$9 million effort will tackle soft biofouling on naval vehicles

When a new ship is launched into seawater, microscopic organisms immediately begin to build up on the hull. Within hours, this layer of bacterial biofilm starts to secrete sticky substances.

The thin, slimy coating continues to grow, making it easier for algae and plant-like growth to accumulate on the surface in fuzzy patches. 

The result is an uneven, rough surface on the ship’s hull that increases drag and resistance, drives up fuel consumption, generates noise and vibrations, and clogs or obscures sensors.

To advance the fundamental knowledge of the science of biofouling and its interaction with naval and marine vehicles at sea, the Office of Naval Research has awarded $9 million to a multi-university partnership as part of the agency’s Multidisciplinary University Research Initiatives program (MURI). 

Led by Virginia Tech, the five-year project includes researchers from Cornell University, the George Washington University, Georgetown University, and the U.S. Naval Academy. The team will conduct landmark experimental measurements, develop datasets, and deliver novel instrumentation and techniques that will be scalable and easily adapted for wide use across Navy facilities and laboratories. 

A foul, multivariable problem

The research will focus on three primary thrusts, including development of new measurement techniques, a deeper look at the biology and materials side with the creation of artificial and cultured biofilms, and development of unprecedented experimental datasets on the interactions between turbulence, biofouling, compliant surfaces, and acoustics.

“Scientifically, this is incredibly difficult to study because biofouling is a highly variable, living ecosystem,” said William Devenport, Alumni Distinguished Professor and lead on the project. 

Growth of the film depends on factors such as whether the vessel is in motion and where it operates globally. To achieve repeatable experiments that allow study of the system’s multiscale, multivariable dynamics, the researchers will develop artificial and cultured biofilms that mimic real-world conditions.

Noise adds another layer of complexity. “From a fluid dynamics and acoustics standpoint, the noise occurs when the biofilm, the surface on which it forms, and the flow together produce a turbulent boundary layer that generates pressure fluctuations,” said Devenport. “Water is heavy, about one ton per cubic meter. Those pressure fluctuations effectively thump on the hull, in much the same way that air buffets the fuselage of an airplane.

“This seemingly thin layer can have a disproportionate effect on flow behavior and the sound it generates,” he said. “Everything is interactive as the flow controls how the biofilm grows, and the biofilm in turn modifies the flow.”

The collaborators

With a wealth of expertise in fluid dynamics and acoustics, Virginia Tech is uniquely positioned to lead this effort. The university’s capabilities include novel centimeter-scale flow channels, optical and X-ray flow measurement technologies, and the Virginia Tech Stability Wind Tunnel and its current strategic upgrade as part of the Mitchell Hall project.

The project also assembles a transdisciplinary dream team of members: 

• Devenport offers more than 40 years of experience in experimental fluid dynamics and acoustics, managing large interdisciplinary teams and advancing turbulent boundary layer acoustic measurements. 
• Olivier Coutier-Delgosha of Virginia Tech brings innovative approaches using centimeter-scale water channels and x-ray measurement techniques.
• Todd Lowe of Virginia Tech is a recognized leader in optical diagnostics for fluid dynamics.
• Rong Yang of Cornell University specializes in biofouling biology and antifouling, with unique capabilities in biointerface engineering, layered structures for simulated biofouling, and bacteria-based growth.
• Dan Blair of Georgetown University focuses on the mechanical properties of soft and biological materials and advanced tools for quantitative microscopy and rheology. 
• Matt Rau of The George Washington University, an expert in marine microbiology and fluid dynamics, grows and experiments on micro-algal organisms under tightly controlled conditions.
• Philippe Bardet of The George Washington University leads in optical flow measurement and pioneered plenoptic imaging for high-resolution tomographic particle tracking.
• Mike Schultz of the U.S. Naval Academy is widely regarded as the leading authority on flows over biofouling, conducting extensive experiments with both simulated and real growth.

“Once biology enters the picture, the number of variables explodes, and it’s easy to make mistakes if you’re not controlling the right parameters,” said Bardet. “That’s why this project is exciting — it is a truly multidisciplinary effort. We have true biologists and people at the fluid–biology interface, like Rong Yang and Matt Rau. William Devenport is extremely thorough and methodical, and I believe he’s the best person in the U.S. to lead this project.”

Experimental testing will advance through three stages, starting small and increasing in complexity. Parallel experiments will run at Virginia Tech and The George Washington University, using centimeter-scale channels modeled after existing flow loops developed by Coutier-Delgosha.

Midscale experimentation will take place in the U.S. Naval Academy’s Boundary Layer Water Tunnel, to capture the full range of turbulent boundary layer structures, including large-scale motions that interact with biofouling and compliant surfaces.

The final stage will occur in the George Washington University’s High-Reynolds Number Matched Index of Refraction facility, designed for the most realistic and demanding flow studies. This will give researchers a view of turbulence and biofouling at scales that closely match real-world naval environments.

“It’s an exciting project,” said Bardet. “We’re pushing limits in measurement and understanding this complex phenomenon, with applications beyond naval use, such as medical device cleaning or sterilization. Understanding the fundamental problem of how fluid flow interacts with bacteria and how invisible slime layers grow is a rich topic, one that is highly relevant, extremely challenging, and scientifically rewarding.”