Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows – An experimental investigation

• A T-junction of rectangular ducts is subjected to mixed grazing/bias flows.
• The linear scattering matrix is determined for several mixed grazing/bias flows.
• The energy transfer between the hydrodynamic and the acoustic field is studied.
• The energy transfer amount, Strouhal ranges and directions are obtained from the scattering matrix.
• The results are compared to those from T-junctions of circular ducts.

Scattering matrices are determined experimentally and used to study the low-amplitude interaction, between the acoustic and the hydrodynamic fields in a T-junction of rectangular ducts. In particular, combinations of grazing and bias flows are investigated in the study. It is observed that for all flow combinations, waves incident on the junction at the downstream side only are attenuated, while waves incident at the other branches may be amplified or attenuated, depending on the Strouhal number. When bias in-flow is introduced to a grazing flow, there is first an increase and then a decrease in both amplification and attenuation, as the bias in-flow Mach number is increased. Comparing with T-junctions of circular ducts, the interaction is stronger for rectangular duct junctions.