Laboratory synthesis of turbulent boundary layer wall-pressures and the induced vibro-acoustic response
Résumé
Theoretical and practical feasibility is considered of synthesizing spatially correlated random pressure fields whose statistical properties are similar to that generated by a fully-developed Turbulent Boundary Layer (TBL) over a panel. Laboratory synthesis of TBL excitation would provide a cost-efficient approach, complementary to in-flight or wind-tunnel measurements, in order to test potential solutions to reduce the TBL-induced noise, of relevance within both the aeronautical and surface transport sectors. Of particular interest is the use of a near-field array of suitably driven acoustic sources with an important question: how many uncorrelated sources are required per correlation length to approximate a TBL excitation and the induced vibro-acoustic response? Due to the exponential decay of the spanwise correlation length with frequency, real-time TBL synthesis appears to be only feasible in the low frequency range. However, the structural and radiative filtering properties of the panel dramatically reduces the number of sources required, thus allowing a synthesis of the panel vibro-acoustic response beyond the hydrodynamic coincidence frequency using a reasonable number of sources. Such theoretical findings have been confirmed experimentally. Effective methodologies are also proposed for an accurate reproduction of the TBL-induced sound power radiated by a panel when coupled to a cavity.
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