Gas Turbine Handbook : Principles and Practices

52 Gas Turbine Handbook: Principles and Practices
The internal pressure, temperature, and velocity variations
within the gas turbine are shown in Figures 4-1 and 4-2. Note that
compressor work is shown as the pressure rise from a to b. From b to
c, the energy addition due to combustion is shown as a temperature
rise at near constant pressure. In actuality there is some pressure
drop through the combustor. The hot gases are then expanded through
the turbine from point c to d, as evidenced by a drop in pressure and
temperature. In a jet-type gas turbine the temperature and pressure
decreases from d to d" as the gas expands through a jet exhaust nozzle
and creates thrust. In mechanical drive type applications, this energy
is expanded from point d to d' in the form of shaft horsepower. Finally,
the Brayton Cycle can be considered a closed cycle for the gas turbine
if we consider the surrounding atmosphere as the heat sink (as depicted
by the constant pressure from point d' or d" to a).
COMPRESSOR
The compressor provides the high pressure, high volume air
which, when heated and expanded through the turbine section, provides
the power output required by the process (mechanical drive,
Figure 4-2. Courtesy of Rolls-Royce Industrial & Marine Gas Turbines
Limited. Typical pressure, temperature, and velocity profiles
relative to gas turbine engine position.