Experimental study of bathymetry generated turbulence on tidal turbine behaviour

Abstract

In high flow velocity areas like those suitable for tidal applications, turbulence intensity is high and flow variations may have a major impact on tidal turbine behaviour. A three-bladed horizontal axis turbine model (scale 1:20) is positioned in the wake of a square wall-mounted cylinder, representative of specific in situ bathymetric variation, to experimentally study these effects in a current flume tank. Local and global loads are acquired in synchronisation with velocity measurements to study the turbine response to flow fluctuations. Velocity measurements need to be obtained close to the turbine, contrary to what is commonly considered, to properly correlate velocity and loads fluctuations. Results show that the loads phase average and their dispersion evolve according to the sheared velocity profile. We conclude that the turbine load fluctuations directly respond to the low frequency velocity fluctuations and are dominated by the turbulent structures shed from the cylinder. It is then possible to compare the effects of large coherent turbulent structures on the turbine behaviour to cases with more classical free stream turbulence commonly studied. These results provide a substantive database in high Reynolds number flows for further fatigue analysis or recommendations for turbine positioning in such flows.

A Phenomenological Study of Lab-Scale Tidal Turbine Loading under Combined Irregular Wave and Shear Flow Conditions

“…These wave-current interactions may have a direct impact on a HATT performance; for example, rotor thrust and power have been shown to decrease as the turbulence intensity (TI) levels increase [4][5][6][7], and wave-induced rotor load fluctuations can be up to three times the average loads [7][8][9][10][11][12]. A further aspect of the sea conditions faced by tidal devices is the presence of shear in the flow, which can arise due to sea bed interactions or due to the wake of upstream bathymetric features or devices [6,[13][14][15][16][17][18]. The combination of wave and current shear effects in the tidal resource will generate complex loading patterns with extremes loads, oscillatory components and stochastic components.…”

“…There have been many laboratory studies into differing aspects of the three flow artefacts discussed above. There have been many articles focused on quantifying and modelling HATT power production under turbulent flow cases with a focus on spectral characterisation and modelling of loading and power production [6,14,15,[18][19][20][21][22][23][24][25][26]. Many laboratoryscale experiments detail the effects of upstream devices both in low turbulence and high turbulence scenarios with results presented in a phenomenological sense [6,14,15,17,27,28].…”

“…Figure18. Mean power spectral density plots for torque-wise loading (Left) and thrust-wise loading (right) for all three datasets gathered at the D1 case for both CO and JSP experiments.…”

The pressure characteristics analysis of oil pulsation flow based on VMD

“…The early studies of cyclic unstable turbulence in tubes chiefly specialise in the low pulsating amplitude and high frequency of rate of flow, and valuable results have been obtained within the proper resolution of scale parameters and the discussion of the interaction mechanism between shear wave and turbulence 3 – 6 . For example, Xuan et al 7 analysed the dynamics of Reynolds stresses and turbulent kinetic energy (TKE) in Langmuir turbulence exploitation knowledge of large-eddy simulations with the wave phase resolved.…”

Performance and Wake Characterization of a Model Hydrokinetic Turbine: The Reference Model 1 (RM1) Dual Rotor Tidal Energy Converter

“…Sensing capabilities in experimental models enabled observing the impact on rotor performance resulting from varying inflow turbulence intensity, unsteady loading, blade geometry, blade pitch, blade roughness (fouling), rotor yaw, submergence and cavitation, and surface waves [6,7,9,10,[12][13][14]16,18]. In some cases, sensors connected to turbine blades provided unique observations of blade loads under varying operating and unsteady loading conditions [5,15,16,19,20]. Achieving Reynolds number independent performance results continues to be a challenge in small scale experiments, especially when combined with increased blockage ratios [5,17].…”