Learning Forum

[mrdurango]

Hi, I'm working on a hydrocyclone validation and I need to know what it is the turbulent viscosity equation for RNG k-e which depend on a swirl factor, k/epsilon and rotational tensor.

thanks.

[Rob]

The equations are covered in the manual(s), and literature. However, I'd also suggest (very carefully) reading the model limitations and recommendations before choosing a different turbulence model! 

[mrdurango]

The equations are covered in the manual(s), and literature. However, I'd also suggest (very carefully) reading the model limitations and recommendations before choosing a different turbulence model! 

 

Hello rwoolhou , thank you for your answer.

As you suggested, I read in section "12.19.6 Swirl Modification" (from 12.19.6 Swirl Modification) the default swirl constant (  in Equation  12.4-8 ) is set to 0.07 (what is this "swirl constant" in the first place?). However, equation 12.4-8 from RNG Swirl Modification:

 

       eq. 12.4-8

 

only shows the functional dependence on , but not the function itself. From the theoretical point of view, I want to know how this function is included in the model since I have not found any literature (apart from here) where such a relationship is used. We know  (eq. 12.4-7):

 

        eq. 12.4-7

 

My question then is: why this swirl factor is included?  what is "f" in eq. 12.4-8, i.e what is the function that corrects the turbulent viscosity in eq. 12.4-7 by using   and .

 

I would be very grateful if you could point me to any articles about this, since to my knowledge, the k-e model doesn´t incorporate any "swirl factor" in its equations.

 

 

 

 

Thank you for your time. 

 

Marvin.

 

[Rob]

I was referring to the limitation of the 2-equations models: we never use them for cyclones. You need to use the RSM Model and a good quality hex or poly mesh. 

Most of the equations should also have references (use the R19 support: v6 is about 17-18 years old), I can't comment other than to refer you to those: not that they're needed as you'll be reading the limitations! 

[mrdurango]

Hello rwoolhou, thank you for your answer. I looked into the last version of fluent documentation and it says the same I showed you. I know it is not recommended to work with RNG k-e in cyclones, and I have as well used the RSM Model and obtained good results. Apart from this, however, my question persists, what is the "swirl factor" and how it is implemented into the k-e model equations, it seems to me a bit obscure. 

 

Thank you for your time again!

 

Marvin

[Amine Ben Hadj Ali]

The function is not published and is confidential.