Discrete Boltzmann modeling of Kelvin–Helmholtz instability in plasma

The Kelvin–Helmholtz Instability (KHI) with and without external magnetic fields is computationally investigated based on the Discrete Boltzmann Method (DBM). The maximum local Knudsen number in the system is up to more than 0.06. Simultaneously, the density correction induced by the second-order Knudsen number effects near some interfaces is up to more than 10% . This work aims at the kinetic physics that occurs on the length and time scales of particle collisions, which leads to discrete/non-equilibrium effects and may contribute to the observed differences between hydrodynamic predictions and experiments. Through selecting appropriate kinetic moments, the DBM has the capability to describe flow systems ranging from continuum to early transition flow regime. The first- and second-order DBMs with different physical capabilities are constructed. The results of the two DBMs are compared, including the hydrodynamic non-equilibrium and the most relevant thermodynamic non-equilibrium behaviors. It is found that: (i) In KHI, without an external magnetic field, two competing energy transport mechanisms influence the saturation moment of the vortex. (ii) In the presence of an external magnetic field, viscous shear stress and heat flux are enhanced, while the magnetic field suppresses the KHI evolution by inhibiting vorticity transport and inducing secondary vortex structures. This results in an increased local Knudsen number and density difference. (iii) The Atwood number At further amplifies the local Knudsen number and density difference. The maximum density difference first increases and then decreases with At as it suppresses the formation of rotational discontinuities near the saturation moment.