Sustainable Propulsion for AUV Applications

Project Overview

Team-based project developing a propulsion system for biodegradable Autonomous Underwater Vehicle (AUV) applications. The project involved designing and prototyping a propulsion system that is environmentally friendly and efficient for underwater exploration and involved developing a pnuematic outgassing system powered by a pressurized fuel cell of hydrogen peroxide and yeast designed by another team and interfaced with our propulsion system. This project was a pre-thesis capstone project in addition to semster-long coursework for ES96.

Design Choices & Optimization

In designing our propulsion system, our biggest constraints were designing an outgassing system that could both operate efficiently and effectively while still being adaptable for biodegradable materials in further iteration. This ultimately led us to choose the radial outgassing system for its simplicity, robustness, and better performance under low-pressure conditions. Our propulsion team worked alongside a fuel cell team to integrate the propulsion system with the hydrogen peroxide and yeast-powered outgassing system, which involved developing interface goals in which we determined extended bursts of 20-40psi would create a reasonable, yet still effective thrust output. We then went to work designing a propeller with outgassing channels. Our first iteration had the channels externally attached to the prop, but in further hydrodynamics testing, we found that an integrated approach would be more effective and reduce drag. Additionally, our latest propeller design is much more robust than earlier versions.

Parallel Design Comparison

In our design process, we evaluated multiple propulsion system configurations to determine the most efficient, each with its own advantages and limitations. The three we considered included:

• Converging-Diverging Nozzle Outgassing
• Radial Outgassing from Propeller Blades
• Tesla Turbine Powered Propeller

We ruled out the CD nozzle early since our fuel cell cannot provide the steady, high-quality flow it requires, especially at our relatively low (~30 psi) and inconsistent pressure. We then prototyped both the radial outgassing and Tesla turbine designs and found that radial outgassing produced significantly more thrust and efficiency. The Tesla turbine relies on viscous effects, which are far less effective in water, and also requires tighter manufacturing tolerances. Our ultimate result in testing proved the turbine would nearly completely stall under our low-pressure conditions. In contrast, the radial outgassing system is simpler, more robust, and performs better under low-pressure conditions, making it the most practical choice for our application. Additionally, in considering adaptability for biodegradable materials and precision manufacturing, the radial outgassing system proved to be the most viable option due to tolerance constraints.