[Guille1811]

Im modeling the effect of an axial fan via a cilinder subdomain with a general momentum source. I used the coefficient technique to force it to move air at 20 m/s.

I run the model with k-epsilon and the momentum source worked fine with a momentum source coef of -5E2 (see first picture attached) . The problem is the results were not so good in terms of temperature fields etc, so after doing tons of sensitivity analysis of mesh, boundary conditions, timescale factor, initial conditions, etc the only thing left to analize is the turbulence model.

I switched to SST model (with turbulence flux closure for heat transfer and transitional turbulence desactivated, i dont have any data), at first the velocity converged almost immediatelly to 19 m/s and it stayed there for like 100 iterations. During that time the simulation "results" were almost exactly as expected because of some other monitored variables, which indicates this model may be the best suited.

After that 100 iter, the velocity suddenly drop to negative values and stay there for like 100 iter, then it comes back to 20 m/s and stay there but this time the final streamlines are caotic and all over the place (see second picture attached).

I tried with different source coefficients in the range between -1E2 and -1E6 and nothing changed.

Any idea of how i can make the momentum source to work?