• Journal of Aerospace System Engineering
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• v.3 no.4
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• pp.41-49
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• 2009

This paper present result of numerical simulation of premixed combustion around a triangle Bluff Body. And a numerical simulation of a premixed flame stabilization by a bluff body was performed using LES Model. The calculated results from the LES showed a good agreement with experiment data than k-model. Premixture combustion has flammability limit, quenching distance, smallest ignition energy has the combustion quality of the back. Bluff body makes a recirculation zone. Therefor velocity of behind bluff body is very slow. It was caused by slowly position speed and the fire occurred after the Bluff Body. Occurrence of fire it made the waste gas of high speed and the thrust made well.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.35-41
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• 2012

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to complement the previous experimental results of the bluff body stabilized flames [1]. For both fuel ejection configurations against an oxidizer stream, the flame stability was affected mainly by vortex structure and mixing field near bluff body. FDS(Fire Dynamic Simulator) based on the LES(Large Eddy Simulation) was employed to clarify the isothermal mixing characteristic and wake flow pattern around bluff body. The air used atmosphere and the fuel used methane. The result of counter flow configuration shows that the flow field depends on air velocity but the mixing field is influenced on the fuel velocity. At low fuel velocity the fuel mole fraction is below the flammable limit and hence the mixing is insufficient to react. Therefore, as the result, the flame formed at low fuel velocity is characterized by non-premixed flames. For the flow field of co-flow configuration, flame stability was affected by fuel velocity as well as air velocity. the vortex generated by fuel stream has counter rotating direction against the air stream. Therefore, the momentum ratio between air and fuel stream was important to decide the flame blow out limit, which is result in the characteristic of the partially premixed reacting wake near extinction.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.1
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• pp.82-88
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• 2011

The objective of this study is to investigate the validity of the dynamic sub-grid G-equation model to a complex turbulent premixed combustion such as bluff body stabilized turbulent premixed flames for the considering of the realistic engineering application. In this study, a new turbulent flame speed model, introduced by the sub-grid turbulent diffusivity and the flame thickness, is also proposed and is compared with an usual model using sub-grid turbulent intensity and with the experimental data. The calculated results can predict the velocity and temperature of the combustion flow in good agreement with the experiment data.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.198-203
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• 2005

The LES-based level-set flamelet model has been applied to analyze the turbulent propane/air premixed bluff-body flame with a highly wrinkled flame fronts. The present study has been motivated to investigate the interaction between the flame front and turbulent eddies. Special emphasis is given to study the effect of G equation filtering treatment on the precise structure of turbulent premixed flames as well as the effect of sub-grid scale (SGS) eddies on the wrinkling of the flame surface. The level-set/flamelet model has been adopted to account for the effect of turbulence-flame interaction as well as to properly capture the flame front. Numerical results indicate that the present LES-based level-set flamelet approach has a capability to realistically simulate the highly non-stationary turbulent premixed flame.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.386-397
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• 2012

The stability and structure of bluff-body stabilized hydrogen flames were investigated numerically and experimentally. The velocity of coflowing air was varied from subsonic velocity to a supersonic velocity of Mach 1.8. OH PLIF images and Schlieren images were used for analysis. Flame regimes were used to classify the characteristic flame modes according to the variation of the fuel-air velocity ratio, into jet-like flame, central-jet-dominated flame, and recirculation zone flame. Stability curves were drawn to find the blowout regimes and to show the improvement in flame stability with increasing lip thickness of the fuel tube, which acts as a bluff-body. These curves collapse to a single line when the blowout curves are normalized by the size of the bluff-body. The variation of flame length with the increase in air flow rate was also investigated. In the subsonic coflow condition, the flame length decreased significantly, but in the supersonic coflow condition, the flame length increased slowly and finally reached a near-constant value. This phenomenon is attributed to the air-entrainment of subsonic flow and the compressibility effect of supersonic flow. The closed-tip recirculation zone flames in supersonic coflow had a reacting core in the partially premixed zone, where the fuel jet lost its momentum due to the high-pressure zone and followed the recirculation zone; this behavior resulted in the long characteristic time for the fuel-air mixing.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.8
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• pp.1084-1093
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• 2010

Large eddy simulation of turbulent premixed flame stabilized by the bluff body is performed by using sub-grid scale combustion model based on the G-equation describing the flame front propagation. The basic idea of LES modeling is to evaluate the filtered-front speed, which should be enhanced in the grid scale by the scale fluctuations. The dynamic subgrid scale models newly introduced into the G-equation are validated by the premixed combustion flow behind the triangle flame holder. The calculated results can predict the velocity and temperature of the combustion flow in good agreement with the experiment data.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.437-441
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• 2010

LES results of turbulent premixed combustion flows are introduced by using the dynamic sub-grid scale model based on G-equation describing the flame front propagation. The turbulent premixed combustion flows around bluff body and over backward facing step are analyzed to validate present formation. LES of swirling partially premixed combustion flame is also performed to conform the predictive capabilities of LES model and to prompt our understanding for the combustion flows over double cone swirl burner combustor by using CFD-ACE+ commercial code.

• Journal of the Korean Society of Combustion
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• v.7 no.1
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• pp.1-7
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• 2002

Experiments have been performed to investigate the structure of axisymmetric hydrogen diffusion flame in a supersonic coflow air. The characteristics and structure of supersonic flames are compared with those of subsonic flames as the velocity of coflow air increases from subsonic to supersonic velocity of Mach 1.8. Also, the subsonic and supersonic flow fields are analyzed numerically for the non-reacting conditions and the possible flame contours indicated by fuel mass fraction are compared with the measured OH radical distributions. It is found that the flame structure indicates more like a partially premixed flame as the coflow air velocity is increased from subsonic to supersonic regimes; strong reaction zone indicated by intense OH signal is found at the center, which is different from subsonic flame cases. And it is shown that the fuel jet passes along the recirculation zones behind the bluff-body fuel nozzle resulting in relatively long mixing time. This is believed to be the reason of the partially premixed flame characteristics found in the present supersonic flames.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.12
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• pp.1004-1012
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• 2014

In this study, blowoff was investigated in a ducted combustor with the bluff body when acoustic excitation was forced. To observe the flame structure, OH radical chemiluminescence was used and the image was analyzed by using POD (Proper Orthogonal Decomposition) algorithm. Natural gas mainly composed of methane was used as fuel. Blowoff occurred when the equivalence ratio was reduced. Equivalence ratio causing blowoff was measured by changing air flow rate, excitation frequency and sound pressure. Blowoff equivalence ratio was varied depending on the experimental conditions. Vortex frequency behind the bluff body and resonance effect in combustor are the main factors that affect the blowoff equivalence ratios with the excitation.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.149-151
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• 2014

The blowoff phenomenon was experimentally investigated in a ducted combustor according to the acoustic excitation. The blowoff equivalence ratio rapidly increases at specific acoustic excitation frequencies. A resonance phenomenon occurs when the excitation frequency approaches the harmonic frequency of the combustor. The resonance increases the velocity fluctuation in the combustor and the infiltration velocity of the unburned gas in the shear layer. Consequently, the mixture velocity exceeds the burning velocity and the blowoff occurs at the higher equivalence ratio.