Originally Posted by flotus1 (Post 408219)

Is this a picture of the actual mesh you are using?
If yes, add at least prism layers at the walls.

What mach number do you expect in your simulation? How high is the pressure at the inlet and outlet respectively?

Originally Posted by flotus1 (Post 408223)

Since you are experiencing convergence issues, I would try a simulation with a velocity or mass flow inlet, at least to get better initial values for the following simulations.

Getting back to the prism layers, are you sure that the volume jump is better this time?

Additionally, I strongly recommend to use a hexa mesh, especially since the whole geometry basically consists of one hexaeder. A good mesh is one thing less to worry about in CFD;)
This could even be done with the Ansys mesher.

Originally Posted by Far (Post 408232)

instead of symmetry , specify them as slip wall.

Extend domain by some unit lengths at inlet and outlet

Originally Posted by Far (Post 408241)

Specify extended walls as slip so you will not have any boundary layer development or pressure loss.

You can define as slip wall by specifying shear stress = 0. It will have same effect as symmetry. Moreover symmetry condition has some special purpose and it has different mathematical definition.

Originally Posted by Far (Post 408241)

You can define as slip wall by specifying shear stress = 0. It will have same effect as symmetry. Moreover symmetry condition has some special purpose and it has different mathematical definition.

Originally Posted by ghorrocks (Post 386130)

This is described in the documentation.

Symmetry enforces zero normal gradient to all parameters, and a slip wall does not necessarily do this. But for most normal simulations they are equivalent.

And a symmetry plane is required to be planar, but a slip wall can be any shape.

Originally Posted by Martin Hegedus (Post 367117)

In general, slip and symmetry are much the same, if not exactly the same. But, sometimes it is implementation dependent. For example one could have p(-1)=p(1) for symmetry but p(0)=p(1) for wall. Also, the turbulence model boundary conditions could be different. OK, I don't know what it means to have a slip turbulence model, but I guess that depends on what someone is trying to do. Also, a turbulence model could depend on the distance from a surface. So it's possible that setting a far field condition to a wall will affect the turbulence model.

But, the answer, to first order, is that they are the same.

Originally Posted by hossam_ali (Post 408314)

hi i think the problem in ur mesh skewness

u should remesh and decrease the skeness to be less than now and this will decrease the squinsh of the mesh (to be less than 0.9)

Originally Posted by victoryv (Post 408603)

I have tried extending boundaries and slip walls. No use. Still it is diverging.
I will try incompressible flow and velocity inlet and simulate once again.

Originally Posted by RodriguezFatz (Post 408614)

You also had compressible flow? That's too much, you should really try to get simple settings running before switching on all additional equations...
Also, if you explain your case in a thread, please tell people everything about it and don't wait until post #50 to do so...:confused:

Originally Posted by victoryv (Post 418791)

I am facing a new problem now. I got rid of all the previous problems. The solution was taking a lot of time and many iterations to reach steady state. So I have used FMG initialization and pseudo transient method( time step 0.001) to make the convergence faster. When I was trying to find mesh independent solution, after 3rd refinement, the solution (pressure and velocity) started oscillating where it was supposed to reach state.

How did the mesh refinement led to oscillations?
If mesh is not the problem, what could be the problem?