Vortex induced vibrations at high Reynolds numbers on circular cylinders

The Reynolds Number is a fundamental parameter in defining vortex shedding from circular cylinders. Most of the studies of vortex induced vibrations are at subcritical and critical Reynolds Number values and there is a need to understand how the Reynolds Number affects these oscillations. An experimental set-up was created in a large wind tunnel to study vortex induced vibrations at high Reynolds Numbers. The circular cylinder model had a diameter of 0.72 m, allowing Reynolds Numbers up to 6·105 to be reached. The cylinder had a mass ratio value of 35, quite low with respect to other tests in air because of its large dimensions but still high compared to the mass ratios obtainable testing in water. By increasing the model's surface roughness it was possible to reach the postcritical flow regime that produces coherent and highly organized vortex shedding. The set-up permitted the simultaneous measurement both of the instantaneous fluid force calculated integrating surface pressure distribution and the model oscillation. The article describes the results of the tests and compares the characteristics of vortex induced vibrations in postcritical flow regime with subcritical ones.