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... s, but is also employed in auxiliary power units to provide power for aircraft ground operation. The compressor of a turbo shaft engine first raises the pressure of the incoming air, which is then guided into the combustion chamber. After being mixed with vaporized fuel and burned, the hot gas expands completely through two separate turbines. The first turbine drives the compressor; the second delivers horsepower to drive the helicopter rotor. The gas is finally released through an exhaust duct without producing any thrust.
I will now tell you about the five major turbo machinery components of a jet engine: the air intake, compressor, combustion chamber, turbine and exhaust section. Each of these contributes uniquely to the generation of thrust. In any application-subsonic transport or supersonic fighter-the air intake is essentially a fluid flow duct whose task is to process the airflow in a way that ensures the engine functions properly to generate thrust. The intake must be designed to provide the appropriate amount of airflow required by the engine and, furthermore, that this flow when leaving the intake section to enter the compressor will be uniform, stable, and of high quality.
These conditions must be met not only during all phases of flight, but on the ground, with the aircraft at rest and the engine demanding maximum thrust prior to take-off. Good intake design is therefore a prerequisite if installed engine performance is to come close to performance figures obtained at the static test bench. Present-day turbine aero-engines require subsonic flow at the entry to the compressor, even if the aircraft is flying at supersonic speed. The task of the air intake is therefore to decelerate the supersonic external flow to a subsonic speed acceptable to the compressor. In each category of a turbine-driven aero-engine-turbojet, turbofan, turboprop or turbo shaft- the compressor is one of the most important components. It is the task of the compressor to increase the pressure of the airstream's that is furnished by the air intake.
This process is accomplished by supplying mechanical energy ( = work) to the compressor, the rotating blades of which exert aerodynamic forces on the airflow. At the compressor outlet, a stream of highly compressed air is discharged to the combustion chamber, where more energy is added in the form of heat. In a compressor, mechanical energy is converted into pressure energy. The amount of energy required, and the quality of achieved energy conversion, is characterized by compressor performance parameters. The most important parameters are: -compressor efficiency -compressor total pressure ratio -air-flow rate The efficiency parameter denotes the amount of energy supplied to the compressor from the turbine, by means of the rotor shaft, that results in an increase of pressure energy. This parameter, therefore, denotes the amount of loss that is always incurred by converting energy.
Next, there is compressor pressure ratio. This parameter is defined as the ratio of the total pressure at compressor discharge and at compressor entry. The importance of the compressor pressure ratio is because overall engine performance is influenced by this parameter as it bears directly on thrust, fuel consumption, and engine efficiency. Engine weight, too, is directly related to pressure ratio.
An increase in pressure ratio, for instance, may require the number of stages in the compressor to be increased, which will result in higher pressure and temperature levels within the gas generator. This in turn will necessitate a heavier engine overall because not only must the engine be re-designed to withstand the higher stress levels, but usually the combustion chamber and turbine as well. The mass flow rate parameter denotes the airflow volume that the compressor is capable of processing within unit time, usually one second. Apart from the importance of this parameter for thermal cycle analysis, it also permits engine classification with respect to engine size to easily be made. There are basically two types of compressors that are in use today. -the centrifugal-flow compressor, and -the axial-flow compressor. Today centrifugal compressors are used only in small engines such as shaft engines for helicopters, auxiliary power units, turboprop engines, and some low-thrust engines for business aircraft.
The majority of engines, however, employ the axial-flow compressor The principal advantage of the axial compressor is its ability to deliver High Mass flow rates together with large pressure ratios at the same time-features which the centrifugal compressor, due to its method of compression, cannot provide. The axial compressor is usually made up of a large number of individual parts of diverse function. Although the variety of engine makes available on the market differ according to the requirements to individual applications, distinct types of components are typical to any compressor. These are -compressor front frame -compressor casing with stator vanes -rotor with rotor blades -compressor rear frame.
The airflow, after being delivered to the compressor face by the air intake duct, first passes the front frame. This is a ring-shaped single-piece lightweight structure made of aluminum alloy or steel, usually cast and then machined. Characteristic to this component is an outer ring, an inner hub and 6 to 8 streamlined supporting struts. The task of the compressor front frame is to accommodate the rotor front bearing and to transfer rotor forces to the outer casing by means of the supporting struts.
The supporting struts are hollow to accommodate, tubing to lubricate and ventilate the front bearing, and to provide space for electric cables where an electric starter is mounted forward of the shaft. The interior of the hollow struts are also used as a warm air passage for de-icing the struts themselves. The compressor casing is a tube-like construction typically split length-wise to facilitate engine assembly and maintenance. The casing material is usually lightweight titanium forging, but stainless steel has also been used in the past. Modern high-performance engines employ alloy materials that were specifically developed to allow expansion of the case due to heating during engine opera...
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