# Experimental Assessment of Flow, Performance, and Loads for Tidal Turbines in a Closely-Spaced Array

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## Abstract

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## 1. Introduction

#### 1.1. Previous Studies of Tidal Stream Turbine Arrays

#### 1.2. Other Studies Using the Supergen UKCMER Tidal Turbines

## 2. Experimental Set-Up and Methods

#### 2.1. The FloWave Ocean Energy Research Facility

^{2}region of relatively straight uniform flow ($\pm 10\%$) in the tank centre. Baseline turbulence characterisation of the tank’s test area was conducted by Sutherland et al. [26]. Turbulence intensity ${I}_{U}$ at $0.8$ m/s is 5–10% and integral lengthscale ${\ell}_{U}$ is typically in the range 0.1 m to 0.5 m. At the primary turbine location these values are approximately 8% and $0.3$ m.

#### 2.2. Turbines and Instrumentation

#### 2.3. Array Configurations

#### 2.4. Flow Measurements

## 3. Influence of Turbine Arrays on Flow Conditions

#### 3.1. Spatial Analysis of Flow Variation

#### 3.2. Frequency Domain Analysis of Spatial Flow Variation

## 4. Influence of Turbine Array on Loading and Power

#### 4.1. Time-Domain Turbine Response

#### 4.2. Frequency-Domain Turbine Response

## 5. Discussion

## 6. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Abbreviations

AC | Array Configuration |

ADV | Acoustic Doppler Velocimeter/Velocimetry |

FFT | Fast Fourier Transform |

RBM | Root Bending Moment |

TSR | Tip-Speed Ratio |

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**Figure 1.**Sectional schematic of FloWave basin showing: (

**A**) wavemaker paddles around circumference; (

**B**) turning vanes and flow conditioning filters; (

**C**) current drive impeller units; (

**D**) buoyant raisable floor ( 15 mØ) below test area [25].

**Figure 2.**Turbine array installed in FloWave, as the floor descends after installation. Fully instrumented primary turbine (red fairing) in the centre between front turbines (yellow and blue). Array layout and configurations tested are shown in Figure 3. Grid on tank floor relative to tank centre, with 0.5 m spacing.

**Figure 3.**(

**left**) Three turbine array layout, and (

**right**) four configurations tested: AC0 empty tank, AC1 primary turbine only, AC2 upstream turbines only, and AC3 full array.

**Figure 4.**Transect along centreline of array ($Y\phantom{\rule{-1.111pt}{0ex}}/\phantom{\rule{-0.55542pt}{0ex}}D=0$) at hub height. Sub-panels show mean velocity $\overline{U}$, mean velocity relative to empty tank $\Delta \overline{U}$, standard-deviation ${\sigma}_{U}$, and turbulence intensity ${I}_{U}$.

**Figure 5.**Transect along primary turbine centreline ($Y\phantom{\rule{-1.111pt}{0ex}}/\phantom{\rule{-0.55542pt}{0ex}}D=0$), showing inflow and wake at varying rotational speed for configuration AC1, with AC0 for comparison.

**Figure 6.**Variation of flow between turbine locations. Subplots show (left) X–Y velocity vectors relative to turbine/blade positions, and (right) $\overline{U}$$\overline{V}$$\overline{W}$ at points on five streamwise transects. For details of array layout and configurations tested see Figure 3.

**Figure 7.**Example spectral density plots for streamwise velocity component U at seven positions for configuration AC3 with all three turbines operating at 90 rpm.

**Figure 9.**Average and standard deviation of thrust and power of the turbine plus root bending moment of a blade all as a function of rotational speed. Each plot shows these forces/moments for the primary turbine with the front two turbines operating at three different rotational speeds (AC3) and also shows the comparable single turbine case (AC1).

**Figure 10.**Spectral density plots of the thrust and the blade root bending moment experienced by the primary turbine, with the front two turbines (AC3) and from the single turbine case (AC1). All turbines operating at 90 rpm.

**Table 1.**Key turbine dimension (from [17]).

Rotor diameter (mm) | 1200 | ($1D$) | |
---|---|---|---|

Nacelle length (mm) | 1030 | ||

Nacelle diameter (mm) | hub to tower | 120 | |

beyond tower | 160 | ||

Hub height (mm) | 1000 | ($0.83D$) | |

Tower diameter (mm) | 102 | ||

Distance from rotor plane to tower axis (mm) | 486 | ($0.4D$) |

Instrumentation | Variables Measured | Sample Rate [Hz] |
---|---|---|

Vectrino Profiler ADV | Velocity components, U, V, W. | 100 |

Bespoke TST Instrumentation | Torque, T, | 256 |

Thrust, Q, | ||

Streamwise root bending moment, $RBM$, | ||

Rotational position, $\theta $. |

**Table 3.**Thrust and power of the turbine plus root bending moment of a blade for selected rotational speeds. Values given for model scale and full scale equivalent.

Measured Model Scale (0.8 m/s) | Full Scale Equivalent (3.1 m/s) | |||||||
---|---|---|---|---|---|---|---|---|

Array Config. | Front Turbines rpm | Primary Turbine rpm | Thrust [N] | Power [W] | Blade RBM [Nm] | Thrust [kN] | Power [MW] | Blade RBM [MNm] |

AC1 | — | 58 | 225.5 | 125.0 | 25.72 | 761.1 | 1.635 | 1.302 |

AC1 | — | 70 | 244.9 | 127.7 | 27.98 | 826.6 | 1.670 | 1.417 |

AC1 | — | 90 | 263.8 | 124.4 | 30.25 | 890.3 | 1.626 | 1.531 |

AC1 | — | 104 | 267.5 | 114.0 | 30.86 | 902.9 | 1.490 | 1.562 |

AC3 | 58 | 90 | 274.9 | 129.4 | 31.27 | 927.9 | 1.691 | 1.583 |

AC3 | 70 | 90 | 271.4 | 130.6 | 31.47 | 916.1 | 1.707 | 1.593 |

AC3 | 90 | 58 | 234.0 | 129.3 | 26.32 | 789.9 | 1.690 | 1.333 |

AC3 | 90 | 70 | 258.6 | 136.2 | 29.27 | 872.7 | 1.780 | 1.482 |

AC3 | 90 | 90 | 279.9 | 134.6 | 31.96 | 944.7 | 1.759 | 1.618 |

AC3 | 90 | 104 | 290.2 | 129.1 | 33.35 | 979.5 | 1.688 | 1.688 |

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## Share and Cite

**MDPI and ACS Style**

Noble, D.R.; Draycott, S.; Nambiar, A.; Sellar, B.G.; Steynor, J.; Kiprakis, A.
Experimental Assessment of Flow, Performance, and Loads for Tidal Turbines in a Closely-Spaced Array. *Energies* **2020**, *13*, 1977.
https://doi.org/10.3390/en13081977

**AMA Style**

Noble DR, Draycott S, Nambiar A, Sellar BG, Steynor J, Kiprakis A.
Experimental Assessment of Flow, Performance, and Loads for Tidal Turbines in a Closely-Spaced Array. *Energies*. 2020; 13(8):1977.
https://doi.org/10.3390/en13081977

**Chicago/Turabian Style**

Noble, Donald R., Samuel Draycott, Anup Nambiar, Brian G. Sellar, Jeffrey Steynor, and Aristides Kiprakis.
2020. "Experimental Assessment of Flow, Performance, and Loads for Tidal Turbines in a Closely-Spaced Array" *Energies* 13, no. 8: 1977.
https://doi.org/10.3390/en13081977