title: Drag force and surface roughness measurements on freshwater biofouled surfaces.
abstract: The detrimental effect of biofilms on skin friction for near wall flows is well known. The diatom genera Gomphonema and Tabellaria dominated the biofilm mat in the freshwater open channels of the Tarraleah Hydropower Scheme in Tasmania, Australia. A multi-faceted approach was adopted to investigate the drag penalty for biofouled 1.0 m x 0.6 m test plates which incorporated species identification, drag measurement in a recirculating water tunnel and surface characterisation using close-range photogrammetry. Increases in total drag coefficient of up to 99% were measured over clean surface values for biofouled test plates incubated under flow conditions in a hydropower canal. The effective roughness of the biofouled surfaces was found to be larger than the physical roughness; the additional energy dissipation was caused in part by the vibration of the biofilms in three-dimensions under flow conditions. The data indicate that there was a roughly linear relationship between the maximum peak-to-valley height of a biofilm and the total drag coefficient.
authors.affiliation: School of Engineering, University of Tasmania, Hobart, Australia. jessica.andrewartha@utas.edu.au
authors.forename: J
authors.initials: J
authors.lastname: Andrewartha
authors.forename: K
authors.initials: K
authors.lastname: Perkins
authors.forename: J
authors.initials: J
authors.lastname: Sargison
authors.forename: J
authors.initials: J
authors.lastname: Osborn
authors.forename: G
authors.initials: G
authors.lastname: Walker
authors.forename: A
authors.initials: A
authors.lastname: Henderson
authors.forename: G
authors.initials: G
authors.lastname: Hallegraeff
mesh_terms: D001422:Bacterial Adhesion; D018441:Biofilms; D004867:Equipment Design; D005618:Fresh Water / Q000737:chemistry*; D017276:Friction; D008422:Materials Testing; D055585:Physical Phenomena; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013499:Surface Properties