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Fer January 27, 2006 04:42

Which kind of pressure use calculating Drag?
Hi all!

I'm running CFD simulations in order to study the drag of a vehicle. When I think more theoretically how to calculate the drag force (or the Cd coefficient) I have a big doubt. First of all, I understand that the CFD program iterates in order to get the velocity/pressure fields in the fluid domain; once they are obtained, then it calculates the drag by integrating the 'pressure field' and the 'shear stress field' through the body surface. My question is: that 'pressure field' (or altenatively, pressure coefficient Cp) is an static pressure, a total pressure,...?

Another question related with this is: pressures measured in a wind tunnel test by pressure sensors located into the body surface, are static pressures, total,...?

It would be very helpful for me to solve this in order to understand the process and very useful if anybody tells me some kind of literature explaining that.



diaw January 27, 2006 05:42

Re: Which kind of pressure use calculating Drag?
Hi Fer,

Can I respectfully direct you towards reading any number of basic CFD books? CFD-Online has an excellent listing & links to many good ones.

You really need to spend a few months reading all the background information before you begin moving into the simulation phase. Things will then become more clear for you.

Enjoy the journey...


Alex Muthaiah January 27, 2006 07:43

Re: Which kind of pressure use calculating Drag?
Also Refer:

Vehicle AirDynamics by Huccho,Ahmed.Its a fantastic book for know the things watever u asked.


Ahmed January 27, 2006 11:29

Re: Which kind of pressure use calculating Drag?
Diaw How are you doing with your research programme. You see, this is one more example of misunderstanding the meaning of the term "Pressure" or "P" in the Navier Stokes equations, but this man is being honest with himself and is trying to understand it, Cheers and GoodLuck for all who want to understand. Read the introduction to the Kinetic Theory of Gases given in Chapter one of Atomic Physics by Max Born, this is a Dover publication that costs $12.95

diaw January 27, 2006 12:10

Re: Which kind of pressure use calculating Drag?
Hi Ahmed,

My current research work is going very well, with a few major break-throughs - all beginning with a search for a singularity - now I have so many, it is incredible. Pressure is very much an integral part of the whole interplay. An extremely fascinating process.

Thanks for asking... :)

Take care.


Freeman January 27, 2006 13:32

Re: Which kind of pressure use calculating Drag?
Mmmm, I haven't heard this book... were you referring to Aerodynamics of Road Vehicles by W-H Hücho instead? I've been searching in Google a bit and I haven't found this reference...

Could you verify this? Thanks.

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