Impact of mass ratio and surface roughness on vortex induced vibrations

Abstract

Fluid structure interactions have been thoroughly studied in the past few decades due to their high importance in engineering applications. This phenomenon plays an important role for example in offshore risers, high slender buildings, chimney stacks, heat exchangers, etc. The vortices shedding from the bluff body can induce high-amplitude oscillations. This phenomenon is known as vortex-induced vibrations (VIV). In this thesis, a numerical study has been performed to better understand the impact of mass ratio and surface roughness on vortex induced vibrations. The work concentrates on vortex induced vibration in a 2D circular cylinder having different mass ratios and surface roughness at a high Reynolds Number (Re) = 10^4. The cylinder was elastically mounted on a mass-spring-damper system, with 1 degree of freedom (dof). The numerical solution is calculated using Reynolds-averaged Navier–Stokes (RANS) equations with computational fluid dynamic (CFD) tools. All the calculations were performed with kw-sst model. The study results concluded that VIV phenomenon is strongly affected by the mass ratio and surface roughness. Higher mass ratios result in shortening of lock-in region with a decrease in amplitude response. It was concluded from the study that rough cylinders have smaller amplitude response and a narrower lock-in region as compared to smooth cylinders. Vortex modes of 2S, 2P, P+S and 2T were observed in this study which agree well with the amplitude response