Impact of turbulence on power production by a free-stream tidal turbine in real sea conditions

Abstract

An experiment was performed to study the power production by a Darrieus type turbine of the Dutch company Water2Energy in a tidal estuary. Advanced instrumentation packages, including mechanical sensors, acoustic Doppler current profiler (ADCP), and velocimeter (ADV), were implemented to measure the tidal current velocities in the approaching flow, to estimate the turbine performance and to assess the effect of turbulence on power production. The optimal performance was found to be relatively high (C p ~ 0.4). Analysis of the power time history revealed a large increase in magnitude of power fluctuations caused by turbulence as the flow velocity increases between 1 and 1.2 m/s. Turbulence intensity does not alone capture quantitative changes in the turbulent regime of the real flow. The standard deviation of velocity fluctuations was preferred in assessing the effect of turbulence on power production. Assessing the scaling properties of the turbulence, such as dissipation rate, , the integral lengthscale, , helped to understand how the turbulence is spatially organized with respect to turbine dimensions. The magnitude of power fluctuations was found to be proportional to L and the strongest impact of turbulence on power generation is achieved when the size of turbulent eddies matches the turbine size.

A comprehensive assessment of turbulence at a tidal-stream energy site influenced by wind-generated ocean waves

“…November 15,2019 found to strongly increasing the magnitude of the power fluctuations generated by TEC [8] and thus, deteriorating the quality of the electricity supply [9].…”

“…Although, numerous reports of attempts made to quantify the structure of the flow and associated turbulence have been recently reported (e.g., [3,8,15,16,17]), the turbulent features of the tidal flow are still poorly understood and described.…”

“…Acoustic Doppler current profilers (ADCPs) using four diverging beams, are commonly used for flow characterization and TEC performance monitoring at tidal energy sites. Such instruments allow for the estimation of the turbulent kinetic energy (TKE) dissipation rate using either spectral (e.g., [3,8,15]) or structure function methods (e.g., [3,19,20]).…”

One year of measurements in Alderney Race: preliminary results from database analysis

“…[44][45][46]), to determine power quality fluctuations (e.g. [1,11]) and to assess fatigue and extreme loading on TECs (e.g. [9,47,48]).…”

“…Required both for individual TECs and arrays of TECs, an accurate description of a highly energetic and highly turbulent tidal flow helps engineers to improve the performance of TECs (e.g. [10,11]). This contributes to the reliable and predictable production of grid quality power at costs competitive with other forms of energy generation [12].…”