• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.197-206
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• 2009

To improve the aerodynamic efficiency of Smart Unmanned Aerial Vehicle (SUAV), vortex generators and flow fence are applied on the surface and the tip of wing. The initially applied vortex generator increased maximum lift coefficient and delayed the stall angle while it produced excessive increase in drag coefficient. It turns out reduction of the airplane's the lift/drag ratio. The new vortex generators with L-shape and two different height, 3mm and 5mm, were used to TR-S4 configuration to maintain the desired level of maximum lift coefficient and drag coefficient. Flow fence was also applied at the end of both wing tip to reduce the interaction between nacelle and wing when nacelle tilting angles are large enough and produce flow separation. To examine the effect of flow fence, flow visualization and force and moment measurements were done. The variation of the aerodynamic characteristics of SUAV after applying flow control devices are summarized.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.1
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• pp.29-37
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• 2011

PIV measurements of the velocity field, pressure field, vorticity, and turbulent intensity in the rear of curved section of an oil fence with current speed showed that the flow directions in the rear of flow boundary area were similar to those in the front of it. As the current speed increased, the patterns of pressure distribution were changed, and the turbulent flow became more irregular. CFD simulations under the same conditions as the PIV tests showed that the flow patterns of the wake were similar to those by PIV tests in speed of 0.3 m/s and less, but were distinctively deviated from those in 0.4 m/s due to the flexibility of the oil fence, which was not properly taken care of in CFD modeling.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.287-292
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• 2001

The objective of this study is to verify the secondary flow and the total pressure loss distribution in the boundary layer fence installed linear turbine cascade passage and to propose an appropriate height of the boundary layer fence which shows the best loss reduction among the simulated fences. In this study three different boundary layer fence was installed which have different height. This study was performed by numerical method and the result showed the boundary layer fence which has the height of one third of the inlet boundary layer thickness showed the best loss reduction rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.11
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• pp.1552-1558
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• 2002

The blade leading edge is modified to control the secondary flow generated in the turbine cascade with fence by intensifying the suction side branch of the horseshoe vortex. The incompressible Navier-Stokes equations are numerically solved with a high Reynolds number k-$\varepsilon$ turbulence closure model for investigating the vortical flows in the turbine cascade. The computational results of total pressure loss coefficients in the wake region are first compared with experiments for validation. The structure and strength of the passage vortex near the suction surface are examined by testing various geometrical parameters of the turbine blade leading edge.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.8-14
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• 2005

Understanding of the flow past a bluff body close to a moving ground is very important in automobile and aeronautical fields because of aerodynamic characteristic and instability induced by unsteady vortex shedding. The passive control method that mounted the vertical and horizontal plates at the lower surface of the cylinder is studied to suppress the unsteady oscillation motion. When the grounds moves, the diminish of the shear layer on the ground promotes the interaction between the lower and the upper separated shear layers of the cylinder, hence vortex shedding occurs at the lower gap height than the stationary ground.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.1
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• pp.94-99
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• 2008

The characteristics of the flowfield of a square prism having fences on the corner was investigated by the PIV. Strouhal numbers, velocity vectors and velocity profiles around the square prism were observed at various positions of the fences, and Reynolds number of $Re=0.6{\times}10^4{\sim}1.0{\times}10^4$. As the results in case of the prism having fences the Strouhal numbers were all smaller than in case of the prototype prism. In case of the prism having vertical fences on the front corners the concentrated intensity of the vorticity was the strongest and the size of separated shear layer was the largest. While in case of the prism having vertical fences on the rear corners the concentrated intensity of the vorticity was the weakest and the size of separated shear layer was the smallest. Also in this case, the flow separated in front corner was reattached around the rear corner and made circulation.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.853-858
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• 2000

The working fluid from the combustor to the turbine stage of a gas turbine makes various boundary layer thickness. Since the inlet boundary layer thickness is one of the important factors that affect the turbine efficiency. It is necessary to investigate secondary flow and loss with various boundary layer thickness conditions. In the present study, the effect of various inlet boundary layer thickness on secondary flow and loss and the proper height of the boundary layer fences for various boundary layer thickness were investigated. Measurements of secondary flow velocity and total pressure loss within and downstream of the passage were taken under 5 boundary layer thickness conditions, 16, 36, 52, 69, 110mm. It was found that total pressure loss and secondary flow areas were increased with increase of thickness but they were maintained almost at the same position. At the fellowing research about the boundary layer fences, 1/6, 1/3, 1/2 of each inlet boundary layer thickness and 12mm were used as the fence heights. As a result, it was observed that the proper height of the fences was generally constant since the passage vortex remained almost at the same position. Therefore once the geometry of a cascade is decided, the location of the Passage vortex and the proper fence height are appeared to be determined at the same time. When the inlet boundary layer thickness is relatively small, the loss caused by the proper fence becomes bigger than endwall loss so that it dominates secondary loss. In these cases the proper fence hight is decided not by the cascade geometry but by the inlet boundary layer thickness as previous investigations.

• The KSFM Journal of Fluid Machinery
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• v.12 no.2
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• pp.8-16
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• 2009

The objective of this study is to investigate the three-dimensional turbulence flow characteristics of a rotor passage of an one-stage axial flow gas turbine and to investigate the effects of a boundary layer fence installed on the hub endwall of the rotor passage. Secondary flows occurring within the rotor passage (e.g. horseshoe vortex, passage vortex, and cross flow) cause secondary loss and reduce turbine efficiency. To control these secondary flows, a boundary layer fence measuring half the height of the thickness of the inlet boundary layer was installed on the hub endwall of the rotor passage. This study was performed numerically. The results show that the wake and secondary flows generated by the stator reduced the rotor load to constrain the development of cross flow and secondary flow reinforced by the rotor passage. In addition, the secondary vortices occurring within the rotor passage were reduced by the rotation of the rotor. Although, the boundary layer fence induced additional vortices, giving rise to an additional loss of turbine, its presence was shown to reduce the total pressure loss when compared to effects of the case without fence regardless of the relative position of blades by enervating secondary vortices occurred within the rotor passage.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.10
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• pp.810-815
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• 2008

To enhance aerodynamic efficiency of the Smart Un-manned Aerial Vehicle(SUAV) during the transition period, wingtip fence is attached at the end of wing. The application of wingtip fence is to reduce the effect of the separated flow caused by the nacelle on the wing especially when the tilting angle of nacelle is more than 30 degrees. To compare the effect of with and without wingtip fence, flow visualization and measurement of the aerodynamic coefficients using the pyramidal type external balance are done. Result of forces and moments measurement shows that the slope of lift coefficient is increased 18% and rolling moment of SUAV especially 60 & 90-degree tilting is changed in favorable manners with wingtip fence.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.6
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• pp.16-22
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• 2004

Unsteady vortex shedding behind a rectangular cylinder near a wall influences both increasing of drag and dynamic stability of heavy vehicle, bridge or building. Incompressible Averaged Navier-Stokes equation with modified ${\varepsilon}-SST$ turbulence model is adapted for investigating the flow field between the rectangular cylinder and the wall. In case the vortex shedding happens, not only the averaged maximum velocity is higher than other cases, but the position of the maximum velocity is closer to the lower surface of rectangular cylinder. On this study, it is confirmed that the vortex shedding behind a rectangular cylinder can be suppressed by the passive control method added by horizontal and vertical fences to the lower surface of rectangular cylinder.