Gas Turbines - Introduction: DGCA Technical General questions

A gas turbine compresses air, burns fuel in it at nearly constant pressure and expands the gas through a turbine and nozzle. That is the Brayton cycle, and the thrust is Newton's third law at work.

Its 18 questions cover engine types, bypass ratio, spools, ducts and propulsive efficiency. DGCA exam sessions have used 6 of them.

Bypass ratio is bypass airflow over core airflow, so 5:1 means five parts go round the core for each part through it. In a high bypass engine the fan gives most of the thrust. A subsonic convergent duct raises velocity and lowers pressure; a divergent one does the reverse. Pressure peaks at compressor delivery; combustion then adds heat at nearly constant pressure, with a small pressure loss.