Problems with a resistance material

[Anonymous]

Hi,

 I am Kevin and I have two problems with a resistance material.

First, if I change the Constant Loss Coefficient (K-Factor) the Simulation doesn't run again.

I must delete the material and then assign new. Is this a general problem of Autodesk CFD 2015?

Second, if I calculate the K-Factor I use this formula from the help site: 

Then I use the K-Factor, but in the Simulation I can't get at the pressure difference.

And if I double the K-Factor then according to the theory the pressure difference must be twice the original value.

I take the static pressure.

What seems to be the trouble?

Kind regards

Kevin Ölscher

[Jon.Wilde]

Hi Kevin,

There should be no issues with changing the type of resistance - so long as you are always starting the analysis from zero.

Do you have sufficient mesh? We do need a good uniform mesh on a resistance with at least 4-5 elements from inlet to outlet.

Could you share a screenshot of your model so we know what we are talking about?

Kind regards,

Jon

[Anonymous]

Hi Jon,

thanks for your help.

I always starting the analysis from zero. But every time the solver ends by unknown reason.

I use an uniform mesh by the resistance material. But the fluid hasn't an uniform mesh, because of my limited pc power.

In the attachments I share a screenshot.

Kinds regards,

Kevin

[Jon.Wilde · Accepted solution]

Hi Kevin,

You have a pretty short inlet which might cause issues. Typically we recommend a length of 5x the width for the inlet and 10x at the outlet.

Also, your resistances only look to have 2 elements from their inlet face to their outlet. Increase this to 4-5 and things ought to start to improve.

With Volumetric resitances like this, we should be using Advection Scheme 5 (Solve -> Solution Controls -> Advection).

Kind regards,

Jon

[Anonymous]

Hi Jon,

Thank you very much. My simulation works better now.

Kind regards

Kevin