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-   -   how to choose the turbulence intensity and hydraulic diameter (http://www.cfd-online.com/Forums/fluent/114221-how-choose-turbulence-intensity-hydraulic-diameter.html)

 shlgzz March 7, 2013 04:16

how to choose the turbulence intensity and hydraulic diameter

Hello.
I'm facing the problem of choosing turbulence intensity and hydraulic diameter when simulating the flow field of airfoil.
Any kind of help will be appreciated.
Thank you.

 kbaker March 7, 2013 13:08

You mean how to set the values of turbulent intensity and hydraulic diameter? if yes it exist at the inlet boundary just select momentum then set your turbulent quantities but be sure first that you choose a turbulence model for your problem if it laminar turbulent quantities cannot be set under laminar case.

 shlgzz March 7, 2013 23:03

I know where to set the values.However,I don't know how to calculate the values of turbulent intensity and hydraulic diameter.
Could you give me some suggestions?

 macfly March 7, 2013 23:47

 vigii March 8, 2013 02:47

For external flow over a airfoil the Turbulence Intensity would be in the range of 1% and hydraulic diameter should be calculated from formula 4*a/p (a-area;p-perimeter) . You should consider the face(in case of 3d) or edge (in case of 2d) which is normal to the direction of flow.

 shlgzz March 8, 2013 07:40

Thank you.vigii.However,I'm not sure about how to calculate the hydraulic diameter because we don't know the width of airfoil.If provided any information in detail,that would be great.Besides,the material of fluid is air or ideal gas? and how do you specify the turbulence?

 vigii March 11, 2013 01:05

If you could give me your outline of the problem. I could help you out. its better to give your domain model with its dimensions. it would be helpful for calculating the parameters of the concern problem.

 shlgzz March 11, 2013 04:17

2 Attachment(s)
Quote:
 Originally Posted by vigii (Post 413012) If you could give me your outline of the problem. I could help you out. its better to give your domain model with its dimensions. it would be helpful for calculating the parameters of the concern problem.
Thank you.vigii.
Under the incompressible conditions,does the mach number influence the lift coefficient and drag coefficient much?

The attachment shows the domain model of 2 dimensions.The radius of arc is 14 times of chord length.The width of rectangle is 20 times of chord length.I wanna know how to specify the turbulence properly.

 vigii March 11, 2013 05:38

I want to clear myself one thing about your nature of your problem. I think you mean to do subsonic flow analysis for your kind of airfoil. If im right then the Velocity/Mach no. Here, it will have its own effects on Cl and Cd.

Give turbulence intensity as 1%
and hydraulic diameter as length of the arc. (If 2d)

If you are trying to replicate any wind tunnel tests. then can give Hydraulic diameter as 4*a/p

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