A cylindrical structure exposed to fluid flow periodically sheds vortices in the wake. The fluctuating lift and drag forces may cause structural vibrations, which give rise to a complex fluid structure interaction referred to as Vortex Induced Vibrations (VIV). When the wake vortex shedding, frequency is close to the structure fundamental frequency, the VIV amplitude can become relatively large. These large amplitude vibrations can impede system operation and may lead to system failure. This is encountered in many engineering applications including heat exchangers, offshore oil risers, pipelines crossing a river, bridges and chimney stacks.
An approximation of many cases of VIV is a pivoted cylinder permitted to move with two degrees of freedom. Span-wise variation in amplitude creates three-dimensional vortex shedding in the cylinder wake. Particle Image Velocimetry (PIV) is used to quantify the flow development, while displacement sensors are used to characterize the structural response. Video 3 shows flow visualization with PIV particle images of a cylinder undergoing VIV. Videos 4a and b show the vorticity fields for a stationary cylinder and that undergoing VIV.
Video 3. PIV raw particle field for vortex induced vibrations of a pivoted cylinder.
Video 4. Phase averaged vorticity field of a) a stationary cylinder and b) cylinder undergoing vortex induced vibrations.