A Numerical Study on Smart Material Selection for Flapped and Twisted Morphing Wing Configurations

ABSTRACT: The developments of innovative adaptive structures on Unmanned Aerial Vehicles (UAVs), such as morphing wings, can potentially reduce system complexities by eliminating control surfaces and their auxiliary equipment. This technology has the potential of allowing a UAV to adapt to different mission requirements or to execute a particular mission more effectively by maintaining an optimum airfoil section over a range of speeds for different segments of a mission profile. Studies on a number of smart materials candidates are currently available in the open literature to achieve wing morphing. The material selection depends on several factors including fast dynamic response, low weight, capability to operate over a wide range of flight conditions and low power consumption. This paper presents a review on smart materials technologies for UAV morphing wings. A numerical study in terms of power requirements is also presented for two morphing wing concepts: flapped and twisted wing planforms. The energy calculations for both morphing configurations were based on a two-step procedure. The first step consists of computing the aerodynamic energy using an in-house Vortex-Lattice (VL) based program. Subsequently the pressure field obtained from the first step is then mapped into a finite element mesh and the structural strain energy is calculated. The numerical results indicated that flapped morphing wings have a better aerodynamic performance when compared to twisted wings and different morphing levels can be achieved using lighter smart materials with lower specific energy for this configuration.摘要：针对无人机（Unmanned Aerial Vehicles, UAVs）研发的创新性自适应结构（如变形机翼），可通过移除操纵面及其配套设备，有效降低系统复杂度。该技术可使无人机适配不同任务需求，或通过在任务剖面的不同阶段维持最优翼型剖面以适应不同飞行速度，从而更高效地执行特定任务。目前公开文献中已针对多种候选智能材料（smart materials）开展了用于实现机翼变形的相关研究。材料的选择需综合考量多项因素，包括快速动态响应特性、低重量、宽飞行工况适应性以及低功耗。本文综述了面向无人机变形机翼的智能材料技术，并针对两种变形机翼构型——襟翼式与扭转式翼面，开展了功率需求相关的数值研究。两种变形构型的能量计算均采用两步流程：第一步借助自研的基于涡格法（Vortex-Lattice, VL）的程序计算气动能量；随后将第一步得到的压力场映射至有限元网格，并计算结构应变能。数值结果表明，相较于扭转式变形机翼，襟翼式变形机翼具备更优异的气动性能；且针对该构型，可采用更轻质、比能量更低的智能材料实现不同变形程度。