DOI: 10.5061/dryad.1c59zw45d
title: Data from: Performance characteristics and bluff-body modeling of high-blockage cross-flow turbine arrays with varying rotor geometry

description: While confinement is understood to increase the power and thrust
 coefficients of cross-flow turbines, how the optimal rotor geometry
 changes with the blockage ratio---defined as the ratio between the array
 projected area and the channel cross-sectional area---has not been
 systematically explored. Here, the interplay between rotor geometry and
 the blockage ratio on turbine performance is investigated experimentally
 with an array of two identical cross-flow turbines at blockage ratios from
 35% to 55%. Three geometric parameters are varied---the number of blades,
 the chord-to-radius ratio, and the preset pitch angle---resulting in 180
 unique combinations of rotor geometry and blockage ratio. While the
 optimal chord-to-radius ratio and preset pitch angle do not depend on the
 blockage ratio, the optimal blade count increases with the blockage
 ratio---an inversion of the relationship between efficiency and blade
 count typically observed at lower blockage. To explore the combined
 effects of rotor geometry, rotation rate, and the blockage ratio on array
 performance, we utilize two bluff-body models: dynamic solidity (which
 relates thrust to the rotor geometry and kinematics) and Maskell-inspired
 linear momentum theory (which describes the array-channel interaction as a
 function of the blockage ratio and thrust). By combining these models, we
 demonstrate that the array time-average thrust coefficient increases with
 dynamic solidity in a manner that is self-similar across blockage ratios.
 Overall, these results highlight key design principles for cross-flow
 turbines in confined flow and provide insights into the similarities
 between the dynamics of cross-flow turbines and bluff bodies at high
 blockage.
description: This data was collected in the Alice C. Tyler flume at the
 University of Washington using a custom laboratory-scale two-turbine array
 test rig. The raw data for each experiment was processed using custom
 MATLAB code. Further details of the physical system and data acquisition
 methods can be found in the supporting manuscript.
description: # **Data from: Performance characteristics and bluff-body modeling of
 high-blockage cross-flow turbine arrays with varying rotor geometry**
 Dataset: [https://doi.org/10.5061/dryad.1c59zw45d](https://doi.org/10.5061/dryad.1c59zw45d) Supporting Article (*Journal of Renewable and Sustainable Energy*): [https://doi.org/10.1063/5.0272110](https://doi.org/10.1063/5.0272110) Supporting Article (Open-Access on arXiv): [https://doi.org/10.48550/arXiv.2410.19165](https://doi.org/10.48550/arXiv.2410.19165) This dataset represents 180 cross-flow turbine array experiments exploring the effects of the blockage ratio (B), blade count, chord-to-radius ratio (c/R), and preset pitch angle on array performance at high blockage. The experimental methods and results are described in detail in our paper: "Performance characteristics and bluff-body modeling of high-blockage cross-flow turbine arrays with varying rotor geometry. The experiments were conducted in the Alice C. Tyler flume at the University of Washington. ## **Description of data file and variables** The experimental data for all experiments is provided as a single file, `HuntEtAl_GeometryBlockage_dataset.mat`, which contains two variables: `data` and `comments`. ## `data` The `data` variable contains a structure of aggregate array performance data, flow field data, and rotor geometry details for all array experiments. Each row of the structure provides performance, flow field, and geometry data from an individual turbine experiment. Each experiment corresponds to a unique combination of the blockage ratio, blade count, chord-to-radius ratio, and preset pitch angle tested across a range of tip-speed ratios. The fields of `data` are categorized and described below: **Experiment specification** `label`: Identifier of the blockage, blade count, chord-to-radius ratio, and preset pitch angle configuration of each turbine tested. `beta_nom`: Nominal blockage ratio [fraction] corresponding to the experiment. **Geometric specification** * `N`: Number of blades. * `R`: Radial distance to quarter-chord point on blade [m]. * `RPrime`: Radius of the outermost circle swept by the turbine blades [m]. * `cToR`: Chord-to-radius ratio. * `alpha_p`: Preset pitch angle [degrees]. Negative angle corresponds to "toe-out" pitch. * `solidity`: Solidity of each turbine in the array, calculated as Nc/(2*pi*R). * `dynSolidity`: Dynamic solidity of each turbine in the array as a function of solidity and TSR. **Time-average performance** * `TSR`: Time-average tip-speed ratio. * `TSROpt`: Tip-speed ratio corresponding to maximum blade-level array-average performance. * `CP`: Time-average TURBINE LEVEL array-average coefficient of performance as a function of TSR. * `CP_blade`: Time-average BLADE LEVEL array-average coefficient of performance as a function of TSR. * `CP_cycle_std`: Standard deviation of the cycle-average values of CP at each TSR. Equivalent for CP_blade. * `CT`: Time-average array-average coefficient of thrust as a function of TSR. * `CT_cycle_std`: Standard deviation of the cycle-average values of CT at each TSR. * `CL`: Time-average rotor-average coefficient of lateral force as a function of TSR. * `CL_cycle_std`: Standard deviation of the cycle-average values of CL at each TSR. * `CF`: Time-average array-average coefficient of resultant horizontal force (i.e., the vector sum of instantaneous CT and CL) as a function of TSR. * `CF_cycle_std`: Standard deviation of the cycle-average values of CF at each TSR. **Phase-median performance** * `theta`: Azimuthal positions [degrees] that correspond to the provided phase-median data (e.g., `CP_phase`). * `CP_phase`: Phase-median TURBINE LEVEL array-average coefficient of performance as a function of TSR and theta. Rows correpsond to each TSR whereas columns correspond to each theta. * `CP_blade_phase`: Phase-median BLADE LEVEL array-average coefficient of performance as a function of TSR and theta. Rows correpsond to each TSR whereas columns correspond to each theta. * `CT_phase`: Phase-median array-average coefficient of thrust as a function of TSR and theta. Rows correpsond to each TSR whereas columns correspond to each theta. * `CL_phase`: Phase-median rotor-average coefficient of lateral force as a function of TSR and theta. Rows correpsond to each TSR whereas columns correspond to each theta. * `CF_phase`: Phase-median array-average coefficient of resultant horizontal force as a function of TSR and theta. Rows correpsond to each TSR whereas columns correspond to each theta. **Flow parameters** * `Uinf`: Freestream velocity [m/s] as a function of TSR. * `h`: Far upstream dynamic depth [m] as a function of TSR. * `temp`: Water temperature [C] measured during the experiment. * `TI`: Turbulence intensity [%] measured during the experiment. * `beta`: Channel blockage ratio [fraction] as a function of TSR as measured during the experiment. * `Re_D`: Diameter-based Reynolds number as a function of TSR as measured during the experiment. * `Fr_h`: Depth-based Froude number as a function of TSR as measured during the experiment. * `subNorm`: Normalized submergence depth (s/h) as a function of TSR as measured during the experiment. **Linear momentum theory** `ubUinf`: Bypass velocity predicted from open-channel linear momentum theory (normalized by `Uinf`) . `uwUinf`: Wake velocity predicted from open-channel linear momentum theory (normalized by `Uinf`) .' **Bluff-body scaling** `CT_bluff`: `CT` re-scaled by the corresponding bypass velocity, `ubUinf`. `TSR_bluff`: `TSR` re-scaled by the corresponding bypass velocity, `ubUinf`.' `dynSolidity_bluff`: Dynamic solidity calculated using the bluff-body scaled TSR. ## `comments` The `comments` variable contains a structure that describes the meaning and format of each field in the `data` structure as provided above. Each field of `comments` contains a description for the corresponding field in `data`. ## **Code/Software** It is recommended that MATLAB/Octave is used to view this data. The code used to apply open-channel linear momentum theory and bluff-body scaling as described in the manuscript is [openly available on GitHub.](https://github.com/aidan-hunt/turbine-confinement-models)