Experimental Investigation of Spectral Broadening of Sound Waves by Wind Tunnel Shear Layers

Kurzfassung

A detailed experimental investigation of the phenomenon of spectral broadening of monochromatic sound waves by wind tunnel shear layers is presented. The determination of the broadening characteristics as a function of aerodynamic (flow velocity and shear layer characteristics) and acoustic (source and receiver positions, tone frequency) properties is performed in a wind tunnel using two different sound source concepts. The performance of each sound source concept and their equivalence for examining experimentally the effect of spectral broadening is evaluated. The magnitude of the tone broadening by the shear layer was quantified as function of the dimensionless scattering parameter. Furthermore a simple approach for the identification of broadened spectral components of tone spectra is presented and its possibilities and limitations are evaluated in detail.