Calculate shaft power on a power turbine

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HattoriHanzo
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Calculate shaft power on a power turbine

Post by HattoriHanzo » Sat Jun 16, 2007 10:12 am

Im thinking of building a turboshaft engine with a free power turbine from an old turbocharger. The gas generator core will be build on a centrifugal flow compressor and a radial turbine. Axial guide vanes and one axial turbine will be used as a free turbine stage.
I wonder if you guys can help me with calculations to solve the shaft power available on the free turbine output shaft?

I also wonder if you know any free downloads of CFD programs useful for stator/rotor turbine stages?
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HattoriHanzo
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Post by HattoriHanzo » Sat Jun 16, 2007 3:55 pm

Is it possible to use the formula for lift: L=q*S*cl?

I know all the data for the free turbine blades exept cl.

For example:

the flow velocity from the guide vanes through the turbine is 200 m/s, the density of air is 2 kg/m3 and the surface area of each turbine blade is 0,0004m2. And we approximate the cl = 3.

then

L for each turbine blade is = 0,5*2*40000*0,0004*3 = 48 Newton

if the free turbine has 20 blades the total force is 48*20 = 960 Newtons.

Is this a possible and a correct solution to solve the shaft power?
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Ash Powers
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Post by Ash Powers » Sun Jun 17, 2007 3:08 pm

Hattori,

There is a very educational section in the Thomas Kamps book on Model Jet engines that goes into the kind of details you are looking for. Also, without having to spend any loot, you can go to the diygasturbines on yahoogroups.com and refer to the rules of thumb, specifically the ROT on freepower turbines. They have spent a healthy amount of time expanding those documents and IIRC, it has everything you need to determine the amount of shaft power available from a given set of operating parameters and component geometry.

Unfortunately your question has many pre-requisite bits of information before you can even get into calculating the potential shaft power of your FPT - the gas producer's operating parameters are a critical starting point for doing the rest of the maths.

www.yahoogroups.com requires registration and a brief "application" to the various groups - upon acceptance, you'll be afforded all the benefits of what the group has to offer - well worth the small trouble for signing up too.

*Admin: Apologies for sending folks elsewhere - IMHO, PJ is truly the best forum I've seen. :)

Mike Everman
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Post by Mike Everman » Mon Jun 18, 2007 3:14 am

No biggie, Ash. I belong to diygasturbines myself! I'll have to check it out again soon.
Mike
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racketmotorman
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Post by racketmotorman » Mon Jun 18, 2007 9:49 pm

Hi Hattori

To workout the potential power output of a freepower (or any turbine) you need to do a "velocity triangle" for it .
From this "triangle" you readoff the total gas deflection thru the turbine , multiply by the velocity of the turbine blade(at mid blade span) , multiply again by the mass flow , then if using imperial units of measure such as feet/sec , pounds weight etc , divide by 550 (ft lbs/sec/hp ) and divide by 32.2 (gravity)to get the shaft horsepower being developed .

Its kinda simple :-))... even more simple again if using the Metric system where the maths are easier.

Cheers
John

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