The stability of initially axisymmetric vorticity distributions around a cylindrical object were investigated numerically and experimentally. Piecewise constant vorticity rings were simulated and the results are in good agreement with Kizner et al. (2012). More realistic vorticity profiles created by the impulsively started and stopped cylinder were simulated and showed indeed that this vorticity configuration does become unstable. After further investigation this instability was triggered by the cartesian based grid cells and not the vorticity distribution itself. Also the radii of the realistic vorticity profiles were determined and the trend observed in the experiments that longer rotation times give lower order modes were confirmed. Comsol simulations of the flow along the cylinder wall proved that the flow has a 3D character, and those secondary flows might be the cause for the observed instabilities in the experiment.
|Date of Award||31 Aug 2013|
|Supervisor||G.J.F. van Heijst (Supervisor 1), Leon P.J. Kamp (Supervisor 2) & Z. Kizner (External coach)|