In the top row of figures, the background color represents the mean axial velocity, computed using RANS simulations, while the streamlines correspond to the acoustic velocity field calculated assuming an inviscid fluid. The bottom row shows the component of the acoustic velocity normal to the jet (i.e., radial velocity). These plots are presented for three geometries: (a) a straight pipe, (b) a pipe with an expansion, and (c) a pipe with a rounded outlet.