• Proceedings of the KSME Conference
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• 2001.06d
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• pp.765-770
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• 2001

The objective of the present study is to investigate the effects of the various inlet boundary layer thickness on convective heat transfer distribution in a turbine cascade endwall and blade suction surface. In addition, the proper height of the boundary layer fences for various inlet boundary layer thickness were applied to turbine cascade endwall in order to reduce the secondary flow, and to verify its influence on the heat transfer process within the turbine cascade. Convective heat transfer distributions on the experimental regions were measured by the image processing system. The results show that heat transfer coefficients on the blade suction surface were increased with an augmentation of inlet boundary layer thickness. However, in a turbine cascade endwall, magnitude of heat transfer coefficients did not change with variation of inlet boundary layer thickness. The results also present that the boundary layer fence is effective in reducing heat transfer on the suction surface. On the other hand, in the endwall region, boundary layer fence brought about the subsidiary heat transfer increment.

• 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.

• 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.

• 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.20 no.8
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• pp.2670-2680
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• 1996

Effeccs of porous wind fence on surface-pressure around 2-dimensional prism model of triangular cross-section were investigated experimentally. The pressure data were obtained at a Reynolds number based on the model height of Re=2.1*10$^{5}$ . Flow visualization also carried out to investigate the flow structure qualitatively. The mean velocity and turbulent intensity profiles measured at fence location were well fitted to the neutral atmospheric surface boundary layer over the open terrain. Various fences with different porosity and height were tested to investigate their effects on the surface pressure acting on a prism model at different locations. As the results, porous fence with porosity 40 ~ 50% is most effective for abating wind erosion. With decreasing porosity of the fence, pressure fluctuations on the model surface are increased. The mean pressure coefficients are decreased only when the fence height is greater than the model height. The effect of distance between wind fence and triangular prism was not significant, compared to that of the fence porosity and height.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1175-1184
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• 2000

Effects of porous wind fences on the wind erosion of particles from a triangular sand pile were investigated experimentally. The porous fence and sand pile were installed in a simulated atmospheric boundary layer. The mean velocity and turbulent intensity profiles measured at the sand pile location were well fitted to the atmospheric boundary layer over the open terrain. Flow visualization was carried out to investigate the motion of windblown sand particles qualitatively. In addition, the threshold velocity were measured using a light sensitive video camera with varying the particle size, fence porosity $\varepsilon$ and the height of sand pile. As a result, various types of particle motion were observed according to the fence porosity. The porous wind fence having porosity $\varepsilon$=30% was revealed to have the maximum threshold velocity, indicating good shelter effect for abating windblown dust particles. With increasing the sand particle diamter, the threshold velocity was also increased. When the height of sand pile is lower than the fence height, threshold velocity is enhanced.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1496-1508
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• 1997

The effects of porous wind fence on the pressure characteristics around a 2-dimensional prism model of triangular cross-section were investigated experimentally. The fence and prism model were embedded in a neutral atmospheric surface boundary layer over the city suburb. In this study, various fences of different porosity, back fence, inclination angle of prism and location of additional back prisms were tested to investigate their effects on the pressure and wall shear stress of the prism surface. The fence and prism had the same height of 40 mm and Reynolds number based on the model height was Re=3.9*10$^{4}$. The porous fence with porosity 40% was found to be the best wind fence for decreasing the mean and pressure fluctuations on the prism surface. By installing the fence of porosity 40%, the wall shear stress on the windward surface of prism was largely decreased up to 1/3 of that without the fence. This indicates that the porous fence is most effective to abate the wind erosion. Pressure fluctuations on the model surface were decreased more than half when a back fence was located behind the prism in addition to the front fence. With locating several back prisms and decreasing the inclination angle of triangular prism, the pressure fluctuations on the model surface were increased on the contrary.

• Korean Journal of Environment and Ecology
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• v.26 no.5
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• pp.741-757
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• 2012

This study had targeted the Seunghwanglim of Wonju in order to understand the forest vegetation's present condition. And then we compared the change in vegetation of Seunghwanglim for 24years. It was intended to provide basic data for conservation and management. Actual vegetation as a result of investigation, a total area of $56,231m^2$ Quercus serrata forest(7.02%), Acer triflorum forest(5.71%), and Deciduous Broad-Leaved Forest and Pinus densiflora forest(6.4%) were distributed variously. Present condition of the plains forest has 34 kinds of canopy species, 65 kinds of understory species, 70 species of shrubs species, 88 species of total species. And the plains forest has 500 individuals of canopy layer, 1,102 individuals of understory layer. Mean importance percentage of the major species showed Ulmus davidiana var. japonica(15.6%), Acer triflorum(15.2%), Pinus densiflora(11.1%), Quercus serrata(9.8%). Acer triflorum diameter at Ulmus davidiana var. japonica were a relatively wide range. Results of change for 24 years, vegetation of Seunghwanglim was changed from Quercus serrata-Acer triflorum to Ulmus davidiana var. japonica-Acer triflorum. Big trees over than DBH 30cm were surveyed total 18 species, 166 individuals. Increased over than the past 63 individuals. Seunghwanglim was destroyed by reckless past. Since 1990, the outer perimeter fence was installed to control human access. After that, understory layer and shrub layer were developed. And big tree was increased. Which is considered to restore damaged ecosystems. In order to conservation and protection of Seunghwanglim, people have to management and monitor about exotic species such as Robinia pseudo-acacia, Populus tomentiglandulosa, Castanea crenata, Pueraria lobata, etc.