The Jet Engines with 'Digital Twins' | Hacker News Reader

The Jet Engines with 'Digital Twins'

bbc.com

85 pointsM_Grey37 comments

Everything I know about jet engines comes from the fantastic multi-year youtube vlog of AgentJayZ of JetCity, Canada! https://www.youtube.com/user/AgentJayZ

AgentJayZ is a great resource and very entertaining.

Ah... Combustors, combustor liners, vacuum-melted steel, lock-wiring... all the good bits and crazy tolerances explained. Also, reminds me of the Rolls-Royce docu: https://www.youtube.com/watch?v=UazsDDFsS7Q&list=PLFF54B91EB...

Pairs well with some https://youtube.com/arduinoversusevil, https://youtube.com/Abom79 and maybe some https://youtube.com/engineerguyvideo

And, if you like aviation: http://www.flywithcaptainjoe.com

> They’re so difficult to make, in fact, the companies that build aircraft don’t make their own engines.

Airframe manufacturers are prohibited from doing so. The "United" in "United Airlines" harks back to when Boeing, Pratt& Whitney and an airmail company were integrated into a single company.

Today, when an airline buys a commercial airliner, the airframe and engine purchases are separate even though the airframe is specific to a single engine type.

Could they unite those elements of the industry again if given the chance, or has it moved on to just be too specialized?

I found this discussion on Quora:

https://www.quora.com/Why-are-airframes-engines-developed-ma...

And this Wikipedia article:

https://en.wikipedia.org/wiki/Air_Mail_scandal

It sounds like a combination of antitrust concerns and just the fact that airframes and engines don't have much in common.

That was a good read, and I agree with your conclusion.

If you find jet engines interesting, check out AgentJayZ [0] on youtube. He runs a shop in Canada that repairs and overhauls smaller jet engines (think, Learjet size rather than 777 size). He has a mix of good videos, including a long running Q&A series.

[0]: https://www.youtube.com/user/AgentJayZ

The article made it unclear what the difference between a "digital twin" and an engine-specific record is. I assume the difference is that they're building a model of some kind, but you wouldn't know that from searching for [twin] in the article.

It is some tech out of GE Digital that, from what I understand, uses sensor data + machine learning against a digital representation of the system to predict failures and tune performance. A friend of mine just recently took a job at a start-up using this technology (https://veerum.com/about/), however I haven't had a chance to catch up with him and really understand how this stuff works.

There is some more information here: https://www.ge.com/digital/power-digital-twin

https://www.ge.com/digital/blog/rise-digital-twins

It's a part of the Predix platform offering:

In large-scale systems, sensor information can be in different locations separated by great distances. For example, a pipeline system may have some assets in a central terminal as well as assets in the field miles away from the terminal - and all of these must be connected to a single asset model to monitor the health of the system as a whole.

Asset data can be ingested through a REST API using files in JSON format or created using a user interface. The data is stored in a graph database that is optimal for searching hierarchies of assets. Tags that indicate pressure or temperature can be associated with each asset. These tags can then be used to bring in and associate time series data and analytics to build digital twins of a complex asset.

For example, you could create an asset model that describes the logical component structure of all pumps in an organization, and then create instances of that model to represent each individual pump. Or you could create custom modeling elements that meet your unique domain needs if a particular pump has a few differences with the generic version.

https://www.predix.io/services/service.html?id=1171

I was hoping that this was about a discovery that jet engines can become quantum-entangled.

It's all fun and games until a careless measurement causes one set of engines to be "on" and the other to be "off".

You gotta make sure that both entangled engines don't end up on the same plane.

At worst... you'd go in circles. At best you'd just sort of lazily zig-zag to your destination.

"Goddamn it Roger, port #2 is in a superposition of existing and not existing again!" "Calm down Wilco, just take a good hard look at her and she'll settle down."

Rolls Royce publish an excellent book "The Jet Engine" with a great deal of information about the design and manufacture of jet engines. I purchased the latest print edition and it's well worth it. However there is an online PDF of an earlier edition at http://airspot.ru/book/file/485/166837_EB161_rolls_royce_the...

Oh, wow. Grew up with that book in the house (probably the first edition), and yes it is fantastic.

> In the second module an air compressor takes air in and puts it under high pressure, which shrinks the volume of the air and allows the engine to be smaller (because compressed air takes up less space).

Does this reporter know what they're talking about? I always thought compressors were an essential part of a jet engine (compression heats the air, then fuel is sprayed in which auto-ignites, expanding, and turning the turbine blades). Not just because compressed air takes up less space.

The compressor does not heat the air to the ignition point. The flame that is already in the engine provides the ignition, and the flame is prevented from blowing out the back by "flame holders".

https://en.wikipedia.org/wiki/Flame_holder

The ignition at engine start is done with spark plugs.

The purpose of the compressor is to provide dense enough air to support combustion, and the pressure is needed to prevent the exhaust gases from blowing out the front of the engine.

> and the pressure is needed to prevent the exhaust gases from blowing out the front of the engine

Out of curiosity: has that ever happened and how does such an event look like?

I'm pretty sure that you'd need a pretty catastrophic failure of the engine for that to happen, and the event might start to strongly resemble an explosion.

See "compressor stall", https://en.wikipedia.org/wiki/Compressor_stall

A compressor stall can be severe enough to damage or even destroy the engine, though I don't think there's (usually, at least?) actually exhaust blowing out the front.

I read a book in which the author related the story of an F-8 Crusader which suffered an in-flight failure during refueling, causing flame to shoot forward from the intake. Apparently there was photographic evidence, which came in handy when the manufacturer insisted that was impossible. Believe it was one of D.K. Tooker's books, probably "The Second Luckiest Pilot." Very entertaining read, highly recommended if you like vignettes of danger in the skies.

Sure: https://www.youtube.com/watch?v=MQWYhsYfMxE (rather bad quality, good explanation)

There's a supersonic variant called an "unstart" which is very dangerous.

Thanks for the video. Amazing that an aircraft engine is attached to the wing in only such a small area and is not sheared off by the power of such an event...

The engine is designed to shear off if it starts vibrating past a certain amount. It's better than wrecking the wing. The engine mounts are very carefully designed to not be too strong nor too weak.

They're very much like a fuse in an electrical circuit. In fact, they're called "fuse pins".

The concept is not without controversy:

https://www.washingtonpost.com/archive/politics/1993/06/18/b...

The purpose of the compressor is simply to compress the air. It's one step of the Brayton Cycle which is used in gas turbines to convert heat energy into mechanical energy.

https://en.wikipedia.org/wiki/Brayton_cycle

Of tangential relevance: On the aircraft I was trained on, it was SOP to set the igniters = ON when encountering some significant amount of precipitation in flight, as a defense against a water induced snuff-out. (I forget exactly how the precip threshold was determined.)

Otherwise, as parent said, the flame persists following engine start, and so the "spark plugs" (igniters) are not kept active.

the detonation engine, would is sound like a hyperactive V1?

digital twin seems like the first start of a humonculus.

This article does a terrible job at explaining how jet engines work. Spending 10 minutes on wikipedia will give you a better idea. Do look for high vs low bypass. Jet engine s are fascinating, the theory behind them is fairly simple, but a huge challenge to make it happen in the physical world, high temperatures as mentioned but also extremely high rotational speed, which requires parts as close to perfection as possible, and very robust, hairline fractures in engines have resulted in plane crashes.

Much of the little I know about jet engines was sparked by my reading this wonderful article: https://www.americanscientist.org/issues/pub/each-blade-a-si... (which happily is _not_ paywalled).

In particular I learned that each blade is a single crystal! I still find this absolutely mind boggling.

Some people learn in a more hands-on fashion...

https://www.flickr.com/photos/bigiain/4081474667/in/photolis...

(not me, some local guy at a DorkBot meeting way back when...)

I think it does a fairly good job - I read through it in about one minute, and (having already spent some time studying jet engine principles) think it got the essential concepts across. e.g. it doesn't use the word "bypass" but does explain the principle. In such a small amount of space and with the constraints on vocabulary/prior-knowledge assumptions of a mass audience, going into the design tradeoffs of different specific designs is overkill.

I think it does a fairly good job

Yes, I agree. I also loved that they mentioned something I think is really cool --- the gas stream is hotter than the melting point of the turbine blades, and yet the designers have found an ingenious solution.

I actually found that article to be one of the clearest explanations of how a jet engine works I have ever read. It may be exceptionally simplified but that can be a very good thing

Sioux City, Iowa being maybe the most notorious, in the Western world, anyway. Or what we used to call the Western world.

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