TEAMER: Numerical Modeling of Pterofin's Oscillating Hydrofoil

The Pterofin Skimmer is a marine energy system that harnesses energy near the water surface with an oscillating hydrofoil that flaps and pitches. Numerical modeling of the device was performed to inform future design developments, focusing on improvements to the operating profile. The work included a large design parameter sweep using a highly computationally efficient reduced-order blade element momentum theory (BEMT) model. Assumptions inherent in this model limited its accuracy, especially with regards to capturing the dynamics of unsteady flow separation. However, its simplicity allowed for a large parameter sweep, critical for the open-ended, current state of development. The reduced-order modeling provided guidance on interesting design regions where higher-fidelity computational fluid dynamics (CFD) modeling was performed. The CFD model gave a more accurate representation of device performance and helped quantify the error associated with the BEMT results. Complicated unsteady flow dynamics can be challenging to capture, even with CFD. Error in the high-fidelity CFD was quantified via validation comparisons to experimental data from a previous TEAMER project.

The project provided insight into which operational parameters improve performance of the Pterofin device and estimated the error associated with the selected mid-fidelity and high-fidelity modeling techniques. In general, as the flap frequency grows, the discrepancy between CFD and BEMT grows, and for all cases the Cp total predicted by CFD is lower than that predicted by BEMT. The highest Cp total predicted by CFD was 0.177. This project confirms modeling challenges with the optimization of a highly unsteady flow power extraction system but offers some insights into operational strategies to improve performance, including the need for a large pitch amplitude and the use of a non-sinusoidal motion profile. The CFD simulations represent only a few operating conditions from a large parameter space. While efforts were made to identify the best performing cases, higher Cp values may be achievable through unexplored motion profiles, advanced controls, or other means.