Experiments on the dynamics of aspirating cantilevered pipes concurrently subjected to reverse external axial flow

Abstract

The dynamics of a hanging cantilevered pipe conveying fluid upwards (i.e. aspirating fluid) and concurrently subjected to a partially confined (annular) reverse external flow over its upper portion has been investigated experimentally in the present parametric study. The influence of annular confinement, pipe length, eccentric placement of the outer wall of the annulus relative to the central pipe, and a constriction at the inlet or outlet of the outer rigid casing on the system was examined for different external/internal flow velocity ratios, particularly Uo/Ui = 0.015 – 0.80. This study is primarily motivated by its application in solution-mined caverns, specifically for the hydrocarbon storage mode. Two different dynamical behaviours were observed; therefore, the results were categorized into two groups: low Uo/Ui (0.015 – 0.06) and high Uo/Ui (0.20 – 0.80). First-mode flutter was found to be the mode of instability of the aspirating pipe, for all flow velocity ratios, followed by the development of mixed-mode motions at higher flow velocities, for all configurations of the system. Even though the bifurcation diagram trends remained qualitatively unaltered for almost all cases, the onset of instability, amplitude of oscillations, and excitation of mixed-mode motions were affected, suggesting sensitivity of the system to small geometrical variations. The nature of the oscillatory motions appeared to generally be near-intermittent and disordered, with minor variations for different parameters.