An aero-acoustic study of an in-duct flexible plate

In the application of mixing urea with diesel exhaust gases a triangular plate is used to generate turbulence. The present work treats the effect of having a yielding plate on the scattering properties, as well as the source generation of the plate. The acoustics of the plate are modeled by a 2-port model, and the results are compared with strain gauge measurements. Earlier developed over-determination methods have been applied for the determinations of the pressure amplitudes and the scattering matrix. For the source cross spectrum matrix an over-determination method is suggested and applied. The improvements of all methods are studied, and great improvements are indeed observed. The effect of inserting the plate is small when the scattering matrix is considered, however the source cross spectrum matrix shows that the plate generates a broad band component as well as a dipole, Strouhal tone. The effect of the yielding plate is observed to be a decrease in the broad band component of about 2 dB at the Mach number 0.213, and a disruption of the mechanism behind the tonal component. It is suggested for future work that a complete structural dynamic investigation of the yielding plate should be made simultaneously with sound spectra measurements at more, narrower flow velocity increments in order to further analyze the effects of the yielding plate.