Boundary layer hydrodynamics of patchy biofilms

Abstract

Algal biofilms, ubiquitous in aquatic systems, reduce the performance of engineered systems and alter ecosystem processes. Biofilm morphology is dynamic throughout community development, with patchiness occurring due to periodic sloughing, but little is known about how community level physical structure affects hydrodynamics. This study uses high resolution particle image velocimetry (PIV) to examine spatially explicit turbulence over sparse, uniform and patchy biofilm at turbulent Reynolds numbers. All biofilms increase the near-bed turbulence production, Reynolds shear stress, and rotational flow compared to a smooth wall, and non-uniform biofilms have the greatest increase in these parameters, compared with a uniform or sparse biofilm. However, a higher drag coefficient over uniform biofilm compared with non-uniform biofilm indicates that percent coverage (the amount of area covered by the biofilm) is a useful predictor of a biofilm’s relative effect on the total drag along surfaces, and in particular the effect on ship performance.

Keywords:

• Biofouling
• algal biofilm
• turbulence
• roughness
• boundary layer
• PIV

Acknowledgements

The authors are grateful for technical support provided by the USNA Technical Support Division and the USNA Hydromechanics Lab. The authors also wish to acknowledge the detailed and constructive criticism of two anonymous reviewers, which significantly improved the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The instantaneous vector fields used to analyze flow over the patchy biofilm plates are freely available on Zenodo at https://doi.org/10.5281/zenodo.5644626

Additional information

Funding

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