Navier Stokes with very small time steps

General Discussion
1

Hello,

I am trying to solve incompressible transient Navier Stokes equation using very small time steps. I have tried the examples given in the documentation including the projection and NS Uzawa Cahouet Chabart solvers. However if I make the time step smaller than the ones given in those examples solution becomes either unstable or spurious errors emerge. I don’t have much experience with NS. Any help and guidance regarding which type of formulation will be suitable for problems with small time steps will be appreciated. Thanks.

2

The non linear term in exemple FreeFem-sources/examples/tutorial/NSUzawaCahouetChabart.edp at develop · FreeFem/FreeFem-sources · GitHub

the non linear term use the characteristic method, and long time ago S. Piperno show that the method do not converge if the time step go to 0.

So I think you see this.