Study On The Effects Of Phase Difference On Aerodynamic Characteristics Of Double Flapping Wings

Flapping-wing aircrafts attract many scientists and biologists to explore with its advantage: high efficiency and good concealment.The dragonfly has two pairs of wings and under the interaction of the forewings and hindwings,their flight is more stable and maneuverable.The phase difference between fore and hind wings plays a key role in the aerodynamic characteristics.Therefore,the effects of phase difference on aerodynamic characteristics of double flapping wings is studied by numerical in this paper.With guidance of the numerical research results,the phase-difference-control mechanism and the experimental prototype have been designed and fabricated.Finally,the relevant experiments are completed on the experimental platform.The morphological and stroke-kinematic parameters of the calculated model are firstly established.The Navier-Stokes equation is solved by STAR-CCM+,the flow field around the wings is numerically simulated.The the effects of phase difference on aerodynamic characteristics of double flapping wings is analyzed,the results provides theoretical guidance for the design of flapping-wing aircrafts.The aerodynamic characteristics of the wings under different flapping frequencies,advance ratios and phase differences are studied.The results show that: the vertical force curve exhibits a U-shape as the phase difference changes,and the forewings and hindwings have various flow interactions when they are flapping.The interactions includes wake interaction,leading edge vortex interaction and encounter interaction.Compared with the forewings,the hindwings are more affected by the interactions and the degree of interaction increases as the advance ratio increases both forewings and hindwings.There is a positive correlation between the aerodynamic power and the vertical force,indicating that most of the power in the aerodynamic power is used for the generation of vertical force.The advance ratio isn't affect the aerodynamic characteristic of forewings,the oscillation of aerodynamic efficiency of the forewings is mainly determined by the the rotation power.The aerodynamic efficiency of the hindwings changes with the advance ratios,which is because the advance ratio changes the degree of the different interaction's of forewing-hindwing.In order to further study the effects of phase difference on aerodynamic characteristics of double flapping wings,a special screw mechanism which can change the phase difference from 0 to 360° of the forewing-hindwing was designed.Meanwhile a experimental prototype was designed and completed.After testing,the mechanism can effectively change the phase difference between the forewings and hindwings of the prototype.A force measurement experiment was carried out with the prototype on arelevant force measurement platform.The experimental results show that: the experimental data meets to the calculation results and the forces change with time are basically the same under different phase differences.The experimental data shows that the phase difference can change the aerodynamic force of the prototype and the vertical force is maximum when flapping in phase.The law of aerodynamic force changing with phase difference is basically the same at different flapping frequenciesThe research results in this paper enrich the research on the effects of phase difference on aerodynamic characteristics of double flapping wings.And the experimental prototype which designed in this paper provides a theoretical basis and experimental support for the development of the flapping-wing aircraft.