View Abstract

EFFECTS OF ALGAL BIOFILM PATCHINESS ON BOUNDARY LAYER HYDRODYNAMICS (E)

Algal biofilms commonly foul natural and man made aquatic surfaces such as ship hulls, where they impose severe drag and, therefore, economic penalties. Biofilms are often found in high- speed, unidirectional flow environments, such as on ship hulls and riverbeds. Biofilms are algal or bacterial cells embedded in exocellular polymeric substance (EPS), and behave as a viscoelastic solid. When biofilms grow under hydrodynamic stress, they form flexible streamers. This compliant surface with protruding streamers results in complex interactions between biofilms and hydrodynamics. Hydrodynamic forces can result in spatially heterogeneous formation of biofilms and sloughing off of biofilms, leading to patchy coverage. We investigated the effects of biofilm patchiness on high Reynolds number boundary layer hydrodynamics by using high resolution Particle Image Velocimetry (PIV) to visualize flow over biofilms grown under shear on acrylic plates. Biofilm, even with sparse, thin coverage is shown to increase turbulence and Reynolds shear stresses in turbulent boundary layers. Over patchy biofilms, the structure of the boundary layer, including both the velocity and Reynolds shear stress profiles were spatially heterogeneous, as was turbulent kinetic energy and the generation and intensity of turbulent bursts and sweeps, which we investigated using quadrant analysis. The friction coefficient (Cf), which is indicative of drag, increased from 0.007 on a smooth wall to 0.01 over biofilm. Cf also exhibited spatial differences over the patchy biofilms, indicating that as biofilm communities develop they are subject to changing hydrodynamic forces.

Authors

Murphy, E. A., University of Virginia, USA, eam6vf@virginia.edu

Barros, J. M., United States Naval Academy, USA, barros@usna.edu

Schultz, M. P., United States Naval Academy, USA, schultz@usna.edu

Flack, K. A., United States Naval Academy, USA, flack@usna.edu

Steppe, C. N., United States Naval Academy, USA, natunewi@usna.edu

Reidenbach, M. A., University of Virginia, USA, reidenbach@virginia.edu

Details

Oral presentation

Session #:114
Date: 02/27/2017
Time: 17:00
Location: 302 A/B

Presentation is given by student: Yes