ABSTRACT
The equations that govern the motion of a fluid consist of conservation equations, auxiliary relations, and initial and boundary conditions. The first group is preeminent; it includes conservation of mass, relations for linear and angular momentum, an energy equation, and the second law of thermodynamics. These equations are most simply obtained in integral form, from which their differential version can be deduced. Auxiliary equations are principally the constitutive relations that provide equations for the thermodynamic and transport properties. Equations (1.54b) and (1.59) are in this category. They also include equations for properties of interest, such as the vorticity, rate of entropy production, and the skin friction and heat transfer at a wall. Indeed, these last two items are principal engineering concerns. Any fluid flow, of course, is incomplete unless conditions fixing the configuration, such as upstream boundary conditions, wall conditions, etc., are prescribed.
