• 한국전산유체공학회:학술대회논문집
• /
• 2008.08a
• /
• pp.58.3-58.3
• /
• 2008

• 유체기계공업학회:학술대회논문집
• /
• 1998.12a
• /
• pp.105-114
• /
• 1998

Flow field and near-field noise of a centrifugal fan has been studied with an efrcient compressible method and STAR-CD. The flow field of the centrifugal fan is assumed two-dimensional. Most of the compressible studies has been done by inviscid solver because viscous simulation shows little difference. The near field noise is estimated in term s of sound pressure level in frequency domain transformed from the computed pressure fluctuations using FFT. The simulation has been done on various design elements such as impeller blade shapes, the number of blades and cut-off clearance. The comparison shows that the number of blades has a significant effect on near-field noise without losing aerodynamic performance.

• The KSFM Journal of Fluid Machinery
• /
• v.2 no.1 s.2
• /
• pp.43-49
• /
• 1999

Flow field and near-field noise of a centrifugal fan has been studied with an efficient compressible method and STAR-CD. The flow field of the centrifugal fan is assumed to be two-dimensional. Most of the compressible studies have been done by inviscid solver because viscous simulation shows little difference. The near field noise is estimated in terms of sound pressure level in frequency domain transformed from the computed pressure fluctuations using FFT. The simulation has been done on various design elements such as impeller blade shapes, the number of blades and cut-off clearance. The comparison shows that the number of blades has a significant effect on near-field noise without losing aerodynamic performance.

• Transactions of Materials Processing
• /
• v.22 no.6
• /
• pp.323-327
• /
• 2013

In this paper, the flow lines as a function of product design as well as the forging process design are explored using typical application examples. The prediction of flow lines using metal forming simulation technology is introduced along with their characterization. Experimental studies have shown that the metal flow lines have a strong influence on the structural rigidity of the final product. In this study we present several typical applications. One example is the case of severely cut metal flow lines during machining, especially in the region where periodic contacting forces are applied. Another example is the case of abnormal distortion of flow lines which can cause too much elongation or hot shortness due to viscous heating in the region of distortion. A third example is the case of a macrosegregation region which needs to be controlled so it is not adjacent to the region where the force is applied in the use of the final component. An example of weight reduction for an automobile component with improved flow lines is also introduced. These typical applications can provide process engineers with the insight in designing automobile or mechanical components as well as in designing the manufacturing methods to produce various parts.

• Journal of Environmental Science International
• /
• v.13 no.7
• /
• pp.655-660
• /
• 2004

This paper demonstrates the numerical simulation of three dimensional flow pattern for vehicular exhaust dispersion in the street canyons. The wind flow around buildings in urban is computed by the SIMPLEST method. The convection-diffusion equation was used to compute the $NO_X$ concentration level near buildings. Details are given of important boundary conditions and turbulence quantities variations. The simple turbulence model was used for unisotropic viscous effect. A control-volume based finite-difference method with the upwind scheme is employed for discretization equation. The simple turbulence model applied in this study has been verified through comparison between predicted and measured data near buildings. By the predictive results, the updraft induced by the presence of high-rise buildings is important in the transport of street level pollutant out from the street canyons. Our suggestion for reducing ground level pollution is to have high-rise buildings constructed or to reduce the channelling effect of street canyons.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.10a
• /
• pp.281-285
• /
• 2005

Viscous solutions of supersonic jet impinging on a flat wall in a confined plenum are simulated using three-dimensional Navier-Stokes solver. A confined plenum was designed for simulating the missile launch and analyzing the behavior of the exhaust plume, which were accompanied by complex flow interactions with shock and boundary layer. Concerns of this paper are to show accurate simulation of internal flow in confined plenum and to demonstrate the jet flow structure when the jet interacts with a small opening on the side. Objectives of this numerical simulation are to understand the effect of changing the plume exit area of the plenum. Pressure and temperature rise at certain position in the plenum are traced and compared with test data.

• 한국전산유체공학회:학술대회논문집
• /
• 2006.10a
• /
• pp.66-69
• /
• 2006

In the present study, we propose a virtual boundary method for simulation of massive inextensible flexible strings immersed in viscous fluid flow. The fluid motion is governed by the Navier-Stokes equations and a momentum forcing is added in order to bring the fluid to move at the same velocity with the immersed surface. A massive inextensible flexible string model is described by another set of equations with an additional momentum forcing which is a result of the fluid viscosity and the pressure difference across the string. The momentum forcing is calculated by a feedback loop. Simulations of several numerical examples are carried out, inlcuding a hanging string which starts moving under gravity without ambient fluid, a string swimming within a uniform flow and a uniform flow over two side-by side strings. The numerical results agree well with the theoretical analysis and previous experimental observations. Preliminary results of a swimming elongated fishlike body will also be presented.

• 한국전산유체공학회:학술대회논문집
• /
• 2009.11a
• /
• pp.88-92
• /
• 2009

When exposed to uniform magnetic fields externally applied, paramagnetic particles acquire dipole moments and the induced moments interacting with each other lead to the formation of chainlike structures or clusters of particles aligned with the field direction. A direct simulation method, based on the Maxwell stress tensor and a fictitious domain method, is applied to solve flows with magnetic chains in simple shear flow. We assumed that the particles constituting the chains are paramagnetic, and inertia of both flow and magnetic particles is negligible. The numerical scheme enables us to take into account both hydrodynamic and magnetic interactions between particles in a fully coupled manner, enabling us to numerically visualize breakup and reformation of the chains by the combined effect of the external field and the shear flow. Simple shear flow with suspended magnetic chains is solved in a periodic domain for a given magnetic field. Dynamics of interacting magnetic chains is found to be significantly affected by a dimensionless parameter called the Mason number, the ratio of the viscous force to the magnetic force in the shear flow. The effect of particle area fraction on the chain dynamics is investigated as well.

• Journal of Ship and Ocean Technology
• /
• v.8 no.1
• /
• pp.42-50
• /
• 2004

In these ten years, the cavitation and erosion phenomena in the rudder have been increased for high-speed container ships. The cavitation in the rudder blades which is injurious to rudder efficiency is mainly caused by the main flow with a large angle of attack induced by propellers, and the erosion which occurs as a result of repeated blows by shock wave that cavitation collapse may produce was observed in the gap legion of the rudder. However, gap cavitation is not prone to occur in model experiments because of low Reynolds number. So, the viscous effect should be considered for solving the flow of the narrow gap. In order to predict the cavitation phenomena and to improve the performance of the rudder, the analysis of the viscous flow in the rudder gap is positively necessary. In this study, numerical calculation for the solution of the RANS equation is applied to the two-dimensional flow around the rudder gap including horn part and pintle part. The velocity and pressure field are numerically acquired according to Reynolds number and the case that the round bar is installed in the gap is analyzed. For reduced the acceleration that pressure drop can be highly restrained numerically and in model experiment, the cavitation bubbles can be reduced.

• Journal of the Society of Naval Architects of Korea
• /
• v.30 no.1
• /
• pp.104-114
• /
• 1993

In this paper, effects of free surface on viscous flow is investigated. Continuity equation coupled with Navier-Stokes equations are solved numerically by using an artificial compressibility method[1, 2]. The body-fitted generalized curvilinear coordinate system is employed to deal with arbitrary body shape. The IAF scheme with finite difference method is used to solve the equations, and a diagonal algorithm is applied to time-varying Jacobian matrices for the computational economics. Free surface shape is obtained by applying zero pressure condition to still water surface at each time step. A numerical test is made for larminar flow around a circular cylinder vertically piercing the free surface. Computed flow patterns are largely affected by the existance of free surface in low Reynolds number flows treated in this paper. Free surface causes viscous pressure drag to vary much in depth direction in accordance with the variations of flow pattern.