Design and Material Considerations for Gas Turbine Engines
Modern gas turbine engines, whether used for aerospace or power generation applications, are composed of a wide range of components expected to endure varying stressors and temperature conditions. As such, material selection for such powerplants necessitates an understanding of the role that each component plays in the engine’s overall operation. To begin, components must be able to handle high loads and excessive vibration, in addition to being able to resist oil, oxidation, or abrasives entering the engine.
As a result of the engine’s use of high-pressure air and burning fuel to generate power, a majority of components experience high temperatures and/or large temperature gradients. During normal operation, gas turbine engines can exude temperatures up to 1,000 degrees Celsius in the turbine section specifically. Based on the engine’s architecture, this temperature gradient can occur over a very short distance. More than that, temperature gradients may also introduce high thermal stresses and even change the engine’s dimensions through warping.
Despite there being varying environments within the engine, every decision for the design of individual components must be made according to a customer’s requirements. Nevertheless, the base criteria for all engines include general performance parameters, cost, and weight. This criteria is also product-specific, meaning that some designs may place performance over cost. Nonetheless, most design reviews will ultimately concentrate on strength, fatigue capability, weight, and cost. For components in the turbine section, creep resistance and thermal stability are also critical.
For most engine components, a low coefficient of thermal expansion (CTE) is not a primary concern. However, control of thermal expansion plays an important role in the overall performance of an engine. It is important to note that the design process is a trade-off between different factors and their effects on the resulting product. For instance, the positive implication of using a low CTE alloy is offset by a decrease in other properties like corrosion resistance. Beyond the many design challenges associated with low CTE alloys, there are also many reasons why it is impractical to use them.
There are two basic reasons why thermal expansion is important in gas turbine engines: thermal stresses generated in engine components and the control of dimensions in the engine. Generally, thermal stress is due to heat generated during engine operation, resulting from both the compression of gasses and the combustion of fuel. When components are affixed to one another or when one component restrains the other, any variations in thermal expansion between these components produces stress on one side of the interface and opposing stress on the other.
The temperature difference between the coldest and hottest regions of the engine can be hundreds of Kelvins, and because the amount of power drawn from the engine varies during different stages of flight, these thermal gradients differ tremendously. More specifically, some components cool faster than others as a result of heat capacity, thermal conductivity, geometry, and the quantity of impinging airflow. In order to take such factors into consideration, design engineers use computational modeling methods.
A gas turbine engine consists of an array of rotating assemblies like rotating discs, airfoils, and shafts, all of which are contained within a static structure. These assemblies drive air throughout the engine to generate power, and they are supported by a series of bearings that require lubrication. Temperature gradients in the clearances between these components change during operation as well. As such, there are two important design considerations: sealing and control of airflow. Ensuring proper sealing can be complicated because the temperature profile of engines varies both radially and axially.
When two components made from materials with different coefficients of thermal expansion are positioned next to each other and the system is heated to a uniform temperature, each component’s diameters increase by a different amount. Additionally, a nominal gap about half the difference is created. However, if the outermost component were made of a low CTE material, the gap would be minimized or eliminated. With regard to the oil system in engines, keep in mind that oils cannot be heated above the temperature at which they begin to burn, and the temperature difference must not exceed a couple hundred degrees. By doing this, you may limit the amount of thermal expansion mismatch in air-oil systems.
Aviation Distribution is a leading distributor of aircraft parts and components that have been sourced from trusted global manufacturers. With countless ready-to-purchase products in our inventory, customers can easily meet rigid time constraints and inflexible budget requirements. As we offer one-on-one consultations, customers are guaranteed a seamless purchasing process. Kick off procurement with a competitive quote on any featured item and see how Aviation Distribution can serve as your strategic sourcing partner!
Modern gas turbine engines, whether used for aerospace or power generation applications, are composed of a wide range of components expected to endure varying stressors and temperature conditions. As such, material selection for such powerplants necessitates an understanding of the role that each component plays in the engine’s overall operation. To begin, components must be able to handle high loads and excessive vibration, in addition to being able to resist oil, oxidation, or abrasives entering the engine.
As a result of the engine’s use of high-pressure air and burning fuel to generate power, a majority of components experience high temperatures and/or large temperature gradients. During normal operation, gas turbine engines can exude temperatures up to 1,000 degrees Celsius in the turbine section specifically. Based on the engine’s architecture, this temperature gradient can occur over a very short distance. More than that, temperature gradients may also introduce high thermal stresses and even change the engine’s dimensions through warping.
Despite there being varying environments within the engine, every decision for the design of individual components must be made according to a customer’s requirements. Nevertheless, the base criteria for all engines include general performance parameters, cost, and weight. This criteria is also product-specific, meaning that some designs may place performance over cost. Nonetheless, most design reviews will ultimately concentrate on strength, fatigue capability, weight, and cost. For components in the turbine section, creep resistance and thermal stability are also critical.
For most engine components, a low coefficient of thermal expansion (CTE) is not a primary concern. However, control of thermal expansion plays an important role in the overall performance of an engine. It is important to note that the design process is a trade-off between different factors and their effects on the resulting product. For instance, the positive implication of using a low CTE alloy is offset by a decrease in other properties like corrosion resistance. Beyond the many design challenges associated with low CTE alloys, there are also many reasons why it is impractical to use them.
There are two basic reasons why thermal expansion is important in gas turbine engines: thermal stresses generated in engine components and the control of dimensions in the engine. Generally, thermal stress is due to heat generated during engine operation, resulting from both the compression of gasses and the combustion of fuel. When components are affixed to one another or when one component restrains the other, any variations in thermal expansion between these components produces stress on one side of the interface and opposing stress on the other.
The temperature difference between the coldest and hottest regions of the engine can be hundreds of Kelvins, and because the amount of power drawn from the engine varies during different stages of flight, these thermal gradients differ tremendously. More specifically, some components cool faster than others as a result of heat capacity, thermal conductivity, geometry, and the quantity of impinging airflow. In order to take such factors into consideration, design engineers use computational modeling methods.
A gas turbine engine consists of an array of rotating assemblies like rotating discs, airfoils, and shafts, all of which are contained within a static structure. These assemblies drive air throughout the engine to generate power, and they are supported by a series of bearings that require lubrication. Temperature gradients in the clearances between these components change during operation as well. As such, there are two important design considerations: sealing and control of airflow. Ensuring proper sealing can be complicated because the temperature profile of engines varies both radially and axially.
When two components made from materials with different coefficients of thermal expansion are positioned next to each other and the system is heated to a uniform temperature, each component’s diameters increase by a different amount. Additionally, a nominal gap about half the difference is created. However, if the outermost component were made of a low CTE material, the gap would be minimized or eliminated. With regard to the oil system in engines, keep in mind that oils cannot be heated above the temperature at which they begin to burn, and the temperature difference must not exceed a couple hundred degrees. By doing this, you may limit the amount of thermal expansion mismatch in air-oil systems.
Aviation Distribution is a leading distributor of aircraft parts and components that have been sourced from trusted global manufacturers. With countless ready-to-purchase products in our inventory, customers can easily meet rigid time constraints and inflexible budget requirements. As we offer one-on-one consultations, customers are guaranteed a seamless purchasing process. Kick off procurement with a competitive quote on any featured item and see how Aviation Distribution can serve as your strategic sourcing partner!
Share
