SECOND ORDER VISCOSITY APPROXIMATION FOR A RELAXING GAS

If in a moving gas a thermodynamic relaxation process takes place the thermodynamic equilibrium pressure differs from the negative normal stress. To a first approximation the difference is determined by the bulk viscosity of the gas. An already known expression for the bulk viscosity is derived under rather general assumptions about the gas. Furthermore, the difference between thermodynamic equilibrium pressure and normal stress is calculated to a second order approximation. Application of the result to the calculation of shock structure in a relaxing gas shows oscillatory behavior of the upstream flow variables for higher shock strengths. This corresponds to the same behavior of solutions obtained by applying the Burnett-approximation in the kinetic theory of gases to the shock structure problem. © 1969 Springer-Verlag.