Numerical simulation of the interaction between finite-amplitude acoustic fields and flow phenomena in open ducts

Finite-amplitude standing acoustic waves in narrow, open ducts are associated with phenomena such as shock formation, acoustic streaming and generation and shedding of vortices at the open end. Typically, these events are all observed when acoustic particle velocities increase inside the duct, and their appearance also depends strongly on the geometry of the duct. The competing effects of nonlinearity, thermoviscous attenuation and radiation at the open end must all be taken into account to adequately model acoustic propagation inside the duct, and, further, we find it is critical to reproduce correctly the behavior of the Stokes boundary layer. We use a full-wave finite volume axisymmetric code which allows for the coupling of the acoustic field with the aforementioned flow phenomena to identify the values of different parameters leading to generation of vorticity at the open end of the duct, and in particular the propagation of streets of vortices along the Stokes boundary layer inside the duct.