• Journal of Ship and Ocean Technology
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• 제3권4호
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• pp.15-22
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• 1999

It is known that lubrication effect of an air cavity can reduced a drag of a ship. The present study intends to utilize the phenomena for the drag reduction of a passenger ship now operating in a lake. A scaled model of the model when air cavities are formed under the bottom of the model. Model experiments have been performed to determine adequate air supply rates, proper shapes and locations of air supply nozzles. It is shown that energy saving of mere than 10% can be achieved at the design speed of the ship even after excluding additional power consumed for air supplying. Multiple air supply nozzles, if allocated properly, are more effective than single one in resistance reduction of the ship.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.475-478
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• 2002

Maximum drag reduction (MDR) in turbulent channel flow by polymer additives is studied by direct numerical simulation. An Oldroyd-B model is adopted to express the polymer stress because it is believed that MDR is closely related to the elasticity of the polymeric liquids. The Reynolds number based on the bulk velocity and the channel height is 40000. MDR in the present study is $44{\%}$ and this is in a good agreement with the Virk's asymptote. Turbulence statistics are also in good agreements with the experimental observation. In the 'large drag reduction', the decrease of turbulent kinetic energy is compensated by the increase of energy transfer from the polymer to the flow. Therefore, MDR is a dynamic equilibrium state of the energy transfer between the polymer and the flow.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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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.

• 설비공학논문집
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• 제9권3호
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• pp.401-409
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• 1997

The long term drag reduction characteristics of Habon-G solution were investigated in the KIER pilot-scaled district heating simulation system. Test runs were implemented for 30 days without interruption. Pressure drop, flow rate and power consumption of surfactant (Habon-G) solution were regularly observed and compared with those of plain water. The experimental results suggest that the surfactant can be effectively applied to the DH transmission system for considerably long period wthout significant loss of its drag reduction capability even though the concentration of the additive may gradually decrease in the first stage of the experiment because of absorption.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.71-76
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• 2000

This experimental study was conducted to figure out the drag reduction and convective heat transfer in vertical downward two-phase flow with polymer additives. The drag reduction effect were analyzed by using the difference of the pressure drop between the flow with polymer additives and without it. Experimental results show that the pressure drop with polymer additives is less than the pressure drop without polymer in vertical downward two-phase flow. And the convective heat transfer has decreased with increasing the polymer concentration in vertical downward two-phase flow.

• 한국자동차공학회논문집
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• 제4권3호
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• pp.176-186
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• 1996

The phenomena of drag reduction using small quantities of a liner macromolecules has attracted the attention of many experimental investigations. On the other hand drag reduction in two phase flow can be applied to the transport of crude oil, phase change system such as chemical reactor, pool and boiling flow, and to flow with cavitation which occurs pump impellers. But the research on dragreduction in two phase flow is not sufficient. The purpose of the present work is to evaluate the drag reduction by measuring pressure drop, void fraction, mean liquid velocity and turbulent intensity whether polymer additives a horizontal single and two phase system or not. Flow pattern of air-water two phase flow was classified by electrical conductivity probe signal. Velocities and turbulent intensities of signal were measured simultaneously with a Hot-film anemometer.

• Journal of Advanced Marine Engineering and Technology
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• 제23권5호
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• pp.679-686
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• 1999

This study is to investigate the effect of a substantial drag reduction caused by the polymer(A611P) when the working fluids flow to the vertical direction in the vertical cylindrical equipment of closed flow system. The drag reduction is associated with the mechanical degrada-tion thermal degradation and heat transfer. By ignore the heat fluxs within the closed system the pressure drop due to the polymer concentration the flow velocity and flow time have been mea-sured. By taking into account the mechanical and thermal degradation in the closed system an experiment has been focused on the determination of the condition which could improve the pump capacity in the heat union electric power plant. Under the condition of non-boiling it has been found out that the change of heat flux has little influence on the drag reduction.

• 태양에너지
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• 제19권1호
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• pp.37-45
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• 1999

As polymer added in flow, the phenomenon of drag reduction effect was found by many experiments and studies. We divided polymer into three molecular weight($2{\times}10^5,\;4{\times}10^5,\;5{\times}10^5$) and into four concentration(1, 5, 10, 20wppm), then we measured the drag reduction effect in the range Reynolds Number with $30000{\sim}60000$. Finally we found that the most effect drag reduction was that molecular weight is $2{\times}10^5$ with 10wppm concentration. Then the concentration was according to PEO molecular weight, and in general DR increase according to Reynolds Number.

• 대한기계학회논문집B
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• 제34권8호
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• pp.799-807
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• 2010

폴리머 첨가제에 의한 항력감소 난류 채널 유동에 대한 직접수치모사를 스펙트럴 기법을 통해 수치적으로 해석하였다. 마찰속도 및 채널 높이의 절반으로 무차원화한 레이놀즈수는 395 이며, 폴리머 첨가제에 의해 발생하는 폴리머 응력은 FENE-P 모델을 통해 고려하였다. 폴리머 분자의 이완 시간 및 최대 연신 한계와 같은 FENE-P 모델 인자는 항력감소율에 큰 영향을 끼치는 것으로 나타났다. 항력감소율이 낮은 유동과 높은 유동에 대해 항력감소에 따른 난류 통계량의 변화를 조사하였다. 또한, 동일한 항력감소율을 갖는 유동에 대해, 서로 다른 FENE-P 모델 인자가 난류 통계량의 변화에 미치는 영향도 조사하였다. 최종적으로, Li 등(2006) 이 제시한 유변학 인자들과 항력감소율과의 상관관계식을 본 수치해석 결과를 통해 확인하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.60-60
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• 2003