ABSTRACT
The paper presents both state-of-the-art CFD modeling techniques for subsea gas bubble plumes and the subsequent dispersion above sea, and simplified look-up tables where the consequences in terms of distance to flammable gas clouds caused by a subsea gas release are found. Gas transfer from sea to air on the surface (the bubblezone) represents the interface also between separate CFD models for below and above sea. Sintefs CFD models of subsea bubble plumes captures the transient plume behavior, surface dynamics (height of boiling zone, shear layers, radial flow), subsea mass and heat transfer, and it gives transient and stationary boundary conditions for dispersion above sea. It is currently validated for a 10 m water depth experiment. A DNV RP is developed for CFD modeling of dispersion above sea including bubble zone definitions, standard k-ε model and recommendations for the buoyancy turbulence model, air inlet boundary conditions, and how to maintain turbulence downwind. Different commercial CFD codes are often not able to predict the same plume lengths due to default modeling differences, and the current RP gives the modeling details that need to be followed in order to give consistent results. The CFD generated look-up tables are integrated into a tool called PlumePro where the height and distance to the LFL plume can be found given sea depth, release rate and wind speed. PlumePro interpolates in the look-up tables generated from a set of CFD modeling runs where the state-of-art modeling techniques are applied.
