Solving Boundary Layer

aleCinci · February 11, 2016, 10:55

Hi everybody,
I'm setting a low-Re stady-state case using simpleFoam. I'd like to use KOmegaSST turbulent model solving directly the BL because I set y+ lower than 1. I guess I have to set k=0, but how can I set omega at the wall, if I don't want to use any wall-functions?
Thank you in advance.

Gerrit · February 11, 2016, 13:40

Hi,

http://www.cfd-online.com/Wiki/Turbu...ary_conditions
here you can find the initial values you want to calculate.
Setting k=0 means, that the fluctuating part of the velocity is zero. Does that make sense in your case?

Best

aleCinci · February 12, 2016, 07:47

I think that k have to be 0 beacuse the velocity fluctuactions at the wall are 0. I think that with that formulas I can compute omega=0 at the walls but I don't know if it is correct.
Bye

Gerrit · February 12, 2016, 07:55

Hi,

well good question.
The way I did this for "k" was normally to use the kqRWallFunction at walls:

Code:

                type            kqRWallFunction;
                value           uniform 0.1;

and the turbulentIntensityKineticEnergyInlet function at inlet:

Code:

        type            turbulentIntensityKineticEnergyInlet;
        intensity       0.005;       // 0.05% turbulent intensity
        value           $internalField;

I am not very concern about the actual meaning of "value" this time. kqRWallFunction should "know" that at the wall is no velocity and thereby no turbulence. I think sometimes OF simply needs the "value XXX;" line although it does not use it in the end (If I am not correct about this, I am of course happy to be enlightened as well :-) )

By the way: I found these lines in some tutorial files and used them for my simulations. If you search in the tutorials you mostly find what you need.

Best

aleCinci · February 12, 2016, 08:20

I set exactly this function at the inlet patch, in fact I know the initial conditions at the inlet. Actually I'm talking about walls (it is a flat plate placed in the middle of the domain). I don't know if using the omegaWallFuction it automatically will avoid the WallF hence calculate the BL.
Bye

February 11, 2016, 10:55	Solving Boundary Layer	#1
aleCinci New Member Alessandro Cinciripini Join Date: Oct 2015 Posts: 3 Rep Power: 10	Hi everybody, I'm setting a low-Re stady-state case using simpleFoam. I'd like to use KOmegaSST turbulent model solving directly the BL because I set y+ lower than 1. I guess I have to set k=0, but how can I set omega at the wall, if I don't want to use any wall-functions? Thank you in advance.

February 12, 2016, 07:55		#4
Gerrit Member Join Date: Jul 2015 Location: Aalborg Posts: 83 Rep Power: 10	Hi, well good question. The way I did this for "k" was normally to use the kqRWallFunction at walls: Code: type kqRWallFunction; value uniform 0.1; and the turbulentIntensityKineticEnergyInlet function at inlet: Code: type turbulentIntensityKineticEnergyInlet; intensity 0.005; // 0.05% turbulent intensity value $internalField; I am not very concern about the actual meaning of "value" this time. kqRWallFunction should "know" that at the wall is no velocity and thereby no turbulence. I think sometimes OF simply needs the "value XXX;" line although it does not use it in the end (If I am not correct about this, I am of course happy to be enlightened as well :-) ) By the way: I found these lines in some tutorial files and used them for my simulations. If you search in the tutorials you mostly find what you need. Best

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February 11, 2016, 13:40		#2
Gerrit Member Join Date: Jul 2015 Location: Aalborg Posts: 83 Rep Power: 10	Hi, http://www.cfd-online.com/Wiki/Turbu...ary_conditions here you can find the initial values you want to calculate. Setting k=0 means, that the fluctuating part of the velocity is zero. Does that make sense in your case? Best

February 12, 2016, 07:47		#3
aleCinci New Member Alessandro Cinciripini Join Date: Oct 2015 Posts: 3 Rep Power: 10	I think that k have to be 0 beacuse the velocity fluctuactions at the wall are 0. I think that with that formulas I can compute omega=0 at the walls but I don't know if it is correct. Bye

February 12, 2016, 08:20		#5
aleCinci New Member Alessandro Cinciripini Join Date: Oct 2015 Posts: 3 Rep Power: 10	I set exactly this function at the inlet patch, in fact I know the initial conditions at the inlet. Actually I'm talking about walls (it is a flat plate placed in the middle of the domain). I don't know if using the omegaWallFuction it automatically will avoid the WallF hence calculate the BL. Bye