对称面圆周角对轴对称降落伞流场特性的影响

Influence of circular angle in symmetric plane to the flowfield characteristics of an axisymmetric parachute

根据降落伞的特点，通过3点假设（伞衣薄膜、伞的轴对称和流场定常），将三维复杂流动问题转化成二维轴对称问题，以节约计算时间．定义对称面圆周角，保持伞衣幅底部直径和顶孔直径不变，选取对称面圆周角在80°-140°范围内变化，建立一系列轴对称降落伞的计算模型．利用数值模拟手段，求解RNG（Renormalization Group）k-epsilon湍流模型下的N-S方程组，获得与有关单位试验相吻合的计算结果．分析发现对称面圆周角和伞衣幅高度对降落伞阻力影响很小．算例中阻力随对称面圆周角的变化在±0．28％以内．对称面圆周角的变化对轴对称降落伞尾流区流场的拓扑结构没有影响．对称轴上存在2个鞍点，随着对称面圆周角的增大，第1个鞍点的位置几乎不变，第2个鞍点的位置向尾流方向推移．

According to the characteristics of parachute, the 3-D complex flow problem was transformed into an axisymmetric problem with computational timesaving, based on three assumptions （membrane assumption of canopy, axisymmetric assumption of parachute, and steady assumption of flowfield）. After the circular angle in symmetric plane was defined and diameters of parachute bottom and top vent were kept invariable, a series of fluid dynamics computational model were established over circular angle range of 80° - 140°. By solving renormalization group （RNG） k-epsilon turbulence N-S equations, the numerical simulation result is in good agreement with the relative experiments. It is found that the influence of circular angle and parachute height is very small. The changes of drag in samples are below ±0.28 %. The wake topology structure of axisymmetrie parachute is unaltered with the circular angel of symmetric plane changed. There are two saddle points in the axis. With the circular angle in symmetric plane increased, the position of the first saddle point is fixed, and the position of the second saddle point moves wake oriented.