Experimental investigation of lift-up and instability of the viscous flow induced by a rotating cone-cylinder in an enclosure

This paper probes into the flow induced by a rotating cone-cylinder model in an enclosure. Two component particle image velocimetry measurements in the symmetry plane reveal that the rotating cone-cylinder causes an outward jet on the cylinder section, which lifts the rotating boundary layers away from the wall. A large-scale counter-rotating vortex pair sets up with its mutual upwash aligned with the lift-up region. Furthermore, the centrifugal instability induces Taylor vortices in the rotating boundary layer, which are convected by the mean flow field and are lifted away from the surface, causing a high standard deviation. The lift-up phenomenon shows two preferred axial locations: below a critical Reynolds number $Re_{b,c}$, the lift-up occurs close to the cone-cylinder junction, and for Reynolds number higher than $Re_{b,c}$ lift-up is pushed away from the cone-cylinder junction, towards the model base. The value of the critical Reynolds number $Re_{b,c}$ lies within $2 \times 10^3-2.5 \times 10^3$ for the investigated cases.