The turbine is connected to the shaft, which is also connected to the compressor. As the flow passes through the turbine, the total pressure and temperature decrease. This number is always less than 1.0. Using our station numbering , the TPR is equal to pt5 divided by pt4, as shown above. In the axial turbine, cascades of small airfoils are mounted on a shaft that turns at a high rate of speed.
Work is done by the flow to turn the turbine and the shaft.
The enthalpy at the entrance and exit is related to the total temperature at those stations, as shown at the right on the slide. The total temperature is also related to the total pressure for a compressible flow, as shown on the left. The efficiency factor is included to account for the actual performance of the turbine as opposed to the ideal, isentropic performance. In an ideal world, the value of the efficiency would be 1.0. In reality, it is always less than 1.0.