Unsteady hydrodynamics of a full-scale tidal turbine operating in large wave conditions

Gabriel Thomas Scarlett, Brian Sellar, Ton van den Bremer and Ignazio Maria Viola

Renewable Energy, 2019, vol. 143, issue C, 199-213

Abstract: Tidal turbines operate in a highly unsteady environment, which causes large-amplitude load fluctuations to the rotor. This can result in dynamic and fatigue failures. Hence, it is critical that the unsteady loads are accurately predicted. A rotor's blade can experience stall delay, load hysteresis and dynamic stall. Yet, the significance of these effects for a full-scale axial-flow turbine are unclear. To investigate, we develop a simple model for the unsteady hydrodynamics of the rotor and consider field measurements of the onset flow. We find that when the rotor operates in large, yet realistic wave conditions, that the load cycle is governed by the waves, and the power and blade bending moments oscillate by half of their mean values. While the flow remains attached near the blade tip, dynamic stall occurs near the blade root, resulting in a twofold overshoot of the local lift coefficient compared to the static value. At the optimal tip-speed ratio, the difference between the unsteady loads computed with our model and a simple quasi-steady approximation is small. However, below the optimal tip-speed ratio, dynamic stall may occur over most of the blade, and the maximum peak loads can be twice those predicted with a quasi-steady approximation.

Keywords: Tidal turbine hydrodynamics; Fatigue loading; Unsteady aerodynamics; Blade-element momentum theory; Dynamic stall; Wave-induced loading (search for similar items in EconPapers)
Date: 2019
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (10)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:renene:v:143:y:2019:i:c:p:199-213

DOI: 10.1016/j.renene.2019.04.123

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