Date on Master's Thesis/Doctoral Dissertation

8-2014

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Mechanical Engineering

Committee Chair

Lian, Yongsheng

Committee Co-Chair (if applicable)

Bradshaw, Roger

Committee Member

Bradshaw, Roger

Committee Member

Sharp, Keith

Committee Member

Chang, Dar-Jen

Committee Member

Wissink, Andrew

Subject

Leading edges (Aerodynamics); Aerofoils

Abstract

The perching maneuver of natural fliers is a complex motion involving fast change of angle of attack, complicated wing kinematics, large wing deformation and agile body motion control, but the prominent aerodynamic features can be revealed using a simple pitch-up wing motion coupled with a stream wise deceleration. In this dissertation the aerodynamic forces, the leading edge vorterx (LEV) development, and LEV circulation of pitch-up and perching wings are extensively studied at low Reynolds number conditions. 2D and 3D wings of different aspect ratios were linearly pitched up from 0 to 90 at three reduced pitch rates. The numerical investigation was conducted at a Reynolds number of 500 and the flow field was described using the unsteady three-dimensional incompressible Navier-Stokes equations on a set of composite overlapping grids. The Q-criterion was used to identify and isolate the LEV structure from shear layer vorticity. Results have shown that the LEV circulation depends primarily on the wing aspect ratio: increasing wing aspect ratio increased the rate of LEV circulation generation during the pitch-up motion. The reduced pitch rate for the pitch-up motion was found to delay the LEV circulation development when the aspect ratio was greater than two. For perching, pitch rate only altered the LEV propagation away from the wing, and not the magnitude of the circulation.

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