Toward the development of a hydrofoil tailored to passively reduce its lift response to fluid load

Abstract The objective of this research is to explore the possibility of using Passive Adaptive Composite (PAC) on structures to help control the lift generated by hydrofoils on boats such as the International Moth. Introducing composite fibres oriented at off-principal axis angles, allow a foil to passively control its pitch angle to reduce the lift generated at higher boat speeds helping to achieve a stable flight in a wide range of weather conditions. PAC utilises the inherent flexibility of a composite structure to induce a twist response under bending load which could be used to minimise the use of active control systems, or even improve the dynamic response of foils in waves. However, to design flexible foils requires numerical and experimental tools to assess the complex fluid structure interactions involved. This paper evaluates a simplified hydrofoil geometry designed to reduce its lift coefficient with increased flow speed. A coupled Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) methodology is presented to predict flexible foil performance. Validation of these numerical tools is achieved through the use of wind tunnel experiments including full field deformation measurements. Twist deformations resulted in a reduction in the effective angle of attack by approximately 30% at higher flow speeds reducing the foil lift and drag significantly.