Kinetic Description of the Propagation of Plane Sound Waves in a Diatomic Gas

Plane wave solutions for the propagation of sound in a polyatomic gas have been obtained by employing the method of Sirovich and Thurber for polyatomic kinetic models. An asymptotic analysis valid at small frequencies yields the correct continuum limits for the absorption and speed of propagation, and numerical calculations were made for a wide range of frequencies and at several values of the collision number for the relaxation of internal degrees of freedom. Calculations using values of model parameters suitable for nitrogen, oxygen, and air, over a large range of the rarefaction parameter, are in very good agreement with dispersion and absorption measured in these gases.