The first part of the turbofan is the fan. It's also the part that you can see when you're looking at the front of a jet. The fan, which almost always is made of titanium blades, sucks in tremendous quantities of air into the engine. The air moves through two parts of the engine. Some of the air is directed into the engine's core, where the combustion will occur. The rest of the air, called "bypass air", is moved around the outside of the engine core through a duct. This bypass air creates additional thrust, cools the engine, and makes the engine quieter by blanketing the exhaust air that's exiting the engine.
In today's modern turbofans, bypass air produces the majority of an engine's thrust. The compressor is located in the first part of the engine core.
And it, as you probably have guessed, compresses the air. The compressor, which is called an "axial flow compressor", uses a series of airfoil-shaped spinning blades to speed up and compress the air.
It's called axial flow, because the air passes through the engine in a direction parallel to the shaft of the engine as opposed to centrifugal flow. As the air moves through the compressor, each set of blades is slightly smaller, adding more energy and compression to the air. In between each set of compressor blades are non-moving airfoil-shaped blades called "stators".
These stators which are also called vanes , increase the pressure of the air by converting the rotational energy into static pressure. The stators also prepare the air for entering the next set of rotating blades.
In other words, they "straighten" the flow of air. The combustor is where the fire happens. The hot exhaust passes through the core and fan turbines and then out the nozzle, as in a basic turbojet. The rest of the incoming air passes through the fan and bypasses , or goes around the engine, just like the air through a propeller.
The air that goes through the fan has a velocity that is slightly increased from free stream. So a turbofan gets some of its thrust from the core and some of its thrust from the fan.
The ratio of the air that goes around the engine to the air that goes through the core is called the bypass ratio. Because the fuel flow rate for the core is changed only a small amount by the addition of the fan, a turbofan generates more thrust for nearly the same amount of fuel used by the core.
This means that a turbofan is very fuel efficient. In fact, high bypass ratio turbofans are nearly as fuel efficient as turboprops. The combustion chamber consists of a fuel injector system to allow fuel to be ignited and subsequently burned by the high temperature and pressure air.
As the air fuel mixture burns it rapidly expands increases in volume and is forced out of the back into the exhaust stage. The immense energy of the expanding gases is transferred into rotation energy by means of a coaxial shaft connected to the post combustion turbine. The way the exhaust stage produces thrust is a clear manifestation of Newtons 3 rd law. The exhaust gases exit at high velocity out of the rear of the engine, the reaction force of the exhaust gases is in the opposite direction of the exhaust thus it is called thrust.
The large fan is driven by this energy exchange and behaves like a propeller in the case of high bypass Turbofan engines. The expanding gases in the post combustion turbine stage drive the shaft that consequently drives the large fans. The large fan draws air into the bypass and compression chamber, which results in the air being at the correct pressure and temperature to ignited and combusted with the fuel.
But if the turbofan engine requires hot compressed air to combust the air fuel mixture, and if we need to drive the post combustion turbines to drive the fans which drive the compression stage, you may be asking. How does a turbofan engine start? The blades of the fan require rotational energy to start the combustion cycle, so engineers have designed a high-pressure inlet called an Air Turbine Starter.
The air turbine starter is attached to the side of the engine. The air turbine starter is a small pressurized turbine that is driven by a start cart shown below. This happens by way of two concentric shafts—the outer shaft, which couples the high-pressure turbine to the high-pressure compressor, and the inner shaft, which connects the low-pressure turbine to the booster and fan. Only then do the combustion gases leave the thrust nozzle, generating an additional burst of residual thrust.
While in turbojet engines, all the ingested air flows consecutively through compressors, the combustor and turbines, turbofans separate the accelerated air stream behind the fan rotor. Flying and the technologies that make it possible yield a wealth of content for the magazine, which makes for some truly fascinating reading: stories from over one hundred years of history and plenty of exciting features on topics with a bearing on the future of aviation, such as climate change, population growth and limited resources.
Our monthly e-mail newsletter keeps you informed about topics in the world of aviation. Free of charge and can be canceled at any time. In a nutshell: Sustainable aviation Mastermind for MTU production. Huge technology leap: GTF The geared turbofan GTF , the latest generation of turbofan engines, has a special attribute: a reduction gearbox between the fan and the low-pressure shaft together with the low-pressure compressor and actuating low-pressure turbine.
How a modern turbofan engine works in 4 stages 1. Ingestion The fan rotor, the blade wheel at the front, draws in air. Compression Next, the portion of ingested air that flows into the engine core is compressed in the low- and high-pressure compressors. Combustion After compression, the air flows into the combustor.
Expulsion The hot gas races through the high- and low-pressure turbines, each of which has several turbine wheels and numerous blades that are rotated by the exhaust gas stream.
0コメント