Reply To: Conservation issue with a UDS solution

[Luca B.]

Aerosol simulation in Ansys Fluent can require some attentions. The abrupt changes in aerosol mass imbalance and the transient storage term behavior when resuming from an intermediate file can indeed be perplexing. Let me share some general insights from similar Fluent simulation challenges that might help you troubleshoot the problem.

In cases where there is an unreasonably small time step in a transient simulation, it is often related to the mesh size. The time step size is proportional to the mesh size, and if the mesh is not uniform or has varying densities, it can lead to issues like the ones you're experiencing . 

Furthermore, when dealing with multiphase models, it is recommended to use a coupled solver with a pseudo transient option for all steady-state multiphase runs, as it adds a time marching under-relaxation which can help stabilize the solution .

It's also important to ensure that the boundary conditions are set up correctly. Incorrect specification methods, especially for mass flow rate inlets, can lead to problems in solving the model.

Lastly, when simulating particle flows, the particle size can significantly affect the simulation results, and it's crucial to ensure that the maximum number of time steps is sufficient for the particles to be tracked accurately.

While these resources may not directly address the specific issue with the diffusion coefficient and timestep size, they provide a starting point for troubleshooting complex transient simulations in Fluent. It may be beneficial to review the mesh quality, solver settings, and boundary conditions to identify any potential sources of instability in your simulation.