Active shape airfoil control through composite-piezoceramic actuators

The transonic aerodynamic field around a wing section is characterised by a large number of peculiarities, which strongly influence the airfoil performance. In particular, a shock wave located on the wing upper surface strongly interacts with the boundary layer, causing a drag increase, Moreover, wave oscillations may give rise to the undesired aeroelastic phenomenon of buffeting. Aerodynamic studies have pointed out that shape airfoil modifications may lead to performance improvements. The aim of the work is to present a procedure to design and realise a tailored and integrated composite actuator made of an aluminium alloy sheet. The geometry of the skin element is modified by the combined action of a uniform pressure load producing static deformations, and tangential piezoelectric ceramic patches bonded through a laminate connection layer, generating dynamic oscillations. The laminate is aimed at properly insulating the two elements and addressing the energy towards one direction, preferably. Glass fibre/epoxy was selected to this target. The design procedure is made of a first part, devoted at the definition of the sheet thickness law (taking into account the ceramics contributions) that assures the deformed shape following the specific aerodynamic requirements, and a second part, applied to optimise the structure-actuators configuration. Analytical and numerical extensions of available models, able to predict the strain actuation on composite elements with variable thickness under different boundary conditions complete the proposed methodology. According to the obtained results and indications, an experimental "bump" prototype was realised. An experimental campaign is being carried out in order to compare the real behaviour of the skin element with the theoretical predictions: static and dynamic bump deflected shape was measured.