• Korean Journal of Soil Science and Fertilizer
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• v.44 no.2
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• pp.316-319
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• 2011

Biopiles which offer the potential for cost-effective treatment of contaminated soils are above-ground, engineered systems that use oxygen to stimulate the growth and reproduction of aerobic bacteria for degradation of the petroleum constituents adsorbed to soil in excavated soils. This technology involves heaping contaminated soils into piles and stimulating aerobic microbial activity within the soils through the aeration and/or addition of minerals, nutrients, and moisture. Inside the biopile, microbially mediated reactions by blowing or extracting air through the pipes can enhance degradation of the organic contaminants. The influence of a aeration system on the biopile performance was investigated. Air pressure made to compare the efficiency of suction in the pipes showed that there were slightly significant difference between the two piles in the total amount of TPH biodegradation. The normalised degradation rate was, however, considerably higher in the aeration system than in the normal system without aeration, suggesting that the vertical venting method may have improved the efficiency of the biological reactions in the pile.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.377-382
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• 2001

A suboptimal control law in turbulent pipe flow is derived and tested. Two sensing variables ${\partial}p/{\partial}{\theta}\;|_w\;and\;{\partial}{\upsilon}_{\theta}/{\partial}r\;|_w$ are applied with two actuations ${\phi}_{\theta}$ and ${\phi}_r$. To test the suboptimal control law, direct numerical simulations of turbulent pipe flow at $Re_r=150$ are performed. When the control law is applied, a $13{\sim}23%$ drag reduction is achieved. The most effective drag reduction is made at the pair of ${\partial}{\upsilon}_{\theta}/{\partial}r\;|_w$ and ${\theta}_r$. An impenetrable virtual wall concept is useful for analyzing the near-wall suction and blowing. The virtual wall concept is useful for analyzing the near-wall behavior of the controlled flow. Comparison of the present suboptimal control with that of turbulent channel flow reveals that the curvature effect is insignificant.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.135-140
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• 2011

The battery pack, a main component of NEV(Neighborhood Electric Vehicle), needs cooling system when it is charging or discharging to prevent the degradation of the battery charging efficiency. The purpose of this study is to analyse the effects of cooling methods, changing positions of inlet and outlet and changing area ratios of inlet and outlet. It has been observed that in the point of uniform cooling suction from the exit side is more efficient than blowing from the inlet. And there is a suitable inlet/outlet area ratio in maximizing the mass flow rate. The numerical analyse using a commercial code STAR-CCM+ version 4.02 were used for the study.

• Journal of computational fluids engineering
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• v.16 no.3
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• pp.82-87
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• 2011

The battery pack, a main component of NEV(Neighborhood Electric Vehicle), needs cooling system when it is charging or discharging to prevent the degradation of the battery charging efficiency. The purpose of this study is to analyse the effects of cooling methods, changing positions of inlet and outlet and changing area ratios of inlet and outlet. It has been observed that in the point of uniform cooling, suction from the exit side is more efficient than blowing from the inlet. And there is a suitable inlet/outlet area ratio in maximizing the mass flow rate. A commercial code, STAR-CCM+(ver. 4.02), was used for the numerical study.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2625-2630
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• 2008

Horseshoe vortices are formed at the junction of an object immersed in fluid-flow and endwall plate as a result of three-dimensional boundary layer separation. This study shows preliminary results of the kinematics of such horseshoe vortices around a circular cylinder with a cavity (slot) placed upstream to disturb the primary separation line. Through the cavity, no mass flow addition (blowing) or reduction (suction) is applied. The upstream cavity weakens the adverse pressure gradient before the cavity. With the upstream cavity, a single vortex is found to form immediately upstream of the cylinder whereas a typical two vortex system is observed in the absence of the cavity. Furthermore, the strength of the single vortex tends to be reduced, resulting from the interaction with the separated flow convecting directly towards the leading edge of the cylinder.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2708-2712
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• 2008

The objective of this work is to study various vortical structures from controlled circular jet such as trifurcating and blooming jets. The numerical simulations of flow from a circular jet are carried out at $Re_D=4300$ based on the jet-exit velocity and jet diameter using large eddy simulation with the dynamic Smagorinsky model in a cylindrical coordinate system. The excitation for the controlled jet is achieved by combining axial and helical excitations. The axial velocity controlled by blowing and suction at the jet exit has several peaks in their cycle with respect to ratio of axial to helical excitations. This active control changes the spreading angle and vortical structures in the downstream region.

• Journal of the Semiconductor & Display Technology
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• v.20 no.3
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• pp.77-82
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• 2021

This numerical study focuses on the analysis of fume particle dispersion characteristics over the surface of target workpiece in laser micro-hole machining process. The effects of oblique stagnation flow over fume generating machining point are examined by carrying out a series of three-dimensional random particle simulations along with probabilistic particle generation model and particle drag correlation of low Reynolds number. Present computational model of fume particle dispersion is found to be capable of assessing and quantifying the fume particle contamination in precision hole machining which may influenced by different types of air flow patterns and their flow intensity. The particle size dependence on dispersion distance of fume particles from laser machining point is significant and the effects of increasing flow oblique angle are shown quite differently when slot blowing or slot suction flows are applied in micro-hole machining.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.96-107
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• 2001

An unsteady numerical simulation was performed to analyze flow structures behind a local suction/blowing in a flat-plate turbulent boundary layer. The local forcing was given to the boundary layer flow by means of sinusoidally oscillating jet. A version of the unsteady $\kappa$-$\xi$-f(sub)u model (Rhee and Sung 2000) was employed. The Reynolds number based on the momentum thickness was about Re(sub)$\theta$=1700. The forcing frequency was varied in the range 0.011$\leq$f(sup)+$\leq$0.044 with a fixed forcing amplitude A(sub)o=0.4. The predicted results were compared and validated with the experimental data. It was shown that the unsteady locally-forced boundary layer flow is predicted well by the $\kappa$-$\xi$-f(sub)u model. The effect of the pitch angle of local forcing on the reduction of skin friction was also examined.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.72-78
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• 2007

To develop the aerodynamic performance, there are widely two group of studies are achieved. The first one is about design of the vehicles geometry and the second one is about aerodynamic devices. Geometry design is highly credible and stable method. But it is not flexible and each parts are related interactively. So if one part geometry are modified, the other parts are required to be redesigned. The other hand, flow control by aerodynamic device is flexible and modulized method. Though it needs energy, relatively little input makes far advanced aerodynamic performance. Synthetic Jet is one of the second group method. The device repeats suction and blowing motion in constant frequency. According to the performance, the flow which are near the flight surface are served momentum. This mechanism can reduce the aerodynamic loss by boundary layer and separated flow. Synthetic jet actuator has several parameters, that influence the flow control. This study focus the parameters effects of the synthetic jet - orifice geometry, frequency, jet speed and etc.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.497-501
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• 2000

Flow over a sphere is controlled experimentally at $Re=10^5$ using electro-magnetic actuators. The electro-magnetic actuator developed in this study is composed of the permanent magnet electro-magnet membrane and slot. Eight actuators are placed inside the sphere at equally spaced intervals on a latitudinal plane and the position of the control slot is 76 from the stagnation point. Each actuator generates a periodic blowing and suction through the slot at variable frequencies of $10{\sim}140Hz$ and variable amplitudes by controlling electric signals applied to the electro-magnet. Drag on the sphere measured using a load cell is significantly reduced with control at the forcing frequencies larger than the natural shedding frequency $({\approx}14Hz\;at\;Re=10^5)$, whereas drag is slightly increased at the forcing frequency of 10Hz. It is shown from pressure measurement that the static pressure in the rear surface of the sphere is significantly increased with control, indicating that the separation is delayed due to control. Flow visualizations also show that the detaching shear layer is more attracted to the sphere center with control, the separation bubble size is significantly reduced, and motion inside the bubble is very weak, as compared to the case of uncontrolled flow.