ABSTRACT:The flow pattern behind a circular cylinder is associated with various instabilities. These instabilities are characterized by the Reynolds number and include the wake, separated shear layer and boundary layer. Depending on the physical application of the cylinder, increasing the level of turbulence on the surface of the cylinder would be a target for drag reduction or heat transfer enhancement. Particle Image Velocimetry (PIV) has been carried out to investigate the wake region behind a foamed and a finned cylinder. The purpose of this analysis is to investigate the flow characteristics for these two cases. The experiments are conducted for a wide range of Reynolds numbers (based on the mean air velocity and the cylinder diameter) from 1000 to 10000. Two dimensional results of planar PIV reveal the important aspects of the local flow features of the circular finned and foamed cylinders. These include turbulent boundary layer development over the surface and a delayed separation of the flow resulting in a smaller wake size at each speed. The application of Proper Orthogonal Decomposition (POD) to the PIV velocity fields of the two cylinder types is also discussed. The POD computed for the measured velocity fields for all cases shows that the first two spatial modes contain most of the kinetic energy of the flow, irrespective to the cylinder type. These two modes are also responsible for the large-scale coherence of the fluctuations. For three different cylinder types, the first four eigenmodes of the flow field were calculated and their structures were analysed.

No abstract

No abstract

No abstract

No abstract