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송우길 ( Woo Gil Song ),장조원 ( Jo Won Chang ),전창수 ( Chang Su Jeon ) 한국항공운항학회 2009 한국항공운항학회지 Vol.17 No.4
An experimental study was carried out to investigate aerodynamic characteristics on reduced frequency of flapping wings. The half span of the wing is 28cm, and the mean chord length of wing is 10cm. In flight, the Reynolds Number range of birds is about 10(4), and the reduced frequency during a level flight is 0.25. The experimental variables of present study were set to have similar conditions with the bird flight`s one. The freestream velocities in a wind tunnel were 2.50, 3.75 and 5.00㎧, and the corresponding Reynolds numbers were 1.7 × 10(4), 2.5 × 10(4) and 3.3 × 10(4), respectively. The wing beat frequencies of an experimental model were 2, 3 and 4Hz, and the corresponding reduced frequency was decided between 0.1 and 0.5. Aerodynamic forces of an experimental flapping model were measured by using 2 axis load-cell. Inertial forces measured in a vacuum chamber were removed from measuring forces in the wind tunnel in order to acquire pure aerodynamic forces. Hall sensors and laser trigger were used to make sure the exact position of wings during the flapping motion. Results show that the ratio of downstroke in a wing beat cycle is increased as a wing beat frequency increases. The instantaneous lift coefficient is the maximum value at the end of downstroke of flapping wing model. It is found that a critical reduced frequency with large lift coefficient is existed near k=0.25.
차량 형상에 따른 후류 구조 변화 및 공기저항 저감 연구
장진혁(Jin Hyuck Chang),송우길(Woo Gil Song),장조원(Jo Won Chang) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
Rear wakes of a hatchback type vehicle were measured using 3-D hot-wire anemometer at the HKMC model wind tunnel. A relationship between the wake pattern and the shape variations of rear body was studied. The backlite angle (rear glass angle) of hatchback type vehicles was the most important factor on determining the shape of wake. And we proposed the aerodynamic devices based on the results of wake pattern studies.