ANALYSIS OF THE NON-STATIONARY FLOW AROUND A RECTANGULAR CYLINDER

In this work the non-stationary flow around a rectangular cylinder immersed in a steady water flow is investigated through the topological analysis of time resolved PIV velocity fields. The phenomenon considered is characterized by the presence of large scale eddies, which are the main responsible of the hydrodynamic loading on the cylinder. In order to investigate the correlation between the hydrodynamic loading and the flow structures, we have identified and measured the motion of the large scale eddies. The leading and trailing vortices have been characterized by calculating their convection velocities and shedding frequencies. The velocity fields are obtained by means of a particular time resolved PIV system (Malavasi et al. [4]); they are characterized by a 50 Hz time resolution and a spatial resolution of 0.75 cm. The duration of each acquisition is 32 s which correspond to an amount of 1600 velocity fields. The flow field around a rectangular cylinder of chord L=0.18 m and thickness s=0.06 m (aspect ratio L/s=3) has been analyzed separately in three regions: the intrados region, the extrados region and the rear wake region. Upgrading the velocity inversion points (VIP) analysis proposed by Blois and Malavasi [1] for the characterization of the mean flow structures, in this work we have investigated the evolution of th