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 stillone of the major questions in fluid mechanics. The specific character of wall roughness may varysignificantly from case to case. In this paper we show a method for obtaining the roughness functionof an arbitrary rough surface by using resolved RANS simulations. This method is considerablycheaper in terms of resources and time than currently used experimental approaches. The dragcharacterization and roughness function determination is performed for marine coatings withdifferent roughness size. The results are validated by experiments in a rotating disk rig and by datafrom a towing tank for same coatings. Furthermore, the roughness functions obtained areimplemented in wall-function based CFD simulations and the computational results havedemonstrated very satisfactory agreement with experiments