Potential Flow Based Aerodynamic and Aeroelastic Analysis of flapping Wings

The motivation for this research is the importance that the modeling of aerodynamics and aeroelasticity of flapping wings has had in the last decade. The development of flapping wings Micro Air Vehicles (MAV) has captured a huge interest in the recent past, due to the several disciplines involved in the subject. In this dissertation the attention is focused on the flow and its interactions with the structure.

Even though experiments have had a fundamental role in the explanation of the aerodynamics around a flapping wing, it is widely accepted that a key aspect in the development of future flapping wings MAVs is the modeling. The aim of the project is to investigate different techniques for the development of a numerical framework used in the prediction of the unsteady aerodynamic forces on flapping wings.

The understanding of the phenomena occurring on flapping wings is attempted first with very basic models. The research is carried out based on potential flow assumptions: the flow in initially treated as irrotational and inviscid. Although the assumptions are very strong, it is shown that the mechanisms of lift and thrust production can be described, together with the convection of the wake behind the wing. The limitation of potential flow models is the incapacity to describe flows that are separated over a large portion of the wing. The modeling of this issue is particularly important for flapping wings, where the separation is exploited in order tin increase the forces produced.

The development of a Vortex Particle Method (VPM) is attempted, with wake elements released at each time step from all the panels of the airfoil. The advantage of Vortex Particle Methods over panel methods is that they represent more realistically the flow around the wing. The drawback is the greater complexity and longer running times.

Aeroelasticity is discussed as well, as it is believed that the wing flexibility can enhance the performance of flapping wings. The thesis investigates the stability and response of an airfoil connected to a rotational and a linear spring at its elastic axis. Even though the structural model is very simple, it is shown that there might be advantages introducing a certain level of flexibility in the system.

The framework built in this project is not aimed at giving an accurate representation of the forces produced by flapping wings. A methodology that allows to avoid CFD computations is deemed fundamental in the design phase of an aerial vehicle. The final goal of this project is the development of meshless techniques for the aerodynamic analysis of unsteady flows. An essential point that needs deep insight is their inaccuracy compared to CFD. Therefore considerations about the lack of accuracy and ways to improve it are made in order to show that there is a real advantage in the sue of grid-free methods. The results of the analysis are compared with other results found in the literature. In particular, experimental results are considered where possible, otherwise numerical computation shave been taken into account. The first part of the code has been developed in FORTRAN, due to its running time efficiency, while the second part has been developed in C++, because of its ability to handle more complex data structures.