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-   -   My Solution wont Converge!!! (https://www.cfd-online.com/Forums/fluent/36396-my-solution-wont-converge.html)

 Chris April 15, 2005 12:45

My Solution wont Converge!!!

Please Help! My solution WILL NOT converge! It keeps getting close but then diverges again. I have done 6000 iterations at courant no = 2. Then a further 2000 at Courant no = 5. If I increase the courant number after around 3000 iterations the solution diverges!

I only have until Thursday (weds realistically) to finish this project!

Can anyone please look at my .msh file and advise how to improve the mesh.

I also need advice on how to get the solution to converge?

Chris

 Sham April 15, 2005 18:33

Re: My Solution wont Converge!!!

Sham.

 Harish April 15, 2005 22:35

Re: My Solution wont Converge!!!

i'm not sure what your problem is. But you may try using a higher order scheme for the problem and it should work. also check the CFL condition for stability.

Harish

 kiran April 15, 2005 23:36

Re: My Solution wont Converge!!!

pls tell about ur problem and attach ur mesh file. i will c once.if i have any idea about that i will help u.start the iterations with low courant no. 0.1 after some 1000 iterations increase gradually. any how try to complete the project. all the best.

regards kiran

 swarup April 16, 2005 07:17

Re: My Solution wont Converge!!!

Are you solving time dependent flow? Please check your problem set-up and initialization of solution. Also check your boundary conditions and property inputs. In my opinion, you should check these things even if you are not solving a time-dependent flow. I guess you are using Coupled Implicit solver. If not then you should not use Courant Number higher than 2.0 for Explicit solution method. Stick to Courant number of 1 or less to start with and keep it constant for a substantial number of iterations. If you have non-linear changes in variables introduced during calculation, try adaptive time step if relevant. Further deatils are needed to understand the nature of difficulties though. I strongly suggest you to check your inputs and other details.

Swarup.

 samir April 16, 2005 11:17

Re: My Solution wont Converge!!!

Try changing under relaxation parameters.

 Chris April 16, 2005 18:57

Re: My Solution wont Converge!!!

Hello,

I have created a mesh using the mesh edge function. In the main the mesh immediately around the missile (1m radius) is from interval size 0.001 at the missile to interval size 0.1 at the edge of the ellipse. From here until the domain boundaries it extends getting gradually coarser. Hence, I have a fine mesh around the missile and a coarse mesh for the remainder of the computational domain.

I am modelling the fluid flow at M0.8 (then M1.2, then M3.0), at 11km.

Coupled, implicit, 2D, steady, energy eqn on, Sp-Al, air = ideal gas, Sutherland law, Pfarfield, Courant No=5

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