Effect Of Flapping-wing On The Thrust Generated By Wing Vortex And Wake Based On UVLM

Insects are the earliest flying species on the earth.Their flight ability has been optimized by hundreds of millions of years of evolution,and they have been able to hover,jump,accelerate and turn at will.This is not available in existing aircraft.Inspired by biological aircraft such as insects,flapping wing aircraft adopts the movement form of flapping wing that can generate lift and thrust at the same time,which has the advantages of high energy utilization rate,quiet flight process,good maneuverability and convenient takeoff and landing,etc.,and is suitable for short distance limited space tasks in buildings.In recent years,with the development of many emerging disciplines such as microelectronics,materials science,automatic control and finite element analysis,the research on insect-like flapping wing aircraft has developed rapidly.However,as an aircraft with high flight efficiency,small load and complex structure,the development cycle of flapping wing aircraft is long and cross-disciplinary.Therefore,although flapping wing aircraft has made many breakthroughs in recent years,it still falls far short of the requirements in practical application and still has a long way to go.Different from conventional aerodynamics,the unsteady effect has a significant effect on the motion stress of flapping wings,and the unsteady effect is a hot and difficult point in fluid mechanics.With the development of unsteady vortex lattice method(UVLM)and low Reynolds number aerodynamics,recent studies have found the unsteady aerodynamics mechanism unknown before the flapping wing motion.Although most previous studies have focused on the pitching and flapping motion of flapping wing UAV,the aerodynamic influence of wing vortex and trailing vortex on aircraft thrust needs to be studied for more accurate simulation.In this paper,the three-dimensional unsteady vortex lattice method was applied to the flapping wing aircraft model,and the calculation program was developed to obtain the lift and thrust data at different frequencies,amplitude and average pitch angle.In particular,the influence of flapping frequency on the instantaneous thrust generated by wing vortex and trailing vortex was studied by comparing with the experimental data.The results show that the average thrust increases with the increase of flapping frequency,and the thrust produced by the wing vortex is much larger than that produced by the trailing vortex.The thrust ratio of wing vortex and trailing vortex increases with the increase of flapping frequency.This research is helpful to understand the flight mechanism of biology and improve the design of bionic flapping wing aircraft.