modelling wall friction

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 May 6, 2015, 12:22 modelling wall friction #1 New Member   Ronald Thompson Join Date: Mar 2015 Location: Portland, Oregon, USA Posts: 25 Rep Power: 9 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?

 May 6, 2015, 15:56 #2 Member     Ethan Doan Join Date: Oct 2012 Location: Canada Posts: 90 Rep Power: 12 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

 May 6, 2015, 16:17 #3 New Member   Ronald Thompson Join Date: Mar 2015 Location: Portland, Oregon, USA Posts: 25 Rep Power: 9 do i simply put my value of friction coefficient in for the wall roughness boundary condition or is wall roughness a different scale, thanks

 May 6, 2015, 16:53 #4 Member     Ethan Doan Join Date: Oct 2012 Location: Canada Posts: 90 Rep Power: 12 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.

 April 4, 2016, 05:09 Wall roughness height #5 New Member   SRIVATSAN Join Date: Apr 2016 Posts: 1 Rep Power: 0 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.