• Journal of the Korean Society for Aviation and Aeronautics
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• v.12 no.2
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• pp.17-28
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• 2004

In unmanned aerial vehicle (UAV), the high temperature results from friction with the air, combustion of fuel and combustion gas of a nozzle etc. It causes serious problems in the UAV structure. The characteristic analysis of heat resistant metal and ceramic materials and creep analysis for the functionally graded material (FGM) is presented in this paper. FGM is composed of two constituent materials that are mixed up according to the specific volume fraction distribution in order to withstand high heat condition. In addition, the creep behavior of FGM applied in duct structure of an engine is analyzed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.44-52
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• 1987

For the favorable performance of a D.I. diesel engine, it is important to improve the mixture formation process and the ensuing early stage of combustion process. In the present paper, high speed photography was employed to investigate the effectiveness of a cavity digged in a piston crown for some more useful utilization of air. The cavity would function to improve mixing of fuel and air by the increase of turbulence of air and by the impingement of fuel spray on the cavity wall. The results obtained are summarized as follows: (1) From an aspect of thermal efficiency, it is effective to inject the spray tangentially to the cavity wall to enlarge the area of spray evaporation. (2) some deductions obtained from previous investigations using a hot air stream duct are supported by the present results. For example, it is effective for the quick development of flames throughout the combustion chamber to mix the evaporated fuel of main spray with the intermediates brought about by the early stage of combustion of the preceded auxiliary fuel spray.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.842-849
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• 2002

The present study showed that a quantitative analogy of the fully developed laminar flows inorthogonally rotating rectangular ducts and stationary curved rectangular ducts of arbitrary aspect ratio could be established. In order to clarify the similarity of the two flows, the dimensionless parameters $K_{LR}$ =Re/√Ro and Rossby number Ro= $w_{m}$/$\Omega$d in a rotating strait duct were used as a set corresponding to Dean number $K_{LC}$ =Re/√λand curvature ratio λ=R/d in a stationary curved duct. Under the condition that the value of Rossby number and curvature ratio was large enough, the flow field satisfied the ‘asymptotic invariance property’: there were strong quantitative similarities between the two flows such as friction factors, flow patterns, and maximum axial velocity magnitudes for the same values of $K_{LR}$ and $K_{LC}$ .

• Journal of Power System Engineering
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• v.16 no.4
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• pp.44-50
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• 2012

The present numerical study was performed to determine how the two perforated baffles( Inclined angle=$5^{\circ}$; perforation diameter=2cm) placed at a rectangular duct affect heat transfer and associated friction factors. The parametric effects of perforated baffles(3, 6 and 12 holes) and flow Reynolds number ranging from 28,900 to 61,000 on the heated target surface are explored. As for the investigation of heat transfer behaviours on the local Nusselt number with two baffles placed at $x/D_h=0.8$ and $x/D_h=0.8$ of the edge baffles, it is evident that the average Nusselt number increases with increasing number of holes, but the friction factor decreases with an increase in the hole number placed at baffles. The numerical results by commercial code CFX 10.0 are confirmed with the experimental data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.1063-1071
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• 1999

Fine grid calculations are reported for the developing turbulent flow in a curved duct of square cross-section with a radius of curvature to hydraulic diameter ratio ${\delta}=Rc/D_H=3.357 $ and a bend angle of 720 deg. A sequence of modeling refinements is introduced; the replacement of wall function by a fine mesh across the sublayer and a low Reynolds number algebraic second moment closure up to the near wall sublayer in which the non-linear return to isotropy model and the cubic-quasi-isotropy model for the pressure strain are adopted; and the introduction of a multiple source model for the exact dissipation rate equation. Each refinement is shown to lead to an appreciable improvement in the agreement between measurement and computation.

• Journal of Animal Environmental Science
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• v.8 no.2
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• pp.73-78
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• 2002

The experiment was carried out to investigate the optimal air velocity for improving the ventilation efficiency of duct ventilation system used in Korean swine building. The results are followed ; In 2.2 m height of duct, the air velocity of hole was 5.0 m/s as the over level of recommendation. In different hole interval, the air velocity was various of 4.6${\sim}$11.6 m/s in narrow hole interval, 5.4${\sim}$10.9 m/s in broad hole interval. But the air velocity was 6.6${\sim}$7.7 m/s in duct system pierced hole with equal interval, and it was equal velocity in different parts of duct in this hole interval.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.92-104
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• 1993

In the present study, the velocity profiles and entrance length of developing transitional pulsating flows are investigated both analytically and experimentally in the entrance region of a square duct. The systems of conservation equations for transitional pulsating flows in a square duct are solved analytically by linearizing the non-linear convective terms. Analytical solutions are obtained in the form of infinite series for velocity pofiles. The experimental study for the air flow in a square duct(40mm*40mm*4000mm) is carried out to measure velocity profiles and other parameters by using a hot-wire anemometer with a data acquisition and processing system. The distribution of velocity profiles( $u_{ps}$ / $u_{m,ta}$) in the decelerating period is higher than in the accelerating period. The distribution of the axial component of the axial component of velocity in the transitional flow is nearly uniform in the central region of the duct, and decrease rapidly near the wall. The entrance length correlation of the transitional pulsating flows in a square duct is obtained to be $L_{e}$/ $D_{h}$=0.83 $A_{1}$R $e_{ta}$ /(.omega. sup+1)$^{2}$TEX>

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.3
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• pp.1-8
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• 2016

In this study, we evaluated the flow characteristics of various types of waveguide-below-cutoff (WBC) arrays and their shielding effectiveness (SE) of electromagnetic pulses (EMP) based on computational fluid dynamics (CFD). Three types of waveguides were selected for analysis: (1) grid type, (2) honeycomb type, and (3) multi-layer types (2-ply, 4-ply, 6-ply, and 8-ply). To analyze the air flow characteristics, the flow velocities in the longitudinal center of the WBC and the differential pressures between the WBC array inlet and outlet were evaluated. Consequently, we derive the following conclusions: (1) despite an increase in the inlet velocity, the pressure drop of the 6-ply multi-layer type did not significantly increase as compared to that of other types of waveguides (waveguide thickness of 0.1 mm, SE of 100 dB); (2) the grid and honeycomb type had the fastest flow rate of 17.5 m/s, which is approximately 2.5 m/s faster than that at the inlet (waveguide thickness of 1 mm, module size of 30 mm); and (3) the average pressure drop of the grid type waveguide is the lowest in the overall model, whereas that of the 8-ply is the highest (waveguide thickness of 1 mm, module size of 30 mm, and SE of 80, 100 dB).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.441-448
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• 2004

A numerical study was conducted to show the effect of aspect ratio on the analogy of the developing laminar flows between in orthogonally rotating straight duct and in a stationary curved duct of rectangular cross-section. In order. to clarify the similarity of two nows, dimensionless parameters (equation omitted) and Rossby Ro= $w_{m}$$\Omega$ $d_{h}$, in a rotating straight duct were used as a set corresponding to Dean number, (equation omitted), and curvature ratio, λ=R/ $d_{h}$, in a stationary curved duct. Four. different aspect ratios A=0.25, 0.5, 2 and 4 were considered. Under the condition that the magnitudes of Ro and λ were large enough to satisfy the 'asymptotic invariance property' and the aspect ratio was larger than 1, there were strong quantitative similarities between the two flows such as flow patterns, friction factors, and maximum axial velocity magnitudes fur the same values of $K_{LR}$ and $K_{LC}$ . On the other hand, as the aspect ratio decreased below 1 (A=0.25 and 0.5), the difference of the secondary flow intensity between these two flows was enhanced and therefore the analogy of two flows was not so evident as that of the larger aspect ratio (A=2 and 4). 4).nd 4).

• The KSFM Journal of Fluid Machinery
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• v.9 no.1 s.34
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• pp.25-31
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• 2006

The present study investigates the effects of bleed flow on heat/mass transfer and pressure drop in a rotating channel with transverse rib turbulators. The hydraulic diameter $(D_h)$ of the square channel is 40.0mm. The bleed holes are located between the rib turbulators on leading surface and the hole diameter (d) is 4.5 mm. The square rib turbulators are installed on both leading and trailing surfaces. The rib-to-rib pitch is 10.0 times of the rib height(e) and the rib height-to-hydraulic diameter ratio $(e/D_h)$ is 0.055. The tests were conducted at various rotation numbers (0, 0.2, 0.4), while the Reynolds number and the rate of bleed flow to main flow (BR) were fixed at 10,000 and $10\%$, respectively. The results suggest that the heat/mass transfer characteristics in the internal cooling passage are influenced by rib turbulators, bleed flow and the Coriolis force induced by rotation. For the rotating ribbed passage with bleed flow, the heat/mass transfer on the leading surface is hardly affected by bleed flow, but that on the trailing surface decreases due to the diminution of main flow. The results also show that the friction factor decreases with the bleed flow.