The commercial CFD software STAR-CCM+ was used to simulate transportation of viscous oil in a horizontal pipe. The CFD model was first validated against analytical solution for wall shear stress in laminar flows with constant physical properties. The model was then used to investigate the effects of heat loss since the pipe is subjected to cooling by the sea water on the sea bed.
The results show strong thermal stratification across the pipe with cooler fluid at the bottom of the pipe and warmer fluid near the gas-liquid interface. A layer of cooler fluid is also found next to the pipe wall. Higher values for density and viscosity are found in the cooler regions. The higher viscosity in the cooler layer around the wall was found to give a large increase in wall shear stress and therefore higher pressure drop.
Such strong variations in temperature and physical properties across the pipe are difficult to represent by averaged values as used in traditional one-dimensional analysis. The wall shear stress and pressure drop are likely to be under-estimated which could lead to serious problems in operating the pipeline. Three-dimensional CFD method presented in this paper can provide some very valuable information and therefore is an important tool in Computational Flow Assurance.