Erik Kostson
Ansys Employee

Use the surface velocity as an excitation not pressure. Also define a port at the inlet/excitation and a radiation boundary also at the inlet. The surface velocity for a plane duct wave is just surface_velocity = pressure_source/(density*speed of sound). See below how to set the excitation as explained above.

Also make sure your mesh is connected (not sure why it is split in so many cylinders).

All the best