simplest way to predict the behaviour of a gas turbine engine
is to use an ideal one dimensional gas dynamics/
thermodynamic analysis. Assuming the engine operates on an
ideal Brayton cycle, then the problem becomes one of tracking
gas flow through an ideal intake, isentropic compression,
constant pressure combustion and finally isentropic expansion through
a turbine and nozzle.
simple assumptions are needed to allow for the calculations
1. Isentropic intake and
compression (no losses)
2. Constant pressure
combustion. As the flow is relatively slow in the inlet to
the combustion chamber then it can be assumed that the
pressure is roughly equal to the stagnation pressure of the
flow at this point. The stagnation temperature rise is based
on the mass flow rate of fuel injected and its calorific
value, giving rise to an enthalpy change CpTo
3. The turbine provides
all required energy to drive the compressor and/or fan.
4. Isentropic expansion
through the exhaust nozzle back to surrounding ambient
a simple core only engine, the change in velocity of the
exhaust gas compared to inlet stream will be an ideal
measure of the thrust generated.
the mass flow rate of air and fuel through the core of the
the engine is also driving a fan to produce cooler bypass flow then the total
thrust can be found by summing the momentum change to both
bypass and core gas streams.
the following application, the prediction of thrust for a typical
commercial aircraft turbo-fan engine can be investigated. To
explore a range of operating conditions input values can be
Conditions : Altitude, Flight Mach Number
Conditions/Geometry : Compressor Pressure Ratio (CPR), Fan
Pressure Ratio (FPR), Bypass Ratio, Fuel-Air Ratio.
application predicts thrust and specific fuel
consumption based on these input conditions. Note, the solution
does not include any second order effects and does not check
whether the engine is operating within sensible physical