Aeroelastic analysis of bio-inspired flapping wing models

In recent years, the studies on Micro Air Vehicles (MAVs) have increased together with the advances in microtechnology. Especially, flapping-wing MAVs with both the high aerodynamic efficiency in low velocities and the high manoeuvring capability have become a very remarkable research area. The flight characteristics of the birds and insects in nature have led the development of flapping-wing MAVs. The aerodynamics of the insects flying at low Reynolds numbers (<104) and the different structures in their wings have been widely considered in the applications of bio-inspired flapping-wing MAVs. In this thesis study, the aerodynamic and aeroelastic characteristics of the three dimensional (3D) wings inspired by the bumblebee and hawkmoth wings are investigated in detail. The flat wings are modelled by Solidworks, and the vein structures are added to the flat wings by ANSYS/SpaceClaim. Then, the mesh structures are generated by ANSYS/Meshing. In the fluid-flow analysis; 3D, incompressible, laminar, steady, and unsteady Navier-Stokes equations are solved with the computational fluid dynamics (CFD) method by using ANSYS/Fluent. In the structural analysis, the displacement calculations are done with the finite element (FE) method by using ANSYS/Mechanical APDL. The CFD and FE analyses are simultaneously performed by ANSYS/System Coupling for the fluid-structure interaction (FSI) analysis. When the studies in the literature are reviewed, the static response of the insect wing to the steady aerodynamic forces in forward flight and the dynamic response of the insect wing to the unsteady aerodynamic forces in hover have not been investigated in detail. This thesis primarily aims to simulate the one-way FSI of the wings by transferring the aerodynamic forces obtained from the steady-state CFD analysis into the FE solver as a pressure load. The static aeroelastic responses of the wings to the pressure loads at various angles of attack (α=0°–90°) are compared for different materials such as cuticle, aluminium alloy Al-6061, and titanium alloy Ti-6Al-4V. It has been found from the steady-state CFD analysis that the hawkmoth wing has higher aerodynamic efficiency and the wings reach the maximum aerodynamic efficiency at α=5°. It has been seen from the one-way FSI analysis that the maximum tip deflections reach to peak for the wings at α=90°. Another purpose of the current study is to observe the unsteady aerodynamic characteristics of the 3D, rigid wing model inspired by the hawkmoth wing in hover. In this scope, the effects of various kinematic parameters such as wingbeat frequency, stroke amplitude, and stroke plane angle on the aerodynamic forces during hovering flight are investigated. The sinusoidal motion is provided by using a user-defined function (UDF) in order to flap the wing with the pure-plunge motion. It has been found from the unsteady CFD analysis that the mean vertical aerodynamics force is maximum for the high wingbeat frequency, high stroke amplitude, and low stroke plane angle. The results obtained from the numerical analysis are verified with both the convergency of the results in the mesh and time-step refinement studies and the comparison of the results with the data available in the literature. The main purpose of this thesis is to select the suitable wing materials and kinematic parameters from the analyses done and to clearly compare the dynamic aeroelastic responses of the different wing structures inspired by the hawkmoth wing (flat-forewing, veined-forewing, rigid wing, flexible wing) in hover. It is seen from the two-way FSI simulations that the veined-wing with the cuticle material increases the vertical aerodynamic force more.