Fluid structure interaction testing, modelling and development of passive adaptive composite foils

Abstract

High performance foiling catamarans are one of the fastest growing sectors in the sailing and sport industries, allowing athletes to perform in extremely fast and spectacular boats. These boats fly above the water with the aid of foils that not only provide horizontal side-force to counterbalance the aerodynamic forces from the sails, but also deliver vertical force that supports some or all of the mass of the boat. Exploring the possibility of using Passive Adaptive Composite (PAC) on the hydrofoils to control their pitch angle enables the boats to achieve a stable flight in a wide range of weather conditions.

This thesis presents an experimental and numerical evaluation of bend-twist elastic coupling in composite passive-adaptive structures. Due to the lack of experimental validation in Fluid Structure Interaction (FSI) investigations, a full-field deformation of an aerofoil-shaped section under wind loading is measured. Moreover, the influences of structure deflection on flow behaviour are investigated by looking at the changes in flow features evaluated on a transverse plane downstream of the trailing edge. The experimental analysis was carried out at the University of Southampton R. J. Mitchell wind tunnel and involved the use of full-field non-contact measurement techniques such as high speed three dimensional Digital Image Correlation (3-D DIC) and stereoscopic Particle Image Velocimetry (PIV). After assessing the validity and repeatability of the experiments, the research focuses on the development of a numerical FSI investigation that involves the use of a structural and a fluid solver to simulate the aero-elastic behaviour of composite tailored specimens with different internal structures. The numerical analysis is developed as a tool to allow the design of a new structure able to achieve a constant level of lift force (corresponding to the weight of the catamaran) in increased flow speed. During the research project it was proven that the efficiency of the foils can be improved by tailoring the internal structure to induce smart coupled bend-twist toward a wash-out (feather) or wash-in (stall) position under increased loading.

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