Effects of the vibration regime on the spanwise correlation of the aerodynamic forces on a 5:1 rectangular cylinder

It is well known that the spanwise correlation of aerodynamic pressures and forces on vibrating cylinders increases with the amplitude of oscillation. Little knowledge, however, exists on how the nature of the motion, i.e. the degree of freedom in which the body vibrates and the reduced wind velocity, affects such correlation. In this paper, some results are presented of a wind tunnel study aimed at investigating the spanwise correlation of aerodynamic pressure and force fluctuations on a rectangular cylinder with an aspect ratio of 5:1. Measurements were carried out on the stationary cylinder and in four dynamic configurations, each characterised by different values of the heaving and pitching natural frequencies. With varying reduced wind velocity, in each dynamic configuration the three vibration regimes of vortex shedding lock-in, forced motion and flutter were observed in the tests. In the paper only two dynamic configurations are presented, one being that in which the heaving and pitching natural frequencies in still air coincide. This is an interesting case, in which the dynamic response is very much affected by the possibility that the motion has of switching from one degree of freedom to another.