| Reducing fuel consumption of modern aircrafts is at the same time an ecological challenge, because it is associated with a reduction of greenhouse gases emissions, and an economical challenge, because due to fossil energy rarefaction, increases in fuel prices are burning issues. These goals may be achieved by reducing wing drag, and consequently engine power. This project is financed by the Consortium for research and innovation in Aerospace in Quebec (CRIAQ), the Natural sciences and engineering research council of Canada (NSERC), Bombardier Aerospace and Thales Canada, and named 7.1 - Laminar flow improvement on an aeroelastic research wing. It is executed by two universities, Ecole de technologie superieure (ETS) and Ecole polytechnique de Montreal, and also by the National Research Council Canada - Institute for Aerospace Research (NRC-IRA). The aim of this project is to develop an active system in order to delay the laminar-to-turbulent transition appearance on the wing.;To meet the functional requirements of the application, the geometry (length and cross-section) of the SMA active elements and the bias spring characteristics are calculated in this thesis. For that, the first parameter that must be fixed is the force of the bias element, which has to maintain the skin in the nominal position in presence of the aerodynamic suction and without actuation. In order to move the skin, the actuators must fight the force of the bias element and the deformation of the flexible extrados, but are helped for that by the suction force of the aerodynamic loading.;Because shape memory alloys' behaviour is difficult to model, the design process is mostly based on a trial-and-error approach. For this study, a characterization of small-dimensions SMA wires allowed to determine the force-stroke envelope, for a given value of the initial strain, actuation temperature and number of cycle. Then, the actuator geometry for the wing prototype can be defined, thanks to a design method based on a scaling of these results.;A 6 wires configuration, each 1800 mm length and 0.7 mm2 cross-section, and made of nickel-titanium alloy (Ti-50.26 at% Ni) appears to satisfy the requirements of the application, once subjected to a preliminary thermo-mechanical preparation (30% cold rolling and heat treatments at 300°C). These wires are cold-deformed during their installation into the prototype, to generate the strokes and forces required to deform the flexible extrados, once activated.;For this study, a morphing wing prototype is designed and built. It is made of three main components apart the rigid structure: a flexible extrados on which pressure sensors are installed to detect the location of the transition, a controller, and smart actuators which move the flexible extrados through a transmission system. These actuators are made of shape memory alloy (SMA) wires placed in parallel of the bias element. They can modify the wing airfoil geometry depending of the flight conditions. These depend of the flow speed (Mach number varying from 0,2 to 0,35), and the angle of attack, varying from -1° to 2°. Optimised airfoils, which can adapt to each studied configuration, have been developed by Ecole polytechnique. A numerical model describing the flexible extrados behavior is built by the Laboratoire sur les alliages a memoire et les systems intelligents (shape memory alloys and smart systems laboratory), at ETS. The results of these studies show that the extrados profile should be controlled by two individually controlled actuators placed along the wing chord. They must be able to generate 8 mm vertical displacement from their reference position in order to reach the optimized airfoils. The numerical model gives the forces and strokes required at the two actuation lines, which must be generated by the actuators and transmitted to the flexible extrados through the transmission system.;The morphing wing prototype has been experimentally tested three times in a wind tunnel, in October 2008, and then in February and May 2009. The SMA actuators' parameters (forces, displacements, etc.) were measured and compared to the predicted values found during the design process. The experimental results allowed the validation of the methodology developed in this master thesis.;Keywords: Ni-Ti shape memory alloys, actuators, morphing wing, wind tunnel tests. |
