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 Zweeper December 20, 2009 17:03

hydraulic diameter?

2 Attachment(s)
hey, maybe I'm just confused because of the English word for it (sorry, my first language isn't English) but i need help with the "hydraulic diameter" setting in gambit.

The problem is in the attachment. I have to create a wind tunnel with a lorry inside (3D).

in the bundary conditions in fluent i can set up for both inlet and outlet the option specification method: itensity and hydraulic diameter

what is my hydraulic diameter in this case? the hydraulic diameter of the lorry? or the wind tunnel?

Is it the same like the characteristic length of the reynolds number when i want to calculate my reynolds number for this case?

 -mAx- December 21, 2009 02:22

You are in the set-up panel for your inlet.
So you need to enter the hydraulic diameter for the inlet.
Dh = 4. Area / Perimeter

 Zweeper December 21, 2009 06:44

ah okay, so then this formula

http://www.cfd-online.com/W/images/m...bdef9c58cf.png

and when i want to determine the characteristic length of the lorry for the Reynolds number? I should take then Dh with the front side of the lorry?

the problem is that i (until now) just calculated flow within pipes etc.

 -mAx- December 21, 2009 07:43

Sorry, the formula I gave you is for internal flow

 Zweeper December 21, 2009 07:52

ah okay, but which formula is then for external flow?
the formula from my post is the same. im confused with this, sorry.

 Zweeper December 24, 2009 11:47

sorry for the questions, but you already helped me a lot!

now i have another question to fluent. its about the "report" -> "reference values" option. i can change the area there.

Is this area the frontal area of the lorry? (the object i wanna analyse?)

for example, when i have an airfoil with the chord = 1 and a depth = 4, the reference area is then 4, right? or is this area related to the wind tunnel?

greetings!

 -mAx- January 4, 2010 01:44

reference values are given for setting the Cd, Cl and Cx coefficients (related to yor body).
So you have to give those values for your body

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