• 터널과지하공간
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• 제6권1호
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• pp.64-68
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• 1996

Analyzed in this paper is fluid flow in the region near the exhaust and blower ports of the ventilation ducts inside a vehicle tunnel. Theoretical analysis shows that prediction of the energy loss in this region is important for designing the ventilation system. A finite-difference numerical model for the two-dimensional turbulent flow field was used to obtain the flow solution as well as the energy loss. It was shown that the blower-nozzle angle ($\beta$) had an important role in establishing both the pressure gradient and the energy loss, while the effect of the distance between two ports on them was not so significant.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.2-4
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• 2010

Due to rapid progress in the performance of high-end computers, numerical prediction of fluid flow and flow-induced sound is expected to become a vital tool for aero- and hydro- dynamic design of various flow-related products. This presentation focuses on the applications of large-scale numerical simulations to complex engineering problems with a particular emphasis placed on the low-speed flows. Flow field computations are based on a large eddy simulation that directly computes all active eddies in the flow and models only those eddies responsible for energy dissipations. The sound generated from low-speed turbulent flows are computed either by direct numerical simulation or by decoupled methods, according to whether or not the feedback effects of the generated sound onto the source flow field can be neglected. Several numerical examples are presented in order to elucidate the present status of such computational methods and discussion on the future prospects will also be given.

• 한국연소학회:학술대회논문집
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• 대한연소학회 2003년도 제27회 KOSCO SYMPOSIUM 논문집
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• pp.49-56
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• 2003

Mathematical formulation of the zone conditional two-fluid model is established to consider flame-generated turbulence in premixed turbulent combustion. The conditional statistics of major flow variables are investigated to understand the mechanism of flame generated turbulence. The flow field in burned zone shows substantially increased turbulent kinetic energy, which is highly anisotropic due to reaction kinematics across thin flamelets. The transverse component of rms velocities in burned zone become larger than axial component in the core of turbulent flame brush. The major source or sink terms of turbulent kinetic energy are the interfacial transfer by the mean reaction rate and the work terms by fluctuating pressure and velocity on a flame surface.

• 대한기계학회논문집
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• 제19권7호
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• pp.1675-1683
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• 1995

A numerical study of the fluid flow and heat transfer characteristics of the two-dimensional impingement jet with a confinement plate has been carried out. The fluid flow was calculated by solving the full Navier-Stokes equation. In doing that, the well known SIMPLER algorithm was used and the trouble making convection term was discretized according to QUICKER scheme. The energy equation was simply solved by using the SOR method. For the Reynolds number of 10000, two channel heights, say 1.5 and 3.0 times the jet exit width, and two thermal boundary conditions constant wall temperature and constant wall heat flux were considered. Discrete heat sources were flush mounted along the impingement plate at a distance of 0, 2, 3, 4, 5, 6, 10, 12, times the jet exit width from the stagnation point. The length of each heat source is 4 times the jet exit width long. The Nusselt number averaged over each heat source was compared with experiment. Comparison shows that both calculations and experiment have the secondary peak of Nusselt number at downstream of stagnation point, even though there is a little quantitative difference in between. The difference is believed due to abscure thermal boundary condition in experiment and also accuracy of turbulence model used. The secondary peak is shown to be caused by rigorous turbulent flow motion generated as the wall jet flow is retarded and developes into the channel flow without flow reversal.

• 한국소음진동공학회논문집
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• 제21권12호
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• pp.1138-1145
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• 2011

The internal broadband noise of a centrifugal fan in a household refrigerator is predicted using hybrid CAA techniques based on stochastic turbulent synthetic model. First, the unsteady flow field around the centrifugal fan is predicted using computational fluid dynamics(CFD) method. Then, the turbulent flow field is synthesized by applying the stochastic turbulent synthetic technique to the predicted flow field. The aerodynamic noise sources of the centrifugal fan are modeled on a basis of the synthesized turbulent field. Finally, the internal broadband noise of the centrifugal fan is predicted using the boundary element method(BEM) and the modeled sources. The predicted noise spectrum is compared with the experimental data. It is found that the predicted result closely follows the experimental data. The proposed method can be used as an effective tool for designing low-noise fans without expensive computational cost required generally for the LES and DNS simulations to resolve the turbulence flow field responsible for the broadband noise.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.627-632
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• 2011

The internal broadband noise of a centrifugal fan in a household refrigerator is predicted by using hybrid CAA technique based on stochastic turbulent synthetic model. First, the unsteady flow field around the centrifugal fan is predicted using Computational Fluid Dynamics (CFD) method. Then, the turbulent flow field is synthesized by applying the stochastic turbulent synthetic technique to the predicted flow field. The aerodynamic noise sources of the centrifugal fan are modeled on a basis of the synthesized turbulent field. Finally, the broadband noise of the centrifugal fan is predicted using Boundary Element Method (BEM) and the modeled sources. The predicted result is compared with the experimental data. It is found that the predicted result closely follows the experimental data. The proposed method can be used as an effective tool for designing low-noise fans without expensive computational cost required generally for the LES and DNS simulations to resolve the turbulence flow field responsible for the broadband noise.

• 한국유체기계학회 논문집
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• 제4권4호
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• pp.37-42
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• 2001

In the present study, flow characteristics of turbulent oscillatory flow in an oscillator connected to square-sectional $180^{\circ}$ curved duct are investigated experimentally. In order to investigate wall shear stress and pressure distributions, the experimental studies for air flows we conducted in a square-sectional $180^{\circ}$ curved duct by using the LDV system with the data acquisitions and the processing system. The wall shear stress at bend angle of the $150^{\circ}$ and pressure distribution of the inlet (${\phi}=0^{\circ}$) to the outlet (${\phi}=180^{\circ}$) by $10^{\circ}$ intervals of the duct are measured. The results obtained from the experiment are summarized as follows : wall shear stress values in the inner wall we larger than those in an outer wall, except for the phase angle (${\omega}t/{\pi}/6$) of 3, because of the intensity of secondary flow. The pressure distributions are the largest in accelerating and decelerating regions at the bend angle(${\phi}$) of $90^{\circ}$ and pressure difference of inner and outer walls is the largest before and after the ${\phi}=90^{\circ}$.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.346-352
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• 2009

The objective of the present work is to improve numerical predictions of unsteady turbulent swirling flows in the draft tubes of hydraulic power plants. We present Large Eddy Simulation (LES) results on a simplified draft tube consisting of a straight conical diffuser. The basis of LES is to solve the large scales of motion, which contain most of the energy, while the small scales are modeled. LES strategy is here preferred to the average equations strategies (RANS models) because it resolves directly the most energetic part of the turbulent flow. LES is now recognized as a powerful tool to simulate real applications in several engineering fields which are more and more frequently found. However, the cost of large-eddy simulations of wall bounded flows is still expensive. Bypass methods are investigated to perform high-Reynolds-number LES at a reasonable cost. In this study, computations at a Reynolds number about 2 $10^5$ are presented. This study presents the result of a new near-wall model for turbulent boundary layer taking into account the streamwise pressure gradient (adverse or favorable). Validations are made based on simple channel flow, without any pressure gradient and on the data base ERCOFTAC. The experiments carried out by Clausen et al. [1] reproduce the essential features of the complex flow and are used to develop and test closure models for such flows.

• 한국자동차공학회논문집
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• 제3권5호
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• pp.82-89
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• 1995

The three-dimensional fluid motion through the intake port and cylinder of a single DOHC SI engine was investigated with a commercial computational fluid dynamics simulation program, STAR-CD. This domain includes the intake port, intake valves and combustion chamber. Steady induction port flows for various valve lifts have been simulated for an actual engine configuration. The geometry was obtained by direct interface with a three-dimensional CAD software for complicated port and valve shape. The computational grid was generated using the commercial preprocessor ICEM CFD/CAE. Detailed procedures were presented on the generation of the geometry and the block-structured mesh. A standard k-${\varepsilon}$ turbulent model was applied to consider the complexity of the geometry and the fluid motion. The global flow patterns and the distributions of various quantities, such as pressure, velocity magnitude around the valve seat etc., were examined. The computational results, such as mass flow rate, discharge coefficient etc., for various valve lifts were compard with the experimental results and the computational results were found in good agreement with the experiment.

• 대한기계학회논문집B
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• 제23권3호
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• pp.374-387
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• 1999

Two-dimensional turbulent fluid flow and solidification were investigated in a continuous casting process of a steel slab with electromagnetic field. The electromagnetic field was described by the Maxwell equations. The enthalpy-porosity relation was employed to suppress the velocity within a mushy region. A revised low-Reynolds number $k-{\varepsilon}$ turbulence model was used to consider the turbulent effects. It is shown that the temperature gradient in the casting direction in the case with EMBR becomes very weak compared to that of the case without EMBR. The results also show that the velocity profiles of the case with solidification are quite different from those of the case without solidification.