Seabed Scour Characteristics And Prediction Model Of Vertical-axis Tidal-current Turbine

As the world's energy demand increases,many large-scale tidal turbines are installed around the world.When the water flows through the turbine pile foundation,the seabed can be washed.Seabed scour causes the turbine to be unstable or even cause significant economic losses.Therefore,research on the seabed scour induced by tidal current turbine is crucial.However,due to the complicated flow field distribution of vertical axis tidal current turbines,the scientific community is still in the initial stage of seabed scour research.In this paper,a semi-empirical model for the prediction of seabed scour induced by vertical-axis tidal current turbine is proposed through a series of model experiments.The model includes the prediction formula of maximum scouring depth and temporal development of scour depth.This paper also establishes a three-dimensional CFD numerical model for predicting the seabed scour of vertical axis turbines.The proposed CFD model is used to simulate the full-scale turbine scour process.The main research contents and conclusions are as follows:(1)The empirical model for predicting the maximum scouring depth of the vertical axis tidal current turbine is proposed.Two parameters related to turbine are mainly considered: tip clearance and rotor radius.In this study,a series of 3D printed vertical axis turbine models were placed in a circulating water tank to study their local scour characteristics.The current experimental results propose that the maximum scour depth is about 80% deeper than scour induced by single pile.Scour depth increases with the decrease of tip clearance.Scour depth increases firstly and then decrease with the increase of rotor radius.Based on experimental results,an empirical model of seabed scour induced by vertical axis tidal current turbine is proposed to predict the maximum scour depth and scour profiles.(2)The empirical model for predicting the temporal evolution of seabed scour induced by vertical axis turbine is proposed.Temporal scour depths and profiles at various turbine radius and tip clearance were studied by flume experiments.The scour hole develops rapidly in the initial process and grows gradually.The equilibrium of scour hole is reached after 180 mins.Empirical equations are proposed to predict the temporal scour depth around turbine.These equations are in good agreement with the experimental data.(3)The CFD model for simulating seabed scour induced by tidal current turbine is established,and the simulation analysis of the seabed scouring of the full-scale tidal energy turbine is completed for the first time.The numerical model consists of a k-turbulence model,a sediment transport model and a sand-sliding model.The transient flow field calculation is coupled with the bed deformation calculation to simulate the development of the scour hole.The data proves that the proposed CFD model can capture the main features of turbine scouring.However,the numerical model underestimates the equilibrium scouring depth by about 15%–20% compared to the model experiment.Based on the verified numerical model,the scour development process of the full-scale vertical axis tidal current turbine is studied,and the scour depth and the scour hole contour are predicted.In this paper,the scouring mechanism of the vertical axis tidal energy turbine seabed is discussed in detail and the corresponding prediction formula and CFD simulation method are provided.These research results have important guiding significance for turbine scour research and the commercialization of tidal current turbine.