Frequency Averaged Injected Power under Boundary Layer Excitation: An Experimental Validation

On one hand, energy methods usually deal with frequency averaged quantities. Statistical Energy Analysis, for example, uses energy per subsystems and power injected averaged over frequency bands. On the other hand, when a structure is excited by a turbulent boundary layer, its response is calculated using a model of boundary pressure cross spectrum (Corcos, Efimtsov...). Such calculations take into account boundary conditions and exact geometry of the excited structure which is often non necessary for energy methods. A model of Frequency Averaged Injected Power under boundary layer excitation (FAIP model [1]) has been previously proposed as a tool for vibroacoustic pre-design process. The present paper deals with an experimental validation of the FAIP model. To validate this approach, a characterization of the turbulent flow (wall pressure spectrum, velocity profiles, correlation lengths, Corcos' coefficients) have been carried out in the wind tunnel of the Ecole Central of Lyon. In a second step, the power injected into a plate placed onto a dedicated setup has been evaluated measuring the velocity field on the plate with a laser vibrometer. Thus, experimental power injected into the plate has been compared with the one predicted by FAIP model. FAIP model are in good agreement with Experiments showing that FAIP model is able to give accurate estimation of power injected into a plate excited by a turbulent boundary layer (TBL) on the whole frequency range (below, above and at the aerodynamic coincidence frequency). Four plates made in different materials (steel, copper, PVC) and of different geometries have been tested for three free stream velocities (20, 35 and 50 m/s).