• International Journal of Aerospace System Engineering
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• v.1 no.1
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• pp.1-9
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• 2014

In this paper, the effects of the anti-vortex hole angle and blowing ratio on the flat plate film cooling effectiveness were experimentally investigated. For the film cooling effectiveness measurement, pressure sensitive paint technique was applied. The experiments were conducted for cylindrical and anti-vortex film cooling holes, and three blowing ratios of 0.25, 0.5, and 1.0 were tested. Two anti-vortex hole angles of 0 and 15 degree with respect to the flow direction were considered. For the cylindrical hole case, the film cooling effectiveness decreased as the blowing ratio increased because of the coolant lift-off. For the angle anti-vortex hole cases, however, higher blowing ratio resulted in higher film cooling effectiveness due to the reduced actual blowing ratio and diminished kidney vortex. For all blowing ratio, the angled anti-vortex hole case showed the highest film cooling effectiveness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.8
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• pp.688-693
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• 2007

To improve aerodynamic efficiency of the Smart Un-manned Aerial Vehicle(SUAV), vortex generator was applied along the wing upper surface during SUAV tests. Vortex generator, initially used in TR-S2 configuration to enhance lift characteristic, increased lift coefficient. Meanwhile vortex generator produced excessive drag and eventually reduced lift-to-drag ratio. To examine the effect of vortex generator's height, three different heights of vortex generator were used for various SUAV configuration. Vortex generator of 3mm height used in TR-S4 configuration produced 3.1% increase in maximum lift coefficient and 1.5% reduction in lift-to-drag ratio.

• The KSFM Journal of Fluid Machinery
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• v.10 no.4
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• pp.39-46
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• 2007

In large pump station, vortex generation such as free-surface vortex and submerged vortex occurring around pump intake, or at bell-mouth inlet has been an important flow characteristics which should be considered always to keep away the suction of air-entrained or cavitated flow. In this study, a commercial CFD code was used to predict accurately the vortex generation for the specified intake design. These result shows the preliminary result of submerged vortex prediction for the Turbo-machinery Society of Japan Sump Test CFD standard model. At bottom wall, air volume fraction (red color) was found in a large scale to explain the submerged vortex generation at particular operation and configuration condition. And these indicate the free surface formation behind the bell mouth. Particularly, non-uniform approaching flow is a major parameter to govern the occurrence of the free-surface vortex. Futhermore the comparison between turbulence ($k-{\epsilon}$ & $k-{\omega}$ model) mode were executed in this study.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1447-1452
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• 2003

Vortex is very interesting flow phenomena on the heat transfer enhancement. In the present study, naphthalene sublimation technique is used to determine the average and local mass transfer coefficients on the flat plate with vortex generator. A parametric study with Reynolds number and angle of attack is carried out to investigate the heat transfer enhancement. The heat transfer coefficients on the flat plate with rectangular type and delta type vortex generator are compared with those of the flat plate without the vortex generator. Comparing heat transfer coefficients between rectangular type and delta type vortex generator, rectangular type vortex generator has much higher value than delta type vortex generator at the same condition.

• Journal of Hydrospace Technology
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• v.1 no.1
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• pp.1-13
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• 1995

Vortex shedding from a circular cylinder is simulated by means of the discrete vortex method. The shear layer emanating from the separation point is approximated as a sheet vortex which is in turn represented by a sequence of discrete vortices. The strength of these vortices is calculated from the vorticity shedding rate and introduced at a small distance off the side ($\Theta=\pm\pi/2$) of the cylinder surface in regular time step. Sheet vortex cutting, rediscretization and replacement of vortex by vortex segment are put to use to enhance stability of the sheet vortex evolution. The simulated vortex distribution pattern very well reproduces structure like the Karman vortex street. However, as for the force coefficients, the qualitative properties are correctly predicted but some more improvements are needed for the quantitative accuracy.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1377-1382
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• 2004

Flow fields in a half ducted propeller fan have been investigated by three-dimensional Reynolds-averaged Navier-Stokes (RANS) simulations and a vortex core identification technique. The simulation at the design operating condition shows that the tip vortex onset point is located at 30 percent tip chord of the suction surface on the blade tip. There is no interaction between the tip vortex and the adjacent blade, so that the tip vortex smoothly convects to the rotor exit. However, the high vorticity in the tip vortex causes the wake and the tip leakage flow to be twined around the tip vortex and to interact with the pressure surface of the adjacent blade. This flow behavior corresponds well with experimental results by Laser Doppler Velocimetry. On the contrary, the simulation at the low-flowrate operating condition shows that the tip vortex onset point is located at the 60 percent tip chord of the suction surface. In contrast to the design operating condition, the tip vortex grows almost tangential direction, and impinges directly on the pressure surface of the adjacent blade.

• Journal of the Korean Society of Visualization
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• v.15 no.1
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• pp.19-24
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• 2017

In this study, we conduct a numerical experiment of the single 5MW NREL wind turbine and compare the performance of various vortex core identification for the wake behind the wind turbine. In the kinetic analysis of wind turbine, 20% velocity deficit at 200 s is observed, showing wake which contains tip vortex near blade tip and rotor vortex at the center of the wind turbine. Time series of velocity and turbulent intensity show numerical simulation converge to a quasi-steady state near 200 s. In the comparison between methods for vortex identification, ${\lambda}_2$-method has good performance in terms of tip vortex, rotor vortex, vortex during its cascade process compared to vorticity magnitude criteria, ${\Delta}$-method. We conclude that ${\lambda}_2$-method is suitable for vortex identification method for wake visualization.

• Journal of the Korean Society of Clothing and Textiles
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• v.40 no.2
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• pp.305-314
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• 2016

This paper investigated the applicable possibility of PTT and wool staple fibers to the air vortex system as high quality yarns for a high emotional and comfort garment. It was found that the tactile hand of vortex yarn knitted fabrics was harsher than ring and compact yarns knitted fabrics. It was observed that formability and sewability of air vortex yarn knitted fabrics seemed worse than ring and compact yarns due to low tensile and compressional resilience and high bending and shear hysteresis of air vortex yarn knitted fabrics. It revealed that wicking and drying rates of air vortex yarn knitted fabric were better than ring and compact yarns; in addition, the heat keepability of vortex yarn knitted fabric was higher than ring and compact yarns due to low thermal conductivity and max heat flow rate ($Q_{max}$). Any difference of thermal shrinkage between air vortex and ring yarn knitted fabrics was not shown, but pilling characteristic of air vortex yarn knitted fabric was superior. However, it was shown that wicking, drying, thermal property and pilling characteristics of air vortex yarn knitted fabric were superior due to air vortex yarn structure with parallel fibers in the core part and periodical and fasciated twists in the sheath part of the yarns.

• Journal of Mechanical Science and Technology
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• v.20 no.3
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• pp.418-425
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• 2006

The present investigation deals with the study of the internal flow phenomena of the counterflow type vortex tube using experimental testing and numerical simulation. Visualization was carried out using the surface tracing method, injecting dye on the vortex tube wall using a needle. Vortex tube is made of acrylic to visualize the surface particle tracing and the input air pressure was varied from 0.1MPa to 0.3MPa. The experimentally visualized results on the tube show that there is an apparent sudden changing of the trajectory on the vortex tube wall which was observed in every experimental test case. This may indicate the stagnation position of the vortex flow. The visualized stagnation position moves towards the vortex generator with increase in cold flow ratio and input pressure. Three-dimensional computational study is also conducted to obtain more detailed flow information in the vortex tube. Calculated total pressure, static pressure and total temperature distributions in the vortex tube were in good agreement with the experimental data. The computational particle trace on the vortex tube wall is very similar to that observed in experiments.

• Resources Recycling
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• v.6 no.4
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• pp.24-30
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• 1997

The recent trend of recycle of mold scrap is to make high quality secondary ingot which can be used as raw malerial undcr intensive control of scrap. In this study, recycle of aluminum chlp generated atter machinmg process of castings was performed by vortex melting melhod Vortex melting technique was adopted for chip mclting process. The condition far optimal vortcx depth was decided using water mndellng experiment varying the shape, location, rotating speed of stlircr and watcr levcl. Before melting, chips were preheated at room temperame, 200, 300, $ 400^{\circ}C$and then submerged in the mirldle of vortex. The lecovery rale depending on the temperature was examined. As a result vortex depth was influenccd only by shape and rotating speed of stirrer, and the hlghest recovery rate oI 97% was obta~nedw hcn the submerged chip was preheated at $300^{\circ}C.$