Confinement-Exploiting Cross-flow Turbine Arrays

Brian Polagye, University of Washington

ARPA-E SHARKS

Team Overview

Scott Jenne

Elena Blackman

Dr. Richard Wiebe

Dr. Mike Motley

Dr. Brian Johnson

Dr. Steve BruntonDr. Brian Polagye

Dr. Owen Williams

Dr. Jennifer Franck

Technical Overview‣ Control co-design of cross-flow turbine arrays with high confinement

– Exploit confinement, unsteady hydrodynamics, and inter-turbine interactions

– Rapid experimental optimization to full-scale validation through simulation

Experiments

Electrical Model

Est. LCOE

Powertrain efficiency

P, F

Laboratory Control Optimization

P

Control Update

Experiment (PIV)

Simulation

Validated Simulation

Structural Simulation

Full-scale pressure fields

Economic Model

Structural design

Full-scale Evaluation

New Candidate Geometry

ω(θ)

Economic Model

Prior Work‣ Three foundational elements

– Confinement: Betz limit exceeded in experiments1

– Control: Intracycle control experimentally demonstrated > 50 % increase in power output relative to fixed tip-speed ratio2

– Geometry: Preset pitch, chord-radius ratio, and blade count all affect turbine performance

‣ No prior work has identified potential for simultaneous optimization of these factors

– Consequently, we are likely unaware of substantial improvements that are possible for cross-flow turbines

1 McAdam, R.A., Houlsby, G.T. and Oldfield, M.L.G. (2013) Experimental measurements of the hydrodynamic performance and structural loading of the Transverse Horizontal Axis Water Turbine: Part 1. Renewable Energy, 59.

2 Strom, B., Brunton, S., and Polagye, B. (2017) Intracycle angular velocity control of cross-flow turbines. Nature Energy, 2. doi: 10.1038/nenergy.2017.103

Effects of blade number, chord-to-radius ratio, preset pitch angle, and Reynolds number on maximum CP

Project Impact

‣ Benefit to technology developers

– Highlight opportunities in design space

– Apply similar techniques to propriety systems with unsteady fluid dynamics to reduce LCOE (cross-flow turbines, oscillating foils)

‣ Benefit to site developers

– Highlight LCOE reduction potential for confinement-exploiting arrays for all turbine variants

– Motivate approaches to site development beyond micrositing for individual turbines

‣ Benefit to industry

– Potential to increase estimates for technically available resources at river and tidal current sites

Yang, Z., Wang, T., Branch, R., Xiao, Z. and Deb, M., 2021. Tidal Stream Energy Resource Characterization in the Salish Sea. Renewable Energy.

Anticipated Challenges‣ Challenge 1: What if full-scale LCOE is insensitive to

choice of geometry and control strategy?

– Impact: Unable to meet performance targets

– Mitigation: Rapid iteration with validated simulations (performance and flow fields) to identify problem and redirect efforts as early as possible

PIV 2D RANS

Dave, M., Strom, B., Snortland, A., Williams, O., Polagye, B. and Franck, J.A., 2021. Simulations of Intracycle Angular Velocity Control for a Crossflow Turbine. AIAA Journal, 59(3), pp.812-824.

Anticipated Challenges‣ Challenge 2: How can we ensure we haven’t

missed part of the geometric design space?

– Geometric space is vast and difficult to explore experimentally

– Mitigation: Bayesian experimental optimization to identify portions of design space with high uncertainty and potential for low LCOE

– Demonstrated potential to map coordinated control parameter space with 50% fewer experiments

Scherl, I., Brunton, S., and Polagye, B. (2021) Paramter modeling of a two cross-flow turbine array. 14th European Wave and Tidal Energy Conference, Plymouth, U.K., Sep. 5-9.

Path to Target LCOE

‣ Approach

– Step change increase in CP, utilizing potential and kinetic energy in moving water: CP > 1.3

– Maintain high generator and drivetrain efficiencies while employing intracycle control

– Limit CT increase to 1.5x (Compared to 3x increase in CP)

‣ Environmental and societal compatability

– Intracycle control reduces collision risk and noise: achieves high efficiency at relatively low average tip-speed ratio

– “On demand” migration and transportation corridors available shutting down sections of array

7

Tech to Market Plan

‣ Design use cases– Focus on river for remote communities, but

consider potential for large-scale river and tidal currents

– Target LCOE < 8 ¢ / kWh

‣ Demonstrate early-stage market benefits– Reduce need for “micro-siting” individual

turbines

– Apply turbine optimization framework to proprietary designs

‣ Commercialization barriers– Requires “high” confinement to achieve

LCOE targets – elevated environmental and economic risk for initial array