• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1262-1272
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• 2003

A two-dimensional direct numerical simulation is performed to investigate the dynamic behaviors of a single vortex in counter reacting and non-reacting flow field. A predictor-corrector-type numerical scheme with a low Mach number approximation is used in this simulation. A 16-step augmented reduced mechanism is adopted to treat the chemical reaction. The budget of the vorticity transport equation is examined to reveal a mechanism leading to the formation, destruction and transport of a single vortex according to the direction of vortex generation in reacting and non-reacting flows. The results show that air-side vortex has more larger strength than that of fuel-side vortex in both non-reacting and reacting flows. In reacting flow, the vortex is more dissipated than that in non-reacting flow as the vortex approach the flame. The total circulation in reacting flow, however, is larger than that in non-reacting flow because the convection transport of vorticity becomes much large by the increased velocity near the flame region. It is also found that the stretching and the convection terms mainly generate vorticity in non-reacting and reacting flows. The baroclinic torque term generates vorticity, while the viscous and the volumetric expansion terms attenuate vorticity in reacting flow. Furthermore, the contribution of volumetric expansion term on total circulation for air-side vortex is much larger than that of fuel-side vortex. It is also estimated that the difference of total circulation near stagnation plane according to the direction of vortex generation mainly attributes to the convection term.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.449-452
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• 2008

Flow difference between reacting and non-reacting case in a swirl stabilized annular combustor is investigated using 3D Large Eddy Simulation with flamelet turbulent combustion model. The combustor of concern is the LM6000, lean premixed dry low-NOx annular combustor, developed by GEAE. Boundary conditions are based on experimental data. Heat release as a result of combustion put the dilatation of density in primary combustion zone highly increased so that the main swirl stream behind of a swirl cup stretched further downstream than that of non-reacting case. The oval shape of core flow in cross-section to flow direction, which clearly observed in non-reacting case, tends to be circle, and small vorticities in wide range in non-reacting case disappears, but the size of iso-vorticity increase in reacting case.

• 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.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.250-257
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• 2005

Large eddy simulation{LES) methodology used to model a bluff-body stabilized non-reacting flow. The LES solver was implemented on parallel computer consisting 16 processors. To verify the capability of LES code, the results was compared with that of Reynolds Averaged Navier-Stokes(RANS) using $k-{\epsilon}$ model as well as experimental data. The results showed that the LES and RANS qualitatively well predicted the experimental results, such as mean axial, radial velocities and turbulent kinetic energy. However, in the quantitative analysis, the LES showed a better prediction performance than RANS. Specially, the LES well described characteristics of the recirculation zones, such as air stagnation point and jet stagnation point. Finally, the unsteady phenomena on the Bluff-body, such as the transition of recirculation region and vorticity, was examined with LES methodology.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.439-444
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• 2011

Doosan Heavy Industries & Construction Co., Ltd. has been recently developing the gas turbine engine using the biogas as fuel. This paper describes the non-reacting and reacting flow analysis of the combustor which is one of the main components in gas turbine engine. Through CFD analysis, investigation has been performed to evaluate the primary factors for aerodynamic design and to predict combustor behaviors during operation with various fuel distribution ratios. The calculation results are compared with rig test data, which reveals that CFD predictions such as pressure loss, air distribution ratio, and recirculation flow are quite reliable. The trend of NO formation was similar with the test, except the low fuel distribution ratio.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.49-56
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• 2002

A two-dimensional direct numerical simulation is performed to investigate the formation characteristics of a single vortex interacting with $CH_4/N_2$-Air counterflow nonpremixed flame. The numerical method was based on a predictor-corrector scheme for a low Mach number flow. The detailed transport properties and a 16-step augmented reduced mechanism are adopted in this calculation. The budgets of the vorticity transport equation arc examined to reveal the mechanisms leading to the formation, evolution and dissipation of a single vortex interacting with counterflow nonpremixed flame. It is found that the stretching term, which depends on the azimuthal component of vorticity, and radial velocity, mainly generates vortieitv in non-reacting and reacting flows. The viscous and baroclinic torque term destroy the vorticity in non-reacting flow. In addition, the baroclinic torque term due to density and pressure gradient generates vorticity, while viscous and the volumetric expansion terms due to density gradient destroy vorticity in reacting flow.

• 한국연소학회:학술대회논문집
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• 2013.06a
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• pp.123-126
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• 2013

Combustor development requires high fidelity simulation capable of predicting recirculation zone (RZ), temperature field, and pollutant emission. Swirling flow is widely used in combustor for its benefits in efficient mixing and flame stabilization by RZ. Large eddy simulation (LES) is used to calculate swirling flow in an expanding pipe [1], and shows higher accuracy than RANS. Reactive flow modeling using LES and flamelet model is validated with experiments by Barlow et al. [4] and Masri et al. [3]. Finally, heat transfer simulation of Samsung Techwin's combustor liner is presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.320-327
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• 2006

The computations of chemically reacting laminar and turbulent flows are performed using the preconditioned Navier-Stokes solver coupled with turbulent transport and multi-species equations. A low-Reynolds number $k-\varepsilon$ turbulence model proposed by Chien is used. The presence of the turbulent kinetic energy tenn in the momentum equation can materially affect the overall stability of the fluids-turbulence system. Because of this coupling effect, a fully coupled formulation is desirable and this approach is taken in the present study. Choi and Merkle's preconditioning technique is used to overcome the convergence difficulties occurred at low speed flows. The numerical scheme used for the present study is based on the implicit upwind ADI algorithm and is validated through the comparisons of computational and experimental results for laminar methane-air diffusion flame and $ H_2/O_2$ reacting turbulent shear flow. Preconditioning formulation shows better convergence characteristics than that of non-preconditioned system by approximately five times as much.

• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.139-144
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• 2007

A micro cyclone combustor was developed to be used as a component of mobile power generator (MPG). The cyclone combustor was designed so that fuel and air were supplied to the combustion chamber separately to prevent a flash-back. The flame shape stabilized inside the micro cyclone combustor was visualized experimentally and the flow field and the combustion characteristics of the combustor were investigated numerically. The global equivalence ratio (${\Phi}$), defined using the fuel and air flow rates, was introduced to examine the overall flow and flame features of the combustor. The flame stabilization mechanism could be well understood using the velocity distribution inside the combustor. For only non-reacting case, it was found that a weak recirculating zone was formed upper the fuel-supplying tube in case of ${\Phi}$ < 1.0. It was also found that small regions that have a negative axial velocity exist near the fuel injection ports for both of non-reacting and reacting case. It was identify that a flame front was stabilized at the negative axial velocity regions near the fuel injection ports.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.4
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• pp.321-328
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• 2014

The performance characteristics of a subscale diffuser under non-reacting conditions for high-altitude simulation were numerically investigated with respect to different lengths of the secondary throat diffuser. The ratio of the length of the diffuser entrance to the nozzle exit diameter was set to 0, 50, and 100%. In addition, flow characteristics were studied for a range of length-to-diameter ratios of the secondary throat diffuser. An insufficient diffuser entrance length caused contraction of the plume immediately after the nozzle exit. When the length-to-diameter ratio was less than 8, a strong Mach disk was formed inside the diffuser, resulting in a sharp increase in pressure. In addition, flow characteristics in the diverging part of the diffuser were investigated for a range of diverging part lengths. A short diverging part may lead to abrupt pressure recovery, resulting in the possible application of mechanical load to the diffuser.