Optimization shape design and realization of variable camber wing based on compliant mechanisms

Camber morphing aircraft actively change their geometric configurations with different missions and flight conditions to achieve potential aerodynamic performance improvements, which is of significant interest to the aviation community. The adaptive compliant trailing edge is one of the promising camber morphing concepts. It utilizes distributed structural flexibility to transmit motion and force from the actuator, offering a continuous and smooth aerodynamic surface, from which the aircraft suffers less from the weight penalty. However, this concept requests specialized design methodologies, including shape parameterization for variable camber, aerodynamic shape optimization for target shape, and compliant mechanisms synthesis, which remains a challenge. This work proposes a systematical design framework to optimize shape and structural topologies of the variable-camber trailing edge under a given flight condition. The proposed variable-camber trailing edge is then designed and implemented into a real wing section as the prototype. The load-bearing capability and smoothness are verified through wind tunnel tests. The following research topics are carried out in this dissertation: (1) A methodology is presented to address the design problem of variable-camber trailing edge through a hierarchical approach known as the two-level method, where the aerodynamic shape is first optimized, followed by the compliant mechanisms synthesis. The first optimization level integrates an innovative morphing shape parameterization with a high fidelity computational fluid dynamics solver, a hybrid mesh deformation algorithm, and an efficient adjoint-based gradient evaluation method. The class/shape transformation parameterization method is modified to consider the kinematics of a camber morphing airfoil with compliant mechanisms. Furthermore, the first level optimization produces a feasible optimized morphing shape for compliant mechanisms design. The second optimization level provides a complete definition of the hybrid topology optimization problem that combines topology and sizing parameters to synthesize compliant mechanisms based on load path representation. It includes parent lattice specification, initial load path library generation, and actuator integration. The proposed method substantially reduces the required number of parameters and enlarges the design space while improving the optimization efficiency and deformation accuracy. The results show that the deformation error between the present result and the target shape is 1.43‰, suggesting the deformation accuracy 20% higher than that in the literature. The deformation shape of the manufactured variable-camber trailing edge is in good agreement with the finite element model, and maximum deflections of about 22.2 degrees downward and 15.7 degrees upward are achieved. (2) The planner compliant mechanisms for a variable-camber trailing edge are extended to wing segments capable of both chordwise and spanwise trailing edge deformation. Firstly, the straight wing with a sole chordwise morphing trailing edge is developed and built mechanically to validate the proposed morphing concept. Then, by embedding hyper-elastic material in the skin structure, a three-dimensional morphing transition section that elastically lofts between two variable-camber trailing edge devices in a passive and continuous manner is proposed and integrated into the straight wing. Finally, the static and dynamic characteristics of the proposed two morphing trailing edge wing models are evaluated in ground tests. The aerodynamic performance and the deformation under aerodynamic loads are investigated in a low-speed wind tunnel. The results show the load-bearing natural of the proposed compliant morphing trailing edge devices, presenting a smooth and continuous outer mold surface. In particular, a spanwise transition angle of 29 degrees between two adjacent morphing camber trailing edge devices is achieved. (3) The co-relation is constructed between the airfoil shape parametric model and the deformation characteristics of the planner compliant trailing edge model by using machine learning technology. The airfoil shape parameterization scheme is extended to a three-dimensional wing, aiming at efficient static aeroelastic analysis and wing shape optimization. The geometric nonlinear static aeroelastic analysis framework is first validated by comparing wind tunnel test results. The induced drag coefficient and maximum/mean stress are then minimized subject to lift, morphing trailing edge kinematic constraints, and several flight conditions. The results reveal that the morphing trailing edge has the potential for drag reduction and load alleviation. A 2.2% reduction in lift-induced drag is obtained. In addition, 60.5% maximum stress reduction and 75.6% mean stress reduction of the wing’s main spar are achieved using morphing trailing edge for typical cruise conditions. In summary, aiming at establishing a systematic design framework for the variable-camber wing that can be adopted in real aircraft, this work conducts the design, analysis, manufacture, and validation of the variable-camber wing based on compliant mechanisms. The trailing edge shape is optimized subject to aerodynamic performance and kinematic relation of mechanisms. Then, the planner compliant mechanisms are designed and extended to wing segments with morphing trailing edge capable of deforming along chordwise and spanwise. Finally, the ground and wind tunnel tests are carried out for validation. To conclude, this work provides methodologies for designing the variable-camber wing and contributes a reference for developing morphing aircraft in the future.