Influence of the position angle of the small pipeline on vortex shedding flow around a sub-sea piggyback pipeline

The vortex shedding flow past a piggyback pipeline close to a plane boundary is investigated numerically. The piggyback pipeline is comprised of a large pipeline and a small pipeline. The aim of the study is focused on the effects of the position angle of the small pipeline on the vortex shedding and the hydrodynamic forces of the pipeline bundle. The two-dimensional Reynolds-averaged Navier-Stokes equations are solved using the finite element method. The equations are enclosed by the k-ω turbulent model. The ratio of the small pipeline diameter (d) to the large one (D) is 0.2. The Reynolds number based on the free stream velocity (U0) and the large pipeline diameter (D) is Re = 2 ×104. Simulations are carried out for the positional angles (α) of the smaller pipeline relative to the larger one ranging from 0 to 180° with an interval of 15°, and the gaps (G) between the large pipeline and the plane boundary ranging from 0.2 to 0.6D. It is found that the critical gap ratio, below which the vortex shedding is suppressed, is a function of the positional angle of the small pipeline. The effects of the position angle of the small pipeline on the hydrodynamic forces on the pipeline system are investigated numerically.