• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.514-519
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• 2003

The objective of this study is to document the secondary flow and the total pressure loss distribution in the contoured endwall installed linear turbine nozzle guide vane cascade passage and to propose an appropriate contraction ratio of the contoured endwall which shows the best loss reduction among the simulated cases. In this study, three different contraction ratio of contoured endwalls have been tested. This study was performed by experimental method and when the contoured endwall has the contraction ratio of 0.17 on exit height the results showed the best loss reduction.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.87-92
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• 2008

The breakup processes and spray plume characteristics of liquid jets injected in subsonic air cross-flows were experimentally studied. The behaviors of column, penetration, breakup of plain liquid jet and droplet sizes, velocities have been studied in non-swirling cross-flow of air. Nozzle has a 1.0 mm diameter and Lid ratio=5. Experimental results indicate that the breakup point is delayed by increasing air momentum, the penetration decreases by increasing Weber number and the split angle is increased by increasing air velocity or decreasing injection velocity. SMD increases according as increasing height or decreases in accordance with increasing air velocity. This phenomenon is related to the momentum exchange between column waves and cross-flow stream. Droplet vector velocities were varied from 11.5 to 33 m/s. A higher-velocity region can be identified in down edge region at Z/d=40, 70 and 100. Lower-velocity region were observed on bottom position of the spray plume.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.358-363
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• 2008

The spray cross-section characteristics of two-phase spray that using external-mixing nozzle injected into a subsonic cross flow were experimentally studied with various ALR ratio that is $0{\sim}59.4%$. Suction type wind tunnel was used and experiments were conducted to ambient environment. Several plain orifice nozzles with L/d of 30 and orifice diameter of 0.5 mm and orifice length 1.5 mm were tested. Free stream velocity profiles at the injection location were measured using hot wire. Spray images were captured to study collision point and column trajectory. Phase Doppler particle analyzer(PDPA) was utilized to quantitatively measuring droplet SMD, volume flux. Measuring probe of PDPA positions was moved 3-way transverse machine. SMD distributions were layered structure and peaked at the top of the spray plume and low value at bottom of the spray. Volume flux of spray was distributed to the two side region and volume flux quantity decreased when ALR ratio increased. It was found that the perpendicularly injected two-phase spray jet of external mixing into a cross flow showing that mistlike spray moved away from the test section bottom region.

• Journal of the Korean Institute of Gas
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• v.18 no.2
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• pp.21-27
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• 2014

A MILD(Moderate and Intense Low oxygen Dilution) combustion, which is effective in the reduction of NOx, is considerably affected by the recirculation flow rate of hot exhaust gas to the combustion furnace. The present study used a coanda nozzle for the exhaust gas recirculation in a MILD combustor. A numerical analysis was accomplished to elucidate the effect of exhaust gas entrainment toward the furnace with or without a coaxial contractor. The result of the present CFD analysis showed that the entrainment mass flow rate without a coaxial contractor had 18% larger than that with a coaxial contractor when the mixed gas outlet pressure was ambient pressure. On the other hand, if the outlet pressure increased, the mass flow rate with a contractor was larger than that without a contractor. It could be analysed by the entrainment driving force composed with the nozzle throat pressure, inlet and outlet pressures and flow cross sectional area.

• Design & Manufacturing
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• v.13 no.3
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• pp.12-18
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• 2019

Fluid jet polishing is a method of jetting a fluid to polish a concave or free-form surface. However, the fluid jet method is difficult to form a stable polishing spot because of the lack of concentration. In order to solve this problem, MR fluid jet polishing system using an abrasive mixed with an MR fluid whose viscosity changes according to the intensity of a magnetic field is under study. MR fluid jet polishing is not easy to formulate for precise optimal conditions and material removal due to numerous fluid compositions and process conditions. Therefore, in this paper, quantitative data on the factors that have significant influence on the machining conditions are presented using various simulations and the correlation studies are conducted. In order to verify applicability of the fabricated MR fluid jet polishing system by nozzle diameter, the flow pattern and velocity distribution of MR fluid and polishing slurry of MR fluid jet polishing were analyzed by flow analysis and shear stress due to magnetic field changes was analyzed. The MR fluid of the MR fluid jet polishing and the flow pattern and velocity distribution of the polishing slurry were analyzed according to the nozzle diameter and the effects of nozzle diameter on the polishing effect were discussed. The analysis showed that the maximum shear stress was 0.45 mm at the diameter of 0.5 mm, 0.73 mm at 1.0 mm, and 1.24 mm at 1.5 mm. The cross-sectional shape is symmetrical and smooth W-shape is generated, which is consistent with typical fluid spray polishing result. Therefore, it was confirmed that the high-quality surface polishing process can be stably performed using the developed system.

• The KSFM Journal of Fluid Machinery
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• v.11 no.3
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• pp.22-29
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• 2008

Clean and renewable energy technologies using ocean energy give us non-polluting alternatives to fossil and nuclear-fueled power plants to meet establishment of countermeasures against the global warming and growing demand for electrical energy. Among the ocean energy resources, wave power takes a growing interest because of its enormous amount of potential energy in the world. Therefore, various types of wave power conversion system to capture the energy of ocean waves have been developed. However, suitable turbine type is not normalized yet because of relatively low efficiency of the turbine systems. The purpose of this study is to investigate the internal flow and performance characteristics of a cross-flow type hydro turbine, which will be built in a caisson for wave power generation. Numerical simulation using a commercial CFD code is conducted to clarify the effects of the turbine rotation speed and flow rate variation on the turbine characteristics. The results show that the output power of the cross-flow type hydro turbine with symmetric nozzle shape is obtained mainly from Stage 2. Turbine inlet configuration should be designed to obtain large amount of flow rate because the static pressure and absolute tangential velocity are influenced considerably by inlet flow rate.

• Transactions of Materials Processing
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• v.31 no.5
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• pp.281-289
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• 2022

Presently, 3D printers manufactured by material extrusion are economical and easy to use, so they are being used in various fields. However, this study conducted a tensile test on the infill pattern and density of the PLA+ material, due to the limitations of long printing time as well as low mechanical strength. The infill area for the infill density change was measured, using a vision-measuring machine for four infill patterns (concentric, zigzag, honeycomb, and cross) in which the nozzle path was the same for each layer. The tensile strength/weight[MPa/g] and tensile strength/printing time[MPa/min] of the tensile specimens were analyzed. In this study, efficient infill density and patterns are suggested, for cost reduction and productivity improvement. Consequently, it was confirmed that the infill area and infill percentage of the four patterns, were not constant according to the infill pattern. And the tensile strength of the infill density 40% of the honeycomb pattern and infill density 20% of the cross pattern, tended to highly consider the weight and printing time. Honeycomb and cross patterns could reduce the weight of the tensile specimen by 19.11%, 28.07%, as well as the printing time by 29.56%, 52.25%. Tensile strength was high in the order of concentric, zigzag, honeycomb, and cross patterns, considering the weight and printing time.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.1
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• pp.46-52
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• 2000

A computational analysis has been made on fluid flow in a regenerative cooling Passage for a reduced size liquid rocket engine to predict pressure drop and heat transfer rate in it. The contraction/expansion of the cross sectional area of the passage turn out to increases both the pressure loss and the heat transfer rate of the duct. The changes of the cross sectional area near the nozzle throat are effective to protect the throat which suffers from severe thermal load. Also given is the qualitative characteristics of the performance of the regenerative cooling system due to the variation of coolant flow rate.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.3
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• pp.277-283
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• 2000

The heat transfer characteristics for air jet vertically impinging on a flat plate which had a set of hybrid rod were investigated experimentally. The rod had a cross section made with a half of circular cross section and that of rectangular and was installed in front of the plate. The heating surface was given constant heat flux value of 1020 W/$m^2^{\circ]C$ and the problem parameters investigated were jet Reynolds number, nozzle-to-plate spacing and the rod size. The local and local average Nusselt number characteristics were found to be dependent on the rod size because the flow was disturbed by installing the rod. Higher convective heat transfer rate occurred in the whole plate as well as in the stagnation region.

• The KSFM Journal of Fluid Machinery
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• v.17 no.4
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• pp.30-39
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• 2014

The cross flow turbine is economical because of its simple structure. For remote rural region, there are needs for a more simple structure and very low head cross flow turbines. However, in this kind of locations, the water from upstream always flows into the turbine with some other materials such as sand and pebble. These materials will be damage to the runner blade and shorten the turbine lifespan. Therefore, there is a need to develop a new type of cross flow turbine for the remote rural region where there is availability of abundant resources. The new design of the cross flow turbine has an inlet open duct, without guide vane and nozzle to simplify the structure. However, the turbine with inlet open duct and very low head shows relatively low efficiency. Therefore, the purpose of this study is to optimize the shape of the turbine inlet to improve the efficiency, and investigate the internal flow of a very low head cross flow turbine. There are two steps to optimize the turbine inlet shape. Firstly, by changing the turbine open angle along with changing the turbine inlet open duct bottom line (IODBL) location to investigate the internal flow. Secondly, keeping the turbine IODBL location at the maximum efficiency achieved at the first step, and changing the turbine IODBL angle to improve the performance. The result shows that there is a 7.4% of efficiency improvement by optimizing turbine IODBL location (open angle), and there is 0.3% of efficiency improvement by optimizing the turbine IODBL angle.