Power fluctuations in turbulent swirling flows

We report an experimental study of the temporal fluctuations of the total power injected in a swirling flow generated in the gap between two coaxial disks, counter-rotating at a fixed velocity. We use either a free geometry in air or a shrouded one, i.e. with the disks enclosed in a cylindrical vessel. We show that the fluctuations of the power injection are large in both cases (rms amplitude up to 10% of the mean value), but that their statistical properties are qualitatively different. When the flow is confined in a cylindrical vessel, we find that the PDF of the power fluctuations is strongly non-Gaussian and we study the correlations between the power fluctuations and the pressure field at the boundary.