• Journal of computational fluids engineering
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• v.17 no.1
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• pp.16-22
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• 2012

Acoustic pressure field around the centrifugal fan is predicted by a aero-acoustic splitting method. Unsteady flow field is obtained by solving the incompressible Navier-Stokes equations using commercial code, while the acoustic waves generated inside the centrifugal fan and shroud are predicted by solving the far field acoustics analysis. Computational results show that the acoustic waves of BPF tone are generated by interactions of the blades with the shroud. Acoustic results is validated by experimental results This paper describes the influence of geometric parameters on the noise generation from the section of blades and shroud. One of the effective ways to reduce BPF noise is optimization method using Genetic Algorithm, which effectively minimize eccentricity, is suggested. New improving design was developed by optimization method.

• Solar Energy
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• v.9 no.1
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• pp.62-69
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• 1989

This analysis is to investigate the influence of inflow angle when cooling air flows into PC (Printed Circuit) board channels. Flow between PC board channels with heat generating blocks is assumed laminar, incompressible, two-dimensional. Geometric parameters (block spacing (S), block height (H), block width (W) and channel height (L)) are held fixed. Inflow angle variations are $-10^{\circ},\;0^{\circ},\;10^{\circ}$, where uniform heat flux per unit axial length Q (W/m) from heated block surfaces is generated. The governing equations for velocity and temperature are solved by SIMPLE (Semi-Implicit Method Pressure for Linked Equation) algorithm. Nusselt number on each block surfaces is analyzed after a numerical calculation result. The result shows that the assumption on parallel inflow (inflow angle to channel, $0^{\circ}$) to PC board channels can be used without large error even when inflow' angle is varied.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.166-170
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• 2007

An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present studywas 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 34 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.4
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• pp.546-553
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• 2001

A Parametric study is numerically carried out for flow fields in a two-dimensional plane channel with thin obstacles(“baffles and blocks”) mounted symmetrically in the vertical direction and periodically in the streamwise direction. The aim of this investigation is to understand how various geometric conditions influence the critical characteristics and pressure drop. A range of BR(the ratio of baffle interval to channel height) between 1 and 5 is considered. Especially when BR is equal to 3, for which the critical Reynolds number turned out to be minimal, we add blocks in the center region in order to study their destabilizing effects on the flows. It is revealed that the critical Reynolds number is further decreased by the presence of the block.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.783-788
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• 2000

Flow fields in two-dimensional plane channels with thin obstacles("baffles and blocks") mounted symmetrically in the vertical direction and periodically in the streamwise direction are studied numerically to understand how various geometric conditions influence the critical Reynolds number and pressure drop. Changing BR(the ratio of channel to baffle interval) from 1:1 to 1.5, we computed the critical Reynolds number and pressure drop. Especially when BR is 1:3, at which the critical Reynolds number turned out to be minimal, we added blocks in the geometry in order to study their destabiliting effects on the flows.

• Journal of the Korean Society of Industry Convergence
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• v.12 no.1
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• pp.11-18
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• 2009

The air flow and heat transfer characteristics of an air jet impinging on a pedestal heat source has been investigated numerically to examine the effects of geometric parameters such as nozzle-to-pedestal spacing, nozzle diameter and pedestal size. Also, the parameters of Reynolds number, air jet power, supplied heat and thermal conductivity of pedestal have been studied to reveal how these affect the average Nusselt number. Hence, a two-dimensional turbulent model has been developed and adopted to simulate the fluid flow and heat transfer phenomena numerically. The results obtained from the model show that the nozzle-to-pedestal spacing, relative size of nozzle to pedestal and Reynolds number of air jet have a significant influence on the cooling characteristics of heated pedestal. Furthermore, some useful guidelines could be given to the application of cooling the heated pedestal.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.70-77
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• 2004

Comprehensive investigation on the outlet's geometric shapes of a centrifugal blower with higher inlet resistance than an atmospheric pressure is carried out for improvements of its performance. Most unwanted behaviors of such blower are pulsating flows because of unbalance between inflows and outflows in a scroll casing. In order to reduce this undesirable phenomenon a triump is made for both the shape of outlet duct and an accessory structure inserted in the outlet port of the blower. The modification on the shape is concerned with the contraction of cross sectional area and the attached structure is for an intentional obstruction to cause a flow resistance. The details of the modification are examined for different cases and results. The methodologies for the work are performance evaluations including noise level and velocity measurements with PIV Consequently, the performance of improved system is close to that of the system operating with atmospheric pressure at the inlet.

• Journal of KSNVE
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• v.3 no.3
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• pp.271-278
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• 1993

Acoustic characteristics of silencer system are affected by various geometric parameters such as cross sectional geometry, size of chamber, and location of inlet-outlet port. It is impossible to obtain exact solutions of the equations of acoustic wave propagation except few simple cases. So, we resort to numerical techniques to analyze performance of acoustic system. In this work, finite element formulation has been obtained to predict transmission loss of an arbitrary 3-dimensional muffler in the presence of mean flow of low mach number. The effect of the degree of the ellipticity of expansion chambers on the transmission loss has been studied using the resulting finite element equation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.234-235
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• 2008

The surface flatness of heteroepitaxially grown 3C-SiC thin films is a key factor affecting electronic and mechanical device applications. This paper describes the surface flatness of poly(polycrystalline) 3C-SiC thin films according to Ar flow rates and the geometric structures of reaction tube, respectively. The poly 3C-SiC thin film was deposited by APCVD (Atmospheric pressure chemical vapor deposition) at $1200^{\circ}C$ using HMDS (Hexamethyildisilane : $Si_2(CH_3)_6)$ as single precursor, and 1~10 slm Ar as the main flow gas. According to the increase of main carrier gas, surface fringes and flatness are improved. It shows the distribution of thickness is formed uniformly.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.3
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• pp.415-425
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• 1996

This study presents an analytical method of solving the behaviors of arc plasma in a nozzle constricting transferred-type torch and purposes to obtain the basic data for the design of a plasma torch, which can be obtained from the temperature, pressure, velocities and voltage distributions. We have to solve some conservation equations simultaneously and need to know the exact thermal gas properties in order to obtain the correct behaviors of arc plasma. It is also necessary to give the relevant physical or geometric boundary conditions. For the simplicity of analysis, we assumed that (a) the plasma flow is laminar, (b)the local thermodynamic equilibrium, i.e. LTE, prevails over the entire arc column region. The electrode sheath effects were neglected and the nozzle area was excluded from the analysis by assuming that the current flow into the nozzle is zero. We solved the momentum transfer equation including the self-magnetic pinch effect, and obtained the temperature distribution from the energy conservation equation. From this temperature, we could get arc voltage distribution. (author). refs., figs., tabs.