Influence of coaxial cylinders on the vortex breakdown in a closed flow

The effect of stationary cylindrical rods located at the centerline axis on the vortex breakdown (VB) in a closed flow is studied experimentally and numerically. The flow takes place in a cylindrical container with a rotating end wall. The dimensionless numbers characterizing the dynamics of the system are the Reynolds number, based on the angular velocity of the rotating wall, the aspect ratio of the container and dimensionless radius of the rod. We find that the onset of VB, as a function of the Reynolds number, is anticipated for very small values of the rod radius RrRr, while it is delayed for values of RrRr beyond a critical value. In order to characterize this effect, the critical Reynolds number for the appearance of the vortex breakdown as a function of the radius of the stationary rods and the different aspect ratios was accurately determined, using digital particle image velocimetry and numerically using a three-dimensional Navier–Stokes solver. The numerical and experimental results are compared showing an excellent agreement.