Where do I find coefficient values for these 2 formulas? (drag coefficients)

[Tim Leijten]

Hi there,

So I asked a question here how I would calculate the air drag and the wheel drag of a train and I got an answer that made me very happy.
Unfortunately i don't know where i could find the coefficient values required for the formulas.
So i am wondering if someone knows where i can find these values for trains or how I can calucate them myself.
This are the formulas:
Fd = Cd 1/2 p v2 A
and: F = Crr N
So I need to know how i get the Cd and Crr values.(original formulas in the link in the first sentence)


Thanks!

 

[gleem]

Have you tried Googling drag coefficient or coefficient of rolling resistance?

 

[Tim Leijten]

Have you tried Googling drag coefficient or coefficient of rolling resistance?

I have, but I want to calculate them myself.
But i did find something for drag coefficent.
The only values i could find for wheels were in % which i believe is not what i am looking for.

 

[gleem]

I think they are usually determined experimentally. The Wikipedia articles give some guidance and you could look up drag coefficients of locomotives too.

 

[Dale]

@gleem is right, these are usually not calculated theoretically, they are measured, for example in a wind tunnel.

 

[Tim Leijten]

I think they are usually determined experimentally. The Wikipedia articles give some guidance and you could look up drag coefficients of locomotives too.

Thanks, I see.
Do you maybe know if there is some database for that?
Or are these put in like the manuals of locomotives or something?

 

[DrStupid]

Do you maybe know if there is some database for that?

Maybe there are such databases but I don't expect them to be free for everybody. Such experiments are quite expensive and the results are intellectual property of the sponsors.

Or are these put in like the manuals of locomotives or something?

Yes, that should be a good place to look for the coefficients (or something equivalent) if you have access to such documents.

 

[Dr.D]

There was a lot of excellent experimental work done in Nazi Germany (Prandtl, et al) in the 1930's as that nation prepared for war. This work made its way into two large books:
Fluid Dynamic Drag
Fluid Dynamic Lift
both by S.F. Hoerner
These books are rather hard to find, but they are by far the best source I know about.

 

[jrmichler]

In addition to the books listed by Dr.D, which mostly apply to aircraft, there is also Aerodynamics of Road Vehicles by Wolf-Heinrich Hucho.

 

[Tim Leijten]

Okay, thanks!
I think I got an idea where to look.