Torque of Savonius turbine is not convergent
 

Dear all,
I used Fluent 13 to simulate the Savonius turbine with obstacles was placed front of it as attached picture. k-w sst turbulence model and the second order discretisation were selected. However, I could not get convergence with time for Torque of turbine (Cm) while Cm is well convergent with time for the case of without obstacles.
Could you give me some advice, please.
Thanks.

Hi,

Flow is unsteady, so Cm is supposed to be unsteady. You have to consider other scalars to judge convergence. Then you will have an idea about how Cm oscillates.

Regards,

Thanks,
Yes, the flow is unsteady so Cm should be oscillated, however, it should be repeated over one cycle or periodic of time.

Hi fsifsi,

can I ask you how do you evaluate the turbine torque? Do you use the Cm value or the Momentum obtained from Result Reports?

Thanks,

Andrea

I used Cm value

Lower the time step. how did you calculate the time step?