【作者】 张蛟龙； 胡俊； 于勇；

【机构】 北京理工大学飞行器动力学与控制教育部重点实验室；

【摘要】 采用计算流体力学的多域网格划分、动态网格和大涡模拟技术对低展弦比矩形扑翼的三维流场进行了研究。研究发现,在小攻角情况下,前缘涡(LEV)紧贴扑翼上表面。随着攻角的增大,前缘涡逐渐升起,形成"拱形涡"。同时,新的漩涡会不断地在前缘产生。新形成的前缘涡与之前形成的一起构成"多前缘涡"结构,这对扑翼获得高升力是极其重要的。随着缩减频率增加,同一攻角下的前缘涡更加紧凑,且不易从翼面脱落。同时子涡结构减少,流场整体一致性变好。此外,两相邻前缘涡之间间距增加,不利于"多前缘涡"结构的维持。螺旋度分析结果表明,在前缘涡横断面处螺旋度密度较高,说明具有较好一致性的前缘涡内部能量消耗较低。缩减频率越大,其螺旋度密度越高,表明此时前缘涡传递给子涡结构的能量越小,能量利用率越高。此外,对扑翼模型升阻特性的分析表明,随着缩减频率的增加,升力性能不断增强;超过无量纲时间0.2,升阻比表现出极小的差异,说明缩减频率扑翼俯仰运动的升阻性能影响不大。更多还原

【Abstract】 Three-dimensional flow field of a low aspect ratio rectangular wing has been studied using Computational Fluid Dynamics by means of multi domain meshing,dynamic mesh and large eddy simulation technique.The results show that at small AOA,the leading edge vortex(LEV) is closely attached to the upper surface of the wing according to Q-iso surfaces.With the increase of the AOA,the LEV gradually rises up,and an ’arch vortex’ is formed.Meanwhile,new vortexes will continuously generate in the leading edge region.The newly formed LEVs together with the ones in the foregoing consist of ‘multi-LEVs structure’,which is of great significance for maintaining the high lift.With the increase of reduced frequency,the LEV at the identical AOA is more compact and not easy to break off.The number of sub vortex structures decreases,and the overall consistency of flow field becomes better.In addition,the distance between the two adjacent LEVs increases,detrimental to the maintenance of the multi-LEVs structure.Then,the analysis results of helicity indicate that the high helicity exists at the cross section of the LEV,showing that the energy consumption within the LEVs with good consistency is low.And the larger the reduced frequency is,the higher the helicity of the LEV will be,indicating the less energy is transferred to the sub vortex.Besides,the lift and drag characteristic is studied to deepen the understanding of the developments and changes of LEV.The results show that the lift performance will be enhanced with the reduced frequency increasing.Beyond t/T(28)0.2,the lift-drag ratios have little discrepancy,which indicates that the reduced frequency has little influence on the lift-drag ratio of the flapping wing doing the pitching motion.更多还原