User roughness

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konst
Posts: 25
Joined: Sun Sep 17, 2017 7:41 pm

User roughness

Post by konst » Thu May 24, 2018 11:45 am

Dear all,
Could you tell the definition of user roughness parameter which is set up in the GUI. Is it "ks" value (Nikuradze roughness) or "y0" value. Or some other value?
In the source code (https://www.code-saturne.org/cms/sites/ ... ource.html) there is next lines about roughness:

Code: Select all

  688   /* Compute the friction velocity ustar */
  689 
  690   /* Shifting of the wall distance to be consistant with
  691    * the fully rough wall function
  692    *
  693    * ln((y+y0)/y0) = ln((y+y0)/alpha xi) + kappa * 5.2
  694    *
  695    * y0 =  roughness * exp(-kappa * 8.5)
  696    * */
  697   double y0 = roughness*exp(-cs_turb_xkappa*cs_turb_cstlog_rough);
That means user roughness is "ks" value which is ks=30*y0 roughly? Or maybe definition of roughness changes somewhere before?

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