[LSC]

Hi, I am trying to model roughness which I only have the average grain size (0.25mm). How to I convert this value into equivalent sand roughness height? Is there any relationship?

[Andy Chen]

Dear LSC :

Did you simulate open channel on CFX? According your problem that you can use Parker(1991) Ks (sand roughness height)=6.0*D50(average grain size). I use the equation to decide roughness height when I simulated open channel. If you have any question, welcome to discuss with me.

[hmasenger]

Originally Posted by Andy Chen

Dear LSC :

Did you simulate open channel on CFX? According your problem that you can use Parker(1991) Ks (sand roughness height)=6.0*D50(average grain size). I use the equation to decide roughness height when I simulated open channel. If you have any question, welcome to discuss with me.

hi
i am having same problem in sand grain roughness but in pipes .i know e/d equal to 0.001 and i dont know the right equvalent sandgrainroughness .do yo have any idea how to define it?

[energy382]

take a look at the cfx-solver theory guide, chapter 2 "modeling flow near the flow"/"treatment of rough walls"

http://www1.ansys.com/customer/conte.../cfx/xthry.pdf