Learning Forum

[RickJ1]

Hello

I am running a reacting flow of a premixed hydrogen-air mixture into a combustion chamber to simulate a flame in Ansys Fluent. This simulation is steady-state in a 2D-axisymetric geometry. The species its mixture properties are imported through a CHEMKIN file, using the Konnov (2019) mechanism.

When running the simulation through a cluster the results start to differ compared to running on a local computer. When ran through the cluster the flame profile start to get unrealistic and incorrect, but when running the exact same file on the local computer the flame is realistic and correct.

To narrow down the problem, a simulation is ran both on the cluster and the local computer for a cold (non-reacting) flow.

After 3 iterations the continuity already starts to differ, between the local and the cluster.

The file read on the cluster where the simulations “starts” with is initialized on the local computer.

Below a plot is made showing the difference in continuity between the cluster and the local result on the corresponding iteration.

[DrAmine]

Worth trying running on same number of CPU's using same release version and precision and everything set the same: pretty sure due to depth of Convergence.
Moreover any other precautions turned on to deal with stiff chemistry (like ISAT?

[RickJ1]

Release version and precision etc are the same.
The local machine is running on 4 CPU's. I have ran for both 16 and 4 CPU's on the cluster. The 16 CPU's is the one plotted above. For 4 CPU's the differences got even larger compared to the local machine.
ISAT is not used. I am fairly new to Ansys Fluent, but I believe ISAT would not "improve" the results, but only reduces the calculation times right?

[DrAmine]

My question regarding ISAT is just to verify if it is enabled or not as it might affect the way to solution but not the final solution (ISAT is recommended for stiff chemistry to accelerate the chemical reactions calculations).
What can you tell about convergence?