Predicting ship frictional resistance due to biofouling using Reynolds -averaged Navier-Stokes simulations

Biofouling reduces the overall hydrodynamic performance of a ship and increases fuel consumption. Four different fouling resistant coatings were experimentally investigated to study their surface roughness properties, during two years of exposure at sea water. An open source RANS solver, OpenFOAM, with integrated rough wall function model, was verified and validated for frictional and total resistance prediction for smooth (no coating) surface conditions. Next, the solver was validated against available CFD and Empirical results for ship frictional resistance prediction with different levels of slime and fouling. Finally, frictional and total resistance was predicted for a ship hull surface with the experimentally studied coatings. The experimental outputs were used to model surface roughness properties of the ship hull, and predict the resistance performance of the ship after one and two years of exposure at sea, with the studied hull coatings. The study reveals that the determination of frictional resistance alone is not enough to understand the required change in propulsion power requirement due to fouling, total drag resistant prediction is also important. It also shows that coatings with initial low roughness may not retain the low resistance property over a long period of exposure to the sea, comparing to other coatings. Overall, the study concludes that CFD can prove to be a very effective tool to study the effect of biofouling on hull properties.