| With the current decreasing global fossil energy reserves,and the more serious environmental pollution,energy crisis and environmental problems need to be solved urgently,so finding clean renewable energy to substitute for traditional fossil energy is an effective way to solve the problem.Global studies show that current energy can be used as a predictable renewable energy source,which is a new energy source with huge potential for commercial power generation.In order to use the current energy successfully,it is very important to understand the hydrodynamics of tidal current turbine.Although many technologies applied to wind turbines and marine propellers can be used to analyze hydrodynamic characteristics of power flow turbines,there is still a lack of research data in many aspects.The research on the cavitation characteristics of the tidal current turbines is still in the initial stage in the world.In addition,the optimization work on the existing blades is still lacking,especially for the optimization of the cavitation performance of the tidal current turbine.In view of the cavitation problem of the tidal current turbine,the numerical simulation accuracy of the cavitation characteristics of the tidal current turbine and the optimization of the cavitation performance of the blade airfoil were carried out in this paper.The main innovation points are as followed:(1)In this paper,the hydrodynamic performance parametersincluding lift coefficient and drag coefficient of the NACA63-815 airfoil were calculated.The investigation results show thatthe numerical calculation results are consistent with the experimental data.(2)Firstly,SST k-? model and Partially-Averaged Navier-Stokes model were adopted to analyze NACA63-815 airfoil cloud cavitation characteristics,and the difference between the calculated results of the two turbulence models and the experimental values were compared.Secondly,the numerical predictions of the power coefficient and thrust coefficient at different tip speed ratios of the tidal current turbine were carried out.The turbulent characteristics of the tidal current turbine under different cavitation numbers were analyzed using the turbulence model verified by the airfoil.In addition,the accuracy of the two turbulence models for cavitation prediction were compared.The cavity distribution and the influence of cavitation on the tidal current turbine were also analyzed.(3)A multi-objective optimization method based on particle swarm optimization combined with XFoil software which can greatly enhance the optimization efficiency was proposed for the cavitation phenomena of NACA63-815.The method based on Zhukovsky conversion and Theodorsen theory,the shape function method was used to parameterize the airfoil and optimization model was established based on the shape function.In this paper,the optimization is mainly aimed at the minimum surface pressure coefficient of airfoil at large attack angle.At the same time,in order to ensure the hydrodynamic performance of airfoil,the multi-objective optimization function which is combined with the lift coefficient,the coefficient of lift drag ratio and the minimum of the pressure coefficient was established.(4)The NACA63-815 airfoil was optimized by this method mentioned above.The CFD method was also used to comparre the cavitation distributions of the optimized airfoil with the original airfoil at three cavitation numbers(1,1.5 and 2)under two attack angles.The minimum pressure coefficients were increased by 17% and 45.8% respectively,and the maximum lift drag ratios were increased by 6.0% and 61.1%.The optimization results show that the cavitation initial and full cavitation performance of the optimized airfoil have been significantly improved and the hydrodynamic performance has also been improved.The investigation results couldvalidate the accuracy of the optimization method used in the present paper. |
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