TEAMER RFTS 15 Application – Pterofin & NREL – Technical Summary
Background on technology:
The Pterofin Skimmer is a marine energy system that harnesses energy near the water surface with an oscillating hydrofoil. The foil oscillates about a driveshaft in a pendulum motion. During each oscillation, the foil also pitches about its spanwise axis near the end of each swing such that the leading edge remains upstream in the relative flow. A counterbalance and control system regulate the wing motion, and a power system converts that motion into a single direction to turn a generator. The Skimmer has the potential to perform well in low flow environments and can be deployed in shallow areas.
Background on problem being addressed:
Past work on the Skimmer consisted of experimental prototype testing and low-fidelity modeling. Prototype testing demonstrated the viability of the concept but limited the number of parameters that could be tested. Analytical modeling gave a rough estimate of performance, but the models applied did not account for important aspects of operation, such as induction and variable lift coefficients. This work will simulate device performance for a wide range of parameters at higher levels of fidelity to provide insight as to which configurations improve performance, and which should be further optimized.
Statement of intended outcomes and what metrics will be used:
The project’s intended outcomes are: 1) insight into which geometric and operational parameters improve performance; 2) quantify performance for a specific set of parameters; 3) estimate the error associated with mid-fidelity and high-fidelity modeling. The following metrics will be evaluated: driveshaft torque and speed; mechanical power; hydrofoil pitching torque; system thrust. CFD results will be compared to experimental data at lab scale, and BEM results will be compared to CFD results at full scale.
Overview of requested support:
Pterofin is requesting support modeling their Skimmer device. The support consists of running a large parameter sweep using a reduced-order blade element momentum model, which is highly computationally efficient. Assumptions inherent in this model will limit its accuracy, especially with regards to capturing the dynamics of unsteady flow separation. However, its simplicity will allow for a large parameter sweep and provide guidance on which cases should be simulated with a higher-fidelity computational fluid dynamics (CFD) model. The CFD model will give a more accurate representation of device performance and help quantify the error associated with the BEM results. Error in the high fidelity CFD will be quantified with comparisons to previous experimental data.
Rationale for facility selection:
NREL has extensive experience in turbine and hydrofoil modeling, and open-source tools developed by NREL for wind are being adapted for marine turbines. One such tool is OpenFAST, an aero-hydro-elastic engineering model for whole turbines. Due to the unique design and operation of the Pterofin device, relative to traditional turbines, the OpenFAST rotor aero/hydrodynamics module AeroDyn will be run independently. This work requires expert knowledge of AeroDyn and its capabilities as applied to marine energy devices. The NREL team also has significant experience with CFD modeling of marine turbines and hydrofoils, and a large high performance computational resource.
The Pterofin Skimmer is a marine energy system that harnesses energy near the water surface with an oscillating hydrofoil. The foil oscillates about a driveshaft in a pendulum motion. During each oscillation, the foil also pitches about its spanwise axis near the end of each swing such that the leading edge remains upstream in the relative flow. A counterbalance and control system regulate the wing motion, and a power system converts that motion into a single direction to turn a generator. The Skimmer has the potential to perform well in low flow environments and can be deployed in shallow areas.
Background on problem being addressed:
Past work on the Skimmer consisted of experimental prototype testing and low-fidelity modeling. Prototype testing demonstrated the viability of the concept but limited the number of parameters that could be tested. Analytical modeling gave a rough estimate of performance, but the models applied did not account for important aspects of operation, such as induction and variable lift coefficients. This work will simulate device performance for a wide range of parameters at higher levels of fidelity to provide insight as to which configurations improve performance, and which should be further optimized.
Statement of intended outcomes and what metrics will be used:
The project’s intended outcomes are: 1) insight into which geometric and operational parameters improve performance; 2) quantify performance for a specific set of parameters; 3) estimate the error associated with mid-fidelity and high-fidelity modeling. The following metrics will be evaluated: driveshaft torque and speed; mechanical power; hydrofoil pitching torque; system thrust. CFD results will be compared to experimental data at lab scale, and BEM results will be compared to CFD results at full scale.
Overview of requested support:
Pterofin is requesting support modeling their Skimmer device. The support consists of running a large parameter sweep using a reduced-order blade element momentum model, which is highly computationally efficient. Assumptions inherent in this model will limit its accuracy, especially with regards to capturing the dynamics of unsteady flow separation. However, its simplicity will allow for a large parameter sweep and provide guidance on which cases should be simulated with a higher-fidelity computational fluid dynamics (CFD) model. The CFD model will give a more accurate representation of device performance and help quantify the error associated with the BEM results. Error in the high fidelity CFD will be quantified with comparisons to previous experimental data.
Rationale for facility selection:
NREL has extensive experience in turbine and hydrofoil modeling, and open-source tools developed by NREL for wind are being adapted for marine turbines. One such tool is OpenFAST, an aero-hydro-elastic engineering model for whole turbines. Due to the unique design and operation of the Pterofin device, relative to traditional turbines, the OpenFAST rotor aero/hydrodynamics module AeroDyn will be run independently. This work requires expert knowledge of AeroDyn and its capabilities as applied to marine energy devices. The NREL team also has significant experience with CFD modeling of marine turbines and hydrofoils, and a large high performance computational resource.
