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.

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.

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.

A Burning Velocity Correlation for Premixed Hydrogen / Air / Steam Flames

Chae Hoon Sohn,Yong Gi Aum,Suk Ho Chung,Seong Wan Hong,Hee Dong Kim 대한기계학회 1999 KSME International Journal Vol.13 No.3

Effects of inlet blockage of gas-liquid scheme injectoron acoustic tuning for acoustic dampingin a combustion chamber

Chae Hoon Sohn,I-Sun Park 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.2

In a rocket combustor, purely acoustic tuning of gas-liquid scheme injector is studied numerically for acoustic absorption by adopting linear acoustic analysis. Acoustic behavior in the combustor with a single injector is investigated to assure the optimum injector length. Acoustic-absorption effect of the injector is evaluated for cold condition by the quantitative parameter of damping factor as a function of injector length in the chamber for several boundary absorption coefficients. Irrespective of boundary absorption at the chamber wall, it is assured that the optimum tuning-length of the injector corresponds to half of a full wavelength of the first longitudinal overtone mode traveling in the injector with the acoustic frequency intended for damping in the chamber. Although boundary absorption affects little the tuning length of the injector, it appreciably affects damping capacity. Acoustic absorption at the wall increases with boundary absorption coefficient, but purely acoustic-damping effect induced by the tuned injector decreases with the coefficient. As another design parameter, effects of blockage at the injector inlet on acoustic tuning are investigated. It is found that the optimum injector length is shifted depending on the blockage ratio. Suitable combination of injector length and blockage should be made for maximum damping.

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.

A Study on Unsteady Responses of Flames - Calculation of Flame Transfer Function in a Subscale Combustor

Chae Hoon Sohn(손채훈),Jourdain Guillaume,Young Jun Kim(김영준) 한국연소학회 2015 KOSCOSYMPOSIUM논문집 Vol.2015 No.12

Effects of radiation on the uncertainty of flame speed determination using spherically propagating flames with CO/CO₂/H₂O dilutions at elevated pressures

Sohn, Chae Hoon,Chen, Zheng,Ju, Yiguang Elsevier 2015 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.86 No.-

<P><B>Abstract</B></P> <P>This work investigates numerically the effects of spectral dependent radiation on laminar flame speed determination using spherically propagating CH<SUB>4</SUB>/air and H<SUB>2</SUB>/air flames with CO/CO<SUB>2</SUB>/H<SUB>2</SUB>O dilutions at elevated pressures. Three different models, adiabatic, optically thin radiation, and fitted statistically narrow band correlated <I>k</I> (FSNB-CK) models, are employed. The effects of radiation-induced negative burned gas velocity, increased density ratio, and chamber confinement induced flow compression are investigated. It is found that compared to the FSNB-CK model, the adiabatic flame model over-predicts the flame speed by 7% and the optically thin model makes more significant under-prediction. Moreover, this discrepancy increases with pressure. The results also show that a large negative velocity in the burned gas is induced by radiative heat loss and magnified further by the flow compression in a small combustion chamber. The radiation-induced negative burned gas velocity causes an under-estimation of flame speed. Moreover, radiation also increases the density ratio between the burned and the unburned gases. The use of the density ratio of adiabatic flame also causes under-prediction of flame speed. Two radiation corrections taking into account of the negative burned gas velocity and the increased density ratio are recommended for flame speed determination using propagating spherical flame for radiative mixtures. The corrections proposed in this study reduce the uncertainty of flame speed due to radiation.</P>

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

Sohn, Chae-Hoon,Cho, Han-Chang The Korean Society of Mechanical Engineers 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.