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 LSC July 29, 2009 22:01

equivalent sand roughness height

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 August 3, 2009 22:15

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 December 23, 2012 11:26

equivalent sand grain roughness

Quote:
 Originally Posted by Andy Chen (Post 225151) 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 December 23, 2012 12:50

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

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