• 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.

• Polymer(Korea)
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• v.26 no.6
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• pp.752-758
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• 2002

FTIR, FT-Raman, and X-ray diffraction techniques were used to determine chain segregations and lamellar structures of the mixed binary n-paraffins with different chain lengths. The results of three different techniques, infrared spectroscopic studies of crystal field splitting, the Raman longitudinal acoustic mode, and the SAXS long period measurements were compared one another to understand the crystallization mechanism of separated or mixed n- paraffin lamellae.

• Journal of ILASS-Korea
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• v.29 no.1
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• pp.23-31
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• 2024

This study conducted a 3D thermo-acoustic analysis based on the helmholtz solver to analyze the major resonance modes causing combustion instability in a single-can combustor. The experimental investigations were carried out on a test rig designed by the Korea Institute of Machinery & Materials (KIMM) under various conditions of hydrogen co-firing and fuel staging. Through these experiments, two primary unstable frequencies were identified. To determine the resonance modes of these frequencies, a 3D thermo-acoustic analysis was conducted using temperature information from the test rig. The results confirmed that the unstable frequencies observed in the experiments were all longitudinal modes. Additionally, the mode shapes identified in the analysis facilitated a simplification of the exit geometry for the low-order network model, confirming that this did not significantly affect the fundamental resonance modes.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.335-340
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• 2005

Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. The evaporation was observed at atmosphere pressure. The droplet was recorded throughout the entire evaporation process and transient variations of the volume was measured. The evaporation process of oscillating droplet with thermofoil has been also observed to investigate analyzing the resonance effect on the thermal characteristics of droplet. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. During imposing the acoustic wave, the pendant droplet makes a rotating motion in its longitudinal axis which is a new shape oscillation mode. The evaporation rate of a pendant droplet at resonant frequency is significantly enhanced.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.51-56
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• 2005

Acoustic excitations were imposed to coaxial air jet of non-premixed jet flame with hydrogen gaseous injected axially in the center of the flow. The frequencies of excitation were three dominant resonant frequencies at 1L, 2L, 3L. modes including specially 514 Hz (2L-mode) which was estimated theoretically as longitudinal mode of combustor characteristics. The mixing enhancement by acoustic forcing has been investigated quantitatively using PLIF and PIV. The effect of acoustic excitation on combustion process was significant to enhance mixing rate that coincides with specific resonant frequencies. And the behavior of vortex-interaction on flame structure was a good evidence to investigate the phenomenon of shear/mixing layer of fuel-air jet structure. The results obtained in this study concludes that generated streamwise vortex by acoustic excitation has a potential to enhance the mixing rate and abating NOx emissions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.4-5
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• 2002

로켓 엔진의 개발에 있어 성능과 수명(life time)에 가장 문제가 되는 것은 연소 안정성에 있다. 일반적으로 연소 불안정을 야기시키는 것은 3가지로서 축방향(longitudinal), 반경방향(radial)과 접선방향(longitudinal) 모드(mode)가 있다. 이와 같은 모드를 제어하는 방법에는 수동적 제어방법으로 음향공(acoustic cavity)과 배플(baffle)이 있으며, 음향공은 모드에 관계없이 특정한 주파수에 맞추어 체적을 조절하여 음향파(acoustic wave)를 감쇄시키는 것이고 배플은 주파수에 관계없이 접선방향 모드를 제어하는 것이 기본 목적이나 허브(hub)를 설치하여 반경방향 모드까지 제어할 수 있다. 음향공은 엔진의 성능 또는 연소장에는 영향을 주지 않고 작동하는 반면, 배플은 초기 엔진설계를 할 때 고려하지 않으면 후에 배플을 장착하였을 때는 초기 설계의 제한 때문에 장착의 어려움과 성능 및 연소장에 영향을 미쳐 원하지 않는 엔진의 시험 결과를 야기할 수 있다. 본 연구에서는 KSR-III와 동일한 조건의 연소기에서 다양한 배플을 장착하였을 경우에 대하여 성능과 연소장에 대하여 예측하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.236-241
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• 2009

To identify turbulent flow characteristics of non-reacting case resulted from cooling flow injection in a rectangular swirl combustor, 3D Large Eddy Simulation(LES) was implemented and Proper Orthogonal Decomposition(POD) analysis was used for post-processing. The combustor of concern is the LM6000, lean premixed dry low-NOx annular combustor, developed by GEAE. It was observed that increase in speed of shear layer resulted from the inflow of cooling flow caused intensified vorticity magnitude in central toroidal recirculation zone. In the case of vorticity magnitude in corner recirculation zone, however, was weakened. In addition, pressure fluctuation in combustor was damped down and longitudinal acoustic mode was significantly dissipated

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1165-1173
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• 2003

The effects of (1) phonon dispersion on thermal conductivity model and (2) differentiation of group velocity and phase velocity are examined for germanium. The results show drastic change of thermal conductivity regardless of the same relaxation time model. Also the contribution of transverse acoustic (TA) phonon and longitudinal acoustic (LA) phonon on the thermal conductivity at high temperatures is reassessed by considering more rigorous dispersion model. Holland model, which is commonly used for modeling thermal conductivity, underestimates the scattering rate for TA phonon at high frequency. This leads the conclusion that TA is dominant heat transfer mode at high temperatures. But according to the rigorous consideration of phonon dispersion, the reduction of thermal conductivity is much larger than the estimation of Holland model, thus the TA at high frequency is expected to be no more dominant heat transfer mode. Another heat transfer mechanism may exist at high temperatures. Two possible explanations we the roles of (1) Umklapp scattering of LA phonon at high frequency and (2) optical phonon.

• The Journal of the Acoustical Society of Korea
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• v.16 no.2E
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• pp.21-26
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• 1997

We propose to use transverse waves instead of longitudinal waves in a scanning tomographic acoustic microscope (STAM) and new type of multiple-transducer with the functions of muliple-angle and multiple-frequency tomography. Proposed multiple-transducer scheme has three insonification angles and three resonance frequencies in order to operate in the transverse wave mode and multiple-angle and multiple frequency tomography for the STAM. In order to evaluate the performance of proposed transducer scheme we have simulated tomographic reconstruction with back-and-forth propagation(BFP) algorithm. Simulation results showed proposed multiple-transducer scheme is capable of obtaining good resolution with transverse wave mode and multiple-frequency tomography. It is also showed that proposed scheme is an efficient rotation scheme by proportion to the number of projections.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1627-1632
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• 2003

The effect of (1) phonon dispersion in thermal conductivity model and (2) the differentiation of group velocity and phase velocity for Ge is examined. The results show drastic change of thermal conductivity regardless of using same relaxation time model. Also the contribution of transverse acoustic (TA) phonon and longitudinal acoustic (LA) phonon is changed by considering more rigorous dispersion model. Holland model underestimates the scattering rate for high frequency TA, so misleading conclusion, i.e. TA is dominant heat transfer mode at high temperature. But the actual reduction of thermal conductivity is much larger than the estimation by Holland model and high frequency TA is no more dominant heat transfer mode. Another heat transfer mechanism may exist for high temperature. Two possible explanations are (1) high frequency LA by Umklapp scattering and (2) optical phonon.