• International Journal of Fluid Machinery and Systems
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• v.8 no.3
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• pp.169-182
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• 2015

When simulating the dynamic behaviour of a hydro power plant, it is essential to have a good representation of the turbine behaviour. The pressure transients in the system occurs because the flow changes, which the turbine defines. The flow through the turbine is a function of the pressure, the speed of rotation and the wicket gate opening and is, most often described in a performance diagram or Hill diagram. In the Hill diagram, the efficiency is drawn like contour lines, hence the name. A turbines Hill diagram is obtained by performance tests on scaled model in a laboratory. However, system dynamic simulations have to be performed in the early stage of a project, before the turbine manufacturer has been chosen and the Hill diagram is known. Therefore one have to rely on diagrams for a turbine with similar speed number. The Hill diagram is drawn through measured points, so for using the diagram in a simulation program, one have to iterate in the diagram based on curve fitting of the measured points. This paper describes an alternative method. By means of the Euler turbine equation, it is possible to set up two differential equations which represents the turbine performance with good enough accuracy for the dynamic simulations. The only input is the turbine's main geometry, the runner blade in- and outlet angle and the guide vane angle at best efficiency point of operation (BEP). In the paper, simulated turbine characteristics for a high head Francis turbine, and for a reversible pump turbine are compared with laboratory measured characteristics.

• The KSFM Journal of Fluid Machinery
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• v.16 no.3
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• pp.39-47
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• 2013

Effect of semicircular rib or groove on the performance of a rim-seal was evaluated using three-dimensional Reynolds-averaged Navier-Stokes equations. The turbulence was modeled using the one-equation Spalart-Allmaras turbulence closure model. Reynolds number based on the axial chord of the turbine blade was 500,000 at the mainstream outlet. The numerical results for a sealing effectiveness was validated in comparison with experimental data. To examine the effect of the semicircular rib or groove on sealing effectiveness of the rim-seal, location and diameter of the rib or groove were selected as the parameters to be performed. The rim-seals with the semicircular groove showed a higher sealing effectiveness than that with the semicircular rib. The semicircular groove installed on the stator side showed best sealing effectiveness among the numerical simulation results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.6
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• pp.1187-1193
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• 2002

Anodic bonding process has been quantitatively evaluated based on the Taguchi analysis of the interfacial fracture toughness, measured at the interface of anodically bonded silicon-glass bimorphs. A new test specimen with a pre-inserted blade has been devised for interfacial fracture toughness measurement. A set of 81 different anodic bonding conditions has been generated based on the three different conditions for four different process parameters of bonding load, bonding temperature, anodic voltage and voltage supply time. Taguchi method has been used to reduce the number of experiments required for the bonding strength evaluation, thus obtaining nine independent cases out of the 81 possible combinations. The interfacial fracture toughness has been measured for the nine cases in the range of 0.03∼6.12 J/㎡. Among the four process parameters, the bonding temperature causes the most dominant influence to the bonding strength with the influence factor of 67.7%. The influence factors of other process parameters, such as anodic voltage and voltage supply time, bonding load, are evaluated as 18%, 12% and 2.3%, respectively. The maximum bonding strength of 7.23 J/㎡ has been achieved at the bonding temperature of 460$\^{C}$ with the bonding load of 45gf/㎠, the applied voltage of 600v and the voltage supply time of 25minites.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.7 s.262
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• pp.628-634
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• 2007

The present study investigated the heat/mass transfer characteristics in an equilateral triangular channel simulating the leading edge cooling passage in gas turbine blade. Using naphthalene sublimation method and pressure measurement experiments, local mass (heat) transfer and pressure coefficients were obtained. The experiments were conducted with three rotating numbers between 0.0 and 0.1; two channel orientations of $0^{\circ}$ (model A) and $30^{\circ}$ (model B); the fixed Reynolds number of 10,000. The results showed that the channel rotation caused the heat transfer discrepancy between suction and pressure sides. Due to the secondary flow induced by Coriolis force, the high heat transfer appeared on the pressure side. When the channel orientation was $30^{\circ}$ (model B), the secondary flow caused the more uniform heat transfer distribution among leading edge and inner wall on pressure side than that of the model A.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.1
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• pp.137-143
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• 2017

An axial fan has competitive advantages that can make air flow more straight and longer and produce larger air volume than the other kinds of fans. In those reasons, axial fans are widely used for ventilator, 4D cinema, duct, and so on. But, as it was designed and manufactured without any mathematical analysis or computer simulations, it is difficult to develop the performance of axial fans. Actually the axial fan is designed and manufactured in industry by imitation or traditional method. Flow velocity and volume of axial fan are changed by pitch angle, frame, the number of blade, camber angle, and chord length. In this paper, the performance of axial fan was analyzed and by computer program known as CFD. Finally, we have designed a new axial fan whose velocity and volume is improved. The performance of new axial fan is also compared with the of conventional fans experimentally.

• Applied Microscopy
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• v.28 no.3
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• pp.399-414
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• 1998

Glandular trichomes present on the leaf surface of Drosera capensis were examined using transmission electron microscopy. A large number of stalked glands exist on the adaxial surfaces of the leaf blade. The secretory head is composed of two layers of secretory cells, one layer of middle cells, and the inner tracheids. The secretory cells contain rough endoplasmic reticulum, mitochondria, plastids, Golgi apparatus, and vacuoles. The secretory cells show prominent cell wall ingrowth, and thick cuticle restricted on the subcuticular wall. Frequently, the cuticle has some pores, canal-like structures, showing electron -dense granules being penetrated through them. Ultrastructural localization using diaminobenzidine showed the electron-dense deposits in the vacuole. No peroxidase activity was seen in the cell wall and cytolasm. The activity of peroxidase (POX) isozymes in Drosera which isoelectric point (pI) is 3.6 and some anionic POX isozymes which pIs are laid between 3.6 and 4.6 were especially increased according to the development and the formation of glandular trichomes. Also, the activity of some POX isozymes which isoelectric points are laid between 4.6 and 5.1 were increased in the regions of leaves which has trichomes.

• The KSFM Journal of Fluid Machinery
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• v.7 no.3 s.24
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• pp.32-38
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• 2004

Shape of a multi-blades centrifugal fan is optimized by response surface method based on three-dimensional Navier-Stokes analysis. For numerical analysis, Reynolds-averaged Navier-Stokes equations with standard $k-{epsilon}$ turbulence model are transformed into non-orthogonal curvilinear coordinate system, and are discretized with finite volume approximations. Due to the large number of blades in this centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models for economic calculations. Optimizations with and without constraints are carried out. Design variables, location of cur off, radius of cut off, expansion angle of scroll and width of impeller were selected to optimize the shapes of scroll and blades. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, the efficiency was successfully improved. The correlation of efficiency with relative size of inactive zone at the exit of impeller is discussed as well as with average momentum fluxes in the scroll.

• The KSFM Journal of Fluid Machinery
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• v.8 no.3 s.30
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• pp.33-41
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• 2005

The optimum condition is defined as one that best suits the purpose of flocculation; the number of small particles should decrease, while that of large particles should increase. The object of this research was to develop a new impeller and substitute for conventional flocculators. The flow characteristics of turbines and hydrofoil type flocculators in turbulent fluids were observed using a standard $k-{\epsilon}$ Model and a computational fluid dynamics (CFD) simulation program-FLUENT. The experiments were performed to compare PBT(Pitched Blade Turbine) flocculator with twisted hydrofoil type flocculators for velocity distribution, and floe formation at conventional water treatment plants in Korea. As a result of the CED solution, twisted hydrofoil types are similar to hydrofoil flocculators for flow characteristics without regard to the twisted angle, On the other hand, it was established that turbine flocculators are greater than hydrofoil flocculators with flow unevenness and dead zone formation. Twisted hydrofoil type-II (Angle $15{\sim}20^{\circ}$) is the most proper impeller for water flocculation from this point of view with a decreasing the dead zone, maintaining of the equivalent energy distribution and a drawing up of the sedimentation substance from the bottom of the flocculation basin.

• Journal of Energy Engineering
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• v.20 no.2
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• pp.143-153
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• 2011

Offshore wind power(OWP) is one of the most promising renewable energy and gives higher output than onland one due to stronger and consistent wind in offshore. it offsets shortcoming of noise, spatial limit and less affects scenery, and can be built in larger size. Korea has plenty of offshore wind resources as it is surrounded by the sea in three directions. This review describes recent progress in offshore wind turbine and substructure technology. Market trend in local and overseas, Number of papers published and patents registered are analysed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.1
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• pp.1-11
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• 2012

Performance analysis was performed for an autorotating rotor. For a given airspeed, shaft angle, and collective pitch, the steady state of autorotation was judged by using the transient simulation method(TSM), then the thrust, lift, and drag coefficient for that state were computed. Average thrust was calculated from the instantaneous thrusts, in which the TSM was used in blade thrust integration. The analysis method was applied to the model rotor that had been tested by wind tunnel. Some comparison between analysis and test was provided. Two types of two-dimensional airfoil aerodynamic data were utilized in analysis, and they were made by Navier-Stokes Solver in terms of Reynolds and Reynolds-Mach number. The quantitative difference of results using two data set was examined and compared.