Optimization Analyses On Structural Load Of Composite Rotor Based On CFD/CSD Coupling Method

Unsteady rotor load is the main vibration source of helicopter,in the process of rotation,there are both complex unsteady aerodynamic loads and elastic deformations of the elastic blades,which increase the difficulty of rotor aerodynamic and structural analyses,and become the focus of rotor aeroelasticity field.To reduce the structural vibration loads of the composite rotor,it is necessary to optimize the structure of the blades,so three aspects are studied in this thesis: structural loads analysis considering blade elasticity,parametric modeling method of blade sectional structure and optimization design method.The main contents include:In Chapter 1,the research background and significance of this thesis is introduced.The rotor CFD/CSD coupling analysis method used in rotor structural loads optimization,the parametric modeling method of composite blades and the rotor dynamic optimization method are reviewed,the work to be carried out in this thesis is summarized.In chapter 2,the generation method of rotor's moving-embedded grid and numerical simulation of rotor flowfield are established respectively.The "disturbance diffraction method" and Inverse-map method are used to improve the efficiency of hole cutting and donor cells searching in moving-embedded grid system.The grid deformation is conducted by the algebraic method.For predicting the unsteady aerodynamic loads,the rotor CFD method based on the compressible RANS governing equation and one equation S-A turbulence model is established,the high order ROE-MUSCL scheme is used to enhance the accuracy of CFD analysis and the OpenMP method is used for parallel computing acceleration.The UH-60 A rotor and Caradonna-Tung rotor are selected as numerical examples,as a result,the effectiveness of the present CFD method has been validated.In Chapter 3,the rotor structural dynamic analysis method and the CFD/CSD coupling analysis method are established.Based on the moderate deformation beam theory,the Hamilton principle and the finite element method,the motion equations are established for the elastic blades.The blade elastic response and rotor structural loads are calculated by Newmark-Beta method and force integral method respectively.The loose coupling strategy of rotor CFD and CSD analysis is established by taking into account the calculation accuracy and efficiency,and the coupling information exchange is carried out for each circle.The SA349/2 and UH-60 A blades are simulated to demonstrate the effectiveness of the structural dynamics analysis method and the CFD/CSD coupling method.In Chapter 4,the parametric modeling method and sectional properties analysis method for C-type beam-shaped composite blades are established based on the parametric definition of sectional components,which improve the simulation ability of the real structure of the blades and increase the efficiency of blade structure modeling and section analysis.Blade cross sections of different structure design forms are used to verify the validity and robustness of the parametric modeling method,and the case analysis of a box beam is carried out to verify the reliability of VABS section properties analysis.In Chapter 5,the optimization design method is established and applied to the rotor structure design and the rotor structure load optimization.Based on the latin hypercube sampling design of experiment method and the radial basis function(RBF)approximation model,the surrogate model method is established to improve the optimization efficiency.Combining the surrogate model method,the parametric modeling method of blade section and multi-population genetic algorithms,firstly,the design scheme of the baseline blade is obtained by optimizing the section location parameters,then the thicknesses and ply angles of the blade skin and the Z-beam are selected as optimization variables,the 4/rev structural hub loads of the rotor in hover is optimized,and structure design scheme of the optimized blade is obtained.Compared with the baseline blade,the 4/rev rotor hub loads of the optimized blade are significantly reduced.Chapter 6 summarizes the research content,the conclusions and the innovation points of this thesis,and forecasts the future research work.