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The Wenchuan earthquake greatly reduced the forest water conservation capacity along the banks of Minjiang River. With the intensified soil erosion and the rapid increasing sediment transport, the sediment erosion of hydraulic turbines running on the river has become more and more serious, especially of high head Francis turbines. In this study, the k-ε multiphase flow turbulence model was used to calculate the sediment-water flow of a high head Francis turbine with long and short blades in Minjiang River. The distribution pattern of sediment concentration (sediment volume fraction) on the blade surface shows that the sediment particles mainly gather on the outlet edge at 10% of the blade height on the suction surface of the long blade, while the sediment concentration on the surface of the short blade is small. The erosion of the 0Cr13Ni5Mo runner blade was tested by the flow around erosion method, and the erosion amount on the blade surface in the severe erosion area was obtained. Based on the test data of erosion and the numerical calculation results of sediment flow, a formula to calculate the sediment erosion rate of flow passage components with 0Cr13Ni5Mo material was given for turbines operating in Minjiang River. By using this formula, the sediment erosion of flow passage components in hydraulic turbines with 0Cr13Ni5Mo or similar materials operating in Minjiang River can be predicted. [ABSTRACT FROM AUTHOR]

Abstract In-stream hydrokinetic energy conversion devices can be deployed in large scale rivers to produce energy with minimal infrastructure costs. They are however shown to actively interact with the channel bathymetry and sediment transport generating a scour and deposition pattern similar to bridge pier. Symmetric, streamwise, aligned turbine installations have shown to introduce only local effects, yet complex configurations may trigger non-local morphodynamic instabilities. Experimental investigations, based on continuous spatio-temporal measurements of bed topography, explore a number of inflow conditions and siting strategies for axial-flow hydrokinetic turbine models. Results show that asymmetric turbine installations in a portion of the channel cross section may introduce weak non-local deformation of the mean bed topography and alter bedform migration velocities. Geomorphic effects become stronger with increasing shear stress and with rotors deployed up to half of the channel width, resulting in mean flow distortion within the channel cross section and inducing an alternating scour-deposition pattern resembling the signature of steady, forced fluvial bars. Non-local effects can be mitigated, narrowing the turbine array, or amplified, distributing turbines in a vane-like installation, leading to different estimates of energy production averaged at the power plant scale. A discussion on the key quantities governing geomorphic effects and the potential benefits of asymmetric turbine deployments is provided as a preliminary guideline towards the expansion of Marine Hydrokinetic energy in rivers. Highlights • Experiments on axial-flow hydrokinetic turbines in fluvial environment are presented. • Asymmetric turbines siting induces weak non-local mean flow and mean bed distortions. • Cumulative wake effects alter the mean flow and the bedform convection velocity. • Non-local geomorphic effects can be mitigated with strategic array configurations. • Power performance were estimated and included in a new MHK array coefficient. [ABSTRACT FROM AUTHOR]

The location of a wave farm and, in particular, its distance to the coast is one of the key aspects in a wave energy project. The effects of the farm on the coast, which can be instrumental in mitigating storm-induced erosion and thus contribute to coastal defence, are sometimes disregarded in selecting its location, possibly due to the inexistence of an ad hoc methodology. In this context, the objective of this work is to examine the influence of the farm-to-coast distance through a sensitivity analysis in a case study: Perranporth (UK). The impacts of a wave farm on the beach morphology are examined in four scenarios with different farm-to-coast distances using a high-resolution suite of numerical models. The results show that a wave farm closest to the beach offers the highest degree of coastal protection (up to 20% of beach erosion reduction). The downside of this enhanced coastal protection is that the wave resource available at this location would be slightly smaller (approx. 10%) than in the case of the wave farms further from the coast. More generally, we find that the farm-to-coast distance is a critical variable in determining the effectiveness of a wave farm for coastal defence. [ABSTRACT FROM AUTHOR]