大迎角脱体涡流场的螺旋性密度

On Asymmetrical Vortex Flows at High Incidence

采用拟压缩性方法数值求解不可压缩的Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程。提出一种当地时间步长，加快Ｂｅａｍ－Ｗａｒｍｉｎｇ近似因式分解方法的收敛速度。通过在正切拱型旋成柱体的头部施加微小的射流扰动，使得大迎角流场的计算得到与实验结果相符的非对称脱体涡。在流场中引入螺旋性密度的概念，图形描述脱体涡流场中的涡分布。

In some aerospace applications, experiments have already revealed that asymmetry exists for incompressible flow past symmetrical flight vehicle when angle of attack is large.We have seen no generally accepted theoretical explanation of such a phenomenon in the open literature.Previous numerical calculations, including that by the first author et al, can numerically show asymmetry, but we deem that the asymmetry is very likely due to Inherent defects in the methods of calculation used,at least in the case of the first author et al.In this paper we give a numerical method that is without the abovementioned defects,but does lead to asymmetry when a suitably small jet disturbance is applied.In Fig.l,where no disturbance is applied,symmetry is preserved even when angle of attack is 30°.Figs.2 and 3, where jet disturbance is applied, show asymmetrical results that are in agreement with Lamont's test data[5].Our method of calculation is based on well -known principles of incompressible flow.It is worthwile to point out that acceleration in convergence is achieved through our proposed new expression of local time step as given in eq.(3).