20.1 Governing Equations for Viscous Flows
The Navier-Stokes (NS) equaadtions are the governing equations for the viscous compressible flow and hence are the governing equations for hypersonic flows. This section deals with the basics of NS equations and its non-dimensionalization.
Continuity Equation:

Considering steady state conditions we have;

X Momentum Equation:

therefore the L.H.S. simplifies to give X momentum equation in Steady State  Conditions as;

Y Momentum Equation: