[antt]

I am currently analyzing the fluid flow field of a multi-nozzle in three dimensions. However, the following error keeps occurring.

Divergence detected in AMG solver: temperature
absolute pressure limited to 5.000000e+10 in 32400 cells on zone 2

turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 2150 cells

Divergence detected in AMG solver: temperature
Divergence detected in AMG solver: temperature
Divergence detected in AMG solver: temperature
Error at host: floating point exception

===============Message from the Cortex Process================================

Compute processes interrupted. Processing can be resumed.

================================================== ============================

Error: floating point exception
Error Object: ()

Error at Node 2: floating point exception

Error at Node 0: floating point exception

Error at Node 1: floating point exception

Error at Node 3: floating point exception

Error: floating point exception
Error Object: #f

mesh quality is
------------------------------------------
Skewness min 2.5942e-07/max 0.40638
aspect ratio min1.0015/max 3.346
orthogonal quality min 0.84878/max 1.
------------------------------------------

I need advice. please help me..

thank you

[Martin_Sz]

The error message "Divergence detected in AMG solver: temperature" in Ansys Fluent indicates that the solver is having difficulty converging on a solution for the temperature field. Here are some steps you can take to address this issue:

**Understanding the Errors:**

* **Limited Absolute Pressure:** The message "absolute pressure limited to 5.000000e+10 in 32400 cells on zone 2" suggests that the pressure values in some cells (zone 2) are reaching a very high limit. This could be due to an incorrect pressure boundary condition or a physical inconsistency in your model.
* **Limited Turbulent Viscosity:** The message "turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 2150 cells" indicates that the turbulent viscosity is being limited in some cells. This could be happening due to very high or low velocity gradients in those cells.

**Troubleshooting Steps:**

1. **Check Boundary Conditions:** Double-check your pressure boundary conditions for zone 2. Ensure they are set correctly and don't lead to unrealistic pressure values.
2. **Refine Mesh:** A coarse mesh can sometimes lead to convergence issues. Try refining the mesh, particularly in areas with high pressure gradients or complex geometry.
3. **Relaxation Factors:** Adjusting relaxation factors for temperature, pressure, and other relevant variables can sometimes help the solver converge. Start with smaller values and gradually increase them.
4. **Under-Relaxation:** Enable under-relaxation for temperature and pressure. This helps the solver take smaller steps towards the solution during each iteration, potentially avoiding divergence.
5. **Solver Initialization:** Try initializing the solution from a simpler case or a previous converged solution (if available).
6. **Solver Settings:** Experiment with different solver settings like convergence criteria and residuals targets.
7. **Model Geometry:** Review your model geometry for any inconsistencies or sharp corners that might be causing numerical problems.
8. **Material Properties:** Ensure your material properties for temperature and other relevant fields are entered correctly and within reasonable ranges.

[antt]

Originally Posted by Martin_Sz

The error message "Divergence detected in AMG solver: temperature" in Ansys Fluent indicates that the solver is having difficulty converging on a solution for the temperature field. Here are some steps you can take to address this issue:

**Understanding the Errors:**

* **Limited Absolute Pressure:** The message "absolute pressure limited to 5.000000e+10 in 32400 cells on zone 2" suggests that the pressure values in some cells (zone 2) are reaching a very high limit. This could be due to an incorrect pressure boundary condition or a physical inconsistency in your model.
* **Limited Turbulent Viscosity:** The message "turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 2150 cells" indicates that the turbulent viscosity is being limited in some cells. This could be happening due to very high or low velocity gradients in those cells.

**Troubleshooting Steps:**

1. **Check Boundary Conditions:** Double-check your pressure boundary conditions for zone 2. Ensure they are set correctly and don't lead to unrealistic pressure values.
2. **Refine Mesh:** A coarse mesh can sometimes lead to convergence issues. Try refining the mesh, particularly in areas with high pressure gradients or complex geometry.
3. **Relaxation Factors:** Adjusting relaxation factors for temperature, pressure, and other relevant variables can sometimes help the solver converge. Start with smaller values and gradually increase them.
4. **Under-Relaxation:** Enable under-relaxation for temperature and pressure. This helps the solver take smaller steps towards the solution during each iteration, potentially avoiding divergence.
5. **Solver Initialization:** Try initializing the solution from a simpler case or a previous converged solution (if available).
6. **Solver Settings:** Experiment with different solver settings like convergence criteria and residuals targets.
7. **Model Geometry:** Review your model geometry for any inconsistencies or sharp corners that might be causing numerical problems.
8. **Material Properties:** Ensure your material properties for temperature and other relevant fields are entered correctly and within reasonable ranges.

Thank you for the advice. I have one more question. If the analysis works with the same boundary conditions in 2D but diverges in 3D, could it be due to issues with the mesh?

[Martin_Sz]

Originally Posted by antt

Thank you for the advice. I have one more question. If the analysis works with the same boundary conditions in 2D but diverges in 3D, could it be due to issues with the mesh?

probably YES

[LoGaL]

In my experience, the only thing makes fluent crash is a bad mesh. Unless you are simulating really complicated physics such as multiphase/combustion/similar.