[ranjithdj]

Hi all,


I am simulating flow over a bump using SA model. I want to calculate u'v'=2*v_t*S_ij. I can get eddy viscosity (u_t=v_t/density) directly from field function. How to calculate strain rate tensor(S_ij). How to define user function for S_ij?


Thanks
Ranjith

[LuckyTran]

At the bottom of the tree in tools you'll find field functions and there you can create a custom field function. There is an interactive GUI that you can use.



Or do you need help with the formula for Sij?

[bluebase]

Hi Ranjith,

the strain rate is available as field function. However, its a temporary field function which is usually not stored. To get it: open the flow solver and look for the option "Temporary Storage Retained". This will make many intermittent functions available. One of them is called something like Strain Rate Modulus or Strain Rate Tensor Modulus, maybe use the search feature. It's variable name is actually ${StrainRate}.

However, the value of that function represents the total shear rate, or its magnitude, so it's only a scalar without any information about the direction.
I believe, the definition of that Modulus can be found somewhere in the theory guide as well.

If you really need to define a tensor, you might check the documentation on user field functions. In the last couple of versions the support for tensor valued operations have been extended. So you might find a short cut to your desired output

Best, Sebastian

[ranjithdj]

Originally Posted by LuckyTran

At the bottom of the tree in tools you'll find field functions and there you can create a custom field function. There is an interactive GUI that you can use.



Or do you need help with the formula for Sij?

Thank you. I have doubts again.
S_ij within the boundary layer will be only the diagonal matrix right. i.e 2(∂U/∂x+∂V/∂y+∂W/∂z) or I have to take all other components.
How can I get value for ∂U/∂x or ∂V/∂x in StarCCM?

[bluebase]

Hi Ranjith,


search for "Calculating Derivatives with Vector Field Functions" in the manual.


Best, Sebastian

[ranjithdj]

Originally Posted by bluebase

Hi Ranjith,

the strain rate is available as field function. However, its a temporary field function which is usually not stored. To get it: open the flow solver and look for the option "Temporary Storage Retained". This will make many intermittent functions available. One of them is called something like Strain Rate Modulus or Strain Rate Tensor Modulus, maybe use the search feature. It's variable name is actually ${StrainRate}.

However, the value of that function represents the total shear rate, or its magnitude, so it's only a scalar without any information about the direction.
I believe, the definition of that Modulus can be found somewhere in the theory guide as well.

If you really need to define a tensor, you might check the documentation on user field functions. In the last couple of versions the support for tensor valued operations have been extended. So you might find a short cut to your desired output

Best, Sebastian

Thank you, Sebastian. I got the field function by temporary storage for strain rate. Do you know how the strain rate will be calculated? So the below figure shows formula for strain rate. Is that every element of tensor should be calculated or only diagonal?
https://www.google.com/imgres?imgurl...MygMegUIARCKAg

[ranjithdj]

Thank you, Sebastian and LuckyTran