Experiments on the dynamics of a cantilevered pipe conveying fluid and subjected to reverse annular flow

Abstract The dynamics of a pipe conveying fluid and counter-currently subjected to a partially confined external axial flow through a coaxial annular region over its upper portion has been investigated experimentally. Apart from its fundamental aspects, this flow configuration simulates one of the modi operandi of solution-mined caverns utilized for hydrocarbon storage. Beyond the instability, at sufficiently high flow rates, the flexible pipe impacts the rigid coaxial shorter outer tube. The effects of confinement length, i.e., the ratio of the confined length of the pipe to its total length, L ′ / L , and the ratio of external to internal flow velocities, U o / U i , on the onset of instability, as well as the dynamical behaviour of the system with impacting, have been investigated. It was found that for all L ′ / L ratios and a very small value of U o / U i , i.e., U o / U i = 0 . 055 , the system loses stability via flutter in the second mode. Increasing the confinement length ratio expedited the aforementioned flutter. At higher U o / U i ratios, i.e., U o / U i ≥ 0 . 2 , the pipe is subjected to a static deformation, followed by more complex behaviour at higher flow velocities. The post-instability impact displays a rich dynamical behaviour with both periodic and chaotic components. Depending on the various system parameters, mainly the U o / U i and L ′ / L ratios and the internal flow velocity, several types of impacting/sticking behaviour were observed. The pipe may undergo single-sided or two-sided impacting, oscillation over the buckled position and partial or complete rubbing or sticking on the outer rigid tube.