Add-on damping patch efficiency on sound transmission of a thin plate under aerodynamic or acoustic excitation

The turbulent boundary layer excitation is one of the main sources of aircraft interior noise over a large frequency range while the diffuse sound field excitation is often considered as an approximation for noise analysis and noise control evaluation. This paper presents the study of add-on damping patches efficiency under both excitations. The structure of interest here is a simply supported thin plate partially covered with a damping treatment. Numerical results are carried out using an original methodology based on the Minimization of Error on a Sample of Observation Points (MESOP). The transmission loss index is assessed in the frequency range from 50 Hz to 7 kHz. This investigation points out different behaviors: a damping effect is observed only in the critical frequency region under diffuse sound field excitation whereas the transmission loss index is increased by damping over the whole frequency band under turbulent boundary layer excitation. The excitation field appears to be a key factor. The excitation effect on the damping treatment characterization is then observed for two patch sizes. The transmission loss under aerodynamic excitation with varying patch sizes is finally investigated in a context of damping treatments optimization.