1. A Test-Bed Design Characterization of Tidal Turbine Flows Patrick Bates Russell Dunn Jacob Folz Scott Lessard Eric M. Martin Richard Peale University of Maine, Department of Mechanical Engineering Introduction Over the past decade there has been intense development of In-Stream Tidal power generation as a viable sustainable and renewable energy source. Many companies have designed proprietary turbines; little published data exists key aspects of In-Stream tidal turbine flows, including basic performance characteristics, wake flow patterns, turbine array interaction effects and surface profile effects. This poster presents the development of a test platform for efficiently characterizing the performance and flow patterns of scale model tidal turbine designs. The University of Maine and Maine Maritime Academy created this testing capability as part of a larger effort, which aims to create an internal structure that can achieve the following: Procedure Using the designed and fabricated test bed, ran a controlled experiment to develop dimensional and non-dimensional performance curves. Created flow through scaled model of a tidal turbine (Figure 8) in a 100’ long tow tank by attaching test bed to movable carriage (Figure 3) Ran carriage at three controllable speeds and multiple torsional loads Data collected using Data Acquisition System (Figure 7) Discussion The dimensional curves (Figure 11) follows a partial power curve for the high end angular velocity of the turbine. Further data points at lower rotational speeds would provide a full scale power curve for the turbine. This would show the optimum rotational velocity for the turbine to run at its highest power efficiency. In the non-dimensional performance curve (Figure 12), the points collapse to a single curve for the middle and higher flow velocities, indicating that the test apparatus was properly measuring the turbine performance. The lower speed data may have suffered from the lower measurement forces due to the internal friction in the test bed system, but the number of data points collected was insufficient to make any concrete conclusions. Acknowledgements This project was made possible with the contributions by Mick L. Peterson, Meg Smith, Mo Shahinpoor, and the Department of Mechanical Engineering. Rich Kimball and students from Maine Maritime Academy were an essential part in designing, fabricating, and testing the test bed. The AMC and Art Pete aided in the fabrication process, along with Neil Greenberg. References D’Epagnier, Chung, Stanway and Kimball, 2007: An Open sourced Parametric Propeller Design Tool; MTS/IEEE Oceans 2007 Conference, Vancouver, B.C. Zeh,M.: Development of a Six Axis Dynamometer for Tow Tank Testing; Undergraduate Capstone Project, April 2006 Maine Maritime Academy, Castine Me. Figure 1: Tidal Power Site at Bagaduce Narrows Figure 2: Rendering of potential Tidal Turbine Farm Figure 3: Test Bed setup in wave tank Strut: (Figure 6) Hydrodynamic extension Solid, welded, streamlined extension for complete lower driveline submersion Two side-by-side hollow aluminum airfoil struts connect Upper Driveline System to Lower Driveline System Top end of struts welded to connector plate for tensioning chain Bottom end of strut contoured to OD of Nacelle for hydrodynamic efficiency High efficiency chain encapsulated by struts Nylon tube within strut to reduce friction on chain Figure 4: 3D Computer Model of Driveline Figure 7: Wiring Diagram of Data Acquisition Assembly Develop a rapid design/build/test sequence for rapid development of turbine designs Create a series of baseline turbine designs using this rapid development process Generate detailed performance and flow field data for this design, which is publicly available Provide these resources to the public and turbine development community Upper.500” stainless steel drive shaft Three supporting, self aligning Rylon linear bearings Incremental Rotary Encoder coupled to the upper plate shaft DC stepper motor to provide rotational resistance Two ABS skate wheels reducing friction within motor Torque measuring reactant force gimble with a S-Type Load Cell Six-axis dynamometer which suspends driveline with necked slender rods and collects drag force data High efficiency steel chain and nylon sprocket for trasmision of rotational motion from lower to upper driveline Figure 6: 3D Computer Model of Struts Figure 8: 3D printed OpenProp propeller Results Figures 9 -12 show experimental data, equations utilized, and performance curves of the turbine. Collected average steady state angular velocity and average torsional load from Figure 9 to develop dimensional performance curves shown in Figure 11 Applied equations from Figure 10 to show the precision of the test bed and performance of turbine design shown in Figure 12 Figure 9: Raw data from test run Figure 11: Dimensional performance Figure 12: Non-dimensional performance Conclusion A test bed for the testing of scale model tidal turbines was developed and implemented in the University of Maine tow tank. A sample turbine was tested which successfully demonstrated the test beds measurement capabilities. Data was collected over a range of speeds and it was shown that the non-dimensionalized power curves collapsed to a single performance curve as expected. This was used to validate the performance of the test bed measurement system. Figure 1 shows the tidal passage in the Bagaduce narrows, a site being studied by Maine Maritime Academy as a potential tidal energy site. In- Stream tidal turbines extract energy from the kinetic energy of a tidal flow, as opposed to the traditional tidal barrage dam, which utilizes a head rise created by a dam for the energy source. Tidal In-Stream systems would look more like underwater wind farms, using an array of turbines located along high velocity tidal flow channels, as seen in Figure 2. Design The tidal turbine test bed was engineered to test the performance of tidal turbine designs in an overhead carriage tow tank. Many different design matrices were used to select the current design.. The final design Figure 3 shows the entire test bed assembled contained: The Test Bed Five Sub-Assemblies: Instrumentation to read torque, rotational velocity, and frontal force Multidirectional support and force measurement capability Streamlined extension Housing and universal driveline for turbine mounting Data collection of instrumentation output Upper Driveline: (Figure 4) Instrument mounting Data Acquisition: (Figure 7) Acquire, condition, and store data Instrumentation: Angular velocity of shaft – Incremental Rotary Encoder Frontal drag force – 100 lbs. S-Type Load Cell Reaction force from resistance torque – 50 lbs. S-Type Load Cell Signal Conditioners convert instrumentation output to 0-5 Volts DAQ Unit supplies LabVIEW with conditioned data Interactive program for data readout and storage Power Coefficient: Tip Speed Ratio: Figure 10: Equations used in non-dimensional performance curves Figure 5: 3D Computer Model of the Nacelle with a Section View Nacelle & Lower Driveline: (Figure 5) Hydrodynamic driveline containment 3.50” OD, 12” long, internally threaded aluminum pipe UHMW Polyethylene bearing fixture insert Two unsealed stainless steel ball bearings Stainless steel.500” shaft with spherical thrust transmitting end and threaded end for turbine mounting Threaded UHMW tail cone to maintain converging streamline flow Nylon sprocket and stainless steel chain for efficient power transmission Threaded UHMW nose cone to reduce flow separation and support shaft bearing Dynamometer: (Figure 3) Support and force measurement Six-axis force measurement capability Force captured parallel to velocity vector of carriage motion S-Type load cell connected to upper driveline Dynamometer frame bolted to carriage for rigid support Designed and built by Matt Zeh of MMA (Zeh 2006)