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Oscillations of Tethered Bodies as a Result of Fluid – Structure Interaction

When tethered bodies are immersed in a flow, structural oscillations (Vortex Induced Vibrations, VIV) may occur as a result of the interaction between the fluid and the structure. These interactions are common in various applications including tethered ocean buoys, side-scan sonars, aircraft warning spheres in overhead transmission lines and more recently in energy harvesting technologies. On the one hand these vibrations may damage structural integrity while on the other hand they may be beneficial for “green” energy harvesting. In the Environmental Multi-Phase Flow laboratory (EMPFL) headed by Dr. René van Hout, we study fluid-structure interactions of tethered bluff bodies immersed in a uniform flow (Fig.1). These fluid structure interactions can give rise to Vortex-Induced Vibrations (VIV) that are characterized by complex, three-dimensional, coupled fluid-structure behavior. Vortex induced vibrations are characterized by both periodic and non-stationary large amplitude oscillations. We use quantitative time resolved Particle Image Velocimetry (PIV) technique to both track the sphere dynamics as well as flow field characteristics. Results are used to analyze the vortex shedding dynamics (Fig. 2) and fluid forcing associated with the sphere motion.

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Fig. 1. Schematic of laboratory setup

SwirlingStrength

Fig. 2. Illustration of vortex shedding by oscillating tethered sphere, ReD = 1360. Upper row: vector maps; Middle row: vorticity; Lower row: Swirling strength.

References

  1. van Hout R., Krakovich A., Gottlieb O., 2010: Time resolved measurements of vortex-induced vibrations of a tethered sphere in uniform flow. Physics of Fluids 22, Vol. 8: DOI: 10.1063/1.3466660.
  2. Eshbal, L., Krakovich, A., van Hout, R., 2012. Time resolved measurements of vortex-induced vibrations of a positively buoyant tethered sphere in uniform water flow. Submitted to Journal of Fluids and Structures.