TY - JOUR
T1 - Leading-edge vortex formation and transient lift generation on a revolving wing at low Reynolds number
AU - Chen, Long
AU - Wu, Jianghao
AU - Cheng, Bo
N1 - Publisher Copyright:
© 2019 Elsevier Masson SAS
PY - 2020/2
Y1 - 2020/2
N2 - Both the transient formation and the stable attachment of leading-edge vortex (LEV) contribute to the high lift generation of an insect wing when it revolves at high angles of attack. In this study, we examined the LEV formation and the transient lift generation on a revolving wing with Reynolds number at 1500 and aspect ratio at 3, using combined computational and experimental methods. The wing started from stationary with a constant angular acceleration within a prescribed chord length of travel at its radius of gyration (i.e. λa), ranging from 0.25 to 2, and then revolved at a constant velocity. Our results showed that the rate of LEV development saturated when λa<1, resulting in a minimum chord length of travel of 2.5 to arrive at a steady LEV. This minimum travel distance agreed well with the prediction based on the vortex formation criterion proposed in other vortex generators. On the other hand, the instantaneous lift generation was strongly dependent on the instantaneous wing velocity and acceleration and therefore exhibited no saturation as λa decreases, which is seen in the LEV formation. The lift generation was attributed to the evolution of tangential vorticity according to the vortex impulse theory. Finally, the instantaneous volume-averaged LEV circulation at different angles of attack scaled well with the instantaneous velocity normal to the leading edge.
AB - Both the transient formation and the stable attachment of leading-edge vortex (LEV) contribute to the high lift generation of an insect wing when it revolves at high angles of attack. In this study, we examined the LEV formation and the transient lift generation on a revolving wing with Reynolds number at 1500 and aspect ratio at 3, using combined computational and experimental methods. The wing started from stationary with a constant angular acceleration within a prescribed chord length of travel at its radius of gyration (i.e. λa), ranging from 0.25 to 2, and then revolved at a constant velocity. Our results showed that the rate of LEV development saturated when λa<1, resulting in a minimum chord length of travel of 2.5 to arrive at a steady LEV. This minimum travel distance agreed well with the prediction based on the vortex formation criterion proposed in other vortex generators. On the other hand, the instantaneous lift generation was strongly dependent on the instantaneous wing velocity and acceleration and therefore exhibited no saturation as λa decreases, which is seen in the LEV formation. The lift generation was attributed to the evolution of tangential vorticity according to the vortex impulse theory. Finally, the instantaneous volume-averaged LEV circulation at different angles of attack scaled well with the instantaneous velocity normal to the leading edge.
KW - Computational fluid dynamics
KW - Insect flight
KW - Leading-edge vortex
KW - Low Reynolds number
KW - Particle tracking velocimetry (PTV)
UR - https://www.scopus.com/pages/publications/85078665850
U2 - 10.1016/j.ast.2019.105589
DO - 10.1016/j.ast.2019.105589
M3 - 文章
AN - SCOPUS:85078665850
SN - 1270-9638
VL - 97
JO - Aerospace Science and Technology
JF - Aerospace Science and Technology
M1 - 105589
ER -