• Journal of Advanced Marine Engineering and Technology
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• 제29권6호
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• pp.637-644
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• 2005

This paper describes the numerical simulation of the interaction between longitudinal vortices ("common flow up") and a 3-D turbulent boundary layer over a flat plate To analyze the common flow up Produced from vortex generators. the flow field behind the vortex generators Is modeled by the information that is available from studies on a half-delta winglet. Also. the Reynolds-averaged Navier-Stokes equation for three-dimensional turbulent flows. together with a two-layer turbulence model to resolve the near-wall flow, is solved by the method of AF-ADI. The computational results predict that the boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it is directed away from the wall Also. the numerical results. such as Reynolds stresses. turbulent kinetic energy and skin friction characteristics generated from the vortex generators . are reasonably close to the experimental data.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.579-584
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• 2000

Algebraic Reynolds Stress (ARS) model is applied in order to analyze the turbulent flow of wall-attaching offset jet and to evaluate the model's predictability. The applied numerical schemes are upwind scheme and skew-upwind scheme. The numerical results show good prediction in first order calculations (i.e., reattachment length, mean velocity, pressure), while they show slight deviations in second order (i.e., kinetic energy and turbulence intensity). By comparison with the previous results using $k-{\varepsilon}$ model, ARS model predicts better than the standard $k-{\varepsilon}$ model, however, predicts slightly worse than the $k-{\varepsilon}$ model including the streamline curvature modification. Additionally this study can reconfirm that skew-upwind scheme has approximately 25% improved predictability than upwind scheme.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.321-327
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• 2000

This study represents numerical analysis in top opening rectangular with a heating source. The governing equations were solved by a finite volume method, a SIMPLE algorithm was adopted to solve a pressure term. The top boundary with free surface was calculated by energy balance condition. As the results of simulations, the magnitudes of the velocity vectors and isotherms were very small at the lower space of a heating source. The mean Nusselt numbers are increased proportionally to the Grashof number, the heat transfer at Y/H=0.25 was greater than other positions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.823-826
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• 2002

Experiments were conducted to show the characteristics of the flow on unventilated parallel plane jets. Measurements of mean velocity components and turbulent intensities were carried out with a particle image velocimetry. The measurements range of these experiments was Reynolds number of 5300 based on the nozzle width and the cases of nozzle-to-nozzle distance were 4, 6, 8, and 10 times the width of the nozzle. Results show that a recirculation zone with a sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plate. The positions, where maximum value of mean turbulent intensities and mean turbulent kinetic energy show, were at the same position with the merging point. The spread of jets in the merging region increases more rapidly than that of jets in the converging and the combined region. As nozzle-to-nozzle distances were increased, it was shown that merging and combined lengths were shorter.

• 대한기계학회논문집
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• 제19권3호
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• pp.751-762
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• 1995

The snapshot method is introduced to approximate the coherent structures of planar jet flow. The numerical simulation of instantaneous flow field is analyzed by SIMPLE algorithm. An ensemble of realizations is collected using a sampling condition that corresponds to the passage of a large scale vortex at positions 4 and 6 diameters downstream from the nozzle. With snapshot mothod we could treat the data efficiently and approximate coherent structures inhered in the planar jet flow successfully 94% of total turbulent kinetic energy with 10 terms of Karhunen-Loeve expansions. Finally, In accordance with the recent trend to try to explain and model turbulence phenomena with the existence of coherent structures, in the present study, we express the underlying coherent structures of planar jet flow in the minimum number of modes by calculating Karhunen-Loeve expansions in order to improve to understanding of jet flow and to make the information storage and management in computers easier.

• Journal of Advanced Marine Engineering and Technology
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• 제36권1호
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• pp.109-117
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• 2012

본 논문은 매연여과장치(DPF)의 Inlet Pipe 길이를 5가지 경우로 변화시켜, 이 변화가 유동장에 미치는 영향을 살펴보았다. 실험 방법으로서는 PIV 계측과 상용코드를 사용하여 수치해석을 수행 하였으며, 그 결과 PIV와 CFD는 87%로 일치하는 상관성을 보였다. 또한 동일한 유속 조건일 때 Inlet Pipe 길이가 20mm일 때 안정적이고 높은 압력 값을 보여 매연여과율을 높일 수 있을 거라 사료된다.

• 소음진동
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• 제6권6호
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• pp.709-715
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• 1996

In recent years, the piping vibration in many Power Plants is being increased by the aged generating facilities due to a long time use. Generally, the pressure fluctuations associated with the flow-induced excitations in this case are broadband in nature. Mainly, the dominant sources of vibration are a vortex-shedding, plane waves and boundary layer turbulence. The peak level of the spectrum is proportional to the dynamic head. A severe disturbance in pipeline results in the generation of intense broadband internal sound waves which can propagate through the piping system. The characteristic frequencies of operating loads of 20%, 57%, 70%, 100% are 4 - 6 Hz and coincide with the results from impact hammering test and FEM analysis. We chose the wire energy absorbing rope restraint as a vibration reduction method after reviewing the various conditions such as site, installing space and economic cost etc. After installation, the vibration level was reduced about 54% in velocity.

• 한국분무공학회지
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• 제15권3호
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• pp.109-114
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• 2010

The implementation of gelled propellants systems offers high performance, energy management of liquid propulsion, storability, and high density impulse of solid propulsion. The present study focused on the macroscopic spray characteristics of liquid sheets formed by triplet impinging jets of non-Newtonian liquids which are mixed by Carbopol 941 0.5%wt. The results are compared to experiments conducted on spray images which formed by triplet impinging jets concerning with airassist effect at center orifice. When gel propellants are injected by doublet impinging jets at low pressure and high pressure, closed rim pattern shape appeared by polymeric effect from molecular force and showed inactive atomization characteristics, because of extensional viscosity related by restriction of atomization process and breakup time delay of turbulence transition. As increasing mass flow rate of the air(increasing GAR), spray breakup level is also increased.

• Nuclear Engineering and Technology
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• 제44권1호
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• pp.33-42
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• 2012

In the present study, CFD is employed to investigate phenomena occurring during a process of thermal stratification in U-bent pipes at transitional Reynolds number. URANS evaluation had been chosen for its low computational costs during transient analysis and for the evaluation of modeling performance in these conditions. Application of CFD at transitional Reynolds number and buoyancy driven flows indeed contains deeper uncertainties in relation to the range of applicability for hydrodynamic and thermal models. The methodology applied in the work points out, through validations with the basic problems constituting the complex stratified phenomenon, the applicability of the current turbulence modeling. Accurate predictions have been found in relation to transitional Reynolds number in bent pipes and region of stability induced by the gravitational field. On the other hand the defects introduced in the unstable region of the U bent pipe, are discussed in relation to the adopted modeling.

• 상하수도학회지
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• 제28권1호
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• pp.73-81
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• 2014

One-dimensional flux theory (1DFT) is conventionally used for design of secondary clarifier of wastewater treatment plant. However, the 1DFT cannot describe turbulence, density current, shape parameters of the clarifier. In this study, we optimized the configurations of influent guide baffle and effluent baffle through the simulation using computational fluid dynamics (CFD) and its verification by particle image velocity (PIV) test. The energy dissipating inlet (EDI) without influent guide baffle ($0^{\circ}$) showed the best efficiency for minimizing downward velocity under the center well of the clarifier. The lowest velocity distribution around the effluent weir region could be obtained with the McKinney baffle (EB-2). The performances of the influent and effluent baffles were clearly verified by PIV test results.