The Numerical Simulation Study Of Electrodynamic Aerobraking Of Hypersonic Spacecraft In Rarefied Regime

Behind the bow shock which is in front of the hypersonic vehicle whose velocity is usually greater than mach 12, the main species of the rarefied air N2 and O2 almost will dissociate into atoms N and O due to the extraordinarily high temperature, and the electronic state modes of lots of atoms are excited. So, positive ions and electrons come out because of the spontaneous ionization process between some atoms. And then, the collisions between the produced electrons and neutral particles lead to some other forms of ionization process.If the magnetic dipole is placed in the front of the vehicle, the charged particles affected by the magnetic field move as the Larmor cyclotron, then many circles of induced current form. Obviously the current suffer the Lorenz force in the magnetic field. It is known that one element of Lorenz force is in the opposite direction of the velocity of the coming flow by analysis. As a result, the flow behind the shock is decelerated, meanwhile, the shock intervals increase. When the vehicle re-entries into the upper of the atmosphere, we can consider take this method to decelerate the capsule.Currently, the DSMC method has been widely used to hypersonic rarefied flow, micro rarefied flow and so on, but it still is challenged to simulate weakly ionization flow using DSMC. On one hand, some properties of electron are different from the charged or not heavy particles that the mass is lighter about 5 order of magnitude and the velocity is higher around 2 order of magnitude, which cause the sampled time step for electron is less 2 order of magnitude at least, on the other hand, the charged particles are also affected by the electric potential filed of the other charged particles, and this situation cannot described by the existed molecule modes. These are both the main difficulties in simulating weakly ionization with DSMC method.According to advice given by Bird, the electroneutrality hypothesis is available when the characteristic dimension is larger much than the Debye dimension, which means the produced positive ion and the electron are restricted in a sphere whose radius is the Debye dimension. This idea has been proved feasible by Bird. So in this paper we use this method to simulate the rarefied pure nitrogen atmosphere with weakly ionization affected by magnetic field and show the effect results varies with the magnetic density. In the end, we explore the possibility that the capsule in the upper atmosphere take the method considered above to make aero-braking.