Vortex breakdown: the “bubble” formation mechanism

Vortex breakdown is a widespread phenomenon that affects vortices with axial flow such as leading-edge vortices over delta wings, flame holders in combustion devices and atmospheric tornadoes. It consists of an abrupt change in the flow topology where the flow decelerates and diverges as if a solid obstacle was present in the flow. The structure of the vortex varies slowly in the streamwise direction and then, suddenly, the structure changes drastically with the formation of an axisymmetric recirculation region.

The main objective of the present project is to investigate numerically the on-set of the recirculation “bubble” typical of the breakdown state. Then, by combining numerics and theory a reduced system of equations, which is simpler than the full Navier-Stokes equations and that is able to capture the main features of the vortex dynamics, will be determined.
Direct numerical simulations will be carried out using the in-house spectral solver implemented in Matlab.

Supervisor: Francesco Viola