[Knowledge]

Hi everyone!

I am simulating a model, and is only interested in the heat transfer behavior. I need to do a lot of simulations and due to limited time and space on my computer I was wondering if it was possible to reduce the computational calculations as I am only interested in the heat transfer.

Thank you much

[karachun]

Replace Fluid domains with convection BC.

[Gert-Jan]

You can freeze the fluids and turbulence by setting expert parameters:

solve fluids = f
solve turbulence = f

Then CFX only solves the remaining equations, like energy.
In this way, you can solve a temperature field in a frozen flow field with various boundary conditions. This is of course only valid if the coupling between energy and fluids is negligible.

[Opaque]

Originally Posted by Gert-Jan

You can freeze the fluids and turbulence by setting expert parameters:

solve fluids = f
solve turbulence = f

Then CFX only solves the remaining equations, like energy.
In this way, you can solve a temperature field in a frozen flow field with various boundary conditions. This is of course only valid if the coupling between energy and fluids is negligible.

and, the flow field was properly converged in the previous calculation. If there is a mass imbalance in the frozen field, it would show up in the heat transfer calculation. The negligible coupling also implies minimal temperature dependency (better none) of properties required for the flow: viscosity and density

[Knowledge]

Hi

I am not expert in CFX and therefor as the manual recommend I should not change the expert control parameters if I am not experienced. Would you mind giving me a step by step description on how to change these parameters?

[Knowledge]

I was wondering if it was possible to do it that way.

CFX-pre --> "output control" --> "Resuls" --> for "option" --> selected variables for "output variable list" --> temperature

Is it possible?

[aero_head]

Originally Posted by Knowledge

Hi

I am not expert in CFX and therefor as the manual recommend I should not change the expert control parameters if I am not experienced. Would you mind giving me a step by step description on how to change these parameters?

Hello Sara,

To change the expert parameters, right click on the Solver folder and choose "Insert>Expert Parameter". Most of the parameters will appear in the GUI panel that comes up. If you need one that doesn't come up (i.e. an undocumented one), just add any of the ones shown to create the Expert Parameter object then right click on it and choose "Edit in Command Editor" to insert the parameter manually.

[aero_head]

Originally Posted by Knowledge

I was wondering if it was possible to do it that way.

CFX-pre --> "output control" --> "Resuls" --> for "option" --> selected variables for "output variable list" --> temperature

Is it possible?

Sure, it is possible but defeats the purpose of your question, since this would not reduce the number of computational calculations. Monitor points just monitor specified parameters, it would still calculate everything else as normal.

[Knowledge]

Originally Posted by aero_head

Sure, it is possible but defeats the purpose of your question, since this would not reduce the number of computational calculations. Monitor points just monitor specified parameters, it would still calculate everything else as normal.

But what is the difference between monitoring and calculation?
Can the monitoring option not reduce the simulation time my simulation takes approximatly a whole day right now and takes a lot of space on my harddisk

[aero_head]

Originally Posted by Knowledge

But what is the difference between monitoring and calculation?
Can the monitoring option not reduce the simulation time my simulation takes approximatly a whole day right now and takes a lot of space on my harddisk

Monitoring a value lets you keep track of the parameter during the simulation. The calculation of everything else will continue as normal. Again, the only way to solely calculate certain parameters is to modify the T/F statements in the expert parameters.

You can try it out I know you said you are not an expert, but it is okay, because you are AWARE of what you will be modifying. They put that sentence in the manual because they don't want people changing expert parameters without knowing the repercussions. Since you now know what changing these settings will do, you are an 'expert' for that particular section

The only other way I can think of to only calculate certain parameters is to write and implement your own code, specifying what you want the solver to calculate (I've only done this once).

[Gert-Jan]

As I mentioned earlier, in a frozen flow field, you can solve the energy equation solely by setting the other equations to false. Then since you only solve an energy equation that is not coupled to anything, you can simply increase the auto time scale from 1 to 10, 10000, 100000, or what so ever. Just give it a try untill you pushed it too far. Then the solver solves the equation at very high speed for you in a short period of time. You only need to make absolutely sure that:

- your energy residuals are low
- the temperature in your monitoring points are constant.
- your energy imbalance is zero (energy in = energy out).

Then you can be sure that your energy equation is solved accurately. And again, remember your flow is frozen, so your solution only makes sense if there is no coupling between energy and any other variables. If you have an ideal gas, then you are already in trouble. Same hold for an temperature dependent viscosity. But judge for yourself.

Don't hesitate to use expert parameters. You are already an expert since you are suspicious on the action that you take. Credits for you.