On the measurement of VIV lift force coefficients at high Reynolds numbers

Abstract

The objective of the research was the measurement of the VIV lift force coefficient in-phase with velocity Clv and in-phase with acceleration Cla for a pipe section with large length over diameter ratio of L/D ~18 at high Reynolds numbers of Re > 1E4. The coefficients are measured for a forced oscillation pipe in a steady flow and can be directly used as input parameter for pragmatic riser VIV prediction models. Risers are vertical pipelines that transport fluids from the oil well on the seabed to the production facility in the free water surface. The risers in deep water are extremely slender structures, having length over diameter ratio of more than L/D = 1E3. The risers in deep water behave as a flexible string-like structure with low structural damping, which makes them susceptible for resonant vibrations. The vibrations caused by the vortex shedding in the downstream wake of the riser are known as Vortex Induced vibration (VIV) and occur when the frequency of the vortex shedding coincides with one or more of the natural frequencies of the riser. The VIV of the riser poses large challenges for the design of the risers, in particular related to metal fatigue.