Numerical modeling of a sagging pipeline using an Eulerian two-phase model

Abstract

The scour below a sagging pipeline is studied using a combination of a k-epsilon flow model and an Eulerian two-phase model, the modeling system being a part of the FLUENT CFD package. Both flow–particle and particle–particle interactions are considered in the model and the predicted bed profile changes are evaluated against data of a published laboratory experiment. In the configuration considered, the sagging is manifested in two steps: (1) the local scour around the pipeline is allowed to develop fully; and (2) the pipeline is lowered to the scour hole in a controlled fashion until it reaches the bottom of the scour hole. Three sagging velocities are simulated, and predicted scour profiles agree well with the laboratory data. Differences of scour evolution are noted for different sagging velocities, for which possible reasons were advanced. General characteristics of flow fields, including turbulence, suspension of particles and sediment transport are described paying attention to their dependence on the pipeline sagging. The scour profiles simulated are also in good agreement with a LES-based numerical study reported earlier.

Keywords:

• pipeline
• scour
• sagging
• two-phase flow

Acknowledgment

This work was funded by ONR contracts # N00014-01-1-0349 and N00014-04-1-0621.