[steven1]

Hi,

In my case, i want to use the transition SST model or the transition k-kl-omega model. But i don't know how to determine the intermittency and the laminer kinetic energy.

Does someone know how to calculate them?

Thank you.
Steven

[Far]

You dont need these quantities.

[steven1]

Originally Posted by Far

You dont need these quantities.

Thank you for your reply.
So what should i fill in the blank?

[Far]

Are you talking about transition models of Fluent? If yes then you dont need to input any parameters for these models except turbulence length scale and turbulence intensity if you have info about them.

If you dont have info about length and intensity then you can use these parameters (can be used in parametric study) :

For turbulence length scale you take it as 30% of chord length and turbulence intensity can be taken as < 1% for low distrubence such as in wind tunnels, 1-5% in normal free stream conditions and >5% in highly disturbed upstream flow.

[steven1]

Ok, thank you, so i can i will have a try.

[steven1]

Originally Posted by Far

Are you talking about transition models of Fluent? If yes then you dont need to input any parameters for these models except turbulence length scale and turbulence intensity if you have info about them.

If you dont have info about length and intensity then you can use these parameters (can be used in parametric study) :

For turbulence length scale you take it as 30% of chord length and turbulence intensity can be taken as < 1% for low distrubence such as in wind tunnels, 1-5% in normal free stream conditions and >5% in highly disturbed upstream flow.

hello, i still have a question. how can i judge whether my results are correct? for example, when i use k-epsilon standard-wall function, if my yplus are between 30 and 300, i'ill accept the results.
Thank you.

[arohr]

Originally Posted by Far

Are you talking about transition models of Fluent? If yes then you dont need to input any parameters for these models except turbulence length scale and turbulence intensity if you have info about them.

If you dont have info about length and intensity then you can use these parameters (can be used in parametric study) :

For turbulence length scale you take it as 30% of chord length and turbulence intensity can be taken as < 1% for low distrubence such as in wind tunnels, 1-5% in normal free stream conditions and >5% in highly disturbed upstream flow.

Hi Far,

I know I'm bringing up a very old post but this one is the only thread which directly has my question in it.
I am in search of the literature or direction from the solvers on where the relations of turbulence length scales is described. I am trying to use the transition-SST 4 equation model and want to make sure I am inputting reasonable values for length scale (my flow generally boils down to a cylinder in cross-flow).
In fluent's user's guide I see they bring up a relationship of 0.07*L for length scale, where L is characteristic duct size. I am hesitant to use this because my overall analysis is a free shear flow. I am also dealing with a very large Reynolds (on the order of 10^5) and am hesitant to use values meant for wall-bounded flows.
The experiment I am comparing against gave me turbulence intensity of their tunnel so I don't need to worry there. Any help would be greatly appreciated.

[Far]

What i have learned is that "Length scale has minimum to no effect on transition"

Rule of thumb is to take length scale = 0.3 L.

Or you can hit & trail and check it.