Features of Bulk Viscosity Simulation in Carbon Dioxide

The aim of this work is to build an adequate model for calculating the bulk viscosity in carbon dioxide and to evaluate its contribution to the normal mean stress under various conditions. Bulk viscosity characterizes the finite time of energy exchange between the translational and internal degrees of freedom Bulk viscosity in carbon dioxide is considered in the one-temperature approximation devel-oped using the Chapman ‒ Enskog method taking into account the rotational and vibrational degrees of freedom, as well as complex mechanisms of vibrational relaxation including intra-and inter-mode vibrational energy transitions. Chemical reactions are not included to the model. Two models for the bulk viscosity coefficient in CO 2 are considered: the model based on the exact kinetic theory methods, as well as the model representing the bulk viscosity coefficient as a sum of independent contributions of rotational and vibrational degrees of freedom. The latter model predicts that in carbon dioxide at room temperature, the bulk viscosity coefficient may exceed that of shear viscosity by several orders of magnitude and, thus, make a significant contribution to the stress tensor. In this work, it is shown that the use of a consistent theoretical approach does not allow separating the bulk viscosity into independent rotational and vibrational contributions. Vibrational relaxation times are evaluated using different models.