Vibroacoustics Under Aerodynamic Excitations

Abstract

This paper gives a number of energy considerations related to the flow induced vibration and noise predictions. In this context, reduced modeling of structural-acoustic issues are the main red line of the work. The present paper deals thus with equivalent “rain on the roof” (ROF) excitations, which allow the modeling of spatially correlated broadband sources by statistically independent point forces. ROF excitation largely simplifies the expressions of the joint acceptance functions and can be easily modeled using finite element method (FEM). Two approaches are presented here and an equivalent model of excitation is developed and validated on acoustic and aerodynamic excitations, such as diffuse field or turbulent boundary layer (TBL) excitations. The first idea, considers the equivalence over the extended physical domain. It allows equivalent ROF excitation only for frequencies over the acoustic coincidence effect. The second method is based on the wavenumber space equivalence. Validation of this approach has been carried out for different acoustic and aerodynamic excitations, and for different structural boundary conditions. Numerical experiments show that this approach gives acceptable results for a wide frequency range specifically for TBL excitations. Then, the problem of the structural–acoustic response under aerodynamic sources is considered further. The structure is a composite structure of arbitrary thickness and anisotropy. The fully coupled system is modeled using a Statistical Energy Analysis like (SEA-like) approach, and the energetic characteristics for each subsystem are computed and compared to the direct FEM solution. The error of the reduced model calculations for each frequency band is presented and the limits of the reliability of the reduction are explored. Different strategies concerning the reduction process parameters are investigated in order to optimize the accuracy with respect to time efficiency. The loading applied to the model comprises typical random distributed excitations, such as a ‘rain-on-the-roof’ excitation, a diffused sound field and a Turbulent Boundary Layer (TBL) excitation.