The effect of imperfections on the emergence of three-dimensionality in stationary vortex breakdown bubbles

We conduct detailed simulations in order to investigate the structure of steady vortex breakdown bubbles. Careful examination of all experimental visualizations reveals a number of ubiquitous features, such as the existence of dye inside the bubble and asymmetries in its downstream end. We show numerically that such features can be attributed to imperfections in the setup of the experimental apparati, imperfections that may be minimized with careful manufacturing and setting up of the rig, but are never completely eliminated. We study such forced breaking of symmetry for imperfections of an order of magnitude typical to those of realistic experimental setups.