Flow-induced vibration of a cube orientated at different incidence angles

Abstract

This study experimentally investigates the transverse flow-induced vibration (FIV) of an elastically mounted cube at three different incidence angles of α=0∘, 20∘ and 45∘, corresponding to two centreplane mirror-symmetric cases and one asymmetric case. The FIV response is characterised by analysing the vibration amplitude and frequency responses, together with the fluid force coefficients and phases, over the reduced velocity range of 1.2⩽U∗⩽16. Here, U∗=U∕(fnwH), with U the free-stream velocity, fnw the natural frequency of the system in quiescent fluid (water) and H the frontal projected width of the body. It was found in the α=0∘ case that two synchronisation regions could be identified, where the periodic body vibration was synchronised with oscillatory shear layers. The vibration amplitude was found to increase with U∗ in the second synchronisation region, with the largest value of Amax∗≃0.74 observed at the highest U∗ value tested. In the asymmetric orientation case of α=20∘, a synchronisation region occurred over 6.0<U∗<8.6, where the amplitude tended to increase to its local peak of Amax∗≃0.25 at U∗=8.6. For higher U∗ values, synchronisation was lost, but the cube still exhibited high amplitude oscillations. However, in the α=45∘ case, while the vibration amplitude tended to increase with U∗ (i.e. Amax∗≈0.3 at U∗=16), the FIV response was found to be desynchronised over the entire U∗ range. The findings indicate that body vibration is strongly coupled with the oscillatory separating shear layers for all α cases, which can result in significant vibration.