# Problem with Convergence!!

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 February 20, 2008, 03:49 Problem with Convergence!! #1 Elleana Guest   Posts: n/a Hi all, Could some one please tell me what are the general causes of convergence problems. Iam doing simple heat transfer analysis the continuity equation seems to oscillate up and down along with the x, y and Z velocities. Reducing the resuduals does not seem change the situation much. Can some one please lend their thoughts on this. I have checked the boundary condition and mesh seems to be fine. Cheers Elleana

 February 20, 2008, 07:01 Re: Problem with Convergence!! #2 Amit Guest   Posts: n/a Check the order of scheme you r using, first try with first order scheme than after sufficient convergence switch to higher order scheme.

 February 20, 2008, 07:20 Re: Problem with Convergence!! #3 Elleana Guest   Posts: n/a Hi, Iam working on first order. i havent turned the second order yet. Cheers Elleana

 February 20, 2008, 07:34 Re: Problem with Convergence!! #4 Armin Guest   Posts: n/a hi,if you are solving this problem employing Segregated Method it is some time helpful to make some changes to the under relaxation factors, in case of heat transfer temperature and energy under relaxation factors are important, other relaxation factors have a second level of importance, be careful although you might be able to make the solutions converge they might be inaccurate, changing momentum under relaxation factor is effective, moreover if you are using coupled method changing the Courant number and also implementing adaptive grid might help the solution converge, it is a lot more helpful if you can specify the conditions of your problem, thereby I can help you better.

 February 20, 2008, 09:01 Re: Problem with Convergence!! #5 Elleana Guest   Posts: n/a HI Armin, Thanks for your reply. There is a louvre on the left hand side of the building which is 8m * 27m *2.8m. there are thermal mazes placed at eaqual distances on the path of the flowing air on both sides of the 8m width. the air inturn flows in a zig zag way around these obstructions. the idea is to cool down the external air to an extet to reduce the work of the air handling by a factor. i have declared a velocity inlet and a pressure outlet with temperature boundary condition for the walls of the thermal maze. From what iam witnesing it is creating excess turbulence inside. is it a good idea to solve the flow and energy equations first. use them as a initial solution and solve the turbulence equations. Cheers Elleana

 February 23, 2008, 06:53 Re: Problem with Convergence!! #6 armin Guest   Posts: n/a Dear Ellena solving the flow and energy at first can be useful especially when you are working with high speeds, on the other side if the method of your solution is segregated you can change the relaxation factors especially momentum, and also you can gradually change the boundary condition without the necessity to initialize the solution ,decreasing the momentum coefficient can converge your solution.

 February 23, 2008, 16:37 Re: Problem with Convergence!! #8 Carlos Guest   Posts: n/a P.S. Run isothermal simulations first and then use those to initialize thermal simulations, this is good practice at first. However, with more confidence and experience you can get a converged solution for a 2nd order/Quick model with heat transfer, species transport and get convergence - from scratch! Its all down to the quality of the mesh and model set up. Carlos.

 February 28, 2008, 02:44 Re: Problem with Convergence!! #9 Elleana Guest   Posts: n/a Hi Carlos & Armin, Thank you very much for the valuable tips. My apologies for sending a delayed email as i was on a break. I have followed the steps and its working fine now. Thanks Kind regards Elleana

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