• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.690-700
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• 1994

The effects of thermal stratification on the flow of a stratified fluid past a circular cylinder were examined in a wind tunnel. In order to produce strong thermal stratifications, a compact heat exchanger type variable electric heater is employed. Linear temperature gradient of up to $250^{\circ}C/m$ can be well sustained. The velocity and temperature profiles in the cylinder wake with a strong thermal gradient of $200^{\circ}C/m$ were measured and the smoke wire flow visualization method was used to investigate the wake characteristics. It is found that the temperature field effects as an active contaminant, so that the mean velocity and temperature profiles can not sustain their symmetricity about the wake centerline when such a strong thermal gradient is superimposed. It is evident that the turbulent mixing in the upper half section is stronger than that of the lower half of the wake in a stably stratified flow.

• Journal of Korea Water Resources Association
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• v.38 no.8 s.157
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• pp.691-698
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• 2005

A series of experiments has been performed to investigate the flapping motion, which has been generally considered as an intrinsic characteristic of plane flow, of the horizontal merging buoyant jet discharged into stationary ambient water. For Horizontal merging buoyant jets, the flapping motions has been observed and the average onsets of flapping motion coincided with the start of merging transition. The Strouhal number, which describes the measure of frequency of vortices on the flow boundary with respect to the local properties of the flow, varies and converges to a constant value over merging transition. Considering the merging transition and the variation of local flow properties, the characteristics of flapping motion of plane flow can be applied to merging buoyant jets.

• Journal of the Korean Society for Railway
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• v.15 no.6
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• pp.531-536
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• 2012

This study presents a result on aero-acoustic characteristics of pantograph panheads. To analyze the fluid flow around the panhead and resulting sound radiation, simple models of panhead were used in the numerical simulations called Lattice-Boltzmann method. The simulation results were verified using the wind tunnel test. The main aerodynamic noise was generated from the vortex shedding which is characterized by the Strouhal number, flow speed and geometry. The reduction in the radiated noise with simultaneously achieving increased lifting force was implemented for the simple rectangular geometry used in this study. Also, it was shown that the radiated sound power was significantly reduced by minimizing vortex shedding using through-holes or streamline shapes.