Steady flow instability in an annulus with deflectors at rotational vibration

International audienceExperimental study and direct numerical simulation of dynamics of an isothermal low-viscosity fluid are done in a coaxial gap of a cylindrical container making rotational vibrations relative to its axis. On the inner surface of the outer wall of the container, semicircular deflectors are placed regularly, playing the role of flow activators. As a result of vibrations, the activators oscillate tangentially. In the simulation a two-dimensional configuration is considered, excluding the end-wall effects. In the experiment a container with large aspect ratio is used. Steady streaming is generated in the viscous boundary layers on the activators. On each of the latter, beyond the viscous domain, a symmetric vortices pair is formed. The steady streaming in the annulus has an azimuthal periodicity. With an increase in the vibration intensity, a competition between the vortices occurs, as a result of which one of the vortices (let us call it even) approaches the activator and the other one (odd) rolls away and couples with the vortices from the neighbouring pairs. Streamlines of the odd vortices close on each other, forming a flow of a cogwheel shape that encircles the inner wall. Comparison of the experiment and the simulation reveals an agreement at moderate vibration intensity