Dynamics of sheared gases

When the characteristic length associated to the gradient of at least one h ydrodynamic field becomes comparable to the mean free path, standard hydrod ynamics does not apply. Situations like this are particularly evident in sh eared gases. A gas-dynamics valid for sheared gases derived from Boltzmann' s equation is presented in a compact form in two and three dimensions. The equations are then reduced to the case of stationary planar flow where they are seen to imply highly nonlinear transport equations. The gas-dynamic eq uations correctly describe, for example, the observed shear thinning and he at flux not orthogonal to the isotherms. The shape of all the hydrodynamic fields can be obtained with extraordinary precision. (C) 1999 Elsevier Scie nce B.V. All rights reserved.