Turbine Cooling Air in a Jet Engine
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- เผยแพร่เมื่อ 20 ต.ค. 2024
- The mysterious source and pathways for turbine cooling air in a turbojet engine. The Canadair Sabre 6 was built in Canada under license from North American Aviation. It was a slightly modified design of the F-86F, and it used a Canadian designed and produced engine: the Orenda 14 turbojet.
While restoring one, I had all the pieces in place to show how turbine cooling air gets where it is needed.
Other videos about cooling air, by title. Copy into the search box on my channel page...
Working on a Turbojet: 3 -Turbine Cooling Air
Air-Cooled Blades - Turbine Engines: A Closer Look
Cooling Air 3 - Rear Bearing
Combustor Liners - Turbine Engines: A Closer Look
Heat, upon HEAT. Why turbine temp is so important.
Cool Your Jets
Great subject and thanks for your posts. I'm a qualified diesel mechanic 60 years old now and I spent around 8/10 years working on compressors and steam turbines in the local refinery.
I have always been interested in jet engines mostly because I'm a mechanic of course I'm curious.
I've learned a hell of a lot from you and I'm eternally grateful. Thank you.
THANK YOU for all your hard work. I've learned A LOT from watching the Channel. 🤠
Always satisfying my need for fine details. Thanks
re: parts operating in atmosphere hot enough to melt them
Alec Steele toured a steel foundry and his host pointed out the blast furnace nozzles are made of copper that survives due to its better heat conductivity than iron.
The turbine engine's dynamic balance of heat and pressure and speed is an absolute work of art.
Well done once again J
Thanks for the reply. Love your videos. Always been obsessed with aircraft since I was a kid living in pmq on C.F.B Trenton.
Thank you! 👍❤
Muchas gracias por su dedicación y generosidad. Un saludo.
Best explanation
Very informative, I learned a lot. Thanks
What is the benefit from you ceramic-coating the old Orenda blades? Does that allow you to run the engine hotter, i.e. get more power, or is it more about increasing the blade life (reducing creep, thermal stress etc.)?
PS - great video!
The second reason, and also as extra protection from a possible hot start.
Nice video, agentjayz!
The Rolls Royce book, 'The Jet Engine', actually has a fairly detailed diagram of cooling air from HP and LP compressors to everywhere it gets to, and some smaller drawings of cutaways with more detail.
Given the multitude of ways that compressor air can leak around inside an engine, it seems like it would be difficult to troubleshoot an undesired compressor air leak. Is that even a thing in gas turbines, or is the volume so high that it doesn't really matter?
In this engine, air can only leak from three places:
The external lines, which is cause by failed gaskets, and is easily found and remedied.
The mating split lines between cases, which doesn't really ever happen due to width, flatness, and enormous clamping pressure.
The rear seal of the compressor, shown here. It needs to be critically adjusted. If it was too tight, the turbine would get insufficient cooling air. If it was too big a gap, you would lose a couple % of power produced.
Also, your last point is true.
Honestly, if you had a half inch hole drilled in the compressor case anywhere... air would blast out with a surprising roaring fury... and the engine would be just fine.
11:15 cooler? How does that impact performance? Longevity? Can ceramic coated blades be used along with water injection?
We do not increase the fuel flow or EGT. The coating is to protect and extend the service life of the blades.
Do these engines have any ‘purposeful’, directed air cooling of the exterior turbine case to compensate for thermal expansion and maintain clearance of the turbine blades to the inner case wall? Using compressor bleed ACC active or TCC turbine clearance control can’t recall the name. Or does this engine pre-date that technological complication?
Yes, the Orenda pre-dates that tech. What I call modern engines feature Active Cooling Control.
That is interesting.
Are the air cooling passages in the blades cut with EDM, or some other process?
Love your content. Thank you!
There are different methods used. Sometimes EDM, sometimes lasers, and I'm sure other proprietary secrets.
Fair enough. Thank you!
@@AgentJayZ
@@Marr_SC As a kid, my dad was one of the lead engineers on the TF-39 before he moved over to CF-6. We frequently got to tour GE's Evendale plant. I remember once seeing the facility where they were drilling those holes using an early (circa 1970) variant of EDM. Lots of machines lined up side by side because the process was so slow, and there are a *lot* of holes to drill.
You need to be careful about the terminology here. I would use the term 'cooling passages' for the internal cavities in the blade. Those 'passages' are typically formed during the casting process using ceramic cores, which are then leached out chemically.
The tiny holes you see emerging on the surface of the blade are usually referred to as 'film cooling holes' or 'effusion cooling holes', depending on their precise function. The ones emerging at the trailing edge of the blade are usually referred to as 'trailing edge ejection holes'. Unlike the other cooling holes they are not producing an insulating layer of air on the surface of the blade - obviously! Their function is to cool the trailing edge internally.
EDM was commonly used in my day, 20 plus years ago.
I didn't know you did additional "improvements" - I knew you ceramic coated the blades, but I assumed that was in the service manual.
I'd be curious to know if there are any other improvements you make when you (re-)build an engine, outside the scope of the service documentation of the time.
This engine was developed before ceramic coatings. the only other thing we do is spend more time balancing the rotating assembly to a smaller final imbalance value than the factory did.
I followed .. there is no tube or pipe involved with the turbine disk cooling air. There *is* one for the bearing .. which you clarified .. settled in my book.
In this engine. Each design is different.
@@AgentJayZ yeah .. but you're absolved in my mind as far as how you mention the patreon video goes, my understanding is the question was specifically regarding the turbine disk.
All reconciliatory
Thanks it is intresting
I have a strange unrelated question about a airplane ID book I just got.
The previous owner crossed out "turboprop" every time it was used, maybe 150 times throughout the book.
Why would they do that?
Perhaps the subject wasn’t a turboprop 🤷♂️.
The previous owner was abused by the Allison T-56/501 engine.
Never assume that graffiti or vandalism has any meaning... Or... maybe the previous owner did not understand what the word meant.
Assuming competence is behind the action of others can be a dangerous thing to do.
I've been going through these comments for 30 minutes this morning, and I have deleted two, because they contained ignorance presented as knowledge by people who did not understand what they were talking about.
That's about average for any day, but I'm not done yet.
Cheers.
@@AgentJayZ Perhaps he was he something of a pedant in relation to gas turbine engine terminology? Could he have possibly preferred the now almost defunct term 'propeller turbine' engine? Much of the terminology we now use has become commonplace and accepted because of custom and practice.
Question: why should the term 'turbojet' refer solely to a jet engine that doesn't have a bypass flow.? All it describes is an engine with a turbine that produces a propulsive jet.
Answer: because the term was applied as shorthand term to the early jet engines, which were 'straight through' engines. Incidentally, Frank Whittle wanted to call his jet engine a 'gyrone'.
Originally, Rolls-Royce used the term 'bypass turbojet engine' for engines such as the Conway and the Spey (it's there in early editions of the 'Jet Engine' book). In principle, there's nothing wrong it as a descriptive term, but 'turbofan' is now commonplace. However, it's actually just another shorthand term. which was invented by our American cousins and is now accepted - even by R-R.
@@grahamj9101 A direct translation of the Swedish terms are "single stream engine" (turbojet) and "double stream engine" (turbofan), but I think it is old terminology and most people say "turbofläkt" (turbofan) now.
I saw that older jet engines like the J79 had black smoke trails. In our older diesels and racing engines we ran rich to help cool the pistons and combustion chambers. Is this also done in those older jet engines?
The J79 originally had inefficient combustors and fuel nozzles. Upgrades on the later models eliminated the smoke trail.
The earlier jets all had a slightly less prominent trace of black smoke to the exhaust. Progress in the design of combustion has eliminated that from all turbine engines.
@@AgentJayZ..Thanks
Did water injection add to the black smoke?
@@mattyh2180 Very definitely!
That's why B-52Hs still produce a lot of smoke on take-off. When they eventually get their new Rolls-Royce F130 engines and become B-52Js, they will not have water injection and should be smoke free.
Also, if you have ever seen a Harrier at an air show, you may have noticed that, in the hover, the exhaust from the 'hot' rear nozzles can suddenly become much smokier. The Pegasus has water injection, intended for a 'short lift wet' take-off rating at maximum weight, but I think that display pilots sometimes use it for effect.
@grahamj9101 I wonder if the harrier uses it to reduce the risk of hot air ingestion at lower altitude close to the ground.
Did you have an approx cfm of the cooling air flow? Curious of the mass flow.
It's a small percentage of total mass flow. Only the engineers who designed the engine would know the amount.
Thanks for an amazing video as always. I wonder if the thermal barrier coating can also be applied to the inside of piston engines(piston crown and maybe the valve etc) to reduce the cooling requirements especially in air cooled engines. It remains to be seen if the coating can resist pressure pulses and solvent like effects of fuel.. hmm. Maybe someone has done the experiment already. Do you know where they sell ceramic coating in small quantities?
Many racing piston engines use thermal barrier coatings on the piston crown. Not sure about the valves, but I would expect to work, and also the surface of the combustion chamber in the head.
@@AgentJayZ thank for replying 😁 do you think that the piston tbc is the same stuff used in jet shops? I read up online how some specialist builders use plasma stuff to put on the ceramic on the pistons and i saw you mention plasma gun so i was wondering
What is the ceramic coating you use? A long shot.... but I'm wondering for a hobbiest how well the thermal barrier coating would work for 3D printed plastic parts - to experiment with a custom turbine for even 30 or 60 seconds.
Component Repair Engineer here. In theory, TBC would protect the plastic internals for a brief period, no study has been performed (that I am aware of) as to the efficacy of TBC protected polymers. The problem I see would be the application of the TBC. It is applied through a process that would be beyond the glass transition temperature of most of the 3D printed polymers (EBPVD, APS, HVOF, etc... *google the processes*).
It would be prohibitively expensive for the home gamer, assuming a supplier would even bother to quote such a thing.... It would be less expensive to use the 3D print as the basis for a casting of your choice of material.
The ceramic is applied using a plasma torch spray. If you've got a plastic than can handle 5000 degree heat, you'll be a billionaire very soon.
F86 BABY WOOOOOOOOOOOOOOO
Hello jay, thanks for the video.
When looking at mechanical drawing of jet engines I always wonder why are the compressor disks extending inward towards the center of rotation without making conact with the shaft (apart from first and last disk)? I would instintively think that more rotating mass is bad but that ought not to be the truth. So do you know what purpuse does this design have? I would bet it is something that has to do with structural integrity and vibration dampening but I would love to know the exact reason.
Love the content, bye :)
Now go and find a cross-sectional drawing (not a simplified diagram) of a Rolls-Royce Avon, or a Tyne/Spey/Conway. You will see that the compressor discs are connected to a central shaft by means of 'hairpin' shaped extensions from the disc, which have splined couplings with the shaft.
Similarly, If you can find a cross-sectional drawing of an Armstrong Siddeley Sapphire, or a Viper/Mamba, you will see that the compressor discs also have a central shaft.
Other engines of that era had various means of joining the compressor discs together, but without a central shaft. For example, Bristol used both a rim bolted arrangement and long bolts through the webs of the discs: take a look at an Olympus or a Pegasus.
With the development of laser welding, more recent engines have dispensed with mechanical fasteners (nuts and bolts to you), and the discs are welded together at (or near) their rims. It results in a lighter construction, with an altogether better mechanical integrity. A central shaft is no longer necessary: the welded 'drum' forms a much larger and stiffer shaft.
@@grahamj9101 thanks for the answer!
When you replace different parts of the engine, which one bears the serial number? Or in another words, if you put a couple of engines together, whose plaque you put on the final one?
That's a very good question, and one with many possible answers. These engines all had a military service history, after which they were sold to collectors without any documentation so engine logs were started at the time of sale.
...
several decades later
...
I start with a good candidate for restoration, and I use that data plate. I may change out a great number of parts and assemblies. We keep the original serial number, and start a new log book with zero TSO, or time since overhaul.
I have spoken with several operators of these aircraft, and they have told me this is acceptable to them.
Thanks for the reply. A fan of your channel since the first time I've seen your videos.
I always thought it was interesting that modern turbojet engines run with no/little smoke at mil. No smoke in burner. And then has yellow smoke until the engine "cools down" back to mil. Any idea what would cause that?
Yellow/orange smoke is caused by the formation of Oxides of Nitrogen (NOx). In that specific case, its caused by the high temperature oxidation of atmospheric nitrogen (known as Thermal NOx) - when the burner is turned off, excess O2 which was being consumed when in AB is allowed to react at the high temperatures of the AB section to form orange NOx until temps cool down. There’s also Fuel NOx but that’s another case.
@@GlutenEruption It's true that nitrogen oxides can be coloured - it is specifically nitrogen dioxide which has the orange-red colour, all the other nitrogen oxides are colourless. Hence RFNA (red fuming nitric acid), which gets its colour from having excess nitrogen dioxide dissolved in it.
However, the quantities of nitrogen oxides produced in an engine are not likely to be enough to see the colour of it in the exhaust. It takes several percent at minimum to see the colour, whereas the concentration in engine exhaust is going to be in the parts per million range, a tiny fraction of a percent at most. This is because the vast majority of the oxygen in the air will be consumed by burning the fuel, leaving hardly any left over to react with nitrogen. Gas turbines do of course use most of the air they draw in as cooling air or dilution air, but once the combustion products from the flame have been diluted, the temperature is not going to be high enough for the production of nitrogen oxides.
Heaven is a place on Earth and it is a jetshop in Canada 😉
On the turbine disks that feed the cooling holes at the roots of the blades, does the disk work a bit like a centrifugal compressor in that it flings the cooling air out towards the edge and into the blades?
There would be some effect like that, but I would not say that it's working like a centrifugal compressor.
It's working like a centrifuge. Difference? No actual gas path, no impeller, and no diffuser.
There are two common methods (with variations) of feeding cooling air to the turbine blades.
The first method uses a 'mini-disc' or 'coverplate', which is usually on the front face of the turbine disc . The cooling air is introduced at a low radius into the space between the coverplate and the disc, to flow outwards and into the roots of the turbine blades. There is definitely a pumping effect and some coverplates do actually have radial vanes on their inner faces to enhance the effect.
The second method uses pre-swirl nozzles at the radius of the blade roots. These are effectively miniature nozzle guide vanes, which accelerate the cooling air circumferentially, so that it enters the spaces between the blade roots at the correct angle.
It does mean that the cooling air is entering the blades at a lower pressure as compared to the first method, so that there is relatively less pressure to drive the flow through the internal passages and out through the cooling holes. However, it does have the advantage of providing a cooling air supply at a relatively lower temperature, and it was R-R's preferred method for the RB211 engines. However, looking at various illustrations, it appears that they have gone for the coverplate method in the Trent engines.
Thank you, it must have been the cover plate version I saw in some image.
Do you know by which factor the rate of heat transfer changes through ceramic coating?
Ceramics are like rock, which is not as good at conducting heat as metal is. For both heat and electricity, metals are conductors, and ceramics are insulators.
I think the first engine to use air cooled turbine blades was the General Electric YJ 93.
Perhaps it was the first US engine to have cooled turbine blades, with drilled radial cooling passages. However, both BMW and Junkers used cooled turbine blades in their engines towards the end of WWII. They were relatively crude and fabricated from sheet metal, with the cooling used to provide an acceptable, but still relatively short life, using (not very) heat resistant steels.
were you ever a maintainer in the Canadian Armed Forces?
All of the engines I work on were at one time in service with the RCAF, but I have always been a civilian.
At 5:49, you caught yourself out, didn't you, AgentJayZ? You referred to the 'bearing chamber', went on to use the term 'combustion chamber', and then denied that it was a 'chamber'. You've irritated me before with this denial and I've pointed out that the Orenda Illustrated Parts Catalog(ue), which you have shown us previously, uses the term 'combustion chamber'.
I'll tell you and your subscribers yet again that the term 'combustion chamber' was in use long before I was even born, let alone before I laid a spanner (wrench) on a jet engine: Frank Whittle used the term way back in the 1930s. I suggest that you respect this and accept it.
After all, I've had to accept the use of the Johnny-come-lately term 'combustor' across the industry. I even used it on some of my drawings back in the 1970s, when I was responsible for combustion system design at R-R IMD.
Alright, I give. This is the second time in two days you have beat me.
More on that in the the next video.
Jeez... you're such an engineer.
I still say the turbine engine community needs to fight the Oxford English Dictionary... and Common Sense will be in the audience.
Edit: I should say, sir that although it seems like we are arguing on this minor point, you are effectively a partner on this channel. The gate keeper robots are extremely strict, and often flag comments with the word good, because they mistake it for god.
Anyway, they hold those comments for my review.
There are many each day, and I carefully read each before approving them for release.
Your comments, whenever they are held in such a way, I approve without even reading, because I know you only deal in facts and information. Such is my respect for your input.
Nobody else gets that treatment. It's important to me that you know that.
@@AgentJayZ Of course, I had no idea that I was getting preferential treatment, nor have I ever expected it. Thank you for telling me: I will now ensure that I respect it at all times.
I might have been brought up in the motor trade here in the UK (US = auto repair business), with 'hands on' experience at an early age, but I had a career lifetime in gas turbine engine design. That career began in Coventry, the city of Frank Whittle's birth, which was also Auto City UK when I was a young man. That experience will be in my blood for the rest of my days (I'm now in my 80th year).
I have a huge respect for your 'hands-on' knowledge and experience, which, of course, I could only get 'second hand' after my basic training. I recall an event during a placement in the Rocket Department at Ansty. We were doing a flow check in the engine build shop on something (I can't remember what) and we could see bubbles in a sight glass, which puzzled us.
I suddenly realised that a union nut was probably loose and picked up a spanner/wrench to tighten it. The fitter I was working with grabbed my wrist extremely firmly to stop me.
As I was a technical apprentice and not a craft apprentice, the union rules prohibited me from doing so. I could have caused a strike!
@@AgentJayZ PS I've had some light-hearted fun over the years with the "two nations divided by a common language" issue. After all, it has happened (and sometimes still happens) between Bristol and Derby. For example: snubber/clapper, thrust bearing/location bearing: (turbine annulus) flare/hade: blow-off valve/bleed valve - are some that immediately come to mind.
However, being more serious for a moment, all I'm asking for is that long-standing and different gas turbine engine terminology on this side of the pond is at least recognised and accepted as being valid.
A few years ago, I had a row on your channel with a guy who rejected the fact that, here in the UK, we have long used the term 'angle of incidence' for the difference between the air/gas angle and the geometric angle at the leading edge of an aerofoil (you say airfoil, we say aerofoil). I even quoted the fact that this had been recognised back in 1944 by Langewiesche in his book 'Stick and Rudder', which may still be in print.
Similarly, I was ridiculed by another guy for telling him that British engines had reheat, not afterburning. I pointed out the fact that the engines I'd worked on (including the Olympus 593) had Reheat Fuel Control Units: he just would not accept this.
I found those comments offensive, insulting and unacceptable, both personally and for the engineers who have gone before me.
TKS, Mestre!
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