# Design Optimization of a Cross-Flow Air Turbine for an Oscillating Water Column Wave Energy Converter

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## Abstract

**:**

## 1. Introduction

## 2. CFD Setup

#### 2.1. Numerical Model

#### 2.2. Data Analysis

## 3. Experimental Setup

#### 3.1. Experimental Apparatus

#### 3.2. Measurement Instruments and Experiment Procedures

^{®}ULS sensor (model: USS 20130; FSC: 200–1300 mm; resolution: 0.18 mm) was employed to measure the piston displacement precisely, although the piston motion was governed by the servo motor within the preset period and stroke. With the measured piston displacement, the flow rate through the turbine was calculated. The pressure transducer (model: DWSD0020R1AA; FSC: 0–20 kPa; accuracy: 0.075% of FSC) was used to measure differential pressure between the inlet and outlet of the turbine. Digital signals from all sensors were transmitted to data logger (model: PT-1624 Powertron) and stored simultaneously.

## 4. Results and Discussion

#### 4.1. Geometric Optimization

#### 4.2. Overall Performance in Reciprocating Flows

#### 4.3. Validation of Numerical Model with Experiment Result

## 5. Conclusions

- The optimized model had 36 blades of the rotor with 3 mm thickness and 0.38 throat width of the nozzle.
- The geometric optimization of the nozzle was the most sensitive among the selected design variables. This indicates greater possibility for enhancing its performance in future work.
- The maximum efficiency of the optimized model was 0.611, which was 1.7% larger than that of the reference model.
- The band width of the model significantly widened as the flow coefficient increased.
- The optimized model in reciprocating flows had more improved operating range with higher efficiency than the steady-state performance, but the peak performance decreased by 4.3%.
- The averaged difference between the numerical result and the experimental result was 3.5%, which indicates that the numerical model was able to predict the turbine performance with high accuracy.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 5.**Effect of thickness and number of rotor blades on the turbine performance at 350 rpm constant rotational speed.

**Figure 6.**Effect of rotational speed and number of rotor blades on the turbine performance with 3 mm blade thickness.

**Figure 7.**Effect of nozzle throat width on the turbine performance with 700 rpm and 3 mm blade thickness.

**Figure 8.**Comparison of velocity vectors between NZ = 0.26 and 0.38 at ω = 700 rpm, Nb = 36, and t* = 3 mm.

**Figure 12.**Comparison of the reference and optimized model performance in steady and reciprocating air flows by CFD.

**Figure 13.**Comparison of the cycle-averaged performance of numerical and experimental turbines in reciprocating air flows.

Design Parameter | Value |
---|---|

Outer diameter, D1, (m) | 0.3 |

Inner diameter, D2, (m) | 0.24 |

No. of blades, Nb | 24, 30, 36 |

Thickness of blades, t*, (mm) | 3, 4, 5 |

Nozzle entry angle, δ, (°) | 90 |

Angle of attack, α, (°) | 18 |

Blade inlet angle, β1, (°) | 30 |

Blade exit angle, β2, (°) | 90 |

Rotor and nozzle width, W, (m) | 0.4 |

Rotational speed, ω, (rpm) | 350 and 700 |

$\mathrm{Nozzle}\text{}\mathrm{throat}\text{}\mathrm{width},\text{}\mathrm{NZ},\text{}{S}_{0}/{R}_{1}\delta $ | 0.26 (original), 0.3, 0.34, 0.38 |

Design Parameter | Value |
---|---|

Outer diameter, D1, (m) | 0.3 |

Inner diameter, D2, (m) | 0.24 |

Width of turbine, W, (m) | 0.4 |

Tip clearance, (mm) | 1 |

No. of blades, Nb | 36 |

Thickness of blades, t*, (mm) | 3 |

Nozzle entry angle, δ, (°) | 90 |

Angle of attack, α, (°) | 18 |

Blade inlet angle, β1, (°) | 30 |

Blade exit angle, β2, (°) | 90 |

Rotor and nozzle width, W, (m) | 0.4 |

Rotational speed, ω, (rpm) | 350 and 700 |

$\mathrm{Nozzle}\text{}\mathrm{throat}\text{}\mathrm{width},\text{}\mathrm{NZ},\text{}({S}_{0}/{R}_{1}\delta )$ | 0.38 |

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**MDPI and ACS Style**

Kang, H.-G.; Lee, Y.-H.; Kim, C.-J.; Kang, H.-D.
Design Optimization of a Cross-Flow Air Turbine for an Oscillating Water Column Wave Energy Converter. *Energies* **2022**, *15*, 2444.
https://doi.org/10.3390/en15072444

**AMA Style**

Kang H-G, Lee Y-H, Kim C-J, Kang H-D.
Design Optimization of a Cross-Flow Air Turbine for an Oscillating Water Column Wave Energy Converter. *Energies*. 2022; 15(7):2444.
https://doi.org/10.3390/en15072444

**Chicago/Turabian Style**

Kang, Hong-Goo, Young-Ho Lee, Chan-Joo Kim, and Hyo-Dong Kang.
2022. "Design Optimization of a Cross-Flow Air Turbine for an Oscillating Water Column Wave Energy Converter" *Energies* 15, no. 7: 2444.
https://doi.org/10.3390/en15072444