Reynolds Number Effect on Velocity Field and on Coherent Structures behind a Cylinder

The Particle Image Velocimetry was used to investigate the coherent structures behind a cylinder under moderate Reynolds number. Dynamical decomposition method was used to detect flow patterns having similar frequency as the vortex shedding frequency which is given by Strouhal number. The flow field has two-dimensional nature only for time-averaged flow. The instantaneous snapshots are fully 3-D. The wake is full of spanwise as well as streamwise oriented vortical structures causing periodical changing in the pressure field