Experimental Investigation of the Turbulent Boundary Layer of Surfaces Coated With Marine Antifoulings

Abstract

Turbulent boundary-layer measurements have been carried out on flat surfaces coated with two different new generation marine antifoulings. The coatings were applied on 1-m-long test sections that were fitted in a 2.1-m-long flat plate setup. The measurements were carried out in two different recirculating water tunnels by means of two-component laser Doppler velocimetry and were compared with measurements of a smooth steel reference surface and a surface covered with sand grit. Both coatings exhibited an increase in frictional resistance compared to the reference surface, but the increase was significantly smaller for the Foul(ing) Release coatings than for the Tin-free SPC coating. The coatings did not significantly affect the boundary-layer thickness. When expressed in inner variables, the coatings did not have an effect on the turbulence intensity profiles, but when expressed in outer variables, the coatings affected the near-wall turbulence intensities.

Modern approaches to marine antifouling coatings

“…Candries and Atlar [19] recorded an average increase in friction velocity of between 10-14% for foul release systems and between 13.4-23.5% for tin-free SPC. Differences in coating application techniques can influence the surface roughness of coatings with an overall increase in the frictional resistance in roller applied FRCs than spray coated FRCs reported [19].…”

“…Biofouling affects the latter by increasing the average hull roughness and wall shear stress. The effects of antifouling coatings, such as self-polishing copolymer (SPC) and foul release coatings (FRCs), on the hydrodynamic boundary layer have been shown to have little influence on either its thickness or shape factor, although friction velocity was increased [19]. The negative effects of biofilm roughness on drag were studied by Shultz and Swain [20] and the importance of this initial biological growth on the mean and turbulence profiles of marine vessels were highlighted.…”

Numerical simulation of turbulent boundary layers of surfaces covered with foul release and antifouling coatings

“…As the flow continues across the body, it becomes more and more turbulent in the transition region, until it eventually becomes a turbulent flow. The length of the transition region can vary due to several factors including surface roughness, pressure and velocity fluctuations (Candries, 2001). The turbulent boundary layer is assumed to consist of two main regions: an inner region and an outer region.…”

“…The whole roughness regime is subdivided into three regimes, and the formulas proposed by Cebeci and Bradshaw based on Nikuradse's data are adopted to compute ΔB for each regime (Cebeci, T., and Bradshaw, P. (1977). For the hydrodynamically smooth regime ≤ 2.25:…”

Effect of ship hull form on the resistance penalty from biofouling

“…1933; Cebeci and Bradshaw 1977) and antifouling coatings (Johansson 1984;Schultz 2004;Candries and Atlar 2005). As shown in Figure 1, ΔU + can be collapsed for disparate roughness geometries in the fully rough regime (ie high Reynolds number) by use of the so-called equivalent sand-roughness height k s .…”