Comparison of flow structures behind rigid and flexible finite cylinders

Abstract

Flows over bluff bodies are closely related to aero- or hydro-dynamic forces on structures. In bio-mimetic applications, flexible structures are usually employed, and quantitative flow information is essential for optimizing structural design. In this study, the flow behind a flexible cylinder is compared with the flow behind a rigid cylinder using flow visualization, time-resolved particle image velocimetry (PIV), and proper orthogonal decomposition (POD) modal analysis. The spectral analysis demonstrates that the oscillatory motion of a flexible cylinder strongly influences the flow behind the cylinder. The flows behind the rigid and flexible cylinders are clearly different near the free end of the cylinder. The downwash flow from the free end of the flexible cylinder is relatively weak compared to the rigid cylinder. Behind the tip of the flexible cylinder, large-scale vortices are shed and they are propagated downstream. However, such flow phenomena are not observed behind the rigid cylinder. These results could be used as basic data in the design process of bio-inspired structural applications.