Undamped transverse-only VIV of a diamond cylinder at low Reynolds numbers

Abstract

There have been only a few investigations lately to analyze the flow-induced vibrations of a diamond cylinder, i.e. a square cylinder inclined at 45 ∘ to the free-stream at low and high Reynolds numbers, Re. However, for transverse vortex-induced motions of diamond cylinders at low Re, features of response branching, mean surface pressure, wake modes and fluid loading are less explored. We investigate numerically at Re=100, undamped hydroelastic vortex-induced vibrations of a diamond cylinder over a well-resolved U∗ range of 1 to 12. The order of magnitude of the maximum response as well as branching of response of the diamond oscillator are analogous to those of the circular cylinder and depart considerably from the ones of a square cylinder at zero incidence. Interestingly, the mean lift from this nominally symmetric cross-section deviates from zero at U∗ values of 3.5 and 4.2 corresponding to the quasi-periodic initial branch and periodic lower branch, respectively. At U∗=3.5 corresponding to low amplitude oscillations, three distinct asymmetric wake modes are identified: asymmetric 2S and two one-sided modes of different nature. The well known asymmetric P+S mode is identified at U∗=4.2 relating to high amplitude oscillations.