Influence of coaxial cylinders on vortex breakdown in a closed flow

TL;DR

This study investigates how fixed cylindrical rods along the centerline influence vortex breakdown in closed flows, revealing that small rods enhance while larger rods suppress vortex breakdown, supported by experimental and numerical analysis.

Contribution

The paper provides the first combined experimental and numerical analysis of how coaxial cylinders affect vortex breakdown, including a simple model applicable to open flows.

Findings

Small rods enhance vortex breakdown

Larger rods suppress vortex breakdown

Excellent agreement between experiments and simulations

Abstract

The effect of fixed cylindrical rods located at the centerline axis on vortex breakdown (VB) is studied experimentally and numerically. We find that the VB is enhanced for very small values of the rod radius $d$, while it is suppressed for values of $d$ beyond a critical value. In order to characterize this effect, the critical Reynolds number for the appearance of vortex breakdown as a function of the radius of the fixed rods and the different aspect ratios was accurately determined, using digital particle image velocimetry. The numerical and experimental results are compared showing an excellent agreement. In addition, a simple model in order to show that this effect also appears in open pipe flows is presented in the appendix.