Reduction of barnacle recruitment on micro-textured surfaces: Analysis of effective topographic characteristics and evaluation of skin friction

This study investigates five designed micro-textured surfaces and their effects on barnacle fouling and hydrodynamic drag. Three of the micro-textures were developed in the present study and evaluated together with two commercial riblet films. All micro-structures were arranged as longitudinal grooves with different profile depths, widths and angles of inclination. In field tests the recruitment of the barnacle Balanus improvisus on micro-textured surfaces and smooth controls was evaluated. All micro-textured surfaces reduced recruitment, and the most efficient texture reduced recruitment by 98%. For some micro-textures the reduction of recruitment declined as settlement intensity increased. In a correlative analysis, the trigonometric inclination of the micro-structures explained most of the recruitment reduction. The steepest angle of inclination caused a massive reduction in barnacle settlement. Surface micro-structures may affect the boundary-layer flow and the hydrodynamic drag (skin friction) of the surface. The skin friction was empirically measured in a flow channel using a sub-set of the tested microtextures. The measurements of skin friction showed that the orientation of the microstructures is important, with a minimum friction when the grooves are parallel to the flow. For one of the micro-textures the skin friction was ca 10% lower compared to a hydraulically smooth surface. It is concluded that, depending on the flow speed, micro-textures will not significantly increase skin friction when arranged parallel to the flow, even at moderate protrusion through the viscous sub-layer.