Multi-field Coupling Numerical Study On Plasmasonic Sheath Of Hypersonic Flying Craft

When hypersonic vehicles fly at more than 5 times of the speed of sound,hypersonic air flows near the aircraft.The different energy relaxation processes and a lot of complicated chemical reactions,such as dissociation,ionization,excitation,recombination et al.These effects lead to the formation of a thin layer of plasmasonic sheath covering the surface of the hypersonic vehicle.Electromagnetic wave propagation through a plasma sheath to maintain communications to hypersonic vehicles has been a huge challenge to the design of hypersonic vehicles,since the electromagnetic wave could be reflected,absorbed and refracted by the plasma sheath,that causes the so-called blackout.There is no doubt that a well understanding of the interaction of electromagnetic waves with the plasma sheath is the key to the solution of blackout,while an accurate prediction of the plasma sheath properties is a prerequisite condition to start the study of this interaction.Motivated by those,in this paper,a thermos-chemical non-equilibrium physics-mathematics model is established,and the commercial CFD software USim are used to numerically study the characteristics of the plasma sheath,especially the electron density and the collision frequency of electron-neutral particle.The two-temperature(i.e.,the translational-rotational temperature and vibrational-electron temperature)and 7 species with 18 reactions are assumed to deal with the thermodynamic and chemical non-equilibrium respectively.What? more,the results of two-temperature model are compared with those of one-temperature model.The one-temperature model is firstly adopted to numerically descript the plasma sheath in the flight test RAM-C ? at attitude of 61 km with different velocities.The space distributions of the temperature,pressure,velocity and number densities of different species are obtained.The comparison between the calculated results of the electron number density and the experimental data is analyzed to verify the reliability of the computational code.Based on the benchmark,a more realistic dual-temperature multi-field coupling model is used to numerically simulate the formation of the plasma sheath of RAM-C ? at attitudes of 61 km and 71 km.And the distributions of the temperatures,velocity,electron number density and collision frequency of electrons and each neutral component are given here,and the most attentions are paid to the parameter distributions along the stagnation line.The calculated results show the exist of the detached shock wave and the huge differences of plasma parameters between the both sides of the shock.It also can be shown that the non-equilibrium effect is the most obvious in the head region;the peak value of electron number density can reach 1020m-3,and the collisions of electrons and neutral particles are dominated by the collisions with nitrogen molecular,with the magnitude of collision frequency 109 s-1.While the attitude has minor effect on the electron number density.