Aerodynamic Shape Design and Validation of an Advanced High-Lift Device for a Regional Aircraft with Morphing Droop Nose

Hindawi International Journal of Aerospace Engineering Volume 2019, Article ID 7982168, 21 pages https://doi.org/10.1155/2019/7982168 Research Article Aerodynamic Shape Design and Validation of an Advanced High-Lift Device for a Regional Aircraft with Morphing Droop Nose Alessandro De Gaspari 1 2 1 and Frédéric Moens 2 Department of Aerospace Science and Technology, Politecnico di Milano, 20156 Milano, Italy Aerodynamics Aeroelasticity and Acoustics Department, ONERA, The French Aerospace Lab, 92190 Meudon, France Correspondence should be addressed to Alessandro De Gaspari; Received 15 April 2018; Accepted 4 December 2018; Published 27 March 2019 Academic Editor: Mauro Pontani Copyright © 2019 Alessandro De Gaspari and Frédéric Moens. 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. In the present work, the aerodynamic shape design of an advanced high-lift system for a natural laminar flow (NLF) wing, based on the combination of a morphing droop nose and a single slot trailing edge flap, is presented. The paper presents both the aerodynamic design and optimization of the NLF wing and the high-lift configuration considering the mutual effects of both flap devices. Concerning the morphing droop nose (DN), after defining the parameterization techniques adopted to describe the geometry in terms of morphing shape and flap settings, the external configuration is obtained by an aerodynamic shape optimization procedure able to meet geometrical constraints and the skin structural requirements due to the morphing. The final performance assessment of the three-dimensional high-lift configurations is performed by high-fidelity aerodynamic analyses. The design procedure is applied to a twin-prop regional aircraft equipped with a natural laminar flow wing. The morphing droop nose is compatible with an NLF wing that requires the continuity of the skin and, at the same time, extends the possibilities to improve the performances of the class of regional aircraft which usually are not equipped with conventional leading edge devices. Additionally, the morphing technology applied to the flap allows the design of a tracking system fully integrated inside the airfoil geometry, leading to a solution without external fairings and so with no extra friction drag penalty for the aircraft. 1. Introduction In the field of the innovative high-lift device technologies, the active camber morphing represents an interesting concept, due to its capabilities to improve the aerodynamic performances and to redefine the takeoff and landing maneuvers configurations, offering the possibility to be immediately installed on the existing wing without the need to replace the structural wing box. One of the main devices that allow changing the wing camber is the morphing droop nose. Many applications of this concept are described by Friswell in [1]. Around 1973, Boeing performed a wind tunnel test comparison on a wing equipped with hinged leading and trailing-edge flaps, and then with smooth variable-camber flaps that provided large improvements [2]. More than ten years later, Boeing started several research programs aimed at embedding active camber devices on board a military aircraft [3–5]. In the Advanced Fighter Technology Integration (AFTI) program, by NASA and USAF, the F-111 wing was equipped with control surfaces, driven by electrohydraulic actuators, based on sliding panels for the lower trailing edge, and composite flexible panels for the upper trailing edge and for the leading edge. The AFTI/F-111 flight tests confirmed a performance increase of 20% in terms of aerodynamic efficiency and 15% in terms of distributed load on the wing, keeping constant the bending moment [6, 7]. One of the most important contributions to the design of morphing droop nose comes from Monner, who developed different concepts during the years. At the beginning, he tried to replace the leading edge ribs with several plates, fitting into 2 the airfoil shape, and connected each other with rigid hinges, whereas the skin is free to slide along the airfoil contour by means of joint and stringers that restore the required stiffness [8, 9]. The rib elements were optimized to minimize the hinge stress. Afterwards, Monner continued his collaboration with EADS, within the SmartLED project, to realize a patent smart leading edge device to be used in a typical high-lift application and to replace the droop nose installed on the A380. This morphing droop nose was optimized to reach a deflection of 20 deg, keeping smooth the external surface. Recently, different EU projects, such as SADE and SARISTU, started from Monner’s work to design a portion of a full-scale morphing droop nose composed of two main parts: a compliant skin and a rigid kinematic mechanism obtained by an integrate design [10]. Other projects also concerned the development of morphing flap [11, 12] and morphing trailing edge [13, 14] devices for the load control in both high-speed and low-speed conditions. Nowadays, one of the most technologically advanced companies in the field of adaptable shape structures is FlexSys Inc. which developed specific tools for the design of devices based on the compliant structure concept. They cover different fields of application, including morphing wing equipped with seamless and hingeless leading and trailing edge devices, without any rigid mechanism [15, 16]. They are strongly focused on obtaining completely continuous and smooth surfaces able to optimize the aerodynamic efficiency in different flight conditions. A compliant flap system was designed to maximize the laminar boundary layer over a wide lift coefficient range by continuously optimizing the shape throughout the mission. This technology was successfully installed on the NASA Gulfstream aircraft by replacing the original flap. The work presented in this manuscript starts in the framework of EU-funded Clean Sky 2 REG-IADP AG2 project, where innovative high-lift device technologies, able to achieve new design requirements and suitable to be applied to the natural laminar flow (NLF) wing of a Green Regional Aircraft, have been investigated. In a first step, the wing shape of the reference Green Regional Aircraft has been redesigned to obtain a large portion of natural laminar flow on both surfaces at cruise and off-design flight conditions. The aircraft configuration equipped with this new NLF wing has been used as baseline for the design of innovative high-lift devices to be considered at takeoff and landing conditions. A morphing droop nose installed on the wing of an existing Regional Aircraft provides significant aerodynamic benefits because this kind of medium-size civil aircraft are usually not equipped with conventional leading edge devices. Moreover, the morphing droop nose allows redesigning the baseline wing shape that can be optimized considering (...truncated)