de Laval turbine

Has anyone ever built a model of a de Laval turbine? I mean one with a real
de Laval nozzle, that put out some power.
Or do you know of a good text about them? Most are either too simple or
they're too abstract on the engineering theory side.
I'd like to build a model of one, but not just a steam windmill. I'd
like to have some real de Laval nozzles on it.
Thanks to any steamers who know about these motors.
--
Ed Huntress
Reply to
Ed Huntress
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Maybe you can find a copy of:
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Some info here:
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Looks like the critical bit of science is the nozzle accelerates the steam jet to the speed of sound (and above? I assume speed of sound for the material being run through the throat) in the constriction, then the jet hits the divergent part of the nozzle and speeds up yet a bit further.
Interesting stuff, and doubly cool since that principal is used in rocket nozzle design.
So anything convergent-divergent is a de Laval nozzle. Sounds like you could test nozzle designs just by measuring the speed of the output jet (somehow!).
I like the brief mention here:
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" Nowadays steam turbines are the preferred power source of electric power stations and large ships, although they usually have a different design--to make best use of the fast steam jet, De Laval's turbine had to run at an impractically high speed."
An impractically high speed- that makes it a cool project right there!
Dave
Reply to
spamTHISbrp
Ed,
At the following address is a very good little book on the design and manufacture of model steam turbines:
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Also Model Engineer magazine has had articles on this subject from time-to-time.
Wolfgang
Reply to
wfhabicher
--There are a couple of articles in Model Engineer, including some clever ways of cutting the buckets. I messed around with 'em ages ago and wound up writing a little cnc program to make aeorfoil-shaped buckets and a steerable inlet jet; kinda fun. The rotor was no more than 1-1/2" dia tho..
Reply to
steamer
IIRC, Lindsay had some old reprints and archive.org had some stuff buried in their old steam power books. Some of the older books are lighter on the math and heavier on the practice, intended more for the guys that had to maintain them. The impulse turbine is kind of dead, the electric motor took over for running the stuff they used to use it for, haven't seen mention of them except as historical objects in any recent texts. When you shrink to model sizes, subtle curves in full- size practice start resembling straight lines anyway.
Stan
Reply to
stans4
Yeah, but supersonic steam jet + rocket nozzles + linear equiv. speed of the rotor at about 1/2 the steam jet speed =3D lotsa fun!
Where else are you going to get that much excitement with 1 moving part? ;)
Dave
Reply to
spamTHISbrp
GE turbines are/were impulse rather than reaction based for the HP and IP cylinders as were GEC in the UK and Alcatel-Alstom in France. That's something like 50% of the installed base in the world. Impulse turbines are certainly not kind of dead, I walked past two impulse rotors this afternoon in the erecting shop at work!
Mark Rand RTFM
Reply to
Mark Rand
A De Laval (impulse) turbine does not imply supersonic operation. It implies that all of the expansion is done in the fixed blades and the energy is extracted in the moving blades by changing the direction of the steam.
In fact all large turbines will have supersonic conditions in the LP stages merely due to the size of the blades, the rotor speed and the quantity of steam flowing through them. Tip speed on a typical 3000rpm 660MW turbine last stage is about 1400mph. The steam is actually going slower than this (the blade peripheries do travel faster than the steam), but still supersonic.
If you want a worrying statistic, the force trying to pull the blades out of the rotor on a last stage blade is about 1000 tonnes per blade with a typical 46" blade :-)
Mark Rand RTFM
Reply to
Mark Rand
I don't know about now, but I was under the impression that large steam turbines for years were hybrids, with one or two impulse stages followed by a series of reaction stages.
-- Ed Huntress
Reply to
Ed Huntress
And the speed of sound at the transition stage in a convergent/divergent (de Laval) nozzle occurs in a gas state in which it's much higher than the speed of sound in the atmosphere.
-- Ed Huntress
Reply to
Ed Huntress
Maybe you can find a copy of:
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Some info here:
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Right. Which is much higher than the speed of sound in the atmosphere.
I forget most of the dynamics, but it's pretty wild.
Well, de Laval invented the thing (I think), so they use his name on it when it's applied to steam turbines. There are old engineering texts I've seen that provide formulas for all of the dimensions, based on steam temperature, superheat, pounds of steam produced, and so on.
Even the little ones made for doing farm jobs, around the turn of the 20th century, turned at speeds around 30,000 rpm. I have no idea how they held together, given the state of metallurgy at that time.
-- Ed Huntress
Reply to
Ed Huntress
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Thanks, Dave. I'm collecting a good set of references here. I have them all saved for the next rainy weekend.
-- Ed Huntress
Reply to
Ed Huntress
That's one of the things I most want to see. I don't have time to reinvent it all.
I'd like to make something around 6" diameter, if I can.
Thanks, Ed.
-- Ed Huntress
Reply to
Ed Huntress
I've tried plucking out information from old steam books, but they've generally been disappointing. There was one I saw years ago that analyzed some of de Laval's actual production models, and that was great. But I have no idea how to find it now.
Anyway, it's one of those pursuits that's a good challenge, and I'd like to fool with it as I have time.
-- Ed Huntress
Reply to
Ed Huntress
It tends to be a graduation rather than completely one or the other. It tends to be more impulse at the HP end and more reaction at the LP end, but there are/were major differences in proportion. Causes problems when major companies merge, you don't always end up with an optimum design :-|
The major difference in philosophy is that in an impulse design all the pressure drop is across the diaphragms (fixed stages). So you can make the rotor similar to a series of disks on a thinner shaft. This way, the interstage glands where all the pressure drop is (diaphragm to rotor) are shorter, due to being on a smaller diameter. The blade tip seals are far less significant doe to the token pressure drop across the moving stage. Because there's no pressure drop across the moving blades, there's no end-thrust issue. The disks even have (pressure) balance holes to ensure this.
Reaction design turbines tend to be made with a barrel type rotor since the pressure drop across fixed and moving blades is similar, so you can't benefit from a shorter length of gland and you don't want a great big pneumatic piston effect generating end thrust on each stage. Obviously on a double flow cylinder, the end thrusts should balance. but on a single flow cylinder you've got problems.
You can also play games like 100% impulse near the centre and 100% reaction near the tips for long blades. CFD is wonderful :-)
regards Mark Rand RTFM
Reply to
Mark Rand
It sounds like more formulas and calculations than I would do for fun. d8-)
'Too bad Tesla's turbine didn't pan out the way he thought it would. It sure would make life simpler.
-- Ed Huntress
Reply to
Ed Huntress
Not all! The old Canadian Pacific steamships Princess Marguerite, and Princess Patricia, had single stage impulse turbines.
Steve R.
Reply to
Steve R.
--Tellyawhat I'll take some photos today; somewhere I've got a little display I made that illustrates the steps required to machine a complete rotor.
--That's massive! IIRC the one Bill Lear made for his sand racer only had a 4" dia rotor and was rated over 100hp!
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steamer

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