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Turbulent boundary-layer structure of flows over freshwater biofilms


Walker, JM and Sargison, JE and Henderson, AD, Turbulent boundary-layer structure of flows over freshwater biofilms, Experiments in Fluids: Experimental Methods and Their Applications to Fluid Flow, 54, (1628) pp. 1-17. ISSN 0723-4864 (2013) [Refereed Article]

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Copyright 2013 Springer-Verlag Berlin Heidelberg

DOI: doi:10.1007/s00348-013-1628-x


The structure of the turbulent boundary-layer for flows over freshwater biofilms dominated by the diatom Tabellaria flocculosa was investigated. Biofilms were grown on large test plates under flow conditions in an Australian hydropower canal for periods up to 12 months. Velocity-profile measurements were obtained using LDV in a recirculating water tunnel for biofouled, smooth and artificially sandgrain roughened surfaces over a momentum thickness Reynolds number range of 3,000–8,000. Significant increases in skin friction coefficient of up to 160 % were measured over smooth-wall values. The effective roughnesses of the biofilms, ks, were significantly higher than their physical roughness measured using novel photogrammetry techniques and consisted of the physical roughness and a component due to the vibration of the biofilm mat. The biofilms displayed a k-type roughness function, and a logarithmic relationship was found between the roughness function and roughness Reynolds number based on the maximum peak-to-valley height of the biofilm, Rt. The structure of the boundary layer adhered to Townsend’s wall-similarity hypothesis even though the scale separation between the effective roughness height and the boundary-layer thickness was small. The biofouled velocity-defect profiles collapsed with smooth and sandgrain profiles in the outer region of the boundary layer. The Reynolds stresses and quadrant analysis also collapsed in the outer region of the boundary layer

Item Details

Item Type:Refereed Article
Keywords:Biofouling, turbulent boundary layer, hydropower, roughness
Research Division:Engineering
Research Group:Fluid mechanics and thermal engineering
Research Field:Turbulent flows
Objective Division:Energy
Objective Group:Renewable energy
Objective Field:Hydro-electric energy
UTAS Author:Walker, JM (Dr Jessica Walker)
UTAS Author:Henderson, AD (Associate Professor Alan Henderson)
ID Code:87277
Year Published:2013
Funding Support:Australian Research Council (LP1010700)
Web of Science® Times Cited:14
Deposited By:NC Maritime Engineering and Hydrodynamics
Deposited On:2013-11-12
Last Modified:2017-11-08

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