Unstable Phenomenon in Flow through a Pipe System with a Cross Pipe : 1st Report, Generation of Flow Instability and Its Condition

Abstract

The phenomenon, that the flow rate of a loop with a cross pipe switches nonperiodically between a high level and a low level under certain flow conditions was found and experimentally investigated by using air and water. The flow behaves as if a bistable flow state exists like a flow in fluidics. It is observed by a flow visualization technique (spark tracing method and air injection method) that the switching synchronizes with the generation and the collapse of a swirl flow through opposing laterals of the cross pipe. The pressure loss coefficient of branching at the low flow rate level is about twice as much as that at the high flow rate level.