Fundamentals (thermodynamics, thrust, engine layouts, station numbering)
What this domain tests
The Fundamentals domain checks whether you can reason from the Brayton cycle to real engine behavior: how pressure ratio and turbine inlet temperature set efficiency and specific work, how thrust is produced, how engine layouts differ, and how stations are labeled. Expect numeric thrust questions and layout comparisons rather than pure definitions.
Core rules
- The ideal Brayton cycle has isentropic compression, constant-pressure heat addition, isentropic expansion, and constant-pressure heat rejection. Thermal efficiency rises with pressure ratio; specific work peaks at a moderate pressure ratio.
- Net thrust for a single stream is Fn = mdot(Ve - V0) + (pe - p0)Ae. At a convergent nozzle with no pressure thrust, only the momentum term remains.
- A turbofan splits thrust between core and bypass; bypass ratio is bypass mass flow divided by core mass flow. Turboprop and turboshaft extract shaft power; residual jet thrust is small.
- Station numbering: 0 free stream, 1 inlet entry, 2 compressor/fan face, 3 compressor exit, 4 combustor exit (turbine inlet), 5 turbine exit, 7 nozzle entry, 9 nozzle exit. Variants exist, so read definitions.
Worked example
A turbojet passes 50 kg/s, exits at 600 m/s, flight speed 200 m/s, exit pressure equals ambient. Fn = 50(600 - 200) = 20,000 N = 20 kN. If exit pressure were 5 kPa above ambient over 0.4 m2, pressure thrust would add 2,000 N, giving 22 kN.
Traps
Using gross thrust when the question asks net; forgetting pressure thrust; assuming station numbers are universal; confusing bypass ratio with mass-flow ratio.