[saeed jamshidi]

Hello,

I'm going to dive into K-omega SST turbulence model, and I'v noticed about Menter's wall BC for Omega.
Would you please help me to clarify nu and y?
y is the first cell hight close to the wall not y+?
Is nu=kinematic viscosity?, for example (nu_water=1e-6) otherwise what is the kinematic viscosity at the wall?
thanks.

omega
type fixedValue;
value uniform (calculated with Menter's recommended wall BC, i. e. 

omegawall=60*nu/(beta*y^2), with nu=kinematic viscosity at the wall, 

beta=0.075 and y=normal distance between the first fluid node and the nearest wall);

[arjun]

Everything seems good except the factor would be 6 and not 60.

[saeed jamshidi]

Dear arjun, thank you for the reply.

The formula is as follows:

omega_wall = 10 * 6 * nu / ( 0.075 * y^2 )

So, you confirm that y is the first cell hight and nu is the kinematic viscosity?

Besides, I would appreciate it if you verify my K, omega and nut BCs on the wall for y+=1;

omega:

    wall
    {
        type             fixedValue;   
        value          uniform  63775; //according menter BC.
    }

K:

    wall
    {
        type            fixedValue;
        value           uniform 1e-12;
    }

nut:

     wall
    {
        type fixedValue;
	value uniform 0;
    }

Currently, I am pretty sure about K & omega BC types and values, nevertheless, I have doubt for nut type because I've seen in CFD online some threads, calculated type is considered on the wall.

[arjun]

Nu and y are what you said.


The factor of 10 seems arbitrary to me but if its working for them then who am i to argue.

This seems to be something people are doing differently.

[NotOverUnderated]

Originally Posted by arjun

Nu and y are what you said.


The factor of 10 seems arbitrary to me but if its working for them then who am i to argue.

This seems to be something people are doing differently.

That factor is not arbitrary. It is in the original paper of menter [1]:



Reference:

[1] F. R. Menter, ‘Two-equation eddy-viscosity turbulence models for engineering applications’, AIAA Journal, vol. 32, no. 8, pp. 1598–1605, 1994, doi: 10.2514/3.12149.

[arjun]

Originally Posted by NotOverUnderated

That factor is not arbitrary. It is in the original paper of menter [1]:



Reference:

[1] F. R. Menter, ‘Two-equation eddy-viscosity turbulence models for engineering applications’, AIAA Journal, vol. 32, no. 8, pp. 1598–1605, 1994, doi: 10.2514/3.12149.

Its arbitrary in reference paper too. He never derived how he came to that factor. Besides other people use other values. StarCCM uses 2.5 and not 10.

Do you have a paper that derives that factor 10 and shows that it is not something that author came up with and have defite value of 10.

[saeed jamshidi]

Thank you for your opinions.

Yeah, it's kind of controversial issue.

However, I saw wolf dynamics tutorial, and it was declared that omega value just on the wall could be a large value.

[arjun]

Originally Posted by saeed jamshidi

Thank you for your opinions.

Yeah, it's kind of controversial issue.

However, I saw wolf dynamics tutorial, and it was declared that omega value just on the wall could be a large value.

Yes, different people do different things. I guess based on their experience and ideas. I prefer 2.5 as value as it seems to produce good results.