Oscillations of Subsonic Flow in an Abruptly Expanding Circular Duct

摘要

Subsonic flow in an abruptly expanding duct driven from a pressure reservoir, which shows self-excited oscillations of considerable amplitude was studied by visualization and acoustic pressure measurements. Depending on the pressure drop in the duct and its dimensions, three distinct types of flow oscillations are observed. These are characterized by symmetrical and antisymmetrical oscillations of the separated jet in the abruptly expanding section, and symmetrical oscillations of the jet periodically separating and reattaching to the wall. The oscillations are accompanied by intensive noise, with an intensity of 40 dB above the turbulence noise level.