The Research Of Structural Design And Integrated Optimization Of Variable-thickness Morphing Airfoil Based On CFD/CSD Technology

Application of smart materials and structures on wings and aircrafts is one of the hot issues in the field of aircraft design recently.A variable-thickness wing actuated by shape memory alloy(SMA)has been designed and fabricated in this paper.Aimed at the main problems existing in design of morphing airfoils and adaptive optimal deformation of aerodynamic configuration,a set of methodologies appropriate for design process of cooling system design applied on SMA wires and aerodynamic optimization are established.The variable-thickness wing consists of a support frame and a elastic deformable envelop.And a novel solution is put forward to solve the problem of rapid cooling for the SMA actuators.Simultaneously,mathematical and experimental analysis of the cooling system are implemented to verify the effectiveness of the cooling system.To obtain the optimal aerodynamic configuration in the deforming procedure of the morphing wing,a adjoint optimization method based on control theory of the partial differential equation is developed.Then a numerical method based on CFD/CSD technology is developed and relevant computational codes were compiled on the platform of Fortran and Matlab.Eventually,numerical examples under different flight conditions are carried out to verify the feasibility of the method.The main research work includes the following sections:(1)Airfoil profile of NASA SC(2)-0518 is employed as a prototype to design the variable-thickness morphing wing which has the uniform section along the wing span.A linear-displacement actuator is designed based on SMA wire to drive deformation of the upper envelop.In order to achieve rapid cooling for heated SMA wires,a tube-telescoping forced convection cooling system is presented.Based on one-dimensional intraductal flow equations,mathematical model of the cooling process of SMA is established.And based on the above theoretical analysis,air-bleeding pressure and time of gas tank are predicted,cooling time both under natural cooling and forced convection cooling conditions were calculated as well.To verify the accuracy of mathematical analysis,tests of the cooling time in both cooling conditions are conducted.(2)For the computation of viscous flow-field governing equations and adjoint equations associated with N-S equations,a uniform numerical method for low-speed/high-speed flows is developed.AUSM flux-vector splitting scheme and Jst central scheme are employed for the discretization of convective flux and viscous flux,respectively.By the introduction of precondition for time-derivative,LU-SGS implicit scheme is applied to improve the computational efficiency and stability,S-A and SST models are employed for turbulent flow-field calculation as well.Based on cell-centered finite volume method,multi-blocks structure grids are established for aerodynamic analysis and optimization.To realize the mesh deformation caused by the variation of aerodynamic configuration,the commercial software ICEM-CFD scripting tool is utilized to achieve rapid reconstruction of the grid.By calculation tests conducted under two typical flight conditions,the accuracy of flow-field solver,effectiveness of precondition method and convergence property of the LU-SGS scheme were investigated.(3)In this case that aerodynamic loads and driving forces of SMAs are applied on the upper flexible envelop,coupled numerical analysis through the applications of CFD and CSD technologies.For the establishment of governing equation for elastic deformation of the extrados,combined the stress state of plate-bending based on Mindlin plate theory with plane-stress a new incompatible curved rectangular shell element is obtained.Then finite element models of envelop and elastic flake are established based on the above shell element.Radial-Basis-Function(BRF)method is introduced to achieve the accurate interpolation of aerodynamic loads and deformation displacements between the flow-field and structure-field interfaces.And loose-coupling approach is introduced for the coupled-field computation.Using the displacements results of CSD,the mathematical relationship between variations of aerodynamic configuration and linear displacements of SMA actuators is derived.(4)Based on Control Theory of partial differential equations,optimal design of wing shape has been converted to a control problem of the aerodynamic shape optimization,which takes up the aerodynamic performance as the objective function and N-S equations as the constraints.By setting the coefficients of variations of flow-field variables in expressions of the objective function gradient equal to 0,adjoint equations and corresponding boundary conditions are derived.So that the calculation amount of objective function gradient is reduced to 2 times the amount of calculation of N-S equations regardless of the number of design variables.For convenience of solving by uniform discrete approach,adjoint equations are turned into the same forms as N-S equation.With the contrast of traditional ergodic calculation in two free-stream conditions of 30m/s and 0.6Ma,it has shown that the optimal method based on adjoint equations of flow-field has the better efficiency and accuracy.The novel optimal approach should have broad prospects and applications in design of morphing wings.