旋翼机对降落伞工作性能的影响

Effects of rotorcraft on aerodynamic performance of parachute

摘要:

为研究旋翼机对降落伞工作性能的非定常影响,建立一套适用于旋翼机伞降系统非定常复合流场的数值模拟方法。首先,采用PISO（pressure implicit split operator）算法和Reliazable k-ε湍流模型,以提高瞬态计算效率和粘性计算精度,准确捕捉流场尾涡细节变化。其次,建立了高效的动态网格更新模型,结合Diffusion Smoothing和Remeshing两种网格更新方法,对不同变形尺度的网格进行分类处理.在此基础上,研究了旋翼扰动下物伞系统的非定常尾流特征和降落伞气动特性的变化。 结果表明:旋翼转动使前体尾流区长度增加,尾流对降落伞影响增强,伞衣入口的流场结构呈不对称分布；前体尾部负涡量区逐渐上移,与伞衣入口的负涡量区相连通,促进了伞衣尾涡的脱离,伞衣尾流区的旋涡数量明显增加；另一方面,旋翼转动扰乱了前体表面的涡流分布,形成旋转涡流区,前体尾流中的脱落涡流区范围变小,受涡量黏性耗散的影响,进入伞衣的旋涡强度减弱.随着旋翼转速增加,伞衣外侧压力不变,内侧压力和压强系数均逐渐减小,内外压差减小,降落伞的平均阻力系数逐渐减小。

Abstract:

To study the unsteady effects of rotorcraft on the aerodynamic performance of parachute, a numerical simulation method for the unsteady compound flowfield of rotorcraft-parachute system was established. First, the pressure implicit split operator (PISO) algorithm and Reliazable k-ε model were applied to improve the efficiency of transient calculation and the accuracy of viscosity calculation, and the detail changes in the wake vortex were accurately captured. Subsequently, an efficient dynamic mesh updating model was established, and the Diffusion Smoothing and Remeshing methods were adopted to classify meshes with different deformation scales. Then, the unsteady wake characteristics of the rotorcraft-parachute system and the aerodynamic characteristics of the parachute were studied. Results show that the rotor increased the length of the frontal wake area. The influences of the wake on the parachute were increasing, and the flowfield structure at the entrance of the parachute was asymmetrically distributed. The negative vorticity area at the tail of the rotorcraft gradually moved up and connected with the negative vorticity area at the entrance of the canopy, which promoted the separation of the vorticity from the canopy. The number of vortices in the wake increased significantly. On the other hand, the rotor disrupted the vortex distribution around the rotorcraft, which formed a rotating vortex region. The range of shedding vortex in the wake became smaller. The vorticity magnitude entering the canopy was weakened due to the vorticity viscous dissipation. With increasing rotor speed, the outer pressure of canopy remained the same, but the inner pressure and pressure coefficient gradually decreased, and the pressure difference was reduced, so the average drag coefficient of the parachute gradually decreased.