| Biofilms rapidly colonize materials exposed in marine environments. While biocide-containing antifouling (AF) coating systems are effective in controlling macrofouling, they can become colonized by low form algae and slimes. These have been shown to cause an increase in skin friction drag. This effect may be magnified on non-toxic, foul-release coatings, which contain no biocide to combat biofilm buildup. While the penalties associated with macrofouling are well known, the effects of low form algae and diatomaceous slime films is not as well established. This study compares the mean and turbulent boundary layer velocity structure of surfaces covered with marine biofilms of known composition with those of a smooth surface. The purpose was to provide a basis for the prediction and modeling of flows over biofilms attached to full scale marine vehicles.;A nominally zero pressure gradient, turbulent boundary layer flow was generated on a flat plate fixture mounted in the Harbor Branch Oceanographic Institution recirculating water tunnel. Measurements were made using a two-component laser Doppler velocimeter (LDV). Profiles of the mean and turbulent, axial and wall-normal velocity components, including the longitudinal-plane Reynolds shear stress were measured. Boundary layer similarity laws were used to determine the skin friction coefficient (c;It was found that biofilms had a significant impact on the velocity structure in the boundary layer. Increases in c;The variability in biofilms (cover, thickness, and morphology) prevents scaling lab results to ship frictional resistance with a high degree of certainty. Nevertheless, an attempt was made to use a roughness allowance procedure and a similarity-law analysis to predict ship scale frictional resistance. Both indicated significant increases in skin friction for ship scale surfaces covered with biofilms. |
