Isentropic flow of a perfect gas in a nozzle
Fluid mechanics-One-dimensionnal compressible flow

Its profile must therefore be such that it dresses exactly the flow vein studied in paragraph 2. So, for example, if the pressure in the nozzle varies from p ₀ to zero in the direction of flow, the profile must converge, then diverge, and the outlet cross-section must be infinite. The inlet cross-section will itself be infinite if the inlet velocity is zero.

In practice, the theoretical flow conditions are never met and, in particular, the fluid viscosity...