In this paper, an experimental investigation on the flow structures in a turbulent bounda- ry layer employing a special laser light sheet-Hydrogen bubble flow visualization technique is described. It is observed that ...In this paper, an experimental investigation on the flow structures in a turbulent bounda- ry layer employing a special laser light sheet-Hydrogen bubble flow visualization technique is described. It is observed that the high/low speed streaks are directly related to the hairpin or horseshoe-like vortices. This observation can give a better understanding of the physical mechanism in the turbulent boundary layer.展开更多
Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles.The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble v...Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles.The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble visualization and the Particle Image Velocimetry(PIV)techniques.There are three near-wall topological patterns with different Angles of Attack(AoAs):the separation bubble,the Leading-Edge Vortex(LEV)and the high Ao As flow.For the separation bubble pattern,two saddles and two foci form in the middle of the model.The features of the LEV pattern are the leading-edge separation lines.The topological characteristics of the separation lines are changed by the interaction between the LEV and the Wing-Tip Vortex(WTV).For the high Ao As flow pattern,four unstable foci are found at the forewing and the hindwing respectively.The angle between the trajectory of the WTV and the model increases with increasing Ao A even though the slope of the WTV angle versus Ao A curve declines at the moderate AoAs.展开更多
文摘In this paper, an experimental investigation on the flow structures in a turbulent bounda- ry layer employing a special laser light sheet-Hydrogen bubble flow visualization technique is described. It is observed that the high/low speed streaks are directly related to the hairpin or horseshoe-like vortices. This observation can give a better understanding of the physical mechanism in the turbulent boundary layer.
基金funded by the National Natural Science Foundation of China (No. 11721202)。
文摘Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles.The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble visualization and the Particle Image Velocimetry(PIV)techniques.There are three near-wall topological patterns with different Angles of Attack(AoAs):the separation bubble,the Leading-Edge Vortex(LEV)and the high Ao As flow.For the separation bubble pattern,two saddles and two foci form in the middle of the model.The features of the LEV pattern are the leading-edge separation lines.The topological characteristics of the separation lines are changed by the interaction between the LEV and the Wing-Tip Vortex(WTV).For the high Ao As flow pattern,four unstable foci are found at the forewing and the hindwing respectively.The angle between the trajectory of the WTV and the model increases with increasing Ao A even though the slope of the WTV angle versus Ao A curve declines at the moderate AoAs.
