CFD computations are conducted at full scale in order to determine the airflow around the above-water hull and the superstructure of the vessel. These studies highlight the local wind conditions and the exhaust dispersion on the relevant open decks (especially helideck) and at other locations (e.g. path of helicopter approach, air intakes for engine and ventilation).
The CFD model retains all components of the vessel above the water line with influence on the airflow, including the major air intakes, while small-scale details are omitted (e.g. railings, antennae). The oncoming wind profile is approximated by a standard atmospheric power law unless the customer specifies a different wind profile.
The computations are performed using HSVA's flow solver FreSCo+, a finite-volume code well-suited for the simulation of turbulent flow around complex geometries. For highly unsteady aerodynamics simulations, a hybrid RANS-LES turbulence treatment is applied: In this so-called DES approach, the dominant energetic eddies in the bulk of the flow field are resolved in a LES sense, while the near-wall behaviour is approximated by a RANS k-ω-SST closure. The dispersion of exhaust gases over the decks is included via a two-phase volume-of-fluid (VOF) method.
Time averaged flow field, typical of RANS computation results.
Instantaneous flow field from a DES computation.
These DES simulations are known to be superior to the present industrial standard of RANS-based computational aerodynamics. Especially the simulation of exhaust-gas transport is significantly improved when a DES turbulence treatment is considered instead of a pure RANS approach.