Numerical Simulation Of The Free Surface Effect For Vertical Axis Tidal Current Turbine

Environmental disruption caused by the decreasing reserves of traditional energy structure prompted developing new energy resources to became the essential assurance for human society.Tidal energy,an abundant and steady resource,has emerged the significant research value.Typically,the hydro-turbine which can convert tidal energy to rotary mechanical energy has attracted the attention of global experts.Floating vertical axis tidal current turbine owns great advantage versus other kinds of turbines,which embodies in random orientation of incoming flow and simple repair process to unit structure.In terms of the previous research so far,the working conditions of turbine were simplified to the exploration of homogenous incoming flow in unlimited depth.However,the construction selection to immersion depth of free surface and the effect to performance of turbine caused by wave must be considered with actual environment.Also,the application of replacing 3D model with 2D model caused the neglect of vorticity condition on blades' top.Hence,3D turbine model was applied to explore the influence of free surface in latter contents as well as the turbine performance affected by wave.First of all,the model of 3D blades with periodic rotation in conditions of unlimited depth,free surface and inerratic wave was built,which in order to analyze whether the free surface could influence the performance of turbine.The model of sliding mesh was applied to simulate the stress condition of rotated blades and the influence on power of turbine.Secondly,the analysis to the influence on turbine stress and power which is cause by different immersion depth in static water was explored as well.Lastly,the first-order regular wave was created in order to understand the condition of dynamic stress and power of turbine as well as figuring out the influence rule of wave's period and amplitude.Simulated data of CFD showed: The existence of free surface will increase the power of water turbine at low speed ratio,and will reduce the power of water turbine at high speed ratio.The existence of wave will reduce the power of water turbine and have no influence at the average force on the water turbine,but it will increase the amplitude of force on the water turbine.The increase of wave amplitude will reduce the efficiency of the water turbine.The increase of the wave cycle will also reduce the efficiency of the water turbine.The discussion and results demonstrated the significant future direction of designing and constructing floating vertical axis tidal current turbine in actual environment and also laid the foundation for further theoretical research on free surface effect.