Aerodynamic roughness length to equivalent sand-grain roughness?

Shanny · July 12, 2019, 01:51

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)

AlexanderZ · July 12, 2019, 04:17

you may try to find something here
https://www.sciencedirect.com/search...rtBy=relevance

best regards

Shanny · August 19, 2019, 21:01

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.

mimarilker · November 15, 2019, 10:16

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?

mz_uon · August 7, 2020, 11:50

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

July 12, 2019, 01:51	Aerodynamic roughness length to equivalent sand-grain roughness?	#1
Shanny 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)

August 19, 2019, 21:01	Solved	#3
Shanny 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.

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July 12, 2019, 04:17		#2
AlexanderZ Senior Member Alexander Join Date: Apr 2013 Posts: 2,363 Rep Power: 34	you may try to find something here https://www.sciencedirect.com/search...rtBy=relevance best regards

November 15, 2019, 10:16		#4
mimarilker New Member anarchitect Join Date: Jan 2017 Posts: 3 Rep Power: 9	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
mz_uon Member Join Date: Apr 2020 Posts: 76 Rep Power: 6	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