Influence of geometrical parameters on the hysteresis of flutter onset in confined configurations

Abstract

The interaction between a flow and a flexible structure can provide fascinating insight into the vortex shedding phenomenon and any propagation and mixing characteristics, which relate to a plethora of applications such as heat transfer, snoring, musical instruments, or propulsion mechanisms. In this investigation, the influence of confinement on the flapping behaviour of a flexible flag is explored. In particular, hysteresis, one of the least understood aspects of flapping flags, and its sensitivity on both the flexural rigidity of the flag and the confinement ratio is addressed. For the same test-section dimensions and flag material, variations in the flag thickness and flag length enable a range of mass ratios (M∗) and confinement ratios (C∗) to be studied. Pressure measurements and high-speed imaging allow quantification of the hysteretic behaviour. The results demonstrate that although confinement ratio does not contribute to the existence of hysteresis, the relation between the critical reduced velocities and the mass ratio is sensitive to the degree of confinement.