Periodic vortex shedding in the turbulent wake of a disk

The periodic behavior of a turbulent wake behind a thin, sharp-edged disk was studied experimentally at a Reynolds number of 12,500 based on disk diameter. Velocity measurements were made using hot wire anemometers. The mean velocity, fluctuation intensity, periodic frequency, and periodic signal to noise ratio were measured for the circular disk as well as for various other thin axisymmetric shapes to compare the basic periodic properties of the various wakes. The Strouhal number was equal to 0.13 over a large Reynolds number range for all disk shapes if the length scale was based on the diameter of a circular disk with the same drag coefficient. A detection scheme was devised to allow conditional sampling of the periodic phenomenon without externally influencing the flow. Using these measurements it was found that the observed periodicity was due to a vortex pattern which developed within four diameters downstream of the disk.