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“This film is from Lewis Flight Propulsion Laboratory, now known as NASA Glenn Research Center. The film looks at addressing the problem of turbine inlet temperature and the benefits of air-cooled blades. A promising blade is the fabrication of cast air-cooled blades using a lost wax technique. Video is in color and has sound.”
Langley Film L-708
Public domain film from NASA, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization.
A turbine blade is the individual component which makes up the turbine section of a gas turbine. The blades are responsible for extracting energy from the high temperature, high pressure gas produced by the combustor. The turbine blades are often the limiting component of gas turbines. To survive in this difficult environment, turbine blades often use exotic materials like superalloys and many different methods of cooling, such as internal air channels, boundary layer cooling, and thermal barrier coatings.
In a gas turbine engine, a single turbine section is made up of a disk or hub that holds many turbine blades. That turbine section is connected to a compressor section via a shaft (or “spool”), and that compressor section can either be axial or centrifugal. Air is compressed, raising the pressure and temperature, through the compressor stages of the engine. The pressure and temperature are then greatly increased by combustion of fuel inside the combustor, which sits between the compressor stages and the turbine stages. That high temperature and high pressure fuel then passes through the turbine stages. The turbine stages extract energy from this flow, lowering the pressure and temperature of the air, and transfer that energy to the compressor stages along the shaft. This is process is very similar to how an axial compressor works, only in reverse.
The number of turbine stages varies in different types of engines, with high thrust, high bypass ratio, engines tending to have the most turbine stages.[citation needed] The number of turbine stages can have a great effect on how the turbine blades are designed for each stage. Many gas turbine engines are two shaft designs, meaning that there is a high pressure shaft and a low pressure shaft. Other gas turbines used three shafts, adding an intermediate pressure shaft between the high and low pressure shafts. The high pressure turbine is exposed to the hottest, highest pressure, air, and the low pressure turbine is subjected to cooler, lower pressure air. That difference in conditions leads the design of high pressure and low pressure turbine blades to be significantly different in material and cooling choices even though the aerodynamic and thermodynamic principles are the same.
Turbine blades are subjected to very strenuous environments inside a gas turbine. They face high temperatures, high stresses, and a potentially high vibration environment. All three of these factors can lead to blade failures, which can destroy the engine, and turbine blades are carefully designed to resist those conditions.
Turbine blades are subjected to stress from centrifugal force (turbine stages can rotate at tens of thousands of revolutions per minute (RPM) and fluid forces that can cause fracture, yielding, or creep failures. Additionally, the first stage (the stage directly following the combustor) of a modern turbine faces temperatures around 2,500 °F (1,370 °C), up from temperatures around 1,500 °F (820 °C) in early gas turbines. Modern military jet engines, like the Snecma M88, can see turbine temperatures of 2,900 °F (1,590 °C)…
A key limiting factor in early jet engines was the performance of the materials available for the hot section (combustor and turbine) of the engine. The need for better materials spurred much research in the field of alloys and manufacturing techniques, and that research resulted in a long list of new materials and methods that make modern gas turbines possible.. One of the earliest of these was Nimonic, used in the British Whittle engines.
The development of superalloys in the 1940s and new processing methods such as vacuum induction melting in the 1950s greatly increased the temperature capability of turbine blades. Further processing methods like hot isostatic pressing improved the alloys used for turbine blades and increased turbine blade performance.[6] Modern turbine blades often use nickel-based superalloys that incorporate chromium, cobalt, and rhenium.
Aside from alloy improvements, a major breakthrough was the development of directional solidification (DS) and single crystal (SC) production methods…
