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high-bypass turbofan
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High-bypass turbofan
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high-bypass turbofan

engine
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High-bypass turbofan
High-bypass turbofan Figure 5: High-bypass turbofan with two-spool core and mixed-flow jet.

A high-bypass turbofan engine is a type of jet engine designed for high propulsive efficiency, meaning the exiting jet velocity is close to the aircraft's flight speed. This is achieved by having most of the air bypass the engine's core and go directly to an exhaust nozzle. The bypass ratio, which is the ratio of bypass air to core air, is a key classification. High-bypass engines have ratios from 5 to 8, while ultrahigh-bypass engines (UBEs) have ratios of 9 to 15 or higher.1

These engines are common in the transonic flight speed regime (Mach 0.75 to 0.9). While higher bypass ratios offer better fuel efficiency, very large fans can increase weight and installation challenges. Ultrahigh-bypass engines may use a gearbox to connect a high-speed turbine to a large, slow-rotating fan.1

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2 Britannica Sources
  1. jet engine - Medium-bypass turbofans , high-bypass turbofans , and ultrahigh-bypass engines
  2. jet engine - Low-bypass turbofans and turbojets

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