Numerical Simulation of a Passive Control of the Flow Around an Aerofoil Using a Flexible, Self Adaptive Flaplet.
Numerical Simulation of a Passive Control of the Flow Around an Aerofoil Using a Flexible, Self Adaptive Flaplet.
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DOI：
10.1007/s10494-018-9914-6
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Pinelli A
中科院分区：
文献类型：
--
作者：
Rosti ME;Omidyeganeh M;Pinelli A
几乎所有的鸟类都使用自激活羽毛来调整它们的翅膀特征，以延迟失速或减轻其不利影响(例如，在着陆期间或由于阵风而突然增加攻角)。一些羽毛被认为是流动分离的结果，并与流动相互作用，产生了对非定常涡量场的有益修改。受鸟类羽毛的启发，在飞机上使用自适应襟翼需要了解导致上述空气动力学益处的物理机制，并确定最佳襟翼的特性，包括它们的尺寸、位置和理想的制造材料。在此框架下，本文的数值研究分为两部分。首先，在一个简化的场景中，我们确定了使安装在翼型上的襟翼在大迎角下能够通过改变其长度、位置和固有频率来增加升力和改善气动效率的主要特征。随后，通过详细的直接数值模拟分析，了解了由与流场相互作用引起的小斑块运动所带来的气动效益的来源。参数研究表明，优化襟翼可以使NACA0020翼型在迎角为20度时的平均升力增加约20%。在弦雷诺数为2×104的情况下，对安装了优化襟翼的翼型周围的流场进行了直接数值模拟，结果表明，翼型吸力侧大的回流气泡的循环通过是引起翼型襟翼运动的主要原因。反过来，当襟翼被向下推时，诱导的飞机喷流将后缘涡移到更下游，远离机翼，缓和由这些涡流产生的下压力，并调节当选择最佳折线布局时看起来更有组织的脱落周期。
Self-activated feathers are used by almost all birds to adapt their wing characteristics to delay stall or to moderate its adverse effects (e.g., during landing or sudden increase in angle of attack due to gusts). Some of the feathers are believed to pop up as a consequence of flow separation and to interact with the flow and produce beneficial modifications of the unsteady vorticity field. The use of self adaptive flaplets in aircrafts, inspired by birds feathers, requires the understanding of the physical mechanisms leading to the mentioned aerodynamic benefits and the determination of the characteristics of optimal flaps including their size, positioning and ideal fabrication material. In this framework, this numerical study is divided in two parts. Firstly, in a simplified scenario, we determine the main characteristics that render a flap mounted on an aerofoil at high angle of attack able to deliver increased lift and improved aerodynamic efficiency, by varying its length, position and its natural frequency. Later on, a detailed direct numerical simulation analysis is used to understand the origin of the aerodynamic benefits introduced by the flaplet movement induced by the interaction with the flow field. The parametric study that has been carried out, reveals that an optimal flap can deliver a mean lift increase of about 20% on a NACA0020 aerofoil at an incidence of 20o degrees. The results obtained from the direct numerical simulation of the flow field around the aerofoil equipped with the optimal flap at a chord Reynolds number of 2 × 104 shows that the flaplet movement is mainly induced by a cyclic passage of a large recirculation bubble on the aerofoil suction side. In turns, when the flap is pushed downward, the induced plane jet displaces the trailing edge vortices further downstream, away from the wing, moderating the downforce generated by those vortices and regularising the shedding cycle that appears to be much more organised when the optimal flaplet configuration is selected.
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