Abstract
Abstract The need for hydrokinetic turbine wake characterisation and their environmental impact has led to a number of studies. However, a small number of them have taken into account mobile sediment bed effects. The aim of the present work is to study the impact of the presence of a horizontal-axis three-bladed turbine with the flow and a mobile sediment bed. We use a series of laboratory experiments with a scaled modelled turbine installed in a flume with a mobile sandy bed at the bottom. Acoustic instruments were used to monitor flow, suspended sediment and bed behaviour. Results show a velocity decrease of about 50% throughout the water column and no flow recovery after a distance of 15 rotor diameters. Clearly visible ripples in the absence of the model turbine were replaced by horseshoe-shaped scour pit in the near wake region, and a depositional heap in the far wake. Suspended sediment differences were recorded in the streamwise direction with a possible effect of the wake as far as 15 rotor diameters. These results imply potentially important effects on the efficiency of turbine arrays, if the flow were to be lower than expected, on turbine foundations and modify coastal sediment transport.
Highlights
Energy from renewable sources is widely available from water, geothermal heat, sun, wind, biomass and wave-tidal sources
This study aims to address this gap and present for the first time an investigation of the interaction between the sediment triad flow, suspended sediment and bed [15], and a modelled turbine using experiments in a flume
Results from the ADV point measurements are presented in Fig. 7 for the mean velocity in the streamwise (U) direction, displaying the ratio of the mean velocity measured with the scaled turbine (Ufix) normalised by the mean velocity measured at x=D 1⁄4 0, y=D 1⁄4 0 location in absence of scaled turbine (Uofix)
Summary
Energy from renewable sources is widely available from water, geothermal heat, sun, wind, biomass and wave-tidal sources. Their use remains extremely difficult due to conversion processes, limited efficiencies, infrastructure, land availability, systems reliability and environmental impact [1]. The growing interest in hydro kinetic turbines and tidal stream turbines toward commercial developments requires improved understanding of the implications of array deployments. Environmental effects may include changes to both physical and ecological processes Examples of such effects are the turbid wakes 30e150 m wide and up to 10 km long which have been observed downstream of offshore wind farm arrays [2,3]. Deployments of tidal stream turbines (TST) could produce large wakes, even though the underpinning mechanisms would be more complicated due, in part, to the combination of a support structure and the moving turbine
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