# False diffusion in Lid driven cavity

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 May 13, 2020, 16:47 False diffusion in Lid driven cavity #1 New Member   Mudit Mehta Join Date: Mar 2020 Posts: 15 Rep Power: 6 Please Help!!! Hello, Can someone please explain how a false diffusion will look like in Lid driven cavity problem. (Reynolds number = 100) I am using first order upwind scheme for the discretization of convective terms in steady state navier stokes equation and using SIMPLE method.

May 13, 2020, 17:32
#2
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Filippo Maria Denaro
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Quote:
 Originally Posted by Mudit2208 Please Help!!! Hello, Can someone please explain how a false diffusion will look like in Lid driven cavity problem. (Reynolds number = 100) I am using first order upwind scheme for the discretization of convective terms in steady state navier stokes equation and using SIMPLE method.

You are working on a test-case that has no analytical solution. we already discussed such issue. The numerical diffusion can act as if you are solving the lid-driven cavity at a smaller Re. But that is locally determined by the cfl value. For the steady case you need to consider the grid size.
However, your question is not well stated.

 May 13, 2020, 17:38 #3 New Member   Mudit Mehta Join Date: Jun 2019 Posts: 3 Rep Power: 6 The grid size i have taken is 65x65 and 21x21. I have generated u, v, p countours, streamlines, u velocity along vertical geometric centre of cavity and v velocity along horizontal centre of cavity. Can we look at false diffusion from here? I have values to compare from ghia et. al. of u velocity along vertical line and v velocity along horizontal line.

May 13, 2020, 17:41
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Filippo Maria Denaro
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Quote:
 Originally Posted by Mudit The grid size i have taken is 65x65 and 21x21. I have generated u, v, p countours, streamlines, u velocity along vertical geometric centre of cavity and v velocity along horizontal centre of cavity. Can we look at false diffusion from here? I have values to compare from ghia et. al. of u velocity along vertical line and v velocity along horizontal line.

You can only perform a grid refinement study and report the velocity profiles at each grid.

 May 13, 2020, 17:42 #5 New Member   Mudit Mehta Join Date: Jun 2019 Posts: 3 Rep Power: 6 Okay. Thank you so much

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