Vortex shedding characteristics around a circular cylinder with flexible film

In this paper, an experimental study about the influence of flexible film on the vortex shedding characteristics behind a cylinder has been performed with increasing Reynolds number (Re) and the ratio of flexible film length to cylinder diameter (L/D). The smoke-wire technique is implemented for flow visualization. The detailed statistics and vortex shedding structures associated with pressure fluctuations owing to a flexible film behind a cylinder are presented. The focus of this paper is on efforts to reveal the influence on the distribution of fluctuation pressure and the frequency of vortex shedding resulting from flapping flexible film with different parameters of L/D. Our experimental results mainly reveal that when the flexible film is in asymmetric flapping mode behind the cylinder, the peak distribution of fluctuating pressure coefficients C-pf will deviates from central area. The Strouhal number decreases with the increase of LID. For L/D=3, the Strouhal number also decreases with increasing Re. It is found that the peak of fluctuating pressure spectrum is closely related with the non-dimensional parameter L/D, and the vortex shedding frequency obviously decreases with increasing of L/D. The fluctuating signal of flapping flexible film for L/D=5 effectively offsets the fluctuating signal behind a cylinder itself, and the peak of fluctuating pressure spectrum does not occur at Re=2500. Nevertheless, for L/D=3, the amplitude of fluctuating pressure spectrum obviously exceeds that of fluctuating pressure spectrum of L/D=0. Our results further reveal that flapping flexible film effectively controls the vortex shedding behind a cylinder with increasing of L/D. However, for L/D=3, the flapping flexible film results in harmonic excitation mode. (C) 2019 Published by Elsevier Masson SAS.