Some unsteady aerodynamics relevant to insect-inspired flapping-wing micro air vehicles

Abstract

Flapping-wing micro air vehicles, based on insect-like apping, could potentially ll a niche in the current market by o ering the ability to gather information from within buildings. The aerodynamics of insect-like apping are dominated by a large, lift-enhancing leading-edge vortex (LEV). Historically, the cause and structure of this vortex have been the subject of controversy. This thesis is primarily intended to provide insight into the LEV, using computational uid dynamics coupled with validating experiments. The problem is simpli ed by breaking down the complex kinematics involved in insect-like apping and examining only a part of these kinematics; rstly in 2D, before progressing to 3D sweeping wing motions. The thesis includes discussion of published literature in the eld, highlighting gaps and inconsistencies in the current knowledge. Among the contributions of this thesis are: descriptions of the e ects of changing Reynolds number and angle of attack for 2D and 3D ows; clari cation of terminology and phenomenology, particular in the context of 2D ows; and detailed descriptions of the development and structure of the LEV in both 2D and 3D cases, including discussion of Kelvin-Helmholtz instability. The issues of Strouhal number, delayed leading-edge separation, dynamic stall and the Wagner e ect are also considered. Generally, the LEV is shown to be unstable in 2D cases. However, in 3D cases the LEV is seen to be stable, even if Reynolds number is increased. The stability of the LEV is found to be critically dependent on wing aspect ratio.