• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.68-72
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• 2006

Vertical fence has the coherent flow structure in front of the fence. In the present study, the wake change due to the flow separator in front of the vertical fence was experimentally investigated. Quantitative method was applied to study the separated shear flow field. The results show the flow separator changes the downstream shear flow and alters the curvature of separated shear layer As the freestream velocity increased, the reattachment length also increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.1
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• pp.47-53
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• 2008

The effect of periodic blowing and suction of upstream flow on the separated shear flow behind the vertical fence was experimentally investigated. The fence was submerged in the turbulent shear flow and DPIV method was used to measure the instantaneous velocity fields around the fence. Periodic blowing and suction flow was precisely generated by the syringe pump. Spanwise nozzle made 2D planar periodic jet flow in front of the fence and the effect of frequency and maximum jet velocity was studied. From the results, the reattachment length can be reduced by 60% of uncontrolled fence case under the control.

• Wind and Structures
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• v.5 no.2_3_4
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• pp.329-336
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• 2002

The along-wind response of a surface-mounted elastic fence under the action of wind was investigated numerically. In the computations, two sets of equations, one for the simulation of the unsteady turbulent flow and the other for the calculation of the dynamic motion of the fence, were solved alternatively. The resulting time-series tip response of the fence as well as the flow fields were analyzed to examine the dynamic behaviors of the two. Results show that the flow is unsteady and is dominated by two frequencies: one relates to the shear layer vortices and the other one is subject to vortex shedding. The resulting unsteady wind load causes the fence to vibrate. The tip deflection of the fence is periodic and is symmetric to an equilibrium position, corresponding to the average load. Although the along-wind aerodynamic effect is not significant, the fluctuating quantities of the tip deflection, velocity and acceleration are enhanced as the fundamental frequency of the fence is near the vortex or shedding frequency of the flow due to the occurrence of resonance. In addition, when the fence is relatively soft, higher mode response can be excited, leading to significant increases of the variations of the tip velocity and acceleration.

• Journal of the Korean Society of Visualization
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• v.8 no.1
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• pp.13-18
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• 2010

An experimental investigation of the flow around a vertical fence was carried out using a PIV velocity field measurement technique. The vertical fence was embedded in a turbulent boundary layer. The instantaneous velocity fields measured at cross-sectional planes reveal complex longitudinal vortices that vary in size and strength, developing from the upstream location. In the instantaneous vorticity and velocity field data, the shear flow separated from the fence top is highly turbulent and shows unsteady flow characteristics. The topography of the ensemble averaged velocity fields, especially the separation bubble formed behind the fence, shows that the spatial distributions of streamwise velocity (U) and vertical (V) are symmetric, the spanwise velocity (W) is skew-symmetric with respect to the central xy-plane(z=0).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.5
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• pp.708-715
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• 1998

The shelter effect of a porous wind fence on a triangular prism was experimentally investigated in a circulating water channel. A porous fence of porosity .epsilon.=38.5% was installed in front of the prism model. The fence and prism model were embedded in a turbulent boundary layer. The instantaneous velocity fields around the fence and prism model were measured by using the instantaneous velocity fields around the fence and prism model were measured by using the 2-frame PTV(Particle Tracking Velocimetry) system. By installing the fence in front of the prism, the recirculation flow region decreases compared with that of no fence case. The porous fence also decreases the mean velocity, turbulent intensity and turbulent kinetic energy around the prism. Especially, at the top of the prism, the turbulent kinetic energy is about half of that without the fence.

• 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.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.772-776
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• 2001

The flow structures of turbulent shear layer behind oil fences with different tip configurations were investigated experimentally using flow visualization and PIV velocity field measurement. An oil fence was installed in a circulating water channel and the flow structure around the fence tip was mainly analyzed in this experiment. The four tip configurations tested in this experiment are knife edge; semi-circle edge, circular edge and rectangular edge. The 300 instantaneous velocity fields were measured using the single-frame PIV system and they were ensemble averaged to give the mean velocity field and spatial distribution of turbulent statistics. Free stream velocity was fixed at 10ms/sec and the corresponding Reynolds number based on the fence height was Re=4000. As a result, for the oil fence with rectangular edge, the streamwise velocity component was decreased. On the other hand it was increased for the oil fence with circular edge. For all four fences tested in this study, general flow pattern of the lower shear layer is analogous but the upper layer shows difference depending on the tip configurations. The oil fence with circular edge has more diffusive upper shear layer than that of the others. The shear layer of the oil fence with rectangular edge has relatively thin thickness. The oil fence with circular edge was found to be proper shape for tandem fence.

• 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.

• Proceeding of KASS Symposium
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• 2006.05a
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• pp.91-101
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• 2006

We have conducted the study about the shelter effect against the wind by using the wind fence with various porosities and the measured distance from the wind fence, in three different types of it ; (Circle wind fence, Vertical wind fence, Horizontal wind fence) The shelter effect and turbulence characteristics of the selected wind barrier is throughly investigated by wind tunnel test. flow characteristics of velocities and turbulences behind wind fence were measured using hot-wire anemometer. we characterize the turbulence behind the wind fence by varying the porosity of 0 %, 20 %, 40%, and 60%, and the distances from the wind fence from 1 H to 9 H with maintaining the uniform flow velocity of 6 m/s. In addition, we investigated the overall characterization of the wind fence by measuring total of twenty eight points on the wind fence, which forms the lattice structure on it with seven points in lateral direction and four points in vertical direction. The results of analysis from the circle wind fence indicate that the degree of the turbulence is lowered and the velocity of the wind is decreased when the porosity of 40 % are used at the distance from 3 H to 9 H. On the other hand, the vertical, horizontal wind fence with the porosity of 20% is more advantageous at the distance of 2 H to 9 H. For the effectiveness of the wind fence depending on the position, the center part is the greatest and it decreases at the edges with 10 % to 30 % less than that of at the center.

• 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.