Life, death, and propagation of an isolated turbulent blob fed by vortex loops*

We create and sustain an isolated blob of turbulence by repeatedly firing together vortex loops.

In the steady state, our PIV and 3D PTV measurements reveal that the blob consists of a turbulent core (Re_lambda = 50 - 300) surrounded by comparatively quiescent fluid. By examining the mass and enstrophy flux, distribution of energy and enstrophy, and turbulent statistics, we assemble a full picture of its three-dimensional structure, onset, and tunability. When the injection of vortex rings stops, a spherical front that separates the turbulent core from the quiescent surroundings propagates in the chamber, and the turbulence decays. By using a simple low-order closure model, we construct a spatially-extended description of the turbulence propagation, and compare its predictions of energy profile and non-diffusive dynamics with data.