Morphing airfoils are airfoils with enhanced geometry adaptability. While conventional airfoils (wings and empennages) are provided with simple devices - like rudders or flaps -which control a very limited number of geometry degrees of freedom, an increasing number of innovative ideas are being implemented into unconventional airfoil concepts in which geometry is managed by a large number of degrees of freedom. Additionally or alternatively, the word 'morphing' often implies managing airfoil geometry in a smooth way, avoiding pattern discontinuities which are typical in the classic, mechanism-oriented design of airfoil geometry control devices. Most approaches to morphing airfoils involve exploiting structural flexibility in order to produce the desired geometry changes. This leads to concepts with a high degree of shape adaptability, attractive lightweight potential and inherent smoothness in geometry management. However, it demands for large efforts in design and optimisation. One of the major challenges is constituted by the presence of restrictions which impose upper stiffness limits: structures which are to be kept flexible in some sense require coupled design procedures in which interactions with deformation-sensitive loads like aerodynamic, actuator and inertia loads must be analysed in more detail. In this context, classic theoretical approaches like box-girder analysis and beam-based aeroelastic wing models have to be revisited by extending them to the additional deformation degrees of freedom, in order to provide adequate tools for conception and preliminary design as well as a basis for efficient optimisation procedures. This paper presents an analytical approach to shape-adaptable airfoils with compliant ribs. The stress distribution and deformation behaviour of thin-walled airfoils with closed section is analysed, where cross-section deformations - unlike most classic theories - are allowed within given boundaries. Then the structural model is coupled with a proper aerodynamic operator in order to analyse the most relevant static aeroelastic phenomena. Morphing airfoils with closed girder structure and deformable ribs can be efficiently analysed by means of a revisited thin-walled beam theory in which one additional degree of freedom for the cross-section deformation is explicitly taken into account. The deformation behaviour of the structure is then described by a set of ordinary differential equations in which an additional section deformation function appears together with the functions related to the conventionally analysed beam behaviour, consisting of bending, shear, torsion and axial deformation. A new internal reaction as well as a set of section moments also appears in the theory as a consequence of the extended deformability of the cross-section. A de-coupling procedure allows defining a set of generalised displacement functions each of which is ruled by a separate equation. The theory can be extended to the case of more than one cross-section deformation degree of freedom without substantial problems. The presented analytical model can be advantageously used to perform aeroelastic calculations and to analyse aeroelastic stability and response. In particular, it can help analysing the effect of design variables (like the spokes layout of an airfoil of the belt-rib kind and the resulting deformation mode) on the aeroelastic behaviour and play an important role in the aeroelastic design of shape-adaptable airfoil structures. Efficient tools for aeroelastic design are basic to the successful development of morphing structures based on structural compliance, not only to avoid dangerous coupling phenomena but also to exploit aeroelastic amplification effects in order to realise the desired geometry changes with reduced actuator size and energy.


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    Title :

    Three-dimensional structural and aeroelastic analysis of morphing airfoils


    Additional title:

    3-dimensionale Struktur- und Aerodynamik-Analyse von veränderlichen Strömungsprofilen


    Contributors:


    Publication date :

    2005


    Size :

    8 Seiten, 1 Tabelle, 5 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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