Study On The Hydrodynamic Performance Of The Combined Vertical Axis Tidal Turbine

As an important component of renewable energy,the marine energy has many advantages,such as rich resources reserves and little impact on the environment.As a part of ocean energy,the tidal current has many advantages,such as the high energy density and broad prospect of exploitation and utilization.Compared with the horizontal axis turbine,vertical axis turbine has the advantages of simple structure,easy of manufacture,no influence on the flow direction.However,there are some problems with the vertical axis turbines,such as the shortcomings of self-starting,low energy extraction efficiency at low rotational speed,the periodic unsteady flow-field during operation,which will affect its scale and commercial development.Therefore,this paper adds an internal layer which is the S-type turbine to the H-type turbine,and the performance of this new lift-resistance vertical axis turbine is studied by the CFD numerical simulation method.Firstly,the equations of motion and force analysis of S-type turbine and H-type turbine are established.The two-dimensional numerical simulation is presented,and the correctness of the numerical simulation is verified.The influence of geometric parameters(overlap ratio)and motion parameters(tip speed ratio)of S-type turbine on the hydrodynamic performance of the turbine is studied.And the results showed that it is appropriate to work at the low tip speed ratio,and it is found that the torque coefficient decrease with the increase of the tip speed ratio,and there is an optimal tip speed ratio that makes the power coefficient be the maximum.The Savonius water turbine with the overlap ratio can reduce or even eliminate the negative moment,thus it can improve the performance of the Savonius water turbine.In addition,the influence of the tip speed ratio of the H-type turbine on the hydrodynamic performance of the turbine was studied.The results of the study show that the power coefficient of the H-type turbine and the tip speed ratio are approximately related to a parabola,and there is an optimal tip speed ratio that makes the power coefficient be the maximum.Compared with the Savonius turbine,the H-type turbine is suitable for higher tip speed ratio.and the best power coefficient is better.Finally,this paper analyzes the hydrodynamic performance and self-starting of the vertical axis turbine.And mainly the influence of geometric parameters(inner-outer diameter ratio,radius ratio)of the vertical axis turbine on the hydrodynamic performance and self-starting is studied,and then it is compared with the H-type turbine.The results show that the existence of the S-type turbine improves the self-starting performance of the turbine,and the mutual interference between the S-type turbine with the H-type turbine will reduce the power coefficient of the turbine to a certain extent.Therefore,all of above can provide references for the design and optimization of the vertical axis turbine.