Numerical Analysis Of The Dynamic Stall Characteristics And Shape Optimization Of Low Reynolds Number Revolving Wing

Insects in nature are capable to perform remarkable flapping flight,achieving high aerodynamic efficiency and high maneuverability,as well as highly stable hovering flight.Dynamic stall,or delayed stall associated with leading edge vortex(LEV)is considered as one of the prominent mechanisms of lift-enhancement in flapping-wing aerodynamics in insect flight,which has also been confirmed in revolving wings in low Reynolds(Re)number regime.Recently,motivated by the development of micro air vehicles(MAV)and multi-rotor drones,more studies have been focused on the low Re dynamic stall mechanisms in concert with revolving wings.However,it is still unclear why this delayed stall at low Res performs remarkably distinguished from that at high Res.In this study,a hawkmoth wing-like geometric model and a revolving kinematic model with an impulsive accelerated start was built as the quasi-steady model of flapping wings.Systematic parametric study was carried out on stall characteristics in terms of two key parameters in the control equations of insect flight,namely Re and aspect ratio(AR).Research into Re effect over a wide range from 100 up to 5.4×10~5 shows that in the low Res regime where most insects fly,the revolving wing likely does not stall in a conventional sense:there is no trend that lift turns to reduce at some critical angle of attack(AoA)but keeps increasing with Res until reach certain margin.Research into AR effect over 5.56 to 11.12indicates that the vortex structures vary with notably while aerodynamic forces insensitive to the studied AR range.Smaller AR wing model achieves better efficiency.Based on these findings,a method was further proposed to optimize the revolving wing design in terms of wing shape with consideration of a design point.With this method,the attached leading-edge vortex near the wing root were more stable and aerodynamic efficiency better,and lift force was effectively enhanced 15%while the wing area reduced 40%。Overall,our studies into the Reynolds number and aspect ratio effect on dynamic stall mechanism and shape optimization method for revolving wing may provide reference for the insect-sized MAV design.