Poster R15 - Quantifying Shear Stress of Small-Scale Turbulent Flow for Testing Marine Bacterial Growth

Introduction: Understanding the growth of marine biofilms requires accurately replicating their natural environment, including temperature, media nutrient content, and flow dynamics. In marine environments, particularly on aquatic vessels, biofilms experience turbulent flow and high shear stress, which contribute to their distinctively thin and dense growth patterns. Traditional flow experiments with large basins and high-volume pumps do not offer the precision needed for studying small-scale samples like bacteria. A feasible alternative is the use of a custom-designed flow channel with a small cross-section, allowing for a required high shear stress and ensuring a developed flow field over the sample. This setup typically involves a long channel and a carefully designed transition region between channels of varying geometries. Particle image velocimetry (PIV) is employed to visualize and quantify the flow field near the solid boundary, enabling accurate shear stress measurements.

Materials and

Methods: Optical coherence tomography (OCT), a laser scanning technique, was used to capture longitudinal cross-sectional images of fluid flow seeded with particles, which were then analyzed using PIV concept to assess differences in shear rate across varying Reynolds numbers and surface roughness. Experiments were conducted at Reynolds numbers of 1,000, 3,000, 5,000, and 10,000, using phantoms with different sandpaper roughness values. The fluid, seeded with titanium dioxide, was imaged over 250 frames using OCT, and the PIV software was utilized to calculate the shear rate.

Results, Conclusions, and Discussions: The PIV analysis successfully tracked particle images and calculated shear rates, revealing significant differences between the shear rates on top flat surfaces and bottom rough surfaces. This indicates the system’s capability to detect subtle changes in shear stress. Notably, the impact of surface roughness on shear stress was found to increase with higher Reynolds numbers.
This study demonstrates a robust method for examining flow mechanics that influence biofilm growth and development. By combining this approach with controlled nutrient and temperature settings, it is possible to closely mimic aquatic environments. This integration aids in developing more accurate biofilm models, enhancing our understanding and management of biofilm-associated issues on marine vessels.

Acknowledgements (Optional): This research was funded by NIH COBRE, NSF EPSCoR, and DARPA Project