Affiliations: Departmenf of Aerospace and Mechanical Engineering,
Korea Aerospace University, Hwajeon-dong, Deokyang-gu, Goyang city,
Gyeonggi-do, 412-791, Republic of Korea | Department of Aeronautical Science and Flight
Operation, Korea Aerospace University, Hwajeon-dong, Deokyang-gu, Goyang city,
Gyeonggi-do, 412-791, Republic of Korea. E-mail: jwchan@kau.ac.kr | Department of Aerospace Engineering, Korwa Air Force
Academy, Ssangsuri, Namil-myun, Chungwon-gun, Chungbuk-do. 363-849, Republic of
Korea
Abstract: An unsteady flow visualization and force measurement were carried
out in order to investigate the effects of the reduced frequency of a
dragonfly-type model. The flow visualization of the wing wake region was
conducted by using a smoke wire technique. An electronic device was mounted
below the test section in order to find the exact position angle of the wing
for the visualization. A load-cell was employed in measuring aerodynamic forces
generated by a plunging motion of the experimental model. To find the period of
the flapping motion in real time, trigger signals were also collected by
passing laser beam signals through the gear hole. Experimental conditions were
as follows: the incidence angles of the fore-and hind wing were 0° and
10°, respectively, and the reduced frequencies were 0.150 and 0.225. The
free-stream velocities of the flow visualization and force measurement were 1.0
and 1.6 m/sec, respectively, which correspond to Reynolds numbers of 3.4
× 10^3 and 2.9 × 10^3. The
variations of the flow patterns and phase-averaged lift and the thrust
coefficients during one cycle of the wing motion were presented. Results showed
that the reduced frequency was closely related to the flow pattern that
determined flight efficiency, and the maximum lift coefficient and lift
coefficient per unit of time increased with reduced frequency.
