Structural And Material Optimum Design Of Concentrator

Concentrator is the core of concentrator augmented wind turbine.The structure of the comcentrator has a great effect on the air velocity in the parallel tube and the flow separation in the diffusion tube of concentrator,and then has a great effect on its property in concentrating wind energy.Therefore,its structure needs to be optimized.The material selection of concentrator has a great effect on its cost and security.So,its material selection needs to be optimized.Before the structural optimization and the material optimization,the reliability analysis needs to be done for the computational fluid dynamics method used in the optimization.(2)Study the reliability of the computational fluid dynamics method used in the optimizationThe modeling and simulation has been done based on the control equations in computational fluid dynamics,the fundamental equations of turbulence,the solving methods of turbulence,the viscosity model of turbulence.The vehicle tests for concentrator and the setting of the point for testing wind speed are stated.Compared with velocity inlet boundary condition,adopting the mass flow inlet boundary condition enables the calculation for shrinkage pipe and parallel pipe to be more accurate.Therefore,in terms of inlet boundary condition,the mass flow inlet is adopted.According to the grid independence test,when the Relevance Center and the relevance of the grid division is Fine and 70 respectively,it’s reliable of the calculations on qualitative prediction and can be used to optimize the structure of the concentrator.In addition,the relative error of the most calculations is less than 10% in the installation section of wind turbine and the demand for quantitative prediction is met basically.The Reynolds number independence test is performed on the basis of the grid independence test.The final results indicate that the relative error’s variation of calculations is small when the calculation is performed by using different Reynolds number.Hence,the error will be small if the Reynolds number used in current flow field is a little different from the Reynolds number used in vehicle tests.And the relative error is the smallest if the calculated Reynolds number is adopted in flow field calculation.(3)Study the structural optimization for the concentratorIn the structural optimization,a new diffuser is added to the outer edge of the diffuser of the original concentrator.The length of the generatrix of newly added diffuser is d.α is the angle between the generatrix and the vertical direction.A series of concentrator models are obtained by adopting different d and α.In order to get the highest-performing concentrator,these concentrator models of different structures are analyzed and compared by using computational fluid dynamics method.Mechanisms of influence of the newly added diffuser on the property of the concentrator are analyzed in the structural optimum design.The performance of concentrator is due to whether or not the flow separation takes place near the inner wall of diffuser.If the flow separation takes place,the performance of concentrator will be greatly influenced.Basically,the flow separation affects the radial diffusion of the airflow within the diffuser from the axis to the inner wall of the diffuser.The closer the location where the radial diffusion appears is to the exit of the parallel pipe,the better property of concentration.The mark of the radial diffusion is the positive pressure gradient appearing from the axis to the inner wall of the diffuser.If it appears,the radial diffusion will take place;if it doesn’t appear,the radial diffusion will be impeded and the property of concentration will get worse.If the location that the positive pressure gradient first appears is close,the lower the static pressure is,the better property of concentration.The reason that the newly added diffuser of final optimization model can improve the concentrating performance of concentrator is that the airflow will be speeded up when it flows towards the outer edge of the newly added diffuser along the exterior wall of diffuser.The velocity of airflow is very high on the outer edge of the newly added diffuser and the low pressure area can even be formed behind the newly added diffuser.It forms a strong suction effect on the inside of concentrator,enhances the wind speeds at the installation section of wind turbine inside the parallel pipe of concentrator and improves the performance of concentrator.D is the internal diameter of the parallel pipe of concentrator,d and α are the length of generatrix and the angle between the generatrix and the vertical direction respectively.Mechanisms of influence of different d and α on the property of concentrator is analyzed in the paper.The model 4-40 of which d is 0.4D and α is 40°is the optimal model in the 42 different selected optimization models.(4)Study the material optimization for the concentratorThe material-optimum design has been made with the optimized concentrator.The stress on the concentrator made of the selected materials caused by wind load in certain wind velocity is calculated using fluid-structure integration.This material may be used to make concentrator if the maximum stress is less than the fracture stress of the selected material.The grid independence test for solid field is carried out to insure the reliability of the simulation result.The analysis shows that the accuracy of the fluid-structure interaction analysis meets the requirement when the element size of body grid and face grid is less than 0.015 m and the grid number is more than 216379.In order to minimize error,the grid division method that the element size of body grid and face grid is 0.009 m is adopted to the grid division of solid field and the subsequent calculation.The concentrators made of Polycarbonate,Polyethylene Wood-Plastic Composite,Polymethyl methacrylate are studied by fluid-structure interaction software respectively.The results indicate that the maximum stress on the concentrator made of the selected materials caused by wind load at the wind speed of 25 m/s is all far less than the fracture stress of the selected material.The maximum deformation of corresponding three selected materials is merely 5.9548 mm.The structural strength and rigidity of the three material are suitable for design requirements.Therefore,the three materials may be used to make concentrators.As for the material that the fracture stress,the Young modulus,the Poisson ratio will change with the temperature,the way of material optimization is presented.