伞衣透气性对翼伞气动特性的影响

Effects of canopy's air permeability on parafoil aerodynamic performance

为了提高翼伞的飞行性能,需要研究伞衣织物透气性对翼伞气动特性的影响。使用不可压雷诺时均Navier-Stokes(RANS)方程模拟伞衣外部流场,建立了包含附加动量源项的多孔介质域控制方程模拟伞衣,对2种透气性材料模型和无透气性影响传统模型的气动特性和流场分布进行了二维和三维定常数值模拟。数值结果表明,求解多孔介质域控制方程可以得到较准确的伞衣透气速度,伞衣表面的湍流度急剧增加;使用较大透气量材料制作伞衣时,升力系数大幅下降,阻力系数大幅上升,同时会造成内腔泄压影响翼伞的外形保持;使用微透气量材料制作伞衣时,升力系数在小迎角时小于不透气模型,在大迎角时大于不透气模型,较小的透气速度能在大迎角时延缓边界层分离。

In order to enhance the flight performance of parafoil, the effects of canopy fabric＇ s air perme- ability on parafoil aerodynamic performance were studied. The canopy external flow field was modeled by the incompressible Reynolds-averaged Navier-Stokes （RANS） equations, and the governing equations for porous medium domain with an additional momentum source term were established to model the canopy. For two material models with air permeability and one traditional model without air permeability, the aerodynamic char- acteristics and distribution of the two-dimensional and three-dimensional flow field were numerically simulated under steady condition. The results indicate that the canopy seepage velocity is available by solving the gover- ning equations of porous medium domain, and the canopy external turbulivity increases sharply. The lift coeffi- cient decreases and drag coefficient increases significantly when the canopy is made of large air permeability fabric, and furthermore the inner cavity pressure dropping affects the aerodynamic shape maintaining of parafoil. The lift coefficient is less than that in impermeable case at small angle of attack, and is greater than that in impermeable case at large angle of attack when the canopy is made of slight air permeability fabric be- cause mild seepage velocity can delay the boundary layer separation at large angle of attack.