The Current Understanding of the Spectral Broadening Effect by Turbulent Shear Layers

Abstract

In aeroacoustic open jet wind tunnel testing the sound propagation through the turbulent wind tunnel shear layers is accompanied by several effects which may distort the original signal. One of these effects is the so-called “spectral broadening”. This phenomenon results in a reallocation of acoustic energy of the sound wave into other frequencies. In case of a tonal sound source this effect leads to difficulties in the interpretation of aeroacoustic measurement results and can also lead to uncertainties by the determination of absolute levels. In the context of aeroacoustic measurements of counter rotating open rotors and propellers these issues become more and more important.