Study On Evolution Of Disturbance In Supersonic Boundary Layer Of Weekly Ionized Gas On A Flat Plate With Imposed Magnetic Field

In this paper, steady base flow and nonlinear evolution of second mode instability wave in weekly ionized Mach 4.5 boundary layer on flat plate with six different imposed magnetic fields are simulated by direct numerical simulation. The imposed magnetic fields are generated by placing two-dimensional magnetic dipoles below the flat plate surface. The N-S equations with the applied magnetic force terms are taken as the governing equations. By comparing with the results got without imposed magnetic field, the following conclusions are drawn:1. The imposed magnetic fields generated by placing two-dimensional dipoles below the flat plate surface exert similar effects on the pressure of flow field, that is, the pressure is caused to fluctuate which means the existence of favorable pressure gradient and adverse pressure gradient, the number of the peaks of pressure is the same with the one of extremes of the absolute value of magnetic force's component in x direction( f x) In boundary layer, the locations of pressure's crests are almost the same with the ones where the absolute value of f x reaches its extremity, while out of boundary layer, there is a hysteresis of the locations of pressure's crests to the ones where the absolute value of f x reaches its extremity , and the further away from the boundary layer, the more significant the hysteresis is. The degree of imposed magnetic fields'effects on pressure of flow field varies and is mainly determined by the strength of the imposed magnetic field, and it is not very sensitive to the different arrangements of the magnetic dipoles.2. The imposed magnetic fields generated by placing two-dimensional dipoles below the flat plate surface also impose similar effects on steady base flow, which means, the flow in the vicinity of the boundary layer is retarded by the imposed magnetic fields, this results in the thickening of boundary layer; the normal velocity is strongly modified by the imposed magnetic fields; skin friction coefficient is reduced everywhere on the flat plate. The degree of imposed magnetic fields'effects on steady base flow varies and is also mainly determined by the strength of the imposed magnetic field, and it is also not very sensitive to the different arrangements of the magnetic dipoles.3. The imposed magnetic fields generated by placing two-dimensional dipoles below the flat plate surface also have similar effects on nonlinear evolution of second mode instability wave, it means, the second mode instability wave is substantially stabilized by the imposed magnetic fields, the degree of stabilization varies and is also mainly determined by the strength of the imposed magnetic field, and it is also not very sensitive to the different arrangements of the magnetic dipoles.