Non-equilibrium sound propagation using the orientation-free discrete kinetic theory

Computations using orientationfree discrete velocity models for the dispersion relationship of ultrasound propagation in monatomic hardsphere gases (or gases composed of systems of vortices) are presented. Comparisons with previous verified fixedorientation results for the propagation of the sound mode of ultrasound in rarefied gases show that if collective excitations are considered, orientationfree discrete velocity models can provide more physical insight. We also address the symmetry and limits of these models.