The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically.After an initial start from rest,the wing is made to execute an azimuthal rotation(sweepin...The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically.After an initial start from rest,the wing is made to execute an azimuthal rotation(sweeping)at a large angle of attack and constant angular velocity.The Reynolds number(Re)considered in the present note is 480(Re is based on the mean chord length of the wing and the speed at 60% wing length from the wing root).During the constant-speed sweeping motion,the stall is absent and large and approximately constant lift and drag coefficients can be maintained.The mechanism for the absence of the stall or the maintenance of large aerodynamic force coefficients is as follows.Soon after the initial start,a vortex ring,which consists of the leading-edge vortex(LEV),the starting vortex,and the two wing-tip vortices,is formed in the wake of the wing.During the subsequent motion of the wing,a base-to-tip spanwise flow converts the vorticity in the LEV to the wing tip and the LEV keeps an approximately constant strength.This prevents the LEV from shedding.As a result, the size of the vortex ring increases approximately linearly with time,resulting in an approximately constant time rate of the first moment of vorticity,or approximately constant lift and drag coefficients. The variation of the relative velocity along the wing span causes a pressure gradient along the wing- span.The base-to-tip spanwise flow is mainly maintained by the pressure-gradient force.展开更多
基金supported by the National Key Technology R&D Program(2012BAD32B03)the Cooperative Innovation Foundation of Industry,Academy and Research Institutes(BY2013015‐10)in Jiangsu Province of China~~
基金The project supported by the National Natural Science Foundation of China(10232010)
文摘The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically.After an initial start from rest,the wing is made to execute an azimuthal rotation(sweeping)at a large angle of attack and constant angular velocity.The Reynolds number(Re)considered in the present note is 480(Re is based on the mean chord length of the wing and the speed at 60% wing length from the wing root).During the constant-speed sweeping motion,the stall is absent and large and approximately constant lift and drag coefficients can be maintained.The mechanism for the absence of the stall or the maintenance of large aerodynamic force coefficients is as follows.Soon after the initial start,a vortex ring,which consists of the leading-edge vortex(LEV),the starting vortex,and the two wing-tip vortices,is formed in the wake of the wing.During the subsequent motion of the wing,a base-to-tip spanwise flow converts the vorticity in the LEV to the wing tip and the LEV keeps an approximately constant strength.This prevents the LEV from shedding.As a result, the size of the vortex ring increases approximately linearly with time,resulting in an approximately constant time rate of the first moment of vorticity,or approximately constant lift and drag coefficients. The variation of the relative velocity along the wing span causes a pressure gradient along the wing- span.The base-to-tip spanwise flow is mainly maintained by the pressure-gradient force.
基金This work was supported by the National Natural Science Foundation of China(Grant No.12072013)the China Postdoctoral Science Foundation(Grant Nos.BX20220368,and 2022M720356)Beijing Municipal Natural Science Foundation(Grant No.20L00003).
