Wall and Boundary Scale (SST)

b4kerman · February 7, 2018, 05:50

I am running a simulation using the SST model and the "Wall and Boundary Scale" in the Solver Manager is decreasing to e-5 in the first iterations and is constant after that. I am used to no value after the first iterations instead of a constant value. Is this ok or is there some problem regarding my mesh?

ghorrocks · February 7, 2018, 06:08

The solver does a diffusion based solution using the solver to get the wall scale variable - which is the distance from the nearest wall. Usually this equation converges quickly to a tight tolerance and then stops, while the rest of the simulation progresses with the other equations (which are much harder to solve).

So this is normal behaviour.

b4kerman · February 7, 2018, 06:13

Perfect, thanks!

elia_l · October 30, 2018, 07:51

Quote:

Originally Posted by ghorrocks

The solver does a diffusion based solution using the solver to get the wall scale variable - which is the distance from the nearest wall. Usually this equation converges quickly to a tight tolerance and then stops, while the rest of the simulation progresses with the other equations (which are much harder to solve).

So this is normal behaviour.

Sorry ghorrocks, I havent clear what this indicator means. you just said "the distance from the nearest wall"... the distance of what? Could you kindly explain more in depth the concept?

Really thanks in advance.

ghorrocks · October 30, 2018, 17:50

The variable is the distance to the nearest wall of the node. That's all, very simple.

elia_l · October 31, 2018, 00:30

thanks a lot ghorrocks! i supose it is expressed using the adimensional form (y+), isn't it? and the value shown by the chart each iteration is the RMS or MAX value (depending on selection) all over the domain walls, is it right?
thanks again in advance

Opaque · October 31, 2018, 08:59

The default plot in the solver manager for Wallscale is the RMS residual as the solution is converging. Once the solution has converged to the specified criteria, the equation is no longer solved.

In some releases shows as a constant residual from there on, in other releases the line is no longer plotted and it stops at the iteration when convergence was achieved.

The wall distance is computed from the wallscale equation solution, see documentation for details.

February 7, 2018, 05:50	Wall and Boundary Scale (SST)	#1
b4kerman New Member Patrick Join Date: Jan 2017 Posts: 10 Rep Power: 9	I am running a simulation using the SST model and the "Wall and Boundary Scale" in the Solver Manager is decreasing to e-5 in the first iterations and is constant after that. I am used to no value after the first iterations instead of a constant value. Is this ok or is there some problem regarding my mesh?

February 7, 2018, 06:08		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,863 Rep Power: 144	The solver does a diffusion based solution using the solver to get the wall scale variable - which is the distance from the nearest wall. Usually this equation converges quickly to a tight tolerance and then stops, while the rest of the simulation progresses with the other equations (which are much harder to solve). So this is normal behaviour. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

October 30, 2018, 17:50		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,863 Rep Power: 144	The variable is the distance to the nearest wall of the node. That's all, very simple. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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February 7, 2018, 06:13		#3
b4kerman New Member Patrick Join Date: Jan 2017 Posts: 10 Rep Power: 9	Perfect, thanks!

October 31, 2018, 00:30		#6
elia_l New Member Join Date: Oct 2018 Posts: 22 Rep Power: 8	thanks a lot ghorrocks! i supose it is expressed using the adimensional form (y+), isn't it? and the value shown by the chart each iteration is the RMS or MAX value (depending on selection) all over the domain walls, is it right? thanks again in advance

October 31, 2018, 08:59		#7
Opaque Senior Member Join Date: Jun 2009 Posts: 1,875 Rep Power: 33	The default plot in the solver manager for Wallscale is the RMS residual as the solution is converging. Once the solution has converged to the specified criteria, the equation is no longer solved. In some releases shows as a constant residual from there on, in other releases the line is no longer plotted and it stops at the iteration when convergence was achieved. The wall distance is computed from the wallscale equation solution, see documentation for details.