Understanding the Exhaust Section of the Gas Turbine Engine

The gas turbine engine is a widely used engine type for aircraft, utilizing the combustion of fuel and air mixtures to produce the propulsive force needed for achieving flight. As the ignition of fuel and air mixtures results in a stream of hot, expanding exhaust gases, there needs to be a system in place to rid the engine of this byproduct after it is used to drive assemblies. With the exhaust section of the gas turbine engine, spent gases are expelled rearward at a high velocity to achieve more thrust as well as to mitigate turbulence.

In order to efficiently remove exhaust from the engine while producing more thrust, a number of components must work together. While parts may vary depending on the engine, the most common components of the exhaust section are the exhaust cone, tailpipe, and exhaust nozzle. As the exhaust gases pass through the turbine section and spin it, they are then captured by the exhaust cone. With a diverging passage existing between an outer duct and an inner cone, the velocity of exhaust begins to drop and pressure will rise as it passes through the cone. This also creates a solid flow of gases that can then be directed to the exhaust nozzle.

For the exhaust cone to optimally function, it contains an outer shell/duct, inner cone, and various hollow struts or tie rods that act as supports for the duct and cone. The outer shell or duct is most often produced with stainless steel due to its heat resistance and strength. For the assembly to carry out its task, the shell or duct is also fitted with thermocouple bosses for exhaust temperature thermocouples. If there needs to be support for the inner core, tie rods or hollow struts may be used. Radial struts, while also supporting the cone, serve to straighten exhaust gases that swirl inside the system. As the inner cone is placed near the turbine disk and turbine wheel, gases move through without turbulence as well.

If the gas turbine engine features a tailpipe, the structure is most often designed to be semi-flexible. In some instances, a bellows arrangement may also be implemented, and this allows for the assembly to be moved while conducting installation and maintenance procedures as well as during thermal expansion. With the use of the bellows arrangement, the tailpipe can be protected from hazards such as warping which is the result of stress. Due to the immense heat that regularly moves through the tailpipe, it is important that there is protection for surrounding airframe components so that they are not affected by heat radiation. While there are a variety of solutions for this issue, insulation blankets and shrouds are the most common.

The insulation blanket of a gas turbine engine will typically consist of multiple layers of aluminum foil that are each separated with fiberglass materials. While the insulation blanket is beneficial for the integrity of surrounding airframe components, its main role is actually to maintain heat within the system so that significant heat loss is not avoided. This is due to the fact that hotter temperatures will enable higher performance for the engine.

For the exhaust nozzle, the construction of the assembly will dictate whether the velocity of expelled gas is subsonic or supersonic. Converging and converging-diverging designs are the two primary types and the nozzle itself may either have a fixed or variable opening. The fixed opening is the most simplistic type, and it has no moving parts. It is important that the size of the fixed-area opening is optimal for the aircraft and its engine as an opening that is too small may choke the engine while much larger sizes may result in wasted thrust. Variable-area exhaust openings are mostly used when an afterburner or augmenter is implemented to the assembly. When either device is activated, the nozzle will increase its open area to accommodate the increased mass flow. When the device is not in use, the opening will decrease in size.

With the intensive operations that the gas turbine engine and exhaust section undertake, it is important to have all assemblies regularly maintained so that aging or damaged parts can be repaired or replaced before they pose a hazard. ASAP NSN Parts is a leading distributor of gas turbine engine components, aviation components, and highly demanded NSN parts. As a premier purchasing platform dedicated to quality assurance, we operate with AS9120B, ISO 9001:2015, and FAA AC 00-56B certification and accreditation. Begin the purchasing process with a competitive quote in just 15 minutes when you fill out and submit an Instant RFQ form as provided on our website today.


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