Research On Flow Field Characteristics And Design Of Horizontal Axis Tidal Current Turbine Blade

Tidal current energy has become one of the most poten tial renewable energy for it is environmentally friendly,stable,predictable and rich in reserves.If a cost-effective capturing method could be developed,tidal current energy could alleviate the energy crisis and environmental problems.The horizontal axis tidal current turbine is one of the most developed tidal current energy conversion devices.However,due to its low energy conversion efficiency,it is still a long way from its commercialization.The rotor blade is the key component of tidal turbine i n the process of converting the kinetic energy of current into electric energy.The blade design largely determines the energy conversion efficiency of the tidal turbine.Therefore,a well-designed blade profile is the key factor of the horizontal axis tidal current turbine design.Based on the above problems,in this paper,the flow field characteristics of the traditional horizontal axis tidal current turbine are analyzed by using computational fluid dynamics method(CFD).Three types of tidal turbines with winglets are designed and the hydrodynamic performances are studied.Furthermore,the influences of the design variables of winglet on the energy conversion efficiency of tidal turbine are investigated.Firstly,the energy crisis and the environmental problems in the world are described,the characteristics of tidal energy and tidal turbines are presented and the current research status of horizontal axis tidal current turbines is analyzed.Thereby,the research direction of the flow field characteristics and design methods of the horizontal axis tidal current turbine is determined.Secondly,the subsequent research method of the hydrodynamic performance of the tidal turbine is determined by introducing the Betz theory,the blade element momentum theory and the computational fluid dynamics.Next,the computational model of tidal turbine is verified by numerical uncertainty assessment.Based on the CFD results,the flow field characteristics of the traditional horizontal axis tidal current turbine are analyzed,and the pressure distribution characteristics of the turbine blade and vorticity magnitude contour with streamlines behind the blade tip are presented.Then,the winglet technique is introduced to the design of horizontal axis tidal current turbine.The trapezoid tip turbine,the triangle tip turbine and the hybrid tip turbine are designed,and their hydrodynamic performances are investigated by CFD and compared with that of the traditional horizontal axis tidal current turbine.The numerical results show that the three designed tidal turbines with winglets all could reduce the intensity of the tip vortex and improve the power coefficient a t the optimum tip speed ratio(TSR).The winglet designs improve the power production by improving the torque near the blade tip and decreasing the intensity of tip vortices at the same time.Finally,the influences of bending direction and design variables of winglet on the energy conversion efficiency of tidal turbine are investigated.The results demonstrate that the performance of the tidal turbine could be improved only when the winglet bent towards the suction side.In addition,the energy conversion efficiency are affected by the winglet length,tip chord and cant angle,and the proper designed variables could acquire power increase of horizontal axis tidal current turbine at the whole conditions.