Vortex shedding flow around a pipeline with a spoiler is simulated by solving the Navier-Stokes equations. The effect of spoilers on the velocity profile under the pipe and the seabed shear stress were investigated by a series of numerical tests. It was found that the attachment of a spoiler increased both the flow rate through the gap between pipe and seabed, and the shear stress on seabed. The increases are quantified for different spoiler lengths and gap ratios.
Installation of offshore pipelines normally involves mechanical trenching, pipeline laying and backfilling. The process of trenching, laying and backfilling contributes significantly to the total cost of a hydrocarbon field development. Previous research found that pipeline laid on the seabed can sometimes bury itself under natural environmental conditions. The process is refered to as pipeline self-burial. Pipeline self-burial often starts with the scrouing of seabed material under the pipeline. Then the pipeline sinks into the scour hole due to it's own weight. As the pipeline sinks into the scour hole, the flow field and the seabed shear stress around the pipe adjusts themselves accordingly. Up to a certain point, the scouring ceases and is replaced by the natural backfillinf of the trench. This completes the self-burial process. It is obvious that natural self-burial of pipelines depends on many factors such as scour depth, extent and rate. Past research found that attchment of a spoiler on top of a pipeline enhances the process of pipeline self-burial by increasing local scour depth, extent and rate (Hulsbergen 1984&1986, Hulsbergen and Bijker, 1989). The speculation on the reason tbr scour enhancement by spoiler was that the spoiler increases the flow underneath the pipe due to additional blockage offered by the spoiler (Chiew. 1992 & 1993).
