Value of Cmu for RANS turbulence models

[st268]

Hello,

I am using the Rij-epsilon SSG turbulence model and have noticed that Cmu is being set to 0.42 in my turbulence initialization. I had thought that this constant was normally around 0.09. In fact in the user guide it states that code_saturne sets this as 0.09 yet it is most definitely 0.42 in my xml file.

Anyone have any ideas as to why this is? It is the same for k-e model also (appears as 0.42 in my xml files)

cmu = 0.42;
k = 1.5*(0.02*uref)^2;
eps = k^1.5*cmu/almax

Any help would be appreciated!

Thanks and best regards,

Susan

[Yvan Fournier]

Hello,

This should occur only if you choose to initialize turbulence values using a formula, which you can edit.
The example (initial) formula was fixed on Oct 30, so it should be in version 3.0.3, but in any case, you can just edit the turbulence initialization formula in the GUI and fix the value.

When not using a user formula (letting the code do initialization by reference values), it will use the correct value of cmu in any case (0.42 being a typo/mixup with kappa).

Regards,

Yvan

P.S. 3.0.4 should be released within a few days, so you might prefer to wait before installing 3.0.3.

[st268]

Hi Yvan,

Thanks for the quick reply. I changed Cmu manually as you suggested in my new runs, and noticed that it appears correct in the listing file so I am not too worried about it.

Just to note though, that this appeared for me when I had chosen initialise turbulence from reference values not formula.

<turbulence model="Rij-SSG">
<initialization choice="reference_value" zone_id="1">
<formula>cmu = 0.42;
k = 1.5*(0.02*uref)^2;
eps = k^1.5*cmu/almax;</formula>

Thanks for your help

Susan

PS: I am using 3.1.0, I will be upgrading to the latest version when it is released