A gas turbine engine exhaust system is paramount for heat dissipation and performance, ensuring that spent gases are optimally expelled from the engine after combustion. While varying engines may contain different components and complex assemblies, the common function of all exhaust parts is to direct spent gases out of the engine in such a way that an efficient exit velocity is reached without causing turbulence.
The main sections of the gas turbine engine include the exhaust cone, tailpipe, and exhaust nozzle. The exhaust cone is the section of the aircraft engine that follows the turbine assembly, and it gathers the expanding gases that pass through the turbine blades so that they may be directed into a solid flow. By converting the stream of gas, the exhaust cone can cut down the velocity of the gas while increasing its pressure. For the design of the exhaust cone, the section contains an outer shell, inner cone, multiple radial hollow struts, and tie rods for support.
The outer shell of the assembly is tasked with collecting exhaust gases, and it often comes in the form of a stainless steel assembly which is connected to the turbine case rear flanges. If there is a need for temperature thermocouples within the assembly, the duct may be designed with thermocouple bosses. The struts are also attached to the outer duct, and they serve as supports for the inner cone which sits in the middle of the exhaust duct. Struts are also useful for straightening the flow of exhaust, ensuring that they exit at a proper angle for beneficial operations. The inner cone is placed near the rear face of the turbine disk, and it serves to prevent exiting exhaust gases from causing turbulence. The inner cone may also feature a small hole at the exit tip, and this allows for air circulation to cool the turbine wheel.
The tailpipe is the next major section of the aircraft gas turbine engine, and they are often designed with semiflexible characteristics. For certain tailpipe constructions, a bellows arrangement may be implemented for the means of moving the tailpipe during thermal expansion, maintenance, and installation. With such capabilities of movement, the tailpipe is less at risk of warping under stress. As the high temperatures of combustion can result in heat radiating from the exhaust cone and tailpipe, engineers often implement insulation for the protection of airframe components. While there are numerous solutions that may serve for thermal protection, shrouds and insulation blankets are the most common as they can protect assemblies and increase performance.
The exhaust nozzle is the final section of the engine, and it may be a converging design for subsonic gas velocities or a converging-diverging design for the means of supersonic gas velocities. The nozzle opening may also have a fixed or variable area, the fixed area being fairly simplistic due to its lack of moving parts. It is important that fixed area nozzles are optimally designed so that the engine does not choke during operations and can achieve optimal thrust. When an augmenter or afterburner is implemented in the engine, the exhaust nozzle will come in the form of the variable area type as it will need to extend its open area to accommodate the increased mass of flow. If the augementer or afterburner is shut-off, the exhaust nozzle can adjust to a smaller opening.
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