[vbchris]

Is there a difference in hardware requirements between transient and steady-state simulations, generally speaking?

I have been working a lot with transient phase change models and would like to know if there are any special considerations for a workstation which runs models locally. Typically mesh sizes ~500k to ~2mill.

[flotus1]

For transient simulations that write a lot to disk during the simulation, the speed of the hard drive can become an additional bottleneck. Same for post-processing such simulations, e.g. when creating an animation. In my opinion, a decent SATA SSD is a must-have for any proper workstation. NVMe SSDs can provide even faster read/write speed if necessary.
Other than that, a GUI can hold back a transient simulation that runs rather fast. In that case, either reduce the output update interval or run in batch mode.

[CLane]

Thanks, does RAM bandwidth requirements differ much?
I assumed bandwidth requirements are proportional to mesh size and not solver type?

I am running Fluent and OpenFOAM with unstructured meshes.

[flotus1]

The problem size does not change the code balance. As long as the model is too large to fit into cache entirely, you are limited by memory bandwidth to the same extent. And 500k cells is definitely too large to fit into any L3 cache.

[LuckyTran]

The steady and transient solvers are virtually identical.

Any problem worth considering will be limited by RAM bandwidth. If you are not limited by bandwidth, then either you are not doing CFD the right way or your problem is too simple and there is nothing to consider. The bigger the mesh, the more you will be limited by bandwidth. But if you get a new workstation, or any recent hardware, there are few options for bandwidth. You either have 2/3/4 memory channels. It is usually a very easy choice (whatever is within your budget).

Then you go for optimizing the other (and probably more significant) bottlenecks. As already mentioned, writing files fastly is a huge bottleneck in transient simulations if that is what you are trying to do.

The hardware requirements don't change from steady to transient per se. But in steady state you don't need to output the solution at every iteration because you are interested in the final converged solution. A new opportunity arises in transient simulations since now you have the option to save the solution every time-step. This would be like writing the solution every iteration in a steady case (but no one really does that because the information is useless). But in transient simulations, that data is usable to some people.

[Simbelmynë]

Originally Posted by flotus1

Other than that, a GUI can hold back a transient simulation that runs rather fast. In that case, either reduce the output update interval or run in batch mode.

I remember Fluent 6.3 ran much faster with the GUI minimized


This was true regardless of transient or steady-state simulation though (as you noted it was more connected to the update interval of the residuals). Also, Linux did not have the same problem, it was only present under Windows, which is strange considering the relatively poor GPU driver development on Linux.

[flotus1]

A later Fluent version could be greatly sped up by moving the mouse back and forth. Fun times.