CFD Wall Shear Stress Benchmark in Stratified-to-Annular Transitional Flow Regime

Multiphase transport phenomena are an integral part of flow assurance design in subsea systems. One area of importance in subsea design is carbonic corrosion and how this affects the material selection and thickness. Corrosion prediction strongly depends upon the fluid flow regime, whereby a pragmatic interpretation of the effects of flow on corrosion mechanisms is used. It is postulated that the lack of agreement between corrosion modelling and corrosion field data is more likely due to the inadequate consideration of the multiphase flow regime during design, rather than any limitations in the corrosion models employed. This suggests a better representation of flow regime will provide greater confidence in the corrosion modelling predictions. Wall shear stress is an important parameter in corrosion models; as corrosion inhibitor removal from the wall increases with increasing wall shear stress and therefore escalates the corrosion rates. This parameter is a direct measure of the viscous energy loss within the turbulent boundary layer, and it is related to the intensity of turbulence in the fluid acting on the wall. It is not a force on the wall from the flowing fluid but, rather, a force within the flowing fluid at the wall. Therefore an adequate corrosion prediction has to take into account the flow behaviour accurately.