Observations on wake of a circular disk during starting

A wake created by two circular disks in a water channel was observed experimentally during the starting stage using a hydrogen bubble method of flow visualization. Acceleration of the free stream was nearly constant during starting. A vortex sheet separating from the disk edges was found. The diameter and abcissa of the vortex increased linearly. Reverse flow was observed in the center of the wake. In the transition stage, the vortex became asymmetric and disintegrated into chaotic and violent flow. A series of photographs of the starting vortex is presented.