Modelling of a SMA Blade Twist System Suited for Demonstration in Wind Tunnel and Whirl Tower Plants

Abstract

In this work, the modeling of a demonstrator of a morphing system aimed at altering the twist of a rotorcraft blade is presented. The device was conceived for two different representative environments: the wind tunnel plant of the University of Bristol and the whirl tower facility of the DLR, for tests in fixed and wing rotary configurations, respectively. The concept, conceived and matured within the European Project of SABRE, is based on shape memory alloys, SMA. This technology was selected for its intrinsic compactness and solidity, which better meet the requirements of a typical blade structure, being extremely flexible and subjected to relevant inertial loads. A dedicated structural layout was conceived to favor the working modality of the SMA torsional system; this architecture was tailored both to absorb the typical actions occurring onto a blade and to assure a certain level of pre-twist necessary for the SMA strain recovery. The activation of the SMA was performed through an electrothermal helicoidal coil wrapped around it. A dedicated network of sensors was integrated within the structure to measure the impact of the different actions on the blade system. This subsystem, functional to shape reconstruction operations, is capable of splitting the contribution of the loads to pure twist and flapping. At first, the requirements imposed by the two test facilities were elaborated together to the operational needs, arriving at the issue of the most relevant specifications. Secondly, the conceptual and advanced design were considered, demonstrating, first, the feasibility of the concept and, then, its compliance with the test environment. The work ends with two different layouts, conceived respectively for the tests in fixed and rotary wing configurations. For both of them, a performance estimate was addressed, and a discussion on the advantages and disadvantages was presented.