The Effect of Biofilms on Turbulent Flow over Permeable Beds

Kazemifar, F.; Blois, G.; Aybar, M.; Calleja, P.P.; Nerenberg, R.; Sinha, S.; Hardy, R.J.; Best, J.; Sambrook Smith, G.H.; Christensen, K.T.

Abstract

Despite an increasingly large body of work advancing our understanding of flow interactions occurring at the interface of a turbulent flow overlying a permeable bed, little is known concerning how such flow may be affected by the presence of biofilms, which exist in nearly all aquatic environments. This paper quantifies the effects on flow exerted by biofilms grown over experimental laboratory permeable beds until biofilm detachment, and then compares this to the residual effects after its detachment. The investigation is conducted in a flow channel by immersing two‐dimensional permeable beds with idealized geometry and different porosities in order to explore different bed permeabilities. Sequences of increasingly higher flow velocity conditions followed by lower flow, were considered to explore the effect of detachment. Measurements were performed using particle image velocimetry. The total wall shear stress and friction velocity were found to increase in the presence of pre‐grown biofilm, and decrease after biofilm detachment, when compared at the same pump frequency. The dimensionless Reynolds stresses, at constant pump frequency, collapsed for different bed configurations in the outer layer, while for the inner layer, the presence of biofilm led to a decrease in dimensionless Reynolds stress. Quadrant analysis shows that this decrease was primarily due to a reduction in strong Q2 contributions. These results suggest that models for flow and transport over permeable media in aquatic environments cannot neglect the role of biofilms in modifying turbulence.

Citation

Kazemifar, F., Blois, G., Aybar, M., Calleja, P., Nerenberg, R., Sinha, S., Hardy, R., Best, J., Sambrook Smith, G., & Christensen, K. (2021). The Effect of Biofilms on Turbulent Flow over Permeable Beds. Water Resources Research, 57(2), Article e2019WR026032. https://doi.org/10.1029/2019wr026032

• Journal Article Type: Article
• Acceptance Date: Dec 8, 2020
• Online Publication Date: Dec 14, 2020
• Publication Date: 2021-02
• Deposit Date: Jan 19, 2021
• Publicly Available Date: Dec 14, 2021
• Journal: Water Resources Research
• Print ISSN: 0043-1397
• Electronic ISSN: 1944-7973
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 57
• Issue: 2
• Article Number: e2019WR026032
• DOI: https://doi.org/10.1029/2019wr026032
• Public URL: https://durham-repository.worktribe.com/output/1281351