Experimental characterization of vibro-acoustic properties of an aircraft fuselage

Modern turbo-prop engines have been identified as an efficient alternative to jet engines for the propulsion of next generation short range aircraft. However, the benefit in operating efficiency comes along with disadvantages related to engine noise and noise transmission into the aircraft cabin. Numerical models used for response analysis often show significant deviations in the medium frequency range up to 500 Hz. Model validation based on experimental modal data is often not possible due to the high modal density that aircraft fuselage structures exhibit in this frequency range. A method is presented that provides a meaningful correlation of the results of vibration tests on aircraft fuselage structures with corresponding numerical predictions. The correlation criterion used is inspired by statistical energy analysis and is based on kinetic energies integrated over frequency bands and spatially integrated over surface areas of the fuselage structure. The objective is to indicate frequency bands where the finite element model needs to be adjusted to better match with experimental observations up to 500 Hz and to locate the areas where these adjustments should be applied. The application of the kinetic energy correlation criterion comes along with several requirements on the test equipment, test installation and testing procedures. An effort has been spent to extent well defined testing procedures stemming from aircraft ground vibration testing into the medium frequency range. As a result, a test method is presented that has been applied in a test campaign on a full-scale aircraft fuselage structure to validate the proposed correlation criterion based on kinetic energies.