
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• 1987

Thermoacoustic oscillation of an air column induced by heated wires is investigated analytically and experimentally. Acoustic power generation from a single heater wire is estimated based on the result of heat transfer analysis and expressed in terms of the efficiency factor indicating the conversion efficiency from heat to acoustic energy. It is shown that the efficiency factor becomes maximum when the wire radius is the order of the coustic boundary layer thickness and the flow velocity is close to the thermal diffusion velocity. Onset condition of the column oscillation is obtained by equating the acoustic power generation at the heater to the power loss due to thermoviscous dissipation at the tube wall and the convection and radiationloss at the open ends of the tube. In estimating the acoustic power generation, the heater is treated as a stretched single wire by correcting the flow velocity to take into account the interactions between adjacent heater wires. Experiment is performed by using a spiral heater of 1mm diameter in an air column of 37mm diameter. The heat input to drive the oscillation is measured and compared with the theoretical prediction. A good agreement is found between the theory and experiment, which is regarded as a substantial verification of the present analysis.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.235-238
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• 1998

파이프의 양 끝단에 심한 온도구배가 형성될 때 음향이 발생한다는 사실은 이미 알려진 사실이다. 본 연구는 열구동식 열음향냉동기를 구현하기 위해서 1단계로 열원에 의한 음향발생을 달성하고자 했다. 이를 위해 1/4 파장의 열음향 발생장치를 설계 및 제작하여 실험에 사용하였다. 열음향 발생기는 직경 3cm, 길이 16cm의 공명관에 가열부, 박판집적체, 고온부 및 저온부의 열교환기로 구성되며 발생음의 기본주파수는 520Hz로 설계하였다. 고온부를 38$0^{\circ}C$로 가열한 결과 열음향발생기의 개구부로부터 1m 떨어진 곳에서 최초 음압측정값이 약 112dB, 음향출력으로 약 1와트에 해당하는 값을 얻었다. 박판집적체에 급격한 온도구배가 형성되면서 주변의 기체가 자발적인 진동을 하여 형성된 음향동력중 일부는 공명관 벽에 흡수되고 일부는 열교환기에서 점성에 의해 소산된다. 따라서 실제로 음향으로 변하는 부분은 이들을 감한 부분인데 실험결과 약 53%의 음향 생성효율을 달성했으며 이는 스위프트 등이 얻었던 결과보다 우수하다.

• 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.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.2
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• pp.131-139
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• 1988

The thermoacoustic oscillation induced in an air column with variable cross section area is investigated theoretically and experimentally. The onset condition of the oscillation is derived by equating the acoustic power production to the power dissipation. The power production at the heater is predicted by using the efficiency factor obtained by heat transfer analysis for a single wire in a uniform cross flow and considering the interference between heater wires. The power dissipation is estimated by measuring the attenuating coefficient from the pressure decay curve. The theoretical prediction to the onset condition of the oscillation is confirmed experimentally. The effect of the variation of the column cross section area on the onset condition is presented.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.809-813
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• 2010

For the purpose of developing a modeling technique for reduced-order dynamics of thermoacoustic instability, we constructed an electrically heated Rijke tube and measured the pressure oscillation inside the tube. Analysing the measured pressure data showed that the instability generated three major oscillation modes, among which the first mode frequency quite well matches the result from a rough acoustic analysis. As a continuing research, a data-based modeling technique for the thermoacoustic instability will be developed in the near future.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.2
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• pp.221-228
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• 1997

A strong combustion-driven sound from a surface burner made of a perforated metal fiber plate for premixed gas was investigated to clarify the physical mechanism of its generation. A simple model was developed for the acoustic power generation in terms of the heat transfer response function and the acoustic impedance of the burner. The acoustic impedance of the perforated metal fiber placed on the open exit was measured and the heat release response of the burner to the oscillating flow associated with the acoustic disturbance was expressed in terms of a response function. It was found that the power is generated by the heat release in response to the downstream particle velocity, in contrast to the upstream velocity in the case of the Rijke oscillation driven by a heater placed in the lower half of a columm with upstream flow. The measured frequencies of the oscillation were in agreement with the estimated resonance frequencies and their excitation was varied with the combustion conditions. For the same fuel rate, the excited frequency increases with the air ratio if it is low but decreases with the ratio if not so low. Such frequency characteristics were explained by assuming a heat release response function with a time constant and it was shown that the excited frequency decreases as the time constant increases.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.373-380
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• 1988

The effect of sound on the heat transfer from an isothermal cylinder in cross flow is investigated by numerical analysis. The modeling is made for the laminar incompressible flow fluctuating in the range of the Reynolds number, 5.leq.Re.leq.35, by the sinusoidal acoustic field. The instantaneous response of the flow and heat transfer is simulated for various frequencies. It is shown that the heat transfer amplitude decreases and the phase lags behind the flow velocity with increase in the frequency. The time-mean effects of the acoustic field on the flow field and heat transfer, known as the acoustic and thermoacoustic streaming, are analyzed. The time-mean heat transfer coefficients are decreased around the forward stagnation point but increased in the wake region. Such a local difference in heat transfer coefficients is a function of the frequency and becomes greatest at some frequency. However, with balance between the local increase and decrease, the overall heat transfer coefficient is almost unaffected by sound.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.1
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• pp.42-49
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• 2021

As a measure of susceptibility on the combustion instability, thermo-acoustic instabilities in rocket combustion system was considered for the estimation of the operational stability margin. Growth rate, which governs the asymptotic stability behavior of the system, was determined from the dynamic data measured during combustion tests in order to understand the dynamic characteristics of combustor system. Frequency transform technique was first applied to determine the system parameters such as growth rate and/or damping coefficient for an interested mode from the time series pressure data, and the PDFs of pressure amplitude were extracted from the amplitude envelope of pressure oscillation for the stochastic analysis.