Nuclear magnetic resonance measurements of fluctuations in air–water two-phase flow: Pipe flow with and without “disturbing” section

In this paper we describe a new NMR sequence designed to measure the liquid mass flux and the liquid momentum flux fluctuations in a two-phase flow, in order to study the action of the flow on transverse mechanical structures. An upward air–water bubbly flow is investigated in a circular pipe under atmospheric pressure and room temperature for two geometrical configurations: with and without a “disturbing” section. Results show that the addition of the “disturbing” section on the experimental set-up led to the appearance of an instability phenomenon that greatly influences the relative intensity of both mass and momentum liquid flux fluctuations. Moreover, the spectral analysis of the former quantities demonstrates that the fluctuations of the liquid space fraction play a major role in the behavior of the liquid momentum flux fluctuations.