• Journal of computational fluids engineering
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• v.10 no.3 s.30
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• pp.43-47
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• 2005

In this study, the numerical and dynamic simulation on staging problem including forward jet mechanism is conducted. The forward jet plays a vital role in staging, which jets out from aftbody. This staging environment needs full dynamic characteristics study and flow analysis for securing staging safety. Present study performs dynamic simulation of forebody and aftbody with flow analysis using the Chimera grid scheme which is usually used for moving body simulations. As a result, the separation mechanism using forward jet well work in staging for given initial conditions and reverse thrust, chamber pressure variation from experiments. Furthermore, it is found that the technique using forward jets for staging is excellent for securing the separation safety.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.165-170
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• 2003

Centrifugal blowers are widely used for air handling units in industry applications. The blower has a centrifugal impeller and a scroll casing including a driving component such as an electric motor. The impeller takes forward or backward blades to induce flows into the blower. Comprehensive investigation according to the two kinds of blades is systematically carried out for a guidance of design. It is observed that flow rate of the blower with forward blades is larger than that of the system with backward blades. The reason is due to larger velocity from the rotating forward blades and the tendency is validated by a parallel experiment with a wind tunnel. Numerical analysis for the system shows detail information inside the blades and the casing. A series of figures to show the flow details offers deep understanding of a centrifugal blower with different blades.

• Journal of computational fluids engineering
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• v.9 no.1
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• pp.10-17
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• 2004

Comprehensive investigation according to the two kinds of blades is systematically carried out for a design of the centrifugal blower. The motivation of this work is due to demand of enhanced flow rate with higher inlet pressure, such as air purifiers adopting several filters. It is observed that flow rate of the blower with forward blades is larger than that of the system with backward blades. The reason is due to larger outlet velocity from the rotating forward blades and the tendency is validated by a parallel experiment with a wind tunnel. Numerical analysis for the blower system shows detail information between the blades and inside the casing. A series of figures to show the flow details offers deep understanding of a centrifugal blower with the two different blades.

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.302-312
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• 2004

This work developed improved slip factor model and correction method to predict flow through impeller in forward-curved centrifugal fan. Both steady and unsteady three-dimensional CFD analyses were performed to validate the slip factor model and the correction method. The results show that the improved slip factor model presented in this paper could provide more accurate predictions for forward-curved centrifugal impeller than the other slip factor models since the present model takes into account the effect of blade curvature. The correction method is provided to predict mass-averaged absolute circumferential velocity at the exit of impeller by taking account of blockage effects induced by the large-scale backflow near the front plate and flow separation within blade passage. The comparison with CFD results also shows that the improved slip factor model coupled with the present correction method provides accurate predictions for mass-averaged absolute circumferential velocity at the exit of impeller near and above the flow rate of peak total pressure coefficient.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.916-923
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• 2000

Numerical study of three-dimensional turbulent flow in a forward curved centrifugal fan is presented. Standard $k-{\varepsilon}$ turbulence model and non-orthogonal curvilinear coordinates arc used to consider the turbulent flow field and complex geometry. Finite Volume approach is adopted for discretization scheme and structured grid system is used to help convergence. Multiblock grid system is used for flow field and divided into five domains that are inlet, outlet, impeller, tip clearance and scroll. It is assumed that the flow field is steady and incompressible. These numerical results are compared with the experimental data inside a rotor and at the fan outlet. Most important flow features are captured through this numerical approach. Finally details of flow field inside a fan are described and analyzed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.05a
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• pp.79-82
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• 1999

This paper presents a study of cold combined forward-backward extrusion product. The case of product with thin wall in piercing process occur defects of deformation and breakdown during piercing process and the center web of product with thin thickness cause flow defect. Such defect is made by the difference of material flow. Methods of the material flow control in the two directions and forming process to remove this flow defect is proposed. The effectiveness of the proposed methods is examined by comparison experiment and finite element simulation.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.312-317
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• 2001

Modifying effects of the rectangular forward step for suppressing the unsteady pressure fluctuation during interaction between the upstream vortical flow with the edge are studied numerically. The vortical flow is modeled by a point vortex, and the unsteady pressure coefficient is obtained from the velocity and the potential field. To investigate the effects of the edge shape the rectangular forward step is chamfered with various angles. Calculation show that the pressure peaks become decreased by increasing the vortex height as well as the chamfering angle. The pressure amplitudes are very sensitive to the change of the initial vortex height. From this study we can find out that the chamfered edge has two effects; the one is that it suppresses the pressure amplitude generated from the edge, and the other is that it decreases the time variation of unsteady pressure fluctuation. These modifying concepts can be applied to attenuate the self-sustained oscillation mechanism at the open cavity flow.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.433-436
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• 2009

This study is concerned with an effect of frictional condition in a forward/backward combined extrusion process. Generally, the material flow of the billet is influenced by the corners of the die cavity, the ratio in reduction in area, and thickness ratio of backward can thickness to forward can thickness. In addition, the frictional condition in contact area between the billet and the punch/die also affect the material flow. This paper investigated the effect of frictional condition for variable friction factors. The FEM simulation has been carried out in order to examine the effect of frictional condition. Deformation patterns and flow characteristics were examined in terms of design parameters such as extruded length ratio etc. Die pressure exerted on the die-workpiece interface is calculated by the simulation results and analyzed for safe tooling. Therefore the numerical simulation works provide a combined extrusion process of stable cold forging process planning to avoid the severe damage on the tool.

• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.174-180
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• 1998

Numerical study of three-dimensional turbulent flow in a forward curved centrifugal fan is presented. Standard $k-{\varepsilon}$ turbulence model and non-orthogonal curvilinear coordinates are used to consider the turbulent flow field and complex geometry. Finite Volume approach is adopted for discretization scheme and structured grid system is used to help convergence. Multiblock grid system is used for flow field and divided into five domains that are inlet, outlet, impeller, tip clearance and scroll. It is assumed that the flow field is steady state and incompressible. This numerical work is performed with commercial CFD-ACE code developed by CFD Research Corporation, and the results are compared wi th the experimental data

• Transactions of Materials Processing
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• v.3 no.3
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• pp.291-301
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• 1994

In the simultaneous forward-backward extrusion the effects of some process variables including area reduction, stroke advance, materials(Al 2024 and commercial pure copper) on the extrusion load, plastic flow and height ratio of upper to lower extruded parts are experimentally investigated and analyzed. Grid-marking technique is employed to visualize the plastic flow. The influence of using split and original specimen on the extrusion load and height ratio is evaluated by experiments. Experimental results show that the plastic flow if oriented to the part of lower area reduction in the begining but it is usually variated during the overall process. The configurations of plastic deformation and plastic flow are dependent on the working materials and the lubricational conditions.