Reply #65: Turbofans and rotors. N1 and N2.

[Make7]

Most of today's turbine engines are dual-rotor engines, meaning there are two distinct sets of rotating components. The rear compressor, or high-pressure compressor, is connected by a hollow shaft to a high-pressure turbine. This is the high rotor. The rotors are sometimes called spools, such as the "high spool." In this text, we will use the term rotor. The high rotor is often referred to as N2 for short.

The front compressor, or low-pressure compressor, is in front of the high-pressure compressor. The turbine that drives the low-pressure compressor is behind the turbine that drives the high-pressure compressor. The low-pressure compressor is connected to the low-pressure turbine by a shaft that goes through the hollow shaft of the high rotor. The low-pressure rotor is called N1 for short.

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A turbofan engine is simply a turbine engine where the first stage compressor rotor is larger in diameter than the rest of the engine. This larger stage is called the fan. The air that passes through the fan near its inner diameter also passes through the remaining compressor stages in the core of the engine and is further compressed and processed through the engine cycle. The air that passes through the outer diameter of the fan rotor does not pass through the core of the engine, but instead passes along the outside of the engine. This air is called bypass air, and the ratio of bypass air to core air is called the bypass ratio.

Schematic

The air accelerated by the fan in a turbofan engine contributes significantly to the thrust produced by the engine, particularly at low forward speeds and low altitudes. In large engines, such as the engines that power the B747, B757, B767, A300, A310, etc., as much as three-quarters of the thrust delivered by the engine is developed by the fan.

http://fromtheflightdeck.com/Stories/turbofan

RC wrote:

The first Picture are parts from a military air craft.

Perhaps you could walk us through the identification process that would substantiate your statement. Or at least provide some kind of source for that information. Or even just a picture. Kind of like this one of a ?pic">RB211-535E4.

-Make7