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Old   December 19, 2010, 03:44
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Hi.
I want to make a simulation for a airfoil for i solute it with FLUENT.
I must use the k-e turbulent model but i do not know how i make the mesh near the wall of airfoil. I have read that the Y plus of first cell must be within 30-300 for standard wall function. However, How can i compute the Y length of cells for i make the mesh arround the foil
NACA0012and also ,I want some tutorials about ernal flow around airfoil or cylinder with Reynolds number at nearly 50000.
Thanks
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Old   December 19, 2010, 05:36
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Quote:
Originally Posted by MANFEIZHANG View Post
Hi.
I have read that the Y plus of first cell must be within 30-300 for standard wall function. However, How can i compute the Y length of cells for i make the mesh arround the foil NACA0012
First, evaluate drag coeff as c_f=0.074Re_L^{-1/5}, where L is the chord length.
Then calculate friction stress \tau_w=1/2 c_f\rho U^2 and friction velocity u_*=\sqrt{\tau_w/ \rho}

Then we have
y^+ = y u_* / \nu where \nu is the kinematic viscosity
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Last edited by ignat; December 19, 2010 at 07:07.
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Old   December 24, 2010, 04:55
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thanks,ignat
now ,i had done some examples by k-e model ,y+=0.0001m,Angle of Attack is 12(re=50000,the chord length is 1m),but from the result ,i can't find the shedding vortex,may i have your email ? i have some details to talk with you,ok?
looking forward to your reply .merry christmas
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Old   December 24, 2010, 08:27
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Originally Posted by MANFEIZHANG View Post
y+=0.0001m
y+ is dimensionless parameter. What does it mean "m"?
May be it is dimension value?

Optimal y+ near the wall is about 1 (dimensionless!) for calculation without wall function and 10-100 for calculation with wall functions. But never 0.0001!
Did you estimate friction velocity u* for your case?

I am not expert in aerodynamics but i think shedding vortex does not obligatory occur. It depends on many circumstances.

regards.
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