Error in interpolating data?

Lighto · October 18, 2018, 11:26

Hello everyone,

I am a new Fluent-user and I have a very simple question (I think).

I have defined some custom field functions such as the laminar and turbulent stresses in a k-w-RANS simulation, using viscosity-lam, viscosity-turb, turb-kinetic-energy, density and the gradients. I saved the single components of the stresses (i.e. 12 color-by per time-step) and a combination of them (also defined as a CFF - called "scalar-stress") on some particles injected at the inlet of my domain. To check if "scalar-stress" was correct, I tried to recombine manually (i.e. with matlab) the stresses using the output files but I obtained a different result comparing it to what Fluent has saved as "scalar-stress".

So basically my conclusion is: combining some variables in Fluent is different than doing it in post-processing, but why?
Is this an interpolation issue?

LuckyTran · October 18, 2018, 13:57

How do you calculate gradients in matlab?

Lighto · October 18, 2018, 19:21

I do not calculate gradients in matlab. I save directly $\sigma_{xx},...,\tau_{zx}$ both for laminar and turbulent. Then sum them and do the same calculations I do in Fluent.

October 18, 2018, 11:26	Error in interpolating data?	#1
Lighto New Member Davide Join Date: Jun 2018 Posts: 10 Rep Power: 8	Hello everyone, I am a new Fluent-user and I have a very simple question (I think). I have defined some custom field functions such as the laminar and turbulent stresses in a k-w-RANS simulation, using viscosity-lam, viscosity-turb, turb-kinetic-energy, density and the gradients. I saved the single components of the stresses (i.e. 12 color-by per time-step) and a combination of them (also defined as a CFF - called "scalar-stress") on some particles injected at the inlet of my domain. To check if "scalar-stress" was correct, I tried to recombine manually (i.e. with matlab) the stresses using the output files but I obtained a different result comparing it to what Fluent has saved as "scalar-stress". So basically my conclusion is: combining some variables in Fluent is different than doing it in post-processing, but why? Is this an interpolation issue?

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October 18, 2018, 13:57		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	How do you calculate gradients in matlab?

October 18, 2018, 19:21		#3
Lighto New Member Davide Join Date: Jun 2018 Posts: 10 Rep Power: 8	I do not calculate gradients in matlab. I save directly $\sigma_{xx},...,\tau_{zx}$ both for laminar and turbulent. Then sum them and do the same calculations I do in Fluent.