# Divergence Only with Second Order Discretization

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 August 6, 2009, 11:03 Divergence Only with Second Order Discretization #1 New Member   Ryan Join Date: Jul 2009 Location: Windsor Posts: 9 Rep Power: 16 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

 August 5, 2022, 03:46 #2 New Member   Berke Bayraktar Join Date: Aug 2022 Posts: 2 Rep Power: 0 Same problem. Have you any solutions??

 August 11, 2022, 17:08 #3 New Member   Ahmed Join Date: Sep 2019 Posts: 1 Rep Power: 0 1. Check the grid quality. 2. Try to lower CFL number and then increase it gradually as the solution advanced. Good Luck

 Tags compressible, courant, divergence, second order