Continuous Adjoint-Based Aero-structural Multi-disciplinary Design Optimization

Multidisciplinary design optimization for aircrafts is one of the most interesting issues of the aircraft designers.In the present work,on unstructured mesh,an aerostructural multidisciplinary design optimization system has been developed based on continuous adjoint optimization method,including aerodynamic single-disciplinary optimization,aerostructural analysis method on the basis of a linear quadrilateral shell element theory and high-fidelity aerostructural multidisciplinary design optimization methods.On the basis of Euler equations and unstructured mesh,a continuous adjoint aerodynamic single-disciplinary optimization approach is presented.Firstly the continuous adjoint equations and boundary conditions are derived on the unstructured mesh.Secondly the numerical solution method is proposed including spatial discretisation methods(JST sheme and second-order Roe scheme)and time discretization methods(Explicit 4-stage Runge-Kutta scheme and Implicit LU-SGS scheme),especially the second-order Roe-type upwind method and LU-SGS method developed in the work are more robust and efficient.The numerical solution of the flow control equations and the continuous adjoint equations is accelerated through MPI parallel technology,and the effect of different spatial discretization methods of the flow control equations and the continuous adjoint equations to the adjoint solutions.The geometry shape parameterization method is Free Form Deformation technology,the moving grid method used here is linear spring analogy which is easy to perform and the optimization method is Sequence Quadratic Program method which is able to deal with the linear or nonlinear optimization problems with or without constraints.The gradients evaluated from continuous adjoint method are compared with those from finite difference method to validate the accuracy.At last aerodynamic single-disciplinary optimization for ONERA M6 wing and DPW-W1 wing is implemented,which shows that the continuous adjoint method in the work is sound and efficient.An aerostructural analysis method based on a linear quadrilateral shell element has been developed.This shell element is based on Hellinger-Reissner variational principle,where the stress resultants and the displacement variables are independent.The element stiffness matrix is computed analytically which is fast and efficient.Each node of the element has 5/6 degrees to be able to deal with intersections between the elements.Aerostructural analysis method is tight coupling method.The PARDISO solver project is used to compute the structural equilibrium equations which are linear equations.PARDISO is from intel MKL library,which is a parallel direct solution method and is able to efficiently solve linear equations with large condition number.The information transfer method between the two disciplines of aerodynamics and structre is Thin Plate Spline method(TPS).The moving grid method applied here is linear elasticity method which is robust very much.Then the simulation results for classic cases of the shell element is presented to verify the correction and accuracy and the ability for the intersection of the shell theory.At last the aerostructural analysis for DPW-W1 wing is researched.A high-fidelity aerostructural multidisciplinary design optimization system for aircraft is built up based on the continuous adjoint method.Three optimization cases is presented here,including: aerodynamic single-discipilinary optimization considering the deformation of the static elasticity,aerostructural multidisciplinary design optimization based on continuous adjoint method and finite difference method and aerostructural multidisciplinary design optimization based on one-way coupling adjoint method.And the results of the above three optimization are compared with those of aerostructural analysis of aerodynamic single-discipilinary optimization,which shows the importance and necessity of multidisciplinary design optimization in aircraft design.