Performance Analysis of Hydrofoil Shaped and Bi-Directional Diffusers for Cross Flow Tidal Turbines in Single and Double-Rotor Configurations

Stefania Zanforlin, Fulvio Buzzi and Marika Francesconi
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Stefania Zanforlin: Department of Energy, Systems, Territory and Constructions Engineering, University of Pisa, l.go Lucio Lazzarino, 56122 Pisa, Italy
Fulvio Buzzi: Department of Energy, Systems, Territory and Constructions Engineering, University of Pisa, l.go Lucio Lazzarino, 56122 Pisa, Italy
Marika Francesconi: Department of Energy, Systems, Territory and Constructions Engineering, University of Pisa, l.go Lucio Lazzarino, 56122 Pisa, Italy

Energies, 2019, vol. 12, issue 2, 1-25

Abstract: With the aim of finding efficient solutions for cross flow turbine (CFT) bi-directional diffusers able to harvest non perfectly rectilinear tidal currents, a 2D CFD analysis of ducted CFTs was carried out with focus on the effects of diffuser shape and yaw angle. The HARVEST hydrofoil shaped diffuser, equipped with a pair of counter-rotating turbines, and a bi-directional symmetrical diffuser were compared in terms of coefficient of power ( C P ), torque ripple, overall thrust on diffuser and wake characteristics. Slightly better C P were predicted for the symmetrical diffuser, due to the convergent walls that address the flow towards the blade with a greater attack angle during early and late upwind and to the viscous interactions between the turbine wakes and strong vortices shed by the diffuser. A C P ’s extraordinary improving resulted when yaw increased up to 22.5° for the hydrofoil shaped and up to 30° for the symmetrical diffuser. Similar behaviour in yawed flows also occurred in case of a ducted single rotor, demonstrating that it is a characteristic of CFTs. The insertion of a straight throat in the diffuser design proved to be an effective way to mitigate torque ripple, but a C P loss is expected.

Keywords: tidal currents; cross flow turbine; diffuser; vortex shedding; yawed flows (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2019
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (6)

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