Pulsating pipe flow instability perturbed by a trip wire

This study is concerned with the phenomenon of flow instability in the entrance region of a pulsating pipe flow perturbed by a trip wire at the inlet, where the flow was uniform at the core with a thin boundary layer on the wall. First of all, it is illustrated by a case without the installation of a trip wire that small disturbance developed in the accelerating phase of pulsation, which was well explained by the inflection-point instability mechanism. Subsequently, one of the cases studied with the installation of a trip wire indicates that the inflection-point instability mechanism still played the key role, but the instability was promoted further upstream. On the other hand, there were cases of which the flow instability development was rather due to the viscous effect mainly, which was decaying in a certain downstream region, followed by a renewal growth with irregular fluctuations.