A simple mechanism for controlling vortex breakdown in a closed flow
  This work is focused to study the development and control of the laminar vortex breakdown of a flow enclosed in a cylinder. We show that vortex breakdown can be controlled by the introduction of a small fixed rod in the axis of the cylinder. Our method to control the onset of vortex breakdown is simpler than those previously proposed, since it does not require any auxiliary device system. The effect of the fixed rods may be understood using a simple model based on the failure of the quasi-cylindrical approximation. We report experimental results of the critical Reynolds number for the appearance of vortex breakdown for different radius of the fixed rods and different aspect ratios of the system. Good agreement is found between the theoretical and experimental results. 
C. Cabeza, Gustavo Sarasua, Arturo C. Marti, and Italo Bove