The converge of unsteady problems?
 

Dear Sir or Madem,

I am very sorry to trouble you .However as a new user of Fluent, I need some help indeed.

Now I am calculating the pusatile flow of blood in the vessels. To check the accuracy of result, first I build a straight cylinder,then give it pusatile inlet velocity and zero outlet pressure. The length of the cylinder is more than 10 times of the dimmeter. I think if the calculation is right, the velocity of the outlet will be equal to the inlet.

Yes,when the velocity is in the increasing state, the outlet velocity can keep up with the inlet velocity very well. However in the decreasing state, the outlet velocity can not keep up with the inlet velocity...

So I try to slove this problem in these days by using different outlet condition(outlet flow ratio equals to 1),increasing the iteration numbers of each time step and changing the relax factors of momentum and pressure. But the result is still bad similarly .

Have you ever happened to this problem before and how do you deal with it?

Sorry to bother you a lot!

And thanks for your help very much!

Best wishes, Zhang Junmei

Re: The converge of unsteady problems?
 

I worked on a similar problem, with airflow in straight cylinders. I used to keep outlet boundary condition as "Outflow" and inlet one as "velocity inlet". And I never observed any such problem. What are your boundary conditions?