• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.895-905
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• 2001

This paper presents vector fields, three dimensional mean velocities, turbulent intensities, turbulent kinetic energy and Reynolds shear stresses measured in the X-Y plane of the gas swirl burner with a cone type baffle plate by using an X-type hot-wire probe. This experiment is carried out at the flow rates of 350 and 450ℓ/min which are equivalent to the combustion air flow rate necessary to release 15,000 kcal/hr in a gas furnace. The results show that the maximum axial mean velocity component exists around the narrow slits situated radially on the edge of a burner. Therefore, there is some entrainment of ambient air in the outer region of a burner. The maximum values of turbulent intensities occur around the narrow slits and in front of a burner up to X/R=1.5. Moreover, the turbulent intensity components show a relatively large value in the inner region due to the flow diffusion and mixing processes between the inclined baffle plate and the swirl vane. Consequently, the combustion reaction is expected to occur actively near these regions.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.811-814
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• 2002

Using a mathematical theory, we show that the optimality condition of a turbulent diffuser with maximum pressure recovery at the exit is zero shear stress along the wall. The optimal diffuser shape is designed through iterative procedures by using the $k-{\varepsilon}-{\nu}^{2}-f$ turbulence model for flow simulation. The Reynolds number based on the bulk mean velocity and the channel height at the diffuser entrance is 18,000. We also perform large eddy simulation to validate the shape design results and investigate the flow characteristics near the zero-skin friction wall. Results from large eddy simulation show that the skin friction is slightly higher than zero but is still very small as compared to that of the flat plate boundary layer flow Although the time-averaged wall shear stress is slightly above zero along the diffuser wall, instantaneous flow reversals occur intermittently. The streamwise mein velocity shows an asymptotic behavior of the half-power-law near the wall where the skin friction is close to zero.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1022-1025
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• 2003

Although the globe is the most typical valve to control high pressure drop in piping system, it is very hard to figure out the characteristics of flow field in the globe valve caused by its complex geometry. So there is very few studies to find out flow characteristics of globe valve. In this study, numerical analysis for flow field in the globe valve is carried out using the Fluent code which is commercial CFD program. Pressure drop through the globe valve is also measured to verify the results come from numerical analysis. Comparing experiment with numerical analysis, two results are very close to each other. Also finite element method is employed to evaluate the safety of globe valve using the results coming from the flow analysis to make the boundary conditions for FEM analysis. Maximum stress appears on the inlet channel of valve where inlet flow runs against. Because the maximum stress between 11.7 MPa to 3.6 MPa is within 3.4% of yield stress. the structural safety of valve is considered to be very sound

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1491-1496
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• 2009

Fluid flow and structural analyses of an electronic expansion valve (EEV) using CO2 as a working refrigerant are carried out to estimate the mass flow rate and maximum stress. An engineering sample EEV that the orifice diameter is 1.8 mm was fabricated. The mass flow rates were measured at various EEV inlet temperatures and pressures for several EEV openings using experimental heat pump system. The sample EEV has over 35 MPa burst pressure and the maximum mass flow rate of CO2 through the EEV increased to 100 g/s at full opening condition.

• The KIPS Transactions:PartB
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• v.14B no.4
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• pp.241-248
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• 2007

An L-curve corner detection method is proposed for the determination of the regularization parameter in optical flow estimation. The method locates the positive peak whose curvature difference from the just right-hand negative valley is the maximum in the curvature plot of the L-curve. while the existing curvature-method simply finds the maximum in the plot. Experimental results show that RMSE of the estimated optical flow is greater only by 0.02 pixels-per-frame than the least in the average sense. The proposed method is also compared with an existing curvature-method and the adaptive pruning method, resulting in the optical flow estimation closest to the least RMSE.

• Transactions of Materials Processing
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• v.9 no.1
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• pp.72-79
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• 2000

Dynamic recrystallization (DRX), which may occur during hot deformation, is important for the microsturctural evolution of 304 stainless steel. Especially, the current interest in modelling hot rolling demands quantitative relationships among the thermomechanical process variables, such as strain, temperature, strain rate, and etc. Thus, this paper individually presents the relationships for flow stress and volume fraction of DRX as a function of processing variables using torsion tests. The hot torsion tests of 304 stainless steel were performed at the temperature range of 900~110$0^{\circ}C$ and the strain rate range of 5x10-2~5s-1 to study the high temperature softening behavior. For the exact prediction of flow stress, the equation was divided into two regions, the work hardening (WH) and dynamic recovery (DRV) region and the DRX region. Especially, The flow stress of DRX region could be expressed by using the volume fraction of DRX (XDRX). Since XDRX was consisted of the critical strain($\varepsilon$c) for initiation of dynamic recrystallization (DRX) and the strain for maximum softening rate ($\varepsilon$*), that were related with the evolution of microstructure. The calculated results predicted the flow stress and the microstructure of the alloy at any deformation conditions well.

• Journal of Biomedical Engineering Research
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• v.17 no.1
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• pp.49-60
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• 1996

An experimental investigation was performed under steady flow condition to assess hydrodynamic performance of floating-type monoleaflet polymer valves (MLPV) withdifferent leaflet thickness. The St. Jude Medical valve (SJMV) was also used for comparison test. Pressure drops of MLPVS are larger than those for other types of polymer valves and mechanical valves. Furthermore, the thicker is the leaflet thickness of the polymer valve, the larger are the corresponding pressure drop. The velocity profiles for MLPs reveal a large reversed flow region downward to the valve position. The maximum wall shear stresses of MLPVS at a flow rate of $30{\ell}$/min are in the range 50-130 dyn/$cm^2$, and the corresponding maximum Reynolds shear stresses are in the range of 100-500 dyn/$cm^2$, respectively, which are beyond the allowable limit clinically. In contrast, floating-type monoleaflet polymer valves show better hydrodynamic performance in leakage volume. From the designing point of view, it may be concluded that the optimum thickness of leaflet for better hydrodynamic performance is one of the Important parameters.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.05
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• pp.241-246
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• 1995

An experimental investigation was performed under steady flow condition to assess hydrodynamic performance of floating-type monoleaflet polymer valves (MLPV) with different leaflet thickness. The St. Jude Medical valve (SJMV) was also used for comparison tests. Pressure drops of MLPVs are larger than those for other types of polymer valves and mechanical valves. Furthermore, the thicker is the leaflet thickness of a polymer valve, the larger arc the corresponding press drop. The velocity profiles for MLPV reveal a large reversed flow region downward to the valve position. The maximum wall shear stresses of MLPVs at a flow rate of 30 l/min are in the range $54-130\;dyn/cm^2$, and the corresponding maximum. Reynolds shear stresses are in the range of $100-500\;dyn/cm^2$, respectively. Both arc beyond the allowable limit clinically. In contrast, floating-type monoleaflet polymer valves show better hydrodynamic performance in leakage volume. From the designing point of view, it can be concluded that the optimum thickness of leaflet for better hydrodynamic performance is one of the important parameters.

• Wind and Structures
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• v.22 no.6
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• pp.663-684
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• 2016

Conical vortices generated at the corner regions of large-span flat roofs have been investigated by using the Particle Image Velocimetry (PIV) technique. Mean and instantaneous vector fields for velocity, vorticity, and streamlines were measured at three visual planes and for two different flow angles of $15^{\circ}$. The results indicated that conical vortices occur when the wind is not perpendicular to the front edge. The location of the leading edge corresponding to the negative peak vorticity and maximum turbulent kinetic energy was found at the center of the conical vortex. The wind pressure reaches the maximum near the leading edge roof corner, and a triangle of severe suctions zone appears downstream. The mean pressure in uniform flow is greater than that under turbulent flow condition, while a significant increase in the fluctuating wind pressure occurs in turbulent streams. From its emergence to stability, the shape of the vortex cross-section is nearly elliptical, with increasing area. The angle that forms between the vortex axis and the leading edge is much smaller in turbulent streams. The detailed flow structures and characteristics obtained through FLUENT simulation are in agreement with the experimental results. The three dimensional (3-D) structure of the conical vortices is clearly observed from the comprehensive arrangement of several visual planes, and the inner link was established between the vortex evolution process, vortex core position and pressure distribution.

• Journal of Advanced Marine Engineering and Technology
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• v.12 no.1
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• pp.53-61
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• 1988

Most of the recent for the flow field hydrofoil in partially cavitating condition are the ones which are linearized, and the problem of cavity end region for hydrofoil is not verified. This paper deals with a study on characteristics of end region flow field for partially cavitating hydrofoil by using a characteristics of shear turbulence flow and nonlinear cavity flow theory. The results obtained as follows : 1) Shear layer thickness is decreased gradually going to the end section of hydrofoil. When attack angle is large, it is appeared largely at the region of partial cavitation after its collapsing. 2) The fluctuation velocity of a second-degree relative direction have minimum value at the front of hydrofoil or at the end of hydrofoil. The difference for the validity of attack angle is appeared largely at the surrounding of .chi.$_{e}$ point. 3) The fluctuation velocity of transverse direction decrease from the maximum thickness of cavitation to the end of hydrofoil, but it undergoes largely the effect of pressure recovery. The difference is larger at the region of partial cavitation after its collapsing than at the of hydrofoil. 4) The distribution of Reynolds stress have maximum values at the region of partial cavitation after its collapsing and the end of foil, and the larger attack angle, the larger the distribution of value.e.