Numerical Investigation On The Influence Of Corrugation Location Distribution On Aerodynamic Performance Of Dragonfly Airfoils

Micro air vehicle has a wide application prospect in military and civil fields.With the requirements of miniaturization development,micro air vehicle is faced with aerodynamic problems at low Reynolds number.In low Reynolds number environment,traditional smooth airfoils will be affected by viscosity effect,resulting in laminar flow separation and other conditions,which limits its aerodynamic performance.Therefore,it is of certain engineering significance to develop airfoils with high aerodynamic performance inspired by the morphological characteristics of insect wings with strong flying ability.Dragonfly,as the outstanding flyer in nature,has two significant characteristics of its wings: corrugated structure in cross section and tandem aerodynamic layout of front and rear wings.As a significant morphological feature of dragonfly wings,corrugated structure can improve wing strength,but its aerodynamic influence at low Reynolds number has not been reached a unified conclusion.In this paper,computational fluid dynamics（CFD）method is applied to study the effect of corrugated position distribution on the unsteady aerodynamic performance of single wing and tandem wing in gliding and flapping flight states.Firstly,by studying the influence of chord position distribution of corrugation on aerodynamic performance of single wing,the flow law of corrugated airfoils is revealed,and the influence of chord position distribution of corrugation is summarized.When The Reynolds number is 1500,the vortex in the trailing edge corrugation absorbs the leading edge vortex,which makes the leading edge vortex closer to the wall,delays the shedding of the leading edge vortex,and increases the negative pressure on the upper wing surface,so that the gliding aerodynamic performance of the airfoil is optimal when the corrugation is at the trailing edge.The change of Reynolds number has no effect on this phenomenon.However,in flapping flight,the larger Angle of attack flapping causes large-scale flow separation around the flow,and the aerodynamic performance of airfoils is insensitive to surface corrugation structure,so the change of the chord position of the corrugation has less impact on aerodynamic performance than that of gliding flight.Secondly,the corrugation of upper and lower wings of a single wing are distinguished,and the influence of corrugation distribution of upper and lower wings on aerodynamic performance of airfoils is revealed.The result shows that: no matter in gliding or flapping flight,the trailing edge corrugation of the upper wing surface can improve the negative pressure of the surface,which is beneficial to the improvement of the aerodynamic performance of the airfoils,the corrugation of the lower wing surface will reduce the positive pressure of the surface and adversely affect the aerodynamic performance of the airfoils.Finally,the influence of the chord position of the corrugation in tandem wings is studied,and the influence of the chord position distribution of the corrugation on the aerodynamic interaction mechanism of front and rear wings is revealed.The result shows that: in gliding flight,the tandem wing whose corrugation is located at the trailing edge of the front wing has the best aerodynamic performance,when the front and rear wing flapping at 0°phase difference,the aerodynamic force produced by the tandem wing is the largest.In the two flight states,the change of forewing corrugation structure has no obvious effect on the rear wing,when the rear wing corrugation is located at trailing edge,the aerodynamic performance of the front wing can be improved,but this improvement is not obvious when the front and rear wing are flapping at 180°phase difference.