Numerical Study on Flow Around Circular Conduits in Tandem Arrangement at Higher Re of O (10⁶)

Risers are vertical offshore circular conduits that connects the reservoir beneath the water surface to a fixed or floating platform at the water surface, when the riser are subjected to sea currents the flow started to separate from its outer surface and vortices are formed in the downstream leads to vortex shedding. So there is need to spoil vortex shedding and suppress Vortex-induced vibration (VIV) to prevent damage on structures and on the other hand there is equal chance for utilization of energy as sustainable source from the ocean currents. The present numerical study is the done on larger diameter circular conduits which is used to draw cold water from deeper water depths for floating barge desalination plant deployed by National Institute of Ocean Technology (NIOT) would be susceptible to vortex-induced vibrations. Two such conduits held together in tandem arrangement using spacer is studied extensively for higher Re of O (106) in this work. The aspect ratio (L∕D) of the cylinder is an important parameter to be considered. In this study modeling of cylinder for aspect ratio of 9 is chosen to capture the 3D effect along the length of the cylinder. The present work is focused on studying flow behavior around the conduits and its vortex shedding using commercial CFD software STAR-CCM+. The numerical simulation was carried out at Re of O (106) for tandem arrangement of 2D center to center spacing of Re ranging from 0.8 × 106 to 3.2 × 106. In this orientation the effect of lift, drag and pressure variation along the length and also on circumference of conduits was analyzed and it is correlated with the various flow velocities of circular conduits.