SimScale CAE Forum

Solver Fatal Error - Different Dimensions on a Convective CFD analysis

I am trying to simulate forced convection in a small room used as an oven. I am doing a convective heat transfer, steady state, using the k-epsilon turbulence model. When I run the simulation, the solver quickly gives a Fatal Error. The solver log error reads:
[25] Different dimensions for =
dimensions : [1 -1 -1 0 0 0 0] = [0 -1 -1 0 0 0 0]

This shows up several times in the log. I have 6 velocity inlets (vents supplied with hot air by a fan), and a pressure outlet. The rest are walls. I have tried changing the boundary conditions but keep getting this error. Has anyone come across something like this?

The link to the project is: Furnace Heating / Ventilation

Thanks in advance for any help.

Hi @rtrowbridge!

@PowerUsers_CFD and I are having a look at it asap and get back to you as soon as we know more about this issue.

All the best!


Thank you. Some more information - I ran this as a CHT analysis (using a different mesh with 2 regions) and got the same error.

Hi @rtrowbridge!

One of our engineers is having a look at it. Getting back to you as soon as I know more.

All the best!


Hi @rtrowbridge!

Can you now try if the simulation works? Please note that some faces and/or interfaces are unassigned. A no-slip wall boundary will be assumed for unassigned faces, and a thermal coupling for unassigned interfaces as you might have seen when creating a run.

Please get back to me and tell me if everything works fine now!




Thanks for looking into this. I ran the convection, k-epsilon, analysis again in my project and got the same error. Did someone copy my project and make changes to the copy? If so, can you provide a link to that? I don’t see it in the public projects.

Earlier today I ran this as a laminar convection analysis and it ran fine. The dimension error seems to be related to the turbulence model.

I have a question concerning transient analysis too. Someone has asked me if it is possible to simulate heat transfer in a room like this over a 20 minute span. I looked over how the transient analysis is done, and this long of a time frame doesn’t seem practical because the time steps would have to be very small to keep the Courant Number low. It would take too many steps. Is there a way to do a transient analysis over such a long time span, or is this generally just done for short time ranges (under a second long)?


Thanks a lot for the feebdack Rick!

I will forward your message to the engineer and he will get back to you as soon as possible!

Cheers and all the best!


@rtrowbridge Rick, to address the k-epsilon failure, I just copied and ran “Convective heat transfer” simulation. It does not have the dimensions issue anymore, but fails due to numeric-related reason, I assume a different discussion. Could you make sure to save your simulation once and then run?


Thank you. I reran the k-epsilon analysis without changing anything again and did get a different error this time.

I am having a different issue with a conjugate heat transfer analysis for this same project. This is the simulation titled Refined-CHT-Laminar-80Deg in the project. I am getting a fatal solver error that the maximum number of iterations was exceeded. I thought it may be because the mesh was too coarse, so I refined the multi region mesh and still get this error. From looking at the solver log, it appears that the solver for the enthalpy of the solid region is what is exceeding the 1000 iterations. The solid region enthalpy solver was defaulted to GAMG. I reran this as a smooth solver with .0001 absolute and relative tolerance and had the same error. I did not define the boundary conditions for the interfaces of the solid and fluid region because I want them to be thermally coupled. Do you have any ideas how I can solve this numerical issue? Note that I have also lowered the inlet velocity just to make sure that wasn’t the cause.