磁场中弱电离气体二维平板超音速边界层扰动演化研究

Study on evolution of disturbance in supersonic boundary layer of weakly ionized gas on a flat plate with imposed magnetic field

数值模拟了6种不同外加磁场下M_(?)=4.5、弱电离的二维平板边界层的基本流场及边界层中第二模态不稳定波的非线性演化。发现:外加磁场使边界层附近同一y处的流向速度减小从而使边界层的厚度增加;很大程度地改变法向速度;壁面摩擦系数减小:很大程度地抑制第二模态不稳定波的增长。这些影响主要决定于外加磁场的强度,而对外加磁场的产生方式不很敏感。外加磁场的存在还使得压力产生波动,在边界层内,压力波峰的位置与流向磁场力绝对值极大的位置基本一致:在边界层外,压力波峰的位置滞后于流向磁场力绝对值极大的位置,并且离边界层越远,这种滞后就越明显。

In this paper, steady base flow and nonlinear evolution of second mode instability wave in weekly ionized Mach 4.5 botmdary layer on flat plate with six different imposed magnetic fields are simulated by direct numerical simulation. It is found that due to the existence of imposed magnetic fields, streamwise velocity in vicinity ofwall is diminished which results in the thickening of boundary layer; normal x clocity is tremendously altered; skin friction coefficient is declined; the evolution of second instability wave is strongly depressed. It is also found that the influences mentioned above are not very sensitive to the arrangement of the magnetic dipoles but mainly determined by the strength of imposed magnetic fields. Pressure is caused to fluctuate and in boundary layer, the locations of pressure＇s crests are almost the same with the ones where the absolute value offi reaches its extremity, while out of botmdary layer, there is a hysteresis, and the further away from the boundary layer, the more significant the hysteresis is.