On the fluid dynamics of spin-over in a partially filled cylinder

This work provides a comprehensive account of the flow within a cylinder with a free surface and an intermediate aspect ratio (liquid height to cylinder radius, L/R=0.5), undergoing spin-over: the rotation of the entire cylinder about its vertical axis is impulsively reversed from solid body rotation to the same angular velocity in the opposite direction. The transient unstable fluid flow arising from this has not previously been characterized. This study employs two-dimensional, two-component particle image velocimetry, planar laser-induced fluorescence, and three-dimensional computational fluid dynamics side by side to capture the spin-over process in full. A thorough investigation of the fluid flow established within the bulk of the fluid, as well as in the endwall and sidewall boundary layers, is provided to reveal the intricate interplay between those regions in time. The investigation goes through the various flow stages during spin-over, including the primary and secondary endwall boundary layer separations, the generation of type I/type II waves, and the behavior of the Taylor–Görtler vortices in the sidewall boundary layer, as well as the late-stage establishment of geostrophic flow through Ekman pumping. The impact of increasing the Reynolds number, Re, and Froude number, Fr, is also investigated (2504<Re<25 043; 0.02<Fr<1.07), shedding light on secondary endwall boundary layer separations and the onset of three-dimensional turbulence. The findings have implications for diverse fields, from the fluid dynamics in rotating bioreactors to geophysical and astrophysical systems.