CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CFX (http://www.cfd-online.com/Forums/cfx/)
-   -   first node in turbulence model (http://www.cfd-online.com/Forums/cfx/18617-first-node-turbulence-model.html)

Franco Belosi August 20, 2001 04:10

first node in turbulence model
 
I'm a beginner with CFD (CFX4.3): in dealing with the k-epsilon turbulence model I've to set the first node at y+>11.Since y+ is a function of the unknown friction velocity how can I estimate the first grid position? Are there any empirical relationships which allow a crude estimate of the friction velocity? Thank you in advance for anybody helping me.

Jonas Larsson August 20, 2001 11:17

Re: first node in turbulence model
 
Yes, you can estimate the wall-distance you need to get a certain y+. There is even a nice little free online calculator which will do it for you - you can find a link to it in the Resources/Calcs/Misc section of CFD Online.

Herve August 21, 2001 08:20

Re: first node in turbulence model
 
In the manual you will see that you can set a USRSCAL (user scalar) to return the y+ values and plot it.

Regarding u*, for open channel for example you can use the crude assumption that a mean u* = sqrt(g*R*So) where g is the gravitational acceleration, R the hydraulic radius and So the energy gradient.


All times are GMT -4. The time now is 22:47.