| With the continuous consumption of fossil fuels,the environmental and energy problems have become serious,all countries are vigorously developing renewable energy.As a clean and renewable energy,the tidal current energy has become a hot spot for research.However the ocean environment in which the tidal current energy power generation device is located is very complex,the hydrodynamic characteristics of the turbine can be influenced by the free-surface,wave and immersion depth of the tip of blade,which will affect the efficiency of power system.At present,the researches of hydrodynamic characteristics of turbine are mostly carried out under the condition without free-sureface and current is uniform flow,these experiments do not take into account the common effects of current,wave and free-surface.Therefore,in this paper,the flow field and hydrodynamic characteristics of turbine which is in the environment of existing free-surface,current and wave are studied by theory method and numerical simulation.The study can provide theoretical and data support for hydrodynamic performance and load prediction of horizontal axis turbine,and provide important reference for the blade strength design and the platform motion response analysis.First,by consulting a lot of data,this paper summarized the theoretical research and experimental research development of tidal horizontal axis turbine and tidal current power generation technology,the theoretical basis and numerical method of the viscous CFD numerical simulation technology are introduced in this paper.For the problem of unbounded flow,the research is based on CFD theory and Star CCM+ software,and mesh the numerical model of horizontal axis turbine,the meshing method and the number of grids are studied to prove that they are independent of the numerical simulation results,the nnumerical simulation results are compared with the experimental results in order to verify the effectiveness of the numerical simulation method,a CFD simulation method about the flow field and the hydrodynamic characteristics horizontal axis turbine in unbounded flow is extablished.Based on that,the overlapping grid technology is further applied to calculate the hydrodynamic performance and flow field of horizontal axis turbine with free-surface or free-surface and wave.The advantage of this method is that the application of overlay grid technology can rapidly change wave parameters,free surfaceheight and the movement mode of hydraulic turbines,this method can effectively improve the computation speed.For the problem of free-surface effect,three working conditions(no free-surface,static water surface and wave)with the same tip depth are simulated by CFD simulation method,the capacity usage ratio and the axial load coefficient with the speed ratio change curves of the horizontal axis turbine are obtained.Through the analysis of the results,the influence of the free-surface on the horizontal axis turbine hydrodynamic characteristics is obtained,the influence of different tip immersion depth on the hydrodynamic coefficient of the horizontal axis impeller is further explored.For the problem of wave effect,this research change wave frequency and amplitude to calculate CFD simulation.Then it can acquire change rules about the capacity usage ratio and axial load coefficient on the water turbine with the change of wave frequency and amplitude.Considering that the periodic motion of the waves can affect the vibration amplitude and velocity of fluid which near the surface,it is necessary to study the effect of Energy utilization coefficient and axial load coefficient with the change of the ratio of the amplitude and the immersion depth.After the study,it can get the rule of water turbine flow field characteristics with the change of wave frequency and amplitude by analyzing flow field characteristics at each working condition. |
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