This short video is a result of the CFD simulation of flow in a Francis turbine, operating at high load. Depending upon the level of excessive circumferential velocity component at the outlet of the runner, vortical structures rotate around the central coherent structure while travelling in the direction of the draft tube.
More information about the CFD simulation with the zonal LES turbulence model can be obtained in the paper:
Jošt, D., Škerlavaj, A., Morgut, M., Mežnar, P., and Nobile, E., 2015. Numerical simulation of flow in a high head Francis turbine with prediction of efficiency, rotor stator interaction and vortex structures in the draft tube. Journal of Physics: Conference Series 579(1), 012006. doi:10.1088/1742-6596/579/1/012006