Sound separation probes for flowing duct noise measurements

In order to understand the propagation of broadband sound from a device such as a jet engine, it is necessary to make fluctuating pressure measurements in the ducted airstream. However, in a flowing duct, fluctuating pressure energy can be due to both turbulence and sound travelling in the duct. By using the principal that sound waves and turbulent flow pressure perturbations travel at different velocities, a probe has been developed that provides the data necessary to separate the energy due to sound from that due to turbulence. A mini-computer based FFT analysis of the probe measurements provides the overall level of the broadband sound in the duct as well as the spectral distribution of the sound energy.