Roughness effects of diatomaceous slime fouling on turbulent boundary layer hydrodynamics

Abstract

Biofilm fouling significantly impacts ship performance. Here, the impact of biofilm on boundary layer structure at a ship-relevant, low Reynolds number was investigated. Boundary layer measurements were performed over slime-fouled plates using high resolution particle image velocimetry (PIV). The velocity profile over the biofilm showed a downward shift in the log-law region (ΔU⁺), resulting in an effective roughness height (k_s) of 8.8 mm, significantly larger than the physical thickness of the biofilm (1.7 ± 0.5 mm) and generating more than three times as much frictional drag as the smooth-wall. The skin-friction coefficient, C_f, of the biofilm was 9.0 × 10⁻³ compared with 2.9 × 10⁻³ for the smooth wall. The biofilm also enhances turbulent kinetic energy (tke) and Reynolds shear stress, which are more heterogeneous in the streamwise direction than smooth-wall flows. This suggests that biofilms increase drag due to high levels of momentum transport, likely resulting from protruding streamers and surface compliance.

Keywords:

• Biofilm
• turbulence
• drag
• roughness
• PIV
• boundary layer

Acknowledgements

The authors thank three anonymous reviewers for insightful comments and criticism which improved this manuscript. The authors are also grateful to the staff of the USNA Hydromechanics Lab, especially Mark Pavkov, Dan Rhodes and Michael Stanbro, for technical support and care and maintenance of the dynamic slime facility.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The data from this study are openly available in the data repository Zenodo at https://doi.org/10.5281/zenodo.1175014

Additional information

Funding

This work was supported by the US Office of Naval Research Grant #N0001417-WX-00846; the US Office of Naval Research Grant #N00014-15-1-2560; the US National Science Foundation Graduate Research Internship Program Fellowship #2014162109; and the US National Science Foundation Graduate Research Fellowship Program #DDGE-1315231.