Optimization Study On The Blade Profiles Of A Horizontal Axis Tidal Turbine Based On BEM-CFD Model

Ocean currents can be an important part of renewable energy.With its low cost,low ecological impact and wide adaptability,tidal turbine had gradually become a hot research field in ocean energy.In China,the development of tidal turbine was still in its infancy.The key to improve the efficiency of a horizontal axis tidal turbine was to increase the energy conversion efficiency of its rotor.Based on this,this paper developed an optimization model of horizontal axis tidal tumines.It realizeed the automatic optimization on blade profiles of horizontal axis tidal turbines with high efficiency,which saved the design cost.This optimization model was of great significance to design horizontal axis tidal turbines.Firstly,based on the traditional blade element momentum theory,a BEM calculation program was compiled on the MATLAB to calculate the axial force and tangential force of the target rotor.The power coefficient and the thrust coefficient were calculated.The required airfoil lift and drag coefficient were calculated by the CFD method.At the same time,the influence of Reynolds number and blade thickness were taken into account in this model.The correction coefficient of tip loss and the factor of high axial induction were also added.With the source terms introduced into the CFD model,the BEM-CFD model was built.In this model,the rotor was simplified into a disc model,and the characteristic of the rotor was expressed by the source terms calculated by the BEM theory.The source terms were put into the CFD model to simulate a peripheral flow field.Compared with the experimental data,it was proved that the BEM-CFD model can better simulate the influence of non-uniform inflow,free surface fluctuation effect and supporting structure on the performance of tidal turbine.Then,an optimization model based on ISIGHT platform for a horizontal axis tidal turbine was proposed.The pitch angle distribution and the chord length distribution of turbine blades were taken as the optimization variables,and the power coefficient and the thrust coefficient were selected as the optimization objectives.The Bezier curve parameterization and response surface model were introduced to realize the optimization automatically and efficiently.Results showed that at the optimum operating condition of the target turbine,the power coefficient was increased by 0.96%and the thrust coefficient was reduced by 2.36%.Finally,considering the multi-operating conditions,the average and variance values of the power coefficients under all working conditions were selected as the objective functions.And results showed that the optimized rotor's power coefficient increased from 0.2674,0.4255 and 0.4385 to 0.3261,0.4612 and 0.4514 when the tip speed ratios were at 4,6 and 8.The average power coefficient increased from 0.3892 to 0.4050,and the variance from 0.0061 to 0.0033.