近自由表面仿生翼三维非定常流动控制和减阻机理的实验研究

Pelicans are good at flying in ground effect above water surface for foraging,they open the primary feathers at the wing tips to control the tip vortices,in order to adapt the variation of flying height and speed. In this way, they can achieve lift enhancement,drag reduction and keep flying stability. The flow field around pelican is disturbed by unsteady water wave, the physical characteristics are different from that of flying in free space, the geometric profile of the primary feathers are also different,the mechanism of the flow control of the primary feathers is unknown up to now.Inspired by this phenomena,we propose to conduct an experimental simulation of a bionic wing in ground effect in a wind-wave tunnel.In order to solve the problem of the drag reduction and keep flying stability,a Tomographic-PIV system is used to capture the 3D flow structure around the wing tip,and the aerodynamic parameters such as lift/drag forces and pressure distribution on the wing are measured as well, so as to inveatigate the relativey between flow structure of bionic wing tips and aerodynamic loads of the wing.By comparison and analysing, we will try to reveal the mechanism of the flow control of the bionic wing in different geometric profiles,and illustrate the physical principle of the drag reduction and lift enhancement of the bionic wing at the condition of the gas-wave coupling.Due to the speciel experimental condition in this project,new mechanical phenomena are expecting to be explored,therefore, this project is valuable to be implemented.As well, the results of is study will be use for reference to design of Wing in ground effect vehicle.

鹈鹕擅长利用地面效应做掠水面觅食飞行，它将翼尖羽毛张开，起到对翼尖涡的主动控制作用，以适应飞行姿态、高度、速度等因素的变化，实现增升减阻和保持飞行稳定性。鹈鹕翼面流场受波浪非定常扰动，力学特性与在自由空间飞行时区别明显，翼尖羽毛的几何控制姿态也完全不同，目前对其流动控制机理尚缺乏了解。为此，本项目拟在风浪槽中采用装有仿生翼尖的机翼模拟鹈鹕翼的飞行状态，针对近自由表面波动干扰下翼尖仿生装置如何实现增升减阻和改善飞行稳定性这一问题，以Tomo-PIV(层析PIV)技术测量翼尖三维速度场及演化，结合气动参量的测量，通过探讨翼尖三维非定常流动特性与气动载荷之间的关联性以及流场结构与自由表面相互作用关系，揭示不同姿态翼尖仿生装置的流动控制机理，阐明气液耦合条件下仿生翼增升减阻的内在物理根源，发现新的力学现象和力学机制，因此本项目具有重要的基础研究价值和科学意义，并对地效飞行器的优化设计有借鉴作用。

本项目以鹈鹕利用地面效应做掠水飞行时张开翼尖初级飞羽对翼尖涡进行主动流动控制为研究对象，采用多种不同形式翼尖帆片为仿生增升减阻装置，利用风洞和拖曳水槽实验模拟了鹈鹕的飞行姿态，进而深入探讨了地面效应条件下翼尖仿生装置如何实现增升减阻和改善飞行稳定性的机理，通过探讨翼尖三维非定常流动特性与气动载荷之间的关联性以及流场结构与自由表面相互作用关系，发现了不同形式翼尖仿生装置的流动控制效能的差异，并发现了新的力学现象。主要研究结果有：1）地面效应条件下仿生机翼升力线随攻角的增长偏离线性规律，越靠近地面，升力线弧度越大；2）短梯形翼尖帆片的增升效果优于长梯形帆片和椭圆梯形帆片，且攻角越大翼尖帆片的流动控制效能越高；3）翼尖帆片对翼尖涡的耗散以及翼尖涡向下游发展过程中的涡合并现象，显著降低了机翼的诱导阻力，是机翼的升阻比增加的主要因素之一；4）发现了翼尖涡在地面附近由于镜像涡的诱导产生展向运动，增加了翼尖涡的间距，也是诱导速度和诱导阻力降低的原因之一；5）梯形帆片的失速特性优于椭圆形帆片，具有较好的流动控制效能；6）机翼在波浪型表面附近升阻力的周期性变化与翼尖涡环量的周期性变化相对应。因此本项目所发现的流动现象和流动机理具有重要的基础研究价值和科学意义，并在工程上对于地效飞行器增升减阻或无人飞行器的长航时飞行优化设计有一定的应用前景。