Experimental modal analysis has become in the past years a sophisticated and reliable tool to assess the dynamic behaviour of structures. This is why AVIO, in collaboration with the Politecnico di Torino, decided to start a comprehensive test campaign on a large component of one of the aeronautical engines which are currently in production. As many typical aeronautical devices, the item must bear both high dynamic and thermal stresses. In order to identify the vibration behaviour of the part, its modal parameters had been measured and matched with the results of a finite element model. The structure under investigation is a metallic and thin shell of almost cylindrical shape and it was studied in laboratory conditions. A random input was applied by an electrodynamical shaker in order to excite the cylinder mainly in its radial direction but with non negligible tangential and axial force components. In the freefree configuration a large set of acceleration data was acquired for a total of 320 points, each in three directions, in order to correctly define not only the system poles but also its mode shapes. The measures took five days and were accomplished in 54 runs because of two main reasons: the limited number of channels in the acquisition system and the need of limiting the added mass on the thin shell. A dedicated support had also been designed and manufactured with the aim of correctly simulating the real boundary conditions, which are quite particular and should allow the thermal expansion of the cylinder: in this configuration only 30 triaxial acceleration signals were measured in five runs. All data have been independently processed by two modal parameters estimation techniques, namely the stochastic subspace identification in the time domain (SSI) and the rational fraction polynomial method in the Z domain (FRPZ). The system is almost axisymmetrical and in fact the experimental results show the presence of couples of modes with very close frequencies and very similar mode shapes, thus confirming the theoretical predictions. Some highlights on the practical implementation of the two techniques are given together with a comparison and comments on their result.


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    Title :

    Experimental modal analysis of an aeronautical engine component


    Contributors:
    Fasana, A. (author) / Garibaldi, L. (author) / Giambra, M. (author) / Plancher, M. (author) / Marchesiello, S. (author)


    Publication date :

    2008


    Size :

    12 Seiten, 4 Bilder, 3 Tabellen, 8 Quellen



    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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