基于滑移网格技术的翼伞动导数分析

Calculation of Dynamic Derivatives for Parafoil Based on Sliding Mesh Technique

翼伞在航天回收领域有着广泛的应用前景,为了提高对翼伞动稳定性认识,文章针对某型号的翼伞进行动导数的分析。基于滑移网格技术,采用计算流体学的方法对翼伞进行了三维数值模拟。重点分析了翼伞做小幅度俯仰、偏航和滚转运动时的动导数,通过改变攻角和减缩频率这两项重要参数,获取了多组力矩系数迟滞曲线,利用时间平均法对非定常气动力数据进行处理,得到了翼伞绕三个坐标轴的阻尼系数。计算结果表明:翼伞在小攻角下做小幅度强迫运动时,在俯仰和滚转方向上阻尼导数为负,翼伞具有俯仰和偏航方向上的动稳定性,在偏航方向阻尼导数为正,翼伞不具有偏航方向的动稳定性;攻角和减缩频率的选取均会影响翼伞阻尼导数的计算结果,其中,攻角的增加不仅能影响迟滞环面积的大小还能影响迟滞环的动态特性,使翼伞的动稳定性发生变化,而减缩频率的改变仅影响迟滞环面积的大小,对偏航方向的动稳定性没有影响。

Parofil in the field of spacecraft recovery has widely prospect.To improve the understanding of dynamic stability of the specific parafoil,the dynamic derivative of a type of parafoil is analyzed in this paper.Based on the Computational Fluid Dynamics(CFD),a three-dimensional numerical simulation was completed by using sliding mesh.The emphasis is on the analysis of the small amplitude pitch,yaw and roll oscillation.Furthermore,different angles of attack and the reduction of frequency are choose to achieve the hysteresis curve of moment coefficient,and a time average method was built to calculate damp dynamic derivative around three axes.The results show that when the parafoil moves in small amplitude oscillatory motion at small angle of attack,the dynamic derivative is negative in the direction of pitch and roll.It has the dynamic stability in pitch and roll direction.However,in the yaw direction,the dynamic derivative is positive which means that it is unstable.Angle of attack and the reduce frequency would affect the dynamic derivative of parafoil,the increment of angle of attack can not only affect the size of hysteresis loop but also the dynamic characteristics of hysteresis loop,thus changing the dynamic stability.However,reducing frequency only affects the size of hysteresis loop,the dynamic stability will not change.