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VORTICITY DYNAMICS IN THE LEADING EDGE VORTEX ON REVOLVING WINGS
Restricted (Penn State Only)
Master of Science
Date of Defense:
April 07, 2017
Bo Cheng, Thesis Advisor
Kenneth Brentner, Committee Member
leading edge vortex
The presence of a stable leading edge vortex(LEV) is the most distinguishing feature of flapping wing flight. Delayed stall due to this stable LEV allows insects and birds to maintain a high lift coe cient even at high angles of attack. A necessary condition for a stable LEV is revolving motion, as Lentink and Dickinson discovered. However, there is currently no congruent theory or mechanism to fully explain stable LEV. This research is focused on the fundamental condition of the stable LEV in revolving wings, which represent the stable rotating phases of flapping wings. A revolving rectangular wing with constant angle of attack and rotational speed is simulated in queiscent fluid. By changing Reynolds number and aspect ratio of the wing, relative magnitudes of every term of di erent vorticity transport mechanisms are investigated by calculating the terms in the vorticity transport equation. As a result, tilting of the planetary vorticity due to a vertical gradient of spanwise flow(PVTr) is found to assist the stability of LEV by canceling out a portion of vorticity. Regardless of Reynolds numbers and aspect ratios, PVTr is the most consistent stabilizing factor. Since PVTr is derived from Coriolis force, this conclusion is not only consistent with but further details the e ect of Corilois force on the stability of LEV that Lentink and Dickinson suggested.
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