Turbine Blade Cooling Air Pathways 

I belt and polish those blades daily. It's crazy the amount of work that goes into them from start to finish.

Incredible how heavy some of these older turbine blades seem to be - they must be pulling like crazy on the shaft at high RPMs. Anyway - thanks for showing all these, amazing stuff. Would be fun to see how they manufacture the blades and get those tiny holes in there.

At prima machine training the past few weeks. I manufacture and produce these parts. I love your videos. I make replacement parts for most of what you show.

Investment casting was revived and refined to make the complex internals of blades. It was state of the art in the 1970's when I studied it formally as part of Materials Science, Thermodynamics and Fluid Mechanics. There were of course gaping chasm of untold wisdom. Which is why I'm watching this channel.

I'm not a turbine engine engineer, but I have some training in heat exchanger design. The objective here is to maximize the heat transfer to the cooling air while minimizing the mass flow rate of the cooling air, since this is what costs compressor power and therefore fuel consumption. Yes, the Series flow path potentially increases the max temperature of the cooling air in the blade, but this also means that the cooling air has absorbed more heat per mass. Sure, you could just restrict the outlet of air, but then the air is moving very slowly inside the blade, which reduces the heat transfer coefficient. And then you also have a thermal gradient within the air in the blade that results in the air at the tips being hotter, whereas with the series path, the temperatuee gradient of the air in the blade will somewhat average out radially. This temperature gradient will also be present in the air exiting the film cooling holes. The series path will have more pressure drop, but you likely have more differential pressure than you need for the convective cooling path because the exit pressure is somewhere between the stage inlit and stage outlet pressures, whereas the film cooling exit pressure is the turbine inlet pressure.

What baffles me when I look at the engineering of these turbine engines is how the designers and engineers manage the complexitiy within their process. When I am doing my little tinkering projects as a hobbyist I always try to keep it as simple and functional as possible. But a solution to an upcoming design problem often leads to a feature that comes with its own challenges, requirements and issues. And this spiral of fixes and more issues can grow really fast. I do not even dare to think of the level of complexity when designing rocket or gas turbine engines. Keeping it simple yet efficient and effective is really an art form.

This is what I keep explaining to my pilot friends when they start talking about a mythical small, efficient, low cost turbine engine. The key is the temperature differential, or how hot you can run the turbine itself. The key to keeping the turbine buckets (aka blades) cool enough to survive a large temperature differential is through cooling air inside of it, and a film of protective cooling air surrounding it as protection from the combustion heat. The physics of moving air around tiny little passages gets harder and harder to do, and even more difficult to manufacture. Making a 250hp gas turbine engine that is efficient and cheap, is simply not possible, at least not in any means we have today. Film cooling was used in the V2 rocket engine in WW2, quite effectively.

As I watch this mams videos. I realize his education is way beyond an average gas turbine engine mechanic. He has a very good understanding of very complex concepts in design and heat transfer technologies and metallurgy. Metallurgy is a subject that is more difficult than a nuclear physicist. Metallurgy is so complex that many will specialize in a group of metals such as non ferrous, ferrous, Titanium and it's alloys, Grasses and bronze, etc... I used to teach Metallurgy and am impressed with his knowledge of so many of these areas of expertise. I also was a welding engineer who built gast tibine engine hot zone components, mostly combustion cans. Someday I want to visit his shop and learn more in person. My last bucket list thing to do while alive. May visit after I pass...😅

When I worked at a combined cycle plant, we had rotor cooling air. Bleed air was passed through a water to air heat exchanger (aka kettle boiler). This cooled the air and added some heat to the feed water for the steamer setup. Siemens SGT5000F

Great video as always! Some pertinent terms you could throw into this conversation (to help tie together everything you're talking about) are 'surface area', 'choked flow', 'dwell time', and 'gas density'. Yes, lots of fluid dynamics and thermodynamics math over both our heads (and I'm even in the mass flow measurement business!). In short, we're trying to pass a low molecular weight gas over a much higher molecular weight metal to draw (lots of) heat energy away. Or at least enough to maintain a nice safety margin on the metalurgical temp limits. Some 30+ years ago I met a guy (working as a car mechanic in Tucson AZ ironically) who apparently revolutionized the manufacturer of these cooled turbine blades; specifically for private jet sized engines. Interesting fellow, not sure what he was doing working on my Honda with that kind of resume! Anyway, it was great to finally see a breakdown (literally!) on what theses blades are all about. Thanks again for making these videos.

It's still amazing to me that those early gas turbine engines, and even piston engines, were designed and built by extremely smart people with nothing but pencil, paper, slide rules, and a vision of what they wanted to achieve. No computers or AI modeling, just ingenuity.

Informative. I did not know that some were air cooled. Thank you for video

In a reciprocating engine, the boundary layer usually does a good job at insulating the metal bits from peak combustion temperatures. Undet knock however, supersonic waves scour the boundary layer from the surface often resulting in holes burnt through piston tops. A gas turbine situation is a little different mainly because there's no respite from heat so sustaining a cooler boundary layer requires some "help" in the form of air bleeds.

Rolls has been GROWING titanium single crystal blades for their "Trent" series ... with internal passages and surface holes somehow grown in place. The process is proprietary and secret.

The HPT blades on the Rolls-Royce Trent 1000 TEN have a life of 1000 cycles (flights) mandated by EASA (if they last that long before cracking due to creep) and cost around $25,000 USD each

I would love it if you ground down more turbine blades to discuss cooling paths and heat management.

AJZ, thank you for your explanation and demonstration.

I spend around 30 plus years measuring the position and angle of various jet engine cooling holes. The F110 engine ( f16 motor) for an example in first stage nozzle has around 600 cooling hole two vane noozle. The first stage blades and vanes are in the hottest place in a jet engine.

A lot of less expensive jet engines like general aviation turboprops and helicopter turboshafts still have uncooled turbine blades that look like the one from the early 50s.

The pressure in the combustion chamber can not exceed the pressure in the compressor. The pressure is assumed as constant ideally. However it drops a little.

Thanks.

@agentjayz, cheers buddy. You might be surprised how similar “modern” turbine blades are in similarity to earlier turbofans. The huge difference is in the coatings applied, and that can go into an episode all of its own. Well coatings normally contain RE elements that are very, very expensive. In development we would start with full thickness coatings and then thin it out for “war on cost” until it looks like swiss cheese and go from there. There is just no substitute for rhenium, its just how low can you go (material life vs. cost). Then we could get into military engines vs. commercial and different cost concerns blah blah blah 😂. We are total nerds buddy ✈️.

Jumo 109-004B Orkan engines had hollow bleed air cooled blades.

G'day Jay, Yay Team ! A beautiful Explainification ; I enjoyed every bit Of it... Thankyou. As regards your Parting Question, "Who makes Cars with Wooden Spoked Wheels today (?)... Nobody !" Well, um, probably because I posted a Video showing two of my grandfather's Wheelwrighting Tools which I'd cleaned and oiled-up for their first use in 25 years (and then, I was using them for the first time since 1936 when my grandfather last made a Wagon Wheel Spoke with them)... ; The mighty RU-vid Algae-Rythm has been feeding me with back-catelogue Uploads from @ Engels Coach Workshop Channel... Whereas I use the 1905 Patent Tools on my grandfather's Brace & Bit, Dave Engel has a pair of Drill-Presses, one with a Spoke-Pointer and the other with a Spoke-Tennon Cutter... He scratch-built Full Size Replicas of the 3 Wagons in the Death Valley Borax Wagon-Train - which used to operate from 1892 till 1896 or something....; each Rear Wheel from all of 3 Wagons , weighed 1,080 Pounds, before fitting - and he built all three complete, working Wagons, two Ore-Carriers holding 8 Cubic Yards each and a Water-Wagon holding 6 tons or so to water the 16 to 24 Mules it took to haul the Wagon-Train out from the Mine. At age 15 I helped Dad to shape & fit one of the last of 6 Pairs of Sulky-Shafts which his father had bought pre-sawn in 1936, there were 3 pairs still in stock in 1976 (!) {and the old man had no trouble selling the two remaining pairs...}. Not long after that, he was asked to fit a pair of Steel Tyres to two Wooden Wheels, for an old Combination Harvester being restored, and I was enlisted to help in the second one of them. I've flown behind two Propellers which I designed, laminated with Ancestral G-Clamps, carved with the inherited Drawknife & Spokeshaeves, and shaped with the Grandparental Wood-Rasps....(!) ; so I sort of barely almost know enough to understand & appreciate what an amazing (Remnant) Expert Master Craftsman he actually is. And his Production Values are Superb. Do yourself a favour, maybe And check out the answer to your Question.... Look him up...(?) ! He's not churning out Wheels for Henry's Model-Ts But he is Still making an apparently handsome living, as a Wheelwright, Making and Repairing & Restoring Wooden Wheels, and Horse-Drawn Vehicles. Commercially, with a Main-Street Shopfront Workshop FULL of the most wonderfully Specialised Tools... I really enjoy watching the pair of you..., because You and he are like two Peas in Parallel Pods, On different pathways, Both in relentless Pursuit of preserving the Old Machinerys, in the Olden Ways, Least it all be forgot...(!). Kinda thing. Just(ifiably ?) sayin'. Such is life, Have a good one... Stay safe. ;-p Ciao !

The manufacture of those things is very data intense. Everything in the process is logged, a few of each batch gets X-Rayed and that data is stored away for a very long time for traceability. If they make one today and it fails 30 years from today, the investigator will be able to track back to the initial making of the thing. At least that is supposed to be how it works. Pretty fascinating process, IMO to make so many and record so much and yea, each one cannot cost $1M...not practical.

Seeing you present these blades that had a bad day it made wonder: How much damage can a jet engine absorb and still be repairable? Or put another way; at what point do you consider an engine a total loss?

where i work we do steel stacks the can hold 800°C ...we had numerous connected to a gas turbine generators ...thats some crasy ass technical solutions in those stacks. we didnt went to aircool the liners yet :D:D. when the inlet is of the size of two buses its 99.9 chance its one of those.

23:48 just give me the damn torque table hahaha. So true Jay

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There is another book Irwin E Treager Aircraft Gasturbine engine technology. Very practical book like the Jeppesen one.

Seeing the size of the internal cooling passages on some of those blades brings a side question to my mind: Is there a secondary effect of reducing the mass of the blade, so reducing the forces on the blade root?

The CF6-6 and the TF-39 had the two in one blades. They called them buckets.

Cooled cooling air for the turbine, AgentJayZ? Yes, it was done years ago - by the Russians in one of their military turbofans. If you trawl the internet, you might be able to find a photo of a sectioned engine with a mass of small tubes in the bypass duct. I did look at cooled cooling air and putting a heat exchanger in the bypass duct of a future military engine project at R-R Bristol, many years ago. Having told you this, I hope that I don't get a knock at the door and get taken away by some men in dark suits.

A notable professor once said, "Let the rest of the world worry about water". When a civilizations ability to move is ruled by exothermic reaction, where your wallet releases heat, and now is even given cooling holes so it can release more heat! Then we have reached the maximum potential of a turbine blade and the said societies ability to evolve. Therefore it's up to the individual to fight for their right in how their ability to move is ruled. Physics that include an endothermic reaction would loosen this shackle, cool the wallet, reduce the need of exotic geometric shapes and balance the equation allowing evolution to continue. Change comes from the bottom!

I think the logic behind the serpentine configuration has to do with making the air do more work until it it ‘uses up’ its ability to absorb heat thus making a specific mass of air do more work than simply one pass of the same mass. Sorry for that long sentence…

I was watching a talk on this here RU-vid by the chap that wrote the “The Secret Horse Power Race” book, he mentioned that BMW when developing a turbo charger for the FW190 engine used air cooling for the turbine due to a lack of Nickel needed to make high temperature steel. I’ve failed to find other mentions of this on the net.

Do you have a video showing the pto from turbine shafts. More to the point which axle is it taken from. My interest is heli engine

I wonder if the computer on a modern engine varies the compressor bleed air to the different cooling pathways during different operatig conditions? I know we are extracting smaller and smaller effiencies from modern engines, and varying the bypass air might account for several percents of thermal efficiency at cruising conditions.

Jay - What is the approximate thickness of the ceramic coating applied to the solid turbine blades to extend their service life ?

Something I've wondered about for a long time: what is the smallest feasible gas turbine engine (either axial or centrifugal)? I've seen pretty tiny ones (like IDK maybe 4" diameter) but can they be made smaller still? And if not, what is the limiting factor? I can think of a couple of candidates: 1) strength of materials (the smaller they are the faster they spin, right? So at some point everything will fly apart at the rotational speeds required); 2) thermodynamic: smaller turbines means less space available for gas expansion; 3) engineering: the smaller you go, the more microscopic the tolerances get.

Can you show a pathway of supplying air to discs and blades for air cooled blades?

I have a related question. I read somewhere recently that one way to significantly reduce drag on a torpedo (as in a torpedo from a submarine) is to eject compressed air out of the torpedo nose so that the torpedo essentially moves through a near-still (relative to the torpedo) envelope of air (which would have significantly less drag than moving through the water). Leaves me wondering if the cooling air ejected out of the leading edge of a turbine blade, which at that point would be moving at the same, or very nearly the same, speed as the blade, helps reduce drag on the blade?

Can the cooling air be intercooler to lower it's temperature? Would that be worth the hassle? Maybe air that was too cold would cause thermal shock to the blades?

Excellent presentation, sir. Question: possible to use low-pressure air from the early compressor stage passing through an intercooler to lower the temperature of high-pressure air from later stages of the compressor in order to increase the cooling capacity for turbine blad cooling? ~just curious~ 👍

Apologies because its not fully relevant. Its eh almost relevant though. It is about engine cooling. I recently found out that Top fuel dragsters are cooled by their fuel. Because they run on almost pure Nitro which has its own oxygen supply they actually can and do use more fuel than air. (a car or jet, burns about 15 times more air by weight than fuel) Dragsters have about 40 fuel injectors, some in the supercharger and other parts of the airflow. So the fuel is providing almost all of the lubrication and cooling. thats why they choose to run them on a mix that uses more fuel than air.

Maybe a stupid question, but is it possible to have regeneratively cooled blades (similar to rocket engine combustion chamber) by running fuel trough them? I guess coking would be a problem…

I wonder if they somehow injectionmold those or theyre drilled after?

Does GE or any other aircraft Engine manufacturer make a triple spool engine like the Rolls-Royce RB211 Trent, they were the first bleed air turbine cooling turbojet cause I have seen possibly from you How's the pt6 going updates please

How do they make those blade with all the holes inside? No wonder they are $10,000 each.

Is there possibility to cool that cooling air between compressor and turbine blade?

There is one detail I don't understand. Pressure of gasses after combustion should be much higher than pressure in compressor. Then how come products of combustion don't flow inside the air passages of blade and heat it even more ? Possible explanation is venturi effect, but without calculation/simulation it's not easy to judge which way gas is going to flow.

How the fuck are they manufactured? Amazing things.

Did the person who was supposed to attach that 737 max door to the fuselage,(which susequently detached there from), finish, or even start reading that 2nd book shown? I can't imagine so. 🤣

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I love Pink Floyd

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