Jump of azimuthal velocity in a creeping two-fluid swirling flow

Abstract

This work reveals a jump of azimuthal velocity at the interface that can be important for vortex bioreactors. The rotating lid controls the flow of two fluids in a vertical cylindrical container, the other walls of which are stationary. Near the lid, a centrifugal force pushes the upper fluid toward the sidewall, thereby developing its centrifugal meridional circulation. This motion drives the bulk counter-circulation in the lower fluid at a slow rotation. The use of sunflower oil for the upper fluid, alcohol-glycerine solutions for the lower fluid and the assembly of averaged PIV images allow measuring velocity and visualizing pattern even in a creeping motion. This advanced experimental method helps to detect velocity jumps occurring at the interface.