Bypass duct

Schematic turbofan engines. The high-bypass engine (top) has a large fan that routes much air around the turbine; the low-bypass engine (middle) has a smaller fan routing more air into the turbine; the turbojet (bottom) has zero bypass, and all air goes through the turbine.

In aviation, a bypass duct is a passage within a turbofan engine that allows a portion of the air, known as bypass air, to flow around the engine's core, or combustion chamber. This bypass air is accelerated by a fan and then expelled through the rear of the engine, contributing significantly to the overall thrust.

Here's a more detailed explanation:

Bypass Air:

The air that bypasses the engine core, typically flowing through a large fan in the front of the engine.

Thrust:

The bypass air is accelerated by the fan and then expelled out of the engine, creating thrust.

Engine Cooling and Noise Reduction:

The cool bypass air can be mixed with the hot exhaust air at the back of the engine, which helps cool the exhaust and reduce engine noise.

Bypass Ratio:

The ratio of bypass air to core air flow is known as the bypass ratio. High-bypass engines, common in commercial airliners, are more fuel-efficient and quieter than low-bypass engines, which are typically used in military aircraft for higher performance.

Turbofan Engine:

Turbofan engines, also known as fanjet or bypass engines, produce thrust using a combination of jet core efflux and the accelerated bypass air.