Onset of vortex shedding around a short cylinder

This paper presents results of three-dimensional direct numerical simulations (DNS) and global linear stability analyses of a viscous incompressible flow past a finite-length cylinder with two free flat ends. The cylindrical axis is normal to the streamwise direction. The work focuses on the effects of aspect ratios (in the range of 0.5 <= AR <= 2, cylinder length over diameter) and Reynolds numbers (Re <= 1000 based on cylinder diameter and uniform incoming velocity) on the onset of vortex shedding in this flow. All important flow patterns have been identified and studied, especially as AR changes. The appearance of a steady wake pattern when AR <= 1.75 has not been discussed earlier in the literature for this flow. Linear stability analyses based on the time-mean flow has been applied to understand the Hopf bifurcation past which vortex shedding happens. The nonlinear DNS results indicate that there are two vortex shedding patterns at different Re, one is transient and the other is nonlinearly saturated. The vortex-shedding frequencies of these two flow patterns correspond to the eigenfrequencies of the two global modes in the stability analysis of the time-mean flow. Wherever possible, we compare the results of our analyses to those of the flows past other short-AR bluff bodies in order that our discussions bear more general meanings.

Automated summary

This paper presents the results of numerical simulations and linear stability analyses on the flow past a cylinder. The effects of aspect ratios and Reynolds numbers on vortex shedding are investigated, and a new steady wake pattern is discovered.