Relationship between Actual and Stagnation Properties

The relation between enthalpy h, stagnation enthalpy h₀, and kinetic energy  is:

For an ideal gas with constant specific heat, Eq. (6.15) can be written as:

Since  = γRT, where γ = c_p0/c_v0

For an isentropic process,

Values of  are given as a function of M in Table 6.1 for the value of γ = 1.40.

 

Table 6.1 One-dimensional insentropic compressible-flow functions for an ideal gas with constant specific heat and molecular weight and γ = 1.4

The conditions at the throat of the nozzle can be found by putting M = 1 at the throat. The properties at the throat are denoted as an asterisk (*) and are referred to as critical properties.

 

Table 6.2 gives these ratios for various values of k.

 

Table 6.2 Critical properties for isentropic flow of an ideal gas