Higher moments of the velocity distribution function in dense-gas shocks

Large–scale molecular dynamics simulations of a Ms = 4.3 shock in dense argon (ρ = 532 kg/m3, T = 300 K) and a Ms = 3.6 shock in dense nitrogen (ρ = 371 kg/m3, T = 300 K) have been performed. Results for moments (up to order 10) of the velocity distribution function are shown. The excess even moments of the shock–normal velocity component (i.e., in the direction of shock propagation) are positive for most parts of the shock wave, but become negative towards the hot side of the shock before reverting back to zero. The even excess moments of the shock–parallel velocities and the odd moments of the shock–normal velocity do not change signs within the shock. The magnitude of the excess moments increases with the order of the moment, i.e., the higher moments correspond less and less to those of a Maxwell–Boltzmann distribution.