Question aboutTrefftz plane analysis?

[mezah]

Hello every one
I would like to learn more about trefftz plane theory which is used to calculate induced drag.
Is it an effective method to calculate induced drag?
can i used it with propeller and wind turbine instead of an aircraft wing?

thanks in advance

 

[berkshire]

Here is a link to it.

http://www.edforall.net/index.php/e...s/1926-trefftz-plane-analysis-of-induced-drag

B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[mezah]

Thanks for the link but i was hoping for some kind case study or at least solved examples

 

[patprimmer]

You will find that many here will help you find the answer rather than just giving it out. By doing this we tend to not encourage students who are to lazy to do their own homework.

Regards
Pat
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[MiketheEngineer]

What Pat is saying - I think - is go BUY the book, read it and then if you don't understand something - we will try to help..

 

[mezah]

All my respect to the rules but i am not searching for someone to solve my home work - that if i have one - all i need is a text book or a paper where i can find more detailed discussion about the subject rather than just a part of a presentation which is a little bit obscure for me.

I asked two more question which i can't answer by reading 3 pages, what i need is an opinion based on experience.
Appreciate your help and i have no intention to break any rules.

 

[rb1957]

Pat's response is because you don't show us you understand the material and ask a very general question.
so too berkshire's (so he gives you a link to the material).

if you're saying you've read the material but don't "get it", i'd suggest starting with an earlier lecture and see if that helps. maybe if you ask a specific question about the derivation, maybe someone will give you a nice response (but don't count on it !).

assuming you know the material, and you're asking is it applicable to propeller drag analysis, i'd point out the initial assumptions "invisid, incompressible" fliud. i'd suggest that flow around a propeller is not incompressible (tip speeds are often close to mach 1), and so it probably doesn't apply (unless they derive a compressible version later in the lecture.

 

[patprimmer]

By propeller, I presume you mean aircraft not boat propeller. Of course there are similarities, but one does operate in a compressible medium and the other in a non compressible medium.

This is far from my area of expertise, but I think a propeller can be treated as a wing, except that the air speed over the wing increases with dia as does effective pitch unless that is corrected for in the design.

Even if you are not a student which I will quite happily take your word for, simplistic or very wide general questions still tend to downgrade the site and attract student style posts which we mostly really don't want to bother with.

Regards
Pat
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[rb1957]

pat, sure a prop blade is like a wing, with some differences (as you've noted, rotation speed changes the AoA along the blade, the blade is twisted to compensate). the key issue is flow around a blade is compressible, and this method (i've only looked at the 1st page of the link above) says "incompressible fluid" ... a typical assumption, reasonable for subsonic wing analysis but IMHO dubious for a blade.

 

[KENAT]

Dubious for an aircraft propeller at high rpm, but maybe not for a wind turbine so long as effective tip speed doesn't get too high.

Assume the OP means HAWT, or do you actually mean VAWT?

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[mezah]

KENAT i agree with you, incompressible flow is a safe assumption when we are dealing with HAWT since the speed and hence the Mach number are small.

rb1957 This method used - as i understand - to calculate the induced drag, and since the induced is caused by the downwash which lead to change the angle of the Lift which lead to another component of lift in the free stream direction namely induced drag.
All this has nothing to do with the compressibility effect, so i think the incompressible, inviscid, irrational flow assumption - even for high speed propeller - is safe.

MiketheEngineer What i am trying to say is: all i want is the NAME of the book so i can BUY it

 

[rb1957]

ok, i missed the wind turbine reference.

don't we use CFD for this (calculating drag) these days ? looking quickly at the calc, you need the flow veolcity over some control volume, something you'll only get from CFD; but then don't CFD codes calc drag for you ?

maybe go to the MIT opencourseware site (the origin of the previous link) and look for similar lectures, maybe there are references and examples ?

maybe you're too focused on this specific analysis ? maybe google "induced drag".

"to calculate the induced drag, and since the induced is caused by the downwash which lead to change the angle of the Lift which lead to another component of lift in the free stream direction namely induced drag." ... this seems circular ! induced drag is drag caused by lift (as opposed to form drag) you use it to determine the drag polar of a wing.

 

[mezah]

Unfortunately, there is no solved example for this course

 

[rb1957]

ok, but are you using CFD to analyze the blade ? doesn't CFD calc the drag of the airfoil ??

are you trying to do some hand calcs to verify the CFD ?

i found this site "

http://www.pdas.com/induced.html"

by googling "induced drag worked example". it has links to some more work/books on the subject.
even googling "trefftz plane analysis" got lots of hits (surprisingly) so there are sources out there (that you can find for yourself).

is this for school ??