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RISS 인기검색어
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- 저자 : 사공웅(Woong Sagong) (검색결과 3 건)
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사공웅(Woong Sagong),전우평(Woo-Pyung Jeon),최해천(Haecheon Choi) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
The sailfish and swordfish are known as the fastest sea animals. They have a long bill, which has been regarded as a drag-reduction device by the separation delay through turbulence generation. In the present study, we investigate the hydrodynamic characteristics of sailfish and swordfish through the wind-tunnel experiment. From the direct measurement of drag forces on the fishes, we find that the drag coefficients of sailfish and swordfish are comparable to or smaller than those of other fishes such as the dogfish, tuna, dolphin and trout. The role of bill is also investigated in this study. The drag with the artificial short bill is smaller than that with the original bill, indicating that the bill does not make any role in reducing drag. From the velocity measurement near the body surface, we find that the flow separation does not occur even with the short or smooth bill, and thus there is no need to generate turbulence using the bill for the form-drag reduction.
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이욱(Wook Yi),사공웅(Woong Sagong),최해천(Haecheon Choi) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
In this study, a passive control using a boat-tail device is conducted for a three-dimensional car model in ground proximity. We consider various boat-tails and investigate the mechanism of drag reduction by them. By varying the length and slant angle of boat-tail, we obtain drag reductions up to 40%. From the oil-surface flow visualization and hot-wire measurement, the drag reduction by the boat-tail is characterized by the shearlayer instability and reattachment on the boat-tail, forming a small separation bubble at the upstream part of boat-tail surface, resulting in the delay of main separation and drag reduction. At high slant angles, the flow fully separates and drag is nearly same as that of no control.
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보트-테일 장치에 의한 3차원 모형 운송체의 항력감소의 메커니즘
이욱(Wook Yi),사공웅(Woong Sagong),최해천(Haecheon Choi) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
The boat-tail device decreases a significant amount of drag on a three-dimensional model vehicle. However, the detailed mechanism of drag reduction by the boat tail has not been clearly found. To clarify the mechanism of its drag reduction, we conduct an experiment for flow over a three-dimensional model vehicle in ground proximity. We consider various boat tails and conduct force and velocity measurements near the boat tail and oil-surface visualizations. The slant angle of boat tail shows a great effect on drag reduction and the maximum drag reduction is 45%. The flow separation at a small slant angle occurs at the trailing edge of the boat tail. At an intermediate angle, separated flow reattaches on the boat-tail surface by forming a small secondary separation bubble which provides strong near-wall momentum, resulting in the delay of main separation and a significant drag reduction. The flow fully separates at the leading edge of boat tail and the drag reaches that of no control at a large slant angle.
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