SKYWORX

Most modern passenger and military aircraft are powered by gas turbofans engines. They inhale massive amounts of air and blow it out the back to generate thrust. As an example, the GE90 can produce up to 115,000 pounds of thrust. That's about the weight of ten elephants. Times that by two for each wing!

 

Airplane engines are comprised of a fan, compressor, combustor, and turbine. The fan, situated at the front, is the largest in diameter and provides a majority of the thrust. Some of the air continues on to the compressor which squeezes the air, raising its temperature and pressure. The air is ignited with fuel in the combustor, raising its temperature further. The turbine extracts some of the power from the high energy flow and helps drive the compressor and fan, which are all connected together by a central shaft.

 

I spent just over five years as a turbine durability engineer at a major aerospace manufacturer. The job is best summarized as such: part investigator, part mad-scientist, and part artist. A concentrated blend of science and engineering went into every thing we did.

 

Turbine components experience an extremely harsh environment. The hardware must withstand a combination of high heat, pressure, and stress, especially those exposed to the "hot-gas" path. All the while, the parts must survive several thousand hours under such conditions without failure. Durability engineers, along with other disciplines, utilize advanced technology, like protective thermal barrier coatings and high-temperature super nickel alloys, and creative cooling schemes with intricate cast-in features to give them a fighting chance. At takeoff, blades can glow red-orange to yellow-white from the intense heat and experience about ten tons of force from the rotational speed.

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Turbine durability is a balancing act aimed at reducing part temperatures while using the least amount of cooling air to do it. The cooling air is pumped through small cavities and features built into the components. The cavities also help reduce material and weight. Flow rate, area, speed (or mach number), pressure, and heat transfer rate are all important aspects that must be tweaked and controlled for.

 

The challenge is to mitigate the four main modes of distress: corrosion (chemical reaction with gaseous environment which is accelerated at high temperature, or put simply, burning), creep (permanent deformation or elongation over long time-scales at high temperature and force), thermal mechanical fatigue (cracking due to temperature and stress cycles), and coating spallation (erosion and removal of protective coating).