Transition Process of Frequencies of the Pure Tone Caused by Vortex Shedding in a Pipeline Containing a Double Orifice

Experimental investigations of the generation of resonant sound by flow in a pipeline containing two closely spaced orifice plates were performed. The frequencies of the tone generated were examined in detail when the velocity was increased from 3 to 25 m/s. In order to determine the convection velocity of vortices formed between the two plates, the measurements of the phase of fluctuating velocity were made using a hot-wire anemometer. The vortex shedding frequency is locked-in the pipe modes, but indicates a slight increase with an increase in the flow velocity. The ratio of the distance between the two orifice plates to the spacing of vortices is expressed by m+ε, where m is an integer and ε is a decimal part. It was found that the value of εdecreases with increasing flow velocity within the range from 0 to 0.5, and a change of the number of vortex or frequency jump occurs when ε reaches a limit value.