In this paper a novel experimental investigation into the vortex formation in the wake of a fixed and an oscillating circular cylinder is presented. The aim of the study is to acquire a better understanding of the complex three-dimensional vortex flow around the cylinder at high Reynolds numbers, as well as to set up a method for the validation of CFD for riser VIV applications. The Reynolds number in the experiments ranged from 40,000 to 200,000.
A 200 mm rigid cylinder of 3.4 m length was towed at constant speed in a 210 m long towing basin. The fluid loads on the cylinder were measured and state-of-the-art 3 component Particle Image Velocimetry (PIV) measurements were carried out in a 2-D plane of 400 × 700 mm in the downstream wake of the cylinder. A fixed cylinder and a oscillating cylinder were tested. The range of amplitudes and frequencies was tested for the oscillating cylinder in the lock-in region. The tests give new insight in the vortex synchronisation and will provide a valuable set of data for future CFD-code validation.
One of the grand challenges in the offshore industry is still the assessment of the motions of a circular cylinder in waves and current for application to risers or riser bundles up to 10,000 feet water depth. Here the fatigue life is dominated by the VIV phenomena and also the possibility of riser collision is governed by VIV effects. The nature of the vortex induced vibration (VIV) problem relates to a hydro-elastic problem in which the vibrations are triggered by force fluctuations due to the generation of vortices. The force fluctuations in return are strongly influenced by the subsequent motions of the riser in a truly coupled fashion.
