Modal analysis by holographic interferometry of a turbine blade for aircraft engines

Michele Arturo Caponero; Alberto De Angelis; V. R. Filetti; S. Gammella

doi:10.1117/12.195517

Abstract

Within the planning stage devoted to realize an innovative turbine for an aircraft engine, an experimental prototype has been made. Several measurements have been carried out to experimentally verify the expected structural and dynamic features of such a prototype. Expected properties were worked out by finite elements method, using the well-known Nastran software package. Natural frequencies and vibration modes of the designed prototype were computed assuming the turbine being in both `dynamic condition' (rotating turbine at running speed and temperature), and in `static condition' (still turbine at room temperature). We present the experimental modal analysis carried out by time average holographic interferometry, being the prototype in `static condition;' results show the modal behavior of the prototype. Experimental and computed modal features are compared to evaluate the reliability of the finite elements model of the turbine used for computation by the Nastran package; reliability of the finite elements model must be checked to validate results computed assuming the turbine blade is in hostile environments, such as `dynamic condition,' which could hardly be tested by experimental measurements. A piezoelectric transducer was used to excite the turbine blade by sine variable pressure. To better estimate the natural vibration modes, two holographic interferograms have been made for each identified natural frequency, being the sensitivity vector directions of the two interferograms perpendicular to each other. The first ten lower natural frequencies and vibration modes of the blade have been analyzed; experimental and computed results are compared and discussed. Experimental and computed values of natural frequencies are in good agrement between each other. Several differences are present between experimental and computed modal patterns; a possible cause of such discrepancies is identified in wrong structural constraints imposed at nodes of the finite elements model. Slight structural differences among different blades of the same prototype turbine are pointed out and discussed.

Citation Download Citation

Michele Arturo Caponero, Alberto De Angelis, V. R. Filetti, S. Gammella, "Modal analysis by holographic interferometry of a turbine blade for aircraft engines", Proc. SPIE 2342, Interferometry '94: Photomechanics, (30 November 1994); doi: 10.1117/12.195517; https://doi.org/10.1117/12.195517

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