• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.497-508
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• 1985

본 논문에서는 일양한 예혼합 기류중에 놓여진 원주 후류의 고온 순환류에 의 해 보지되는 난류 예혼합 화염을 대상으로 해서 유동의 가시화 및 온도와 이온전류의 변동의 측정에 의해서 화염의 구조를 조사한 결과, 원주 보염기 후류의 재순환 영역부 근에 형성된 전단층에 있어서는 코히렌트(Coherent)구조의 화염이 되고 하류부에서는 불규칙한 3차원 와(渦)에 지배되는 전파성 화염이 형성 되었다. 온도변동에 대한 쌍 봉성의 확율밀도분포와 이온전류변동에 대한 3개의 피이크의 확율밀도분포는 엷은 반 응면을 사이에 두고 미연혼합기괴와 기연가스괴가 서로 접하는 주름 상층류화염 또는 층류화염편의 구조에 대응하며, 코히렌트 와(渦)에 지배되는 화염에 있어서는 거시적 혼합은 코히렌트 와의 거동에 지배되나 그 구조는 주름상층류 화염과 일부 강한 전단 력을 받는 부분에는 분산 반응영역의 구조임이 밝혀졌다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.10
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• pp.28-37
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• 2004

A two-dimensional direct numerical simulation was performed to investigate the evolution and vortical structure of a single vortex in reacting and non-reacting jet flow fields. A predictor-corrector-type numerical scheme with a low Mach number approximation was used, and a two-step global reaction mechanism was adopted as the combustion model. Through the comparisons of single vortex behaviors in reacting and non-reacting jet flow fields, it was found that the evolution characteristics and vortical structure of the single vortex were significantly influenced by a outer vortex that was generated from the buoyance effect as well as the chemical heat release. Furthermore, it was also identified that the differences of the vortical structure in reacting and non-reacting jet flow fields were mainly attributed to the thermal expansion, Baroclinic torque and buoyance effect.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3B
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• pp.231-237
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• 2009

This study presents a numerical model to simulate density currents developing two dimensionally. The ${\kappa}-{\varepsilon}$ model is used for the turbulence closure. Elliptic flow equations are solved by the finite volume method. In order to investigate the applicability of the numerical model, discontinuous density currents are simulated numerically. The vortices due to the instability at the interface are simulated, showing a good agreement with the experimental visualizations in the literature. It is also investigated that the transition from slumping phase to inertial phase occurs when a bore generated at the end wall overtakes the front. However, the propagation of the density current is retarded compared with the experimental results. Two-dimensional modeling seems to have an effect on underestimating the front velocity of the density current.

• Journal of Advanced Marine Engineering and Technology
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• v.13 no.4
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• pp.33-39
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• 1989

A turbulent premixed flames of layer formed between burned hot gas and unburned mixture were investigated by means of schlieren photograph with fluctuations of temperature and ion current. The combustion intensity between burned hot gas and shear layer was higher than the intensity between unburned mixture and shear layer. A wrinkled laminar flame and flamelet were appeared at downstream to exist and distributed reaction zone was at upstream as a result of analyzed probability density functions of temperature fluctuation. The initial combustion intensity of reaction zone of eddy between burned hot gas and shear layer was higher than that of final, flowing downstream, and vice versa between unburned mixture and shear layer.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1661-1668
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• 1990

In a turbulent premixed flame stabilized by the streamline step, and dominated by a coherent eddy, a flame micro-structure was investigated with analyzing the signals of temperature, the ion current, and schieren phtographs simultaneously. Generally the contours of large scale coherent eddies of schlieren photographs was considered as the flame front, however, the main reaction can be occurred within the eddy as a structure of fine flamelets scale. The surrounding burned gas of flamelets could not propagate to a unburned mixture, obstructing flamelets from propagating to a unburned mixture. Consequently, it could restrain flashback. The main reaction region was found to be located at higher temperature of the burned gas rather than at maximum rms of fluctuating temperature. The peak probability of higher temperature was 6 times greater than that of lower temperature. As it was difficult to infer a flame structure from PDF distribution of the fluctuating temperature in form of bimodal shape, it should be taken into consideration with other informations related to the sensitive flame front, for instance, ion current.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.1
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• pp.133-140
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• 2002

This article presents an application of a large-scale structural mixing model(Broadwell et at. 1984) to the blowout of turbulent reacting cross flow jets. Experimental observations, therefore, aim to identify the existence of large-scale vortical structure exerting an important effect upon the flame stabilization. In the analysis of common stability curve, it is seen that the phenomenon of blowout are only related to the mixing time scale of the two flows. The most notable observation is that the blowout distance is traced at a fixed positions according to the velocity ratio at all times. Measurements of the lower blowout limits in the liftable flame are qualitatively in agreement with the blowout parameter $\xi$, proposed by Broadwell et al. Good agrement between the results calculated by a modified blowout parameter $\xi$'and the present experimental results confirms the important effect of large-scale structure in the stabilization feature of blowout.