Rosti Marco E, Omidyeganeh Mohammad, Pinelli Alfredo
1Linné Flow Centre and SeRC (Swedish e-Science Research Centre), KTH Mechanics, SE 100 44 Stockholm, Sweden.
2School of Mathematics, Computer Science and Engineering, City, University of London, London, EC1V 0HB UK.
Flow Turbul Combust. 2018;100(4):1111-1143. doi: 10.1007/s10494-018-9914-6. Epub 2018 Apr 26.
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 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 can deliver a mean lift increase of about 20 on a NACA0020 aerofoil at an incidence of 20 degrees. The results obtained from the direct numerical simulation of the flow field around the aerofoil equipped with the flap at a chord Reynolds number of 2 × 10 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 flaplet configuration is selected.
几乎所有鸟类都会使用自激活羽毛来调整翅膀特性，以延迟失速或减轻其不利影响（例如在着陆时或由于阵风导致攻角突然增加时）。据信，一些羽毛会因气流分离而弹出，并与气流相互作用，对不稳定涡度场产生有益的改变。受鸟类羽毛启发，在飞机上使用自适应襟翼，需要了解产生上述空气动力学益处的物理机制，并确定襟翼的特性，包括其尺寸、位置和理想的制造材料。在此框架下，本数值研究分为两部分。首先，在一个简化场景中，我们通过改变襟翼的长度、位置和固有频率，确定安装在大攻角翼型上的襟翼能够提供增加升力和提高空气动力学效率的主要特性。随后，通过详细的直接数值模拟分析，来理解襟翼与流场相互作用引起的运动所带来的空气动力学益处的来源。已进行的参数研究表明，在20度入射角下，一个[此处原文缺失具体襟翼相关内容]可使NACA0020翼型的平均升力增加约20。在弦雷诺数为2×10的情况下，对装有[此处原文缺失具体襟翼相关内容]襟翼的翼型周围流场进行直接数值模拟得到的结果表明，襟翼运动主要是由翼型吸力面上一个大回流泡的周期性通过引起的。反过来，当襟翼向下推动时，诱导平面射流将后缘涡旋进一步向下游推移，远离机翼，减轻这些涡旋产生的下压力，并使脱落周期变得规则，当选择[此处原文缺失具体襟翼相关内容]襟翼配置时，脱落周期似乎更加有组织。
