Numerical Study of Gap to Diameter Ratio Effects in Steady Current under Offshore Pipelines

The performance of a standard turbulence model in simulation of hydrodynamics of a steady current around a circular cylinder above a wall is examined. Mechanism of vortex shedding and effect of different gap to diameter ratios (0.1, 0.35 and 0.5) on the bed shear stress are also demonstrated. The flow field is computed with solving the Reynolds Averaged Navier-Stokes equations (RANS);whereas the seabed under pipeline is treated as a plane boundary and a no-slip boundary condition on pipe surface, is considered. The governing equations are solved using finite volume method in a Cartesian coordinate system. Based on the numerical solutions, the flow field and its induced vortex shedding are studied. It is found that a turbulence model can well predict the flow hydrodynamics with accounting vortex shedding around a pipeline near seabed; consequently, it can be easily applied for simulation of scour under offshore pipelines.

Keywords:

Reynolds Averaged Navier Stokes Equations , turbulence model , vortex shedding , gap to diameter ratio and local scouring