Excitation of Self-Sustained Oscillations by a Flow of Liquid in a Cylindrical Duct with two Diaphragms

We study the flow of a viscous incompressible liquid in a cylindrical duct with two serial diaphragms by finding the numerical solutions of nonstationary Navier–Stokes equations. It is shown that, within a certain range of Reynolds numbers, the flow of liquid in the region between the diaphragms is characterized by the presence of an unstable shear layer. A series of sequential vortices formed in the shear layer generates self-sustained oscillations of the velocity profile in the opening of the second diaphragm. It is shown that the analyzed system also has two stable modes of periodic oscillations with different frequencies. These oscillations may play the role of an acoustic source in the duct.