seanreit

My Feedback: (60)

I had understood that there are some applications where turbine blades are being wallowed out and running fuel inside the blade to cool it to get the hot section hotter.

Am I completely off base here? I understand that if there was even a minute crack it could cause a major problem and maybe even be a bomb, but I toured an xray facility a year ago, and I thought they told me they were xraying the blades to assure that the fluid was not waring down the inside of the turbine blades. Today in a conversation, I was not as sure as I thought I was.

TO be more specific, I thought this was being tested or used in the F-111.

Can anyone clear this up for me?

KC36330

allot of turbine blades have holes through them for cooling (mostly high pressure bypass air), it regulates temp fluctuations in the blades and cuts down dramatically on thermal stress of the blades, it also allows for a higher max operating temp of the turbine which increases thermal efficiency.

causeitflies

Never heard of fuel going through the blades but as KC said most use air for cooling for higher more efficient temps.

mr_matt

My Feedback: (10)

It is air going through the hollow blades, never heard of fuel. They run fuel through rocket nozzles to cool them but I have not heard of turbines doing this

causeitflies

Sean, the "fluid" they were referring to was probably air.

ossie

Sean, maybe you heard the term ' film cooling'
Here's a brief description - http://www.me.umn.edu/labs/tcht/measurements/what.html
Cheers Os

Woketman

My Feedback: (6)

This is called regenerative cooling. An example: LH2 in the SSMEs (Space Shuttle Main Engines) goes through small tubes that surround the engine nozzle before entering the combustion chamber. This serves two purposes: it cools the nozzle (keeps it from melting, which it would!) and pre-heats the liquid hydrogen prior to it meeting up with the O2.

The Russkies actually use LO2 for regenerative cooling ( [X(] ) in a few of their engines. A dicey situation if even a minute leak occurs!!!

Square Nozzle

My Feedback: (1)

I spent 41 years working on engines at Pratt & Whitney and have never heard of using any "fluid" other than high compressor air to cool the turbine blades. The air is pumped into the blade roots from a duct system that we called TOBI (tangential onboard injection). The interior or the blade has cast in passages that direct the air to critical areas of the blade. Then the air is exited from the blade through holes in the blade airfoil surface to provide film cooling of the exterior. I doubt very seriously that any liquid could survive in the turbine section of the engine even before it got to the blades.

WHMC

My Feedback: (15)

Only turbine I can think of using fuel pressure for something was the GE CJ805. Convair 880/990. They had variable inlet guide vanes operated using fuel pressure. WHMC

seanreit

My Feedback: (60)

Ok, I knew you guys could straighten me out, I am usually pretty good at regurgitating what I hear, it is certainly possible that either he did not know what he was talking about when originally speaking to me, or worse case scenario, a sign of aging is I am making up memories..... []

It sure sounded cool at the time nonetheless. Thanks guys,

Sean

Woketman

My Feedback: (6)

As long as we are making up memories....

"Sean, remember that time that I let you fly my Isobar and all went well and its a_s did not burn off?" Yeah, right!

Gordon Mc

My Feedback: (11)

I thought you were gonna say:

"Sean, remember that time 6 years ago when I loaned you $100,000.00 and you promissed to repay it this year at 35% APY interest ?"

Robrow

Typically the HP turbine blades are working in temps around double their melting point temp. Regenerative cooling is used big time on modern jets particularly in the environmental control systems, the cold air units have an uncanny resemblance to our microturbine engines with a compressor, turbine and shaft connecting them.

Those big F1 engines on the old Saturn V were certainly something to behold and they burned highly refined kero (RP-1) if I remember rightly.

Rob.

SJN

This is cool

How can a rocket engine that generates 5,000 degree steam and 13,800 pounds of thrust form icicles at the rim of its nozzle? It's cryogenic. The Common Extensible Cryogenic Engine, CECE for short, has completed its third round of intensive testing. This technology development engine is fueled by a mixture of -297 degree Fahrenheit liquid oxygen and -423 Fahrenheit liquid hydrogen.

The engine components are super-cooled to similar low temperatures. As CECE burns its frigid fuels, gas composed of hot steam is produced and propelled out the nozzle creating thrust. The steam is cooled by the cold engine nozzle, condensing and eventually freezing at the nozzle exit to form icicles. Using liquid hydrogen and oxygen in rockets will provide major advantages for landing astronauts on the moon. Hydrogen is very light but enables about 40 percent greater performance (force on the rocket per pound of propellant) than other rocket fuels. Therefore, NASA can use this weight savings to bring a bigger spacecraft with a greater payload to the moon than with the same amount of conventional propellants. CECE is a step forward in NASA's efforts to develop reliable, robust technologies to return to the moon and a winter wonder.

Woketman

My Feedback: (6)

The -297 and -423 are ONLY at sea level atmospheric pressure. And yes, there can be a huge performance advantage to LOX/LH2, but it does not come free: they are cryogenic and therefore must be stored refirgerated and under pressure. That means you have to use them sometime soon or loose a lot to boil-off. To keep it simple back in Apollo days, they used storable hypergolic (they ignite on contact) propellants to make life easy and reliable. You need to ignite LOX/LH2. And when you are on the moon counting on that engine to get you back into lunar orbit to start your way home, that thing BETTER light! The Apollo LM HAD to work as long as you can open the pre-valves!

Mike Emilio

Sean, , ,

I did some inspections on the F404 engine parts, used on the F18 aircraft.
Then I remembered this thread and took a few pics.

These pictures are of the blades used on the GE F404 engine.

All the blades are hollow inside, except for compressor blades.

The first stage is a rather large configuration, with a double set of blades.
The other stages are very much smaller.

Notice that they have intake porting on one end.

Air is pushed thru these ports, and exits via a row of smaller holes on the inside surface of the trailing edge.

This is done to help keep the blade temperature down.

Square Nozzle

My Feedback: (1)

Sorry Mike but those are turbine inlet guide vanes. They are also air cooled typically using external plumbing that brings air in from the high compressor. The blades fit into the turbine disc with a fir tree looking root attachment.

SJN

pics

Woketman

My Feedback: (6)

Anyone know for certain why they have that serrated-looking trailing edge? My guess is some sort of boundary layer control, but that does not make a lot of sense if it is the trailing edge! Unless it is to prep the airflow for the next stage.

causeitflies

I think because the material is much thinner at the trailing edge and there is more cooling needed there.

Mike Emilio

The blades are assembled into a large ring representing either compressor, or turbine end. The process is about the same for either one.
They are then poured with a low temperature alloy, I think it was called Kirksite. This stops them from vibration during the grinding operation. The entire ring is put into a rotary fixture, then ground as an entire assembly.

The Kirksite is melted out merely with very hot water.

These blades were basically rejects that would not properly fit into the grinding wheel/fixture.

Here's the fir tree types. Also from the F18, F404 engine.

Mike Emilio

These are hollow parts. It might look serrated, but it's actually a full row of .022" holes, where the air exits.

That's a .022" dia drill that I stuck in one of the holes.

Woketman

My Feedback: (6)

Thanks Mike, that makes sense.

Mike Emilio

That's exactly what the engineers said as well.
The trailing edge takes quite a beating with the heat.

Harley Condra

My Feedback: (4)

Mike,
"Kirksite" is composed of 94% zinc, and 6% aluminum, and has a melting point of 725° F. Too high for hot water.
Kirksite is now being used for an alloy in injection molding, but has been more commonly used as the die in drop hammer die sets. The punch, or the part of the hammer die set that gets dropped, is made of lead.


I believe you must have meant "Cerrobend", which melts at 158° F, which is well within the range of hot water.

I use these three shapes of cerrobend ingots for building weights.
The top one weighs 1.35 Lbs., the center one weighs 1.93 Lbs., and the hex shaped one is 2.4 Lbs.