Advection/Diffusion

kamakura117 · March 24, 2012, 22:02

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

kamakura117 · March 25, 2012, 23:27

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.

kamakura117 · March 27, 2012, 14:06

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.

kamakura117 · March 27, 2012, 14:08

Contour/Vector plots...

March 24, 2012, 22:02	Advection/Diffusion	#1
kamakura117 New Member N/A Join Date: Jul 2010 Posts: 29 Rep Power: 15	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

March 25, 2012, 23:27		#2
kamakura117 New Member N/A Join Date: Jul 2010 Posts: 29 Rep Power: 15	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.