• Proceedings of the KSRS Conference
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• v.2
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• pp.1007-1010
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• 2006

This study investigates the spatial structure of the total cloud liquid water content Q fields over the Northwest Pacific Ocean during winter monsoon. The distributions of Q have been estimated from the brightness temperatures of the ocean - atmosphere system $T_B(f)$, where f is frequency, measured by AQUA AMSR-E in January -March 2003. Marine strati (St) and stratocumuli (Sc) are typical for winter monsoon season. They were analysed using mainly high-frequency channel at f = 36.5 GHz, vertical polarisation. $T_B$ data were accompanied by the data on near surface wind speed, air temperature and humidity from the nearest meteorological stations. Tow one-dimensional spectra were computed for downwind and crosswind sections of Q fields. The AMSR-E antenna field of view (14-8 km) and the cloud field sizes (100-1000 km) restricted the spatial scales. The results of case study Jan 31 2003 are presented. Scale-invariant spectrum is typical. In the cases of extended St levels a spectral slope equals about -1.7, conforming to classical -5/3 of turbulence theory. For Sc cases the absolute magnitude of spectral slope is rather higher, as a rule. The value is about -2. In the case when cloud streets are presented, a strait line form of spectrum is less reliable with a slope being rather lower (about -1.4).

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.15-21
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• 1999

The flow characteristics around KRISO 300K VLCC double-body model have been experimentally investigated in a closed-type subsonic wind tunnel. The local mean velocity and turbulence statistics including turbulent intensity. Reynolds shear stress and turbulent kinetic energy were measured using a x-type hot-wire probe. The measurements were carried out at several transverse stations of the stern and near wake regions. The surface flow was visualized using on oil-film technique to see the flow pattern qualitatively. The flow in the stern and near wake region revealed complicated three-dimensional flow characteristics. The VLCC model shows a hook-shaped wake structure behind the propeller boss in the main longitudinal vortex region. The thin boundary layer at midship was increased gradually in thickness over the stern and evolved into a full three-dimensional turbulent wake.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.6
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• pp.24-32
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• 2004

The effects of guide vanes and tip clearances on the characteristics nf axial flow fans are investigated both computationally and experimentally. Performance test of fans carried out in full scale shows considerable effects of tip clearance between rotor tip and duct on the characteristics of fans. The tested results are compared with the computation based on the finite volume method to solve the Navier-Stoke equations with $textsc{k}$-$\varepsilon$ turbulence model. The comparison shows good agreements between experimental and computational results. In addition, the effects of shape of guide vanes are numerically studied. The results show that increased volume of separated region around the guide vane reduces the recovery of tangential component of kinetic energy in the wake, resulting in loss of efficiency

• Wind and Structures
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• v.8 no.2
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• pp.79-88
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• 2005

This paper deals with a unified way for calculating vortex-induced vibrations (Aeolian vibrations in transmission line parlance) of undamped single overhead conductors. The main objective of the paper is to identify reduced parameters which would unify the predicted vibration response to the largest possible extent. This is actually done by means of a simple mathematical transformation resulting, for a given terrain (associated to a given wind turbulence intensity), into a single, unified response curve that is applicable to any single multi-layered aluminium conductor. In order to further validate the above process, the predicted, unified response curve is compared with measured response curves drawn from tests run on a full-scale test line using several aluminium-conductor-steel-reinforced (ACSR), all-alloy-aluminium-conductor (AAAC) and aluminium-conductor-alloy-reinforced (ACAR) conductors strung at different tensions. On account of the expected scatter in the results from such field tests, the agreement is shown to be good. The final results are expressed by means of only four different curves pertaining to four different terrain characteristics. These curves may then be used to assess the vibration response of any undamped single, multi-layer aluminium conductor of any diameter, strung at any practical tension.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.12
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• pp.1163-1168
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• 2009

The power quality of wind energy becomes more and more important in connecting wind-farms to the grid, especially weak grid. This paper presents the simulation of a wind farm of a permanent magnet synchronous generator (PMSG) and a doubly fed induction generator (DFIG). Flicker mitigation is performed by using PMSG as a static synchronous compensator (STATCOM) to regulate the voltage at the point of common coupling (PCC). A benefit of the measure is that integrating two function of to control the active power flow and to reduce the voltage flicker in a wind farm. Simulation results show that controlling PMSG is an effective and economic measure in reducing the flicker during continuous operation of grid connected wind turbines regardless of short circuit capacity ratio, turbulence intensity and grid impedance angle.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.247-251
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• 2010

It is very difficult to understand and estimate the heat transfer and flow characteristics in the combustor, which is one of main components in the Auxiliary Power Unit (APU), because its flow filed has very complex structure. In this paper, specified is characteristics of injection and flow through different air goles in the liner, which consist of large circular holes film cooling holes, and tangential air swirl holes. The durability of the liner depends on whether the surface of the liner is exposed to the hot gas over 1000 $^{\circ}C$ of a temperature or net. It is proved that the locations of hot spots estimated from the calculation using CFD are matched well with that from the test. In this study, CFD simulations were performed to examine the heat transfer and temperature distributions in and about a liner wall with film cooling on the wall. This computational study is based on the ensemble average continuity, compressible Navier-Stokes, energy, and PDF combustion equations closed by the standard $k-{\varepsilon}$ turbulence model with standard wall functions for the gas phase and the Fourier equations for conduction in the solid phase.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1005-1014
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• 2004

Experiments were done for the three dimensional unsteady flow in a counter-rotating axial flow fan under peak efficiency operating condition. Flow fields in a counter rotating axial flow fan were measured at cross-sectional planes of the upstream and downstream of each rotor. Cross sectional flow patterns were investigated through the acquired data by the 45$^{\circ}$ inclined hot-wire. Flow characteristics such as tip vortex, secondary flow and tip leakage flow were confirmed through axial, radial and tangential velocity vector plot. It has been found that the radial and tangential velocity components disappeared, while the axial velocity component highly increased as soon as the tip vortex was generated. It has been observed that secondary flow and turbulence intensity which were increased by the front rotor were dissipated passing through the rear rotor. As the result the energy loss of the counter rotating axial flow fan decreased at the downstream of rear rotor. Also, it has been verified that tip vortex pattern of the rear rotor was dampened because the tip vortex generated by front rotor was mixed with that of the rear rotor.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.202-212
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• 1985

Numerical and experimental studies are presented for turbulent flows and heat transfer in annular channel with circumferential fins on the inner tube in a double pipe heat exchanger. Flow and heat transfer characteristics are periodically fully developed, and complex flow patterns are shown. Numerical calculations are executed by using modified TEACH-2E computer program based on the standard k-.epsilon. turbulence model. Mean velocity, turbulent kinetic energy, and Reynolds stress distributions are measured with the hot wire anemometer. Static pressures on the outer wall of the pipe are measured for three pitch-height ratios and several Reynolds numbers. Numerical predictions generally show reasonable results in comparison with experimental results. When the pitch-height ratio is about 5.0 and other geometric parameters are fixed in this paper, maximum heat transfer is achieved. Reattaching flow patterns appeared in this region. As the pitch between fins is increased beyond 5.0, mean Nusselt numbers are decreased and the pressure drop through one pitch almost remains.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.155-158
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• 2002

In general, TVC(Thermal Vapor Compressor) is used to boost/compress a low pressure vapor to a higher pressure for further utilization. The one-dimensional method is simple and reasonably accurate, but cannot realize the detail as like the back flow and recirculation in the mixing chamber, viscous shear effect, and etc. In this study, the axisymmetric How simulations have been performed to reveal the detailed flow characteristics for the various ejector shapes. The Navier-Stokes and energy equations are solved together with the continuity equation In the compressible flow fields. The standard $k-{\epsilon}$ model is selected for the turbulence modeling. The commercial computational fluid dynamic code FLUENT software is used for the simulation. The results contain the entrainment ratio under the various motive, suction and discharge pressure conditions. The numerical results are compared with the experimental data, and the comparison shows the good agreement. The three different flow regimes (double chocking, single chocking and back flow) have been clearly distinguished according to each boundary pressure values. Also the effects of the various shape variables (nozzle position, nozzle outlet diameter, mixing tube diameter, mixing tube converging angle, and etc.) are quantitatively discussed.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.1
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• pp.31-35
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• 2016

For reaction injection molding (RIM) polyurethane was mixed in the mixing head by impingement mixing, injected into the mold, and cured quickly, as soon as the mold is filled. The shape of the nozzle in the mixing head is critical to improve the quality of polyurethane. To achieve homogeneous mixing, an intensive turbulence energy in the mixing nozzle is essential. In this study, a mixing nozzle for RIM was designed, and mixing efficiency was investigated based on experiment. Experiments were conducted with different combinations of nozzle tips and exit diameter to measure the mixing efficiency by measuring jet force and investigating mixing image with high speed camera. Jet force increased gradually and reaches steady state conditions. The jet force depended on shape of nozzle tip and outlet sizes. These results suggest that optimized nozzle configurations are necessary for high efficiency mixing with RIM.