# SST model with rough wall?

 Register Blogs Members List Search Today's Posts Mark Forums Read

 November 29, 2005, 05:48 SST model with rough wall? #1 David Guest   Posts: n/a Hi, all Through changing the CCL of wall roughness parameter, it could set the roughness height when SST model is employed, and the solver works normally. The results of simulated boundary layers with rough wall differ from the ones with smooth wall, and the former seem more reasonable. But in some metarials it said that the representation of roughness in this model is not entirely consistent and straighforward. I think it maybe the reason why CFX could not set roughness under SST model. Who could give the internal explaining of this problem?

 November 29, 2005, 12:07 Re: SST model with rough wall? #2 Mike Guest   Posts: n/a There's some extra parameters that need to be set in the CCL to make SST with rough walls consistent, which is why you cannot pick it in CFX-Pre. The CCL should be similar to the following: BOUNDARY : MyWall Boundary Type = WALL Location = WALL BOUNDARY CONDITIONS : WALL INFLUENCE ON FLOW : Option = No Slip END WALL ROUGHNESS: Option = Rough Wall Roughness Height = 0.0002 [m] END TURBULENT WALL FUNCTIONS : Option = Scalable Minimum Yplus = 2.5 END END END Be sure to include the Minimum Yplus parameter and use a value of 2.5, as shown. You will also need to set the following expert parameter: FLOW: EXPERT PARAMETERS: effective viscosity type = 2 END END Details on why these are required would have to come from CFX Support. Regards, Mike

 November 29, 2005, 20:26 Re: SST model with rough wall? #3 David Guest   Posts: n/a Mike, Thank you for your detail guide of setting the roughness parameter!

 November 30, 2005, 00:37 Re: SST model with rough wall? #4 Sam Guest   Posts: n/a Hi Mike, I thought the default value for min Y+ is about 11.06 if scalable wall function is used. How do you determine what value is appropriate anyway?

 November 30, 2005, 12:22 Re: SST model with rough wall? #5 Mike Guest   Posts: n/a Hi Sam The default value is normally 11.06 as you say, and should usually be left alone. This value corresponds to the edge of the viscous sublayer for a smooth wall. However, rough walls break up the viscous sublayer so a different formulation is required for the min Y+. You shouldn't need to worry about determining what value is appropriate, but in this case the code doesn't automatically change the min Y+, which is one reason why you can't pick rough walls in CFX-Pre.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post mehrdadeng CFX 10 February 25, 2011 06:25 DarrenC FLUENT 0 December 13, 2009 09:33 Vincent CFX 7 September 10, 2007 16:49 raik Main CFD Forum 3 May 6, 2007 07:51 CFDworker CFX 1 January 27, 2006 13:42

All times are GMT -4. The time now is 04:10.