Effect of material stiffness on the motion and flow near the free end of a finite cylinder surface

Abstract

Flexible structures are common in nature and biomimetic applications. A detailed understanding of their interactions with fluid is essential for the optimisation of structural design. The material stiffness has a strong influence on the motion and flows around the body. In this study, the effect of material stiffness on the motion and flow was experimentally investigated. Cylinders with various rotational stiffnesses ranging from 0.610 N·mm to 0.274 N·mm were produced by changing the degree of cross linking of polydimethylsiloxane. The motion and flow near the free end of the cylinders were examined using a high-speed imaging technique, time-resolved particle image velocimetry, and a proper orthogonal decomposition (POD) modal analysis. Consequently, the primary direction of the motion is altered from the inline to cross-flow direction as the stiffness decreases. The cylinder motion is observed to strongly affect the on flows near the free end, and the length and width near the wake are affected by the vibration magnitude of the cylinder along the inline and cross-flow directions. Vortex shedding occurs near the free end when the motion along the cross-flow direction is larger than 0.1D. These flow structures only propagate downstream behind the flexible cylinders having a relatively weak oscillating motion along the inline direction. The present results could be utilised as basic data in the design of bio-inspired cylinder-shaped structural applications, and relevant computational fluid dynamics (CFD) analyses.