# equivalent sand roughness height

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 July 29, 2009, 22:01 equivalent sand roughness height #1 Member   LSC Join Date: May 2009 Posts: 58 Rep Power: 8 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?

 August 3, 2009, 22:15 #2 Member   Yi-Lang Chen Join Date: May 2009 Posts: 58 Rep Power: 8 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.

December 23, 2012, 12:26
equivalent sand grain roughness
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hamed
Join Date: Apr 2009
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Rep Power: 8
Quote:
 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?

 December 23, 2012, 13:50 #4 Senior Member   Christoph Join Date: May 2011 Location: Germany Posts: 182 Rep Power: 9 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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