Marano, Aniello Daniele (2022) Vibroacoustic Optimal Design and Structural Scalability of Composite Wing for the Next Generation Civil Tiltrotor. [Tesi di dottorato]

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his dissertation presents the up-scaled process of an innovative composite wing for the Next Generation Civil Tiltrotor. Inspired from the Technological Demonstrator wing, the purpose is to investigate the up-scaling process of its structural architecture to realize a new high lift, low drag wing optimized to improve downwash impingement in helicopter mode and increase the total fuel capacity. About the wing primary structure, for the wingbox, a curvilinear rear spar is used instead of the straight spars associated with the conventional transport wings. Additionally, the composite structure is considered for the wing design because it has larger ratios in the strength-to-weight and the stiffness-to-weight than those for the metallic structure, which can further reduce the total tiltrotor structural weight and fuel consumption. High speed and maneuverability, and at the same time, low vibration and noise are the most important features of the new generation rotorcrafts and tiltrotors. Tiltrotors manufacturers are trying to bring tiltrotor technology to the civil aviation market by reducing the interior vibration and noise level so to make the competitiveness of tilt-rotor aircraft greatly improved for this purpose. For tilt-rotor aircraft, the aeroacoustics has a great influence on the interior noise. The in-flight noise test campaign carried out on board of the AW609 LHD tiltrotor is described in this thesis. These tests were performed with the main goals to validate an experimental setup in a fully new environment and the assessment of a data analysis procedure and to better investigate the problem of noise and then obtain satisfactory levels of comfort for passengers of the NGCTR. The use of the lightweight composite could lead to enhanced flexibility of the wing, which may cause many aeroelastic problems such as large deflections, the onset of flutter and whirl flutter, loss of control, etc. Whirl flutter clearance, crashability requirements and, wing box structural layout design are all considered to address some of these problems through multidisciplinary design, analysis, and optimization studies in this work. In this context, some laboratory activities on the sidelines of scalability were conducted to become more confident with the aeroelastic phenomena treated. In particular, a series of activities in the vibrations test field modal testing and experimental treatment of the whirl flutter phenomenon are presented. Several numerical and structural dynamics tests were performed to confidently and validate the Multi-Input Multi-Output methods. A section of the thesis shows the design, development, and testing of a small-scale unpowered experimental test rig with a multi-blade propeller to demonstrate the aeroelastic phenomenon of Whirl Flutter investigated by means of Operational Modal Analysis. The discussion experimentally and numerically introduces the sensitivity analyses as the shaft inertia and stiffness parameters and, the air stream speeds vary and the definition of the whirl flutter stability diagram, identifying for which speed conditions the shaft-propeller system is free from flutter. The best solution of the NGCTR wing while satisfying different design constraints is investigated employing a multi-objective optimization process implemented in the Multicella tool. Research studies show the possible benefits of using Multicella for wing preliminary design in terms of time-saving with respect to the Finite Element Model approach. Several optimization studies are conducted to show the influence of different composite materials to achieve the optimal stiffness distribution to reach the total structural weight minimization and maximum margin of safety requirements.

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