Knowledge-Based Shape Optimization of Morphing Wing for More Efficient Aircraft

Hindawi Publishing Corporation International Journal of Aerospace Engineering Volume 2015, Article ID 325724, 19 pages http://dx.doi.org/10.1155/2015/325724 Research Article Knowledge-Based Shape Optimization of Morphing Wing for More Efficient Aircraft Alessandro De Gaspari and Sergio Ricci Department of Aerospace Science and Technology, Politecnico di Milano, Via La Masa 34, 20156 Milano, Italy Correspondence should be addressed to Sergio Ricci; Received 31 March 2015; Revised 22 July 2015; Accepted 31 August 2015 Academic Editor: Ning Qin Copyright © 2015 A. De Gaspari and S. Ricci. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. An optimization procedure for the shape design of morphing aircraft is presented. The process is coupled with a knowledgebased framework combining parametric geometry representation, multidisciplinary modelling, and genetic algorithm. The parameterization method exploits the implicit properties of the Bernstein polynomial least squares fitting to allow both local and global shape control. The framework is able to introduce morphing shape changes in a feasible way, taking into account the presence of structural parts, such as the wing-box, the physical behaviour of the morphing skins, and the effects that these modifications have on the aerodynamic performances. It inherits CAD capabilities of generating 3D deformed morphing shapes and it is able to automatically produce aerodynamic and structural models linked to the same parametric geometry. Dedicated crossover and mutation strategies are used to allow the parametric framework to be efficiently incorporated into the genetic algorithm. This procedure is applied to the shape design of Reference Aircraft (RA) and to the assessment of the potential benefits that morphing devices can bring in terms of aircraft performances. It is adopted for the design of a variable camber morphing wing to investigate the effect of conformal leading and trailing edge control surfaces. Results concerning four different morphing configurations are reported. 1. Introduction The very challenging targets of new environmental requirements for transport aircraft force the researchers to look for more advanced aircraft configurations, based on more efficient aerodynamics and structures together with more sophisticated flight control systems. Focusing on European transport, it appears as clear that the pressure will increase for large scheduled European carriers to reequip their short haul fleets with more fuel-efficient types, in order to remain competitive with low-cost rivals and to ensure they will not be unduly penalized when European emissions trading comes into full force. The Bréguet range equation [1, 2] combines aerodynamic, propulsion, and structural figures of merit and suggests acting on both the aircraft empty weight and the lift over drag ratio, in order to improve the modern aircraft efficiency. Many are the approaches investigated during recent years trying to improve all the Bréguet equation terms, such as advanced and unconventional configurations able to improve aircraft efficiency, new materials and structural concepts, active controls to peak loads reduction and flight control improvements, more efficient engines, and alternative fuels [3]. Certainly morphing technologies offer potential benefits for a more efficient aircraft and for this reason literature reports many and different morphing concepts even if a clear evaluation of their real benefits is not available yet [4– 7]. One of the key challenges for morphing technologies is represented by the identification of the most suitable actuation concept able to reduce the actuation energy and the mechanism weight. While current aircraft are already equipped with systems able to introduce in-flight geometrical variations such as wing area change, variable camber, and retractable landing gear, the morphing of next generation still has challenges and leads to the design of morphing wings based on conformable control surfaces [8]. In particular, the variable wing camber morphing, considered as the capability to change the airfoil 2 shape without surface discontinuities often based on the adoption of ad hoc designed flexible skins [9], appears as an efficient way to maximize the lift over drag ratio and to reduce the fuel consumption over the entire flight envelope. However, the design of this kind of morphing devices requires developing specific procedures able to assist the engineers during both the design [10–12] and the benefits evaluation phases. Currently, this target is commonly addressed by means of dedicated multilevel and multiobjective optimization procedures [13]. Multilevel capabilities allow performing the optimization of morphing shapes and the design of the morphing mechanism separately [14]; multiobjective techniques help to design aircraft able to adapt its shape to optimize the performances along the cruise or at a wide range of different flight conditions. The design of morphing wing devices must combine two opposite requirements, often named kinematic and structural requirements, respectively: a flexible structure so to minimize the energy necessary to adapt its shape as expected and at the same time an enough rigid structure able to maintain the new shape under the aerodynamic loads when the morphing mechanism is not actuated. The approach proposed by the authors [15] is based on the optimization of aerodynamic, stiffness, and actuation sequentially, passing through the definition of a family of optimal morphing shapes associated with a group of as many flight conditions. Hence, the design of morphing mechanism depends on the availability of the optimal shapes that must be achieved when it is actuated and that are computed before the mechanism is known. In this way the optimal shapes guarantee the aerodynamic performances, while the mechanism can be optimized considering both kinematic and structural requirements. The key problem is that the allowable shape variation laws depend on the type of mechanism, while the mechanism design depends on the shape changes that the mechanism must be able to reach. For this reason, in recent years many efforts have been made aiming at considering energy and actuation requirements [16–18], as well as structural constraints [19], directly during the aerodynamic shape optimization. The work presented in this paper focuses on the first level of a wider morphing design framework having the following capabilities: wing shape optimization able to combine aerodynamic performances with optimal deformation of the skins (first level); optimal design of compliant mechanism able to produce, once actuated, the optimal shape coming out from the first level (second level); integration of the morphing devices into a high-fidelity model repr (...truncated)