Unsteady Hydrodynamic Characteristics Analysis Of Floating Vertical Axis Tidal Turbine

With the rapid growth of the world’s demand for energy,energy shortages and environmental pollution problems have become increasingly severe.Therefore,it is urgent to increase the proportion of new energy sources such as renewable energy.Marine renewable energy has great development advantages and utilization value,among which tidal energy with strong predictability has an important strategic position in marine renewable energy.Vertical axis tidal turbine is the core component of tidal energy conversion systems with simple structure,free from flow direction restriction and convenient assemblage maintenance.Its unsteady hydrodynamics in turbulence,wave and platform shaking motion brings great challenges to system optimization design and control.In order to ensure the energy efficiency,structural reliability and power stability of the system,it is urgent to quickly and accurately predict the numerical method of hydrodynamic load of turbine.In this paper,the unsteady hydrodynamic numerical method of vertical axis turbine is established based on the unsteady double-multiple stream tube model to study the hydrodynamic characteristics of floating vertical axis tidal turbine in complex marine environment.The composition and working principle of floating vertical axis tidal turbine system are summarized.Based on the blade element momentum theory of vertical axis turbine,the important hydrodynamic parameters of the turbine are given,and the steady double-multiple stream tube method is developed.Based on potential flow theory,the time domain motion equation and mooring equivalent stiffness of floating platform are derived.Based on the steady double-multiple stream tube method,the dynamic virtual blade model is introduced,combined with the dynamic stall model to simulate the dynamic stall effect of the vertical axis tidal turbine to improve the accuracy of numerical calculation;combined with the dynamic inflow model to simulate the vertical axis tidal turbine in the unsteady flow field to ensure the stability of the calculation.Integrating the above models and applying discrete methods and numerical algorithms,the hydrodynamic numerical method of the unsteady vertical axis turbine is established,and the validity is verified.Based on the above method,the unsteady hydrodynamic characteristics of turbine under the steady flow field of uniform flow and shear flow are calculated and analyzed.Considering the unsteady of tidal flow field in the complex marine environment,the unsteady hydrodynamic characteristics of turbines under the conditions of gradual flow,sudden flow and turbulence are studied.Considering the fluid particle motion induced by wave,the unsteady hydrodynamic characteristics of the turbine under wave action are studied,and the influence of wave parameters on the unsteady hydrodynamic characteristics of the turbine is analyzed.The hydrodynamic coefficients of the floating platform are calculated by AWQA software,the mooring equivalent stiffness is calculated by catenary theory,and the hydrodynamics of the turbine is calculated by unsteady double-multiple stream tube method.Based on the timedomain motion equation,the coupling numerical method of floating vertical axis turbine is established.The above method is applied to analyze the coupling law between the floating platform motion and the hydrodynamic force of the vertical axis turbine.