• Proceedings of the KSME Conference
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• 2000.04b
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• pp.447-452
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• 2000

The low-emission and high-performance diesel combustion is an important issue in the combustion research community. In order to understand the detailed diesel flame field involving the complex Physical Processes, It Is quite desirable to study diesel spray dynamics, auto-ignition and spray flame propagation. Dynamics of fuel spray is a crucial element for air-fuel mixture formation flame stabilization and pollutant formation. In the present study, the diesel RCM (Rapid Compression Machine) and the Electric Control injection system have been designed and developed to investigate the effects of injection Pressure, injection timing, and intake air temperature on spray dynamics and diesel combustion processes. In terms of the macroscopic spray combustion characteristics it is observed that the fuel jet atomization and the droplet breakup processes become much faster by increasing the injection pressure and the spray angle. With increasing the cylinder pressure there is a tendency that the shape of spray pattern in the downstream region tends to be spherical due to the increase of air density and the corresponding drag force. Effects of intake temperature and injection pressure on auto-ignition is experimently analysed and discussed in detail.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.1
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• pp.43-48
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• 2013

In this study, the performance of an impeller according to blade length and pitch angle was studied experimentally by building a variable pitch impeller while changing blade length to review the effect of blade length and pitch angle on a fan's performance. The pitch angle was changed in six steps from $20^{\circ}{\sim}45^{\circ}$ at intervals of $5^{\circ}$ while the blade lengths were changed to 90 mm, 100 mm, 110 mm and 120 mm with an identical airfoil shape while carrying out the experiment. The results are summarized as follows: The air flow per static pressure of axial fans increased linearly with increase of pitch angle, but the high static pressure showed a decrease at a pitch angle of $35^{\circ}$. The shaft power increased proportionally to the pitch angle at all blade lengths; the larger the pitch angle, the larger the measured increase of shaft power. This is because the drag at the fan's front increases with the pitch angle. In the axial fans considered in this research, the flow and increase of static pressure amount increased up to a pitch angle of $30^{\circ}$ but decreased rapidly above $35^{\circ}$.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.1105-1117
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• 2023

In this study, the pressure drop behavior of single- and two-phase flows of air and water through the porous beds filled with uniform and non-uniform sized spherical particles was examined. The pressure drop data in the single-phase flow experiments for the uniform particle beds agreed well with the original Ergun correlation. The results from the two-phase flow experiments were analyzed using numerical results based on three types of previous models. In the experiments for the uniform particle beds, the data on the two-phase pressure drop clearly showed the effect of the flow regime transition with a variation in the gas flow rate under stagnant liquid condition. The numerical analyses indicated that the predictability of the previous models for the experimental data relied mainly on the sub-models of the flow regime transitions and interfacial drag. In the experiments for the non-uniform particle beds, the two-phase pressure loss could be predicted well with numerical calculations based on the effective particle diameter. However, the previous models failed to accurately predict the counter-current flooding limit observed in the experiments. Finally, we propose a relation of falling liquid velocity into the particle bed by gravity to appropriately simulate the CCFL phenomenon.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.1-6
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• 2011

In this study, wind tunnel test were conducted to improve an aerodynamic performance of HEMU400X pantograph system with 4 types of pantograph housing models. Experimental models were 1/4 scaled pantograph system, 1/4 scaled ground plate which is scaled down to real roof shape of HEMU-400x, and 4 types of pantograph housing models. The free stream of wind tunnel were 20, 40, 60, 70m/s. The lift and drag forces were measured with 2-axis load cell. And, Total pressure were measured with rake in the wake region of panhead. In addition, Surface flow visualization by tufts were performed to know flow characteristics around pantograph housing. According to the results of force tests and surface visualizations, pantograph housing shape is important part because the shape affects to pantograph system. Therefore, it is considered that adaption of pantograph housing is more advantageous to decrease drag and acoustic noise.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.2
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• pp.59-65
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• 2017

When an anchor is dropped into the sea, there exists a danger of collision on the pipeline and subsea cables in the seabed. This collision could cause huge environmental disasters and serious economic losses. In order to secure the safety of subsea structures such as pipelines and subsea cables from the external impact, it is necessary to estimate the exact external force through the anchor's terminal velocity on the water. FLUENT, a computational fluid dynamic program, was used to acquire the terminal velocity and drag coefficient computation. A half-symmetry condition was used in order to reduce the computational time and a moving deforming mesh technique also adapted to present hydrostatic pressure. The results were examined with the equation based on Newton's Second Law to check the error rate. In this study, three example cases were calculated by stockless anchors of 5.25 ton, 10.5 ton, and 15.4 ton, and for the onshore experiment dropped height was back calculated with the anchor's terminal velocity in the water.

• Atmosphere
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• v.17 no.3
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• pp.231-240
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• 2007

The flow regimes of continuously stratified flow over a double mountain and the effects of a double mountain on wave breaking, upstream blocking, and severe downslope windstorms are investigated using a mesoscale numerical model (ARPS). According to the occurrence or non-occurrence of wave breaking and upstream blocking, three different flow regimes are identified over a double mountain. Higher critical Froude numbers are required for wave breaking and upstream blocking initiation for a double mountain than for an isolated mountain. This means that the nonlinearity and blocking effect for a double mountain is larger than that for an isolated mountain. As the separation distance between two mountains decreases, the degree of flow nonlinearity increases, while the blocking effect decreases. A rapid increase of the surface horizontal velocity downwind of each mountain near the critical mountain height for wave breaking initiation indicates that severe downslope windstorms are enhanced by wave breaking. For the flow with wave breaking, the numerically calculated surface drag is much larger than theoretically calculated one because the region with the maximum negative perturbation pressure moves from the top to the downwind slope of each mountain as the internal jump propagating downwind occurs.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.179-184
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• 2012

This study was performed to find out the measurement criteria of slip resistance from analysis of human gait and slips. Many kinds of slip resistance testers were developed based on mechanical friction testers. But, there are, as yet, no unambiguous slip resistance measurement methodologies and generally accepted safety criteria or safety thresholds for estimating slipping hazard exposures. Also, there are variety of measuring conditions between those testers. The measurement criteria should be tested within the range of human slipping conditions observed in biomechanical studies. It's results should clearly consider whether the devices reflect the human slipping conditions. In this study a dragsled type friction tester, which was constructed in accordance with ISO 15133 basically, was used. Test conditions were set in order to determine the range of measurement criteria. It is shown that drag velocity should be more than 1 m/s, acceleration be more than 10 $m/s^2$, contact time be less than 0.1sec, and contact pressure be within 350~400 kPa.

• Journal of computational fluids engineering
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• v.7 no.4
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• pp.35-41
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• 2002

The projectile afterbodies for zero-lift drag reduction has been analyzed using the Navier-Stokes equations with the κ-εturbidence model. The numerical method of a second order upwind scheme has been used on an unstructured adaptive grid system. Base drag reduction methods that have been found effective on axisymmetric bodies are boattailing, base bleed, base combustion, locked vortex afterbodies and multistep afterbodies. In this paper, turbulence flow and pressure charateristics have been studied for geometries of multistep afterbodies. The important geometrical and flow parameters relevant to the design of such afterbodies have been identified by step number, length and height. The flow over multistep aftoerbodies or base have many kinds of compressible flow characteristics including expansion waves at the trailing edge, recompression waves, separation and recirculating flow in the base region, shear flow and wake flow. The numerical results have been compared and analyzed with the experimental data. The flow characteristics have been clearly shown.

• Transactions of the KSME C: Technology and Education
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• v.2 no.1
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• pp.39-46
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• 2014

This study presents computational analysis of aerodynamic characteristics of two-dimensional airfoil sections with elastic flap attached at the trailing edge. EDISON_CFD was utilized to simulate the incompressible turbulent flow around the foil and MIDAS_IT was employed to estimate the deflection of the flap under the pressure loading. Using iterative procedure, the terminal deflection was estimated and the resulting lift-drag ratio indicates that the favorable effect of the flap is expected within certain amount of angle of attack.

• Journal of computational fluids engineering
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• v.21 no.3
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• pp.48-54
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• 2016

In the present work, numerical simulations were conducted on the scaled model of the BWB type UCAV in the subsonic region using ANSYS FLUENT V15. The prediction method was validated through comparison with experimental results and the effect of the twisted wing was investigated. To consider the transitional flow phenomenon, ${\gamma}$ transition model based on SST model was adopted. The coefficients of lift, drag and pitching moment were compared with experimental results and the pressure distribution and streamlines were investigated. The twisted wing decreases the lift force but increases lift-to-drag ratio through delay of stall and leading edge vortex's movement to the front, also the non-linearity of the pitching moment is decreased.