• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1659-1666
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• 2001

The objective of this study was to investigate the characteristics of air flow and heat transfer caused by trapezoid rods array in impinging air jet system. Trapezoid rods have been set up on front of flat plate to act as a turbulence promoter. Local Nusselt numbers were determined as a function of three parameters : (a) the space from re(Is to heating surface(C=1, 2, 4mm), (b) the pitch between each rods(P=30, 40, 50mm), (c) the distance from nozzle exit to flat plate(H/B=2, 6, 10). The measurements were compared with those of the experiment without trapezoid rods. As a result, when rods are installed in front of the impinging palate, the acceleration of the flow and the eddies due to the rods seem to contribute to the heat transfer enhancement. Heat transfer performance was best under the condition of C=1mm and as the pitch is 30mm. The maximum rate of heat transfer augmentation is about 1.9 times greater compared to that without trapezoid rods.

• Journal of Energy Engineering
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• v.21 no.2
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• pp.187-193
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• 2012

In this study, it was experimentally investigated the effect of the clearances distance between the rod and the impinging plate on characteristics of the thermal flow. For the heat transfer enhancement of wall jet region, the right triangle and the square rods were arranged in front of the impinging plate with various clearance distances. As results, the heat transfer enhancement rate of potential core region at H/B=2 was higher than that of transition region at H/B=10. In this experiment range, the maximum heat transfer enhancement rate was about 46 % higher at the square rod with H/B=2 and C=1mm compared with the flat plate. The heat transfer enhancement rate of the right triangle rod was on average about 3 to 8 % higher than that of the square rod, regardless of the clearance.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.4
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• pp.243-252
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• 2021

The present study aims to investigate the interaction of a wire-type turbulence stimulator and the laminar boundary layer on a flat plate by flow field measurement. For the towing tank tests, a one-dimensional Laser Doppler Velocimetry (LDV) attached on a two-axis traverse was used to measure the streamwise velocity component of the boundary layer flow in zero pressure gradient, disturbed by a turbulence stimulator. The wire diameter was 0.5 and 1.0 mm according to the recommended procedures and guidelines suggested by the International Towing Tank Conference. Turbulence development by the stimulator was identified by the skin friction coefficient, mean and Root Mean Square (RMS) of the streamwise velocity. The laminar boundary layer with the absence of the wire-type stimulator was similar to the Blasius solution and previous experimental results. By the stimulator, the mean and RMS of the streamwise velocity were increased near the wall, showing typical features of the fully developed turbulent boundary layer. The critical Reynolds number was reduced from 2.7×10⁵ to 1.0×10⁵ by the disturbances caused by the wire. As the wire diameter and the roughness Reynolds number (Rek) increased, the disturbances by the stimulator increased RMS of the streamwise velocity than turbulent boundary layer.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.1
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• pp.18-28
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• 2022

The turbulence stimulation effect of studs for boundary layer over a flat plate was investigated through the flow measurement in KRISO cavitation tunnel. For the test, Laser Doppler Velocimetry (LDV) and three flat plate models were used: (1) flat plate without studs; (2) flat plate with one stud row; (3) flat plate with two stud rows. The dimension and location of stud rows and the inflow speed were selected considering test conditions for standard-sized model ships in KRISO towing tank. The boundary layer characteristics of test models were analyzed and compared in terms of mean velocity profiles, turbulence intensity profiles, boundary layer thickness, and shape factor. In the case of the flat plate without studs, transition from laminar to turbulent flow occurred around Re_x=3.83 ~ 5.19 × 10⁵. In the case of flat plates with stud rows, the flow rapidly changed into turbulent flow right after passing the first stud row. In the state where turbulence was already developed, the second stud row slightly increased the turbulence intensity near the top of the stud, but did not significantly affect the boundary layer characteristics such as mean velocity distribution, boundary layer thickness, and shape factor.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2010.04a
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• pp.59-63
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• 2010

Seven different size of orifice were applied in a constant volume combustion chamber for evaluating the effects of torch-ignition on combustion. The initial flame development and flame propagation were analyzed by the mass fraction burn and combustion enhancement rate. The combustion pressures were measured to calculate the mass fraction burn and the combustion enhancement rates. In addition, the flame propagations were visualized by the shadowgraph method for the qualitative comparison. The result showed that the combustion pressure and mass burned fraction were increased when using the torch-ignition device. The combustion enhancement rates of torch-ignition cases were improved in comparison with conventional spark ignition. Finally, the visualization results showed that the torch-ignition induced faster burn than conventional spark ignition due to the earlier transition to turbulent flame and larger flame surface, during the initial stage.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.92-97
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• 2005

A series of combustion test was done to verify the optimization result of a gas generator for a 10 ton thrust liquid rocket engine. An injector element is F-O-F impinging type injector and the test was conducted with kerosene/LOX propellants. Test results of combustion temperature and pressure show a very good agreement with optimal design result and verify that the design method was properly established. And turbulence ring revealed its effectiveness in enhancing combustion gas mixing and temperature difference in the radial direction showed only less than 15K. Also turbulence ring induced only 3.2% pressure loss in the combustion chamber, which is far less than conventional level observed in a gas turbine engine. Axial temperature distribution also shows that turbulence ring could effectively reduce about 10% or more in gas generator length if its location is properly selected.

• Journal of Wind Energy
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• v.13 no.4
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• pp.26-41
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• 2022

Three similarities (i.e., geometrical similarity, kinematic similarity and dynamic similarity) between a prototype and model must be satisfied to perform an experiment for a floating offshore wind turbine (FOWT). For dynamic similarity, most of the model tests in ocean engineering basins are performed based on the Froude number, so the scale effect for the wind turbine of an FOWT occurs by different Reynolds numbers between the prototype and model. In this study, various model test techniques for overcoming the scale effect of the wind turbine part of the FOWT are investigated. Firstly, model test techniques using simple approaches are reviewed, and the advantages and disadvantages of the simple approaches are summarized. Secondly, the model test techniques in recent projects that apply improved approaches are introduced including advantages and disadvantages. Finally, new approaches applying digitalization are reviewed, and the characteristics of the new approaches are introduced.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.260-267
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• 2001

The objective of this study was to investigate the characteristics of jet flow and heat transfer caused by trapezoid rods array in impinging jet system. In this study, trapezoid rods have been set up in front of flat plate to serve as a turbulence promoter. The bottom width of trapezoid rod was W=4, 8mm and oblique angle were $80^{\circ}$. The space from rods to the heating surface was C=1, 2, 4mm, the pitch between each rods was P=30, 40, 50mm, and the distance from nozzle exit to flat plate was H=100, 500mm. This results were compared with the case without trapezoid rods. As a result, when rods are installed in front of the impinging plate, the acceleration of the jet flow and the eddies due to the rods seem to contribute to the heat transfer enhancement. Among test conditions, the heat transfer performance was best for the condition of W=8mm, C=1mm, P=30mm and H/B=10. The maximum heat transfer rate is about 1.9 times larger than that without trapezoid rods.

• Water for future
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• v.25 no.1
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• pp.111-119
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• 1992

This paper is concerned with the actual comparison analysis for the freshening process in the two selected experimental reservoirs. At the deep freshening reservoir, the salinity and depth of the freshwater layer were estimated by simulation technique using the quantitative equation for the two-layered flow structures. First of all, it is shown that the effects of underdrainage conduit in the lower layer were reported more effective for the control of upper layer salinity comparing with the case of no underdrainage conduit. Further the results of computation were later compared with the real observed values and the relating parameters of the salt-balance equation are conformed even though approximately. Finally it was represented that the salinity of upper layer is easily diluted not only by the tidal gate but also by the underdrainge conduit in the lower layer of the freshening reservoir.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.565-571
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• 2001

The objective of this study was to investigate the characteristics of air flow and heat transfer caused by trapezoid rods array in impinging air jet system. In this study, trapezoid rods have been set up on front of flat plate to act as a turbulence promoter. Local Nusselt numbers were determined as a function of three parameters: (a) the space from rods to heating surface(C=1, 2, 4mm), (b) the pitch between each rods(P=30, 40, 50mm), (c) the distance from nozzle exit to flat plate(H/B=2, 6, 10). And this research compared the above with the experiment without trapezoid rods. As a result, heat transfer performance was best under the condition of C=1mm and as the pitch is 30mm. In this case, maximum rate of heat transfer augmentation is about 1.9 times greater compared to that without trapezoid rods.