Measurements and Prediction of Friction Drag of Hull Coatings

The prediction of the friction drag from surfaces with different types and shapes of roughness is still one of the major questions in fluid mechanics. The specific character of wall roughness may vary significantly from case to case. In this paper we show a method for obtaining the roughness function of an arbitrary rough surface by using resolved RANS simulations. This method is considerably cheaper in terms of resources and time than currently used experimental approaches. The drag characterization and roughness function determination is performed for marine coatings with different roughness size. The results are validated by experiments in a rotating disk rig and by data from a towing tank for same coatings. Furthermore, the roughness functions obtained are implemented in wall-function based CFD simulations and the computational results have demonstrated very satisfactory agreement with experiments