VORTICITY DYNAMICS IN THE LEADING EDGE VORTEX ON REVOLVING WINGS

Restricted (Penn State Only)
Author:
Chung, Hojae
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 07, 2017
Committee Members:
  • Bo Cheng, Thesis Advisor
  • Kenneth Brentner, Committee Member
Keywords:
  • Aerodynamics
  • Insect flight
  • Insect
  • LEV
  • leading edge vortex
  • Revolving wing
  • Revolving motion
  • Rossby number
  • Rossby
  • Planetary vorticity
  • Vorticity equation
  • Vorticity
Abstract:
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.