A turbofan splits incoming air into two streams: a cool bypass flow accelerated only by the front fan (blue particles, outer duct), and a core flow that also passes through the compressor, combustor and turbine before exiting hot (orange/red particles, centre duct). Net thrust is the combined momentum added to both streams.
mdot = rho * A_fan * V_face (air mass flow, kg/s)
mdot_core = mdot / (1 + BPR)
mdot_bypass = mdot * BPR / (1 + BPR)
F = mdot_core * Ve_core + mdot_bypass * Ve_bypass (static thrust, N)
Ambient density ρ falls exponentially with altitude (ρ = ρ0·e−h/H), so the same throttle setting moves less air — and makes less thrust — high up, exactly as it does on a real aircraft.
- Throttle (N1) — fan/core rotational speed as a percentage of maximum; drives mass flow and exhaust velocity.
- Bypass ratio — how much air goes around the core versus through it; high-bypass engines (airliners) trade raw exhaust speed for efficiency, low-bypass (fighters) do the opposite.
- Altitude — thinner air reduces mass flow and thrust at a fixed throttle.
- Afterburner — injects extra fuel into the core exhaust for a large, inefficient thrust boost, shown as the long secondary flame.
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This is the same core+bypass architecture used in every modern airliner and most military jet engines — the bypass ratio is the single biggest lever airframers pull to trade fuel efficiency against thrust density.