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MANFEIZHANG December 19, 2010 03:44

k-e model
 
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

ignat December 19, 2010 05:36

Quote:

Originally Posted by MANFEIZHANG (Post 287748)
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

MANFEIZHANG December 24, 2010 04:55

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

ignat December 24, 2010 08:27

Quote:

Originally Posted by MANFEIZHANG (Post 288365)
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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