# Aerodynamic roughness length to equivalent sand-grain roughness?

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 July 12, 2019, 01:51 Aerodynamic roughness length to equivalent sand-grain roughness? #1 New Member   Shannon Kieran Join Date: Jul 2019 Posts: 3 Rep Power: 6 Hi, I am carrying out a Fluent simulation for a city block. In order to set the appropriate surface roughness for the wall boundary condition for the ground surface, I need to specify the sand-grain roughness height (Ks). However, because it is an atmospheric boundary layer problem, not a pipe system, the surface roughness parameters I do have are the aerodynamic roughness length (zo), and also approximate drag cofficient (Cd). I've had a look at the theory guide, user guide and also various textbooks but haven't had any luck finding out how I can convert zo or Cd to an equivalent approximate Ks. Any assistance would be appreciated! (I am a university student)

 July 12, 2019, 04:17 #2 Senior Member   Alexander Join Date: Apr 2013 Posts: 2,309 Rep Power: 33 you may try to find something here https://www.sciencedirect.com/search...rtBy=relevance best regards

 August 19, 2019, 21:01 Solved #3 New Member   Shannon Kieran Join Date: Jul 2019 Posts: 3 Rep Power: 6 Just thought I would post the following in case anyone has the same question later on. I eventually found the answer to my question in this article: Blocken B, Stathopoulos T, Carmeliet J. 2007. CFD simulation of the atmospheric boundary layer:– wall function problems. Atmospheric Environment 41(2): 238-252. © Elsevier 2007.

 November 15, 2019, 10:16 #4 New Member   anarchitect Join Date: Jan 2017 Posts: 3 Rep Power: 8 I have read this article for numerous times, but it does not offer an exact solution. Could you please share how you solved your problem?

 August 7, 2020, 11:50 #5 Member   Join Date: Apr 2020 Posts: 76 Rep Power: 5 This paper offers a direct solution to equivalent sand grain height, as is needed to be input in Fluent for ABL simulation http://www.cobee2018.net/assets/pdf/p/063.pdf

 Tags roughness height, wall boundary conditions