On the formation of Taylor-Görtler structures in the vortex induced vibration phenomenon

Abstract

In this work, the three-dimensional structure of the boundary layer in the context of the vortex induced vibration of a circular cylinder is presented and investigated for the first time. Large-eddy simulations of a low mass ratio () two-degrees of freedom circular cylinder at the subcritical Reynolds number and zero damping () for several reduced velocities of the system have been performed. A detailed description of the flow topology at the cylinder boundary layer and in the near wake for the three branches of structural response, i.e. the initial (I), super-upper (SU) and lower (L) branches, is presented. In the SU branch, the boundary layer becomes three-dimensional due to the emergence of streamwise vortices which are associated to the onset of a centrifugal instability that occurs twice every cycle. This is the first time a centrifugal instability in a freely vibrating system is reported. The streamwise structures with alternating vorticity, called here Taylor-Görtler vortices, are described and characterised. It is shown that their wavelength is in agreement with that of other centrifugal instabilities observed in forced sinusoidal oscillating cylinders.