Vortex stability and breakdown - Survey and extension

The precipitating conditions, phenomena and effects of vortex breakdown and stability are discussed. Breakdown occurs when a stagnation point appears, followed by the appearances of flow reversal and downstream turbulence. Laboratory techniques such as edge and trailing vortices, tangential jets and vane vortex generators for studying vortex formation are reviewed. Two types of breakdown have been identified: bubble and spiral. Transcritical wave theory is outlined, noting that the concept of critical flow is central to any description of breakdown. Consideration is given to the stability or instability of vortex cores at infinite Re. It is shown that the breakdown point may be estimated by computing the Froude number. Experimental data demonstrate that axisymmetric modes grow during propagation in a variable vortex waveguide. The wave loses stability because of three-dimensional perturbations after a critical amplitude is reached.