Analysis of magnetohydrodynamic drag character for hypersonic vehicles

In hypersonic flight, a very high temperature area can form ahead of the nose of aerocraft due to the shock aerodynamic heating, which leads to air weakly ionized. Many researchers have demonstrated that it is effective to control flow by utilizing the interaction between weakly ionized air and a magnetic field. Most of previous researches focus on magnetohydrodynamic (MHD) heat shield, because the Lorentz force can increase the shock stand-off distance, further reduce convective heat flux. In this study, the MHD force effect is mainly considered, and the MHD drag characters under different types of magnetic field are discussed.The numerical simulation of hypersonic hemispherical flow field with external magnetic field is carried out by using a low magnetic-Reynolds MHD model. Three kinds of simple ideal magnetic fields (axial, radial and circle uniformly distributed magnetic field) are compared and analyzed. The influence and mechanism of the structure of the flow field, the aerodynamic drag and the Lorentz resistance of different magnetic fields are analyzed. It is found that under the radial ‘extrusion’ effect of the axial magnetic field, the shock wave shape is protruded and a ‘saturation phenomenon’ of pressure exists on the wall; the radial magnetic field has the axial ‘extrusion’ effect, the larger magnetic field intensity will lead to the formation of the high temperature area of the shoulder, and the induced electric field in the circle magnetic field leads to the poor effect of increasing resistance. Then the flow fields of two special magnetic fields (dipole magnetic field and solenoid magnetic field) are compared, and the radial ‘dilatation’ effect is found to be different from the ideal magnetic field. Compared with the Lorentz force under the different magnetic fields, the Lorentz force in the radial magnetic field is found to be concentrated in the high temperature area of the shoulder, and the Lorentz force is generally small under the circle magnetic field. The direction near the standing point will have an adverse effect, i.e., the resistance increases. In the specially distributed magnetic field, the direction of Lorentz force near the shoulder is approximately parallel to that of the shoulder, while the direction near the standing point is approximately perpendicular to the axis. Compared with the dipole magnetic field, the solenoid magnetic field with high Lorentz force region is close to the shoulder, so it will have good resistance enhancement effect. The influence of the dipole magnetic field on the wall pressure is weak. The effect of increasing resistance, caused by the magnetic field induced electric field, evolves from weak to strong in the following sequence:radial magnetic field, solenoid magnetic field, axial magnetic field, dipole magnetic field and circle magnetic field.