Numerical investigation on interaction mechanisms between flow field and electromagnetic field for nonequilibrium inductively coupled plasma

Abstract

In this paper, the inductively coupled plasma (ICP) wind tunnel, which is widely used in the development of thermal protection system for reentry vehicle in the aerospace field, is studied. The distribution properties and the interaction mechanism of the flow field and electromagnetic field are investigated by numerically solving the multi-physics fields coupling among the flow field, electromagnetic field, thermodynamic field and turbulent field. In the numerical simulation, the thermochemical non-equilibrium plasma magneto-hydrodynamic model is used to accurately simulate the high-frequency discharge, Joule heating, energy conversion, and internal energy exchange of air ICP. Finally, the distribution of electron temperature, particle number density, Lorentz force, Joule heating rate, velocity, pressure and electric field strength of air plasma are obtained through the multi-physics field coupling calculation. The results show that the plasma flow is in a thermodynamic non-equilibrium state near the torch wall in the induction coil region and that the Lorentz force plays an important role in controlling the momentum transfer. A strong eddy flow occurs between the inlet and the second turn of the inductive coil. The eddy flow has a close relationship with the negative pressure gradient and the electromagnetic heating phenomenon in the induction coil region. The radial Lorentz force is always negative. This indicates that the free electrons are generated near the wall due to the fact that the skin effect are always subjected to a force making them move to the central axis of the ICP torch. The maximum value of the radial Lorentz force is 3.95 times higher than that of the axial Lorentz. This indicates that the momentum transfer is predominantly radial. The Joule heating effect of the air particles is also affected by the radial Lorentz force. The maximum value of <i>E</i><sub>I</sub> is 2.9 times larger than the real part of electric field, <i>E</i><sub>R</sub>. The positive <i>E</i><sub>I</sub> is generated by the free electrons inside the plasma. The number density of free electrons reaches a maximum value at a distance of 5.5 mm far from the inner wall surface of the torch below the second induction coil. 91% of N<sub>2</sub> are dissociated into atomic N near the central axis. The maximum electron and translational temperature simulated in this paper are 9921 K and 8507 K, respectively.