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Old   March 24, 2012, 23:02
Unhappy Advection/Diffusion
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Hello,

I am writing a advection/diffusion script in MATLAB for a driven cavity problem. I am using the SIMPLE method with power law convection approximations and using Numerical Heat Transfer and Fluid Flow by Patankar as my guiding text. I have completely written the code, but the solution does not converge. I was hoping that someone with experience could send me a PM and help me diagnose the issues I am having.

Many thanks,

Jesse
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Old   March 25, 2012, 23:27
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Update: I got the code working, but only when I apply very low relaxation factors (u,v = 0.15, p = 0.08) that have to get lower as I refine the grid. Does anyone have any indication as to why this might be the case? I figured it might most likely be due to a mass imbalance, due to how I average on the periphery nodes... but the solvers are fully consistent with each other in their treatments. The continuity, \nabla \vec{u} is roughly 1e-7 in each node. I imagine this is sufficiently zero.

Anyone have any ideas?

Thanks.
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Old   March 27, 2012, 14:06
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Update 2: So, with very small relaxations factors (.01 for pressure, and .07 for velocity) I can somewhat match, with a 25 x 25 grid, the reference solution for the lid driven cavity. I am beginning to suspect an issue with either the pressure correction or the non-linearity treatments. Scanning over the code many times, I can not find any issue in their development. I've attached some results.
Attached Images
File Type: png V&V_res_2.png (7.8 KB, 8 views)
File Type: png V&V_v_ben_2.png (7.5 KB, 6 views)
File Type: png V&V_u_ben_2.png (7.2 KB, 6 views)
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Old   March 27, 2012, 14:08
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Contour/Vector plots...
Attached Images
File Type: png V&V_v_2.png (22.9 KB, 4 views)
File Type: png V&V_u_2.png (23.0 KB, 5 views)
File Type: png V&V_p_2.png (20.6 KB, 4 views)
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