Shock Front Thickness and Bulk Viscosity in Polyatomic Gases

Abstract

The thickness of shock fronts in carbon dioxide and nitrous oxide gases has been measured by the light reflectivity method. The thickness of these fronts are in agreement with thicknesses predicted theoretically when only shear viscosity and heat conduction effects are considered. They demonstrate that the contribution of any real bulk viscosity is small. The molecular vibrations are not excited in the shock front and hence the large sound absorption in these gases in excess of that calculated using shear viscosity can only come from the vibrational excitation process. Real bulk viscosity in ideal gases is not a manifestation of vibrational excitation but only of the rotational excitation process.