• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.4
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• pp.53-62
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• 2006

Two-dimensional steady flowfields generated by transverse injection jets into a supersonic mainstream are numerically simulated. Fine-scale turbulence effects are represented by a k-${\omega}$ SST two-equation closure model which includes $y^+$ effects on the turbulence model. Solution convergence is evaluated by using Grid Convergence Index(GCI), a measure of uncertainty of the grid convergence. Comparison is made with experimental data and other turbulence models in term of surface static pressure distributions, the length of the upstream separation region, and the penetration height. Results indicate that the k-${\omega}$ SST model correctly predicts the mean surface pressure distribution and the upstream separation length for low static pressure ratios. However, the numerical predictions become less consistent with experimental results as the static pressure ratio increases. All these results are taken within 1% error band of grid convergence.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.6305-6314
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• 2015

This study presents numerical simulations of mean flow and turbulence structure of an open channel with submerged vegetation. Filtered Navier-Stokes equations are solved using large-eddy simulation (LES). The immersed boundary method (IBM) is employed based on a Cartesian grid. The numerical result is compared with experimental data of Liu et al. (2008) and shows that simulated results coincided reasonably with experimental data within the average error of 10%. Strong vortices are generated at the interface between vegetated and non-vegetated regions with spanwise extent. The generation of turbulence induced by shear at the interface is interfered with wake turbulence, resulting turbulence intensity maximum. Turbulence produced by shear affects the flow in vegetated region and the penetration depth increases with an increase in the submergence ratio. This result can be used to understand sediment transport mechanisms in the vegetated region.

• Journal of ILASS-Korea
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• v.29 no.1
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• pp.32-37
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• 2024

Macroscopic visualization of non-evaporating sprays was experimentally conducted to investigate spray tip penetration and spray angle under low-density conditions, corresponding to an early injection strategy. Furthermore, injectors with varying injection angles (146° and 70°) and numbers of holes (8 and 14) were employed to examine the impact of injector configuration. Compared to the baseline injector, 8H146, which has 8 holes and a 146° injection angle, the spray tip penetration of the 8H70 injector was found to be longer. This can be attributed to higher momentum due to a smooth flow field between the sac volume and the nozzle inlet, which is located closer to the injector tip centerline. The increase in velocity led to intense turbulence generation, resulting in a wider spray angle. Conversely, the spray tip penetration of the 14H70 injector was shorter than that of the 8H70 injector. The competition between increased velocity and decreased nozzle diameter influenced the spray tip penetration for the 14H70 injector; the increase in momentum, previously observed for the 8H70 injector, contributed to an increase in spray tip penetration, but a decrease in nozzle diameter could lead to a reduction in spray tip penetration. The spray angle for the 14H70 injector was similar to that of the 8H146 injector. Moreover, injection rate measurements revealed that the slope for a narrow injection angle (70°) was steeper than that for a wider injection angle during the injection event.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.97-103
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• 2008

Unsteady three-dimensional flowfields generated by transverse fuel injection into a supersonic mainstream are simulated with a DES turbulence model. Comparisons are made with experimental results in term of the temporal eddy position and eddy formation frequency. The vorticity field around the jet exit is also analyzed to understand the formation mechanism of the jet vortical structures. Results indicate that the DES model correctly predicts the convection characteristics of the large scale eddies. However, it is also observed that the numerical results slightly overpredict the eddy formation frequency. The jet vortical structures are developed from the competing vortices in the recirculation region of upstream boundary.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.97-103
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• 2008

Unsteady three-dimensional flowfields generated by transverse fuel injection into a supersonic mainstream are simulated with a DES turbulence model. Comparisons are made with experimental results in term of the temporal eddy position and eddy formation frequency. The vorticity field around the jet exit is also analyzed to understand the formation mechanism of the jet vortical structures. Results indicate that the DES model correctly predicts the convection characteristics of the large scale eddies. However, it is also observed that the numerical results slightly overpredict the eddy formation frequency. The jet vortical structures are developed from the competing vortices in the recirculation region of upstream boundary.

• International Journal of High-Rise Buildings
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• v.1 no.2
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• pp.73-80
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• 2012

In order to use sea breezes to counter the heat island phenomena, i.e. to promote urban ventilation, it is necessary to clarify the effect of building morphology and height on large-scale wind fields. In this study, the sea breeze in the vicinity of the Kanto Plain in Japan is simulated using a mesoscale meteorological model incorporating an urban canopy model, and the inland penetration of sea breezes is accurately reproduced. Additionally, a mean kinetic energy balance within a domain (Control Volume; CV) moving along the sea breeze is analysed. From the results, it is clarified that the sea breeze is interrupted by the resistance and turbulence caused by buildings at the centre of Tokyo. The interruption effect is increased in accordance with the height of these buildings. On the other hand, adverse pressure gradients interrupt in the internal region.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.53-56
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• 2004

The mixing characteristics of a multiple transverse injection system in a scramjet combustor were studied with numerical methods. The distance among injectors on mixing characteristics were investigated. The three-dimensional Wavier-Stokes equations including k-w SST turbulence model were solved. It was shown that the mixing characteristics of a multiple transverse injection system were very different from those of a single and a dual injection system; the rear injection flow was strongly influenced by blocking effect due to the momentum flux of the front injection flow and thus had higher expansion and penetration than the front injection flow. The multiple injection system had higher mixing rate, higher penetration but had more losses of stagnation pressure than the single injection system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.53-60
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• 2002

Based on the analyses of the single transverse injection in supersonic flow fields, the mixing characteristics of dual transverse injection of hydrogen in supersonic air flow are studied with computational methods. Three-dimensional Navier -Stokes and the k-$\omega$ SST turbulence model were used. A parametric study is conducted with the variation of the distance between two injectors. The flow patterns and the mixing characteristics of two injection flows are very different from each other, and the flow patterns and the mixing characteristics of the rear injection flow are strongly influenced by those of the first injection flow. The increase of the distance between two injectors up to a specific distance results in the increase of mixing rate and penetration of fuel. However, the increase of the distance over the specific distance results in the decrease of mixing rate and penetration of fuel. From the results it can be stated that there exists a distance between two injectors for optimum mixing characteristics.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.407-413
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• 2011

VIC (Vortex-In-Cell) method for viscous incompressible flow is presented to simulate the wake behind a modified NACA16 foil. With uniform rectangular grid, the velocity in field is calculated using streamfunction from vorticity field by solving the Poisson equation in which FFT(Fast Fourier Transform) is combined with 2nd order finite difference scheme. Here, LES(Large Eddy Simulation) with Smagorinsky model is applied for turbulence calculation. Effective viscosity is formulated using magnitude of strain tensor(or vorticity). Then the turbulent diffusion as well as viscous diffusion becomes particle strength exchange(PSE) with averaged eddy viscosity. The well-established panel method is combined to obtain the irrotational velocity and to apply the no-penetration boundary condition on the body panel. And wall diffusion is used for no-slip condition numerical results of turbulent stresses are compared with experimental results (Bourgoyne, 2003). Before comparing process, LES(Large Eddy Simulation) SGS(Subgrid scale) stress is transformed Reynolds averaged stress (Winckelmans, 2001).

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.6
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• pp.8-22
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• 1995

Three dimensional numerical study of non-evaporating and evaporating spray characteristics was performed in a quiescent and motoring condition of direct injection diesel engine. The calculation parameter was breakup model. The breakup models used were Reitz & Diwakar model and TAB model. The modified k-${\varepsilon}$ turbulence model considering the compressibility effect due to the compression and expansion of piston was used. The calculation results of the spray tip penetration and tip velocity using the TAB model showed similar trends comparing with the experimental data. Although the evaporation rate was not nearly affected with the breakup model at the higher injection pressure, in the low injection case, the evaporation rate result using the TAB model became higher than that of R&D model. The evaporation rate was increased with the injection pressure due to the vigorous interaction with the gas field.