Divergence Only with Second Order Discretization
 

Hello All,

I am simulating a single phase supersonic gas flow in a convergent-divergent de-Laval type nozzle.

I am using the density based implicit formulation (2D, steady state), along with the standard k-epsilon viscous model. I have defined the ideal gas law for compressible flow in the Density field for the Gas (in the materials panel) along with the Sutherland viscosity law. I defined the operating pressure to be atmospheric. As well, I have enabled the Intensity & Hydraulic Diameter option in the drop down menu for the boundary conditions (due to the internal flow of my simulation)

Boundary Conditions are as follows:
Main Inlet - pressure of 6.15 atm and temperature of 500 K, intensity ratio of 3% and the default hydraulic diameter of 1m.
Outlet - atmospheric gauge pressure and 300 K, intensity ratio of 3% and the default hydraulic diameter of 1m.
Walls - enabled specified shear and temperature.

My Problem:
After the solution has converged using first order discretization, I change to second order discretization for improved accuracy and iterate again. To my dismay, the solution diverges quickly even when Fluent reduces the Courant number as low as 0.05.

Therefore, I propose the following questions:

1 - Why does the solution not converge using second order?
2 - Is there something wrong with my set-up that would cause the solution to converge with first order but diverge with second order?
3 - How do I fix this?

If anyone can help me with this topic it would be greatly appreciated...

Thanks,
Ryan

Same problem. Have you any solutions??

1. Check the grid quality.
2. Try to lower CFL number and then increase it gradually as the solution advanced.

Good Luck