Surface y+ manual calculation

Yur · October 11, 2011, 08:56

Hi guys,

I need toget the surface y+ results for internal flow. I have the following equation now, but it's not showing me the correct values. Could somebody give me a solution for this.

surface_yplus = (y_velocity*cell_size)/char_viscosity;

The y_velocity is the downstream velocity direction. The cell_size is different for each region in the geometry and the char_viscosity is just a constant.

ps. It's a low speed simulation (0.75 m/s)

Thanks in advance.

bluebase · October 23, 2011, 12:53

Hi Yur,

may be it's late:

Check your formula again and compare with http://www.cfd-online.com/Wiki/Dimen...e_%28y_plus%29

u_star is not the downstream velocity.

When you follow the link for friction velocity one gets:
u_star = sqrt( tau_w / rho )

Follow the link for wall shear stress to get a formula to compute tau_w.

I hope this is helpful.

Sebastian.

October 11, 2011, 08:56	Surface y+ problem	#1
Yur New Member Join Date: Aug 2011 Posts: 17 Rep Power: 14	Hi guys, I need toget the surface y+ results for internal flow. I have the following equation now, but it's not showing me the correct values. Could somebody give me a solution for this. surface_yplus = (y_velocitycell_size)/char_viscosity; The y_velocity is the downstream velocity direction. The cell_size is different for each region in the geometry and the char_viscosity is just a constant. ps. It's a low speed simulation (0.75 m/s) Thanks in advance. Last edited by Yur; October 11, 2011 at 10:00.*

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October 23, 2011, 12:53		#2
bluebase Senior Member Sebastian Engel Join Date: Jun 2011 Location: Germany Posts: 566 Rep Power: 20	Hi Yur, may be it's late: Check your formula again and compare with http://www.cfd-online.com/Wiki/Dimen...e_%28y_plus%29 u_star is not the downstream velocity. When you follow the link for friction velocity one gets: u_star = sqrt( tau_w / rho ) Follow the link for wall shear stress to get a formula to compute tau_w. I hope this is helpful. Sebastian.