Effects of an annular porous layer on vortex-induced vibrations of an elastically-mounted circular cylinder

Abstract

A numerical study is conducted on vortex-induced vibrations (VIVs) of an elastically supported circular cylinder wrapped by a porous layer at a Reynolds number of Re=150. The cylinder is allowed to vibrate only in the transverse direction. The mass ratio and damping ratio of the system are kept constant at mr=2 and ζ = 0.01, respectively. The effects of Darcy number (10−6≤Da≤50), the dimensionless thickness of the porous layer (ep=0,0.25,0.5,1) and reduced velocity (3≤ur≤20) on the vortex shedding pattern, displacement amplitude, displacement frequency as well as lift and drag coefficients are investigated. Results show that increasing Darcy number causes the displacement amplitude of the cylinder to decrease. Moreover, values of Da smaller than 10−4 resemble the wake structures of the bare cylinder. In these low Darcy numbers (also for the bare cylinder) the 2S* mode is observed only at ur=5. However, at higher values of Darcy number the region of 2S* mode is extended to higher values of reduced velocity. Also, except for the limiting cases of very high or very small values of Darcy number (10−6 or 50), the sudden decrease in the displacement amplitude at the end of the traditional lock-in regime is eliminated from the response of the system.