액체 로켓엔진에서 선형 연소 안정한계에 미치는 유한화학반응 효과

손채훈,박이선,허환일 朝鮮大學校 機械技術硏究所 2005 機械技術硏究 Vol.8 No.1

로켓엔진에서 선형 연소 안정한계에 미치는 유한화학반응의 열적 효과를 조사하였다. 안정한계를 평가하기위해 3차원 연소실에서 유한화학반응을 채택한 반응 유동장 계산으로부터 구한 유통변수들을 사용하였다. 주요 유통변수들의 값은 유한화학반응 모델의 채택으로 인해 상당히 달라졌으며 결과적으로 안정한계도 수정되었다. 유한화학반응은 열적 관점에서 안정성 향상에 기여함을 알았다. In this study, thermal effect of finite-rate chemistry on stability are investigated. To evaluate stability limits, various flow variables from reactive flow fields are required. The flow variables are obtained from CFD analyses with finite-rate chemistry adopted in three dimensional chamber. When finite reaction is adopted, the establishment of reactive flow field is delayed. Accordingly. major flow variables are modified and the calculated stability limits are affected moderately by finite-rate chemistry. It is found that finite-rate chemistry contributes to stability enhancement in thermal point of view.

음향모드 분할 현상을 피하는 음향공명기 동조방법에 대한 수치적 연구

박이선,손채훈 朝鮮大學校 機械技術硏究所 2004 機械技術硏究 Vol.7 No.2

음향불안정을 억제하는 수동제어기구 중 하나인 음향공명기의 mode split을 일어나지 않게 동조시키기 위해서는 고유주파수의 음향에너지 특성에 따른 정확한 동조가 필요하다. 여기서는 고유주파수를 응용해서 정확한 동조를 시킬 수 있는 방법을 소개하겠다. 음향공명기 모델로서 Helmholtz 형태의 공명기가 채택되었고, 진동해석을 통해 고유주파수를 구하였다. 유해 모드로 알려져 있는 제1종방향 음향모드와 제1접선방향 음향모드를 새로운 해석 방법에 의한 감죄를 통해 검증을 하였으며, peak의 좌우의 음향에너지가 균형을 이루게 함에 따라 mode split 된 peak이 1개의 peak으로 변화하는 과정을 나타내었다. 이를 토대로 mode split 없는 감쇠를 위해서는, 억제하고자 하는 음향모드의 peak을 중심으로 한 좌우의 음향에너지가 균형을 이룰 때 모드분할 현상이 나타나지 않으면서 그 음향모드를 감쇠시킬 수 있게 동조시킬 수 있음을 알 수 있었다. Acoustic behavior in gas turbine combustion chamber with acoustic cavity is numerically investigated by adopting linear acoustic analysis. Helmholtz-type resonator is employed as a cavity model to suppress acoustic instability passively. The tuning frequency of acoustic cavity is adjusted by varying the length of acoustic cavity. Through harmonic analysis, acoustic pressure responses of chamber to acoustic oscillating excitation are shown and the resonant acoustic modes are identified. Acoustic damping effect of acoustic cavity is quantified by damping factor. As the tuning frequency 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 damping effect is degraded significantly. A method to tune acoustic resonator preveting acoustic-mode split is suggested considery energy balance between left and of the peak response right sides.

On the Method for Hot-Fire Modeling of High-Frequency Combustion Instability in Liquid Rocket Engines

Chae Hoon Sohn,Woo-Seok Seol,Alexander A. Shibanov,Valery P. Pikalov 대한기계학회 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.6

This study presents the methodological aspects of combustion instability modeling and pro­vides the numerical results of the model (sub-scale) combustion chamber, regarding geometrical dimensions and operating conditions, which are for determining the combustion stability boundaries using the model chamber. An approach to determine the stability limits and acoustic characteristics of injectors is described intensively. Procedures for extrapolation of the model operating parameters to the actual conditions are presented, which allow the hot-fire test data<br/> to be presented by parameters of the combustion chamber pressure and mixture (oxidizer/fuel) ratio, which are customary for designers. Tests with the model chamber, based on the suggested scaling method, are far more cost-effective than with the actual (full-scale) chamber and useful for injector screening at the initial stage of the combustor development in a viewpoint of combustion instabilities.

Effects of Various Baffle Designs on Acoustic Characteristics in Combustion Chamber of Liquid Rocket Engine

Chae Hoon Sohn,Seoug-Ku Kim,Young-Mog Kim 대한기계학회 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.1

Effects of various baffle designs on acoustic characteristics in combustion chamber are numerically investigated by adopting linear acoustic analysis. A hub-blade configuration with five blades is selected as a candidate baffle and five variants of baffles with various specifications are designed depending on baffle height and hub position. As damping parameters, natural-fre­quency shift and damping factor are considered and the damping capacity of various baffle designs is evaluated. Increase in baffle height results in more damping capacity and the hub position affects appreciably the damping of the first radial resonant mode. Depending on baffle height, two close resonant modes could be overlapped and thereby the damping factor for one resonant mode is increased exceedingly. The present procedure based on acoustic analysis is expected to be a useful tool to predict acoustic field in combustion chamber and to design the passive control devices such as baffle and acoustic resonator.<br/>

Hot-Fire Injector Test for Determination of Combustion Stability Boundaries Using Model Chamber

Chae Hoon Sohn,Woo-Seok Seol,Alexander A. Shibanov,Valery P. Pikalov 대한기계학회 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.9

This study realizes the conceptual method to predict combustion instability in actual full-scale combustion chamber of rocket engines by experimental tests with model (sub-scale) chamber. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions, and hot-fire test procedures were followed to obtain stability boundaries. From the experimental tests, two instability regions are presented by the parameters of combustion-chamber pressure and mixture (oxidizer/fuel) ratio, which are customary for combustor designers. It is found that instability characteristics in the chamber with the adopted jet injectors can be explained by the correlation between the characteristic burning or mixing time and the characteristic acoustic time. In each instability region, dynamic behaviors of flames are investigated to verify the hydrodynamically-derived characteristic lengths of the jet injectors. Large-amplitude pressure oscillation observed in upper instability region is found to be generated by lifted-off flames.

Hot- Fire Injector Test for Determination of Combustion Stability Boundaries Using Model Chamber

Sohn Chae Hoon,Seol Woo-Seok,Shibanov Alexander A.,Pikalov Valery P. The Korean Society of Mechanical Engineers 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.9

This study realizes the conceptual method to predict combustion instability in actual full-scale combustion chamber of rocket engines by experimental tests with model (sub-scale) chamber. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions, and hot-fire test procedures were followed to obtain stability boundaries. From the experimental tests, two instability regions are presented by the parameters of combustion-chamber pressure and mixture (oxidizer/fuel) ratio, which are customary for combustor designers. It is found that instability characteristics in the chamber with the adopted jet injectors can be explained by the correlation between the characteristic burning or mixing time and the characteristic acoustic time: In each instability region, dynamic behaviors of flames are investigated to verify the hydrodynamically-derived characteristic lengths of the jet injectors. Large-amplitude pressure oscillation observed in upper instability region is found to be generated by lifted-off flames.

Thermo-kinetic dynamics of near-limit cool diffusion flames

Sohn, Chae Hoon,Han, Hee Sun,Reuter, Christopher B.,Ju, Yiguang,Won, Sang Hee Elsevier 2017 Proceedings of the Combustion Institute Vol.36 No.1

<P><B>Abstract</B></P> <P>The dynamics of near-limit cool diffusion flames are investigated experimentally and numerically by studying transient flame evolution and instability. In order to observe the effects of chemistry-transport coupling on ignition and instability in a cool diffusion flame, diffusion flames of n-heptane and pure oxygen are sensitized by ozone in a counterflow burner. First, it is found from experimental observations that the immediate addition of ozone to the oxidizer side of a frozen flow either initiates a cool diffusion flame or triggers a two-stage ignition into a hot flame. Second, a cool flame near its extinction limit can be destabilized by a perturbation of the fuel mole fraction, eventually leading to flame extinction. The recorded flame chemiluminescence signals reveal repeated flame oscillations before extinction. Next, details of the transient dynamics of near-limit cool diffusion flames are explored through numerical calculations by adopting the same perturbation method. Experimental observations of unsteady flame initiation and instability are simulated, and it is found that the ignition process is highly sensitive to the perturbed ozone mole fraction and that the ignition delay times in a counterflow configuration are significantly affected by the diffusive transport of species with high concentration. The instability mechanism of a cool flame is found to be distinct from that of diffusive-thermal instability. The results show that the instability behavior of a cool flame is a thermo-kinetic instability, which is triggered and controlled by the chemical kinetics associated with the OH radical population in the negative temperature coefficient chemical kinetic regime coupled with heat production and loss.</P>

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

Sohn, Chae-Hoon,Cho, Han-Chang The Korean Society of Mechanical Engineers 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.9

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.

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

Chae Hoon Sohn,Han Chang Cho 대한기계학회 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.8

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.

Combustion Stability Characteristics of the Model Chamber with Various Configurations of Triplet Impinging-Jet Injectors

Sohn Chae-Hoon,Seol Woo-Seok,Shibanov Alexander A. The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.6

Combustion stability characteristics in actual full-scale combustion chamber of a rocket engine are investigated by experimental tests with the model (sub-scale) chamber. The present hot-fire tests adopt the combustion chamber with three configurations of triplet impinging-jet injectors such as F-O-O-F, F-O-F, and O-F-O configurations. Combustion stability bound-aries are obtained and presented by the parameters of combustion-chamber pressure and mixture (oxidizer/fuel) ratio. From the experimental tests, two instability regions are observed and the pressure oscillations have the similar patterns irrespective of injector configuration. But, the O-F-O injector configuration shows broader upper-instability region than the other configurations. To verify the instability mechanism for the lower and upper instability regions, air-purge acoustic test is conducted and the photograph or the flames is taken. As a result, it is found that the pressure oscillations in the two regions can be characterized by the first impinging point of hydraulic jets and pre-blowout combustion, respectively.