Session: 41-03 Small-scale Wind Turbines

Paper Number: 121978

121978 - Design Guidelines for Arrays of Closely Spaced Darrieus Turbines 

Given the significant power coefficient enhancement that Darrieus turbines experience when installed in proximity to each other, deploying two or more closely spaced Darrieus turbines has become an attractive solution for wind applications and, mostly, in the case of hydrokinetic applications. The present study provides design guidelines for closely spaced counter rotating hydrokinetic Darrieus turbines by identifying the mutual power augmentation trends. Each individual rotor within the array is labelled based on its rotational direction relative to the neighbouring turbine, namely: inward, outward, or a combination of both. The analysis is carried out by means of two-dimensional Computational Fluid Dynamics (CFD) simulations, and it includes the assessment of instantaneous blade forces and generated torque. These aspects are examined in conjunction with the locally sampled kinematic data for each blade. The latter allowed the computation of lift and drag coefficients, contributing to a more comprehensive understanding of the physical mechanisms at play in such compact setups. The study shows that a consistent power augmentation mechanism is present regardless of the number of deployed turbines, and also in the case of an odd number of rotors that is usually not investigated in the literature. This mechanism results from suppressing the streamtube expansion thanks to the flow blockage between adjacent rotors, making the angle of attack increase, and thus in turn increasing the generated lift. This effect is more prominent at higher tip-speed ratios thanks to the narrower angle of attack cyclic variation and the higher flow blockage, shifting the optimal tip-speed ratio to higher values for arrays setups compared to standalone turbines.

Presenting Author: Omar Sherif Mohamed University of Florence

Presenting Author Biography: Omar was born in Ismailia, Egypt. He received a Bachelor of Science in Mechanical Engineering in 2017, and a Master of Science in Renewable Energy Engineering in 2020, both from the British University in Egypt. During his studies, Omar has worked as a Research Assistant at both Centre for Advanced Materials and Centre for Renewable Energy of the British University in Egypt from 2018 to 2021.
Starting from January 2022, he is attending the PhD course in Industrial Engineering at the University of Florence. His research interests include CFD and low-order modelling of wind turbines, VAWTs for low wind speed applications, passive and active boundary layer control for turbine blades, and the development of Darrieus turbines for small watercourses.

Authors:

Omar Sherif Mohamed University of Florence
Pier Francesco Melani University of Florence
Giuseppe Soraperra HE-PowerGreen s.r.l.
Alessandra Brighenti HE-PowerGreen s.r.l
Francesco Balduzzi University of Florence
Alessandro Bianchini University of Florence