[dynamic]

Hi,
im currently trying to model the flow around an object in a tank using the K-epsilon solver, the object is attached to one of the concrete walls of the tank and i want to see what effect the friction of the concrete has on the acceleration of the flow around the object.

my question is how do I add in the friction coefficient of the concrete into my model?

[edoan]

You should be able to specify a wall roughness in the boundary conditions. You cant use it with enhanced wall functions though. you can use a K-e with standard wall functions or a k-w model

[dynamic]

do i simply put my value of friction coefficient in for the wall roughness boundary condition or is wall roughness a different scale, thanks

[edoan]

You cant use the friction coefficient for the wall roughness value you need to specify your wall roughness value in height like millimeters. im not really sure how to take a friction coefficient and turn it into a wall roughness. You could enter various values of wall roughness until your simulation gives you the correct skin friction drag corresponding to your friction coefficient.

[Srivatsan]

I found moody chart useful in guessing the wall roughness from the friction coefficient. from the darcy weisbach factor and reynolds number, the chart gives you e/d ratio.